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

Abstract

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 ≥ 0.96) for instantaneous water fluxes (tested range: 0.3−0.7 m/s), cumulative water fluxes (50−600 L/cm2), and cumulative nitrate fluxes (0.4−5.1 g/cm2). 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.