Jones The relationship between 2011 Accepted

The relationship between fine sediment and macrophytes in rivers.
Jones, J.I.1, Collins, A.L.2,4, Naden, P.S.3, Sear, D.S.4
1 School of Biological and Chemical Sciences, Queen Mary University of London, Mile End
Road, London, E1 4NS, UK
2 Soils Crops and Water, ADAS, Woodthorne, Wergs Road, Wolverhampton, West Midlands,
WV6 8TQ, UK
3. CEH Wallingford, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford,
Oxfordshire, OX10 8BB, UK
4 School of Geography, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

Running head: fine sediment and macrophytes


Abstract
The interplay between erosion and deposition are fundamental characteristics of river basins.
These processes result in the delivery, retention and conveyance of sediment through river
systems. Although the delivery of sediment to rivers is a natural phenomenon, in recent years
there has been increasing concern about the enhancement of sediment loadings as a result of
anthropogenic activities. The presence of macrophytes in river channels tends to increase the
retention of fine sediment leading to changes in bed composition. However, a complex
relationship exists between macrophytes and fine sediment: macrophytes affect the
conveyance of fine sediment and are, in turn, affected by the sediment loading. This review
deals with these two reciprocal effects and, in particular, summarises the available evidence
base on the impact of fine sediment on macrophytes. Increased inputs of fine sediment appear
to have both direct and indirect impacts on the macrophyte community, altering light
availability, and the structure and quality of the river bed. The nature of these impacts
depends largely on the rate of deposition and the nature of the material deposited. Changes in
macrophyte community composition may ensue where the depositing material is more
nutrient rich than the natural river bed. Many of the changes in macrophyte flora that occur
with increased fine sediment inputs are likely to closely parallel those that occur with
increased dissolved nutrient availability. If attempts to manage nutrient inputs to rivers are to

achieve their goals, it is critical that fine sediment-associated nutrient dynamics and transfers
are considered.
Key words:
Aquatic plants, deposition, suspended solids, turbidity, conveyance, fluvial dynamics


Introduction
The interplay between erosion and deposition represents a fundamental characteristic of river
systems which has important implications for channel processes and ecological functioning.
Although the delivery of sediment to rivers is a natural phenomenon, in recent years there has
been increasing concern about the influence of human activities on the amount of fine
sediment (i.e. < 2 mm in size encompassing inorganic sand (<2000 to >62 µm), silt (<62 to
>4 µm) and clay (<4 µm), and organic particles) delivered to rivers. The mobilization of fine
sediment to rivers is enhanced by activities such as agriculture (e.g. Collins & Walling, 2007),
forestry operations (e.g. Davies & Nelson, 1993), construction (e.g. Angermeier, Wheeler &
Rosenberger, 2004), mining (e.g. Turnpenny & Williams, 1980) and the urbanization of
catchments (e.g. Hogg & Norris, 1991), with the quality, quantity and timing of the sediment
loads received by rivers being dependent on key sources and delivery pathways.
Increased inputs of fine sediment can lead to marked physical modifications of the river
environment (Owens et al., 2005) with consequent ecological impacts (Waters, 1995, Wood
& Armitage, 1997, Wood & Armitage, 1999, Bilotta & Brazier, 2008). Here, we review the
relationships between fine sediment and aquatic macrophytes (photosynthetic organisms
easily visible with the naked eye, including vascular plants, bryophytes and macroalgae). A
complex relationship is evident: macrophytes create a diversity of flow conditions which
affects the conveyance of fine sediment and, in turn, macrophytes are affected by the
sediment load. We will deal with these two reciprocal effects in turn, though in reality, they
are closely interlinked.
The impacts of macrophytes on sediment transfer and conveyance
Aquatic macrophytes are an artificial (multiphyletic) group of large (macroscopic)
photosynthetic organisms usually growing with their roots in soil (or water) above which is a

layer of water. Due to their physical presence, macrophytes physically block the volume
available for water movement as well as creating flow resistance (Green et al., 2006, Bal &
Meire 2009). This results in turbulent energy dissipation, creating areas of low velocity and
bed shear stress that encourages deposition of fine organic and inorganic particles (Barko,
Gunnison & Carpenter, 1991, Barko & James, 1998). The extent to which macrophytes affect
the flow is dependent upon the morphology, flexibility and density of stems (Sand-Jensen &
Mebus, 1996, Sand-Jensen, 1998, Sand-Jensen & Pedersen, 1999, Asaeda; Fujino &
Manatunge, 2005, Cotton et al., 2006, Naden et al., 2006, Puijalon & Bornette, 2006),
Wharton et al., 2006, Bornette et al., 2008, Puijalon et al., 2008). The greater the resistance
of the plants present, the greater the retention of sediment (Sand-Jensen et al., 1989, SandJensen, 1998, Gurnell et al., 2006). The term macrophyte encompasses a wide range of
morphologies. Broadly these can be described as emergent, floating leaved, submerged, and
encrusting dependent on where the plant structures are relative to the water surface and
substrate, with individual species often displaying plasticity among these growth forms (e.g.
Puijalon & Bornette, 2006). Although the relationship is not absolute, these four categories
largely correspond with declining stiffness and resistance as progressively less supportive
tissue (largely correlated with dry:fresh mass) is required to maintain the position of the
photosynthetic parts of the plant. A further category of plants, namely trees including all


woody plants and other large woody debris, could be included together with macrophytes as
they represent a particularly large resistance to flow and are associated with high rates of
sediment accretion, with considerable influence on the geomorphology of rivers (Gurnell,
Blackall & Petts, 2008, Sear et al., 2010). For the purposes of this paper we will exclude
large wood and trees, choosing instead to focus on herbaceous plants more typically regarded
as macrophytes.
Effects on flow
Despite this heterogeneity of morphology, aquatic macrophytes tend to spread by vegetative
growth, forming stands (close groupings of individual shoots) which are relatively
homogeneous (within the stand). Although each individual shoot has a boundary layer that
influences exchange of dissolved substances (Black, Maberly & Spence, 1981) and can be

measured (Jones, Eaton & Hardwick, 2000b), whole stands of macrophytes can be treated as
a coherent hydraulic units (Sand-Jensen & Pedersen, 1999). While there are a range of
different definitions (Statzner, Lamouroux, Nikora and Sagnes, 2006), Luhar, Rominger and
Nepf (2008) summarise the average distributed morphology of macrophyte stands as the
frontal area per unit volume, a, and use this parameter to describe the influence of sparse and
dense stands of macrophytes on water velocity and turbulence1. Where stands are sparse
(Drag coefficient x frontal area index, CDah < 0.1), the velocity profile within the stand
resembles a turbulent boundary layer with relatively high velocity within the vegetated layer
and high turbulent stress at the bed (see Figure 1a). Under these conditions, rates of sediment
deposition and remobilisation within the stand are only slightly altered compared to those in
unvegetated regions, and the macrophytes have little influence on the conveyance of
suspended sediment. However, where stands are dense (CDah > 0.1), the velocity within the
vegetation is significantly reduced and a shear layer or mixing layer is developed above the
vegetation canopy. This shear layer results in the generation of large coherent KelvinHelmholtz vortices, whose strength and penetration into the vegetation layer is determined by
the balance between the shear production and canopy dissipation of the turbulent eddies
(Nepf et al., 2007; see Figure 1b). Under these conditions bed shear stress is reduced,
sediment is advected into the canopy and sediment accumulates. Once produced, the vortices
pass down the plant stand with a characteristic frequency (Ghisalberti & Nepf, 2009) which,
dependent upon the flexibility of the shoots and flow (Patil & Singh, 2010), cause coherent
waving of the surface of the plant stand, known as the monami (mo = aquatic plant, nami =
wave (Ackerman & Okubo, 1993)), and reduce drag on the plant (Ghisalberti & Nepf, 2006,
Ghisalberti & Nepf, 2009).
Clearly drag, morphology and density have a significant influence on whether plant stands
encourage the accumulation of sediment (Luhar et al., 2008). However, drag and shoot
morphology are not fixed; dependent on flow velocity, macrophyte shoots can bend and
compress, reducing height, frontal area and, consequently drag (Sand-Jensen, 2003, Green,
2005b, O'Hare, Hutchinson & Clarke, 2007, Sand-Jensen, 2008, Sand-Jensen & Pedersen,
2008). The flexibility of shoots (and morphology) is critical in determining the extent to
which drag can be reduced in faster flows (Green, 2005d, Green, 2005b). Shoot flexibility
1

