Seasonal response of nitrogen exchange fluxes to crab disturbance at sediment-water interface in coastal tidal wetlands

Coastal wetlands are hotspots for nitrogen(N)cycling,and crab burrowing is known to transform N in intertidal marsh soils.However,the underlying mechanisms remain unclear.This study conducted field experiments and used indoor control test devices to investigate the seasonal response of nitrogen to crab disturbance at the sediment-water interface in coastal tidal flat wetlands.The results showed that crab disturbance exhibited significant seasonality with large seasonal differences in cave density and depth.Due to crab disturbance,nitrogen fuxes at the sediment-water interface were much greater in the box with crabs than in the box without crabs.In summer,NH-N showed a positive flux from the sediment to the overlying water,but NO2-N and NOg-N showed positive fluxes from the sediment to the overlying water only in early stages.In winter,NH-N showed a positive flux from the sediment to the overlying water,but NO-N and NO,-N both exhibited positive and negative fluxes.These results indicated that the presence of crab burrows can cause the aerobic layer to move downward by approximately 8-15 cm in summer and directly promote nitrification at the sediment surface.

The application of Yangtze Estuary Tidal Wetlands Geographic Information System

Yangtze Estuary Tidal Wetlands Geographic Information System (YETWGIS) is a comprehensive software system for environmental management and decision of Yangtze estuary tidal wetlands. Based on MapObjects components technology, Data Mining technology, mathematical modeling method and Visual Basic language, this software system has many functions such as displaying, editing, querying and searching, spatial statistics and analysis, thematic map compiling, and environmental quality evaluation. This paper firstly outlined the system structure, key techniques, and achieving methods of YETWGIS, and then, described the core modules (the thematic map compiling module and environmental quality evaluation model module) in detail. In addition, based on information entropy model, it thoroughly discussed the methods of environmental quality evaluation and indicators' weight calculation. Finally, by using YETWGIS, this paper analyzed the spatial distribution characteristics of Heavy Metal and Persistent Organic Pollutants (POPs) of the Yangtze estuary tidal wetlands in 2002, and evaluated the environmental quality of the Yangtze estuary tidal wetlands in 2003.

Heavy metal distribution of natural and reclaimed tidal riparian wetlands in south estuary, China

We evaluated the distribution and accumulation of Cd, Cr, Cu, Ni, Pb and Zn in two plant species （Scirpus tripueter Linn. and Cyperus malaccensis Lam.）, in water and soils sampled from the reclaimed tidal riparian wetlands （RTRWs） and the natural riparian wetlands （NRWs） in the Pearl River Estuary （PRE）. The results showed that the concentrations of studied heavy metals in soils exceeded the eco-toxic threshold recommended by US EPA. The concentrations of Cd, Cr and Zn in plants may lead to toxic effiects. The heavy metal concentrations were high in water and low in soils of RTRWs compared with that in the NRWs. The accumulation of heavy metals in the roots of plants was higher in NRWs than those in RTRWs while the opposite result was found for heavy metal accumulation in shoots. Based on the bioaccumulation and translocation factors, the plants in NRWs had a higher capacity to accumulate heavy metals while higher abilities to transport heavy metals from roots to shoots were observed in RTRWs. Heavy metal contaminations in RTRWs were dominated by anthropogenic sources from both side uplands and river water, whereas in NRWs, the metal accumulations were simultaneously affected by anthropogenic and natural factors

Marsh persistence under sea-level rise is controlled by multiple,geologically variable stressors

Introduction:Marshes contribute to habitat and water quality in estuaries and coastal bays.Their importance to continued ecosystem functioning has led to concerns about their persistence.Outcomes:Concurrent with sea-level rise,marshes are eroding and appear to be disappearing through ponding in their interior;in addition,in many places,they are being replaced with shoreline stabilization structures.We examined the changes in marsh extent over the past 40 years within a subestuary of Chesapeake Bay,the largest estuary in the United States,to better understand the effects of sea-level rise and human pressure on marsh coverage.Discussion:Approximately 30 years ago,an inventory of York River estuary marshes documented the historic extent of marshes.Marshes were resurveyed in 2010 to examine shifts in tidal marsh extent and distribution.Marsh change varied spatially along the estuary,with watershed changes between a 32%loss and an 11%gain in marsh area.Loss of marsh was apparent in high energy sections of the estuary while there was marsh gain in the upper/riverine section of the estuary and where forested hummocks on marsh islands have become inundated.Marshes showed little change in the small tributary creeks,except in the creeks dominated by fringing marshes and high shoreline development.Conclusions:Differential resilience to sea-level rise and spatial variations in erosion,sediment supply,and human development have resulted in spatially variable changes in specific marsh extents and are predicted to lead to a redistribution of marshes along the estuarine gradient,with consequences for their unique communities.

Spatio-temporal characteristics and causes of changes in erosion-accretion in the Yangtze （Changjiang） submerged delta from 1982 to 2010

The Yangtze delta＇s response to accelerating river damming and irrigation is a topic of global concern. This research analyzed the general erosion-accretion of the submerged delta front, the spatio-temporal changing pattern in different sub-regions, the geomorphological changes in typical cross-sections, and the geomorphological causes of the four main sub-regions（the eastern tidal wetland of Chongming–CM, the Hengsha shoal–HS, the Jiuduansha wetland–JDS, and the eastern tidal wetland of Nanhui–NH）. Data sources include topographic data measured at high-resolution, sediment load at Datong Station, and the corresponding estuary construction information. Major findings are：（1） in general, the study area had slightly eroded（the erosion area ratio was 51.83% and the accretion area ratio was 48.17%） from 1982 to 2010, and it had experienced a shift of “erosion-accretion- erosion”. The spatio-temporal change of geomorphology was also significant in the eight sub-regions, excluding constant erosion in the North Channel;（2） evolution in eastern and northern CM and HS, northern JDS, and the region within the 5 m isobath of NH was dominated by vertical deposition, which was the opposite of that in southern CM and HS, and the region within the 5 m isobath of eastern and southern JDS;（3） on the whole, the encompassed surface areas（ESAs） of the 2 m and 5 m isobaths kept increasing, and the annual growth rates reached 10.42 km^2/yr and 7.99 km^2/yr respectively during 1982–2010（however, four sub-regions exhibited disagreements）, and in the whole region and all sub-regions, the ESA of the 10 m isobath decreased, while the ESA of the 15 m isobath changed slightly during the period and remained stable;（4） being less influenced by the estuarine engineering, CM was the only sub-region where the ESA of the isobath decreased in accordance with the decline of the sediment load. Major conclusions are that estuarine engineering projects play an increasingly important role in affecting the submerged delta against the macro-background of the reduction of sediment load, the change of ESA and the distribution of isobaths. Along with the accelerating construction of the Shanghai International Shipping Centre and reclamation project, the geomorphological evolution of the submerged delta will become more complex and thus deserves frequent monitoring in the future.