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20 pages, 6693 KiB

Open AccessArticle

Divergent Geochemical Pathways of Carbonate Aquifer Evolution in a Classic Karst Terrain: (2) Groundwater Source Delineation Using Regional Water Chemistry Data

by Sarah Asha Burgess, Tracy D. Branam and Lee J. Florea

Water 2023, 15(19), 3436; https://doi.org/10.3390/w15193436 - 29 Sep 2023

Cited by 2 | Viewed by 1465

Abstract

Springs provide ideal monitoring points for groundwater chemistry, which are important for managing groundwater resources. The chemistry of these spring waters aggregate geochemical reactions along the flow path. In this paper, part two of a two-part investigation, 104 perennial springs in the classic [...] Read more.

Springs provide ideal monitoring points for groundwater chemistry, which are important for managing groundwater resources. The chemistry of these spring waters aggregate geochemical reactions along the flow path. In this paper, part two of a two-part investigation, 104 perennial springs in the classic karst landscape of the Mitchell Plateau, Indiana, USA were sampled at base flow. Many of these springs are historically important for domestic, agricultural, commercial, and recreational use. Multifactor analysis of field measurements, principal ions, and stable isotopes revealed five primary clusters of springs emerging from the Mitchell Aquifer. Two clusters represented earth-alkaline-type karst groundwater that were discriminated by temperature and inorganic carbon concentration. Two other clusters comprised mineralized alkaline-earth-type groundwater with excess alkalis and elevated sulfate. The fifth cluster appeared to be groundwater that included meteoric and mineralized sources. Using the longitudinal data over two years from part one of this investigation, two mixing lines were used to describe the data set. The mixing lines pointed to sources of sulfur in mineralized springs from deep brines and from evaporite dissolution. Collectively, these regional data allow for a better delineation of water types and differentiation between the Upper and Lower Mitchell Aquifer. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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18 pages, 4142 KiB

Open AccessArticle

Divergent Geochemical Pathways of Carbonate Aquifer Evolution in a Classic Karst Terrain: (1) Polygenetic Cave Development Identified Using Longitudinal Groundwater Geochemistry

by Sarah A. Burgess, Lee J. Florea and Tracy D. Branam

Water 2023, 15(19), 3410; https://doi.org/10.3390/w15193410 - 28 Sep 2023

Cited by 1 | Viewed by 1505

Abstract

Carbonic acid and sulfuric acid speleogenesis describe a dichotomy between epigenetic and hypogenetic caves and carbon and sulfur cycling in karst, but do not acknowledge the global spectrum of cave formation. This paper, part one of a two-part investigation, tests and revises speleogenetic [...] Read more.

Carbonic acid and sulfuric acid speleogenesis describe a dichotomy between epigenetic and hypogenetic caves and carbon and sulfur cycling in karst, but do not acknowledge the global spectrum of cave formation. This paper, part one of a two-part investigation, tests and revises speleogenetic models from a classic karst landscape using dissolved ion concentrations δ¹³C_DIC, and δ³⁴S in water samples collected at four sites across the Bluespring and Lost River karst basins in the Mitchell Plateau, Indiana, USA. Analyses revealed elevated sulfur in both karst basins but differently sourced; H₂S (δ³⁴S = −14.2‰) evolved from petroleum seeps in Bluespring Caverns accounted for up to 61% of sulfur in the cave stream, while evaporite beds (δ³⁴S = [+14.50‰, +17.91‰]) of the St. Louis Limestone contributed up to 100% of sulfur at Orangeville Rise, a terminal spring of the Lost River karst basin. These results have implications for carbon–sulfur cycle linkages, particularly the potential acceleration of carbon flux from sulfuric acid dissolution in otherwise epigenetic settings. We suggest a new paradigm for speleogenesis in the North American midcontinent—speleogenesis in the Mitchell Plateau and similar settings is not epigenetic or hypogenetic, but instead polygenetic with competing chemical processes varying across space and time. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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12 pages, 3231 KiB

Open AccessArticle

Characteristics of Dissolution Changes in Carbonate Rocks and Their Influencing Factors in the Maocun Basin, Guilin, China

by Chunmeng Mo, Shenglin Xin, Fen Huang, Jianhua Cao and Junbo Xiao

Water 2023, 15(18), 3285; https://doi.org/10.3390/w15183285 - 18 Sep 2023

Cited by 1 | Viewed by 1476

Abstract

Karstification and the global carbon cycle are closely related. Understanding the features of dissolution variations in carbonate rocks and the variables influencing carbonate dissolution is crucial for producing reliable estimates of karst carbon sinks. The seasonal variations in carbonate dissolution rates and the [...] Read more.

