Measuring and modeling suspended sediment and nutrient yields in a mixed-land use watershed of the central United States

Dissertation advisor: Jason A. Hubbart, Ph.D.Includes vita.Science-based information is needed to better understand mixed-land-use contributions of suspended sediment and nutrient loads to receiving water bodies. Water samples were analyzed for suspended sediments and nutrients using a nested-scale experimental watershed study design (n=836 samples x 5 gauging sites) in an urbanizing mixed-land use watershed of the central USA. Highly variable annual precipitation was observed during the four year study period (2010-2013) with the greatest suspended sediment and nutrient yields during 2010 (record setting wet year) and least yields during 2012 (extreme drought year). Estimated annual suspended sediment yields ranged from 16.1 t km-2 yr -1 during 2012 to 313.0 t km-2 yr -1 during 2010. Annual total inorganic nitrogen and total phosphorus yields exceeded 10.3 and 2.04 kg ha-1 yr -1 from the agricultural dominated headwaters. Multiple linear regression analyses indicated significant (CI = 0.05) relationships between pollutant loading, annual total precipitation (positive correlate), urban land use (positive correlate), forested land use (negative correlate), and wetland land use (negative correlate). Results highlight the need for ongoing studies, and improved best management practices designed to reduce suspended sediment and nutrient loading in mixed-land use watersheds globally.Includes bibliographical references

Measuring and modeling stream and air temperature relationships in a multiland use watershed of the central United States

A nested-scale experimental watershed study design approach was used in an urban watershed of the central U.S. to investigate stream water temperature (Tw) variability during water year's 2011, 2012, and 2013. Drought conditions were observed during water year 2012 when total annual precipitation was approximately 340 mm less than the 30 year record. Sudden increases of >1 ??C within a 15 minute time interval in Tw (Tw surges) following summer thunderstorms were observed at urban sites. Differences in mean Tw between gauging sites were significantly (p=0.02) correlated to urban land use and downstream distance as discharge increased. Linear and nonlinear regression analyses were performed between Tw and air temperature (Ta) data at time scales ranging from 15 minute to seasonal time steps. Additionally, the linear Tw model used in the Soil and Water Assessment Tool (SWAT), and a new processed based Tw model that accounts for hydrology were evaluated. Significant (p>0.05) differences in model efficiency were not found between the linear Tw model used in SWAT and the new process based Tw model. Results from this study will provide land managers with quantitative information and Tw models needed to make informed management decisions and improve water quality in urban watersheds

Characterizing Land Use Impacts on Channel Geomorphology and Streambed Sedimentological Characteristics

Land use can radically degrade stream physical habitat via alterations to channel geomorphology and sedimentological characteristics. However, independent and combined influences such as those of agricultural and urban land use practices on channel geomorphology and substrate composition remain poorly understood. To further understanding of mixed land use influence on stream physical habitat, an intensive, 56 km hydrogeomorphological assessment was undertaken in a representative mixed land use watershed located in Midwestern USA. Sub-objectives included quantitative characterization of (1) channel geomorphology, (2) substrate frequency and embeddedness, and (3) relationships between land use, channel geomorphology, and substrate frequency and embeddedness. Channel geomorphology, and stream substrate data were directly measured at survey transects (n = 561) every 100 m of the entire 56 km distance of the reference stream. Observed data were averaged within five sub-basins (Sites #1 to #5) nested across an agricultural-urban land use gradient. Multiple regression results showed agricultural and urban land use explained nearly all of the variance in average width to depth ratios (R2 = 0.960; p = 0.020; n = 5), and maximum bank angle (R2 = 0.896; p = 0.052; n = 5). Streambed substrate samples of pools indicated significantly (p \u3c 0.001) increased substrate embeddedness at agricultural Site #1 (80%) located in the headwaters and urban Site #5 (79%) located in the lower reaches compared to rural-urban Sites #2 to #4 (39 to 57%) located in the mid-reaches of the study stream. Streambed substrate embeddedness samples of riffles that ranged from 51 to 72% at Sites #1 and #5, and 27 to 46% at Sites #2 to #4 were significantly different between sites (p = 0.013). Percent embeddedness increased with downstream distance by 5% km−1 with the lower urban reaches indicating symptoms of urban stream syndrome linked to degraded riffle habitat. Collectively, observed alterations to channel morphology and substrate composition point to land use alterations to channel geomorphology metrics correlated with increased substrate embeddedness outside of mid-reaches where bedrock channel constraints accounted for less than 3% of substrate frequency. Results from this study show how a hydrogeomorphological assessment can help elucidate casual factors, target critical source areas, and thus, guide regional stream restoration efforts of mixed-land-use watersheds

Assessing the Difference between Soil and Water Assessment Tool (SWAT) Simulated Pre-Development and Observed Developed Loading Regimes

