Plankton and seston of a Colorado (U.S.A.) alpine lake: The winter anomaly and the inlet‐outlet budget

Long Lake, Colorado, at an altitude of 3209 m, is oligotrophic and has an annual ice cover of 240 days. Greatest phytoplankton biomass (mostly μ‐algae) was attained in April and May under thick ice and snow. The Zooplankton was sparse; Cyclops was most abundant in winter, but cladocerans and rotifers had no seasonal maxima. The lake had a total water replacement of 38.7 times per year. Heavy June runoff flushes cut more than 99% of the plankton. On an annual basis, about twice as much plankton biomass is lost through the outlet as comes in through the inlet. Total monthly organic seston sedimentation (fallout) rates for the whole lake ranged from 16.1 kg in October to 730.8 kg in June. Total annual seston production (balance) was 8.0 g organic matter or 4.24 g carbon/m 2 .