Minnesota Lakes Research Articles

Increased mercury concentrations in walleye and yellow perch in lakes invaded by zebra mussels.

Zebra mussels (Dreissena polymorpha) are invasive species that alter ecosystems and food webs with the potential to affect aquatic mercury cycling and bioaccumulation in fishes, although the effect of zebra mussels on fish tissue mercury has not been tested in inland lakes. We assessed differences in fish tissue mercury concentrations and food webs in Minnesota lakes with and without zebra mussels while controlling for other lake and watershed characteristics. Mercury concentrations in adult walleye (Sander vitreus) and yellow perch (Perca flavescens) were 72 % and 157 % higher, respectively, in lakes containing zebra mussels compared to uninvaded lakes. Mercury in young of year (age-0) fish was also elevated, with mercury concentrations 97 % and 82 % higher in age-0 walleye and yellow perch, respectively, in zebra mussel lakes. Walleye mercury concentrations exceeded 0.22 ppm - a threshold triggering more restrictive human consumption advisories for sensitive populations - at a 23 % smaller size, and average-sized walleye (420 mm) exceeded this threshold at a rate of 77 % in invaded lakes, compared to 35 % in uninvaded lakes. Walleye and yellow perch relied more on littoral resources in lakes with zebra mussels but did not feed at meaningfully higher trophic levels. Increased fish tissue mercury in lakes invaded by zebra mussels have consequential implications for fisheries and human health.

The gut microbiome and resistome of yellow perch (Perca flavescens) living in Minnesota lakes under varying anthropogenic pressure

Anthropogenic activities can significantly impact wildlife in natural water bodies, affecting not only the host's physiology but also its microbiome. This study aimed to analyze the gut microbiome and antimicrobial resistance gene profile (i.e., the resistome) of yellow perch living in lakes subjected to different levels of anthropogenic pressure: wastewater effluent-impacted lakes and undeveloped lakes. Total DNA and RNA from gut content samples were extracted and sequenced for analysis. Results indicate that the gut resistome and microbiome of yellow perch differ between lakes, perhaps due to varying anthropogenic pressure. The resistome was predominated by macrolide resistance genes, particularly the MLS23S group, making up 53 % of resistome sequences from effluent-impacted lakes and 73 % from undeveloped lakes. The colistin resistance gene group (mcr) was detected in numerous samples, including variants associated with Aeromonas and the family Enterobacteriaceae. The gut microbiome across all samples was dominated by the phyla Proteobacteria, Firmicutes, and Actinobacteria, with the opportunistic pathogens Plesiomonas shigelloides and Aeromonas veronii more abundant in effluent-impacted lakes. Metagenomic analysis of wild fish samples offers valuable insights into the effects of anthropogenic pressures on microbial communities, including antimicrobial resistance genes, in water bodies.

Performance and cost advantage of stocking locally sourced Walleye fry into southern Minnesota lakes

AbstractObjectiveA genetically distinct strain of Walleye Sander vitreus (southern Minnesota strain [SMS]) persists in southern Minnesota lakes despite decades of stocking more easily obtained strains from outside of the region. Because of the regional performance advantage inferred by this persistence, we conducted in situ experiments to compare survival and stocking cost of SMS Walleye fry against those of a frequently stocked northern Minnesota strain (Mississippi headwaters strain [MIS]) to determine whether it is beneficial to expand SMS fry stocking in lieu of historic practices.MethodsWe conducted four paired stockings of oxytetracycline‐marked SMS fry and MIS fry into six southern Minnesota lakes and then sampled the fish as fall fingerlings during 2018, 2019, 2021, and 2022. We then used fluorescent microscopy and parentage‐based tagging techniques to discern the stocked strains for comparison of growth and survival. We also obtained production and stocking cost data from agency records to calculate relative stocking costs.ResultBy the end of their first summer, SMS Walleye from all but two stockings exhibited higher survival than MIS Walleye. Despite higher initial costs to produce SMS fry, their higher survival to fall fingerlings made the stocking of SMS fry more cost effective than MIS fry stocking. Natural reproduction was also identified in several stocked lakes, most of which consisted of either high or increasing levels of SMS ancestry.ConclusionA local strain can outperform nonlocal strains at a level that can overcome additional costs of developing a new egg source. In addition, natural reproduction of local‐strain Walleye may reduce or eliminate the need for future stocking.

