Impact of Water Column Acidification on Protozoan Bacterivory at the Lake Sediment-Water Interface

Abstract

Although the impact of acidification on planktonic grazer food webs has been extensively studied, little is known about microbial food webs either in the water column or in the sediments. Protozoon-bacterium interactions were investigated in a chronically acidified (acid mine drainage) portion of a lake in Virginia. We determined the distribution, abundance, apparent specific grazing rate, and growth rate of protozoa over a pH range of 3.6 to 6.5. Protozoan abundance was lower at the most acidified site, while abundance, in general, was high compared with other systems. Specific grazing rates were uncorrelated with pH and ranged between 0.02 and 0.23 h-1, values similar to those in unacidified systems. The protozoan community from an acidified station was not better adapted (P = 0.95) to low-pH conditions than a community from an unacidified site (multivariate analysis of variance on growth rates for each community incubated at pHs 4, 5, and 6). Both communities had significantly lower (P < 0.05) growth rates at pHs 4 and 5 than at pH 6. Reduced protozoan growth rates coupled with high grazing rates and relatively higher bacterial yields (ratio of bacterial-protozoan standing stock) at low pH indicate reduced net protozoan growth efficiency and a metabolic cost of acidification to the protozoan community. However, the presence of an abundant, neutrophilic protozoan community and high bacterial grazing rates indicates that acidification of Lake Anna has not inhibited the bacterium-protozoon link of the sediment microbial food web.

Short-Term Effects of Low pH on the Microfauna of an Activated Sludge Wastewater Treatment System

“…The results of our small-scale experiments suggest that microfaunal organisms in an activated sludge wastewater treatment system may be able to survive at low pH levels of 4.5 to 5.5, that is, below the stated optimum of pH 6.5 to 8.0 (Benefield andRandall 1988, Pennak 1989). Similarly, in an acidified lake with a pH range of 3.6 to 6.4, Tremaine and Mills (1991) found protozoan abundance to be highest at pH 5.0 to 5.3. However, the temperature of the sludge environment in wastewater treatment is also an important factor to consider.…”

“…Given the complex organic nature of the activated sludge, a wide range of buffering reactions might be involved. Tremaine and Mills (1991) suggested that anaerobic microbial reduction of iron and sulfate might buffer pH in lake sediments, sufficient to maintain a neutrophilic protozoan community.…”

Toxic effects of chemicals on microorganisms

“…The protozoan community from an acidified station (sediment-water interface of an acid mine drainage) was not better adapted to low-pH conditions than a community from an unacidified site. 80 The sed-iment buffering was probably sufficient to maintain a neutrophilic protozoan community.…”

Caracterização limnológica e avaliação de efeitos ambientais causados por efluente de mina de urânio sobre populações microbianas planctônicas da represa das Antas, Caldas (M.G.).

“…Associado ao fluxo de biomassa, os protozoários bacterívoros tem se mostrado eficientes mineralizadores de nitrogênio e fósforo, reciclando o carbono e os nutrientes via cadeia alimentar microbiana, sendo especialmente importantes em ecossistemas pobres em nutrientes, como os ambientes oligotróficos, onde as interações tróficas estão tensamente relacionadas (TREMAINE;MILLS, 1991;GONZÁLEZ, 1999;SIMEK et al 2001).…”