The Use of Microbial Enzyme Activities to Identify Fecal Pollution Sources in Surface Waters

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A total maximum daily load (TMDL), which is the calculated total amount of pollutant that a waterbody can receive from point and non-point sources, is established for streams that do not meet their designated use criteria. Physical, chemical, and biological water quality parameters are used to attempt to identify pollution sources. Microbial enzyme activity (mg/mL) is used to monitor the changes in the microbial community by identifying changes in their metabolism. The health of a stream can be monitored by the presence and absence of microorganisms due to the response of the microbial community to prolonged pollution exposure. To fully understand the metabolic activity, MEA data are compared to other factors including biochemical oxygen demand (BOD), nitrogen, phosphate, total coliform and Escherichia coli concentrations. Dissolved oxygen refers to the amount of oxygen used by microorganisms to degrade organic carbon, which reduces the survivability of aerobic organisms. Nitrogen and phosphate compounds from anthropogenic sources are readily dissolved into water and are limiting nutrients for microorganisms. Total coliforms and E. coli determine the fecal contamination in the waterbody. All of these factors are used to determine point and nonpoint pollution sources. From February 2014 to January 2016, water and sediment samples were collected monthly from 16 sites along Sinking Creek in Northeast Tennessee. During the two-year study, physical and field parameters were measured. Water samples were analyzed for chemical parameters including alkalinity, hardness, and BOD. Using an ion chromatograph, the concentration of phosphates and nitrates in the samples was measured. For biological parameters, the water sample was used to obtain total coliform and E. coli data using the Colilert enzyme substrate test. MEA data were collected from triplicate sediment samples collected at each site. These sediment samples were tested for acid and alkaline phosphatase, glucosidase, galactosidase, and dehydrogenase enzymes. The substrate for these enzymes was added to the respective sample, incubated for approximately 24 hours, and analyzed by colorimetric spectrophotometry to obtain absorbance. The enzyme concentration was calculated by comparing the absorbance to a generated standard curve. The results for the measured parameters were compared to identify correlation between the MEA concentrations and other biological and chemical parameters. The microbial activity should show a holistic view of changes in the waterbody, which should correlate with the other factors. A direct relationship between E. coli, total coliforms, nitrate, phosphate concentrations, and MEAs was expected. A correlation should be seen between MEAs and BOD data, due to an increase in oxygen demand during microbial metabolism. By examining multiple parameters together, the results would provide the necessary information to determine remediation efforts for the waterbody.

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