Predicting responses to climate change using a joint species, spatially dependent physiologically guided abundance model.

Predicting the effects of warming temperatures on the abundance and distribution of organisms under future climate scenarios often requires extrapolating species-environment correlations to climatic conditions not currently experienced by a species, which can result in unrealistic predictions. For poikilotherms, incorporating species' thermal physiology to inform extrapolations under novel thermal conditions can result in more realistic predictions. Furthermore, models that incorporate species and spatial dependencies may improve predictions by capturing correlations present in ecological data that are not accounted for by predictor variables. Here, we present a joint species, spatially dependent physiologically guided abundance (jsPGA) model for predicting multispecies responses to climate warming. The jsPGA model uses a basis function approach to capture both species and spatial dependencies. We apply the jsPGA model to predict the response of eight fish species to projected climate warming in thousands of lakes in Minnesota, USA. By the end of the century, the cold-adapted species was predicted to have high probabilities of extirpation across its current range-with 10% of lakes currently inhabited by this species having an extirpation probability >0.90. The remaining species had varying levels of predicted changes in abundance, reflecting differences in their thermal physiology. Though the model did not identify many strong species dependencies, the variation in estimated spatial dependence across species suggested that accounting for both dependencies was important for predicting the abundance of these fishes. The jsPGA model provides a new tool for predicting changes in the abundance, distribution, and extirpation probability of poikilotherms under novel thermal conditions.

Estimating ethanol correction factors for δ13C and δ15N isotopic signatures of freshwater zooplankton from multiple lakes

AbstractIn freshwater systems, δ13C and δ15N stable isotopes can be used to differentiate between pelagic and littoral energy sources and to quantify trophic position. In these ecosystems, crustacean zooplankton are frequently used to characterize the pelagic baseline. Zooplankton samples are often preserved prior to processing and analysis, which can affect isotopic signatures. Variability in preservation effects across studies make it difficult to determine if and how to correct for preservation effects. Here, we develop a correction factor for ethanol preservation and present a flexible statistical method that can be updated with additional data to increase its applicability. We collected zooplankton from five lakes in Minnesota, USA encompassing wide isotopic ranges (δ13C from −37.23‰ to −23.96‰; δ15N from 3.07‰ to 14.44‰). Changes in zooplankton δ13C and δ15N signatures were quantified using a Bayesian hierarchical model predicting fresh values from ethanol‐preserved values. Ethanol preservation increased δ13C by a factor of 1.158 (95% CI 0.866–1.441) and had a negligible effect on δ15N (slope = 1.077; 95% CI 0.833–1.359). Lake‐specific values did not differ from the overall relationship. K‐fold and leave‐one‐out cross validation tests verified that both models were accurate; RMSE of predicted δ13C = 0.701 and RMSE of predicted δ15N = 0.590. Our correction factors could be applied to other systems in which baseline δ13C and δ15N values fall within the range of our study, and this approach also enables the inclusion of data from additional lakes to estimate new corrections.

High‐volume plankton tow net sampling improves eDNA detection of invasive zebra mussels (Dreissena polymorpha) in recently infested lakes

AbstractAquatic invasive species are a serious and growing threat to biodiversity. Zebra and quagga mussels (Dreissena polymorpha and D. rostriformis bugensis) are freshwater invaders causing substantial ecological and economic damage across Europe and North America. Early detection of invasive mussels and other non‐indigenous species is increasingly needed to prevent their establishment and spread. Environmental DNA (eDNA) techniques potentially offer higher sensitivity monitoring tools to complement more conventional methods for surveying adult and juvenile mussels and veliger larvae. eDNA assays are typically performed on small‐volume (0.5–5 L) water samples that are concentrated by filtration prior to extraction and downstream processing. Sampling using a towed plankton net of a larger (64 μm) pore size can process orders of magnitude larger water volumes with the potential for increasing eDNA detection sensitivity. We compared the sensitivities of high‐volume plankton tow net water sampling to filter sampling in three recently infested lakes in Canada and Minnesota, USA. Paired filtration and tow net samples were analyzed for Dreissena DNA using an established quantitative polymerase chain reaction assay for the genus. Higher yields of Dreissena eDNA (more DNA copies) were recovered from plankton tow than from filtered samples in all 33 paired comparisons. In some cases, plankton tow samples were positive for Dreissena eDNA while lower‐volume filtering produced a false negative detection. Our results demonstrate the effectiveness of plankton tow net sampling for eDNA early detection of invasive mussels, a method that can be used exclusively or as a supplement to filter sampling. Our results further suggest that eDNA testing could be incorporated into monitoring programs that routinely use plankton tows for visual detection of invasive mollusk larvae, as well as other aquatic invasive and non‐invasive species ranging from plankton to metazoans, including many fish.

