Freshwater benthic algal population and community changes due to acidity and aluminum‐acid mixtures in artificial streams

Abstract

AbstractCommunities of freshwater benthic algae were exposed to water acidified daily to pH 4.8 alone and in mixtures with 50, 100, or 500 μg L−1 Al. Daily acidification to nominal pH 4.8 in acidified treatments exposed algae to a range of pHs that led to a variety of Al species of different toxicity. Calcium concentrations in stream water were higher in acidified and Al treatments on day 1, and dissolved Al in stream water was higher in the highest Al treatment on days 1, 7, and 28; otherwise acid and Al treatments did not significantly alter Al and Ca in the exposure water. Calcium bioaccumulation by periphyton was lower in acidified and Al treatments on all sampling days. Concentrations of Mg in water and periphyton did not differ between treatments. The artificial stream system generated alkalinity to buffer acidified water; the amount of generated alkalinity returned to approximately the same levels for the first week, but the amount of alkalinity generated during the second week appeared to decline, and acid‐only and acid‐Al mixtures diverged in their ability to generate alkalinity during the third and fourth weeks. Aluminum in acidified water inhibited abundance of diatoms and green and blue‐green algae more than the effects of acid stress alone. The green filamentous alga Mougeotia showed a slight (but not statistically significant) increase in abundance in the acid‐only treatment. The middle‐Al treatment (nominally 100 μg L−1 Al and acid) generated more alkalinity and had higher abundance of some algal taxa on days 14 and 28, even though measured Al concentrations in water and periphyton fell between low‐ and high‐Al‐treatment levels. Community‐level tests, combining a taxonomic analysis of algal population abundance with chemical analysis of water and bioaccumulation, provide valuable insight to assess anthropogenic stress.