Authigenic sulfide minerals and their sulfur isotopes in sediments of the northern continental slope of the South China Sea and their implications for methane flux and gas hydrate formation

This is a report of the study of the authigenic sulfide minerals and their sulfur isotopes in a sediment core (NH-1) collected on the northern continental slope of the South China Sea, where other geophysical and geochemical evidence seems to suggest gas hydrate formation in the sediments. The study has led to the findings: (1) the pyrite content in sediments was relatively high and its grain size relatively large compared with that in normal pelagic or hemipelagic sediments; (2) the shallowest depth of the acid volatile sulfide (AVS) content maximum was at 437.5 cm (> 2 mu mol/g), which was deeper than that of the authigenic pyrite content maximum (at 141.5-380.5 cm); (3) delta S-34 of authigenic pyrite was positive (maximum: +15 parts per thousand) at depth interval of 250-380 cm; (4) the positive delta S-34 coincided with pyrite enrichment. Compared with the results obtained from the Black Sea sediments by Jorgensen and coworkers, these observations indicated that at the NH-1 site, the depth of the sulfate-methane interface (SMI) would be or once was at about 437.5-547.5 cm and the relatively shallow SMI depth suggested high upward methane fluxes. This was in good agreement with the results obtained from pore water sulfate gradients and core head-space methane concentrations in sediment cores collected in the area. All available evidence suggested that methane gas hydrate formation may exist or may have existed in the underlying sediments.

Pretreatment Method for Nitrogen Isotopic Analysis of Nitrate in Seawater

A suitable method for the pretreutment of dissolved nitrate samples in seawaters for nitrogen isotopic analysis was established. First, the seawater samples were processed by removing nitrite and amonium. Then Devard's alloy was added in sample for conversion of dissolved nitrate to ammonium. The sample was distilled, and then the ammonium condensate was collected with zeolite. after distillation, the collected condensate was filtered and prepared for determining nitropic values. Some tests of the method were conducted. The distillation condition, the influence of salinity on nitrogen isotopic analysis, absorption of ammonium onto zeolite and an improved method on a large volume of seawater were discussed in this study. The results showed that the distillation step had an average recovery of (104.9 +/- 4.2) % (n = 6) when distillating every 300 mL aliquot of the sample under a strong alkaline condition with 0.5 g devard's alloy and a distillation time of 30 min. The nitrogen isotopic fractionation decreased markedly when salinity was increased from 0% to 0.5%; further increase(1% - 3.5%) showed little effect. The adsorption rate of ammonium onto zeolite had a high yield of (95.96 +/- 1.08) % (n = 6) in average. An improved collection method was used to process a large volume of seawater with several distillations, and had good effect on analysis. The method had been applied to analyze water samples collected from Changjiang estuary. The analytical results indicate that the method is suitable for delta N-15 analysis of dissolved nitrate in seawaters. The present method could provide valuable information about the source and cycle mechanism of dissolved nitrogen in estuary waters.

Enrichment of stable carbon and nitrogen isotopes of plant populations and plateau pikas along altitudes

Stable carbon and nitrogen isotope ratios were measured in plant populations and plateau pikas to determine enrichment in stable isotopes of three alpine meadow ecosystems at different elevations in the Qinghai-Tibet Plateau. The results indicated that stable carbon isotope signatures of plant populations at the three locations showed significant variations, delta C-13 of plant populations showed an enrichment of 0.86 parts per thousand per 1000 in over the linear proportion of the altitudinal response, while stable nitrogen isotopes showed no apparent difference. The stable nitrogen isotopes of plateau pikas became significantly isotopically heavier along altitudinal gradients and showed an enrichment of 3.17 parts per thousand/km. Stable carbon isotopes showed no significance, however, and the enrichment of 0.448 parts per thousand/km. delta C-13 and delta N-15 in plateau pikas were not significantly correlated. There appeared to be segregation between the metabolism of stable carbon and nitrogen isotopes of plateau pikas. Variances in metabolic rate at lower water availability and temperatures are presumed to be the main cause of enrichment of stable nitrogen isotopes along altitudinal gradients. Attention should be paid to construct trophic positions and to trace food chain information based oil an isotopic enrichment model.

