Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
Integrated Science Lab - IceLab, Umeå University, Umeå, Sweden.
Glob Chang Biol. 2019 Feb;25(2):504-521. doi: 10.1111/gcb.14521. Epub 2018 Dec 14.
Productivity and trophic structure of aquatic ecosystems result from a complex interplay of bottom-up and top-down forces that operate across benthic and pelagic food web compartments. Projected global changes urge the question how this interplay will be affected by browning (increasing input of terrestrial dissolved organic matter), nutrient enrichment and warming. We explored this with a process-based model of a shallow lake food web consisting of benthic and pelagic components (abiotic resources, primary producers, grazers, carnivores), and compared model expectations with the results of a browning and warming experiment in nutrient-poor ponds harboring a boreal lake community. Under low nutrient conditions, the model makes three major predictions. (a) Browning reduces light and increases nutrient supply; this decreases benthic and increases pelagic production, gradually shifting productivity from the benthic to the pelagic habitat. (b) Because of active habitat choice, fish exert top-down control on grazers and benefit primary producers primarily in the more productive of the two habitats. (c) Warming relaxes top-down control of grazers by fish and decreases primary producer biomass, but effects of warming are generally small compared to effects of browning and nutrient supply. Experimental results were consistent with most model predictions for browning: light penetration, benthic algal production, and zoobenthos biomass decreased, and pelagic nutrients and pelagic algal production increased with browning. Also consistent with expectations, warming had negative effects on benthic and pelagic algal biomass and weak effects on algal production and zoobenthos and zooplankton biomass. Inconsistent with expectations, browning had no effect on zooplankton and warming effects on fish depended on browning. The model is applicable also to nutrient-rich systems, and we propose that it is a useful tool for the exploration of the consequences of different climate change scenarios for productivity and food web dynamics in shallow lakes, the worldwide most common lake type.
水生生态系统的生产力和营养结构是由底栖和浮游食物网区的正、负相互作用产生的，这些相互作用受到全球变化的影响。本研究利用一个浅水湖泊食物网的过程模型对此进行了探讨，该模型包括底栖和浮游两部分（非生物资源、初级生产者、食草动物、肉食动物），并将模型预测结果与在贫营养池塘中进行的褐变和变暖实验结果进行了比较，这些池塘中栖息着北方湖泊群落。在低营养条件下，模型有三个主要预测：（a）褐变减少光的穿透并增加养分供应，从而减少底栖生物并增加浮游生物的产量，逐渐将生产力从底栖区转移到浮游区；（b）由于主动选择栖息地，鱼类对食草动物施加自上而下的控制，主要受益于两种生境中生产力较高的生境中的初级生产者；（c）变暖会放松鱼类对食草动物的自上而下的控制，并减少初级生产者的生物量，但与褐变和养分供应的影响相比，变暖的影响通常较小。实验结果与模型对褐变的大多数预测一致：随着褐变，光穿透、底栖藻类生物量和底栖动物生物量减少，而浮游营养物质和浮游藻类生物量增加。与预期一致的是，变暖对底栖和浮游藻类生物量有负面影响，对藻类生物量和底栖动物和浮游动物生物量的影响较弱。与预期不一致的是，褐变对浮游动物没有影响，而变暖对鱼类的影响取决于褐变。该模型也适用于富营养系统，我们提出，它是探索不同气候变化情景对浅水湖泊生产力和食物网动态影响的有用工具，浅水湖泊是世界上最常见的湖泊类型。