Karstification and the global carbon cycle are closely related. Understanding the features of dissolution variations in carbonate rocks and the variables influencing carbonate dissolution is crucial for producing reliable estimates of karst carbon sinks. The seasonal variations in carbonate dissolution rates and the primary factors affecting carbonate dissolution in the Maocun watershed, Guilin, are examined under external source water (Xiaolongbei), karst water (Beidiping), and the mixed external source water and karst water (Bianyan) conditions. In this work, the characteristics of carbonate dissolution rates in several water bodies are investigated using field sampling and indoor experimental measurements. A correlation analysis is performed to analyze the key environmental factors impacting carbonate dissolution. The findings demonstrate that there is a clear seasonal and regional variation in the rate of the dissolution of carbonate rocks. The seasonal characteristics of the carbonate dissolution rate are summer > autumn > spring > winter. The carbonate dissolution rate ranges from −0.023 to 0.258 mg/cm²/d, with a mean value of 0.068 mg/cm²/d. The variation in carbonate dissolution rates on a spatial scale is characterized by exogenous water (Xiaolongbei) > exogenous water mixed with karst water (Bianyan) > karst water (Beidiping). As the rate of carbonate erosion in the Maocun basin is influenced by many factors, the correlation analysis shows that the main controlling factors for the rate of carbonate erosion in the Maocun basin are flow, the saturation index, pH, and pCO₂. Seasonal variations in carbonate dissolution rates are mainly influenced by pCO₂ and the flow rate, and the spatial variations are mainly influenced by pH and the saturation index. The results of this study are important for the scientific assessment of karst development in the study area and the accurate estimation of karst carbon sinks. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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15 pages, 3528 KiB

Open AccessArticle

Source, Distribution and Transformation of Organic Matter in a Subtropical Karst Reservoir

by Jianhong Li, Tao Zhang, Junbing Pu, Xiangling Tang, Yincai Xie and Qiong Xiao

Water 2023, 15(18), 3255; https://doi.org/10.3390/w15183255 - 13 Sep 2023

Viewed by 1204

Abstract

In order to improve the understanding of the global carbon cycle and the stability of karst carbon sinks, it is necessary to better understand the source, distribution and transformation characteristics of organic matter (OM) in aquatic ecosystems. Here, stable isotope ratios (δ¹³ [...] Read more.

In order to improve the understanding of the global carbon cycle and the stability of karst carbon sinks, it is necessary to better understand the source, distribution and transformation characteristics of organic matter (OM) in aquatic ecosystems. Here, stable isotope ratios (δ¹³C and δ¹⁵N), elemental analysis (C/N ratios), and lipid biomarkers were analyzed for dissolved organic matter (DOM) (<0.7 μm), particulate organic matter (POM) (>0.7 μm) of water, and organic matter from sediment cores (SCOM) to identify the sources, distribution, and transformation of OM in a subtropical karst reservoir. The results showed that short-chain (C14–20) n-alkyl lipids were more abundant than long-chain (C21–34) n-alkyl lipids in both the DOM and SCOM samples, indicating that bacteria were the primary sources of these lipids, while terrestrial organic matter (OM) made only a minor contribution to the n-alkyl lipid pool, and aquatic plants (macrophytes) OM contributed major contribution to the n-alkyl lipid pool in POM. Microbial activity and lipid degradation were more pronounced in the DOM. Furthermore, terrigenous and macrophyte-derived lipids were found to be more abundant in POM than in DOM and SCOM, suggesting that they are relatively resistant to degradation compared with phytoplankton-derived OM. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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21 pages, 8325 KiB

Open AccessArticle

Phosphate in Aqueous Solution Adsorbs on Limestone Surfaces and Promotes Dissolution

by Liang Li, Wenhai Wang, Zhiwei Jiang and Anzhong Luo

Water 2023, 15(18), 3230; https://doi.org/10.3390/w15183230 - 11 Sep 2023

Cited by 1 | Viewed by 1743

Abstract

The use of large quantities of phosphorus-containing fertilizers has resulted in an increase in phosphorus content in the groundwater system, and phosphorus can be adsorbed on the surface of carbonate rocks, affecting their dissolution process and thus carbon sequestration and sink enhancement in [...] Read more.

