The incidence and variation of bacteria in a stock dam : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University
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Date
1974
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Massey University
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Abstract
The effects of agricultural activities, including grazing and fertilizer application, and environmental factors, on the incidence and variation of bacteria in a stock dean were investigated. A survey of water quality at sites around the edge of a dam was carried out over a period of 15 months. Samples were analysed for water temperature, pH, turbidity, dissolved oxygen, 5-day biochemical oxygen demand (BOD5), total and soluble phosphorus, total nitrogen, ammonia, nitrite, nitrate,
total plate count (TPC), total coliform (TC), faecal coliform (FC) and faecal streptococcal (FS) counts. The bacterial content of faecal samples from animals around the dam and of littoral sediments were determined. Experiments with incubation of fresh and sterilized pond water samples were carried out to examine the effects of trophic status and nitrate and phosphate addition on bacterial growth and survival. The presence of grazing animals and wildlife around the dam resulted in significant increases in BOD5
, turbidity, FS and FC counts. Turbidity, ammonia, nitrate, log10
TPC, log10
TC and log10
FC were positively correlated with the amount of rainfall in the 5 days prior to sampling. While dissolved oxygen saturation was positively correlated with water temperature, ammonia, nitrate, log10
TPC and log10
TC exhibited a negative correlation. Ammonia, nitrate and log10
TPC were correlated with turbidity, and log10
TPC was correlated positively with ammonia and nitrate concentrations. Fertilizer application resulted in slightly increased phosphate concentrations. The bacterial content of cattle and goose faeces was similar to those reported in the literature, with FC/FS ratios less than 0.01. FC and FS bacteria were observed to grow in sterilized pondwater samples in pure cultures and in a community of indigenous bacteria harvested from the water. Addition of phosphate and nitrate, and increasing trophic status caused growth stimulation in both pure culture and in the mixed community. In fresh samples, while indigenous bacterial populations increased, indicator bacteria survived longer in less eutrophic water. It was concluded that BOD5
, turbidity, FC and FS counts were good indicators of animal pollution in this situation. Land drainage and mixing of dam sediments resulted in increased indigenous bacterial counts and chemical enrichment. While the physico-chemical nature and trophic status of the water may have influenced bacterial growth and survival, direct pollution, land drainage and mixing of sediments were overriding factors. The concentrations of faecal indicator bacteria encountered suggested that pathogenic organisms such as Salmonella could be present in littoral water and bottom sediments.
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Keywords
Water pollution, Agricultural pollution, Agriculture Environmental aspects