[If individual submerged shoots or submerged parts of shoots have a characteristic frontal area, Af, and the
stand is h high and contains m shoots per unit bed area, the stand has a frontal area index ah = mAf]


appears to be related to the proportion of structural tissues, which can be cellulose, lignin or
biogenic silica (Schoelynck et al., 2010). As the drag force also influences the likelihood of
physical damage to the plant and uprooting, flow velocity – itself a function of water
discharge and channel morphology as well as plant growth – influences the distribution of
macrophyte species. Hence, flexible taxa, with dissected leaves and easily compressible
shoots are typical of high velocities, whereas stiff, erect, and often emergent taxa
predominate in lower velocities (Sand-Jensen et al., 1989, Sand-Jensen & Mebus, 1996). In
the highest velocities only encrusting forms can persist, typically low-stature haptophytes
(plants lacking rooting structures; e.g. mosses and attached algae) growing over the surface of
stones.
The higher drag within plant stands can divert flow around the stand, resulting in increased
velocities, and increased scouring, in the unvegetated region, although actual rates of erosion
will depend on sediment characteristics and flow velocity (Sand-Jensen et al., 1989, Gambi,
Nowell & Jumars, 1990, Sand-Jensen & Madsen, 1992, Sand-Jensen & Mebus, 1996).
Diversion of flows and scouring appears to occur when macrophytes occupy less than 0.4 of
the bed area (from work undertaken with stands of eelgrass (Zostera marina L.); Ghisalberti
& Nepf, 2009) and where macrophytes occupy the margins of the river channel (Gurnell et
al., 2006). Where increased flows around individual stands occur, the stands take on a
characteristic shape (see Figure 2): erosion at the sides of the stand cause deviation from
radial expansion of the stand such that stands become elongated and streamlined in the flow
direction (Sand-Jensen & Pedersen, 2008). Growth of stands in such a form results in a lower
increase in frontal area (ah) relative to volume (and therefore biomass) when compared to
radial growth, which would produce a spherical form (Sand-Jensen & Pedersen, 2008). Over
larger areas of macrophyte coverage (e.g. eelgrass beds) self organisation can result in banded
patterns, as stems encourage deposition but erosion increases with distance from the leading

edge (Bouma et al., 2009, van der Heide et al., 2010). At higher densities of macrophytes
(>0.4 of bed) studies of stands of eelgrass, indicated that there was insufficient coherence in
the channels between plant stands and velocities are reduced throughout, potentially resulting
in sediment accumulation in both the vegetated and unvegetated regions (Ghisalberti & Nepf,
2009). It should be noted that where flows are low and nutrient levels high, dense growth of
filamentous algae (e.g. Cladophora spp.) can cover 100% of the bed resulting in extensive
accretion of sediment.
Visual observation indicates that the diversion of flows around stands of macrophytes can
cause increased erosion of banks and modification of channel morphology. The distribution
of macrophytes within a river channel has considerable influence on the overall resistance to
flow, and can be summarised, in part, by a blockage factor describing the proportion of the
channel filled with macrophytes (Green, 2005a, Green, 2005c, Green, 2006). Over a wide
range of macrophyte densities, blockage factor is a better predictor of the total resistance to
flow than the morphology of individual stands (Green, 2006, Luhar et al., 2008).
Field measurement of water velocity within and around stands of submerged macrophytes has
been undertaken by many workers, using a variety of techniques, including salt dilution (e.g.
Madsen & Warncke, 1983), hot-wire anemometry (e.g. Losee & Wetzel, 1988, Sand-Jensen


& Mebus, 1996, Sand-Jensen & Pedersen, 1999, Bass, Wharton & Cotton, 2005 ),
electromagnetic current metering (e.g. Green, 2005d), acoustic Doppler velocimetry (e.g.
Naden et al., 2006, Wharton et al., 2006)). Such work has embraced a range of flow
conditions from lakes (Losee & Wetzel, 1993) to fast flowing rivers (e.g. Wharton et al.,
2006), and coastal beds of seagrasses (Ackerman & Okubo, 1993) and kelp (Jackson &
Winant, 1983). The velocity profiles produced tend to show a significant reduction within
dense stands of macrophytes, with velocities deep within dense stands being reduced by an
order of magnitude compared to velocities outside the stand (Madsen & Warncke, 1983,
Losee & Wetzel, 1988, Sand-Jensen & Mebus, 1996, Sand-Jensen & Pedersen, 1999, Cotton
et al., 2006, Wharton et al., 2006) but with less of a reduction (Sand-Jensen, 1998), and even
local acceleration (Naden et al., 2006, Wharton et al., 2006), within sparse stands. The

particular form of measured velocity profiles reflects the position of the profile relative to
both the channel topography (Gurnell et al., 2006), the location with respect to and within
individual macrophyte stands (Sand-Jensen, 1998, Wharton et al., 2006), and how much of
the water column is occupied by the vegetation (Naden et al., 2006). The conditions of
reduced flow and reduced turbulence within macrophyte stands are conducive to the trapping
and retention of fine sediment, and fine sediment tends to accumulate (Sand-Jensen et al.,
1989, Sand-Jensen, 1998, Clarke, 2002). Rates of accumulation vary dependent upon both the
supply of fine sediment and the extent to which the macrophytes reduce velocity and
turbulence (Sand-Jensen & Mebus, 1996, Sand-Jensen, 1998), which is largely a function of
the vegetation density and position of the macrophyte stand (Green, 2006, Gurnell et al.,
2006, Luhar et al., 2008). Flexibility of macrophytes further influences the accretion of fine
sediment: the occurrence of the monami creates high velocities towards the tail of stands of
flexible macrophytes and encourages erosion in this region (Sand-Jensen & Mebus, 1996,
Sand-Jensen, 1998) whereas large coherent vortices, and subsequently substantial deposition,
occur in the lea of less flexible plant stands (Green, 2005d).
Sediment accumulation
Several workers have measured rates of accumulation of sediment (Table 1), indicating that
substantial amounts of material can be retained within stands of plants. Even where rates of
accumulation have not been measured, it is clear that the substrate below macrophyte stands
can contain significantly more fine sediment than unvegetated areas (Clarke & Wharton,
2001, Clarke, 2002). This accumulation of fine sediment results in changes in bed
morphology (Corenblit et al., 2007) that can further reinforce accumulation: pronounced
changes in bed morphology have been recorded in stands of a variety of species of
macrophyte (James, Barko & Butler, 2004). It should be noted that as well as habitat
modification through increased deposition and sediment retention, by diversion and
acceleration of flows around dense stands of macrophytes, their presence results in
modification of bed and channel morphology through increased erosion in the unvegetated
regions.
As a biologically active component of the river landscape, many species of macrophytes
undergo seasonal fluctuations in biomass as they grow and die-back in the autumn or after

flowering (mosses and liverworts are a notable exception where standing stock may represent
several years’ growth). These fluctuations in biomass result in seasonal variation in the rate of
accumulation, typically with high rates of fine sediment accumulation over the spring and
early summer followed by intense erosion of the accumulated material over the autumn and
winter, once the plants have died back and the stands are no longer capable of retaining the
sediment at a time of increasing river flows (Dawson, 1978, Dawson, Castellano & Ladle,
1978, Dawson, 1981, Champion & Tanner, 2000, Kleeberg et al., 2009). Downstream loss of
retained material can occur with increased flow (Sand-Jensen et al., 1989, Sand-Jensen, 1998,
Schulz et al., 2003, James et al., 2004), or after weed cutting and other management practices
(Svendsen & Kronvang, 1993). However, the coincidence of increased autumn/winter
discharge with reduced strength of macrophytes as they die back, leads to increased
likelihood of breakage or uprooting of macrophytes and the remobilisation of accumulated
material, a process that is exacerbated by the lower stability and poor rooting medium
presented by the accumulated sediment (Kleeberg et al., 2009). The likelihood of stem
breakage compared to uprooting will depend on the strength of the stems and their resistance
to flow. It should be noted that disturbance from flow can occur at any time, such that plant
cover appears to be highest in rivers where the variability in flow is lowest (Riis et al., 2008).
As a consequence of reduced resistance, higher velocities have been recorded where there
have been plant stands once the plants have died back (Wharton et al., 2006). An annual
cycle of sediment accretion by Ranunculus penicillatus subsp. pseudofluitans (Syme)
Webster, followed by invasion by Rorripa nasturtium-aquaticum (L.) Hayek with further
accretion, followed by intense erosion and loss of Rorripa and the majority of the
Ranunculus biomass from the stand has been described as being typical of chalk stream
headwaters (Dawson, 1978, Dawson et al., 1978, Heppell et al., 2009). A similar sequence of
accumulation and erosion has been described for Danish streams where dense stands of
submerged plants, typically Ranunculus peltatus Schrank or Callitriche spp., encourage
accretion of sediment and succession to emergent (Berula erecta (Hudson) Cov., Veronica
anagallis-aquatica L., Mentha aquatica L.) and eventually terrestrial species which are then

washed out during high discharge, although Sand-Jensen (1997) stresses that the return period
(or eventual succession to terrestrial vegetation) is dependent upon the frequency of high
flow events (which is also true for the R. penicillatus subsp. pseudofluitans – R. nasturtiumaquaticum). It should be noted that increasing accumulation of sediment can be associated
with increasing biomass and changing morphology, from submerged to emergent, of
individual species, as well as with species succession. A similar seasonal accretion of nutrient
rich, fine sediment has been observed within the less dense stands of arrowhead, Sagitaria
sagitifolia L., as biomass increases during the peak of the growing season, with subsequent
extensive erosion of accumulated material, and release of nutrients, in the autumn and winter
(Kleeberg et al., 2009). As stands of submerged macrophytes grow, flow is directed into
unvegetated areas where erosion of the bed may occur (Dawson, Castellano & Ladle, 1978;
Kleeberg et al., 2009). Despite local increases in velocity, average velocity tends to decline,
and flow depth increases with increasing biomass of macrophytes (Gurnell & Midgley, 1994,
Jones et al., 2008), although this relationship is influenced by how evenly macrophyte
biomass is distributed across the channel: an uneven distribution has less of an effect. Where
macrophyte stands have substantial overwintering biomass, fluctuations in sediment accretion


are likely to be less pronounced, although this relationship will be confounded by stream
power: less powerful rivers are less likely to remove plant biomass and accumulated sediment
during winter flows. Nevertheless, it does appear that in many cases the accumulation of fine
sediment within stands of macrophytes may represent transient storage rather than long term
retention. This has important implications for the net transfer of fine sediment-associated
nutrients and contaminants through macrophyte-dominated river systems.
The occurrence of different macrophyte species is influenced by substrate composition, as
well as water depth, chemistry and velocity (Haslam, 1978). Most of these parameters are
influenced by accretion of fine sediment, which in turn has the potential to affect macrophyte
species that are capable of growing at that position (see below). Hence, accretion of fine
sediment has the tendency to encourage species succession, particularly towards terrestrial
species.
Ecological Engineering

