Global diagnosis of land-atmosphere coupling based on water isotopes.

Land-atmosphere coupling (LAC) plays a significant role in weather and climate and is related to droughts and heatwaves. We propose a simple and efficient LAC diagnosis method based on the analysis of water isotopes in atmospheric water vapour and precipitation. Using the method, we identify the primary LAC hotspot regions of the globe and reveal the seasonality of LAC strength. We find that LAC strength exhibits a relationship with latitude. Low latitudes present stronger LAC strength and contribute more significantly to the overall LAC area compared to boreal middle and high latitudes. It's important to note that LAC primarily manifests in the troposphere and is detected in the lower stratosphere of low latitudes, with limited influence observed in the stratosphere. However, the impact of LAC is noticeable in the upper stratosphere in boreal middle and high latitudes. Moreover, the seasonality of LAC strength is pronounced. On a global scale, the season with the strongest LAC is boreal autumn in the Northern Hemisphere but boreal summer in the Southern Hemisphere. Notably, this pattern does not exhibit a seesaw effect between the two hemispheres. Our isotope-based LAC diagnosis method captures the major LAC hotspots found in previous work and validates the seasonality of LAC within these hotspots. This substantiates the reliability and effectiveness of our isotope-based approach.

Health risks of shallow groundwater in the five basins of Shanxi, China: Geographical, geological and human activity roles.

Rapid economic development often leads to groundwater degradation, posing health risks to those who rely on it. The groundwater discharge conditions in basins are poor. The health risk of shallow groundwater in basins needs more attentions. The health risk of shallow groundwater in the five basins of Shanxi Province, China was discussed based on the hydrochemical evolution of shallow groundwater and the water quality assessment. The results showed that arsenic (As) and chromium (Cr) in the shallow groundwater of the basins caused prominent health risks followed by fluoride (F) and nitrate (NO3-). The non-carcinogenic risks of As, F and NO3- to children were higher than that to adults, and the carcinogenic risks of As and Cr were higher for adults than children. Various hydrogeochemical reactions, geological conditions, climatic factors, and human activities are closely related to groundwater health risks, and basin topography is considered as one of key factors. Water-rock interaction, dedolomitization and cation exchange are the natural processes in the evolution of groundwater hydrochemistry, while agricultural and mining activities are the anthropogenic factors causing groundwater degradation. The leaching/dilution effects of infiltration precipitation in the basin-mountain systems cause distinct temporal changes in the chemical composition and health risks of the groundwater in the basins. Differences in climate and farming practices among the basins further complicate the spatio-temporal changes. The basin-mountain system is conducive to the convergence and enrichment of water flow and solutes in the basins, which aggravates the degradation of groundwater quality. This study highlights that the combined influences of geographical and geological factors and anthropogenic activities amplify the human health risks of groundwater in the basins.

Water diversion induces more changes in bacterial and archaeal communities of river sediments than seasonality.

Previous studies have demonstrated that seasonal variation is often the most important factor affecting aquatic bacterial assemblages. Whether anthropogenic activities can dominate community dynamics remains unknown. Based on 16S rRNA high-throughput sequencing technology, this study revealed and compared the relative influence of water diversions and seasonality on bacterial and archaeal communities in river sediments from a region with obvious seasonality. The results indicate that the influence of water diversion on bacteria and archaea in water-receiving river sediments exceeded the influence of seasonal variation. Water diversion affected microbes by increasing EC, salinity, water flow rate, and organic matter carbon and nitrogen contents. Seasonal variations affected microbes by altering water temperature. Diversion responders but no season responders were classified by statistical methods in the microbial community. Diversion responder numbers were related to nitrogen concentrations, complex organic carbon contents and EC values, which were mainly affected by water diversion. With the joint impact of water diversion and seasonality, the correlations of bacterial and archaeal numbers with environmental factors were obviously weakened due to the increases in the ecological niche breadths of microorganisms. Natural seasonal changes in bacterial and archaeal communities were totally altered by changes in salinity, nutrients, and hydrological conditions induced by anthropogenic water diversions. These results highlight that human activity may be a stronger driver than natural seasonality in the alteration of bacterial and archaeal communities.

