Browsing by Subject "eutrophication"

Now showing 1 - 11 of 11
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    Abiotic Mechanisms for Cyanobacteria Physiology and Distribution in Lakes: A Multi-Scale Approach
    (2018-05) Wilkinson, Anne
    Harmful Algal Blooms (HABs) are a ubiquitous ecological and public health hazard because they are comprised of potentially toxic freshwater microorganisms, called cyanobacteria. Cyanobacteria are capable of accumulating in large concentrations in fresh-water ecosystems during summer and producing a toxin (microcystin) that in high concentration can be harmful to humans and animals. The occurrences of toxic HABs are highly spatially and temporarily variable in freshwater ecosystems and are difficult to predict. These HABs can be governed by abiotic environmental conditions including water temperature structure, light, nutrient abundance, and mixing. This dissertation increases the understanding of abiotic environmental conditions, i.e. different mixing scales, on the physiology and distribution of cyanobacteria in nutrient invariant eutrophic systems using field and laboratory studies. In the laboratory, we investigated the effect of small-scale turbulence on the growth and metabolism of Microcystis aeruginosa. The laboratory bioreactor setup included two underwater speakers, generating a quasi-homogeneous turbulent flow, comparable to field values in the lacustrine photic zone (Reλ =0, Reλ =33 and Reλ =15). The results suggest that turbulence mediates the metabolism of Microcystis aeruginosa, quantified by the net oxygen production, oxygen uptake, and inorganic carbon uptake, which is not manifested in changes in growth rate. In the field, we investigate the abiotic drivers for cyanobacteria and microcystin vertical distribution using a research station 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 distributions of cyanobacteria biovolume (BV) and microcystin concentrations (MC) using easily measurable physical lake parameters. The analysis of vertical heterogeneity of cyanobacteria in the entire water column revealed high positive correlations among BV stratification, surface water temperature, stratification stability, quantified by the Schmidt stability. During strong stratification, the MC and BV accumulated above the thermocline and were highly correlated. Although, the cyanobacteria BV is significant only above the thermocline during stratification where cyanobacteria are exposed to high phosphate, temperature and light, there is still further vertical variability to explain within this region. Two types of BV distributions were observed above the thermocline. The first distribution depicted BV uniformly distributed over the diurnal surface mixed layer (SL). The second BV distribution displayed local BV maxima near and under the surface in the SL. A quantitative relationship was developed to determine the probability of observing a uniform distribution as a function of the surface Reynolds number (ReSL), the dimensionless ratio of inertial to viscous forces, over the SL. The uniform distribution was observed for ReSL>50,000. The outcome of this analysis is the first step towards the quantification and prediction vertical stratification of cyanobacteria biovolume and microcystins as a function of local meteorological and physical conditions in a stratified lake.
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    Characterization of streams and rivers in the Minnesota River Basin Critical Observatory: water chemistry and biological field collections, 2013-2016
    (2017-09-06) Dolph, Christine, L.; Hansen, Amy, T.; Kemmitt, Katie, L.; Janke, Ben; Rorer, Michelle; Winikoff, Sarah; Baker, Anna; Boardman, Evelyn; Finlay, Jacques, C.; dolph008@umn.edu; Dolph, Christine, L.
    This dataset was collected to inform the Water, Sustainability and Climate Minnesota River Basin Observatory, and was supported by the National Science Foundation under Grant No. 1209402 Water, Sustainability and Climate (WSC) – Category 2, Collaborative: Climate and human dynamics as amplifiers of natural change: a framework for vulnerability assessment and mitigation planning. The dataset contains point locations, watershed areas and water quality information for 231 ditch, stream, river and wetland sites located in the Le Sueur River, Chippewa River, Cottonwood River, Cannon River, Wantonwan River and Blue Earth River basins of Minnesota. Study sites ranged in size from 1st order ditches and streams to an 8th order river. Each of these sites was sampled at least once between 2013-2016 (most sites were sampled multiple times) for one or more of the following parameters: 1) water chemistry (total dissolved nitrogen, nitrate-N, nitrite-N, ammonium-N, particulate nitrogen, soluble reactive phosphorus, total dissolved phosphorus, particulate phosphorus, total phosphorus, dissolved organic carbon, dissolved inorganic carbon, particulate carbon, chlorophyll a, total suspended solids, volatile suspended solids, delta-H-2 and delta-O-18 stable isotopes of site water, specific UV absorbance (SUVA) of site water, fluorescence index (FI) of site water); 2) stable isotopes (delta-C-13, delta-N-15, delta-H-2) of invertebrate consumers, particulate carbon and potential food sources; 3) denitrification rates and characteristics of benthic sediment in agricultural drainage ditches; and 4) stream discharge. This dataset also includes spatial data files containing study site locations and watershed areas delineated for each site.
