The influence of cascade reservoir construction on sediment biogenic substance cycle in Lancang River from the perspective of phosphorus fractions

doi:10.1016/j.ecoleng.2020.106051

Ecological Engineering

Volume 158, 1 December 2020, 106051

https://doi.org/10.1016/j.ecoleng.2020.106051 Get rights and content

Highlights

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The upstream XW Reservoir sediment showed low BAP and high inert P content.
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The downstream NZD Reservoir sediment showed high BAP and low inert P content.
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P in the sediment of the cascade reservoirs has totally different control factors.
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The sediment trapped in upstream reservoir highlights the regional sediment role.

Abstract

The impact of the development of cascade reservoirs on the biogenic substance cycle is an important scientific issue for the future sustainable development of the Lancang-Mekong River. The vertical distribution of phosphorus (P) fractions of Xiaowan (XW) and Nuozhadu (NZD) Reservoir sediment in Lancang River were studied to better understand the environment influence of cascade deep reservoir for the first time. The results showed that the P concentration in the overlying water and the P content in sediment of the upstream XW Reservoir was higher than that of the downstream NZD Reservoir, but the P bio-availability (BAP) in sediment were lower than that of the NZD Reservoir. The sediment of the XW Reservoir showed low BAP content and high inert P content. In the contrast, the sediment of the NZD Reservoir showed high BAP content and low inert P content. The P in the sediment of the two reservoirs has totally different control factors, which indicates that the biogenic substance cycles mechanisms of two reservoirs are significantly different under the influence of the cascade reservoir. The less sediment source of downstream reservoir highlights the role of regional sediment in turn. The biogenic substance of the regional sediment plays an important role in the downstream reservoir sediment.

Introduction

The Earth system is changing dramatically as the result of anthropologic activities. It is reported that rivers play an important role in Earth system and most rivers around the world are under the regulation of 45,000 large dams since 1930s.(Dams, 2000). Dams can promote human economic development by flood control, power generation, water supply, etc. Nevertheless impacts of dams are generally well known, include the following changes: net water balance (Vösösmarty et al., 1997), flow regime (Batalla et al., 2004; Mcclelland et al., 2004), water level (Lu and Siew, 2006; Wang et al., 2013), sediment transport disruption (Topping et al., 2000; Walling and Fang, 2003; Willis and Griggs, 2003), and channel morphology (Xu, 1996; Bondar and Blendea, 1997; Brandt, 2000; Villanueva, 2003). The impact of dam on river hydrology has received particular attention while the impact of cascade reservoir construction on biogenic substance cycle is relatively minor.

Phosphorus (P) is a major nutrient in surface water environment and has been considered as the limiting factor for primary production in aquatic ecosystems (Elser et al., 2007; Conley et al., 2009). Over the past many years, there are increasingly numbers of anthropologic activities and this makes the supply rate of P to water bodies been profoundly influenced, and this has resulted in eutrophication. Excessive P enrichment in aquatic ecosystems frequently leads to the appearance of water quality deterioration, harmful phytoplankton blooms, and other serious environmental and human health problems (Smith et al., 1999; Smith and Schindler, 2009).

Sediment, as a fundamental part of surface water system, is the sink or source of biogenic substance (such as nitrogen and phosphorus) in aquatic environments (Chon et al., 2012). Once the biogenic substance enters into water, it tends to transfer to sediment through biochemical and physical processes (Carpenter, 2005; Zhu et al., 2013). However, due to frequent hydrodynamic disturbances and the physical and chemical factor changes, P accumulated in the sediment could be released into the overlying water (Zhu et al., 2013), thus this will cause the water pollution or eutrophication. The internal P loading has been receiving more and more attention in recently (Smolders et al., 2006).

There are many P species in sediment, such as P binding to aluminum oxides, interior Fe oxides and calcium, some of which can be easily bio-available and some are inert (Zhou et al., 2001). Considering P fractions rather than total phosphorus (TP) will have a great contribution in evaluating the trophic conditions of freshwater (Wang et al., 2006; Zhu et al., 2012). Moreover, P can be divided into various species with different methods for certain purposes. The chemical sequential extraction method (Psenner et al., 1988), which modified into four species including loosely bound P (ex-P), reductant soluble P (BD-P), metal oxide bound P (NaOH-P) and calcium bound P (HCl-P) (Hupfer et al., 1995), is widely used to identify the P contribution to surface water system eutrophication (Fytianos and Kotzakioti, 2005; Gao et al., 2005; Zhang et al., 2013).

