Browsing by Subject "Lake management"

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    Community assembly, invasion, and management of aquatic plant communities
    (2022-12) Verhoeven, Michael
    Determining what mechanisms drive native species declines and what governs their recovery is foundational to understanding community change, and successfully applying this knowledge to limit further losses or restore degraded ecosystems. Efforts to reduce invasive plant populations are often considered critical for halting degradation of native plant communities and fostering their subsequent recovery or restoration. To assess whether management of two invasive plants—Eurasian watermilfoil (Myriophyllum spicatum) and curlyleaf pondweed (Potamogeton crispus)—is likely to foster recovery of native aquatic plant communities, I integrate experimental and observational methods to study community assembly processes in aquatic plants. Chapter 1 builds the foundation for subsequent studies by constructing an observational monitoring database, compiled from more than 500,000 plant observations collected by disparate sources over a 19-year period. In Chapter 2, I use niche models to unpack how patterns of dominance seen in P. crispus and M. spicatum have likely arisen through different mechanisms, predicting direct competition with native species is less likely for P. crispus than M. spicatum. The aquatic plants database is used in Chapter 3 to assess invader control for boosting native plant communities in real-world management projects, with a focus on comparing the two invaders to test predictions from niche models. I show that limitations of monitoring data constrain estimation of causal effects of management. This limits the generalizability of the findings, highlighting the need for more strategic allocation of aquatic plant monitoring efforts and improved tracking of management interventions. In Chapter 4 I synthesize results of a 4-year, in-lake field experiment and the 19-year, statewide observational data, using community assembly theory to ascribe changes in plant communities to three major mechanisms (invader competition, environmental conditions, and regional species pools) and assess the scales at which these mechanisms shape aquatic plant communities. The results highlight complexity and interactivity of community assembly in this system, with mixed evidence for each mechanism and strong differences across scales. This research demonstrates that contrary to common dogma in aquatic plant management, invaders’ relationships with recipient communities are nuanced, and that invader control alone is insufficient to achieve restoration.
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    Exploring hydraulic residence in Minnesota's Sentinel Lakes: implications for management
    (2014-08) Engel, Lee Charles
    Lake systems present a challenge in determining how water associated solutes cycle with time. Lake hydraulic residence time is an important lake management variable dependent on several factors including: volume, watershed size, location within a watershed and climatic variability. The stable isotopes of hydrogen (Deuterium expressed as δD) and oxygen (δ18O) can provide some hydrologic insight to lake water quality management. Analyzing the stable isotopic composition of lake water δD and δ18O over time can aid in identifying source water input mixing and evaporative processes. Lake water δD and δ18O were compared to the isotopic composition of atmospheric water vapor which has a known isotopic concentration at specific latitudes and air temperatures (Burns and McDonnell, 1998; Dansgaard, 1964). Study lakes were sampled spring, summer, and fall over a three year period. Deviations in the amplitudes of fractionated lake water compared to water vapor was modeled to predict hydraulic residence time for twenty-four lakes throughout Minnesota. Results suggest hydraulic residence time was dynamic; variations occurred with annual source water contributions, watershed size and connectivity. Ranges of annual hydraulic residence time among individual lakes were as great as 18.8 years and as small as 0.4 years. δD and δ18O values were plotted in relation to the Meteoric Water Line (MWL) for all study lakes. A gradient of δD and δ18O values were found in relation to latitude. Lighter values ofδD and δ18O were found in northern Minnesota compared to southern Minnesota. Variations in seasonal δD and δ18O created annual amplitudes that provide insight into lake water budgets and residence times. The use of δD and δ18O offer water quality managers a tool to better understand, protect, and remediate lakes and their watersheds.