东湖沉积物中氮磷形态分布的研究

武汉东湖是具有代表性的城市浅水型湖泊.在2004年采用现场调查、布点检测和实验室化学性质分析等方法,对东湖西南部的子湖--庙湖的沉积物柱芯的氮和磷进行了形态分析,对其垂直剖面分布和季节性变化进行了调查.研究表明,沉积物中氮的赋存特征和变化规律为:总氮平均含量1.62～3.17g/kg,在垂直剖面上表现为随沉积深度的增加而降低的趋势;其含量随季节变化有周期性的规律,春季沉积物中总氮的含量是1 a中最少的,夏季开始增加,秋冬季总氮量达到最大.因受沉积物总氮和埋藏环境的双重影响,沉积物中铵态氮平均含量的季节性变化规律与总氮相似,春季铵态氮的含量最少为117.66mg/kg,夏秋季含量达到最大为216.20mg/kg,冬季稍有减少.沉积物中各形态磷的垂直赋存特征为:在0～10em沉积深度内,总磷(TP)含量0.255～3.36g/kg、不稳态磷(LP)含量0.192～11.00mg/kg、铁结合磷(Fe-P)含量13.47～1379.91mg/kg和铝结合磷(Al-P)含量7.77～317.64mg/kg,均有明显的"表层富积"现象,其含量随深度的增加而迅速减少,通常>10 cm后这些磷形态的含量保持稳定.结果表明,造成湖泊水体富营养化的污染源有外源和内源,当外源截污后,内源沉积物中的营养盐仍可能使湖泊处于富营养化状态;磷仍然是东湖最主要的限制性营养元素,春季湖区沉积物中铁结合磷比例最大,占沉积物TP的44.30%,说明庙湖水域污染程度严重.

Vertical Distribution of Species of Nitrogen and Phosphorus in the Sediments of Donghu Lake

Donghu Lake is a typical urban shallow lake. Miaohu Lake was analyzed in Southwest of Donghu Lake. Characteristics of nitrogen and phosphorus in sediment cores were analyzed and assessed with investigation and chemical analysis in laboratory in 2004. Vertical distributions and seasonal changes of nitrogen and phosphorus chemical species in the sediments of two sampling sites were examined and analyzed. The results showed that concentration of TN decreased with the increase of sediment depth and the concentration of the mean TN was 1.62~3.17 g/kg. The concentration of TN reached its minimum in spring, and began to increase in summer. The concentration of TN reached its maximum till autumn and winter. Dissolved ammoniac nitrogen (DAN) was controlled by both the content of TN and the sediment environment, so the vertical profiles and seasonal changes of DAN presented the same trend as those of TN. The lowest concentration of DAN was 117.66 mg/kg in spring, and the highest concentration of DAN was 216.20 mg/kg in summer and autumn. It was decreasing in winter. Vertical profiles of phosphorus species showed that total phosphorus (TN), labile phosphorus (LP), Al- and Fe- bound phosphorus (Al-P, Fe-P) were characterized by a similar distribution pattern and enrichment in the upper 0~10cm sediment layers. The concentration decreased steeply within 10cm sediment layers, then it became steady. The concentration of TP, LP, Fe-P and A1-P was 0.255~3.36 g/kg, 0.192~11.00 mg/kg, 13.47~1379.94 mg/kg and 7.77~317.64 mg/kg, respectively. The results indicate that sources of pollution which cause water body in the lake eutrophication have the extraneous source and the internal one. After the extraneous sources are truncated, nutrient salt in sediments still possibly causes the lake to be at the eutrophication condition. Phosphorus is the most restricting nutritious element in Donghu Lake.The proportion of Fe-P is the biggest in spring and its proportion is 44.30%. These show that pollution is serious in Miaohu Lake.