Sedimentary Environment Evolution In Representative Kelp (Laminaria Japonica)-cultured Region (Harny Bay) And Inner Hydrodynamic Mechanism

This paper addresses the evolution of sediment environment and the alteration of hydrodynamics in the Harny Bay, which is a representative region of kelp(Laminaria Japonica) culture, in light of hydrological records, field measurements, station–based monitoring, remote sensing interpretation, bathymetric charts and so on. Due to the large–scale culture of kelp, the seabed under kelp canopy come to steadier than before and contrastly the regions outside on the boundary turn unsteadier owing to stepped–up turbulent flow. Thinning tendency of grain size and enrichment of organic matter is both indicated. The kelp rafts block the upper 5 m water, forcing transmission path of SPM altered and changing spatial distribution of SPM. The grain size of surficial SPM is mainly affected by coupling of wave field and tidal currents, dissimilarly grain size of bottom SPM on water–sediment interface under kelp canopy is obviously finer than outside regions, indicating the possible role of kelp. Based on multi–source images analysis, SPM contour showed that high–value SPM outside is hardly attain kelp–farming area. Additionally, environmental evolution information arisen by kelp cultural activities is also recorded by Sediment core. The results showed that Ever since 1980's Grain–size of Core HN01 turns thinner gradually and the vertical distribution of OC contents also indicated that biological accumulation is faster owing to biological detritus released from kelp (Laminaria Japonica). The distribution of nutrients indicates that the consumption of DIN in farming area is evident. As to the hydrodynamic force under kelp canopy, evidence provided that large–scale kelp(Laminaria Japonica) have alter the erosion/accretion pattern of seabed in the cultural area by means of reducing the hydrodynamics condition(most likely wave damping and flow confusion). The analog results from SWAN model indicate that the wave damping effect is related to the rafts quantity and the magnitude of incoming wave energy. The wave damping coefficient result from kelp rafts varies from 0.2 to 0.4 based on in–situ observation. The interaction among kelp rafts and water in the boundary regions is so complicated that reflection, diffraction and energy dissipation among boundary should be included to interpret evolution of sedimentary environment.