Van Meter Kimberly J, Basu Nandita B
Department of Earth & Environmental Sciences, University of Waterloo, Waterloo, ON, Canada.
Department of Earth & Environmental Sciences, University of Waterloo, Waterloo, ON, Canada; Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, ON, Canada.
PLoS One. 2015 May 18;10(5):e0125971. doi: 10.1371/journal.pone.0125971. eCollection 2015.
Nutrient legacies in anthropogenic landscapes, accumulated over decades of fertilizer application, lead to time lags between implementation of conservation measures and improvements in water quality. Quantification of such time lags has remained difficult, however, due to an incomplete understanding of controls on nutrient depletion trajectories after changes in land-use or management practices. In this study, we have developed a parsimonious watershed model for quantifying catchment-scale time lags based on both soil nutrient accumulations (biogeochemical legacy) and groundwater travel time distributions (hydrologic legacy). The model accurately predicted the time lags observed in an Iowa watershed that had undergone a 41% conversion of area from row crop to native prairie. We explored the time scales of change for stream nutrient concentrations as a function of both natural and anthropogenic controls, from topography to spatial patterns of land-use change. Our results demonstrate that the existence of biogeochemical nutrient legacies increases time lags beyond those due to hydrologic legacy alone. In addition, we show that the maximum concentration reduction benefits vary according to the spatial pattern of intervention, with preferential conversion of land parcels having the shortest catchment-scale travel times providing proportionally greater concentration reductions as well as faster response times. In contrast, a random pattern of conversion results in a 1:1 relationship between percent land conversion and percent concentration reduction, irrespective of denitrification rates within the landscape. Our modeling framework allows for the quantification of tradeoffs between costs associated with implementation of conservation measures and the time needed to see the desired concentration reductions, making it of great value to decision makers regarding optimal implementation of watershed conservation measures.
在人为景观中，经过数十年施肥积累的养分遗留问题，导致保护措施实施与水质改善之间存在时间滞后。然而，由于对土地利用或管理方式改变后养分消耗轨迹的控制因素理解不全面，量化这种时间滞后一直很困难。在本研究中，我们开发了一个简约的流域模型，用于基于土壤养分积累（生物地球化学遗留）和地下水流动时间分布（水文遗留）来量化流域尺度的时间滞后。该模型准确预测了爱荷华州一个流域中观察到的时间滞后，该流域41%的面积已从行播作物转变为原生草原。我们探讨了溪流养分浓度随自然和人为控制因素变化的时间尺度，这些因素从地形到土地利用变化的空间格局。我们的结果表明，生物地球化学养分遗留的存在增加了时间滞后，使其超出仅由水文遗留导致的时间滞后。此外，我们表明最大浓度降低效益根据干预的空间格局而变化，优先转换集水区尺度流动时间最短的地块能按比例带来更大的浓度降低以及更快的响应时间。相比之下，随机转换模式导致土地转换百分比与浓度降低百分比之间呈1:1关系，而与景观内的反硝化率无关。我们的建模框架能够量化与实施保护措施相关的成本与实现预期浓度降低所需时间之间的权衡，这对决策者在流域保护措施的优化实施方面具有重要价值。
