Minnesota Lakes Research Articles

Distribution and toxic potential of alkylphenols, nonylphenol ethoxylates, and pyrethroids in Minnesota, USA lake sediments

This study provided the first assessment of pyrethroids and pyrethrins in Minnesota, USA lake sediments, and the second one for alkylphenols (APs) and nonylphenol ethoxylates (NPEs). Surficial sediments were collected in 2017 from 30 small to medium-sized lakes, encompassing a variety of watershed land uses and ecoregions. These lakes were targeted from a pool of 50 randomly selected lakes included in the National Lakes Assessment (NLA) study. Sixty percent of the study lakes ( n = 18) had at least one detection of a contaminant of emerging concern (CEC). 4-Nonylphenols (4-NP) had the highest detection frequency (46.7%), followed by 4-nonylphenol monoethoxylates (4-NP1EO; 26.7%), bifenthrin (26.7%), 4-nonylphenol diethoxylates (3.3%), and resmethrin (3.3%). The prevalence of 4-NP was consistent with the degradation of high production NPEs in the environment. All other CECs and pyrethrins were not detected. No CECs were detected in the three most remote lakes, located in forested northeastern Minnesota, where atmospheric deposition would be the most likely source of contamination. The concentrations of detected CECs were below levels of concern to benthic invertebrates. Lakes associated with crop land use and the Upper Midwest ecoregion had the highest number of detections for 4-NP, 4-NP1EO, and bifenthrin. Lakes impacted by development had significantly higher ( p < 0.05) 4-NP and 4-NP1EO concentrations than lakes with other watershed land uses, while there was no significant difference ( p > 0.05) between land use categories for bifenthrin. For the first time, ambient background threshold values were calculated for 4-NP, 4-NP1EO, and bifenthrin to provide an indication of ambient sediment quality conditions represented by diffuse anthropogenic sources. This study demonstrated the benefit of analyzing CECs in sediments from small to medium-sized lakes, for which the random sampling design of future NLA studies could be utilized to fully assess the distribution and toxic potential of select CECs nationwide. • CECs have not been well studied in bed sediments from small to medium-sized lakes. • Alkylphenols, nonylphenol ethoxylates, and pyrethroids are CECs of interest. • These CECs were analyzed in surficial sediments collected from 30 Minnesota lakes. • CEC concentrations were below levels of concern to benthic invertebrates. • Watershed land uses affected the distribution of some CECs, but not for bifenthrin.

Iron filings application to reduce lake sediment phosphorus release

Natarajan P, Gulliver JS, Arnold WA. 2021. Iron filings application to reduce lake sediment phosphorus release. Lake Reserv Manage. 27:143–159. Surface water impairments due to excess phosphorus loading from the watershed and internal recycling from sediments have been reported worldwide. This study investigated the application of iron metal filings to lake sediments as a method to control sediment phosphorus release. Using batch studies, a zero-valent iron filings material was selected for laboratory dosing experiments with lake sediment cores. Iron filings doses of 0 (control), 0.01, 0.1, and 1 g/cm2 were added to sediment cores collected from a eutrophic lake in Minnesota, United States, to determine the impacts of iron addition on the oxic and anoxic phosphate (PO4-P) flux at 20 C and 10 C in the laboratory. Under oxic conditions, PO4-P release did not occur from the sediments, and low water column PO4-P concentrations were maintained in the iron-dosed and control cores. After switching to anoxic conditions, the 0.1 and 1 g/cm2 iron doses continued to reduce or fully prevent sediment PO4-P flux. The enhanced supply of iron in the sediments was found to reduce the porewater PO4-P, resulting in no apparent PO4-P diffusion across the sediment–water interface and low PO4-P in the overlying water under oxic and anoxic conditions. Further evaluation using in situ experiments is needed to assess the effectiveness of iron filings addition in sequestering sediment phosphorus under natural conditions.

