Department of Physics, Chemistry and Biology (IFM)

Phosphorus Fractionation-BAP

 Bioavailable P are the part of the P forms that are readily available and are released during certain environmental conditions like, redox-sensitive potential and changes in pH. The forms of P that constitute BAP are the Loosely-P, the Fe-P and the Al-P. From the study a total of 14.5% which translates to 0.148g P/kg DM of the TP was estimated to be the BAP in the 0-5 cm depth region (Fig. 1). The 5-10 cm depth region had a BAP amounting to 9.66% (0.0812 g P/Kg DM) of the TP (Fig 2). Al-P, is known to be the most available P for algal consumption (Dorich et al., 1984; Zhou et al., 2001). It was observed that, in both depths studied, BAP forms comparatively minimum composition in the fractions elucidated. However, it is worth mentioning that, these BAP stands a chance of being released during certain environmental conditions and when released, would have dire consequences on the ecosystem (Hesse, 1971).  The fractionation scheme showed a trend of Residual P > Al-P > Ca-P > Fe-P > Loosely-P.

Pattern and Spatial distribution of P

The general observation from the study showed concentration of P tends to decrease with depth. Decomposition of organic matter, microbial activity and reduction of Iron oxides play a vital role in influencing vertical distribution of P, thus the difference in depths (Sundy et al, 1992; Reddy et al., 1996).

Transect along the latitudinal plane showed significance for TP within the 5-10 cm depth. TP in both depths decreased from the inlet to the outlet (Figs 5 and 6). The same was recorded for BAP (Figs 3 and 4). This observation is expected for TP due to particles being high at the inlet as compared to the outlet (Braskerud et al., 2000), though seen in wetlands. The variation observed in the pattern of distribution could be due to the sampling strategy used and also since effluents from the surrounding sites are not channeled through a common inlet and also might probably be different in compositions. 

Sediment P flux

Sediment P release recorded -0.07 and 0.60 µg/g for oxic and anoxic treatments respectively. Sediment P flux for oxic condition had an average of -6.43µgd^-1m^-2 whiles anoxic condition had an average of 120.17 µgd^-1m^-2. Significant difference was recorded between the two incubation with a p-value of 0.007.

 Anoxic incubation data saw an exponential increase from start and started leveling off from day 16, however, samples from site 1, 5 and 6 kept on increasing exponentially. The oxic condition on the other hand was almost a 0 concentration and reduced to negatives in subsequent days, this general trend notwithstanding did not apply to some of the sampling sites, where they tend to fluctuate between the negatives and positives. This was somewhat similar to the observation made by Penn et al., 2000. This trend was attributed to the removal of P from the overlying water due to the formation of a microlayer on the sediment surface (Penn et al., 2000). Trophic classification of lakes is known to be positively correlated to the sediment P release (Nürnberg et al. (1986).

From data, oxic treatment generally recorded no release of sediment P contrary to that of the anoxic. Though the general trend of oxic treatment recorded a negative concentration value, it is however worth noting that in some cases there were positive sediment P release which is contrary to traditional knowledge. The trend of positive sediment P flux (desorption) is in line with studies (Nriagu and Dell 1974; Boström et al. 1982; Hupfer et al. 2004). This trend is attributed to either the increased degree in saturation of P binding sites in the sediment or microbial degradation of organic material. It is also postulated that, shallow lakes with large surface areas can experience the desorption of P even in oxic conditions. This tends to show the importance of studying P release in oxic conditions especially in shallow lakes thus controlling it release. The p value of 0.007 affirms the fact that depletion of DO causes release of P from sediments.