Abstract:
Taking Gaoqiao mangrove of Zhanjiang Mangrove National Nature Reserve as the study area, six
sediment cores were sampled along two sample lines A and B, which were perpendicular to the coastline,
and spatial distribution features of physicochemical properties and enrichment pattern of metal trace in
sediment cores were analyzed. The content of metals, including major metals (Al, Fe and Mg) and trace
metals (As, Co, Cr, Cu, Mn, Ni, Pb and Zn) and their possible relationships with physicochemical
properties (particle size, pH, exchangeable base cations, total nitrogen, total phosphorus, and organic
matter) in core sediment samples were evaluated. Analysis of physicochemical properties revealed that an
overall predominance of silt and sand in the study area, the concentration of clay, silt and sand of
sediment were (134)%,(3912)% and (4816)%, respectively, organic matters varied from
0.2% to 3.7%, 2.5 -7.3 for pH value, 1.4 -16.4 cmol/ kg for exchangeable base cations, 0.01% -0.2% for total nitrogen, and 130 - 435 mg/ kg for total phosphorus. The sediment quality parameters
including grain size, pH value, exchangeable base cations, organic matter, total nitrogen and phosphorus
were not significant (P 0.05) between A and B sample lines. The metal concentrations in sediment
obtained in this study decreased in the following order,Al (4.5% -19.2%), Fe (1.0% -4.7%), Mn
(50.4 -163.4 mg/ kg), Cr (24.4 -43.0 mg/ kg), Zn (14.4 -52.1 mg/ kg), Pb (11.3 -34.9 mg/
kg), Ni (3.5 -19.4 mg/ kg), Co (3.0 - 7.7 mg/ kg), Cu (1.4 - 9.6 mg/ kg), As (1.4 - 5.8 mg/
kg), Mg (0.2 - 0.9 mg/ kg). The difference was significant (P 0.05) among contents of metals
excluding Co, Cu, As and Fe. The concentrations of Cr, Cu and Mn on line A were much higher than on
line B. Spatial distribution varied markedly in physicochemical properties. The sand content and pH
value increased with increasing distance from the seawall. Organic matter, total nitrogen and total
phosphorus were affected by mangrove community type and hydrodynamics. Physicochemical properties
varied obviously in vertical direction, parameters of physicochemical properties ( not including sand
content in surface layer) were the highest, and decreased gradually from top to bottom layer. With
increasing distance from the seawall, the metal concentration in core sediment decreased gradually with
the tidal level but varied with metals; therefore, tidal level was not the solo factor affecting metal
distribution in horizontal level. Similar to the trends of physicochemical properties, hierarchical variation
in metal concentration was presented in a vertical direction: concentrations of metals were the highest in
surface layer, and decreased gradually from top to bottom layer. Correlation analysis showed that organic
matters were positively correlated with finer particles (P 0.01), but negatively correlated with pH value
and sand content (P 0.01). A significantly negative correlation was detected between metal content
and sand content, and metal concentration had no correlation with pH value. The metal concentration was
positively correlated with exchangeable base cations, organic matter and fine particles (P 0.01). The
associated or homologous features were detected according to the significant correlation among the metals.