Niche conservatism and spread explain introgression between native and invasive fish.

Hybridisation can be an important driver of evolutionary change, but hybridisation with invasive species can have adverse effects on native biodiversity. While hybridisation has been documented across taxa, there is limited understanding of ecological factors promoting patterns of hybridisation and the spatial distribution of hybrid individuals. We combined the results of ecological niche modelling (ENM) and restriction site-associated DNA sequencing to test theories of niche conservatism and biotic resistance on the success of invasion, admixture, and extent of introgression between native and non-native fishes. We related Maxent predictions of habitat suitability based on the native ranges of invasive Eastern Banded Killifish (Fundulus diaphanus diaphanus Lesueur 1817) and native Western Banded Killifish (Fundulus diaphanus menona Jordan and Copeland 1877) to admixture indices of individual Banded Killifish. We found that Eastern Banded Killifish predominated at sites predicted as suitable from their ENM, consistent with niche conservatism. Admixed individuals were more common as Eastern Banded Killifish habitat suitability declined. We also found that Eastern Banded Killifish were most common at sites closest to the presumed source of this invasion, whereas the proportion of admixed individuals increased with distance from the source of invasion. Lastly, we found little evidence that habitat suitability for Western Banded Killifish provides biotic resistance from either displacement by, or admixture with, invasive Eastern Banded Killifish. Our study demonstrates that ENMs can inform conservation-relevant outcomes between native and invasive taxa while emphasising the importance of protecting isolated Western Banded Killifish populations from invasive conspecifics.

Non-linear effects on the population performance of Bighead Carp under different maturation schedules.

Bighead Carp currently threatens to invade the Laurentian Great Lakes from the Mississippi River, but the novel climatic conditions it will encounter by expanding northwards could affect its population performance. Bighead Carp in colder climates exhibits slower growth and matures later, with later maturation typically leading to larger adult size and increased fecundity and survival. Accordingly, the life-history strategies of Bighead Carp at its northern range limits could differ from those observed in its current invaded range. To explore how population performance could differ across changing environmental conditions, we used a stage- and age-based matrix population model parameterized with values reported for Bighead Carp populations around the world. The model was used to evaluate how different ages of maturity and their resulting impacts to body size, survival, and fecundity could impact rates of population growth and establishment. Age of maturity had a non-linear effect on population growth, with maturation at intermediate ages (4-6 years) resulting in better performance. However, performance differed less between maturation ages when fecundity was allowed to increase disproportionately with body size. Greater population growth at younger ages of maturity suggest that invasion at lower latitudes could enable establishment in fewer years due to faster rates of development in warmer temperatures. Across all maturation schedules, population growth was most sensitive to the recruitment of age-1 individuals and least sensitive to adult survival, and vital rates overall varied more in their contribution to population growth at younger ages of maturity. Thus, understanding the factors that control age-1 recruitment would inform projections of population performance for Bighead Carp in the Laurentian Great Lakes. Supplementary Information: The online version contains supplementary material available at 10.1007/s10530-023-03126-z.

Occurrence and biomagnification of perfluoroalkyl substances (PFAS) in Lake Michigan fishes.

We measured perfluoroalkyl substances (PFAS) in prey and predator fish from Lake Michigan (USA) to investigate the occurrence and biomagnification of these compounds in this important ecosystem. Twenty-one PFAS were analyzed in 117 prey fish obtained from sites across Lake Michigan and in 87 salmonids collected in four lake quadrants. The mean concentration of sum (∑) PFAS above the method detection limit was 12.7 ± 6.96 ng g-1 wet weight in predator fish (all of which were salmonids) and 10.7 ± 10.4 ng g-1 in prey fish, with outlier levels found in slimy sculpin, Cottus cognatus (187 ± 12.2 ng g-1 ww). Perfluorooctanoic sulfonic acid (PFOS) was the most frequently detected and most abundant compound of the 21 PFAS, occurring in 98 % of individuals with a mean concentration of 9.86 ± 6.36 ng g-1 ww without outliers. Perfluoroalkyl carboxylates (PFCA) concentrations were higher in prey fish than in predators, with some compounds such as perfluorooctanoic acid (PFOA) being detected in higher frequency in prey fish. Besides PFOS, detection of several long-chain (C8-C12) PFCAs were observed in >80 % of the prey fish. Overall, the observed concentrations in Lake Michigan fish were lower than those reported in other Laurentian Great Lakes except for Lake Superior. Biomagnification factors (BMFs) for PFOS exceeded 1.0 (range, 1.80 to 5.12) in all predator-prey relationships analyzed, indicating biomagnification of these compounds, whereas BMFs of other long-chain PFCAs varied according to the fish species. PFAS were found in all fish species measured from Lake Michigan and commonly biomagnified from prey to predator fish, strongly suggesting a dietary connection.

