Stream chemistry responses to bark beetle disturbance and changing atmospheric deposition in alpine and forest headwater catchments

Abstract

The extent of alpine land cover influences the chemistry of streams draining mountain catchments and may determine how they respond to ecosystem change. During the first two decades of the 2000s, the Southern Rockies, USA, experienced both severe bark beetle infestation and significant decreases in atmospheric nitrogen (N) and sulfur (S) deposition. To evaluate the consequences of these events, we compared the chemistry of samples collected during 2004–2006 and 2017–2019 in streams draining 18 headwater catchments comprised of mixtures of forest and alpine land cover. Stream total dissolved N, nitrate, and sulfate concentrations increased linearly with the proportion of alpine cover within the study catchments. Consistent with regional patterns in atmospheric deposition, stream nitrate decreased and ammonium increased, though stream sulfate was unchanged. Differences in solute concentrations between the sampling periods were greatest in catchments with the highest proportion of alpine cover and were minimal in fully forested catchments. This relationship demonstrates the sensitivity of catchments with alpine headwaters to changing nutrient deposition and, conversely, the capacity for nutrient retention by non‐host vegetation to buffer the impacts of beetle‐related tree mortality in fully forested catchments.

Citation

Rhoades, Charles C.; Fegel, Timothy S.; Rhea, Allison E.; Starr, Banning; Elder, Kelly. 2026. Stream chemistry responses to bark beetle disturbance and changing atmospheric deposition in alpine and forest headwater catchments. Hydrological Processes. 40: e70644.