The stable isotope hydrology of Sable Island, Nova Scotia, Canada with implications for evaluating the water budget of wild horses

We investigated the stable isotope hydrology of Sable Island, Nova Scotia, Canada over a five year period from September, 2017 to August, 2022. The delta 2H and delta 18O values of integrated monthly precipitation were weakly seasonal and ranged from -66 to -15 parts per thousand and from -9.7 to -1.9 parts per thousand, respectively. Fitting these monthly precipitation data resulted in a local meteoric water line (LMWL) defined by: delta 2H = 7.22 +/- 0.21 center dot delta 18O + 7.50 +/- 1.22 parts per thousand. Amount-weighted annual precipitation had delta 2H and delta 18O values of -36 +/- 11 parts per thousand and -6.1 +/- 1.4 parts per thousand, respectively. Deep groundwater had more negative delta 2H and delta 18O values than mean annual precipitation, suggesting recharge occurs mainly in the winter, while shallow groundwater had delta 2H and delta 18O values more consistent with mean annual precipitation or mixing of freshwater with local seawater. Surface waters had more positive values and showed evidence of isolation from the groundwater system. The stable isotopic compositions of plant (leaf) water, on the other hand, indicate plants use groundwater as their source. Fog had delta 2H and delta 18O values that were significantly more positive than those of local precipitation, yet had similar 17O-excess values. delta 2H values of horsehair from 4 individuals lacked seasonality, but had variations typical to those of precipitation on the island. Differences in mean delta 2H values of horsehair were statistically significant and suggest variations in water use may exist between spatially disparate horse communities. Our results establish an important initial framework for ongoing isotope studies of feral horses and other wildlife on Sable Island.