Analysis of diets of upland buzzards using stable carbon and nitrogen isotopes

We measured the stable carbon and nitrogen isotope ratios for muscles of the upland buzzards (Buteo hemilasius) and their potential food sources, plateau pikas (Ochotona curzoniae), Qinghai voles (Lasiopodomys fuscus), plateau zokors (Myospalax fontanierii), and several passerine bird species at the alpine meadow in Maduo county, Guoluo prefecture of Qinghai province, People's Republic of China, to provide diet information of upland buzzards, highlighting different diet composition of upland buzzards exposed to different locations. The results demonstrated that stable carbon isotope ratios of upland buzzards, passerine birds, plateau pikas, plateau zokors, and Qinghai voles were -24.42 +/- 0.25parts per thousand, -22.89 +/- 1.48parts per thousand, -25.30 +/- 1.47parts per thousand, -25.78 +/- 0.22parts per thousand, and -25.41 +/- 0.01parts per thousand, respectively, and stable nitrogen isotope ratios were 7.89 +/- 0.38parts per thousand, 8.37 +/- 2.05parts per thousand, 5.83 +/- 1.10parts per thousand, 5.23 +/- 0.34parts per thousand, and 8.86 +/- 0.06parts per thousand, respectively. Fractionation of stable carbon and nitrogen isotope ratios between upland buzzards and their food were 1.03parts per thousand and 2.11parts per thousand, respectively. Based on mass balance principle of stable isotopes and the Euclidean distance mixing model, upland buzzards depended mainly on plateau pikas as food (74.56%). Plateau zokors, Qinghai voles, and passerine birds only contributed a small proportion (25.44%) to diets of upland buzzards. The results were closely accordant with analyses of stomach contents and food pellets, which firmly supported the feasibility of using stable carbon and nitrogen isotope ratios to investigate diet information of upland buzzards. Another study based on stable carbon isotopes showed that upland buzzards living in the Haibei prefecture (another prefecture located in the southeast Qinghai province) mainly preyed on passerine birds (64.96% or more) as food supply. We were alarmed by the preliminary results that widespread poisoning activities of small mammals could reshape the food composition of upland buzzards, influencing the stability and sustainability of the alpine meadow. Bio-control on rodent pests should be carried out rather than the chemical measures.

巴丹吉林沙漠及其南缘地区的水化学和环境同位素特征与环境演变

The Badain Jaran Desert lies on the Alashan Plateau in western Inner Mongolia. Because of huge dunes, permanent lakes and on the northern fringe of the Asian summer monsoon, the Badain Jaran Desert has been drawing attentions of many experts. And they have made great progress in dune’s geomorphology, botany in desert, paleoclimate change and other study areas. We analyzed environmental isotope and ion chemistry in lakes and groundwater of the desert and southeastern area, and collected some other evidences from 14C dating, fossils and archeology. According to chemical analysis, we discuss the difference spatial character of ion chemistry and environmental isotope in lakes and groundwater of the desert and adjacent. Contrasting with ion chemistry and isotope results in other arid area, we argue origin of groundwater and lakes in the desert area, and get a preliminary understanding of desert lakes’ evolution during Holocene. Some main conclusions were drawn as follows: 1. It has a obvious difference in hydrophysical parameters between lakes and groundwater in the desert and margin. 2. The results of ion analysis show that Na+ and Cl- are dominant in most lakes of the desert. Meanwhile, Na+ 、Cl- and HCO3- are dominant in groundwater of the desert and adjacent, and alsoMg2+、Ca2+、and NO3- have more percentage than in lakes. 3. Owing to different solubilities, the conten of main ions in water varies with the content of TDS. Whereas the content of TDS is over 100 g/L, the content of SO42-、HCO3-、Mg2+and Ca2+ in lakes descend. 4. The result of isotope analyzing indicate the lakes and groundwater in southeast desert have a similar vaporing trend with the groundwater in the southeast margin of the desert. It imply there would have some kind of contact between groundwater in margin and lakes of southeast desert. 5. Contrasting with isotope results of groundwater in other arid area, it show that the groundwater in the desert and Yabulai area should be phreatic water which have a low water table. Therefore, we conclude that the groundwater in southeast part of the desert and southern margin mainly are recharged by precipitation of local abundant rainfall and groundwater of low mountain of southern area. 6. And all of these evidences, which are different from salinity, the content of CO32- and geological data, show that the bigger northern lake group and southeastern lake group in the desert have different groundwater replenishing system because a fold belt lie between of the two group lakes and obstruct them in landform. and HCO3- 7. The 14C dating results of fossil and lacustrine deposits show that there maybe have a wider range of shoreline during early and middle Holocene than today. 8. By the discovery and study of some pieces of pottery and fine stoneware, we preliminary conclude that there maybe have some certain amount of early human activities in the Badain Jaran Desert.

