SS4.13 Water Quality of Lakes, Rivers and Coastal Zones
Date: Thursday, June 13, 2002
Time: 11:45:00 AM
Location: Carson B
 
ArhonditsisGB, University of Washington, Seattle, USA, georgea@u.washington.edu
Brett, M, T, University of Washington, Seattle, USA, mtbrett@u.washington.edu
Frodge, J, D, King County Department of Natural Resources, Seattle, USA, Jonathan.Frodge@METROKC.GOV
 
ENVIRONMENTAL CONTROL AND LIMNOLOGICAL IMPACTS OF A LARGE RECURRENT SPRING BLOOM IN LAKE WASHINGTON, USA
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Lake Washington’s, USA, limnological processes are strongly dominated by a recurrent diatom bloom which occurs during March and April. During this bloom epilimnetic chlorophyll concentrations peak on average at 10 g/L, which is 3.2 times higher than concentrations seen during summer stratification. Lake Washington does not experience a consistent fall bloom. We have conducted statistical analyses and developed a mechanistic model in order to unravel the factors driving this dramatic spring bloom, and to assess the impact of this bloom on Lake Washington’s overall limnology. The bloom is initiated as the lake progresses from winter deep mixing (and light limited) conditions and collapses as summer stratification (and nutrient limitation) sets up. The initial phase of the spring bloom is quite consistent from year to year, whereas the latter phase of the bloom is highly variable. During the bloom inorganic nitrogen and phosphorus concentrations as well as water clarity decline, and pH and oxygen saturation increase. Because this bloom is strongly dominated by highly nutritious diatoms it likely has an inordinate impact on zooplankton and fisheries production in this lake.