广州流溪河氮磷浓度的季节变化和空间分布特征

Seasonal and spatial variation of nitrogen and phosphorus concentrations in Liuxi River in Guangzhou

广州市流溪河横跨北回归线,是典型的热带-亚热带过渡区河流。为了解该河流的营养盐分布特征,设置了20个采样点,于2015年2月至2017年2月进行季节性采样,共开展了8次水质监测,利用多元统计方法分析了主要营养盐(氮和磷)的季节动态和空间分布,并探讨影响营养盐时空分布的主要因素。结果表明:TN和TP的浓度范围分别为0.29~11.88 mg·L^(-1)与0.01~0.59 mg·L^(-1),TN浓度枯水期高于丰水期,总体上受降雨量的调节和河水稀释效应的影响; TP浓度丰水期高于枯水期,总体上受降雨量的调节及外源输入的影响; TN与TP在枯水期具有相似的季节变化特征,而在丰水期季节变化特征差异大;NO_3^--N和TN浓度的空间变化趋势相似,分为三个区段:流溪河水库上游的中值区河段,流溪河水库下游到街口大桥处的低值区河段和街口大桥下游的高值区河段,流溪河上游的两座大型水库对营养盐的滞留是导致其空间差异的主要因素之一; NH_4^+-N和TP浓度沿流域上游至下游总体上呈上升的趋势;三级河流氮和磷浓度显著高于一级河流和二级河流,河流氮、磷浓度与土地利用类型显著相关,建筑用地、裸露地和耕地所占比例的扩大会增加水体中TP、NH_4^+-N和NO_3^--N的浓度,而增加林地面积有助于水土保持和减少水体中氮、磷浓度。因此,上游水库的调节和下游城镇地区增加林地面积等方式对改善流溪河水质具有积极作用。

Liuxi River,across the Tropic of Cancer,is a typical river in transition between tropics and subtropics. To understand the seasonal and spatial variation of nutrient concentrations in the river,eight investigations on water quality were carried out at 20 sites covering the whole river from February 2015 to February 2017. We analyzed the seasonal dynamics and spatial distribution of N and P concentrations and the potential affecting factors by multivariate statistical methods.The concentrations of TN and TP ranged from 0.29 to 11.88 mg·L^-1 and 0.01 to 0.59 mg·L^-1,respectively. TN concentration in the dry season was higher than that in the flood season,regulated by rainfall and affected by river dilution. TP concentration in the flood season was higher than that in the dry season,which was regulated by rainfall and significantly affected by exogenous input. Seasonal variations of TN and TP were similar in the dry season,but different in the flood season. Spatial variations of NO3^--N and TN concentrations were similar,which could be divided into three distinct sections： the mid-value section of upstream of Liuxihe Reservoir,the low-value section from downstream of the Liuxihe Reservoir to the Jiekou Bridge,and the high-value section of downstream of Jiekou Bridge. Nutrient retention in two large reservoirs located in the upstream was one of the main factors accounting for the spatial difference. The concentrations of NH4^＋-N and TP increased from upstream to downstream. The concentrations of N and P were significantly higher in the third-order stream than in the first-and second-order streams,which were significantly correlated with the land use types. The high proportion of building land,open land and cultivated land increased the concentrations of TP,NH4^＋-N and NO3^--N,while the increased proportion in forest land contributed to soil and water conservation and reduced the concentrations of N and P in the river. Therefore,the regulation of upstream reservoirs and the increase of forest land in downstream urban areas are helpful to improve the water quality of Liuxi River.