Hydrogeochemical and isotopic assessment of the origin of NO_(3)^(−)and N-NH_(3)contents in the aquifer located in a closed lacustrine volcano-sedimentary basin in the metropolitan area of Mexico City

To explain the presence and spatial distribution of NO_(3)^(−)and N-NH_(3)in the Aquifer of the Metropolitan Area of Mexico City(AMAMC),a hydrogeochemical and isotopic analysis using^(13)C DIC(as well as the stable isotopes^(18)O and^(2)H)in groundwater was conducted.This aquifer is located in an old closed lacustrine volcano-sedimentary basin;some wells hosted in the semi-confined zone contain high N-NH_(3)concentrations,while others present NO_(3)^(−)contents in the recharge zones(hosted in an oxidizing environment).In this study,a change in the isotopic signature(primarily in^(18)O and^(2)H)was observed from the recharge zones to the basin center in some of the wells with high NO_(3)^(−)concentrations,this behavior can be attributed to evaporation during the incorporation of recently infiltrated water.In addition,the results for^(13)C(along with ^(2) H)in wells with the highest N-NH_(3)concentrations exhibited an atypically broad range of values.Results indicated the occurrence of hydrogeochemical and/or biochemical processes in the aquifer(in an oxidizing or reducing environment),such as organic degradation,bacterial decomposition(primarily in the ancient Lake Texcoco and which acts as a natural sink for carbon,nitrogen,sulfur,and phosphorus),besides rock weathering and dissolution,which may be responsible for a very marked isotopic modification of the^(13)C(and,to a lesser extent,2 H).Methanotrophic bacterial activity and methanogenic activity may be related to N-NH_(3)removal processes by oxidation and residual water incorporation respectively,whereas the increase in the NO_(3)^(−)content in some wells is due to the recent contribution of poor-quality water due to contamination.

Use of δ^(18)O, δ^(13)C and NO_(3)^(-) to identify hydrogeochemical processes related to contamination in an aquifer located in central Mexico

In this work,an isotopic analysis of δ^(18)O,δ^(13)C,and NO_(3)^(-) concentrations was carried out to identify the origin and the processes related to the contamination of an aquifer located in the state of Guanajuato,Mexico.The research identified the possible sources of δ^(13)C in groundwater.During groundwater flow,CO_(2) participates in different hydrogeochemical reactions in which the dissolution of carbonates or biochemical processes related to biodegradation stand out.Isotopic data of δ^(13)C,δ^(18)O,and the hydrogeochemical behavior of NO_(3)^(-) and HCO_(3)^(-) in water,in addition to isotopic data and the chemical composition of limestones in the study area,were determined to establish the isotopic signature and the processes undergone by the rocks.The isotopic signature of rock and water samples indicated that metamorphic limestones contributed with carbon dioxide to deep groundwater,while in the upper aquifer,bacterial metabolic reactions during nitrification–denitrification could modify the isotopic signature of δ^(13)C in some wells,although atmospheric contribution also plays a role.The modification of the carbon isotopic component is related to the precipitation of calcite in specific regions of the study area,input of atmospheric CO_(2),and soil(e.g.the possible participation of C4-type plants in the assimilation-release of carbon).This process is not confirmed or completely ruled out in this study since agriculture is excessively developed throughout the region.The joint interpretation of isotopic values and the hydrogeochemical behavior of major and conservative elements help in identifying possible pollution processes in which different carbon sources are related.

A review of lignans from genus Kadsura and their spectrum characteristics

Kadsura belongs to the Schisandroideae subfamily of Magnoliaceae.Plants from genus Kadsura are widely distributed in the South and Southwest of China.The plants of the genus are widely used as folk medicine for a long time in history,with the functions of relieving pain,promoting 'qi' circulation,activating blood resolve stasis,and applications in the treatment of rheumatoid arthritis and gastroenteric disorders.Lignans are the primary characteristic constituents with various biological activities of plants from genus Kadsura.This paper summarized 81 lignans isolated from the plants of genus Kadsura over the past eight years(from 2014 to 2021),which belong to five types:dibenzocyclooctadienes,spirobenzofuranoid dibenzocyclooctadienes,aryltetralins,diarylbutanes and tetrahydrofurans.Each type of these lignans possess typical characteristics in proton magnetic resonance(^(1)H NMR) and carbon-13 nuclear magnetic resonance(^(13)C NMR) spectra,the NMR regularities of these types of lingans were summarized,which provided a useful reference for the structural analysis of lignans.The relationships between lignans and pharmacodynamics were also systematically analyzed,lignans were predicted to be the quality markers(Q-marker) of Kadsura genus.