CHEMICAL CHARACTERISTICS OF SUBURBAN PONDS ACROSS A LAND USE GRADIENT

Suburban ponds represent understudied, yet highly important, aquatic ecosystems. An integrated chemical, biological, and landscape based study on the relationships between suburban land use, water chemistry, and amphibian (green frog, Rana clamitans) reproductive health was conducted on 19 ponds in south-central Connecticut. The biological results are presented in a companion paper. The ponds included forested (control) and suburban (residences on septic or sewer systems) sites. At each pond, shallow monitoring wells were installed near the shoreline, and surface and groundwater samples were collected for analysis of 54 elements by inductively-coupled-plasma/mass spectrometry and inductively-coupled-plasma/atomic emission spectrometry. Although groundwater and surface water distributions of the various elements were highly variable, representing complex geologic and land use relationships, there were several consistent trends. Concentrations of B, Ca, Mg, and Na increased with increasing development and road density. Using groundwater/surface water distributions of Sr, B, and rare earth elements, the sites could be categorized as ponds with similar groundwater/surface water conditions, ponds undergoing net-water exportation (dominated by evaporation), and ponds undergoing net-water importation (precipitation and runoff). Several ponds showed fractionation of As and the transition metals Zr, Mo, Mn, Fe, and Co between groundwater and surface water as the result of geochemical processes. Concentrations and distributions of the major elements are consistent with water-rock interactions and geochemistry of the groundwater, although there is anthropogenic enrichment of many elements including Li, K, Rb, Sr, Ba, and U. Concentrations of most elements in the pond waters were low, relative to streams, due to the absence of point-source discharges and limited non-point sources in the small drainage areas. However, several trace elements detected in the ponds, including As and Cd, have been reported to be “metalloestrogens” and have the potential to interfere with frog and other vertebrate reproduction. This type of complex inorganic chemical and hydrological understanding is essential to assessing complex biological processes.