Inter-annual variation in submerged macrophyte community biomass and distribution: the influence of temperature and lake morphometry

Abstract

We monitored the biomass and distribution of submerged macrophyte communities in five lakes in the Eastern Townships of Quebec, Canada, in two climatically different growing seasons. Early season warm temperatures allowed for much deeper macrophyte colonization (25–170%), an average of 300 g m −2 greater wet weight biomass (g m −2) and a 45–1160% increase in whole lake biomass in warm 1998 compared to a cooler 1997. In contrast, the inter-year variation in underwater light climate had no effect on macrophyte colonization as water column turbidity was generally higher in the warmer year, although irradiance did affect the distribution and biomass within seasons. The positive relationship between phytoplankton and whole system macrophyte biomass observed in this study cautions that the negative relationship in highly eutrophic shallow systems does not appear applicable to deeper systems characterized by lower macrophyte biomass to lake volume ratios. Earlier growing seasons, as predicted by climate change models, would result in greater biomass and distribution of submerged macrophyte communities, thereby modifying the structure and functioning of north temperate lakes. The effect will be a function of lake morphometry and most pronounced in shallow systems.