Research

22 pages, 9722 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Assessment of Surface Hydrological Connectivity in an Ungauged Multi-Lake System with a Combined Approach Using Geostatistics and Spaceborne SAR Observations

by Yueqing Chen, Lili Wu, Guangxin Zhang, Y. Jun Xu, Zhiqiang Tan and Sijia Qiao

Water 2020, 12(10), 2780; https://doi.org/10.3390/w12102780 - 06 Oct 2020

Cited by 3 | Viewed by 2494

Abstract

Connectivity metrics for surface water are important for predicting floods and droughts, and improving water management for human use and ecological integrity at the landscape scale. The integrated use of synthetic aperture radar (SAR) observations and geostatistics approach can be useful for developing [...] Read more.

Connectivity metrics for surface water are important for predicting floods and droughts, and improving water management for human use and ecological integrity at the landscape scale. The integrated use of synthetic aperture radar (SAR) observations and geostatistics approach can be useful for developing and quantifying these metrics and their changes, including geostatistical connectivity function (GCF), maximum distance of connection (MDC), surface water extent (SWE), and connection frequency. In this study, we conducted a geostatistical analysis based on 52 wet and dry binary state (i.e., water and non-water) rasters derived from Sentinel-1 A/B GRD products acquired from 2015 to 2019 for China’s Momoge National Nature Reserve to investigate applicability and dynamics of the hydrologic connectivity metrics in an ungauged (i.e., data such as flow and water level are scarce) multi-lake system. We found: (1) generally, the change of GCF in North–South and Northeast–Southwest directions was greater than that in the West–East and Northwest–Southeast directions; (2) MDC had a threshold effect, generally at most 25 km along the W–E, NW–SE and NE–SW directions, and at most 45 km along the N–S direction; (3) the flow paths between lakes are diverse, including channelized flow, diffusive overbank flow, over-road flow and “fill-and-merge”; (4) generally, the values of the three surface hydrological connectivity indicators (i.e., the MDC, the SWE, and the conneciton frequency) all increased from May to August, and decreased from August to October; (5) generally, the closer the distance between the lakes, the greater the connection frequency, but it is also affected by the dam and road barrier. The study demonstrates the usefulness of the geostatistical method combining Sentinel-1 SAR image analysis in quantifying surface hydrological connectivity in an ungagged area. This approach should be applicable for other geographical regions, in order help resource managers and policymakers identify changes in surface hydrological connectivity, as well as address potential impacts of these changes on water resources for human use and/or ecological integrity at the landscape level. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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18 pages, 8354 KiB

Open AccessArticle

Effects of Irrigation Discharge on Salinity of a Large Freshwater Lake: A Case Study in Chagan Lake, Northeast China

by Xuemei Liu, Guangxin Zhang, Jingjie Zhang, Y. Jun Xu, Yao Wu, Yanfeng Wu, Guangzhi Sun, Yueqing Chen and Hongbo Ma

Water 2020, 12(8), 2112; https://doi.org/10.3390/w12082112 - 25 Jul 2020

Cited by 19 | Viewed by 3221

Abstract

The salinization of freshwater lakes by agricultural activities poses a threat to many lake ecosystems around the world. Quantitative, medium- to long-term studies are needed to understand how some common agricultural practices, such as the discharge of crop irrigation in the vicinities of [...] Read more.

The salinization of freshwater lakes by agricultural activities poses a threat to many lake ecosystems around the world. Quantitative, medium- to long-term studies are needed to understand how some common agricultural practices, such as the discharge of crop irrigation in the vicinities of large lakes, may affect lake salinization. In this study, hydrological, hydrodynamics, water quality and meteorological datasets were used to analyze the long-term spatial-temporal variations of water salinities of a major lake, the Chagan Lake, in Northeast China. An integrated hydrodynamics-salinity model was used to simulate lake water salinity changes taking place at different times and locations, including (i) salt accumulations during a non-frozen period, and (ii) the time when water salinity may reach a significant threshold (1 psu) that jeopardizes a major environmental and economic value of this lake (i.e., the cultivation of local fish species). The results confirmed that Chagan Lake was indeed undergoing salinization in the ten year period between 2008 and 2018. The spatial-temporal patterns of the salinization processes were identified. For instance, (i) the mean salinity of the lake water was found to be 0.55 psu in the summer season of the region and 0.53 psu in the winter, and (ii) between May to October the salinity was up to 0.62 psu in the western region of the lake. The rate of salt accumulation was found to be 97 ton per annum during the non-frozen period. The simulation predicted that by 2024 the lake water will become sub-saline (salinity > 1.07 psu) which is toxic to fish species, if the current practice of irrigation discharge into the lake continues. In the scenario that the amount of irrigation discharges into the lake doubles, the western region of the lake will become sub-saline within one year, and then the whole lake within three years. Overall, this study has produced results that are useful to authorities around the world, for balancing the risks and benefits of developing crop irrigation fields in areas surrounding large freshwater lakes. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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19 pages, 3265 KiB

