Abstract
Long River is a small tributary typical of the Three Gorges Reservoir. In order to clarify the influence of hydro-meteorological factors and human regulation of the reservoir water level on the water environment, we monitored water environment parameters at six sites along Long River for three years, and were able to assess the degree to which variation in the water environment was affected from the micro-scale to macro-scale processes. We found that the water environment parameters have obvious seasonal variation and spatial distribution patterns. From upstream to the estuary, the influence of the backwater was gradually enhanced, whereas the influence of inflow gradually weakened. The distance coefficient between the samples in the backwater area and control sites in the upstream and the Yangtze River had a significant longitudinal gradient pattern (ANOVA, p < 0.05). Through redundancy analysis (RDA) forward selection, we found that cumulative precipitation, water level, cumulative net radiation, daily average temperature, daily net radiation, and daily precipitation all had significant influences on the water environment of the Long River (global permutation test, p < 0.05). The perennial backwater area was mostly affected by water level fluctuations (explaining 39.9% of data variation), whereas the fluctuation backwater area and the upstream inflow area were most affected by cumulative precipitation (explaining 42.9% and 44.0% of data variation, respectively). On the macroscale, the contribution rate of monthly change to the variation of water environment variables reached 54.9%, and the contribution rate of geographical change to the variation of water environment variables was only 7.2%, indicating that the water environment of Long River was mainly affected by exogenous input factors driven by the monsoon climate. Furthermore, we showed that the spatial interpolation method combined with the distance coefficient can easily and efficiently describe the complicated dynamic influences of the upstream inflow and the Yangtze River backwater on the water environment in the Long River bay. The conclusions are helpful in explaining the driving mechanisms of the water environment in the tributaries of the Three Gorges Reservoir, which can provide reference for water environmental protection and management in the Three Gorges Reservoir.
Highlights
The operation of the Three Gorges Project (TGR) has produced tremendous social and economic benefits [1,2]
The major water environment parameters followed distinct distribution patterns, in which TN, TP, and EC gradually increased from the backwater end to Long River estuary (LRE), while Chl.a and CODMn occur at higher values in the midstream
Among parts of Long River (LR), the perennial backwater area was mostly affected by fluctuating of water level (WL), while the fluctuation backwater area and the upstream inflow area were mostly affected by rainfall
Summary
The operation of the Three Gorges Project (TGR) has produced tremendous social and economic benefits [1,2]. The construction of the dam has had a number of ecological effects, changing the water area of TGR from the original natural river to a canyon-type reservoir. The natural eco-hydrological rhythm of the river has been changed as well. Humans manually control the water level, which has become an important factor affecting the water environment of the TGR [3]. The impounding of the reservoir itself has had significant negative effects on the water environment. The most prominent problem is the deterioration of water quality in the tributaries and the bay, as well as consequent eutrophication and water blooms [1,4], all of which have attracted widespread concern
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