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A clear need exists to understand the role that water table fluctuations play in mobilizing nutrients in soils and shallow groundwater near streams, particularly in dry Mediterranean watersheds, which experience marked wetting and drying seasonal patterns. As groundwater level varies, so does the supply of inorganic nitrogen and organic carbon from different soil layers, which affects processes such as coupled nitrification-denitrification and the chemistry of groundwater that flows to streams. Along discharging groundwater flow paths, carbon-rich soils release dissolved organic carbon (DOC), which biogeochemically reacts with nitrogen (N) and oxygen (O) as groundwater levels rise and become saturated. For understanding the biogeochemical dynamics in N at the interface between soils and groundwater, a cylindrical, meter-long polyvinyl chloride (PVC) soil column was constructed and filled with heterogeneous soil and aquifer layers of decreasing organic matter with depth. A cyclical water level cycle was imposed for 16 days using influent to the column from local groundwater at the experimental site with < 1 mg nitrate-N/L. Water table dynamics were monitored with a pressure sensor, tensiometer, and two soil moisture sensors. Vertical arrays of redox sensors and pore water samplers were used to observe changes in pore water chemistry. Water samples were analysed for pH, ammonium-N (NH4-N), nitrate-N (NO3-N), nitrite-N (NO2-N), and DOC. Soil samples were taken for microbial activity and solid chemistry analysis. Near the soil-aquifer transition, nitrate accumulates under aerobic conditions and DOC from organic matter is mobilized under anaerobic conditions. Preliminary pore water analysis shows that during wetting cycles, there is an increase in dissolved inorganic N (NO3+NO2) near the surface (57 mg N/L at 40 cm depth) but a decrease in DIN concentrations in deeper layers (0.92 mg N/L at 55-100 cm depth), suggesting that nitrification and denitrification processes stratified with depth. The results illustrate the significance of groundwater level fluctuations on DIN and DOC cycling and mobilization in Mediterranean riparian soils during wetting events.

Water tables in floodplain aquifers rise and fall over a variety of timescales in response to changes in recharge, discharge, floods, and water use. To investigate the effects of water table fluctuations on DOC delivery to groundwater, an experiment was conducted at two Mediterranean sites: a pristine forested stream and an urban coastal floodplain. Groundwater was pumped into and out of the bottom of the soil column at varying rates to simulate water table fluctuations over a period of 16 days. Flooding events were imitated by inundating the top of the column with water sourced from nearby surface water features. The effects of repeated wetting and drying events on carbon mobilization, DOM quality, and geochemical responses were measured. Preliminary analysis reveals strong downward movement of DOC from soil layers after wetting events. SUVA at 254 nm increased with DOC concentrations compounds within pore waters during wetting events. During initial water table fluctuations, redox potential near the soil-aquifer interface was relatively stable but declined after subsequent wettings. Forthcoming analyses will also examine changes in the humification, fluorescence, and freshness indices of DOM from excitation-emission matrices. This study shows the influence of multiple saturation events on carbon mobilization and shallow groundwater biogeochemistry in unique floodplains.

Quantifying the transfer of organic carbon (OC) from the terrestrial to the riverine ecosystems is of crucial importance to fully appreciate the carbon cycle at the catchment, regional and global scales. Dissolved Organic Carbon (DOC) represents one of the main forms in which terrestrial OC is leached to inland waters and the oceans. Its concentration in streams, rivers and lakes is critical for aquatic metabolism but also for the transport of metals and pollutants. In the past years, several studies in different experimental catchments observed increasing trends in DOC concentration in rivers, possibly linked to changes in land use and hydrologic regime. Moreover, these studies unveiled how hydrologic variability imposes a strong control on DOC transport with streamflow producing events disproportionately contributing to the overall DOC export. In this study, we explore the interaction between water and carbon cycles in the critical zone of an alpine catchment in order to quantify the flux of DOC exported from the soil to the stream via superficial or subsuperficial runoff. We couple the Water Age theory to unravel the time water spends within hillslopes with the Reactivity Continuum model to quantify the degradation of DOC along the transport. The model is applied to the Oberer Seebach basin (Austria) for which extensive time series of streamflow DOC concentration and hydrological variables are available at high-frequency resolution (sub-daily measurements). For a subset of the DOC samples, the excitation emission matrices and the absorbance spectra are also available and allow deriving information on the quality and reactivity of DOC. We reproduce DOC concentration estimating the travel time distribution of water and assuming it dictates the time available for the continuous degradation of the DOC mixture. Results show that the model is able to well reproduce DOC streamflow concentration, capturing its complex relation with streamflow discharge over the three years of observations. In addition, the framework allows the estimation of the reactivity distribution of the exported DOC. To validate these results, we compare the estimated average reactivity with multiple fluorescence and absorbance indexes calculated from data, revealing significant correlations.

Este artículo contiene 14 páginas, 1 tabla, 7 figuras., Stream dissolved oxygen (DO) dynamics are an outcome of metabolic activity and subsequently regulate ecosystem functions such as in-stream solute and sediment reactions. The synchronization of DO signals in and across stream networks is both a cause and effect of the mode and timing of these functions, but there is limited empirical evidence for network patterns of DO synchrony. We used high frequency DO measurements at 42 sites spanning five catchments and stream orders to evaluate DO signal synchrony in response to variation in light (a driver of photosynthesis) and discharge (a control on DO signal spatial extent). We hypothesized that stream network DO synchrony arises when regional controls dominate: when light inputs are synchronous and when longitudinal hydrologic connectivity is high. By complement, we predicted that DO signal synchrony decreases as light becomes more asynchronous and stream flows decline or become discontinuous. Our results supported this hypothesis: greater DO signal synchrony arose with increasing light synchrony and flow connectivity. A model including these two controls explained 70% of variation in DO synchrony. We conclude that DO synchrony patterns within- and across-networks support the current paradigm of discharge and light control on stream metabolic activity. Finally, we propose that DO synchrony patterns are likely a useful prerequisite for scaling subdaily metabolism estimates to network and regional scales., This project was supported by The Loire-Bretagne Water Agency and the Rhône-Méditerranée-Corse Water Agency. J.D. was also supported by the EUR H2O’Lyon, French ANR-17-EURE-0018 grant. S.B. work was funded by the CANTERA (RTI2018-094521-B-100) and EVASIONA (PID2021-122817-NB-100) projects and a Ramon y Cajal fellowship (RYC- 2017-22643) from the Spanish Ministry of Science, Innovation, and Universities and AEI/FEDER UE. A.L. was supported by the program Beatriu de Pin os, funded by the Government of Catalonia and the Horizon 2020 research and innovation program (BP-2018-00082). JPZ work was partially supported by US NSF awards (1846855, 1916567) and a fellowship from the Collegium - Lyon, Institute for Advanced Study.

Este artículo contiene 9 páginas, 4 figuras, 1 tabla., The relevance of wastewater treatment plant (WWTP) effluents in fluvial networks is increasing as urbanization grows in catchments. Urban-sourced fine particles from WWTP effluents deposit and accumulate in the streambed sediment of receiving streams over time and can fuel respiration rates, which can thus potentially increase rates of biogeochemical reactions and CO2 emissions to the atmosphere. We aimed to provide a quantitative assessment of the influence of WWTP-sourced fine particles deposited in the streambed sediment on stream metabolic activity for 1 year in an intermittent Mediterranean stream. More nutrientrich and metabolically active fine particle standing stocks were observed downstream of the WWTP, propagating to the end of the 820 m study reach, especially during the dry period (i.e., when the dilution capacity of the stream to WWTP inputs is, This work was supported by an NSF EAR-Postdoctoral Fellowship and a Marie Curie Individual Fellowship (833702MICROPATH) to J.D.D., AEI/FEDER UE and Spanish Office for Research (MINECO) funded MEDSOUL (CGL2014-59977-C3-2-R) and Eco-Reactors (PGC2018- 101975-B-C22) to E.M., and a Ramon y Cajal fellowship (RYC-2017-22643), NICUS (CGL2014-55234-JIN) and CANTERA (RTI2018-094521-B-100) to S.B.

