PS 41-134 - Long-term stream chemistry patterns in a boreal watershed underlain with discontinuous permafrost

Abstract: High-latitude ecosystems are being disproportionately impacted by climate change compared to the global average. The consequences of climate change in boreal ecosystems are evident in declining permafrost extent, amplification of positive climate feedback loops, and alteration of the timing and intensity of hydrologic events. Interior Alaska is in the zone of discontinuous permafrost, the rapid thaw of which could have implications on carbon and nutrient cycling in headwater streams. We examined stream chemistry over a 20-year period in three headwater catchments of the Caribou-Poker Creeks Research Watershed (CPCRW) in interior Alaska. These catchments vary in permafrost underlay (4-53%) and size of drainage area. The goal of the study was to evaluate patterns in stream solute concentrations to determine how permafrost thaw and climate change-related trends in temperature alter carbon cycling in high-latitude watersheds. Using long-term datasets from the Bonanza Creek Long-Term Ecological Research (BNZ) database, we analyzed inter and intra-annual patterns of discharge, geochemical solutes (Ca²⁺, Mg²⁺, SO₄^2-, and DIC), and nutrients (NO₃^-, TDN, DON, TDP, and DOC). By separating solutes into these categories, we were able to analyze long-term trends in nutrient transport and weathering processes. We performed the analysis using the EGRET R package that carries out the analysis using Weighted Regression on Time, Discharge, and Season (WRTDS) and the Thiel-Sen approach. Here we show that organic components (DOC and DON) have decreased significantly over the study period while other solutes have had no significant change or have slightly increased. Preliminary results indicate significant negative yearly trends for dissolved organic carbon (DOC; -2 to -3.5 % per year) and of larger magnitude for dissolved organic nitrogen (DON; -9.0 to -13.1 % per year). Positive yearly trends are significant for dissolved inorganic carbon (0.7 to 1.1 % per year), while there was no significant trend for weathering solutes such as Ca²⁺, and Mg²⁺. Further, there are differences in solute trends between catchments. The high permafrost extent site had a positive yearly trend with nitrate, but a slightly lower magnitude trend for DON than the lower permafrost sites. In conclusion, a decrease in permafrost extent will have ramifications on nutrient and carbon cycling in boreal headwater streams.