Photochemistry limits primary production
Immobilization of dissolved phosphorus in bacteria and on photochemically-formed particles can contribute to a phosphorus limitation of primary production in headwater environments that receive waters rich in soil dissolved organic matter.
In situ experiments were done to determine the effects of the photochemical degradation of dissolved organic matter (DOM) and subsequent formation of particulate matter on dissolved phosphorus (P) concentrations in surface waters. The results revealed increasing concentrations of particulate phosphorus (PP) and particulate organic carbon (POC) in exposed samples with increasing exposure time (cumulative irradiation energy). Based on an enumeration of bacteria in the samples, we estimated the contribution of biotic and abiotic processes to the PP production. The abiotic PP formation ranged from 56 – 83 % and 50 – 95 % of the total PP in the exposed and control samples, respectively. The remainder was assumed to be bacterial P uptake. Despite the overlapping intervals, biotic and abiotic PP productions were usually higher in exposed samples than in controls. The PP and POC production was affected by the properties of DOM, such as its humic content and freshness index. We hypothesize that the observed immobilization of dissolved P in bacteria and on photochemically-formed particles can contribute to a P limitation of primary production in headwater environments that receive waters rich in soil DOM.