One- and Three-Dimensional Hydrodynamic, Water Temperature, and Dissolved Oxygen Modeling Comparison

Understanding and modeling water quality in a lake/reservoir is important to the effective management of aquatic ecosystems. The advantages and disadvantages of different water quality models make it challenging to choose the most suitable model; however, direct comparison of 1-D and 3-D models for lake water quality modeling can reveal their relative performance and enable modelers and lake managers to make informed decisions. In this study, we compared the 1-D model MINLAKE and the 3-D model EFDC+ for water temperature, ice cover, and dissolved oxygen (DO) simulation in three Minnesota lakes (50-m Carlos Lake, 23.5-m Trout Lake, and 5.6-m Pearl Lake). EFDC+ performed well for water temperature and DO simulation in the open water seasons with an average root mean square error (RMSE) of 1.32 °C and 1.48 mg/L, respectively. After analyzing the ice thickness with relevant data, it was found that EFDC+ calculates a shorter ice cover period and smaller ice thickness. EFDC+ does not consider snowfall for ice thickness simulation. The results also revealed that EFDC+ considers spatial variance and allows the user to select inflow/outflow locations precisely. This is important for large lakes with complex bathymetry or lakes having multiple inlets and outlets. MINLAKE is computationally less intensive than EFDC+, allowing rapid simulation of water quality parameters over many years under a variety of climate scenarios.

A lack of genetic diversity and minimal adaptive evolutionary divergence in introduced Mysis shrimp after 50 years.

The successes of introduced populations in novel habitats often provide powerful examples of evolution and adaptation. In the 1950s, opossum shrimp (Mysis diluviana) individuals from Clearwater Lake in Minnesota, USA were transported and introduced to Twin Lakes in Colorado, USA by fisheries managers to supplement food sources for trout. Mysis were subsequently introduced from Twin Lakes into numerous lakes throughout Colorado. Because managers kept detailed records of the timing of the introductions, we had the opportunity to test for evolutionary divergence within a known time interval. Here, we used reduced representation genomic data to investigate patterns of genetic diversity, test for genetic divergence between populations, and for evidence of adaptive evolution within the introduced populations in Colorado. We found very low levels of genetic diversity across all populations, with evidence for some genetic divergence between the Minnesota source population and the introduced populations in Colorado. There was little differentiation among the Colorado populations, consistent with the known provenance of a single founding population, with the exception of the population from Gross Reservoir, Colorado. Demographic modeling suggests that at least one undocumented introduction from an unknown source population hybridized with the population in Gross Reservoir. Despite the overall low genetic diversity we observed, F ST outlier and environmental association analyses identified multiple loci exhibiting signatures of selection and adaptive variation related to elevation and lake depth. The success of introduced species is thought to be limited by genetic variation, but our results imply that populations with limited genetic variation can become established in a wide range of novel environments. From an applied perspective, the observed patterns of divergence between populations suggest that genetic analysis can be a useful forensic tool to determine likely sources of invasive species.

