Growth of aquatic plants in Southern Ontario impoundments in relation to phosphorus, nitrogen and other factors

In 1969-70 species composition and standing crops of macrophytes and phytoplankton were studied in both natural and man-made impoundments, located within a 90 km radius of Toronto. The total hardness of the epilimnial waters ranged from 53 to 307 ppm and the pH from 6.9 to 8.4. Total alkalinities ranged from 60 to 223 ppm. Total and soluble phosphorus concentrations varied between 0.010 to 0.065 and 0.002 to 0.019 ppm, respectively. Nitrates averaged from less than 0.01 to 1.91 ppm and nitrites from 0.001 to 0.070 ppm. Surface concentrations of Kjeldahl nitrogen ranged from 0.24 to 1.37 ppm and ammonia from 0.010 to 0.634 ppm. Stratification was strongest in the deep kettle lakes and flooded sand pits and was weakest in those shallow impoundments having appreciable flushing throughout the year. The plankton of the shallow impoundments with extensive stands of macrophytes consisted chiefly of diatoms, flagellates and green algae. In contrast, blooms of blue-green algae were characteristic of the kettle lakes and the deepest pond, where macrophyte growth was restricted due to light penetration. Significant correlations were found between the concentrations of phosphorus and iron in the plant tissues and in the epilimnial waters but none were found for nitrogen or manganese. There were no significant correlations between the concentrations of these elements in the plants and in the sediments. When the quantities of minerals contained in the samples of macrophytes were prorated per hectare, it was evident that these plants removed large quantities of nutrients from their environment. For example, a stand of elodea in one pond contained 89 Kg/ha N and 7 Kg/ha P at the time of sampling. The implications of these findings in aquatic weed control and nutrient removal are emphasized.