Data for: Hydraulic Shortcuts Increase the Connectivity of Arable Land Areas to Surface Waters

Surface runoff represents a major pathway for pesticide transport from agricultural areas to surface waters. The influence of man-made structures (e.g. roads, hedges, ditches) on surface runoff connectivity has been shown in various studies. In Switzerland, so-called hydraulic shortcuts (e.g. inlets and maintenance manholes of road or field storm drainage systems) have been shown to influence surface runoff connectivity and related pesticide transport. Their occurrence, and their influence on surface runoff and pesticide connectivity have however not been studied systematically.To address that deficit, we randomly selected 20 study areas (average size = 3.5 km²) throughout the Swiss plateau, representing arable cropping systems. We assessed shortcut occurrence in these study areas using three mapping methods: field mapping, drainage plans, and high-resolution aerial images. Surface runoff connectivity in the study areas was analysed using a 2x2 m digital elevation model and a multiple-flow algorithm. Parameter uncertainty affecting this analysis was addressed by a Monte Carlo simulation. With our approach, agricultural areas were divided into areas that are either directly connected to surface waters, indirectly (i.e. via hydraulic shortcuts), or not connected at all. Finally, the results of this connectivity analysis were scaled up to the national level using a regression model based on topographic descriptors and were then compared to an existing national connectivity model.Inlets of the road storm drainage system were identified as the main shortcuts. On average, we found 0.84 inlets and a total of 2.0 manholes per hectare of agricultural land. In the study catchments between 43 and 74 % of the agricultural area is connected to surface waters via hydraulic shortcuts. On the national level, this fraction is similar and lies between 47 and 60 %. Considering our empirical observations led to shifts in estimated fractions of connected areas compared to the previous connectivity model. The differences were most pronounced in flat areas of river valleys.These numbers suggest that transport through hydraulic shortcuts is an important pesticide flow path in a landscape where many engineered structures exist to drain excess water from fields and roads. However, this transport process is currently not considered in Swiss pesticide legislation and authorisation. Therefore, current regulations may fall short to address the full extent of the pesticide problem. However, independent measurements of water flow and pesticide transport to quantify the contribution of shortcuts and validating the model results are lacking. Overall, the findings highlight the relevance of better understanding the connectivity between fields and receiving waters and the underlying factors and physical structures in the landscape.

地表径流是农药从农业区域向地表水体迁移的主要途径。已有多项研究证实，人工构筑物（如道路、树篱、沟渠）会对地表径流连通性产生影响。在瑞士，所谓的水力捷径（hydraulic shortcuts）——例如道路或农田暴雨排水系统的进水口与检修井——已被证明会影响地表径流连通性及相关的农药迁移过程。然而，目前尚未有研究对这类捷径的分布及其对地表径流和农药迁移连通性的影响开展系统性探究。为填补这一研究空白，我们在瑞士高原全域随机选取了20个研究区域（平均面积=3.5 km²），所有区域均代表典型的耕作农田系统。我们采用三种测绘手段——野外实地测绘、排水规划图纸与高分辨率航空影像——对研究区内的水力捷径分布情况进行了排查。研究采用2米×2米分辨率的数字高程模型（digital elevation model）与多流向算法，对研究区内的地表径流连通性展开分析；针对该分析涉及的参数不确定性问题，我们通过蒙特卡洛模拟（Monte Carlo simulation）进行了处理。通过本研究的分析框架，农业区域被划分为三类：直接连通地表水体的区域、间接（即通过水力捷径）连通的区域，以及完全不连通的区域。最后，本研究基于地形特征参数构建回归模型，将连通性分析的结果尺度上推至全国尺度，并与现有国家级连通性模型开展对比。研究发现，道路暴雨排水系统的进水口是最主要的水力捷径类型；平均而言，每公顷农业用地对应0.84个进水口与总计2.0个检修井。在本次研究的流域内，43%至74%的农业区域通过水力捷径与地表水体相连；在全国尺度下，该占比相近，处于47%至60%之间。相较于此前的连通性模型，本次基于实测观测的研究使得连通区域的估算占比发生了变化，这种差异在河谷平缓区域表现得最为显著。上述结果表明，在大量布设工程构筑物以排除农田与道路积水的景观中，通过水力捷径的迁移是一条重要的农药运移路径。但目前瑞士的农药立法与登记审批流程尚未纳入这一迁移过程，因此现行法规可能未能全面覆盖农药污染问题的全部影响范围。不过，当前仍缺乏针对水流与农药迁移的独立实测数据，无法量化水力捷径的贡献并验证模型结果。总体而言，本研究结果凸显了深化认识农田与受纳水体间连通性、以及景观中相关影响因素与物理构筑物的必要性。