Landscape Models for Simulating Water Quality at Point, Field, and Watershed Scales

In the last four decades, a plethora of models has been developed to simulate nonpoint-source (NPS) pollutant fate and transport at point, field, and watershed scales. Developed by experts in various disciplines, these models tend to reflect the needs of those disciplines. For example, the original intent of the solute transport models was to determine impact of water, nutrient, and salts on plant growth. Later, these models were extended to examine solute transport in the vadose zone to assess possible contamination of soil and groundwater. Similarly, a number of field- and watershed-scale models have been developed by linking together submodels of system components to quantify best management practice (BMP) effectiveness and watershed-level impact. New model users are often unaware of the suite of models available and are often uncertain about the appropriateness of models for their situation. The goals of this article are to discuss why NPS pollutant models were developed at various spatial scales (i.e., scale issues), briefly review commonly used models, and reflect on the future of landscape NPS models. Since the computational power of computers has significantly increased, automated data acquisition systems that can capture and transmit data at high resolution are being used, software that can handle large volumes of data has been developed, and improved chemical analysis capabilities are being developed, we conclude this article with the projection that development of a scale-independent model that can address complex issues of the next century by coupling state-of-the-art understanding of multiple hydrogeological, geochemical, and microbiological processes is possible. Future improvement in these models will result in a more scientific and robust approach for managing NPS pollutants.