OCEANOGRAPHIC PROCESSES OF CORAL REEFS: Physical and Biological Links in the Great Barrier Reef - Chapter 3 docx

Landcover and Water
Quality in River
Catchments of the Great
Barrier Reef Marine Park
Andrew K.L. Johnson, Robert G.V. Bramley,
and Christian H. Roth
CONTENTS
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Methods and Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
The Herbert River Catchment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Landcover. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Surface Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Contemporary Broadscale Landcover Change
in GBRMP Catchments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Landcover Change in the Herbert River Catchment . . . . . . . . . . . . . . . . . . . . 26
Water Quality in the Herbert River Catchment . . . . . . . . . . . . . . . . . . . . . . . . 27
Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
INTRODUCTION
The Great Barrier Reef Marine Park (GBRMP) covers an area of approximately
350,000 km
2
and spans almost 2,000 km of the east coast of Queensland, Australia.
The GBRMP is a marine ecosystem that is recognised internationally for its unique
biological and physical features. Fifteen river catchments, covering an area of
approximately 375,000 km
2
, drain directly into the GBRMP (Figure 1). Land use in

these catchments is dominated in areal terms by grazing. Cropping, particularly sugar-
cane production, is a major user of land resources in a number of catchments and is
predominantly located on fertile coastal floodplains immediately adjacent to
GBRMP waters (Table 1).
3
19
© 2001 by CRC Press LLC
20 Oceanographic Processes of Coral Reefs
TABLE 1
Approximate Area of Major Land Uses in Catchments Adjoining the GBRMP
1996
Catchment Catchment Percentage of Catchment Area
Name Area (km
2
) Forest
a
Pristine
b
Grazing
c
Crops Urban
NE Cape
d
43,300 4.3 33.9 61.7 0.05 0.05
Daintree 2,130 37.7 31.7 26.7 1.9 2.0
Mossman 490 30.4 11.0 44.6 10.1 3.9
Barron 2,180 36.4 2.0 47.7 6.8 6.9
Mulgrave Russell 2,020 16.9 25.1 38.9 13.3 5.8
Johnstone 2,330 25.3 12.8 41.6 15.9 4.4
Tully 1,690 62.5 2.1 20.7 11.1 3.7

Murray 1,140 32.9 27.3 29.6 7.0 3.3
Herbert 10,130 9.5 9.7 71.1 7.0 2.7
Black 1,080 18.0 9.3 67.4 1.1 4.2
Haughton 3,650 0.8 10.8 74.0 10.9 3.5
Burdekin 129,860 1.0 1.3 94.8 1.0 2.0
Don 3,890 0.2 2.6 91.3 2.8 3.1
Proserpine 2,490 9.6 4.0 74.6 7.5 4.3
O’Connell 2,440 7.6 4.4 70.5 11.1 6.5
Pioneer 1,490 22.7 6.1 48.5 17.9 4.7
Shoalwater Bay-Sarina
e
11,270 1.3 41.6
f
44.1 10.3 2.7
Fitzroy 152,640 6.7 2.3 87.5 3.3 0.2
Curtis Coast
g
9,225 12.2 11.3 68.9 0.57 6.7
Total area 369,480 28,007 39,830 284,056 13,597 3,990
Total (%) 7.6 10.8 76.9 3.7 1.1
a
Comprises state forests and timber reserves.
b
Comprises national parks and other reserves.
c
Comprises unimproved and improved pastures.
d
Comprises Jacky Jacky Creek, Olive-Pascoe, Lockhart, Stewart, Jeannie, Normanby, and Endeavour
catchments.
e

Comprises Plane Creek, Styx, Shoalwater Creek, and Water Park Creek catchments.
f
Approximately 65% of this area occupied by the Shoalwater Bay Field Training Area of the Australian
Defence Forces.
g
Comprises Calliope, Boyne, and Baffle Creek catchments.
Source: QDPI, 1993; EPA, 1999; Johnson et al., 1999.
Current environmental trends suggest a decline in coastal terrestrial and riverine
systems, and on the adjacent GBRMP marine environment (Anonymous, 1993;
Arthington et al., 1997). The vegetation of many of the river catchments adjoining the
GBRMP has been extensively cleared (Russell & Hales, 1996) since the mid-19th
century. Freshwater wetlands and riparian forests once covered large areas of coastal
floodplains which are now used for agriculture (Tait, 1994; Johnson et al., 1999).
© 2001 by CRC Press LLC
Landcover and Water Quality in River Catchments 21
Prior to clearing, these wetlands would have provided extensive buffer strips and
freshwater habitats adjacent to coastal river systems, estuaries, and shorelines.
Clearing, notably for sugarcane cultivation, has left only remnants of these ecosys-
tems (Russell et al., 1996). Present-day wetlands and riparian forests in many catch-
ments are frequently narrow and sparsely vegetated and have been invaded by exotic
weeds (Johns et al., 1997). It is likely those wetlands and riparian forests in such poor
condition have suffered a corresponding degradation of their intrinsic ecological val-
ues (Arthington et al., 1997).
The status of freshwater wetlands and riparian forests in river catchments adja-
cent to the GBRMP has been reviewed superficially by a number of authors
(Arthington & Hegerl, 1988; Anonymous, 1993; Blackman et al., 1996). Accounts
have increasingly confirmed their very high biological richness, diversity, geograph-
ical extent, importance as habitat for a similarly rich and diverse biota, and funda-
mental role in ensuring the health of key GBRMP ecosystems. Of the 19 Queensland
wetlands identified as having national importance (Blackman et al., 1996), 8 are