Open AccessArticle

Reservoir-Induced Hydrological Alterations Using Ecologically Related Hydrologic Metrics: Case Study in the Beijiang River, China

by Jiakai Du, Xushu Wu, Zhaoli Wang, Jun Li and Xiaohong Chen

Water 2020, 12(7), 2008; https://doi.org/10.3390/w12072008 - 15 Jul 2020

Cited by 12 | Viewed by 2289

Abstract

Anthropogenic activities have a tremendous impact on water ecosystems worldwide, especially in China. To quantitatively evaluate the hydrological alteration connected with aquatic lives and river ecological risks, we took the Beijiang River located in South China as the case study and used ecosurplus [...] Read more.

Anthropogenic activities have a tremendous impact on water ecosystems worldwide, especially in China. To quantitatively evaluate the hydrological alteration connected with aquatic lives and river ecological risks, we took the Beijiang River located in South China as the case study and used ecosurplus (defined as ecological carrying capacity exceeding ecological consumption)/ecodeficit (defined as ecological consumption exceeding carrying capacity) and Indicators of Hydrological Alterations to evaluate hydrological changes. The Ecologically Relevant Hydrologic Indicators were employed to select the key indices of Indicators of Hydrological Alterations, and the eco-environmental water demand calculation provide an effective way for the reservoir operation. Results showed that: (1) High flows contributed more to the ecodeficit, while low flows contributed more to the ecosurplus; (2) the ecodeficit in some parts of the river basin might exceed the ecosurplus after reservoir construction, especially along the main stream; and (3) the determination of eco-environmental water demand is a feasible way for improving the environment by controlling reservoirs. The current study can help guide the optimization of hydrological operation in the basin toward making the ecosystem healthier and has potential to further provide a reference for other basins in terms of hydrological alterations driven by anthropogenic activities. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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17 pages, 4416 KiB

Open AccessArticle

Human Activities and Climate Variability Affecting Inland Water Surface Area in a High Latitude River Basin

by Liwen Chen, Guangxin Zhang, Y. Jun Xu, Shengbo Chen, Yanfeng Wu, Zongting Gao and Haiyang Yu

Water 2020, 12(2), 382; https://doi.org/10.3390/w12020382 - 31 Jan 2020

Cited by 15 | Viewed by 3368

Abstract

Spatiotemporal changes in the surface area of inland water bodies have important implications in regional water resources, flood control, and drought hazard prediction. Although inland water bodies have been investigated intensively, few studies have looked at the effect of human activities and climate [...] Read more.

