Regulation of Vegetation and Evapotranspiration by Water Level Fluctuation in Shallow Lakes

Qiang Liu,Liqiao Liang,Chunhui Li,Xiaomin Yuan,Shuzhen Li,Xuan Wang,Sirui Yan,Miao Li

doi:10.3390/w13192651

Abstract

Water level fluctuations play a critical role in regulating vegetation distribution, composition, cover and richness, which ultimately affect evapotranspiration. In this study, we first explore water level fluctuations and associated impacts on vegetation, after which we assess evapotranspiration (ET) under different water levels. The normalized difference vegetation index (NDVI) was used to estimate the fractional vegetation cover (Fv), while topography- and vegetation-based surface-energy partitioning algorithms (TVET model) and potential evaporation (Ev) were used to calculate ET and water evaporation (Ep). Results show that: (1) water levels were dramatically affected by the combined effect of ecological water transfer and climate change and exhibited significant decreasing trends with a slope of −0.011 m a−2; and (2) as predicted, there was a correlation between water level fluctuation at an annual scale with Phragmites australis (P. australis) cover and open-water area. Water levels also had a controlling effect on Fv values, an increase in annual water levels first increasing and then decreasing Fv. However, a negative correlation was found between Fv values and water levels during initial plant growth stages. (iii) ET, which varied under different water levels at an annual scale, showed different partition into transpiration from P. australis and evaporation from open-water area and soil with alterations between vegetation and open water. All findings indicated that water level fluctuations controlled biological and ecological processes, and their structural and functional characteristics. This study consequently recommends that specifically-focused ecological water regulations (e.g., duration, timing, frequency) should be enacted to maintain the integrity of wetland ecosystems for wetland restoration.

Highlights

Increases in the frequency and magnitude of climate extremes [1,2], over the past several decades, in combination with anthropogenic activities have dramatically altered wetland hydrological regimes [3], leading to the widespread degradation of aquatic ecosystems at a global scale [4]
Alterations in hydrological regimes can result in a series of changes in physical, chemical and biological environments [5], as well as affecting the biota and ecosystems of shallow lakes [6,7]
Water level fluctuations play a critical role in maintaining the ecosystem integrity of shallow lake systems

Summary

Introduction

Increases in the frequency and magnitude of climate extremes [1,2], over the past several decades, in combination with anthropogenic activities (e.g., water level changes from the reservoirs and dams throughout the world) have dramatically altered wetland hydrological regimes [3], leading to the widespread degradation of aquatic ecosystems at a global scale [4]. Understanding interactions between hydrological regimes, biota and ecosystem processes can help maintain the integrity of wetlands and aid in wetland restoration [6,7,8]. Under the influence of climatic change and anthropogenic activity, hydrological regimes have deviated from their natural processes [6]. Dams, which contribute to water security, energy supply and flood protection, have fragmented freshwater species habitats [10], leading to connective shifts between hydrological regimes, organic matter and nutrients (e.g., [7,11])

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Methods

Discussion

Conclusion