located in areas immediately adjacent to or within the GBRMP. While the present sta-
tus of these ecosystems is known, there have been no detailed assessments of histor-
ical changes in coastal wetlands and riparian forests in GBRMP catchments.
Similarly, while the current extent of landcover in river catchments adjoining the
GBRMP is generally known, the spatial and temporal distribution of landcover since
European settlement is poorly understood.
The aim of this chapter is to describe broad-scale changes in landcover in
GBRMP catchments and to examine in detail changes that have occurred using a case
study undertaken in the lower Herbert River catchment. We also describe the likely
impact that these changes have had on the water quality of the Herbert River. While
the focus of the chapter is not on the impacts of these changes per se, we discuss sig-
nificant issues that are central to the maintenance and function of estuarine and
marine ecosystems in the GBRMP.
METHODS AND MATERIALS
THE HERBERT RIVER CATCHMENT
The Herbert River catchment drains an area of approximately 10,000 km
2
to the Coral
Sea and is the largest of the river systems located in Australia’s sub-humid to humid
tropical northeast (latitude 15 to 19°S, longitude 145 to 146°E) (Figure 2). Average
annual rainfall is approximately 2500 mm. Mean annual runoff for the catchment is
4991 ϫ 10
9
m
3
or 493 mm, and the rainfall-to-runoff ratio approximately 37%
(Hausler, 1991).
Natural vegetation consists predominantly of open Eucalyptus and Melaleuca
woodlands, with areas of open grassy plains and dense Melaleuca wetlands.
Rainforest patterns occur on the creek and river levees and on some of the northern

ranges. Large areas of the upper catchment remain under natural vegetation, although
much of the lower catchment has been cleared for crop production or exotic pas-
tures. Agricultural and pastoral activities are the largest users of land (in area) in the
© 2001 by CRC Press LLC
22 Oceanographic Processes of Coral Reefs
catchment. The catchment has a population of approximately 18,000 (1993 Census),
of which 75% are located in the lower catchment.
LANDCOVER
A desktop study was conducted to collect data from a range of published and unpub-
lished sources on landcover in catchments adjoining the GBRMP. This activity drew
heavily on work undertaken by the Queensland Statewide Landcover and Tree Study
(SLATS) (QDNR, 1999a and 1999b). The study utilised Landsat Thematic Mapper
(TM) imagery (spatial accuracy Ϯ30 m) and ground surveys to map changes in
woody vegetation cover (where woody vegetation was defined as approximately 12%
foliage projective cover or greater) between 1988, 1991, 1995, and 1997.
The study attempted to map vegetation change for all perennial woody plants
of sizes that could be distinguished by Landsat TM imagery. Accuracy of areal
interpretation for the whole state was reported as Ϯ8% at a 95% confidence interval.
Error data associated with misclassification were not reported, although incidences
of misclassification in areas of pasture and in highly fragmented landscapes (e.g.,
narrow riparian zones in coastal areas) were acknowledged. Anecdotal evidence from
field-workers also suggests the existence of substantive misclassification in grazing
lands (A. Ash, personal communication). QDNR (1999a and 1999b) describes the
method used in more detail.
Landcover in the Herbert River catchment was visually interpreted from scanned
and rectified 1:25,000 aerial photography acquired in 1943, 1961, 1970, 1977, 1988,
and 1992 (spatial accuracy Ϯ7 m) and 1:10,000 digital orthophotography acquired in
1993, 1994, and 1995 (spatial accuracy Ϯ1 m). An unsupervised classification of
SPOT Panchromatic and MSS imagery was used to map landcover in 1996 (spatial
accuracy Ϯ10 m).

