Food Web Of Benthic Macroinvertebrates In A Second Order River Of Qingjiang River Basin

A food web can directly describe feeding pattern, trophic pathway and energy flow in a community. Macrozoobenthos is one of the main ecological groups of aquatic community, and plays an important role in material cycling and energy flow in aquatic ecosystem. However, there are very few studies conducted on the ecological function of this group in China. Therefore, food web of macroinvertebrates in Tanqigou Stream, a second order river of Qingjiang River basin, was investigated during from 2006 to 2008. The main work covered the calculation of secondary production, foregut content analysis, trophic basis analysis of secondary production, and construction of connectance food web and energy flux food web. The results were as follows:(1) The analysis of trophic bases showed that Tanqigou Stream was a detritus-based and allochthonous-input-dependent river. Except Thienemanimyia lentiginosa, amorphous detritus composed the highest proportions of gut content and contributed most to production for the dominant species: for four mayflies up to 84.38%-77.81%, 74.70%-62.01% respectively; for two caddisflies up to 63.82%-85.35%, 47.44%-70.89%; and for two herbivore chironomids Paratanytarsus parthenogeneticu and Eukiefferiella potthasti Lehman up to 84.46%-86.89%, 68.60%-80.12% respectively. Amorphous detritus accounted for 73.12% of gut content for T. lentiginos, but it only contributed 36.15% of its secondary production, while animal material occupied 14.95% of its gut content, yet contributed 51.64% of its production. Besides amorphous detritus, vascular plant detritus, filamentous algae, diatoms, filamentous fungi were also principal food resources for macroinvertebrates in the Stream.(2) Temporal and spatial patterns of ingestion for the four dominant mayflies were also examined. With respect to seasonal variation or different sampling stations, there was little difference in feeding selection of the four species, but significant variation were observed in absolute value of their ingestion. Temporally, the total daily ingestion of four mayflies in spring (up to 2690.40mg/m2) and summer (up to 2301.37mg/m2) was markedly higher than those in autumn (up to 1232.01mg/m2) and in winter (up to 483.67 mg/m2). Spatially, the total daily ingestions of the four mayflies in S2, S5 and S6 were larger than those in other three sampling stations, among which the maximum was in S5 at 13302.20mg/m2, while the minimum occurred in S1 up to 1530.61mg/m2. Taken as a whole, the temporal and spatial pattern of ingestion for the mayflies kept generally stable with the total amount ranks: Electrogena sp.>Indobaetis sp.>Choroterpes sp.>Caenis sp. except for several local fluctuations.(3) Connectance food web and energy flux food web of the macroinvertebrates in Tanqigou Strean in April 2006 to March 2007 were constructed. The former included 5 basal food resources, 4 top species, 27 intermediate species, the predator-prey ratio was 0.36, and the number of linkages was 152, the trophic connectance was 0.16, the maximum chain length was 3, and the mean chain length was 2.21. The Latter was mainly formed by weak linkages. Assuming that the proportion of energy flow through weak linkages was at least 30% in all pathways, there were 36 weak linkages, accounting for 60.31% of the total linkages (63) in the energy flux food web.Our research tried to provide an insight into the function of macroinvertebrates in the view of feeding relationship and quantitative energy flow in order to understand self-operational mechanism of rivers more deeply, which forms a scientific foundation for their sustainable development.