Phytoplankton and Macrophyte Response to Increased Phosphorus Availability Enhanced by Rainfall Quantity

Abstract

Rainfall patterns are becoming more extreme in the northeastern US and are expected to intensify with an increase in extreme precipitation events and a greater frequency of short-term drought. In Northwest Bay, an undeveloped, primarily forested sub-watershed of Lake George, NY, stream discharge and phosphorus loading in 2006 exceeded that of 2007 by more than 3-fold due to unusually heavy rainfall in 2006 and below average rainfall in 2007. The additional phosphorus loading to the open water positively influenced chlorophyll concentrations in 2006, while porewater soluble phosphorus significantly correlated to precipitation in both 2006 and 2007. The elevated porewater concentrations in early summer of 2006 provided a nutrient advantage that resulted in tissue phosphorus in 3 macrophyte species to more than double while no change in nitrogen or carbon was detected. It is believed that the heavy late spring/early summer rainfall in 2006 saturated soils creating additional stormwater run-off and increasing groundwater seepage that supplied ample phosphorus resulting in enhanced phytoplankton biomass and macrophyte uptake of phosphorus.