| Through hydrologic cycles, nonpoint source (NPS) pollutants generated by human activities at a local scale are accumulated into a broad-scale water quality problem. A watershed approach is required to address the cumulative impact of NPS problems. Nonetheless, what is the optimal size for watershed management is an on-going debate. To explore the effects of scale on landscape properties, hydrologic processes, and land-water interactions, an Iowa watershed encompassing some 11,000 km2 was first decomposed into four hierarchical levels, which contained 7, 11, 31, and 149 sub-watersheds, respectively, using GIS techniques. Hydrologic processes and landscape properties were then quantified for each of the 198 sub-watersheds using hydrologic modeling and pattern analysis techniques. Based on the simulated results and selected indices of landscape patterns, relationships between landscape patterns and hydrologic processes were established at discrete levels and translated to other levels within the watershed hierarchy. How dominant factors controlling the land-water interaction change with scale and errors resulting from scaling was finally evaluated. This case study reinforced the importance of scaling issues in resource management and exemplified how the effects of scale on spatial patterns, processes, and pattern-process interactions can be explored through a hierarchically structured framework using GIS techniques and statistical analyses. |