Game fish response to dredging of a eutrophic urban lake in Minnesota

Mundahl ND, Hoisington J. 2020. Game fish response to dredging of a eutrophic urban lake in Minnesota. Lake Reserv Manage. 37:170–185. We compared relative abundances, average weights, and growth rates of 6 game fish species before and after the 1999–2001 partial dredging of Lake Winona, a eutrophic, urban lake in Minnesota, to determine whether lake dredging sustainably changed fish population structure to the benefit of anglers. Relative catch rates (trap nets, gill nets, electrofishing) and growth rates were obtained from various fish population assessments and lake surveys conducted by the Minnesota Department of Natural Resources (MN DNR) from 1980 to 2016 for both Lake Winona and Lake Oscar, an ecologically similar lake that has not been dredged. Before-after control-impact (BACI) analyses revealed that compared to Lake Oscar, relative catch rates in Lake Winona after dredging declined significantly for bluegill (Lepomis macrochirus), black crappie (Pomoxis nigromaculatus), and northern pike (Esox lucius), and increased significantly for walleye (Sander vitreus) and largemouth bass (Micropterus salmoides). Average weights of yellow perch (Perca flavescens) and pike increased significantly after dredging. Only black crappie displayed improved growth after dredging. Largemouth bass catch rates for quality- and preferred-size fish increased in postdredging surveys. Although predredging data are lacking, population size structures and relative weights of bluegill, crappie, and bass post dredging were within ranges that meet MN DNR management objectives. Overall, dredging of Lake Winona was followed by improved quality and structure of game fish populations in this system, something that decades of previous biomanipulation and macrophyte management had not accomplished.

Stable isotope patterns in lake food webs reflect productivity gradients

AbstractStable isotopes 13C and 15N are often used in lake ecosystems to assess energy sources and trophic positions, respectively. However, δ13C and δ15N are also influenced by internal biogeochemical processes in epilimnetic and hypolimnetic habitats in lakes, but the extent to which biogeochemical processing mediates isotope values between these two habitats, and whether these patterns are influenced by lake productivity is not known. We sampled δ13C and δ15N in epilimnetic mussels, Chaoborus, cisco (Coregonus artedi), and seston and zooplankton in the epilimnia and hypolimnia of 22 Minnesota (USA) lakes ranging from oligotrophic to eutrophic. We also measured lake temperature–oxygen profiles and light levels to assess factors influencing isotope patterns. Isotope samples were baseline‐corrected using epilimnetic mussels in each lake (sample—mussel) to control for watershed‐level differences in isotope values. Results showed δ13C in epilimnetic and hypolimnetic zooplankton, hypolimnetic seston, Chaoborus, and cisco became more depleted in δ13C relative to epilimnetic mussels in low‐productivity lakes where light penetrated into the hypolimnion, while epilimnetic seston δ13C stayed similar to mussel δ13C in all lakes. This pattern was likely due to hypolimnetic phytoplankton in clearwater lakes incorporating more respired CO2, which is depleted in δ13C, and subsequently passing depleted δ13C values up the food chain. Results also showed habitat differences in δ15N with epilimnetic and hypolimnetic zooplankton, hypolimnetic seston, Chaoborus, and cisco becoming more enriched relative to epilimnetic mussels in low‐productivity lakes with higher O2 levels in the hypolimnion, while epilimnetic seston δ15N remained similar to mussel values. The δ15N pattern is consistent with the idea that denitrification and microbial degradation enriched hypolimnetic seston relative to epilimnetic seston in low nutrient lakes, while enhanced epilimnetic primary production enriched epilimnetic δ15N seston relative to hypolimnetic seston in high nutrient lakes. Our results indicate isotopic differences between epilimnetic and hypolimnetic organisms that change along productivity gradients and suggest that microbial processes and the light regime are important drivers.