Lake characteristics drive concordant trophic responses across ecosystems in three top predator fish species

Understanding similarities in trophic ecology of top predators is crucial given their influences on food webs. We sampled walleye ( Sander vitreus), northern pike ( Esox lucius), and muskellunge ( Esox masquinongy) from 17 Minnesota (USA) lakes and used δ13C and δ15N to estimate littoral carbon use, trophic position, and isotopic niche size of each species. All three species showed large inter-lake variability yet had concordant trophic responses across lakes, as littoral carbon use, trophic position, variability in littoral carbon and trophic position, and niche size were all positively related among species across lakes. Concordant responses were driven by a few key lake variables, with trophic position positively related to proportion littoral area and depth of hypoxic water, littoral carbon positively related to depth of hypoxic water and presence of zebra mussels ( Dreissena polymorpha), and niche size inversely related to lake area. Our results indicate that lake characteristics may influence food webs via consistent effects on multiple top predators. They also show that the amount of suitable habitat can be important for the ecosystem size hypothesis for trophic position.

Beyond Phosphorus: Salinization as a driver of eutrophication symptoms in North American lakes

The acceleration of global urbanization continues to fuel concerns surrounding water quality impairments in urban lakes, particularly eutrophication. Eutrophication of freshwater environments is generally assumed to be driven by increased anthropogenic phosphorus (P) supplies which can alleviate limitations on primary production. Salinization is also recognized as a stressor on urban freshwater quality, particularly in cold temperate climate regions where salts are applied to road surfaces as de-icing agents. While the ecological damages caused by P enrichment and salinization to freshwaters are both well established, thus far, their impacts on water quality have only been considered independently. Although improvements to the management of urban stormwater and wastewater have decreased P inputs to freshwater systems in recent decades, many lakes worldwide remain eutrophic, as indicated by declining dissolved oxygen (DO) concentrations and rising dissolved inorganic P (DIP) concentrations in the hypolimnion. Our previous study of an urban freshwater lake in Ontario, Canada, showed that persistent eutrophication symptoms are linked to salinization associated with impervious land cover expansion, rather than increased external P loading. In this research, we present a multiple decade of water chemistry data analyses for several other urban lakes in Ontario, Wisconsin, and Minnesota to determine how increased lake salinization rates intersect with water temperature and morphometry to alter water column stratification, thus, increasing eutrophication symptoms. Our trend analysis shows progressive salinization (observed through significant increases in chloride or electrical conductivity) of all the lakes investigated. Calculations of lakes mixing indices over time show that, on average, lake stratification is becoming more stable with increased salinity playing a crucial role in enhancing lake stratification. Overall, salinity is becoming a stronger regulator of water density than temperature in the cold temperate urban freshwater lakes of North America. The increasing salinity trends are accompanied by increasing hypolimnion hypoxia and increasing DIP to total P (TP) ratios in all lakes, thereby demonstrating the mechanistic link between salinization and internal P loading. Rising salinity intensifies water column stratification, in turn, reducing the oxygenation of the hypolimnion and enhancing internal P loading from the sediments. These results highlight that stricter management of de-icing salt application rates should be considered to control lake eutrophication symptoms in cold climate regions.

A comparison of survey method efficiencies for estimating densities of zebra mussels (Dreissena polymorpha).

Abundance surveys are commonly used to estimate plant or animal densities and frequently require estimating detection probabilities to account for imperfect detection. The estimation of detection probabilities requires additional measurements that take time, potentially reducing the efficiency of the survey when applied to high-density populations. We conducted quadrat, removal, and distance surveys of zebra mussels (Dreissena polymorpha) in three central Minnesota lakes and determined how much survey effort would be required to achieve a pre-specified level of precision for each abundance estimator, allowing us to directly compare survey design efficiencies across a range of conditions. We found that the required sampling effort needed to achieve our precision goal depended on both the survey design and population density. At low densities, survey designs that could cover large areas but with lower detection probabilities, such as distance surveys, were more efficient (i.e., required less sampling effort to achieve the same level of precision). However, at high densities, quadrat surveys, which tend to cover less area but with high detection rates, were more efficient. These results demonstrate that the best survey design is likely to be context-specific, requiring some prior knowledge of the underlying population density and the cost/time needed to collect additional information for estimating detection probabilities.