The ability of macrophytes to encourage accretion of sediment, and hence modify bed
morphology and encourage succession, has led to suggestions of positive feedbacks and
ecosystem engineering (the creation or modification of habitats) by certain species of
macrophyte (Corenblit et al., 2007, Peralta et al., 2008, Corenblit et al., 2009). Although
meaningful field tests of community level differences due to positive feedback processes are
difficult to procure, it is clear that macrophytes can induce change in habitats, and thus have
marked consequences for themselves and other organisms, both in the habitat patches
occupied by macrophyte stands and in areas outside the stand where the flow is affected
(Reise et al., 2009).
The impacts of fine sediment on macrophytes
Suspended particles
As well as affecting how macrophytes influence sediment transfer and conveyance,
macrophyte morphology has an influence on how fine sediment impacts their growth and
survival. As macrophytes require light for photosynthesis, the position of the photosynthetic
parts of the plant relative to the water surface is a key control. Any increase in the turbidity of
the water column caused by suspended fine sediment will reduce light availability, and hence
photosynthesis, and have an impact on the growth of submerged macrophytes, as has been
shown with clay additions to experimental streams (Parkhill & Gulliver, 2002). At its most
extreme, constant high turbidity from fine sediment and other particulates suspended in the
water column can attenuate light to such an extent that submerged macrophytes are excluded
from all but the shallowest (usually marginal) areas (Vermaat & De Bruyne, 1993). Although
the impact of fine sediment turbidity on light attenuation has a less pronounced effect on
emergent and floating leaved macrophytes, where the majority of the photosynthetic parts are
above the water column, the submerged parts can contribute substantially to the


photosynthetic capability of such species, particularly early in the growing season
(Delbecque, 1983).
Nevertheless, high concentrations of inorganic fine sediments in the water column do not
tend to occur for prolonged periods, being strongly associated with high flow events;

sustained high densities of fine particulates tend to be of biological origin (phytoplankton)
rather than eroded inorganic sediment. Where mining activity has resulted in sustained high
levels of turbidity, such as streams influenced by placer gold mines in Alaska (LaPerriere et
al., 1983, Van Nieuwenhuyse & LaPerriere, 1986, Lloyd, Koenings & LaPerriere, 1987, Pain,
1987), there is a negative correlation between turbidity (as Nephelometer Turbidity Units:
NTU) and primary production (g O2 m-2 day-1). A similar reduction in primary production,
benthic cholorophyll and diatom density was reported downstream of gravel extraction in a
French river (Rivier & Seguier, 1985). Lloyd et al. (1987) developed a model that related
turbidity to gross primary production, where an increase from 1 to 5 NTU resulted in a
decrease of 3-13 % of gross primary production, and an increase from 1 to 25 NTU a
decrease of 13-50 %. However, isolating the effect of turbidity on light availability from the
other effects of sediment on macrophytes (see below) is difficult, and requires modelling of
light attenuation and determination of the relationship between light and
photosynthesis/growth (Sand-Jensen & Madsen, 1991). Using this approach Vermaat and De
Bruyne (1993) established that low light availability due to turbidity (from suspended
sediment and phytoplankton) resulted in almost total exclusion of macrophytes in the River
Vecht. In the River Spree turbidity (primarily phytoplankton) was responsible for a 45%
reduction in light availability at a depth of 0.5 m, although this only had a significant effect
on macrophyte growth when combined with shading attributable to bankside vegetation and
periphyton (Köhler, Hachoł & Hilt, 2010).
Abrasion by the passage of suspended fine inorganic particles can damage macrophytes,
particularly submerged plants. The submerged leaves of macrophytes tend to be thinner than
emergent leaves and lack a cuticle (Sculthorpe, 1985), adaptations to increase light harvesting
and gas exchange underwater (Spence & Crystal, 1970a, Spence & Crystal, 1970b). An
unfortunate consequence of these adaptations is that submerged leaves are more fragile than
emergent or floating ones, and may be more prone to damage by suspended particles.
However, it is only at prolonged high concentrations that suspended particles are likely to
cause noticeable physical damage to macrophytes and such an effect has yet to be
demonstrated in the field (Waters, 1995). Furthermore, at the high concentrations required to
cause significant physical damage other, indirect, effects are apparent that tend to exclude

submerged macrophytes.
Deposited particles
Although particulates tend to settle out of the water column (dependent upon the size, weight,
and floc formation of particle and the hydrodynamics of the situation) this does not
necessarily remove their ability to attenuate light: if particulates settle onto the photosynthetic
parts of the plant and remain there, their presence will reduce the light available to the plant


beneath. The presence of plant structures within the water column causes particles to deposit
on the plants (see Palmer et al., 2004 for details of effects). Furthermore, due to the close
proximity of deposited particles scattering of light is enhanced. Hence, the attenuation
coefficient of deposited material is greater than the same material in suspension (Sand-Jensen
& Borum, 1984, Sand-Jensen, 1990, Vermaat & Hootsmans, 1991). In fact periphyton (the
layer of algae, bacteria, fungi, organic and inorganic particles that grows attached to
submerged surfaces including plants) can contribute more to the overall attenuation of light
than water depth (Sand-Jensen & Borum, 1984, Sand-Jensen, 1990, Beresford, 2002). As
algae are direct competitors for the light used in photosynthesis, they tend to contribute
disproportionately to light (particularly when measured as Photosythetically Active
Radiation) attenuation by periphyton. However, settled fine sediments can have a significant
impact on light attenuation, with the extent of attenuation dependent upon the concentration
and opacity of sediment particles. If the particles are translucent they can actually improve
the passage of light through periphyton by acting as a conduit through more optically dense,
particularly algal, parts of the layer (Losee & Wetzel, 1983). Nevertheless, any increased
attenuation due to a layer of deposited material will result in reduced photosynthesis and
growth of macrophytes.
Following ideas from lakes (Phillips, Eminson & Moss, 1978, Jones & Sayer, 2003), it has
been suggested that increased periphyton growth occurs with increased nutrient loading to
rivers, with subsequent impacts on the growth of macrophytes (Hilton et al., 2006). The
effect of shading by periphyton on the growth of river macrophytes has been shown (Köhler
et al., 2010), although the relationship between nutrients and periphyton is less clear (Jones &

Sayer, 2003, O'Hare et al., 2010). Nevertheless, to date there has been no attempt to
discriminate between the effects of increased shading as a consequence of deposited fine
sediment and those as a consequence of increased algal growth.
Aquatic macrophytes counter the build up of settled particulates and algal growth by the
growth of new surfaces. Despite incorrect assertions that periphyton has to reduce the light
available to the plants to below the compensation point (irradiance where gross
photosynthesis = respiration) to have an impact on macrophyte growth (O'Hare et al., 2010),
any reduction in the light below the saturation point (irradiance where any increase does not
result in increased photosynthesis) will have an impact (Sand-Jensen & Madsen, 1991). A
positive feedback will be entered, and plants excluded, when the reduction in photosynthesis
is sufficient to reduce growth such that the rate of periphyton accumulation (either by growth
or deposition) is faster than the production of new leaves. Whilst the production of new
leaves has obvious cost to the plant, the strategy can help fast growing plants keep ahead of
settling particles. Slower growing species are more vulnerable to being smothered by fine
sediment, particularly short stature, encrusting species such as mosses and liverworts, and
communities dominated by these groups (e.g. low nutrient upland streams) are likely to be
particularly sensitive to increased inputs of fine sediment. The abundance of mosses declined
markedly in river types where they had previously been a major component of the community
when fine sediment was experimentally added to rivers in New Zealand (Matthaei et al.,
2006). Similar effects are seen on attached algae (periphyton) growing on stones, and


although many species of diatom (i.e. Raphidae) are capable of migrating through layers of
deposited material (Eaton & Moss, 1966), deposition of fine sediment leads to a reduction in
periphyton standing stock (Cline, Short & Ward, 1982, Yamada & Nakamura, 2002) and
production (Van Nieuwenhuyse & LaPerriere, 1986, Parkhill & Gulliver, 2002).
The deposition of material on the leaves of macrophytes has an additional impact on
photosynthesis. The surfaces of the submerged parts of macrophytes are surrounded by a
viscous sub-layer where flow is laminar and parallel to the leaf surface (Leyton, 1975). This
viscous sub-layer is a major restriction on the diffusion of gasses into and out of the plant

