Stream chemistry response to external perturbations at Sleepers River
Abstract
The carbon and nitrogen cycles at the catchment scale are largely driven by biogeochemical processes and environmental conditions. Microbial reactions that process carbon and nitrogen species are sensitive to both chemical (pH, substrate availability) and climatic (temperature, moisture) conditions. External perturbations (acid rain, climate change) may influence carbon and nitrogen dynamics, though the nature of their influence is difficult to differentiate due to confounding factors over daily to decadal time scales. We focus our study on the Sleepers River Research Watershed in Vermont, which has exhibited increasing dissolved organic carbon (DOC) but relatively stable nitrate concentrations over the past three decades. The primary driver of increased stream DOC has long been debated as either recovery from acid rain or climate change. At Sleepers River, acid deposition peaked in the late 20th century and has since decreased. At the same time, climate change has increased temperatures and storm frequency and altered snowmelt events. Here we ask: (1) What factors and processes drive the temporal trends of DOC and nitrate at Sleepers River? (2) What is the relative influence of climate change and recovery from acidification on stream chemistry and biogeochemical reaction rates? To address these questions, we use a watershed reactive transport model, HBV-BioRT, to simulate the biogeochemical reactions and hydrologic transport of carbon and nitrogen species at Sleepers River. The model was first calibrated to reproduce chemical variations in soil water, groundwater, and streamwater. By manipulating the meteorological forcing, rainfall chemistry, and biogeochemical reactions in the model, we show that acidic precipitation leads to lower DOC and higher nitrate concentrations in the stream, while less acidic precipitation leads to higher DOC and lower nitrate concentrations. Different climate change scenarios also demonstrated the influence of temperature and storm frequency on solute generation (reaction rates) and transport to streams (flushing events). This work underscores the importance of external perturbations on solute dynamics, as the combined effects of recovery from acidification and climate change may lead to long-term changes in carbon and nitrogen transport and transformation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H41B..01S