The relative importance of cisco (Coregonus artedi) in the diets of common loons (Gavia immer) among a set of cisco refuge lakes in Minnesota

Common loon ( Gavia immer (Brünnich, 1764)) foraging patterns and the relative importance of cisco ( Coregonus artedi Lesueur, 1818) in the diets of loons were evaluated for the Whitefish Chain of Lakes, a set of coldwater cisco refuge lakes in Minnesota, USA. Environmental DNA metabarcoding of loon fecal samples detected 15 fish species. Yellow perch ( Perca flavescens (Mitchill, 1814)), mimic shiner ( Notropis volucellus (Cope, 1865)), and cisco were the most prominent prey detected across the study lakes. We observed a shift in fish species consumed, with increases in detections of mimic shiner and cisco DNA among loon fecal samples collected in August and September. In some locations, suitable oxythermal habitat became restricted throughout the summer, forcing cisco into surface waters, which potentially increased their vulnerability to loon predation. Conversely, large foraging aggregations of loons were observed during late summer through fall at locations with ample oxythermal habitat and abundant cisco populations. We hypothesize that cisco were sought by loons as a high-calorie prey resource prior to migration. Conservation efforts directed at preserving water quality in important cisco refuge lakes are likely to benefit common loons through enhancement of both the forage base, for resident and migrating birds, and breeding habitat suitability.

Sulfide Immobilization: Investigating the Impact of a Protective Sulfide-Bearing Layer Formed by Siderite (FeCO3)

Sulfate-rich wastewater poses ecological hazards to freshwater ecosystems, and sulfate is highly regulated in many Minnesota lakes. Biological sulfate reduction results in the reduction of sulfate to sulfide, and this process is used to remediate acid mine drainage. Theoretically, the aqueous sulfide can be immobilized into a solid-phase material and removed from the aqueous system. This study focuses on sulfide immobilization using iron-bearing waste minerals. Specifically, the extent of reaction of siderite (FeCO3), an abundant ferrous mineral in some mining wastes, with sulfide was studied. Mildly acidic batch reactors containing powdered siderite were consecutively injected with a sodium sulfide solution. Solid reaction products were identified and characterized using powder X-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Mackinawite (FeS) appeared to be the most abundant product, with greigite (Fe3S4) also detected. Results reveal that the immobilization capacity of sulfide by siderite is limited by the concentration of the Fe2+(aq) presented in the system immediately before the initial sulfide exposure as the Fe2+(aq) levels are not replenished after sulfidation. These results improve our understanding of the sulfidation of siderite and provide insight to improve the viability of using siderite-containing mining waste rock in a sulfate remediation technology.

530 Utilization of Advanced Practice Provider for Quality Virtual Burn Care

Abstract Introduction From the plains of North Dakota to the lakes of Minnesota and beyond, for our patient population, telemedicine has grown to be an important burn care delivery method. Specialized burn care is essential to ensure successful patient outcomes from burn injury. Our institution utilizes an advanced practice provider (APP) either physician assistant or nurse practitioner to lead the telemedicine care instead of the burn surgeon. Given most of the burn care is non-operative management, an APP can deliver burn expertise and high-quality care to the burn patient. Methods A retrospective chart review performed via data extraction from the electronic medical record at a single ABA-verified Burn Center. Dates of review ranged from January 1, 2022, through June 30, 2022. Patient population was Regions Hospital Outpatient Burn Clinic and Telemedicine Clinic volumes. Data review included patient location, mode of visit (in-person or virtual), and time to >95% healed. Inclusion was acute burns of all ages and mechanisms of injury. Exclusion was non-burn wounds, scar management and frostbite patients. Results A total of 1300 (87%) of all outpatient visits performed by APPs with 328 (25%) of these visits conducted via telemedicine. Varying by month, 7-13% of patients were treated exclusively via telemedicine not requiring any in-person burn care. When comparing the patient distance from the burn center (1-50 miles and >50 miles) and time to >95% healed, there was no correlation. Patients who were treated exclusively via telemedicine, lived an average of 205 (5-580) miles from the burn center, had an average TBSA of 2.2 (0.25-55) % and had an average of 18.3 (7-62) days until 95% healed. Compared to patients treated in-person only or combination of in-person and telemedicine, lived an average of 91 (1-631) miles, had an average TBSA of 2.5 (0.25-67) % and had an average of 24.6 (5-80) days until 95% healed. Conclusions A burn telemedicine program led by APPs can facilitate remote expert burn care, all while maintaining standard of care. Limitations were a narrow review window, single center retrospective analysis, and the exact date for time to 95% healed is difficult to determine due to interval follow up windows. Our goal is to further review and analyze our telemedicine and clinic data to optimize burn care delivery with the utilization of APPs, investigate quality of care indicators within telemedicine and reduce transfers and travel for specialized burn care. Applicability of Research to Practice APP led telemedicine improves surgeon availability to do hands on treatment in the Burn Center and allows for outreach and specialized expertise to be delivered across remote distances. It allows for the ability to triage patients and optimize burn clinic resources. Telemedicine can be performed in any location and reduce travel. Telemedicine is reimbursable. Barriers include wound care supply access, technological limitations, state licensing and institutional credentialing.

