韩江口及邻近海域夏季营养盐和溶解有机质的河口化学特征

Estuarine chemistry characteristics of nutrients and dissolved organic matter in the Hanjiang River Estuary and adjacent coastal areas during summer

韩江三角洲(包括韩江、榕江和练江)为我国六大三角洲之一,但该海域生源要素的河口化学特征知之甚少.2010年夏季开展了韩江口及邻近海域营养盐、有色溶解有机质(CDOM)来源、分布及河口行为的初步调查.走航及断面温、盐分布显示,韩江口夏季存在南、北两个羽流区且水体层化明显.溶解无机氮、硝酸盐、硅酸盐与吸收系数(a 350)、类腐殖质荧光组分呈表观保守混合行为,而亚硝酸盐、铵盐、活性磷酸盐及类蛋白质组分随盐度波动较大.北羽流混合区硅酸盐河端外推值高于南羽流混合区,说明韩江流域硅酸盐风化作用强于榕江流域.北羽流混合区a 350以及类腐殖质组分的河端外推值高于韩江干流及入海口,表明在河口低盐度区存在添加作用.与东南沿海其他河流相比,韩江具有特征性的高硅酸盐∶溶解有机氮浓度比(1.9)和低CDOM丰度,人为影响程度相对较小,韩江口海域表现为潜在性磷限制特征.

The Hanjiang River Delta(including Hanjiang,Rongjiang and Lianjiang)is among the six largest deltas in the coastal areas of China,yet little is known about the estuarine chemistry characteristics of biogenic elements in this subtropical estuary.The sources,distribution,and estuarine behavior of nutrients,chromophoric dissolved organic matter(CDOM)in the Hanjiang River Estuary(HRE)and adjacent coastal areas were investigated during summer of 2010.The trajectory and sectional distribution of water temperature and salinity showed a strong stratification accompanying with the north and south plumes in the HRE during summer.Dissolved inorganic nitrogen(DIN),nitrate,and dissolved silicate(DSi)exhibited conservative mixing behaviors,alongside the absorption coefficient a 350 and humic-like fluorescence components.Reactive phosphate,nitrite,ammonium and protein-like components fluctuated with salinity.The effective DSi concentrations of freshwater end-member in the north plume mixing zone were higher than those in the south plume mixing zone,indicating that silicate weathering was stronger in the Hanjiang basin than in the Rongjiang basin.The higher effective concentrations of a 350 and humus-like fluorescence in the north plume mixing zone,compared to the downstream Hanjiang River,indicate their addition in the low salinity area of the estuary.The Hanjiang River showed a typical high fluvial c(DSi)∶c(DIN)ratio(1.9)and low CDOM concentration compared to other rivers in Southeast China,suggesting relatively small anthropogenic perturbation.The HRE showed a potential phosphorus limitation characteristics.