Reconstruction of a regional, 12,-yr silica decline in lakes by means of fossil sponge spicules

Abstract

We conducted a broad reconnaissance for freshwater upwelling along the southeastern coast of Sweden from Båstad 5 km northward. A 300- × 350-m area of sandy seabed, 0– 2 m deep, was selected for detailed mapping and study. Results were similar regardless of whether measurements were taken with a bottom-contact electrical-conductance sediment probe, by suction of the upper centimeter of the seabed, or with seepage meters. While the point measurements (suction samples and seepage meters) provided an estimate of seepage flux, the sediment-probe reconnaissance provided confidence that a large area of groundwater discharge was not overlooked. The nearshore discharge (0–50 m offshore) probably originates from a shallow aquifer and the offshore discharge (50–220 m offshore) from a buried, confined aquifer.