Nature Environment and Pollution Technology

Lakhi Prasad Hazarika ¹, Debojit Baruah ², Ranjit Dutta ²

Affiliations
1 Department of Zoology, North Lakhimpur College, North Lakhimpur-787 031, Assam, IN
2 Department of Botany, Lakhimpur Girls' College, North Lakhimpur-787 031, Assam, IN

Abstract

Critically endangered Ganges River Dolphin (Platanista gangetica gangetica Roxb.) is found in substantial numbers in the downstream of Subansiri river, a major tributary of the River Brahmaputra. Best estimates of 21, 23 and 26 dolphins were recorded in 2005-06, 2006-07 and 2007-08 respectively. Until recently, the Subansiri river was considered one of the safe havens for residential dolphin due to relatively healthy downstream environment coupled with awareness of river bank inhabitants. Water environment of the un-damming Subansiri river strongly influence the existence of dolphin population. However, compositional changes of their distribution may have occurred after regulation of the river by the 2000 MW Lower Subansiri Hydroelectric Projects, whose construction has begun. Only 25 cumec/sec water will be released to the downstream after operation of the project against the present minimum flow discharge of 188 cumec/sec. This huge irreversible reduction (87.60%) in water discharge will make the downstream extremely vulnerable for this IUCN's red listed mammal, the dolphin. Flushing of reservoir sediment will accelerate the degradation by increasing, decreasing the riverbed and water table respectively. To protect the ecological and social security of the downstream, in general, and Ganges dolphin in particular, the minimal environmental flows for long term sustaining of the recently declared India's national aquatic animal is to be calculated and executed accordingly.

Keywords

Dolphin, Downstream, Hydroelectric Project, Northeast India, Subansiri River.

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Ranjit Dutta ¹, Debojit Baruah ¹, S. K. Sarma ², Lakhi Prasad Hazarika ³

Affiliations
1 Department of Botany, Lakhimpur Girls' College, P.O. Khelmati, Lakhimpur-787 031, Assam, IN
2 Department of Botany, Gauhati University, Guwahati, Assam, IN
3 Department of Zoology, North Lakhimpur College, Assam, IN

Abstract

Pre-impact studies of the 2000 MW lower Subansiri dam have been carried out from January 2006 to December 2006 on certain hydrobiological aspects of downstream of the river Subansiri viz., physicochemical parameters, phytoplankton, zooplankton and freshwater fish diversity. The water quality is suitable for planktonic and fish diversity. In thedownstreamof proposed dam, a total of 199 taxa have been recorded and identified which include 48 species of algae, 23 species of zooplankton, and 128 species of freshwater fishes belonging to 9 orders, 27 families and 78 genera.

Keywords

River Hydrobiology, Plankton, Fishes, Subansiri River Dam.

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Debojit Baruah ¹, Lakhi Prasad Hazarika ², Ranjit Dutta ¹

Affiliations
1 Department of Botany, Lakhimpur Girls College, Lakhimpur-787 031, Assam, IN
2 Department of Zoology, North Lakhimpur College, Lakhimpur-787 031, Assam, IN

Abstract

Downstream of River Subansiri showed a biologically controlled healthy ecosystem along with riparian zones and catchment forests which are hot spots of species before the hydel projects were undertaken. This important natural corridor for the energy flow, nutrient cycling and species diversity would certainly be altered due to the construction of 2000 MW lower Subansiri dam in three orders viz., first order impact (hydrology) through alteration in the flow regime, discharge control resulting from damming of river, reduced flow variability and total volume of runoff, and water quality (physical, chemical and biological changes). Second order impacts through changes in sediment transport, floodplain morphology, river water turbidity affecting the biota directly, alteration in primary production (plankton, riparian vegetation), and the third order impact through the habitat degradation due to changes in flow regime, water quality, loss of breedingground for threatened fishes like Tor tor, Tor putitora, fish diversity, fishery production, creating barrier for upstream and downstream migratory fishes as well as endangered aquatic mammal Platanista gangetica, loss of genetic diversity of indigenous deep water rice varieties as well as important native species and thereby affecting the food production capacity and livelihood security of the people who depend on the downstream.

Keywords

River Subansiri, Lower Subansiri Dam, Downstream Impacts, Species Diversity.

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