洱海湖心区沉积柱芯营养盐垂向分布及时间演化特征

The Vertical Distributions and Temporal Evolution Characteristics and of Nutrient Concenctration in the Sediment Core at the Center of Lake Erhai

连续的沉积物记录为研究湖泊富营养化的长期过程提供了可能。分析了洱海湖中心沉积柱的营养盐浓度垂向分布和沉积物年代记录,并结合湖心水质变化情况,研究了洱海沉积物营养盐的时间演化特征及生态意义。结果显示:Cal.AD 1960年以前,洱海沉积物营养盐稳定在较低水平,总有机碳(TOC)平均质量分数为1.45%,总氮(TN)平均质量分数为0.20%,总磷(TP)质量分数低于1 000 mg·kg^(-1);Cal.AD 1960年以后,TOC和TN质量分数均急剧升高,尤其在1990年之后呈直线上升态势,最高值分别为5.8%和0.84%,TP质量分数从1 000 mg·kg^(-1)。左右直线上升至1 345 mg·kg^(-1),反映了洱海近几十年来的人为富营养化加剧过程。沉积物TP与TOC、TN呈极显著正相关(P=0.001),TOC与TN的Pearson相关系数最大。洱海沉积物的TOC/TN比值总体比较稳定,数值在5.8~11.5之间波动,反映出这3种营养物质的藻类同源性。沉积物的营养物累积过程伴随水质变化呈不断恶化趋势,1990年后沉积物营养盐的时间演变规律与湖心区水质随时间的变化趋势基本一致。洱海表层沉积物TN、TP浓度明显高于东部平原湖区的湖泊,其营养盐内源负荷不容忽视。与同地区湖泊相比,沉积物TN浓度水平与抚仙湖和滇池相当,而TP浓度明显低于这两个湖泊,说明洱海沉积物对P仍具有较强的吸附容量及潜在缓冲能力。

Continuous sediment records provide the possibility to study the long-term process of lake eutrophication. This study conducted an analysis on sedimentary total phosphorus (TP), total nitrogen (TN), total organic carbon (TOC) and C/N ratio in the sediment core at the central area of Lake Erhai, and their historical evolution characteristics. The results indicated that, before Cal.AD 1960, the nutrient content in sediment was kept low level, with the mean values of TOC, TN and TP were 1.45%, 0.20% and 1 000 mg·kg-1 respectively, which were dominated by natural process. Since Cal. AD 1960s, the contents of TOC, TN and TP in sediment ascended sharply to 5.8%, 0.84% and 1 345 mg·kg-1 respectively. Specially after 1990, the growth rate of nutrient contents in sediment accelerated, reflecting the intensification of anthropogenic eutrophication in Lake Erhai in recent decades. Sedimentnutrient accumulation process is accompanied by a deterioration trend of water quality. After 1990, the time evolution of nutrients inthe sediment column and nutrient concentration variation over time at the center of the lake area are basically the same. There was asignificant positive correlation among TOC, TN and TP in the sediments (P=0.001),and Pearson correlation coefficient between TOC and TN was the highest. Moreover, TOC/TN ratio of sediments in Lake Erhai is relatively stable, with values ranging from 5.8 to 11.5, indicating these nutrient indicators had high homology of algae. The nutrient concentration in the surface sediments of Lake Erhai were significantly higher than those of the lakes located in the eastern plain lake region, which indicated that release potential of nutrients in sediment of Lake Erhai can’t be neglected. Compared with other lakes in the same geographical region, TN content of Lake Erhai was equivalent to those of Lake Dianchi and Lake Fuxianhu, while TP content was much lower than those of the two lakes. It can be concluded that the sediments of Lake Erhai had high phosphate adsorption capacity and buffer capacity to P input.