Water salinity and productivity recorded by ostracod assemblages and their carbon isotopes since the early Holocene at Lake Qinghai on the northeastern Qinghai-Tibet Plateau, China

Lake Qinghai, the largest saline lake in China, is a closed-basin lake with a salinity of 16 g/L and is situated in the sensitive semi-arid zone between the Asian monsoon-controlled area and the westerly jet stream-influenced area. With the support of the International Continental Drilling Program (ICDP), Lake Qinghai was drilled in 2005 using the ICDP GLAD800 drilling system. Two ostracod species, i.e., Limnocythere inopinata and Eucypris mareotica, were found only in the upper 5.15 m of the drilled core 1F, covering 12 ka, where the depths of 5.15 to 3.15 m (12.0-7.4 ka) are dominated by E. mareotica and the depths of 3.15 to 0 m (7.4 ka-present) are dominated by L inopinata. The presence of the ostracod Eucypris mareotica was related to the high salinity of the water ( exceeding 30 g/L), and the dominant species of ostracod (Limnocythere inopinata) was related to the brackish water (3-16 g/L) in the Lake Qinghai area (Li et al., 2010). The changes in the carbon isotope in the modem ostracod shells were related to the water salinity and productivity on the lake bottom in Lake Qinghai (Li et al., 2012). On this basis, this study evaluated the changes in lake salinity and productivity and their relation to climatic change using changes in the relative abundances of ostracod fossil species assemblages and the stable carbon isotope in ostracod shells from core 1F and other published data (e.g., total organic carbon content, delta C-13(TOC) and ice core delta O-18). The single occurrence of ostracod Eucypris mareotica and the highest average delta C-13 values (-02 parts per thousand) in their shells indicated that the lake salinity and productivity were very high, a phenomenon that was related to the high temperature and low lake level (caused by intense evaporation even though the precipitation increased sharply) in the early Holocene. The deceased abundance of ostracod E. mareotica and the lowest average delta C-13 values (-2.0 parts per thousand.) in ostracod shells showed that the lake salinity and productivity decreased because of the increased lake level and decreased temperatures in the middle Holocene. Finally, the lake level decreased, but the water salinity and the lake productivity gradually increased because of the high E/I ratio related to the increased temperature in the late Holocene.</p

Ion-Exchange Method for Nitrogen Isotope Analysis of Nitrate in Soil

The N isotopic composition of nitrate in soil extraction samples can deliver critical information regarding the soil N cycle for biogeochemical processes. Here, we present a preparatory ion-exchange resin method for the N isotope analysis of NO3- in saturated CaSO4 soil extracts. This method showed that the NO3- in saturated CaSO4 soil extracts could be effectively separated from SO42- and other anions to avoid interference from the large amounts of coexisting anions in soil extracts. The nitrate recovery rate ranged from 95.54 to 105.04%. The resulting average natural abundance of N-15 (delta N-15) values of the KNO3 solutions and the KNO3-CaSO4 solutions were +6.04 +/- 0.03 parts per thousand (n = 6) and +6.03 +/- 0.12 parts per thousand (n = 6), respectively. The average delta N-15 value of the KNO3 salt was +6.07 +/- 0.06 parts per thousand (n = 12). Therefore, we concluded that N isotopic fractionation did not occur throughout the process. In addition, the delta N-15-NO3- values of natural soils extracted using saturated CaSO4 were reproducible between separate analytical runs. The standard deviations of the delta N-15-NO3- for the three different soils were +/- 0.17 parts per thousand (n = 4), +/- 0.04 parts per thousand (n = 3), and +/- 0.34 parts per thousand (n = 3). Our ion-exchange method was effective at separating NO3- from other anions in the soil extracts and was suitable for measuring the delta N-15-NO3 of saturated CaSO4 soil extracts.</p

Occurrence of Organochlorine Pesticides in Surface Soils from College School Yards of Xi'an, China

In this study, surface soil samples from 14 representative college school yards in Xi&#39;an, the capital city of Shaanxi province, China, were collected and analyzed for 21 organochlorine pesticides (OCPs). The total concentrations were in the ranges of 0.2-67.0 ng/g. HCHs and DDTs were the most dominant compounds among the 21 OCPs, and their concentrations ranged from 0.1-8.5 to 0.1-56.3 ng/g, respectively. Source identification analysis indicated that the residues of HCHs and DDTs were mostly due to historical use of these chemicals or from other source regions. The quality of all the Xi&#39;an college school yard soils except sample XAUAT was classified as low pollution by OCPs according to the National Environmental Quality Standards for Soils of China (GB15618-1995).</p

Carbon chain length distribution in n-alkyl lipids: A process for evaluating source inputs to Lake Qinghai

