Watershed Glossary

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ablation - loss of snow and ice through combination of sublimation (solid to gas) and melting (solid to liquid)

absorption - water movement into rocks and soil by natural processes of infiltration by precipitation or snowmelt, movement into sinkholes or other openings, or directly from atmospheric moisture

acid - a substance that dissociates in water to form a solution with more H+ ions than OH- ions; has a pH less than 7

acidity - acidity is the capacity to neutralize base. The more acid a solution, the more base that must be added to raise the pH to an acceptable level. Acidity is an important consideration when developing treatment solutions to address the pollution and degradation of streams from highly acidic waters due to practices of the mining industry, particulary the coal-mining industry in Pennsylvania.

Acidity is the opposite of alkalinity with both based on the carbonate system. The acidity of a water source is generally attributable to the carbonate molecules H2CO3 and HCO3- and sometimes to strong acids, namely, H+.

acre-feet - a measure of reservoir capacity, the volume needed to cover 1 acre (43,560 sqare feet) to a depth of 1 foot

aerobic - processes or conditions in the presence of oxygen

algae - single-celled, colonial, or multicellular aquatic plants having chlorophyll but lacking true leaves, stems, or roots

alkaline - refers to a substance with the capacity to neutralize acid

alkalinity - alkalinity is the capacity to neutralize acid. The alkalinity of a natural water source is largely defined by the carbonate system.

The presence of large quantities of alkalinity in water sources that are impacted by mining is very important in preventing highly acidic conditions. It is quite common to add alkalinity to a water source to raise the pH. Alkalinity is commonly added in the solid form of calcium carbonate (CaCO3), also known as limestone. When limestone dissolves in water, the calcium carbonate molecule dissociates and large concentrations of CO32- are released into solution which will chemically bond with H+ ions. When all the H+ ions have chemically bonded with the CO32- molecules, CO32- and HCO3- will accumulate in solution, increasing the alkalinity of the water source and also raising the pH

The general method for measuring alkalinity is the potentiometric titration technique. This method involves continuously adding volumes of acid with a certain concentration to a water sample until the pH of the water reaches a specified endpoint. "Potentiometric" refers to the use of a pH meter to identify when the desired pH has been reached. The amount of acid added is converted to equivalent mg CaCO3/L and reported along with the titrated pH endpoint.

allochthonous - referencing sources of organic material that are outside the aquatic system, such as leaves and twigs

alluvium - deposits of clay, silt, sand, gravel, or other particulate material that has been deposited by a stream or other body of running water in a streambed, on a flood plain, on a delta, or at the base of a mountain

ammonia/ammonium -

anaerobic - processes or conditions in the absence of oxygen

aquaculture - farming of plants, fish, or shellfish

aquatic - references a relationship to freshwater ecosystems

aquiclude - a rock layer with very low porosity such to be virtually impermeable

aquifer - a water bearing geologic formation, usually referring only to those formations capable of yielding a useable quantity of water. A confined aquifer has relatively impermeable rock (an aquitard or aquiclude) above and below. If a confined aquifer has a downward grade from its recharge zone, groundwater can become pressurized and can create an artesian well. Unconfined aquifers allows free flow of water from the surface and the saturated zone of the aquifer.

aquitard - a rock layer with low porosity that permits limited groundwater movement

artesian water/artesian well - water that flows freely from an unconfined aquifer under pressure without the need of a pump

autochthonous - referencing sources of organic material within the aquatic system, such as photosynthesizing algae and plants

autotroph - an organism that produces complex organic molecules from simple inorganic molecules using light (photoautotroph) or chemical reactions (chemoautotroph) as an energy source; includes plamnts, algae, and some bacteria


bankfull - a stream stage (elevation) where flooding is incipient, where additions to flow volume will cause the stream to move out of the stream channel onto the floodplain; bankfull height can often be determined, during lower flows, by stream bank characteristics such as breaks in the bank slope, depositions of fine materials at the scour mark, rock discoloration, absence of perennial vegetation, or root hair exposure; bankfull width is distance across channel between bankfull indicators or the width of the channel at bankfull discharge