Landcover boundaries were mapped onto a geo-referenced digital base (spatial
accuracy Ϯ10 m) in ARCINFO GIS. The classification methodology (Johnson et al.,
1999 and 2000) drew heavily on previous vegetation (Tracey, 1982; Blackman et al.,
1992; Perry, 1995) and soil (Wilson & Baker, 1990) surveys in the region. Validation
of mapping units and mapped boundaries was conducted in 1996 by vehicle and foot
traverses. Approximately 150 sites were visited. Classification of units and bound-
aries not inspected in 1996 was undertaken by extrapolation from equivalent photo-
graphic units.
In addition to mapping observed landcover, an estimate of landcover prior to
European settlement (circa 1860s) in the Herbert was developed from a simple rule
base that related remaining stands of native vegetation and the known distribution of
soils, topography, relief, hydrology, and rainfall. A time series was developed to elu-
cidate spatial and temporal change in landcover (Johnson et al., 1999).
SURFACE WATER QUALITY
A number of sites were selected to reflect the major landcover classes, soil types
(Wilson & Baker, 1990; Wood, 1984, 1985, and 1988), and sub-catchments in the
lower Herbert floodplain (Figure 3) on the basis that water sampled at any given site
reflected the biophysical characteristics of the land upstream of that site.
© 2001 by CRC Press LLC
Landcover and Water Quality in River Catchments 23
Beginning in October 1992, surface grab samples of river water were taken at
each of these sites at monthly intervals and also in response to rainfall events of inten-
sity greater than 50 mm d
Ϫ1
. The samples were collected either by lowering a bucket
from a bridge at a point above the centre of the flowing part of the channel, or more
directly by wading into the stream. The samples were collected in acid-washed poly-
ethylene bottles and were stored in a portable refrigerator for transfer back to the lab-
oratory. On each sampling occasion, the distance between the surface of the water
and a fixed arbitrary point such as a bridge rail was also measured for later estima-

tion of actual water depth and then discharge.
The laboratory procedures used in this study have been detailed by Muller et al.
(1995). Total concentrations of nitrogen (N) and phosphorus (P) were determined
according to USEPA (1984) methodology. Total suspended solids (TSS) were deter-
mined by gravimetric measurement of the amount of particulate material retained on
0.45 ␮m cellulose acetate filter papers.
For the analysis of land use impact on water quality, the landcover classification
(Figure 3) was simplified into land under sugarcane, grazing (i.e., improved grazing
or Eucalyptus-dominated patterns), and forestry (i.e., plantation forestry or natural
rainforest). This was done to simplify the attribution of water quality differences,
given that for the majority of sites, several land uses exist upstream of those sites (i.e.,
water quality measurements made at a particular site may integrate the effects of
more than one landcover class). This simplification of landcover categories is also
consistent with the results of Hunter and Walton (1997), who found that in the
Johnstone catchment, whilst it was possible to discriminate between the effects of
intensive and non-intensive land uses on water quality, it was not possible to dis-
criminate within these broad groupings.
For the purposes of the present study, time of sampling was treated as an inde-
pendent variable because although several authors (e.g., Hunter et al., 1996 and ref-
erences therein; Mitchell et al., 1996 and 1997) have demonstrated the strong
seasonality of riverine discharge and water quality in north Queensland rivers and
their links to the strongly seasonal climate, our purpose here was to examine the
effects of landcover on water quality.
RESULTS
CONTEMPORARY BROADSCALE LANDCOVER CHANGE
IN
GBRMP CATCHMENTS
Tables 2 and 3 show contemporary woody vegetation changes in GBRMP catchments
for the period 1991 to 1997. They show:
• Large areas of woody vegetation converted to pasture in the Fitzroy,

Burdekin, Normanby, Don, Proserpine, and Baffle Creek catchments,
implying a change from extensive grazing woodlands to more intensive
forms of grazing on improved pastures
• Large areas converted to crops in the Herbert, Murray, Haughton, Plane
Creek, and Fitzroy catchments
© 2001 by CRC Press LLC
24 Oceanographic Processes of Coral Reefs
TABLE 2
Rates of Change from Woody Vegetation to Other Landcover Classes in
GBRMP Catchments 1991–1995
Rate of Woody Vegetation Change (km
2
yr
Ϫ1
)
Catchment Catchment New %
Name Area (km
2
) Regrowth
a
Pasture
b
Crops
c
Forest
d
Urban
e
Total Area
Jardine 3,288 0.1 0.07 0 0 0 0.07 0.002

