Lewis David Bruce, Grimm Nancy B
Global Institute of Sustainability, Arizona State University, P.O. Box 873211, Tempe, Arizona 85287-3211, USA.
Ecol Appl. 2007 Dec;17(8):2347-64. doi: 10.1890/06-0031.1.
In urban catchments of arid central Arizona, we investigate how the export of mineral and organic nitrogen (N) in storm runoff is regulated by interactions between local landscape characteristics and broader scale storm features. First, we test whether N export is more a function of (1) processes that affect N concentration in runoff or (2) the propensity of the catchment to convey rainfall as runoff. With data pooled across catchments, the mass of N in export (load) is determined by processes regulating runoff N concentration. There are exceptions when catchments are examined individually, where N load from some catchments is determined by the hydrologic responsiveness of the catchment. Second, we investigate the relationship between N export and catchment features. Loads per catchment area were greater from more impervious catchments, probably because impervious catchments held more N in a mobilizable phase and conveyed more rainfall as overland flow. Loads per area were lower from larger catchments, possibly owing to more N-retention hot spots in larger catchments. Catchments with the greatest N exports were those with commercial land use, and loads decreased as development became less prevalent or as residential replaced industrial land use. Third, we investigated how catchment features moderated direct responses of N export to storms. Export was less correlated with storm features in catchments that were larger, more pervious, and less industrial. Results support an "N build and flush" hypothesis, which purports that there is little biotic processing of N deposited to arid, urban surfaces with little organic matter. The rate and duration of deposition determine the size of the mobile N pool. Any amount of rainfall capable of generating overland flow would entrain nearly all mobilizable N and export it from the catchment. Nonetheless, these results suggest that, even with daunting seasonal and interannual variability in storm conditions, material export can be reduced by managing intrinsic catchment features.
在亚利桑那州中部干旱地区的城市集水区，我们研究了暴雨径流中矿物质和有机氮（N）的输出是如何受到当地景观特征与更大尺度暴雨特征之间相互作用的调节的。首先，我们测试氮输出更多地是（1）影响径流中氮浓度的过程的函数，还是（2）集水区将降雨作为径流输送的倾向的函数。利用跨集水区汇总的数据，输出（负荷）中氮的质量由调节径流氮浓度的过程决定。当单独检查集水区时存在例外情况，一些集水区的氮负荷由集水区的水文响应性决定。其次，我们研究了氮输出与集水区特征之间的关系。不透水集水区每集水区面积的负荷更大，可能是因为不透水集水区在可移动相中保留了更多的氮，并将更多的降雨作为地表径流输送。面积较大的集水区每面积的负荷较低，可能是由于较大集水区中有更多的氮保留热点。氮输出最大的集水区是那些有商业用地的集水区，随着开发变得不那么普遍或住宅取代工业用地，负荷会下降。第三，我们研究了集水区特征如何调节氮输出对暴雨的直接响应。在面积更大、渗透性更强且工业化程度更低的集水区，输出与暴雨特征的相关性较小。结果支持“氮积累与冲刷”假说，该假说认为，沉积到几乎没有有机物的干旱城市表面的氮几乎没有生物处理过程。沉积的速率和持续时间决定了可移动氮库的大小。任何能够产生地表径流的降雨量都会夹带几乎所有可移动的氮并将其从集水区输出。尽管如此，这些结果表明，即使暴雨条件存在令人生畏的季节性和年际变化，通过管理集水区的内在特征仍可减少物质输出。