bankfull discharge - the discharge at bankfull height is the dominant channel forming flow and usually as a recurrence interval of 1 to 2 years

base - a substance that dissociates in water to form a solution with more OH- ions than H+ ions; has a pH greater than 7

base flow - the sustained flow of a stream in the absence of any precipitation, snowmelt, or other runoff

bedrock - the solid rock beneath soil, loose sediments and other unconsolidated material

benthic - referencing bottom dwelling or bottom oriented

benthos - usually refers to the collection of bottom dwelling organisms

biodiversity - variation in the assemblage of distinct types of organisms in a given ecosystem, biome, or larger geographical area and can refer to and includes genetic diversity within a species, species diversity within an ecosystem, and ecosystem diversity within a region or within the biosphere

biomass - amount of organisms, measured as total weight per unit of area

biomonitoring - using organisms to assess or monitor environmental conditions

buffering capacity - the capability of a natural system or a managed water system to 'neutralize' additions of acids or bases without correspondingly large changes in pH. In natural systems, buffering capacity is of greatest importance in considering stream, river of lake response to atmospheric deposition of acidic pollutants (acid rain) or response to pollution from mining drainage.

The carbonate system is the main group of molecules that determine how well a natural water source can "buffer" the addition of acid without the pH dropping rapidly. The molecules of the carbonate system that largely attribute to this ability to buffer large drops in pH are HCO3-, CO32-, and OH-These molecules are bases and when H+ (acid) is added to the water source, the H+ ions will chemically bond with the bases. For example:

OH- + H+ —-> H2O;
CO32- + H+ —-> HCO3-;
HCO3- + H+ —-> H2CO3

When the only carbonate mineral in solution is H2CO3, all the alkalinity has been used up since there are no carbonate molecules left for the H+ ions to chemically bond with.

If mostly basic carbonate molecules are in solution (HCO3-, CO32-, and OH-), the pH is correspondingly basic (almost always >7). Conversely, if the carbonate molecules in solution are mostly H2CO3, the pH is correspondingly acidic (< 7). The larger the concentration of basic molecules, the more H+ ions that can be added to the water source without the pH dropping rapidly to a low level. If more acid is added to the system than can chemically react with the basic molecules, all carbonate molecules will be in the form of H2CO3 and the pH will drop to a very low level, as happens with acid mine drainage of very low pH (= 2 or 3).


cfs - cubic feet per second , a measure of discharge or stream flow volume

caddisfly - member of the insect order Trichoptera; an indicator organism in biological assessment of stream health, part of the EPT (Ephemeroptera, Plecoptera, Trichoptera) complex or metric used in biodiversity indices

capillary action - movement of a liquid through the porous spaces in a solid such as soil, through plant roots, and through the capillary blood vessels in our bodies due to the forces of adhesion, cohesion, and surface tension

catchment - drainage basin or watershed

collectors - members of a functional feeding group that acquire and ingest very small particles of detritus (FPOM or fine particulate organic material). Collectors can be further ditinguished as filterers that use constructed nets or anatomical structures such as hairs to trap food items from the current, or as gatherers that collect detritus that has fallen out of suspension and is lying on bottom or is mixed with bottom sediments

complete metamorphosis - a life cycle that includes the pupal stage, usually described as egg-larva-pupa-adult (ELPA)

condensation - process of water vapor coalescing into water droplets

cone of depression - occurs due to pumping groundwater where drawdown of the surface of the saturated zone, water table, in an unconfined aquifer is most severe closest to the well. In a confined aquifer, the reduction is in head pressure not the surface of the saturated zone

consumptive use - that portion of water withdrawn that is evaporated, transpired by plants, consumed by humans or livestock, or used without return by industry

CPOM - coarse particulate organic material

cyanobacteria - also called blue-green algae


detritus - dead and decomposing animal or plant material

detritivore - organism that consumes detritus

diatom - a unicellular algae with silica-containing cell walls, often of intricate design

