Conductivity as a tracer of agricultural and urban runoff to delineate water quality impacts in the northern Everglades Matthew C. Harwell & Donatto D. Surratt & Dorianne M. Barone & Nicholas G. Aumen Received: 2 July 2007 / Accepted: 19 December 2007 / Published online: 26 January 2008 # U.S. Fish and Wildlife Service, U.S. Department of Interior 2008 Abstract Agricultural and urban runoff pumped into the perimeter canals of the Arthur R. Marshall Loxahatchee National Wildlife Refuge (Refuge), a 58,320-ha soft-water wetland, has elevated nutrients which impact the Refuge interior marsh. To best manage the Refuge, linkages between inflows to the perimeter canals and environmental conditions within the marsh need to be understood. Conductivity, which typically is high in the canals and lowest at the most interior sites, was used as a surrogate tracer to characterize patterns of constituent transport. The Refuge was initially classified into four zones based upon patterns and variability in conductivity data: Canal Zone; Perimeter Zone (canal to 2.5 km into the interior); Transition Zone (2.5 to 4.5 km from the canal); Interior Zone (>4.5 km from the canal). Conductivity variability declined from the Perimeter to the Interior Zone, with the highest variability in the marsh observed in the Perimeter Zone and the lowest variability observed in the Interior Zone. Analysis of other water quality parameters indicated that conditions in the Perimeter and Transition Zones were different, and more impacted, than in the Interior Zone. In general, there was a positive relationship between structure inflows and canal phosphorus concentrations, including discharges from treatment wetlands and bypasses of untreated water. This classification approach is applica- ble for stratified sampling designs, resolving spatial bias in water quality models, and in aiding in management decisions about resource allocation. Keywords A.R.M. Loxahatchee National Wildlife Refuge . Chloride . Nitrogen . Nutrients . Oligotrophic wetland . Phosphorus . Soft water . South Florida . Sulfate Introduction The Everglades developed as a rainfall-driven system with surface waters low in nutrients and other inorganic ions. More than half of the original spatial Environ Monit Assess (2008) 147:445–462 DOI 10.1007/s10661-007-0131-3 M. C. Harwell (*) : D. D. Surratt : D. M. Barone : N. G. Aumen Department of Interior—Everglades Program Team, Boynton Beach, FL 33473, USA e-mail: matthew_harwell@fws.gov N. G. Aumen c/o A.R.M. Loxahatchee National Wildlife Refuge, 10216 Lee Rd., Boynton Beach, FL 33473, USA Present address: M. C. Harwell : D. D. Surratt c/o A.R.M. Loxahatchee National Wildlife Refuge, 10216 Lee Rd., Boynton Beach, FL 33473, USA Present address: D. M. Barone Florida Atlantic University, Boca Raton, FL 33431, USA