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Hypolimnetic metabolism in Lake Washington: Relative effects of nutrient load and food web structure on lake productivity 1
Author(s) -
Lehman John T.
Publication year - 1988
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1988.33.6.1334
Subject(s) - hypolimnion , epilimnion , water column , eutrophication , environmental science , nutrient , plankton , anoxic waters , primary production , environmental chemistry , ecology , ecosystem , biology , chemistry
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 nitrification 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 independently from 14 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 significantly lower during an episode of cultural eutrophication in the 1960s. Rates of primary production and hypolimnetic processes decreased in response to changes in nutrient income when effluents from waste treatment plants were diverted from the lake. After a period of recovery from eutrophication, Lake Washington experienced a second basinwide perturbation involving alteration of the planktonic herbivore community. The change in food web structure failed to produce a response comparable to that of altered nutrient loading. Despite inferred changes in algal growth rates and in species composition, total primary productivity and rates of hypolimnetic metabolism did not change.