Spatio-Temporal Distribution and Driving Factors of Organic Carbon in Qiandaohu Reservoir during Summer Storm
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摘要: 近年来，极端降雨事件在全球发生的强度和频率不断增加，这可能对大型深水水库水体有机碳的时空分布产生深远影响. 为探究强降雨事件对千岛湖有机碳的时空分布特征及影响机制，于2020年5—8月逐月采集了典型大型深水水库——千岛湖100个调查点位水样，分析了千岛湖夏季水体总有机碳(TOC)、溶解性有机碳(DOC)和颗粒有机碳(POC)浓度的时空分布特征和影响因素，重点探讨了强降水过程对有机碳浓度、通量和储量的影响. 结果表明：①2020年5—8月千岛湖TOC、DOC和POC浓度平均值分别为2.06、1.73 和0.33 mg/L，随着强降雨开始，5—7月TOC、DOC浓度呈逐渐上升趋势，而雨量急剧下降的8月(几乎无雨)，浓度也随之显著下降；水平分布上，5—7月有机碳浓度高值在全库的分布范围逐渐扩大，整体具有河流区到湖泊区逐渐降低趋势. ②新安江入库碳通量(FTOC、FDOC、FPOC)约占全库25条主要河流总入库碳通量的69%，降雨期间5—7月总入库FTOC分别是8月的11、36和41倍；5—8月有机碳储量(RTOC、RDOC、RPOC)平均值分别为44 611、38 452和6 159 t，6月、7月的总入库碳通量均占当月全库水体碳储量的1/5，所占比例分别8月的35和28倍. ③DOC和POC浓度与叶绿素a(Chla)、悬浮颗粒物(SS)、有机悬浮颗粒物(OSS)、无机悬浮颗粒物(ISS)、CODMn和TP浓度均呈极显著(P<0.01)正相关，与透明度(SD)呈极显著(P<0.01)负相关. 研究显示：千岛湖有机碳主要受浮游植物内源生产过程以及外源输入过程共同决定，而这两个过程受水文气象因素的综合影响，强降雨过程是千岛湖有机碳时空变化的关键驱动力；强降雨也是有机碳通量升高的关键控制因子，并且高入库碳通量会对全库水体碳储量产生强烈冲击.Abstract: Intensity and frequency of extreme rainfall events are increasing globally, which may strongly influence the biogeochemical processes of organic carbon in freshwater reservoirs. In order to clarify the spatial-temporal distribution characteristics of organic carbon and driving factors in Qiandaohu Reservoir, water samples were collected from 100 survey sites monthly from May to August in 2020. And the concentrations of total organic carbon (TOC), dissolved organic carbon (DOC), and particulate organic carbon (POC) in samples were analyzed. The results showed that the average TOC, DOC and POC concentrations in the reservoir from May to August in 2020 were 2.06, 1.73 and 0.33 mg/L, respectively. With the onset of heavy rainfall, TOC and DOC concentrations gradually increased from May to July, and decreased significantly in August when rainfall decreased sharply (almost no rain). In terms of horizontal distribution, the distribution range of high value of organic carbon concentration gradually expanded in the whole reservoir from May to July, and gradually decreased from inflows to the reservoir. The carbon fluxes (FTOC、FDOC、FPOC) of the Xin'anjiang inflow river accounted for 69% of the total inflow carbon fluxes of 25 major rivers. Moreover, total inflow FTOC of 25 major rivers in May, June and July was 11, 36 and 41 times of that of August, respectively. The mean values of organic carbon storage (RTOC, RDOC and RPOC) from May to August were 44,611, 38,452 and 6,159 t, respectively. The total inflow carbon flux in June and July accounted for one fifth of the whole storage in water body, which were 35 and 28 times of that in August, respectively. The changes of DOC and POC concentrations were significantly correlated with chlorophyll a (Chla), suspended particulate matter (SS), organic suspended particulate matter (OSS), inorganic suspended particulate matter (ISS), CODMn and TP concentrations (P<0.01), and negatively correlated with transparency (SD) (P<0.01). This indicates that the organic carbon in Qiandaohu Reservoir was mainly determined by the endogenous production process and exogenous input process of phytoplankton, and the two processes were influenced by hydrometeorological factors. Heavy rainfall is also a key control factor for the increase of organic carbon flux, and high inflow carbon flux will have a strong impact on the carbon storage in the whole reservoir.
