Innovative Method to predict Water Quality in Coastal Areas for Ecosystem

溶解氧是影响生态系统水质的关键因素之一。外界条件，如降水、温度、风向、风速和营养盐负荷等，通过几条途径影响溶解氧，其中一些特征时间较短，不足一天。年或季节平均法不能很好地估计溶解氧的小时变化，因为它具有较短的特征时间，而某些季节特征时间较长。为了估计溶解氧浓度，人们认为用随机方法而不是确定性方法是有用的。根据东京湾、新知湖和博田湾的观测资料，对东京湾、新知湖和博田湾的低溶解氧发生情况进行了随机调查。在博田湾，温跃层下的溶解氧浓度主要取决于下层的厚度，而不是叶绿素a浓度、光量子通量、沉积物耗氧速率等，利用它们可以较高精度地估算溶解氧的变化。东京湾东北风时，在温跃层发育和水温高于15度的共同作用下，出现无氧含硫水体的“蓝潮”。“蓝潮”的发生与风能和水体重心的变化有明显的相关性。利用一种测量水面以上大气混合层中氮氧化物变化的方法，研制了河口氮氧化物大尺度观测系统。

Dissolved oxygen is one of the key factors on water quality for ecosystem. External conditions such as climate conditions including precipitation, temperature, wind direction and speed and nutrient loading, some of which have shorter characteristic time less than one day, influence dissolved oxygen through several paths. The yearly or seasonal average methods are ineffective to estimate hourly change of dissolved oxygen because it has a short characteristic time with some seasonally long ones. In order to estimate dissolved oxygen concentration, a stochastic method, instead of a deterministic one, is considered useful. In this study, occurrence of low dissolved oxygen concentration was stochastically investigated based on observation date in Tokyo Bay, Lake Shinji and Hakata Bay. In Hakata Bay, dissolved oxygen concentration under the thermocline depends on the thickness of the lower layr more than chlorophyll-a concentration, light quantum flux, sediment oxygen consumption rate, etc. Using them, the dissolved oxygen changes were estimated with high accuracy. In Tokyo Bay, "blue tide", which is water body with oxygen-free and contains reduced sulfur, occurs under both of the development of thermocline and water temperature higher than 15 degree when wind of north-east blows. The occurrence of "blue tide" is clearly correlated with wind energy and the change of the center of gravity of water body. The development of a large scale observation system on nitrogen oxide in an estuary was developed by using a method to measure changes of nitrogen oxide in the mixing layr of the atmosphere above the water surface.