More Like this

1. Long-term change in the concentration-discharge relationship reveals controls on watershed exports of dissolved organic carbon

   https://doi.org/10.22541/essoar.175285266.66333339/v1  

   Solomon, Christopher T; Bernhardt, Emily S; Driscoll, Charles T; Green, Mark B; McDowell, William H (July 2025, ESS Open Archive)

   Dissolved organic carbon (DOC) export from watersheds by streams is an important, changing component of the global carbon cycle. We examined the controls on DOC export by quantifying changes in the DOC concentration-discharge relationship from 1992 through 2022 for nine forested headwater catchments at the Hubbard Brook Experimental Forest in the northeastern United States. We observed a strong increase in the intercept of the log-log concentration-discharge relationship between 2005 and 2017 and a weak increase in the slope of that relationship between 2002 and 2021, along with seasonal and watershed-level differences. The intercept, which indicates the average stream DOC concentration at a given discharge, was strongly and inversely related to ionic strength of the soil solution as predicted by electrolyte solubility theory. This relationship varied among watersheds, perhaps because of soil pH. The intercept was not strongly related to annual precipitation or air temperature. DOC export ranged from 13 to 153 kg C ha-1 y-1 among study watersheds and years, and was correlated with annual precipitation and discharge. Historical data suggest that DOC export has probably increased over the past 50 years, likely due both to increases in precipitation and runoff and to increases in the intercept and slope of the concentration-discharge relationship. Our results suggest the potential for long-term legacy effects of acidification on DOC solubility and stream DOC concentrations in acid-sensitive watersheds, despite reductions in acid deposition, as mineral weathering slowly replenishes the ionic strength of soil solutions. 

   more » « less
2. High Frequency Monitoring and Nitrate Sourcing Reveals Baseflow and Stormflow Controls on Total Dissolved Nitrogen and Carbon Export Along a Rural‐Urban Gradient

   https://doi.org/10.1029/2023WR036750  

   Delesantro, Joseph M; Duncan, Jonathan M; Riveros‐Iregui, Diego; Whitmore, Keridwen M; Band, Lawrence E (October 2024, Water Resources Research)

   Abstract Efforts to reduce nitrogen and carbon loading from developed watersheds typically target specific flows or sources, but across gradients in development intensity there is no consensus on the contribution of different flows to total loading or sources of nitrogen export. This information is vital to optimize management strategies leveraging source reductions, stormwater controls, and restorations. We investigate how solute loading and sources vary across flows and land‐use using high frequency monitoring and stable nitrate isotope analysis from five catchments with different sanitary infrastructure, along a gradient in development intensity. High frequency monitoring allowed estimation of annual loading and attribution to storm versus baseflows. Nitrate loads were 16 kg/km²/yr. from the forested catchment and ranged from 68 to 119 kg/km²/yr., across developed catchments, highest for the septic served site. Across developed catchments, baseflow contributions ranged from 40% of N loading to 75% from the septic served catchment, and the contribution from high stormflows increased with development intensity. Stormflows mobilized and mixed many surface and subsurface nitrate sources while baseflow nitrate was dominated by fewer sources which varied by catchment (soil, wastewater, or fertilizer). To help inform future sampling designs, we demonstrate that grab sampling and targeted storm sampling would likely fail to accurately predict annual loadings within the study period. The dominant baseflow loads and subsurface stormflows are not treated by surface water management practices primarily targeted to surface stormflows. Using a balance of green and gray infrastructure and stream/riparian restoration may target specific flow paths and improve management. 

   more » « less
3. Pulse of the Storm: 2024 Hurricane Helene’s Impact on Riverine Nutrient Fluxes Across the Oconee River Watershed in Georgia

   https://doi.org/10.3390/environments13020076  

   Bhattacharjee, Arka; Stamm, Grace; Myrick, Blaire; Basapuram, Gayatri; Dutta, Avishek; Duttagupta, Srimanti (January 2026, Environments)

