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1. Understanding links between water-quality variables and nitrate concentration in freshwater streams using high frequency sensor data

   https://doi.org/10.1371/journal.pone.0287640  

   Kermorvant, Claire; Liquet, Benoit; Litt, Guy; Mengersen, Kerrie; Peterson, Erin E.; Hyndman, Rob J.; Jones, Jeremy B.; Leigh, Catherine (June 2023, PLOS ONE)

   Larsen, Stefano (Ed.)

   Real-time monitoring usingin-situsensors is becoming a common approach for measuring water-quality within watersheds. High-frequency measurements produce big datasets that present opportunities to conduct new analyses for improved understanding of water-quality dynamics and more effective management of rivers and streams. Of primary importance is enhancing knowledge of the relationships between nitrate, one of the most reactive forms of inorganic nitrogen in the aquatic environment, and other water-quality variables. We analysed high-frequency water-quality data fromin-situsensors deployed in three sites from different watersheds and climate zones within the National Ecological Observatory Network, USA. We used generalised additive mixed models to explain the nonlinear relationships at each site between nitrate concentration and conductivity, turbidity, dissolved oxygen, water temperature, and elevation. Temporal auto-correlation was modelled with an auto-regressive–moving-average (ARIMA) model and we examined the relative importance of the explanatory variables. Total deviance explained by the models was high for all sites (99%). Although variable importance and the smooth regression parameters differed among sites, the models explaining the most variation in nitrate contained the same explanatory variables. This study demonstrates that building a model for nitrate using the same set of explanatory water-quality variables is achievable, even for sites with vastly different environmental and climatic characteristics. Applying such models will assist managers to select cost-effective water-quality variables to monitor when the goals are to gain a spatial and temporal in-depth understanding of nitrate dynamics and adapt management plans accordingly. 

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2. Water chemistry time series for Beaverdam Reservoir, Carvins Cove Reservoir, Falling Creek Reservoir, Gatewood Reservoir, and Spring Hollow Reservoir in southwestern Virginia, USA 2013-2023

   https://doi.org/10.6073/pasta/7d7fdc5081ed5211651f86862e8b2b1e  

   Carey, Cayelan C; Howard, Dexter W; Hoffman, Kathryn K; Wander, Heather L; Breef-Pilz, Adrienne; Niederlehner, B R; Haynie, George; Keverline, Ryan; Kricheldorf, Michael; Tipper, Evelyn (April 2024, Environmental Data Initiative)

   Depth profiles of dissolved organic and inorganic carbon and total and dissolved nitrogen and phosphorus were sampled from 2013-2023 in five drinking water reservoirs in southwestern Virginia, USA. The five drinking water reservoirs are: Beaverdam Reservoir (Vinton, Virginia), Carvins Cove Reservoir (Roanoke, Virginia), Falling Creek Reservoir (Vinton, Virginia), Gatewood Reservoir (Pulaski, Virginia), and Spring Hollow Reservoir (Salem, Virginia). Beaverdam, Carvins Cove, Falling Creek, and Spring Hollow Reservoirs are owned and operated by the Western Virginia Water Authority as primary or secondary drinking water sources for Roanoke, Virginia, and Gatewood Reservoir is a drinking water source for the town of Pulaski, Virginia. The dataset consists of depth profiles of water chemistry samples measured at the deepest site of each reservoir adjacent to the dam. Additional water chemistry samples were collected at a gauged weir on Falling Creek Reservoir's primary inflow tributary, as well as surface samples at multiple upstream and inflow sites in Falling Creek Reservoir 2014-2023 and Beaverdam Reservoir in 2019 and 2020. One upstream site at Beaverdam Reservoir was sampled at depth in 2022. Inflow sites at Carvins Cove Reservoir were sampled from 2020-2023. The water column samples were collected approximately fortnightly from March-April, weekly from May-October, and monthly from November-February at Falling Creek Reservoir and Beaverdam Reservoir, approximately fortnightly from May-August in most years at Carvins Cove Reservoir, and approximately fortnightly from 2014-2016 in Gatewood and Spring Hollow Reservoirs, though sampling frequency and duration varied among reservoirs and years. 

