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Newsletter and Technical Publications GLOSSARY Aerobic refers to system in which some oxygen is present. Agrochemicals are pesticides and fertilizers developed artificially for agricultural use. Airshed is the portion of the atmosphere that provides inputs of materials to a lake or reservoir. Airsheds have local components and often include regional or even hemispheric components because of long-distance transport. Algae are small, often microscopic, aquatic plants in a water body. They exist either as phytoplankton (i.e., free-floating cells) or as periphyton (i.e., filamentous algae attached to rocks or other underwater objects). Algicides are chemical compounds used to kill algae. Anaerobic refers to system in which oxygen is not present. Anoxic refers to the condition of the lack of dissolved oxygen, i.e., deoxygenated water. Anthropogenic refers to everything originating from human source. Aquaculture refers to artificial cultivation or growth of fish, crayfish and other aquatic organisms for use as food, particularly in fishponds and similar structures. Aquatic environment is a general phrase that indicates the combination of physical, chemical and biological conditions present in lakes, reservoirs, wetlands, rivers and oceans. Backward linkages (of eutrophication) are the source of an externality and forward linkages are the areas the externality influences. In most cases, eutrophication is linked to the production decisions of water users. These are referred to as production externalities. A feature of a production externality is there are goods that people care about, but are not sold on markets. The lack of markets for externalities causes problems. Benthic invertebrates are aquatic organisms, such as insect larvae, bivalves, amphipods and various worms, that live in the sediments of aquatic environments. Biomanipulation refers to use of native or artificially introduced biological organisms, for example, algae-eating zooplankton, to treat eutrophication, as contrasted with the use of chemicals or other non-natural control measures. Biomass is the total mass of living material in a given body of water. BOD5 is biological oxygen demand originating from the degradation of organic matter by microorganisms during 5 days. Buffering capacity is a measure of the ability of a system to meet changes imposed from the environment by minor changes in the system. Chemical fertilizers are man-made chemical compounds containing mainly nitrogen, phosphorus and potassium and sometimes other elements to enhance plant growth. In contrast, natural fertilizers are different products of the nature. Chlorophyll is the green pigment in a plant cell that absorbs the solar energy in the process of photosynthesis of new organic matter. COD is chemical oxygen demand and is measured as the amount of oxygen supplied by the chemical oxidation agent chromate to degrade organic matter by chemical means. Cost/benefit analysis is a process comparing the cost of a given action, such as pollution control programme, with the expected benefits of the action, such as better water quality. The comparison usually is expressed in strictly monetary terms. Cs137 is a radioactive isotope of the element cesium. Decision-tree refers to a chart or graph of alternative options deemed necessary to achieve specific goals. The specific options are chosen on the basis "yes" or "no" responses to specific questions asked sequentially in the chart. DEHP (diethylhexylphthalate) is a chemical used in several industries, particularly in the plastics industry. Dial oxygen sags refers to the diurnal changes in oxygen caused by the diurnal variation of the photosynthesis, which is producing oxygen. Diel cycles are the changes in environmental conditions that occur over a 24 hour period. Diffuse or non-point pollution source refers to pollution coming from many widely spread sources in contrast to point source, where one point (often a pipeline) can be indicated. It is not possible to collect the pollutants coming from diffuse sources. Therefore it is necessary to find solutions which do not build on environmental technology (also called end-of-the pipeline technology). Discount rate, r, is the premium that people are willing to pay, expressed as a percentage over a specified period. Funds received today are worth, at the end of the first period, a total of (1+r) times the amount of funds. Equivalently, an amount of funds to be received at the end of the period are worth 1/(1+r) times that amount at the beginning of the period. Discrepancies between the public or social interest and the private interest stem from the fact that certain costs or benefits, associated to production and consumption activities, are not internalized by the agents giving place to a gap between the social price that should prevail under conditions of perfect competition and the private price that is actually observed in the market. From an environmental standpoint, those non-internalized costs are related to activities causing natural resource degradation or exhaustion, and pollution. When the case is of production activities with negative environmental impacts, its marginal private cost of production and the costs of environmental degradation and restoration compose the marginal social cost of a given good. Ecology is the study of the distribution and abundance of organisms and the physicochemical and biological processes that determine the structure and function of ecosystems. Ecotone is the transition zone between two ecosystems, such as the shoreline of a lake, which is an ecotone between the lake and the land (i.e., between aquatic and terrestrial ecosystems). Effluent is the liquid waste from municipal sewage, industrial and septic sources, which is released to surface waters, such as lakes, reservoirs and streams. Endorheic lakes are inland drainage lakes that do not have surface flow outlet. Examples are: Lake Chad, Aral Sea, Dead Sea. Endorheic lakes are inland drainage lakes that do not have surface flow outlet. Examples are: Lake Chad, Aral Sea, Dead Sea. Epilimnion refers to the upper mixed layer in lakes and reservoirs. Euphotic zone is the upper portion of a lake or reservoir where sufficient light is present to support growth of aquatic plants. Eutrophic lake or water reservoir is a water body receiving large amount of nutrients from its watershed. It is characterized by high photosynthetic activity and low water transparency. Externalities are variously known as external effects, external economies and diseconomies, spill over and neighbourhood effects. Externalities involve an interdependence of utility and/or production functions; they represent the beneficial or adverse effect, which the activities of one firm or household causes on those of another firm or household. A negative externality or diseconomy represent certain costs caused by an activity which are not perceived as such by the firm causing them but they do have effects on other activities and agents or to society as a whole. Fish yield is a description of the quantity of fish, which is expected to be produced or caught in a water body, as a function of nutrient supply and other water body characteristics. Flushing rate is the time required for the whole volume of a lake or reservoir to be replaced. Fluvial flux is the transport of material by rivers and is expressed in terms of an amount of material per unit time and per unit area of cross section. Food web structure refers to the number of organisms at different trophic levels in a community. Examples of trophic levels include primary producers, such as algae or other aquatic plants, herbivores and predators. Gully is a small channel for water, such as an artificial channel dug at the edge of a field, or a natural channel in rock. (continued)
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