STRUCTURE AND FUNCTION OF BENTHIC ALGAL COMMUNITIES IN AN EXTREMELY ACID RIVER¹

Abstract

The composition of algal species and pigments and the structural and functional characteristics of the algal community were investigated in an acid stream of southwestern Spain, the Río Tinto. The algal community had low diversity and showed few seasonal differences. It was mainly made up of Klebsormidium flaccidum Kütz. (Silva, Mattox & Blackwell) that produced long greenish or purplish filaments, Pinnularia acoricola Hust. (producing brown patches) and Euglena mutabilis Schmitz. The algal filaments made up a consistent biofilm that also included fungal hyphae, iron bacterial sheaths, diatoms, and mineral particles. HPLC analyses on Río Tinto samples showed that undegraded chl accounted for 67% of the total chl in the filamentous patches but were a minority in the brown patch (2.6%). The brown patch had a concentration of carotenoids eight times lower than that observed in the green patch. When chl concentrations were weighted for the proportion of the different patches on the streambed, undegraded chl a accounted for 89.2 mg chl a·m−2 of stream surface area (5.4 g C·m−2). This high algal biomass was supported by relatively high nutrient concentrations and by a high phosphatase activity (Vmax = 137.7 nmol methylumbelliferyl substrate·cm−2·h−1, Km = 0.0045 μM). The remarkable algal biomass in Río Tinto potentially contributed to the bacterial–fungal community and to the macroinvertebrate community and emphasizes the role that the algae may have in the organic matter cycling and energy flow in extreme systems dominated by heterotrophic microorganisms.

Acid mine drainage affects the development and function of epilithic biofilms in streams

“…The significant negative relationship between PHOS:LAMP ratios and pH supports this finding because higher concentrations of metals often are present in more severely affected AMD streams with lower pH. Elevated PHOS activity has been observed in other acidic rivers with high concentrations of Al (Gross 2000, Sabater et al 2003, and elevated microbial PHOS activity was associated with increasing acidity in a recent study on leaf breakdown along an acidity gradient in Appalachian streams (Simon et al 2009). …”

Phosphorus limitation of algae living in iron-rich, acidic lakes

“…High alkaline phosphatase activities would subsequently be expected in lakes with a low SRP concentration and are often used as an indicator for P-limited algal communities (Beardall et al 2001), but in the acidic mining lakes alkaline phosphatase activity (measured at pH 9) was highest in the lake with the highest SRP concentration. The increased alkaline phosphatase activities in the Fe-rich lakes is in accordance with increased phosphatase activities in the benthic community of the Fe-rich acid mining drainage of the Rio Tinto (Sabater et al 2003). Also, in a saline, sulphaterich lake, high phosphatase activities were detected although SRP concentrations were high (Waiser & Robarts 1995).…”

Biofilm Bacterial Community Structure in Streams Affected by Acid Mine Drainage

“…Klebsormidium can be a good indicator of iron concentrations in water (35), while diatoms, such as Navicula, are known to remain active in very acidic (pH Ͻ3.0) environments (19). Increases in algal biomass and primary production have previously been observed following stream acidification (pH Ͻ5.0) and may be attributed to reduced grazing pressure by macroinvertebrates and the low-pH preference of some algal species (such as Klebsormidium sp., which may be found in abundance in highly acidic freshwater environments [33]). The increased abundance of bacterial DNA in the more acidic streams may be directly related to the increased abundance of algae such as Klebsormidium sp., which provide a large surface area for bacterial attachment while also exuding labile dissolved organic matter, stimulating bacterial growth (30).…”