Water-quality Parameters

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The Bard Water Lab analyzes
samples for sewage-indicating bacteria, turbidity, chlorophyll a, colored dissolved organic material (CDOM), phycocyanin, and optical brighteners (OB). We also have samplers record temperature and conductivity data. These water-quality indicators are interrelated: a change in one indicator impacts all of the others. By analyzing these indicators, the Bard Water Lab is able to monitor this relationship. The lab maintains a data archive for the Saw Kill Watershed Community that houses historic water-quality data, maps of subbasins, riparian buffers, wetlands, impervious surfaces, and dams in the Saw Kill watershed, as well as a collection of the relevant literature. 


Turbidity is a measure of particles suspended in water; it is measured in NTRs (nephelometric turbidity units) or JTRs (Jackson turbidity units). The presence of minute particles in water diminishes its clarity. Turbidity increases from stormwater runoff in eroded areas, the removal of stream-bank vegetation, in-stream dredging and other disturbances, waste discharges, excess algae, decaying organic materials, and debris in streams.

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Normal temperature ranges vary among lakes, streams and rivers depending on geography and climate. Water temperature also changes during daily and seasonal cycles, and weather events. The presence of bank vegetation, especially trees and shrubs that extend over the water, helps maintain a lower water temperature. Warmer water encourages algal blooms, changes metabolic rates in aquatic organisms, and affects water chemistry.

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Salt (sodium chloride) content in fresh water is assessed by measuring chlorides--soluble mineral compounds dissolved in water--in milligrams per liter (mg/L) of water. However, salt content can also be measured through conductivity, or the ability of water to conduct an electrical current through charged particles within the water. These particles include salts, minerals, chlorides, sulfides, and carbonate compounds. Values are reported in microsiemens per centimeter (uS/cm). “Specific conductance” measures conductivity at specific water temperatures.

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Sewage-indicating Bacteria

The Enterolert and Colilert assays are used to measure Enterococci, and Total Coliforms and Escherichia coli (E. coli), respectively. Total coliforms include bacteria found in soil, surface waters, and human and animal waste. Fecal coliforms  are a group of bacteria found in the digestive tracts of warm-blooded animals, including humans, and are excreted in feces. Within the fecal coliform group, E. coli is the best indicator of fecal pollution and the possible presence of pathogens.

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Chlorophyll A

Chlorophyll allows plants (including algae) to photosynthesize, i.e., use sunlight to convert simple molecules into organic compounds. Chlorophyll a is the predominant type of chlorophyll found in green plants and algae. Chlorophyll a is a measure of the amount of algae growing in a water body. It can be used to classify the trophic condition of a water body. Although algae are a natural part of freshwater ecosystems, too much algae can cause aesthetic problems such as green scums and bad odors, and can result in decreased levels of dissolved oxygen.

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