Spatiotemporal changes in the surface area of inland water bodies have important implications in regional water resources, flood control, and drought hazard prediction. Although inland water bodies have been investigated intensively, few studies have looked at the effect of human activities and climate variability on surface area of inland waters at a larger scale over time and space. In this study, we used MODIS (MOD13Q1) images to determine water surface area extent at 250 m spatial resolution. We then applied this algorithm with MOD13Q1 images taken at 16-day intervals from 2000 to 2018 to a large river basin in China’s northeast high latitude region with dense stream network and abundant wetlands to investigate spatiotemporal distribution and dynamics of inland water bodies. The study identified 209 ponds, lakes, and reservoirs with an average total surface area of 2080 km² in the past 19 years. The total water surface area fluctuated largely from 942 km² to 5169 km², corresponding to rainfall intensity and flood. We found that the total water surface area in this high latitude river basin showed an increasing trend during the study period, while the annual precipitation amount in the river basin also had an increasing trend concurrently. Precipitation and irrigation significantly contributed to the monthly change of water surface area, which reached the highest during June and August. The increase of water surface area was significant in the lower basin floodplain region, where agricultural irrigation using groundwater for rice production has progressed. Four nationally important wetland preserves (Zhalong, Xianghai, Momoge, and Chagan Lake) in the river basin made up nearly 50% of the basin’s total water surface area, of which Zhalong, Xianghai, and Momoge are designated by The Ramsar Convention as wetland sites of international importance. Seasonally, these water bodies reached their maximal surface area in August, when both the monsoon weather and agricultural discharge prevailed. This study demonstrates that water surface area in a high latitude river basin is affected by both human activities and climate variation, implying that high latitude regions will likely experience more changes in surface water distribution as global climate change continues and agriculture becomes intensified. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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15 pages, 3161 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Long Short Term Memory Networks and the Hydrological Model in Runoff Simulation

by Hongxiang Fan, Mingliang Jiang, Ligang Xu, Hua Zhu, Junxiang Cheng and Jiahu Jiang

Water 2020, 12(1), 175; https://doi.org/10.3390/w12010175 - 08 Jan 2020

Cited by 90 | Viewed by 10505

Abstract

Runoff modeling is one of the key challenges in the field of hydrology. Various approaches exist, ranging from physically based over conceptual to fully data driven models. In this paper, we propose a data driven approach using the state-of-the-art Long-Short-Term-Memory (LSTM) network. The [...] Read more.

Runoff modeling is one of the key challenges in the field of hydrology. Various approaches exist, ranging from physically based over conceptual to fully data driven models. In this paper, we propose a data driven approach using the state-of-the-art Long-Short-Term-Memory (LSTM) network. The proposed model was applied in the Poyang Lake Basin (PYLB) and its performance was compared with an Artificial Neural Network (ANN) and the Soil & Water Assessment Tool (SWAT). We first tested the impacts of the number of previous time step (window size) in simulation accuracy. Results showed that a window in improper large size will dramatically deteriorate the model performance. In terms of PYLB, a window size of 15 days might be appropriate for both accuracy and computational efficiency. We then trained the model with 2 different input datasets, namely, dataset with precipitation only and dataset with all available meteorological variables. Results demonstrate that although LSTM with precipitation data as the only input can achieve desirable results (where the NSE ranged from 0.60 to 0.92 for the test period), the performance can be improved simply by feeding the model with more meteorological variables (where NSE ranged from 0.74 to 0.94 for the test period). Moreover, the comparison results with the ANN and the SWAT showed that the ANN can get comparable performance with the SWAT in most cases whereas the performance of LSTM is much better. The results of this study underline the potential of the LSTM for runoff modeling especially for areas where detailed topographical data are not available. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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15 pages, 2096 KiB

Open AccessArticle

The Periodic Response of Tidal Flat Sediments to Runoff Variation of Upstream Main River: A Case Study in the Liaohe Estuary Wetland, China

by Haifu Li, Lifeng Li, Fangli Su, Tieliang Wang and Peng Gao

Water 2020, 12(1), 61; https://doi.org/10.3390/w12010061 - 22 Dec 2019

Cited by 4 | Viewed by 2494

Abstract

(1) Background: To reveal the intrinsic relationship between the tidal flat sediments in an estuary wetland and the runoff from the upstream river. This research was conducted in the tidal flats of the Liaohe estuary wetland. (2) Methods: The ¹³⁷Cs and ²¹⁰ [...] Read more.