海底金属矿床充水条件及矿坑突水的断层效应研究

The Xinli mine area of Sanshandao mine is adjacent to the Bohai Sea and its main exploitable ore deposit occurs in the undersea rock mass. The mine is the biggest undersea gold mine of China after production. The mine area faces a latent danger of water bursting, even sudden seawater inrush. There is no mature experience in undersea mining in China so far. The vein ore deposit is located in the lower wall of a fault; its possible groundwater sources mainly include bittern, Quaternary pore water and modern seawater. To ensure the safety of undersea mining, to survey the flooding conditions of the ore deposit using proper measures and study the potential seawater inrush pattern are the key technical problems. With the Xinli mine area as a case study, the engineering geological conditions of the Xinli mine area are surveyed in situ, the regional structural pattern and rock mass framework characteristics are found out, the distribution of the structural planes are modeled by a Monte Carlo method and the connectivity coefficients of rock mass structural planes are calculated. The regional hydro-geological conditions are analyzed and the in-situ hydro-geological investigation and sampling are performed in detail, the hydrochemistry and isotopes testing and groundwater dynamic monitoring are conducted, the recharge, runoff, discharge conditions are specified and the sources of flooding are distinguished. Some indices are selected from the testing results to calculate the proportion of each source in some water discharge points and in the whole water discharge of the Xinli mine area. The temporal and spatial variations of each water source of the whole ore deposit flooding are analyzed. According to the special project conditions in the Xinli mine area, the permeability coefficient tensors of the rock mass in Xinli mine area are calculated based on a fracture geometry measurement method, in terms of the connectivity and a few hydraulic testing results, a modified synthetic permeability coefficient are calculated. The hydro-geological conceptual and mathematical model are established，the water yield of mine is predicted using Visual Modflow code. The spreading law of surrounding rock mass deformation and secondary stress are studied by numerical analysis; the intrinsic mechanism of the faults slip caused by the excavation of ore deposit is analyzed. The results show that the development of surrounding rock mass deformation and secondary stress of vein ore deposit in the lower wall of a fault, is different from that in a thick-big ore deposit. The secondary stress caused by the excavation of vein ore deposit in the lower wall of a fault, is mainly distributed in the upper wall of the fault, one surface subsidence center will occur. The influences of fault on the rock mass movement, secondary stress and hydro-geological structures are analyzed; the secondary stress is blocked by the fault and the tensile stress concentration occurs in the rock mass near the fault, the original water blocking structure is destructed and the permeable structure is reconstructed, the primary structural planes begin to expand and newborn fissures occur, so the permeability of the original permeable structure is greatly enhanced, so the water bursting will probably occur. Based on this knowledge, the possible water inrush pattern and position of the Xinli mine area are predicted. Some computer programs are developed using object-oriented design method under the development platform Visual Studio.Net. These programs include a Monte Carlo simulation procedure, a joint diagrammatizing procedure, a structural planes connectivity coefficient calculating procedure, a permeability tensor calculating procedure, a water chemical formula edit and water source fixture conditions calculating procedure. A new computer mapping algorithm of joint iso-density diagram is raised. Based on the powerful spatial data management and icon functions of Geographic Information System, the pit water discharge dynamic monitoring data management information systems are established with ArcView.

陕西关中盆地地热水循环的同位素研究

Geothermal resource is rich in Guanzhong Basin, but as to its cycle characteristic, there has been lack of systematic study so far. Blind exploitations lead to water-temperature reducing, the decrease of spring flow rate and so on. Based on groundwater system and hydrogeological and hydrological geochemical theory, this paper studied the recycling type of geothermal water and analyzed the resources of dissolved inorganic carbon (DIC) and sulfate. The origin of the internal geothermal water is ice and snow in Qinling Mountain and Liupan Mountain above 1400m. The precipitation and surface water entered the deep part of the basin along piedmont faults, heated and water-expansion increased. The karst groundwater comes from meteoric water of the bare carbonate rock area in the North Mountains. Geothermal-water DIC mainly came from the dissolution of carbonate rock in the deep part of Guanzhong Basin, sulfate of Xi’an depression and Lishan salient came from the dissolution of continental evaporate , and sulfate of Gushi depression and Xianli salient came from co-dissolution of continental and marine evaporate. The above results supply science basis for reasonable exploitation and sustainable utilization of the geothermal water in Guanzhong Basin.