This webpage serves as a reference for the High Rock Lake Water Quality Dashboard and contains information on the datasets integrated into the maps. Each tab on the portal is outlined and described below. This work was supported by several students and faculty, including David Bjorkback (NCCU student), Michael Berryann (NCCU/NCAT student), Marlene Perrin (NCCU student), Dr. Chris Zarzar (TruWeather Solutions), Dr. Rakesh Malhotra (NCCU faculty), and Dr. Courtney Di Vittorio (WFU).
Field Sampling
EEG Field Data Survey: The research team collected grab samples from May 2022 through October 2023 to calibrate the satellite models. The samples were processed in Dr. Kyana Young’s lab at Wake Forest University to estimate Chlorophyll-a (Chl-a), color dissolved organic matter (CDOM), and Total Suspended Solids (TSS). Chl-a was estimated using the EPA 445 method (Arar and Collins, 1997) and a Trilogy fluorometer with a non-acidification module. The APHA-AWWA-WEF (2005) method was used for TSS, and the Ocean Optics protocol was used for CDOM (Mueller et al., 2003). All samples were stored in a cooler and processed within 24 hours of collection. This dataset is also published in an online database that is used for global satellite model calibration (Lehmann et al., 2022). Time series of Chl-a, CDOM, and TSS
Yadkin Riverkeeper Swim Guide Data: This program and data collection effort is managed by the Yadkin Riverkeeper (YRK) and hosted on their website: https://www.yadkinriverkeeper.org/swim-guide. YRK staff and volunteers collect samples in areas that are used for recreation and measured E. coli levels; high values indicate high fecal coliform counts and pose a public health threat. This program is broadly managed by Swim Drink Fish Canada (formerly Lake Ontario Waterkeeper) and can be used by any public interest club, organization, or agency to share information with the public.
Watershed Boundaries: This layer shows the High Rock Lake watershed and sub-watersheds delineated using StreamStats (https://www.usgs.gov/streamstats). Each lake arm was delineated to outline areas that are contributing sediment and nutrient loads to different sections of the lake.
Lake Median Chl-a for September: This map of median Chl-a values in September was derived from Sentinel-2 satellite imagery using the model calibrated by the research team, described here. This is an aggregated map from images spanning from July 2016 through August 2024 and highlights how Chl-a levels vary throughout the lake around the peak of the growing season, when Chl-a values are typically high.
2022 IR Overall Stream Assessment
The 2022 NC Integrated Water Quality Assessment Report evaluates surface water quality statewide as required under the Clean Water Act, assessing whether waterbodies meet their designated uses for recreation, aquatic life, and water supply. Using data from recent years, the report classifies streams and water bodies into categories based on the degree of impairment, with Category 5 waters identified as impaired and requiring a Total Maximum Daily Load (TMDL) for pollutants. The assessment uses monitoring data to assign status at the waterbody and, where appropriate, the watershed level, ensuring more precise geographic representation of impairments. Results indicate continued water quality challenges in several areas, particularly related to parameters like nutrients, pathogens, and sediment, while many waters continue to fully support their designated uses. The 2022 IR also introduces improved mapping and data
Google Earth Engine Dual Map Viewer
This tab links to the Google Earth Engine Dual Map Viewer Application and allows users to interact with satellite-derived lake water quality maps of Chl-a and TSS alongside true-color images. The full methodology and model performance that is behind this tool is described here. Users can select specific dates, choose which map they would like to view, use the slider to compare images side-by-side, and download individual maps as a geotiff file (which can be imported into GIS software for viewing). Note that the maps take time to load after making a selection; this is largely due to the high computing expense associated with the atmospheric correction algorithm that is initiated when a new selection is made.
Google Earth Engine Time Series Inspector
This tab links to the Google Earth Engine Time Series Inspector Application and allows users to view time series of Chl-a and TSS alongside the most recent TSS or Chl-a map of the lake. The full methodology and model performance that is behind this tool is described here. Users can select a point or draw a rectangle or polygon within the lake. If selecting a region, the median value within the area is calculated for each image. After the time series Chl-a and TSS plots render, users can open the chart in a new tab by clicking on the arrow in the upper right corner and download the data to a csv file.
