Human Impact on the Sedimentary Environment of the Intertidal Zone Since about 200 Years in Beibu Bay，the Southern China

Abstract:

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 Bay were used in order to discuss the human impact on sedimentary environment since 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 of 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 1930AD 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 of 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.