(1) Background: To reveal the intrinsic relationship between the tidal flat sediments in an estuary wetland and the runoff from the upstream river. This research was conducted in the tidal flats of the Liaohe estuary wetland. (2) Methods: The ¹³⁷Cs and ²¹⁰Pb dating technique was used to reconstruct the time correspondence between tidal flat sediments and runoff, and the periodic response was explored between the changes in the tidal flat sediments and runoff based on the spectrum analysis method. (3) Results: The average sedimentation rate in the tidal flat was 2.24 cm·year⁻¹ during the past 50 years. The amount of fine sediment particles deposited on the estuary tidal flat was directly related to the amount of sediments transported by the river and inversely proportional to the ability of rivers to transport fine matter. The high frequency reproduction cycle of 14–15 years in the flood season flow and 5–6 years in the annual sediment discharge of the Liaohe River correspond to the high and low frequency reproduction cycles of the median size of sediments in Liaohe estuarine wetland tidal flats. (4) Conclusions: The research clarified the hydrological constraints of the action law between Liaohe River runoff and the estuarine sediments. The periodic response between Liaohe River runoff and the sediment was established. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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12 pages, 2361 KiB

Open AccessArticle

Impacts of Land Use and Land Cover on Water Quality at Multiple Buffer-Zone Scales in a Lakeside City

by Wenqin Huang, Jingqiao Mao, Dejun Zhu and Chenyu Lin

Water 2020, 12(1), 47; https://doi.org/10.3390/w12010047 - 20 Dec 2019

Cited by 28 | Viewed by 4534

Abstract

Understanding the effect of land use/land cover (LULC) on water quality is essential for environmental improvement, especially in urban areas. This study examined the relationship between LULC at buffer-zone scales and water quality in a lakeside city near Poyang Lake, which is the [...] Read more.

Understanding the effect of land use/land cover (LULC) on water quality is essential for environmental improvement, especially in urban areas. This study examined the relationship between LULC at buffer-zone scales and water quality in a lakeside city near Poyang Lake, which is the largest freshwater lake in China. Representative indicators were selected by factor analysis to characterize the water quality in the study area, and then the association between LULC and water quality over space and time was quantified by redundancy analysis. The results indicated that the influence of LULC on water quality is scale-dependent. In general, the LULC could explain from 56.9% to 31.6% of the variation in water quality at six buffer zones (from 500 m to 1800 m). Forest land had a positive effect on water quality among most buffer zones, while construction land and bare land affected the representative water quality indicators negatively within the 1200 m and 1500 m buffer zones, respectively. There was also a seasonal variation in the relationship between LULC and water quality. The closest connection between them appeared at the 1000 m buffer zone in the dry season, whereas there was no significant difference among the buffer zones in the wet season. The results suggest the importance of considering buffer-zone scales in assessing the impacts of LULC on water quality in urban lakeshore areas. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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21 pages, 17895 KiB

Open AccessArticle

A Study on the Response of the Hydrodynamic Environment to the Morphology of Radial Sand Ridges in the Coastal Waters of Jiangsu

by Changjun Qi, Lejun Ma, Qinggai Wang, Yuan Zhai, Jixuan Li and Hanwen Zhang

Water 2019, 11(10), 2190; https://doi.org/10.3390/w11102190 - 21 Oct 2019

Cited by 1 | Viewed by 2704

Abstract

A two-dimensional hydrodynamic model for the waters off the coast of Jiangsu, where there are radial sand ridges (RSRs) (hereinafter, the RSR area), was established based on measured topographic, tide level and tidal current data. Considering the complex topographic and geomorphic characteristics of [...] Read more.

A two-dimensional hydrodynamic model for the waters off the coast of Jiangsu, where there are radial sand ridges (RSRs) (hereinafter, the RSR area), was established based on measured topographic, tide level and tidal current data. Considering the complex topographic and geomorphic characteristics of the RSR group in this area, an unstructured grid was used for the calculation. A four-layer refinement was applied to the grid from outside to inside to better fit the complex topography. The simulations were performed to examine the response of the hydrodynamic environment to the morphology of the RSRs in three scenarios, namely, when there are natural RSRs, no RSRs, and partially reclaimed RSRs. When there are no or partially reclaimed RSRs, the tidal current field still exists in a radial pattern in the RSR area. The radial tidal current field is relatively stable and is not controlled by the morphologies of the RSRs. The topographic changes do not alter the distribution pattern of the radial tidal current field but do affect the local current fields. When there are no RSRs, the flood currents can directly reach Jianggang. Under practical conditions, the RSRs block the tidal currents during a flood tide to some extent. This phenomenon is particularly pronounced when the RSRs are partially reclaimed. For example, during an ebb tide, when the tidal currents encounter sand ridges or reclamation areas, their streamlines bend, and they flow around the obstacles. This change will affect the material transport, sediment deposition and seabed erosion. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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17 pages, 3064 KiB