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    Data and R code supporting "A hidden Markov model for ecosystems exhibiting alternative stable states"
    (2021-01-20) Vitense, Kelsey; Hanson, Mark A; Herwig, Brian R; Zimmer, Kyle D; Fieberg, John R; viten003@umn.edu; Vitense, Kelsey
    This repository contains the data and R code used to conduct the analyses in the article "Using hidden Markov models to inform conservation and management strategies in ecosystems exhibiting alternative stable states" in Journal of Applied Ecology.
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    Eagle Lake Pollution Control Project: Assessment of Lake Improvement
    (Water Resources Research Center, University of Minnesota, 1979-06) Latterell, Joseph J.; Abbott, Robinson S.; Straw, Thomas E.; Van Alstine, James B.; Myette, Charles F.
    In this study of the response of Eagle Lake, Kandiyohi County, MN, to the removal of septic effluent, detailed studies of the biological, chemical, sedimentological, hydrological and physical conditions in the lake were conducted. Comparisons of the data collected in this fifth year study were made with benchmark data. An annual hydrologic budget for Eagle Lake was prepared for the 1978 water year. Results show that the amount of water that flowed through Eagle Lake in the 1978 water year was 6,719 acre-feet. Inflow to the lake comprised 45 percent surface water, 22 percent groundwater, and 33 percent precipitation. Water out of the system comprised 72 percent surface water, less than 1 percent groundwater, 25 percent evaporation, and slightly greater than 2 percent net change in lake storage. Several observations give evidence of an improvement in the quality of Eagle Lake waters after the installation of a peripheral sewage collection line. One such observation is the decrease in total nutrient loads of nitrogen and phosphorus at the spring turnover 1978. However, increases in the phytoplankton biomass and the shifts in the most abundant species with the Blue-Green algae assuming dominance do no t indicate an improvement in water quality. The interpretation of our observations has been compiled by the increased nutrient load of the surface water inlets, especially that which resulted from unseasonably heavy rains flushing large quantities of nutrient rich and biologically active waters stored behind a beaver dam during weeks 24 to 28, 1978.
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    Nutrient dynamics in Minnesota watersheds
    (2016-12) Boardman, Evelyn
    While excess nitrogen (N) and phosphorus (P) from anthropogenic activities are known to contribute to the eutrophication of aquatic ecosystems, curbing their inputs poses a management challenge due to poorly understood interactions between land cover, nutrient inputs, and climate. In chapter 1 we examined nutrient inputs, losses, and retention in Minnesota watersheds, across a gradient of environmental variables. Fertilizer inputs were dominant sources of N and P inputs to agricultural watersheds, driving hydrologic losses. Greater runoff decreased retention, suggesting the interactive effects of climate, hydrological modifications, and high nutrient inputs contribute to sustained high hydrologic exports. In chapter 2 we examined the factors controlling concentration-discharge relationships describing P and sediment mobilization in agricultural watersheds in Minnesota. P and sediment were concentrated with greater discharge at most sites. Mean concentrations were elevated by anthropogenic land uses, and bluffs were positively related to particulate concentrations. The mobilization of P is highly sensitive to discharge and its different forms deserve explicit consideration in management strategies.
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    The Phytoplankton of Minnesota Lakes - A Preliminary Survey
    (Water Resources Research Center, University of Minnesota, 1971-06) Brook, A.J.
    Between the years 1965 and 1967, phytoplankton collections were taken in the summer from nearly 200 lakes in a diversity of areas throughout the State. About 220 taxa of euplanktonic algae were identified. The analysis of the Minnesota lake phytoplankton indicates there is a diminution in species diversity in the course of the evolutionary progression as lakes change in character from oligotrophy to eutrophy. Many of the markedly eutrophic lakes have suffered severe disturbance of the natural system due to artificial enrichment. Eutrophic lakes in Minnesota are typically dominated in summer and early fall by water blooms of blue green algae as is usual in most productive lakes of temperate regions. Microcystis aeruginosa, M. wesenbergii, Coelosphaerium naegelianium, Aphanizomenon flos aquae, numerous species of Anabena, Lyngbya birgei, and Gloetrichia echinulata are most common.