Different Responses of Bacterial and Archaeal Communities in River Sediments to Water Diversion and Seasonal Changes.

In recent years, different responses of archaea and bacteria to environmental changes have attracted increasing scientific interest. In the mid-latitude region, Fen River receives water transferred from the Yellow River, electrical conductivity (EC), concentrations of Cl- and Na+ in water, total phosphorus (TP), and Olsen phosphorus (OP) in sediments were significantly affected by water transfer. Meanwhile, temperature and oxidation-reduction potential (ORP) of water showed significant seasonal variations. Based on 16S rRNA high-throughput sequencing technology, the composition of bacteria and archaea in sediments was determined in winter and summer, respectively. Results showed that the dominance of bacterial core flora decreased and that of archaeal core flora increased after water diversion. The abundance and diversity of bacterial communities in river sediments were more sensitive to anthropogenic and naturally induced environmental changes than that of archaeal communities. Bacterial communities showed greater resistance than archaeal communities under long-term external disturbances, such as seasonal changes, because of rich species composition and complex community structure. Archaea were more stable than bacteria, especially under short-term drastic environmental disturbances, such as water transfer, due to their insensitivity to environmental changes. These results have important implications for understanding the responses of bacterial and archaeal communities to environmental changes in river ecosystems affected by water diversion.

Characteristics of aquatic bacterial community and the influencing factors in an urban river.

Bacteria play a critical role in environmental and ecological processes in river ecosystems. We studied the bacterial community in the Ganjiang River, a major tributary of the Yangtze River, as it flowed through Nanchang, the largest city in the Ganjiang River basin. Water was sampled at five sites monthly during the wet season, and the bacterial community was characterized using Illumina high-throughput sequencing. A total of 811 operational taxonomic units (OTUs) were observed for all samples, ranging from 321 to 519 for each sample. The bacterial communities were maintained by a core of OTUs that persisted longitudinally and monthly. Actinobacteria (41.17% of total sequences) and Proteobacteria (31.80%) were the dominant phyla, while Firmicutes (mostly genus Lactococcus) became most abundant during flooding. Temperature and flow rate, rather than water chemistry, were the main factors influencing the bacterial community in river water. Temperature was the best individual parameter explaining the variations in OTU abundance, while flow rate was the best individual parameter explaining the variations in phylum abundance. Except for Proteobacteria, the relative abundance of bacterial phyla did not differ significantly between sites, and the degrees of influence of urban landscape on the bacterial community were estimated to be 17%-34%.

[Distribution Characteristics and Source of Fluoride in Groundwater in Lower Plain Area of North China Plain: A Case Study in Nanpi County].

There is an obvious regional contradiction between water resources and agricultural produce in lower plain area of North China, however, excessive fluorine in deep groundwater further limits the use of regional water resources. In order to understand the spatial distribution characteristics and source of F(-) in groundwater, study was carried out in Nanpi County by field survey and sampling, hydrogeochemical analysis and stable isotopes methods. The results showed that the center of low fluoride concentrations of shallow groundwater was located around reservoir of Dalang Lake, and centers of high fluoride concentrations were located in southeast and southwest of the study area. The region with high fluoride concentration was consistent with the over-exploitation region of deep groundwater. Point source pollution of subsurface drainage and non-point source of irrigation with deep groundwater in some regions were the main causes for the increasing F(-) concentrations of shallow groundwater in parts of the sampling sites. Rock deposition and hydrogeology conditions were the main causes for the high F(-) concentrations (1.00 mg x L(-1), threshold of drinking water quality standard in China) in deep groundwater. F(-) released from clay minerals into the water increased the F(-) concentrations in deep groundwater because of over-exploitation. With the increasing exploitation and utilization of brackish shallow groundwater and the compressing and restricting of deep groundwater exploitation, the water environment in the middle and east lower plain area of North China will undergo significant change, and it is important to identify the distribution and source of F(-) in surface water and groundwater for reasonable development and use of water resources in future.

