考虑到俄亥俄州有大量的池塘和小湖泊，池塘里的鱼死亡是罕见的事件. However, they do occur every year, and some years are worse than others. Visiting your pond and seeing many dead fish floating around would no doubt cause you concern, particularly if the fish population is to your satisfaction. 鱼 kills can result from a variety of causes but the most common are weather, 池塘植被, 以及两者的相互作用. The critical parameter of these scenarios is oxygen level. 氧气对水生生物至关重要，应保持在4ppm(每百万份水中的氧气含量=每升水的毫克数)或更高的水平. 这篇文章将重点介绍这三个常见的原因，以及你能做些什么来减少池塘里冬天或夏天鱼死亡的可能性. If you experience a fish kill and you suspect it is the result of disease or chemical spill, contact your county Extension Agent for assistance.
冻死
冬季氧气循环
在冬天, the contribution of oxygen from photosynthesis by green plants and algae is greatly reduced. This is caused by the normal fall die-off of plants and algae due to cold water. 另外, 那些留下来的绿色植物产生较少的氧气，因为它们在冷水中新陈代谢减慢. This does not mean that oxygen levels are much lower in winter. 事实上，情况正好相反. 在未冻的池塘里, high oxygen levels will occur during winter because the oxygen needs are less in cold water. 水生动物(主要是鱼类)的新陈代谢和耗氧分解过程在冷水中大大减少. Also, cold water contains more oxygen than does the warm water of summer. 强劲的冬季风也保持了池塘水的循环，并在冬季不断增加氧气. 这些因素结合在一起，即使植物在冬季提供的氧气很少，也可以防止在未结冰的池塘中发生冬杀. Problems, if they are to occur, will happen once ice forms on the pond.
冬杀是如何发生的
Oxygen depletion scenario during winter ice cover. 氧含量以百万分之一(ppm)表示，并显示总体水平和趋势.
初冬
冬杀是在长时间的冰覆盖期间氧气显著下降的结果. Figure 1 illustrates the sequence of events that can lead to winterkill. As long as the pond is open or partially open, oxygen levels remain high. 这是因为空气中氧气的扩散和风的搅动向水中添加的氧气比用于动物代谢和植物分解的氧气要多. 对于那些很少暴露在风中的有遮蔽的池塘也是如此.
冬季中期
When ice forms, neither wind nor diffusion from the air contribute oxygen to the water. 氧气的唯一来源变成了少数剩余的藻类和植物产生的少量氧气. If the ice remains thin and clear, 植物和藻类的氧气生产可以继续，因为足够的阳光可以穿透冰，使光合作用发生. 这种产物几乎可以补偿持续进行的呼吸和分解所消耗的物质. If the ice remains into mid-winter or thickens slightly, oxygen levels will begin to decline by 1-2 parts per million. 这是因为每天池塘里的植物和动物消耗的氧气略多于产生的氧气. At this point, however, the pond still has sufficient oxygen.
冬末
当冰持续到冬末，变得相当厚甚至更厚时，一个严重的问题就会出现, 被雪覆盖着. This reduces the amount of sunlight reaching the plants and algae, thereby substantially reducing the amount of oxygen produced. Since metabolism and decomposition continue unabated, oxygen levels begin to drop and can approach levels that threaten fish survival. In cold water, oxygen levels less than 2-3 ppm for an extended time will begin to kill fish. If levels drop to 1-2 ppm or lower throughout the pond, a complete fish kill will result.
Factors Influencing the Likelihood of a 冻死
严冬——到目前为止，这是决定冬季被杀可能性的最重要因素. A mild winter means little or no ice and thus, no winterkill due to low oxygen levels. A harsh winter greatly increases the chances of problems. Ice thickness and clearness is important. 如前所述, thickening ice over time results in less and less light being available for photosynthesis. Perhaps the worst thing that can occur is for the snow to cover the ice. 经常, 只要没有积雪，就避免冬杀(除非冰很厚，而这种情况在俄亥俄州很少发生)。. 冰面上四英寸厚的湿雪几乎消除了阳光的穿透，氧气含量也会迅速下降.
