J. Koski-vahala et al., Phosphorus mobilization from various sediment pools in response to increased pH and silicate concentration, J ENVIR Q, 30(2), 2001, pp. 546-552
Phosphorus (P) release from sediment particles to the interstitial water ha
s been studied extensively, but the contribution of different inorganic P p
ools in sediment under differing environmental conditions is not fully unde
rstood. This study was undertaken to get more detailed information about th
e chemical mobilization mechanisms. Phosphorus mobilization from reserves b
ound by Al, Fe, and Ca compounds in response to increased pH and to inorgan
ic silicon (Si) enrichments was investigated using a sequential fractionati
on analysis and an isotope-labeling technique. The aerobic sediment of Lake
Vesijarvi had a high P retention capacity, and Fe-bound P was the largest
inorganic P pool as well as the main source of released P. High Si addition
(47 mg Si L-1 sediment) released more P to the interstitial water than did
the elevation of pH from 6.6 to 9.5, since Si lowered the resorption of re
leased P onto hydrated Al oxides. This finding reveals that P equilibrium b
etween Fe-bound and Al-bound P in sediments regulates P net mobilization to
the interstitial water under aerobic conditions. Furthermore, elevated pH
combined with high Si enrichment had a positive synergistic effect, resulti
ng in the most substantial P mobilization. This synergism may cause a self-
fueled increase in the internal loading of P. It accentuates the effect of
diatom sedimentation on P fluxes in eutrophic lakes with high pH and may fa
vor the appearance of bloom-forming cyanobacteria.