渤海南部海域沉积物中吸附态无机氮的地球化学特征

GEOCHEMICAL CHARACTERISTICS OF ADSORBED INORGANIC NITROGEN IN THE SOUTH BOHAI SEA SEDIMENTS

用分相浸取的方法对采集于渤海南部海域的 2 9个站位的沉积物样品 (表层样站 2 7个 ,柱状样站 2个 )中的吸附形式的无机氮 (包括NH4 N和NO3 N)和总氮 (TN)进行了研究 ,探讨了它们的地球化学分布特征及其控制因素。研究表明 ,在表层沉积物中 ,NH4 N在渤海中央盆地由东北向西南方向递增 ,在中央区域有两个异常高值区 ,莱州湾内分布较为均匀 ,渤海湾南部为一低值区 ,向北逐渐增大。NO3 N在渤海中央盆地由东西两侧向中央递增 ,渤海湾和莱州湾内均沿着离岸方向递减。渤海南部表层沉积物中吸附态氮占TN的 3 2 8% ,表层沉积物中吸附形式的氮以NO3 N为主 ,占 83 7% ;NH4 N主要受有机质含量 (OC)、氧化还原环境(Es)、黏土矿物组成的影响 ;NO3 N主要受水体NO3 N浓度和分布的控制。NH4 N随沉积深度增加而增加 ,NO3 N随深度增加而减小。TN的分布主要受陆源物质输入及沉积物粒度控制。研究区TN高而OC低且二者相关性较差 ,间接说明TN中有相当部分是以无机氮 (IN)的形式存在 。

The adsorbed inorganic nitrogen (including NH 4-N and NO 3-N) in sediments is considered as an 'active' part of the total nitrogen and could be released to the water while the environment changes (such as physical, chemical, biological, geological condition). It plays an important part in the process of N transportation across the sediment-water interface and the nutrient supply, which therefore, could have influence on the primary productivity in the marginal sea and further control marine biogeochemical cycling of nutrients. 27 surface and 2 core sediment samples collected in Sept. 1998 in the south Bohai Sea were used for studying the adsorbed inorganic nitrogen(include NH 4-N and NO 3-N)and total nitrogen (TN). The samples were immediately sealed in plastic bags and taken to laboratory. The lab procedures are proper amount of samples and dry them for 12-14h at 60℃; obtain (1000±0.1)mg for subsamples; place the subsamples in 50ml plastic centrifuge tubes; add 20.00ml 1.0 mol/L KCl solution and vibrate them for 20 min at 25℃; then centrifuge them 10min(4000r/min); extract the clear supernatant to determine the content of NH 4-N and NO 3-N.The control was set up simultaneously; put (100±0.1)mg dried sediment samples into 50ml glass tubes, add 20ml oxidative agent(0.24mol/L NaOH, 0.074mol/L K 2S 2O 8) to the tubes, and shake them; then oxidize them for 40min at 120℃ in high-pressure sterilizing utensil. After the oxidant cooled, the tubes were taken out and centrifuged. The solution was used for determining total nitrogen (TN). Results showed that the adsorbed inorganic nitrogen account for only 3.28% of total nitrogen, including 0.56% NH 4-N and 2.72% NO 3-N. The adsorbed NH 4-N was mainly from anoxic mineralization of organism, thus, its distribution was controlled by the content of organism, Es and pH, and the characters of clay. The content of NO 3-N was higher than that of NH 4-N and NO 3-N was the predominant species of adsorbed nitrogen in this region, which showed that the mineralization of organisms was weak and couldn't provide much nutrient for primary productivity, and the terrestrial input NO 3-N was the dominating nutrient source. The content of adsorbed NO 3-N decreased with depth in core sediments, while NH 4-N decreased with depth in 0-10cm layer then increased slightly. TN distribution was mostly controlled by terrestrial inputs and sediment grain size. Compared with other sea regions, the content of TN was higher while the organic carbon content was little in the southern Bohai Sea sediments. The vertical distribution of TN was complex, which was maybe caused by the complicated sedimentary. The ratio of OC to TN content was abnormal low and the content of TN was not correlative with that of OC, which showed that a quite part of TN in southern Bohai Sea sediment was inorganic origin. The high inorganic nitrogen in south Bohai Sea sediments was the concentration result of coast terrestrial IN inputs. Therefore, various existence forms of nitrogen in sediments should be differentiated and their controlling factors should be judged in order to deeply study the biogeochemical cycling of nitrogen in marine environment.