Recent Human Activities Research Articles

Bibliometric analysis of research progress on karst groundwater pollution

The hydrological conditions in karst areas are complex. Due to the special karst structure, the surface and aquifers are closely connected through surface karsts, sinkholes, etc., making the karst aquifers vulnerable to pollution. In recent years, human activities and climate change have also exacerbated this phenomenon. Understanding the key knowledge and research status of karst groundwater pollution is an important prerequisite for subsequent research. Based on the CiteSpace software, this paper analyzed the related papers on karst groundwater pollution in the core database of Web of Science, intending to sort out the research results in this field and explore potential research hotspots. Analysis results show that: (1) In recent years, the number of publications and citations in this field has gradually increased, and there is a large space for research and development; (2) The United States, China, Germany are the countries that have contributed the most in this field. The number of research results in this field supported by the National Natural Science Foundation of China is in a leading position in the world; (3) The identification and protection of the vulnerability of karst aquifers, modeling of groundwater flow and pollutant migration are the main research directions. Water chemical analysis, tracer experiment and numerical modeling are the main research methods in this field; (4) The migration of organic micro-pollution, the trace of groundwater flow, the distribution of biodiversity and control factors, the characterization of karst conduits and the simulation of conduit flow, and the development of new tracer isotope fractions are potential development directions and breakthrough points in this field. In general, the research on karst groundwater pollution in the future is inseparable from the cross-integration of various disciplines, the mutual verification of multiple methods, and the introduction of new technological methods.

Genetic Structure and Population Demography of White-Spotted Charr in the Upstream Watershed of a Large Dam

White-spotted charr (Salvelinus leucomaenis leucomaenis) is an anadromous fish that has been severely harmed by human land-use development, particularly through habitat fragmentation. However, the anthropogenic impacts on populations of this species have not been evaluated, except those on small dammed-off populations. Using multiplexed ISSR genotyping by sequencing, we investigated the genetic structure of white-spotted charr in four tributaries in the upper section of the Kanayama Dam in the Sorachi River, Hokkaido Island, Japan. There were no distinct genetic structures (FST = 0.014), probably because some active individuals migrate frequently among tributaries. By model-flexible demographic simulation, historical changes in the effective population size were inferred. The result indicates that the population size has decreased since the end of the last glacial period, with three major population decline events, including recent declines that were probably associated with recent human activities. Nevertheless, populations in the watershed upstream of the Kanayama Dam are still expected to be at low risk of immediate extinction, owing to the large watershed size and the limited number of small check dams. An effective conservation measure for sustaining the white-spotted charr population is to maintain high connectivity between tributaries, such as by providing fishways in check dams during construction.

Small coastal streams-Critical reservoirs of genetic diversity for trout (Salmo trutta L.) in the face of increasing anthropogenic stressors.

We used microsatellite markers to investigate levels and structuring of genetic diversity in trout (Salmo trutta L.) sampled from 16 rivers along the south coast of Cornwall in southwest England. This region is characterized by many small coastal streams with a few larger catchments. At a regional level, genetic structuring of contemporary populations has been influenced by a combination of events, including the last Ice Age and also more recent human activities over the last millennium. All populations are shown to have gone through strong genetic bottlenecks, coinciding with increased exploitation of mineral resources within catchments, beginning during the Medieval period. At more local levels, contemporary human‐induced habitat fragmentation, such as weir and culvert construction, has disproportionally affected trout populations in the smaller catchments within the study area. However, where small catchments are relatively unaffected by such activities, they can host trout populations with diversity levels comparable to those found in larger rivers in the region. We also predict significant future loses of diversity and heterozygosity in the trout populations inhabiting small, isolated catchments. Our study highlights how multiple factors, especially the activity of humans, have and continue to affect the levels and structuring of genetic diversity in trout over long timescales.

