Xuehua Duan

Sediment pollution and its effect on fish through food chain in the Yangtze River

Abstract Suspended sediment adsorbs pollutants from flowing water in rivers and deposits onto the bed. However, the pollutants accumulated in the river bed sediment may affect the bio-community through food chain for a long period of time. To study the problem the concentration of heavy metals (Cr, Cd, Hg, Cu, Fe, Zn, Pb and As) in water, sediment, and fish/invertebrate were investigated in the middle and lower reaches of the Yangtze River during 2006-2007. The concentrations of heavy metals were 100-10,000 times higher in the sediment than in the water. Benthic invertebrates had relatively high concentrations of heavy metals in their tissues due to their proximity to contaminated sediments. Benthic invertivore fish had moderately high concentrations of heavy metals whereas phytoplanktivore fish, such as the silver carp, accumulated the lowest concentration of heavy metals. The concentrations of Cu, Zn, and Fe were higher than Hg, Pb, Cd, Cr, and As in the tissue samples. The concentration of heavy metals was lower in the river sediments than in the lake sediments. Conversely, the concentration of heavy metals was higher in river water than in lake water. While a pollution event into a water body is often transitory, the effects of the pollutants may be long-lived due to their tendency to be absorbed in the sediments and then released into the food chain. The heavy metals were concentrated in the following order: bottom material > demersal fish and benthic fauna > middle-lower layer fish > upper-middle layer fish > water.

Effect of streambed sediment on benthic ecology.

Abstract Benthic macroinvertebrates have been commonly used as indicator species for assessment of aquatic ecology. Streambed sediment, or substrate, plays an important role in habitat conditions for macroinvertebrate communities. Field investigations were done to study the benthic diversity and macroinvertebrate compositions in various stream substrata. Sampling sites with different bed sediment, latitude, and climate were selected along the Yangtze River, the Yellow River, the East River, and the Juma River, in China. The results show that benthic community structures found in different substrata clearly differ, while those found in substrata of similar composition and flow conditions but in different macroclimates are similar. The study, thus, demonstrates that the benthic macroinvertebrate community is mainly affected by substrate composition and flow conditions, but is generally unaffected by latitudinal position and macroclimate. Taxa richness of the macroinvertebrate community was found to be the highest on hydrophyte-covered cobbles, high on moss-covered bedrock, and low on clay beds and cobble beds devoid of plant biomass. Sandy beds are compact and unstable, thus, no benthic macroinvertebrates were found colonizing such substrata. Aquatic insects account for most of the macroinvertebrates collected in these rivers. Different insects dominate in different types of substrata: mainly EPT species (Ephemeroptera, Plecoptera, Trichoptera) in cobble, gravel, and moss-covered bedrock; and Chironomidae larvae in clay beds. The relation between the number of species in the samples and the size of the sampling area fits a power function of the species area. One square meter (1m 2 ) is suggested as the minimum sampling area. A substrate suitability index is proposed by integrating the suitability of sediment, periphyton, and benthic organic materials for macroinvertebrates. The biodiversity of macroinvertebrates increases linearly with the substrate suitability index. Benthic taxa richness increases linearly with the suitability index.

Effects of pollution on macroinvertebrates and water quality bio-assessment

Many large rivers in China have an inflow of contaminated water. Water pollution caused by urban sewage and agriculture, and occasionally pollution events from industries have become a significant stress on aquatic ecology. Pollution affects the biodiversity of the aquatic community and the species composition changes from natural species to tolerant species. The species composition of aquatic animals may reflect water pollution level. Extremely non-uniform distributions of functional feeding groups occurred as a result of high nutrient levels. A combination of chemical and biological methods constitutes the best approach for biological monitoring studies that measure water quality. Macroinvertebrates were used as bio-assessment indicator to determine the environmental quality of given water body. In this study, samples of water and macroinvertebrates were taken from several dozen sites in 14 rivers in China with different pollution levels, including the Yangtze, East, Weihe, Songhua, Yongding, and Panlong rivers. Macroinvertebrates were identified to genus or family level. Water samples were classified into different water quality grades according to the concentration of different substances. Five biological indices: taxa richness (S), density (D), total BMWQ score (t-BMWQ), average BMWQ score (a-BMWQ), and the family biotic index (FBI) were used for biological assessment of water quality. Analyzing macroinvertebrates’ occurrence in different water quality levels, taxa-specific indicators, which are defined as the taxa of macroinvertebrates that live in a certain water quality level but do not exist in other water quality levels were proposed for water quality bio-assessment. Leptophlebiidae, Siphlonuridae, Arctopsychidae, Perlidae, and Antocha sp. are the taxa-specific indicators for very good or good water quality; Chironomidae, Lymnaeidae, Tubifex sp., Limnodrilus sp., Limnoperna lacustris, Corbicula sp., Macrobrachium sp., Planorbidae, Glossiphoniidae, and Branchiura sp. are the taxa-specific indicators for very poor water quality; and Psychomyiidae and Hydroptilidae are the taxa-specific indicators for moderate water quality.

