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• SRP dynamics in streambed sediments are complex and heterogeneous over small scales. • SRP concentrations closely linked to iron and possibly manganese redox cycling. • High porewater SRP close to streambed surface likely derived from P-rich sediments. • Oxic cap may limit SRP flux to stream but is temporally and spatially discontinuous. Streambed sediment and groundwater represent important stores of soluble reactive phosphorus (SRP) in freshwater catchments yet their contributions to watershed SRP loads remain unclear. This study evaluates the spatio-temporal variability and geochemical and hydrologic controls on porewater SRP in the streambed along an agricultural reach, including the influence of groundwater-surface water interactions. High porewater SRP (>1000 µg/L) and high available sediment-bound SRP were observed in low groundwater discharge zones, specifically in the shallow (≤0.1 m) streambed sediments. Porewater SRP concentrations were linked to iron and possibly manganese redox cycling with more-reducing conditions consistently coinciding with high SRP. Porewater SRP varied temporally but distinct seasonal changes across the stream reach were not observed. A shallow oxic cap that may limit SRP release to the stream was observed in the very shallow streambed but its presence was spatially and temporally discontinuous. Finally, data indicate P-rich shallow streambed sediments are the likely source of the observed high SRP porewater concentrations in the streambed rather than incoming groundwater from the adjacent fields. Overall, the findings highlight the complexity of SRP dynamics in agricultural streambeds and provide insight into processes governing the timing and location of SRP loading streams. [ABSTRACT FROM AUTHOR]

Rivers suffer from multiple stressors acting simultaneously on their biota, but the consequences are poorly quantified at the global scale. We evaluated the biological condition of rivers globally, including the largest proportion of countries from the Global South published to date. We gathered macroinvertebrate‐ and fish‐based assessments from 72,275 and 37,676 sites, respectively, from 64 study regions across six continents and 45 nations. Because assessments were based on differing methods, different systems were consolidated into a 3‐class system: Good, Impaired, or Severely Impaired, following common guidelines. The proportion of sites in each class by study area was calculated and each region was assigned a Köppen‐Geiger climate type, Human Footprint score (addressing landscape alterations), Human Development Index (HDI) score (addressing social welfare), % rivers with good ambient water quality, % protected freshwater key biodiversity areas; and % of forest area net change rate. We found that 50% of macroinvertebrate sites and 42% of fish sites were in Good condition, whereas 21% and 29% were Severely Impaired, respectively. The poorest biological conditions occurred in Arid and Equatorial climates and the best conditions occurred in Snow climates. Severely Impaired conditions were associated (Pearson correlation coefficient) with higher HDI scores, poorer physico‐chemical water quality, and lower proportions of protected freshwater areas. Good biological conditions were associated with good water quality and increased forested areas. It is essential to implement statutory bioassessment programs in Asian, African, and South American countries, and continue them in Oceania, Europe, and North America. There is a need to invest in assessments based on fish, as there is less information globally and fish were strong indicators of degradation. Our study highlights a need to increase the extent and number of protected river catchments, preserve and restore natural forested areas in the catchments, treat wastewater discharges, and improve river connectivity. [ABSTRACT FROM AUTHOR]

It has been proposed that biomonitoring may benefit from the use of metabolomics (the study of all small molecules in an organism) to detect sub-lethal organism stress through changes in the metabolite profile (i.e., the metabolome). However, to integrate the metabolome into biomonitoring programs the amount of natural variability among and within populations of indicator taxa must be established prior to generating a reference condition. This study determined variation in the metabolome among ecoregion and stream of origin in the northern crayfish (Faxonius virilis) and if that variation inhibited detection of stressor effects at sites exposed to human activities. We collected crayfish from seven minimally disturbed streams (i.e., reference streams), distributed across three level II ecoregions in central Canada and compared their metabolomes. We found ecoregion and stream origin were poor predictors of crayfish metabolomes. This result suggests crayfish metabolomes were similar, despite differing environmental conditions. Metabolomes of crayfish collected from three stream sites exposed to agricultural activity and municipal wastewater (i.e., test sites) were then compared to the crayfish metabolomes from the seven reference streams. Findings showed that crayfish metabolomes from test sites were strongly differentiated from those at all reference sites. The consistency in the northern crayfish metabolome at the studied reference streams indicates that a single reference condition may effectively detect impacts of human activities across the sampled ecoregions. • Application of metabolomics may enhance bioassessment of ecosystems. • Crayfish metabolomes from reference streams did not differ among ecoregion or stream. • Natural variation did not impede detection of impacts of human activity. • Regional reference conditions could include streams from multiple ecoregions. [ABSTRACT FROM AUTHOR]