Lake Martin, Louisiana sediments as a record of geomorphology, paleoenvironment, and human activities

There are relatively few lake sediment records from the southeastern United States that span sufficient time to characterize the environment prior to substantial anthropogenic disturbance. This has made it difficult to characterize the magnitude and timing of the impact of industrial human activities within the context of natural variability. The objective of this study was therefore to use weight percent organic matter, carbon to nitrogen ratios, carbon and nitrogen isotopes, and weakly bound lead concentrations from Lake Martin, a small oxbow lake in southern Louisiana, to (1) characterize natural variability in lake carbon and nitrogen cycling within the last several millennia in a vastly understudied region of the US and (2) assess the impact of recent human activities such as agriculture, land-use change, and industrial activities on the water and sediment quality of the lake. The basal sediments from Lake Martin are distinctive in color and character and likely derive from a large paleo-lake that catastrophically drained in the late Holocene. The last 1100 years of the record demonstrates a gradual transition from a system with moderate amounts of terrestrial materials to one dominated by aquatic organic matter likely due to the transition from a lotic to lentic system. Coincident with when the Acadians settled in the Lafayette area around 200 years ago, further changes are apparent in the sediment record, but do not display the hallmark signs of either land-use change or cultural eutrophication. This may be because lake levels are low and led to the efficient oxidation and recycling of organic matter.

Study of sediment deposition at Tanjung Laboh due to jetty structural

Changes in coastal areas are due to factors such as natural factors. In recent years human activities and coastal development have contributed greatly to the change of the coast. Concerned with this problem, a study was conducted on the coast of Tanjung Laboh in March 2019 to collect oceanographic data related to coastal change. The purpose of this study was to compare the distribution of sediment size in jetty structure areas and unstructured areas. Specific gravity has been compared between sampling lines A, B, C and D. The study area has been divided into three zone and every sampling line is in between of 80 meters. Field work to collect current velocity data was done during high tide. Estimates of sediment accumulation were carried out by comparing sediment characteristics obtained in structured and unstructured areas that related to current velocity. The results show that the beach profile is silty clay. The current velocity is also found to be low at 0.044 m/s to 0.218 m/s. In conclusion, the sediment transportation and sediment deposition can be influence by current velocity of a coastal and factor of any barrier. Test have been carried out shows that different particles size distribution around jetty structure and without jetty structure.

Spatiotemporal trends of atmospheric Pb over the last century across inland China

Sedimentary records from remote regions contain pollutants derived dominantly from atmospheric input, and thus have the potential to trace past atmospheric pollution history. Based on seventeen sediment records from relatively remote areas of China, atmospheric Pb pollution history during the last century was studied. These records suggest only occasionally slight pollution before ~1950 and display synchronous Pb enrichment processes since the 1950s, implying the start of widespread atmospheric Pb pollution in China. This corresponded well with the beginning of socio-economic development after the establishment of the People's Republic of China. However, owing to the Chinese Cultural Revolution, a roughly unchanged atmospheric Pb status was found in the 1960–70s except on the Qinghai-Tibetan Plateau, where atmospheric Pb still increased gradually caused by long-range atmospheric transport of pollutants from southwest Asia. In ~1980–2000, atmospheric Pb experienced the greatest increase, resulting from rapid development of extensive economy after the Reform and Opening-up in 1978. After ~2000, atmospheric Pb generally stopped increase due to the phasing out of leaded gasoline, but it remained high, with the highest in Southwest China, medium in Northeast China, central North China and the Qinghai-Tibetan Plateau, and the lowest in the southeast Mongolia Plateau and West China. This study reveals spatio-temporal variations of atmospheric Pb in inland China under the influence of recent human activities, providing an important supplement for understanding global Pb pollution in the Anthropocene.

