SUMMARY. 1. Macroinvertebrates were sampled in the riffles of fifty-eight streams from three regions of the Himalaya (Anapuma, Langtang and Everest) in ...
Freshwater Biology (1993) 30, 169-180
Macroinvertebrate communities in streams in the Himalaya, Nepal SIMON D. RUNDLE,* ALAN JENKINS* AND S.J. ORMEROD* * Catchment Research Group. School of Pure and Applied Biology. University of Wales Cardiff. PO Box 915. Cardiff CFl 3TL, UK ^ Institute of Hydrology, Crowmarsh Cifford, Wallingford, Oxon OXIO 8BB, UK Author for correspondence: Dr Simon Rundle
SUMMARY 1. Macroinvertebrates were sampled in the riffles of fifty-eight streams from three regions of the Himalaya (Anapuma, Langtang and Everest) in Nepal. A semiquantitative method with identification to family level was used to describe communities on-site. 2. Stream physicochemistry was assessed and the community structure of macroinvertebrates was related to chemistry, physiography (substratum composition, altitude and size), geographical location and the dominant land use in each catchment (terraced agriculhire, forest or scrub). Community data were analysed by ordination PECORANA) and classification (TWINSPAN). 3. The concentration of cations in stream water decreased significantly with altitude. Chemistry also differed between regions; sites from Anapurna had a higher pH and conductivity than those in the other two areas. 4. Communities were dominated by aquatic insect larvae, with Ephemeroptera, in particular the Baetidae, most numerous across sites. 5. There were, nevertheless, differences in community structure between sites, which were related closely to stream physicochemistry. Ordination scores were strongly correlated with altitude, magnesium concentration and substratum composition. Classification was also linked to altitude and chemistry, differentiating high-altitude sites with low silica concentrations from others. Sites from the Anapuma and Everest regions, with their contrasting chemistry, were also separated. 6. Community structure was also related to land use: streams draining catchments dominated by terraced agriculture had different communities from those in scrub or forest. This result was confounded, however, by the strong relationship between land use, altitude and chemistry; sites in terracing were at lower altitude, had higher concentrations of silica and a higher proportion of fine sediments than those in the other land-use types. 7. Overall, our data indicate that natural features of the relief and geology in the Himalaya create strong gradients in their invertebrate faunas, but that activities of man may have an effect on stream structure and ecology through catchment management. Introduction Knowledge of stream ecology in tropical and subtropical areas of the developing world is extremely limited. Studies of macroinvertebrates tend to focus
° " °^^ ^ ^ ^ ^'*^^ (Bishop, 1973; Stout & Vandermeer, 1975; Hynes, 1975a,b; Turcotte & Harper, 1982; Dudgeon, 1983,1988; Benzie, 1984; Ginon & Statzner, 1985) or one taxonomic group (e.g. Kimmins, 1964); to date, only one study has compared communities 169
170 S.D. Rundle, A. Jenkins and S.}. Ormerod from a large number of streams (Williams & Hynes, 1971). Moreover, work has also concentrated on systems at low altitude, the only information on high mountain streams coming from South America (lilies, 1964; Turcotte & Harper, 1982) and Africa (Williams & Hynes, 1971). At present, a major gap exists in our knowledge of high altitude streams from Asia. Situated between the Indian subcontinent and China, the Himalayan mountains lie on the biogeographic divide between the Oriental and Palearctic zones, and span a large range in altitude (to 8848 m OD) and climate, being affected by sharply seasonal runoff. However, this area is increasingly affected by human influence through deforestation, agriculture and tourism. Together, these features underscore the need for a greater hydrobiological research effort than has been made hitherto. Here we present the first extensive survey of macroinvertebrates from medium to high altitude streams in the Himalaya of Nepal. We assess relationships between stream chemistry, physiography and the distribution, abundance and community structure of macroinvertebrates. We also investigate differences in commuruty composition between regions, and in streams draining different types of land use. Site Description The streams were situated in three regions (Fig. 1). They included tributaries of five rivers, all in the Ganges drainage system: the Modi Khola (Anapurna region), the Shorong and Hinku Kholas (Everest region) and the Helambu and Langtang Kholas
