摘要
尽管外部营养盐的输入量下降了约30%,但在芬兰湾的开阔海区并没有出现相应的改善。20世纪90年代末向芬兰湾中的氮排放量达到了每年120000t,而每年磷的排放量为7000t。就其表面水域而言,芬兰湾海区营养盐的单位面积排放量是整个波罗的海营养盐平均单位面积排放量的2～3倍。尽管排放量有所下降,但在20世纪90年代中期海表和近海底的水域中磷酸盐的浓度仍呈上升趋势。导致这种状况发生的主要原因可能是20世纪90年代芬兰湾东部海域沉积物与水的交界处氧气状况的恶化导致了内部营养盐排放的增多,但20世纪80年代和90年代初期这一海区的供氧状况相对较好。根据在芬兰湾近海获取的实验数据,表层沉积物和水之间的磷酸盐-磷的通量已减少到平均值,13kg/km^2·d。这与在波兰湾开阔海区测量到的能够代表其变化趋势的磷含量相符。沉积物流出物中氮和磷的低比率在一定程度上解释了芬兰湾的初级生产中氮受到的限制。
Despite a decrease of about 30% in the external nutrient inputs, no corresponding improvement has been observed in the state of the open Gulf of Finland. At the end of the 1990s the external nutrient load to the Gulf totalled 120 000 tonnes (t) yr-1 of nitrogen (N) and 7000 t yr-1 of phosphorus (P). Relative to its surface area, the nutrient load of the Gulf is 2 to 3 times the average of the Baltic Sea. Despite the decrease in loading, an increase in the phosphate-P concentration was observed both in the surface and near-bottom layers around the mid-1990s. The reason for this development was most probably the acceleration of internal loading, triggered by poor oxygen conditions at the sediment-water interface of the eastern Gulf, where the oxygen conditions weakened during the 1990s, after being relatively good in the 1980s and the early 1990s. On the basis of experimental data from the coastal Gulf of Finland, the phosphate-P flux from the reduced surface sediment to water averaged 13 kg km-2 d-1. This corresponds to total amounts which can explain the observed trends of P in the open Gulf. The low N:P ratio of the sediment efflux can partly explain the N limitation of primary production in the Gulf.
