01988, by the American Society of Limnology and Oceanography, Inc. Hypolimnetic metabolism in Lake Washington: Relative effects of nutrient load and food web structureon lake produ.ctivityl

The general metabolism of carbon, oxygen, phosphate, nitrate, and silicate in the hypolimnion of Lake Washington is examined from 23 yr of record. Magnitudes of net consumptive and regenerative processes in the water column and sediments are identified and stoichiometries of regeneration in situ are calculated. Aerobic respiration appears to be almost equally divided between the water column and sediment surface. Net vitrification is more rapid in the water column, and silicate regeneration is confined to the sediment surface. Nutrients do not accumulate on average at the Redfield ratio. Rates of hypolimnetic oxygen consumption are compared to production rates inferred indepen-dently from “C and oxygen bottle assays. A third of all gross primary production is respired in the hypolimnion of Lake Washington during spring and summer, but the proportion was signifi-cantly lower during an episode of cultural eutrophication in the 1960s. Rates of primary production and hypolimnetic processes decreased in response to changes in nutrientincome when effluents from wastetreatmentplants were dive~ed from the lake. After a period of recovery from eutro-phication,.LakeWashington experienceda second basinwide perturbationinvolving alterationo