Background and purpose Abdominal aortic aneurysm (AAA) is a multifactorial disease characterized by chronic inflammation, oxidative stress, and proteolytic activity in the aortic wall. Targeting Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway is a promising strategy for chronic inflammatory diseases. We investigated the vasculoprotective role of suppressor of cytokine signalling-1 (SOCS1), the negative JAK/STAT regulator, in experimental AAA. Experimental approach A synthetic, cell permeable peptide (S1) mimic of SOCS1 kinase inhibitory domain to suppress STAT activation was evaluated in the well-established mouse model of elastase-induced AAA by monitoring changes in aortic diameter, cellular composition, and gene expression in abdominal aorta. S1 function was further evaluated in cultured vascular smooth muscle cells (VSMC) and macrophages exposed to elastase or elastin-derived peptides. Key results S1 peptide prevented AAA development, evidenced by reduced incidence of AAA, aortic dilation and elastin degradation, partial restoration of medial VSMC, and decreased inflammatory cells and oxidative stress in AAA tissue. Mechanistically, S1 suppressed STAT1/3 activation in aorta, downregulated cytokines and metalloproteinases, and altered the expression of cell differentiation markers by favouring anti-inflammatory M2 macrophage and contractile VSMC phenotypes. In vitro, S1 suppressed the expression of inflammatory and oxidative genes, reduced cell migration, and reversed the phenotypic switch of macrophages and VSMC. By contrast, SOCS1 silencing promoted inflammatory response. Conclusion and implications This preclinical study demonstrates the therapeutic potential of SOCS1-derived peptide to halt AAA progression by suppressing JAK/STAT-mediated inflammation and aortic dilation. S1 peptide may therefore be a valuable option for the treatment of AAA.

A unified conceptual framework for river corridors requires synthesis of diverse site-, method- and discipline-specific findings. The river research community has developed a substantial body of observations and process-specific interpretations, but we are still lacking a comprehensive model to distill this knowledge into fundamental transferable concepts. We confront the challenge of how a discipline classically organized around the deductive model of systematically collecting of site-, scale-, and mechanism-specific observations begins the process of synthesis. Machine learning is particularly well-suited to inductive generation of hypotheses. In this study, we prototype an inductive approach to holistic synthesis of river corridor observations, using support vector machine regression to identify potential couplings or feedbacks that would not necessarily arise from classical approaches. This approach generated 672 relationships linking a suite of 157 variables each measured at 62 locations in a fifth order river network. Eighty four percent of these relationships have not been previously investigated, and representing potential (hypothetical) process connections. We document relationships consistent with current understanding including hydrologic exchange processes, microbial ecology, and the River Continuum Concept, supporting that the approach can identify meaningful relationships in the data. Moreover, we highlight examples of two novel research questions that stem from interpretation of inductively-generated relationships. This study demonstrates the implementation of machine learning to sieve complex data sets and identify a small set of candidate relationships that warrant further study, including data types not commonly measured together. This structured approach complements traditional modes of inquiry, which are often limited by disciplinary perspectives and favour the careful pursuit of parsimony. Finally, we emphasize that this approach should be viewed as a complement to, rather than in place of, more traditional, deductive approaches to scientific discovery.

The importance of riparian zones in shaping the hydrology and biogeochemistry of forest headwater catchments has been well-established in the last couple of decades. However, most studies rely on single catchment approaches or focus on a single ecoregion. Here, we present a multiple-site approach using data from four catchments located in four European ecoregions and encompassing a wide range of hydrological and biogeochemical conditions: the boreal Krycklan, the temperate Rappbode, the sub-humid Mediterranean Font del Regàs, and the semi-arid Mediterranean Fuirosos.At long temporal scales, both climate and topography interrelate to determine the dominant source layer (DSL), i.e. the riparian zone depth stratum that contributes the most to water and solute fluxes to streams. Generally, shallower DSLs are found in wetter climates characterized by higher ratios of annual precipitation to potential evapotranspiration (e.g. boreal), but locally can occur in the flatter contributing areas defined by higher topographic wetness indexes. Riparian soils show large differences in carbon and nutrient content across ecoregions. Mediterranean riparian soils are characterized by lower organic matter content and small dissolved organic carbon (DOC) exports from deeper, mineral layers, resulting in overall lower stream DOC concentrations compared with the temperate and, especially, the boreal sites. On the other hand, the denitrification potential of the Mediterranean riparian zones, especially at the semi-arid site, is limited due to drier conditions that oxygenate the riparian soils and may even promote nitrification, resulting in higher stream nitrate (NO3-) concentrations compared to the boreal site. The denitrification potential of the temperate site is counterbalanced by a significantly higher nitrogen deposition compared to the other sites.At the event scale, antecedent soil moisture conditions and associated hydrological connectivity within the catchments becomes an important factor defining solute export from riparian profiles and hysteresis patterns between riparian groundwater tables and stream discharge. Generally, the wetter conditions in the boreal site generate anticlockwise patterns between groundwater tables and discharge, indicating high catchment hydrological connectivity. Clockwise patterns are characteristic of the Mediterranean sites and imply low hydrological connectivity, except during very wet antecedent conditions. The temperate site is characterized by linear patterns and intermediate conditions. Solutes displaying relatively high concentrations in the riparian profile are generally transport limited, especially during events preceded by dry conditions, whereas source limitation occurs during events preceded by wet conditions, especially for solutes displaying relatively low concentrations. We highlight that multiple-site approaches can help identifying common patterns and differences in riparian hydrological and biogeochemical functions across ecoregions, as well as the factors driving these patterns and the resulting dynamics of stream water chemistry.

Este artículo contiene 25 páginas, 6 figuras., Hyporheic zones increase freshwater ecosystem resilience to hydrological extremes and global environmental change. However, current conceptualizations of hyporheic exchange, residence time distributions, and the associated biogeochemical cycling in streambed sediments do not always accurately explain the hydrological and biogeochemical complexity observed in streams and rivers. Specifically, existing conceptual models insufficiently represent the coupled transport and reactivity along groundwater and surface water flow paths, the role of autochthonous organic matter in streambed biogeochemical functioning, and the feedbacks between surface-subsurface ecological processes, both within and across spatial and temporal scales. While simplified approaches to these issues are justifiable and necessary for transferability, the exclusion of important hyporheic processes from our conceptualizations can lead to erroneous conclusions and inadequate understanding and management of interconnected surface water and groundwater environments. This is particularly true at the landscape scale, where the organizational principles of spatio-temporal dynamics of hyporheic exchange flow (HEF) and biogeochemical processes remain largely uncharacterized. This article seeks to identify the most important drivers and controls of HEF and biogeochemical cycling based on a comprehensive synthesis of findings from a wide range of river systems. We use these observations to test current paradigms and conceptual models, discussing the interactions of local-to-regional hydrological, geomorphological, and ecological controls of hyporheic zone functioning. This improved conceptualization of the landscape organizational principles of drivers of HEF and biogeochemical processes from reach to catchment scales will inform future river research directions and watershed management strategies., The work of Stefan Krause and David M. Hannah has been funded through NERC NE/L003872/1 and through the UNESCO UniTwin network: Ecohydrological Interfaces and the Birmingham Institute of Global Innovation. Aaron Packman was supported by United States National Science Foundation (NSF) award number EAR-1734300. Adam S. Ward was supported by NSF Award EAR 1652293, Department of Energy award DE-SC0019377, the Burnell and Barbara Fischer Faculty Fellowship at Indiana University, and the University of Birmingham’s Institute for Advanced Studies. This research was sponsored by the Office of Biological and Environmental Research within the Office of Science of the U.S. Department of Energy (DOE), as part of the Environmental System Science supported Critical Interfaces Science Focus Area project at the Oak Ridge National Laboratory (ORNL).