Diet Patterns and Niche Overlap of Muskellunge and Co‐Occurring Piscivores in Minnesota Lakes

AbstractMuskellunge Esox masquinongy, Northern Pike E. lucius, Walleye Sander vitreus, and Largemouth Bass Micropterus salmoides are popular sport fish that often co‐occur in aquatic systems. Although numerous studies have investigated interactions among these species, the simultaneous evaluation of diet patterns and niche overlap among all four species has not been conducted. Our experimental design aimed to quantify diet overlap among Muskellunge and the other piscivores, while lakes without Muskellunge were also sampled to compare the diets of the other piscivores in their presence or absence. Diets of piscivores from 10 Minnesota lakes were collected via gastric lavage and quantified using an index of relative importance. Diets of individual species were compared among seasons and predator length categories, and among‐species comparisons were also conducted by season and relative to Muskellunge presence using permutational multivariate ANOVA (PERMANOVA). Muskellunge consumed a wide range of prey, whereas Northern Pike and Walleye diets consisted primarily of Yellow Perch Perca flavescens and centrarchids. Largemouth Bass consumed more invertebrates, especially crayfish Faxonius spp. No species exhibited seasonal diet shifts, but diets were different among length categories for all species except Walleye. Although nonmetric multidimensional scaling ordinations indicated shared prey use, PERMANOVA results indicated that the diets of Muskellunge and Largemouth Bass were most different from each other and the other piscivores' diets across all seasons. Conversely, Northern Pike and Walleye diets were similar regardless of season or Muskellunge presence. Finally, lake‐scale habitat variables were correlated with piscivore diets, and Yellow Perch abundance was correlated with Walleye diets. Our results indicate that while Muskellunge, Northern Pike, Walleye, and Largemouth Bass can coexist in a variety of lakes, populations of important prey and habitat variables should be examined before management actions (e.g., stocking) are implemented to ensure adequate prey availability and to ensure that competition among these piscivores is not increased to the detriment of existing fisheries.

Variability of microplastic loading and retention in four inland lakes in Minnesota, USA

Microplastic pollution (plastic particles < 5 mm) has potentially harmful impacts on aquatic ecosystems. Understanding the factors that impact microplastic loading and distribution within aquatic ecosystems is crucial for assessing potential threats from microplastics. Here we examine the extent of microplastic pollution in the surface waters and sediments of four small inland lakes in Minnesota, USA that represent a range of human impacts as well as a variety of watershed and lake characteristics. Surface water particulates and benthic sediments were collected in the summers of 2019 and 2020 to examine the loading of microplastics into these lakes and their distribution throughout the ecosystems. Lower size cut offs were set at 330 μm for surface water particulate samples and 250 μm for sediment samples. Watershed to surface area ratio (WS:SA) and urban development were the most influential factors on microplastic loading. Surface water microplastic concentrations ranged from 27,000 microplastics km−2 in Elk Lake (small WS:SA and minimally developed) to 152,000 microplastics km−2 in White Iron Lake (large WS:SA and low development). Concentrations in benthic sediments ranged from 30 microplastics kg−1 dry sediment in White Iron Lake (forested watershed) to 270 microplastics kg−1 dry sediment in Peltier Lake (urbanized watershed) and were not directly correlated to surface water concentrations. Results from this study highlight the characteristics of small lakes that influence spatial and temporal variability in microplastic loading, retention, and deposition of microplastics to sediments. Further, this study demonstrates the difficulties of accurately predicting microplastic loading and the importance of comprehensive sampling to account for the variability of microplastic loading and distribution in smaller inland lakes.