Morphological Variation of Cisco across Gradients of Lake Productivity

AbstractThe effects of lake productivity and late‐summer hypolimnetic oxygen on the size and shape of Cisco Coregonus artedi were examined in 27 Minnesota lakes. Geometric morphometry analyses of specimens captured in vertical gill nets indicated that Cisco in more productive lakes with hypoxic hypolimnia were larger, with deeper bodies, shorter snouts and caudal peduncles, and longer fins. Cisco in unproductive lakes with oxygenated hypolimnia were smaller, with slender bodies, longer snouts and caudal peduncles, and shorter fins. The effect of hypolimnetic oxygen on depths utilized by Cisco and the resulting vulnerability to predation was an important driver of shape and fin length. Deeper body depths and longer fin lengths were possibly a response to greater vulnerability to predation when hypoxic hypolimnia limit coldwater refugia for Cisco, which are forced to inhabit shallower depths near warmwater predators such as Walleye Sander vitreus and Northern Pike Esox lucius. Differences in size and shape relationships of Cisco in lakes on and off the Canadian Shield were also detected. The availability of late‐summer habitat, depth‐mediated predation risk, and growth potential appear to be important ecological drivers of morphological variation in Cisco.

An invasive fish promotes invasive plants in Minnesota lakes

Abstract Biological invasions can greatly alter ecological communities, affecting not only the diversity and abundance but also composition of invaded assemblages. This is because invaders’ impacts are mediated by characteristics of resident species: some may be highly sensitive to invader impacts while others are unaffected or even facilitated. In some cases, this can result in invasive species promoting further invasions; in particular, herbivory by introduced animals has been shown to disproportionately harm native plants, which can indirectly benefit non‐native plants. Here, we investigated whether such patterns emerged through the effects of an invasive fish species on lake plant communities. Specifically, we tested whether invasion of Minnesota (U.S.A.) lakes by Cyprinus carpio (common carp), an omnivorous, benthivorous fish known to reduce abundance and richness of aquatic plants, differentially affected native versus non‐native plant species. We applied statistical models to a large, long‐term monitoring dataset (206 macrophyte taxa recorded in 913 lakes over a 20‐year time period) to test whether carp altered community composition, to identify which macrophyte species were most sensitive to carp and determine whether species characteristics predicted carp sensitivity, and to characterise consequences of carp invasion on lake‐level vegetation attributes. We found that carp exerted strong selective pressure on community composition. Native macrophytes, those with a more aquatic growth form, and those considered less tolerant of disturbance (i.e. higher coefficients of conservatism) were more sensitive to carp. Conversely, no introduced macrophytes exhibited sensitivity to carp and all had higher probabilities of occurrence as carp abundance increased. The net effect of carp invasion was a shift toward less species‐rich plant communities characterised by more non‐native and disturbance‐tolerant species. These results have several implications for conservation and management. First, they reinforce the need to prevent further spread of carp outside of their native range. Where carp have already established, their control should be incorporated into efforts to restore aquatic vegetation; this may be an essential step for recovering particular plant species of high conservation importance. Furthermore, reducing carp abundance could have ancillary benefits of reducing dominance by invasive plant species. Lastly, where carp cannot be eliminated, managers should target native macrophytes that are relatively tolerant of carp in shoreline plantings and other revegetation efforts.

The relationship between biodiversity and wetland cover varies across regions of the conterminous United States.

Identifying the factors that determine the spatial distribution of biodiversity is a major focus of ecological research. These factors vary with scale from interspecific interactions to global climatic cycles. Wetlands are important biodiversity hotspots and contributors of ecosystem services, but the association between proportional wetland cover and species richness has shown mixed results. It is not well known as to what extent there is a relationship between proportional wetland cover and species richness, especially at the sub-continental scale. We used the National Wetlands Inventory (NWI) to model wetland cover for the conterminous United States and the National Land Cover Database to estimate wetland change between 2001 and 2011. We used a Bayesian spatial Poisson model to estimate a spatially varying coefficient surface describing the effect of proportional wetland cover on the distribution of amphibians, birds, mammals, and reptiles and the cumulative distribution of terrestrial endemic species. Species richness and wetland cover were significantly correlated, and this relationship varied both spatially and by taxonomic group. Rather than a continental-scale association, however, we found that this relationship changed more closely among ecoregions. The species richness of each of the five groups was positively associated with wetland cover in some or all of the Great Plains; additionally, a positive association was found for mammals in the Southeastern Plains and Piedmont of the eastern U.S. Model results indicated negative association especially in the Cold Deserts and Northern Lakes & Forests of Minnesota and Wisconsin, though these varied greatly between groups. Our results highlight the need for wetland conservation initiatives that focus efforts at the level II and III ecoregional scale rather than along political boundaries.

