Boreal Acid Sulfate Soil Microbial Communities

Metal sulfide-rich sediments occur widely in many coastal areas surrounding the Gulf of Bothnia region of the Baltic Sea. Since the last ice age; land uplift has resulted in these sediments rising above the sea level; and due to the typically high economic value of coastal areas; Microbial being draining for e.g. infrastructure or agricultural uses.

The oxidation of metal sulfides in PASS material (leading to ASS) is similar to the well studying generation of acid mine drainage from sulfide minerals and the commercial process of biomining; In these processes, the metal sulfide bond is chemically oxidizing by ferric iron to produce soluble metal(s) and depending on the type of mineral, either thiosulfate or elemental sulfur.

Soil microbial communities

The mineral dissolution is catalyzing by acidophilic microorganisms; (optimal pH for acidophile growth < 5 and extreme acidophiles < 3) that oxidize the ferrous iron to regenerate the chemical oxidan;t and convert the reduced sulfur to sulfuric acid.

This parameter positively correlated with the occurance of predicted heterotrophic acidophilic; organisms of the Acidimicrobiacaea and Acidimicrobiales. The closest correlation however was observing to unassigned members of the Proteobacteria; which could indicate their placement in sulfur-oxidizing acidophilic clades. Nevertheless, the generally low predictive strength of the measuring chemical parameters strongly suggesting that low pH and high metal mobility were not the dominant factors that selected for the microbial communities.

Swedish acid sulfate

The deepest Flarkbäck sample had very different geochemical characteristics such as a higher pH and Co, Ni, Zn, and Mn concentrations typical for PASS material. However, the relative proportions of OTUs aligning with ferrous iron and sulfur compound oxidizing Nitrosomonadaceae and Ferrovaceae raises thepossibility that this soil depth was in the process of being oxidized into an ASS.

Despite environmental concerns related to the release of metals and acid; the occurrence of acid sulfate soils has been largely neglected in boreal environments. The results of this study showing that Swedish acid sulfate soils are being oxidizing; that this oxidation is likel catalyzing by acidophilic microorgansisms; and that creating an anoxic environment by flooding an acid sulfate soil has begun to reverse the process of acid generation. However, in contrast to studies on the eastern Baltic coast; principal coordinate analysis does not indicate low pH and high metal concentrations to be the dominant factors; shaping the microbial community.