No abstract

Knowledge on the ecology of streams at extreme altitudes is relatively sparse. We conducted a preliminary survey of the macroinvertebrate fauna of Tibetan streams in June 2009 and August 2011 and compared streams with different water sources. We collected quantitative samples of macroinvertebrates and measured physicochemical variables at 16 sites (8 each sampling year) at altitudes ranging from 4315 to 5065 m a.s.l. and grouped the sites into 3 types according to origin: glacier-fed, rain-fed, and lake-outlets. We identified 38 taxa, with a mean of 8.9 taxa per site. Overall the benthic fauna was dominated by insects (71%), mainly Diptera (especially Chironomidae). Ephemeroptera, Plecoptera, and Trichoptera were found at nearly all sites but mostly in low numbers; however, the fauna was significantly different in the 2 sampling years, especially due to the proportions of Chironomidae (68% in June 2009 and 10% in August 2011) and Baetidae (6% vs. 35%, respectively). The 3 stream types had significantly different faunas. Rain-fed streams had the highest total taxon richness (γ-diversity), but glacier-fed streams had a slightly higher taxon turnover rate (β-diversity). Percent glacial cover in the catchment and water turbidity explained most of the variability in taxon richness. Although not particularly taxon rich compared to other high-altitude streams, the Tibetan stream fauna showed considerable spatial variability. The fast retreat of the glaciers and permanent snow fields in Tibet makes further studies on distribution patterns and driving forces for aquatic biodiversity urgent.

Figure 2. Tibetan pilgrim offering hot yak butter tea upon our arrival at a sacred lake.

The fast increase in temperature on the Tibetan Plateau, with anticipated future changes in aquatic ecosystems and biodiversity, highlights the urgent need for ecological data on the sparsely studied Tibetan running waters. In the present study we surveyed eight Tibetan streams to obtain data on densities, feeding selectivity and trophic position of the stone loach Triplophysa. Benthic algae, detritus, macroinvertebrates and fish were quantified and collected for stable isotope and stomach content analysis. Triplophysa density (mean 0.70 individuals m–2, maximum 1.6 individuals m–2) decreased with altitude and increased with the percentage cover of fine substratum. Glacier-fed sites tended to have the lowest fish densities, whereas the highest densities were found near lakes. Mean fish length (4.1–9.6cm) was positively related to the percentage cover of coarse substratum. Triplophysa was omnivorous, but the composition of the stomach contents varied greatly between sites and among individuals. Algal matter was ingested at most sites, but macroinvertebrates (Chironomidae, Baetidae and Simuliidae) dominated the ingestion (average 50–100%). The trophic position of Triplophysa, identified from δ15N (‰) of the biota, varied between 2.6 and 4.2 among localities (mean 3.6) and was inversely related to the biomass of benthic algae, but unrelated to quantities of other potential food sources.