Sensitivity of using stable water isotopic tracers to study the hydrology of isolated wetlands in North Florida

Abstract

Hydrology of forested wetlands is critical to the ecosystem functions and services of the forests. Our understanding of the hydrology of those wetlands, however, is very limited most likely due to the tediousness and costs of monitoring those scattered small wetlands by the traditional methods. Stable isotope ratios of oxygen (δ18O) and hydrogen (δ2H) in water may provide us a much simpler alternative to study the hydrology of those wetlands. We investigated the sensitivity and resolution of using natural stable water isotopes to quantify the hydrology of those isolated wetlands in the forests of North Florida. The observed Local Meteoric Water Line (LMWL) [δ2H = 7.7*δ18O + 9.2 (r2 = 0.97, n = 202)] followed closely to the Global Meteoric Water Line (GMWL), indicating the local rains were formed following a general isotopic equilibrium condition. Using data collected between 2014 and 2017, we observed a negative linear correlation between monthly total rain and the weight of its isotopic signature. There was no significant effect of temperature or humidity on the isotopic signatures of the rains. The water isotopes of the ephemeral ponds and sinks, on the other hand, were significantly enriched relative to the precipitation. The local evaporation lines (LEL) of the studied ephemeral ponds and sinks indicated significant evaporation. The isotope data indicated that the ephemeral Pond 55 and Pond 12 were rain fed while the water source to Blue Sink was a mixture of precipitation and groundwater. We showed that the significant differences in stable water isotopic signatures among the precipitation (especially during tropical storms and hurricanes), surface water and ground water can be used to trace the hydrological budgets and processes of forested wetlands in North Florida.