The effects of the reverse seasonal flooding on soil texture within the hydro-fluctuation belt in the Three Gorges reservoir, China

Abstract

Purpose The formation of the large hydro-fluctuation belt at the altitude of 145-175 m, following the construction of the Three Gorges Dam, developed from the terrestrial system in the Three Gorges reservoir. This research mainly concerned the effects of the resultant reverse seasonal flooding on soil texture. Materials and methods Four field experimental plots were designed with sample belts and quadrats at the head, middle, and tail sections of the reservoir area. Stratified soil samples were collected, followed by analysis of soil structure and soil grain size of the collected samples. Results and discussion The reverse seasonal flooding significantly changes texture and nutrient of riparian soil. The percentages of silt and clay formations were greatest at the lower hydro-fluctuation belt, followed by the middle and upper hydro-fluctuation belt, respectively. The percentage of silt and clay particles at 150 m was greater than that of 170 m by 18.12%. Conversely, the percentage of sand particles at the upper hydro-fluctuation belt ranked the highest, and followed by the middle and lower hydro-fluctuation belt, respectively. The percentage of sand particles at 170 m was higher than that at 150 m by 19.72%. Soil texture type changed with increasing altitude gradient, from silt loam, loam, then to sandy loam. Reverse seasonal flooding also promotes silt and clay permeation, and deposition from surface soil to subsurface soil, increasing homogeneity in grain structure between soil layers. This change in soil texture is associated with changes in soil nutrients. The content of soil organic matter, total nitrogen, total phosphorus, and total potassium varied significantly among soil texture types, with loam having the highest soil nutrient concentration and sandy loam having the lowest. Conclusions The reverse seasonal flooding promotes the deposition of clay and silt within the hydro-fluctuation belt, inducing the total texture change of loam to silt loam. However, the structures and attributes of soil texture varied along the altitude gradient, as the exposed and submersed season and time span of riparian soil changed with the increase of altitude.

Branches and Leaves Growth Patterns in Myricaria laxiflora Remnant Populations Are Affected by Human-altered Water Level Fluctuations

“…Responses in branch and leaf functional traits to the water level gradient Water level uctuations are important ecological processes that in uence the ecosystem in water leveluctuating regions (Matthew et al, 2019). Under the in uence of water level uctuations, the ecological environment at the water level-uctuating region exhibits clear spatial heterogeneity, where environmental factors including emergence period, emergence time and soil water content are signi cantly different across the water level conditions (Wang et al, 2018). Caused by the environmental heterogeneity, branch and leaf growth traits of riparian plants also exhibit spatial variations across the water level conditions (Spencer et al, 2004;McCoy-Sulentic et al, 2017;Duan et al, 2017).…”

“…When the water level gradually decreased in early September, M. laxi ora plants emerged and quickly restored their vegetative growth, and then began to ower and set fruits within a week (Chen and Xie, 2009). After the construction of the Three Gorges-Gezhou Dam cascade hydropower station, because human regulation on river discharge is conducted to ful ll the needs of ood prevention and power generation, the water level uctuation pattern in the habitat of M. laxi ora remnant populations was signi cantly altered: the emergence time of habitats is delayed, average periods of emergence was shortened from 220 days to 190 days; the ooding retreat rapidly during the growth restart period; also, and the water level in the winter dry season dramatically decreased (Wang et al, 2018;Duan et al, 2016;Sun et al, 2007). We investigated the branch and leaf growth traits in populations across a water level condition during the growth restart period after emergence to understand the pattern of branch and leaf growth traits changing with water level gradient and the phenotypic plasticity.…”

Effects of soil water conditions on seedling regeneration in Myricaria laxiflora remnant populations

“…Remnant M. laxiflora populations exist between 41 and 46 m altitude. The soil type of this site is Haplic Alisol (depth, 30–40 cm), the soil organic matter content ranged 10.0–16.0%, and the soil bulk density and porosity ranged 35.52–61.81% and 1.05–1.81 g cm −3 , respectively (Chen, Guan, et al, ; Chen, Wu, et al, ; Chen & Xie, ; Wang et al, ).…”

Linkages between soil organic carbon fractions and carbon-hydrolyzing enzyme activities across riparian zones in the Three Gorges of China

“…Water submergence can also reduce the input of fresh OC from plant litter and root exudates because of less oxygen availability for plant roots 35 . Meanwhile, enzyme activities could be indirectly affected by soil pH and microclimates under large hydroelectric project 1,5,36 . For instance, Amendola et al 5 have found that increase in soil moisture results in higher enzyme activities, with soil becoming dry condition, the substrate diffusion and oxygen content can limit enzyme activities.…”

“…Since the completion of the Three Gorges Dam in 2008, a total area of 350 km 2 water level fluctuation zone has been formed in the Three Gorges Reservoir with water level fluctuation from 145 m above sea level in summer (May to September) to 175 m in winter (October to April) 1,38 . The reversal of submergence time and prolonged inundation dramatically lead to change in soil moisture, pH and vegetation types 32,34 , and these changes ultimately affect soil C cycling and enzyme activities.…”