On the probability of ecological risks from microplastics in the Laurentian Great lakes.

The Laurentian Great Lakes represent important and iconic ecosystems. Microplastic pollution has become a major problem among other anthropogenic stressors in these lakes. There is a need for policy development, however, assessing the risks of microplastics is complicated due to the uncertainty and poor quality of the data and incompatibility of exposure and effect data for microplastics with different properties. Here we provide a prospective probabilistic risk assessment for Great Lakes sediments and surface waters that corrects for the misalignment between exposure and effect data, accounts for variability due to sample volume when using trawl samples, for the random spatiotemporal variability of exposure data, for uncertainty in data quality (QA/QC), in the slope of the power law used to rescale the data, and in the HC5 threshold effect concentration obtained from Species Sensitivity Distributions (SSDs). We rank the lakes in order of the increasing likelihood of risks from microplastics, for pelagic and benthic exposures. A lake-wide risk, i.e. where each location exceeds the risk limit, is not found for any of the lakes. However, the probability of a risk from food dilution occurring in parts of the lakes is 13-15% of the benthic exposures in Lakes Erie and Huron, and 8.3-10.3% of the pelagic exposures in Lake Michigan, Lake Huron, Lake Superior, and Lake Erie, and 24% of the pelagic exposures in Lake Ontario. To reduce the identified uncertainties, we recommend that future research focuses on characterizing and quantifying environmentally relevant microplastic (ERMP) over a wider size range (ideally 1-5000 µm) so that probability density functions (PDFs) can be better calibrated for different habitats. Toxicity effect testing should use a similarly wide range of sizes and other ERMP characteristics so that complex data alignments can be minimized and assumptions regarding ecologically relevant dose metrics (ERMs) can be validated.

Aqueous Geochemical Controls on the Sestonic Microbial Community in Lakes Michigan and Superior.

Despite being the largest freshwater lake system in the world, relatively little is known about the sestonic microbial community structure in the Laurentian Great Lakes. The goal of this research was to better understand this ecosystem using high-throughput sequencing of microbial communities as a function of water depth at six locations in the westernmost Great Lakes of Superior and Michigan. The water column was characterized by gradients in temperature, dissolved oxygen (DO), pH, and other physicochemical parameters with depth. Mean nitrate concentrations were 32 µmol/L, with only slight variation within and between the lakes, and with depth. Mean available phosphorus was 0.07 µmol/L, resulting in relatively large N:P ratios (97:1) indicative of P limitation. Abundances of the phyla Actinobacteria, Bacteroidetes, Cyanobacteria, Thaumarchaeota, and Verrucomicrobia differed significantly among the Lakes. Candidatus Nitrosopumilus was present in greater abundance in Lake Superior compared to Lake Michigan, suggesting the importance of ammonia-oxidating archaea in water column N cycling in Lake Superior. The Shannon diversity index was negatively correlated with pH, temperature, and salinity, and positively correlated with DO, latitude, and N2 saturation. Results of this study suggest that DO, pH, temperature, and salinity were major drivers shaping the community composition in the Great Lakes.

Pesticide Prioritization by Potential Biological Effects in Tributaries of the Laurentian Great Lakes.