Genetic diversity and differentiation in populations of invasive Eurasian (Myriophyllum spicatum) and hybrid (Myriophyllum spicatum×Myriophyllum sibiricum) watermilfoil

AbstractPopulation genetic studies of within- and among-population genetic variability are still lacking for managed submerged aquatic plant species, and such studies could provide important information for managers. For example, the extent of within-population genetic variation may influence the potential for managed populations to locally adapt to environmental conditions and control tactics. Similarly, among-population variation may influence whether specific control tactics work equally effectively in different locations. In the case of invasive Eurasian watermilfoil (Myriophyllum spicatumL.), including interspecific hybrids with native northern watermilfoil (Myriophyllum sibiricumKom.), managers recognize that there is genetic variation for growth and herbicide response. However, it is unclear how much overall genetic variation there is, and how it is structured within and among populations. Here, we studied patterns of within- and among-lake genetic variation in 41 lakes in Michigan and 62 lakes in Minnesota using microsatellite markers. We found that within-lake genetic diversity was generally low, and among-lake genetic diversity was relatively high. However, some lakes were genetically diverse, and some genotypes were shared across multiple lakes. For genetically diverse lakes, managers should explicitly recognize the potential for genotypes to differ in control response and should account for this in monitoring and efficacy evaluation and using pretreatment herbicide screens to predict efficacy. Similarly, managers should consider differences in genetic composition among lakes as a source of variation in the growth and herbicide response of lakes with similar control tactics. Finally, laboratory or field information on control efficacy from one lake may be applied to other lakes where genotypes are shared among lakes.

Characterization of Proteins from Zebra Mussel Shells

Wisconsin and Minnesota lakes are under attack from invasive Zebra Mussels, Dreissena polymorpha, a freshwater mussel species native to Eurasia. The Zebra Mussels were introduced to the Great Lakes around 1985–1986 and have continued to aggressively invade the surrounding areas of Minnesota and Wisconsin. Outcompeting native species, including fish, for food sources, Zebra Mussels are thriving. Oddly, this confluence of attributes, i.e., fast growth but undesired presence, offers a unique opportunity to capitalize on the economic potential of this invasive species’ presence in Wisconsin. Previously we have extracted and optimized the protocol for extracting proteins from Zebra Mussel shells. The extracted proteins will be analyzed to find their identity using MALDI‐TOF MS characterization. This will be the next step in determining a possible commercial use in a large pool representing an underutilized potential resource that is also a pest.

Regional measurements and spatial/temporal analysis of CDOM in 10,000+ optically variable Minnesota lakes using Landsat 8 imagery

Information on colored dissolved organic matter (CDOM) is essential for understanding and managing lakes but is often not available, especially in lake-rich regions where concentrations are often highly variable in time and space. We developed remote sensing methods that can use both Landsat and Sentinel satellite imagery to provide census-level CDOM measurements across the state of Minnesota, USA, a lake-rich landscape with highly varied lake, watershed, and climatic conditions. We evaluated the error of satellite derived CDOM resulting from two atmospheric correction methods with in situ data, and found that both provided substantial improvements over previous methods. We applied CDOM models to 2015 and 2016 Landsat 8 OLI imagery to create 2015 and 2016 Minnesota statewide CDOM maps (reported as absorption coefficients at 440 nm, a440) and used those maps to conduct a geospatial analysis at the ecoregion level. Large differences in a440 among ecoregions were related to predominant land cover/use; lakes in ecoregions with large areas of wetland and forest had significantly higher CDOM levels than lakes in agricultural ecoregions. We compared regional lake CDOM levels between two years with strongly contrasting precipitation (close-to-normal precipitation year in 2015 and much wetter conditions with large storm events in 2016). CDOM levels of lakes in agricultural ecoregions tended to decrease between 2015 and 2016, probably because of dilution by rainfall, and 7% of lakes in these areas decreased in a440 by ≥3 m-1. In two ecoregions with high forest and wetlands cover, a440 increased by >3 m-1 in 28 and 31% of the lakes, probably due to enhanced transport of CDOM from forested wetlands. With appropriate model tuning and validation, the approach we describe could be extended to other regions, providing a method for frequent and comprehensive measurements of CDOM, a dynamic and important variable in surface waters.