Jacky Jacky Creek 2,916 0 0 0 0 0 0 0
Olive-Pascoe 4,199 0 0 0 0 0 0 0
Lockhart 2,847 0 0 0 0 0 0 0
Stewart 2,694 0 0 0 0 0 0 0
Jeannie 3,886 0.02 0 0 0 0 0 0
Normanby 24,319 0.07 4.74 5.93 0 0.23 10.91 0.045
Endeavour 2,063 0.07 0 0.15 0 0.14 0.29 0.014
Daintree 2,130 0.01 0.13 0.12 0 0 0.26 0.012
Mossman 490 0.03 0 0.01 0 0.05 0.07 0.014
Barron 2,180 1.61 0.4 1.42 0.14 0.15 2.1 0.096
Mulgrave-Russell 2,020 0.04 0.05 0.73 0.03 0.12 0.94 0.047
Johnstone 2,330 0 0.4 1.21 0.03 0.02 1.65 0.071
Herbert 10,130 0.54 1.35 18.55 2.65 0.33 22.88 0.226
Tully 1,690 0 0.03 0.85 0 0.05 0.93 0.055
Murray 1,140 1.15 0 7.66 0.08 0.06 7.79 0.683
Burdekin 129,860 5.15 5.29 0.4 0 1.16 6.85 0.005
Black 1,080 0.53 0.22 0.94 0 0.22 1.38 0.128
Ross 1,346 0.75 0.43 0 0 0.61 1.04 0.077
Haughton 3,650 6.37 1.9 3.31 0 1.06 6.28 0.172
Don 3,890 2.68 3.42 0.05 0 0.12 3.59 0.092
Proserpine 2,490 3.03 2.85 0.35 0 0.09 3.29 0.132
O’Connell 2,440 0.55 2.31 0.22 0.11 0.06 2.69 0.110
Pioneer 1,490 0 0.21 0.03 0 0 0.24 0.016
Plane Creek 2,547 1.32 2.67 4.97 0.1 0.11 7.85 0.308
Styx 3,018 0.59 3.85 0 0 0.09 3.93 0.130
Shoalwater Creek 3,698 0.71 1.19 0 0 0.07 1.26 0.034
Water Park Creek 1,756 1.18 0.72 0.42 1.1 0.2 2.44 0.139
Fitzroy 152,640 25.07 17.34 0.5 0.01 0.45 18.28 0.012
Calliope 2,204 0.11 0.59 0 0 0.68 1.28 0.058
Boyne 2,473 0.02 0.72 0 0 0.35 1.07 0.043

Baffle Creek 4,106 1.14 1.55 0.93 0.01 1.33 3.82 0.093
Total 369,480 52.84 52.43 48.75 4.26 7.75 113.18 0.069
a
New regrowth is defined as areas which have changed from non-woody to woody within the period.
b
Areas cleared to pasture. Includes clearing for grazing, rural residential, future urban land use, native
forestry on private land, privately owned plantations cleared to pasture.
c
Cleared for growing crops.
d
State forest clearing including plantation and native forest. Includes cleared private plantations that are
replanted.
e
Cleared for mining, infrastructure, and urban development.
Source: QDNR, 1999a.
© 2001 by CRC Press LLC
Landcover and Water Quality in River Catchments 25
TABLE 3
Rate of Change from Woody Vegetation to Other Landcover Classes in
GBRMP Catchments 1995–1997
Rate of Woody Vegetation Change (km
2
yr
Ϫ1
)
Catchment Catchment New %
Name Area (km
2
) Regrowth
a

Pasture
b
Crops
c
Forest
d
Urban
e
Total Area
Jardine 3,288 0 0.02 0 0 0.11 0.13 0.004
Jacky Jacky Creek 2,916 0 0 0 0 0.01 0.01 0.000
Olive-Pascoe 4,199 0 0 0 0 0 0 0.000
Lockhart 2,847 0 0 0 0 0.04 0.04 0.001
Stewart 2,694 0 0 0 0 0 0 0.000
Jeannie 3,886 0 0 1.6 0 0.34 1.93 0.050
Normanby 24,319 0 0.14 0 0 0.63 0.77 0.003
Endeavour 2,063 0.04 0.16 4.4 0.01 0.38 4.94 0.239
Daintree 2,130 0 0.09 0.17 0.07 0 0.34 0.016
Mossman 490 0 0.03 0.07 0.01 0.13 0.24 0.049
Barron 2,180 0.05 1.22 5.69 0.3 0.53 7.74 0.355
Mulgrave-Russell 2,020 0.05 0.1 0.11 0 0.23 0.44 0.022
Johnston 2,330 0.05 0.71 0.85 0.01 0.01 1.57 0.067
Herbert 10,130 7.54 2.92 7.59 0.23 0.92 11.66 0.115
Tully 1,690 0.09 0 1.41 0.01 0.12 1.54 0.091
Murray 1,140 1.63 0.45 3.4 0.22 0.08 4.15 0.364
Burdekin 129,860 5.57 14.72 1.24 0 2.92 18.88 0.015
Black 1,080 1.8 1.6 1.73 0.03 0.27 3.62 0.335
Ross 1,346 0.65 1.24 0.02 0 1.37 2.63 0.195
Haughton 3,650 2.93 0.72 10.81 0 0.51 12.04 0.330
Don 3,890 2.39 1.39 1.19 0 0.26 2.84 0.073

