SMALL FARM PONDS: OVERLOOKED FEATURES WITH IMPORTANT IMPACTS ON WATERSHED SEDIMENT TRANSPORT

Despite their size, small farm ponds are important features in many landscapes. Yet hydrographical databases often fail to capture these ponds, and their impacts on watershed processes remain unclear. For a 230-km(2) portion of central Texas, United States (U.S.), we created a historical inventory of ponds and quantified the accuracy of automated detection methods under varying drought conditions. In addition, we documented pond dredging/enlargement events and identified sites that had been abandoned. We also analyzed sediment cores from downstream reservoirs to track changes in watershed sediment transport. Over 75years, pond densities increased more than 350% - to among the highest documented in the U.S. - and the ability of automated methods to detect these ponds was highly dependent on drought severity (R-2=0.96). Approximately 5% of ponds present in the 1950s were no longer present in 2012, while 33% were dredged between 1937 and 2012. Downstream reservoir sedimentation has decreased by an average of 55% as ponds have increased in number. These findings suggest that small ponds and the maintenance of trapping efficiency have large-scale impacts on sediment dynamics. Accurately accounting for these storage effects is vital to water resource planning efforts.