| 三峡库区澎溪河河段间水华程度差异及其机制 |
| 摘要点击 2735 全文点击 2798 投稿时间：2022-04-01 修订日期：2022-04-29 |
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| 中文关键词 三峡库区|澎溪河|断面|水华|长江回水|内源磷迁移 |
| 英文关键词 Three Gorges Reservoir area|Pengxi River|sections|algal blooms|backwater from Yangtze River|migration of internal phosphorus |
| 作者 | 单位 | E-mail | | 罗晓佼 | 西南大学资源环境学院, 重庆 400715
国家级三峡库区水环境监测与模拟国际科技合作基地, 重庆 400715 | 843261942@qq.com | | 张钘 | 西南大学资源环境学院, 重庆 400715
国家级三峡库区水环境监测与模拟国际科技合作基地, 重庆 400715
重庆市万州区土肥与农业生态保护站, 重庆 404199 | | | 黄伟 | 西南大学资源环境学院, 重庆 400715
国家级三峡库区水环境监测与模拟国际科技合作基地, 重庆 400715 | | | 胡鹏飞 | 西南大学资源环境学院, 重庆 400715
国家级三峡库区水环境监测与模拟国际科技合作基地, 重庆 400715 | | | 谭炳圆 | 西南大学资源环境学院, 重庆 400715
国家级三峡库区水环境监测与模拟国际科技合作基地, 重庆 400715 | | | 张磊 | 西南大学资源环境学院, 重庆 400715
国家级三峡库区水环境监测与模拟国际科技合作基地, 重庆 400715 | echozhanglei@swu.edu.cn |
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| 中文摘要 |
| 三峡大坝蓄水以来,库区50%一级支流水华频发,且不同支流水华高发断面的地理位置不同,受干流影响程度存在差异.为探讨水华暴发的河段差异,及其与长江回水的关系,以库区一级支流澎溪河为例,在2019年春季水华季,进行了间隔期一周、总时长一个月的采样,从河口至上游设置7个采样断面(PX1~PX7),根据各断面的垂向水温和电导率特征推断长江回水的影响范围和形式;并通过对水华高发的高阳平湖断面(PX5)和分别距其4 km的上游断面(PX6)和下游断面(PX4)的水文、水质和底泥营养盐等指标,探究断面间水华暴发程度的差异及其机制.结果表明,水华季澎溪河下游(PX1~PX4)的ρ(Chl-a)较低,为14.55~44.00μg·L-1,上游(PX5~PX7)则达到42.66~175.40 μg·L-1,其中PX5的ρ(Chl-a)最高时达413.00 μg·L-1,显著高于其余位点(P<0.05).温度和电导率结果显示,4~5月长江干流回水从中下层潜入澎溪河,下游(PX1~PX4)处于长江干流回水与澎溪河上游来水的交汇区域,水体不稳定,不利于水华暴发;而澎溪河中上游(PX5~PX7)未直接受到长江干流回水的影响,营养交换以垂向为主.PX4~PX6的水体各层的n(TN)/n(TP)和n(DTN)/n(DTP)均值多数远高于16,水体营养盐为磷限制状态.采样期内,PX5底泥全磷均值为相距仅4 km的上游PX6断面的91%,而其表层水体总磷为PX6的180%.产生该现象的原因为PX5水面宽度是PX6的3.6~4.7倍,PX5过风距离更长,在库区多河谷少风和低风速条件下,风浪对PX5的扰动强于PX6,导致PX5底泥释放的营养盐更易补给表层水体,故PX5处水华最严重.可见,导致库区支流水华的主要原因是水体分层稳定性和内源磷的供应.水体分层稳定性主要受干流回水影响;而中上游水体内源磷的供应受库区支流特殊水体分层现象(表密度层)的影响,其受天气扰动的时间和程度可用于预测预警水华暴发的时间和规模. |
| 英文摘要 |
| Since the impoundment of the Three Gorges Dam, 50% of the first-order tributaries in the reservoir area have had frequent algal blooms but with variations regarding the geographical locations of the seriously bloomed sections and the scope of the latter being influenced by the mainstream. This study took the Pengxi River, a first-order tributary of the reservoir area, as an example in order to explore the difference in eutrophication among the river sections and the influence of the Yangtze River on its tributaries. During the spring bloom season of 2019, sampling was carried out in one-week intervals for a total duration of one month. Seven sampling sections (PX1-PX7) were set up from the confluence to upstream. According to the profiles of vertical water temperature and conductivity of each section, the influence scope and form of the backwater of the Yangtze River were inferred; in addition, severity differences and mechanisms of algal blooms among sections were explored through the comparison of the hydrology, water quality, and sediment nutrients among Gaoyang Lake (PX5), which has had serious algal blooms, and the upstream (PX6) and downstream (PX4) sections of PX5, which are both 4 km away from PX5. The results showed that during the sampling month, the average ρ(Chl-a) in the confluence area of the Pengxi River (PX1-PX4) and in the upstream (PX5-PX7) were in the range of 14.55-44.00 μg·L-1 and 42.66-175.40 μg·L-1, respectively. The ρ(Chl-a) of PX5 was up to 413.00 μg·L-1, which was significantly higher than that of other sections (P<0.05). Temperature and conductivity results showed that the backwater from Yangtze River flowed into the Pengxi River from the middle and bottom layers during the period from April to May. The confluence (PX1-PX4) sections were in the intersection area of the backwater from Yangtze River and the upstream of the Pengxi River; thus, the waterbody was unstable, which was not conducive to the formation of algal blooms. However, the upstream (PX5-PX7) sections were not directly affected by the backwater from Yangtze River, leading the nutrient exchange mainly vertically. Most averages of n(TN)/n(TP) and n(DTN)/n(DTP) of PX4-PX6 were all greater than 16, indicating a phosphorus-limited state. During sampling, the average sediment total phosphorus of PX5 was 91% of that in upstream PX6, which was only 4 km away, whereas the surface water total phosphorus of PX5 was 180% of that in PX6. The important reason for this phenomenon is that the water surface width of PX5 was 3.6-4.7 times that of PX6, indicating longer wind fetch in the former section. Owing to the mountainous landscape in the Three Gorges Reservoir (TGR) region where windy weather is rare, the disturbance effect of wind and waves on PX5 was stronger than that of PX6, and the nutrients released from the sediment at the PX5 section caused by wind and waves resupplied the surface water more easily, causing more serious algal blooms at PX5 than those at the remaining sections in the Pengxi River. The main causes of the algal blooms in the tributaries of the TGR area lied in the stability of water stratification and the supply of internal phosphorus. The stability of water stratification was mainly affected by the backwater from Yangtze River, and the supply of internal phosphorus in the algal bloom season was affected by the special water stratification phenomenon of the tributaries of TGR—the "surface density layers." The duration and degree of weather disturbance to the surface density layers can be used to predict the time and scale of algal blooms. |
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