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    Proceedings of Conference on Inland Lake Renewal and Shoreland Management
    (Water Resources Research Center, University of Minnesota, 1972-06) Water Resources Research Center
    The program of the Conference included an introduction and overview of the program of the Inland Lake Demonstration and Shoreland Management Project of Wisconsin. Reports were presented on selected lake renewal activities, selected shoreland management and development activities, and shoreland management educational programs. Projects were described involving chemical inactivation of nutrients, nutrient exclusion/dilutional pumping, rehabilitation of a small flowage, urban runoff, characterization private controls for recreational land development, shoreland development, and lake rehabilitation legislation and programs. The progress of Minnesota's shoreland program and activities in lake demonstration projects was described. Alum was used successfully for chemical inactivation of nutrients in an overfertilized small lake in Wisconsin. Dilutional pumping resulted in some success in reducing the phosphorus content of another lake. Plastic sheeting, in combination with sand and gravel blankets on the bed of a millpond, was used to control aquatic plants. With regard to water-oriented recreational developments, it was suggested that an automatic property owners association can provide a mechanism for maintaining and managing the common open space and facilities to which individual lake lot owners have common rights. A nationwide survey disclosed that explicit statutes saying that a local unit of government or State agency is authorized to project, manage, or rehabilitate lakes are rare. The 1969 session of the Minnesota Legislature passed the Shoreland Management Act requiring each county to adopt a shoreland management ordinance to help combat lake problems. Considerable progress has been made in implementing the provisions of the Act.
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    Proceedsings of Conference on Inland Lake Renewal and Shoreland Management
    (Water Resources Research Center, University of Minnesota, 1972-06) Water Resources Research Center
    The program of the Conference included an introduction and overview of the program of the Inland Lake Demonstration and Shoreland Management Project of Wisconsin. Reports were presented on selected lake renewal activities, selected shoreland management and development activities, and shoreland management educational programs. Projects were described involving chemical and inactivation of nutrients, nutrient exclusion/diluational pumping, rehabilitation of a small flowage, urban runoff, characterization private controls for recreational and development, shoreland development, and lake rehabilitation legislation and programs. The progress of Minnesota’s shoreland program and activities in lake demonstration projects was described. Alum was used successfully for chemical inactivation of nutrients in an overfertilized small lake in Wisconsin. Dilutional pumping resulted in more success in reducing the phosphorus content of another lake. Plastic sheeting, in combination with sand and gravel blankets on the bed of a millpond, was used to control aquatic plants. With regard to water-oriented recreational developments, it was suggested that an automatic property owners association can provide a mechanism for maintaining and managing the common open space and facilities to which individual lake lot owners have common rights. A nationwide survey disclosed that explicit statutes saying that a local unit of government or State agency is authorized to project, manage, or rehabilitate lakes are rare. The 1969 session of the Minnesota Legislature passed the Shoreland Management Act requiring each county to adopt a shoreland management ordinance to help combat lake problems. Considerable progress has been made in implementing the provisions of the Act.
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    Shallow lakes in Minnesota: Can we predict the good, the bad, and the vulnerable?
    (2018-12) Vitense, Kelsey
    Shallow lakes (i.e., lakes with maximum depth <5 m) provide critical habitat for wildlife and afford recreational opportunities for the public, including fishing and waterfowl hunting. However, many shallow lakes have degraded conditions resulting from anthropogenic disturbances, such as excessive nutrient inputs from land conversion to agriculture and alteration of natural hydrology leading to increased connectivity of surface waters and colonization by disruptive fish species. These degraded shallow lakes experience frequent and sometimes toxic algal blooms, which decrease the utility of lakes to the public. Additionally, reduced water clarity leads to the loss of submerged aquatic vegetation (SAV), which provide an important food source for waterfowl. Mathematical models tell us that the changing conditions of shallow lakes are reflective of alternative stable states, where lakes can be in either a turbid, algae-dominated state with little to no SAV or a clear, healthy state supporting abundant SAV. These states are stable in the sense that lakes will stay in one of the two states due to strong positive feedback loops (e.g., SAV take up nutrients that algae need, release chemicals toxic to algae, and provide a home to zooplankton that eat algae) unless: (1) there is a sudden disturbance to the system that forces the lake into the other state, or (2) a key component of the system slowly but steadily changes until a threshold is reached, at which point the lake “snaps.” The first case is akin to swinging a hammer to break a pencil in half and the second is like bending a pencil with increasing pressure until it breaks. Much is known about the causes of shifts between clear