Este artículo contiene 14 páginas, 5 figuras, 2 tablas., Wastewater treatment plant (WWTP) effluents alter water chemistry and in-stream nutrient uptake rates of receiving freshwaters, thus changing the magnitude and fate of the nutrients exported. In Mediterranean regions, the dilution capacity of receiving streams can vary strongly over time due to the seasonal occurrence of floods and droughts, causing temporal variability of nutrient uptake. We assessed the temporal patterns and the controlling factors of net nutrient uptake in an intermittent Mediterranean stream receiving WWTP effluent inputs. We compiled the longitudinal concentration profiles of ambient dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) along a 800 m reach on 47 sampling dates between 2001 and 2017, encompassing a wide range of hydrological conditions. We estimated net nutrient uptake in the receiving stream. In 72% of the dates, high rates of net ammonium uptake co-occurred with net releases of either nitrate or nitrite. This pattern suggests that the receiving stream has a high nitrification capacity. Conversely, 75% of the dates did not show any longitudinal pattern in SRP concentration, suggesting that uptake and release processes for this element were either counterbalanced or both occurred at very low rates. Finally, net ammonium uptake was low when the stream had a low dilution capacity (< 40%) and ammonium concentration was high. Overall, we demonstrate that consideration of the receiving stream’s dilution capacity is imperative to the management of freshwaters to guarantee an adequate dilution of WWTP effluent inputs and avoid saturation of in-stream nutrient uptake capacity under low flow conditions in urban landscapes., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This study was funded by the projects “EcoReactors” (PGC2018-101975-B C22), “CANTERA” (RTI2018- 094521-B-100) and “Fluvial P-removal” (PID2019-111803RB-I00) from I + D program of the Spanish Ministry of Science, Innovation, and Universities. AL was supported by the program Beatriu de Pinós (BP-2018–00082) from the Government of Catalonia and the European Commission. JLJL was supported by a Marie Skłodowska-Curie Individual Fellowship (H2020-MSCA-IF-2018, RIPARIONS ref: 834363). SB was supported by a Ramon y Cajal fellowship (RYC-2017–22643) from the Spanish Ministry of Science, Innovation, and Universities.

Plastics, especially microplastics (

Este artículo contiene 14 páginas, 7 figuras, 2 tablas., Headwater streams are control points for carbon dioxide (CO2) emissions to the atmosphere, with relative contributions to CO2 emission fluxes from lateral groundwater inputs widely assumed to overwhelm those from in-stream metabolic processes. We analyzed continuous measurements of stream dissolved CO2 and oxygen (O2) concentrations during spring and early summer in two Mediterranean headwater streams from which we evaluated the contribution of in-stream net ecosystem production (NEP) to CO2 emission. The two streams exhibited contrasting hydrological regimes: one was non-perennial with relatively small groundwater inflows, while the other was perennial and received significant lateral groundwater inputs. The non-perennial stream exhibited strong inverse coupling between instantaneous and daily CO2 and O2 concentrations, and a strong correlation between aerobic ecosystem respiration (ER) and gross primary production (GPP) despite persistent negative NEP. At the perennial stream, the CO2–O2 relationship varied largely over time, ER and GPP were uncorrelated, and NEP, which was consistently negative, increased with increasing temperature. Mean NEP contribution to CO2 emission was 51% and 57% at the non-perennial and perennial stream, respectively. Although these proportions varied with assumptions about metabolic stoichiometry and groundwater CO2 concentration, in-stream CO2 production consistently and substantially contributed to total atmospheric CO2 flux in both streams. We conclude that in-stream metabolism can be more important for driving C cycling in some headwater streams than previously assumed., S.B. work was funded by the CANTERA (RTI2018-094521-B-100) and EVASIONA (PID2021-122817-NB-100) projects and a Ramon y Cajal fellowship (RYC-2017-22643) from the Spanish Ministry of Science, Innovation, and Universities and AEI/FEDER UE. A.L. was supported by the program Beatriu de Pin os, funded by the Government of Catalonia and the Horizon 2020 research and innovation program (BP-2018-00082). J.L.J.L. was funded by the project RIPARIONS granted by the European Commission through a Marie Skłodowska Curie Individual Fellowship (H2020-MSCA-IF-2018-834363) and by the Spanish Government through a Juan de la Cierva grant (FJCI-2017-32111). M.J.C. and L.K. were supported by funds from the National Science Foundation (DEB1442140 and DEB1557028).

Effluents from wastewater treatment plants (WWTP) affect water chemistry and in-stream nutrient uptake capacity from receiving freshwaters, thus altering the amount and fate of nutrients exported. In Mediterranean regions, the dilution capacity of receiving streams to buffer the WWTP biogeochemical fingerprint can vary seasonally due to changes in hydrologic conditions. We assessed the temporal patterns and controls on nutrient uptake in an intermittent Mediterranean stream receiving WWTP effluent inputs. We compiled data on longitudinal profiles of ambient concentrations of dissolved inorganic nitrogen and phosphorus along a 800 m reach on 47 sampling dates between 2001 and 2017 that cover a wide range of hydrological conditions. Data were used to estimate net nutrient uptake in the receiving stream. Ammonium concentration decreased along the reach in 72% of dates, and these decreases were coupled with increases of either nitrite or nitrate. This phenomenon suggests that the stream acted as a hot spot of nitrification. Conversely, concentration of phosphorus did not show any longitudinal pattern in 75% of dates, suggesting that uptake and release processes for this element were commonly counterbalanced. Finally, ammonium net uptake decreased when the stream had a low dilution capacity, suggesting that excess of available nutrients associated with WWTP inputs control de temporal variation of the bioreactive capacity of the receiving streams. Overall, this study suggests that water management should consider the biogeochemical interplay between WWTP operation and the functioning of receiving streams as a strategy to improve stream water quality in urban landscapes.

Este artículo contiene 17 páginas, 7 figuras, 1 tabla., Surface-groundwater interactions in intermittent rivers and ephemeral streams (IRES), waterways which do not flow year-round, are spatially and temporally dynamic because of alternations between flowing, non-flowing and dry hydrological states. Interactions between surface and groundwater often create mixing zones with distinct redox gradients, potentially driving high rates of carbon and nutrient cycling. Yet a complete understanding of how underlying biogeochemical processes across surface-groundwater flowpaths in IRES differ among various hydrological states remains elusive. Here, we present a conceptual framework relating spatial and temporal hydrological variability in surface water-groundwater interactions to biogeochemical processing hotspots in IRES. We combine a review of theIRES biogeochemistry literature with concepts of IRES hydrogeomorphology to: (i) outline common distinctions among hydrological states in IRES; (ii) use these distinctions, together with considerations of carbon, nitrogen, and phosphorus cycles within IRES, to predict the relative potential for biogeochemical processing across different reach-scale processing zones (flowing water, fragmented pools, hyporheic zones, groundwater, and emerged sediments); and (iii) explore the potential spatial and temporal variability of carbon and nutrient biogeochemical processing across entire IRES networks. Our approach estimates the greatest reach-scale potential for biogeochemical processing when IRES reaches are fragmented into isolated surface water pools, and highlights the potential of relatively understudied processing zones, such as emerged sediments. Furthermore, biogeochemical processing in fluvial networks dominated by IRES is likely more temporally than spatially variable. We conclude that biogeochemical research in IRES would benefit from focusing on interactions between different nutrient cycles, surface-groundwater interactions in non-flowing states, and consideration of fluvial network architecture. Our conceptual framework outlines opportunities to advance studies and expand understanding of biogeochemistry in IRES., This study is based upon work from COST Action CA15113 (SMIRES, Science and Management of Intermittent Rivers and Ephemeral Streams, www.smires.eu), supported by COST (European Cooperation in Science and Technology). A.S. was supported by the InterNet Project (Eawag Discretionary Funds, Ernst Gohner ¨ Foundation and Gelbert Foundation), S.A. was supported by the Israel Science Foundation (grant 682/17). G. W. was supported by Klima- and Energiefonds within the ACRP program (PURIFY - KR17AC0K13643). S.B. was supported by the Spanish Government through “Ramon ´ y Cajal” fellow (RYC-2017-22643). HP.G. was supported by the Leibniz Foundation via the IGB household. O.S. was supported by the German Research Foundation (DFG grant SU 405/10- 1). A.W. was additionally supported by Klima- and Energiefonds within the ACRP program (PURIFY - KR17AC0K13643). V.P. is partially funded by the Environmental Protection Agency (Ireland) (EPA). U.R. was supported by a grant from the German Research Foundation (RI 2093/2- 1). S.O. was partially supported by the German Research Foundation (DFG grant SU 405/10-1). O.T. was partially supported by the National Strategic Reference Framework (NSRF). D.vS. was supported by a “Serra Húnter” Fellow. M.I.A. was supported by the “Juan de Cierva” postdoctoral program funded by the Spanish Ministry of Science, Innovation and Universities (Ref: IJC2018-036969-I).

