DEVELOPMENT OF STANDARD DIGITIZING PROCEDURES TO ASSESS TEMPORAL CHANGES IN SMALL, ANTHROPOGENIC PONDS USING HISTORICAL AERIAL PHOTOGRAPHS AND GIS

Small, anthropogenic water bodies (ponds) have become a recent topic of study due to their abundance and their effects on sedimentation, water budgets, nutrient cycles (including carbon), water quality, and local ecology. However, problems exist with determining pond inventories accurately and evaluating their cumulative effects. Other studies have compared ponds detected by automated remote sensing techniques, specifically spectral detection of water-dominated pixels, to ponds that were identified and digitized from aerial photographs. Unfortunately, automated methods using the most common and widely available multispectral imagery (Landsat ETM+) detect only about 60% of known ponds, and typical digitizing methods, though an improvement, lack standard repeatable procedures. In this study, we developed standardized digitizing techniques that can be used by any researcher. Our methods include analysis of tree shadows, pond water turbidity, aquatic vegetation, and tonal and color differences in aerial photographs. The result was a preliminary handbook for standardized pond digitizing. The standard techniques were used to assess temporal changes in pond abundance and size from a time-series of historical aerial photographs (1944 – 2008) in a small basin in eastern Kansas. Our study showed that between 1944 and 2008 the number of ponds in the basin increased from 179 to 480, total water area increased from 2.8% of the basin to 11.8%, and average pond size increased from 1834 m² to 2843 m². Also, a relationship seems to exist between fluctuations in precipitation and pond size within the study basin. Our study demonstrates the effectiveness of historical aerial photographs, GIS, and a standardized digitization method to collect data to monitor environmental change. Systematic investigations such as this are essential for advancing automated pond detection techniques and will allow for more accurate pond inventories of larger regions. Pond inventory studies are necessary for further assessments of the cumulative effects of ponds on a region’s hydrology, geochemistry and ecology.