Analytical dataset: Effects of climate variability on snowmelt and implications for organic matter in a high elevation lake

Few paired lake-watershed studies examine long term effects of climate
on the ecosystem function of lakes in a hydrological context. We use
thirty-two years of hydrological and biogeochemical data from a
high-elevation site in the Sierra Nevada of California to characterize
variation in snowmelt in relation to climate variability, and explore
the impact on factors affecting phytoplankton biomass. The magnitude
of accumulated winter snow, quantified through basin-wide estimates of
snow water equivalent (SWE), was the most important climate factor
controlling variation in the timing and rate of spring snowmelt.
Variations in SWE and snowmelt led to significant differences in lake
flushing rate, water temperature, and nitrate concentrations across
years. On average in dry years, snowmelt started 25 days earlier and
proceeded 7 mm/d slower, and the lake began the ice-free season with
nitrate concentrations ~2 uM higher and water temperatures 9 C warmer
than in wet years. Flushing rates in wet years were 2.5 times larger
than dry years. Consequently, particulate organic matter
concentrations, a proxy for phytoplankton biomass, were 5 – 6 uM
higher in dry years. There was a temporal trend of increase in
particulate organic matter across dry years that corresponded to lake
warming independent of variation in SWE. These results suggest that
phytoplankton biomass is increasing as a result of both interannual
variability in precipitation and long term warming trends. Our study
underscores the need to account for local-scale catchment variability
that may affect the accumulation of winter snowpack when predicting
climate responses in lakes.