Distribution abundance and seasonality of benthic macroinvertebrates of a hill stream

Abstract

xiii newlineABSTRACT newlineHimachal Pradesh in the northwest region of the Himalayan biodiversity hotspot is home to a network of seasonal and perennial streams, which embody a vital source of water for irrigation and drinking purposes besides fisheries. Ecological integrity of these water bodies at lower and middle elevations has been severely impacted because of various anthropogenic activities. The aim of this study was to investigate how benthic macroinvertebrate communities were affected in a stream flowing through rural-urban landscape dotted with human settlements, agriculture fields, industrial units, and denuded and forested hills. Talheri stream in the Giri River Watershed and close to Shoolini University campus near Solan Town was sampled at monthly intervals for a period of two years. It was characterized by the insect orders Ephemeroptera, Trichoptera and Diptera, mostly predominated by tolerant species and sensitive Plecoptera being completely absent. Biotic indices such as ETP taxa, Shannon diversity index, Margalef species richness and Hilsenhoff Biotic Index indicated disturbance and moderate pollution at the stream. newlineHeterogeneous substratum of the stream and diverse physicochemical variables of water appeared to have influenced distribution of macroinvertebrates, which were represented by 30 morpho taxa. Among dominant taxa, nymphs of Baetis (Baetidae, Ephemeroptera) were well represented on hard substrates like rocks, pebble and cobble where as Caenis (Caenidae, Ephemeroptera) nymphs and Cryptochironomus (Chironomidae, Diptera) larvae were pervasive at all riffle microhabitats as well as connected pools. Sessile filter-feeding larvae of Simulium sp. were found abundantly at the stable rocky site with well-oxygenated fast flowing water currents as rocks provided suitable substratum for their attachment and high flow supplied ample food. Pools supported higher abundance of Baetis sp. 1, Micronecta sp. (Corixidae, Hemiptera), Psychoda sp. (Psychodidae, Diptera), Burmagomphus sp. (Gomphidae, Odonata) and Ephemerella sp. 1 (Ephemerellidae, Ephemeroptera), possibly, because of drift, protection from scouring during spates and adaptability to lentic waters. Physicochemical parameters and abundance of macroinvertebrates exhibited seasonal variations. The wet monsoon season was marked with lower macroinvertebrate population compared to dry season. Temporal fluctuations in the abundance of dominant species were studied, and their correlations with physicochemical variables newlinexiv newlinewere determined. These correlations were significant for Caenis sp. with water temperature and pH, and for Baetis sp.2 and Cryptochironomus sp. 2 with alkalinity. newlineRegarding functional feeding groups, collector-gatherers were dominant at all microhabitats and shredders were completely absent. This pattern was consistent among both years. Two way ANOVA was performed to enumerate tests of significance between various metrics. A key for the identification of benthic macroinvertebrates of Talheri stream is provided. newlineKeywords: Benthic macroinvertebrates, biotic indexes, temporal variations, microhabitats, disturbance, Himalayas, Himachal Pradesh. newline