The impacts of a linear wastewater reservoir on groundwater recharge and geochemical evolution in a semi-arid area of the Lake Baiyangdian watershed, North China Plain.

Sewage leakage has become an important source of groundwater recharge in urban areas. Large linear wastewater ponds that lack anti-seepage measures can act as river channels that cause the deterioration of groundwater quality. This study investigated the groundwater recharge by leakage of the Tanghe Wastewater Reservoir, which is the largest industrial wastewater channel on the North China Plain. Additionally, water quality evolution was investigated using a combination of multivariate statistical methods, multi-tracers and geochemical methods. Stable isotopes of hydrogen and oxygen indicated high levels of wastewater evaporation. Based on the assumption that the wastewater was under an open system and fully mixed, an evaporation model was established to estimate the evaporation of the wastewater based on isotope enrichments of the Rayleigh distillation theory using the average isotope values for dry and rainy seasons. Using an average evaporation loss of 26.5% for the input wastewater, the estimated recharge fraction of wastewater leakage and irrigation was 73.5% of the total input of wastewater. The lateral regional groundwater inflow was considered to be another recharge source. Combing the two end-members mix model and cluster analysis revealed that the mixture percentage of the wastewater decreased from the Highly Affected Zone (76%) to the Transition Zone (5%). Ion exchange and redox reaction were the dominant geochemical processes when wastewater entered the aquifer. Carbonate precipitation was also a major process affecting evolution of groundwater quality along groundwater flow paths.

Using major ions and δ15N-NO3(-) to identify nitrate sources and fate in an alluvial aquifer of the Baiyangdian lake watershed, North China Plain.

In semi-arid regions, most human activities occur in alluvial fan areas; however, NO3(-) pollution has greatly threatened the shallow groundwater quality. In this paper, δ(15)N-NO3(-) and multi-tracers were used to identify the origin and fate of NO3(-) in groundwater of the Baiyangdian lake watershed, North China Plain. The investigation was conducted in two typical regions: one is the agricultural area located in the upstream of the watershed and another is the region influenced by urban wastewater in the downstream of the watershed. Results indicate that the high NO3(-) concentrations of the upstream shallow groundwater were sourced from fertilizer and manure or sewage leakage, whilst the mixture and denitrification caused the decrease in the NO3(-) concentration along the flow path of the groundwater. In the downstream, industrial and domestic effluent has a great impact on groundwater quality. The contaminated rivers contributed from 45% to 76% of the total recharge to the groundwater within a distance of 40 m from the river. The mixture fraction of the wastewater declined with the increasing distance away from the river. However, groundwater with NO3(-) concentrations larger than 20 mg l(-1) was only distributed in areas near to the polluted river or the sewage irrigation area. It is revealed that the frontier and depression regions of an alluvial fan in a lake watershed with abundant organics, silt and clay sediments have suitable conditions for denitrification in the downstream.

Estimating the submarine groundwater and nutrients discharge of Yellow River delta with cross-section method.

In this paper, cross-section method was used to estimate the groundwater and nutrients discharge fluxing to the Bohai Sea from the Yellow River Delta. The flux of shallow phreatic groundwater (within 10 m) in the Yellow River Farm discharging into sea was 2.9x10(-5) m3/m d in 2004 and 3.1x10(-5) m3/m d in 2005. Time distribution monthly mean flux is consistent with the Yellow River's runoff but taking on lag effect. And the volume of the phreatic water discharging from the whole delta is 3.71-3.77x10(3) m3, which is 2x10(-5)% of the Yellow River's annual runoff. The transport amount of shallow confined water (buried depth 15-20 m) from 2004 to 2005 was 5.7-6.2x10(-3) m3/m d in the Yellow River delta, 0.0037-0.004% of the runoff of Yellow River. There is low concentration of NO3-, NH4+ and PO4(3-) but high dissolved SiO2 in the shallow confined aquifer. Despite the high concentration of phreatic nitrate, it weakly influences the seawater because of the little flux of discharge into sea.