Background Abdominal aortic aneurysm (AAA), a degenerative vascular pathology characterized by permanent dilation of the aorta, is considered a chronic inflammatory disease involving innate/adaptive immunity. However, the functional role of antibody‐dependent immune response against antigens present in the damaged vessel remains unresolved. We hypothesized that engagement of immunoglobulin G (IgG) Fc receptors (FcγR) by immune complexes (IC) in the aortic wall contributes to AAA development. We therefore evaluated FcγR expression in AAA lesions and analysed whether inhibition of FcγR signaling molecules (γ‐chain and Syk kinase) influences AAA formation in mice. Methods FcγR gene/protein expression was assessed in human and mouse AAA tissues. Experimental AAA was induced by aortic elastase perfusion in wild‐type (WT) mice and γ‐chain knockout (γKO) mice (devoid of activating FcγR) in combination with macrophage adoptive transfer or Syk inhibitor treatment. To verify the mechanisms of FcγR in vitro, vascular smooth muscle cells (VSMC) and macrophages were stimulated with IgG IC. Results FcγR overexpression was detected in adventitia and media layers of human and mouse AAA. Elastase‐perfused γKO mice exhibited a decrease in AAA incidence, aortic dilation, elastin degradation, and VSMC loss. This was associated with (1) reduced infiltrating leukocytes and immune deposits in AAA lesions, (2) inflammatory genes and metalloproteinases downregulation, (3) redox balance restoration, and (4) converse phenotype of anti‐inflammatory macrophage M2 and contractile VSMC. Adoptive transfer of FcγR‐expressing macrophages aggravated aneurysm in γKO mice. In vitro, FcγR deficiency attenuated inflammatory gene expression, oxidative stress, and phenotypic switch triggered by IC. Additionally, Syk inhibition prevented IC‐mediated cell responses, reduced inflammation, and mitigated AAA formation. Conclusion Our findings provide insight into the role and mechanisms mediating IgG‐FcγR‐associated inflammation and aortic wall injury in AAA, which might represent therapeutic targets against AAA disease., Our work suggests a pathogenic role of IgG IC interaction with activating FcγR present in infiltrating and VSMC during AAA formation. These results support the investigation of novel immunotherapeutic strategies targeting FcγRs and/or downstream molecules to inhibit humoral immune damage in AAA

Background and Aims Diabetic nephropathy is the leading cause of chronic kidney disease worldwide. Hyperglycemia in concert with cytokines activate Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway and induce gene expression of many inflammatory and oxidative stress mediators, which are critical events at all stages of diabetic kidney disease. Suppressor of cytokine signaling 1 (SOCS1) is a STAT-inducible protein and a negative feedback regulator of JAK/STAT pathway. The microRNA-155 is an epigenetic modulator of SOCS1 gene by repressing its translation and, at the same time, is a transcriptional target of STAT, thus completing another regulatory loop of JAK/STAT pathway. Therefore, our aim was to explore the interplay between miR-155 and JAK/STAT/SOCS1 axis in experimental diabetic nephropathy. Method In streptozotocin-induced type 1 diabetic aged mice (wild-type and apolipoprotein E (apoE) knockout) we analyzed the kidney levels of miR-155 and markers of renal damage, inflammation and oxidative stress. In vitro, the expression of miR-155, SOCS1 and STAT1 in mesangial, tubuloepithelial and macrophage cell lines were modulated by silencing/inhibition or overexpression/mimicking experiments to further determine the JAK/STAT pathway activation and expression of downstream target genes. Results In vivo, type 1 diabetes significantly upregulated miR-155 expression in kidneys from both wild-type and apoE knockout mice (1.8- and 4.5-fold vs respective non-diabetic controls). The miR-155 levels directly correlated with parameters of renal damage (serum creatinine, albuminuria, kidney-to-body weight ratio and renal score) and the mRNA expression of chemokines (Ccl2 and Ccl5) and pro-oxidant enzymes (Nox2 and Nox4), but inversely with antioxidant genes (Sod1 and Cat). In vitro, the expression of miR-155 was increased in renal cells and macrophages exposed to hyperglycemia and/or inflammatory conditions. Overexpression of miR-155 reduced SOCS1 expression, enhanced STAT1 and STAT3 activation and pro-inflammatory cytokines and chemokines (Il6, Tnfa, Ccl2 and Cxcl10) expression. By contrast, miR-155 antagonist upregulated SOCS1 and had a protective effect on renal cells by decreasing STAT1/3 phosphorylation and pro-inflammatory gene expression. Additionally, loss- or gain-of function experiments indicate a direct implication of SOCS1 in the regulation of miR-155 expression by STAT transcription factors. Conclusion Our study indicates a pro-inflammatory role of miR-155 in diabetic kidney disease by downregulating renal expression of SOCS1. Therefore, antagonism of miR-155 may have a renoprotective effect in diabetic nephropathy through SOCS1-mediated feedback inhibition of JAK/STAT overactivation. Ongoing in vivo studies with miR-155 inhibitor in experimental diabetes will clarify its role in the development and progression of diabetic nephropathy.

Human activities negatively impact water quality by supplying excessive nutrients to streams. To investigate the capacity of streams to take up nutrients from the water column, we usually add nutrients to stream reaches, calculate the fraction of added nutrients that is taken up, and identify the environmental conditions controlling nutrient uptake. A common idea is that nutrient uptake increases with increasing water residence time because of increased contact time between solutes and organisms. Yet, water residence time only partially explains the temporal and spatial variability of nutrient uptake, and the reasons behind this variability are still not well understood. In this talk I’ll present a study which shows that good characterization of spatial heterogeneity of surface-subsurface flow paths and bioactive hot spots within streams is essential to understanding the mechanisms of in-stream nutrient uptake. The basis of this study arises from the use and interpretation of nutrient uptake results from the Tracer Additions for Spiraling Curve Characterization (TASCC) method. This model has been rapidly adopted to interpret in-stream nutrient spiraling metrics (e.g, nutrient uptake) over a range of concentrations from breakthrough curves (BTCs) obtained during pulse solute injection experiments. TASCC analyses often identify hysteresis in the relationship between spiraling metrics and concentration as nutrient concentration in BTCs rises and falls. The mechanisms behind these hysteresis patterns have yet to be determined. We hypothesized that difference in the time a solute is exposed to bioactive environments (i.e., biophysical opportunity) between the rising and falling limbs of BTCs causes hysteresis in TASCCs. We tested this hypothesis using nitrate empirical data from a solute addition combined with a process-based particle-tracking model representing travel times and transformations along each flow path in the water column and hyporheic zone, from which the bioactive zone comprised only a thin superficial layer. In-stream nitrate uptake was controlled by hyporheic exchange and the cumulative time nitrate spend in the bioactive layer. This bioactive residence time generally increased from the rising to the falling limb of the BTC, systematically generating hysteresis in the TASCC curves. Hysteresis decreased when nutrient uptake primarily occurred in the water column compared to the hyporheic zone, and with increasing the distance between the injection and sampling points. Hysteresis increased with the depth of the hyporheic bioactive layer. Our results indicate that the organisms responsible for nutrient uptake are confined within a thin layer in the stream sediments and that the bioactive residence time at the surface-subsurface water interface is important for nutrient uptake. I will end the talk illustrating how these findings can have important implications for in-stream nutrient uptake within the context of restoration practices addressed to modify the hydro-morphological characteristics of stream channels.

