Can nutrient pathways and biotic interactions control eutrophication in riverine ecosystems? Evidence from a model driven mesocosm experiment.
Can nutrient pathways and biotic interactions control eutrophication in riverine ecosystems? Evidence from a model driven mesocosm experiment.
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DOI：
10.1016/j.watres.2017.02.062
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发表时间：
2017-05
期刊：
影响因子：
12.8
通讯作者：
C. Jäger;Jeske Hagemann;D. Borchardt
中科院分区：
文献类型：
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作者：
C. Jäger;Jeske Hagemann;D. Borchardt
生态理论预测，底栖生物与浮游生物初级生产的相对重要性通常沿着河流的连续体从下游的底栖藻类占主导地位转变为上游的浮游藻类占主导地位。然而，驱动这些栖息地中藻类之间相互作用的潜在机制、其控制因素以及对河流生态系统的影响，人们仅得到部分了解。我们使用简化的数值模型对主导生态过程进行了机械分析，并研究了非生物因素和生物相互作用如何通过改变资源竞争来影响底栖和浮游藻类。我们将模型的结果与模拟模型参数空间的阶乘介观实验的结果进行比较。结果表明，底栖和远洋藻类生物量的时间发展以及优势模式的转变具有显着的相似性。我们特别分析了养分供给途径（从潜流带上升流、直接供给地表水或通过这两种途径）和河流深度梯度放牧的影响。我们的结果表明，底栖藻类的分离、浮游藻类的下沉和养分供应途径是决定各自藻类生物量分布的关键过程，特别是在浅层和中深系统中。增加养分供应会增加藻类生物量，但不会改变相互作用的一般模式。光照减少会降低浮游藻类的优势，但会增加溶解的营养物质。在中等到高放牧率下，藻类生物量可以由食草动物控制，但是，在高放牧率下，溶解的养分会在地表水中积累。我们的结果表明，为了理解和解释河流生态系统的富营养化现象，需要明确考虑营养途径、资源竞争和放牧的内部控制。因此，对自来水系统进行生态有效的富营养化管理必须超越对营养物排放的控制或实现受纳水域的限制阈值，但需要考虑营养物途径（地表水与地下水）以及从低阶河流生态系统到高级河流生态系统的生物控制的转变。
Ecological theory predicts that the relative importance of benthic to planktonic primary production usually changes along the rivers' continuum from a predomination of benthic algae in lower stream orders to a predomination of planktonic algae at higher orders. Underlying mechanisms driving the interaction between algae in these habitats, its controlling factors and consequences for riverine ecosystems are, however, only partly understood. We present a mechanistic analysis of the governing ecological processes using a simplified, numerical model and examine how abiotic factors and biotic interactions influence benthic and planktonic algae by changing resource competition. We compare the outcome of the model with the results of a factorial mesocosm experiment mimicking the parameter spaces of the model. The results show a remarkable similarity with regard to the temporal development of benthic and pelagic algal biomass and shifting dominance patterns. In particular we analyse the effects of the pathways of nutrient supply (upwelling from the hyporheic zone, direct supply to the surface water, or via both pathways) and grazing in a gradient of river depths. Our results show that detachment of benthic algae, sinking of planktonic algae and the pathway of nutrient supply are key processes determining the respective algal biomass distributions particularly in shallow and intermediate deep systems. Increasing nutrient supply increases algal biomasses, but does not change the general pattern of the interactions. Decreasing light supply decreases the dominance of planktonic algae, but increases dissolved nutrients. At intermediate to high grazing rates algal biomass can be controlled by grazers, but however, at high grazing rates, dissolved nutrients accumulate in the surface water. Our results indicate that nutrient pathways, resource competition and internal control by grazing need to be considered explicitly for the understanding and explanation of eutrophication phenomena in riverine ecosystems. As a consequence, ecologically effective eutrophication management of running water systems has to go beyond the control of nutrient emissions or the achievement of limiting threshold values in the receiving waters, but requires the consideration of the nutrient pathways (surface water versus groundwater) and the shifting biological controls from lower to higher order stream ecosystems.