(Black et al., 1981). Layers of periphytic algae have been shown to act as hydraulically
smooth surfaces where the measured thickness of the viscous sub-layer increases linearly
with the thickness of the periphyton attached to the leaf surface (Jones et al., 2000b). Thus,
any increase in the thickness of this layer due to the deposition of fine sediment on the plant’s
surfaces will increase the distance across which the dissolved gasses carbon dioxide and
oxygen must diffuse, considerably reducing the rate of photosynthesis (Black et al., 1981,
Jones, Eaton & Hardwick, 2000a).
Where rapid accretion of sediment occurs, large sections of plants can become buried, which
can result in total loss of macrophytes (Edwards, 1969, Brookes, 1986). Again rapid growth
can enable some species of macrophyte to cope with being smothered. The production of
adventitious roots, i.e. roots that arise from stem tissues, is a further advantage if stems
become buried. Fast growing, emergent species are particularly adept at coping with being
smothered; when road construction resulted in the rapid deposition of large quantities of
sediment in the river, Ranunculus penicillatus subsp. pseudofluitans could not cope with
being smothered whereas Rorippa nasturtium-aquaticum continued to grow through the
deposited material (Brookes, 1986). However, when deposition rates are high even rapidly
growing species cannot persist (Edwards, 1969, Brookes, 1986).
The effects of burial of macrophytes by deposits of fine sediment is not solely restricted to
growing shoots; the burial of seeds, turions, tubers and other reproductive propagules affects
their ability to establish. Different sensitivities to burial are apparent among taxa (Xiao et al.,
2010) and plant propagule type (e.g. seeds versus turions (Van Wijk, 1989)). Typically, larger
propagules are capable of establishing from a greater depth of sediment than smaller ones
(Van Wijk, 1988, Van Wijk, 1989), but other characteristics, such as a light requirement for
germination (Coble & Vance, 1987) or oxygen availability (Wu et al., 2009), may determine
the impact of sediment deposition on propagule establishment. The differences in the ability
to cope with smothering must in part explain the succession of species that occurs as
sediment accretes within stands of macrophytes (see above), but other changes, especially in
flow and light conditions, must also play a role.
Bed composition
Even where the deposition of fine sediment does not bury macrophytes, accretion of sediment

can alter the composition of the bed of the river (Barko et al., 1991). Hence, the medium into
which the plants are rooting changes in quality, with a number of inter-related consequences.


The deposition of fine sediment may reduce the grain size distribution of the bed, thereby
potentially increasing erodibility and the likelihood that plants will be uprooted during high
flow events. The extent of remobilisation is dependent on bed sediment quality (grain size,
dry weight or organic content), hydrodynamics (bed shear stress, velocity) and bed structure
(hiding effects). In the case of cohesive sediment, deposition history, dewatering, and
biological activity will also be important influences on sediment consolidation and surface
sealing (Krishnappan, 2007). However, the relative importance of these parameters is highly
variable and rates of sediment remobilisation are context specific (El Ganaoui et al., 2004).
At its most extreme whole banks of deposited sediment can be eroded together with whole
beds of associated macrophytes (Dawson, 1981). Whereas macrophytes tend to produce
extensive root networks in coarse grained sediments, either as a stronger holdfast or to
sequester the scarcer nutrients in such sediments, resulting in a reduced likelihood of
uprooting and a more stable sediment (Boeger, 1992), fine sediments tend to encourage
shallow rooting with the opposite effects. In part, such reduced rooting may be due to the
increased nutrient availability in fine sediments (Wang et al., 2009), but the reduced pore
size, and hence lower oxygen penetration by diffusion or mass flow (Pretty, Hildrew &
Trimmer, 2006), must also play a role. Furthermore, as deposited fine sediments tend to have
a high organic content, microbial activity results in further oxygen depletion, with a
consequent impact on root penetration and the stability of the plants growing on such
sediments; plants become increasingly prone to dislodging/uprooting. Whilst the growth of
sweet flag, Acorus calamus L., a species adapted to growing in highly anoxic soil, was
correlated with fertility, it was negatively correlated with organic content (Pai & McCarthy,
2005). As sediments accrete there is a tendency for those macrophyte species that produce
shallow, adventitious roots to be favoured, i.e. rapidly growing, rank species (Dawson et al.,
1978, Brookes, 1986, Clarke & Wharton, 2001) such as Potamogeton pectinatus L., Elodea
and related species, Sparganium spp. and Rorippa nasturtium-aquaticum. Where deposited

sediments are deep, anoxic and loose only emergent species with access to aerial oxygen, and
those that float above the accreting sediment, such as Glyceria fluitans (L.) R.Br. and
Glyceria maxima (Hartman) O.Holmb., are capable of persisting (Willby & Eaton, 1996). In
fast flowing upland streams, where the macrophyte flora is mainly confined to encrusting
mosses growing over the surface of stones, the accumulation of relatively nutrient rich, fine
sediment patches (often initiated by the presence of mosses) can lead to an increase in species
richness and area of the stream bed colonised by macrophytes.
Nutrient availability
Further changes occur as nutrients become more available in the rooting medium as
sediments accrete. Fine sediments tend to have high availability of biologically available
inorganic nutrients and organic matter (Stutter, Langan & Demars, 2007): as sediments
accrete so the rooting medium becomes more fertile. Furthermore, under the anaerobic
conditions that develop in deposited fine sediments microbial activity tends to mineralise
organic nutrients. Transformations and availability of sedimentary phosphorus are largely
controlled by the environmental conditions within and directly above the sediment, with pH
and redox potential (eH) of particular importance (Boström et al., 1988a, Boström, Persson &


Broberg, 1988b, Enell & Lofgren, 1988, Pettersson, Boström & Jacobsen, 1988). The main
phosphorus transformations in the top 20-30cm of freshwater sediments are related to the
decomposition of organic phosphorus and the subsequent adsorption of the orthophosphate
produced (Martinova, 1993). The behaviour of nitrogen within freshwater sediments is poorly
understood. However, it is clear that organic nitrogen can be mineralised under anoxic
conditions, and that the ammonia produced can be accessed by macrophytes. As conditions
within deposits of fine sediment do not favour nitrification (i.e. lack of oxygen) ammonia
may accumulate in these zones. This can be of great benefit to the plants: the nitrogen
recycled in the deposits of fine sediment accumulated within stands of Ranunculus
penicillatus ssp. pseudofluitans (Syme) S. Webster appears to be assimilated by the plants in
preference to sources of dissolved nitrogen in the river water (Trimmer, Sanders & Heppell,
2009). Where anoxic conditions occur with plentiful labile organic matter (a frequent

condition in deposited fine sediment) denitrification can result in a reduction of nitrate, with
potential release of nitric and nitrous oxide (Faafeng & Roseth, 1993, Trimmer et al., 2009).
The rate of denitrification is strongly correlated to the percentage carbon and nitrogen of the
sediments, and the percentage of particles less than 100µm (Garcia-Ruiz, Pattinson &
Whitton, 1998). The production of methane in deposits of fine sediment occurs also, and
much of this methane is vented to the atmosphere via aerenchyma (gas filled channels in the
plants connecting roots to shoots) in the macrophytes (Sanders et al., 2007). Similarly,
emergent (Dacey, 1980, Dacey & Klug, 1982, Dacey, 1987, Armstrong, Armstrong &
Beckett, 1992) and submerged (Sand-Jensen, Prahl & Stocholm, 1982, Caffrey & Kemp,
1991, Flessa, 1994) macrophytes can actively conduct oxygen via arenchyma to their roots by
a variety of mechanisms (e.g. Knudsen diffusion, Venturi convection, photosynthetic and
humidity pressurisation) where it is released to oxidise the surrounding sediment.
Such changes in nutrient availability in the sediment can lead to increased production by
macrophytes (Chambers & Kalff, 1985, Chambers & Prepas, 1990, Chambers et al., 1991,
Carr & Chambers, 1998, Sagova-Mareckova, Petrusek & Kvet, 2009). Although certain
elements (e.g. nitrogen) may be available in surplus in existing sediments (Carr & Chambers,
1998, Thomaz et al., 2007), increases in phosphorus availability in the sediment in particular
result in increased growth of macrophytes (Chambers et al., 1991, Carr & Chambers, 1998,
Heaney et al., 2001, Sagova-Mareckova et al., 2009). Again, increasing nutrient availability
encourages succession towards more rapidly growing, rank species (Barko et al., 1991,
Bornette et al., 2008). Initially this can lead to an increase in species richness if the unimpacted site was very poor in nutrients (Langlade & Décamps, 1995), but this soon turns to
a decline in richness as competitively dominant species are encouraged (Langlade &
Décamps, 1995, Assani, Petit & Leclercq, 2006, Bornette et al., 2008). The few experiments
that have been undertaken indicate competitive replacement under increased fertility
(Potamogeton pectinatus replaced Ranunculus penicillatus subsp. pseudofluitans under
increased water phosphorus (Spink et al., 1993); Hydrilla verticillata (L. f.) Royle over
Vallisneria americana Michx. with increased sediment fertility (Van, Wheeler & Center,
1999); competitive ability of Elodea nuttallii (Planch.) St. John and Myriophyllum spicatum
L. increased with increasing sediment fertility (Angelstein et al., 2009)). However, there is a
balance between the benefits of increasing nutrient availability in deposited fine sediments

