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1. Deep denitrification: Stream and groundwater biogeochemistry reveal contrasted but connected worlds above and below

   https://doi.org/10.1016/j.scitotenv.2023.163178  

   Severe, Emilee; Errigo, Isabella M.; Proteau, Mary; Sayedi, Sayedeh Sara; Kolbe, Tamara; Marçais, Jean; Thomas, Zahra; Petton, Christophe; Rouault, François; Vautier, Camille; et al (July 2023, Science of The Total Environment)
2. Exploring dissolved organic carbon cycling at the stream–groundwater interface across a third-order, lowland stream network

   https://doi.org/10.1007/s10533-017-0404-z  

   Ruhala, Sydney S.; Zarnetske, Jay P.; Long, David T.; Lee-Cullin, Joseph A.; Plont, Stephen; Wiewiora, Evan R. (January 2018, Biogeochemistry)
3. Where groundwater seeps: Evaluating modeled groundwater discharge patterns with thermal infrared surveys at the river-network scale

   https://doi.org/10.1016/j.advwatres.2021.104108  

   Barclay, J.R.; Briggs, M.A.; Moore, E.M.; Starn, J.J.; Hanson, A.E.H.; Helton, A.M. (February 2022, Advances in Water Resources)
4. Multi-Scale Temporal Patterns in Stream Biogeochemistry Indicate Linked Permafrost and Ecological Dynamics of Boreal Catchments

   https://doi.org/10.1007/s10021-021-00709-6  

   Webster, Alex J.; Douglas, Thomas A.; Regier, Peter; Scheuerell, Mark D.; Harms, Tamara K. (October 2021, Ecosystems)

   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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5. Numerical modeling of groundwater‐driven stream network evolution in low‐relief post‐glacial landscapes

   https://doi.org/10.1002/esp.5278  

   Cullen, Cecilia; Anders, Alison M.; Lai, Jingtao; Druhan, Jennifer L. (November 2021, Earth Surface Processes and Landforms)

   In the low-relief post-glacial landscapes of the Central Lowlands of the United States, fluvial networks formed and expanded following deglaciation despite the low slopes and large fraction of the land surface occupied by closed depressions. Low relief topography allows for subtle surface water divides and increases the likelihood that groundwater divides do not coincide with surface water divides. We investigate how groundwater transfer across subtle surface water divides facilitates channel network expansion using a numerical model built on the Landlab platform. Our model simulates surface and subsurface water routing and fluvial erosion. We consider two end-member scenarios for surface water routing, one in which surface water in closed depressions is forced to connect to basin outlets (routing) and one in which surface water in closed depressions is lost to evapotranspiration (no routing). Groundwater is modeled as fully saturated flow within a confined aquifer. Groundwater emerges as surface water where the landscape has eroded to a specified depth. We held the total water flux constant and varied the fraction of water introduced as groundwater versus precipitation. Channel growth is significantly faster in routing cases than no-routing cases given identical groundwater fractions. In both routing and no-routing cases, channel expansion is fastest when ~30% of the total water enters the system as groundwater. Groundwater contributions also produce distinctive morphology including steepened channel profiles below groundwater seeps. Groundwater head gradients evolve with topography and groundwater-fed channels can grow more quickly than channels with larger surface water catchments. We conclude that rates of channel network growth in low-relief post-glacial areas are sensitive to groundwater contributions. More broadly, our findings suggest that landscape evolution models may benefit from more detailed representation of hydrologic processes. 

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