AQUATIC EFFECTS OF ACIDIC DEPOSITION - CHAPTER 12 (END) doc

309

Definitions

Acid anion

—Negatively charged ion that does not react with hydro-
gen ion in the pH range of most natural waters.

Acid–base chemistry

—The reaction of acids (proton donors) with
bases (proton acceptors). In the context of this book, this means the
reactions of natural and anthropogenic acids and bases, the result
of which is described in terms of

pH

and

acid neutralizing capacity

of the system.

Acid cation

—Hydrogen ion or metal ion that can hydrolyze water to
produce hydrogen ions, for example, ionic forms of aluminum,
manganese, and iron.

Acid mine drainage

—Runoff with high concentrations of metals
and sulfate and high levels of acidity resulting from the oxidation
of sulfide minerals that have been exposed to air and water by
mining activities.

Acid neutralizing capacity (ANC)

—The equivalent capacity of a
solution to neutralize strong acids. The components of ANC include
weak bases (carbonate species, dissociated organic acids, alumino-
hydroxides, borates, and silicates) and strong bases (primarily,
OH

-

). In the National Surface Water Survey, as well as in most
other recent studies of acid–base chemistry of surface waters, ANC
was measured by the Gran titration procedure.

Acidic deposition

—Transfer of acids and acidifying compounds from
the atmosphere to terrestrial and aquatic environments via rain,
snow, sleet, hail, cloud droplets, particles, and gas exchange.

Acidic episode

—An

episode

in a water body in which

acidification

of surface water to an

acid neutralizing capacity

less than or equal
to zero occurs.

Acidic lake or stream

—A lake or stream in which the

acid neutral-
izing capacity

is less than or equal to zero.

Acidification

—The decrease of

acid neutralizing capacity

in water

or

base saturation

in soil caused by natural or anthropogenic
processes. Paleolimnologists use this term to specify diatom-in-
ferred decrease in pH, because ANC is not often reconstructed
using diatoms.

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310

Aquatic Effects of Acidic Deposition

Acidified

—Pertaining to a natural water that has experienced a de-
crease in

acid neutralizing capacity

or a soil that has experienced
a reduction in

base saturation

.

Acidophilic

—Describing organisms that thrive in an acidic envi-
ronment.

Alkalinity

—The equivalent sum of HCO

3
-

+ CO

2-

+ OH

-

minus H

+

,
that is, buffering conferred by the bicarbonate system; the terms
ANC and alkalinity are sometimes used interchangeably. ANC
includes alkalinity plus additional buffering from dissociated or-
ganic acids and other compounds.

Analyte

—A chemical species that is measured in a water sample.

Anion

—A negatively charged ion.

Anion–cation



balance

—A method of assessing whether all ions have
been accounted for and measured accurately; in an electrically
neutral solution, such as water, the total charge of positive ions
(

cations

) equals the total charge of negative ions (

anions

).

Anion deficit

—The concentration of measured

cations

minus mea-
sured

anions

; usually the result of unmeasured organic anions or
analytical uncertainty and often used as a surrogate for organic
anion concentration.

Anion exchange/adsorption

—A reversible process occurring in soil
by which anions are adsorbed and released.

Anion reduction

—The process by which NO

3
-

is reduced to N

2

O or
N

2

(nitrate reduction or

denitrification

) and SO

4
2-

is reduced to S

2-

(

sulfate reduction

). Nitrate reduction and sulfate reduction can be
mediated by plants during growth; the reduced N and S are as-
similated into the growing plant. Denitrification and dissimilatory
sulfate reduction are mediated by bacteria in anoxic zones in soils,
sediment, or the water column. In the absence of oxygen, bacteria
use the energy derived from these two reduction reactions in the
decomposition of organic matter.

Anthropogenic

—Of, relating to, derived from, or caused by humans
or related to human activities or actions.

Assemblage

—A group of taxa recorded in a sample (e.g., the group
of taxa preserved in a sedimentary section).

Background sulfate

—Estimated pre-industrial (pre-1850) concentra-
tion of sulfate in surface waters or precipitation.

Base cation

—An alkali or alkaline earth metal cation (Ca

2+

, Mg

2+

,
K

+

, Na

+

).