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3. Linking Water Age, Nitrate Export Regime, and Nitrate Isotope Biogeochemistry in a Tile‐Drained Agricultural Field

   https://doi.org/10.1029/2023WR034948  

   Yu, Zhongjie; Hu, Yinchao; Gentry, Lowell E; Yang, Wendy H; Margenot, Andrew J; Guan, Kaiyu; Mitchell, Corey A; Hu, Minpeng (December 2023, Water Resources Research)

   Abstract Accurately quantifying and predicting the reactive transport of nitrate () in hydrologic systems continues to be a challenge, due to the complex hydrological and biogeochemical interactions that underlie this transport. Recent advances related to time‐variant water age have led to a new method that probes water mixing and selection behaviors using StorAge Selection (SAS) functions. In this study, SAS functions were applied to investigate storage, water selection behaviors, and export regimes in a tile‐drained corn‐soybean field. The natural abundance stable nitrogen and oxygen isotopes of tile drainage were also measured to provide constraints on biogeochemical transformations. The SAS functions, calibrated using chloride measurements at tile drain outlets, revealed a strong young water preference during tile discharge generation. The use of a time‐variant SAS function for tile discharge generated unique water age dynamics that reveal an inverse storage effect driven by the activation of preferential flow paths and mechanically explain the observed variations in isotopes. Combining the water age estimates with isotope fingerprinting shed new light on export dynamics at the tile‐drain scale, where a large mixing volume and the lack of a strong vertical contrast in concentration resulted in chemostatic export regimes. For the first time, isotopes were embedded into a water age‐based transport model to model reactive transport under transient conditions. The results of this modeling study provided a proof‐of‐concept for the potential of coupling water age modeling with isotope analysis to elucidate the mechanisms driving reactive transport. 

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4. N ₂ O ₅ reactive uptake kinetics and chlorine activation on authentic biomass-burning aerosol

   https://doi.org/10.1039/c9em00330d  

   Goldberger, Lexie A.; Jahl, Lydia G.; Thornton, Joel A.; Sullivan, Ryan C. (October 2019, Environmental Science: Processes & Impacts)

   We examined the reactive uptake of dinitrogen pentoxide (N 2 O 5 ) to authentic biomass-burning aerosol (BBA) using a small chamber reservoir in combination with an entrained aerosol flow tube. BBA was generated from four different fuel types and the reactivity of N 2 O 5 was probed from 30 to 70% relative humidity (RH). The N 2 O 5 reactive uptake coefficient, γ (N 2 O 5 ), depended upon RH, fuel type, and to a lesser degree on aerosol chloride mass fractions. The γ (N 2 O 5 ) ranged from 2.0 (±0.4) ×10 −3 on black needlerush derived BBA at 30% RH to 6.0 (±0.6) ×10 −3 on wiregrass derived BBA at 65% RH. Major N 2 O 5 reaction products were observed including gaseous ClNO 2 and HNO 3 and particulate nitrate, and used to create a reactive nitrogen budget. Black needlerush BBA had the most particulate chloride, and the only measured ClNO 2 yield > 1%. The ClNO 2 yield on black needlerush decayed from an initial value of ∼100% to ∼30% over the course of the burn experiment, suggesting a depletion of BBA chloride over time. Black needlerush was also the only fuel for which the reactive nitrogen budget indicated other N-containing products were generated. Generally, the results suggest limited chloride availability for heterogeneous reaction for BBA in the RH range probed here, including BBA with chloride mass fractions on the higher end of previously reported values (∼17–34%). Though less than fresh sea spray aerosol, ∼50%. We use these measured quantities to discuss the implications for nocturnal aerosol nitrate formation, the chemical fate of N 2 O 5 (g), and the availability of particulate chloride for activation in biomass burning plumes. 

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5. Modification of a dual‐chamber denitrification bioreactor with a surface water pumping system

   https://doi.org/10.1002/agg2.20399  

   Hartfiel, Lindsey M.; Craig, Andrew J.; Soupir, Michelle L. (September 2023, Agrosystems, Geosciences & Environment)

   Core Ideas A subsurface drainage‐fed bioreactor was retrofitted with a supplemental surface water pumping system. Design criteria of the pumping system are presented along with challenges and future recommendations. Pumped bioreactor systems show promise for the treatment of alternative nitrate‐laden sources of water. Pumped bioreactors have the potential to remove nitrate beyond the typical drainage season. 

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