要了解湖泊中的鱼类死亡,我们需要了解这些水体的一些关键物理特征。经历季节的湖泊的一个重要特征是温跃层。随着夏季湖水的表面积水升温,温度梯度得以建立,底部附近有更密集,更冷的水,顶部附近有更温暖的水。虽然风通常可以在水周围甩动,足以彻底混合,并从深处带出冷的,富含氧气的水,但是温跃层阻挡了这一过程。混合仅发生在温跃层之上,保持温水缺氧并促进鱼类死亡。这并不奇怪,只是随着你走得更深的温度变化并不是渐进的。相反,在几米处有一个尖锐的不连续性,上面有温暖的水,下面有冷水。分界线是温跃层。切断两大块水对鱼类来说非常重要。在白雪皑皑的地区,鱼类死亡也可能在冬季发生,而且这也是一个氧气问题。在特别严寒的冬季,雪可以沉积在湖面冰上,阻挡阳光到达水面。结果,藻类死亡并分解,消耗氧气,并且几乎没有鱼可用。这些品系的作者观察到鱼类杀灭条件造成的特殊表现。在冬末中西部的一个小湖上,数十只鲶鱼聚集在冰冷的空气中的一个洞中,以便在无氧水中存活。一只红尾鹰已经充分发挥了这种意想不到的赏金,从洞口边缘摘下了几条绝望的鱼。并非所有鱼类死亡都是溶解氧波动的结果。许多类型的污染物对水生生物有毒,并且当以足够高的浓度释放时可能导致灾难性事件。以下是一些主要鱼类死亡的例子:2016年春季,死鱼出现在越南超过200公里的海岸线上。据保守估计,死鱼的数量超过100吨,代表了数百万条鱼。该地区的人民严重依赖渔业,对鱼类的杀戮产生了负面影响,这也影响了养殖鱼类和贝类。越南人民愤怒地回应,指责不同级别的政府允许工业严重污染水域。愤怒的长期目标是一个大型钢铁厂,排放海岸线的废物,但政府花了几个星期正式确定该公司,Formosa Ha Tinh Steel负责。排出的化学物质包括酚类,氢氧化铁和氰化物。据“亚洲时报”报道,该钢铁制造商据报同意支付5亿美元的赔偿金。
格鲁吉亚的Ogeechee河于2011年5月遭遇了一次重大的鱼类死亡。除鳄鱼,海龟和鸟类外,还发现了有毒物质释放的受害者,38,000条鱼死亡。尸体散布在70多英里的河岸上。 King America Finishing纺织厂因非法释放甲醛,氨和过氧化氢而被判有罪。涉及采矿废物的事故通常会导致鱼类死亡。 Mount Polly矿山灾害涉及水坝失效,释放了大量有毒的尾矿并影响了红大马哈鱼的种群。在许多采矿区域,酸性矿山排水降低了流动pH值,足以杀死鱼类(例如在科罗拉多州和新墨西哥州的金王矿井中)。 2003年夏天,在罗德岛沃里克附近的纳拉甘西特湾,有超过一百万条鱼死亡。原因是由于一场真正强烈的降雨事件造成的低氧条件,倾倒了大量含有污染性营养废物的径流。在夏末,温暖的海水藻类增殖,然后沉没并消失,它们的分解在整个水柱中消耗了大量的氧气

新西兰梅西大学环境工程Assignment代写:海洋环境

To understand fish kills in lakes, we need to understand a few key physical characteristics of these bodies of water. An important feature of lakes experiencing seasons is the thermocline. As the surface waters of a lake warm up in the summer, a temperature gradient gets established, with denser, colder water near the bottom and warmer water near the top. While winds can usually whip around water enough to thoroughly mix it and bring up cold, oxygen-rich water from the depths, the thermocline blocks that process. Mixing only occurs above the thermocline, keeping the warm waters oxygen-poor and facilitating fish kills. That is not at all surprising, except that the temperature change as you go deeper is not gradual. Instead, there is a sharp discontinuity a few meters down, with warmer waters above, and cold water locked in below. The dividing line is the thermocline. This cutting off of the two large masses of water is very significant for fish. In snowy regions, fish kills can happen in winter too and there again it is a question of oxygen. During particularly severe winters, snow can lay thick over lake ice, blocking sunlight from reaching the water. As a result, algae die off and decompose, consuming oxygen, and leaving little of it available for fish. The author of these lines has observed a peculiar manifestation resulting from fish kill conditions. On a small lake in the Midwest in late winter, dozens of catfish congregated at a hole in the ice gulping air to survive the oxygen-less water. A red-tailed hawk had made the best of this unexpected bounty, picking off a few desperate fish from the edge of the hole. Not all fish kills are the result of fluctuations in dissolved oxygen. Many types of pollutants are toxic to aquatic life and can cause catastrophic events when released at high enough concentrations. Here are some examples of major fish kills: In spring 2016, dead fish turned up on over 200 km of coastline in Vietnam. Conservative estimates put the number of dead fish recovered at over 100 tons, representing millions of fish. Heavily relying on the fishing industry, the people in that region were negatively affected by the fish kill which also impacted farm-raised fish and shellfish. The Vietnamese population responded with outrage, accusing the different levels of government of allowing industries to heavily pollute waters. Anger was long aimed at a large steel factory which discharges waste off the coastline, but it took several weeks for the government to formally identify the company, Formosa Ha Tinh Steel, as responsible. The discharged chemicals included phenols, iron hydroxide, and cyanide. According to Asia Times, the steel manufacturer reportedly agreed to pay $500 million in compensation. The Ogeechee River in Georgia experienced a major fish kill in May 2011. Victim of a toxic release, 38,000 fish were found dead, in addition to alligators, turtles, and birds. The carcasses were spread out over 70 miles of river banks. The King America Finishing textile plant was found guilty of illegally releasing formaldehyde, ammonia, and hydrogen peroxide. Accidents involving mining waste commonly lead to fish kills. The Mount Polly Mine Disaster involved a dam failure, releasing huge amounts of toxic mine tailings and affecting a sockeye salmon population. In many mining regions, acid mine drainage lowers stream pH enough to kill fish (for example in the Gold King Mine spill in Colorado and New Mexico). In the summer of 2003, over a million fish died in the Narragansett Bay near Warwick, Rhode Island. The cause was low oxygen conditions brought about by a really intense rain event dumping tons of runoff containing polluting nutrient waste. In the late summer, warm waters algae proliferated and then sank and died off, their decomposition using up vast amounts of oxygen throughout the water column.​

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