坦噶尼喀湖东北部入湖河流表层沉积物中磷的形态和分布特征

磷是坦噶尼喀湖生态系统中必不可少的营养元素,直接决定湖体初级生产力的高低,进而影响到周边居民对于动物蛋白的获取来源.为了解坦噶尼喀湖磷的外源输入,选择湖泊东北部的入湖河流,对表层沉积物(16个样点)中总磷(TP)和各形态磷含量及其分布特征进行分析,并探讨磷的形态分布特征与土地利用方式之间的相关关系.结果表明,入湖河流沉积物TP含量为73.05~239.94 mg/kg,平均含量为152.64±55.37 mg/kg,其中最高值出现在马拉加拉西河口.采用Psenner法对磷进行连续浸提并比较不同形态磷含量,由高及低依次为铁铝结合态磷(Fe/Al-P)钙结合态磷(CaP)有机磷(Org-P)残渣态磷(Res-P)弱吸附态磷(Labile-P).土地利用类型对TP及各形态磷含量影响较大,其中TP含量表现为河口湿地城镇附近林草地区,表明地表径流和人类活动会对TP含量产生影响,而对于不同形态磷含量,Laible-P、Fe/Al-P、Org-P含量均表现为河口湿地林草地城镇附近,Ca-P、Res-P含量均表现为城镇附近河口湿地林草地.分析沉积物理化性质与各磷形态之间的相关性,发现沉积物总氮(TN)、有机质和总有机碳与Fe/Al-P、LabileP和TP相关性较好,与Org-P、Ca-P和Res-P相关性较差,表明TN和有机质的输入,会伴随沉积物中磷含量的升高,其增量的赋存形态主要为氧化还原敏感态磷和Labile-P.沉积物粒径组成与各磷形态含量存在相关性,细粒径沉积物与各形态磷含量呈显著正相关,粗粒径沉积物与各形态磷呈显著负相关,表明细小颗粒更易吸附磷.

Phosphorus fractions and their spatial distribution in surface sediments of inflow rivers in the northeastern Lake Tanganyika

Phosphorus is an essential nutrient in the Lake Tanganyika ecosystem, which determines the lake''s primary productivity, and subsequently influences the animal protein sources for riparian residents. To understand the external inputs of phosphorus to the Lake Tanganyika, 16 surface sediment samples from the rivers which flow into the northeastern lake were collected and analyzed to understand the content and spatial distribution of the total phosphorus (TP), and the relationship between land use pattern and the spatial distribution of different phosphorus forms. The TP content in surface sediment varied from 73.05 to 239.94 mg/kg, with an average content of 152.64±55.37 mg/kg, and the highest content was observed at Malagarasi river mouth. Using the sequential extraction method(Psenner) the phosphorus fractionation distribution of sediments was analyzed. The results showed that sequences of the contents of different phosphorus forms was Fe/Al-P > Ca-P > Org-P > Res-P > Labile-P. The TP content was highest in the estuarine wetlands, followed by that in urban areas, and the lowest content was in the woodland. It implies that land use had significant impacts on the content of TP and phosphorus forms. The patterns also implied that surface runoff and human activities would be the causes of the TP accumulation in the surface sediment of inflowing rivers. The spatial distribution of different phosphorus forms differed from that of TP. The highest content of Liable-P, Fe/Al-P and Org-P were observed in the estuarine wetland, and then followed by those in the woodland.The urban area had the lowest contents. The highest contents of Ca-P and Res-P were found in urban area, and then followed by estuarine wetland. The woodland had the lowest content. According to the correlation analyses between the contents of different P forms and particle size of sediments, total nitrogen (TN), loss of ignition (LOI), and total organic carbon (TOC), it was found that TN, LOI and TOC had significantly positive correlations with the Fe/Al-P, Labile-P and TP contents, while they had weak correlations with Org-P, Ca-P and Res-P. It indicated that the input of TN and organic matter would increase the content of phosphorus in the sediment, and the incremental P forms were Fe/Al-P and Liable-P. There were significant and positive correlations between fine particle sediments and the contents of different phosphorus forms, while significant and negative correlations existed between coarse sand and the contents of phosphorus forms. These results indicate that fine particle sediments are easier to adsorb the phosphorus.