Joel Christopher Hoffman

Worldwide, freshwater systems contain more than 18,000 fish species^1,2,3, which are critical to the functioning of these ecosystems⁴ and are vital cultural and economic resources to humans^5,6,7; despite this value, fish biodiversity is at risk globally^8,9. In the USA, leading threats to fish communities in rivers and streams include climate change and invasive fish introductions and game fish stocking by humans^{10,11,12,13,14}. Here we harmonized US federal biomonitoring datasets with 389 species spanning 27 years (1993–2019) and 2,992 sites to analyse trends in fish biodiversity. In cold streams (past summer stream temperatures below 15.4 °C), fish abundance and richness declined by 53.4% and 32% over 27 years, respectively, and uniqueness increased. Periodic (large-bodied, late-maturing) fishes increased, and opportunists (small-bodied, short generation time, ‘r-selected’) decreased, possibly due to proliferation of native or introduced game fishes. In warm streams (stream temperatures greater than 23.8 °C), fish abundance and richness increased by 70.5% and 15.6% over 27 years, respectively, and communities homogenized. Small opportunistic fishes replaced large periodic fishes. Intermediate streams (stream temperatures 15.4–23.8 °C), representing the average stream, had minimal changes in fish biodiversity through time. Interactions between warming and introduced fish were associated with increased rates of degradation to local fish biodiversity. Given the magnitude of these changes in a relatively short time span, there is an urgent need to curb degradation of fish biodiversity caused by fish introductions and warming water temperatures.

Purpose of Review During a combined sewer overflow (CSO) event, the capacity of a sewer system is exceeded, and untreated sewage, wastewater, and stormwater are released into nearby water bodies. CSOs occur in urban areas due to heavy precipitation, which is expected to occur more frequently and at higher intensity in certain regions of the world due to increasing climate variability. After a CSO, humans can be exposed to pathogens through recreational activities and contaminated drinking water. While previous research has quantified the impacts of CSOs on water quality indicator species and described the effects of CSOs on coastal wetland ecosystems, there is limited research on the potential human health impacts of CSOs. We conducted a literature search of peer-reviewed epidemiological studies that investigated associations between CSOs and human health outcomes. Recent Findings Our literature search and screening methods returned eight studies on the association between CSOs and gastrointestinal (GI) illness in Europe and North America. Our selected peer-reviewed publications included five different study designs: time series, case-crossover, retrospective cohort, case-control, and case time series, with study periods including years 2002 to 2019. Summary The included studies showed evidence of a positive association between CSOs and GI illness, and one study suggested that sewer infrastructure improvements may decrease the burden of GI illness in future decades.

Objective: The potential for environmental DNA (eDNA) to disperse widely from source organisms enables high detection efficiency but raises questions about eDNA's ability to differentiate fine-scale spatial patterns relative to conventional fish capture data. Methods: We evaluate these questions in the St. Louis River estuary—a hydrologically and spatially complex coastal system within Lake Superior that supports a diverse assemblage of resident and migratory fish species—via comparison of eDNA metabarcoding (12S and 16S loci) to multigear capture survey data from 2 years and two seasons. Results: The eDNA and capture surveys collectively yielded 68 fish species: 2 species detected only by capture, 27 detected only by eDNA, and 39 shared across both survey types but having generally higher occurrence frequencies with eDNA than capture. Six species detected only by eDNA were unexpected, having no prior records in the Lake Superior basin. Data from paired eDNA and capture stations showed little relationship between the two survey types, with capture yielding species at stations that eDNA did not, eDNA detecting species in different habitats and distant locations from any captures, and assemblage patterns homogenized in eDNA surveys relative to capture surveys. Conclusions: Our study finds that eDNA is a sensitive tool for assessing species presence at the system scale but that capture surveys may better yield the fine-scale spatial distribution information of interest to fisheries and habitat managers, especially in spatially and hydrologically complex systems.

Remediation to Restoration to Revitalization (R2R2R) is a framework to identify social and ecological relationships between coastal and estuarine revitalization and aquatic sediment remediation or habitat restoration projects. Undertaking ecological restoration projects along coasts and estuaries provides an opportunity to support and enhance human communities’ well-being by improving and protecting aquatic and riparian habitat and reconnecting communities with the water. To consider both human and biophysical dimensions simultaneously, a community-based decision support process that considers community values with potential ecological outcomes is required. We employed the R2R2R framework to relate ecological restoration to ecosystem services (ES) and associated human benefits such as safe fishing, boating, swimming opportunities, and subsistence food gathering. This case study involved a comparative analysis of contamination remediation and habitat restoration design alternatives for Mud Lake, an embayment of the St. Louis River near Duluth, Minnesota. We also conducted a community values analysis to compare the potential community wellbeing impacts resulting from changes in ecosystem services associated with restoration alternatives. We found the mix of ES provided at Mud Lake varied among decision alternatives, resulting in trade-offs among alternatives and likely differences in well-being outcomes. Our study shows that when there are multiple ecological and social tradeoffs associated with a restoration project, considering ES with community values contributes to more equitable decision-making and can mitigate negative impacts to well-being. We argue the R2R2R framework is useful for establishing a community of practice for integrating ES and community values into decision-support for remediating coasts and estuaries along the Great Lakes.

Understanding carbon (C) dynamics in large lake ecosystems poses challenges due to their size, causing uncertainty in their contribution to the global C cycle. Here, we used autonomous underwater vehicles to calculate upper mixed‐column (UMC) metabolism in Lake Superior. We paired 7 years of high‐resolution dissolved oxygen and temperature data from 17 glider missions with in situ meteorological data to calculate daily gross primary production, ecosystem respiration, and net ecosystem metabolism. We found the UMC of Lake Superior to be net heterotrophic (primary production < ecosystem respiration) most of the time, suggesting its role as a net source of CO₂ to the atmosphere. Heterotrophy was pronounced during cold and transitional days (2 y⁻¹, which is twice the rate of C it fixes from the UMC itself.