Diptera - the insect order of true flies, two-winged flies, that includes house flies, horse flies, mosquitoes, midges, black flies, and craneflies among others

discharge - the volume of water that passes a given point in a given amount of time

dissolved oxygen - the levels of dissolved oxygen (DO) in natural waters and wastewaters depend on the physical, chemical, and biochemical activities in the water source. Low DO concentrations can have harmful effects on aquatic life that require oxygen for survival. Low DO concentrations result from oxygen-demanding pollutants that serve as a food source for aquatic microorganisms. These aquatic microorganisms use oxygen in their metabolism and are capable of surviving at lower DO levels than higher life forms thereby, lowering DO levels in the water creating a harmful environment for aquatic life of higher life forms. Most oxygen-demanding pollutants are organic compounds (i.e. municipal waste), but ammonia nitrogen is an important inorganic pollutant.

dissolved solids - total dissolved solids (TDS) represents the portion of the sample (water, wastewater, effluent) that passes through a filter of a particular size. Generally, a pore size of 0.45 mm is considered to be adequate to differentiate between microscopic particulate and dissolved material. The final result, after evaporation and drying, represents the total dissolved solids.

Total dissolved solids results are limited to providing a measure of the total water soluble fraction and do not reveal the quantity or type of individual contaminants in the sample.

drainage basin - land area where precipitation that falls drains to a particular water body or defined point on a water body, same as watershed or catchment

drawdown - the lowering of the groundwater surface, or water table, by pumping. Can also refer to lowering of a reservoir.


ecology - the science that studies the relationships of organisms to their environment

ecosystem - all of the component organisms of a community and the environment that forms an interacting system

effluent - water that flows outward from a lake, or from a treatment system such as a sewage treatment plant

embeddedness - a measure of the degree to which gravel, cobble and boulder substrate is covered or sunken into fine sediments such as silt, sand or mud

Ephemeroptera - insect order of mayflies, important indicator organism for stream health; part of the EPT (Ephemeroptera, Plecoptera, Trichoptera) complex or metric used in biodiversity indices

epilimnion - in a thermally stratified lake or reservoir, the upper layer of water with virtually uniform temperature

erosion - process by which particles of soil or rock are loosened by weathering and then carried away by wind or water, or wearing of stream bed and bank materials by direct action of the water or by abrasive materials carried in the water

estuary - a partially enclosed coastal body of water with one or more rivers flowing into it and with a connection to the ocean

eutrophic - an aquatic environment that is enriched with nutrients, especially nitrogen and phosphorus, leading to increased organic production and undesirable effects on aquatic ecosystems and uses

evapotranspiration - the sum of evaporation from water surfaces, moist soil and other land surfaces, and transpiration of plants


filterer - a collector organism feeds on small particles of organic material suspended in the water using constructed nets (caddisflies), internal sieves with siphons (clams and mussels), or brush-like tufts of hair on the head (black fly larva) or on legs (Isonychia amyfly nymphs)

flood - the temporary overflow of water from adjacent streams, rivers, lakes or oceans onto lands not normally covered by water

flood, 100 year - a flood with a 1 per cent chance of being equaled or exceeded in any given year

flood plain - land outside of a stream channel defined by the highest probable maximum flood, or the area inundated by a flood of a designated recurrence interval

flood stage - the stream elevation at which bank overlow begins onto land of the flood plain

flood way - a part of the floodplain designated to be kept free of obstructions such a buildings so as to allow movement of flood water

