Pyrite from acid mine drainage promotes the removal of antibiotic resistance genes and mobile genetic elements in karst watershed with abundant calcium carbonate.

More information is needed to fully comprehend how acid mine drainage (AMD) affects the phototransformation of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in karst water and sewage-irrigated farmland soil with abundant carbonate rocks (CaCO3) due to increasing pollution of AMD formed from pyrite (FeS2). The results showed FeS2 accelerated the inactivation of ARB with an inactivation of 8.7 log. Notably, extracellular and intracellular ARGs and mobile genetic elements (MGEs) also experienced rapid degradation. Additionally, the pH of the solution buffered by CaCO3 significantly influenced the photo-inactivation of ARB. The Fe2+ in neutral solution was present in Fe(II) coordination with strong reducing potential and played a crucial role in generating •OH (7.0 µM), which caused severe damage to ARB, ARGs, and MGEs. The •OH induced by photo-Fenton of FeS2 posed pressure to ARB, promoting oxidative stress response and increasing generation of reactive oxygen species (ROS), ultimately damaging cell membranes, proteins and DNA. Moreover, FeS2 contributed to a decrease in MIC of ARB from 24 mg/L to 4 mg/L. These findings highlight the importance of AMD in influencing karst water and sewage-irrigated farmland soil ecosystems. They are also critical in advancing the utilization of FeS2 to inactivate pathogenic bacteria.

Identifying the source and transformation of riverine nitrates in a karst watershed, North China: Comprehensive use of major ions, multiple isotopes and a Bayesian model.

Nitrate (NO3-) contamination of surface water is a globally concern, especially in karstic regions affected by intensive agricultural activities. This study combines hydrochemistry, and environmental isotopes (δ2HH2O, δ18OH2O, δ15NNO3, and δ18ONO3) with a Bayesian isotope mixing model (Simmr) to reduce the uncertainty in estimating the contributions of different pollution sources. Samples were collected from 32 surface water sites in the Yufu River (YFR) watershed, North China, in September and December 2019. The results revealed that NO3--N was the predominant form of inorganic nitrogen that caused the deterioration of water quality in the watershed, accounting for approximately 58% of the total nitrogen (TN). The hydrochemical compositions and nitrate isotopes indicated that NO3- mainly originated from soil nitrogen (SN), ammonium fertilizer (AF), but nitrate fertilizer (NF), manure and sewage (M&S) and atmospheric precipitation (AP) were limited. The isotopic composition of nitrate in the upper reaches of the watershed was mainly affected by microbial nitrification, while the mixture of multiple sources was the dominant nitrogen transformation process in the mid-lower reaches of the watershed. Simmr model outputs revealed that SN (56.5%) and AF (29.5%) were the primary contributor to riverine NO3- pollution, followed by NF (7.1%), MS (3.6%), and AP (3.4%) sources. Moreover, an uncertainty index (UI90) of the isotope mixing showed that SN (0.73) and AF (0.67) had the highest values, followed by NF (0.22), M&S (0.22) and AP (0.10). Chemical fertilizer and SN collectively contributed >50% of nitrate during the two sampling campaigns. These results indicated that reducing the application of nitrogen fertilizers and rational irrigation are the keys to alleviate of NO3- pollution. The study is helpful in understanding the source and transformation of riverine NO3- and effectively reducing NO3- pollution in karst agricultural rivers or watersheds.

Sources and selective preservation of organic matter in the karst watershed: evidence from sediment records in a plateau deep lake, Southwestern China.

Human activities have greatly altered terrestrial carbon (C) dynamics associated with vegetation cover and land use changes, thereby influencing the C sink in downstream ecosystems. However, the transport and preservation of organic C from soils that experience serious erosion in the karst area are scarce, particularly at catchment scales. In this study, chemical characteristics of organic matter (OM) isolated from the topsoil, overlying water, and lake sediments, as well as subsequent source identification, were inferred from the molecular, spectroscopic, and carbon isotopic (δ13C) signatures in a typical karst catchment, Southwestern China. The results indicated that the elemental compositions of the calcareous soil and paddy soil significantly differed from the yellow soil. High similarities existed in the fluorescence spectra of humic substances (HS) extracted from the front two soil types with those of lake sediments, indicating the homogeneous nature of OM molecular structure. The C/N ratios of six dissolved OM fractions and sedimentary HS along with δ13C values consistently reflected the primary terrestrial source. It was estimated to account for 60% of total organic C in sedimentary OM by end-member mixing modeling in accordance with soil erosion intensity and large recharge coefficient of this catchment. The evolution of soil loss and lake productivity can be well deduced from sediment records of organic C content, C/N ratio, and the specific information of HS. This research highlighted that the composition, source, and fate of OM in the karst lake was mainly dominated by the terrestrial C flux, rather than in-lake production. Furthermore, soil type and erosion intensity have significant effects on the nature of eroded OM and ultimate preservation.

