Community Characteristics Of Aquatic Insects And Bioassessment For Water Quality In Lower Order Streams

In order to clarify the community characteristics of aquatic insects, 3 kinds of 9 lowerorder streams of representative old growth forests, second growth forests and farmlands inLiangshui national natural reserve and Maoershan experimental forestry centre were selectedfor the first time, through the collecting and identifying of the aquatic insects, as well asdetermining the physical and chemical index of stream water quality, the community constitute,seasonal dominant concentration and foundational feeding group were analyzed, the waterquality was assessed by biological indicator, Shannon-Weiner diversity index, communitysimilarity index and biotic index, which provides foundational data and theory support forfurther studying of aquatic insects in aquatic ecosystem.The conclusions as follows:(1) As a result, 4907 aquatic insect individuals were collected, belonging to 38 families 8orders. Trichoptera, Ephemeroptera, Plecoptera and Diptera were dominant groups, theirnumbers of individuals account for 91.14% of all the aquatic insects. The total number ofaquatic insects in old growth forest streams was the most, 58.98%, more than that in secondgrowth forest streams, and the total number in farmland streams was the least, only 8.34%. Thespecies diversity of second growth forest streams was better than those of old growth forest andfarmland streams, and the foundational feeding groups in second growth forest streams werebalanced; in old growth forest streams the proportion of shredder was the biggest, accountingfor 44.16%; in farmland streams the proportion of filterer was the biggest, accounting for65.77%. The quantity of aquatic insect individuals in riffle was more than 1 times of that inpool.(2)The stream habitat quality was investigated with 10 indices, including the livingground substance of sub-fluvial animals, characteristic of ground substance in pool and widthof vegetation in both banks, etc. The results showed that there were no obvious difference ofstream habitat quality between old growth forest and second growth forest streams, whereas,they had remarkable difference with that of farmland streams (P＜0.05), combining with thequantity of collected aquatic insect individuals, which proved that good habitat quality maycontribute to the species diversity of aquatic insect and the increasing of quantity of individuals.(3) The width, depth and flow speed of three kind of stream were maximum in August,meanwhile, species diversity also achieved maximum, proved that abundant runoff can speedup the circulation of materials, promote the reproduction of aquatic insects. The temperatureand content of dissolved oxygen were 2 old growth factors for aquatic insects, the optimumtemperature was 7℃-11℃, dissolved oxygen was about 10mg/L in old growth forest.streams; the optimum temperature was 10.5℃-14℃, dissolved oxygen was 6 mg/L-10 mg/L in secondgrowth forest streams; when dissolved oxygen was enough, temperature remarkably affects thesurvival of aquatic insects in farmland streams. The pH value in 3 kinds of streams was 6.5-7.0,suitable for the survival of aquatic insects according to the fishery pH value standard (6.5-8.5).(4) The determination result of organic matter indicated that in August the CPOMcontent in old growth forest streams was extremely different with those of the other 2 kinds ofstreams (P＜0.01), whose content reached as high as 565.283 g/m~2, abundant CPOM providedrich food for shredders. The seasonal variation rule of filter and gatherer was consistent withFPOM in old growth forest streams. The difference of suspended algae content seasonalvariation was extremely remarkable in second growth forest streams (P＜0.01), the content inMay was 9.08 and 12.11 times of those in August and October, respectively, the illuminationwas old growth factor. The content of inserted algae in farmland streams was the most, thesecond growth forest streams was less, the old growth forest streams was the least, in addition,there was restrictive effect between the content of inserted algae and the community of scrapers.(5)The results of water quality assessment showed that, using different factors such as thedissolved oxygen, total nitrogen, ammonia and total phosphorus, the conclusions were quitedifferent. For example, water quality wasⅠgrade by dissolved oxygen, but wasⅤgrade bytotal nitrogen in old growth forest streams. The physical and chemic features of water werecomplex, influenced by many factors, existing extremely complex physical and chemicalprocess between various factors, if water quality was assessed by mere single factor, there wasbigger deviation, but this problem can be solved by biological monitor.(6)The Odontoceridae, Neoephemeridae and Capniidae were selected as biologicalindicators for good stream water based on tolerance valuess of aquatic insects and sample sites.There was relationship between seasonal dominant concentration of aquatic insects and theassessment results of water quality with Shannon-Weiner diversity index, the species diversityreduced gradually with the increasing of water pollution degree. The analysis of communitysimilarity index showed water quality of old growth forest and second growth forest streamsdid not influence the composition of aquatic insect community, but in farmland streams therewas moderate influence. The results of biotic index showed water quality were good in anytimeexcept the water quality of farmland streams was light pollution in October.