| The stream hyporheic zone is an ecotone of surface water–ground water interactions, which is rich in biodiversity, and is an important component of stream ecosystem. The macroinvertebrates are at the top of food webs in the hyporheic zone and directly influence the matter and energy dynamics of the system. They are potential indicators of river ecological health, adjust environmental purification and buffer functions, and play an important role in stream ecosystems. The macroinvertebrate of hyporheic zone in a typical mountain river are studied through field investigations and experiments, including habitat characteristic of hyporheic zone, recolonization processes of hyporheic microinvertebrate, composition and distribution of the hyporheic macroinvertebrate, influence of environmental factors on community structure and distribution of hyporheic macroinvertebrates, difference between hyporheic macroinvertebrate and benthic macroinvertebrate. The main contents and researeh results are summarized as follows:(1) In this study, we analysis the 10 parameters of habitat characteristics in hyporheic zone. The results indicated that the substrates of riverbed are gravel and cobble mainly, the heterogeneity have no significant difference, and the ranges of PFS are 4.59~11.97%, and the ranges of vertical hydrological gradient(VHG) sre 0.15~0.73 mm/s. The temperature of interstitial water displays a substantial correlation with temperature of surface water, and is affected by the air temperature. Principal components analysises based on the habitat parameters indicate that the 5 parameters including percentage of fine sediment(PFS), median diameter(D50), vertical hydrological gradient(VHG) and temperature of interstitial water, could represent the habitat characteristics of hyporheic zone completely.(2) The composition and distribution of the hyporheic macroinvertebrate were investigated using artificial substrates in the upper reaches of Heishuitan River in August, December 2013 and April 2014. The results indicated that a total of 27 microinvertbrate species were identified in all three seasons. In summer, 22 species were identified, and the proportion of aquatic insect is 81.8%. 16 species were identified both in winter and spring, and the proportion of aquatic insect is 75.0% and 62.5% respectively. The density of macroinvertebrate assemblage in summer was significant lower than that of winter and spring, and was the highest in spring. The biomass of macroinvertebrate assemblage in winter was significant higher than that of summer and spring, and was the lowest in summer. Species richness, Shannon-Wiener index and Pielou index all have no significant difference among three seasons. The density and richness of macroinvertebrate were decreased with bed depth, and had found maximum invertebrate density within the top 20 cm of the stream bed. Collector-filterer and collector-gatherer were the dominant functional feeding group in all three seasons. The community structure and temporal–spatial distribution of macroinvertebrate were determined by interactions and life history strategy of macroinvertebrate, and physical-chemical factors of hyporheic zone.(3) The recolonization processes of hyporheic microinvertebrate communities were studied using artificial substrates in a mountain stream. Our results indicate that the individual density of microinvertebrates showed the J type growth curve from 7 to 29 days, declined suddenly after 29 days, and showed a fluctuating trend after 55 days. The trend of decline after 29 days was not only influenced by environmental capacity and interspecific competition, but also by external environment factors. During this period, sustained rainfall caused floods in the study area. The richness of macroinvertebrates showed an increasing trend from 1 to 29 days and a fluctuating trend after 29 days. The biomass of macroinvertebrates generally showed an increasing trend. The richness, density, and biomass of macroinvertebrate communities showed no significant difference at 29, 71, and 83 days(P > 0.05). The Shannon-Wiener and Pielou indices also showed no significant difference at 55, 71, and 83 days(P > 0.05). The species density before and after disturbance was used to indicate the recovery state of the community. However, in the long time scale, using only species density did not accurately reveal the recovery state of the stream ecosystem, because of the influence of environmental factors and life history strategy. According to the comprehensive analysis based on these trends and the principal component analysis of species abundance in different recolonization time, macroinvertebrate communities of the hyporheic zone tend to stabilize after 55 days. The dominant species were Camptochironomus sp., Corbicula fluminea, Baetis sp., Cinygmina sp., Hydropsyche sp. and a member of the Psephenidae. In all 28 species macroinvertebrates, 20 species were aquatic insects, which comprised the dominant assemblage of macroinvertebrates. Collector-filterers and collector-gatherers were the dominant functional feeding groups during the whole process. The recolonization of hyporheic microinvertebrate communities is an interactive process of its own resilience and external environment factors. The resilience of communities was determined by the life history strategy, adaptability, and interspecific and intraspecific interactions of species. The external environment factors include the environmental capacity, drought, and flood. In the initial stage of recolonization, the most important factor was the structure of hyporheic zone that controlled acroinvertebrate moving into the habitat, the life history strategy was the most important factor in the interim period, and in the stable period, the combined effect of the environmental and biological factors influenced the composition and distribution of the macroinvertebrate community in the hyporheic zone.(4) The habitat characteristics of hyporheic zone could be represented by physical and chemical parameters of sediment, interstitial water and hyporheic exchange in hyporheic zone. In order to study the micro-scale influence of environmental factors on community structure and distribution of hyporheic macroinvertebrates, we chose 5 sites to investigate hyporheic macroinvertebrate and habitat characteristics in the upper reaches of Heishuitan River. Our results indicated that totally 29 species of macroinvertebrates were collected in study reach, and aquatic insect was the dominant group of macroinvertebrates. The density, biomass and richness of macro-invertebrate were decreased with bed depth. The composition and distribution of the hyporheic macroinvertebrates were determined by median diameter(D50) of sediments, vertical hydrological gradient(VHG) and vertical hydraulic conductivity(Kv), and the most important factor is D50. Besides that, the food sources and interactions of macroinvertebrates may also play an important role. All of these factors form a complex natural filter to control the composition and distribution of the hyporheic macroinvertebrates.(5) In this study, we analyzed the difference between hyporheic macroinvertebrate and benthic macroinvertebrate of 5 sites in upper reaches of Heishuitan River. The results indicated that there are some common dominant species and some unique species in these two communities. The analysis of Similarities show that these two communities are only little different(R=0.272,P<0.05). The results indicated that hyporheic zone is the refuge of macroinvertebrate during abrupt change term of environmental conditions, also is the source for benthic invertebrates to recolonization. |
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