The use of large quantities of phosphorus-containing fertilizers has resulted in an increase in phosphorus content in the groundwater system, and phosphorus can be adsorbed on the surface of carbonate rocks, affecting their dissolution process and thus carbon sequestration and sink enhancement in carbonate rocks. Therefore, in this study, limestone was exposed to 2 mg/L and 100 mg/L phosphate solutions for 12 d through static batch adsorption experiments. The hydrochemical results showed that in 100 mg/L phosphate solution, a substitution reaction occurred to produce CaHPO₄ precipitate, while the concentration of each ion in 2 mg/L phosphate solution was relatively stable and in dynamic equilibrium; combined with XRD and XPS analyses, the main mechanism of phosphate adsorption may be chemical precipitation, which is preferentially adsorbed to Ca sites on carbonate rocks, and the surface deposits are mainly CaHPO₄ and a small amount of Mg₂PO₄(OH). The FTIR spectra were obtained in the range of 1040 cm⁻¹–1103 cm⁻¹ for observed phosphate vibrations, and the υ₃ (asymmetric stretching) mode was more significant in the experimental group with a higher phosphate concentration. Raman spectra located near 149 cm⁻¹ and 275 cm⁻¹ involved Ca²⁺ or Mg²⁺ relative translations and vibrations, corroborating the FTIR spectroscopic results; a combination of XRD, XPS, FTIR, and Raman spectra confirmed that phosphate adsorption on limestone may be due to the interaction of electrostatic, chemical precipitation, and ligand exchange mechanisms. In addition, the SEM-EDS results showed that, with the combined effect of the water–rock chemical reaction and physical adsorption, metal–phosphorus phase precipitation was formed on the limestone surface, which promoted the dissolution of limestone and may have an unfavorable effect on the carbon sequestration and sinking of carbonate rocks. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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19 pages, 10863 KiB

Open AccessArticle

Geochemistry of Weathering Cover and the Main Influencing Factors in Karst Area of Guilin, Southwest China

by Huaying Wu, Zhongcheng Jiang, Qibo Huang, Funing Lan, Hongwei Liao, Tengfang Li and Chenhui Huang

Water 2023, 15(16), 2944; https://doi.org/10.3390/w15162944 - 15 Aug 2023

Cited by 3 | Viewed by 1576

Abstract

The chemical weathering of carbonate rocks is the main form of interaction between earth spheres in the karst critical zone. The karst weathering cover, which is composed by residua from carbonate rocks weathering, contains important information about the climate environment and material cycle. [...] Read more.

The chemical weathering of carbonate rocks is the main form of interaction between earth spheres in the karst critical zone. The karst weathering cover, which is composed by residua from carbonate rocks weathering, contains important information about the climate environment and material cycle. We present the chemical composition of weathering covers in karst area of Guilin, Guangxi province, analyze their weathering process and strength, and compare them with the other weathering covers in other karst area in China, including Yunnan, Guizhou, Hunan, and Qinghai Tibet Plateau. The results showed: (1) the chemical composition of Guilin weathering covers were similar to that of carbonate weathering covers in other areas of China, and had the common characteristics of uniform distribution of chemical composition in the profile and obvious enrichment of Fe, Al and trace elements. During the formation of carbonate weathering cover and the residua, the rapid dissolution of Ca and Mg had an important impact on the migration and enrichment of other elements. (2) The chemical index of alteration (CIA) of carbonate weathering covers in Guilin and other karst areas of China was much larger than that in the upper crust (UCC) (60.13), which showed strong chemical weathering characteristics of the humid and hot climate. (3) The weathering process of carbonate rock was different from that of silicate and loess. In the early stage of carbonate rock weathering, soluble components (calcite and dolomite) had been rapidly dissolved and leached. All the carbonate weathering residua was measured to be in the stage of K₂O weathering and Al₂O₃ increasing. Therefore, the weathering degree of carbonate weathering cover was mainly determined by the leaching of K₂O and the increase of Al₂O₃. As a result, there was no correlation between CIA and Na/K (molar ratio), but was a significant negative correlation between CIA and K/Al (molar ratio) in the carbonate weathering cover. (4) The CIA values of weathering residua and carbonate weathering cover in southern China were negatively correlated with latitude, reflecting the influence of climate factors. From the influence of lithology, the chemical compositions of parent rock can affect the CIA of weathering cover, and the content of insoluble matter in carbonate rock was negatively correlated with CIA. From the influence of topography, the CIA value of weathering residua decreased from the high to the low position and from the shallow to the deep part of the profile. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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21 pages, 5092 KiB

