Isotope Signatures of the Precipitation and Natural Waters in the Forests of North Florida.

Hydrological process and water balances of forests are critical to their ecosystem functions and services. However, our understanding of those processes and balances is limited in the isolated wetlands of Apalachicola National Forest (ANF) in north Florida. We initiated a study using hydrogen and oxygen isotopic signatures of waters to understand the hydrologic processes and balances of those isolated wetlands. We report here the baseline information of the isotopic signatures of waters in two isolated wetlands in ANF. Our results indicated a local Meteoric Water Line (LMWL) of d²H = 7.8*d¹⁸O + 8.8 (n=187) that followed closely the Global Meteoric Water Line (GMWL) of d²H = 8*d¹⁸O + 10. We observed no significant correlation between rain amount and isotopic signature, except the largest and most intense rains from named tropical storms and hurricanes. Those intense rains were typically associated with the most depleted oxygen and hydrogen values. We observed the most enriched (and with the narrowest range of) d¹⁸O (-7.3 to +0.9 ‰, n =63) and d²H (-45.0 to +10.9 ‰, n=63) values of rains during the winter (December to February) and spring (March to May) seasons. In contrast, more depleted isotope values were observed in the rains of summer and fall seasons (d¹⁸O: -14.3 to +1.3 ‰; d²H: -108 to +11.5 ‰; n=94). We were also able to establish preliminary local evaporation lines (LEL) for some water bodies within the ANF like d²H = (5.3, 5.4, 5.4)*d¹⁸O + (–3.0, –5.4, –5.7) (n=34, 68, 69) for Pond 55, Pond 12 and Blue Sink, respectively. These data along with groundwater isotopic signature that we are currently collecting, can help us better understand the hydrological processes and balances of those isolated wetlands in ANF.