   Tropical cyclones can rapidly alter watershed chemistry by shifting hydrologic pathways and mobilizing stored nutrients, yet these disturbances often remain undetected when storms cause little visible flooding or geomorphic damage. During Hurricane Helene 2024, intense rainfall across the Oconee River watershed in Georgia generated sharp increases in discharge that triggered substantial nutrient export despite minimal physical alteration to the landscape. High-frequency measurements of nitrate, phosphate, and sulfate in urban, forested, and recreational settings revealed pronounced and synchronous post-storm increases in all three solutes. Nitrate showed the strongest and most persistent response, with mean concentrations increasing from approximately 1–3 mg/L during pre-storm conditions to 6–14 mg/L post-storm across sites, and remaining elevated for several months after hydrologic conditions returned to baseline. Phosphate concentrations increased sharply during the post-storm period, rising from pre-storm means of ≤0.3 mg/L to a post-storm average of 1.5 mg/L, but declined more rapidly during recovery, consistent with sediment-associated mobilization and subsequent attenuation. Sulfate concentrations also increased substantially across the watershed, with post-storm mean values commonly exceeding 20 mg/L and maximum concentrations reaching 41 mg/L, indicating sustained dissolved-phase release and enhanced temporal variability. Recovery trajectories differed by solute: phosphate returned to baseline within weeks, nitrate declined gradually, and sulfate remained elevated throughout the winter. These findings demonstrate that substantial chemical perturbations can occur even in the absence of visible storm impacts, underscoring the importance of event-based, high-resolution monitoring to detect transient but consequential shifts in watershed biogeochemistry. They also highlight the need to better resolve solute-specific pathways that govern nutrient mobilization during extreme rainfall in mixed-use watersheds with legacy nutrient stores and engineered drainage networks. 

   more » « less
4. Freeze–thaw processes and intense rainfall: the one-two punch for high sediment and nutrient loads from mid-Atlantic watersheds

   https://doi.org/10.1007/s10533-017-0417-7  

   Inamdar, Shreeram; Johnson, Erin; Rowland, Richard; Warner, Daniel; Walter, Robert; Merritts, Dorothy (April 2018, Biogeochemistry)

   Large runoff, sediment, and nutrient exports from watersheds could occur due to individual extreme climate events or a combination of multiple hydrologic and meteorological conditions. Using high-frequency hydrologic, sediment, and turbidity data we show that freeze–thaw episodes followed by intense winter (February) rainstorms can export very high concentrations and loads of suspended sediment and particulate organic carbon (POC) and nitrogen (PN) from mid-Atlantic watersheds in the US. Peak suspended sediment (> 5000 mg L−1), POC (> 250 mg L−1) and PN (> 15 mg L−1) concentrations at our 12 and 79 ha forested watersheds for the February rainfall-runoff events were highest on record and the fluxes were comparable to those measured for tropical storms. Similar responses were observed for turbidity values (> 400 FNU) at larger USGS-monitored watersheds. Much of the sediments and particulate nutrients likely originated from erosion of stream bank sediments and/or channel storage. Currently, there is considerable uncertainty about the contribution of these sources to nonpoint source pollution, particularly, in watersheds with large legacy sediment deposits. Future climate projections indicate increased intensification of storm events and increased variability of winter temperatures. Freeze–thaw cycles coupled with winter rain events could increase erosion and transport of streambank sediments with detrimental consequences for water quality and health of downstream aquatic ecosystems. 

   more » « less
5. Long‐Term Stream Chemistry Patterns in a Boreal Watershed Underlain With Discontinuous Permafrost

   https://doi.org/10.1029/2025JG009126  

   Kraus, K L; Jones, J B (December 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract The consequences of climate change on boreal ecosystems are evident in declining permafrost extent, amplifying positive climate feedback loops, and altering the timing and intensity of hydrologic events. Thawing permafrost in the discontinuous permafrost zone could affect carbon and nutrient cycling in stream ecosystems. We examined stream chemistry and climate trends over a 20+‐year period across catchments in the Caribou Poker Creeks Research Watershed underlain with varying extents of permafrost (4%–53%). The study aimed to evaluate patterns in dissolved inorganic carbon (DIC,pCO₂), dissolved organic carbon (DOC), nitrogen (Dissolved organic nitrogen, and NO₃⁻), geochemical solutes (Ca²⁺, Mg²⁺, SO₄²⁻), and discharge to determine how altered terrestrial flowpaths and climate change‐related trends in temperature and precipitation have transformed solute transport in high‐latitude watersheds during the ice‐free season. We analyzed long‐term trends in stream chemistry using Thiel‐Sen analysis and a mixed effects model to quantify the influence of abiotic factors on solute concentrations. Results indicate significant declines in DOC (−109.0 to −169.9 μg L⁻¹ yr⁻¹) andpCO₂(−24.1 ppmv yr⁻¹) in higher permafrost extent sub‐catchments. The highest permafrost catchment is experiencing the greatest amount of change, contrasting sharply with opposite to fewer trends in the catchments with lower permafrost extent. Model results indicate the importance of moisture conditions and discharge (p < 0.05), especially for changes in organic solutes. As climate change progresses, the role of these abiotic factors and permafrost thaw will remain important for solute transport dynamics in boreal headwater streams, with consequences for in‐stream communities and downstream solute yields. 

   more » « less