Heavy metals,polycyclic aromatic hydrocarbons and organochlorine pesticides in the surface sediments of mangrove swamps from coastal sites along the Leizhou Peninsula,South China

Contents of heavy metals,polycyclic aromatic hydrocarbons (PAHs),dichlorodiphenyltrichloroethanes (DDTs) and hexachlorcyclohexanes (HCHs) in surface sediments from mangrove areas of the Leizhou Peninsula were analyzed in July and November 2005. Risk assessment criteria applied by Long E R et al. (1995) and Long E D et al. (1998) (effects range low,ERL; effects range mean,ERM) of chemicals in sediments from the gulf or estuary were used to assess the potential ecological risks of heavy metals,PAHs,DDTs and HCHs to aquatic organisms in the studied area. The results indicated that the average contents of zinc,nickel,chromium,lead,copper,arsenic and mercury were (61.97 ± 55.87),(59.99 ± 39.01),(47.93 ± 28.37),(26.64 ± 13.00),(23.45 ± 41.96),(9.32 ± 3.62),(0.14 ± 0.18) mg/kg in dry weight in the sediment samples collected from five studied sites in the Leizhou Peninsula,respectively. Cadmium was not calculated due to its content being below the detection limit (< 0.3 mg/kg). The average levels of Cr,Cu,Ni,Pb,Zn and Hg exceed their background values. The average contents of Ni were higher than ERM. The contents of PAHs in the sediments from the five studied sites were (79.78 ± 43.70) ng/g in dry weight,far lower than ERL(4 022 ng/g). The contents of DDE,DDD and DDTs in the sediments from five studied sites were (2.60 ± 4.68),(17.52 ± 27.25),(27.78 ± 46.64) ng/g in dry weight respectively,clearly higher than ERL,and the average contents of DDT were (7.66 ± 15.93) ng/g in dry weight,much higher than ERM. HCHs could be detected in the sediments only from Gaoqiao sampling site,with the average contents (0.07 ± 0.08) ng/g in dry weight.

Anisotropy analyses of population distribution patterns

Direction-dependence,or anisotropy,of spatial distribution patterns of vegetation is rarely explored due to neglect of this ecological phenomenon and the paucity of methods dealing with this issue.This paper proposes a new approach to anisotropy analysis of spatial distribution patterns of plant populations on the basis of the data resam-pling technique(DRT)combined with Ripley’s L index.Using the ArcView Geographic Information System(GIS)platform,a case study was carried out by selecting the popula-tion of Pinus massoniana from a needle-and broad-leaved mixed forest community in the Heishiding Nature Reserve,Guangdong Province.Results showed that the spatial pattern of the P.massoniana population was typically anisotropic with different patterns in different directions.The DRT was found to be an effective approach to the anisotropy analysis of spatial patterns of plant populations.By employing resam-pling sub-datasets from the original dataset in different direc-tions,we could overcome the difficulty in the direct use of current non-angular methods of pattern analysis.