Evaluating a primary carbonate pathway for manganese enrichments in reducing environments

Most manganese (Mn) enrichments in the sedimentary rock record are hosted in carbonate minerals, which are assumed to have formed by diagenetic reduction of precursor Mn-oxides, and are considered diagnostic of strongly oxidizing conditions. Here we explore an alternative model where Mn-carbonates form in redox-stratified water columns linked to calcium carbonate dissolution. In ferruginous Brownie Lake in Minnesota, USA, we document Mn-carbonates as an HCl-extractable phase present in sediment traps and in reducing portions of the water column. Mn-carbonate becomes supersaturated in the Brownie Lake chemocline where dissolved oxygen concentrations fall below 5 μM, and Mn-oxide reduction increases the dissolved Mn concentration. Supersaturation is enhanced when calcite originating from surface waters dissolves in more acidic waters at the chemocline. In the same zone, sulfate reduction and microaerobic methane oxidation add dissolved inorganic carbon (DIC) with negative δ13C. These observations demonstrate that sedimentary Mn enrichments may 1) develop from primary carbonate phases, and 2) can occur in environments with dissolved oxygen concentrations <5 μM. Primary Mn-carbonates are likely to originate in environments with high concentrations of dissolved Mn (>200 μM), and where Mn and Fe are partitioned by S cycling, photoferrotrophy, or microaerophilic Fe-oxidation. A shallow lysocline enhances Mn-carbonate production by providing additional DIC and nucleation sites for crystal growth. This carbonate model for Mn-enrichments is expected to be viable in both euxinic and ferruginous environments, and provides a more nuanced view of the relationships between Mn and carbon cycling, with applications throughout the rock record.

Invasive species and biotic homogenization in temperate aquatic plant communities

AbstractAimBiotic homogenization (BH), a reduction in the distinctness of species composition between geographically separated ecological communities in a region, is an important but underappreciated potential consequence of biological invasions. While BH theory has always considered invasions, it has generally been in a relatively narrow context that the cosmopolitan nature of invasive species increases BH because of their shared presence across many locations. We sought to evaluate this component of BH as well as broader effects of invasive species on BH through changes in native communities, including overall reductions in species richness or shifts in species composition.LocationMinnesota, USA.Time period2002–2014.Major taxa studiedAquatic macrophytes, including both vascular plants and attached macroalgae.MethodsWe used surveys of aquatic macrophyte communities from 1,102 shallow lakes in Minnesota, USA (including 248 lakes with repeated surveys) to evaluate relationships between invasion, native species and BH.ResultsWe found that the presence of invasive species was associated with BH and that this pattern was reflected in both the total community (i.e., with invasive species included) and in the composition of the native species community alone. We found that invaded lakes were more compositionally similar to each other than uninvaded lakes, but that both groups were becoming more similar over time—despite neither group exhibiting declines in species richness. This pattern was largely driven by shifts in the native community itself, with common species becoming more widespread and rare species becoming rarer.Main conclusionsInvasive species increase measures of community similarity through their own presence in multiple locations, and also by influencing the composition of native species. These patterns have important implications for conservation and management and suggest that BH should be considered more widely in evaluating the impacts of biological invasions and developing response strategies.