Base cation buffering

—The capacity of a watershed soil or a sediment
to supply base cations (Ca

2+

, Mg

2+

, K

+

, Na

+

) to receiving surface

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Definitions

311
waters in exchange for acid cations (H

+

, Al

3+

); may occur through
cation exchange in soils or weathering of soil or bedrock minerals.

Base cation supply

—The rate at which base cations can be supplied
to buffer incoming acid cations; this rate is determined by the
relative rate of mineral weathering, the availability of base cations
on exchange sites, and the rate of mobile anion leaching.

Base saturation

—The proportion of total soil

cation exchange capac-
ity

that is occupied by exchangeable

base cations

, that is, by Ca

2+

,
Mg

2+

, K

+

, and Na

+

.

Bedrock

—Solid rock exposed at the surface of the earth or overlain
by saprolites or unconsolidated material.

Benthic

—Referring to bottom zones or bottom-dwelling organisms
in water bodies.

Bias

—A systematic difference (error) between a measured (or pre-
dicted) value and its true value.

Bioassay

—Measurement of the response of an organism or group of
organisms upon exposure to

in situ

environmental conditions or
simulated environmental conditions in the laboratory; also referred
to as toxicity test.

Biological effects

—Changes in biological (organismal, populational,
community-level) structure and/or function in response to some
causal agent; also referred to as biological response.

Biological significance

—The quality of being important in maintain-
ing the structure and/or function of biological populations or com-
munities.

Calculated conductance

—The sum of the products of individual

ionic species and their known equivalent conductance values,
measured under specified conditions. Calculated conductance of-
ten is compared with measured conductance as a quality assur-
ance procedure.

Calibration

—Process of checking, adjusting, or standardizing oper-
ating characteristics of instruments or coefficients in a mathemat-
ical model with empirical data of known quality. The process of
evaluating the scale readings of an instrument with a known stan-
dard in terms of the physical quantity to be measured.

Carbonaceous particles

—A collective term referring to carbonaceous
spherules resulting from coal and oil combustion, as well as soot
particles from wood burning. Carbonaceous particles are well pre-
served in lake sediments, where they can be used to infer past coal,
oil, or wood-burning activities.

Catchment

—See

watershed

.

Cation

—A positively charged ion.

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312

Aquatic Effects of Acidic Deposition

Cation exchange

—The interchange between a cation in solution and
another cation on the surface of any surface-active material such
as clay or organic matter.

Cation exchange capacity

—The sum total of exchangeable cations
that a soil can adsorb.

Cation leaching

—Movement of cations out of the soil, in conjunction
with mobile anions in soil solution.

Cation retention

—The physical, biological, and geochemical process-
es by which cations in watersheds are held, retained, or prevented

from reaching receiving surface waters.

Chronic acidification

—See

long-term acidification

.

Chrysophyte

—Members of the classes Chrysophyceae and Synuro-
phyceae that are covered by siliceous scales. Like the diatom valves,
chrysophyte scales are taxonomically diagnostic and well-pre-
served in lake sediments. These algae have flagella and live in the
open water (euplankton) of a lake.

Circumneutral

—Close to neutrality with respect to

pH

(neutral pH
is equal to 7); in natural waters, pH 6 to 8.

Close-interval sectioned sediment core

—Refers to PIRLA-II cores

whose recent sediments were sectioned at very close intervals (0.25
cm) so as to establish a fine temporal resolution.

Conceptual model

—Simplified or symbolic representation of proto-
type or system behavior and responses.

Conductance

—See

specific conductance

.

Confidence limits

—A statistical expression, based on a specified
probability, that estimates the upper and/or lower value (limit) or
the interval expected to contain the true population mean.

Decomposition

—The microbially mediated reaction that converts
solid or dissolved organic matter into its constituents (also called
decay or mineralization).

Denitrification

—Biologically mediated conversion of nitrate to gas-
eous forms of nitrogen (N

2

, NO, N

2

O); denitrification occurs during
decomposition of organic matter.

Diatom

—Alga in the class Bacillariophyceae that are characterized
by cell walls composed of two siliceous halves, known as valves
(two valves equal a frustule). These siliceous valves are taxonom-
ically diagnostic and well-preserved in lake sediments, so past
diatom assemblages can be interpreted from their fossil remains.