Watersheds of the Great Lakes Basin (USA/Canada) are highly modified and impacted by human activities including pesticide use. Despite labeling restrictions intended to minimize risks to nontarget organisms, concerns remain that environmental exposures to pesticides may be occurring at levels negatively impacting nontarget organisms. We used a combination of organismal-level toxicity estimates (in vivo aquatic life benchmarks) and data from high-throughput screening (HTS) assays (in vitro benchmarks) to prioritize pesticides and sites of concern in streams at 16 tributaries to the Great Lakes Basin. In vivo or in vitro benchmark values were exceeded at 15 sites, 10 of which had exceedances throughout the year. Pesticides had the greatest potential biological impact at the site with the greatest proportion of agricultural land use in its basin (the Maumee River, Toledo, OH, USA), with 72 parent compounds or transformation products being detected, 47 of which exceeded at least one benchmark value. Our risk-based screening approach identified multiple pesticide parent compounds of concern in tributaries of the Great Lakes; these compounds included: eight herbicides (metolachlor, acetochlor, 2,4-dichlorophenoxyacetic acid, diuron, atrazine, alachlor, triclopyr, and simazine), three fungicides (chlorothalonil, propiconazole, and carbendazim), and four insecticides (diazinon, fipronil, imidacloprid, and clothianidin). We present methods for reducing the volume and complexity of potential biological effects data that result from combining contaminant surveillance with HTS (in vitro) and traditional (in vivo) toxicity estimates. Environ Toxicol Chem 2023;42:367-384. Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Integrating invasive species risk assessment into environmental DNA metabarcoding reference libraries.

Environmental DNA (eDNA) metabarcoding has shown promise as a tool for estimating biodiversity and early detection of invasive species. In aquatic systems, advantages of this method include the ability to concurrently monitor biodiversity and detect incipient invasions simply through the collection and analysis of water samples. However, depending on the molecular markers chosen for a given study, reference libraries containing target sequences from present species may limit the usefulness of eDNA metabarcoding. To explore the extent of this issue and how it may be resolved to aid biodiversity and invasive species early detection goals, we focus on fishes in the well-studied Laurentian Great Lakes region. First, we provide a synthesis of species currently known from the region and of non-indigenous species identified as threats by international, national, regional, and introduction pathway-specific fish risk assessments. With these species lists, we then evaluate 23 primer pairs commonly used in fish eDNA metabarcoding with available databases of sequence coverage and species specificity. Finally, we identify established and potentially invasive non-indigenous fish that should be prioritized for genetic sequencing to ensure robust eDNA metabarcoding for the region. Our results should increase confidence in using eDNA metabarcoding for fisheries conservation and management in the Great Lakes region and help prioritize reference sequencing efforts. The ultimate utility of eDNA metabarcoding approaches will come when conservation management of existing fish communities is integrated with early detection efforts for invasive species surveillance to assess total fish biodiversity.

∼14 000 years of geochemical and isotopic data from Lake Simcoe, Canada.

This dataset contains measurements of modern water and ancient core materials from Lake Simcoe, the fourth largest lake wholly in Ontario, Canada. These data consist of: (i) oxygen, hydrogen and carbon isotope (δ 18O, δ 2H and δ 13C) compositions for modern water samples; (ii) physical measurements of one piston core, PC-5; (iii) δ 13C and δ 18O values of ostracods collected from PC-5, and (iv) δ 13C and δ 18O values of ancient DIC and water, respectively, inferred from item (iii). Physical measurements performed on core PC-5 include magnetic susceptibility, mineralogy and grain size. Mass accumulation rates are also reported. These data will be of interest to those aiming to better characterize the timing and pathway of meltwater flow during and following deglaciation of the Laurentide Ice Sheet in the Laurentian Great Lakes region. These data will also be useful to researchers investigating the influence of deglaciation on the oxygen and carbon isotope systematics of ancient lake environments. A discussion of these data is available in "A ∼14 000-year record of environmental change from Lake Simcoe, Canada" [1].

Factors driving the spatial distribution of microplastics in nearshore and offshore sediment of Lake Huron, North America.

Offshore and nearshore sediment samples from Lake Huron, North America, were analysed for microplastics. Normalized abundances ranged from 59 to 335,714 particles per kg of dry weight sediment (p kg-1 dw). Of the four main basins of Lake Huron, the North Channel contained the greatest microplastic abundances, averaging 47,398 p kg-1 dw, followed by Georgian Bay (21,390 p kg-1 dw), the main basin (15,910 p kg-1 dw) and Saginaw Bay (1592 p kg-1 dw). Results indicate that greater lake depths (p = 0.004), associated with finer grained sediment (p = 0.048), are significant zones of deposition. Regression analysis reveals that source-driven factors generally do not account for microplastic abundances and distribution. Instead, process-driven hydrodynamic forces such as waves and surface currents could be driving distribution and deposition into the offshore environment. The findings suggest that these often overlooked processes should be considered when investigating microplastics quantity in bottom sediment of large lakes.

Alternative migratory strategies related to life history differences in the Walleye (Sander vitreus).

