National-scale remotely sensed lake trophic state from 1984 through 2020.

Lake trophic state is a key ecosystem property that integrates a lake's physical, chemical, and biological processes. Despite the importance of trophic state as a gauge of lake water quality, standardized and machine-readable observations are uncommon. Remote sensing presents an opportunity to detect and analyze lake trophic state with reproducible, robust methods across time and space. We used Landsat surface reflectance data to create the first compendium of annual lake trophic state for 55,662 lakes of at least 10 ha in area throughout the contiguous United States from 1984 through 2020. The dataset was constructed with FAIR data principles (Findable, Accessible, Interoperable, and Reproducible) in mind, where data are publicly available, relational keys from parent datasets are retained, and all data wrangling and modeling routines are scripted for future reuse. Together, this resource offers critical data to address basic and applied research questions about lake water quality at a suite of spatial and temporal scales.

Initial test results for a passive surface water fluxmeter to measure cumulative water and solute mass fluxes.

The theoretical concept and initial test results of a Passive Surface Water Fluxmeter (PSFM) to directly and simultaneously measure cumulative water and solute mass fluxes in surface water flow systems are presented. The PSFM consists of a symmetric hydrofoil that is vertically installed in a stream and one or more sorbent columns that are connected to the nonuniform flow field around the hydrofoil. Depending on the ambient flow velocity, a flow occurs through each column, which elutes portions of initially present "resident" tracers in the column, while, at the same time, solutes in the water (e.g., contaminants or nutrients) are retained in the sorbent column. Quantification of the resident tracer mass remaining and the mass of solutes sorbed in the column enables determination of the local cumulative or time-averaged water and solute mass fluxes. Laboratory flume experiments show good agreement with independent measurements (R(2) > or = 0.96) for instantaneous water fluxes (tested range: 0.3-0.7 m/s), cumulative water fluxes (50-600 L/cm(2)), and cumulative nitrate fluxes (0.4-5.1 g/cm(2)). Future work is required to validate the PSFM performance under a larger range of flow velocities, transient flow, and transport conditions and for different hydrofoil shapes.