Guangming Zhao

Distribution, sources and potential toxicological significance of polycyclic aromatic hydrocarbons (PAHs) in surface soils of the Yellow River Delta, China.

PAH concentrations of 61 surface soil samples collected from the Yellow River Delta (YRD), China were measured to determine occurrence levels, sources, and potential toxicological significance of PAHs. The total concentrations of ∑PAHs ranged from 27 to 753 ng/g d.w., with a mean of 118±132 ng/g. The highest concentrations was found in the mid-southern part of the YRD (753 ng/g), which was associated with the oil exploration. The ratios indicated that the PAHs throughout the YRD were mostly of pyrogenic origin; while various sites in mid-southern part in the region were derived mainly from the petrogenic sources. Multivariate statistical analyses supported that the PAHs in surface soils of the YRD were principally from the coal and biomass combustion, petroleum spills, and/or vehicular emissions. The toxic assessment suggested that the PAHs in soils were at low potential of ecotoxicological contamination level for the YRD.

Vulnerability of Eco-Hydrological Environment in the Yellow River Delta Wetland

ABSTRACT Gao, M.; Liu, S.; Zhao, G.; Yuan, H.; Wei, C.; Wu, Y., and Tang, J., 2014. Vulnerability of eco-hydrological environment in the Yellow River delta wetland. We investigated the relationship between groundwater head and oceanic tidal fluctuations in the Yellow River Delta wetland through on-site hydrological monitoring. Shallow groundwater heads were obviously affected by oceanic tide along the coastal zone. The ranges of the wetland zone can be readily assessed by measuring fluctuation amplitudes or lags. The results show that the influence radius is approximately 12 km to 18 km (when the correlation coefficient is 0.7 to 0.8) under the joint actions of oceanic tide and shallow groundwater seepage flow in clayey silt coastal wetland. A cross-sectional sketch of the coastal wetland model is developed based on monitoring data of groundwater and oceanic tidal fluctuations to study the vulnerability of the eco-hydrological environment in the Yellow River Delta wetland. The coastal wetland consists of three zones (the groundwater seepage zone, the tidal-induced transitional zone, and the tidal zone) with distinctly different hydraulic properties. Analytical solutions are used to estimate the vulnerability of the eco-hydrological environment in the wetland aquifer located in the NE part of the Yellow River Delta wetland, Shandong Province, China. Our results show that changes in the shallow groundwater quality of the wetland are significantly affected by natural factors, such as strong cutoff in the lower reaches, storm tides, and human engineering activities. The northern coastal wetland may be submerged without damp proof when the height of a storm tide reaches 2.4 m. The depth of shallow groundwater and the salinity gradient are key factors that contribute to the vulnerability of the ecological environment. The vulnerability of the eco-hydrological environment is derived from the joint actions of groundwater dynamics, hydrochemistry, and tidal-induced processes under sedimentary stress and water pressure.

Surface sediment properties and heavy metal pollution assessment in the Shallow Sea Wetland of the Liaodong Bay, China

Liaodong Bay, a semi-enclosed bay located in northeastern China, is impacted by the discharges of five rivers. We analyzed 100 surface sediment samples from the Shallow Sea Wetland of Liaodong Bay for grain size and concentrations of organic carbon (Corg) and heavy metals. The ranges of the heavy metal concentrations were 2.32-17μg/g (As), 0.025-1.03μg/g (Cd), 18.9-131μg/g (Cr), 4.6-36.1μg/g (Cu), 0.012-0.29μg/g (Hg), 13.7-33.9μg/g (Pb), and 17.4-159μg/g (Zn). Pollution assessments revealed that some stations were moderately to highly polluted with As, Cd, and Hg. Severe pollution was apparent in the Xiaoling River estuary; lower concentrations of heavy metals were observed in other river mouths, where the sediments were more coarse. The distributions of the heavy metals were closely associated with Corg and grain size.

Inter-annual variability of area-scaled gaseous carbon emissions from wetland soils in the Liaohe Delta, China

Global management of wetlands to suppress greenhouse gas (GHG) emissions, facilitate carbon (C) sequestration, and reduce atmospheric CO2 concentrations while simultaneously promoting agricultural gains is paramount. However, studies that relate variability in CO2 and CH4 emissions at large spatial scales are limited. We investigated three-year emissions of soil CO2 and CH4 from the primary wetland types of the Liaohe Delta, China, by focusing on a total wetland area of 3287 km2. One percent is Suaeda salsa, 24% is Phragmites australis, and 75% is rice. While S. salsa wetlands are under somewhat natural tidal influence, P. australis and rice are managed hydrologically for paper and food, respectively. Total C emissions from CO2 and CH4 from these wetland soils were 2.9 Tg C/year, ranging from 2.5 to 3.3 Tg C/year depending on the year assessed. Primary emissions were from CO2 (~98%). Photosynthetic uptake of CO2 would mitigate most of the soil CO2 emissions, but CH4 emissions would persist. Overall, CH4 fluxes were high when soil temperatures were >18°C and pore water salinity <18 PSU. CH4 emissions from rice habitat alone in the Liaohe Delta represent 0.2% of CH4 carbon emissions globally from rice. With such a large area and interannual sensitivity in soil GHG fluxes, management practices in the Delta and similar wetlands around the world have the potential not only to influence local C budgeting, but also to influence global biogeochemical cycling.

Records of Compaction Subsidence of Argillaceous Sediments in the Modern Yellow River Delta

The distributary lobe of the modern Yellow River Delta formed after 1855 was 15 m in thickness before it was abandoned, where the compaction subsidence has reached as high as 2.28∼3.87 m in the past 30 years. The compaction ratio of clayey silty sand (25.8%) is 1.7 times greater than that of silty sand (15.2%). It means that the compaction process has basically terminated. On the other hand, the compaction subsidence of underlying sediment is quite limited and shows an insignificant difference. For example, for the underlying sediment of 20∼30 m in thickness, the subsidence varies between 0.2 and 0.28 m. The average compaction ratio of clayey silty sand is 0.91%, while that of silty sand is 1.19%, and the average compaction ratio of all sediment is 1%. Theres a negative exponential function relationship between porosity and burial depth of the sediment, and the higher the clay content, the more difficult it is for pore water to drain. The superficial sediments contribute more to the compaction subsidence than the underlying strata.

Carbon sequestration and its controlling factors in the temperate wetland communities along the Bohai Sea, China

The carbon sequestration rate (CSR) in deltaic wetlands is associated with the nutrient balance, sediment (soil) accretion rate (SAR) and geological and climatic conditions. To explore the relationships between these factors, micronutrients; C, N, and P concentrations; and ages determined using either paleosols or radiometric dating with 210Pb were analysed from a total of 14 cores from the Yellow River delta (YRD) and Liaohe delta (LHD) wetlands, collected in 2007 and 2012 respectively. With the exception of Ca, concentrations of N, organic C, Cu, Zn, Fe, Mn, Mg, K, Al and H+ were significantly higher in the wetland soils of the LHD, but organic CSR was virtually identical at the two sites, ~140gCm–2year–1 at sites above mean sea level (MSL). SAR and organic CSR at LHD sites below MSL were ~2.8 times the corresponding rates at sites above MSL. SAR and total CSR were much higher in the YRD than LHD because of the much greater accumulation rate of CaCO3 in the YRD. Organic CSRs were primarily controlled by SAR in both deltaic wetland systems. However, organic CSRs were much more sensitive to changes in SARs in LHD wetlands than YRD wetlands.