Constraining invader dominance: Effects of repeated herbicidal management and environmental factors on curlyleaf pondweed dynamics in 50 Minnesota lakes

Abstract Curlyleaf pondweed (Potamogeton crispus) is one of the most widespread and widely managed aquatic invasive plants in North America. Despite decades of management, the efficacy of long‐term management strategies and the effects of environmental drivers on curlyleaf pondweed populations remain uncertain. To evaluate the effects of management and environmental factors on within‐lake distribution and local density of curlyleaf pondweed, we collated monitoring data from point–intercept surveys collected by a variety of lake managers across Minnesota, U.S.A. Using this dataset, comprising 177 lake‐years of plant data, we examined the influence of herbicide treatment, water clarity, snow depth, and ice cover duration on curlyleaf pondweed distribution and density between 2006 and 2015. We evaluated the effects of herbicides on curlyleaf pondweed at three time points relative to treatment: within year, carryover effects the following year, and cumulative effects over multiple years of treatment. All three temporal measures were associated with significant reductions of curlyleaf pondweed. Additionally, herbicidal management reduced both the density and distribution of curlyleaf pondweed. Given that herbicide management led to reductions that carried over into future years, managers may be able to design multi‐year treatments to reduce total management effort over time. We also found strong effects of environmental conditions on curlyleaf pondweed. Elevated lake productivity and decreased winter snow cover were associated with increased springtime distributions of curlyleaf pondweed, whereas duration of winter ice cover had no influence. The influence of productivity suggests that reductions of this invasive species may be an ancillary benefit of water‐quality improvements that lower lakes’ trophic status. Our results also show that decreased winter snow cover, as predicted under climate change, could exacerbate problematic growth of curlyleaf pondweed. Harnessing monitoring data from multiple projects, as this study does, allows for robust inference about environmental and management constraints on macrophytes. Because of environmental and management variability, we suggest that treatment regimens follow an adaptive management cycle, with outcomes of management monitored and evaluated, and strategies updated accordingly. It is also vital to continue monitoring both managed and unmanaged lakes to enable stronger inferences about treatment effectiveness.

Troy D. Zars: a personal tribute to a scientist, colleague, and friend

I knew Troy for nearly 15 years, and in that time I don’t recall hearing any childhood stories like those in seemingly every personal statement I’ve read from aspiring scientists or medical students. No stories about hours spent gazing at an anthill. I don’t recall hearing about shelves crowded with insects collected on Styrofoam, or animal skulls kept in a shoebox under his bed. If these collected crania existed, it was more likely because Troy was a crack shot with a pellet gun than a need to know adaptations in the dentition of local squirrel populations. I don’t recall hearing about science projects taken to the Iowa State Capitol to share with politely interested legislators. But I do recall hearing about spending the entirety of the daylight hours in the summer, with his brother Doug, finding where the crappie were biting. About crystal clear water on a lake in Minnesota that you didn’t quite need to know the exact location of, just in case you were thinking of going and plundering the walleye within. I definitely heard about triumphs as a starting lineman not only for his high school football team, but the mighty Norse of Luther College. I heard about summer warehouse jobs in sweltering Iowa Julys. And I saw, firsthand, love and commitment and family. Troy’s story demonstrates that the finest scientists are not just cultivated in narrow STEM curricula that begin at age 5. They are just as likely to be football-playing fishermen, fathers, husbands, and friends who can navigate an operant conditioning paradigm during the week, and dance a polka and produce a magnificent smoked pork shoulder on Saturday. Nature and an independent spirit and a little bit of mischief is a different kind of Magnet school. And it gave us truly one of the best.

Co-limitation by N and P Characterizes Phytoplankton Communities Across Nutrient Availability and Land Use

Historically, freshwater lakes have been widely assumed to be singly limited by phosphorus (P) because the dominant paradigm assumes that nitrogen fixation (N2 fixation) will compensate for any nitrogen (N) deficits. However, a growing body of evidence demonstrates that primary producer response to nutrient manipulation most frequently indicates co-limitation by N and P. Differences in N and P supply ratio have been shown to influence the identity and severity of nutrient limitation, but whether N and P concentration and the ratio of N to P concentrations can explain the frequency of co-limitation in aquatic primary producer assemblages remains unclear, especially in ecosystems subject to human perturbation that strongly increase nutrient availability. We determined how resource availability influences nutrient limitation by N and P of phytoplankton primary production across 12 lakes in Minnesota that vary in watershed land use and lake nutrient levels. We measured epilimnetic lake metabolism and indicators of N2 fixation to evaluate their influence on nutrient limitation status of planktonic algal assemblages. Despite large differences in land use (agricultural, urban, and suburban) and water column N and P availability, planktonic algal response to nutrient manipulation was consistently characterized by co-limitation by N and P across years and months. Neither P availability (as concentrations of total and inorganic forms) nor N2-flux rate predicted responses to nutrient additions. N availability significantly influenced responses of phytoplankton to nutrient additions across years, but this effect was small. The ratio of total N to total P significantly influenced the response to single additions of N and P (these effects were negative and positive, respectively) in summer 2013. Importantly, higher lake primary production and heterocyte count (number of nitrogen fixing cells) were also associated with a stronger, positive response to N + P addition. Overall, these data suggest that planktonic algal assemblages are predominantly characterized by co-limitation by N and P despite large and diverse human impacts on nutrient inputs. Additionally, higher rates of primary production increase the likelihood of co-limitation. Together, these results further support the paradigm shift toward dual management of N and P in aquatic ecosystems.

