Distribution patterns of macroinvertebrate communities in a Chinese floodgate-regulated river and their relationships with river longitudinal connectivity
Introduction
In China, floodgates are usually built in rivers located in regions that experience water shortage principally because of navigation and irrigation needs. In floodgate-regulated rivers, the river sections between floodgates maintain higher water levels, which do not fundamentally change in comparison to the previous natural conditions. The construction of floodgates results in a lack of river longitudinal connectivity, a fragmented habitat, especially during dry seasons, a potential decline in the value of ecosystem services and a loss of biodiversity (Branco et al., 2012; Monaghan et al., 2005; Wohl et al., 2016). At the river scale, the hydrological connectivity is known to influence biogeochemical fluxes, food web structure and biodiversity patterns of macroinvertebrate, macrophyte and fish assemblages (Aarts et al., 2004; Lasne et al., 2007; Paillex et al., 2009; Robinson et al., 2004). Restoring hydrological connectivity at different scales is necessary for species conservation and restoration of ecological processes and is currently a worldwide concern (Besacier-Monbertrand et al., 2014). Studies have shown that macroinvertebrates have high species richness in dynamically connected waterbodies, and the α-diversity of macroinvertebrates can achieve a maximum value at a moderate level of hydrological connectivity; in contrast, the β-diversity seems to decline with the degree of connectivity (Castella et al., 1991; Petts and Greenwood, 1985; Robinson et al., 2004). These observations are in accordance with the “intermediate disturbance hypothesis,” which states that higher species diversity is expected in waterbodies that connect with intermediate frequency (Amoros et al., 1999; Connell, 1978; Petts and Greenwood, 1985). Moreover, increasing hydrological connectivity levels could promote species diversity and enhance the introduction of alien species after restoration measures (Gallardo et al., 2008; Paillex et al., 2009).
In China, the Shaying River basin is recognized as experiencing serious flood events that frequently occur during the wet season. Since 1949, many floodgates have been built in the Shaying River basin to enable the full utilization of water resources and flood control. To date, the Shaying River is thus highly regulated. The river was historically abundant in fishery resources, but aquatic organisms, especially fish, almost vanished in most reaches of the river during a period of serious water pollution (Shu et al., 2014). Since 1994, with the implementation of water pollution prevention in the Huai River basin, the water quality of the Shaying River has improved considerably (Chen and Shen, 2004). In recent years, monitoring results have shown that the ecological conditions have also improved, demonstrating the effectiveness of the pollution control measures (Shu et al., 2014).
The relationships between macroinvertebrate communities and river connectivity at different landscape scales has been emphasized and confirmed in many studies (Castella et al., 1991; Dou et al., 2016; Lasne et al., 2007; Leigh and Sheldon, 2009; Saltveit et al., 1994), but these cases were mainly limited in exploring the relationships between lateral connectivity and macroinvertebrate assemblages. Studying the effects of river fragmentation caused by hydraulic projects and subsequent environmental changes on aquatic communities and then developing management and conservation strategies are very important (Cellot et al., 1994). In this study, the Li River and the middle and lower reaches of the Shaying River were selected to investigate the effects of floodgates on macroinvertebrate communities by comparing the communities of the two contrasting rivers and exploring their relationships with longitudinal connectivity. This study was based on the following hypotheses: 1) there will be differences in biotic structure and water quality between regulated and more natural river reaches, 2) the longitudinal connectivity can be affected by floodgates in river systems, and 3) there will be a strong relationship between the distribution patterns of macroinvertebrate communities and longitudinal connectivity.
Section snippets
Study area
The Shaying River basin (112°45′-113°15′E, 34°20′-34°34′N) is located at the transitional zone between the warm temperate zone and the subtropical zone, with a warm temperate semi-humid continental climate and distinct four seasons (Fig. 1). Northerly winds prevail in winter, while southwest winds prevail in summer. The mean annual temperature is 14.5–15.0 °C and varies seasonally, with an extreme maximum temperature of 41.5 °C and an extreme minimum temperature of −22.8 °C. The rainfall in the
Physicochemical characteristics of the reaches in both rivers
During April and September, reaches 1–5 had lower values of CODMn and CODCr than reaches 6–10. Additionally, reaches 6–7 had higher BOD5 values than the other reaches during both months. The values of AN in reaches 1–4 were higher than those in reaches 5–10 in April, but in September, the values in reaches 3 and 9–10 were relatively higher than those in other reaches. The TP values in reaches 1–5 were lower than those in reaches 6–10 in both months (Table 1 and Table 2). In both months, reach 1
Comparison of macroinvertebrate communities in both rivers
Although the Li Shaying rivers had similar ratios of molluscs and scrapers, their species compositions were significantly different, and this difference was related to the abundance changes of the dominant species. The different communities in both rivers were mainly reflected in the differences in the percentages of aquatic insects, crustaceans and the dominance and sub-dominance of different taxa; additionally, these results were verified by statistical analyses, such as ANOSIM and SIMPER.
Competing interest statement
The authors declare that no conflicts of interest exist in the submission of this manuscript, and the manuscript has been approved for publication by all authors. On behalf of my co-authors, I declare that the work described was original research that has not been published previously, and it is not under consideration for publication elsewhere, in whole or in part. All listed authors have approved the manuscript.
Author contributions
Juxiang Hu and Cuizheng Wei conceived and designed the experiments. Shiyun Chi performed the experiments, analyzed the data and wrote the manuscript. Jun Hu and Jinxiu Zheng provided advice. Ming Li improved the English.
Acknowledgements
This study was funded by the National Natural Science Foundation of China (Nos. 51409178 and 51509169) and Special Funds for Public Industry Research Projects of the National Ministry of Water Resources (No. 201501030). The authors thank Qiang Shen, Aiming Zhu, and Shaobo Gao for field assistance.
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