Crop, Soil, and Environmental Sciences Department, Division of Agriculture, University of Arkansas, Fayetteville, AR 72701, USA.
Water Sci Technol. 2011;64(4):945-52. doi: 10.2166/wst.2011.712.
The concept of critical source areas of phosphorus (P) loss produced by coinciding source and transport factors has been studied since the mid 1990s. It is widely recognized that identification of such areas has led to targeting of management strategies and conservation practices that more effectively mitigate P transfers from agricultural landscapes to surface waters. Such was the purpose of P Indices and more complex nonpoint source models. Despite their widespread adoption across the U.S., a lack of water quality improvement in certain areas (e.g. Chesapeake Bay Watershed and some of its tributaries) has challenged critical source area management to be more restrictive. While the role of soil and applied P has been easy to define and quantify, representation of transport processes still remains more elusive. Even so, the release of P from land management and in-stream buffering contribute to a legacy effect that can overwhelm the benefits of critical source area management, particularly as scale increases (e.g. the Chesapeake Bay). Also, conservation tillage that reduces erosion can lead to vertical stratification of soil P and ultimately increased dissolved P loss. Clearly, complexities imparted by spatially variable landscapes, climate, and system response will require iterative monitoring and adaptation, to develop locally relevant solutions. To overcome the challenges we have outlined, critical source area management must involve development of a 'toolbox' that contains several approaches to address the underlying problem of localized excesses of P and provide both spatial and temporal management options. To a large extent, this may be facilitated with the use of GIS and digital elevation models. Irrespective of the tool used, however, there must be a two-way dialogue between science and policy to limit the softening of technically rigorous and politically difficult approaches to truly reducing P losses.
自 20 世纪 90 年代中期以来，人们一直在研究由源和输移因素同时作用而产生的磷（P）流失关键源区的概念。人们普遍认识到，确定这些关键源区有助于制定管理策略和保护措施，从而更有效地减轻农业景观向地表水转移的 P 量。这就是 P 指数和更复杂的非点源模型的目的。尽管这些方法在美国得到了广泛应用，但某些地区（例如切萨皮克湾流域及其某些支流）的水质改善情况并不理想，这对关键源区管理提出了更严格的要求。尽管土壤和施用 P 的作用很容易定义和量化，但输移过程的代表性仍然更加难以捉摸。即便如此，土地管理和河流缓冲带中 P 的释放仍会造成遗留效应，从而抵消关键源区管理的好处，特别是在规模增加（例如切萨皮克湾）的情况下。此外，减少侵蚀的保护性耕作可能导致土壤 P 的垂直分层，最终导致溶解态 P 流失增加。显然，由空间变异性景观、气候和系统响应带来的复杂性将需要迭代监测和适应，以制定出具有地方相关性的解决方案。为了克服我们所概述的挑战，关键源区管理必须开发一个“工具箱”，其中包含几种方法来解决 P 局部过剩的根本问题，并提供空间和时间管理选择。在很大程度上，这可以通过使用 GIS 和数字高程模型来实现。然而，无论使用何种工具，都必须在科学和政策之间进行双向对话，以限制对技术上严格且政治上困难的方法的软化，从而真正减少 P 流失。
