Relative Importance of Phosphorus Supply to Phytoplankton Production: Fish Excretion versus External Loading

Abstract

In laboratory tanks with bream (Abramis brama), perch (Perca fluviatilis), and roach (Rutilus rutilus) concentrations of phosphorus and nitrogen increased with time. Phosphorus was mainly released as soluble molybdate-reactive phosphorus (SRP); nitrogen almost exclusively as ammonium. The release increased with the species' tendency to forage on littoral sediments and with a smaller fish size. Bioassays with the test algae Selenastrum capricornutum showed that released phosphorus was readily available to algal growth. The total supply of phosphorus to the epilimnion of Lake Gjersjøen was calculated from the external supply from the tributaries and the estimated phosphorus release from total roach biomass. From May to October 1980 phosphorus release from the roach population contributed about the same order of magnitude as the total phosphorus loading from the watershed. During the period with the most serious phosphorus depletion to the phytoplankton (July, August, and September), the phosphorus supply from fish was about double that of the external phosphorus supply, confirming the important role of sediment-feeding fish populations in the eutrophication processes of lakes.

Aquatic insect diversity in two temple ponds of Silchar, Assam, N.E. India and their conservation values

“…Significant positive correlation between DO and PO 3− 4 could be due to the fact that high sunlight penetration and PO 3− 4 concentration increased phytoplankton in the pond which in turn produced more DO. The significant positive relationship of pH with PO 3− 4 is due to the fact that at high pH, phosphorus is released from sediment during summer (Brabrand et al, 1990) (Table II).…”

Long-term changes in the littoral benthos of a Norwegian subalpine lake following the introduction of the European minnow (Phoxinus phoxinus)

“…Several studies report an increase in primary production in lakes after fish stocking (Leavitt et al 1994;McNaught et al 1999;Parker et al 2001;Zimmer et al 2001). This is explained by the fact that fish make nutrients from terrestrial and benthic sources available for the pelagic community (Brabrand et al 1990;Tatrai 1987). This is probably of less importance in Øvre Heimdalsvatn where minnow is predominantly restricted to the shallower parts of the lake (Museth et al 2002).…”

Can fish introductions alter nutrient cycles in previously fishless high-latitude lakes?

“…N and P not assimilated by trout (egested in faeces) would not be immediately available to phytoplankton. In contrast, assimilated nutrients subsequently evacuated (excreted in urine) were assumed to be directly available to primary producers and to contribute to internal load (Brabrand et al, 1990;Lall, 1991).…”

“…This mechanism should further magnify the nutrient load to the lakes derived from fish presence, although the uptake of these sequestered nutrients is not always linear (Vanni et al, 2013). Similarly, fish egestion does not immediately affect nutrient dynamics of the lakes, as the portion of fish diet that is egested is, for the largest part, not readily available to primary producers without prior microbial breakdown (Brabrand et al, 1990;Vanni, 1996). However, eventually, egestion might stimulate the growth of bacterial decomposing organisms, and consequently enhance the growth of mixotrophic phytoplankton such as cryptophytes (Boros et al, 2014).…”