滤食性双壳类对浅水湖泊底栖-水层耦合作用的影响：水体变清的机理

Benthic-pelagic coupling is one of the key processes determining the characteristics of shallow lake ecosystems. Aiming at the scientific question of how filter-feeding bivalves increase water clarity in shallow lakes, the hypothesis of the proposed study is: filtering by filter-feeding bivalves not only decreases pelagic algae biomass, but also favors the growth of benthic algae by increasing light penetration. In addition, the bivalves can enhance the growth of benthic algae by increasing the total nitrogen concentrations, ratio of nitrogen:phosphorus in overlying water, while the growing benthic algae can depress the growth of pelagic algae by decreasing phosphorus (P) concentrations in overlying water by taking up P and by reducing the sediment release of P. These processes further increase water clarity in shallow lakes. To test these hypothesized effects of benthic filter-feeding bivalves on the benthic-pelagic coupling, the biomasses of benthic and pelagic algae, total suspended solids (TSS), total nitrogen, and ratio of nitrogen:phosphorus in the overlying water and light intensity on the sediment surface will be measured in mesocosm experimental aquatic ecosystems with and without filter-feeding bivalves. Then, N enriched experiments will be conducted to evaluate the effect of N and N:P on the growth of benthic algae. In combination with the results from the mesocosm experiments, the possible ways that filter-feeding bivalves may be enhancing growth of benthic algae will be explored. Finally, experiment of nutrient fate will be conducted to evaluate the nutrient release from bivalve and the sediment release affected by the animal. The results of this study will shed light on the mechanisms forming and maintaining the clear water state of shallow lakes and also have important implications for the conservation and restoration of shallow lakes.

底栖-水层耦合作用是决定浅水湖泊生态系统特征的关键过程之一。针对滤食性双壳类如何使水体变清的科学问题，我们假设：其直接滤食不仅降低浮游藻类密度，还利于底栖藻类生长；同时其还可提高水中总氮含量、氮:磷比促进底栖藻类生长，而底栖藻通过吸收和抑制沉积物释放等过程降低水层磷，进一步限制浮游藻类生长以提高水体透明度。通过构建中型水生系统，设置具有和没有滤食性双壳类两种处理，通过监测底栖、浮游藻类及水中总固体悬浮物、氮、氮:磷及光照变化，分析其对底栖-水层耦合作用影响；结合氮添加实验，探索其促进底栖藻类增长的途径；并通过滤食性双壳类对营养盐归趋的影响实验，揭示其使浅水湖泊水体变清的机理。该研究有助于进一步揭示浅水湖泊清水态形成与维持机理，同时可为湖泊保护与修复提供参考。

底栖-水层耦合作用是决定浅水湖泊生态系统特征的关键过程之一。但该过程受滤食性双壳类影响。针对其如何影响底栖-水层耦合过程进而使浅水湖泊变清的科学问题,进行以下研究：.中型系统实验中发现：滤食性双壳类可显著降低浮游藻类密度，降低水中的磷浓度，增强了水体底部的光照，提高水体透明度，改善水质。但不同种类滤食性底栖双壳类演替，若生物量相同，则未能进一步增强水体透明度。.原位中型系统实验中，也发现富营养化水体中，背角无齿蚌虽对TN影响不显著，但降低了TP、浮游藻类Chl a和TSS含量，增加了TN:TP比值，表明背角无齿蚌可改善富营养化水体水质；幼龄蚌的滤水速率高于成年蚌；幼龄蚌的滤水速率春季最大，夏季最小；而在水质良好的清水态系统中，背角无齿蚌反提高了水中总磷和铵态氮含量，表明其未能进一步改善清水态水体水质。.研究也发现，滤食性双壳类不仅能滤食水体颗粒物,降低TSS，也可代谢增加水中的氮、磷等含量；提高TN:TP比值。TN及TN:TP比值的提高利于促进底栖藻类生长。.同时，研究了背角无齿蚌、苦草及其共存对水质的影响，发现：背角无齿蚌可降低浮游藻类生物量；苦草降低了TN、NO3-、TP及浮游藻类Chl a；蚌草共存显著降低了氮、磷及浮游藻类Chl a；背角无齿蚌对苦草的生长起到促进作用，实验结束时蚌草共存组的苦草干重及株高显著高于草处理组。.该研究揭示了滤食性双壳类使水体变清的机理，为水生系统保护与修复提供参考，具有重要理论和应用价值。相关结果发表在PLoSONE, Reviews in Fish Biology and Fisheries, Ecological Engineering, Environmental Science and Pollution Research, Hydrobiologia, Inland Waters, Knowledge and Management of Aquatic Ecosystems和生态学杂志上。