Wanxiang Jiang

Impacts of cascade run-of-river dams on benthic diatoms in the Xiangxi River, China

The ecological effects of small run-of-river dams on aquatic ecosystems are poorly understood, especially on downstream benthic algal communities. We examined impacts of such dams on the benthic diatom community at a regional scale in the Xiangxi River, China. A total of 90 sites were visited, which were divided into five habitats (H1–H5) according to impact extent of each dam. Using partial least squares (PLS) modeling, we developed two predictive models (diatom species richness and total diatom density) based on environmental variables of an unregulated habitat (H1). These models were then used to predict species richness and total densities at impacted habitats (H2–H5) and residuals, i.e. the differences between observed and predicted values, were used to evaluate impact strength of flow regulation. Significant impacts of flow regulation on diatom species richness were detected at three impacted habitats (H3–H5), where observed species richness were significantly higher—70.6, 63.9 and 46.6%, respectively—than predicted values. Then, possible mechanisms for observed impacts were discussed. Further research is necessary to address the potential negative impacts of cascade run-of-river dams on other aquatic organisms in different seasons, and to explore more appropriate mechanisms for such impacts, which may lead to sustainable management strategies and help to determine the optimal ecological water requirement for the Xiangxi River.

Temporal impacts of a small hydropower plant on benthic algal community

To explore the temporal impacts of a small hydropower plant (SHP) on benthic algal community, monthly samples from November 2005 to June 2006 were taken in a reach of the Xiangxi River, China. During the study period, a total of 116 taxa were recorded and diatoms were the most abundant group, accounting for 60.42 % of total taxa. Our study showed that operation of the SHP had significant impacts on river systems: (1) distinct physicochemical conditions between control and impaired sites; (2) remarkable increase of chlorophyll-a concentration, total algal densities, and decrease of Shannon-Wiener diversity index, evenness at impaired sites during the dry period (e. g., November, December, January, February and March); (3) profound impacts on overall benthic algal community in dry periods (e. g., November, December, January, February, March, May and June). However, the rainfall or the periodical connectivity of channel appeared to decrease the impacts of the SHP on the benthic algal community (e. g., April and May). We suggest that a minimal discharge should be preserved during the dry period and a basal flow kept for the maintenance of fluvial connectivity of the river water, which would provide more sustainability to the benthic algal community as well as other aquatic organisms.

Macroinvertebrate relationships with water temperature and water flow in subtropical monsoon streams of Central China: implications for climate change

Effects of global climate change on freshwaters are still poorly known, particularly in systems where they interact with other environmental variables. Using data from a subtropical monsoon stream in Central China, we assessed the relationships between a macroinvertebrate community and variations in temperature and water flow. We then used these data to assess potential changes under different climate change scenarios. Winter macroinvertebrate abundance and richness decreased with increasing water temperature during the last six years. However, effects of climate on biotic metrics in summer were less clear. Partially constrained ordination revealed that variations in community composition could not be explained clearly by individual climatic variables, but total dissolved solids and total nitrogen were more important. Over the period 1978-2008, average annual air temperature in the study area increased by 0.6 degrees C, whereas total annual water flow declined. Projections suggest that further winter warming of 1 degrees C could decrease the macroinvertebrate abundance and richness by 11.1 % and 6.0 %, respectively. One unit increase in the smoothed sea surface temperature (SSST) during winter could increase the abundance and richness by 38.2 % and 21.1 %, respectively. With further global change effects likely in future, our data highlight the importance of the conservation of mountainous streams in the upper Yangtze River.

Assessing impact of acid mine drainage on benthic macroinvertebrates: can functional diversity metrics be used as indicators?