The purpose of this research was to assess the difference between Soil and Water Assessment Tool (SWAT) simulated pre-development and contemporary developed loading regimes in a mixed-land-use watershed of the central United States (US). Native land cover based on soil characteristics was used to simulate pre-development loading regimes using The Soil and Water Assessment Tool (SWAT). Loading targets were calculated for each major element of a pre-development loading regime. Simulated pre-development conditions were associated with increased retention and decreased export of sediment and nutrients when compared to observed developed conditions. Differences between simulated pre-development and observed developed maximum daily yields (loads per unit area) of suspended sediment (SS), total phosphorus (TP), and total inorganic nitrogen (TIN) ranged from 35.7 to 59.6 Mg km−2 (SS); 23.3 to 52.5 kg km−2 (TP); and, 113.2 to 200.8 kg km−2 (TIN), respectively. Average annual maximum daily load was less during simulated pre-development conditions when compared to observed developed conditions by ranges of 1307 to 6452 Mg day−1 (SS), 0.8 to 5.4 kg day−1 (TP), and 4.9 to 26.9 kg day−1 (TIN), respectively. Hydrologic modeling results indicated that the differences in annual maximum daily load were causally linked to land use and land cover influence on sediment and nutrient loading. The differences between SWAT simulated pre-development and observed contemporary loading regimes from this study point to a need for practical loading targets that support contemporary management and integrated flow and pollutant loading regimes

A Case-Study Application of the Experimental Watershed Study Design to Advance Adaptive Management of Contemporary Watersheds

settings Open AccessFeature PaperArticle A Case-Study Application of the Experimental Watershed Study Design to Advance Adaptive Management of Contemporary Watersheds by Jason A. Hubbart 1,*,Elliott Kellner 2 andSean J. Zeiger 3 1 West Virginia University, Institute of Water Security and Science, Davis College of Agriculture, Natural Resources and Design, Schools of Agriculture and Food, and Natural Resources, 3109 Agricultural Sciences Building, Morgantown, WV 26506, USA 2 West Virginia University, Institute of Water Security and Science, Davis College of Agriculture Natural Resources and Design, Division of Plant and Soil Sciences, 3011 Agricultural Sciences Building, Morgantown, WV 26506, USA 3 School of Natural Resources, University of Missouri, 203-T ABNR Building, Columbia, MO 65211, USA * Author to whom correspondence should be addressed. Water 2019, 11(11), 2355; https://doi.org/10.3390/w11112355 Received: 14 September 2019 / Revised: 30 October 2019 / Accepted: 6 November 2019 / Published: 9 November 2019 (This article belongs to the Special Issue Integrated Water Resources Research: Advancements in Understanding to Improve Future Sustainability) Download PDF Browse Figure Review Reports Cite This Paper Abstract Land managers are often inadequately informed to make management decisions in contemporary watersheds, in which sources of impairment are simultaneously shifting due to the combined influences of land use change, rapid ongoing human population growth, and changing environmental conditions. There is, thus, a great need for effective collaborative adaptive management (CAM; or derivatives) efforts utilizing an accepted methodological approach that provides data needed to properly identify and address past, present, and future sources of impairment. The experimental watershed study design holds great promise for meeting such needs and facilitating an effective collaborative and adaptive management process. To advance understanding of natural and anthropogenic influences on sources of impairment, and to demonstrate the approach in a contemporary watershed, a nested-scale experimental watershed study design was implemented in a representative, contemporary, mixed-use watershed located in Midwestern USA. Results identify challenges associated with CAM, and how the experimental watershed approach can help to objectively elucidate causal factors, target critical source areas, and provide the science-based information needed to make informed management decisions. Results show urban/suburban development and agriculture are primary drivers of alterations to watershed hydrology, streamflow regimes, transport of multiple water quality constituents, and stream physical habitat. However, several natural processes and watershed characteristics, such as surficial geology and stream system evolution, are likely compounding observed water quality impairment and aquatic habitat degradation. Given the varied and complicated set of factors contributing to such issues in the study watershed and other contemporary watersheds, watershed restoration is likely subject to physical limitations and should be conceptualized in the context of achievable goals/objectives. Overall, results demonstrate the immense, globally transferrable value of the experimental watershed approach and coupled CAM process to address contemporary water resource management challenges

Assessing the Difference between Soil and Water Assessment Tool (SWAT) Simulated Pre-Development and Observed Developed Loading Regimes

The purpose of this research was to assess the difference between Soil and Water Assessment Tool (SWAT) simulated pre-development and contemporary developed loading regimes in a mixed-land-use watershed of the central United States (US). Native land cover based on soil characteristics was used to simulate pre-development loading regimes using The Soil and Water Assessment Tool (SWAT). Loading targets were calculated for each major element of a pre-development loading regime. Simulated pre-development conditions were associated with increased retention and decreased export of sediment and nutrients when compared to observed developed conditions. Differences between simulated pre-development and observed developed maximum daily yields (loads per unit area) of suspended sediment (SS), total phosphorus (TP), and total inorganic nitrogen (TIN) ranged from 35.7 to 59.6 Mg km−2 (SS); 23.3 to 52.5 kg km−2 (TP); and, 113.2 to 200.8 kg km−2 (TIN), respectively. Average annual maximum daily load was less during simulated pre-development conditions when compared to observed developed conditions by ranges of 1,307 to 6,452 Mg day−1 (SS), 0.8 to 5.4 kg day−1 (TP), and 4.9 to 26.9 kg day−1 (TIN), respectively. Hydrologic modeling results indicated that the differences in annual maximum daily load were causally linked to land use and land cover influence on sediment and nutrient loading. The differences between SWAT simulated pre-development and observed contemporary loading regimes from this study point to a need for practical loading targets that support contemporary management and integrated flow and pollutant loading regimes

