CAUSES OF POLLUTION
Many causes of pollution including sewage and fertilizers contain nutrients such as nitrates and phosphates. In excess levels, nutrients over stimulate the growth of aquatic plants and algae. Excessive growth of these types of organisms consequently clogs our waterways, use up dissolved oxygen as they decompose, and block light to deeper waters.
This, in turn, proves very harmful to aquatic organisms as it affects the respiration ability or fish and other invertebrates that reside in water.
Pollution is also caused when silt and other suspended solids, such as soil, washoff plowed fields, construction and logging sites, urban areas, and eroded river banks when it rains. Under natural conditions, lakes, rivers, and other water bodies undergo Eutrophication, an aging process that slowly fills in the water body with sediment and organic matter. When these sediments enter various bodies of water, fish respirationbecomes impaired, plant productivity and water depth become reduced, and aquatic organisms and their environments become suffocated. Pollution in the form of organic
material enters waterways in many different forms as sewage, as leaves and grass clippings, or as runoff from livestock feedlots and pastures. When natural bacteria and protozoan in the water break down this organic material, they begin to use up the oxygen dissolved in the water. Many types of fish and bottom-dwelling animals cannot survive when levels of dissolved oxygen drop below two to five parts per million. When this occurs, it kills aquatic organisms in large numbers which leads to disruptions in the food chain.
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許多汙染包括汙水和肥料的起因包含營養素譬如硝酸鹽和磷酸鹽。過份水平, 營養素刺激水生植物和海藻成長。這些類型過份成長有機體因而堵塞我們的水路, 用途被溶化的氧氣當他們分解, 並且阻攔光對更深的水。這, 反過來, 證明非常有害對水生有機體當它影響居住在水中的呼吸作用能力或魚和其它無脊椎。汙染並且導致當泥沙和其它暫停的固體, 譬如土壤, washoff 犁了領域、建築和採伐的站點, 市區, 和腐蝕了河岸當下雨。在自然情況下, 湖、河, 和其它水身體接受Eutrophication, 用沉積和有機物慢慢地填裝水身體的老化過程。當這些沉積輸入各種各樣的水體, 魚respirationbecomes 被削弱, 工廠生產力和水深度成為減少, 並且水生有機體和他們的環境成為窒息。汙染以有機材料的形式送進水路以許多不同的形式作為汙水, 和葉子和草剪報, 或作為決賽從家畜肉肥育場和牧場地。當自然細菌和protozoan 在水中劃分這份有機材料, 他們開始用盡氧氣被溶化在水中。許多類型魚和底部住宅動物無法生存當被溶化的氧氣下落的水平在二到五份以下每百萬。當這發生, 它殺害水生有機體在大數字導致中斷在食物鏈。參考資料： 123