Secondary biological pump driven by food web interactions : A case study in Lake Biwa for gloval environmental issues

为了了解水生生态系统对全球环境变化的响应，我们研究了生物和分解过程与营养、光照和水温等环境变量的关系，以及生物制品沉积通量与食物链的关系。1)浮游植物的初级生产主要受5 m以上土层磷的限制，而5 m以下受光强的限制。2)细菌的分解速率受表层磷和低表层水温的限制。3)沉积通量约占浮游植物日产量的12%，浮游植物产量大部分被表层浮游动物和细菌消耗。4) 20-30%的沉降通量被片足类细胞吸收。5)沉降通量随降水和微浮游藻类繁殖的季节变化而变化。琵琶湖生物生产分解速率和沉积通量受光照、水温、食物网结构等物理变量的强烈影响。此外，它们与河流流入的营养物质密切相关。这些结果表明，控制降水、光照、水温和养分的气候变化通过生物生产-分解和颗粒有机质垂直运输过程直接影响水生生态系统。

To understando responses of aquatic ecosystems to global environmental change, we studied biological and decomposition processes in relation to environmental variables such as nutrients, light and water temperature, and relations between sedimentation flux of biological products and food chains.1) Primary production of phytoplankton was limited by phosphorus in the layr above 5 m deep but by light intensity below 5 m deep. 2) Decomposition rate by bacteria was limited by phosphorus in the epilimnion and by water temperature in the hypolimnion.3) Sedimentation flux corresponded with 12% of daily production of phytoplankton and most of the phytoplankton production were consumed by zooplankton and bacteria in the epilimnion. 4) 20-30% of the sedimentation flux were assimilated by Amphipoda gammarid in the aphotic zone. 5) The sedimentation flux changed seasonally depending on precipitation and propagation of microplanktonic algae such as Fragilaria crotonensis.Biological production-decomposition rates and the sedimentation flux in Lake Biwa were strongly influensed by physical variable like light and water temperature, and food web structure. Further, they related closely to nutrients inflowing from rivers. These results suggest that climate change controlling precipitation, light, water temperature and nutrients influences directly acquatic ecosystems through processes of biological production-decomposition and vertical transportation of particulate organic matter.