Vertical heterogeneities of cyanobacteria and microcystin concentrations in lakes using a seasonal In situ monitoring station

A high frequency, high resolution, seasonal research station was deployed to quantify a wide range of local meteorological conditions, water temperature, and water chemistry, including phycocyanin, in two different eutrophic stratified Minnesota lakes. The monitoring effort was coupled with discrete weekly sampling measuring nutrients, cyanobacteria composition, and microcystin concentrations. Our objective was to describe the vertical and seasonal distributions of cyanobacteria biovolume (BV) and microcystin concentrations (MC) using physical lake variables. Two types of BV distributions were observed above the thermocline upward in the water column. The first distribution depicted BV uniformly distributed over the diurnal surface layer (hSL), and the second BV distribution displayed local BV maxima. A quantitative relationship was developed to determine the anticipation of observing a uniform distribution as a function of the surface layer Reynolds number (ReSL), the dimensionless ratio of inertial to viscous forces. The uniform distribution was observed systematically for ReSL > 50,000. MC was observed to accumulate above the thermocline and have a vertical distribution similar to BV, thus depending on ReSL. This is important for directing sampling efforts, because it narrows the range of BV and MC heterogeneity above the thermocline, and suggests a vertical sampling protocol to detect potential maxima and compute representative depth-average concentrations. We explored the temporal variability of the MC to BV ratio, spatially averaged in the epilimnion (MCep/BVep). The maximum MCep/BVep occurred before the maximum BVep and specifically, during the onset of significant biomass growth in both lakes. This observation is notable because the maximum MCep occurs before the visual signs of enhanced cyanobacterial accrual are less recognizable to the public and to monitoring efforts. Our findings could have important implications for predicting MC distribution and guiding monitoring strategies for quantifying MC concentrations in small stratified lakes.

Exploring the soundscape of small freshwater lakes

Monitoring freshwater ecosystems using passive acoustics is a largely unexplored approach, despite having the potential to yield information about the biological, geological and anthropogenic activity of a lake or river system. The state of Minnesota, located in the upper Midwest of the USA and nicknamed ‘land of 10,000 lakes’, provides an interesting case study for soundscape research, because lakes offer ecological, recreational and economic value throughout the area. The underwater soundscape was monitored at fifteen small lakes <10 km2 on representative days in winter (during 100% ice cover) and summer 2018 using a hydrophone suspended 2 m below the water's surface. Median broadband sound pressure level (100–12,000 Hz) was significantly lower in winter (57.2 dB re 1μPa) compared to summer (66.7 dB re 1μPa), possibly because low frequency wind sounds were reduced in winter. Recordings suggest small freshwater lakes in Minnesota have a relatively pristine soundscape, where vocalizing aquatic animals may hold acoustic niches. However, sound from anthropogenic activity was also present in the study lakes. Ice auger and motorboat sound increased the intensity of the soundscape by 10 dB and overlapped the frequency range (300–1000 Hz) of biological sounds in the environment, that may be important to aquatic life. Understanding current baseline sound levels in ecologically significant freshwater lakes, like those in this study, is the first step in determining any potential consequences of anthropogenic sound. Moving forward, baseline sound levels provide vital evidence for scientists and governing bodies to make proactive decisions for soundscape conservation.