Dissolved inorganic carbon

—The sum of dissolved (measured after
filtration) carbonic acid, bicarbonate, and carbonate in a water sample.

Dissolved organic carbon

—Organic carbon that is dissolved or un-
filterable in a water sample (0.45

µ

m pore size).

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Definitions

313

Drainage basin

—See

watershed

.

Drainage lake

—A lake that has a permanent surface water inlet
and outlet.

Dry deposition

—Transfer of substances from the atmosphere to ter-
restrial and aquatic environments via gravitational settling of large
particles and turbulent transfer of trace gases and small particles.

Dynamic model

—A mathematical model in which time is included
as an independent variable.

Empirical model

—Representation of a real system by a mathematical
description based on experimental or observational data.

Episodes

—A subset of hydrological phenomena known as events.
Episodes, driven by rainfall or snowmelt, occur when

acidification

takes place during a

hydrologic event

. Changes in other chemical

parameters

, such as aluminum and calcium, are frequently associ-
ated with episodes.

Episodic acidification

—The short-term decrease of

acid neutralizing
capacity

from a lake or stream. This process has a time scale of
hours to weeks and is usually associated with

hydrological events

.

Equivalence point

—The point at which, during a titration, the con-
centration of proton donors equals the concentration of proton
acceptors.

Equivalent

—Unit of ionic concentration, a mole of charge; the quan-
tity of a substance that either gains or loses one mole of protons
or electrons.

Eutrophication

—A process of accelerated aquatic primary produc-
tion in response to nutrient enrichment that ultimately can result
in oxygen depletion and changes in biological community structure
and function.

Evapotranspiration

—The process by which water is returned to the
air through direct evaporation or transpiration by vegetation.

Forecast

—To estimate the probability of some future event or condi-
tion as a result of rational study and analysis of available data.
Frame—A structural representation of a population providing a sam-
pling capability.
Gran analysis—A mathematical procedure used to determine the
equivalence points of a titration curve for acid neutralizing capacity.
Ground water—Water in a saturated zone within soil or rock.
Groundwater flow-through lake—A seepage lake that receives a
substantial amount of groundwater input. Although there is no
clear distinction between this type of lake and a groundwater
recharge lake, groundwater flow-through lakes have been opera-
tionally defined as having silica concentrations greater than or
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314 Aquatic Effects of Acidic Deposition
equal to 1.0 mg L
-1
or, in Florida, potassium concentrations greater
than or equal to 15 µeq L
-1
.
Groundwater recharge lake—A seepage lake that receives little or

no groundwater input, but discharges water to the groundwater
system. This type of lake is also known as a mounded or perched
seepage lake. Operationally, groundwater recharge lakes have been
defined as having silica concentrations less than 1.0 mg L
-1
or
potassium concentrations less than 15 µeq L
-1
.
Hindcast—To estimate the probability of some past event or condition
as a result of rational study and analysis of available data.
Hydraulic residence time—A measure of the average amount of time
water is retained in a lake basin. It can be defined on the basis of
inflow/lake volume, represented as “RT,” or on the basis of outflow
(outflow/lake volume) and represented as τ
W
. The two definitions
yield similar values for fast-flushing lakes, but diverge substantial-
ly for long-residence time seepage lakes.
Hydrologic(al) event—Pertaining to increased water flow or dis-
charge resulting from rainfall or snowmelt.
Hydrologic(al) flow paths—Surface and subsurface routes by which
water travels from where it is deposited by precipitation to where
it drains from a watershed.
Hydrology—The science that treats the waters of the earth—their
occurrence, circulation, and distribution; their chemical and phys-
ical properties; and their reaction with their environment, including
their relationship to living things.
Index sample—As defined in the NSWS, a sample or group of sam-
ples taken from a certain place at each sampling unit (lake or stream