Lake sediments generally contain a mixture of terrestrial and aquatic source inputs, and determining the major inputs is important for understanding geological records in paleoenvironment and paleoclimate research. In this study we describe the distribution of n-alkanes and n-fatty acids (FAs) in representative modern plants from around Lake Qinghai. We found a significant difference in the average length of n-FA carbon chains (ACL Fa(16-32)) in terrestrial (23.3) and aquatic plants (18.6). The results reveal that ACL Fa(16-32) may essentially serve as a proxy for evaluating the major source inputs to lake sediments. Assessment of surface sediments from the lake showed that the FAs originated from a mixture of inputs, with the aquatic source input predominant at most sites. Additionally, the delta D values of sediment mid-chain n-acids (C-22) showed a relationship with the ACL Fa(16-32) proxy: an increased Fa ACL corresponded to more negative hydrogen isotope ratio values. We suggest that different sources should be considered and ACL Fa(16-32) could be a potential calibration proxy before using delta D values to extract reliable isotopic information from lake water. More attention should be paid to source inputs and their relationship to other geochemical proxies in future studies of lake sediments.</p

Calibration of the U (37) (K') index of long-chain alkenones with the in-situ water temperature in Lake Qinghai in the Tibetan Plateau

Long-chain alkenones (LCAs) can potentially be used as indicators to understand past variations in lacustrine environments. Previous research has suggested that the relationship between the temperature and the unsaturation index of LCAs should be calibrated individually, because of the possible variations in the alkenone-producing algal species in the lacustrine environment. In this work, we have calibrated U (37) (K&#39;) of water filter samples against the in-situ water temperature in Lake Qinghai, Tibetan Plateau. There are significant relationships between U (37) (K&#39;) and the water temperature, a non-linear relationship was derived. Because the U (37) (K&#39;) values did not respond sensitively at lower temperatures, we suggested that a quadratic regression (U (37) (K&#39;) =0.0011xT (2)-0.0201xT+0.1959, n=15, r (2)=0.74) was appropriate than linear regression to represent the relationship between the in-situ temperatures and U (37) (K&#39;) . Meanwhile, the U (37) (K) correlation relationship was not more significant than U (37) (K&#39;) index in our study. Because of the C-37:4 effects by salinity change, we suggest U (37) (K) is not as robust as the U (37) (K&#39;) index as a temperature proxy, at least for the salt lake in the Tibetan Plateau. The calibration of the U (37) (K&#39;) index in this work has provided a new understanding of historic climatic changes in the Tibetan Plateau.</p

Characterization and Risk Assessment of PolychlorinatedBiphenyls in City Park Soils of Xi’An, China

Polychlorinated biphenyl (PCB) concentrations in surface soil samples (0&ndash;10 cm) from 23 city parks (8 urban and 15 suburban) from Xi&rsquo;An, China were presented. The average concentration of R7 PCBs among all the sites was 1.68 ng g-1 dry weight. High detection frequency (100 %) of PCB 28 and PCB 52 suggested wide occurrence of PCB contaminations in Xi&rsquo;An. Among these PCBs, PCB 28, 52 and 153 were the most dominant compounds (14.9 %, 39.3 % and 9.5 % of the R7 PCBs on average, respectively). &lsquo;&lsquo;Urban fractionation effect&rsquo;&rsquo; was found in Xi&rsquo;An. In other words, PCB concentrations were higher in the urban city park soils than those in suburban park soils. The PCB contamination in Xi&rsquo;An city park soils were at a low level based on the Dutch guideline. However, dioxinlike PCB congeners were detected from 12 parks, which indicated further investigation was urgently required in future. Furthermore, total PCB concentrations were used to evaluate the cancer risk via ingestion, dermal and inhalation and the results showed that the total cancer risk was at the very low level in this area.</p

Occurrence of Organochlorine Pesticides in Farmland Soils of Xi'an, China

In this study, 25 representative farmland soil samples from suburban areas in Xi&#39;an, the capital city of Shaanxi province, China, were collected and analyzed for 20 organochlorine pesticides (OCPs). The concentrations were in the ranges of 0.22-11.24 ng g(-1) for HCHs (sum of alpha, beta, gamma and delta-HCH, avg. 3.56 ng g(-1)), 0.76-56.30 ng g(-1) for DDTs (sum of p,p&#39;-DDT, p,p&#39;-DDD, p,p&#39;-DDE, avg. 12.80 ng g(-1)), 0.47-12.95 ng g(-1) for CHLs (sum of heptachlor, heptachlor epoxide isomer B, alpha-chlordane and gamma-chlordane, avg. 5.90 ng g(-1)), 0.64-31.51 ng g(-1) for other organochlorine pesticides (sum of aldrin, dieldrin, endrin, endosulfan I, endosulfan II, endosulfan sulfate, endrin aldehyde, endrin ketone and methoxychlor, avg. 11.89 ngg(-1)). HCHs, DDTs and CHLs were the most dominant compounds among the 20 organochlorine pesticides. Source identification analysis indicated that the residues of HCHs, DDTs and CHLs were mostly due to historical use of these chemicals or from other source regions. The quality of Xi&#39;an farmland soil was classified as low pollution by organochlorine pesticides according to the national environmental quality standards for soils of China (GB15618-1995).</p

