Targeting for nonpoint source pollution reduction: A synthesis of lessons learned, remaining challenges, and emerging opportunities.

The ability to identify, target, and treat critical pollution source areas on a landscape is an ongoing challenge for water quality programs that seek to address nonpoint source (NPS) pollution. In this article, we develop a conceptual framework for targeting program design, and review recent experience with the implementation of targeting programs that corresponds with a wide range of program characteristics. Through this review, we emphasize that the complex and locally dependent nature of NPS generation and transport makes it impossible to define a narrow set of rules to guide targeting programs everywhere. Instead, we evaluate key features of NPS targeting in several different contexts, highlighting lessons learned from recent experience. This synthesis of targeting program design and implementation points toward several areas of opportunity for improved NPS policy, however more research is needed to systematically document changes in behavior and pollutant loads. The lack of monitoring data at refined scales presents a major obstacle to targeting program success. This paper synthesizes new opportunities and ongoing challenges for the implementation of targeting in NPS water quality programs.

The Promise, Practice, and State of Planning Tools to Assess Site Vulnerability to Runoff Phosphorus Loss.

Over the past 20 yr, there has been a proliferation of phosphorus (P) site assessment tools for nutrient management planning, particularly in the United States. The 19 papers that make up this special section on P site assessment include decision support tools ranging from the P Index to fate-and-transport models to weather-forecast-based risk calculators. All require objective evaluation to ensure that they are effective in achieving intended benefits to protecting water quality. In the United States, efforts have been underway to compare, evaluate, and advance an array of P site assessment tools. Efforts to corroborate their performance using water quality monitoring data confirms previously documented discrepancies between different P site assessment tools but also highlights a surprisingly strong performance of many versions of the P Index as a predictor of water quality. At the same time, fate-and-transport models, often considered to be superior in their prediction of hydrology and water quality due to their complexity, reveal limitations when applied to site assessment. Indeed, one consistent theme from recent experience is the need to calibrate highly parameterized models. As P site assessment evolves, so too do routines representing important aspects of P cycling and transport. New classes of P site assessment tools are an opportunity to move P site assessment from general, strategic goals to web-based tools supporting daily, operational decisions.