Nitrogen and Phosphorous Excretion Rates by Tubificids from the Prahova River (Romania)
Nitrogen and phosphorous exchange at the water–sediment interface is controlled both by complex physico-chemical factors and biological processes. Zoobenthos excretion is one of the most important processes in the mineralization of sedimented organic mater. In polluted freshwaters, tubificid worms are among the dominant components of the benthic community. Rates of ammonium and inorganic phosphate excretion by tubificids were experimentally assessed. They were related to the tubificid abundance in a stream ecosystem polluted with municipal and industrial wastewater. The relationship between these rates and temperature were investigated within the range of 4–23 °C. Relatively constant excretion rates were obtained for both nutrients in the first 8 h of excretion, ranging between 0.076 and 0.226 µg N mg d.w.-1 h-1 and 0.0065–0.01 µg P mg d.w.-1 h-1, respectively. Q10 values of 2.52 for ammonium and 1.31 for phosphate were calculated. If we presume that all excreta eventually enters the water column, then we can calculate that these invertebrates potentially add 39.17 mg N m-2 day-1 and 0.49 mg P m-2 day-1. These values accounts for 17.16 and 7.56% of the nutrient load in the river water, respectively.