HUMAN IMPACT ON THE INTERTIDAL ENVIRONMENT IN BEIBU GULF OVER THE LAST 200 YEARS

Multiple approaches including ²¹⁰Pb dating, grain-size distribution and heavy metal elements (Hg, Cd, As, Pb, Cu, Cr, and Zn) concentration of sediments from two cores in the intertidal zone of Beibu Gulf were used for exploring the human impact on sedimentary environment for the last 200 years. The average sedimentation rate of cores YX07 and YX05 is 0.45 cm/a and 0.37 cm/a, respectively. The two cores span the last 231 and 210 years. The downcore concentration of heavy metal elements generally shows a contrary trend as mean grain-size, suggesting that heavy metal elements tend to be rich in finer grain-size materials. The similar values and stable downcore variation in ratio of trace elements (La/Th) in sediments of the both cores indicate that the sediment sources of the two cores are similar and not changed through time. The sedimentary environment before 1930 was influenced by nature factors, whereas largely influenced by human activity after the time. The mean grain-size became coarser since about 1930, possibly resulted from strengthened physical erosion of soils by stronger anthropogenic impact. Moreover, the 2~3 times increase in Al-normalized heavy minerals such as As, Pb, and Cu since the time suggests that vast industry and domestic wastewater was poured to the estuarine and coastal area, and thus deteriorated the environment of the intertidal zones.