https://hdl.handle.net/10012/22428

The only wild, self-sustaining population of endangered whooping crane (Grus americana) breeds within a remote, pond-rich, groundwater discharge region in and adjacent to Wood Buffalo National Park where there is concern for habitat degradation by climate change. Due to their small area and volume, shallow ponds respond rapidly to changes in climate and are vulnerable to desiccation, which can reduce breeding success by altering food availability and encounters with predators. Hydrological information is scant in this remote region, and longer time-series of data are needed to anticipate how shallow water breeding habitat will respond to future climate warming. Here, contemporary measurements (2022-2023) at three shallow ponds that range from weakly to strongly connected to groundwater are integrated with paleolimnological analyses, which span the past ~300-400 years and capture the cold, arid Little Ice Age and subsequent warming, to improve understanding of hydrological responses to climate variation. Correspondence of pond water ẟ18O inferred from sediment carbonate (carbonate-inferred ẟ18Opw) with contemporary measurements of pond water ẟ18O indicates that carbonate-inferred ẟ18Opw provides a reliable methodology to reconstruct past variation in pond water ẟ18O. Evidence suggests two of the three ponds desiccated during the mid- and late 1700s when the climate of the Little Ice Age was arid. At pond SK 31, where connectivity to groundwater is weak, carbonate-inferred ẟ18Opw increased during this interval and exceeded the contemporary estimate of the terminal basin steady-state isotope composition, indicating strongly negative water balance prevailed due to evaporation. Similar strong net evaporation and near-desiccation has been detected during the same time interval from a record of cellulose-inferred lake water δ18O at a shallow upland lake located ~175 km to the south (Wolfe et al., 2005), which provides confidence in the interpretations based on carbonate-inferred δ18Opw at SK 31. At pond SK 58, where connectivity to groundwater is strong but desiccation occurred in 2023 and 2024 likely by vertical seepage, the stratigraphic record of carbonate-inferred δ18Opw reveals no evidence of enrichment by evaporation during the mid- and late 1700s. A distinctive peak in C/N ratios in sediment deposited ~1790 suggests, however, that an apparently rare desiccation, or near-desiccation, event may have occurred by vertical seepage when SK 31 and PAD 5 also nearly desiccated by evaporation. Smaller C/N-ratio peaks in ~1908 and ~1998 may capture two other short-lived near-desiccation events at SK 58. Recent observed desiccation at SK 58 in 2023-2024 occurred when unusually arid climate conditions resulted in a decline in water level of 60 cm in Great Slave Lake to the lowest levels recorded by the 84-year-long record. At pond SK 26, low carbonate-inferred ẟ18Opw values throughout the ~280-year record provide no evidence of drawdown by evaporation and suggest there may have been shifting sources and discharge of groundwater, which may be indicative of the spatial and temporal variability of past hydrological conditions across this complex landscape. Overall, pond desiccation, including the recent drying of SK 58, appears to be a largely rare occurrence since 1800 but may become increasingly common with ongoing climate change.

https://hdl.handle.net/10012/22428