Journal
ECOSYSTEMS
Volume 25, Issue 5, Pages 1189-1206Publisher
SPRINGER
DOI: 10.1007/s10021-021-00709-6
Keywords
nitrate (NO3-); dissolved organic matter (DOM); multivariate autoregressive state-space (MARSS) models; flowpaths; wavelets; concentration-discharge relationships; storms; time series analysis; nitrate isotopes
Categories
Funding
- Department of Defense Strategic Environmental Research and Development Program [RC-2507]
- Bonanza Creek Long-Term Ecological Research Program - National Science Foundation [DEB-1636476]
- USDA Forest Service, Pacific Northwest Research Station [RJVA-PNW-01-JV-11261952-231]
- Consortium of Universities for the Advancement of Hydrologic Science, Inc.
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Temporal patterns in stream chemistry provide integrated signals describing the hydrological and ecological state of whole catchments. Analyzing these patterns in permafrost-influenced boreal catchments in Interior Alaska revealed the positive influence of permafrost on fDOM export and the differences in solute dynamics between catchments with varying extents of permafrost. This study highlights the importance of understanding the impact of permafrost thaw on catchment hydrology and biogeochemistry.
Temporal patterns in stream chemistry provide integrated signals describing the hydrological and ecological state of whole catchments. However, stream chemistry integrates multi-scale signals of processes occurring in both the catchment and stream. Deconvoluting these signals could identify mechanisms of solute transport and transformation and provide a basis for monitoring ecosystem change. We applied trend analysis, wavelet decomposition, multivariate autoregressive state-space modeling, and analysis of concentration-discharge relationships to assess temporal patterns in high-frequency (15 min) stream chemistry from permafrost-influenced boreal catchments in Interior Alaska at diel, storm, and seasonal time scales. We compared catchments that varied in spatial extent of permafrost to identify characteristic biogeochemical signals. Catchments with higher spatial extents of permafrost were characterized by increasing nitrate concentration through the thaw season, an abrupt increase in nitrate and fluorescent dissolved organic matter (fDOM) and declining conductivity in late summer, and flushing of nitrate and fDOM during summer rainstorms. In contrast, these patterns were absent, of lower magnitude, or reversed in catchments with lower permafrost extent. Solute dynamics revealed a positive influence of permafrost on fDOM export and the role of shallow, seasonally dynamic flowpaths in delivering solutes from high-permafrost catchments to streams. Lower spatial extent of permafrost resulted in static delivery of nitrate and limited transport of fDOM to streams. Shifts in concentration-discharge relationships and seasonal trends in stream chemistry toward less temporally dynamic patterns might therefore indicate reorganized catchment hydrology and biogeochemistry due to permafrost thaw.
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