Nutrients and Major-Ions Measured in Water-Quality Samples Collected from Four North Texas Reservoirs (ver. 2.0, September 2020)

In cooperation with Dallas Water Utilities (DWU), the U.S. Geological Survey (USGS) measures nutrient and major-ion concentrations in selected reservoirs in north Texas. This data release documents the results from water-quality samples collected from Ray Hubbard Lake, Grapevine Lake, Ray Roberts Lake, and Lake Lewisville during 2016 -18. The study began in water year 2016 (WY16) with monthly sampling of Ray Hubbard Lake. A water year is defined as the 12-month period from October 1 through September 30 and is designated by the calendar year in which it ends. During this first year, water-quality samples were analyzed for nutrients only (nitrogen, phosphorous, and multiple species of each nutrient). In water year 2017 (WY17), the study design changed to quarterly sampling, expanded to include Grapevine Lake, and added the analysis of major ions (Calcium, Chloride, Fluoride, Magnesium, Potassium, Silica, Sodium, and Sulfate). In water year 2018 (WY18), the study design further expanded to include quarterly sampling of Ray Roberts Lake and Lake Lewisville. Each reservoir currently (2019) has eight sampling sites. Water-quality samples are collected at a minimum of five equidistant depths, including top and bottom depths, at each site. Samples are analyzed for nutrients, major ions, and bromide by the USGS National Water Quality Laboratory (NWQL). Water-quality field properties (dissolved oxygen, pH, specific conductance, temperature, and Secchi depth) are also measured at each sampling site.