Department of Botany, University of Wisconsin - Madison, 430 Lincoln Drive, Madison, WI, 53706, USA.
Marquette University, 1225 W. Wisconsin Ave., Milwaukee, WI, 53233, USA.
J Environ Manage. 2021 Apr 15;284:112019. doi: 10.1016/j.jenvman.2021.112019. Epub 2021 Feb 1.
Fertilizers and manure applied to cropland to increase yields are often lost via surface erosion, soil leaching, and runoff, increasing nutrient loads in surface and sub-surface waters, degrading water quality, and worsening the 'dead zone' in the Gulf of Mexico. We leverage spatial and temporal variation in agricultural practices and precipitation events to examine how these factors affect stream total phosphorus (TP) concentrations and loads in the Sugar River (Wisconsin), recently listed as impaired. To perform our analysis, we first collected water quality data from 1995 to 2017 from 40 sites along the Sugar River and its tributaries. Starting in 2004, three dairy farms expanded to become concentrated animal feeding operations (CAFOs) in this watershed. We then estimated how time of year, stream position, discharge volume, and proximity to the newly expanded CAFOs affected TP concentrations and loads. Total P concentrations, which ranged from 0.02 to 1.4 mg/L and often exceeded the EPA surface water standard of 0.1 mg/L, increased with increases in stream discharge and proximity to dairy operations, peaking in early spring to mid-summer coincident with extreme precipitation events. Our empirical analysis also shows that TP concentrations downstream from the newly permitted CAFOs increased by 19% relative to upstream concentrations. When examining total daily phosphorus loads (concentration × discharge) from this 780 km watershed, we found that loads ranged from 5.88 to 4801 kg. Compared to upstream TP loads, those downstream from the CAFOs increased by 91% after the expansions - over four times that of concentration increases - implying that the rate of downstream phosphorus transfer has increased due to CAFO expansion. Our results argue for standards that focus on loads rather than concentrations and monitoring that includes peak events. As agriculture intensifies and extreme rainfall events become more frequent, it becomes increasingly important to limit soil and TP runoff from manure and fertilizer. Siting CAFOs carefully, limiting their size, and improving farming practices in proximity to CAFOs in spring and early summer could considerably reduce nutrient loads.
农田中为提高产量而施加的化肥和粪肥经常通过地表侵蚀、土壤淋溶和径流而流失，增加了地表水和地下水的养分负荷，导致水质恶化，并使墨西哥湾的“死区”情况恶化。我们利用农业实践和降水事件的时空变化来研究这些因素如何影响糖河（威斯康星州）的总磷（TP）浓度和负荷，该河流最近被列为受损河流。为了进行分析，我们首先从糖河及其支流的 40 个地点收集了 1995 年至 2017 年的水质数据。自 2004 年以来，三个奶牛场在该流域扩展成为集中式动物饲养场（CAFO）。然后，我们估计了一年中的时间、河流位置、流量和与新扩展的 CAFO 的接近程度如何影响 TP 浓度和负荷。总磷浓度范围从 0.02 到 1.4mg/L，经常超过 EPA 地表水标准的 0.1mg/L，随着河流流量的增加和与奶牛场的接近程度的增加而增加，在早春到夏中与极端降水事件同时达到峰值。我们的实证分析还表明，在新许可的 CAFO 下游，TP 浓度相对于上游浓度增加了 19%。当检查这个 780km 流域的总日磷负荷（浓度×流量）时，我们发现负荷范围从 5.88 到 4801kg。与上游 TP 负荷相比，在 CAFO 扩张后，下游负荷增加了 91%——是浓度增加的四倍多——这意味着由于 CAFO 扩张，下游磷转移的速度增加了。我们的研究结果表明，标准应该侧重于负荷而不是浓度，并且监测应该包括高峰事件。随着农业的集约化和极端降雨事件的发生频率增加，限制粪肥和化肥的土壤和 TP 径流变得越来越重要。在春季和初夏，仔细选址 CAFO，限制其规模，并改善 CAFO 附近的农业实践，可以大大减少养分负荷。