BACKGROUND: While Pace of Life Syndrome predicts behavioural differences between individuals with differential growth and survival, testing these predictions in nature is challenging due to difficulties with measuring individual behaviour in the field. However, recent advances in acoustic telemetry technology have facilitated measurements of individual behaviour at scales not previously possible in aquatic ecosystems. METHODS: Using a Walleye (Sander vitreus) population inhabiting Black Bay, Lake Superior, we examine whether life history characteristics differ between more and less mobile individuals as predicted by Pace of Life Syndrome. We tracked the movement of 192 individuals from 2016 to 2019 using an acoustic telemetry study, relating patterns in annual migratory behaviour to individual growth, and seasonal changes in optimal thermal-optical habitat. RESULTS: We observed two consistent movement patterns in our study population-migratory individuals left Black Bay during late summer to early fall before returning to the bay, whereas residents remained within the bay year-round. The average maximum length of migrant Walleye was 5.5 cm longer than residents, and the sex ratios of Walleye caught during fall surveys was increasingly female-biased towards the mouth of Black Bay, suggesting that a majority of migrants were females. Further, Walleye occupancy outside of Black Bay was positively associated with increasing thermal-optical habitat. CONCLUSIONS: Walleye in Black Bay appear to conform to Pace of Life Syndrome, with migrant individuals gaining increased fitness through increased maximum size, which, given size-dependent fecundity in this species, likely results in greater reproductive success (via greater egg deposition vs. non-migrants). Further, apparent environmental (thermal) controls on migration suggest that migratory Walleye (more so than residents) may be more sensitive to changing environmental conditions (e.g., warming climate) than residents.

Aggregated occurrence records of invasive European frog-bit (Hydrocharismorsus-ranae L.) across North America.

BACKGROUND: European frog-bit (Hydrocharismorsus-ranae L.; EFB) is a free-floating aquatic plant invasive in Canada, the United States and India. It is native to Europe and northern and western Asia and is believed to have first been introduced to North America in Ottawa, Ontario in 1932. It has since spread by way of the St. Lawrence River and connected waterways to southern Ontario and Quebec and parts of the northern United States. Invasive European frog-bit occurs in freshwater coastal wetlands and inland waters, where it can form dense mats that have the potential to limit recreational and commercial use of waterways, alter water chemistry and impact native species and ecosystems. Data on the past and present distribution of this invasive species provide geospatial information that can be used to infer the pattern of invasion and inform management and monitoring targeted at preventing secondary spread. Our EFB dataset contains 12,037 preserved specimen and observation-based occurrence records, including 9,994 presence records spanning two Canadian provinces and ten U.S. states and 2,043 absence records spanning five U.S. states. The aggregated EFB dataset provides a curated resource that has been used to guide a Michigan management strategy and provide information for ongoing efforts to develop invasion risk assessments, species distribution models and decision-support tools for conservation and management. NEW INFORMATION: Specimen-based and observation-based occurrence data were accessed through nine digital data repositories or aggregators and three primary sources. Twenty-six percent of the data are new records not previously published to a data repository or aggregator prior to this study. We removed duplicate data and excluded records with incorrect species identifications. Occurrence records without coordinates were georeferenced from recorded locality descriptions. Data were standardised according to Darwin Core. This aggregated dataset is the most complete account of EFB occurrence records in its North American invasive range.

RAD-tag and mitochondrial DNA sequencing reveal the genetic structure of a widespread and regionally imperiled freshwater mussel, Obovaria olivaria (Bivalvia: Unionidae).

Obovaria olivaria is a species of freshwater mussel native to the Mississippi River and Laurentian Great Lakes-St. Lawrence River drainages of North America. This mussel has experienced population declines across large parts of its distribution and is imperiled in many jurisdictions. Obovaria olivaria uses the similarly imperiled Acipenser fulvescens (Lake Sturgeon) as a host for its glochidia. We employed mitochondrial DNA sequencing and restriction site-associated DNA sequencing (RAD-seq) to assess patterns of genetic diversity and population structure of O. olivaria from 19 collection locations including the St. Lawrence River drainage, the Great Lakes drainage, the Upper Mississippi River drainage, the Ohioan River drainage, and the Mississippi Embayment. Heterozygosity was highest in Upper Mississippi and Great Lakes populations, followed by a reduction in diversity and relative effective population size in the St. Lawrence populations. Pairwise F ST ranged from 0.00 to 0.20, and analyses of genetic structure revealed two major ancestral populations, one including all St. Lawrence River/Ottawa River sites and the other including remaining sites; however, significant admixture and isolation by river distance across the range were evident. The genetic diversity and structure of O. olivaria is consistent with the existing literature on Acipenser fulvescens and suggests that, although northern and southern O. olivaria populations are genetically distinct, genetic structure in O. olivaria is largely clinal rather than discrete across its range. Conservation and restoration efforts of O. olivaria should prioritize the maintenance and restoration of locations where O. olivaria remain, especially in northern rivers, and to ensure connectivity that will facilitate dispersal of Acipenser fulvescens and movement of encysted glochidia.