Effect of preservation on the δ13C value of dissolved inorganic carbon in different types of water samples

Recent studies have shown that the stable carbon isotope compositions of dissolved inorganic carbon (&delta;13CDIC) of water samples preserved with HgCl2 and CuSO4 vary. Furthermore, mercury and cuprum compounds are toxic to the human or biological system and require proper waste disposal. To test the effect of preservation on the &delta;13C value of DIC in different types of water samples, a set of water samples with different DIC concentrations was preserved using different methods, including preserving with inhibitors (CuSO4 or HgCl2), preserving under frozen conditions, filtering through a 0.4&mu;m paper filter, and the DIC species precipitated in the form of solid BaCO3. Our results show that &delta;13CDIC values of the samples preserved with CuSO4 and HgCl2 become more positive with increased storage time. The &delta;13CDIC of the water samples preserved under frozen conditions and the precipitated DIC as BaCO3 are also more positive than original water samples. However, the &delta;13C values were relatively stable for up to 90 days in all water samples filtered through the 0.4&mu;m paper filter and stored under cool conditions (0&ndash;4 ◦C). Therefore, we suggest that the better method for the storage of water samples is to filter the samples through a 0.4&mu;m paper filter while out in the field and preserve them under cool conditions, thereby avoiding the use of preservatives.</p

Vertical distributions of organochlorine pesticidesand polychlorinated biphenyls in an agricultural soil corefrom the Guanzhong Basin, China

The concentrations and distributions of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), and polychlorinated biphenyls (PCBs) in an agricultural soil core in the Guanzhong Basin, China were determined. Overall, p,p&rsquo;-DDT and p,p&rsquo;-DDE were dominant contaminants and accounted for approximately 48.4 and 23.3 % of the total detected DDTs. Low chlorinated PCBs (PCB 28 and PCB 52) were generally detected at higher concentrations and more frequently than high chlorinated PCBs. The peak values of &sum;DDT (12.92 ng/g), &sum;HCH (2.25 ng/g), and &sum;PCB (3.44 ng/g) occurred in the 10&ndash;15, 15&ndash;20, and 5&ndash; 10 cm sections, respectively. The negative correlation between the organochlorine pesticide (OCP) concentrations and the soil depths and the relatively high p,p&rsquo;- DDT/p,p&rsquo;-DDE ratios in the surface soils indicated that these chemicals were recently used illegally, despite their official ban in 1983. The increase in the ratio of &alpha;-/&gamma;-HCH with increasing soil depth indicated that the use of lindane decreased relative to the use of technical HCHs in recent years.</p

Carbon isotopic composition of branched tetraether membrane lipids in a loess-paleosol sequence and its geochemical significance

Carbon isotopes of organic matter have been widely used in quantitative reconstruction of paleovegetation and paleoclimate since they are sensitive to vegetation and environmental changes. However, the effect of transformation of soil organic matter after burial remains unclear. The carbon isotopes of brGDGTs, which were likely produced by heterotrophic bacteria in soil or peat, provide an opportunity to fill this gap. In this study, we investigated the stable carbon isotopic composition of brGDGT-derived alkane spanning the last 60 kyr in the Lantian loess-paleosol sequence from the southern Chinese Loess Plateau, as well as its relationship with &delta;13C values of total organic carbon (TOC) and other established climatic proxies. The results show that the &delta;13C values of brGDGTs were slightly depleted (ca. 1&ndash;2&permil;) relative to TOC, and a good linear relationship between them was observed. These support a heterotrophic lifestyle of brGDGT-producing bacteria and suggest that &delta;13C values of brGDGTs may have potential use in paleovegetation reconstruction. The similar variations between &delta;13C values of brGDGTs and TOC in the soil core also suggest that the effect of soil organic matter transformation after burial may have limited impact on the environmental significance of &delta;13C values of TOC. In comparison with &delta;13C values of the TOC, the widely used proxy for past vegetation changes, the &delta;13C values of brGDGTs seem more specific and sensitive in the Lantian profile due to its specific origin and stable chemical structure.</p