巢湖流域水体溶解性有机氮分布特征及其消减特性研究

Understanding the sources, compositions, chemical characteristics and degradation features of dissolved organic nitrogen (DON) in waters of a lake watershed with different sub-basin characteristics and pollution levels is one of the key issues to scientifically elucidate nitrogen cycle in the lake ecosystem. Nevertheless, basic information regarding systemic studies on DON in lake watershed is still limited at present due to poor investigations. In our project, Lake Chaohu watershed, a complex and typical watershed with different sub-basin and pollution levels, is the representative, and those the revealing of the concentration, spatial distribution characteristics and seasonal changes of DON in waters, the illustrating of the sources and components of DON, analyzing change trend and difference of DON, and the quantifying the degradation process of different DON fractions and its influencing factors were main research contents. Those accurate determinations of DON compositions in the different samples from waters, source identification of DON for whole watershed and quantitative determination of DON degradation process in lake should be resolved. The innovations of the project were the recognization of the differences of DON and its affecting factors in waters among various sub-basins and pollution levels. The method of DON determination in waters and source identification for Lake Chaohu watershed can be established, and the spatio-temporal variation of DON in whole watershed and its influencing mechanism can be exposited. The degradation characteristics of different DON composition can be comprehensive understood. The research findings of this project would be improving the understanding of exogenous nitrogen input and control, nitrogen cycle in the lake ecosystem.

了解湖泊流域不同子流域特征和不同污染程度水体溶解性有机氮来源、组分、化学特征和消减特性是科学理解湖泊水生态系统氮循环过程的关键科学问题，目前这方面的研究较薄弱。本项目以东部典型富营养化湖泊巢湖不同子流域特征和污染程度水体为对象，以揭示溶解性有机氮的含量、空间分布特征以及季节性变化，阐明溶解性有机氮来源、组成、季节性变化规律及其差异性，定量表征水体溶解性有机氮不同组分消减过程及影响因素等为研究内容。拟解决水体中溶解性有机氮组分测定方法、来源解析、定量表征溶解性有机氮消减过程等关键问题，拟在识别不同子流域特征和污染程度水体溶解性有机氮差异及其影响机制方面创新。通过本项目研究可以建立水体溶解性有机氮组分测定及源解析方法；揭示水体溶解性有机氮时空分布差异及其影响机制；综合表征溶解性有机氮不同组分的消减特性。本项目成果对于理解湖泊流域水生态系统外源氮输入和控制、氮循环过程将具有重要推动作用。

了解湖泊水体溶解性有机氮来源、组分、化学特征和消减特性是科学理解湖泊水生态系统氮循环过程的关键科学问题，可为湖泊流域管理提供基础支撑。本项目首先解决了的水中DON精确测定的预处理方法，采用纳滤（NF）预处理的方法对水样进行预处理，可减少DON测定的标准偏差，并确定了NF270为DON预处理用膜。市政污水是湖泊水体DON的一个重要来源，研究结果表明城市污水处理厂进水中DON的浓度在4.65-8.01mg/L之间，出水在0.74~1.81 mg/L，均以小分子量DON为主，经A2O工艺处理后，去除率在67.5%-87.4%之间；各处理工艺段中溶解氨基酸主要以溶解结合氨基酸（DCAA）为主，出水中游离氨基酸（DFAA）占DON的比例低于1%，DCAA约占DON的1.0%~6.4%。巢湖水体DON春季浓度平均为0.307mg/L，夏季DON平均浓度为0.214mg/L，秋季DON平均浓度为0.166mg/L，冬季平均浓度为0.288mg/L，冬、春季DON总体高于夏、秋季，DON可以为藻类的繁殖提供氮源，是巢湖水体中氮循环中的重要部分，内源性DON的增加导致夏季DON浓度高于秋季；受城市工业和生活废水污染的西湖区DON浓度总体上高于受农业废水污染的东湖区。不同湖区DON/TN比例具有明显的季节性差异，春、冬季高于夏、秋季，由于受微生物的作用，春季DON比例最高；受农业面源污染的东湖区DON/TN的比例明显高于受城市生活污染和工业污染的西湖区。相关分析结果表明DON是水体有机物的重要组成部分。夏、秋季巢湖水体中有机污染物主要来自外源，春、冬季巢湖水体天然有机物可能更多来自内源。巢湖水体中DON主要集中在小于1KDa小分子区间内，小于1KDaDON所占比例在46%-69%之间，受市政污水影响的西湖区中小分子量DON所占比例高于受农业面源污染的东湖区。东部平原湖区非通江湖泊比通江湖泊具有更高的DON浓度。人类活动过程中高程度的农田土地利用导致高的DON浓度。相关分析结果表明，DON浓度受温度、海拔、降雨、水文和农田土地利用的控制。夏季浮游藻类和微生物对生物可利用的DON的吸收导致夏季平均DON浓度（0.004–0.666 mg/L）低于冬季(0.006–0.335 mg/L)。本项目成果对于理解湖泊流域水生态系统外源氮输入和控制、氮循环过程将具有重要推动作用。