FPOM - fine particulate organic material


gage height - the height of the water surface above a gage datum or zero point, often used interchangeably with stage

gaging station - a site on a stream, river, or lake where observations and hydrologic cata are collected

gpm - gallons per minute, a measure of discharge more commonly used for pipes, sluices and other regulated flows

grazer - also known as scraper, an aquatic organism that feeds on the periphyton layer of algae and bacteria that grows tightly attached to substrate surfaces

grey water - wastewater from clothes washing machines, showers, tubs, and kitchen sinks

groundwater - water located beneath the ground surface in soil pore spaces and in the fractures of rock formations

groundwater recharge - the process of surface water moving into the groundwater, naturally occuring by precipitation infiltrating into soils and other porous layers and by losing segments of streams, can also refer to the volume added to groundwater by this process


hardness - a water quality parameter that indicates the concentration of alkaline salts in water

headwaters - the source and upper reaches of a stream; the tributaries to a reservoir; the waters upstream of a designated point on a stream; or sometimes refers to all of the streams of a river system except the main stem

herbivore - organism that consumes plants or plant materials

heterotroph - an organism that uses organic carbon, by consuming autotrophs, for growth; includes animals, most fungi, and most bacteria and protists

hydrologic cycle - the water cycle; the cyclic transfer of water vapor from the Earth's surface via evapotranspiration into the atmosphere, from the atmosphere via precipitation back to earth, and through runoff into streams, rivers, and lakes, and ultimately into the oceans

hydrology - the science that studies the behavior of water in the atmosphere, on the surface of the earthm, and underground

hypolimnion - in a thermally stratified lake or resevoir, the lower stratum of water, below the thermocline, in which water temperature is virtually uniform

HUC - hydrologic unit code, a categorization scheme that assumes unique numeric designations

hyporheic - referencing an underground or subterranean aquatic environment


impaired - a waterbody is considered impaired when it does not attain its water quality standards. The impairment can be due to a single pollutant, multiple pollutants, thermal pollution, or unknown pollutants. Water quality standards are established to provide for a water body's designated use(s) and so standards can vary from one water body to another when there are differences in designated use, or a water body can meet some but not all of its designated uses. In Pennsylvania, water bodies that fail to attain the water quality standards for their designated use(s) are listed, according to section 303(d) of the Clean Water Act, on the Integrated Water Quality Report published biannually by the PA Department of Environmental Protection.

impermeable layer - a layer of solid material, such as rock or clay, that does not allow water to pass through

impervious surfaces - manmade components of a watershed that do not allow precipitation to infiltrate for recharge of groundwater or to provide base flow for local streams. Precipitation falling on impervious surfaces will either evaporate or runoff potentially causing flooding and other stormwater management problems and carrying pollutants flushed from surfaces. Roof tops, roadways, parking lots, compacted agricultural soils, and intensively managed lawns and landscapes all can increase runoff.

infiltration - the flow of a liquid into a substance through pores or small openings, specifically the movement of precipitation into permeable soil and rock layers


JTU/Jackson Turbidity Unit - this method of measuring turbidity or lack of clarity in water uses transmission of light as its measure and so can have some effect from substances dissolved in the water that attenuate certain wavelengths. the original test used a candle that was viewed through a column of water but current tests, often used by volunteer watershed groups as inexpensive alternatives to more expensive meters based on light scattering by suspended particles (a more meaningful methodology), use instead a black and white target viewed through a column of sample water. The test parameters are generally adjusted so that turbidity reported as JTUs is equivalent to turbidity reported as NTUs.


Kjeldahl nitrogen (TKN) - sum of organic nitrogen, ammonia (NH3), and ammonium (NH4+)


leaching - the process of water dissolving salts, nutrients, pesticides or other soluble pollutants contained in a layer of soil and carrying these solutes away or to a deeper soil layer

lentic - references still or standing freshwater such as lakes or ponds

limnetic - references freshwater or aquatic (vs marine) environments

littoral - references a coastal zone that includes the intertidal zone in marine environments, from high-water mark of high tides to the elevation that is permanently submerged. In freshwater lake environments, it usually refers to the shallow water zone, often defined as 15 feet or less, where the majority of rooted and floating vascular plants are found

load - mass per unit time, water quality measurements it refers to the amount of a substance under consideration that is carried by water flow during a specified time period

lotic - references moving freshwater such as creeks and rivers


MCL (maximum contaminant level) - the designation given by the U.S. Environmental Protection Agency (EPA) to water-quality standards promulgated under the Safe Drinking Water Act. The MCL is the greatest amount of a contaminant that can be present in drinking water without causing a risk to human health.

