Role of bottom sediments in sustaining plankton production in a Lake ecosystem — Experimental demonstration using enclosed water bodies in a shallow eutrophic Lake

Using large enclosures set in Lake Suwa, experimental studies were conducted to examine the effects of bottom sediments on plankton production in a natural lake ecosystem. Successive changes in biotic and abiotic components in two types of enclosure with and without bottom sediments were surveyed throughout a one-month period in the early fall of 1985. Remarkable differences were found between the two types of enclosure with regard to the time courses of abundance of chlorophyll, PON, PP, TN, TP and zooplankton as well as those of POC/PON and POC/Chl ratios and primary production rate in terms of mg N m−2 day−1. Quantitative examination of the major causes of these differences revealed that the release of nitrogen and phosphorus from the bottom sediments was significantly effective for sustaining the active production of phytoplankton cells with a high nitrogen and phosphorus content, subsequently resulting in active zooplankton growth.