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1. Physical and stoichiometric controls on stream respiration in a headwater stream

   https://doi.org/10.5194/bg-20-3353-2023  

   Dorley, Jancoba; Singley, Joel; Covino, Tim; Singha, Kamini; Gooseff, Michael; Van Horn, David; González-Pinzón, Ricardo (January 2023, Biogeosciences)

   Abstract. Many studies in ecohydrology focusing on hydrologictransport argue that longer residence times across a stream ecosystem shouldconsistently result in higher biological uptake of carbon, nutrients, andoxygen. This consideration does not incorporate the potential forbiologically mediated reactions to be limited by stoichiometric imbalances.Based on the relevance and co-dependences between hydrologic exchange,stoichiometry, and biological uptake and acknowledging the limited amountof field studies available to determine their net effects on the retentionand export of resources, we quantified how microbial respiration iscontrolled by the interactions between and the supply of essential nutrients (C, N, and P)in a headwater stream in Colorado, USA. For this, we conducted two rounds ofnutrient experiments, each consisting of four sets of continuous injectionsof Cl− as a conservative tracer, resazurin as a proxy for aerobicrespiration, and one of the following nutrient treatments: (a) N, (b) N+C,(c) N+P, or (d) C+N+P. Nutrient treatments were considered to be knownsystem modifications that alter metabolism, and statistical tests helpedidentify the relationships between reach-scale hydrologic transport andrespiration metrics. We found that as discharge changed significantlybetween rounds and across stoichiometric treatments, (a) transient storagemainly occurred in pools lateral to the main channel and was proportional todischarge, and (b) microbial respiration remained similar between rounds andacross stoichiometric treatments. Our results contradict the notion thathydrologic transport alone is a dominant control on biogeochemicalprocessing and suggest that complex interactions between hydrology, resourcesupply, and biological community function are responsible for drivingin-stream respiration. 

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2. When does a stream become a river?

   https://doi.org/10.1002/rra.4185  

   Czuba, Jonathan_A; Allen, George_H (July 2023, River Research and Applications)

   Abstract The distinction between a “stream” and “river” is imprecise and vague despite the popular usage of the terms across disciplines for describing flowing waterbodies. Based on an analysis of named flowing waterbodies in the continental United States, we suggest a bank‐to‐bank channel width of 15 m as a working threshold in defining smaller “streams” from larger “rivers.” 

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3. Nitrate Loads From Land to Stream Are Balanced by In‐Stream Nitrate Uptake Across Seasons in a Dryland Stream Network

   https://doi.org/10.1029/2024JG008117  

   Handler, Amalia_M; Helton, Ashley_M; Grimm, Nancy_B (November 2024, Journal of Geophysical Research: Biogeosciences)

   Abstract Exploring nitrogen dynamics in stream networks is critical for understanding how these systems attenuate nutrient pollution while maintaining ecological productivity. We investigated Oak Creek, a dryland watershed in central Arizona, USA, to elucidate the relationship between terrestrial nitrate (NO₃⁻) loading and stream NO₃⁻uptake, highlighting the influence of land cover and hydrologic connectivity. We conducted four seasonal synoptic sampling campaigns along the 167‐km network combined with stream NO₃⁻uptake experiments (in 370–710‐m reaches) and integrated the data in a mass‐balance model to scale in‐stream uptake and estimate NO₃⁻loading from landscape to the stream network. Stream NO₃⁻concentrations were low throughout the watershed (<5–236 μg N/L) and stream NO₃⁻vertical uptake velocity was high (5.5–18.0 mm/min). During the summer dry (June), summer wet (September), and winter dry (November) seasons, the lower mainstem exhibited higher lateral NO₃⁻loading (10–51 kg N km⁻² d⁻¹) than the headwaters and tributaries (<0.001–0.086 kg N km⁻² d⁻¹), likely owing to differences in irrigation infrastructure and near‐stream land cover. In contrast, during the winter wet season (February) lateral NO₃⁻loads were higher in the intermittent headwaters and tributaries (0.008–0.479 kg N km⁻² d⁻¹), which had flowing surface water only in this season. Despite high lateral NO₃⁻loading in some locations, in‐stream uptake removed >81% of NO₃⁻before reaching the watershed outlet. Our findings highlight that high rates of in‐stream uptake maintain low nitrogen export at the network scale, even with high fluxes from the landscape and seasonal variation in hydrologic connectivity. 

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4. Robust Subspace Approximation in a Stream

   Levin, Roie; Sevekari, Anish; Woodruff, David P. (January 2018, NeurIPS)
5. Prairie stream metabolism recovery varies based on antecedent hydrology across a stream network after a bank‐full flood

   https://doi.org/10.1002/lno.12182  

   Ruffing, Claire M.; Veach, Allison M.; Schechner, Anne; Rüegg, Janine; Trentman, Matt T.; Dodds, Walter K. (September 2022, Limnology and Oceanography)

   ABSTRACT Intermittent streams are characterized by significant periods of low to no flow, yet are also frequently subjected to flashy, high floods. Floods alter ecosystem function and result in variable successional patterns across the stream network. Yet, the timing of restored function after floods in intermittent stream networks is relatively unexplored. We measured recovery of stream ecosystem function using rates of gross primary production (GPP), ecosystem respiration (ER), net ecosystem production (NEP), and the primary production to respiration ratio (P/R) across eight locations in the Kings Creek drainage basin with differing preflood conditions (previously dry [intermittent] or flowing [perennial]) over a 30‐d period following a 2‐yr return interval flood. We found that all metabolic rates (GPP, ER, NEP, P/R) varied primarily by time (days since flood) and antecedent flow, but not spatial network position (i.e., drainage area). Intermittent sites exhibited high rates of ER (0.17–3.33 g dissolved oxygen [DO] m⁻²d⁻¹) following rewetting compared to perennial sites (0.03–1.17 g DO m⁻²d⁻¹), while GPP, NEP, and P/R were slower to recover and varied less between sites of differing preflood conditions. Metabolic rates were not strongly influenced by other environmental conditions. A large proportion of variation was explained by the random effect of location. Our results suggest that metabolism is temporally asynchronous and highly heterogenous across intermittent watersheds and that antecedent hydrology (drying prior to rewetting) stimulates heterotrophic activity, likely dependent on terrestrially derived organic matter and nutrient subsidies. 

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