Browsing by Subject "Nutrient criteria"

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    An Evaluation of Water Quality Parameters and Flow Dynamics in High Rock Lake, North Carolina to Assist in the Development of Nutrient Criteria for Lakes and Reservoirs in the State
    (2018-04-26) Rudd, Morgan
    High Rock Dam, located in Rowan and Davidson Counties in North Carolina, was constructed on the Yadkin River in 1927. High Rock Lake (HRL) is primarily fed by the Yadkin River and several smaller tributaries, draining a total area of 3974 square miles. HRL has been on the 303d list of impaired waters since 2004 due to elevated levels of turbidity, chlorophyll-a, and pH. North Carolina currently has surface water standards for chlorophyll-a (40 µg/L), turbidity (25 NTU- lakes), and pH (<6 or >9), but not for nutrients. NC DEQ chose HRL as a pilot study to help develop nutrient criteria for lakes throughout the state. There is a high degree of spatial variability in water quality in HRL. Turbidity, total nitrogen, and total phosphorus decrease with increasing proximity to the dam, whereas chlorophyll-a is most elevated within the mid-section of the lake. Phytoplankton taxonomic assemblage varies according to lake section, with the lower-section of the lake experiencing the most elevated levels of cyanobacteria. Riverine discharge appears to influence chlorophyll-a and biovolume, and future studies should aim to identify the impact of discharge on phytoplankton assemblage. An improved understanding of discharge-water quality relationships can help guide nutrient criteria development for the state’s reservoirs, particularly for reservoirs with short residence times (days-weeks).
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    Redefining algal bloom management pathways in North Carolina
    (2020-04-23) Greif, Jake; Roth, Lindsay; Swann, Kristine; Townsend, Tristen; Watson, Caroline
    Algal blooms are a common occurrence in North Carolina lakes and reservoirs, and recent data suggests they are occurring more frequently. Due to environmental, health, and economic impacts of these occurrences, the North Carolina Department of Environmental Quality (NCDEQ) is invested in understanding the trends in drivers of harmful algal blooms. This project analyzes Ambient Lake Monitoring Data sourced from the Division of Water Resources within NCDEQ to assess potential strategies for both identifying harmful algal blooms and managing the overall occurrences of algal blooms for North Carolina lakes and reservoirs. Our objectives were to: 1) define reference conditions in lakes and reservoirs in North Carolina, 2) predict waterbodies most at risk of algal blooms based on physical and spatial factors, 3) analyze and make recommendations for phytoplankton thresholds, 4) determine temporal trends in blooms, and 5) compare North Carolina water quality criteria the with nationwide policy landscape.  Reference conditions were estimated by taking the median value of monthly 25th percentiles from the most sampled months (May – September) for chemical and biological data. Relative to other ecoregions, the Piedmont’s reference values were consistently high for chemical and biological data; further, the reference conditions for phytoplankton metrics in the Piedmont often exceed current bloom and dominance criteria set by NCDEQ, suggesting it is typical for the Piedmont to experience algal blooms even under the best circumstances. Principal component and redundancy analyses were also performed to assess the relationships among phytoplankton and environmental variables. Results show cyanobacteria vary differently than most other algal groups and are highly associated with chlorophyll-a and nutrients. In order to determine the physical and spatial drivers that make waterbodies vulnerable to algal blooms, we created linear models to predict algal bloom indicators from physical and land use characteristics. Our results suggest that the most vulnerable systems are small reservoirs with dense stream networks that are surrounded by land uses producing high nutrient loads. These findings highlight potential avenues for improved bloom management, such as updating inconsistent bloom criteria and increasing monitoring of at-risk waterbodies. Future studies may incorporate additional physical and spatial characteristics such as precipitation, finer resolution watershed data, and more detailed data about reservoirs including residence time, reservoir order, and reservoir age. Bloom criteria were assessed by calculating the percent of samples which would be classified as potentially harmful algal blooms based on NCDEQ criteria. Unit density and biovolume metrics were found to classify samples across the state inconsistently, with 53.4% and 14.6% in exceedance, respectively. Additionally, sample data were compared to World Health Organization (WHO) guidelines for safe recreational waters using the metric of cyanobacteria cell density. Based on WHO guidelines, 78.3% of samples would be considered at least a moderate risk to human health and 54.6% would be considered a high risk. These results suggest NCDEQ may benefit