and the costs of growing in an unstable, anoxic medium. Hence, dependent upon the nature of
the sediment that is deposited and changes that occur with accretion, the succession of
species growing on accreting sediment are likely to take different trajectories (Figure 3). As
species typical of low-nutrient substrates are slow-growing, in situations where the deposited
sediments are relatively inert (sands) there will be a tendency for loss of macrophytes. Where
macrophytes do occur on deposited inert sediments they will in turn tend to increase the
fertility and encourage further growth. Where deposits are more fertile the trajectory of
community change will depend largely on the stability of the deposited sediment. Deposits of
nutrient rich sediment (relative to the unaltered bed) are likely to lead to succession in the
macrophyte community towards faster-growing, competitively-dominant, usually taller rank
species typical of nutrient-rich environments (e.g. Potamogeton pectinatus, Elodea, Glyceria,
Rorippa, Sparganium). In fast flowing streams, areas of sediment accretion will suppress
slow growing moss species and encourage growths of moss and vascular plant species typical
of more nutrient-rich conditions. Where deposits are stable, fast growing, emergent species
(or emergent forms) will predominate and eventually terrestrial species will colonise if the
deposited material accretes to the water surface. Where the deposits are loose, unstable and
highly organic, the community will tend to lose macrophytes rooted directly into the
deposited sediment and move towards floating mats of vegetation (e.g. of Glyceria or
Rorippa) and, in the absence of flushing flows, sediment will eventually fill beneath floating
mats of vegetation and terrestrial species invade (Figure 3). Irrespective of the nature of the
deposited material, slow-growing and low-stature species typical of low-nutrient
environments, such as many species of moss, are likely to be lost where loads of fine
sediments are increased substantially.
The evidence available indicates that changes in the macrophyte community as a
consequence of enhanced deposition of fine sediment derived from human activities in the
catchment closely parallel those that are typically associated with increased dissolved nutrient
loads (i.e. reduced light penetration to the bed, loss of low-stature slow-growing species,
increases in competitively dominant rank species). Correct attribution of the cause of such

changes in the flora is vital if appropriate management decisions are to be based on such
evidence. Whilst there is often a high degree of commonality in the cause of increased
dissolved nutrient and fine sediment loads to river systems, they are frequently derived from
different sources and follow different delivery pathways through the catchment. Thus, there
are different implications for the management of the sources of these two different inputs. To
date, there is no method available to attribute any differences in the macrophyte flora to these
two potential causes. More evidence of the equivalent and separate impacts on macrophytes
of these two pressures, dissolved nutrients and fine sediments, is required to develop a
method that can discern between them.
Conclusion
Whilst there are several works describing the impact of macrophytes on the retention of
sediment and associated substances, there are relatively few describing the converse. This is a
fundamental gap in the knowledge of an important stressor of European rivers, which should
be addressed. Existing evidence, although limited, indicates that increased inputs of fine


sediment have both direct and indirect impacts on the macrophyte community in receiving
waters, altering light availability, and the structure and quality of the river bed. The nature of
these impacts depends largely on the rate of deposition of fine sediment and the nature of the
material deposited. Where deposition rates are high and deposited material largely inert and
unstable (sands) the impacts are obvious and plant loss a common feature, but where the
depositing material is more nutrient rich subtle changes in macrophyte community
composition may ensue. Many of the changes in macrophyte flora that occur with increased
fine sediment inputs are likely to parallel closely those that occur with increased dissolved
nutrient availability. This is important since it underscores the influence of sediment-bound
nutrients entering river systems in directing change in macrophyte communities. Since the
methods developed for assessing nutrient impacts on rivers are based on the presence and
cover of indicative species (Holmes et al., 1999), the impacts of increased fine sediment and
associated nutrient inputs have the potential to confound assessments of nutrient impact per
se and lead to false attribution of the causes of stress on the receptor. If attempts to manage

nutrient inputs to river basins are to successfully achieve their goal of improving ecological
status, it is critical that the impact of enhanced fine sediment loads is considered at the same
time. Biological impacts frequently result from multiple stressors acting on aquatic
ecosystems. The challenge is to continue unravelling the additive, synergistic and
antagonistic nature of the interplay between these multiple stressors.


Acknowledgements: The authors gratefully acknowledge the funding provided by the
Department for Environment, Food and Rural Affairs (contract WQ0128; Extending the
evidence base on the ecological impacts of fine sediment and developing a framework for
targeting mitigation of agricultural sediment losses). Thanks are extended to Patrick
Armitage, John Murphy, Kris Bal and an anonymous referee for comments on an earlier
draft.


References
Ackerman, J.D. & Okubo, A. (1993) Reduced mixing in a marine macrophyte canopy.
Functional Ecology, 7, 305-309.
Angelstein, S., Wolfram, C., Rahn, K., Kiwel, U., Frimel, S., Merbach, I. & Schubert, H.
(2009) The influence of different sediment nutrient contents on growth and
competition of Elodea nuttallii and Myriophyllum spicatum in nutrient-poor waters.
Fundamental and Applied Limnology, 175, 49-57.
Angermeier, P.L., Wheeler, A.P. & Rosenberger, A.E. (2004) A conceptual framework for
assessing impacts of roads on aquatic biota. Fisheries, 29, 19-29.
Armstrong, J., Armstrong, W. & Beckett, P.M. (1992) Phragmites australis: Venturi- and
humidity- induced pressure flows enhance rhizome aeration and rhizosphere
oxidation. New Phytologist, 120, 297-207.
Asaeda, T; Fujino, T; Manatunge, J. (2005) Morphological adaptations of emergent plants to
water flow: a case study with Typha angustifolia, Zizania latifolia and Phragmites
australis, Freshwater Biology, 50, 1991-2001.

Assani, A.A., Petit, F. & Leclercq, L. (2006) The relation between geomorphological features
and species richness in the low flow channel of the Warche, downstream from the
Butgenbach dam (Ardennes, Belgium). Aquatic Botany, 85, 112-120.
Bal, K. & Meire, P. (2009) The influence of macrophyte cutting on the hydraulic resistance of
lowland rivers. Journal of Aquatic Plant Management, 47, 65-68.
Barko, J.W., Gunnison, D. & Carpenter, S.R. (1991) Sediment interactions with submersed
macrophyte growth and community dynamics. Aquatic Botany, 41, 41-65.
Barko, J.W. & James, W.F. (1998) Effects of submerged aquatic macrophytes on nutrient
dynamics, sedimentation, and resuspension. In: The Structuring Role of Submerged
Macrophytes in Lakes. (Eds E. Jeppesen & M. Søndergaard & M. Søndergaard & K.
Christophersen), pp. 197-214. Springer-Verlag, New York.
Bass, J.A.B., Wharton, G. & Cotton, J.A. (2005 ) Flow disturbance by in-stream
macrophytes: a hot-wire anemometry and scaffold system for measuring fine-scale
velocity patterns and mapping sediment deposits and habitat structures Materials and
Geoenvironment, 52, 189.
Beresford, A.L. (2002) The dynamics of plant-associated invertebrate and periphyton
communities in lakes. PhD, Queen Mary, University of London.
Bilotta, G.S. & Brazier, R.E. (2008) Understanding the influence of suspended solids on
water quality and aquatic biota. Water Research, 42, 2849-2861.
Black, M.A., Maberly, S.C. & Spence, D.H.N. (1981) Resistances to carbon dioxide in four
submerged freshwater macrophytes. New Phytologist, 89, 557-568.
Boeger, R.T. (1992) Influence of substratum and water velocity on growth of Ranunculus
aquatilis L. (Ranunculaceae). Aquatic Botany, 42, 351-360.
Bornette, G., Tabacchi, E., Hupp, C., Puijalon, S. & Rostan, J. C. (2008) A model of plant
strategies in fluvial hydrosystems. Freshwater Biology, 53, 1692-1705
Boström, B., Andersen, J.M., Fleischer, S. & Jansson, M. (1988a) Exchange of phosphorus
across the sediment - water interface. Hydrobiologia, 170, 229-244.
Boström, B., Persson, G. & Broberg, B. (1988b) Bioavailability of different phosphorus
forms in fresh-water systems. Hydrobiologia, 170, 133-155.
Bouma, T.J., Friedrichs, M., van Wesenbeeck, B. K., Temmerman, S, Graf, G. & Herman, P.