Human well-being and natural capital indictors for Great Lakes waterfront revitalization.

Revitalization of natural capital amenities at the Great Lakes waterfront can result from sediment remediation, habitat restoration, climate resilience projects, brownfield reuse, economic redevelopment and other efforts. Practical indicators are needed to assess the socioeconomic and cultural benefits of these investments. We compiled U.S. census-tract scale data for five Great Lakes communities: Duluth/Superior, Green Bay, Milwaukee, Chicago, and Cleveland. We downloaded data from the US Census Bureau, Centers for Disease Control and Prevention, Environmental Protection Agency, National Oceanic and Atmospheric Administration, and non-governmental organizations. We compiled a final set of 19 objective human well-being (HWB) metrics and 26 metrics representing attributes of natural and seminatural amenities (natural capital). We rated the reliability of metrics according to their consistency of correlations with metric of the other type (HWB vs. natural capital) at the census-tract scale, how often they were correlated in the expected direction, strength of correlations, and other attributes. Among the highest rated HWB indicators were measures of mean health, mental health, home ownership, home value, life success, and educational attainment. Highest rated natural capital metrics included tree cover and impervious surface metrics, walkability, density of recreational amenities, and shoreline type. Two sociodemographic covariates, household income and population density, had a strong influence on the associations between HWB and natural capital and must be included in any assessment of change in HWB benefits in the waterfront setting. Our findings are a starting point for applying objective HWB and natural capital indicators in a waterfront revitalization context.

Identifying chemolithotrophic and pathogenic-related gene expression within suspended sediment flocs in freshwater environments: A metatranscriptomic assessment.

The introduction and proliferation of pathogenic organisms in aquatic systems is a serious global issue that consequently leads to economic, financial, and health concerns. Health and safety related to recreational water use is typically monitored through water quality assessments that are outdated and can be misleading. These traditional methods focus on broad taxa groups, provide no insight into the active community or source of contamination, and the sediment compartments (bed and suspended) are often overlooked. To bridge this knowledge gap, our study aimed to 1) examine the metatranscriptome of the microbial community associated with suspended sediment (SS) in freshwater systems; 2) explore the influence of SS in tributaries to the littoral zone of the receiving lake; and 3) compare the SS fraction with previously reported nearshore bed sediment data. Samples were collected seasonally from Lake St. Clair and Lake Erie. Beaches in this region are influenced by both agriculture runoff and continued urban expansion. Results show that both adjacent tributary and beach SS have similar microbial functional diversity and are strongly correlated by site and season. We identified expression of transcripts encoding sequences with similarities to genes involved in nine bacterial infectious disease pathways, including legionellosis (sdhA) and Vibrio cholerae pathogenesis. According to MG-RAST gene categories, lake samples typically showed higher overall expression (p < 0.05) of transcripts with similarities to genes involved in infectious disease pathways compared to the tributaries, with summer upregulated (p < 0.05) compared to fall. Our data suggests SS acts as a strong vector for pathogen transport, making this facet an important area for further research as it pertains to human health regarding recreational water use. To our knowledge, this work is the first to investigate SS in aquatic microbial communities using metatranscriptomic analyses and has significant potential to help address growing issues of microbial contamination impacting freshwater security.

Disturbances to energy metabolism in juvenile lake sturgeon (Acipenser fulvescens) following exposure to niclosamide.