from updating current bloom criteria to classify samples more consistently; furthermore, the inclusion of cyanobacteria cell density as a metric may allow NCDEQ to have assessments more comparable to international guidelines. Algal temporal trends were analyzed by running a mixed model with year as a fixed effect and waterbody as a random effect to account for temporal inconsistency in monitoring efforts. Chlorophyll-a was found to increase by 1.4 µg/L per year in May and decrease by 1.3 µg/L per year in September. Cyanobacterial relative abundance was found to increase by 1% per year in May and August, and 2% per year in June and September. Our results indicate a seasonal shift in algal blooms, occurring earlier in the year, and an increase in cyanobacteria dominance, which could lead to an increase in toxins being produced in waterbodies. Administrative codes for 47 states were assessed for nutrient criteria standards and associated sub-sectioning trends (site-specific, statewide, ecoregional, hydromorphic, designated use) and water quality parameters (chlorophyll-a, total nitrogen, total phosphorus, clarity). Nationally, it is common for states to subsection nutrient criteria in multiple ways to apply criteria to narrowed conditions. Most states have multiple water quality parameters used within criteria. These trends were further broken down by North Carolina ecoregions to find the ranges in nutrient criteria values used in bordering states that share ecoregions in common with North Carolina. North Carolina’s existing nutrient criteria for chlorophyll-a fall approximately midway within these ecoregional ranges, and as NCDEQ moves forward with revising nutrient criteria for lakes and reservoirs, these ecoregional ranges can be used as a reference. NCDEQ is revising nutrient criteria for lakes and reservoirs at a site-specific scale presently, and while this may be the most efficient method of setting the criteria, other options of sub-sectioning could be useful including sub-sectioning based on ecoregion or physical characteristics. Further modeling of chlorophyll-a by ecoregion or physical attribute are needed to assess these options. Based on our results, potential management improvements that NCDEQ could implement include changing water monitoring schedules, updating bloom criteria, and prioritizing lake monitoring based on certain physical and spatial characteristics. Additionally, NCDEQ may benefit from further investigating what drivers contribute to increasing algal blooms and cyanobacteria dominance, and how those drivers concurrently change with a changing climate.
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    Which Nutrient Criteria Should States and Tribes Choose to Determine Waterbody Impairment?: Using Science and Judgments to Inform Decision-making
    (2007-12-12) Kenney, Melissa A
    Nutrients are the number one water pollution problem for U.S. lakes, reservoirs, and ponds. Excessive nutrients, such as nitrogen and phosphorus, lead to eutrophication, a condition that can include low oxygen levels, noxious algal blooms, and fish kills. Since eutrophication is a condition that manifests itself differently in different systems, there is not a criterion variable with a clear threshold that can be used to set the criterion level. This dissertation presents an approach to address the question: How should States and Tribes choose nutrient criteria to determine eutrophication-related impairments of the designated use? To address this question I used a combination of water quality modeling and decision analysis to determine the optimal nutrient criterion variables and levels. To choose criterion variables that are predictive of the designated use, I utilized statistical models (structural equation models, multiple regression, and binomial regression model) to link the measured water quality variables to expert elicited categories of eutrophication and the designated uses. These models were applied successfully to single waterbodies, the Kissimmee Chain-of-Lakes region, and the State of North Carolina to assess which candidate criterion variables were the most predictive. Additionally, the models indicated that the variables that were most predictive of eutrophication were also the most predictive of the designated use. Using the predictive nutrient criteria variables, I applied a decision-analytic approach to nutrient criteria setting in North Carolina. I developed a nutrient criteria value model that included two submodels, a water quality model and a multiattribute value model. The submodels were parameterized using a combination of water quality data, expert elicitation data, and utility assessments. The outcome of the nutrient criteria value model is the overall expected value for a criterion level choice; the optimal criterion level would be the choice that maximized the expected value. Using the preferences of North Carolina environmental decision-makers and a total phosphorus criterion variable, the optimal criterion level was between 0.03 mg/L and 0.07 mg/L. Ultimately, I hope this research will establish methodology used to set appropriate water quality criteria.