Lake Victoria: Structure and Function of a Tropical Ecosystem

9318085克林维多利亚湖是数百万人的基本食物和经济资源。在过去的30年里，生态系统发生了惊人的变化。浮游植物的生产力增加了2 - 3倍，生物量增加了10倍。水的清晰度、氧含量和二氧化硅浓度都大大降低了。地方性鱼类的巨大多样性（300种）已经全部消失，部分原因是导致这些变化的因素：(1)尼罗河鲈鱼的引入改变了食物网，(2)盆地或大气的养分输入引起的富营养化，(3)最近的气候变化改变了水柱结构，造成了有利于蓝草藻类生长的混合模式和底部水域氧气的损失。虽然有证据表明，这些组成部分中的每一个都对维多利亚的变化做出了贡献，但不可能确定它们的相对重要性以及它们如何相互作用于我们对生态系统功能的完整理解。%%%理论预测在热带湖泊中有一个弱的营养级联，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无法解释湖泊生产力的变化。这是因为生物地理控制的结果在高温和不间断的温度下是不同的，还是通过营养相互作用或气候变化存在未被识别的反馈？在这项研究中，我们将探索这些明显的矛盾，并测试这些基本但未经证实的假设。将采用调查和实验方法来推断营养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。建模方法将用于识别重要的捕食者-猎物相互作用，并将这些结果综合为食草动物影响的定量估计。食物网相互作用模型将被用来评估湖泊过去、现在和未来的营养状态。我们将利用硅藻、色素、甲壳类动物和元素沉积的古湖泊学记录作为基准，在生态系统尺度上测试过程调节及其整合机制。

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.