While taxonomic metrics are common indicators for assessing impact of acid mine drainage (AMD) on macroinvertebrates, functional diversity metrics are scarcely used. We tested the hypothesis that functional diversity metrics could be used as indicators for assessing impact of AMD on macroinvertebrates. Differences in both taxonomic metrics and functional diversity metrics were examined among sites with varying levels of AMD impact. AMD led to loss of sensitive functional groups and resulted in low functional diversity in the impacted sites. Functional richness, functional Shannons index and functional Brillouins index were significantly correlated with all key AMD parameters. Compared to taxonomic metrics, functional diversity metrics had higher correlations with most key AMD parameters. Functional diversity metrics were more informative than taxonomic metrics for assessing impact of AMD on macroinvertebrates since they were more effective at indicating mild or moderate AMD pollution. Functional Shannons index and functional Brillouins index were the most precise metrics.

Multi-scale temporal dynamics of epilithic algal assemblages: evidence from a Chinese subtropical mountain river network

Research on multi-scale temporal dynamics of lotic algal assemblages remains scarce. In this study, we analyzed epilithic algae sampled monthly from a Chinese subtropical mountain river network from 2004 to 2007, by using a multivariate time series modeling approach. We hypothesized that (1) multi-scale temporal dynamics exist within algal communities; (2) physical and chemical conditions drive algal temporal dynamics; and (3) tributary sites differ in algal temporal changes. This study revealed 2–4 site-specific algal temporal dynamics, contributed by 23–45% component taxa. Among the time-related taxa, percentages of high profile guild taxa were higher than both the low profile and the motile guild taxa. Several algal temporal dynamics were found to be driven by water temperature, conductivity, or current velocity, within which influences of conductivity at two sites resulted in directional changes in algal communities. Furthermore, tributary sites differed in algal temporal changes when compared to the two mainstream sites. Our findings imply that natural fluctuations and agricultural disturbance together shaped algal temporal dynamics in the studied river network. In conclusion, for accurately tracking algal temporal dynamics, we recommend that long-term and high-frequency biomonitoring protocols are developed. Moreover, both the mainstream and tributary sites should be monitored simultaneously.

Inter-annual patterns in the stability and persistence of stream macroinvertebrate communities: relationship with water physicochemical parameters

The relationships between temporal patterns of macroinvertebrate community and water physicochemical parameters were investigated in the Xiangxi River, which is the largest tributary to the Three Gorges Reservoir (TGR) in Hubei province, China. The construction of the TGR has strongly impacted the Xiangxi River watershed, but inter-annual patterns in stream macroinvertebrate communities have not been examined. We sampled water and macroinvertebrates monthly from 2004 to 2006. We assessed the persistence (similarity between years of species assemblage) and stability (similarity between years with respect to relative abundance of species in the community) of the macroinvertebrate community by the Bray–Curtis distance. The relationship between changes in water physicochemical conditions and changes in community structure were assessed with linear regression. The results showed that both the physical and chemical conditions of the water differed significantly among years. Similarly, the macroinvertebrate community structure and composition were significantly different among years. The compositional persistence was positively and significantly related to the physical condition, supporting the Habitat Templet Theory and indicating the importance of physical habitat protection. This study provides information for environmental assessment, which can be used to develop sustainable management strategies.

Identifying community thresholds for lotic benthic diatoms in response to human disturbance

Although human disturbance indirectly influences lotic assemblages through modifying physical and chemical conditions, identifying thresholds of human disturbance would provide direct evidence for preventing anthropogenic degradation of biological conditions. In the present study, we used data obtained from tributaries of the Three Gorges Reservoir in China to detect effects of human disturbance on streams and to identify disturbance thresholds for benthic diatoms. Diatom species composition was significantly affected by three in-stream stressors including TP, TN and pH. Diatoms were also influenced by watershed % farmland and natural environmental variables. Considering three in-stream stressors, TP was positively influenced by % farmland and % impervious surface area (ISA). In contrast, TN and pH were principally affected by natural environmental variables. Among measured natural environmental variables, average annual air temperature, average annual precipitation, and topsoil % CaCO3, % gravel, and total exchangeable bases had significant effects on study streams. When effects of natural variables were accounted for, substantial compositional changes in diatoms occurred when farmland or ISA land use exceeded 25% or 0.3%, respectively. Our study demonstrated the rationale for identifying thresholds of human disturbance for lotic assemblages and addressed the importance of accounting for effects of natural factors for accurate disturbance thresholds.