Proserpine 2,490 1.5 3.56 10.27 0 0.16 13.99 0.562
O’Connell 2,440 0.49 1.13 2.84 0 0.1 4.06 0.166
Pioneer 1,490 0 1.36 0.92 0.02 2.76 5.07 0.340
Plane Creek 2,547 0.53 0.58 19.58 0.01 0.18 20.34 0.799
Styx 3,018 1.14 5.39 0.91 0 0.12 6.43 0.213
Shoalwater Creek 3,698 0.79 1.47 0.04 0 0.24 1.73 0.047
Water Park Creek 1,756 0.26 1.06 0.4 1.06 0.82 3.34 0.190
Fitzroy 152,640 0.69 17.28 4.05 0.18 0.31 21.83 0.014
Calliope 2,204 0.03 0.93 0.01 0.05 0.33 1.32 0.060
Boyne 2,473 0.02 0.37 0 0 0.1 0.47 0.019
Baffle Creek 4,106 1.03 7.43 1.03 0.09 2.5 11.06 0.269
Total 369,480 29.27 66.07 80.33 2.3 16.48 165.15 0.102
a
New regrow this defined as areas which have changed from non-woody to woody within the period.
b
Areas cleared to pasture. Includes clearing for grazing, rural residential, future urban land use, native
forestry on private land, privately owned plantations cleared to pasture.
c
Cleared for growing crops.
d
State forest clearing including plantation and native forest. Includes cleared private plantations that are
replanted.
e
Cleared for mining, infrastructure, and urban development.
Source: QDNR, 1999b.
© 2001 by CRC Press LLC
26 Oceanographic Processes of Coral Reefs
• Large areas of woody regrowth occurring in the Fitzroy, Burdekin, and
Herbert catchments
• Small areas converted to urban and forest uses in all catchments

These tables show that in terms of the total catchment area delivering to the
GBRMP, the current rate of woody vegetation change is small. They indicate, how-
ever, that the rate of change from woody vegetation to agriculture remains high in a
number of catchments. In the smaller coastal catchments it is reasonable to expect that
these changes are most likely to be occurring on the fertile coastal floodplains imme-
diately adjacent to the GBRMP. In contrast to the bigger basins, in particular the
Fitzroy and the Burdekin, substantial conversion of woody vegetation to more inten-
sive agricultural use is taking place in the interior of these basins (e.g., Brigalow Belt).
The SLATS data presented here should be interpreted with caution. First, it is
important to point out that substantial areas of woody vegetation (e.g., the Brigalow
Belt in the Fitzroy and Burdekin basins) have been cleared prior to the last decade, so
that current rates do not adequately reflect the absolute change in land use. Moreover,
in some instances the SLATS methodology has not always been able to correctly clas-
sify vegetation or landcover classes. An example of this occurs in the Normanby
catchment where large areas have been misclassified as regrowth and cleared for
crops (see EPA, 1999; Johnson et al., 1999).
Photointerpretation of chronosequences of aerial photos coupled with spatial
analysis in GIS and underpinned by adequate ground truthing is a more reliable
means of assessing landcover change, but is both an expensive and time-consuming
methodology, restricting it to more detailed analysis in selected case studies. In the
section that follows we describe in detail the changes that have occurred in the catch-
ment of the Herbert River using such a case study approach.
LANDCOVER CHANGE IN THE HERBERT RIVER CATCHMENT
Landcover in the lower Herbert has changed substantially since European settlement
in the 1860s. Johnson and Ebert (2000) describe changes in the catchment as a whole
and show that since European settlement, approximately 7.5% of the total catchment
area has been converted from native vegetation to other landcover types (95% con-
verted to agriculture). It is likely that landcover in the middle catchment has remained
unchanged due to its inaccessibility and more recent (post-1950) status as a national
park. Landcover in the upper catchment has also remained virtually unchanged over

the last 140 years, with only small areas (i.e.,Ͻ1%) being converted to mining, agri-
culture, and urban uses. However, the increase in grazing pressure and change in fire
regimes experienced since European settlement have caused a marked structural
change in plant communities in the upper catchment and shifted the balance between
shrub and herbaceous layers (Johnson et al., 2000).
Johnson et al. (1999 and 2000) focussed on changes in the lower Herbert (i.e.,
the area immediately adjacent to the GBRMP) and showed that significant changes
in landcover have occurred in this part of the catchment (Figures 4 and 5). It can be
seen that prior to settlement, the area was dominated by open grassland, rainforest
© 2001 by CRC Press LLC
Landcover and Water Quality in River Catchments 27
patterns, mangrove patterns, Eucalypt woodlands, and Melaleuca communities.
However, by the 1940s large losses of rainforest patterns and Melaleuca-dominated
patterns had occurred and much of the native grassland had been converted either to
grazing or sugarcane. Landcover remained relatively stable throughout the 1960s and
early 1970s. However, the period between 1977 and 1996 saw a rapid expansion in
the area under sugarcane.
The consequences of this expansion have resulted in a decrease of approximately
65% in the area of Melaleuca-dominated patterns (comprising a 43% decrease
between 1943 and 1996), a 60% decrease in the area of beachside vegetation, a 20%
decrease in the area of Eucalypt woodland, and a 10% decrease in the areas of rain-
forest patterns when compared to pre-European estimates. In contrast, the area of
mangrove communities and open water has remained relatively stable since 1943,
while the area of sugarcane has more than tripled between 1943 and 1996. As
expected, the area of urban and industrial landcover has increased since European
settlement, although the total area alienated is small within the context of total catch-
ment area (i.e., Ͻ0.5%).
WATER QUALITY IN THE HERBERT RIVER CATCHMENT
Water quality, as expressed by median concentrations of TSS, significantly decreases
in the lower Herbert catchment as the proportion of upstream land area under sugar-