Urban Stormwater Temperature Surges: A Central US Watershed Study

Impacts of urban land use can include increased stormwater runoff temperature (Tw) leading to receiving water quality impairment. There is therefore a need to target and mitigate sources of thermal pollution in urban areas. However, complex relationships between urban development, stormwater runoff and stream water heating processes are poorly understood. A nested-scale experimental watershed study design was used to investigate stormwater runoff temperature impacts to receiving waters in a representative mixed-use urbanizing watershed of the central US. Daily maximum Tw exceeded 35.0 °C (threshold for potential mortality of warm-water biota) at an urban monitoring site for a total of five days during the study period (2011–2013). Sudden increases of more than 1.0 °C within a 15 min time interval of Tw following summer thunderstorms were significantly correlated (CI = 95%; p < 0.01) to cumulative percent urban land use (r2 = 0.98; n = 29). Differences in mean Tw between monitoring sites were significantly correlated (CI = 95%; p = 0.02) to urban land use practices, stream distance and increasing discharge. The effects of the 2012 Midwest USA drought and land use on Tw were also observed with maximum Tw 4.0 °C higher at an urban monitoring site relative to a rural site for 10.5 h. The current work provides quantitative evidence of acute increases in Tw related to urban land use. Results better inform land managers wishing to create management strategies designed to preserve suitable thermal stream habitats in urbanizing watersheds

Assessing Environmental Flow Targets Using Pre-Settlement Land Cover: A SWAT Modeling Application

Determining environmental flow requirements to sustain aquatic ecosystem health remains a challenge. The purpose of this research was to quantify the extent of current flow alterations relative to baseline hydrologic conditions of a simulated historic flow regime prior to anthropogenic flow disturbance (i.e., pre-settlement flows). Results allowed assessment of the efficacy of environmental flow targets based on pre-settlement land cover in a contemporary mixed-land-use catchment (i.e., urban, agricultural, and forested). Pre-settlement flows were simulated using the Soil and Water Assessment Tool (SWAT). Pre-settlement land cover, based on soil physical characteristics, was used to simulate pre-settlement flows with the SWAT model. Environmental flow targets were calculated for each flow element of a historic flow regime (magnitude, frequency, duration, timing, and rate of change). Urban (20% of watershed area) and agricultural development (42% of watershed area) were correlated to decreased median daily stream flow by 0.8 m3 s−1 (percent difference = −115%), increased maximum daily flow by 22 m3 s−1 (percent difference = 13%), and a 34% increase in daily flow variability. High flow frequency increased by 45–76% following development. Results highlight a need for consideration of environmental flow targets appropriate for watersheds already modified by existing land use, and point to a need for long-term, broad-scale, and persistent efforts to develop achievable environmental flow recommendations, particularly in rapidly urbanizing mixed-land-use watersheds

A Case-Study Application of the Experimental Watershed Study Design to Advance Adaptive Management of Contemporary Watersheds

Land managers are often inadequately informed to make management decisions in contemporary watersheds, in which sources of impairment are simultaneously shifting due to the combined influences of land use change, rapid ongoing human population growth, and changing environmental conditions. There is, thus, a great need for effective collaborative adaptive management (CAM; or derivatives) efforts utilizing an accepted methodological approach that provides data needed to properly identify and address past, present, and future sources of impairment. The experimental watershed study design holds great promise for meeting such needs and facilitating an effective collaborative and adaptive management process. To advance understanding of natural and anthropogenic influences on sources of impairment, and to demonstrate the approach in a contemporary watershed, a nested-scale experimental watershed study design was implemented in a representative, contemporary, mixed-use watershed located in Midwestern USA. Results identify challenges associated with CAM, and how the experimental watershed approach can help to objectively elucidate causal factors, target critical source areas, and provide the science-based information needed to make informed management decisions. Results show urban/suburban development and agriculture are primary drivers of alterations to watershed hydrology, streamflow regimes, transport of multiple water quality constituents, and stream physical habitat. However, several natural processes and watershed characteristics, such as surficial geology and stream system evolution, are likely compounding observed water quality impairment and aquatic habitat degradation. Given the varied and complicated set of factors contributing to such issues in the study watershed and other contemporary watersheds, watershed restoration is likely subject to physical limitations and should be conceptualized in the context of achievable goals/objectives. Overall, results demonstrate the immense, globally transferrable value of the experimental watershed approach and coupled CAM process to address contemporary water resource management challenges