interrelationship between nutrients and chlorophyll-a in an urban stormwater lake during the ice-covered period

urban stormwater lakes in cold regions are ice-covered for substantial parts of the winter. it has long been considered that the ice-covered period is the “dormant season,” during which ecological processes are inactive. however, little is known about this period due to the historical focus on the open-water season. recent pioneering research on ice-covered natural lakes has suggested that some critical ecological processes play out on the ice. the objective of this study was to investigate the active processes in ice-covered stormwater lakes. data collected during a two-year field measurement program at a stormwater lake located in edmonton, alberta, canada were analyzed. the lake was covered by ice from november to mid-april of the following year. the mean value of chlorophyll-a during the ice-covered period was 22.09% of the mean value for the open-water season, suggesting that primary productivity under ice can be important. nitrogen and phosphorus were remarkably higher during the ice-covered period, while dissolved organic carbon showed little seasonal variation. under ice-covered conditions, the total phosphorus was the major nutrient controlling the ratio of total nitrogen to total phosphorus, and a significant positive correlation existed between total phosphorus and chlorophyll-a when the ratio was smaller than 10. the results provide preliminary evidence of the critical nutrient processes in the stormwater lake during the ice-covered period.