The evolution of hydrochemical and isotopic signatures from precipitation, surface water to groundwater in a typical karst watershed, Central Texas, USA.

The Upper Cibolo Creek (UCC) karst watershed in Central Texas, USA, represents a portion of the drainage area that supplies water to the recharge zone for the Edwards Aquifer. However, the surface water-groundwater interactions along the UCC are not well quantified, and the hydraulic interactions are important for water budget and water quality of the aquifer. In this study, we investigated the evolution of hydrochemical and isotopic signatures (δ18O, δ2H and d-excess) from precipitation, surface water to groundwater in the UCC watershed from 2017 to 2019, and investigated surface water-groundwater interactions using samples from 14 creeks/spring sites. Factor analysis for the observed parameters demonstrates that changes in water hydrochemistry are primarily controlled by human activity, precipitation input, and water-rock interaction. Hierarchical clustering analysis of temporal isotope variations confirms that significant surface water-groundwater interactions occur in the UCC watershed. We identified relationships between nitrate concentrations at creek/spring sites and land-use conditions, and nitrate input sources were determined utilizing the dual-isotope analyses (δ15N and δ18O) of nitrate. This study provides capacity for a more precise assessment of water resources and water quality in Central Texas.

[Dynamic Changes in Hydrochemical Characteristics and Influencing Factors in the Karst Watershed Flood Process].

The hydrochemistry of river water in a karst basin has a rapid response to the rainstorm/flood process, which is an important process of the karst carbon cycle and should not be ignored. Based on the dynamic monitoring of the hydrochemical characteristics of the flood process in the Yangshuo section on November 8-12, 2015, the dynamic change in the main ions and the influencing factors were analyzed, and the concentration and flux of inorganic carbon from different sources were calculated. The results showed that the hydrochemistry types in different stages of the flood area belonged to the Ca-HCO3 type. The ions were mainly sourced from carbonate weathering, and affected by silicate weathering, rainfall, and human activities. Because of the hydrological process, the weathering strength of carbonate rocks sharply weakened at the beginning of the flood, and then gradually increased. The concentrations of HCO3-, Ca2+, and Mg2+ sharply decreased at the beginning of the flood, then gradually increased, and continued to increase in the second flood process because of the waterlogging in the karst system. Because of the waterlogging, the reaction time between water and rock become longer; thus, the concentrations are higher. The dynamic changes in SO42-, Cl-, Na+, and K+ were mainly affected by precipitation and human activities. At the beginning of the flood, the concentrations of SO42-, Cl-, Na+, and K+ increased because the runoff takes more ions sourced from activities. The concentrations of SO42-, Cl-, Na+, and K+ decreased with the decrease of easily transported substances. At the lowest point of concentration, SO42- and Cl- were mainly sourced from precipitation, and Na+ and K+ were mainly sourced from precipitation and silicate weathering. The weathering of carbonates by carbonic acid was the main source of inorganic carbon, accounting for 74.3% of total inorganic carbon on average. Because of the input of sulfuric/nitric acid, the contribution of the weathering of carbonates by sulfuric/nitric acid to the inorganic carbon cannot be ignored, and the contribution increased significantly in the flood, up to 31.7%. The geological carbon sinks before the flood, and during the first and second flood processes in the Yangshuo section were 1.28×108, 5.28×108, and 11.52×108 g·d-1, respectively. The geological carbon sink before the flood was equal to the annual average flux, whereas the geological carbon sink in the flood process was several times that of the annual average flux. Moreover, because of the significant difference in the weathering strength of carbonate rocks during the two floods, there was also a significant difference in the amount of geological carbon sink under the same discharge.