Impact of ionic aluminium on extracellular phosphatases in acidified lakes

Abstract

We studied direct inhibiting effects of aluminium (Al) on extracellular phosphatases produced by the plankton of acidified lakes in the Bohemian Forest. In laboratory experiments we tested the effect of different Al concentrations (0-1000 microg l(-1)) on kinetic parameters of acid phosphatases (pH optimum approximately 5.0) at pH between 4.5 and 5.2. We observed a significant reduction of an apparent substrate affinity at Al concentrations between 300 and 1000 microg l(-1) at pH 4.5 and 4.8 (but not at 5.2). In contrast, maximum acid phosphatase activity (AcPA) remained unchanged. Such behaviour of saturation kinetics is compatible with the assumption that ionic Al acts as a competitive inhibitor of acid phosphatases. To decide whether the observed Al effects could be explained alternatively by complexation of Al with substrate, we tested statistically the best fits of data with both possible models (competitive versus complexation). Experimental results supported the competitive hypothesis rather than the complexation model suggested originally by some authors. Furthermore, we tested the Al effect within a wide range of pH from 4.0 to 6.0. For pH values < 5.2, the results of an Al-pH matrix experiment gave a more detailed picture: the higher the Al concentration, the wider the pH range in which Al could negatively affect AcPA. The ecological ramifications of this effect were evaluated in the context of field AcPA data on three strongly acidified lakes.

Impacts of alum residues from Morton Jaffray Water Works on water quality and fish, Harare, Zimbabwe

“…The water-soluble monomeric Al is comprised of hydroxyl, fluoride, silicate, carbonate and sulphate complexes as well as the aquo-Al (Prolo et al, 2007). It is this labile inorganic monomeric Al that has been implicated in toxicity studies concerning Al and aquatic biota, including fish (Giller and Malmquist, 1998;Bittl et al, 2001), particularly the hydroxyl complexes; Al 3+ , Al(OH) 2 + and Al(OH) 2+ , (Sharma, 2003).…”

“…Bittl et al (2001) explained this for Al as being due to Al affecting the metabolism of phosphorous (P) probably due to P immobilization in river basins resulting in limited quantities of P in lakes or disturbance of in-lake P cycling. The mechanism through which Al exerts its effects in aquatic organisms, particularly fish, seems to be interference with the ionic and osmotic balance as well as respiration resulting from coagulation of mucus on the gills (DWAF, 1996;Phippen and Horvath 1998;Bjerknes et al, 2003;Sharma, 2003).…”

Biological recovery of the Bohemian Forest lakes from acidification

“…The internal P cycle and P availability for phytoplankton in the Bohemian Forest lakes remains obviously disrupted as a consequence of acidification Bittl et al, 2001). During this survey, we did not observe any significant general change in phytoplankton biomass in comparison with the 1999 data.…”

“…Bacteria are superior competitors to phytoplankton for P under low P (Currie & Kalff, 1984). Furthermore, the growth of both bacteria and phytoplankton may be limited due to inactivation of their extracellular phosphatases at high concentrations of Al i (Bittl et al, 2001). Another common feature of CN, CT, and RA is very low zooplankton biomass as a result of an absence or very low abundances of planktonic Crustacea, which leads to the persisting dominance of the microbial loop in pelagic food webs of these lakes (Vrba et al, 2003a).…”

“…This is most likely the result of complex conditions accompanying current changes in lake water chemistry. Although Al i concentration decreased, suggesting a possible reduction of its inhibitory effect on extracellular phosphatases (Bittl et al, 2001), P immobilisation by Al part still remains very important at the current pH in PL (Kopáček et al, 2004(Kopáček et al, , 2006b.…”