Characterizing the roles of hydrological processes, climate change and Lesser Snow Geese on ponds in Wapusk National Park using isotopic methods

The Hudson Bay Lowlands (HBL) have experienced pronounced warming during the past ∼50 years. Wapusk National Park (WNP) was created in 1996 to protect a representative area of the HBL and is dominated by >10,000 shallow lakes and ponds. These ponds provide key habitat for wildlife, yet little information is available on how they have responded and will continue to respond to climate change. To address this knowledge gap, water isotope tracers were used to examine the hydrological response of ∼40 shallow ponds in WNP, spanning three ecotypes (coastal fen, interior peat plateau-palsa bog and boreal spruce), to seasonal changes in meteorological conditions during 2010 and 2011. Additionally, paleolimnological techniques were used on a sediment core extracted from a coastal fen pond to address the dual impacts of climate warming and expansion of the Lesser Snow Geese (LSG) population.;Samples for water isotope composition were collected from the study ponds during the spring, summer and fall of 2010 (7-9 June, 28-30 July and 22-24 September) and 2011 (14-16 June, 28-30 July and 22-24 September). Four isotopic frameworks were developed and assessed to decide which framework was most suitable for interpreting the oxygen and hydrogen isotope compositions from 2010 and 2011. The year-specific isotopic framework best characterized the ponds in 2010 and 2011. The year-specific framework was calculated using 2010 and 2011 flux-weighted temperature and relative humidity, as well as an estimate of the terminal basin steady-state isotope composition established from an evaporation pan. The isotopic composition of pond input water (SI) was calculated using a coupled isotope tracer approach and individual water balances were expressed as a ratio of evaporation to inflow (E/1).;Seasonal patterns in hydrological conditions for ponds in each of the three ecotypes were similar during 2010 and 2011. The boreal spruce ponds were consistently isotopically-depleted and maintained positive pond-water balances throughout the ice-free season. Conversely, ponds in the other ecotypes displayed greater evaporative enrichment during mid-ice-free season and, in two cases, underwent complete desiccation during 2010. Most ponds showed late season isotopic trajectories towards the Global Meteoric Water Line (GMWL) indicating strong influence of rainfall to the pond-water balances. Ponds that were closest to Hudson Bay and ponds with larger surface areas maintained low E/I ratios, while ponds further inland and ponds that had smaller surface areas had more variable E/I ratios. Lastly, ponds with hydrological connections to other sources of water had low E/I ratios, while ponds without hydrological connections had variable E/I ratios. Overall, ponds in the coastal fen that were a distance away from Hudson Bay, and interior peat plateau-palsa bog ecotypes may be most vulnerable to the effects of climate change, if future conditions are characterized by a longer ice-free season and greater evaporation relative to precipitation.;Paleolimnological analysis was completed on WAP 21, a pond in the coastal fen ecotype that was visibly affected by LSG, to reconstruct long-term hydroecological conditions. A sediment core was extracted from WAP 21 in July 2010 and analyzed for loss-on-ignition (organic matter, mineral matter, CaCO3), organic carbon and nitrogen elemental and isotope compositions, as well as cellulose oxygen isotope compositions, which were used to reconstruct pond water oxygen isotope compositions Over the past ∼40 years, loss-on-ignition data have shown that there has been an increase in the accumulation of organic matter, reflecting an increase in productivity, while low C/N and an increase in delta 15N values indicate that there has been an increase in nitrogen availability. In addition, there has been an exponential increase in sedimentation rate. The increase in productivity in the pond coincides with an expansion in LSG populations in WNP. The sensitivity of WAP 21 to climate changes (i.e., LIA) and recent LSG population increases indicates that the pond may continue to undergo broad shifts if climate warming and increasing LSG populations continue. (Abstract shortened by UMI.).