M. J. (2009) Density-dependent linkage of scale-dependent feedbacks: a flume study
on the intertidal macrophyte Spartina anglica. Oikos, 118, 260-268


Brookes, A. (1986) Response of aquatic vegetation to sedimentation downstream from river
channelization works in England and Wales. Biological Conservation, 38, 351-367.
Caffrey, J.M. & Kemp, W.M. (1991) Seasonal and spatial patterns of oxygen production,
respiration and root-rhizome release in Potamogeton perfoliatus L. and Zostera
marina L. Aquatic Botany, 40, 109-128.
Carr, G.M. & Chambers, P.A. (1998) Macrophyte growth and sediment phosphorus and
nitrogen in a Canadian prairie river. Freshwater Biology, 39, 525-536.
Chambers, P.A. & Kalff, J. (1985) The influence of sediment composition and irradiance on
the growth and morphology of Myriophyllum spicatum L. Aquatic Botany, 22, 253263.
Chambers, P.A. & Prepas, E.E. (1990) Competition and coexistence in submerged aquatic
plant communities: The effects of species interactions versus abiotic factors.
Freshwater Biology, 23, 541-550.
Chambers, P.A., Prepas, E.E., Hamilton, H.R. & Bothwell, M.L. (1991) Current velocity and
its effect on aquatic macrophytes in flowing waters. Ecological Applications, 1, 249257.
Champion, P.D. & Tanner, C.C. (2000) Seasonality of macrophytes and interaction with flow
in a New Zealand lowland stream. Hydrobiologia, 441, 1-12.
Clarke, S.J. (2002) Vegetation growth in rivers: influences upon sediment and nutrient
dynamics. Progress in Physical Geography, 26, 159-172.
Clarke, S.J. & Wharton, G. (2001) Sediment nutrient characteristics and aquatic macrophytes
in lowland English rivers. Science of the Total Environment, 266, 103-112.
Cline, L.D., Short, R.A. & Ward, J.V. (1982) The influence of highway construction on the
macroinvertebrates and epilithic algae of a high mountain stream. Hydrobiologia, 96,
149-159.
Coble, T.A. & Vance, B.D. (1987) Seed germination in Myriophyllum spicatum L. . Journal
of Aquatic Plant Management, 25, 8-10.
Collins, A.L. & Walling, D.E. (2007) Sources of fine sediment recovered from the channel

bed of lowland groundwater-fed catchments in the UK. Geomorphology, 88, 120-138.
Corenblit, D., Steiger, J., Gurnell, A.M. & Naiman, R.J. (2009) Plants intertwine fluvial
landform dynamics with ecological succession and natural selection: a niche
construction perspective for riparian systems. Global Ecology and Biogeography, 18,
507-520.
Corenblit, D., Tabacchi, E., Steiger, J. & Gurnell, A.M. (2007) Reciprocal interactions and
adjustments between fluvial landforms and vegetation dynamics in river corridors: A
review of complementary approaches. Earth-Science Reviews, 84, 56-86.
Cotton, J.A., Wharton, G., Bass, J.A.B., Heppell, C.M. & Wotton, R.S. (2006) The effects of
seasonal changes to in-stream vegetation cover on patterns of flow and accumulation
of sediment. Geomorphology, 77, 320-334.
Dacey, J.H.W. (1980) Internal winds in water lilies: an adaptation for life in anaerobic
sediments. Science, 210, 1017-1019.
Dacey, J.H.W. (1987) Knudsen-transitional flow and gas pressurization in leaves of Nelumbo.
Plant Physiology, 85, 199-203.
Dacey, J.H.W. & Klug, M.J. (1982) Ventilation by floating leaves in Nuphar. American
Journal of Botany, 69, 999-1003.
Davies, P.E. & Nelson, M. (1993) The effect of steep slope logging on fine sediment
infiltration into the beds of ephemeral and perennial streams of the dazzler range,
Tasmania, Australia. Journal of Hydrology, 150, 481-504.


Dawson, F.H. (1978) The seasonal effects of aquatic plant growth on the flow of water in a
stream. In: Proceedings of the European Weed Research Society Fifth Symposium on
Aquatic Weeds. pp. 71-78, Amsterdam.
Dawson, F.H. (1981) The downstream transport of fine material and the organic-matter
balance for a section of a small chalk stream in Southern England. Journal of
Ecology, 69, 367-380.
Dawson, F.H., Castellano, E. & Ladle, M. (1978) The concept of species succession in
relation to river vegetation and management. . Verhandlungen der internationalen

Vereinigung für Limnologie, 20, 1429-1434.
Delbecque, E.J.P. (1983) A comparison of the periphyton of Nuphar lutea and Nymphaea
alba. The distribution of diatoms on the underside of floating leaves. In: Periphyton
of freshwater ecosystems. (Ed R.G.Wetzel), pp. 41-47. Dr. W. Junk Publishers, The
Hague.
Eaton, J.W. & Moss, B. (1966) The estimation of numbers and pigment content in epipelic
algal populations. Limnology and Oceanography, 11, 584-595.
Edwards, D. (1969) Some effects of siltation upon aquatic macrophyte vegetation in rivers.
Hydrobiologia, 34, 29-37.
El Ganaoui, O., Schaaff, E., Boyer, P., Amielh, M., Anselmet, F. & Grenz, C. (2004) The
deposition and erosion of cohesive sediments determined by a multi-class model.
Estuarine Coastal and Shelf Science, 60, 457-475.
Enell, M. & Lofgren, S. (1988) Phosphorus in interstitial water - methods and dynamics.
Hydrobiologia, 170, 103-132.
Faafeng, B.A. & Roseth, R. (1993) Retention of nitrogen in small streams artificially polluted
with nitrate. Hydrobiologia, 251, 113-122.
Flessa, H. (1994) Plant-induced changes in the redox potential of the rhizospheres of the
submerged vascular macrophytes Myriophyllum verticillatum L and Ranunculus
circinatus L. Aquatic Botany, 47, 119-129.
Gambi, M.C., Nowell, A.R.M. & Jumars, P.A. (1990) Flume observations on flow dynamics
in Zostera marina (eelgrass) beds. Marine Ecology-Progress Series, 61, 159-169.
Garcia-Ruiz, R., Pattinson, S.N. & Whitton, B.A. (1998) Denitrification in river sediments:
relationship between process rate and properties of water and sediment. Freshwater
Biology, 39, 467-476.
Ghisalberti, M. & Nepf, H. (2006) The structure of the shear layer in flows over rigid and
flexible canopies. Environmental Fluid Mechanics, 6, 277-301.
Ghisalberti, M. & Nepf, H. (2009) Shallow Flows Over a Permeable Medium: The
Hydrodynamics of Submerged Aquatic Canopies. Transport in Porous Media, 78,
385-402.
Green, J.C. (2005a) Comparison of blockage factors in modelling the resistance of channels

containing submerged macrophytes. River Research and Applications, 21, 671-686.
Green, J.C. (2005b) Further comment on drag and reconfiguration of macrophytes.
Freshwater Biology, 50, 2162-2166.
Green, J.C. (2005c) Modelling flow resistance in vegetated streams: review and development
of new theory. Hydrological Processes, 19, 1245-1259.
Green, J.C. (2005d) Velocity and turbulence distribution around lotic macrophytes. Aquatic
Ecology, 39, 1-10.
Green, J.C. (2006) Effect of macrophyte spatial variability on channel resistance. Advances
in Water Resources, 29, 426-438.
Gurnell, A.M., Blackall, T.D. & Petts, G.E. (2008) Characteristics of freshly deposited sand
and finer sediments along an island-braided, gravel-bed river: The roles of water,
wind and trees. Geomorphology, 99, 254-269.


Gurnell, A.M. & Midgley, P. (1994) Aquatic weed growth and flow resistance - influence on
the relationship between discharge and stage over a 25 year river gauging station
record. Hydrological Processes, 8, 63-73.
Gurnell, A.M., Van Oosterhout, M.P., De Vlieger, B. & Goodson, J.M. (2006) Reach-scale
interactions between aquatic plants and physical habitat: River Frome, Dorset. River
Research and Applications, 22, 667-680.
Haslam, S.M. (1978) River Plants. The macrophytic vegetation of water courses., Cambridge
University Press, Cambridge.
Heaney, S.I., Foy, R.H., Kennedy, G.J.A., Crozier, W.W. & O'connor, W.C.K. (2001) Impacts
of agriculture on aquatic systems: lessons learnt and new unknowns in Northern
Ireland. Marine and Freshwater Research, 52, 151-163.
Heppell, C.M., Wharton, G., Cotton, J.A.C., Bass, J.A.B. & Roberts, S.E. (2009) Sediment
storage in the shallow hyporheic of lowland vegetated river reaches. Hydrological
Processes, 23, 2239-2251.
Hilton, J., O'hare, M., Bowes, M.J. & Jones, J.I. (2006) How green is my river? A new
paradigm of eutrophication in rivers. Science of the Total Environment, 365, 66-83.

