WINTER PRECIPITATION DRIVES MILLENNIAL-SCALE LAKE SEDIMENT BIOGEOCHEMICAL TRENDS IN A FIRE-PRONE SUBALPINE LANDSCAPE

Wildfire activity has increased in forests of western North America over the past several decades. Fires influence the cycling of carbon, nitrogen, and other biologically important elements in soils and vegetation. Past research utilizing lake records from three subalpine lakes in northern Colorado (Hinman, Gold Creek, and Summit) showed that charcoal-inferred fire events over the last ~2500 years caused an average ~20-year increase in carbon, nitrogen, and sulfur concentrations in sediments, while titanium and other metals found in terrestrial mineral material decreased. These relatively short-term impacts were superimposed onto millennial-scale trends in the biogeochemical proxies (Ti, Si, K, Ca, Al, S, P, C, N, δ¹³C, δ¹⁵N). Since climate, vegetation, and soil formation affect biogeochemical processes in lakes, we used principal component (PC) analysis to characterize the dominant modes of variability in the proxies at each site. We compared PC one and PC two with regional paleoenvironmental reconstructions to investigate overlying mechanisms (e.g., climate, fire frequency, vegetation, soil carbon, etc.) potentially driving biogeochemical trends. Preliminary results indicate that reconstructions of winter precipitation are significantly correlated with PC one at Summit (r = 0.51, p < 0.01) and Gold Creek (r = -0.36, p < 0.01) lakes and that the strength of this relationship is related to lake elevation and amount of precipitation delivered to the watershed. These results are consistent with variations in winter precipitation as an important driver of millennial-scale trends in sediment biogeochemistry, particularly in high-elevation subalpine lakes. If true, then future changes in mountain snowpack would be expected to shift the biogeochemical states of subalpine lakes, potentially affecting their response to disturbance events like wildfire.