cane increases (Figure 6a). In contrast, as the proportion of upstream land area under
grazing increases, median concentrations of TSS tend to be significantly lower; a
similar but non-significant effect is observed for forestry. These results remain essen-
tially unchanged irrespective of whether sampling sites which reflect the very large
areas in the upper part of the Herbert catchment under grazing are included (Figure
6a) or excluded (Figure 6b) from the analysis, and also when other indices of water
quality (e.g., fractions of N and P) are used, as concentrations of TSS and total N and
total P are intercorrelated (Figure 7).
The use of median concentrations as an indicator of water quality does not reflect
the highly variable fluctuations of TSS and nutrients as the result of major rain events
(Mitchell et al., 1996 and 1997), but rather can be assumed to better characterise
the longer-term trends of low flow or base flow concentrations (i.e., a measure of
“chronic” impact levels). Benthic faunas in tropical freshwater systems seem to be
adapted to short-term “peaks” in key water quality parameters given the naturally
high variations of flow, so assessing “chronic” changes in the levels of nutrient con-
centrations may be a more meaningful method for assessing land use impacts on
water quality in tropical systems (R. Pearson, personal communication). In the
absence of robust discharge data for most of the sites sampled as part of the Herbert
study, a more simplistic approach for assessing the likely contribution of the major
forms of landcover in the Herbert toward sediment and nutrient discharge was used.
All sites were grouped into three classes of landcover: sugarcane, grazing
(Eucalyptus dominated patterns ϩ improved pastures), and forestry (plantation
forestry ϩ natural rainforest), depending on which of these three land uses was pre-
dominant upstream of any one sampling point. The threshold criterion to discriminate
© 2001 by CRC Press LLC
28 Oceanographic Processes of Coral Reefs
between relative dominance of any land use was Ͼ45%, with relative dominance in
many cases Ͼ60%. Water quality parameters (TSS, total N and P) were then plotted
as box plots. Numbers of samples analysed ranged from n ϭ 160 to 262, n ϭ 110 to
177, and n ϭ 104 to 185 for TSS, total N, and total P, respectively.

As evidenced in Figure 8, sugarcane as a predominant land use clearly yields a
significantly greater variation in concentrations of TSS, total N and P compared to
grazing and forestry, with maximum values measured in high flow (i.e., 0.9 per-
centile) — an order of magnitude or more than low flow values (i.e., 0.1 percentile).
There is also a clear tendency for a greater variation and generally higher values
of water quality parameters under grazing when compared to forestry. The data
collected as part of this water quality study have been summarised by Bramley and
Muller (1999).
DISCUSSION
The extent and nature of vegetation clearance can provide a useful indicator of envi-
ronmental quality in GBRMP catchments, particularly given the significant link to
water quality demonstrated above. As well as providing a direct indicator of the
impact of agricultural and pastoral development on native vegetation, vegetation
clearance can also act as an indicator of general ecosystem disturbance. Studies such
as the ones reported in this chapter can assist decision-makers in assessing resource
condition and addressing the broader requirements of natural resource policy devel-
opment and planning.
The evidence presented in this chapter clearly demonstrates a reduction in the
area of native vegetation in GBRMP catchments. It also quantifies a substantial
reduction in the area of native vegetation in the lower Herbert River catchment over
the last 50 years. The trends observed on the Herbert River floodplain are not unique.
For example, in the Johnstone River catchment, the area of coastal wetlands has
decreased by approximately 60% since 1951 (Russell & Hales, 1996). The most sig-
nificant losses have been of freshwater wetlands, particularly Melaleuca communi-
ties. Melaleuca forests, notably those to the south of the Johnstone estuary, have been
reduced by approximately 78%. There have also been significant reductions in other
wetland categories, including a 64% reduction in palm- and pandanus-dominated
wetlands and a 55% reduction in freshwater reed swamps. Freshwater wetlands to the
north and west of the confluence of the North and South Johnstone Rivers have also
almost entirely disappeared during this period. In contrast, the area of mangrove pat-

