基于LDA模型的松花江河道氮素时空分布规律研究

Spatio-temporal distribution of nitrogen concentration in Songhua River basin based on LDA models

河道氮素浓度是评价水体环境质量的重要指标,受污染来源、河道流量及自净能力等影响,各河段的氮素时空分布规律不同。为了对松花江流域整体水质状况有更加全面和深刻的认识,本文采用LDA(Latent Dirichlet Allocation,潜在狄利克雷分布)模型方法,以松花江流域2006—2010年水质观测数据为基础,进行了氮素时空分布规律的分析和研究,归纳得出了河道断面氨氮和总氮时空分布状况的典型模式,并对不同模式所代表的实际含义进行了解释和归因分析。年内氮素浓度分布可归纳为分别代表高、中、低的3种模式,在全流域内,氨氮3种模式出现的概率为1:3:3,而总氮3种模式出现的概率为1:1:1。氮素浓度极值分布亦可归纳为3种模式,分别表示氮素浓度最高值出现在枯水期、平水期和丰水期;在全流域内,氨氮3种模式出现的概率分别为6:2:1,总氮3种模式出现概率为2:1:1。点、面源污染负荷时空分布的不同可能是造成不同水质断面氮素时空分布不同的主要因素。

Nitrogen concentration is an important indicator for evaluating water quality of rivers and lakes Its spatio-temporal distribution often varies significantly across different river reaches owing to differences in pollutant source, river flow, self-purification capability, and some other factors. To obtain a comprehensive and in-depth understanding of the water quality in the Songhua River basin, we have developed a latent Dirichlet allocation （LDA） model for analysis on spatio-temporal distribution of nitrogen over this basin based on its observation data of 2006 to 2010. Results showed typical distribution patterns of ammonia nitrogen （NH3-N） and total nitrogen （TN） in the river channels, and their meanings were interpreted and analyzed. Annually, nitrogen concentration took three distribution pattems as typical behaviors at high, medium and low concentration levels respectively. In the whole basin, probabilities of NH3-N distribution in these patterns are 1：3：3 respectively while probabilities of TN distribution are 1：1：1. The distribution of peak nitrogen concentration were also conceptualized into three patterns that frequently occur in dry, normal and wet seasons respectively. On average over the basin, their corresponding probabilities are 6：2：1 for NH3-N and 2：1：1 for TN. In addition, this study revealed that differences in pollution loads of the point source and non-point source are possibly the main cause of the difference in spatio-temporal distributions of nitrogen over different river cross sections.