Monitoring the spatio-temporal dynamics of the wetland vegetation in Poyang Lake by Landsat and MODIS observations

Poyang Lake, the largest freshwater lake of China, provides critical ecological functions for water circulation and biodiversity conservation as a dynamic wetland system. However, recent climate change and human activities exerted strong pressures on this ecosystem. In this paper, we applied object-based image analysis (OBIA) and Radom Forests (RF) classifier to ten Landsat images to examine the land cover composition and its change during 1987–2017 low water season at Poyang Lake. NDVI time series (2000–2017) derived from MODIS imagery was used to document the changes of vegetation growth status. To investigate the potential driving mechanism of the inundation patterns, we differentiated the spatial-temporal changes of vegetation coverage and NDVI accumulation on eight elevation bands. Major result indicates that the vegetation area increased by 15.5% of the lake area during 1987–2017. A much faster-increasing rate (58.0 km2 year−1) can be observed during 2001–2009 as compared to that of the overall study period (18.4 km2 year−1). Analysis of NDVI accumulation showed that 42.1% of the lake's area displayed a significant increasing trend during 2000–2017. Spatially, the increase of vegetation area and NDVI accumulation mainly took place in the 11–12 m elevation band in the lower lake center. Early dry season and prolonged exposure period after the operation of Three Gorges Dam (TGD) was the major reason for the spatio-temporal evolution of the wetland vegetation in Poyang Lake. The Lake's water level started to fall below 12 m before 9th November might cause a boost of vegetation growth in the low lake center, and in turn, triggering xerophilization for the vegetation in the highlands and a shift in foraging patterns of waterbirds due to phenology variations. The findings of this study provide a clear reference for sustaining the inter-annual stability of the ecosystem by controlling the depth of water in the lake.

Impacts of Recent Climate Trends and Human Activity on the Land Cover Change of the Abbay River Basin in Ethiopia

The Abbay River Basin, which originates in Ethiopia, is a major tributary and main source of the Nile River Basin. Land cover and vegetation in the Abbay River Basin is highly susceptible to climate change. This study was conducted to investigate the trends of climate change for a period of thirty-six years (1980–2016) within selected stations of the basin by using the innovative trend analysis method, Mann–Kendall test, and Sen’s slope estimator test to investigate the mean annual precipitation and temperature variables. Changes in land cover and vegetation in the Abbay River Basin were studied for a period of thirteen years (2001–2013) by using remote sensing, GIS analysis, land cover classification, and vegetation detection methods to assess the land cover and vegetation in the basin. In addition, Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), and Transformation Matrix were employed to analyze the spatial and temporal patterns of land cover and vegetation impacted by changes in climate. The result reflects that the trend of average annual temperature was remarkably increased (Φ = 0.12, Z = 0.75) in the 36-year period, and the temperature was increased by 0.5°C, although precipitation had slightly decreased during the same period. In the thirteen years’ period, forest land and water resource decreased by 3429.62 km2 and 81.45 km2, respectively. In contrast, an increment was observed in grassland (2779.33 km2), cultivated land (535.34 km2), bare land (43.08 km2), urban land (0.65 km2), and wetland (152.66 km2) in the same period. In the study, it was also observed a decrease of an NDVI value by 0.1 was observed in 2013 in the southern part of the basin. The findings of the present study illustrate a significant change in eco-hydrological conditions in the ARB with an adverse impact on the environment. Hydroclimatic changes caused the increase in temperature and decreasing trend in precipitation which significantly impacted the land cover and vegetation in the basin. The changes in land cover were mostly caused by global and local climate influence which mainly affects the hydroclimate and eco-hydrology systems of the basin. The result is consistent with that of the previous studies conducted elsewhere. The findings of this paper could help researchers to understand the eco-hydrological condition of the study basin and become a foundation for further studies.

