Historical Changes in the Distribution and Abundance of Constructed Ponds in Response to Changing Population Density and Land Use

In the United States most ponds are constructed for varying purposes and at varying historical rates, yet little attention is paid to their presence or ecological impact. We evaluated changes in pond density, landscape position with respect to streams, and rates of pond construction and loss within a watershed in southeastern Pennsylvania and northern Delaware that has experienced increases in population density and associated changes in land use. Based on aerial photographs taken on nine dates between 1937 and 2005, and maps prepared in 1883, abundances of all water bodies declined slightly from 1883 to 1937, then increased 18-fold during the remainder of the study period. Most ponds in 1883 (94.6%) were 'in-line' impoundments receiving stream inflows, whereas 'off-line' water bodies without inflows represented 77.3% of total ponds in 2005. Pond loss rates averaged 3.2%/year between 1883 and 1946, but declined to 0.16%/year between 1946 and 2005. Because of their changing abundance and landscape position, ponds are assuming rapidly changing ecological roles within the watershed.