LONG-TERM LIMNOLOGICAL DATA FROM THE LARGER LAKES OF YELLOWSTONE-NATIONAL-PARK, WYOMING, USA

Long-term Limnological data from the four largest lakes in Yellowstone National Park (Yellowstone, Lewis, Shoshone, Heart) are used to chara cterize their limnology and patterns of temporal and spatial variabili ty. Heart Lake has distinctively high concentrations of dissolved mate rials, apparently reflecting high thermal inputs. Shoshone and Lewis l akes have the highest total SiO2 concentrations (averaging over 23.5 m g L-1), apparently as a result of the rhyolitic drainage basins. Withi n Yellowstone Lake spatial variability is low and ephemeral for most m easured variables, except that the Southeast Arm has lower average Na concentrations. Seasonal variation is evident for Secchi transparency, pH, and total-SiO2 and probably reflects seasonal changes in phytopla nkton biomass and productivity. Total dissolved solids (TDS) and total -SiO2 generally show a gradual decline from the mid-1970s through mid- 1980s, followed by a sharp increase. Ratios of Kjeldahl-N to total-PO4 (KN:TP) suggest that the lakes, especially Shoshone, are often nitrog en limited. Kjeldahl-N is positively correlated with winter precipitat ion, but TP and total-SiO2 are counterintuitively negatively correlate d with precipitation. We speculate that increased winter precipitation , rather than watershed fires, increases N-loading which, in turn, lea ds to increased demand for TP and total SiO2.