Rivers transport pathogenic microorganisms (including fecal indicator bacteria and human enteric viruses) from point and non-point sources over long distances, posing a direct risk for human health. Yet, pathogens in surface waters can be deposited and transitorily immobilized and accumulated together with other fine particles in streambed sediments, mostly within the top few centimeters. These dynamic fine particle standing stocks retain and delay downstream transmission of pathogens during baseflow conditions, but contribute to their resuspension and transport downstream during stormflow events. Direct measurements of pathogen accumulation in streambed sediments are rare. Further, it is unknown whether pathogen accumulation is constrained near to the point source inputs or if the continuous deposition and resuspension of pathogens results in the transmission of active pathogens further downstream. In this study, we analyze fine particle standing stocks along a 1 km reach of an intermittent Mediterranean stream receiving inputs from the effluent of a wastewater treatment plant (WWTP), during a summer drought when the effluent constituted 100% of the stream flow, and thus, large accumulation and persistence of pathogens along the streambed was expected. We measured abundance of total bacteria, Escherichia coli (as a fecal indicator bacteria), and presence of enteric rotavirus (RoV) and norovirus (NoV). We also monitored environmental variables such as water temperature, dissolved oxygen, total benthic particulate matter, and fraction of organic matter. Abundance of E. coli, based on qPCR detection, was high (~ 1 ng/μL) along the first 100 m downstream of the WWTP effluent input, and we found trace amounts of RoV and NoV. Furthermore, E. coli was present along the first km downstream of the WWTP effluent input with a logarithmic decline in concentration with distance. These results were combined with a particle tracking model that uses stream water velocity as an input and accounts for hyporheic exchange, pathogen immobilization, degradation and resuspension during baseflow and stormflow conditions. Model results indicate that even at very low flows ( 1km), but that the extent of longitudinal transport varies among pathogen types. These results demonstrate that benthic standing stocks of fine particles act as hot spots of pathogen accumulation in streams, and that the interplay between immobilization, degradation, the extent of resuspension and downstream transport during storms and time between storms determine pathogen concentrations in the streambed.

The ‘Dominant Source Layer’ (DSL) is defined as the riparian zone (RZ) depth stratum that contributes the most to water and solute fluxes to streams. For any given period of time, the DSL position is inferred from the relationship between RZ groundwater table and stream runoff by assuming that lateral fluxes at any given RZ soil depth are proportional to the groundwater table – stream runoff curve. In forest headwaters, the DSL approach can be used to explain timing and amount of water and solute transferred from RZs to streams.Here, we used the DSL conceptual framework to investigate the potential impact of future climate changes on the long-term mobilization of water and solutes in a subhumid Mediterranean headwater catchment. We used the rainfall-runoff model PERSiST and synthetic temperature, precipitation, and inter-event length scenarios to simulate reference (1981–2000) and future (2081–2100) stream runoff in the catchment. Simulated stream runoff was then used to estimate RZ groundwater tables, and thus, the DSL position, based on the characteristic RZ groundwater table – stream runoff relationship previously established for this catchment. Our simulations indicate that future changes in temperature and precipitation will lead to reductions in stream runoff and water exports, and that the DSL will move down by as much as ca. 30 cm. As a result, shallow organic-rich layers in the RZ may only be hydrologically activated during sporadic large rainfall events predicted for the most extreme inter-event length scenarios. To better understand the transfer of solutes during these large rainfall events, we examined the RZ groundwater table – stream runoff relationship during five large storms for which we had empirical data. We found that this relationship varied among individual storm events depending on antecedent hydroclimatic conditions. Specifically, antecedent drier conditions led to steeper slopes in the RZ groundwater table – stream runoff relationship, which resulted in relatively larger concentrations of dissolved organic carbon (DOC) and nitrate (NO3-) in the stream. A steeper slope of the relationship implies that more RZ layers will be hydrologically connected to the stream, increasing the ‘thickness’ of the DSL and thus the chances for relatively more DOC and NO3- to be mobilized.Overall, we highlight the importance of identifying the layers in the RZ vertical profile that are hydrologically active (i.e., DSLs) and the factors contributing to their temporal dynamics both at long- and short-term scales, to better predict the transfer of water and solutes from catchment soils to forest headwater streams

Este artículo contiene 17 páginas, 6 figuras, 2 tablas., Dissolved organic carbon (DOC) and nitrogen (DON) are important energy and nutrient sources for aquatic ecosystems. In many northern temperate, freshwater systems DOC has increased in the past 50 years. Less is known about how changes in DOC may vary across latitudes, and whether changes in DON track those of DOC. Here, we present long-term DOC and DON data from 74 streams distributed across seven sites in biomes ranging from the tropics to northern boreal forests with varying histories of atmospheric acid deposition. For each stream, we examined the temporal trends of DOC and DON concentrations and DOC:DON molar ratios. While some sites displayed consistent positive or negative trends in stream DOC and DON concentrations, changes in direction or magnitude were inconsistent at regional or local scales. DON trends did not always track those of DOC, though DOC:DON ratios increased over time for ~30% of streams. Our results indicate that the dissolved organic matter (DOM) pool is experiencing fundamental changes due to the recovery from atmospheric acid deposition. Changes in DOC:DON stoichiometry point to a shifting energynutrient balance in many aquatic ecosystems. Sustained changes in the character of DOM can have major implications for stream metabolism, biogeochemical processes, food webs, and drinking water quality (including disinfection by-products). Understanding regional and global variation in DOC and DON concentrations is important for developing realistic models and watershed management protocols to effectively target mitigation efforts aimed at bringing DOM flux and nutrient enrichment under control., National Institute of Food and Agriculture, Grant/Award Number: 1016163, 1019522 and 1022291; Natural Environment Research Council, Grant/Award Number: NE/K010689/1; NSF EPSCoR, Grant/ Award Number: EPS-1929148; Division of Environmental Biology, Grant/ Award Number: 1545288 and 1556603; European Regional Development Fund, Grant/Award Number: RTI2018-094521- B-100 and RYC-2017-22643

The Tracer Additions for Spiraling Curve Characterization (TASCC) model has been rapidly adopted to interpret in‐stream nutrient spiraling metrics over a range of concentrations from breakthrough curves (BTCs) obtained during pulse solute injection experiments. TASCC analyses often identify hysteresis in the relationship between spiraling metrics and concentration as nutrient concentration in BTCs rises and falls. The mechanisms behind these hysteresis patterns have yet to be determined. We hypothesized that differences in the time a solute is exposed to bioactive environments (i.e. biophysical opportunity) between the rising and falling limbs of BTCs causes hysteresis in TASCCs. We tested this hypothesis using nitrate data from Elkhorn Creek (CO) combined with a process‐based particle tracking model representing travel times and transformations along each flow path in the water column and hyporheic zone, from which the bioactive zone comprised only a thin superficial layer. In‐stream nitrate uptake was controlled by hyporheic exchange and the cumulative time nitrate spend in the bioactive layer. This bioactive residence time generally increased from the rising to the falling limb of the BTC, systematically generating hysteresis in the TASCC curves. Hysteresis decreased when nutrient uptake primarily occurred in the water column compared to the hyporheic zone, and with increasing the distance between the injection and sampling points. Hysteresis increased with the depth of the hyporheic bioactive layer. Our results emphasize that good characterization of spatial heterogeneity of surface‐subsurface flow paths and bioactive hot spots within streams is essential to understanding the mechanisms of in‐stream nutrient uptake.

