Lake Victoria: Structure and Function of a Tropical Ecosystem

9318085 Kling湖维多利亚是数百万人的基本食物和经济资源。 在过去的30年里，生态系统发生了显著和令人震惊的变化。 浮游植物生产力增加了2至3倍，生物量增加了10倍。 水的透明度、氧含量和二氧化硅浓度已显著降低。 当地鱼类的巨大多样性（300种）已经全部消失，部分原因是促成这些变化的成分：（1）尼罗河鲈鱼的引入改变了食物网，（2）来自流域或大气的营养物质输入造成的富营养化，以及（3）最近的气候变化改变了水柱结构，并导致混合模式有利于蓝草藻类的发展和底部沃茨的氧气损失。 %虽然有证据表明，这些组件中的每一个都对维多利亚的变化做出了贡献，但由于我们对生态系统功能的完全理解，无法确定它们的相对重要性以及它们如何相互作用。 理论预测在热带湖泊中存在弱的营养级联，这一预测显然与维多利亚湖的观测结果不一致。 磷驱动的富营养化模型不能解释湖泊生产力的变化。 这是因为在高温和不间断的温度下，地理控制的结果是不同的，还是通过营养相互作用或气候变化存在未被认识的反馈？ 在这项研究中，我们将探讨这些明显的矛盾，并测试这些基本的，但未经证实的假设。 调查和实验的方法将被用来推断养分限制的特异性和强度，并估计重要的生物和化学过程的速率。 一个建模方法将被用来确定重要的捕食者-猎物的相互作用，并将这些结果合成到定量估计草食动物的影响。 食物网相互作用模型将被用来评估以前，现在和未来的湖泊营养状态。 我们将使用硅藻，色素，甲壳类动物和元素沉积的变化的古湖泊记录作为基准，在测试的过程调节机制和它们在生态系统尺度上的整合。

9318085 Kling Lake Victoria serves as the basic food and economic resource for millions of people. The last 30 years have produced remarkable and alarming changes in the ecosystem. Phytoplankton productivity has increased 2 to 3-fold and the biomass has increased 10-fold. Water clarity, oxygen content, and silica concentrations have been dramatically reduced. The tremendous diversity of endemic fishes (300 species) has been all lost, due in part to the components that have contributed to these changes: (1) alteration of the food web by the introduction of Nile perch, (2) eutrophication caused by nutrient inputs from the basin or atmosphere, and (3) recent changes in climate that have modified water-column structure and caused mixing patterns to favor development of bluegrass algae and the loss of oxygen in bottom waters. %%% Although there is evidence that each of these components has contributed to the changes in Victoria, it is impossible to determine their relative importance and how they interact die to our complete understanding of ecosystem function. Theory predicts a weak trophic cascade in a tropical lake, a forecast clearly at odds with the observations in Lake Victoria. The phosphorus-driven eutrophication models fail to explain the change in productivity of the lake. Is it because the outcome of biogeographical control is different at high and uninterrupted temperatures, or is there an unrecognized feedback through trophic interactions or variations in climate? In this research we will explore these apparent contradictions and test these basic but unproved hypotheses. %%% A survey and experimental approach will be used to deduce the specificity and intensity of nutrient limitation, and to estimate the rates of important biological and chemical processes. A modeling approach will be used to identify the important predator-prey interactions, and to synthesize these results into quantitative estimates of herbivore impacts. Food web interaction models will be employed to evaluate previous, current, and future trophic states of the lake. We will use the paleolimnological record of change in diatoms, pigments, crustaceans, and element deposition as a benchmark in testing the mechanisms of process regulation and their integration at the ecosystem scale.