Open AccessArticle

Influence of Anthropogenic Sulfuric Acid on Different Lithological Carbonate Weathering and the Related Carbon Sink Budget: Examples from Southwest China

by Yincai Xie, Yupei Hao, Jun Li, Yongli Guo, Qiong Xiao and Fen Huang

Water 2023, 15(16), 2933; https://doi.org/10.3390/w15162933 - 14 Aug 2023

Cited by 3 | Viewed by 1412

Abstract

Accurate estimate of carbonate weathering and the related carbon sink flux induced by anthropogenic H₂SO₄ is of great significance for improving understanding of the hydrogeochemical evolution and the global carbon cycle. Here, to quantitatively evaluate the influence of anthropogenic H [...] Read more.

Accurate estimate of carbonate weathering and the related carbon sink flux induced by anthropogenic H₂SO₄ is of great significance for improving understanding of the hydrogeochemical evolution and the global carbon cycle. Here, to quantitatively evaluate the influence of anthropogenic H₂SO₄ on different lithological carbonate weathering and the related carbon sink budget, karst spring water in the typical limestone and mixed limestone–dolomite catchments in Yaji and Beidiping affected by acid precipitation in southwest China were sampled monthly for the analysis of hydrochemical and δ¹³C_DIC characteristics. Results show for the period of sampling (August 2013 to December 2014) that the average contribution rates of atmospheric inputs and carbonate weathering to total dissolved cations are 2.24% and 97.8%, and 3.09% and 96.9% in Yaji and Beidiping, respectively. The δ¹³C_DIC values (−17.0% to −14.7‰) and the [Ca²⁺ + Mg²⁺]/[HCO₃⁻] (0.98 to 1.25) and [Ca²⁺ + Mg²⁺]/[HCO₃⁻ + SO₄²⁻] (approximately 1) equivalent ratios of samples prove that H₂CO₃ and H₂SO₄ simultaneously participate in carbonate weathering. The contribution rates of H₂SO₄ to [Ca²⁺ + Mg²⁺] and [HCO₃⁻] produced by carbonate weathering in Yaji and Beidiping are 0–30% and 0–18%, and 0–37% and 0–23%, with average values of 14% and 7%, and 19% and 11%, respectively, suggesting that the influence of H₂SO₄ on different lithological carbonate weathering is different. H₂SO₄ precipitation participating in carbonate weathering increases the weathering rate by 14–19%, whereas it decreases the flux of karst carbon sink by 7–11% in Southwest China. Therefore, anthropogenic acids have influenced the global carbon cycle and climate change by carbonate weathering due to the large karst areas in the world, and their influences on different lithological carbonate weathering should not be ignored in the regional and global carbon cycles in future studies. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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20 pages, 10329 KiB

Open AccessArticle

Traceability and Biogeochemical Process of Nitrate in the Jinan Karst Spring Catchment, North China

by Kairan Wang, Xuequn Chen, Zhen Wu, Mingsen Wang and Hongbo Wang

Water 2023, 15(15), 2718; https://doi.org/10.3390/w15152718 - 27 Jul 2023

Viewed by 1155

Abstract

Accurate identification of nitrate (NO₃⁻) sources is critical to addressing groundwater pollution, especially in highly vulnerable karst aquifers. The groundwater hydrochemistry and δ¹⁵N_NO3 and δ¹⁸O_NO3 isotopes were analyzed in samples taken from the Jinan [...] Read more.