Este artículo contiene 13 páginas, 4 figuras, 2 tabals., Fine particulate organic matter (FPOM) accumulated in streambeds is a major component of organic matter budgets in headwater streams and greatly affects productivity and metabolism of stream communities. The spatiotemporal distribution of benthic FPOM in the stream, as well as its quantity and quality, depend on inputs from different source types. These can be natural such as soils, streambanks and riparian vegetation, or anthropogenic such as effluents from wastewater treatment plants (WWTP). In addition, stream flow is a key driver of FPOM dynamics, which influences the balance between its transport and accumulation in the streambed. Yet, the link between FPOM dynamics and its effects on stream metabolism is still largely unknown. The aim of this study was to investigate the influence of stream channel hydromorphology on water transport and streambed accumulation of fine particulate matter (FPM) (mineral and organic fractions), FPOM (organic fraction) and its quality (characterized by %OM, %C, %N and the C:N molar ratio). In addition, we quantified the metabolic activity associated with FPM at the habitat scale, and its potential contribution to whole-reach ecosystem respiration using the resazurin-resorufin bioreactive tracer as a proxy for aerobic respiration. We also characterized water transport and metabolic activity with combined additions of hydrological and bioreactive tracers at the reach scale. The study was conducted in the Cànoves stream (Catalonia, NE Spain) downstream of a WWTP that contains three reaches that were hydromorphologically modified using bioengineering techniques. Slower local velocities at the habitat scale increased accumulation of FPM, but did not influence the spatial variability of its quality. Instead, FPM quality declined further downstream from the WWTP. Accumulation of FPM did not increase metabolic activity, but higher %OM of FPM and lower C:N ratios favored the microbial metabolic activity efficiency (normalized by the gram of FPM). Reach-scale metabolic activity was higher in reaches with higher water exchange rate and longer relative travel times, highlighting hydromorphology as an important driver of microbial metabolic activity at the reach-scale. This demonstrates that the interplay of hydrologic exchange and residence time in streambed sediments associated with the microbial metabolic activity of FPOM can ultimately influence reach-scale metabolic activity., This project was supported by a Marie Curie Individual Fellowship (833702 - MICROPATH) and an NSF EAR-Postdoctoral Fellowship to JD and project MEDSOUL (CGL2014-59977-C3-2-R) from the Spanish Office for Research (MINECO).

Herein we investigated the structural and cellular effects ensuing from the cyclization of a potent inhibitor of JAK2 as mimetic of SOCS1 protein, named PS5. The introduction of un-natural residues and a lactam internal bridge, within SOCS1-KIR motif, produced candidates that showed high affinity toward JAK2 catalytic domain. By combining CD, NMR and computational studies, we obtained valuable models of the interactions of two peptidomimetics of SOCS1 to deepen their functional behaviors. Notably, when assayed for their biological cell responses mimicking SOCS1 activity, the internal cyclic PS5 analogues demonstrated able to inhibit JAK-mediated tyrosine phosphorylation of STAT1 and to reduce cytokine-induced proinflammatory gene expression, oxidative stress generation and cell migration. The present study well inserts in the field of low-molecular-weight proteomimetics with improved longtime cellular effects and adds a new piece to the puzzled way for the conversion of bioactive peptides into drugs.

The chronic activation of the Janus kinase/signal transducer and activator of the transcription (JAK/STAT) pathway is linked to oxidative stress, inflammation and cell proliferation. Suppressors of cytokine signaling (SOCS) proteins negatively regulate the JAK/STAT, and SOCS1 possesses a small kinase inhibitory region (KIR) involved in the inhibition of JAK kinases. Several studies showed that KIR-SOCS1 mimetics can be considered valuable therapeutics in several disorders (e.g., diabetes, neurological disorders and atherosclerosis). Herein, we investigated the antioxidant and atheroprotective effects of PS5, a peptidomimetic of KIR-SOCS1, both in vitro (vascular smooth muscle cells and macrophages) and in vivo (atherosclerosis mouse model) by analyzing gene expression, intracellular O2&bull, &minus, production and atheroma plaque progression and composition. PS5 was revealed to be able to attenuate NADPH oxidase (NOX1 and NOX4) and pro-inflammatory gene expression, to upregulate antioxidant genes and to reduce atheroma plaque size, lipid content and monocyte/macrophage accumulation. These findings confirm that KIR-SOCS1-based drugs could be excellent antioxidant agents to contrast atherosclerosis.

© 2020 by the authors., Studies exploring how different sources of dissolved organic matter (DOM) influence in-stream dissolved organic carbon (DOC) uptake at the ecosystem scale are scarce in the literature. To fill this knowledge gap, we examined the relationship between DOM sources and in-stream net DOC uptake (UDOC) in a sub-humid Mediterranean stream. We considered four reach-scale scenarios occurring under natural conditions that differed in predominant DOM sources (groundwater, leaf litter, and/or upstream water). Results showed that groundwater inputs favored in-stream net DOC uptake, while leaf litter inputs promoted in-stream net DOC release. However, there was no clear effect of DOM source mixing on the magnitude of UDOC. Further, the variability in UDOC within and among scenarios was mostly explained by stream DOC concentration, suggesting that DOC availability limits microbial activity in this stream. DOM composition became a controlling factor of UDOC variability only during the leaf litter period, when stream DOC concentration was the highest. Together, these results suggest that the capacity of headwater forested streams to process DOC is closely tied to the availability of different DOM sources and how they vary over time and along the river network., This research was funded by the Spanish Ministry of Science, Innovation, and Universities through the projects CANTERA (RTI2018-094521-B-100) and MEDFORESTREAM (CGL2011-30590). Anna Lupon held a Juan de la Cierva (FJCI-2016-28416) and a Beatriu de Pinós (BP-2018-00082) grants. Núria Catalán received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement (No.839709). Susana Bernal was supported by the Ramon y Cajal fellowship (RYC-2017-22643).

Diabetic nephropathy (DN) is a multifactorial disease characterized by hyperglycemia and close interaction of hemodynamic, metabolic and inflammatory factors. Nuclear factor-&kappa, B (NF-&kappa, B) is a principal matchmaker linking hyperglycemia and inflammation. The present work investigates the cell-permeable peptide containing the inhibitor of kappa B kinase &gamma, (IKK&gamma, )/NF-&kappa, B essential modulator (NEMO)-binding domain (NBD) as therapeutic option to modulate inflammation in a preclinical model of type 2 diabetes (T2D) with DN. Black and tan, brachyuric obese/obese mice were randomized into 4 interventions groups: Active NBD peptide (10 and 6 &micro, g/g body weight), Inactive mutant peptide (10 &micro, g/g), and vehicle control. In vivo/ex vivo fluorescence imaging revealed efficient delivery of NBD peptide, systemic biodistribution and selective renal metabolization. In vivo administration of active NBD peptide improved albuminuria (&gt, 40% reduction on average) and kidney damage, decreased podocyte loss and basement membrane thickness, and modulated the expression of proinflammatory and oxidative stress markers. In vitro, NBD blocked IKK-mediated NF-&kappa, B induction and target gene expression in mesangial cells exposed to diabetic-like milieu. These results constitute the first nephroprotective effect of NBD peptide in a T2D mouse model that recapitulates the kidney lesions observed in DN patients. Targeting IKK-dependent NF-&kappa, B activation could be a therapeutic strategy to combat kidney inflammation in DN.

