Pond Ecology


ecology

The former pond at the Stroud Preserve in East Bradford Township.


       This document describes “what makes ponds tick”, covering information about the effects of physical habitat and water chemistry on the plants and animals that together characterize regional pond communities. The intended audience consists of working professionals in the environmental sciences, but the presentation is at a level that should be accessible with careful reading to non-scientists with an interest in learning more about their ponds. Our focus is on ponds of Chester County, southeast PA (Fig. 1).
ecology

Fig. 1. Major watersheds of Chester County, southeast Pennsylvania.

       Just how small a water body must be to be called a pond is problematic. Although ponds may differ substantially as ecological systems from larger lakes, there is no firm or widely accepted basis for classifying water bodies as ponds vs. lakes (Søndergaard et al. 2005, DeMeester et al. 2005). The term “pond” is nonetheless in widespread use among researchers as well as non-professionals, and definitions have been provided in a number of papers. Biggs et al. (2005) proposed that ponds are “water bodies between 1 m2 and 2 ha in area”, including both natural and constructed, temporary or permanent waters (see also Oertli et al. 2005). Most of the ponds described here are less than 1 ha (2.5 acres); smaller garden pools are not considered, and excellent descriptions of larger lakes are provided elsewhere.
       Ponds, like lakes and reservoirs, are often termed “lentic”, or still-water, systems, distinguishing them from streams and rivers (“lotic” systems with flowing water). As shown by Downing et al. (2006), areal size is a principal determinant of the number of water bodies present in most parts of the globe (the frequencies of particular size classes decline in approximately inverse fashion to size itself).
number of ponds

Fig. 2. The size distribution of ponds in Chester County. Pond areas are shown on a log scale. As can be seen in the figure, smaller ponds are progressively more abundant down to a size of about 0.1 ha, but then appear to become less common, presumably because detecting them in aerial photos becomes more difficult.


       Below a threshold of approximately 0.1 ha, ponds in Chester County appear to become less abundant (Fig. 2), but this is likely due to a decline in our ability to detect very small ponds in aerial photos (the densities of very small ponds are probably underestimated). When the frequency of water bodies within a size class is multiplied by average size, a further pattern becomes apparent (Downing et al. 2006); the aggregate surface area of small water bodies, of the size described here, may exceed that of larger size classes. Pond size is one of the most important ecological attributes affecting water chemistry, the rate at which ponds accumulate sediments, and the abundance of aquatic species. Size matters!