Assessment of the chlorine demand and disinfection byproduct formation potential of surface waters via satellite remote sensing

The ability of satellites to assess surface water quality indicators such as colored dissolved organic matter (CDOM) suggests that remote sensing could be a useful tool for evaluating water treatability metrics in considering potential drinking water supplies. To explore this possibility, 24 surface water samples were collected throughout Minnesota, USA with wide ranging values of CDOM (a440; 0.41–27.9 m-1), dissolved organic carbon (DOC; 5.5–47.6 mg/L) and specific ultraviolet absorbance at 254 nm (SUVA254; 1.3–5.1 L/mg-M). Laboratory experiments were performed to quantify chlorine demand and the formation of two classes of halogenated disinfection byproducts (DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), using the uniform formation conditions (UFC) test. Chlorine demand and THMUFC were linearly correlated with CDOM (R2 = 0.97 and 0.91, respectively), indicating that CDOM is a useful predictor of these parameters. On the other hand, data comparing di- and tri-HAAUFC with CDOM were better fit by a logarithmic relationship (R2 = 0.73 and 0.87, respectively), while mono-HAAUFC was linearly correlated with CDOM (R2 = 0.46) but only for low-to moderately-colored waters (a440 ≤ 11 m−1). The correlations relating chlorine demand and DBPUFC values with CDOM were coupled with satellite CDOM assessments to estimate chlorine demand and DBPUFC values for all surface waters larger than 0.05 km2 in the state of Minnesota, USA. The resulting maps suggest that only 21.8% of Minnesota lakes would meet both the THM and HAA maximum contaminant levels, but only when pre-disinfection treatment removes 75% of DBP precursors. There are limitations to determining CDOM using satellites for high color surface waters (a440 > 11 m−1), however, leading to underpredicted values for CDOM, chlorine demand, and DBPUFC. Overall, the results demonstrate the potential benefits of satellite remote sensing for assessing potential drinking water sources and water treatability metrics.

Optimization of Shell Grinding Techinques for Purification of Proteins from Zebra Mussel Shells

Wisconsin and Minnesota lakes are under attack from invasive Zebra Mussels, Dreissena polymorpha, a freshwater mussel species native to Eurasia. The Zebra Mussels were introduced to the Great Lakes around 1985–1986 and have continued to aggressively invade the surrounding areas of Minnesota and Wisconsin. Outcompeting native species, including fish, for food sources, Zebra Mussels are thriving. Oddly, this confluence of attributes, ie fast growth but undesired presence, offers a unique opportunity to capitalize on the economic potential of this invasive species' presence in Wisconsin. Here we examine the protein content found in the Zebra Mussel's shell, and optimization of the protocol for extracting proteins from this matrix, with particular emphasis on techniques for grinding the shells. This will be the first step in determining a possible commercial use in a large pool representing an underutilized potential resource that is also a pest.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Holocene Carbon Burial in Lakes of the Uinta Mountains, Utah, USA

Recent research suggests that organic matter sequestered in lake sediment comprises a larger component of the global carbon cycle than once thought, yet little is known about carbon storage in mountain lakes. Here, we used a set of sediment cores collected from lakes in the Uinta Mountains (Utah, USA) to inform a series of calculations and extrapolations leading to estimates of carbon accumulation rates and total lacustrine carbon storage in this mountain range. Holocene rates of carbon accumulation in Uinta lakes are between 0.1 and 20.5 g/m2/yr, with an average of 5.4 g/m2/yr. These rates are similar to those reported for lakes in Greenland and Finland and are substantially lower than estimates for lakes in Alberta and Minnesota. The carbon content of modern sediments of seven lakes is notably elevated above long-term Holocene values, suggesting recent changes in productivity. The lakes of the Uintas have accumulated from 6 to 10×105 Mt of carbon over the Holocene. This is roughly equivalent to the annual carbon emissions from Salt Lake City, Utah. Based on their long-term Holocene rates, lakes in the Uintas annually sequester an amount of carbon equivalent to the emissions of &lt;20 average Americans.