Response of water and energy exchange to the environmental variable in a desert-oasis wetland of Northwest China

Abstract

A case study on a desert-oasis wetland ecosystem in the arid region of Northwest China measured the seasonal and interannual variation in energy partitioning and evapotranspiration to analyse the response of water and energy exchange on soil moisture, groundwater, and environmental variables. Energy partitioning showed a clear seasonal and interannual variability, and the process of water and energy exchange differed significantly in the monthly and interannual scales. The net radiation was 7.31 MJ m À2 · day À1 , and sensible heat flux accounted for 50.42% of net radiation in energy fluxes, 40.56% for latent heat flux, and 9.02% for ground heat flux. The parameters in energy fluxes were best described by a unimodal curve, whereas sensible heat flux followed a bimodal curve. Variations in the daily evapotranspiration and crop evapotranspiration also exhibited a single peak curve with annual values of 569.84 and 644.47 mm, respectively. Canopy conductance averaged 20.77 ± 13.75 mm s À1 and varied from 0.16 to 83.96 mm s À1 during the two hydrological years. The variation in water and energy exchange reflected environmental conditions and depended primarily on vapour pressure deficit, net radiation, soil moisture, and water depth. Although the effects of precipitation on evapotranspiration showed that the response of this ecosystem to climate changes was not obvious, the variation of air temperatures had a strong influence on evapotranspiration, resulting in a significant increase in evapotranspiration (R = 0.730; P < 0.01). μ 2 , wind speed at 2-m height; ℧, decoupling factor 6102 B. LIU ET AL.

Hysteretic response of sap flow in Scots pine (Pinus sylvestris) to meteorological forcing in a humid low‐energy headwater catchment

“…Regarding the meteorological controls on plant water use, many studies have found fairly good linear relationships at the daily scale between transpiration and radiation and vapour pressure deficit ( VPD ), which are two major controlling factors as shown recently, for example, for plants in a desert‐oasis wetland of northwest China (Liu, Zhao, Wen, & Zhang, ), Scots pine in a boreal, humid Scottish catchment (Wang, Tetzlaff, Dick, & Soulsby, ), and tropical montane cloud forest in São Paulo Brazil (Eller, Burgess, & Oliveira, ). However, at the sub‐daily scale (i.e., hourly), the linear relationships between Ec and environmental variables have been shown to be weaker in most studies (Ma et al, ; Tie, Hu, Tian, Guan, & Lin, ; Wang et al, ).…”

Hydrochemical Characteristics Jointly Determine the Transport and Cycling of Soil Carbon, Nitrogen, and Phosphorus in an Arid Chinese Wetland

“…When soil particles adsorb Mg 2+ and Ca 2+ from the groundwater, this increases the concentration of Na + in the soil solution. Generally, shallow groundwater strongly dilutes ions in the soil solution in riparian wetlands, which is why the ion concentrations are lower than in a saltmarsh wetland (Liu et al, 2014(Liu et al, , 2017(Liu et al, , 2019. Thus, concentration of the soil solution through ET combines with ion adsorption and release to alter hydrochemical characteristics such as the Mg 2+ /SO 4 2− ratio in wetlands.…”

“…At the same time, high C, N, and P also mean that there may be little exchange of soil nutrients between the arid wetlands and their external environment. In saline wetlands in arid regions, the irrigation backwater is also one of the main water sources which are rich in salt ions and nutrient elements because of fertilizer application in agricultural activity (Liu et al, 2014(Liu et al, , 2017(Liu et al, , 2019. On the one hand, salt ions and nutrient elements are transported toward the soil surface through capillary rise from shallow groundwater and irrigation water with continuous evapotranspiration, leading to salt accumulation and nutrient enrichment near the soil surface.…”

“…These changes can lead to high spatial and temporal heterogeneity in the distribution of biogeochemical processes in arid wetlands (Couto et al, 2013;Drexler et al, 2013;Weston et al, 2014). In arid wetlands, precipitation is rare, so the effluence of shallow groundwater, agricultural irrigation, and river water are the main water sources (Liu et al, 2014(Liu et al, , 2017. Seasonal and interannual variability in precipitation and groundwater depth affects the freshwater (river) discharge into wetlands and influences the transport of watershed-derived nutrients and sediments (Neubauer, 2013;Pont et al, 2002).…”

Assessing the large-scale plant-water relations using remote sensing products in the humid subtropical Pearl River Basin in south China

“…The relationship is commonly characterized as linear increase of plant water use with increasing moisture within a certain range above which plant water use maintains its potential rate and will be limited mainly by energy (Novák et al, 2005). Noticeably, some studies observed a parabolic relationship between plant water use and soil moisture (Zhao and Liu, 2010) or groundwater level (Liu et al, 2014a).…”