Research in the river corridor commonly focuses in two study designs. One research strategy focuses on physical, chemical, and/or biological dynamics and feedbacks, emphasizing local variation and interaction over larger-scale context. A second study design focuses on gradients arising in response to non-local controls (e.g., climate, tectonic setting), with an emphasis on broad trends over smaller-scale “noise”. Here, we present a comprehensive set of measurements and calculated metrics describing physical, chemical, and biological conditions collected at 62 sites in the river corridor within a 5th order basin including more than 150 variables at each site. The size and scope of this data set allows us to assess which variables have spatial structure in the basin using spatial semivariograms and regressions with discharge and drainage area. We ask how physical, chemical, and biological sub-systems co-vary using a principal components analyses. Next, we explain both spatial structure and local variance simultaneously using support vector machine regression techniques that reveal possible nonlinear, multivariate relationships that may direct future research. Key outcomes from this study include (1) an introduction to an open-source, comprehensive characterization of the river corridor, (2) interpretations of both broad trends and local variance in the river corridor, and (3) a summary of which metrics have the most explanatory power and why within the study system.

Lateral carbon flux through river networks is an important and poorly understood component of the global carbon budget. This work investigates how temperature and hydrology control the production and export of dissolved organic carbon (DOC) in the Susquehanna Shale Hills Critical Zone Observatory in Pennsylvania, USA. Using field measurements of daily stream discharge, evapotranspiration, and stream DOC concentration, we calibrated the catchment-scale biogeochemical reactive transport model BioRT-Flux-PIHM (Biogeochemical Reactive Transport–Flux–Penn State Integrated Hydrologic Model, BFP), which met the satisfactory standard of a Nash–Sutcliffe efficiency (NSE) value greater than 0.5. We used the calibrated model to estimate and compare the daily DOC production rates (Rp; the sum of the local DOC production rates in individual grid cells) and export rate (Re; the product of the concentration and discharge at the stream outlet, or load). Results showed that daily Rp varied by less than an order of magnitude, primarily depending on seasonal temperature. In contrast, daily Re varied by more than 3 orders of magnitude and was strongly associated with variation in discharge and hydrological connectivity. In summer, high temperature and evapotranspiration dried and disconnected hillslopes from the stream, driving Rp to its maximum but Re to its minimum. During this period, the stream only exported DOC from the organic-poor groundwater and from organic-rich soil water in the swales bordering the stream. The DOC produced accumulated in hillslopes and was later flushed out during the wet and cold period (winter and spring) when Re peaked as the stream reconnected with uphill and Rp reached its minimum. The model reproduced the observed concentration–discharge (C–Q) relationship characterized by an unusual flushing–dilution pattern with maximum concentrations at intermediate discharge, indicating three end-members of source waters. A sensitivity analysis indicated that this nonlinearity was caused by shifts in the relative contribution of different source waters to the stream under different flow conditions. At low discharge, stream water reflected the chemistry of organic-poor groundwater; at intermediate discharge, stream water was dominated by the organic-rich soil water from swales; at high discharge, the stream reflected uphill soil water with an intermediate DOC concentration. This pattern persisted regardless of the DOC production rate as long as the contribution of deeper groundwater flow remained low ( % of the streamflow). When groundwater flow increased above 18 %, comparable amounts of groundwater and swale soil water mixed in the stream and masked the high DOC concentration from swales. In that case, the C–Q patterns switched to a flushing-only pattern with increasing DOC concentration at high discharge. These results depict a conceptual model that the catchment serves as a producer and storage reservoir for DOC under hot and dry conditions and transitions into a DOC exporter under wet and cold conditions. This study also illustrates how different controls on DOC production and export – temperature and hydrological flow paths, respectively – can create temporal asynchrony at the catchment scale. Future warming and increasing hydrological extremes could accentuate this asynchrony, with DOC production occurring primarily during dry periods and lateral export of DOC dominating in major storm events.

Lateral carbon flux through river networks is an important and poorly-understood component of the global carbon budget. This work investigates how temperature and hydrology control the production and export of dissolved organic carbon (DOC) in the Susquehanna Shale Hills Critical Zone Observatory in Pennsylvania, USA. We applied the catchment-scale hydro-biogeochemical reactive transport model BioRT-Flux-PIHM to simulate the DOC dynamics. We estimated the daily DOC production rate (Rp; the sum of local DOC production rates in individual modeling grid cell) and the daily DOC export rate (Re; the product of concentration and discharge at the stream outlet) to downstream ecosystems. Simulations showed that Rp varied by less than an order of magnitude and primarily hinged on seasonal temperature change. In contrast, Re varied by more than three orders of magnitude with a strong dependence on discharge and hydrological connectivity. During summer, high temperatures led to high atmospheric water demand (and evapotranspiration) that dried and disconnected hillslope to stream. Rp reached its maximum but Re was at its minimum. The stream only exported DOC from the organic-poor groundwater and from soil water in the narrow organic-rich swales with enriched DOC such that DOC accumulated in the catchment. During the wet period (winter and spring), Rp reached its minimum but Re peaked because the stream was re-connected to a greater uphill area, flushing out the stored DOC. The model reproduced the observed concentration discharge (C–Q) relationship characterized by a flushing-dilution pattern with a rise in concentrations to a maximum (flushing) at a threshold discharge and then followed a general dilution with concentrations decreasing with discharge. This pattern was explained by the comparable contribution of organic-poor deeper groundwater and soil water from organic-rich swales at the minimum flow, maximized percentage contribution of soil water from organic-rich swales at the low flow regime, and increased contribution of uphill soil water interflow from uphill with less DOC at the high flow regime. This pattern persisted regardless of DOC production rate as long as the contribution of deeper groundwater flow remained low ( 18 %, the flushing-dilution C–Q pattern shifted towards a flushing-only pattern with DOC concentrations increasing with discharge. This study illustrates the temporal asynchrony of DOC production, mostly controlled by temperature, and DOC export, primarily governed by hydrological flow paths at the catchment scale. The occurrence of warmer and more extreme hydrological events in the future could accentuate this asynchrony, with major lateral export of DOC dominated by a few major storm events whereas DOC is produced and stored in the catchment in the prolonged drought periods.

Addition of isotopically labeled dissolved forms of nitrogen (N) and carbon (C) in streams has revealed that microbes associated with leaf litter can assimilate solutes from the water column. However, whether this assimilation varies among leaf litter species and at different decomposition stages is still largely unknown. Here, we explore differences in the uptake of NH4‐N and acetate from water column among leaf litter of five riparian tree species at five different times of decomposition. To do so, we conducted a 24 h addition of 15N‐NH4 and 13C‐acetate at constant rate to estimate the microbial uptake of these solutes from the water column. We measured microbial cellobiohydrolase activity and decomposition rates (k) associated with each leaf litter type to examine their influence on NH4‐N and acetate uptake. We found that mass specific N‐uptake (μg N mg N−1 d−1) was relatively constant during leaf litter decomposition whereas mass specific C‐uptake (mg C g C−1 d−1) increased over time. Among leaf litter species, cumulative values of N‐uptake during the study period were negatively related to leaf litter k whereas cumulative values of C‐uptake were positively related to k. Our study indicates that leaf litter species and their decomposition stage are important for understanding the reliance of leaf‐associated microbes on dissolved inorganic nitrogen and dissolved organic carbon from the water column.

