Seepage characteristics were identified for L-31N, a canal and levee system which separates the East Everglades from urban areas. The site (110 km2) is located near Tamiami Trail and Krome Avenue in Miami-Dade County, Florida.

This site has been extensively monitored for groundwater stage, surface water stage and flow, and rainfall due to a municipal wellfield (West Wellfield) located within 2 kilometers of the Everglades and concerns over the impacts of this wellfield on seepage rates. To augment this monitoring program a stable isotope investigation was initiated through the current study along with the installation of seepage meters within the Everglades.

Results indicate that the stable isotopes of water (*18O and *D) can be used as natural tracers of Everglades waters and that a gradient exists in the isotopic composition of shallow groundwater (3 m depth) as one proceeds from the Everglades toward urban areas. During the dry season Everglades waters are highly evaporated due to high temperature and intense solar radiation acting upon shallow surface waters. The evaporated nature of these waters was confirmed by *D analysis coupled with *18O results which indicated that these waters fall below the meteoric water line. Results further indicate that as enriched Everglades groundwaters travel toward urban areas these waters are diluted by lighter, less evaporated waters. These lighter waters possibly originate from rainwater which rapidly infiltrates in urban areas. The net result is a net decrease in *18O toward urban areas. Surface water infiltration rates were observed to increase within the Everglades as Levee L-31N is approached from the west and that areas immediately adjacent to the levee serve as a sink for isotopically light water (e.g. rainwater). The municipal water supply which draws from depths greater than 13 meters is isotopically enriched suggesting that a portion of its supply originates from within the Everglades.

¹ Solo-Gabriele, H.M., Sternberg, L., Ibler, G., and Nemeth, M., 1998. "A Seepage Study of the East Everglades." Abstracts of the 1998 Spring Meeting of the American Geophysical Union, Boston, Massachusetts, EOS Supplement, April 28, 1998. p.S93.

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