ALO docView - Seasonal abundance and community structure of Chironomidae in two contrasting high alpine streams (2000)

											/ 7 pages
Seasonal abundance and community structure o... (2000)

	Verh. Internat. Verein. Limnol. 27 1596-1601 Stuttgart, November 2000 Seasonal abundance and Community structure of Chironomidae in two contrasting high alpine streams Leopold Füreder, Cornelia Schütz, Rainer Burger and Manfred Wallinger Introduction In high alpine areas, located between the tree line and the permanent snow line, three types of streams can generally be distinguished: glacier-fed (kryal), spring-fed streams (krenal) and rain- or snow-melt dominated (rhithral) streams (Ward 1994, Milner & Petts 1994). Each of these stream types has a dif- ferent set of abiotic conditions, which affect the invertebrate fauna in different ways (Tockner et al. 1997, Füreder 1999). The invertebrates of high alpine streams consist of members of specific Orders some of which are able to survive the most unfavor- able conditions. Within the insect orders, chirono- mids usually are dominant in high alpine streams. Especially in glacial streams, chironomids of the genus Diamesa are the predominant benthic animals within the aquatic insect Community (Bretschko 1969, Steffan 1974, Kownacka & Kownacki 1975). Ward (1994) and Milner & Petts (1994) have summarized the abiotic and biotic features of alpine streams and Milner & Petts (1994) presented a conceptual model where glacial rivers and their com- munities can be explained given the influence of temperature, channel form and stability. However, many aspects in high alpine stream ecol- ogy still remain incomplete. Although the summer dominance of Diamesinae is the common feature of high alpine streams, the winter Situation has not been described in detail. The aim of this study is to compare the chironomid Community from two high alpine streams located above the tree line and to describe the seasonal and longitudinal patterns. Study area The presented study is part of a long-term ecological investigation in the Austrian Central Alps where we are comparing two streams with contrasting abiotic conditions (Füreder et al. 1998) in terms of the aquatic insect Community and the environmental conditions responsible for its distribution and its trophic relationship. Our study area is located 100 km southwest of Innsbruck, Tyrol, in the Ötztal Mountains (Fig. 1). The two streams are both low order, 2nd and 3rd before they discharge into the Gurgler Ache (Table 1). Rotmoosache, the glacial stream, drains barren land (a glacial retreat) and Alpine tundra Vegetation. Due to its origin, the environmental conditions such as discharge, turbidity, nutrient concentration and chemical composition are highly seasonal (Fig. 2). Diurnal changes in these parameters become very significant during high discharge fluctuations in summer (Füreder et al. 1998). The conditions in Königsbach, the spring-fed stream, are more stable, and are altered slightly by snow melt in early summer and heavy rain events during the snow-free period. The discharge base flow rate is quite similar to the Rotmoosache; however, summer peaks are less pronounced (max. 1,836.2 compared to 3,004.8 L s" 1 , Table 1, Fig. 2). Methods In order to describe seasonal abundances and the Community structure of the chironomid Community, quantitative benthic samples were taken monthly using a Surber Sampler (rectangular sampling area of 0.09 m 2 , 100 um mesh; Schütz et al. 1998). Three replicates at four sampling sites per stream, sampled monthly from July 1996 to June 1997, were used for this comparison. The benthic samples were sorted into major invertebrate groups and determined into species where possible. At each Station the physical and chemical environ- ment was monitored, using temperature-logging Sys¬ tems at seven stations, discharge measurements using a dip stick, and pH and conductivity readings taken at every sampling period and each Station. Concen- trations of organic and inorganic matter (suspended solids, AFDW) were obtained from field samples. Monthly measurements of water chemistry included alkalinity, ammonia, nitrate, sulfate, chloride, total phosphorus, dissolved organic carbon, sodium, potassium, calcium and magnesia. Replicate samples 0368-0770/00/0027-01596 $ 1.50 ©2000 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart