•CUE increased with greater PRE and RAD but decreased with higher TEM.•WUE increased with greater PRE and TEM but decreased with greater RAD.•CUE showed an insignificant decreasing trend from 2001 to ...2019 in China.•WUE showed a significant increasing trend from 2001 to 2019 in China.•Human activities contribute more than climate change to CUE and WUE.
Carbon-use efficiency (CUE) and water-use efficiency (WUE) are critical parameters for evaluating the exchange of carbon and water in ecosystems, influenced by climate change and human activities. Quantifying the relative contributions of climate change and human activity to CUE and WUE is essential in the context of global warming and rapid land use transformation. This study assessed spatiotemporal variations in CUE and WUE and evaluated their interconnections with climate factors through comprehensive trend and partial correlation analyses. Furthermore, it explored the responses of CUE and WUE variations to climate change and human activities across distinct geographical zones in China from 2001 to 2019, employing multiple regression residual trend analysis. Our analysis suggested that annual average CUE was 0.57 and annual average WUE was 1.47 g C kg−1H2O. Spatially, CUE demonstrated an increase in northern China but a decline in the southern regions, while WUE exhibited a contrasting trend. Generally, CUE exhibited a positive correlation with increased precipitation (PRE) and solar radiation (RAD) but displayed a negative association with elevated air temperature (TEM). Conversely, WUE showed an increase with greater PRE and TEM but a decrease with heightened RAD. Notably, it was revealed that human activities exerted a more significant impact on CUE and WUE in China than climate change. However, climate change played an important role in some areas with low populations, such as the Qinghai–Tibet Plateau. The results will improve the understanding of the carbon and water coupled process in terrestrial ecosystems, which is helpful to optimize the allocation of ecological resources and maintain ecosystem balance.
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•An isotope-mixing model and label approach was used to determine SPOC sources.•Resuspension (45.27%) and algae (31.57%) were the main sources for SPOC.•Water movement and climate ...variations affected seasonal dynamics in different sources.•Buried OC through assimilating DIC from carbonate rock weathering was ~10.84 tC/a.
The biological carbon pump (BCP) effect is a key mechanism in karst surface freshwater ecosystems, and can transform inorganic carbon from carbonate weathering into organic carbon via photosynthesis and sedimentation. In the process, an understanding of particulate organic carbon sources, their flux, and their variability is important for understanding BCP effects, but these relative processes are still poorly understood. Therefore, we used a sediment trap experiment to collect settling particulate organic carbon (SPOC) and conducted a systematic study to understand the sources and factors that influence SPOC, as well as determine the amount of SPOC generated by the BCP effect by combing meteorological data monitoring and modern hydrochemical monitoring in the Dalongdong (DLD) reservoir, a karst groundwater-fed reservoir. Based on δ13C, δ15N, and molar C/N data, as well as relative models, the SPOC sources came from algae, resuspened matter, soil, and domestic sewage. Among these, resuspension (45.27%) and algae (31.57%) were the main sources for SPOC. Thus, the seasonal variations in different sources were mainly affected by water movement caused by climate changing with respect to air temperature and rainfall. In addition, domestic sewage discharge in the DLD reservoir also affected the sources for SPOC. The results suggested that the SPOC from algal sources in the DLD reservoir was 17.07 gC/m2/a at the surface and 9.26 gC/m2/a at the bottom via the BCP process. The SPOC deposition efficiency (OCDE) of algae was 54.25%. Organic carbon from algal source via the BCP effect at the surface of water column was finally deposited and buried in sediment. According to estimation of historical data, the stored organic carbon through assimilating DIC from carbonate rock weathering by BCP effect was as much as 10.84 tC/a. The quantity of organic carbon stored and fixed by BCP effect cannot be ignored in the reservoirs.
In recent years, after the implementation of large-scale ecological restoration projects, karst areas in the South China Karst have become global “greening” hot spots. However, the biodiversity, ...ecosystem quality, and security patterns in karst areas are still severely affected. The reason for this is that despite the execution of karst desertification control projects, the lag mechanism of forest ecosystem functions and services is still unclear. Therefore, we analyze the progress in the research related to desertification control and the improvement of regional forest ecosystem function through a systematic literature review approach. The results show that the major landmarks achieved so far include the following aspects: based on the karst desertification control area, we have elucidated the driving factors of forest ecosystem change, discovered the ecological security pattern of landscape optimization and reconstruction, revealed the internal mechanism of forest system structure optimization and stability enhancement, overcome the technical constraints of forest water–fertilizer coupling, introduced a strategy for regulating functional traits to improve the growth and development of vegetation, proposed strategies to enhance carbon sequestration in forests and the efficiency of microbial carbon use, and created models and paths to realize the value of forest products. The key scientific issues to be addressed in the future mainly comprise the following: the effects of spatial heterogeneity on forest ecosystems, disturbances in landscape reconfiguration caused by human activities, the work mechanisms of the combination and configuration of the niche in structural optimization, the response of species configuration to the water cycle, the coupled relationship between biodiversity and soil properties, the screening and construction of the plant germplasm resource base, the functional trade-offs/synergistic mechanisms of karst forest ecosystems, the creation of policies for forest product in terms of rights, trading, and compensation, and systematic research on the extended industrial chain of forest ecosystems, its service potential, and so on.