Hogg, I.D. & Norris, R.H. (1991) Effects of runoff from land clearing and urbandevelopment on the distribution and abundance of macroinvertebrates in pool areas of
a river. Australian Journal of Marine and Freshwater Research, 42, 507-518.
Holmes, N., Newman, J., Chadd, S., Rouen, K., Saint, L. & Dawson, F. (1999) Mean Trophic
Rank: A User ’s Manual. R&D Technical Report. E38. Environment Agency, Bristol.
Jackson, G.A. & Winant, C.D. (1983) Effect of a kelp forest on coastal currents. Continental
Shelf Research, 2, 75-80.
James, W.F., Barko, J.W. & Butler, M.G. (2004) Shear stress and sediment resuspension in
relation to submersed macrophyte biomass. Hydrobiologia, 515, 181-191.
Jones, J.I., Eaton, J.W. & Hardwick, K. (2000a) The effect of changing environmental
variables in the surrounding water on the physiology of Elodea nuttallii. Aquatic
Botany, 66, 115-129.
Jones, J.I., Eaton, J.W. & Hardwick, K. (2000b) The influence of periphyton on boundary
layer pH conditions: a microelectrode investigation. Aquatic Botany, 67, 191-206.
Jones, J.I. & Sayer, C.D. (2003) Does the fish–invertebrate–periphyton cascade precipitates
plant loss in shallow lakes? Ecology, 84, 2155-2167.
Jones, K.L., Poole, G.C., Woessner, W.W., Vitale, M.V., Boer, B.R., O'Daniel, S.J., Thomas,
S.A. & Geffen, B.A. (2008) Geomorphology, hydrology, and aquatic vegetation drive
seasonal hyporheic flow patterns across a gravel-dominated floodplain. Hydrological
Processes, 22, 2105-2113.
Kleeberg, A., Köhler, J., Sukhodolova, T. & Sukhodolov, A. (2009) Effects of aquatic
macrophytes on organic matter deposition, resuspension and phosphorus entrainment
in a lowland river. Freshwater Biology, 55, 326-345.
Köhler, J., Hachoł, J. & Hilt, S. (2010) Regulation of submersed macrophyte biomass in a
temperate lowland river: Interactions between shading by bank vegetation, epiphyton
and water turbidity. Aquatic Botany, 92, 129–136.
Langlade, L.-R. & Décamps, O. (1995) Accumulation de limon et colonisation végétale d’un
banc de galets. Comptes Rendu del l'Académie des Sciences Paris, Sciences de la vie,
317, 1073-1082.
Laperriere, J.D., Bjerklie, D.M., Simmons, R.C., Van Nieuwenhuyse, E., Wagener, S.M. &
Reynolds, J.B. (1983) Effects of gold placer mining on interior Alaska stream

ecosystems. In: Managing water resources for Alaska's development. (Ed J.W.
Aldrich), pp. University of Alaska, Institute of Water Resources Report IWR-105
Fairbanks, Alaska.


Leyton, L. (1975) Fluid behaviour in biological systems., Clarendon Press, Oxford.
Lloyd, D.S., Koenings, J.P. & Laperriere, J.D. (1987) Effects of turbidity in fresh waters of
Alaska. North American Journal of Fisheries Management, 7, 34-45.
Losee, R.F. & Wetzel, R.G. (1983) Selective light attenuation by the periphyton complex. In:
Periphyton of freshwater ecosystems. (Ed R.G.Wetzel), pp. 89-96. Dr. W. Junk
Publishers, the Hague.
Losee, R.F. & Wetzel, R.G. (1988) Water movement within submersed littoral vegetation.
Verhandlungen der internationalen Vereinigung für Limnologie, 23, 62-66.
Losee, R.F. & Wetzel, R.G. (1993) Littoral flow rates within and around submersed
macrophyte communities. Freshwater Biology, 29, 7-17.
Luhar, M., Rominger, J. & Nepf, H. (2008) Interaction between flow, transport and vegetation
spatial structure. Environmental Fluid Mechanics, 8, 423-439.
Madsen, T.V. & Warncke, E. (1983) Velocities of currents around and within submerged
aquatic vegetation. Archiv für Hydrobiologie, 97, 389-394.
Martinova, M.V. (1993) Nitrogen and phosphor compounds in bottom sediments mechanisms of accumulation, transformation and release. Hydrobiologia, 252, 1-22.
Matthaei, C.D., Weller, F., Kelly, D.W. & Townsend, C.R. (2006) Impacts of fine sediment
addition to tussock, pasture, dairy and deer farming streams in New Zealand.
Freshwater Biology, 51, 2154-2172.
Naden, P., Rameshwaran, P., Mountford, O. & Robertson, C. (2006) The influence of
macrophyte growth, typical of eutrophic conditions, on river flow velocities and
turbulence production. Hydrological Processes, 20, 3915-3938.
Nepf, H., Ghisalberti, M., White, B. & Murphy, E. (2007) Retention time and dispersion
associated with submerged aquatic canopies. Water Resources Research, 43.
O'Hare, M.T., Clarke, R.T., Bowes, M.J., Cailes, C., Henville, P., Bissett, N., Mcgahey, C. &
Neale, M. (2010) Eutrophication impacts on a river macrophyte. Aquatic Botany, 92,

173-178.
O'Hare, M.T., Hutchinson, K.A. & Clarke, R.T. (2007) The drag and reconfiguration
experienced by five macrophytes from a lowland river. Aquatic Botany, 86, 253-259.
Owens, P.N., Batalla, R.J., Collins, A.J., Gomez, B., Hicks, D.M., Horowitz, A.J., Kondolf,
G.M., Marden, M., Page, M.J., Peacock, D.H., Petticrew, E.L., Salomons, W. &
Trustrum, N.A. (2005) Fine-grained sediment in river systems: Environmental
significance and management issues. River Research and Applications, 21, 693-717.
Pai, A. & McCarthy, B.C. (2005) Variation in shoot density and rhizome biomass of Acorus
calamus L. with respect to environment. Castanea, 70, 263-275.
Pain, S. (1987) After the gold rush. New Scientist, 115, 36-40.
Palmer, M.R., Nepf, H.M., Pettersson, T.J.R. & Ackerman, J.D. (2004) Observations of
particle capture on a cylindrical collector: Implications for particle accumulation and
removal in aquatic systems. Limnology and Oceanography, 49, 76-85.
Patil, S. & Singh, V.P. (2010) Characteristics of Monami Wave in Submerged Vegetated
Flow. Journal of Hydrologic Engineering, 15, 171-181.
Parkhill, K.L. & Gulliver, J.S. (2002) Effect of inorganic sediment on whole-stream
productivity. Hydrobiologia, 472, 5-17.
Peralta, G., Van Duren, L.A., Morris, E.P. & Bouma, T.J. (2008) Consequences of shoot
density and stiffness for ecosystem engineering by benthic macrophytes in flow
dominated areas: a hydrodynamic flume study. Marine Ecology-Progress Series, 368,
103-115.
Pettersson, K., Boström, B. & Jacobsen, O.S. (1988) Phosphorus in sediments - speciation
and analysis. Hydrobiologia, 170, 91-101.


Phillips, G.L., Eminson, D. & Moss, B. (1978) A mechanism to account for macrophyte
decline in progressively eutrophicated freshwaters. Aquatic Botany, 4, 103-126.
Pretty, J.L., Hildrew, A.G. & Trimmer, M. (2006) Nutrient dynamics in relation to surfacesubsurface hydrological exchange in a groundwater fed chalk stream. Journal of
Hydrology, 330, 84-100.
Puijalon, S. & Bornette, G. (2006) Phenotypic plasticity and mechanical stress: biomass

partitioning and clonal growth of an aquatic plant species. American Journal of
Botany, 93, 1090-1099.
Puijalon, S.; Bouma, T.J.; Van Groenendael, J.. & Bornette, G. (2008) Clonal plasticity of
aquatic plant species submitted to mechanical stress: escape versus Resistance
strategy. Annals of Botany, 102, 989-996.
Reise, K.; Bouma, T.J.; Olenin, S. & Ysebaert T. (2009) Coastal habitat engineers and the
biodiversity in marine sediments. Helgoland Marine Research, 63, 1-2.
Riis, T., Suren, A.M., Clausen, B. & Sand-Jensen, K. (2008) Vegetation and flow regime in
lowland streams. Freshwater Biology, 53, 1531-1543.
Rivier, B. & Seguier, J. (1985) Physical and biological effects of gravel extraction in river
beds. In: Habitat modification and freshwater fisheries. (Ed J.S. Alabaster).
Butterworth, London.
Sagova-Mareckova, M., Petrusek, A. & Kvet, J. (2009) Biomass production and nutrient
accumulation in Sparganium emersum Rehm. after sediment treatment with mineral
and organic fertilisers in three mesocosm experiments. Aquatic Ecology, 43, 903-913.
Sand-Jensen, K. (1990) Epiphyte shading: its role in resulting depth distribution of
submerged aquatic macrophytes. Folia Geobotanica et Phytotaxonomica, 25, 315320.
Sand-Jensen, K. (1997) Macrophytes as biological engineers in the ecology of Danish
streams. In: Freshwater Biology. Priorities and Development in Danish Research.
(Eds K. Sand-Jensen & O. Pedersen), pp. 74-101. G.E.C. Gad, Copenhagen,
Denmark.
Sand-Jensen, K. (1998) Influence of submerged macrophytes on sediment composition and
near-bed flow in lowland streams. Freshwater Biology, 39, 663-679.
Sand-Jensen, K. (2003) Drag and reconfiguration of freshwater macrophytes. Freshwater
Biology, 48, 271-283.
Sand-Jensen, K. (2008) Drag forces on common plant species in temperate streams:
consequences of morphology, velocity and biomass. Hydrobiologia, 610, 307-319.
Sand-Jensen, K. & Borum, J. (1984) Epiphyte shading and its effect on photosynthesis and
metabolism of Lobelia dortmanna L. during the spring bloom in a Danish lake.
Aquatic Botany, 20, 109-119.