(Langtang region). The geology of these areas consists predominantly of sediments of Proterozoic, Palaeozoic and Mesozoic age metamorphosed to a low greenschist grade. There are also some areas of gneiss (Lower Himalayan Cr^'stallines), high-grade 'Outer Crystalline' rocks, and marbles (in the Anapuma region). Chir pine forests are the predominant vegetation in the subtropical climatic zone (approx. 1000-1700m). The temperate zone (1700-3000 m) is dominated by forests of oak {Quercus), rhododendron andfir{Abies spectabilis and A. pindrau^). although conifers such as blue pine {Pinus wallichiana). Himalayan hemlock (Tsuga dumosa) and spruce {Picea smithiana). and bamboos {Bambusa sp. and Arundinaria sp.) are also present. In the subalpine zone (3000-3800 m) Himalayan silver fir {Abies spectabilis) and birch {Betula utilis) are dominant on the lower slopes but are replaced by juniper {Juniperus spp.) and bamboo at higher altitude. The alpine zone lies between the tree line and the area of permanent snow cover. Juniper and rhododendron shrubs grow to about 4900 m in this zone; grassland is present in both the subalpine and alpine zones. Glaciers are present at high altitudes and several sites in this study were glacial outflows. Because of the extreme gradients and staple rice crop in the Himalaya, farming consists predominantly of terraced agriculture with rice on irrigated, level terrace (khet land) and maize on rain-fed sloping terrace (bari land); most occupies areas in the foothills (Mahabarat). Terracing includes the removal of native vegetation and the creation of wall and plateau structures over extensive areas. Substantial
TIBET
INDIA 0
100 km
Fig. 1 Map showing locations of the three sampling regions (A, Anapuma; B, Lantang; C, Everest) in the Himalaya of Nepal.
Stream macroinvertebrates in the Himalaya
river discharge is diverted through the khet land, and fertilizers, animal slurry and pesticides are applied to both khet and bad land. Nepal has a monsoon climate with heavy rain from June to September, and snow down to 6000 m OD. A less well-defined winter monsoon occurs from December to end of March, with snow above about 2500 m. Climate varies substantially with altitude. For example, annual rainfall in Pokhara (833 m) is typically around 3500 m with maximum temperatures between 19 and 30°C and minima between 6 and 21°C. In contrast, at Namche Bazar (3450 m) annual rainfall is about 1200 mm and maximum and minimum temperature ranges are 6—16°C and -8—8°C, respectively.
171
portable meters. Concentrations of aruons were determined using ion chromatography and of cations by inductively coupled plasma optical emission spectrophotometry. Subsamples used for these analyses were filtered (0.45 \im) on site into a 1% nitric add fixative. I
Macroinvertebrates
A semi-quantitative method was used to assess macroinvertebrate communities on site. Animals were collected from a riffle in each stream using a 2min kick sample (net mesh 0.9 mm). They were separated from mineral sediments by elutriation, placed in a white sorting tray, and the number of individuals in each morpho-family counted. The level of identification was limited by the restricted literature on stream taxonomy in Asia. However, previous Materials and Methods studies elsewhere have shown that family-level deterSampling was carried out during February and March mination is sufficient for assessing important eco1992, the winter dry season, when climate and stream logical patterns at the community level (e.g. Furse et flows are suitable to permit biological sampling and al, 1984; Corkum, 1989; Rutt, Weatherley & Ormerod, habitat assessment. 1990). Most morpho-families were determined using European keys, although some Asian taxa were found (see Appendix 1). Voucher specimens for each taxon Physicochemistry were collected in the field and confirmed later in Substratum and location variables. The width and sub- the laboratory. Field identification of families in the stratum composition of each stream were assessed on Anisoptera, Zygoptera, Tricladida, Hirudinea, Oligosite. Mean width was calculated from three measurechaeta, Turbellaria and Hydracarina was not possible ments taken at evenly spaced intervals along a repreand was limited for the Diptera and Coleoptera. sentative, 20m length of stream. The substratum was In the Everest region taxa were placed in log abuncharacterized by assessing proportional cover by six dance categories (1-10, 11-100 or 100-1000 indicomponents (as defined by Rutt, Weatherley and viduals per sample). These data were used only Ormerod, 1989) in the same section of stream: bedin community-]eve] analyses and for assessing patrock, boulders (>25cm), cobbles/pebbles (1.5-25cm), terns of distribution. Abundances of taxa from sites gravel (0.06-1.5 cm), silt/mud (
