Browsing by Author "Link, Denver"

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    Data and R code for a zooplankton ethanol storage correction factor.
    (2023-04-05) Blechinger, Tristan; Link, Denver; Nelson, Jenna KR; Hansen, Gretchen JA; blech024@umn.edu; Blechinger, Tristan; University of Minnesota Department of Fisheries, Wildlife, and Conservation Biology
    This data set contains fresh and ethanol fixed zooplankton samples collected from five Minnesota lakes during June 2022. The data were collected with five paired sites at each lake. The samples were filtered to remove detritus, phytoplankton, and predatory invertebrates. After filtering, each sample was split between fresh processing and ethanol storage. Ethanol storage samples remained in storage for approximately one month. Samples were sent to the UC-Davis Stable Isotope Facility for analysis. Stable isotope values in addition to lake name, DOW, and site of collection are included in the data file. Bayesian Hierarchical models were used to establish correction factors for ethanol storage. Statistical analysis was performed using the R package brms and model output can be found in respective .rds files. Details for each file can be found in the readme file.
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    Data and R code for analysis of mercury concentration and food web differences in walleye and yellow perch from Minnesota lakes with and without invasive zebra mussels, 2019 - 2021
    (2023-02-24) Blinick, Naomi S; Ahrenstorff, Tyler D; Bethke, Bethany J; Fleishman, Abram B; Link, Denver; Nelson, Jenna KR; Rantala, Heidi M; Rude, Claire L; Hansen, Gretchen JA; nsblinick@gmail.com; Blinick, Naomi S; University of Minnesota Department of Fisheries, Wildlife, Conservation Biology; Minnesota Department of Natural Resources
    This dataset contains δ13C and δ15N stable isotope data for 3,765 biological samples (fish, littoral macroinvertebrates, and zooplankton) collected from 21 lakes between 2019 and 2021, collaboratively by the University of Minnesota and the Minnesota Department of Natural Resources. In addition, 403 samples have corresponding mercury data, based on laboratory analyses conducted by USGS (Tate et al. 2022).
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    Isotopic Correction Factors for Zooplankton Storage
    (2023) Blechinger, Tristan; Link, Denver; Nelson, Jenna KR; Hansen, Gretchen JA
    Stable isotope analysis is an increasingly popular method of food web monitoring and is leading to an increased understanding of how energy and pollutants move within an ecosystem. This technique involves the use of δ13C and δ15N stable isotopes for specific dietary tracking among trophic levels based on their present ratios; in aquatic ecosystems, zooplankton are frequently used to represent the baseline pelagic trophic level. Upon collection, zooplankton samples are often preserved in ethanol prior to processing and analysis. However, this method has varying effects on isotopic signatures of tissues, leading to a potentially inaccurate isotopic position. In order to determine a correction factor to account for ethanol preservation, zooplankton were collected at 25 sites across five Minnesota lakes. Zooplankton stable isotope data were analyzed using a mixed effects model that showed ethanol preservation leading to significant δ13C enrichment (SE = 0.064, t-value = 17.951) and no significant change in δ15N. The random lake effect had no significant impact on the outcome. This correction factor will enhance the accuracy and efficacy of stable isotope analysis for freshwater food webs by providing more reliable baseline isotope values upon which these studies rely, and provide a procedure for other correction factors to be determined.
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    Mercury concentration and aquatic food web alterations associated with zebra mussel invasion in Minnesota lakes
    (2023-08) Link, Denver
    Zebra mussels (Dreissena polymorpha) are an invasive species documented in 299Minnesota lakes, with 231 of those lakes managed as walleye fisheries. Many ecological changes are associated with zebra mussel invasion, including increased water clarity, depleted pelagic energy resources, expanded littoral zones, deposition of benthic organic matter causing anoxic sediments, and increased benthic energy reliance of food webs. However, the effects of zebra mussels vary among lakes, and few opportunities exist to examine lake ecosystems and food webs pre- and post- zebra mussel invasion. Furthermore, recent evidence has suggested that Dreissenid mussels may impact contaminant bioaccumulation in higher trophic levels, but these effects have not been well-studied in inland lakes. I took two distinct approaches to understanding zebra mussel impacts on food webs and contaminants in fishes. I combined historic Minnesota statewide mercury monitoring data from 1997-2021 coupled with stable isotope data to provide insight into food web dynamics and mercury concentration alterations with zebra mussel invasion. I found the probability of exceeding the Minnesota safe threshold for safe eating of average sized northern pike (Esox Lucius) and walleye (Sander vitreus) ranged from 60%-70%, with zebra mussel lakes having an increased chance. Specifically, mercury concentrations analyzed using Before-After Control-Impact (BACI) study design increased by 8.2% in northern pike and 15.4% in walleye for invaded lakes, while uninvaded systems were stagnant or decreased. To quantify resource use and community structure, food webs in Leech Lake were analyzed pre- and post- invasion using stable isotope analysis of δ13C and δ15N. Fish community response to zebra mussel invasion varied spatially in Leech Lake. Bays on the western shoreline of Leech Lake with heterogeneous habitat increased niche size by 39.81% and fish in those areas relied more heavily on benthic resources following invasion. In contrast to the western bays and to hypothesized effects of zebra mussels, fish from the main basin of Leech Lake, containing mostly homogenous pelagic resources, decreased in niche size by 32.26% and relied more heavily on offshore resources. Taken together, high mercury concentrations in Minnesota northern pike and walleye are exacerbated in zebra mussel lakes. Food web dynamics are variable within the same lake, suggesting preexisting food web structure and access to benthic resources are important to community resilience with zebra mussel invasion.