Impact of Effective Light Climate on Periphyton in the Nutrient Impacted River Ganges

Jitendra Pandey, Usha Pandey


Anthropogenic releases in large regulated rivers are overriding their organic load assimilation
capacity and ability to rejuvenate. Effective light penetration in such water bodies are
constrained by trade-off between organic load and benthic oxygen supply. We investigated the
impact of light climate, as influenced by dissolved organic carbon (DOC) and phytoplankton
shading effect, on periphyton biomass accrual in Ganges during summer low flows.
Periphyton chlorophyll a decreased with increasing growth of phytoplankton and DOC.
Periphyton biomass showed significant negative correlation with DOC (R2=0.9483;
p less than0.0001) and phytoplankton biomass (R2=0.9251; pless than0.0001) and positive correlation with
Secchi depth (R2=0.9506; pless than0.0001). Among taxonomic divisions, Chlorophyta, with 24-60%
of total standing stock, showed higher biomass at sites characterized by moderate nutrients and
DOC levels. Cyanophyta (39-74%) contributed large fraction at eutrophic sites and
Bacillariophyta (2-5%) at moderately eutrophic sites. Cyanophycean alga Phormidium
appeared dominant at sites enriched in nutrients. The study indicated that light attenuation
driven by DOC and phytoplankton is leading to erode benthic primary producers and
redistribution of taxonomic divisions in Ganges, which may, by implication, entail a similar


Atmospheric deposition, Climate change drivers, Dissolved organic carbon, Ganges River, Light climate, Periphyton

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