Integrated hydrometeorological, snow and frozen-ground observations in the alpine region of the Heihe River Basin, China

Abstract. The alpine region is important in riverine and watershed ecosystems as a contributor of freshwater, providing and stimulating specific habitats for biodiversity. In parallel, recent climate change, human activities and other perturbations may disturb hydrological processes and eco-functions, creating the need for next-generation observational and modeling approaches to advance a predictive understanding of such processes in the alpine region. However, several formidable challenges, including the cold and harsh climate, high altitude and complex topography, inhibit complete and consistent data collection where and when it is needed, which hinders the development of remote-sensing technologies and alpine hydrological models. The current study presents a suite of datasets consisting of long-term hydrometeorological, snow cover and frozen-ground data for investigating watershed science and functions from an integrated, distributed and multiscale observation network in the upper reaches of the Heihe River Basin (HRB) in China. Meteorological and hydrological data were monitored from an observation network connecting a group of automatic meteorological stations (AMSs). In addition, to capture snow accumulation and ablation processes, snow cover properties were collected from a snow observation superstation using state-of-the-art techniques and instruments. High-resolution soil physics datasets were also obtained to capture the freeze–thaw processes from a frozen-ground observation superstation. The updated datasets were released to scientists with multidisciplinary backgrounds (i.e., cryospheric science, hydrology and meteorology), and they are expected to serve as a testing platform to provide accurate forcing data and validate and evaluate remote-sensing products and hydrological models for a broader community. The datasets are available from the Cold and Arid Regions Science Data Center at Lanzhou (https://doi.org/10.3972/hiwater.001.2019.db, Li, 2019).

Population density of the spur-thighed tortoise Testudo graeca declines after fire in north-western Africa.

Fire is a key ecological process in several biomes worldwide. Over recent decades, human activities (e.g. rural abandonment, monoculture plantations) and global warming are magnifying the risk of fire, with changes in fire intensity and frequency. Here, we offer the first study that examines the impact of fire on the spur-thighed tortoise Testudo graeca living in a native cork oak forest and pine plantation in north-western Africa. A total of 44 transects (22 burnt and 22 unburnt) were sampled at 8 sites affected by fires of natural cork oak forest and pine plantation with 8 surveys per site in 2015–2017 (264 hours of sampling effort). Tortoise densities were estimated with line-transect distance sampling. The detection probability of tortoises was higher in burnt (0.915) than unburnt (0.474) transects. The density of tortoises was negatively associated with elevation and declined with fire by c. 50% in both forest types. The negative response of T. graeca to fire should be considered in conservation planning of this species in north-western Africa in a future scenario of changes in fire regime.

The visible impacts of human activities constructing hydropower dam on Vietnamese Mekong Delta and conceptual solutions for responses

Abstract. Regarding to the important environmental issues, eco-balance and eco-system should be discussed using long period data analysing and visible result of study. These visible results will be materials for construction of geo-design of the river basin. Both hydrological changes and surface changes of the Mekong delta was analysed with new data using hydrologic model with visible mapping in this study. The Mekong River delta, the third largest delta in the world, is presently shifting from growing to shrinking with its ecosystem and environment seriously degraded. These environmental changes are due to several factors such as 1)ill-planned water management schemes including hydropower dams in the river basin, 2) sediment starvation, 3) increased nutrient inflows, in combination with other human activities including infrastructural extension, riverbed mining, delta subsidence, degradation of coastal mangrove belt, and gaps in governance in the whole Mekong basin under the climate change and sea level rise. Both scientific and management communities have suggested that the rate of Mekong delta shrinking will increase markedly this century. The paper compiled new data and mapping together with recent key studies implying that much of the degradation in the Vietnamese Mekong delta is due to recent human activities, particularly hydropower dams in the entire Mekong river basin.By comparison with period before 1990s when there were no large dams, the natural regime here has changed with the annual sediment load to the delta having decreased by 50–60%, the flood discharges have also decreased, the hydrological seasonal regime has shifted as most of the Mekong River water is now trapped in these large dams, and the salinity intrusion into the delta now occurs earlier by 20–30 days. Further, the river bed is on the average deeper by 0.14 m, to which riverbed mining also contributes. There has been a recent increase of erosion of river banks at 400 locations and coasts. The 66% of all of foreshore is now eroding, and the rate of these events is accelerating with time. If all the proposed mainstream hydropower dams in the Lower Mekong Basin have been built, then the Vietnamese Mekong delta with its ecosystems and about 18 million people face critical issues of sustainability. This presentation also focused on some remedial conceptual solutions that may decrease, but not eliminate, the negative impacts of these dams for the Vietnamese Mekong delta. Non-engineering solutions have the highest propriety, but engineering solutions are needed for protecting eroded coastal foreshore, river bank erosion and the fragile mangrove belt. Toward to realization of SDG’s in this study region, the integrated management system of the river basin would be desired.