mg/L - milligrams per liter

Mg/D - millions of gallons per day

macroinvertebrate - an animal without a backbone that is large enough to see with the unaided eye

mayfly - member of the insect order Ephemeroptera, indicator organism in assesments of stream health, part of the EPT (Ephemeroptera, Plecoptera, Trichoptera) complex or metric used in biodiversity indices, immature mayflies are aquatic nymphs with 2 or 3 "tails" or caudal filaments, a single claw on each tarsus, and gills on most abdominal segments. Mayflies transform first into a flying subadult known as a subimago before casting off a final exuvia to emerge as the fully mature imago adult that will mate. Subimago and imago stages are very brief, usually a day or two at most, and do not take food.

meander - a bend in a stream channel that is created and maintained by erosion on one stream bank and deposition on the opposite bank, as the strteam adjusts its channel slope to the slope of its valley. Meandering is synonomous with sinuosity and is a characteristic of most lowland, valley streams. The meander length, width, and rate of movement will also be affected by flow volume, bed and bank material, and sediment load.

mesotrophic - references waters with intermediate levels of productivity, more than oligotrophic waters, but less than eutrophic waters. Mesotrophic waters are commonly clear water lakes and ponds with beds of submerged aquatic plants and medium levels of nutrients.

municipal water system/supply - usually refers to a water system with at least 15 connections or which regularly supplies 25 people for 60 days


NTU/nephelometric turbidity unit - unit of measure of turbidity (cloudiness) of water, this is unit obtained from turbidity meters that use the scattering of light by particles suspended in water; equivalent to JTU (Jackson Turbidity Unit) that is obtained by observing clarity of water and comparing to a standard of pure water

nitrates - NO3, nitrogen trioxide, nitrates are salts of nitric acid, the nitrate ion had 1 molecule of nitrogen with 3 molecules of oxygen. Nitrate is a significant pollutant that contributes to eutrophic conditions in aquatic and marine environments. The primary sources of nitrate pollution are surface runoff from agricultural lands, and sometimes landscaped areas, where excess nitrate fertilizer was applied, or applied in a manner or at a time that promoted runoff rather than incorporation into plant production. Septic systems, too, can be a source of nitrates, produced as bacteria breakdown nitrogen containing organic compounds. Nitrate is toxic to humans, though it is added to cured meats at low concentrations. In higher concentrations, nitrate in the body interferes with the oxygen-carrying ability of hemoglobin.

nitrites - NO2, nitrogen dioxide, nitrates are salts of nitrous acid, the ion has 1 nitrogen with 2 oxygen molecules. Nitrite is an intermediate compound in the conversion of nitrate to ammonium in the nitrogen cycle. It is toxic to humans and many other life forms though, when nitrate is added to cured meats, much of it converts to nitrite, and the two compounds provide anti-bacterial effect as well as characteristic pink or red color and taste.

nitrogen - a necessary element for life forms as a component of proteins, nucleic acids and other organic compounds

nitrogen cycle - the pathways that elemental, inorganic, and organic forms of nitrogen follow through the environment while being used and transformed by life forms. Human activity and industrial processes have influenced the cycle resulting in imbalances with deleterious effects.

non-point source pollution (NPS) - pollution discharged over a wide land area, not from one specific location. These are forms of diffuse pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities, which are carried to lakes and streams by surface runoff. Non-point source pollution is contamination that occurs when rainwater, snowmelt, or irrigation washes off plowed fields, city streets, or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants, such as nutrients and pesticides.