reach) at a particular time of the year. For the Eastern and Western
Lake Surveys, the index sample was a single sample collected from
the center of each lake at a depth of 1.5 m during the fall turnover
period. For the National Stream Survey, the index sample was the
average of 2 or 3 samples collected during the spring baseflow
period within a stream reach.
Inorganic aluminum—The sum of free aluminum ions (Al
3+
) and
dissolved aluminum bound to inorganic ligands; operationally de-
fined by labile monomeric aluminum.
Labile monomeric aluminum—Operationally defined as aluminum
that can be retained on a cation exchange column and measured
by one of the two extraction procedures used to measure mono-
meric aluminum. Labile monomeric aluminum is assumed to rep-
resent inorganic monomeric aluminum (Al
i
).
Liming—The addition of any base materials to neutralize surface
water or sediment or to increase acid neutralizing capacity.
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Definitions 315
Littoral zone—The shallow, near-shore region of a body of water;
often defined as the band from the shoreline to the outer edge of
the occurrence of rooted vegetation.
Long-term acidification—The decrease of acid neutralizing capacity
in a lake or stream over a period of hundreds to thousands of years,
generally in response to gradual leaching of ionic constituents.
Macrophytes—Macroscopic forms of aquatic vegetation.

Macropore flow—Flow of water through large pores or voids in soil
or rock (macropores), in response to the force of gravity.
Mineral acids—Inorganic acids, e.g., H
2
SO
4
, HNO
3
, HCl, H
2
CO
3
. See
strong acids and weak acids.
Mineralization—Process of converting organic nitrogen in the soil
into ammonium which is then available for biological uptake.
Mineral weathering—Dissolution of rocks and minerals by chemical
and physical processes.
Mitigation—Generally described as amelioration of adverse impacts
caused by acidic deposition at the source (e.g., emissions reduc-
tions) or the receptor (e.g., lake liming).
Mobile anions—Anions that flow in solutions through watershed
soils, wetlands, streams, or lakes without being adsorbed or re-
tained through physical, biological, or geochemical processes.
Model—An abstraction or representation of a prototype or system,
generally on a smaller scale.
Monomeric aluminum—Aluminum that occurs as a free ion (Al
3+
),
simple inorganic complexes (e.g., Al(OH)

n
3-n
, AlF
n
3-n
), or simple
organic complexes, but not in polymeric forms; operationally, ex-
tractable aluminum measured by the pyrocatechol violet method
or the methyl-isobutyl ketone method (also referred to as the oxine
method) is assumed to represent total monomeric aluminum. Mo-
nomeric aluminum can be divided into labile and nonlabile com-
ponents using cation exchange columns.
Monte Carlo method—Technique of stochastic sampling or selection
of random numbers to generate synthetic data.
Natural acids—Acids produced within terrestrial or aquatic systems
through natural, biological, and geochemical processes; that is, not
a result of acidic deposition or deposition of acid precursors.
Nitrification—Oxidation of ammonium to nitrite or nitrate by micro-
organisms. A by-product of this reaction is H
+
.
Nitrogen fixation—Biological conversion of elemental nitrogen (N
2
)
to organic N.
Nitrogen saturation—Condition whereby nitrogen inputs to an al-
pine or forested ecosystem exceed plant uptake requirements.
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316 Aquatic Effects of Acidic Deposition

Nonlabile monomeric aluminum—Operationally defined as alumi-
num that passes through a cation exchange column and is mea-
sured by one of the two extraction procedures used to measure
monomeric aluminum; assumed to represent organic monomeric
aluminum (Al
o
).
Nutrient cycling—The movement or transfer of chemicals required
for biological maintenance or growth among components of the
ecosystem by physical, chemical, or biological processes.
Organic acids—Heterogeneous group of acids generally possessing
a carboxyl (-COOH) group or phenolic (C-OH) group; includes
fulvic and humic acids.
Organic aluminum—Aluminum bound to organic matter, opera-
tionally defined as that fraction of aluminum determined by
colorimetry after sample is passed through a strong cation ex-
change column.
Paleolimnology—The branch of limnology that deals with describing
and interpreting lake histories by studying the information con-
tained in lake sedimentary profiles. This information includes mor-
phological and biogeochemical fossils of past lake biota,
geochemistry, and physical attributes of the sediments. These sed-
iment profiles are usually dated using radioisotopes suited for the
time-scale of interest (for example,
210
Pb).
Parameter—A characteristic factor that remains at a constant value
during the analysis, or a quantity that describes a statistical pop-
ulation attribute.
Pelagic zone—Referring to open-water areas not directly influenced

