Summer nutrient conditions in the lower Holland River prior to diversion of municipal inputs - Field Study 1982-83
Nutrient concentrations in the lower Holland River were monitored during the summers of 1982 and 1983 to provide baseline information prior to the diversion of major municipal phosphorus inputs. Concentrations of phosphorus and nitrogen compounds were generally highest in the Holland River East Branch and lowest near the river mouth. Since the introduction of nutrient control measures and detergent-P legislation in Ontario during the early 1970's, improvements in water quality throughout the lower Holland River were apparent. Mean concentrations of total phosphorus, soluble reactive phosphorus, and chlorophyll a were significantly lower in 1982 compared to water samples collected during 1971 (P<0.05).For example, in 1982 the average total and soluble reactive P concentrations near the river mouth were 218 and 101 ?g P/L, respectively, corresponding to 40 and 49 percent reductions. In 1983, mean soluble reactive P concentrations in the river were not significantly lower than those recorded in 1971. In 1983, Cook Bay had the lowest mean concentrations of total P (50 ?g P/L), soluble reactive P (16 ?g P/L) and corrected chlorophyll a (4 ?g/L) found in this study, corresponding to 75, 86 and 85 percent reductions, respectively. Elevated concentrations of phosphorus, iron and manganese in the lower Holland River and in water impounded from the river by the experimental enclosures demonstrated that during the summer months the river sediments can contribute significant amounts of phosphorus to the overlying water. The internal phosphorus inputs appear to be regulated by oxidation-reduction (redox) potential. Intact sediment cores taken from the Holland River and Holland River East Branch, showed a greater potential for total phosphorus regeneration in the Holland River East Branch sediments. Further recovery of the lower Holland River and Cook Bay may depend upon the extent of phosphorus feedback from the bottom sediments. The diversion of Newmarket and Aurora sewage will reduce river flows. This could increase internal phosphorus loading through stagnation. The expected water quality improvements in Cook Bay could be delayed or masked.