Modelling the impact of changes in the physical environment on plankton succession with special emphasis on Daphnia-algae interactions

预计全球变化将改变湖泊的物理条件。本项目将建立浮游生物演替模型，并将其与一维物理模型相结合，研究物理环境尤其是水温变化对浮游生物演替的影响。在两年的应用期内，浮游生物演替模型将以浮游植物和水蚤为主，因为浮游植物的丰度主要由养分和光照的有效性决定，而水蚤的生长对水温高度敏感。浮游生物演替模型还将以一种简化的方式包括以浮游植物为食的快速生长的微型浮游动物和以水蚤为食的鱼类。将包括解决水蚤发育的不同细节（例如大小结构，化学计量）的子模型，以研究模型细节对相对于现场观测的整体模型行为的重要性。模型校准和验证将基于康斯坦茨湖的大量可用数据集。通过比较极端热条件下浮游生物演替的数据和模型结果，探讨物理环境变化对浮游生物演替的影响是否能够被充分模拟，以及是否可能导致浮游生物群落内部相互作用的转变（匹配-失配）。由于春季和初夏生态系统对外界强迫非常敏感，且物种数量较少，因此初步调查的重点将集中在春季和初夏。全球变暖对海洋物理参数的影响及其对浮游生物演替的影响将通过数值实验进行研究。建模工作将辅以冬末和早春的野外测量，以提供关于浮游生物发育的更好的时间分辨率数据，并提高数据质量，特别是水蚤，这在现有的数据集中相当差，因为在一个浮游动物样本中只有很少的个体。在为期两年的应用期内，视乎模拟工作的结果，我们会将浮游生物演替模型应用于研究一年中的其他时段、其他湖泊、中生态系统，或将模型扩展至考虑其他物种。

Global change is expected to alter the physical conditions in lakes. This project will develop a plankton succession model and combine it with a 1 dimensional physical model to investigate the effect of changes in the physical environment and specifically in water temperature on plankton succession. In the two year application period the plankton succession model proposed will be focused on phytoplankton and Daphnia, because phytoplankton abundance is mainly determined by the availability of nutrients and light, whereas Daphnia growth is highly sensitive to water temperature. The plankton succession model will also include in a simplified fashion fast growing microzooplankton feeding on phytoplankton and the predation of fish on Daphnia. Sub-models resolving different details (e.g. size structure, stoichiometry) of Daphnia development will be included to investigate the importance of model detail on the overall model behaviour with respect to field observations. Model calibration and validation will be based on the extensive data set available for Lake Constance. Comparison of data and model results on the plankton succession in years with extreme thermal conditions will be used to investigate whether the impact of changes in the physical environment on plankton succession can be adequately simulated and possibly leads to a shift in the interactions within the plankton community (match-mismatch). Because the ecosystem in spring and early summer is very sensitive to external forcing and dominated by only a few species, the main part of the investigations will initially concentrate on spring and early summer. Consequences of global warming on the physical parameters and the implications on the plankton succession will be studied using numerical experiments. The modeling work will be complemented by field measurements during late winter and early spring to provide data with a better temporal resolution on the plankton development, and to improve the data quality for especially daphnids, which is rather poor in the existing data set because only few individuals were obtained within one zooplankton sample. Depending on the outcome of the modeling work during the two year application period we will apply the plankton succession model to study other time periods of the year, other lakes, mesocosms or extend the model by considering additional species.