by the shore or bottom.
Perched seepage lakes—See groundwater recharge lake.
Periphyton—Plants that live attached to or closely associated with
surfaces (e.g., on the bottom sediments or macrophytes).
pH—The negative logarithm of the hydrogen ion activity. The pH
scale is generally presented from 1 (most acidic) to 14 (most alka-
line); a difference of one pH unit indicates a ten-fold change in
hydrogen ion activity.
Physiography—The study of the genesis and evolution of land forms;
a description of the elevation, slope, and aspect of a study area.
Piston effect—Hydrological process whereby snowmelt or storm dis-
charge forces water that had been previously stored within the
watershed out of soils and into streams.
Plankton—Plant or animal species that spend part or all of their lives
in open water.
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Definitions 317
Pool—In ecological systems, the supply of an element or compound,
such as exchangeable or weatherable cations or adsorbed sulfate,
in a defined component of the ecosystem.
Population—For the purpose of this book, the total number of lakes
or streams within a given geographical region or the total number
of lakes or streams with a given set of defined chemical, physical,
or biological characteristics; or an assemblage of organisms of the
same species inhabiting a given ecosystem.
Precision—A measure of the capacity of a method to provide repro-
ducible measurements of a particular analyte (often represented
by variance).
Probability sample—A sample in which each unit has a known prob-

ability of being selected.
Project—To estimate future possibilities based on rational study and
current conditions or trends.
Quality assurance—A system of activities for which the purpose is
to provide assurance that a product (e.g., database) meets a defined
standard of quality with a stated level of confidence.
Quality control—Steps taken during sample collection and analysis
to ensure that data quality meets the minimum standards estab-
lished in a quality assurance plan.
Reduction/oxidation (redox) reactions—Reactions in which sub-
stances gain or lose electrons, that is, in which substances are con-
verted from an oxidized to a reduced oxidation state and vice versa.
Regionalization—Describing or estimating a characteristic of interest
on a regional basis.
Retention time—The estimated mean time (usually expressed in
years) that water resides in a lake prior to leaving the system. See
hydraulic residence time.
Salt effect—The process by which hydrogen ions are displaced from
the soil exchange complex by base cations (from neutral salts). The
result is a short-term increase in the acidity of associated water;
also referred to as sea-salt effect.
Saturated flow—Flow of water through the voids in rock or soil at a
pressure greater than atmospheric, that is, under a head of pressure.
Scenario—One possible deposition sequence following implementa-
tion of a control or mitigation strategy and the subsequent effects
associated with this deposition sequence.
Secchi disk depth—A measure of the transparency of water.
Seepage lake—A lake with no permanent surface water inlets or
outlets. Seepage lakes are sometimes divided into two categories:
groundwater recharge lakes and groundwater flow-through lakes.

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318 Aquatic Effects of Acidic Deposition
Short-term acidification—See episode.
Simulation—Description of a prototype or system response to differ-
ent conditions or inputs using a model rather than actually observ-
ing the response to the conditions or inputs.
Simulation model—Mathematical model that is used with actual or
synthetic input data, or both, to produce long-term time series or
predictions.
Species richness—The number of species occurring in a given aquatic
ecosystem, generally estimated by the number of species caught
using a standard sampling regime.
Specific conductance—The conductivity between 2 plates with an
area of 1 cm
2
across a distance of 1 cm at 25˚C.
Steady state—The condition that occurs when the sources and sinks of
a property (e.g., mass, volume, concentration) of a system are in
balance (e.g., inputs equal outputs; production equals consumption).
Steady-state model—A model in which the variables under inves-
tigation are assumed to reach equilibrium and are independent
of time.
Stratified design—A statistical design in which the population is
divided into strata, and a sample selected from each stratum.
Stream order—A method of categorizing streams based on their po-
sition in the drainage network. First-order streams are permanent
streams with no permanent tributaries. Higher-order streams are
formed by the confluence of two or more streams of the next lower
stream order.

