Changes in Water Quality via the Metabolic Process While Penetrating a Sandy Shore in a Shallow, Eutrophic Lake.

Abstract

Lake water swashing up onto a sandy beach area penetrates the sandy layer before returning to the lake shore zone. As a result, materials contained in the lake water are metabolized, and the water quality of the penetrating water improves. To clarify the process involved, water samples were collected in collection vessels buried at locations 0.2, 0.5, 0.8 and 1.1 m from the shoreline, and seasonal changes in water quality were observed. Organic materials in the lake water were seen to decompose in the sandy beach zone with the organic phosphorus turning into inorganic phosphorus, and to then return almost completely to the lake shore zone. Organic nitrogen was turned mostly into nitrate with the concentration of total nitrogen decreasing as the sample site moved farther from the shoreline. The reduced N/P ratio in water penetrating toward the shoreline suggests the possibility of denitrification as the cause for the decrease in nitrogen concentration as the lake water swashed in and was filtered through the sandy layer.