Accurate identification of nitrate (NO₃⁻) sources is critical to addressing groundwater pollution, especially in highly vulnerable karst aquifers. The groundwater hydrochemistry and δ¹⁵N_NO3 and δ¹⁸O_NO3 isotopes were analyzed in samples taken from the Jinan Spring Catchment, which has been affected by urbanization and agricultural activities. The study highlighted the use of hydrochemistry, environmental isotopes, and a multisource linear mixed model for NO₃⁻ source identification and apportionment. The results showed that, controlled by carbonate rocks, the hydrochemical types in both rainy and dry seasons were highly consistent, and HCO₃·SO₄⁻Ca was the dominant type, accounting for 60%. Except for Ca²⁺, Mg²⁺ and HCO₃⁻, the coefficients of variation of other ions were all greater than 0.5 in rainy and dry seasons. The chemical composition of groundwater was mainly controlled by water–rock interaction. Ca²⁺ and HCO₃⁻ were mainly derived from carbonate rock dissolution; K⁺, Na⁺, SO₄²⁻, NO₃⁻ and Cl⁻ were partially derived from atmospheric precipitation. The IsoSource model quantitatively revealed that the majority of the groundwater and surface water was influenced by manure and sewage (M&S) contributing 39.3% and 52.3% in the rainy season, and 37.1% and 56.9% in the dry season, respectively. The NO₃⁻ source fraction rates were in the order M&S > SON > AF > CF > AD. In addition, nitrate pollution control measures and suggestions for different areas are put forward. In rural residential areas, the free discharge of livestock manure and sewage should be strictly controlled. In agricultural planting areas, chemical fertilizers and pesticides should be used rationally to prevent non-point source pollution. In urban areas, the centralized treatment of industrial and residential sewage should be strengthened to prevent point source pollution. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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18 pages, 4659 KiB

Open AccessArticle

The Mechanisms Controlling the CO₂ Outgassing of a Karst Spring–River–Lake Continuum: Evidence from Baotuquan Spring Drainage Area, Jinan City, Northern China

by Wen Liu, Tao Zhang, Haoran Liu, Pengfei Ma, Yue Teng, Qin Guan, Lingqin Yu, Chunwei Liu, Yiping Li, Chuanlei Li, Changsuo Li and Junbing Pu

Water 2023, 15(14), 2567; https://doi.org/10.3390/w15142567 - 13 Jul 2023

Cited by 1 | Viewed by 1525

Abstract

The significance of CO₂ emissions at the water–air interface from inland water bodies in the global carbon cycle has been recognized and is being studied more and more. Although it is important to accurately assess CO₂ emission flux in a catchment, [...] Read more.

The significance of CO₂ emissions at the water–air interface from inland water bodies in the global carbon cycle has been recognized and is being studied more and more. Although it is important to accurately assess CO₂ emission flux in a catchment, little research has been carried out to investigate the spatio-temporal variations in CO₂ emissions in view of a water continuum. Here, we systematically compared the differences and control factors of CO₂ degassing across the water–air interface of a spring–river–lake continuum in the discharge area of Baotuquan Spring in July 2017, which is a typical temperate karst spring area in Jinan city, northern China, using hydrogeochemical parameters, stable carbon isotope values, and CO₂ degassing flux. Affected by the pCO₂ concentration gradient between the water and ambient air, the spring water showed a high CO₂ degassing flux (166.19 ± 91.91 mmol/(m² d)). After the spring outlet, the CO₂ degassing flux in the spring-fed river showed a slight increase (181.05 ± 155.61 mmol/(m² d)) due to river flow rate disturbance. The river flow rate was significantly reduced by the “blockage” of the lake, which promoted the survival and reproduction of phytoplankton and provided favorable conditions for aquatic plant photosynthesis, increasing the plankton biomass in the lake to 3383.79 × 10⁴/L. In addition, the significant decrease in the dissolved inorganic carbon (DIC) concentration and the increase in the δ¹³C_DIC values in the lake also indicated that the photosynthesis of the lake’s aquatic plants resulted in a significant decrease in the pCO₂ concentration, thus limiting the amount of CO₂ off-gassing (90.56 ± 55.03 mmol/(m² d)). Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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23 pages, 7429 KiB

Open AccessArticle

Water Retention Evaluation of Slab Trench on Rocky Desertification Slope in a Karst Area of Southwest China

by Shiya Liu, Cheng Zhou, Shan Gao, Qiming Zhong, Lijuan Fan, Qi Luo, Qun Chen, Zechang Zhou and Xunhong Zhu

Water 2023, 15(8), 1576; https://doi.org/10.3390/w15081576 - 18 Apr 2023

Viewed by 1758

Abstract

Soil erosion and water loss are serious problems on the rocky desertification slopes in the karst dynamic system of southwest China. The lack of soil and shortage of water restrict the ecological restoration of the regional slopes and utility of water resources. Therefore, [...] Read more.

