Ecosystem health indicators in the Ganga Basin (Uttarakhand, India): Biodiversity, spatial patterns in structure and distribution of benthic diatoms, macro-invertebrates and ichthyofauna

Abstract

This is the pioneering attempt to study the spatial patterns in structure of lotic ecosystems that form the Ganga River system in the Himalaya. The diversity of source (glacier-fed [GF], snow-fed [SN] and spring-fed [SF]) and stream-size (both interrelated) across the altitudinal panorama, create numerous habitats that contribute to structural diversity. The spatial patterns in richness, density and taxonomic composition and distribution of benthic diatoms are less affected by source compared with macro-invertebrates but shows strong influence on the distribution of fish fauna that are poikiliotherms, because a glacier-fed river carries ice-cold water (usually <20°C) in contrast to normal waters in spring-fed system (22°C near snowline, 32°C in foothills). The abundance patterns of biota of lower organisation grade (diatoms, macro-invertebrates) do not differ sharply even across distant river basins as they are more influenced by proximate factors; thus the sub-basins of the Alaknanda resemble more by virtue of one basin and there is notable resemblance between distant SF Bemunda (lower Ganga basin) and SF Gomti (East Rāmgangā basin) and even the farthest Yamuna and Rāmgangā. Fish are more sensitive to temperature and current velocities that are related to altitude and hence longitudinal rather than the spatial gradients in the mountains. The lotic ecosystem of Doon Valley harbour rich and diverse diatom flora, macroinvertebrate fauna and ichthyofauna. The examination of trophic, saprobic and ecological status shows that organic pollution, degradation and anthropogenic eutrophication are non-existent in the Lesser Himalayan rivers and streams, but the fragile Doon Valley is under severe anthropogenic stress. This and habitats fragmented by hydropower projects in the major rivers has threatened the iconic game fish Himalayan mahseer in the Ganga.

Potential impacts of non‐native fish on the threatened mahseer (Tor) species of the Indian Himalayan biodiversity hot spot

“…Water discharge is a further key driver of fish distribution patterns in IH rivers, with low ‘environmental flows’ and changes to the annual hydrograph of rivers having profound implications for mahseer. Knowledge gaps relating to the ecological needs and distribution of the numerous mahseer fish species create further obstacles to their protection and sustainable management (Nautiyal et al, ). For example, little robust information is available about their critical spawning and nursery habitat requirements.…”

“…Knowledge gaps relating to the ecological needs and distribution of the numerous mahseer fish species create further obstacles to their protection and sustainable management (Nautiyal et al, 2013). For example, little robust information is available about their critical spawning and nursery habitat requirements.…”

“…The over‐exploitation of fishes and the ecosystems that support them, combined with broader pressures leading to deteriorating environmental conditions (Figure ), are the most probable factors explaining the marked decline in mahseer species observed in some IH rivers (Nautiyal et al, ). Mahseer and many other IH riverine fish species depend on the rocky beds of streams and rivers, many of them in moderately cold climatic regions.…”

Impact of the dams on water and plankton quality of the River Ganga (Gangotri to Vindhyachal)

“…To assess water quality and the impact of environmental change, many groups of organisms have been studied. Previous work of upper stretch is limited to the fish and epilithic diatoms only (Nautiyal et al., 2013a, 2013b, 2013c; Nautiyal et al., 2000; Singh et al., 1994). Plankton occupies the base level of a food chain that leads up to commercially important fisheries.…”

Re‐establishment of fish passage for conserving threatened migratory species of West‐Indian Himalayas

“…The known Himalayan fish fauna including that of Nepal (i.e., Indian and Nepali Himalayas) composes of 346 species. Many of these fishes have specialized local adaptations (Nautiyal, ; Nautiyal & Singh, ). A particular adaptation (ventrally located adhesive organs) of these species is their ability to persist during episodic torrential flows following monsoon rains.…”