Sources and dynamics of nitrate in groundwater in a crystalline terrain of tropical Sri Lanka based on a dual isotope approach.

Nitrate pollution of groundwater is one of the major environmental problems in many parts of the world, mainly due to intensive agriculture and waste disposal. Therefore, understanding the fate of nitrate in aquifer systems is important for sustainable groundwater management. In Sri Lanka, a tropical terrain largely covered by high-grade metamorphic rocks, non-point source pollutants from agricultural lands are the main sources of nitrate in groundwater.

Arsenic toxicity exacerbates China's groundwater and health crisis.

Arsenic (As) contamination is considered a major threat to groundwater quality and human health. The uneven distribution of arsenic contributes to regional variations, creating discrimination related to arsenic enrichment and carcinogenic risk. Here, we have analyzed 2,737 groundwater samples across China, which spans a broad range of geo-environments, climates and land use types.

[Analysis the Source and Spatiotemporal Variation of Dissolved Organic Matter in the Chaohe River Watershed].

Dissolved organic matter （DOM） is widespread in aquatic environments and plays a crucial role in various biogeochemistry processes. Urbanization and anthropogenic activities have significantly altered the source and characteristics of DOM in rivers. Therefore, analyzing the spatial and temporal variation of DOM on a watershed scale to trace its source for effective water quality management is important.

Anthropogenic nitrogen inputs favour increased nitrogen and organic carbon levels in Qinghai-Tibetan Plateau lakes: Evidence from sedimentary records.

The water quality of lakes on the Qinghai‒Tibetan Plateau (QTP) is critical, as the QTP serves as a water tower for billions of people in Asia. However, the lack of long-term successive monitoring data has hampered the knowledge of the current patterns of variation in the nitrogen content in QTP lakes, as well as their future trends. In this study, the variations in the nitrogen content in sediment records from Lake Hurleg and Lake Toson and collected datasets from other lakes on the QTP were analysed.

Dynamic transformation and leaching processes of nitrogen in a karst agricultural soil under simulated rainfall conditions.

Frequent exchange of surface water and groundwater in karst agricultural areas results in soil nutrient loss during rainfall and consequent deterioration of the aquatic environment. To understand nitrogen (N) transformation and leaching processes from karst soil during rainfall events, two typical N fertilizers were added to karst soil and consequently investigated the nitrogenous species using soil column experiments system. The contents of various N forms in the soil and leachate were analyzed, and the net nitrification and the N leaching rates were calculated.

Carbon transfer from land to fluvial networks in a typical karst river-reservoir system.

Although terrestrial ecosystems have been widely recognized as an important atmospheric carbon (C) sink, the net C sink capacity may have been overestimated due to C loss through aquatic ecosystems, particularly in catchments with fragile landscapes and intense human disturbances. Here, we integrated the three primary pathways of aquatic C export, including C burial, gaseous C emissions, and downstream C export, into the terrestrial-aquatic C assessment within the Wujiang River basin (WRB) in Southwest China, a typical karst river-reservoir system with cascade reservoirs. The assessment reports a net landscape C sink of 12.

Unravelling nitrate transformation mechanisms in karst catchments through the coupling of high-frequency sensor data and machine learning.

Nitrate dynamics within a catchment are critical to the earth's system process, yet the intricate details of its transport and transformation at high resolutions remain elusive. Hydrological effects on nitrate dynamics in particular have not been thoroughly assessed previously and this knowledge gap hampers our understanding and effective management of nitrogen cycling in watersheds. Here, machine learning (ML) models were employed to reconstruct the annual variation trend in nitrate dynamics and isotopes within a typical karst catchment.

Elucidating the Composition and Transformation of Dissolved Organic Matter at the Sediment-Water Interface Using High-Resolution Mass Spectrometry.

The exchange and transformation of dissolved organic matter (DOM) at the sediment-water interface are crucial factors in regulating watershed biogeochemistry, with the molecular composition of DOM serving as a pivotal determinant in elucidating this process. High-resolution mass spectrometry (HRMS) is an effective tool for resolving the composition of DOM. By analyzing the compositional characteristics of DOM at the sediment-water interface under three different salinities at the same latitude region in northern China, the findings indicate certain variations in component characteristics of DOM between low-salinity inland waters and high-salinity seawaters, with the former exhibiting greater molecular diversity and higher molecular weights, whereas the latter displayed a higher saturation and bioavailability.

High sensitivity of dissolved organic carbon transport during hydrological events in a small subtropical karst catchment.

Dissolved organic carbon (DOC) and discharge are often tightly coupled, though these relationships in karst environments remain poorly constrained. In this study, DOC dynamics over 13 hydrological events, alongside monthly monitoring over an entire hydrological year were monitored in a small karst catchment, SW China. The concurrent analyses of power-law model and hysteresis patterns reveal that DOC behavior is generally transport-limited due to flushing effects of increased discharge but highly variable at both intra- and inter-event scales.

Elevated nitrogen loadings facilitate carbon dioxide emissions from urban inland waters.

Carbon dioxide (CO) production and emissions from inland waters play considerable roles in global atmospheric CO sources, while there are still uncertainties regarding notable nutrient inputs and anthropogenic activities. Urban inland waters, with frequently anthropogenic modifications and severely nitrogen loadings, were hotspots for CO emissions. Here, we investigated the spatiotemporal patterns of partial pressure of CO (pCO) and CO fluxes (FCO) in typical urban inland waters in Tianjin, China.

Chronic increasing nitrogen and endogenous phosphorus release from sediment threaten to the water quality in a semi-humid region reservoir.

The water quality in the drinking water reservoir directly affects people's quality of life and health. When external pollution input is effectively controlled, endogenous release is considered the main cause of water quality deterioration. As the major nitrogen (N) and phosphorus (P) sources in reservoirs, sediment plays a vital role in affecting the water quality.

Elucidation of the dominant factors influencing NO emission in water-level fluctuation zones in a karst canyon reservoir, southwest China.

The water-level fluctuations zones (WLFZs) are crucial transitional interfaces within river-reservoir systems, serving as hotspots for NO emission. However, the comprehension of response patterns and mechanisms governing NO emission under hydrological fluctuation remains limited, especially in karstic canyon reservoirs, which introduces significant uncertainty to NO flux assessments. Soil samples were collected from the WLFZs of the Hongjiadu (HJD) Reservoir along the water flow direction from transition zone (T1 and T2) to lacustrine zone (T3, T4 and T5) at three elevations for each site.

High-frequency data significantly enhances the prediction ability of point and interval estimation.

Accurate prediction of dissolved oxygen (DO) dynamics is crucial for understanding the influence of environmental factors on the stability of aquatic ecosystem. However, limited research has been conducted to determine the optimal frequency of water quality monitoring that ensures continuous assessment of water health while minimizing costs. To address these challenges, the present study developed a hybrid stochastic hydrological model (i.

Unignorable enzyme-specific isotope fractionation for nitrate source identification in aquatic ecosystem.

Nitrate contamination in aquatic systems is a widespread problem across the world. The isotopic composition (δN, δO) of nitrate and their isotope effect (ε, ε) can facilitate the identification of the source and transformation of nitrate. Although previous researches claimed the isotope fractionations may change the original δN/δO values and further bias identification of nitrate sources, isotope effect was often ignored due to its complexity.

Nitrate transformation and source tracking of rivers draining into the Bohai Sea using a multi-tracer approach combined with an optimized Bayesian stable isotope mixing model.

Excessive levels of NO can result in multiple eco-environmental issues due to potential toxicity, especially in coastal areas. Accurate source tracing is crucial for effective pollutant control and policy development. Bayesian models have been widely employed to trace NO sources, while limited studies have utilized optimized Bayesian models for NO tracing in the coastal rivers.

Dynamic N transport and NO emission during rainfall events in the coastal river.

The coastal zone exhibited a high population density with highly impacted by anthropogenic activities, such as river impoundment to prevent saline intrusion, which resulted in weak hydrological conditions. Rainfall events can result in dramatic changes in hydrological and nutrient transportation conditions, especially in rivers with weak hydrological conditions. However, how the nitrogen transport and NO emissions or biogeochemistry responds to the different types of rainfall events in the weak hydrodynamics rivers is poorly understood.

Identify nitrogen transport paths and sources contribution in karst valley depression area using isotopic approach.

