Separating surface runoff from tile drainage flow in agricultural lowland catchments based on diatoms to improve modeled runoff components and phosphorous transport

无论是发达国家还是发展中国家，在制定可持续战略时，以生态和经济上充分的方式进行水资源综合管理正受到越来越多的关注。SWAT模型等生态水文模型是流域范围内水资源可持续管理的广泛应用工具。然而，流域管理如何推动流域水文平衡和水质的变化，目前仍不是很清楚。这在低地集水区尤其明显，这些集水区具有低水力坡度、平坦的地形、高蓄水潜力、大量瓦片排水以及地表水和地下水密切相互作用的特点。因此，该项目的目标是以德国北部的Kielstau集水区(50平方公里)为例，测试一种生物示踪剂(即硅藻)在探测地表径流和排水径流方面的适用性。基于每日混合、降雨和瓦砾排水采样的硅藻和水质分析，我们的目标是1)量化地表径流对低地河流总流量的贡献，2)根据不同水流成分的硅藻浓度分离地表径流和瓦砾排水径流，并确定磷进入河流的途径，3)将检测到的径流产生和磷的输送过程落实到生态水文SWAT模型新引入的瓦砾排水程序中，以改进常规结构和模型性能。

Integrated water resources management in an ecologically and economically adequate way is receiving more and more attention when it comes to the development of sustainable strategies in either developed or developing countries. Ecohydrological models like the SWAT model are widely applied tools for sustainable management of water resources at river basin scale. Nevertheless it is still not clearly understood, how river basin management drives changes in the hydrological balance and the water quality of catchments. This is especially apparent in lowland catchments characterized by low hydraulic gradients, flat topography, high potential for water retention, a large amount of tile drainages and a close interaction of surface- and groundwater.The objective of this project is thus to test the applicability of a biological tracer (i.e. diatoms) for the detection of surface runoff and drainage flow in the example case of the Kielstau catchment (50 km2) in northern Germany. Based on the diatom and water quality analyses of daily mixed, rain event based river and tile drainage samplings, we aim to1) quantify the contribution of surface runoff to total river discharge in lowlands,2) separate surface runoff from tile drainage flow based on different diatom concentration of each flow component and determine the entry pathways of phosphorus into the river, and 3) implement the detected runoff generation and phosphorous transport processes into the newly introduced tile-drainage routine of the ecohydrological SWAT model to improve the routine structure and the model performance.