Sediment phosphorus speciation and retention process affected by invasion time of Spartina alterniflora in a subtropical coastal wetland of China.

In coastal wetland ecosystems, most phosphorus (P) accumulates in the sediments and becomes a major pollutant causing eutrophication by recycling to the water column in estuary areas, especially exotic plant invasions will change the nutrient cycling. In this study, a large wetland invaded by exotic species Spartina alterniflora for over 15 years was selected to study the sediment P fractionation and its retention for different plant invasion periods. The samples were collected from east to west in September and the sediment P was fractionated into total P (TP), inorganic P (IP), iron/aluminum-bound P (Fe/Al-P), calcium-bound P (Ca-P), and organic P (OP). Additionally, the effect of the invasion period on the wetland P fractionation based on space-time reciprocal principle was investigated. For different S. alterniflora invasion periods, the average TP concentration was 675.37 mg kg-1 with a range of 160.33-1071 mg kg-1. The IP concentration was in the range of 107.33-813.33 mg kg-1 (accounting for 54.4-79.5% of TP), of which Fe/Al-P and Ca-P represented up to 99.4%. In addition, the P retention (RP) was within 41.67-329.67 mg kg-1. We also found that TP, IP, Fe/Al-P, Ca-P, OP, and RP in sediments were negatively correlated with pH (p < 0.05), and were also significantly positively correlated (p < 0.01) with water content and electrical conductivity. There were positive correlations between the various forms of P in the sediments (p < 0.01). However, the most important finding was that invasion time of S. alterniflora had a direct effect on the P speciation and three stages were determined. In the first stage, S. alterniflora mainly consumed the OP of the sediment. In the second stage, S. alterniflora showed great vitality and biological immobilization led to the transforming of IP to OP. In the third stage, all P fractions greatly decreased to values even lower than for the bare beach which indicated that S. alterniflora growth had begun to degenerate. These three stages well explained the P seemingly contradictory increases and decreases apparent in previous studies and provide important information for understanding the effect of S. alterniflora invasion.

Residue levels of HCHs, DDTs and PCBs in shellfish from coastal areas of east Xiamen Island and Minjiang Estuary, China.

Shellfish samples were collected from the coastal cultivating areas of east Xiamen Island and Minjing Estuary, China and analyzed for hexachlorocyclohexanes (HCHs), DDTs and polychlorinated biphenyls (PCBs) by GC. Concentration ranges of HCHs, DDTs and PCBs in the coastal area of east Xiamen Island were 0.18-345, 75.2-2143 and ND-23 ng g(-1) dry wt., respectively; those for Minjiang Estuary were ND-5.07, 21.5-2396 and ND-6.78 ng g(-1) dry wt., respectively. The results showed that the organochlorines were evidently accumulated in marine bivalve molluscs, particularly in oyster. The concentrations of organocholorine pollutants in shellfish samples varied with the sampling locations, the season of collection and organism species, but were generally higher than those in the sediments. The concentrations of DDTs in the shellfish were high as compared with HCHs and PCBs, so that DDTs can be considered as the typical organochlorines in the survey areas. The residue levels and compositions of HCHs, DDTs and PCBs are discussed.