terns has remained almost stable. Of the riparian forests assessed, 72% were in poor
or very poor condition (Russell & Hales, 1996).
Similar phenomena are manifest in the lower Burdekin, lower Pioneer, Fitzroy,
Boyne, Mulgrave-Russell, Barron, Mossman, and Daintree River catchments
(Congdon & Lukacs, 1995). In the Tully and Murray River catchments, less than 20%
of coastal land systems suitable for agricultural production remains under native veg-
etation (Tait, 1994). River catchments north of the Daintree River and in the
Shoalwater and Styx catchments have, in comparison, remained largely undisturbed
either as a result of their isolation or status as a national park (Johnson et al., 1997).
© 2001 by CRC Press LLC
Landcover and Water Quality in River Catchments 29
The importance of peak wet season events to the annual riverine export of nutri-
ents and sediments from the Herbert River has previously been identified (Hunter et
al., 1996 and references therein; Mitchell et al., 1996 and 1997). Bramley and
Johnson (1996) have also highlighted the fact that the concentration of nutrients in
streams draining land under cane tend to be greater than in streams draining other
land uses, but otherwise fall within acceptable levels (ANZECC, 1992), except dur-
ing peak wet season events. The analysis presented here reinforces the role of land
under sugarcane as a source of material for downstream export, particularly with
respect to the “chronic” nature of increased concentrations of sediments and nutri-
ents. However, whilst sugarcane as a land use is apparently the dominant source of
sediment and nutrient in the lower Herbert, it is unclear whether this is coming from
the cane paddocks themselves, or from the banks of the numerous man-made surface
drains which dissect the cane-growing part of the catchment (Prove & Hicks, 1991).
Recent data from Ripple Creek sub-catchment in the Lower Herbert suggest that
plant cane paddocks and farm drains are the greatest sources of sediments, whilst
concentrations of TSS from ratooned paddocks are generally in the same order of
magnitude as in samples taken from adjacent forested streams (F. Visser, personal
communication). This implies that the introduction of green trash blanket harvesting
(GCTB) has had a major beneficial effect in reducing sediment and nutrient discharge

from cane land. As such, the Herbert dataset probably reflects a greatly improved sit-
uation, as samples were collected in a period where most of the cane land in the
Lower Herbert was already under GCTB.
When this study began in 1992, there was a strong public perception that any
environmental degradation affecting the Great Barrier Reef was attributable to the
sugar industry, and specifically that the export of nutrients and sediments from sug-
arcane lands was damaging the world heritage status of the reef (Yellowlees, 1991
and references therein). More recently, the role of the grazing industry has received
attention as a sediment source since grazing is the dominant land use upstream of the
coastal floodplains of many of Queensland’s rivers. Further, overgrazing in many
areas has left soils bare and thus generated a large source of potential suspended
riverine sediment. Some commentators have even questioned the significance of sug-
arcane lands to riverine sediment exports (Crossland et al., 1997). The present results
do not support the view that grazing lands are important sources of sediment on a
unit-area basis. Indeed, they indicate that land under sugarcane and, by implication,
changes in landcover, which involve clearing of trees, have a detrimental impact on
water quality. However, on a catchment basis, given the significantly greater propor-
tion of grazing (even with a significantly lower unit area sediment and nutrient export
rate), it is evident that grazing is likely to be the principle overall contributor of sed-
iment and possibly nutrients to the GBRMP.
It is also clear that unless a change in current land use policy, planning, and man-
agement occurs, then the area of freshwater wetland and riparian forest ecosystems
in many of the catchments adjacent to the GBRMP will be reduced to a very low
level. It is likely that many areas of remnant freshwater wetlands and riverine rain-
forest vegetation are already less than is required to perform as an effective and func-
tional biological unit. While we have made no attempt to evaluate the ecological
status of remaining riparian and wetland areas, a recent ecological audit of river
© 2001 by CRC Press LLC
30 Oceanographic Processes of Coral Reefs
catchments in Queensland (Moller, 1996) has shown that the ecological condition of

remaining riparian vegetation in most developed catchments is “poor” to “very poor”
and the condition of freshwater wetlands “moderate” to “poor.” This is of particular
concern as it further reduces the natural capacity of wetlands to mitigate deteriorated
water quality resultant from land use change. Exceptions occur in catchments that
have suffered little disturbance (e.g., Shoalwater, Styx, NE Cape).
The losses of coastal freshwater wetlands and riparian forests observed in the lower
Herbert and in other catchments adjoining the GBRMP are equivalent to, or exceed,
losses in other parts of Australia. For example, in Victoria, one third of wetlands have
been destroyed, including half the area of non-permanent freshwater wetlands (SEAC,
1996). Some 70% of wetlands on the Swan Coastal Plain, Western Australia have been
lost since European settlement in the early part of the 19th century. Similar trends can
be observed in Southeast Asia where reported losses are as high as 50% in Malaysia,
Thailand, and southern China (UNEP, 1998). What separates the Northeast Australian
experience from the rest of the country, large areas of Southeast Asia, and most of
Europe and the U.S.A., is that such a large proportion of these losses have occurred in
the last 50 years and particularly in the last 20 years. In Europe and the U.S.A., signif-
icant wetland and riparian zone restoration programs were operational 20 years ago, a
time when large-scale losses were occurring in Australia.
Current legislative protection for the environment within the GBRMP predomi-
nantly applies to ecosystems within the park boundaries. There is very little scope for
direct management of adjoining areas such as coastal freshwater wetlands and ripar-
ian forests, even though fundamental linkages between these ecosystems and marine
environments are known. Furthermore, there is an absence of quantitative informa-
tion on the actual impact of landcover change on freshwater or marine ecosystems,
even in heavily studied catchments like the Herbert and Johnstone, and this, together
with the fact that different ecosystems are known to have different capacities to
assimilate change (ANZECC, 1992), mitigates against the introduction of direct
management strategies that are acceptable to all stakeholders. Current attempts by the
Queensland government to address this deficiency through coastal planning have
been unsuccessful. In response, policy, planning, and management reforms are

