摘要
波罗的海的富营养化可能已潜在地增加了蓝藻细菌藻华发生的频率和规模。富营养化导致有机沉积物的增加,底层缺氧状况的加剧以及随后的系统内磷负荷的加重。此外,低氧水体积呈现与无机氮库负相关的关系,提示随低氧程度的增加,总氮的消除也会增加。系统内磷负荷加重和溶解的无机氮消除的增加将导致较低的氮磷比,而低的氮磷比是促进固氮蓝藻细菌藻华发生的主要原因之一。因为波罗的海开阔水域的蓝藻细菌藻华似乎被其内部作用所强有力地调控,因此,外部营养物质消减的影响与尺度相关。在较长的时间尺度上,外部磷负荷的减少可能会降低蓝藻细菌藻华的发生;然而,在较短时间尺度上,内部磷负荷可能会抵消外部磷负荷的降低。这些可诱导内部负荷(增加)、氮清除以及固氮蓝藻细菌占优势的耦合的过程,可被定性地描述为一种具有潜在自驱式的"恶性循环"。为了有效抑制蓝藻细菌藻华以及所有的富营养化征象,削减氮和磷外部负荷似乎是至关重要的。
Eutrophication of the Baltic Sea has potentially increased the frequency and magnitude of cyanobacteria blooms.Eutrophication leads to increased sedimentation of organic material,increasing the extent of anoxic bottoms and subsequently increasing the internal phosphorus loading.In addition, the hypoxic water volume displays a negative relationship with the total dissolved inorganic nitrogen pool,suggesting greater overall nitrogen removal with increased hypoxia.Enhanced internal loading of phosphorus and the removal of dissolved inorganic nitrogen leads to lower nitrogen to phosphorus ratios,which are one of the main factors promoting nitrogenfixing cyanobacteria blooms.Because cyanobacteria blooms in the open waters of the Baltic Sea seem to be strongly regulated by internal processes, the effects of external nutrient reductions are scaledependent.During longer time scales,reductions in external phosphorus load may reduce cyanobacteria blooms;however,on shorter time scales the internal phosphorus loading can counteract external phosphorus reductions.The coupled processes inducing internal\loading,nitrogen removal,and the prevalence of nitrogen-fixing cyanobacteria can qualitatively be described as a potentially selfsustaining °■°■vicious circle.' To effectively reduce cyanobacteria blooms and overall signs of eutrophication,reductions in both nitrogen and phosphorus external loads appear essential.