nutrients - plant nutrients (primarily nitrates and phosphates from animal manure, fertilizers, urban runoff, sewage wastewater, detergents, and other manufactured products) that results in excessive algae growth, to the detriment of other forms of aquatic life from oxygen depletion


oligotrophic - a lake with low primary productivity, the result of low nutrient content. These lakes have low algal production, and consequently, often have very clear waters, with high drinking-water quality. The bottom waters of such lakes typically have ample oxygen; thus, such lakes often support many fish species, like lake trout, which require cold, well-oxygenated waters. The oxygen content is likely to be higher in deep lakes, owing to their larger hypolimnetic volume

osmosis - the movement of water molecules through a thin membrane

outfall - the place where a sewer, drain, or stream discharges; the outlet or structure through which reclaimed water or treated effluent is finally discharged to a receiving water body

oxbow lake - a U-shaped water body that results from a meander being cut off from main channel flow, oxbow alone can refer to a U-shaped bend in a river that is not cut off

oxygen demand - the molecular oxygen that is required to meet the needs of biological and chemical processes in water


ppb - parts per billion

ppm - parts per million

particle size - the diameter, generally in millimeters (mm), of suspended sediment or bed material

clay - 0.00024-0.004 mm

silt - 0.004-0.062 mm

sand - 0.062-2.0 mm

gravel - 2.0-64.0 mm

larger components of stream bed material, not referred to as particles, include:

cobble - 64.0-256.0 mm

boulder - 256.0 mm +

pathogen - a disease-producing agent, usually referring to a living organism such as viruses, bacteria, or fungi

peak flow - the maximum instantaneous discharge of a stream or river at a given location, usually occuring at or near the time of maximum stage

per capita use - the average amount of water used per person during a standard time period, generally per day

percolation - the movement of water through the interstices of a rock or soil

periphyton - a complex film composed of algae, cyanobacteria, microbes and detritus that is attached to submerged surfaces in most aquatic environments and is an important food source for many invertebrates and some vertebrates

permeability - the ability of a material to allow the passage of a liquid, such as water through rocks

pH - an expression of the acidity or alkalinity of a solution, as an approximation of the negative logarithim of the concentration of dissolved H+ ions. pH 7 is neutral, pH below 7 is acid, pH above 7 is base or alkaline

phosphates - naturally occuring forms of phosphorus found in many minerals and also an important compound in biological sysytems as a nutrient for plants and a component in animal tissues (e.g. bone as calcium phosphate). Overuse of phosphate containing fertilizers leads to significant environmental consequences, causing booms in the populations of agae and cyanobacteria in aquatic systems and subsequent eutrophication, oxygen depletion, and population declines of fish, macroinvertebrates and other oxygen dependent organisms. Phosphate is one of the salts contributing to total dissolved solids (TDS).

phreatic zone - the saturated zone of an aquifer below the water table or phreatic surface

Plecoptera - insect order of stoneflies, indicator organism in assesments of stream health, part of the EPT (Ephemeroptera, Plecoptera, Trichoptera) complex or metric used in biodiversity indices

point source pollution - pollutants originating from a single, identifiable source such as gases and particulates from a smokestack, thermal pollution from a power plant cooling water outfall, or industrial pollutants from a discharge pipe

porosity - a measure of the water-bearing capacity of subsurface rock

potable water - water that can be consumed without risk of immediate or long-term harm

precipitation - atmospheric water that is pulled to earth by gravity including rain, snow, and ice pellets.

predators - these aquatic animals feed upon other animals, usually other invertebrates but sometimes vertebrates such as fish. Piercer-predators use modified mouthparts to puncture their prey and draw out body fluids, often after injecting a digestive enzyme to liquify tissues. Engulfer-predators consume prey whole or tear large prey into consumable portions, typically using mouthparts modified for capture, holding, and tearing.