Since the 1960s, invasive sea lamprey (Petromyzon marinus) populations in the Laurentian Great Lakes have been controlled by applying two chemicals, 3-trifluoromethyl-4-nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalicylanilide (niclosamide, aka. Bayluscide®), to streams infested with larval sea lamprey. These "lampricide" applications primarily rely on TFM, and are often combined with 1-2% niclosamide, which increases treatment effectiveness. Niclosamide is also used alone to treat lentic habitats and in rivers with high discharge. However, little is known about niclosamide's possible adverse physiological effects on non-target organisms. Of particular concern is the lake sturgeon (Acipenser fulvescens), which is threatened throughout the Great Lakes basin where its habitat often overlaps with larval lamprey. Because niclosamide is believed to impair ATP production by uncoupling oxidative phosphorylation, we determined how it altered metabolic processes and acid-base balance in young-of-the-year (YOY) lake sturgeon exposed to their 9-h LC50 of niclosamide (0.11 mg L-1) for 9 h. Exposure to niclosamide led to decreased brain ATP and glucose reserves, and increased lactate, with no effect on brain glycogen. In contrast, substantial (60%) reductions in glycogen were observed in liver, suggesting that hepatic glycogen reserves were mobilized to meet the brain's glucose requirements when ATP supply was impaired during niclosamide exposure. Disturbances in carcass included reduced phosphocreatine (65-70%), 2- and 4-fold increases in pyruvate and lactate, and a slight metabolic acidosis, characterized by a 0.1 unit decrease in intracellular pH (pHi). Each of these disturbances were corrected within 24 h following depuration in clean (niclosamide-free) water. We conclude that if lake sturgeon survive exposure to niclosamide, they are able to rapidly replenish their energy stores (glycogen, ATP, phosphocreatine) and correct any corresponding metabolic disturbances within 24 h.

Characterization of polycyclic aromatic hydrocarbons in the Great Lakes Basin using dreissenid mussels.

The National Oceanic and Atmospheric Administration (NOAA), National Centers for Coastal Ocean Science (NCCOS) Mussel Watch Program (MWP), conducts basin-wide monitoring and place-based assessments using dreissenid mussels as bioindicators of chemical contamination in the Laurentian Great Lakes. Polycyclic aromatic hydrocarbons (PAHs) body burden results for the period 2009-2018 were combined into one dataset from multiple MWP studies allowing for a robust characterization of PAH contamination. Patterns in PAH data were identified using descriptive statistics and machine learning techniques. Relationships between total PAH concentration in dreissenid mussel tissue, impervious surface percentages, and PAH relative concentration were identified and used to build a predictive model for the Great Lakes Basin. Significant positive correlation was identified by the Spearman's rank correlation test between total PAH concentration and percent impervious surface. The findings support the paradigm that PAHs are primarily derived from land-based sources. Offshore and riverine locations had the lowest and highest median total PAH concentrations, respectively. PAH assemblages and ratios indicated that pyrogenic sources were more predominant than petrogenic sources and that PAHs at offshore sites exhibited relatively more weathering compared to inshore sites.

Quantifying nonlinear temporal effects of ethanol preservation on round goby (Neogobius melanostomus) anatomical traits.

Geometric morphometrics provides a powerful means of evaluating differences in phenotypic traits among specimens. However, inferences of trait variability can be confounded when measurements are based on preserved samples. We evaluated effects of ethanol preservation on morphology over a 22-week time period for a Laurentian Great Lakes invasive fish, round goby (Neogobius melanostomus, Pallas 1814), using sets of 17 lateral and six dorsal landmarks. We tested whether ethanol preservation affected the magnitude of inter-population variation between individuals collected from lake and river habitats. Generalized least square regression determined that length did not significantly vary through the preservation time series for fish from either population, while mass decreased significantly. Body shape variation was summarized using principal component analysis, which revealed that most preservation-associated changes occurred in the first 14 days. The lateral shape experienced a large magnitude change during the first 24 h in ethanol then only minor changes for the remainder of the study. The dorsal shape began to revert to pre-preservation measurements about 14 days following preservation. Additionally, differences in shape were apparent between the two populations throughout the experiment; however, the magnitude of differences between populations varied depending on whether dorsal or lateral landmarks were considered. Our study demonstrates that tissue responses to ethanol preservation can be more complex than a simple loss of mass, resulting in difficult to predict consequences for geometric morphometric analyses, including variable responses depending on the anatomical region being analyzed.

Occurrence of Arsenic in Nearshore Aquifers Adjacent to Large Inland Lakes.

