云南高原典型湖泊水样氮磷含量随低温储存时间的变化

总氮(TN)、总磷(TP)是评价湖泊水体富营养化的主要指标,而实验分析中的总氮、总磷含量的测定结果受诸多因素(如水样储存方式、储存时间和氮磷赋存状态等)的影响,易造成分析数据的不稳定性。对于云南典型喀斯特地区湖泊水体氮磷含量分析而言,特别是在采样点距实验室距离远、样品数量多的情况下,不能按实验分析标准要求时间完成分析。该研究针对云南九大高原典型湖泊的特殊性和在大批量样品采集、远距离搬运、实验分析需要一定时间的实际情况,选择3个氮磷含量差异较大的抚仙湖、阳宗海和滇池为研究对象,对采样后样品在低温储存条件下随测定时间而发生变化进行分析,探讨样品TN、TP和溶解态氮(DN)、溶解态磷(DP)含量的变化特征,以确定最佳的实验分析时间。研究结果表明:(1)采样后即进行氮磷含量分析结果显示:3个湖泊水样氮磷含量差别明显,同时存在状态不相一致,滇池样品中氮磷含量最高,其TN含量为2.44 mg/L,DN含量为1.47 mg/L,占总氮的60%,TP含量为0.13 mg/L,DP含量为0.02 mg/L,占总磷的15%;阳宗海次之,其中TN含量为0.73 mg/L,DN含量为0.60 mg/L,占总氮的82%,TP含量为0.04 mg/L,DP含量为0.03 mg/L,占总磷的75%;抚仙湖最低,其中TN含量为0.32 mg/L,DN含量为0.28 mg/L,占总氮的90%,TP含量为0.02 mg/L,DP含量为0.01 mg/L,占总磷的50%;(2)样品在低温室(3℃～4℃)随着静置时间的增长,TN、TP含量均呈现降低趋势,说明静置时间对其有影响;其中滇池和阳宗海水样总氮总磷含量降低幅度较大,而抚仙湖较小;(3)样品经过滤后,滇池阳和宗海的水样氮磷含量呈现降低趋势,而抚仙湖则无明显变化。样品储存时间、过滤处理对氮磷含量低的湖泊水样影响较小,对氮磷含量大的湖泊影响较大,尤其是颗粒态氮磷含量较高的样品。由于水样中氮磷存在多种形态,湖泊营养程度不同,在对水样进行氮磷含量测定时,应当考虑水样储存时间和氮磷赋存状态等因素。

Nitrogen and Phosphorus Content Changes of the Lake Wate Samples from the Typical Yunnan Plateau Lakes

The total nitrogen (TN) and total phosphorus (TP) contents in the lake water are widely used to estimate the eutrophication levels of the lakes. However, the laboratory analyses results might be not always reliable and accurate because the analyses procedures are often affected by many factors, i.e., the storage method, duration and conditions, especially when a large number of water samples need to be analyzed. To the TP and TN content analyses of the lakes that mostly developed in Karst area in Yunnan, especially to the large lakes and remotely located lakes, the long transportation distance and large water sampling numbers make it difficult to complete the analyses in a limited time duration. Considering theses actual situations, we selected the Lake Fuxian, in that with a very low TP and TN contents, the Lake Yangzong with a middle level of TN and TP contents, and also Lake Dian (Dianchi) with a relatively high TN and TP contents, to test how the TN and TP contents, and also the dissolved TN and TP would change when the water samples are transported and stored under low-temperature condition. Then to fix the optimal storage time to complete the laboratory analyses procedures. The test results indicate that: 1. The total nitrogen and phosphorus contents of the water sample that obtained immediately after sample taken from Dianchi is the highest, of which the TN content is 2.44 mg/L, with the dissolved nitrogen content is 1.47 mg/L that accounting for 60% of total nitrogen, and the TP content is 0.13 mg/L, with the dissolved phosphorus content is 0.02 mg/L that accounting for 15% of total phosphorus. To the water samples taken from Lake Yangzong, the TN contents is 0.73 mg/L, with the dissolved nitrogen content is 0.60 mg/L, accounting for 82% of the TN, the TP contents is 0.04 mg/L, with the dissolved phosphorus content is 0.03 mg/L, accounting for 75% of the TP. The water samples taken from Lake Fuxian show the lowest TN and TP contents, with the TN content of 0.32 mg/L and dissolved nitrogen content of 0.28 mg/L, that accounting for 90% of the TN, the TP contents is 0.02mg/L, with the dissolved phosphorus content of 0.01 mg/L, accounting for 50% of the TP. 2. Along with the low-temperature storage duration increase, the TN and TP contents of the water samples decrease. The total nitrogen and total phosphorus contents of the water samples taken from Lake Yangzong and Dianchi decrease more than that from Lake Fuxian. 3. With the filtration pretreatment procedure, the TN and TP contents in the lake water samples taken from Lake Yangzong and Dianchi also show a significant decrease, but the difference is not so much in the water sample taken from Lake Fuxian. Our findings indicate the storage duration exert a stronger impact on the higher eutrophication level lake water than that on the lower eutrophication level lake water.In particular, on the water samples with higher contents of detrital nitrogen and phosphorus. Our study result suggests that due to the existence of various forms of nitrogen and phosphorus in water samples and the different nutrient levels in lakes, the storage duration and the occurrence state of nitrogen and phosphorus should be considered when determining the nitrogen and phosphorus contents of water samples.