Modification of the Relative Abundance of Constituents Dissolved in Drinking Water Caused by Organic Pollution: a Case of the Toluca Valley, Mexico

Drinking water contains geogenic elements to which human beings are exposed; in the long term, these elements can be either harmful (As) or beneficial (Mg and Ca) to health. The composition and relative abundance of the constituents in groundwaters are conditioned by the balance between dissolution, precipitation, and oxide-reduction processes also by the nature and spatial arrangement of the materials interacting with the water. In recent decades, human activities and changes in the use of land have led to the accumulation of organic materials and their degradation into nitrogen and phosphorus, which has resulted in a change of the physicochemical composition and quality of drinking water. The main target of the study was to evaluate the effect of contamination by nitrogen and phosphate organic matter on the physicochemical composition of water used for human consumption. The study was conducted in the Toluca Valley aquifer. The determination of parameters in situ and analysis in the laboratory of physicochemical parameters revealed the presence of NO3− (1.0–119 mg L−1), SO42− (6.81–24.70 mg L−1), PO43− (2.50–32.20 mg L−1), and N-NH4+ (0–5.40 mg L−1), which suggested the presence of punctual anthropogenic contamination; this was confirmed using 3D fluorescence to identify the presence of organic matter. The results of Na+ (15.75 mg L−1), K+ (2.66 mg L−1), Ca2+ (8.73 mg L−1), and Mg2+ (8.01 mg L−1) using the ICP technique showed that the water supplied in the area has a low mineral content. Correlation between P and cations Ca2+ (0.844) > Na+ (0.720) > Mg2+ (0.694) > K+ (0.60) indicates that anthropic contamination affects the relative abundance of dissolved constituents in water. The scarcity of essential nutrients in water impacts on public health; it has been reported that deficiency of Ca2+ and Mg2 implies a wide variety of clinical conditions, mainly in the development of cardiovascular diseases.

Distribution of grain size and organic elemental composition of the surficial sediments in Lingding Bay in the Pearl River Delta, China: A record of recent human activity

The Pearl River Delta (PRD) in China is severely affected by intensive human activities. In this study, we used surficial sediments collected in its Lingding Bay (LDB) in December 2016 to analyse the grain size and organic carbon composition and to identify the recent human impact recorded in the sediments. We examined the temporal variations in the spatial distribution of the grain size and organic elemental geochemistry of the surficial sediments by comparison with previous studies. Our study shows that in 2016, there were several patches of coarse-grained sediments, which were not consistent with the hydrodynamic conditions in LDB. Compared with the organic carbon composition in 2005–2006, the δ13C values in 2016 were more negative and the contribution of terrigenous organic matter (TOM) to the surficial sediments was significantly greater. There were also several patches of high TOM values in the outer LDB. The overall coarser sediments and lighter δ13C of organic carbon were in contrast to the decline in the riverine sediment supply and the increased eutrophication in recent decades. Furthermore, the anomalous patches of coarse-grained sediments and terrestrially sourced organic carbon were mainly distributed in the navigation channels and on their adjacent shoals, reflecting channel dredging, dumping, and sand mining activities. Therefore, the origins and spatial distributions of the grain size and organic carbon composition of the surficial sediments in LDB in 2016 were not controlled by hydrodynamic conditions and land–sea interactions, but overwhelmingly by human activities. We suggest that LDB of PRD exemplifies an anthropogenically controlled bay.