Soil erosion and water loss are serious problems on the rocky desertification slopes in the karst dynamic system of southwest China. The lack of soil and shortage of water restrict the ecological restoration of the regional slopes and utility of water resources. Therefore, a new slab trench capable of storing soil and water in layers on rocky desertification slopes is introduced in this paper to promote vegetation restoration. To explore the water-storing and -holding capacity of the new type of vegetated slab trench, five groups of model experiments were carried out on the vegetated slab trench under different rainfall intensities and different numbers of plants. Under rainfall and then following dry conditions, the effects of rainfall intensity and the number of plants on the water-storing and -holding capacity of vegetated slab trench models were compared and analyzed. Water-storing and -holding capacity was further explored in three groups of models with single planting or combinations of plants including water stored only in succulent root plant, only in succulent stem plant, or in mixed plants. The test results show that the new type of vegetated slab trench can effectively help to store and hold water. In the rainfall period, due to the runoff of the rainfall not being considered, the greater the rainfall intensity, the higher the water storage efficiency; the more vegetation implanted, the greater the blocking effect of the plant canopy during falling rainwater, and the more reduction is induced on the water storage efficiency of the vegetated slab trench. In the following dry period, both the succulent root plant and succulent stem plant have strong water storage capacity, but the succulent root plant has a stronger capacity for water storage. The growth status of the mixed plants was better than that of single planting, which may be due to the water complementarities between the succulent root plant and succulent stem plant in a mixed planting manner. This study is important for solving the problem of soil erosion and water loss in rocky desertification slopes, and it helps to restore the ecological environment of the area. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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16 pages, 2098 KiB

Open AccessArticle

Quantitative Study on Improved Budyko-Based Separation of Climate and Ecological Restoration of Runoff and Sediment Yield in Nandong Underground River System

by Peng Liu, Zhongcheng Jiang, Yanqing Li, Funing Lan, Yingjie Sun and Xiangfei Yue

Water 2023, 15(7), 1263; https://doi.org/10.3390/w15071263 - 23 Mar 2023

Cited by 4 | Viewed by 1713

Abstract

Serious soil and water loss affects the economy and the living quality of the population in faulted basins. Since 2002, China has carried out large-scale ecological restoration projects in karst areas. However, the karst faulted basins have experienced complex climatic changes, which makes [...] Read more.

Serious soil and water loss affects the economy and the living quality of the population in faulted basins. Since 2002, China has carried out large-scale ecological restoration projects in karst areas. However, the karst faulted basins have experienced complex climatic changes, which makes it difficult to assess the ecological restoration effects quantitatively. Using the improved Budyko model, basin factor (n) and sediment content factor (C) were divided into climate influence and ecological restoration influence by second-order approximation, and the change ratio of climate influence and ecological restoration on sediment yield and loss was quantitatively calculated in the representative basin of the Nandong Underground River System (NURS). This was carried out in order to effectively distinguish the effects of climate change and ecological restoration on runoff and sediment change in the NURS. Furthermore, this study sought to understand the mechanism of runoff and sediment change and to evaluate the ecological restoration in the faulted basin to provide a scientific basis for the next stage of soil and water conservation policy formulation. The results showed that: (1) Using Pettitt to test the abrupt change of water and sediment in the NURS from 1987 to 2018, we found that 2002 was the abrupt change year of water and sediment in the basin. Before and after the mutation, the runoff and sediment yield decreased significantly, with the change rates of −15.5% and −51.8%, respectively. The decrease in precipitation and the increase in E₀ were not significant, which were −4.5% and 1.4% respectively. (2) By calculating the correlation coefficient and the double logarithm function, it was found that the maximum temperature is the main climatic factor affecting the underlying surface factor n, and precipitation is the main climatic factor affecting the sediment concentration c. (3) Climate change reduced runoff by 77.6%. Ecological restoration has reduced sediment by 51.3 percent. The sensitivity of runoff to maximum temperature was 3.61. The sensitivity of grain yield to precipitation and NDVI was 5.37 and 3.26, respectively. The results show that climate is the main factor of runoff reduction, and ecological restoration is the main factor of sediment reduction. Ecological restoration has greatly reduced sediment production, and ecological engineering has made remarkable progress. However, the reduction of runoff caused by climate change should be paid more attention. The results of these studies will help to better formulate land use management policies for soil and water conservation. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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Review