Open AccessArticle

Dam Effects on Downstream Riparian Wetlands: The Nenjiang River, Northeast China

by Yuexin Zheng, Guangxin Zhang, Yanfeng Wu, Y. Jun Xu and Changlei Dai

Water 2019, 11(10), 2038; https://doi.org/10.3390/w11102038 - 29 Sep 2019

Cited by 35 | Viewed by 5995

Abstract

Many studies have found that damming a river can change downstream hydrology, sediment transport, channel morphology, and fish habitat. However, little is known about river dam effects on downstream riparian wetland dynamics and their quantitative relationship with hydrological alterations. In this study, hydrological [...] Read more.

Many studies have found that damming a river can change downstream hydrology, sediment transport, channel morphology, and fish habitat. However, little is known about river dam effects on downstream riparian wetland dynamics and their quantitative relationship with hydrological alterations. In this study, hydrological time series and wetland distribution data spanning nearly 40 years (1978–2016) before and after the construction of a large dam in 2005 across the Nenjiang River in Northeast China were used to reveal the impact of dam on the downstream discharge regime and wetland degradation. Hydro-statistical and stepwise multiple regression analyses were performed to quantify the relationship of riparian wetland area with a metrics of 33 hydrological indicators. Dam construction caused decline in peak discharge, flood frequency, and magnitude. Moreover, 150 km riparian wetlands along the downstream of the dam was largely reduced. The count and duration of high flow pulses, 1-day maximum, and date of maximum discharge changed significantly after the dam construction. The hydrological changes have made a significant contribution to the 44% reduction in riparian wetlands following the dam construction. Our results indicated that hydrological alterations caused by dam regulation led to the area reduction of downstream riparian wetlands. The findings provide relevant information for developing best dam operation practices to protect and restore downstream wetland ecosystems. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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16 pages, 3510 KiB

Open AccessFeature PaperArticle

Spatiotemporal Variations of Summer Precipitation and Their Correlations with the East Asian Summer Monsoon in the Poyang Lake Basin, China

by Hua Zhu, Ligang Xu, Jiahu Jiang and Hongxiang Fan

Water 2019, 11(8), 1705; https://doi.org/10.3390/w11081705 - 16 Aug 2019

Cited by 16 | Viewed by 3363

Abstract

Poyang Lake Basin (PYLB) is located in Southeastern China where the precipitation is closely related to the East Asian Monsoon. Based on the monthly precipitation data of 18 meteorological stations from 1959 to 2018 in the PYLB, Empirical Orthogonal Function (EOF), Wavelet Analysis, [...] Read more.

Poyang Lake Basin (PYLB) is located in Southeastern China where the precipitation is closely related to the East Asian Monsoon. Based on the monthly precipitation data of 18 meteorological stations from 1959 to 2018 in the PYLB, Empirical Orthogonal Function (EOF), Wavelet Analysis, and Pearson Correlation Analysis were used to investigate the spatiotemporal variations of summer precipitation and their correlations with the East Asian Summer Monsoon (EASM). The results demonstrate that there were two leading modes of summer precipitation at inter-annual time scales: the mode being consistent over the whole area and the mode of opposite relationship between the south/north PYLB. Both modes had obvious trend variations and periodic characteristics. The East Asian Summer Monsoon Index (EASMI) showed a decreasing trend of fluctuation, existing in periods of 2–3 years and 11 years. Cross Wavelet Transform revealed that the time coefficients of the second EOF mode and EASMI had an anti-phase resonance period of 2–3 years. Pearson Correlation Analysis also indicated that there was a significant negative correlation relationship between them. These results not only contribute to an understanding of characteristics of summer precipitation in the PYLB and the influences of the East Asian Summer Monsoon on them but also provide a reference for a regional response to climate change and precipitation prediction. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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16 pages, 2712 KiB

Open AccessArticle

Modelling the Impacts of Bathymetric Changes on Water Level in China’s Largest Freshwater Lake

by Lingyan Qi, Jiacong Huang, Junfeng Gao and Zhen Cui

Water 2019, 11(7), 1469; https://doi.org/10.3390/w11071469 - 16 Jul 2019

Cited by 11 | Viewed by 2976

Abstract

A recent dramatic decline in water level during the dry season in China’s largest freshwater lake (Lake Poyang) significantly influenced water availability and biogeochemical processes. To learn the potential causes of water level decline, this study investigated the hydrodynamic response to bathymetric changes [...] Read more.