Metal oxides that form near sediment-water interfaces in marine and riverine settings are known to act as a sediment trap for pollutants of environmental concern (e.g., arsenic and mercury). The occurrence of these pollutant traps near sediment-water interfaces in nearshore lake environments is unclear yet important to understand because they may accumulate pollutants that may be later released as environmental conditions change. This study evaluates the prevalence of pollutant sediment traps in nearshore aquifers adjacent to large lakes and the factors that affect the accumulation and release of pollutants, specifically arsenic. Field data from six sites along the Laurentian Great Lakes indicate widespread enrichment of arsenic in nearshore aquifers with arsenic sequestered to iron oxide phases. Arsenic enrichment at all sites (solid-phase arsenic >2 µg/g) suggests that this is a naturally occurring phenomenon. Arsenic was more mobile in reducing aquifers with elevated dissolved arsenic (up to 60 µg/L) observed, where reducing groundwater mixes with infiltrating oxic lake water. Dissolved arsenic was low (<3 µg/L) in all oxic nearshore aquifers studied despite high solid-phase arsenic concentrations. The findings have broad implications for understanding the widespread accumulation of reactive pollutants in nearshore aquifers and factors that affect their release to large lakes.

Spatiotemporal controls on septic system derived nutrients in a nearshore aquifer and their discharge to a large lake.

This study evaluates spatiotemporal variability in the behavior of septic system derived nutrients in a sandy nearshore aquifer and their discharge to a large lake. A groundwater nutrient-rich plume was monitored over a two-year period with the septic system origin of the plume confirmed using artificial sweeteners. High temporal variability in NO3-N attenuation in the nearshore aquifer prior to discharge to the lake (42-96%) reveals the complex behavior of NO3-N and potential importance of changing hydrological and geochemical conditions in controlling NO3-N discharge to the lake. While PO4-P was retarded in the nearshore aquifer, the PO4-P plume extended over 90 m downgradient of the septic system. It was estimated that the PO4-P plume may reach the lake within 10 years and represents a legacy issue whereby PO4-P loads to the lake may increase over time. To provide broader assessment of the contribution of septic systems to P and N loads to a large lake, a regional scale geospatial model was developed that considers the locations of individual septic systems along the Canadian Lake Erie shoreline. The estimated P and N loads indicate that septic systems along the shoreline are only a minor contributor to the annual P and N loads to Lake Erie. However, it is possible that nutrients from septic systems may contribute to localized algal blooms in shoreline areas with high septic system density. In addition, disproportionate P and N loads in discharging groundwater may change the N:P ratio in nearshore waters and promote growth of harmful cyanobacteria. The study provides new insights into factors controlling the function of the reaction zone near the groundwater-lake interface including its impact on groundwater-derived nutrient inputs to large lakes. Further, the study findings are needed to inform septic system and nutrient management programs aimed at reducing lake eutrophication.

Outsized nutrient contributions from small tributaries to a Great Lake.

Excessive nitrogen (N) and phosphorus (P) loading is one of the greatest threats to aquatic ecosystems in the Anthropocene, causing eutrophication of rivers, lakes, and marine coastlines worldwide. For lakes across the United States, eutrophication is driven largely by nonpoint nutrient sources from tributaries that drain surrounding watersheds. Decades of monitoring and regulatory efforts have paid little attention to small tributaries of large water bodies, despite their ubiquity and potential local importance. We used a snapshot of nutrient inputs from nearly all tributaries of Lake Michigan-the world's fifth largest freshwater lake by volume-to determine how land cover and dams alter nutrient inputs across watershed sizes. Loads, concentrations, stoichiometry (N:P), and bioavailability (percentage dissolved inorganic nutrients) varied by orders of magnitude among tributaries, creating a mosaic of coastal nutrient inputs. The 6 largest of 235 tributaries accounted for ∼70% of the daily N and P delivered to Lake Michigan. However, small tributaries exhibited nutrient loads that were high for their size and biased toward dissolved inorganic forms. Higher bioavailability of nutrients from small watersheds suggests greater potential to fuel algal blooms in coastal areas, especially given the likelihood that their plumes become trapped and then overlap in the nearshore zone. Our findings reveal an underappreciated role that small streams may play in driving coastal eutrophication in large water bodies. Although they represent only a modest proportion of lake-wide loads, expanding nutrient management efforts to address smaller watersheds could reduce the ecological impacts of nutrient loading on valuable nearshore ecosystems.