江苏近岸海域悬沙浓度的时空分布特征

SEASONAL DISTRIBUTIONS OF THE CONCENTRATIONS OF SUSPENDED SEDIMENT ALONG JIANGSU COASTAL SEA

2006—2007年间的四个季节在江苏近岸海域69个站位采集水样,获取悬沙浓度。通过对TM遥感数据反演,获取该海域四季大面悬沙浓度,并与调查的实测悬沙浓度进行对比。结果显示,大面调查的非同步数据基本可正确反映大区域悬沙浓度的季节与空间分布趋势。悬沙浓度等值线由高至低、由陆向海分布,底层浓度约为表层的2—3倍;废黄河口和长江口外海域为悬沙浓度高值区,而海州湾为低值分布区,东南部陆架区受台湾暖流影响出现低值中心。冬季整个海域悬沙浓度均较高,其次为春季,夏季最低;废黄河口海域的高值中心在不同季节分布位置有所移动。海底沉积物的再悬浮是苏北近岸悬沙最主要的来源,河流输沙量的季节变化是影响长江口海域悬沙浓度变化的关键因子。相关分析结果表明,潮流为影响悬沙浓度分布的主要控制因子;季风、风暴潮和风浪虽对悬沙的分布具有一定的影响,但冬季的低温环境是形成该季节整个海域悬沙浓度显著偏高的重要因素。

Water samples of 69 stations in the South Yellow Sea were collected in the four seasons from 2006 to 2007;and suspended sediment concentrations （SSC） were measured and compared with the data extracted from the remote sensing TM images in corresponding seasons.The results confirmed the effectiveness of the usage of meaured data to analyze the distribution of SSC,even though they were not acquired simultaneously.Correlation analyses between the SSC and the current speed,wind speed,water depth and the wave height indicated that tidal current was the main factor that controlled the SSC distribution pattern.Measurements showed that SSC was higher in the south than that in the north.The minimal value in the north was due to lack of sediment supply and weak hydrodynamics in this area.On the other hand,abundant supply from the land led to large SSC values spreading along the coast.Two peak values were observed in the study area.One was close to the coast of the abandoned Yellow River delta,and the other was close to the North Branch mouth of the Changjiang River.The data in a full year period illustrated that the maximum SSC occurred in winter in contrast to the minimum value observed in summer.SSC was well-distributed in winter whereas many high and low centers were noted in other seasons.The peak value varied in different seasons while it kept constant on the north side of Jianggang around the coast of the abandoned Yellow River delta.Vertical profiles showed that the SSC was higher in the bottom than that in the surface water since the strong bed shear stresses caused re-suspension.In respect to the coastal sea of northern Jiangsu,re-suspension was the critical factor for the continuous high SSC,while seasonal changes of discharge explained the fluctuations of SSC around the Changjiang estuary.Other factors,e.g.sediment sources,monsoon,storm surge,wind and waves,may affect the SSC distribution patterns locally and temporarily.The wind imposed an impact on SSC in winter.The seasonal temperature variation was another possible reason for the highest SSC value in winter,because it might strongly change the sea water viscosity,decrease the sediment settling velocity,increase the bottom shear stress,and increase the SSC significantly in the water column.