Makhtoumi Yashar, Uludere Aragon Nazli, Lark Tyler J
Center for Sustainability and Global Environment, Nelson Institute for Environmental Studies, University of Wisconsin-Madison, Madison, WI, USA.
The Numerical Terradynamic Simulation Group, University of Montana, Missoula, MT, USA.
J Environ Manage. 2025 Aug 19;393:126797. doi: 10.1016/j.jenvman.2025.126797.
Excess nutrients in aquatic systems can cause hypoxia, eutrophication, and algal blooms resulting in substantial modification and losses of ecosystem services. Given limited resources, approaches are needed to address water quality issues efficiently and effectively. Prioritized conservation efforts aim to concentrate resources on areas with the greatest impact and have been shown to be effective in mitigating agricultural non-point source nutrients reaching receiving waters. Here we propose a method leveraging hydrologic and biogeochemical modeling paired with soil and terrain analysis to characterize and select the most suitable fields and conservation practices to acheive nitrogen load mitigation. Our approach prioritizes agricultural fields by taking advantage of the spatial distribution of agricultural nitrogen use efficiency and surplus nitrogen to identify croplands that are likely contributing disproportionately high nitrate loads to river water. We assessed cover cropping, conservation tillage, and cropland-to-grassland restoration as within-field conservation practices to enhance nitrogen retention, targeting areas where the greatest gains toward water quality restoration goals could be achieved. Fields under cover crop and cropland-to-grassland conversion generally increased their nitrogen use efficiency, whereas implementation of conservation tillage showed more mixed responses in different fields and parts of the subbasin. Implementing cover crops on the 35.5 % of cropland (30.1 % of total land area) prioritized for the practice within the watershed reduced nitrate load at the subbasins outlet by 15.5 % (11,399 tons nitrate). Cropland-to-grassland restoration (prioritized on 6.3 % of cropland; 5.3 % coverage of the subbasins) reduced 5.2 % of the total nitrate load. Implementing conservation tillage on 18.7 % of cropland (15.8 % of subbasin) produced the lowest improvement in water quality with 1.8 % reduction in the nitrate load. The observed shifts were largely attributed to changes in the nitrate loss pathways. Cover crop and cropland-to-grassland implementation also influenced subbasins' water flow volume by decreasing the outlet daily discharge, by 28.6 % and 3.7 % respectively. Conservation tillage, however, increased the mean daily discharge by 9.5 %. This analysis effectively combines estimates loads and surpluses across the watershed to pinpoint areas where nitrogen management is most and least efficient, providing land management, policy, and investment decision makers with a clear platform to identify potential water quality issues and sites for effective intervention.
水生系统中的过量养分可导致缺氧、富营养化和藻华，从而导致生态系统服务发生重大改变并丧失。鉴于资源有限，需要采取有效方法来解决水质问题。优先保护措施旨在将资源集中于影响最大的区域，并且已证明在减少农业面源养分进入受纳水体方面是有效的。在此，我们提出一种方法，利用水文和生物地球化学模型，并结合土壤和地形分析，来表征和选择最合适的农田及保护措施，以实现氮负荷的减轻。我们的方法通过利用农业氮利用效率和过剩氮的空间分布来对农田进行优先排序，以识别那些可能对河水造成不成比例的高硝酸盐负荷的农田。我们评估了覆盖作物种植、保护性耕作以及农田恢复为草地等田间保护措施对增强氮截留的作用，目标是那些在实现水质恢复目标方面能够取得最大成效的区域。采用覆盖作物和将农田转变为草地的农田通常提高了它们的氮利用效率，而实施保护性耕作在不同农田和子流域的不同区域表现出更为复杂的响应。在流域内被确定为优先实施该措施的35.5%的农田（占总土地面积的30.1%）上种植覆盖作物，使子流域出口处的硝酸盐负荷减少了15.5%（11399吨硝酸盐）。将农田恢复为草地（优先在6.3%的农田上进行；占子流域面积的5.3%）减少了5.2%的总硝酸盐负荷。在18.7%的农田（占子流域面积的15.8%）上实施保护性耕作对水质的改善最小，硝酸盐负荷仅减少了1.8%。观察到的变化主要归因于硝酸盐流失途径的改变。种植覆盖作物和将农田转变为草地还分别使子流域的日径流量减少了28.6%和3.7%，从而影响了子流域的水量。然而，保护性耕作使平均日径流量增加了9.5%。该分析有效地结合了整个流域的估算负荷和过剩量，以确定氮管理效率最高和最低的区域，为土地管理、政策和投资决策者提供了一个明确的平台，以识别潜在的水质问题和有效干预的地点。