Soil water plays an important role in the ecological restoration of karst areas impacted by rocky desertification (KRD) caused by deforestation. A better understanding of the spatiotemporal dynamics ...and modes of water flow in KRD areas is essential for satisfactory soil water management. This study examines the soil water content (SWC) and stable isotope (δ
18
O and δD) patterns in seven sampling sites along an E-W transect in a typical small karst basin in southwest China over the hydrologic year, February, 2018–January, 2019. The results of this study show that the spatial differences of SWC and soil water δ
18
O (δD) values were smaller but in with clear seasonal variations. Seasonal vertical profiles of soil water δ
18
O (δD) showed a decreasing trend from the surface to a depth of 100 cm in February, April, and June, which reversed August and October. Shallow soil water δ
18
O (δD) and line-conditioned excess (lc-excess) (< 20 cm depth) showed significantly stronger seasonality than the deeper soil water (> 20 cm depth). Enriched soil water δ
18
O (δD) values in the upper 20 cm depth was closely related to the potential evaporation over the 7 days prior to each sampling (PET
7
). Piston flow was the dominant mode of flow in the sampling sites, inferred from the vertical profile characteristics of the soil water δ
18
O (δD). The influence of evaporative processes was limited to the upper 20 cm depth of the soil. The fraction of evaporation losses from soil water storage at the 20 cm depth varied from − 15.8% to 12.3%, based on δD estimates, and from − 13.3% to 14.0% based on δ
18
O. These results are important for effective soil water management in KRD areas that experience seasonal drought.
Arbuscular mycorrhizal (AM) fungi and roots play important roles in plant nutrient acquisition, especially in nutrient poor and heterogeneous soils. However, whether an accumulation strategy of AM ...fungi and root exists in such soils of karst shrubland ecosystems remains unclear. Root traits related to nutrient acquisition (root biomass, AM colonisation, root acid phosphatase activity and N
fixation) were measured in two N
-fixing plants (i.e. Albizia odoratissima (Linn. f.) Benth. and Cajanus cajan (Linn.) Millsp.) that were grown in heterogeneous or homogeneous nutrient (ammonium) soil with and without AM fungi inoculation.
Both of these plants had higher AM colonisation, root biomass and relative growth rate (RGR), but lower N
fixation and root acid phosphatase activity in the rhizosphere in the heterogeneous soil environment, than that in the homogeneous soil environment. Plants grown in the AM fungi-inoculated heterogeneous soil environment had increased root biomass and root acid phosphatase activity compared with those grown in soil without inoculation. AM colonisation was negatively correlated with the N
fixation rate of A. odoratissima, while it was not significantly correlated with the root phosphatase activity.
Our results indicated that enhanced AM symbiosis and root biomass increased the absorptive surfaces for nutrient acquisition, highlighting the accumulation strategies of AM and root traits for plant nutrient acquisition in nutrient poor and heterogeneous soils of the karst shrubland ecosystem.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Karst aquifers are highly heterogeneous, and non-stationary systems in terms of hydrodynamic properties. The investigation of the different transport properties and characteristics of a karst aquifer ...system (KAS) is of great significance for the management and protection of karst aquifers. To investigate the response of discharge (
Q
), suspended sediment (SS), and temperature (
T
) to the precipitation (
P
), we performed correlation, spectral, and wavelet analyses on the hydrologic time series that included mean daily value from 2009/1/1 to 2015/12/31 from the Nandong underground river system (NURS), a large (> 1600 km
2
) karst-groundwater basin in southern China. The long memory effects can be determined from the autocorrelation functions of the
Q
, SS and
T
implied that the NURS has a significant amount of storage. The sharp and narrow cross-correlation function (CCF) peaks and the cross-wavelet transform (XT) power spectrum of the SS vs.
P
indicated that the response of the SS to
P
was shorter than that of the
Q
and
T
, and also indicated that the weak memory effect and small inertia of the karst systems with regard to SS. The CCF and XT power spectrum indicated that an increase in
Q
was the main factor triggering the increase in SS, not precipitation, which is contrary to results determined for other karst springs. Furthermore, the XT and cross-wavelet coherence (TC) of T vs. the air temperature (
T
a
) was used to demonstrate that
T
a
is not a direct control on the
T
in the NURS, which can be misinterpreted when using the traditional correlation and spectral analyses.
