摘要
20世纪60年代后期,已发现波罗的海出现了严重的环境问题,其中包括因有机氯和重金属而导致的生物区系污染,以及日益严重的深水缺氧等。开始把有毒污染物——包括新发现的多氯联苯(PCB)——看作是对波罗的海生态系统的主要威胁,在波罗的海海豹和白尾海雕中发现的生殖受损问题,则意味着也威胁到了人类的食用鱼类。各种应对措施逐渐产生了结果,当今对限制波罗的海毒物污染的斗争已成为国际环境方面的成功实例。计算表明,波罗的海深水耗氧量肯定已有增加,波罗的海营养盐负荷也已有增加,其中氮约为4倍、磷约为8倍。已逐渐积累了生态系统各营养层日益增加的有机生产量证据。首先认为磷限制着波罗的海的初级生产力,但测量很快表明,在开阔的波罗的海本体,除了蓝藻外,真正的普遍限制因素则是氮。今天有关的争论是,磷是否通过限制固氮者而控制了开阔海域生态系统生产力,即使在那里浮游植物明显地受着氮的限制。波罗的海的教训告诉我们,我们新发现的环境问题经历着反复变化,而且科学家可能要花费数十年的时间才能就其成因达成共识。当社会决定采取应对措施时,可能需要几十年时间,这些措施才会产生效果,对自然界来说,则需几十年时间才能得以恢复。由此可见,环境管理决策很难等待科学上的定论。因此,我们应该把环境管理决策视为这样一种经验,它需要被监测、被总结,必要时要加以修改。
Grave environmental problems, including contamination of biota by organochlorines and heavy metals, and increasing deep-water oxygen deficiency, were discovered in the Baltic Sea in the late 1960s. Toxic pollutants, including the newly discovered PCB, were initially seen as the main threat to the Baltic ecosystem, and the impaired reproduction found in Baltic seals and white-tailed eagies implied a threat afso to human fish eaters. Countermeasures gradually gave results, and today the struggle to limit toxic pollution of the Baltic is an international environmental success story. Calculations showed that Baltic deep-water oxygen consumption must have increased, and that the Baltic nutrient load had grown about fourfold for nitrogen and 8 times for phosphorus. Evidence of increased organic production at all trophic levels in the ecosystem gradually accumulated. Phosphorus was first thought to limit Baltic primary production, but measurements soon showed that nitrogen is generally limiting in the open Baltic proper, except for nitrogen-fixing cyanobacteria. Today, the debate is concerned with whether phosphorus, by limiting nitrogen-fixers, can control open-sea ecosystem production, even where phytoplankton is clearly nitrogen limited. The Baltic lesson teaches us that our views of newly discovered environmental problems undergo repeated changes, and that it may take decades for scientists to agree on their causes. Once society decides on countermeasures, it may take decades for them to become effective, and for nature to recover. Thus, environmental management decisions can hardly wait for scientific certainty. We should therefore view environmental management decisions as experiments, to be monitored, learned from, and then modified as needed.