Stable but fragile: long-term dynamics of arctic benthic macrofauna in Baydaratskaya Bay (the Kara Sea)

Climate change and direct impacts of human activity are often considered among the main drivers of ecosystem dynamics; however, their relative importance for high-Arctic marine systems is not clearly understood. The Baydaratskaya Bay (southwestern part of the Kara Sea) was not subject to any human activity until 2011, when the construction of the underwater portion of a gas pipeline began; thus, it is a good place to investigate this issue. We used data on the macrobenthos from 1945 to 2013 to assess temporal variability and reveal either decadal-scale trends or construction impacts on the ecosystem. Until 2013, no evidence of long-term changes was detected in biomass, diversity, species composition, functional structure, and biogeographic attributes of the fauna. The ecological status was permanently evaluated as undisturbed. In 2013, however, an extensive shift occurred in the deep-sea area close to the pipeline trench. Benthic biomass and diversity decreased abruptly; while total abundance increased. The functional structure changed. Large bivalves almost completely disappeared, abundance of gastropods and amphipods dropped sharply, while the abundance of small opportunistic polychaetes increased abruptly. Benthic quality assessment indices indicated the deterioration of the community. The most likely reason for such catastrophic changes was the direct impact of dredging and dumping of sediments during pipeline burial from 2012 to 2013. We conclude that the benthic macrofauna in Baydaratskaya Bay has remained relatively stable over the last several decades without any signs of climate-driven borealization. Recent human activity, however, caused local but rapid and strong response, indicating the high sensitivity and vulnerability of this ecosystem.

Expanding global commodities trade and consumption place the world’s primates at risk of extinction

As a consequence of recent human activities. populations of approximately 75% of the world’s primates are in decline, and more than 60% of species (n = 512) are threatened with extinction. Major anthropogenic pressures on primate persistence include the widespread loss and degradation of natural habitats caused by the expansion of industrial agriculture, pastureland for cattle, logging, mining, and fossil fuel extraction. This is the result of growing global market demands for agricultural and nonagricultural commodities. Here, we profile the effects of international trade of forest-risk agricultural and nonagricultural commodities, namely soybean, oil palm, natural rubber, beef, forestry products, fossil fuels, metals, minerals, and gemstones on habitat conversion in the Neotropics, Africa, and South and Southeast Asia. Total estimated forest loss for these regions between 2001 and 2017 was ca 179 million ha. The average percent of commodity-driven permanent deforestation for the period 2001–2015 was highest in Southeast Asia (47%) followed by the Neotropics (26%), South Asia (26%), and Africa (7%). Commodities exports increased significantly between 2000 and 2016 in all primate range regions leading to the widespread conversion of forested land to agricultural fields and an increase in natural resource extraction. In 2016, US $1.1 trillion of natural-resource commodities were traded by countries in primate range regions. The Neotropics accounted for 41% of the total value of these exports, Southeast Asia for 27%, Africa 21%, and South Asia 11%. Major commodity exporters in 2016 were Brazil, India, Indonesia, Malaysia and South Africa, countries of high primate diversity and endemism. Among the top 10 importers were China, the US, Japan, and Switzerland. Primate range countries lag far behind importer nations in food security and gross domestic product per capita, suggesting that trade and commodity-driven land-use have done little to generate wealth and well-being in primate habitat countries. Modeling of land-use and projected extinction of primate species by 2050 and 2100 under a business as usual scenario for 61 primate range countries indicate that each country is expected to see a significant increase in the number of species threatened with extinction. To mitigate this impending crisis, we advocate the “greening” of trade, a global shift toward a low-meat diet, reduced consumption of oil seed, diminished use of tropical timber, fossil fuels, metals, minerals, and gemstones from the tropics, accompanied by a stronger and sustained global resolve to regulate and reverse the negative impacts of growing unsustainable global demands and commodity trade on income inequality, and the destruction of primates and their habitats.