Sand-Jensen, K., Jeppesen, E., Nielsen, K., Van Der Bijl, L., Hjermind, L., Nielsen, L.W. &
Iversen, T.M. (1989) Growth of macrophytes and ecosystem consequences in a
lowland danish stream. Freshwater Biology, 22, 15-32.
Sand-Jensen, K. & Madsen, T.V. (1991) Minimum light requirements of submerged
freshwater macrophytes in laboratory growth experiments. Journal of Ecology, 79,
749-764.
Sand-Jensen, K. & Madsen, T.V. (1992) Patch dynamics of the stream macrophyte
Callitriche cophocarpa. Freshwater Biology, 27, 277-282.
Sand-Jensen, K. & Mebus, J.R. (1996) Fine-scale patterns of water velocity within
macrophyte patches in streams. Oikos, 76, 169-180.
Sand-Jensen, K. & Pedersen, M.L. (2008) Streamlining of plant patches in streams.
Freshwater Biology, 53, 714-726.


Sand-Jensen, K. & Pedersen, O. (1999) Velocity gradients and turbulence around macrophyte
stands in streams. Freshwater Biology, 42, 315-328.
Sand-Jensen, K., Prahl, C. & Stocholm, M. (1982) Oxygen release from roots of submerged
aquatic macrophytes. Oikos, 38, 349-354.
Sanders, I.A., Heppell, C.M., Cotton, J.A., Wharton, G., Hildrew, A.G., Flowers, E.J. &
Trimmer, M. (2007) Emission of methane from chalk streams has potential
implications for agricultural practices. Freshwater Biology, 52, 1176-1186.
Schoelynck, J., Bal, K., Backx, H., Okruszko, T., Meire, P., & Struyf, E. (2010) Silica uptake
in aquatic and wetland macrophytes: a strategic choice between silica, lignin and
cellulose? New Phytologist 186, 385-391.
Schulz, M., Kozerski, H.P., Pluntke, T. & Rinke, K. (2003) The influence of macrophytes on
sedimentation and nutrient retention in the lower River Spree (Germany). Water
Research, 37, 569-578.
Sculthorpe, C.D. (1985) The biology of aquatic vascular plants., Koeltz Scientific Books,
Königstein, Germany.
Sear, D.A., Millington, C.E., Kitts, D.R. & Jeffries, R. (2010) Logjam controls on

channel:floodplain interactions in wooded catchments and their role in the formation
of multichannel patterns. Geomorphology, 116, 305-319.
Spence, D.H.N. & Crystal, J. (1970a) Photosynthesis and zonation of freshwater macrophytes
I. Depth distribution and shade tolerance. New Phytologist, 69, 205-215.
Spence, D.H.N. & Crystal, J. (1970b) Photosynthesis and zonation of freshwater macrophytes
II. Adaptability of species of deep and shallow water. New Phytologist, 69, 217-227.
Spink, A.J., Murphy, K.J., Smith, S.M. & Westlake, D.F. (1993) Effects of eutrophication on
Ranunculus and Potamogeton. Journal of Aquatic Plant Management, 31, 113-117.
Stutter, M.I., Langan, S.J. & Demars, B.O.L. (2007) River sediments provide a link between
catchment pressures and ecological status in a mixed land use Scottish River system.
Water Research, 41, 2803-2815.
Svendsen, L.M. & Kronvang, B. (1993) Retention of nitrogen and phosphorus in a Danish
lowland river system: implications for the export from the watershed. Hydrobiologia,
251, 123-135.
Thomaz, S.M., Chambers, P.A., Pierini, S.A. & Pereira, G. (2007) Effects of phosphorus and
nitrogen amendments on the growth of Egeria najas. Aquatic Botany, 86, 191-196.
Trimmer, M., Sanders, I.A. & Heppell, C.M. (2009) Carbon and nitrogen cycling in a
vegetated lowland chalk river impacted by sediment. Hydrological Processes, 23,
2225-2238.
Turnpenny, A.W.H. & Williams, R. (1980) Effects of sedimentation on the gravels of an
industrial river system. Journal of Fish Biology, 17, 681-603.
Van, T.K., Wheeler, G.S. & Center, T.D. (1999) Competition between Hydrilla verticillata and
Vallisneria americana as influenced by soil fertility. Aquatic Botany, 63, 225-233.
van der Heide, T., Bouma, T.J., van Nes, E.H., van de Koppel, J., Scheffer, M., Roelofs,
J.G.M., van Katwijk, M.M. & Smolders, A.J.P. (2010) Spatial self-organized
patterning in seagrasses along a depth gradient of an intertidal ecosystem. Ecology,
91, 362-369.
Van Nieuwenhuyse, E. & Laperriere, J.D. (1986) Effects of placer gold mining on primary
production in subarctic streams of Alaska. Water Resources Bulletin, 22, 91-99.
Van Wijk, R.J. (1988) Ecological studies on Potamogeton-pectinatus L I. General

characteristics biomass production and life cycles under field conditions. Aquatic
Botany, 31, 211-258.
Van Wijk, R.J. (1989) Ecological studies on Potamogeton pectinatus L. III. Reproductive
strategies and germination ecology. Aquatic Botany, 33, 271-300.


Vermaat, J.E. & De Bruyne, R.J. (1993) Factors limiting the distribution of submerged
waterplants in the lowland River Vecht (the N.L.). Freshwater Biology, 30, 147-157.
Vermaat, J.E. & Hootsmans, M.J.M. (1991) Periphyton dynamics in a temperature-light
gradient. In: Macrophytes, a key to understanding changes caused by eutrophication
in shallow freshwater ecosystems. (Eds M.J.M. Hootsmans & J.E. Vermaat), pp. 157187. International Institute for Hydraulic and Environmental Engineering, Delft.
Vermaat, J.E., Santamaria, L. & Roos, P.J. (2000) Water flow across and sediment trapping in
submerged macrophyte beds of contrasting growth form. Archiv für Hydrobiologie,
148, 549-562.
Wang, S.R., Jin, X.C., Jiao, L.X. & Wu, F.C. (2009) Response in root morphology and
nutrient contents of Myriophyllum spicatum to sediment type. Ecological
Engineering, 35, 1264-1270.
Waters, T.F. (1995) Sediment in streams: sources, biological effects, and control., American
Fisheries Society Monograph 7, Bethesda, Maryland.
Welton, J.S. (1980) Dynamics of sediment and organic detritus in a small chalk stream.
Archiv für Hydrobiologie, 90, 162-181.
Wharton, G., Cotton, J.A., Wotton, R.S., Bass, J.A.B., Heppell, C.M., Trimmer, M., Sanders,
I.A. & Warren, L.L. (2006) Macrophytes and suspension-feeding invertebrates modify
flows and fine sediments in the Frome and Piddle catchments, Dorset (UK). Journal
of Hydrology, 330, 171-184.
Willby, N.J. & Eaton, J.W. (1996) Backwater habitats and their role in nature conservation on
navigable waterways. Hydrobiologia, 340, 333-338.
Wood, P.J. & Armitage, P.D. (1997) Biological effects of fine sediment in the lotic
environment. Environ. Manage., 21, 203-217.
Wood, P.J. & Armitage, P.D. (1999) Sediment deposition in a small lowland stream Management implications. Regulated Rivers-Research & Management, 15, 199-210.

Wu, J., Cheng, S.P., Liang, W., He, F. & Wu, Z.B. (2009) Effects of sediment anoxia and light
on turion germination and early growth of Potamogeton crispus. Hydrobiologia, 628,
111-119.
Xiao, C., Wang, X., Xia, J. & Liu, G. (2010) The effect of temperature, water level and burial
depth on seed germination of Myriophyllum spicatum and Potamogeton malaianus.
Aquatic Botany, 92, 28-32.
Yamada, H. & Nakamura, F. (2002) Effect of fine sediment deposition and channel works on
periphyton biomass in the Makomanai River, northern Japan. River Research and
Applications, 18, 481-493.


Table 1. Rates of sediment accretion measured in stands of macrophytes.
Macrophyte species

Density

Ranunculus penicillatus subsp. pseudofluitans
Ranunculus penicillatus subsp. pseudofluitans
Ranunculus penicillatus subsp. pseudofluitans

69-826 g DW m

Rate of accumulation
-2

-2

-1

Ref

20-50 % cover

3.1 g m h
0.0075 - 0.088 m3 m-2 annum-1
11.6 - 66.8 kg m-2 annum-1

1
2
3

Ranunculus penicillatus subsp. pseudofluitans
Rorippa nasturtium-aquaticum
Ranunculus penicillatus subsp. pseudofluitans
Callitriche stagnalis
Rorippa nasturtium-aquaticum
Ranunculus peltatus

20-60% cover

0.9 – 23.5 kg m-2 annum-1

3

variable

0.12-1.43 g DW m-2 h-1

4
5

Chara aspera
Alisma gramineum

28 ± 15 g AFDW m-2
125 ± 15 g AFDW m-2

25–45 g N m–2 annum-1
20–30 g P m–2 annum-1
1.08 +/- 0.13 g DW m-2 h-1
3.21 +/- 0.21 g DW m-2 h-1

1 = (Trimmer et al., 2009)
2 = (Wharton et al., 2006)
3 = (Heppell et al., 2009)
4 = (Welton, 1980)
5 = (Svendsen & Kronvang, 1993)
6 = (Vermaat, Santamaria & Roos, 2000)

6
6