Radiocarbon ages of different fractions of peat on coastal lowland of Bohai Bay: marine influence?

Peat in boreholes is the most important ^(14)C dating material used for constructing age framework. 20 bulk peat samples were collected from five boreholes, the ^(14)C ages of two fractions(organic sediment fraction and peat fraction) of the bulk peat samples were investigated by AMS-dating and which fraction is better to help construct an age framework for the boreholes were compared and discussed. The results indicated that the peat fraction give a good dating results sequence in the boreholes, compared with the corresponding organic sediment fraction. And the dating results of organic sediment fraction show 161-6 702 years older than corresponding peat fraction, which was caused by marine influence. Then, we suggest an experience formula as y =0.99 x-466.5 by the correlation analysis for correcting the marine influenced organic sediment ages within the conventional ages between 4 000 to 9 000 yrs BP, and more study should be carried out for the AMS ^(14)C dating of the bulk organic sediments.

Resolving the influence of nitrogen abundances on sediment organic matter in macrophyte-dominated lakes, using fluorescence spectroscopy

A controlled experiment was designed to resolve the influence of nitrogen abundance on sediment organic matters in macrophyte-dominated lakes using fluorescence analysis.Macrophyte biomass showed coincident growth trends with time, but different variation rates with nitrogen treatment. All plant growth indexes with nitrogen addition（N, NH4Cl100, 200, 400 mg/kg, respectively） were lower than those of the control group. Four humiclike components, two autochthonous tryptophan-like components, and one autochthonous tyrosine-like component were identified using the parallel factor analysis model. The results suggested that the relative component changes of fluorescence in the colonized sediments were in direct relation to the change of root biomass with time. In the experiment, the root formation parameters of the plants studied were significantly affected by adding N in sediments, which may be related to the reason that the root growth was affected by N addition.Adding a low concentration of N to sediments can play a part in supplying nutrients to the plants. However, the intensive uptake of NH4^＋may result in an increase in the intracellular concentration of ammonia, which is highly toxic to the plant cells. Hence, our experiment results manifested that organic matter cycling in the macrophyte-dominated sediment was influenced by nitrogen enrichment through influencing vegetation and relevant microbial activity.

Microbial bioavailability of dissolved organic nitrogen(DON) in the sediments of Lake Shankou,Northeastern China

Dissolved organic nitrogen（DON）extracted from Lake Shankou sediments using KCl was isolated into hydrophobic and hydrophilic fractions.The bioavailabilities of the hydrophobic and hydrophilic fractions to three types of bacterial communities collected from sediments,activated sludge and compost products were examined.The DON recoveries obtained by DAX-8 and cation exchange resins treatment were 96.17% ± 1.58% and 98.14% ±0% for the samples obtained from N4 and N14 stations,respectively.After 25 days of incubation at 25℃,most DON（59% to 96%）was degraded.Hydrophilic DON exhibited a higher reduction rate than hydrophobic DON during the growth phase.Untreated wastewater from Changshuihe town was the main degradable DON source to station N4,and 93% of hydrophilic DON and 80% of hydrophobic DON were degraded.Station N14 received a large amount of refractory DON from forest soils and exhibited DON degradation rates of 82% and 71% for the hydrophilic and hydrophobic fractions,respectively.Amino acid contents and fluorescence intensities were also analyzed.Approximately 27% to 74% of amino acids were taken up by day 5,and their concentration gradually increased in the following days due to the decomposition of dissolved proteins.Parallel factor analysis resulted in identification of tryptophan-like proteins,tyrosine-like proteins and FA-like substances.During the growth phase,40%–51% of the tryptophan-like proteins were taken up by bacteria,and the accumulation of tyrosine-like proteins was attributed to the release of biotic substances.The concentration of the FA-like substances decreased due to microbial decomposition.

Arsenic,Iron and Organic Matter in Quaternary Aquifer Sediments from Western Hetao Basin,Inner Mongolia

To investigate geochemical and mineralogical features of sediments from aquifers containing high levels of dissolved arsenic（As） in western Hetao Basin, Inner Mongolia, sediment samples were collected for XRD（X-ray diffraction）, amorphous Fe/Mn oxides, and humic/fulvic acid analyses, in addition to As determination. In the study area, the total As contents in the sediments were in the range 5.3–28.8 mg/kg; while that associated with humic substances in the range 4–9 mg/kg, accounting for 26%–47% of the total As. The results of XRD analysis suggest that clay and silt contain certain small amounts of iron oxides minerals, such as ferrihydrite, hematite and goethite, whereas have higher As and Fe_2O_3 contents. Up to one third of As in the sediments could be extracted by ammonium oxalate, and high As contents were generally found in organic-rich clay or silty clay samples with high FA/HA ratio. As is strongly associated with humic substances and Fe oxyhydroxides, which may be the major sink and source of As in the aquifer sediments.