Restoration of an incised mountain stream using artificial step-pool system

A field experiment using an artificial step-pool system was conducted to restore the Diaoga River, a seriously incised mountain stream in Yunnan-Guizhou Plateau, southwest China. Twenty-four artificial steps, designed to mimic natural step forms, were constructed on three stretches of about 260 m length in the middle reach of the river. Channel topography, hydraulic features, aquatic habitats and stream ecology were monitored for 20 months. Following the construction of the artificial step-pool system, the stream bed development coefficient increased significantly. This indicates that actions helped to dissipate flow energy more effectively, enhancing the stability of the stream bed. The step-pools have effectively controlled the incision and stabilized the river morphology. In addition, they have created multiple habitats for different species and increased the habitat diversity. Improvement of the aquatic ecosystem is confirmed by increased density and taxa richness of benthic macro-invertebrates, which are used as an indicator species to evaluate stream ecology.

Effects of fluvial processes and human activities on stream macro-invertebrates

Benthic macro-invertebrates are vital components of river ecosystems. The effects of fluvial processes and human activities on the distribution of macro-invertebrates were studied through field investigations and experiment. Sixty-one sampling sites on 31 rivers in China were selected to investigate the structures of macro-invertebrate assemblages. The rivers, according to their fluvial conditions, are classified as streams with a stable channel bed, degrading channel bed, aggrading channel bed, and intensive bed load motion. The structures of macro-invertebrate fauna for the four types of rivers are very different. Stable rivers have a large number of individuals, abundant fauna, and high biodiversity; while the density and taxa richness for degrading rivers are small, and those for aggrading rivers are much less; whereas the ecology of rivers with intensive bed load motion are the worst. This paper proposes that streambed stability is the primary influential factor shaping the structure of benthic macro-invertebrate communities. Organic pollution can obviously result in the decrease of biodiversity, in the simplification of macro-invertebrate structures, and in the distortion of functional feeding group composition. In a river with high total nitrogen content, the relative abundance of collector-gatherers is high, and that of collector-filterers, scrapers, shredders, and predators are low. Scrapers, shredders, and predators disappear in severely polluted rivers. The isolation of aquatic habitat results in a distinct decrease of individual numbers and taxa richness. This result demonstrates that the connectivity of aquatic habitat significantly affects macro-invertebrate assemblages. A practical method to calculate a Habitat Suitability Index (HSI) is proposed, integrating the effects of the primary physical (including biotic and abiotic) and chemical factors. The biodiversity and taxa richness increase non-linearly with HSI.

Experimental Study on the Effect of Habitat Isolation on River Ecology

Field investigations and an experiment were conducted in the Juma River, in the suburbs of Beijing, to study the effect of habitat fragmentation on river ecology using benthic macroinvertebrates as indicator species. Three experimental plots were isolated from a relatively undisturbed stream habitat with sheet iron. Benthic assemblages were measured by sampling periodically. The results indicate that the abundance, taxa richness and bio-diversity of invertebrates significantly decrease in the experimental plots owing to the habitat isolation. The smaller the experimental habitat plot, the more significantly these biotic indices decrease. Comparison of the benthic communities shows that the relative abundances of Ephemeroptera and Diptera are reduced significantly in the isolated plots, and that of Odonata and Lamellibranchia increase significantly. It is also found that the benthic communities need time to stabilize after isolation, and then present apparent variation with time. There is a relatively high degree of taxa turnover between isolated plots and the non-isolated reach, which can be attributed to the flight and dispersal of many aquatic insects in their adult stages. However, the benthic communities in isolated plots are not nested subsets of that in the natural non-isolated stream.

Ecological Impacts of Seabuckthorn in the Pisha Sandstone Area

There is an area of more than 11,000 km2 in northwest China which is covered by Pisha Sandstone, a kind of loosely bonded sandstone which was formed during the Tertiary period. The sandstone is hard when it is dry and easily changes into sand when wet. The area has a very high erosion rate (over 20,000 t/km2·yr) and very poor vegetation. Seabuckthorn (Hippophae rhamnoides Linn) has been successfully used to reforest gullies and control erosion in the area. Field investigations have been carried out in the Xizhao gully to study the effects of the species on sediment trapping and ecological improvement. It is found that the seabuckthorn mutualizes with Clinelymus dahurcus Turcz, and the two species form dense double-layer vegetation with well developed middle and understory plant communities. The vegetation cover in the gullies reaches 95%. The forest was developed in the late 1990s (first introduced in 1995), with a sediment trapping efficiency of more than 90%. Rainstorm water has also been stored in the gully within the trapped sediment. The water content in the vegetated gully is about twice as high as the uncontrolled plot. The understory community of the seabuckthorn vegetation is much better than in areas forested with poplar or willow. The taxa richness and the thickness-coverage of the sublayer vegetation in the seabuckthorn area are about twice as high as in the latter two.