A recent dramatic decline in water level during the dry season in China’s largest freshwater lake (Lake Poyang) significantly influenced water availability and biogeochemical processes. To learn the potential causes of water level decline, this study investigated the hydrodynamic response to bathymetric changes during three typical hydrological years by scenario simulation using Environmental Fluid Dynamics Code (EFDC). The simulation results indicated that bathymetric changes resulted in a water level decrease during a low water level period. Inter-annual variation in the decrease rate implied that water level in typical dry and wet years were influenced more significantly than that in moderate hydrological years. A spatial gradient in the distribution of water level changes was also observed, which was mainly concentrated in the main channel. Water velocities also slowed down, weakly corresponding to the decrease in water level during the low water level period. Overall, bathymetric changes caused by sand mining contributed to water level and velocity variations, influencing the stability and sustainability of the lake ecosystem. This study can potentially enhance our understanding of the hydrodynamic processes in Lake Poyang and support water resource management. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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21 pages, 2121 KiB

Open AccessArticle

Dissolved Carbon Transport and Processing in North America’s Largest Swamp River Entering the Northern Gulf of Mexico

by Emily M. DelDuco and Y. Jun Xu

Water 2019, 11(7), 1395; https://doi.org/10.3390/w11071395 - 07 Jul 2019

Cited by 7 | Viewed by 3047

Abstract

Transport and transformation of riverine dissolved carbon is an important component of global carbon cycling. The Atchafalaya River (AR) flows 189 kilometers through the largest bottomland swamp in North America and discharges ~25% of the flow of the Mississippi River into the Gulf [...] Read more.

Transport and transformation of riverine dissolved carbon is an important component of global carbon cycling. The Atchafalaya River (AR) flows 189 kilometers through the largest bottomland swamp in North America and discharges ~25% of the flow of the Mississippi River into the Gulf of Mexico annually, providing a unique opportunity to study the floodplain/wetland impacts on dissolved carbon. The aim of this study is to determine how dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) in the AR change spatially and seasonally, and to elucidate which processes control the carbon cycling in this intricate swamp-river system. From May 2015 to May 2016, we conducted monthly river sampling from the river’s inflow to its outflow, analyzing samples for concentrations and δ¹³C stable isotope composition of DOC and DIC. We found that DIC concentrations in the AR were three times higher than the DOC concentrations on average, and showed more pronounced downstream changes than the DOC. During the study period, the river discharged a total of 5.35 Tg DIC and a total of 2.34 Tg DOC into the Gulf of Mexico. Based on the mass inflow–outflow balance, approximately 0.53 Tg (~10%) of the total DIC exported was produced within the floodplain/wetland system, while 0.24 Tg (~10%) of the DOC entering the basin was removed. The AR’s water was consistently oversaturated with CO₂ partial pressure (pCO₂) above the atmospheric pCO₂ (with pCO₂ varying from 551 µatm to 6922 µatm), indicating a large source of DIC from river waters to the atmosphere as well as to the coastal margins. Largest changes in carbon constituents occurred during periods of greatest inundation of the swamp-river basin and corresponded with shifts in isotopic composition. This effect was particularly pronounced during the initial flood stages, supporting the hypothesis that subtropical floodplains can act as effective enhancers of the biogeochemical cycling of dissolved carbon. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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20 pages, 1673 KiB

Open AccessArticle

Field Investigation on River Hydrochemical Characteristics and Larval and Juvenile Fish in the Source Region of the Yangtze River

by Liangyuan Zhao, Wei Li, Li Lin, Weijie Guo, Weihua Zhao, Xianqiang Tang, Dandan Gong, Qingyun Li and Ping Xu

Water 2019, 11(7), 1342; https://doi.org/10.3390/w11071342 - 28 Jun 2019

Cited by 18 | Viewed by 3664

Abstract

The source region of the Yangtze River (SRYR) is located in the Qinghai-Tibet Plateau, where the climatic conditions and alpine-cold natural conditions are harsh. Field investigations of the hydrochemical characteristics and larva and juvenile fish in rivers of the SRYR were carried out [...] Read more.

