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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. 1416definitions Page 309 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC 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 1416definitions Page 310 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC 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. 1416definitions Page 311 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC 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). 1416definitions Page 312 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC 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 1416definitions Page 313 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC 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. 1416definitions Page 314 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC 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. 1416definitions Page 315 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC 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. 1416definitions Page 316 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC 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. 1416definitions Page 317 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC 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 1416definitions Page 318 Wednesday, February 9, 2000 2:30 PM © 2000 by CRC Press LLC [...]... the validity of the predictions 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... Page 320 Wednesday, February 9, 2000 2:30 PM 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 September 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... 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 unpolymerized 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... 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... 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 performs 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... sulfate in watersheds is held, retained, or prevented from reaching receiving surface waters Sum of base cations (SBC or CB)—Refers to the equivalent sum of Ca2+, Mg2+, Na+, and K+ The term specifically excludes cationic Aln+ and Mn2+ Surficial geology—Characteristics of the earth's surface, especially consisting of unconsolidated residual, colluvial, alluvial, or glacial deposits lying on the bedrock Synoptic—Relating... 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 designed; using a data set quite different from the verification data to determine the validity of the model under conditions for which... theory has been developed and elaborated mainly by ter Braak (1986, 1988) Wet deposition Transfer of substances from the atmosphere to terrestrial and aquatic environments via precipitation, for example, rain, snow, sleet, hail, and cloud droplets Droplet deposition is sometimes referred to as occult deposition © 2000 by CRC Press LLC . CRC Press LLC 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. 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. PM © 2000 by CRC Press LLC 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

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