Karst groundwater provides drinking water for a quarter of Earth's population. However, in intensive agricultural regions worldwide, karst water is commonly polluted by nitrate (NO), particularly in the valley depression areas with well hydrological connectivity. The valley depression aquifers are particularly vulnerable to anthropogenic pollution because their pipes and sinkholes respond quickly to rainfall events and anthropogenic inputs.

Source availability and hydrological connectivity determined nitrate-discharge relationships during rainfall events in karst catchment as revealed by high-frequency nitrate sensing.

Karst terrain seasonal monsoonal rainfall is often associated with high concentrations of nitrate-N in streams draining agricultural land. Such high concentrations can pose problems for environmental and human health. However, the relationship between rainfall events that mobilize nitrate and resulting nitrate export remains poorly understood in karst terrain.

The effect of reservoir expansion from underground karst cave to surface reservoir on water quality in southwestern China.

Due to the excessive exploitation of traditional energy sources, the attention paid to water energy has increased in recent years. As an important means to effectively utilize water energy, reservoirs play an important role in drinking water, irrigation, flood control, and drought resistance. However, utilizing reservoirs often led to water quality issues resulting from the interaction of nutrients and hydrological conditions, especially due to the special structure of karst areas.

The Effect of Rainfall on Aquatic Nitrogen and Phosphorus in a Semi-Humid Area Catchment, Northern China.

The impact of rainfall on water quality may be more important in semi-arid regions, where rainfall is concentrated over a couple of months. To explore the impact of rainfall changes on water quality, e.g.

Hazardous toxic metal(loid)s in top- and deep-soils during the transformation of aquaculture ponds restored to farmland.

The pollution risks due to the soil migration of toxic metal(loid)s (TMs) are a greatly hazard to ecological environment as well as animal and human health. Previous studies have primarily focused on surface contamination while deep soil layers often contain dangerous levels of TMs. We used restored wheat and rice farmlands from aquaculture ponds as a case study to examine the ecological risk and distribution of TMs in soil profiles.

New insight into the response and transport of nitrate in karst groundwater to rainfall events.

Although numerous studies focused on nitrate source, transformation and transport of river water in karst area have been reported, it's still unclear in understanding nitrate main source and transformation in karst groundwater system and how nitrate transport from soil to water during rainfall events in karst critical zone. In order to explore the response and transport of nitrate in karst groundwater to rainfall events, different depths of well water before, during and after rainfall event were sampled, and hillslope runoff, surface runoff of different land-use types during rainfall event were sampled synchronously at a typical karst agricultural catchment in Southwest China. Results showed that fluctuations of EC, pH and DO in deep borehole well (W1) and artesian well (W2) were small, on the contrary, variations of EC and DO in shallow well (W3) were large during sampling period.

Seasonal variation of nitrogen biogeochemical processes constrained by nitrate dual isotopes in cascade reservoirs, Southwestern China.

The increase of affected river reaches by reservoirs has drastically disturbed the original hydrological conditions, and subsequently influenced the nutrient biogeochemistry in the aquatic system, particularly in the cascade reservoir system. To understand the seasonal variation of nitrogen (N) behaviors in cascade reservoirs, hydrochemistry and nitrate dual isotopes (δN-NO and δO-NO) were conducted in a karst watershed (Wujiang River) in southwest China. The results showed that NO-N accounted for almost 90% of the total dissolved nitrogen (TDN) concentration with high average concentration 3.

Characterization of Lignin Compounds at the Molecular Level: Mass Spectrometry Analysis and Raw Data Processing.

Lignin is the second most abundant natural biopolymer, which is a potential alternative to conventional fossil fuels. It is also a promising material for the recovery of valuable chemicals such as aromatic compounds as well as an important biomarker for terrestrial organic matter. Lignin is currently produced in large quantities as a by-product of chemical pulping and cellulosic ethanol processes.

Quadrupole detection FT-ICR mass spectrometry offers deep profiling of residue oil: A systematic comparison of 2ω 7 Tesla versus 15 Tesla instruments.

Mass resolving power is one of the key features of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), which enables the molecular characterization of complex mixtures. Quadrupole (2ω) detection provides a significant step forward in FT-ICR MS performance, as it doubles the resolving power for a given signal acquisition time. Whether this 2ω detection technique truly substitutes for a higher magnetic field remains unknown however.