Lake productivity through a lens of ice: is lake trophic status a seasonally-dependent concept?

Lake trophic status is based on growing season productivity when lakes are relatively warm and light is relatively abundant. Given the increasing awareness of under-ice productivity, one question to ask is: does our perception of lake trophic status change in winter relative to summer? We present a framework to begin to address this question based on the lake trophic stability index (LTSI) – the ratio of summer:winter productivity indicators (e.g., TP, phytoplankton and zooplankton demographics). We hypothesize that the different drivers of lake productivity in summer (e.g., nutrient availability) versus winter (e.g., light limitation) will result in disproportionate seasonal changes in our perception of lake trophic status, with variability in winter physical conditions that affect light availability (snow cover, ice thickness, ice duration) playing a major role. Thus we expect differences in LTSI among lakes, suggesting lake trophic status is a varying, seasonally-dependent concept. We present results from winter and summer sampling in two productive systems in Vermont to demonstrate our proposed framework.