Intertidal Pollution On Benthic Macro-arthropod Community In Mangrove Forest

The community structures of benthic macro-arthropods and principal pollutants in intertidal zone of Dongzhaigang Natural Mangrove Reserves were investigated and tested on December, 2009, March,2010 and July, 2010 respectively. The community structure and diversity of benthic macro-arthropods were studied, and pollutants and heavy metal accumulation of some dominant crab bodies were tested. In addition, The community diversity of benthic macro-arthropods were used as biological indicators at first time, and along with chemical indices of water eutrophication and heavy metal content to evaluate the quality of shallow water and the sedimentary environment in the intertidal zone, and the health of the study area was better assessed by these indicators The detailed results as follows.1. Sampling procedures were conducted at 23 stations on 8 sampling points, and benthic arthropods total 34 species belonging to 2 classes, 14 families were collected and identified; among these Grapsidae and Ocypodidae were the most abundant groups, and Uca arcuata, Perisesarma bidens, Kalliapseudes tomiokaensis, Ilyoplax serrata and another mud crab (Ilyoplax sp.) were the common dominant species. Average density and biomass at different intertidal levels were different but not significantly. However, some significant differences observed between winter and spring and between winter and summer.2. In the entire study area, the number of species, Margalef richness index d, Shannon-Wiener diversity index H′and evenness index J in spring were higher than those in winter, and all the these indices were highest in summer, so that the biological diversity also increased by seasons. Evaluation by Margalef richness index showed the water was moderately polluted in winter, but not in spring or summer.3. The result of eutrophication analysis indicated that all the sampling points were eutrophicated in summer, the nutritional indices of some points were one times higher than the critical level, about 50% of sampling points in spring and winter also appeared eutrophication. The content of COD and chlorophyll a in water were significantly correlated in spring and summer, the correlation coefficients were 0.799 and 0.595, respectively .4. The average organic matter contents of sediments in winter were higher than in summer, and the highest occurred in spring, and higher in high-intertidal than in low-intertidal level,and the highest appeared in middle-intertidal level. Results also showed that the organic matter was profuser in surface soil than that in deep soil. And the quality of Sediments in 78% sampling points were included in the first category, the organic carbon contents were less than 2%.5. The content of heavy metals exceeded the critical value in all the stations, with those in the surface soil higher that in deep soil. The quality of sediment belong to the first category, except the quality of T2 sediment are the second category, The contents of Cu, Pb, Cr and Zn were less than 35mg/kg, 60 mg/kg, 80 mg/kg and 150 mg/kg, the whole study region showed good.6. The density of Mud crab1 (Ilyoplax sp.) was negatively correlated with the organic matter content in sediment. The density and biomass of Kalliapseudes tomiokaensis were significantly positively correlated with chlorophyll a, and its biomass was significantly positively correlated with the contents of heavy metal Pb, Cu and Zn. The biomass of Uca arcuata was significantly positively correlated with chlorophyll a, nutrient indices, and the content of Zn. The biomass of Perisesarma bidens was significantly positively correlated with COD, nutrient indices, the contents of Pb, Cu and Zn.7. The ratio of Nitrogen to phosphorus increased in the order of winter, spring, and summer. Almost all parameters were negatively correlated with the summer water eutrophication, the result is consistent with the eutrophication of water in summer. Content of organic matter in spring can have a significantly negative impact to the average biomass, and only heavy metal Cu and Pb can have a significantly negative impact to the average biomass in the summer.8. Uca arcuata, Perisesarma bidens and Metopograpsus frontalis were dominant species in three tide levels, the average accumulation of Cu and Zn in their muscle were much higher than the amount of Pb and Cr, and the enrichment coefficients of Cu achieved enrichment levels. Among them, Cu of Perisesarma bidens and its enrichment coefficients for Cu is largest, as well as Zn with Uca arcuata.