Genetic variability and structure of the Olive Field Mouse: a sigmodontine rodent in a biodiversity hotspot of southern Chile.

The temperate rainforests of southern Chile, a recognized biodiversity hotspot, were significantly affected by Pleistocene glacial cycles in their southern portion and have been severely disrupted mainly due to recent human activities. Additionally, the landscape is characterized by a series of potential barriers to gene flow, such as the Chacao Channel, Cordillera de Piuche in Chiloé and both the Ancud and the Corcovado gulfs. We used mitochondrial DNA sequences and microsatellite data across several populations to evaluate the genetic variability and structure of the sigmodontine rodent Abrothrix olivacea brachiotis, one of the most common species of small mammals and an inhabitant of these biodiverse forests. Sequencing data showed that along with the recovery of high haplotype variation for this species, there was a low nucleotide diversity between haplotypes, showing no genetic differences between the Chiloé Island and continental populations in southern Chile or through any other geographic barrier in the study area. However, microsatellite data exhibited some level of population structuring. The most evident clusterings were those of the Chiloé Island and that of North Patagonia. These findings are corroborated by a barrier analysis that showed a genetic barrier in the latter areas, whereas the Chacao Channel was not a significant barrier for this rodent. Overall, the genetic variability and structure of A. o. brachiotis was concordant with historical factors, such as the Last Glacial Maximum and the presence of geographic elements that isolate populations.

Identification of the Space-Time Variability of Hydrological Drought in the Arid Region of Northwestern China

Drought monitoring is crucial to water resource management and strategic planning. Thus, the objective of this study is to identify the space-time variability of hydrological drought across the broad arid region of northwestern China. Seven distributions were applied to fitting monthly streamflow records of 16 gauging stations from 10 rivers. Finally, the general logistic distribution was selected as the most appropriate one to compute the Standardized Streamflow Index (SSI). The severity and duration of hydrological droughts were also captured from the SSI series. Moreover, we investigate the relationship between hydrological drought (SSI) and meteorological drought (Standardized Precipitation-Evapotranspiration Index (SPEI)) at different time scales. The results show that drought duration and severity decreased over time in the Aibihu, Irtysh, Kaidu, Aksu, Yarkand, Hoton, Shule, Heihe (upstream), and Shiyang Rivers. However, the Tarim (upstream) and Heihe (middle stream) Rivers showed increasing drought duration and severity and this can be attributed to recent decades human activities. Furthermore, two correlation coefficient patterns between SSI and SPEI were found for the rivers of interest, an “increasing-decreasing” pattern for the Irtysh, Heihe, and Shiyang Rivers, where the precipitation is the main runoff supply, and an “increasing-stable” pattern for Aibihu and the Kaidu, Aksu, Yarkand, Hotan, and Shule Rivers, where glacier melt water provided a relatively high supply of runoff. Our findings are a contribution towards implementing effective water resources evaluation and planning in this arid region.

Nutrient burial and environmental changes in the Yangtze Delta in response to recent river basin human activities

High resolution sediment records in the Yangtze Delta front were constructed to reveal recent environmental changes in response to river basin human activities. Increases in nutrient and organic C influxes that began in the 1950s, together with elevated primary productivity and increased chemical fertilizer application, suggested a shift toward anthropogenic-predominated environmental changes during this period. The depletion of total organic C (TOC), total N (TN), and biogenic Si (BSi), along with the decline in sedimentation rate and coarsening of sediment coincided with the development of hydrological engineering in the river basin from the 1980s. Reservoir Si retention substantially altered river mouth primary productivity community composition from diatoms to non-diatoms, thereby changing the BSi/TOC molar ratio in the sediment profile. Estimation of biogenic component burial fluxes was conducted to assess the variation and potential impacts. A recent dramatic decline in biogenic component burial in the delta area suggested a low nutrient removal efficiency in this region, due to the decrease in sediment discharge. Consequently, more nutrients have been further transported to the inner shelf and open waters instead of being buried in the delta sediment, thereby increasing the environmental pressure in the Yangtze Delta and adjoining coastal area.

