Water Quality and Phytoplankton in Dairy Farm Ponds

Concentrations of chlorophyll a, soluble orthophosphate, dissolved nitrate and nitrite, and associated water quality parameters were measured biweekly from May 1979 to May 1980 in 3 sequential ponds located on a dairy farm. Pond number 1 was located in the immediate vicinity of the barn and feedlot, and demonstrated limnological characteristics of a sewage settling pond Chlorophyll a and soluble orthophosphate averaged 298 mg/m3 and 10.1 mg/l respectively. Dissolved oxygen in pond 1 averaged 3.4 mg/l at the surface but was never present at a depth of 1 m. The presence of a settling pond as the primary recipient of wastes produced by a herd of cattle resulted in downstream impoundments having limnological characteristics highly desirable for the culture of herbivorous fishes. Chlorophyll a in ponds 2 and 3 averaged 103 and 77 mg/m3 respectively. In contrast to pond 1, dissolved oxygen at the surface and 1 m in ponds 2 and 3 averaged 7.0 and 4.2, and 10.1 and 7.8 mg/l respectively. Downstream impoundments also had progressively lower concentrations of soluble orthophosphate, total alkalinity, and total hardness. Significant week to week variation in concentrations of soluble orthophosphate, dissolved nitrate and nitrite, and chlorophyll a occurred, but seasonal trends were not apparent. Magnitude of week to week variations was progressively less in downstream impoundments and during the winter. Week to week variations reflect activity of phytoplankton and the susceptibility of small impoundments to environmental factors.

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