| environ. |
dissolved oxygen The amount of oxygen dissolved in a stream, river or lake is an indication of the degree of health of the stream and its ability to support a balanced aquatic ecosystem. The oxygen comes from the atmosphere by solution and from photosynthesis of water plants. The maximum amount of oxygen that can be held in solution in a stream is termed the saturation concentration and, as it is a function of temperature, the greater the temperature, the less the saturation amount. The discharge of an organic waste to a stream imposes an oxygen demand on the stream. If there is an excessive amount of organic matter, the oxidation of waste by microorganisms will consume oxygen more rapidly than it can be replenished. When this happens, the dissolved oxygen is depleted and results in the death of the higher forms of life (溶解在溪流、河水或湖泊中的氧气浓度，可作为河川的健康程度和维持水生态系平衡能力的指标。水中溶氧来自于大气的溶解和水生植物的光合作用。河川水体所能维持的最大氧气浓度﹐称之为饱和溶氧量﹐其值与温度有关；温度愈高，水中饱和溶氧量愈低。 当有机废弃物排入河川，会导致河川的需氧量增加；而过量的有机物进入水体时，微生物氧化这些有机物所消耗的氧量远快于氧气补充入水的速率，一旦氧气被消耗殆尽，会导致较高等生物的死亡。) |