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图 1 2020年5—8月千岛湖采样点的分布
Figure 1. Distribution of sampling sites in Qiandaohu Reservoir from May to August in 2020
图 2 2020年5—8月千岛湖日降雨量、出入库流量总降雨量和平均气温的变化情况
Figure 2. Variation of daily rainfall, flow (i.e., inflow and outflow), total rainfall and mean temperature in Qiandaohu Reservoir from May to August in 2020
图 3 2020年5—8月千岛湖各水质参数的空间变化特征
Figure 3. Spatial variation characteristics of water quality parameters in Qiandaohu Reservoir from May to August in 2020
图 4 2020年5—8月千岛湖有机碳浓度的月变化特征
注: 不同小写字母表示不同月份有机碳浓度在P<0.01水平上差异显著．
Figure 4. Monthly variation characteristics of organic carbon concentration in Qiandaohu Reservoir from May to August in 2020
图 5 2020年5—8月千岛湖有机碳浓度的垂向分布特征
Figure 5. Vertical distribution characteristics of organic carbon concentration in Qiandaohu Reservoir from May to August in 2020
图 6 2020年5—8月千岛湖有机碳浓度的空间分布特征
Figure 6. Spatial distribution characteristics of organic carbon concentration in Qiandaohu Reservoir from May to August in 2020
图 7 2020年5—8月千岛湖有机碳通量和碳储量随月份的变化
Figure 7. Monthly variation of organic carbon flux and carbon storage in Qiandaohu Reservoir from May to August in 2020
图 8 2020年5—8月有机碳浓度与水质参数的相关性分析(n=400)
Figure 8. Correlation analysis between organic carbon concentration and water quality parameters from May to August in 2020(n=400)
表 1 2020年5—8月千岛湖各水质参数的变化
Table 1. Variation of water quality parameters in Qiandaohu Reservoir from May to August in 2020
月份 Chla浓度/
(μg/L)CODMn浓度/
(mg/L)SS浓度/
(mg/L)OSS浓度/
(mg/L)ISS浓度/
(mg/L)TN浓度/
(mg/L)TP浓度/
(mg/L)SD/m 5 7.75±7.94 1.60±0.48 3.36±2.38 1.62±0.86 1.74±1.83 0.97±0.24 0.02±0.01 2.50±1.13 6 5.20±3.44 1.37±0.25 4.86±5.22 1.36±0.58 3.50±4.82 1.02±0.26 0.02±0.01 2.25±0.85 7 9.98±4.42 1.57±0.26 7.39±8.20 2.17±0.53 5.21±7.97 0.99±0.26 0.03±0.02 1.82±0.54 8 6.84±3.01 1.66±0.33 3.27±1.65 1.89±0.56 1.38±1.60 0.78±0.18 0.02±0.01 2.03±0.66 注：表中数据表示平均值±标准差. 
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表 2 2020年5—8月有机碳浓度与环境因子的相关性分析
Table 2. Correlation analysis between organic carbon concentration and environmental factors from May to August in 2020
项目 POC浓度 Chla浓度 CODMn浓度 TN浓度 TP浓度 SS浓度 OSS浓度 ISS浓度 SD DOC浓度 5月 0.48** 0.78** 0.82** 0.73** 0.57** 0.40** 0.67** 0.09 −0.53** 6月 −0.03 0.39** 0.50** 0.18 0.47** 0.26** 0.47** 0.17 −0.43** 7月 0.29** 0.56** 0.57** −0.29** 0.02 −0.17 0.60** −0.32** 0.06 8月 0.28** 0.35** 0.52** −0.62** −0.17 0.04 0.67** −0.46** 0.12 5—8月 0.20** 0.58** 0.41** 0.18** 0.42** 0.36** 0.58** 0.13** −0.29** POC浓度 5月 1.00 0.67** 0.61** 0.46** 0.60** 0.59** 0.66** 0.39** −0.55** 6月 1.00 0.22* 0.29** 0.09 0.15 0.39** 0.48** 0.36** −0.26** 7月 1.00 0.38** 0.44** −0.18 0.05 0.20* 0.49** 0.10 −0.03 8月 1.00 0.28** 0.22* −0.21* −0.02 0.02 0.35** −0.18 −0.09 5—8月 1.00 0.44** 0.45** −0.02 0.23** 0.33** 0.54** 0.12* −0.32** 注：*表示在0.05水平(双侧)上相关显著；**表示在0.01水平(双侧)上相关显著.
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