Excretion by Benthic Invertebrates as Important Source of Phosphorus in Oligotrophic Ecosystem (Lake Krivoe, Northern Russia)

Abstract

We studied contribution of benthic invertebrates to the dissolved phosphates flux from the bottom sediments to the water in an oligotrophic lake (Lake Krivoe, near the White Sea biological station “Kartesh”, Northern European Russia) in 2009-2013 with the aim to quantify specific (among and within taxa), spatial (littoral and deep sites) and seasonal variability. The excretion rates (Pexc) of soluble reactive phosphorus (SRP) were estimated in experiment with dominating taxa of benthic invertebrates (amphipods, oligochaetes, mollusks, and chironomids), freshly collected from the lake. Mass-specific P excretion rate was calculated as Pexc divided by animal dry mass and further used for calculations of benthic P efflux rates. Also, in other experimental series with and without animals (amphipods) we measured extracellular alkaline phosphatase activity. The results showed that the SRP excretion rates varied significantly between taxa and between different-sized individuals within the same taxa (the SRP excretion rate elevates with an increase in individual weight). Notable spatial and seasonal differences in biomass of benthic animals and phosphorus released by them in the lake were found. The calculated phosphorus efflux by excretory activity of benthic animals was more intensive in littoral sites (up to 14.4 μmol m-2d-1 in July), that 7 times greater than maximum efflux in deep areas (2.2 μmol m-2d-1). The mobile burrowing animals (the amphipods Gammarus lacustris, Monoporeia affinis, and Gammaracanthus loricatus) are able to move from the bottom sediments to water and transfer the nutrient; they contributed 80 % of P flux caused by benthic excretion in the lake and affected the activity of the extracellular alkaline phosphatase, increasing its level in water 3-8 times relative to that in the control (without animals). The high phosphatase activity may increase phosphorus bioavailability by catalyzing hydrolysis of organic phosphorus, and further stimulate primary producers

Keywords

• phosphorus cycle
• excretion
• zoobenthos
• amphipods
• phosphatase activity