The source region of the Yangtze River (SRYR) is located in the Qinghai-Tibet Plateau, where the climatic conditions and alpine-cold natural conditions are harsh. Field investigations of the hydrochemical characteristics and larva and juvenile fish in rivers of the SRYR were carried out in July 2018 with the aim of obtaining further information on the unique ecological environment status of this plateau area. The results of the present research indicated that majority of the river water quality parameters in the SRYR were in the range of class I to class II, according to the classification of the environmental quality standard for surface water (GB3838-2002) in China. Among 12 kinds of metal ions, the concentrations of four major ions occurred in the following order: Ca > Na > Mg > K. The concentrations of eight heavy metal ions (Fe, Mn, Cu, Zn, Pb, Cd, Cr and As) were all within the class I water range based on GB3838-2002. A total of three species of larval and juvenile fish, i.e., Triplophysa stenura (T. stenura), Schizopygopsis microcephalus Herzenstein (S. microcephalus) and Triplophysa bleekeri (T. bleekeri), were collected from 11 sampling sites. It was found that T. stenura covered the widest distribution range and was the most abundant. The results of principal component analysis and canonical correspondence analysis demonstrated that the distribution of S. microcephalus exhibited a positive response to water temperature, a positive response to K and a negative correlation with water temperature were demonstrated in the distribution of T. stenura. T. bleekeri distribution had a positive response to Cu, but negative responses to total phosphorus and total dissolved solid. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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16 pages, 4138 KiB

Open AccessArticle

Response of Wetland Evapotranspiration to Land Use/Cover Change and Climate Change in Liaohe River Delta, China

by Manqing Liu and Deyong Hu

Water 2019, 11(5), 955; https://doi.org/10.3390/w11050955 - 07 May 2019

Cited by 14 | Viewed by 3293

Abstract

This study aims to investigate the effects of land use/cover change (LUCC) and climate change on wetland evapotranspiration (ET), and to identify the importance of the main effect factors in the spatiotemporal dynamics of ET. In the wetland of Liaohe River Delta, China, [...] Read more.

This study aims to investigate the effects of land use/cover change (LUCC) and climate change on wetland evapotranspiration (ET), and to identify the importance of the main effect factors in the spatiotemporal dynamics of ET. In the wetland of Liaohe River Delta, China, the ET of eight growing seasons during 1985–2017 was estimated using the surface energy balance algorithm for land (SEBAL) model with Landsat and meteorological data. Results show that the average relative error of regional ET estimated by the SEBAL model is 9.01%, and the correlation coefficient between measured and estimated values is 0.61, which indicates that the estimated values are reliable. This study observed significant spatial and temporal variations in ET across the region of interest. The distribution of the average and relative change rate of daily ET in the study area showed bimodal characteristics, that is, the lowest trough occurred in 2005, whereas crests occurred in 1989 and 2014. Simultaneously, the daily ET varied with the land use/cover area. Regional daily ET displays highly heterogeneous spatial distribution, that is, the ET of different land uses/cover types in descending order is as follows: water body, wetland vegetation, non-wetland vegetation, and non-vegetation (except water area). Therefore, the spatial pattern of ET is relevant to the land use/cover types to some extent. In addition, the temporal variation of wetland ET is closely related to landscape transformation and meteorological factor change. A strong correlation was found between ET and the weighted values of meteorological factors, with a correlation coefficient of 0.69. Meanwhile, the annual fluctuations of daily ET and the weighted values were relatively similar. Therefore, the findings highlight the importance of using cheap and readily available remote sensing data for estimating and mapping the variations in ET in coastal wetland. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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16 pages, 2531 KiB

Open AccessArticle

Changes in Water Level Regimes in China’s Two Largest Freshwater Lakes: Characterization and Implication

by Junxiang Cheng, Ligang Xu, Wenjuan Feng, Hongxiang Fan and Jiahu Jiang

Water 2019, 11(5), 917; https://doi.org/10.3390/w11050917 - 01 May 2019

Cited by 10 | Viewed by 3649

Abstract

The complex water regimes and fragile ecological systems in Dongting Lake and Poyang Lake, located in the middle reach of the Yangtze River, have been significantly affected by regional climate change and anthropogenic activities. The hydrological data from the outlets of Dongting Lake [...] Read more.

