The distributional pattern of benthic macroinvertebrates in a spring-fed foothill tributary of the Ganga River, western Himalaya, India

Abstract

Benthic macroinvertebrates play important ecosystem roles in the cycling and outflow of nutrients. The benthos transforms organic detritus from sedimentary storage into dissolved nutrients that can be mixed into overlying waters and used by rooted plants (macrophytes) and algae (phytoplankton) to enhance primary productivity. This study examined the distribution pattern of benthic macroinvertebrates in a lesser Himalayan foothill stream from the headwaters (2,200m) to mouth (375m). Five stations (S1 to S5) were established along the 43-km course of the stream. Samples were collected at bi-monthly intervals from January to December 2009. The total density of the benthic macroinvertebrate community increased with decreasing altitude and differed significantly among stations. Dominant orders were Diptera at S1 (Simulidae, 27%) & S5 (Chironomidae 24%), Trichoptera at S2 (Limnephilidae 16%) & S3 (Hydropsychidae 9.9%), and Ephemeroptera (Heptageniidae 9.2%) at S4. Principal component analysis revealed that the characteristic taxa were Simulidae at S1, Limnephildae at S2, Hydropsychiidae, Rhyacophilidae, Tipulidae, Perlodidae, Dryopidae & Notonectidae at S3, Heptageniidae at S4, and Chironomidae, Siphlonuridae, & Agrionidae at S5. Cluster analysis showed one large cluster comprising S1 and S2 as sub-groups with resemblance to S3-S4, and S5 as an outlier. The similarity between the stations S3-S4 was attributed to similar landuse pattern (agriculture) and stream order (II Order), while S1 and S2 were slightly similar due to partial similar forest type (oak forest at S1, pine-oak forest at S2) and stream order. At S5, however, the considerable change in forest type (mixed forest) land-use and stream order (III Order) caused S5 as an outlier in cluster. The variations in the abundant and characteristics taxon at different stations were attributed to change in substratum and land-use patterns.