가막만 환경개선사업이 저서다모류군집에 미친 영향

Abstract

Although the Gamak Bay is one of the well-protected bays in Korea, such regions as northern part of the bay have suffered environmental deterioration by the excessive input of organic matters from untreated sewage effluents and fish and shellfish farms. Furthermore, hypoxia occurred in the northern part every summer when thermocline could make the benthic environmental condition worse. In recent years, there were some efforts to improve environmental quality of the bay, especially in the northern part. Dredging to eliminate polluted superficial sediment was conducted in the northernmost part of the bay between 2001 and 2006. In addition, sewage treatment plant began to operate in January 2005. This study was interested in the effect of a series of activities for the enhancement of the environmental quality on the benthic ecosystem. Specifically, this study focused on the changes of macrobenthic polychaete communities (1) in the oxygen deficient area (northern part) between 2005 and 2006, and (2) throughout the bay in winter of 2005 and 2006. Together with biological approaches, measurements of such environmental variables as sediment composition, organic content, acid volatile sulfide and dissolved oxygen content etc. were carried out. (1) Sediment samples were seasonally taken at 9 stations from February 2005 to November 2006. Of these, 2 stations were located in the control site (central part of the bay). In August 2005, oxygen deficiency occurred in 4 northern part stations and 7 stations were azoic. On the other hand, in August 2006, there were no oxygen deficient stations, but 5 stations were azoic. These results indicated that the hypoxia occurrence area in the northern part of the bay apparently reduced in summer of 2006. Multivariate analyses indicated that seasonal and spatial influence on polychaete communities were different from station to station. Seasonal variation was more pronounced in the innermost part and spatial variation was more apparent in control site. (2) Sediment samples were taken at 20 stations covering the whole bay in February 2005 and 2006. Comparison of the dominant polychaete species from the two years indicated that there was a significant decrease in the density of such potential indicators of organic pollution as Lumbrineris longifolia, Capitella capitata, Mediomastus californiensis and Pseudopolydora paucibrachiata. On the contrary, the density of Euchone alicaudata, Flabelligeridae sp. and Praxillella affinis, generally distributed in unpolluted area, apparently increase. Results from a cluster analysis and MDS ordination indicated that macrobenthic polychaete communities were characterized by their geographical position within the bay. In addition, polychaete communities in the northern part positively changed from 2005 to 2006, indicating that environmental improvement activities in the northern part have the desired results in some aspects.