The complex water regimes and fragile ecological systems in Dongting Lake and Poyang Lake, located in the middle reach of the Yangtze River, have been significantly affected by regional climate change and anthropogenic activities. The hydrological data from the outlets of Dongting Lake (Chenglingji station) during 1955–2016 and Poyang Lake (Hukou station) during 1953–2014 were divided into two periods: the pre-impact period and the post-impact period. Four statistical tests were used to identify the change years: 1979 at Chenglingji and 2003 at Hukou. The indicators of hydrologic alteration and range of variability approach were used to assess alterations in water level regimes. Results show that the severely altered indicators were January water level at both lake outlets, and 1-, 3-, 7- and 30-day minimum water level at Chenglingji, with the degree of hydrological alteration being larger than 85%. The overall degrees of hydrological alteration at Chenglingji and Hukou were 52.6% and 38.2%, respectively, indicating that water level regimes experienced moderate alteration and low alteration or that ecosystems were at moderate risk and low risk, respectively. Changes in water level regimes were jointly affected by climate change and anthropogenic activities. Water level regimes at Dongting Lake outlet were mainly affected by increased rainfall and dam regulation. Decreased rainfall, dam regulation, and sediment erosion and deposition were the main impact factors of water level regimes at Poyang Lake outlet. These changes in water level regimes have greatly influenced both aquatic and terrestrial ecosystems, especially for fish and vegetation communities. This study is beneficial for water resource management and ecosystems protection under regional changes. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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14 pages, 2226 KiB

Open AccessArticle

Poyang Lake Wetland Ecosystem Health Assessment of Using the Wetland Landscape Classification Characteristics

by Hailin You, Hongxiang Fan, Ligang Xu, Yongming Wu, Lizhen Liu and Zhong Yao

Water 2019, 11(4), 825; https://doi.org/10.3390/w11040825 - 19 Apr 2019

Cited by 14 | Viewed by 4604

Abstract

Currently, wetland stability is under threat due to the joint effects of global climate change and human activity, especially in lakes. Hence, it is necessary to evaluate the health status of wetland ecosystems such as lakes, identify the variables causing the wetland degradation [...] Read more.

Currently, wetland stability is under threat due to the joint effects of global climate change and human activity, especially in lakes. Hence, it is necessary to evaluate the health status of wetland ecosystems such as lakes, identify the variables causing the wetland degradation and work to protect the wetlands from the identified variables in the future. Based on fourteen high-resolution autumn remote sensing images from 1989–2013, the classification characteristics and spatial distribution patterns of wetland landscapes in Poyang Lake were studied through quantitative interpretation technology. An established health assessment index system named the EHCI (Ecological Health Comprehensive Index) was used to assess the health status of Poyang Lake. Additionally, the relationship between water regime and health status of wetland landscape distribution of Poyang Lake were investigated by multivariate statistical analysis. The results demonstrated: (1) The total area of three first level (or six second level) types of wetland landscapes showed a stable status, which was long-term maintaining at about 3026 km² from 1989–2013. (2) The water area shows a downward trend, while the areas of vegetation and land-water transition zone show upward trends. (3) The proposed EHCI of the Poyang Lake wetland presented a downward trend. According to the EHCI results from 1989–2013, the health status of Poyang Lake wetland was healthy for two years, unhealthy for four years and sub-healthy for eight years. (4) The water level fluctuation greatly affected the EHCI, and the effect became greater as the water level increased. These results contribute to the understanding of specific effects of hydrological process on the health status of the Poyang Lake wetland. In addition they provide a scientific reference for the maintenance of stable ecosystem functions of the seasonal freshwater lake. These results contribute to the understanding of specific effects of hydrological process on the health status of the Poyang Lake. In addition they provide a scientific reference for the maintenance of stable ecosystem functions of the seasonal freshwater lake. Full article

(This article belongs to the Special Issue Wetland Ecohydrology and Water Resource Management)

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