Bioavailability of phosphorus in agriculturally loaded rivers in southern Finland

Abstract

The potential bioavailability of phosphorus in agriculturally loaded rivers of southern Finland was determined by an algal bioassay and the release of the potentially bioavailable particulate P was estimated by sorption studies. According to the bioassay 0 to 13.2 per cent (mean 5.1%) of the particulate P in river water samples was potentially bioavailable. Dissolved reactive P (DRP) in river waters appeared to be totally bioavailable whereas the dissolved unreactive P appeared not to be utilized by algae. In addition to river waters two lake sediment samples were also assayed. In these samples 0 and 2.6% of the P was bioavailable. The potential bioavailability of particulate P in agriculturally loaded rivers obtained in this study was lower than that reported in studies from other countries. The difference was assumed to arise partly from methodological factors and partly from the nature of the Finnish soils. The EPC (equilibrium phosphate concentration) values indicated that during the period when most of the agricultural loading enters the lakes in Finland, potentially bioavailable P is not released from the particles because of the relatively high DRP concentration in the receiving waters. However, during the algal production period the DRP concentration in lakes decreases below the EPC and potentially bioavailable particulate P is desorbed. The increase in pH during this period may further enhance the desorption of P.

A rainfall simulation study on the relationships between soil test P versus dissolved and potentially bioavailable particulate phosphorus forms in runoff

“…& Aura, E. Relationships between P pools in runoff versus soil test P 1979, Ekholm 1994) and accelerate eutrophication of surface waters in the same manner as dissolved molybdate-reactive phosphorus (DRP) does.…”

Review of robust measurement of phosphorus in river water: sampling, storage, fractionation and sensitivity

“…Numerous techniques have been employed to estimate BAP, including bioassays (e.g. Chamberlain and Shapiro, 1969;Ekholm, 1994), ion exchange resin-impregnated membranes (e.g. Abrams and Jarrell, 1992) and chemical extractions using NaOH and NH 4 F (Sharpley, 2000).…”

Comparison of impacts of human activities and climate change on water quantity and quality in Finnish agricultural catchments

“…Increase in DRP may be especially dangerous as the receiving water body is mainly P limited (Pietiläinen and Räike 1999). Assuming that 5 % of PP is bioavailable (Ekholm 1994) in addition to DRP increase in bioavailable P was 18 % in 1990-2012. In this catchment a large part of the fields was not erosion sensitive and known disadvantages of vegetation cover like increased soluble nutrients (Muukkonen et al 2007) may go over benefits gained by preventing erosion. Ulén et al (2010) found that field experiments in Scandinavia with ploughless tillage showed reductions in TP losses but often increase in DRP losses.…”

“…Later some disadvantages of vegetation cover were found, including the tendency to increase the dissolved P load (Muukkonen et al 2007; UusiKämppä and Jauhiainen 2010; Ulén et al 2010). Ekholm (1994) observed that dissolved reactive phosphorus (DRP) was totally bioavailable but around 5 % (0-13 %) of PP was bioavailable in river waters.…”