Laboratory experiments on bivalve excretion rates of nutrients

Benthic nutrient regeneration may be referred to as a new availability to the water column of significant amounts of nitrogen, phosphorus, and other nutrients, as a consequence of the metabolism of organic matter by the benthos (1). The processes of benthic nutrient regeneration in coastal marine systems are strongly influenced by the presence of abundant macrofauna (2-5). Correct evaluation of the biogenic flux of nutrients due to the excretory activity of infaunal species is therefore an important background of information to investigate the cycling of biophilic elements (nitrogen, phosphorus, and silicon). In field studies, major drawbacks include the difficulty to discern between nutrient upward flux due to animal excretion and a number of local effects, such as microbial mineralization (4,6-8) and uptake (9-14), animal bioturbation and irrigation currents (15-19), tidal currents and wind-generated waves (20-22). Laboratory experiments on the animal excretion rates of nutrients under more controlled conditions represent a useful tool for quantifying the actual biogenic contribution by macrofauna to the total upward flux of nutrients from sediments. Nevertheless, these experiments have often restricted their investigations to ammonium (23-28) or, in a few cases, to ammonium and phosphate (29).