Evidence for nutrient enrichment of high‐elevation lakes in the Sierra Nevada, California

Abstract

Long-term measurements (1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) of nutrients and seston in Emerald Lake (Sierra Nevada, California) have revealed ecologically significant patterns. Nitrate, both during spring runoff and during growing seasons, declined from 1983 through 1995. Declining snowmelt nitrate was caused primarily by changes in snow regime induced by the 1987-1992 drought: years with shallow, early melting snowpacks had lower snowmelt nitrate concentrations owing to less labile N production in catchment soils and longer plant growing seasons. However, nitrate declines during growing seasons carried through the wetter years of 1993-2000 and are likely the result of increased P loading to the lake and the release of phytoplankton from P limitation. Contemporaneous with these changes was an increase in algal biomass and a shift from P limitation toward more frequent N limitation of phytoplankton abundance. Particulate carbon concentrations in the late 1990s were two-to threefold greater than in the early 1980s. These trends were reflected in a larger set of Sierra Nevada lakes sampled as part of synoptic surveys (n ϭ 28). Between 1985 and 1999, nitrate decreased and total P increased in Ͼ70% of the lakes sampled. Our data suggest that lakes throughout the Sierra Nevada are experiencing measurable eutrophication in response to the atmospheric deposition of nutrients.

Recent climate extremes alter alpine lake ecosystems

“…As a result of stable TN and lower total phosphorus (TP) concentrations, TN/TP ratios increased in the 2000s, indicating increasingly strong P-limitation of the phytoplankton. Our results differ from those reported for lakes of the Sierra Nevada, where increasing P inputs are resulting in the eutrophication of highelevation lakes and a trend toward increasing N-limitation (21).…”

Phenology of high-elevation pelagic bacteria: the roles of meteorologic variability, catchment inputs and thermal stratification in structuring communities

“…The lake, situated at 2800 m above sea level in a sparsely forested granitic catchment, is representative of the 44000 highelevation (42500 m above sea level) lakes scattered throughout the Sierra Nevada in size (2.7 ha, 10.5 m z max ), solute chemistry and catchment composition (median slope 31%; surface area 75% exposed granitic and granodioritic rock, 19% montane meadow, 3% sparse conifer, 3% water; Melack and Stoddard, 1991). The lake has been studied for several decades, and its hydrology, biogeochemistry and ecology are well characterized (Sickman et al, 2003b). Emerald Lake is remote, accessible only by an 8 km hike (with 1 km elevation gain) from the nearest road.…”

“…In addition, these systems have large and relatively predictable seasonal variations in nutrient availability, primary production, external inputs and physical properties (Melack et al, 1997). High-elevation and high-latitude ecosystems are recognized as early-warning systems for detecting ecological responses to global environmental changes because of their sensitivity to anthropogenic disturbance and regional climatic shifts (Beniston et al, 1997;Melack et al, 1997;Carrera et al, 2002;Fenn et al, 2003;Sickman et al, 2003b;Morales-Baquero et al, 2006b). Montane lakes worldwide have become increasingly affected by the atmospheric deposition of nutrients and pollutants (Psenner, 1999), factors that directly influence the metabolism and community structure of bacteria (Cotner et al, 1997;Carlson et al, 2002;Haukka et al, 2006).…”

Atmospheric Deposition of Nutrients Shifts Carbon Capture and Storage Trends in Freshwater Tropical Lakes in India

“…We found a consistently rising trend in phytoplankton development (measured in terms of Chl a biomass and GPP) over time in a manner synchronous to atmospheric deposition. In tropical lakes, where light and temperature regimes remain generally optimal, phytoplankton growth is primarily nutrient limited (Yang, 2008) and AD-nutrients delivered directly on water surfaces can be rapidly capitalized by proliferating phytoplankton (Sickman et al, 2003). Unlike boreal and subarctic lakes (Weyhenmeyer and Karlsson, 2009), temperature did not appear a major driver of increasing DOC in the study lakes.…”