The application of combined isotopic and hydrochemical compositions may be useful for evaluating water quality problems in karst aquifers in which it is difficult to distinguish the sources of ...solutes from the natural background of those due to human activities. Multiple isotopes (δ¹³C–DIC, δ³⁴S–SO₄ ²⁻) and chemical parameters were measured in rainwater, groundwater and sewage in order to elucidate the solute sources and impacts from human activities and natural background in the Laolongdong karst catchment in Chongqing Municipality, SW China. Overall, the dissolution of carbonate rock controls Ca²⁺, Mg²⁺ and HCO₃ ⁻ content in rainwater and karst groundwater. SO₄ ²⁻ originated mainly from gypsum dissolution in karst groundwater. Carbonate rocks in the studied site could be dissolved jointly by H₂CO₃ from the natural CO₂–H₂O reaction and other acids (organic acids and HNO₃) from sewage and soils. Sewage discharge from urban areas and agriculture activities lead to the increase of NO₃ ⁻, PO₄ ³⁻ and Cl⁻ in karst groundwater. To protect and sustainably utilize the karst aquifer, sewage originating from urban areas must be controlled and treated and the use of fertilizer should be limited.
Severe soil erosion is a critical issue in karst areas. Due to a lack of surface streams, soils often discharge from karst catchments via groundwater. Quantifying sediment discharge (SD) from karst ...groundwater will help managers to develop effective methods of soil conservation. The time series of the monthly SD and controlling factors (water discharge, precipitation, potential evapotranspiration, and normalized difference vegetation index) of the Nandong Underground River System (NURS), a typical karst underground river catchment in southwest China, from 1998 to 2015 were analyzed. To investigate the changing seasonal characteristics of monthly sediment discharge and controlling factors and predict the variations in monthly sediment discharge, an analysis of variance (ANOVA), seasonal Mann–Kendall test, and seasonal decomposition of time series by loess (STL) were conducted to identify changes in the seasonal characteristics of the SD and the controlling factors on a monthly scale. The results of these analyses indicated that the SD and its controlling factors varied considerably from month to month and the annual soil loss mainly occurred from June to September. The SD gradually decreased during April and May due to the decreasing of precipitation in March and April during the 1998–2015 period. The decrease of rainfall not only reduces the intensity of soil erosion on the surface, but also reduces the flow and velocity of underground rivers, reducing the transport capacity of suspended matter. Our study showed that the bivariate state-space model had the lowest Akaike’s information criterion (AIC) score (− 7.594 and − 7.686) and root mean square error (RMSE) (0.022 × 10
6
m
3
and 0.020 × 10
6
m
3
) values and the highest
R
2
values (0.983 and 0.984) for the calibration and validation periods, and was the best state-space model to describe the temporal distribution of the monthly sediment discharge in the NURS. A method that allows for the correct estimation and evaluation of soil erosion and the determination of the regional soil and water conservation can be useful for better karst catchment management in the NURS.
•δ18O-VPDB and δ13C-VPDB in modern calcite precipitates shows clear seasonal variation.•Isotope kinetic fractionation occurs between parent drip water and depositing calcite.•Kinetic fractionation ...amplifies the equilibrium fractionation value of calcite δ18O (by ∼1.5‰) and δ13C (by ∼1.7‰).
A prerequisite for using cave speleothems to reconstruct palaeoenvironmental conditions is an accurate understanding of specific factors controlling calcite growth, in particular the isotopic partitioning of oxygen (δ18O) and carbon (δ13C) which are the most commonly used proxies. An in situ monitoring study from April 2008 to September 2009 at Xueyu Cave, Chongqing, SW China, provides insight into the controls on calcite growth rates, drip water composition, cave air parameters and δ18O and δ13C isotopic values of modern calcite precipitation. Both cave air PCO2 and drip water hydrochemical characteristics show obvious seasonality driven by seasonal changes in the external environment. Calcite growth rates also display clear intra-annual variation, with the lowest values occurring during wet season and peak values during the dry season. Seasonal variations of calcite growth rate are primarily controlled by variations of cave air PCO2 and drip water rate. Seasonal δ18O-VPDB and δ13C-VPDB in modern calcite precipitates vary, with more negative values in the wet season than in the dry season. Strong positive correlation of δ18O-VPDB vs. δ13C-VPDB is due to simultaneous enrichment of both isotopes in the calcite. This correlation indicates that kinetic fractionation occurs between parent drip water and depositing calcite, likely caused by the variations of cave air PCO2 and drip rate influenced by seasonal cave ventilation. Kinetic fractionation amplifies the equilibrium fractionation value of calcite δ18O (by ∼1.5‰) and δ13C (by ∼1.7‰), which quantitatively reflects surface conditions during the cave ventilation season. These results indicate that the cave monitoring of growth rate and δ18O and δ13C of modern calcite precipitation are necessary in order to use a speleothem to reconstruct palaeoenvironment.