Este artículo contiene 9 páginas, 4 figuras, 2 tablas., Emergent macrophyte species selection is critical for the effectiveness of nature-based engineered solutions aiming to address excess nutrient concentrations in freshwater ecosystems. Yet, the mechanisms with which macrophytes enhance nutrient retention need to be further understood. Here, we compared nutrient retention among 12 artificial flumes fed with effluents from a wastewater treatment plant and subjected to four treatments: absence of macrophytes (control) and presence of three different macrophyte species (Iris pseudacorus L., Phragmites australis L., and Schoenoplectus lacustris L.). We estimated the net and gross nutrient uptake based on the longitudinal profiles of ambient concentrations and on pulse injections of ammonium (NH4 +) and soluble reactive phosphorus. Further, we investigated the influence of subsurface hydrological retention, attributed to the architectural differences in the roots of these macrophytes, on nutrient retention. Results showed a species-specific effect of macrophytes on nutrient retention and confirmed root-associated subsurface hydrological retention as a driving factor. Schoenoplectus showed both high net and gross NH4 + uptake, thereby being the most effective species to address N loading, compared to Iris and Phragmites. This work contributes to improve our mechanistic understanding of the role of emergent macrophytes on nutrient retention in aquatic environments., Funding for this study came from the INTERFACES Marie Curie Initial Training Network project (FP7-PEOPLE-2013-ITN, grant 607150) and MEDSOUL (CGL2014-59977-C3-2-R), NICUS (CGL-2014-55234-JIN), CANTERA (RTI-2018-094521-B-101), Eco-Reactors (PGC2018-101975-B-C21 and PGC2018-101975-B-C22), and FORESTREAM (2017-SGR-976) projects from the I + D program of the Spanish Ministry of Science, Innovation, and Universities. A.A. was supported by the USDA NIFA McIntire Stennis Project #MO-MCNR0008. S.B. was supported by the Ramon y Cajal fellowship (RYC-2017-22643).

Este artículo contiene 25 páginas, 9 figuras., In the Anthropocene, watershed chemical transport is increasingly dominated by novel combinations of elements, which are hydrologically linked together as ‘chemical cocktails.’ Chemical cocktails are novel because human activities greatly enhance elemental concentrations and their probability for biogeochemical interactions and shared transport along hydrologic flowpaths. A new chemical cocktail approach advances our ability to: trace contaminant mixtures in watersheds, develop chemical proxies with high-resolution sensor data, and manage multiple water quality problems. We explore the following questions: (1) Can we classify elemental transport in watersheds as chemical cocktails using a new approach? (2) What is the role of climate and land use in enhancing the formation and transport of chemical cocktails in watersheds? To address these questions, we first analyze trends in concentrations of carbon, nutrients, metals, and salts in fresh waters over 100 years. Next, we explore how climate and land use enhance the probability of formation of chemical cocktails of carbon, nutrients, metals, and salts. Ultimately, we classify transport of chemical cocktails based on solubility, mobility, reactivity, and dominant phases: (1) sieved chemical cocktails (e.g., particulate forms of nutrients, metals and organic matter); (2) filtered chemical cocktails (e.g., dissolved organic matter and associated metal complexes); (3) chromatographic chemical cocktails (e.g., ions eluted from soil exchange sites); and (4) reactive chemical cocktails (e.g., limiting nutrients and redox sensitive elements). Typically, contaminants are regulated and managed one element at a time, even though combinations of elements interact to influence many water quality problems such as toxicity to life, eutrophication, infrastructure corrosion, and water treatment. A chemical cocktail approach significantly expands evaluations of water quality signatures and impacts beyond single elements to mixtures. High-frequency sensor data (pH, specific conductance, turbidity, etc.) can serve as proxies for chemical cocktails and improve real-time analyses of water quality violations, identify regulatory needs, and track water quality recovery following storms and extreme climate events. Ultimately, a watershed chemical cocktail approach is necessary for effectively co-managing groups of contaminants and provides a more holistic approach for studying, monitoring, and managing water quality in the Anthropocene., This work was funded by USDA (award # 2016-67019-25280) and NSF-EPSCoR (#1641157) for supporting collaborations at the AGU Chapman Conference on Extreme Climate Events. Significant funding for data collection/analyses in this paper was provided by NSF EAR1521224, NSF CBET1058502, NSF Coastal SEES1426844, NSF DEB-0423476 and DEB-1027188, NSF RI EPSCoR NEWRnet Grant No. IIA-1330406, EPA ORD, Chesapeake Bay Trust, and Multi-state Regional Hatch Project S-1063.

Streams are important sources of carbon to the atmosphere, though whether they merely outgas terrestrially derived carbon dioxide or mineralize terrestrial inputs of dissolved organic matter (DOM) is still a big challenge in ecology. The objective of this study was to investigate the influence of riparian groundwater (GW) and in-stream processes on the temporal pattern of stream DOM concentrations and quality in a forested headwater stream, and whether this influence differed between the leaf litter fall period (LLF) and the remaining part of the year (no-LLF). The spectroscopic indexes (fluorescence index, biological index, humification index, and PARAFAC components) indicated that DOM had an eminently protein-like character and was most likely originated from microbial sources and recent biological activity in both stream water and riparian GW. However, paired samples of stream water and riparian GW showed that dissolved organic carbon (DOC) and nitrogen (DON) concentrations as well as the spectroscopic character of DOM differed between the two compartments throughout the year. A simple mass balance approach indicated that in-stream processes along the reach contributed to reduce DOC and DON fluxes by 50% and 30%, respectively. Further, in-stream DOC and DON uptake were unrelated to each other, suggesting that these two compounds underwent different biogeochemical pathways. During the LLF period, stream DOC and DOC:DON ratios were higher than during the no-LLF period, and spectroscopic indexes suggested a major influence of terrestrial vegetation on stream DOM. Our study highlights that stream DOM is not merely a reflex of riparian GW entering the stream and that headwater streams have the capacity to internally produce, transform, and consume DOM., Susana Bernal and Anna Lupon were funded by the Spanish Ministry of Economy and Competitiveness (MINECO) with a Juan de la Cierva contract (JCI-2010-06397) and a FPU grant (AP-2009-3711). Susana Bernal received additional funds from the Spanish Research Council (CSIC) (JAEDOC027) and the MICECO-funded projects MED_SOUL (CGL2014-59977-C3-2-R) and NICUS (CGL-2014-55234-JIN).

Efficient NH4+ oxidation is a critical issue in human-impaired streams receiving high N loads from the effluent of wastewater treatment plants (WWTP). Archaeal (AOA) and bacterial (AOB) ammonia oxidizers are strongly photoinhibited in laboratory cultures, so we expected that light availability would affect the distribution of AOA and AOB and NH4+ oxidation rates at the reach scale. We selected 2 contiguous reaches downstream of a WWTP input in La Tordera river (northeastern Spain) that strongly differed in canopy cover (open and shaded). Against expectations and despite significant differences in light availability, the 2 reaches showed similar abundance of AOA and AOB and similar daily rates of ecosystem respiration, gross primary productivity, and NH4+ oxidation. The abundance of ammonia oxidizers was not correlated with biomass in biofilms protected from light, whereas a positive relationship was found for light-exposed biofilms. This result suggests that biomass accrual could provide light protection to ammonia oxidizers in light-exposed biofilms. The contribution of NH4+ oxidation to whole-reach NH4+ uptake reached up to 89%, indicating a high potential for NH4+ oxidation in the 2 reaches. NH4+ oxidation rates were similar between night and day, but their contribution to whole-reach NH4+ uptake tended to be higher at night than during the day. Altogether, these findings highlight that environmental factors other than irradiance drive reach-scale NH4+ oxidation in this urban stream.