Potential Pollutant Sources
Watershed Boundaries: This layer shows the High Rock Lake watershed and sub-watersheds delineated using StreamStats (https://www.usgs.gov/streamstats). Each lake arm was delineated to outline areas that are contributing sediment and nutrient loads to different sections of the lake.
NPDES Wastewater Discharge Permits: This dataset shows locations that have a National Pollutant Discharge Elimination System (NPDES) permit, issued by North Carolina’s Division of Water Resources. These permits are required for surface waters and set limits on flow and pollutant levels (e.g., BOD, nutrients, toxins), require monitoring and reporting, and undergo a public review process. Permits are valid for five years, with fees and possibilities for renewal, modification, or enforcement actions (up to $25,000/day fines) managed under clearly defined procedures.
Fractional Impervious Surface: This Fractional Impervious Surface product is part of the 2019 National Land Cover Database (NLCD) that was developed by the Multi-Resolution Land Characteristics Consortium, a partnership of multiple federal agencies. The data is based on imagery from the Landsat satellites and has a 30-meter resolution. Higher impervious surface fractions increase the quantity and speed of runoff from rain events that enter surface water bodies, impacting erosion rates and surface water quality
NC DWR 2024 Permitted CAFO’s: This record shows the 2019 permitted concentrated animal feeding operations (CAFO’s) documented by the North Carolina Department of Water Resources (NC DWR). Nearly all North Carolina swine farms, as well as wet poultry and cattle, are subject to the requirements of their respective state general permits. Every five years, a new general permit is issued. Dry poultry farms do not require a permit.
Poultry CAFO from Machine Learning: This heat map estimates the location of dry poultry CAFO’s and was obtained from a study that used Deep learning on high resolution imagery (Handan-Nader and Ho, 2019). The location data used to train the models was developed by the Environmental Working Group and Waterkeeper Alliance, with validation by the research team at Stanford. The final dataset is available through a GitHub repository and was downloaded and clipped to the High Rock Lake watershed. Each individual location was manually checked by NCCU student David Bjorkback using high-resolution imagery in ArcPro software, and false positives were removed. A heat map is shown instead of individual locations to avoid drawing attention to individual farms.
Monthly Median Chl-a Maps
This tab contains the monthly median (Jan. – Dec.) Chl-a maps derived from Sentinel-2 satellite imagery using the model calibrated by the research team, described here. These aggregated maps are calculated from all quality-controlled Sentinel-2 images spanning from July 2016 through August 2024 and highlight how Chl-a levels vary seasonally throughout the lake. A 100-meter inside buffer was applied to the lake boundaries to remove pixels along the lake boundary, where chl-a values are impacted by vegetation along the bank. The July map is set as the default view, but users can toggle layers on and off using the layer tool in the right sidebar to see different months.
References
APHA-AWWA-WEF (2005) Standard Methods for the Examination of Water and Wastewater. 21th Edition. New York, Total Solids Suspended, Method 2540 D, 2-55 a 2-59.
Arar, E.J. and G.B. Collins. (1997). Method 445.0: In vitro determination of chlorophyll a and pheophytin a in marine and freshwater algae by fluorescence. Revision 1.2. United States Environmental Protection Agency, National Exposure Research Laboratory
Handan-Nader, C., & Ho, D. E. (2019). Deep learning to map concentrated animal feeding operations. Nature Sustainability, 2(4), 298-306.
Lehmann, M. K. et al. GLORIA - A global dataset of remote sensing reflectance and water quality from inland and coastal waters, PANGAEA, https://doi.org/10.1594/PANGAEA.948492 (2022).
Mueller, J. L., Fargion, G. S., & McClain, C. R. (Eds.). (2003). Ocean Optics Protocols for Satellite Ocean Color Sensor Validation, Revision 4, Volume IV: Inherent Optical Properties: Instruments, Characterizations, Field Measurements and Data Analysis Protocols