鄱阳湖出流水质2004～2014年变化及其对水位变化的响应:对水质监测频率的启示

TEMPORAL VARIABILITY OF WATER QUALITY IN POYANG LAKE OUTLET AND THE ASSOCIATED WATER LEVEL FLUCTUATIONS:A WATER QUALITY SAMPLING REVELATION

通过对鄱阳湖湖口2004~2014年以周为单位的水质指标,包括溶解氧(DO),氨氮(NH_4^+-N)和高锰酸盐指数(COD_(Mn))的变化特征及其与水位响应关系进行分析,并对合理的监测频率进行了探讨。结果表明:(1)就DO,NH_4^+-N和COD_(Mn)而言,鄱阳湖出湖水质在2004~2014年没有显著恶化的趋势,然而在年内呈现明显的周期性变化,其浓度与湖泊水位波动有较显著的负相关性(p<0.01),相关系数分别达到–0.63,–0.67和–0.36;(2)考虑水质指标在湖相状态与河相状态存在显著的差异(p<0.01),概率密度分布曲线进一步表明,在鄱阳湖呈湖相时,湖口NH_4^+-N浓度小于0.25 mg/L的概率为93%,而在河相时仅为32.8%。DO与COD_(Mn)浓度在河湖相的特征与NH_4^+-N相似。因此,在湖相状态下,鄱阳湖出流水质良好的概率更大,而高水位下的稀释作用可能是影响湖泊年内变化的主要控制因素;(3)时间序列分析表明DO,NH_4^+-N和COD_(Mn)存在明显的自相关性,1~2月一次的监测频率基本能够准确的描述NH_4^+-N和DO的动态变化特征,而COD_(Mn)仍需要1~2周一次的监测,从而避免过多的损失动态信息。能够为将来更深入的研究湖泊水情与水质定量关系提供基础和思路,从而为湖泊水环境管理和调控提供对策和建议。

A combination of weekly concentrations of three water quality parameters including dissolved oxygen （DO）, ammonia （NHa＋-N） and chemical oxygen demand （CODMn） for water samples in Poyang Lake outlet during 2004-2014, and corresponding hydrological data were analyzed. Results indicated that DO, NHa＋-N and CODMn did not demonstrate significant inter-annual trends, while remarkable seasonal variations were observed, and notable negative correlation was found between DO, NH4＋-N and CODMn and water level fluctuation, with Pearson coefficients of-0.63, -0.67 and -0.36, respectively. The dataset was further split into lake phase and river phase based on characteristic water level of 14 m. Probability density analysis revealed that in lake phase, there was 93% probability that the NH4^-N concentration would be lower than 0.25 mg/L, while for river phase, the probability went down to 32.8%. Similar results were also obtained for CODMn and DO. In general, the water quality of Poyang Lake outlet was more prone to be better in the lake phase than that in the river phase, further indicating that the dilution effect of high water level was decisive for the variability of water quality in Poyang Lake outlet. Finally, a quite strong autoeorrelation of DO and NH4＋-N was found and the water quality sampling for DO, NH4＋-N and CODMn must be different. DO and NH4＋-N can be monitored monthly or bimonthly, while CODlin must be sampled with more frequency, e.g. weekly or biweekly.