Distribution of phytoplankton in the Three-Gorge Reservoir during rainy and dry seasons

https://doi.org/10.1016/j.scitotenv.2006.03.001Get rights and content

Abstract

After damming of the Yangtze River, in order to explore the impacts of the Three-Gorge Dam (TGD) on the aquatic ecosystem, phytoplankton composition, abundance and biomass spatial distribution were studied in the Three-Gorge Reservoir (TGR), and the closest upstream anabranch Xiangxi River, which is 38 km away from the Three-Gorge Dam (TGD) during August (rainy season) 2004 and April (dry season) 2005. In surveys, 6 transects (2 downstream and 4 cross-stream) and 25 stations have been investigated and 314 samples were collected from the surface to the river bed with water samplers. In TGR, 63 taxa and 60 taxa were identified in the rainy and dry seasons, respectively. In the Xiangxi River, 39 taxa were observed in the rainy and dry seasons. Algal blooms occurred in the Xiangxi River and at the influx region of the Yangtze and Xiangxi in both seasons, but had not occurred prior to damming. In the rainy season, the dominant species was Chroomonas acuta with 1.84 × 107 cells l 1, and in the dry season the dominant species were Asterionella formosa and Cryptomonas ovata with 1.34 × 107 cells l 1 and 1.79 × 106 cells·l 1, respectively. In the main channel of TGR, there were no significant correlations between phytoplankton abundance and the concentrations of the main soluble nutrients. In the Xiangxi River, significant negative correlations were observed between phytoplankton abundance and nitrate (Spearman, p < 0.01, n = 21), phosphate (Spearman, p < 0.05, n = 21) and silicate (Spearman, p < 0.01, n = 21) in the rainy season, and similar correlations were also observed with nitrate (Spearman, p < 0.05, n = 28) and silicate (Spearman, p < 0.01, n = 28), but not with phosphate in the dry season. Since the damming of the Yangtze River, eutrophication in the anabranch within the backwater has occurred and become severe, and the frequency of algal bloom within TGR and anabranches is expected to increase.

Introduction

Large dams have been built in more than 150 countries and most of the 45,000 dams are in the developing countries. The Three-Gorge Dam (TGD), in China, is the world's largest dam, measuring 2335 m long and 185 m high, and the reservoir created by it will have an area of 1080 km2 in 2009 (Wu et al., 2003). The construction of the Three-Gorge Project (TGP) can be divided into three stages: preparation and the first stage (1993–1997), the second stage (1998–2003) and the third stage (2004–2009). As the largest water conservancy in the world, TGP will have a significant impact on biodiversity and ecosystems in the region. Some large-scale dams can even influence the bioactive elements of the geochemical cycle at the global scale (Humborg et al., 1997, Jickells, 1998, Friedl and Wüest, 2002, Ragueneau et al., 2002).

Phytoplankton is sensitive aquatic organisms, and their composition and abundance can reflect the eutrophic situation in a short time (Büsing, 1998, Díaz-Pardo et al., 1998). Thus, phytoplankton is often used to estimate the impact of large-scale dams on the aquatic ecosystem (Humborg et al., 1997, Lancelot et al., 2002).

Although the Yangtze River is the third longest river in the world, there were very few studies on phytoplankton in the Yangtze River before damming by the TGD (Boruzkij et al., 1959, Wang and Liang, 1991). This present paper aims to study: (1) the phytoplankton composition and abundance in TGR and the trend of eutrophication in this region after damming; (2) the responses of the phytoplankton to the changes of the hydrological conditions within TGR in the rainy and dry seasons.

Section snippets

Area description

The Changjiang (Yangtze) River is 6300 km long, has a catchment area of 1.96 × 106 km2 (Chen and Yu, 2001) and an annual water discharge of 9.8 × 1011 m3 (Beardsley et al., 1985). The Three-Gorge Reservoir (TGR), sited at 29°16′–31°25′N, 106°–111°10′E, has a catchment of the typical gorge type and its normal water level is currently maintained at 135 m. Mountains around the reservoir are made of limekiln, granite and shale.

Hydrologic conditions of the Yangtze River have changed markedly since

Species richness and surface abundance of phytoplankton

In the mainstream of TGR in August 2004 (rainy season), 46 genera (63 taxa) were recorded, belonging to 25 families. In April 2005 (dry season), the number was 41 genera (60), belonging to 28 families (Table 2). Taxa composed diatom, chlorophyta, cyanophyta, cryptophyta, euglenophyta and pyrrophyta; chrysophyta were not recorded. Diatoms were common in TGR. In the rainy and dry seasons, diatoms accounted for 46% and 53% of the total taxa, respectively. Numbers of cyanophyta taxa were increased

Discussions

Three-Gorge Project (TGP), the largest water conservancy project ever built, has greatly changed the original Yangtze River ecosystem (Wu et al., 2003), and the impacts of TGD on the environment and water ecosystem have become focuses of world attention. In the present study, we have investigated the dynamics of phytoplankton community structure and abundance in TGR and its anabranch, the Xiangxi River. Since erection of the TGR, algal blooms have been detected in the Xiangxi River and the

Acknowledgements

This study has been supported by National Natural Science Foundation of China (No. 30490232) and the Chinese Academy of Science Project (KSCX-2-1-10).

The algal density was provided by The Ecological and Environment Monitoring Information Center of TGP. Some hydrological data were provided by The Hydrological Information Center of the Chinese Hydrological Department.

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