Dissolved Oxygen (DO) is the amount of gaseous oxygen that is dissolved in water. DO is considered low at levels less than 5mg/l and is lethal to many organisms at levels of less than 3mg/l. DO is probably the most significant indicator of aquatic health because DO is critical for aquatic animals such as fish that "breathe" oxygen through their gills.
Temperature is an important variable because it affects many biological, physical, and chemical processes. For example, temperature affects the amount of oxygen that can dissolve in water. Temperature is measured in either degrees Celsius or Fahrenheit.
Salinity is the concentration of dissolved salts in the water. Salinity is measured in parts salt per thousand parts water (ppt). Salinity ranges from near 0ppt in fresh water to about 35ppt in the ocean. Salinity is an important variable because aquatic plants and animals are adapted to live in certain ranges of salinity.
pH is a measure of the acidity or alkalinity of water (technically, a measure of hydrogen ion activity). The lower the value, the more acidic the water is; the higher the value the more alkaline the water is. The pH of surface waters is usually between 6 and 9.
Fecal Coliform Bacteria are found in the intestines of warm-blooded animals. High numbers of fecal coliform bacteria in a water body can indicate the presence of disease-causing organisms (pathogens). Contaminated waters are unsafe for catching/eating fish and shellfish, swimming and, in extreme cases, even boating.
Nutrients (TKN, Ammonia, NO2, NO3, Total P, Ortho P), natural life-sustaining substances, are critical to maintaining an appropriate balance for the health and productivity of aquatic systems. High levels of nutrients or eutrophication is considered detrimental to aquatic habitats and diminishes the recreational value of these waters. Nitrogen and phosphorus are used as indicators of nutrient enrichment.
Chlorophyll 'a' is a plant pigment whose concentration in water is used as an estimate of algae productivity or phytoplankton biomass. High chlorophyll 'a' concentration is typically associated with conditions symptomatic of eutrophication.
Secchi Transparency is used to estimate the transparency of surface waters. High Secchi transparency is indicative of clear water, while low Secchi readings are associated with light-limiting conditions and degraded waters. The extent of penetration and absorption of light determines the maximum depth at which aquatic plants can grow.
CBOD5 Carbonaceous Biochemical Oxygen Demand, represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter. It is a test used to determine the relative oxygen requirements of wastewaters, effluents, and polluted waters.
Total Suspended Solids (TSS) are the non-filterable portion of solids found in the water column. These contribute to the turbidity, or cloudiness of the water and may clog fish gills, either killing them or reducing their growth rate. Suspended solids also reduce light penetration thus reducing the ability of algae to produce food and oxygen.