Q - symbol used for discharge


rating curve - a graphic representation of the relationship between gage height and stream discharge at a gaging station

reach - can refer to a stream length defined by a set of common characteristics (e.g. the stream between two gaging stations, the stream length for which a particular gage station acts a reliable measure of stage and discharge, a stream section with nearly uniform channel characteristics, etc.

recharge - water that is added to an aquifer such as rainwater infiltrating the ground surface and percolating to the water table

reservoir - a natural or artificial water body of any size used for storage, regulation, and control of water

riffle - a relatively shallow section of stream with nearly uniform depth and greater than average flow velocity with resulting rippled surface waves and which are generally important habitat resources for macroinvertebrates and small fishes

riparian zone - the area of transition from land to stream that can include many forms such as grassland, forestland, wetland. or even non-vegetated. Natural riparian zones are important in stream bank stability and erosion control, for pollutant mitigation and intercepting contaminants in runoff from agricultural and developed land surfaces, in flood control, and as habitat for many organisms

riparian buffer - usually used in referring to a managed, vegetated portion of the riparian zone planted and maintained to enhance one or more of the beneficial effects of a naturally functioning riparian zone

runoff - the portion of precipitation, snow melt, or irrigation water that does not infiltrate the ground and flows across impermeable or saturated surfaces to uncontrolled surface streams, rivers, drains or sewers


saturation zone - refers to the area below the water atble where all pore spaces in soil and cracks and voids in rock strata are filled with water

scrapers - or grazers, are aquatic organisms that feed on the periphyton layer of algae and bacteria that grows tightly attached to substrate surfaces

sediment - fragmented material that originates from weathering of rocks and is transported by, suspended in, or deposited by water or air or is accumulated in beds by other natural agencies. Often sediment refers to mineral particles in suspension in water or recently deposited from suspension but as the plural sediments can refer to any size material deposited from water

sedimentary rock - rock formed of accreted sediments such as sandstone, shale ,and siltstone or formed by accretions of organisms or their secretions such as limestone

settling pond - on open pond used to allow solid pollutants to sink to the bottom for removal from treated water in a wastewater treatment system, a mine drainage treatment system, etc. When enclosed vessels are use to collect solids, they are usually referred to as sedimentation tanks.

sewage treatment plant - a facility that receives wastewater from domestic and some other sources and is designed to remove materials that damage water quality and threaten public health and safety when discharged into receiving streams or bodies of water

sewer - a system of underground pipes that collect and deliver wastewater and/or stormwater to treatment facilities or streams

shredders - invertebrate organisms that chew on intact plant material or large pieces of plant material. Shredder-detritivores feed on material that is in a state of decay and shredder-herbivores consume living plant material.

sinkhole - a depression in the Earth's surface caused by dissolving of underlying limestone, salt, or gypsum. Drainage is provided through underground channels that may be enlarged by the collapse of a cavern roof.

solute - a substance dissolved in another substance forming a solution

solution - a mixture of a solvent and a solute

solvent - a substance in which another substance is dissolved

specific conductance - measure of the ability of water to conduct an electrical current

stonefly - member of Plecoptera order of insects, indicator organism in assesments of stream health, part of the EPT (Ephemeroptera, Plecoptera, Trichoptera) complex or metric used in biodiversity indices, immature stoneflies spend 1 -3 years as aquatic nymphs before transforming to flying adults, have 2 "tails" or caudal filaments, and 2 claws on each tarsus, gills are generally absent from abdominal segments

storm sewer - a sewer that carries only surface runoff, street wash, and snow melt from the land

stream - a natural water course containing water at least part of the year

perennial - stream with surface flow continuously year round

intermittent or seasonal - stream with surface flow in response to seasonal inputs such as snowmelt or seasonal springs

ephemeral - stream with surface flow in response to rainfall, the channel is at all times above the water table

continuous - stream with surface flow at all times throughout its length, without spatial interruptions

interrupted - stream with alternating reaches that could be perennial, seasonal, or ephemeral

gaining - a section of stream that receives water from the zone of saturation

losing - a section of stream that contributes water to the zone of saturation

stream flow - the water discharge that occurs in a natural channel

stream order - method of numbering streams as part of a drainage basin network. The smallest unbranched mapped tributary is called first order, when two first order streams combine, a second-order stream is formed. The next order is designated only when two streams of the same order combine (i.e. a second-order stream entering a third-order stream results in a third-order stream).

