Diel changes of nitrogen species in surface and overlying water of an estuarine lake in summer: Evidence for benthic‐pelagic coupling

Abstract

Diel changes in the concentration of nitrogen species [ammonium, nitrite, nitrate, dissolved organic N, and particulate organic N (PON)] and some biological parameters were monitored in the water column of Lake Shinji, a shallow estuarine lake in Japan. The sediment of the lake was densely inhabited by the filter‐feeding bivalve Corbicula japonica. An overlying water sampler showed that PON at the sediment‐water interface (less than a few millimeters above the sediment) was not depleted; nevertheless, active uptake of PON by C. japonica (10.4 mg‐atoms N m−2 (1−1) is reported. Dissolved and particulate N species showed vertically uniform profiles at night, which we attributed to nocturnal water mixing associated with cooling surface water. These observations suggest benthic‐pelagic coupling between filter‐feeding bivalves and phytoplankton which enables the removal of nitrogen from the eutrophic lake through fisheries yield of bivalves.