Testing the ponds people built

Three kinds of pond

Commission scientists mapped 5,850 natural ponds, excavated ponds and stormwater basins. Excavated ponds intercept groundwater; stormwater basins receive runoff. The project compared their ecological conditions. Commission, Natural and Created Wetlands Study.

The study also assessed vehicle damage and projected development. Natural ponds were generally less exposed to development because many lay in protected areas. Commission, Natural and Created Wetlands Study.

Chemicals and pathogens did not follow one simple pattern

A cooperating USGS team sampled 24 wetlands during 2014–2016. Its 2018 report found more pesticides and greater total pesticide concentrations in stormwater basins than in natural or excavated ponds. Reference wetlands also had fewer pesticides than degraded wetlands. These comparisons linked measured contamination with wetland type and surrounding land use. Smalling and colleagues, USGS report (2018).

The pathogen results were less easily divided into good and bad pond categories. Ranavirus appeared in larvae from four wetlands, including a reference natural pond. The chytrid fungus Bd was detected in animals from all three wetland types, although detection probability was low. Those findings do not establish that creating a basin caused disease, or that a single negative sample proved a pond pathogen-free. Smalling and colleagues, USGS report (2018).

The dragonflies did not supply a simple pollution score

The full report also surveyed adult dragonflies and damselflies and their shed larval skins at thirty-three natural ponds in 2014–2015. It recorded fifty-nine species. Assemblages varied with pond size, tree cover and surrounding development, but did not significantly track several chemical measures or an imported Rhode Island degradation classification. The authors considered habitat structure a potentially stronger influence than surrounding land use, while calling the analysis exploratory. Adult visitors and shed skins supplied complementary evidence, including successful emergence at the surveyed water bodies. Bunnell and colleagues, full wetland report (2018).