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25 pages, 6725 KiB

Open AccessReview

A Review of Heavy Metal Migration and Its Influencing Factors in Karst Groundwater, Northern and Southern China

by Wanjun Zhang, Cunlin Xin and Shi Yu

Water 2023, 15(20), 3690; https://doi.org/10.3390/w15203690 - 22 Oct 2023

Cited by 6 | Viewed by 2611

Abstract

With the substantial increase in karst groundwater pollution, the pollution caused by heavy metal migration has become one of the hottest topics. The migration characteristics of heavy metals in karst groundwater are closely related to the geological environment in which they are found. [...] Read more.

With the substantial increase in karst groundwater pollution, the pollution caused by heavy metal migration has become one of the hottest topics. The migration characteristics of heavy metals in karst groundwater are closely related to the geological environment in which they are found. Therefore, this review focuses on the migration characteristics of heavy metals in karst groundwater in southern and northern China and highlights the effect of different environmental contexts such as atmosphere (precipitation), vegetation, soil, rock, and aquifers on the behavior of heavy metals. It also summarizes existing research methods on heavy metal migration in karst groundwater. Meanwhile, current advances and the future perspectives on karst groundwater heavy metal migration will be presented. It is hoped that this review may shed light on the study of heavy metal migration in karst areas. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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13 pages, 2807 KiB

Open AccessReview

Spatial Distribution and Sources of Organic Matter in the Surface Sediments of Fuxian Lake, SW China

by Kai Zhang, Dongli Li, Xuejun He, Changyuan Xie and Haibo He

Water 2023, 15(4), 794; https://doi.org/10.3390/w15040794 - 17 Feb 2023

Cited by 3 | Viewed by 5700

Abstract

Sedimentary organic matter is an important component of the metabolism of a lake’s ecosystem, and it is generally derived from both the watershed and the primary productivity of a lake. Understanding the sources of organic matter in lakes and lake trophic status is [...] Read more.

Sedimentary organic matter is an important component of the metabolism of a lake’s ecosystem, and it is generally derived from both the watershed and the primary productivity of a lake. Understanding the sources of organic matter in lakes and lake trophic status is important when evaluating the quality of lake ecosystems. We summarize the spatial distribution of total nitrogen (TN), total organic carbon (TOC), TOC/TN (C/N) molar ratios, and organic carbon isotope (δ¹³C_org) of the surface sediments of Fuxian Lake, Yunnan–Guizhou Plateau, Southwest China, which is the second deepest freshwater oligotrophic lake in China. The results show that the distributions of TN, TOC, C/N, and δ¹³C_org of the surface sediments are spatially heterogeneous, which is also the case for the trophic conditions of the lake. Compared with the adjacent eutrophic lakes and typical lakes in other areas with strong human activities, the content of organic matter is at a low level. Meanwhile, the autochthonous organic carbon in the surface sediments was characterized by lower δ¹³C_org (−25.3~−28.5) and C/N (8.7~12.9), suggesting that the biological carbon pump effect plays a significant part in the stability of carbon sinks by coupling with carbonate weathering. Our results emphasize the importance of the carbon sink of coupled carbonate weathering and aquatic photosynthesis in the evolution of the carbon cycle in lakes. Although modern monitoring shows that Fuxian Lake is an oligotrophic lake, there are potential risks of organic nitrogen pollution with respect to surface sediments, especially in northern and southern shallow-water areas. The organic pollution of lakes can be reduced by controlling the discharge of wastewater and reducing the nutrient loading of agricultural runoff. Full article

(This article belongs to the Special Issue Karst Dynamic System and Its Water Resources Environmental Effects)

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