The Lancang River is the upper Mekong section in southwest of China. In the early 1980s, there have been planned to construct fourteen cascade hydroelectric dams and some are completed or under construction till now. Previous studies focused the composition, biomass and biological integrity of phytoplankton (Li et al., 2013), changes in runoff and sediment loads (Zhai et al., 2016), impacts of climate change and human activities on the flow regime (Han et al., 2019) and longitudinal variability of sediment (Guo et al., 2020). It have been reported that more than 80% sediments are trapped for nearly half of the reservoirs in the world (Vörösmarty et al., 2003), and meanwhile sediments also play an important role in the biogenic substance geochemistry cycle. Generally, the sediment vertical P distribution is the history result of P sedimentation as well as of many transformation processes, such as biological uptake, adsorption, desorption, release, diffusion, precipitation, mineralization, etc. However few studies have focused on influence of cascade reservoir construction on sediment biogenic substance cycle. Considering the importance of P in the aquatic ecosystem, the main aim of this study was to (1) study the vertical P distribution sedimentary characteristics in the Lancang River, (2) analysis vertical distribution of P fractions in the deep cascade reservoirs, and (3) study relationship between P fractions and related metals under the influence of sediment trapped in the cascade reservoir.

Section snippets

Study area

The Mekong River, as the largest international river in Asia, passes through six countries (China, Myanmar, Laos, Thailand, Cambodia and Vietnam) and seven climate zones. It originates from Guyong-Pudigao creek and discharges into the South China Sea. The upstream of Mekong River, called Lancang River, flows through Qinghai Province, Tibet Autonomous Region, and the Yunnan Province (Li et al., 2012). The large land slope and huge runoff have brought abundant hydropower resources in Yunnan

Physicochemical characteristics of the overlying water

The physicochemical characteristics distribution of the overlying water in the two reservoirs are shown in Fig. 2 TP and SRP have similar spatial distribution characteristics. The concentration of TP and SRP in XW Reservoir were higher than that in the NZD Reservoir with average concentrations of 0.034 ± 0.019 and 0.020 ± 0.008 mg/L, 0.018 ± 0.013 and 0.007 ± 0.003 mg/L, respectively. Most of the water TP concentrations in the reservoirs were lower than standard three (III) of the Chinese

Conclusions

This study is the first to investigate the vertical profiles of P fractions in the sediment in the XW and NZD Reservoir, which are deep reservoirs in Lancang River. The impact of the development of cascade reservoirs on the biogenic substance cycle is an important scientific issue for the future sustainable development of the Lancang-Mekong River. With the continuous economic development in recent years, the emitted P pollutants have gradually increased, so the TP content in the XW and NZD

Author contributions

Mu Zheng: Writing - Original Draft, Formal analysis. Yuchun Wang: Conceptualization, Methodology. Yao Cheng: Writing - Original Draft, Conceptualization. Ji Lu, Jinkun Wu, Chenchen Chen, Yu Li, Fengxia Zhao, Mingming Hu and Yufei Bao: Investigation and Formal analysis.

Declaration of Competing Interest

None.

Acknowledgments

This research was financially supported by the National Natural Science Foundation of China (U1802241, 91647208, 51509066, 11371117 and 51909053), Research Fund of the State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research (SKL2018ZY04), University Science and Technology Research Project of Hebei, China (ZD2019005) and Graduate Innovation Foundation of Hebei Province (CXZZBS2020152).

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Citation Excerpt :
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The influence of cascade reservoir construction on sediment biogenic substance cycle in Lancang River from the perspective of phosphorus fractions

Highlights

Abstract

Introduction

Section snippets

Study area

Physicochemical characteristics of the overlying water

Conclusions

Author contributions

Declaration of Competing Interest

Acknowledgments

Int. J. Sediment Res.

Mar. Pollut. Bull.

J. Hydrol.

Catena

Sci. Total Environ.

Chemosphere

Ecol. Eng.

Water Res.

Water Res.

Water Sci. Technol.

J. Hydrol.

J. Hydrol.

Water Res.

Sci. Total Environ.

Chemosphere

For. Ecol. Manag.

Ecol. Eng.

Chemosphere

Ecol. Eng.

Water Res.

Water Res.

Procedia Environ. Sci.

Trends Ecol. Evol.

Environ. Pollut.

Sci. Total Environ.

Glob. Planet. Chang.

Glob. Planet. Chang.

J. Great Lakes Res.

Colloids Surf. A Physicochem. Eng. Asp.

Int. J. Sediment Res.

Sci. Total Environ.

Environ. Pollut.

Agric. Water Manag.