Aquatic plant assessment in Cook Bay, Lake Simcoe - Field study July-August 1984
The distribution of macrophytes was effectively determined by the echosounding technique providing precise information on distribution fixed by LORAN navigation. The plant height within the water column was determined and a permanent record established on the echo-tracings which may be duplicated to measure changes in the future. Biomass information (volume and wet weight) are recorded for forty-six locations, and of these, twenty-two biomass records are also reported as dry weight (dw) and ash-free dry weight (afdw). The precise location of each of these collections is fixed by LORAN coordinates, so that measurements can be repeated in the future to determine changes in biomass or species composition. Qualitative collections of all common species were made at eleven locations from the mouth of the Holland River to approximately 4 km into the lake to measure changes in plant nutrient chemistry. There is no clear evidence that proximity to the nutrient resources of the Holland River influenced tissue concentration. A gross calculation based on estimated biomass and tissue phosphorus and nitrogen determinations indicated the early August standing crop organic biomass (afdw) to be 273 tonnes in the 9.5 km2 area supporting aquatic macrophyte growth in southern Cook Bay. These plants contained an estimated 983 kg of phosphorus and 7835 kg of nitrogen. This represents only 12 .4% and 10% of the tissue-bound P and N previously calculated for the standing crop of Dichotomosiphon tuberosus in Lake Simcoe. The procedures employed for mapping underwater plant distribution using echo sounding and LORAN navigation and the method developed to derive ash-free dry weight data using a simple field measurement of volume, represent important new techniques for surveying and measuring aquatic macrophyte growth.