Strong acid anion sum (SAA or C
A
)—Refers to the equivalent sum
of SO
4
2-
, NO
3
-
, Cl
-
, and F
-
. The term specifically excludes organic
acid anions.
Strong acids—Acids with a high tendency to donate protons or to
completely dissociate in natural waters, for example, H
2
SO
4
, HNO
3
,
HCl
-
, and some organic acids. See acid anions.
Strong bases—Bases with a high tendency to accept protons or to
completely dissociate in natural waters, for example, NaOH.
Subpopulation—Any defined subset of the target population.
Sulfate adsorption—The process by which sulfate is chemically ex-

changed (e.g., for OH
-
) or adsorbed onto positively charged sites
on the soil matrix; under some conditions this process is reversible,
and the sulfate may be desorbed.
Sulfate reduction—The conversion of sulfate to sulfide during the
decomposition of organic matter under anaerobic conditions
(dissimilatory sulfate reduction) and the formation of organic
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Definitions 319
compounds containing reduced sulfur compounds (assimilatory
sulfate reduction).
Sulfate retention—The physical, biological, and geochemical process-
es by which sulfate in watersheds is held, retained, or prevented
from reaching receiving surface waters.
Sum of base cations (SBC or C
B
)—Refers to the equivalent sum of
Ca
2+
, Mg
2+
, Na
+
, and K
+
. The term specifically excludes cationic Al
n+
and Mn

2+
.
Surficial geology—Characteristics of the earth's surface, especially
consisting of unconsolidated residual, colluvial, alluvial, or glacial
deposits lying on the bedrock.
Synoptic—Relating to or displaying conditions as they exist at a point
in time over a broad area.
Target population—A subset of a population explicitly defined by a
given set of exclusion criteria to which inferences are to be drawn
from the sample attributes.
Total monomeric aluminum—Operationally defined simple unpo-
lymerized form of aluminum present in inorganic or organic
complexes.
Turnover—The interval of time in which the density stratification of
a lake is disrupted by seasonal temperature variation, resulting in
entire water mass becoming mixed.
Validation—Comparison of model results with a set of prototype
data not used for verification. Comparison includes the following:
using a data set very similar to the verification data to determine
the validity of the model under conditions for which it was de-
signed; using a data set quite different from the verification data
to determine the validity of the model under conditions for which
it was not designed but could possibly be used; and using post-
construction prototype data to determine the validity of the pre-
dictions based on model results.
Valve—One-half of a siliceous cell wall of a diatom. Diatom valves
are identified and counted in lake sediments in paleolimnological
studies. Two valves together are referred to as a frustule.
Variable—A quantity that may assume any one of a set of values
during analysis.

Verification—Check of the behavior of an adjusted model against a
set of prototype conditions.
WACALIB—This is a FORTRAN program by J.M. Line and H.J.B.
Birks that implements regression calibration based on weighted
averaging.
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320 Aquatic Effects of Acidic Deposition
Watershed—The geographic area from which surface water drains
into a particular lake or point along a stream.
Water Year—Hydrologic year that runs from October 1 through Sep-
tember 30. For example, water year 1999 began on October 1, 1998.
Weak acids—Acids with a low proton-donating tendency that tend
to dissociate only partially in natural waters, for example, H
2
CO
3
,
H
4
SiO
4
, and most organic acids. See acid anions.
Weak bases—Bases with a low proton-accepting tendency that tend
to dissociate only partially in natural waters, for example, HCO
3
-
,
Al(OH)
4

-
.
Weighted Averaging—This is a statistical method that can be used
for analyzing environmental gradients with biological response
variables (e.g., diatoms and chrysophytes). The optimum of each
species along a gradient (e.g., pH) is estimated as the average of
all pH values for lakes in which the taxon occurs, weighted by the
taxon's relative abundance (WA regression). Reconstructions cal-
culate a predicted environmental value for an algal assemblage
based on the optima of the species and their abundances (WA
calibration). This method is an approximation of the more formal
procedure of maximum likelihood regression and calibration.
Weighted averaging is computationally much easier and often per-
forms better than maximum likelihood (Birks et al., 1990; Kingston
and Birks, 1990). The theory has been developed and elaborated
mainly by ter Braak (1986, 1988).
Wet deposition—Transfer of substances from the atmosphere to ter-
restrial and aquatic environments via precipitation, for example,
rain, snow, sleet, hail, and cloud droplets. Droplet deposition is
sometimes referred to as occult deposition.
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