Pond Volume—The more water volume (i.e., gallons) in a pond, the less likely the pond will experience winterkill. This is why fish over-winter better in larger and/or deeper ponds. 一个平均6英尺深的一英亩池塘比一个平均只有3英尺深的一英亩池塘有更多的冬季氧气.
分解——一个重要的因素是存在于底部的腐烂有机物的数量. 死亡的水生植物和树叶是冬季发生腐烂的大部分有机物. 覆盖着这些材料的池塘底部比没有这些材料的池塘更有可能经历冬杀. 这就是为什么在夏季水生植物群落非常密集的池塘在严冬最容易被冬杀的原因.
鱼的生物量——冬天池塘里鱼的数量(数量和磅数)也会影响冰下氧气的减少. Even though fish metabolism has slowed during winter, they still require oxygen. 一个有很多鱼的池塘比一个有更少鱼的池塘氧气下降得更快. 这就是为什么养鱼户在冬季密切监测池塘，因为他们将鱼类生物量维持在大大超过正常池塘的水平.
最坏的情况——池塘的主人应该最关心的是在一个寒冷的冬天，因为冰层持续覆盖, there is considerable snow cover on the ice, 这个池塘又小又浅, and the pond contained many aquatic plants the previous summer. 减少冰雪, fewer aquatic plants the previous summer, 池塘越深, the less likely a winter fish kill will occur.
冻死预防
幸运的是，在大多数情况下，冬季鱼类的死亡是可以避免的，部分原因是天气条件. Even in Ohio’s harsh winters, a warm spell can partially thaw a pond for a few days. Oxygen levels quickly rebound when a pond becomes ice-free. One timely warm period of 2-3 days can greatly reduce the possibility of a fish kill.
There are activities the pond owner can do to prevent a winterkill. The most important should occur during pond construction. 池塘的岸线坡度应为3:1，以限制夏季水生植物生长的浅水数量. 夏季水生植被的减少意味着更少的分解，并导致冬季冰下的氧气含量更高. Because deeper ponds experience winterkills less often, it is important to have a maximum depth of 10-12 feet if possible.
What can be done for the existing pond? 任何限制冬季植物分解量的策略都很重要. 有许多方法可以消除或减少夏季水生植被，这将减少下一个冬季发生的耗氧分解的数量. 俄亥俄州立大学推广情况说明书a -3-98控制池塘中的丝状藻类和a -4-98水生杂草的化学控制以及俄亥俄州池塘管理公告描述了控制水生植物的各种策略.
另一个要考虑的活动是安装一个曝气系统，以帮助保持池塘的一小块区域不结冰. 曝气 not only adds oxygen to the water directly via the bubbles and agitation, but the open area allows for considerable diffusion of oxygen into the pond from the air. The aeration system does not need to be run continuously all winter. Rather, turn it on when ice is forming on the pond. Leave it off when the pond is ice-free. 曝气 can be used sparingly in winter to minimize ice cover.
安全注意事项: 曝气 during winter generally prevents safe ice from developing anywhere on the pond.
最后, if your pond is ice-covered and aeration is not an option, fish winterkills can often be prevented by simply removing some of the snow off the ice. 大约25-50%的池塘表面需要保持无雪状态，以保持足够的光照，使充分的光合作用发生. This is particularly effective in small, 浅池塘，那里的水量可能不足以让氧气维持冬天.
安全注意事项: Only remove snow when the ice is safe. Four inches of ice is a good rule to follow before stepping onto the ice to remove snow.
威廉·E. 林奇小.
Extension Associate, Aquatic Ecosystem Management
埃里克·R. 诺兰庄园
Assistant Professor, Natural 365app安卓客户端
Extension Specialist, Natural 365app安卓客户端