Spatial Distribution And Sources Of Nitrate And Perchlorate In Soils And Lakes In Antarctic Ice-free Areas

Nitrate(NO₃^-)and perchlorate(ClO₄^-)are two common substances in the environment.Because they are closely related to human life and health,they have received widespread attention.The NO₃^-in the environment is mainly produced by the chemical reaction between NO_xand atmospheric oxidants,so NO₃^-contains information about the atmospheric oxidation environment.The ClO₄^-in the environment have both anthropogenic source and natural sources,and its natural source is mainly the reaction product of chlorine-containing precursor substances and atmospheric oxidants.Antarctic snow and ice is a natural archive that preserves NO₃^-and ClO₄^-produced in the atmosphere.At present,a series of studies on NO₃^-and ClO₄^-in Antarctic snow and ice have been carried out,but the research on NO₃^-and ClO₄^-in Antarctic ice-free areas is limited to Dry Valley areas.Therefore,it is necessary to conduct research on the concentration level,spatial distribution and possible biogeochemical processes of NO₃^-and ClO₄^-in a wider range of ice-free areas.This study takes the surface soil,soil profile,fresh penguin manure/penguin soil with manure,sediment and lake water samples collected at Broknes Peninsula,Fildes Peninsula and Ross Sea Inexpressible Island during the 27th and 36th Antarctic Scientific Expeditions in China,which is based on the nitrogen and oxygen isotopic composition of NO₃^-to study the source of NO₃^-and the geochemical process it undergoes,it also reveals the concentration level,spatial distribution and influencing factors of ClO₄^-in different medium environments.The preliminary conclusions obtained are as follows:In the surface soil of the Antarctic ice-free zone,the concentration of TOC and nutrients(NO₃^-?NO₂^-?NH₄⁺?PO₄^3-and Si O₃^2-)in the surface soil of the Fildes Peninsula is significantly higher than that of the Broknes Peninsula.There is a certain degree of enrichment of?¹⁵N-NO₃^-in the penguin soil with manure and soil in the vegetation coverage area,and the ratio of?¹⁸O-NO₃^-to?¹⁵N-NO₃^-in the penguin soil with manure indicates that it is likely to have experienced denitrification.Nitrification is the main source of NO₃^-in the surface soil in the Antarctic ice-free zone,the contribution to the NO₃^-in the surface soil of the Broknes Peninsula can reach an average of 89±11%,and the contribution to the Inexpressible Island can reach an average of 89±4%,the average contribution to the Fields Peninsula is 79±12%.There is no correlation between the concentration of ClO₄^-in the surface soils with TOC and other nutrients,there is a significant correlation between TOC and each nutrient at the confidence level of 0.01.The concentration of ClO₄^-in the surface soil in the of Antarctica ice-free area is likely to be affected by leaching,but is less affected by human activities,animal activities and microbial reduction,and mainly comes from atmospheric deposition.In the sediments of the Antarctic ice-free zone,the TOC and nutrient concentration in the sediments of the Fildes Peninsula are significantly higher than those of the Brocknes Peninsula.The nutrient concentration of different lake sediments is quite different,showing different concentration characteristics.The contribution of nitrification to the NO₃^-concentration of the Broknes Peninsula can reach an average of 95±18%.There is no correlation between the concentration of ClO₄^-and TOC in lake sediments,and there is no correlation between the concentration of other nutrients.The concentration of ClO₄^-in the sediments of the Broknes Peninsula is less affected by human activities,animal activities and microbial reduction,while the effects of animal activities on the ClO₄^-concentration in the Fildes Peninsula sediments are more obvious.In the lakes of the Antarctic ice-free zone,due to the influence of penguin activities,the nutrient concentration in the Inexpressible Island lake water is much higher than that of the Broknes Peninsula.The isotope data of the lake water in the Inexpressible Island Reserve indicates that the NO₃^-input from penguin dung in the lake water body is likely to have experienced denitrification,and the ClO₄^-concentration in the water body is much higher than that of the Broknes Peninsula.The contribution of nitrification to NO₃^-in the lakes of the Broknes Peninsula can reach an average of82±10%.And there is no correlation between the concentration of ClO₄^-and the concentration of other nutrients.The ClO₄^-in the lakes of the Broknes Peninsula mainly comes from atmospheric deposition,and the ClO₄^-in the lakes of Inexpressible Island Reserve is obviously affected by penguin activities.In this study,ClO₄^-in the lake water was less affected by the reduction of microorganisms.