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Competency Area 7: Non-point source pollution AEM

PO 73. Identify basic water quality indicators and explain their significance.

Water quality indicators consist of physical, chemical, and biological parameters. People traditionally have used their basic senses of sight, smell, and taste to evaluate water quality suitability, and water that looks turbid and colored (containing total suspended and/or dissolved solids materials) is deemed unfit for drinking. These basic physical indicators are still currently used to determine water quality violations because of the implications for inclusion of other chemical and biological indicators.

Turbid water intercepts light transmission, reducing photosynthesis of aquatic species and interrupting food chain production. Sediments get into fish gills and cover nesting areas. Turbidity may indicate inputs of BOD (Biological Oxygen Demand – a characteristic of many wastewaters) that consume oxygen (measured as dissolved oxygen – DO) vital to benthic (aquatic dwelling) organisms.

Suspended materials are also frequently indicators of P (causing eutrophication – a process where water bodies (like ponds) receive excess nutrients that stimulate excessive plant (weed) growth).

Suspended materials may also be indicators for the presence of total (or fecal and E. coli) coliform inputs (potentially pathogenic organisms to humans). Phosphorus concentrations in pristine natural waters are generally less than 0.05 ppm, so a little P enrichment goes a long way in producing algal blooms. The presence of fecal coliforms or E. coli indicates fecal waste inputs, and their presence in very low numbers restricts water use for swimming and drinking. The ingestion of as few as 10 E. coli organisms of the 0157:H7 strain can result in serious health effects. Off-color (or shininess) of water is an indication of dissolved organic carbon (DOC), which may be produced naturally from decaying plant material, but is also often indicative of wastewater, pesticide, or solvents (oil, grease) inputs.

Ammonium-N is an indicator of wastewater pollution, and concentrations greater than 2 ppm affect fish and other aquatics. Since nitrate-N disrupts oxygen transfer in the blood Methemoglobinemia), the standard drinking water concentration is 10 ppm, but concentrations above 2 to 3 ppm are indicative of nutrient enrichment, and can have adverse effects on many aquatic species. Nitrate-N concentrations above 25 ppm can impact livestock health. The absence of certain aquatic macroinvertebrate (biological) organisms (i.e., mayflies, caddisflies, riffle beetles), or the presence of midges, horsefly, and tubificid worms instead, is often an indication of nutrient enrichment in streams.