Effects of seagrass leaf litter decomposition on sediment organic carbon composition and the key transformation processes

Seagrass leaf litters are an important source of sediment organic carbon(SOC). However, the mechanisms of seagrass leaf litter decomposition influencing SOC composition and the key transformation processes remain unknown. We performed a laboratory chamber experiment to compare the labile organic carbon(OC) composition and the enzyme activities governing SOC transformation between the seagrass group(seagrass leaf litter addition) and the control group. The results showed that the seagrass leaf litter decomposition significantly elevated the salt-extractable carbon(SEC) content and the SEC/SOC. Additionally,the levels of invertase, polyphenol oxidase, and cellulase in the seagrass leaf litters addition group were generally higher than in the control group, which could elevate recalcitrant OC decomposition. Following 24 days incubation, addition of seagrass leaf litter increased the amount of CO_2 released, but decreased the SOC content. Therefore, seagrass leaf litter decomposition leached abundant dissolved OC, which enhanced the activity and transformation of SOC.

The relationship between the black carbon and bisphenol A in sea and river sediments(Southern Baltic)

This study was derived from field investigations to assess bisphenol A（BPA）concentrations in the sea and river sediments of the Gulf of Gdansk.Black carbon（BC）and total organic carbon（TOC）were identified as influencing factors on the accumulation.As a result of the transportation of BC with organic matter via rivers into the Gulf of Gdansk,the highest mean concentrations（11.26 ng BPA/（g dry weight（dw）））,were determined in the sediments of river estuaries.Sediments in coastal stations were characterized by the lowest mean concentrations（5.73 ng BPA/（g dw））.TOC content below 0.1% determined the sorption of BPA on BC particles in sediments,and statistically significant correlation between the concentration of BPA and the BC/TOC ratio was found in these cases.In addition,dependency between the concentration of BPA and the content of BC was discovered in sediments where the BC/TOC ratio was 〉 0.33.

Organic matter and pH affect the analysis efficiency of (31)P-NMR

Solution ^（31）P nuclear magnetic resonance spectroscopy（ ^（31）P-NMR） is a useful method to analyze organic phosphorus（Po）, but a general procedure for the analysis method is lacking.The authors used solution ^（31）P-NMR, which was found to be an effective method for analysis of Po in Haihe River sediment, to analyze the Po in the surface sediment in Eastern China at the regional scale, and found that the Na OH-ethylenediaminetetraacetic acid（EDTA）extraction rate was affected by environmental factors. At the regional scale, the extraction rate showed a positive relationship with loss on ignition, when the extraction rate was lower than 60%. The extraction rate had no relationship with the loss on ignition when the extraction rate was higher than 60%. The extraction rate showed a negative relationship with p H, which means that the extraction rate was higher in acidic sediment and lower in alkaline sediment. The ratio of TC/TN（the ratio of total carbon to total nitrogen） was considered to represent the origin of organic matter in the sediment. The extraction rate was high when the TC/TN ratio was lower than 20, meanwhile the extraction rate decreased as the TC/TN ratio increased. The results show that the origin of organic matter in sediment significantly affects the Na OH-EDTA extraction rate. This study will give theoretical support for building an effective and general solution ^（31）P-NMR analysis method.

Historical record of effects of human activities on absolute and relative concentrations of Polycyclic aromatic hydrocarbons(PAHs) in Lake Chao,China

Polycyclic aromatic hydrocarbons（PAHs）are attracting concern because of their potential toxicity,posing serious threats to health of humans and ecosystems（Kim et al.,2013;Zhao et al.,2016）.Generally,similar to other contaminants＇behaviors（Wu et al.,2001;Zhang et al.,2007,2008;Lu et al.,2009）,PAHs result from natural organic matter and activities of humans,the latter＇s contribution usually outweighing the inputs from other sources（Fernández et al.,2000;Srogi,2007）.