Abundance and primary production of filamentous green algae Zygogonium ericetorum in an extremely acid (pH 2.9) mining lake and its impact on alkalinity generation

Abstract

Summary1. In extremely acid mining lakes, benthic filamentous green algae (Zygnemataceae, Chlorophyta) thrive as effective competitors for limited carbon (C). These algae could supply C for microbial‐mediated benthic alkalinity generation. However, biomass, productivity and impact of the acidobiontic filamentous green algae at pH ≤3 have not previously been determined.2. Periphytic filamentous green algae was mapped by harvesting their biomass from 85 1 × 1 m quadrats in mining lake Grünewalder Lauch. Zygogonium ericetorum colonised water depths between 1.6 and 10.5 m covering 88% of total area. Biomass peaked at 5–6 m depth. Total Zygogonium biomass amounted to 72.2 t dry weight for the whole lake (0.94 km2), which corresponds to 16.1 t C and the accumulation of primary production from 2.2 years.3. Growth of Zygogonium is moderately N, C and extremely P deficient, and seriously stressed by high rates of Fe deposition during summer. Consequently, net primary production (NPP) of Zygogonium, calculated from measured photosynthesis versus irradiance characteristics and calculated underwater irradiance (0.13 g C m−2 year−1) and in situ oxygen measurements (7.8 g C m−2 year−1), corresponds to only 0.3% and 18.1% of pelagic NPP.4. Neither pelagic nor benthic Zygogonium primary production can supply enough C for efficient acidity removal. However, at rates of benthic NPP in summer of 21.4 mg C m−2 day−1, Zygogonium contributed 26% of the C equivalents to remove acidity associated with ferric iron, contributing at least seasonally to efficient alkalinity generation.