subsidence - a drop in the land surface due to ground water being pumped

surface tension - the attraction of a liquid's molecules to one another at the liquid surface

surface water - water on earth's surface such as in streams, lakes, reservoirs or oceans

suspended sediment - very fine particles that remain in suspension in water for a considerable period of time due to the upward components of turbulence and currents and/or by suspension

suspended solids - total suspended solids (TSS) is a measure of all suspended (not dissolved) particles in a solution that do not pass a given filter size. TSS is a commonly measured water quality parameter. Waters high in suspended solids may be aesthetically unsatisfactory for purposes such as bathing or drinking a glass of water out of the sink. In addition, measurement of suspended solids is used as a surrogate for measurement of pathogens since direct measurement of pathogens is extremely difficult.


thermal pollution - a reduction in water quality caused by increasing its temperature, often due to disposal of waste heat from industrial or power generation processes. Thermally polluted water can harm the environment because plants and animals can have a hard time adapting to it

thermal stratification - separation of lake waters into upper and lower regions with nearly uniform temperatures separated by narrow layer (thermocline) where temperature changes abruptly

thermocline - water layer where temperature changes rapdily per unit of depth

total inorganic nitrogen - sum of nitrates, nitrites, and ammonia

total nitrogen - sum of TKN (total Kjeldahl nitrogen), nitrate, and nitrite ( = TKN + NO3 + NO2)

transpiration - process by which water is evaporated from plants surfaces, largely through leaf pores

tributary - a small river or stream that flows into a larger river or stream

Trichoptera - insect order of caddisflies

turbidity - cloudiness or haziness of a fluid caused by particles of suspended solids in the water reducing light transmission by scattering light


unsaturated zone - the zone of aeration between the land surface and the water table


vascular plants - also called tracheophytes, these are higher plants that possess tissues modified to conduct water, minerals and photosynthetic products through the plant, these include ferns, clubmosses, flowering plants and conifers

vernal - referencing or occuring in spring, often as a description for pools that contain water from snowmelt and spring rains but which dry during summer drought


wastewater - water that has been used in homes, industries, and businesses that is not for suitable for reuse unless it is treated

water cycle - the hydrologic cycle ; the cyclic transfer of water vapor from the Earth's surface via evapotranspiration into the atmosphere, from the atmosphere via precipitation back to earth, and through runoff into streams, rivers, and lakes, and ultimately into the oceans

water quality - a term used to describe the chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose

water table - the top of the water surface in the saturated part of an aquifer

water well - a bored, drilled, or driven shaft, or a dug hole whose depth is greater than the largest surface dimension and whose purpose is to reach underground water supplies or oil, or to store or bury fluids below ground

watershed - the land area defined by the drainage of water to a common destination, either a body of water or a specific location on a body of water, and delineated by the highest elevation upslope in all directions from the designated point, e.g. the Susquehanna River watershed is delineated by the high divide line separating the drainage basins of the Ohio River , the Great Lakes, the Potomac River, and the Delaware River from the Susquehanna River basin and water that falls on all the lands included by this divide flow to the Chesapeake Bay at the mouth of the Susquehanna near Havre de Grace and Perryville, Maryland. Watersheds can also be as small as the land area upstream of, and draining to, the point where a small forested headwaters stream flows into your favorite trout stream. The term 'watershed' is synonomous with 'drainage basin' and 'catchment', and can be used on a range of topographic scales.


xeriscaping - landscaping that uses plants that are well adapted to the local area and are drought-resistant, eliminating the need for irrigation


yield - mass per unit time per unit area, in water quality refers to the load of substance considered carried by the water flow from specified area of particular land use (e.g. sediment in runoff from acreage of plowed fields)


zone of aeration - the zone above the water table that water percolates through but which is not saturated, the pores spaces contain some air, and water cannot be pumped from this zone

zone of saturation - the zone in which the permeable rocks are saturated with water and water in the zone of saturation will flow into a well