Wild Rice Lakes in Comparison to Mapped Surficial Sands in Minnesota

Several recent studies have considered the distribution of wild rice (Zizania palustris) compared to a variety of physical and watershed parameters. However, the distribution of wild rice has not been systematically compared to the surficial geology. In this study, a relatively comprehensive list of identified wild rice lakes in Minnesota was compared to the mapped areas of surficial sands. Wild rice is significantly more likely to occur on basins which are within or adjacent to mapped surficial sands. Statewide, an odds ratio of 2.1. indicates that a given lake within the mapped surficial sands has more than twice the odds of wild rice occurrence than a lake outside of the mapped surficial sands. The correlation observed here between mapped surficial sands and wild rice presence suggests that a groundwater-surface water interaction may have more widespread importance for sustaining wild rice populations than previously considered.

Wild Rice Lakes in Comparison to Mapped Surficial Sands in Minnesota

Several recent studies have considered the distribution of wild rice (Zizania palustris) compared to a variety of physical and watershed parameters. However, the distribution of wild rice has not been systematically compared to the surficial geology. In this study, a relatively comprehensive list of identified wild rice lakes in Minnesota was compared to the mapped areas of surficial sands. Wild rice is significantly more likely to occur on basins which are within or adjacent to mapped surficial sands. Statewide, an odds ratio of 2.1. indicates that a given lake within the mapped surficial sands has more than twice the odds of wild rice occurrence than a lake outside of the mapped surficial sands. The correlation observed here between mapped surficial sands and wild rice presence suggests that a groundwater-surface water interaction may have more widespread importance for sustaining wild rice populations than previously considered.

Topography-adjusted Monte Carlo simulation of the adjacency effect in remote sensing of coastal and inland waters

We present a Monte Carlo radiative transfer (RT) code that simulates the top-of-atmosphere (TOA) reflectance of waterbodies considering the adjacency effect. The code is the first open-source tool that supports modeling of the adjacency effect with arbitrary topography. It uses the same atmospheric and aerosol settings as 6S, along with user-input surface reflective properties and topography, allowing users to transition from 1D to 3D RT modeling and characterize the adjacency effect in their study areas. The calculation of radiometric quantities was validated against libRadtran, showing a maximum difference lower than 0.6% in extreme optical settings. Examples of the use of the code are presented in three case studies where modeled and measured radiative properties align with each other. One case study shows that 83.7% of the variance in the near-infrared TOA reflectance of 47 lakes in Minnesota was explained by the adjacency effect, emphasizing the significance of the adjacency effect to atmospheric correction algorithms that use near-infrared bands to retrieve aerosol and glint information. Another case study supports the finding of strong wavelength dependence of the effective sea-surface reflectance in above-water measurements of remote sensing reflectance. The code will support physics-based methods that remove the adjacency effect in atmospheric correction processes, and it has the potential to improve satellite-based monitoring of coastal and inland waterbodies.

Nonlinear water clarity trends and impacts on littoral area in Minnesota lakes

AbstractLake water clarity is an indicator of water quality, trophic status, and habitat condition. Changes in clarity impact lake ecosystems and may reflect land use changes or presence of invasive species. Quantifying temporal changes in water clarity can be challenging because clarity varies seasonally, annually, and spatially within and among lakes. We developed a hierarchical generalized additive model to quantify trends in water clarity (Secchi depth) from 1979 to 2018 for 909 Minnesota lakes, accounting for seasonal and spatial variability. Water clarity increased by 0.41 m across lakes from 1984 to 1988 and 2014 to 2018. Lake‐specific clarity trends varied: clarity did not change significantly in 59.0% of lakes, increased in 34.5% of lakes, and decreased in 6.5% of lakes. Water clarity dynamics caused considerable variability in littoral area between seasons and years. Our results have wide applications in aquatic ecology, including understanding changes to food webs, assessing fish habitat, and evaluating impacts of invasive species.