Evolution of Yellow River Delta Coastline Based on Remote Sensing from 1976 to 2014, China

Coastal regions are threatened by natural processes, such as erosion driven by storm surges and the effect of jetties, as well as by human behavior. The coastline of the Yellow River Delta (YRD) was monitored using the general high-tide line method, which combines Remote sensing (RS) and geographic information system (GIS) technology, using multi-spectral scanner (MSS), thematic mapper (TM), and enhanced thematic mapper plus (ETM+) images of the YRD from 1976 to 2014 as a data source. The results demonstrated that the shape and length of the YRD coastline has changed dramatically since 1976. The course of the Diaokouhe channel has resulted in mainly inland erosion in the north, and is primarily marine erosion; therefore, it was termed an erosion-type estuary. However, the coastline of the Qingshuigou course has moved seaward, demonstrating an accretion stage, and was therefore termed an accretion-type estuary. The coastline advanced forward before 1997 and shrank after 2003 in the southern part of the river mouth, which was due to the shift in the river mouth in 1996. It has continually extended outward in the northern part of the river mouth from 2003 onward. The coastline in the southern part of the river mouth has moved randomly, with the occurrence of both erosion and sedimentation caused by land reclamation and sea wave intrusion. In most cases, the coastline has extended offshore, especially in the northern part of the river mouth. The YRD coastline has changed frequently and rapidly from 1992 to 2014. The river mouth channel, river water and sediments, and precipitation were the major factors affecting the YRD. The YRD coastline was mainly in an accretion stage during flow periods. The erosion rate decreased and tended to be stable during a dry period. The coastline was basically stable when dry periods occurred over a long period. The location of Yellow River ports and sea erosion were the main factors driving coastline changes. The coastline was mainly influenced by the flow path of the Yellow River, with recent human activity also becoming a factor.

Disentangling the relative impacts of climate change and human activities on arid and semiarid grasslands in Central Asia during 1982–2015

In recent decades, climate change and human activities have severely affected grasslands in Central Asia. Grassland regulation and sustainability in this region require an accurate assessment of the effects of these two factors on grasslands. Based on the abrupt change analysis, linear regression analysis and net primary productivity (NPP), the spatiotemporal patterns of grassland ecosystems in Central Asia during 1982–2015 were studied. Further, the potential NPP (NPPP) was estimated using the Thornthwaite Memorial model and the human-induced NPP (NPPH), which was the difference between NPPP and actual NPP, were used to differentiate the effects of climate change and human activities on the grassland ecosystems, respectively. The grassland NPP showed a slight upward trend during 1982–2015, while two obvious decreasing periods were found before and after the mutation year 1999. Additionally, the main driving forces of the grassland NPP variation for the two periods were different. During 1982–1999, climate change was the main factor controlling grassland NPP increase or decrease, and 84.7% of grasslands experienced NPP reduction, while the regions experiencing an increase represented only 15.3% of the total area. During 1999–2015, the areas of increasing and decreasing grassland NPP represented 41.6% and 58.4% of the total area, respectively. After 1999, human activities became the main driving force of the NPP reduction, whereas climate change facilitated grassland restoration. The five Central Asian countries showed widely divergent relative impacts of climate change and human activities on NPP changes. In Uzbekistan and Turkmenistan, anthropogenic decreases in grassland NPP intensified during 1982–2015, while the negative anthropogenic effects on grassland NPP in Kyrgyzstan and Tajikistan moderated. Further analysis identified precipitation as the major climatic factor affecting grassland variation in most areas of Central Asia and overgrazing as the main form of human activity accelerating grassland degradation. This study improves the understanding of the relative impacts of climate change and human activities on grasslands in Central Asia.