These data were compiled to quantify the role of Lake Powell in modulating salinity and reducing overall salt flux from the Upper Colorado River Basin downstream. In addition, these data were used to infer summertime calcite precipitation in Lake Powell (the major proposed sink for salt within the system). The Lake Powell Calcium Magnesium data contains summertime surface water calcium and magnesium concentrations along three transects that span the two major inflows to Lake Powell and the region of Lake Powell closest to the dam. The Modeled Salinity data was used to compare measured total dissolved solid concentrations at Lees Ferry to the instantaneous flow-weighted concentration of total dissolved solid entering the reservoir at any given time. The NWIS-Weighted Inflow Salinity data was used to compare total dissolved salt concentrations made by the Lake Powell Water Quality Monitoring Program to those inferred from upstream gaged sites contained in the National Water Information System. The WRTDS-Output Mass Balance data presents annual mass balance estimates for total dissolved solids, sulfate, bicarbonate, calcium, and chloride in Lake Powell including raw results from Weighted Regressions on Time, Discharge and Season (WRTDS) modeling and estimates of changes in annual reservoir storage.

Three synoptic sampling campaigns were conducted on upper Cement Creek, near Gladstone, Colorado, under low-flow conditions. The first campaign, conducted October 2012, was part of a larger campaign to characterize low-flow water quality in the entire Cement Creek watershed. The second campaign, conducted in September 2019, was designed to quantify metal loading and identify sources of contamination along a 2.5-kilometer study reach. The third campaign, conducted in September 2020, was designed to quantify loads and sources along the same 2.5-kilometer study reach during a test closure of a bulkhead on the Red and Bonita Mine, one of the primary sources of metals within the watershed. Streamflow measurements during the 2012 campaign were conducted using Acoustic Doppler Velocimetry. A continuous, instream injection of a sodium bromide tracer was initiated at the head of the study reach two days prior to the 2019 synoptic sampling campaign and maintained throughout the duration of the campaign. Bromide concentrations were subsequently used to determine streamflow using the tracer-dilution method. Streamflow estimates for the 2020 campaign were developed using a series of sodium chloride slug additions, wherein specific conductivity readings were used as a surrogate for chloride concentration. This data release includes concentration data (inorganic cations and anions), estimated streamflow, and calculated loads for the three sampling campaigns. Tracer data for the continuous tracer injection (2019) and slug additions (2020) are also included. Calculated loads may be used to compare low flow conditions with and without contributions from the Gold King Mine (2012 versus 2019) as well as before and after closure of the Red and Bonita bulkhead (2019 versus 2020). The data release consists of a kmz file showing site locations and the following 9 tables: Table 1, Locations of sampling sites Table 2, Synoptic sampling results, October 3, 2012 Table 3, Synoptic sampling results, September 5, 2019 Table 4, Synoptic sampling results, September 19, 2020 Table 5, Iron speciation results, September 7, 2019 Table 6, Bromide timeseries, September 3-5, 2019 Table 7, Slug addition chloride data, September 19, 2020 Table 8, Slug addition results, September 19, 2020 Table 9, Spatial profiles of streamflow and metal load

This dataset includes geochemical, isotopic, and particle-size data for soil and sediment samples collected at approximately 500 sites in the Clear Lake drainage basin, Lake County, California, between November 2021 and December 2023. Data are also reported for ten soil samples collected during October 2018 soon after the Ranch Fire in the upper Scotts Creek watershed. Samples of lakebed sediment (top four centimeters (cm)) were collected at 26 locations in Clear Lake in September 2023 using an Eckman dredge. Samples collected in tributary watersheds included soils, roadside ditches, streambed sediment, and stream-side sediment (including streambanks, floodplain deposits, colluvium, or alluvium). Some of the streambed sites were sampled on multiple occasions, including a monthly time series during July to December 2023. For 589 samples, the size fraction sieved to less than 0.063 millimeter (mm) was analyzed for the following parameters: 61 elements determined by inductively coupled plasma methods, low-level mercury by cold-vapor atomic absorption spectroscopy, total sulfur and carbon by combustion methods, carbonate carbon, stable isotopes of carbon and nitrogen, total organic carbon, total organic nitrogen, and particle-size distribution. A suite of 101 samples (preserved frozen in the field) was analyzed for nutrient species (forms of phosphorus and nitrogen) as well as particle-size distribution. Version History Summary: First Published: March 2025 Version 2.0: August 2025