Exchange of energy, nitrogen and phosphorus between water, bottom and ice in a near-shore ecosystem of the Sea of Japan

Abstract

The processes taking place at the partioning boundaries of a marine ecosystem are still rather obscure. At a permanent research station, water (in winter, ice) samples were taken throughout the year from 6 different depths, and 16 variables related to productivity and hydrochemistry were determined. Transparent and black-walled bell jars were installed on the sea bottom at depths ranging from 0 to 10 m in order to record rates of photosynthesis, respiration and chemical metabolism. In the region studied, two peaks of phytoplankton development occurred: one in winter and one in summer. The winter one coincided with a rise in orthophosphate and nitrate concentrations; the summer peak, with a rise in water temperature and increase of bottom regeneration. Photosynthesis of bottom diatoms was evidenced for all depths investigated. Ammonia and orthophosphate excretion were recorded in all experiments conducted on soft substrata. The measured rates of regeneration corresponded with the values expected in accordance with seasonal changes in nitrogen and phosphorus concentrations. Turnover rates of nitrogen and phosphorus between water and sediment were about 2 to 4 months. Higher production of coastal sea regions may be partly explained by the proximity of the photic layer to sediments and by the increased regeneration rates of biogenous elements.