and turbid states in shallow lakes. For instance, we know that increases in phosphorus (P) inputs to lakes (i.e., bending the pencil) and colonization of bottom-feeding fish species (i.e., the hammers) are associated with shifts from the clear to turbid state. Conversely, we have observed that reducing P inputs and eradicating problematic species can sometimes, but not always, cause the reverse shift back to the clear state. Mathematical models have helped us understand that the critical P threshold at which a lake transitions from the clear to turbid state is not the same as the critical P threshold at which the lake transitions from the turbid state back to the clear state. That is, once a lake transitions to the turbid state, P must be reduced far below its previous level in the clear state before SAV reappears and restores water clarity. This phenomenon makes shallow lake restoration challenging, and efforts to force lakes into the clear state from the turbid state frequently fail or have only short-term effects. Although we have a deep qualitative understanding of the mechanisms driving these shifts, we lack essential quantitative knowledge to improve our ability to manage shallow lakes. For instance, there has not previously been a formal statistical framework grounded in mathematical theory for alternative stable states to classify the state of a lake, nor to estimate critical P thresholds. We lack models to quantify the vulnerability of lakes to state shifts given various risk factors, including proximity to P thresholds and the abundance and composition of fish populations. And we do not have a way to quantitatively prioritize lakes for management, especially without expending significant resources to physically visit and sample lakes. For this dissertation, I partnered with researchers at the Minnesota Department of Natural Resources and the University of St. Thomas who collected a wealth of data on approximately 130 lakes around Minnesota to address these knowledge gaps. I developed methods to accurately classify lake states, identify key drivers of state transitions, and quantify state transition risk based on these drivers. In Chapter 1, I develop a modeling framework that provides the foundation for the approaches I use in subsequent chapters. I use relative abundances of algae and SAV, as well as differing relationships between P and algal abundance within each state, to classify lake states as clear or turbid. The model explicitly incorporates the structure of a cusp catastrophe bifurcation diagram to estimate critical P thresholds where shallow lakes transition from the clear to turbid state and vice-versa. Using data simulated from a theoretical model describing shallow lake processes, I show that not only does this framework classify lake states and estimate critical P thresholds with high accuracy, it also performs better than existing methods. Chapter 2 uses P threshold estimates from Chapter 1 to provide a way to categorize lakes that has direct management implications: lakes that have low enough P levels such that only the clear state is possible vs. lakes with P levels where the lake may exist in the turbid state. I developed a model to predict the category of a lake using only geospatial predictor variables, such as the amount of agriculture in a lake’s watershed. This model provides a first step for managers to prioritize lakes for management and future sampling efforts without visiting lakes to collect water samples or conduct plant surveys. In Chapter 3, I extend the modeling framework in Chapter 1 to allow for temporal dynamics and estimation of state transition probabilities. I assess how transition risk depends on both resilience variables (e.g., current nutrient levels) and perturbation variables (e.g., change in fish biomass). The model identifies top predictors and combinations of predictors for anticipating state transitions, informing essential data needs for future lake surveys. Finally, Chapter 4 describes the development of an R shiny application that allows users to input lake data and receive a predicted state classification and estimate of transition risk based on the modeling work of Chapter 3. This tool can be used by shallow lake managers to help prioritize lakes for management actions based on estimated transition risk according to observed or hypothetical changes to nutrient levels and biological communities, including fluctuations in fish abundance.
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    Upper Midwest lakes are supersaturated with N2
    (2020-06-22) Loeks-Johnson, Brianna M; Cotner, James B; cotne002@umn.edu; Cotner, James B
    Little is known about the exchange of gaseous nitrogen (N2) with the atmosphere in freshwater systems. Although the exchange of N2, driven by excess or deficiencies relative to saturation values, has little relevance to the atmospheric N2 pool due to its large size, it does play an important role in freshwater and marine nitrogen (N) cycling. N-fixation converts N2 to ammonia, which can be used by microbes and phytoplankton, while denitrification/anammox effectively removes it by converting oxidized, inorganic N to N2. We examined N2 saturation to infer net biological nitrogen processes in 34 lakes across 5° latitude and of varying in trophic status, mixing regime, and bathymetry. Here, we report that nearly all lakes examined in the upper Midwest (USA) were supersaturated with N2 (>85% of samples, n = 248), suggesting lakes are continuously releasing nitrogen to the atmosphere. The traditional paradigm is that freshwaters compensate for N-limitation through N-fixation, but these results indicate that lakes in this region arewere constantly losing N to the atmosphere via denitrification and/or anammox, suggesting that terrestrial N inputs are needed to balance the internal N cycle.