required if remaining coastal ecosystems adjoining the GBRMP are to be protected
or maintained. However, their efficacy is likely to be substantively reduced in the
absence of quantitative information on the ecological impact of landcover change. In
the meantime, it is of course incumbent on the individual landholder to manage his
land in such a way that the risk of offsite and downstream impacts is minimised. For
example, with respect to sugarcane production, Wood et al. (1996) have suggested
improvements to fertiliser management.
CONCLUSIONS
In this chapter we have demonstrated that concerns relating to the conversion of veg-
etation and particularly the decline in riparian and wetland resources in catchments
adjacent to the GBRMP are justified and require further attention. Given that agri-
cultural industries in these areas are operating in the context of an ever-increasing
© 2001 by CRC Press LLC
Landcover and Water Quality in River Catchments 31
community expectation for the preservation of native vegetation (particularly ripar-
ian and wetland areas), conflict over the use of these resources is likely to grow in the
future. On the basis of the Herbert case study, the changes in land use are clearly
affecting water quality and sediment and nutrient discharge to the GBRMP. In assess-
ing the relative importance of the different sources of sediment and nutrient dis-
charge, it is important to differentiate between the unit area contributions and the
absolute export on a catchment basis.
We have demonstrated that the magnitude of the tasks facing policymakers and
resource managers in catchments adjacent to the GBRMP, in terms of the way in
which they manage riparian and wetland areas in the future, remains substantial. The
challenge facing government is to provide a stable environment in which locally rel-
evant decision-making can occur and which is supported with appropriate and viable
monitoring, cost-sharing, and regulatory arrangements. In addition, agricultural
industries, in particular, need to develop their own policies and activities to guide
their future developments within a wider context, and in so doing contribute to a
reversal in the rapid historical decline of vegetation resources, particularly riparian

and wetland ecosystems adjacent, the GBRMP, as well as further minimising the cur-
rent levels of sediment and nutrient export.
ACKNOWLEDGMENTS
This work was supported in part by funding from the Sugar Research and
Development Corporation, the Land and Water Resources Research and
Development Corporation, the CRC for Sustainable Sugar Production, and the
CSIRO Divisions of Tropical Agriculture and Land and Water under the aegis of the
CSIRO Coastal Zone Program. The assistance of the many CSIRO technical staff
members who contributed to the Herbert part of this program is greatly appreciated.
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34 Oceanographic Processes of Coral Reefs
FIGURE 2 Location of the Herbert River catchment.
FIGURE 3 Map of lower Herbert showing the location
of surface water sampling sites: (a) surface hydrology
and subcatchment boundaries and (b) 1992 landcover.
FIGURE 4 Changes in the area of four key landcover
types in the lower Herbert River catchment since
European settlement. The bars for each time period are
from left to right: Eucalyptus-dominated patterns,
Melaleuca-dominated patterns, rainforest patterns, and
sugarcane. (Source: Johnson, A.K.L., Ebert, S.P., &
Murray, A.E. 2000
Australian Geographer 26, 75–86.
Reproduced by permission of Taylor & Francis, Inc.,
.)

FIGURE 1 Location of river catchments draining into
the GBRMP.
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Landcover and Water Quality in River Catchments 35
FIGURE 5 Changes in area of other landcover types in
the lower Herbert River catchment since European set-
tlement. The bars for each time period are from left to
right: beachside vegetation, cleared-unused, open grass-
land, mangrove patterns, other agriculture, open water,
regrowth-degraded vegetation, residential and industrial.
(Source: Johnson, A.K.L., Ebert, S.P., & Murray, A.E.
2000
Australian Geographer 75–86. Reproduced by
permission of Taylor & Francis, Inc.)
FIGURE 6 Land use impacts on median sediment load-
ings in the lower Herbert River. The effects of time of
sampling were ignored for this analysis which is pre-
sented (a) for all sampling sites (Figure 3) and (b) for
sites at which stream order is 5 or less. Numbers in fig-
ures refer to sampling points shown in Figure 3.
FIGURE 7 Correlations between riverine suspended
solids and total nitrogen and phosphorus during a 3-
year water quality monitoring program undertaken in
the lower Herbert River catchment, commencing in
1992. Numbers in figures refer to sampling points
shown in Figure 3. Dotted lines indicate the 95% con-
fidence intervals for the regressions.
FIGURE 8 Relationship between land use and water
quality parameters: (a) total suspended solids; (b) total
N; (c) total P in the Lower Herbert. Lowest values 0.1

percentile, second lowest 0.25 percentile, bar
ϭ median,
second highest value 0.75 percentile, and highest value
0.9 percentile, for each box plot, respectively.
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