This research develops a tracer method that will enable ecosystem managers to identify and apportion nonpoint sources of pollution. This knowledge can be invaluable in directing scarce resources towards improving water quality. The proposed research is efficient, since it adapts a well-established method currently used for identifying natural chemical sources and flow paths in pristine environments, expanding its application to pollution sources across the landscape. The goal is to demonstrate the utility of end member mixing analysis (EMMA) to identify and quantify the relative contribution of multiple nonpoint sources to pollution loads of streams draining Connecticut watersheds. Sources (end members) include precipitation, dry deposition, septic tanks, leaking sewage lines, street drainage, lawn chemicals, roof runoff, agriculture, and weathering. Most of the proposed tracers are measured routinely, to make the method as widely applicable as possible. Additional novel tracers are being identified and evaluated to increase the method’s reliability.
Twenty-nine tracers have been measured and evaluated in the eight end member sources and several impacted streams. The tracers are SO42-, Cl-, Na+, K+, Ca2+, Mg2+, SiO2, HCO3-/ANC, DOC, conductivity, Br-, I-, F-, Li+, Rb+, Sr2+, H2VO4-, MoO42-, H3BO3, Ni, Cu, Zn, UO2(CO3)22-, ClO4-, Pd, caffeine, ibuprofen, 35S, and PAHs, though only a best subset (≈ 12) of these will be used in the final tracer method. (Many of the tracers can be measured simultaneously, so the number of analyses is fewer than the list might suggest.) In addition, two contaminants (NO3-, Hg) are measured to evaluate the tracer method’s ability to identify their sources. Data synthesis includes principal component analysis (to determine the rank of the data), multiple linear regressions, explicit consideration of uncertainty in end member composition during regression, backward estimation of end members, alternative testing, and sensitivity analysis to identify the best subset of tracers.
Supported by NOAA - Connecticut Sea Grant Program