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筑坝与硬化对华北山区河流磷氮迁移的影响研究
Alternative TitleThe effects of damming and hardening on the transport of phosphorus and nitrogen in mountainous rivers of North China
鲍林林
Subtype博士
Thesis Advisor李叙勇
2019-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name理学博士
Degree Discipline生态学
Keyword筑坝 河流 质量平衡 ,磷和氮 迁移,水动力 条件 ,营养状态,Dammed River, Mass Balance, Transport Of Phosphorus And Nitrogen,
Abstract
    随着城市化进程的不断推进,城市河流因景观建设和防洪等需要,进行了大量小型闸坝(如橡胶坝、溢流堰等用以蓄水)和河床与河岸硬化(防止河道侵蚀渗漏)的建设,这种景观储水型筑坝与硬化河流,原有的生态系统的结构和栖息地环境被严重破坏,另一方面,其水体的富营养化问题也日渐突出。但是,相比于湖库水体,筑坝与硬化河流富营养化的生态影响却很少受到关注。因此,为了有针对性的改善筑坝与硬化河流的生态环境,本文以华北永定河流域上游山区河流——清水河-洋河水系 5  个不同程度筑坝与硬化河段为研究区,其中筑坝与硬化程度越高,河流水动力条件弱化程度越高,5河段根据水动力弱化程度划分为高强度、中强度、中低强度、低强度和无水动力弱化河段。本文主要探讨了筑坝与硬化河流的水动力条件改变对营养物质磷氮迁移的影响,以及随后的水体富营养化响应,主要研究成果如下:
(1)根据河道结构、河床底质、水文特征、水质参数和水生生物五类指标构建的河流生态系统健康指数(RHI)方法,评估了河流生态系统健康,结果表明,河道结构和河床底质指标的健康程度与 RHI显著正相关(p  < 0.01),筑坝与硬化等人类活动干扰对河流物理结构的改变,进而导致河床底质和水文特征的改变,是损害河流生态系统健康的主要原因;此外,水生生物较低的多样性和  TP、有机质严重污染也降低了整个水系的生态系统健康水平。
(2)采用质量平衡的方法估算了筑坝与硬化河流中磷氮滞留量和滞留率:高强度水动力弱化的橡胶坝拦蓄河段具有与水库相当的磷(42.5%,7.69 t/yr)、氮(48%,158.1 t/yr)滞留能力;其中磷主要滞留在河段上部几个橡胶坝内(47.6%,其显著高于下游几个河段的-8.3%~9.2%,p < 0.05),而氮以硝氮为主,迁移距离更远滞留在河段中下部(16.2%~26.3%,上部河段为-2.5%~8.0%),因此氮磷原子比(N:P)沿梯级橡胶坝先增加而后降低,浮游植物生长受磷的营养限制(N:P > 16);生物作用的贡献,使得溶解态磷(磷酸盐,86.3%)和氮(硝态氮,66.3%)滞留率均高于颗粒态磷(40.3%)和氮(30.1%),且营养物质在夏季的滞留率最高。但是随着筑坝与硬化程度的增加、水动力条件弱化程度增加,磷氮的滞留效率先增加后降低,表明适当筑坝和河床底质的多样化才有利于磷氮滞留;此外,自然流量的增加能够降低河流对营养物质的滞留率,但是对水动力条件越弱的河段降低作用越低。
(3)以沉积物磷释放潜力(EPCsat)和回归模型研究的筑坝对磷在沉积物和水体之间迁移的影响,表明闸坝建设直接的、间接地改变了河流的理化性质,进而决定了磷在沉积物和水体之间的迁移:在 30  级橡胶坝拦蓄河段内,由于橡胶坝拦截使得流速骤降(从1m3/s到0.01m3/s),悬浮泥沙在第 4号橡胶坝(4#)之前快速沉降,使得点 4#的沉积物细颗粒物含量高于河段入口处的沉积物,所以  4#的 EPCsat(67%)较入口(76%)低;随着系列橡胶坝的梯级拦截,沉积物粒径相对变粗,菹草和浮游植物的加速生长降低了水体磷酸盐浓度,而增加了沉积物生物可利用磷和有机质的含量,因而导致 EPCsat逐渐升高到  90%(河段出口)。
(4)采用藻类生物学指标和回归模型探讨了河流营养状态变化的主要驱动因子:在高强度水动力弱化的橡胶坝拦蓄河流中,随着橡胶坝级数增加水体滞留时间变长,营养程度从中营养(5 ug/L ≤叶绿素 a浓度<   25 ug/L)逐渐升高到富营养(叶绿素a浓度> 50 ug/L,浮游植物细胞 > 100×10  cells/L),流量(解释度为636.8%)和磷浓度(26.3%)是决定其富营养化的主要因素;同等营养物质水平下,水动力条件越弱的河段其浮游植物生长速率较高:即高强度水动力弱化河段(单位距离的浮游植物生长率 18.4  %)> 低强度水动力弱化河段(-3.3 %),中低强度水动力弱化河段(27.9 %)> 无水动力弱化河段(14.7 %),相对应的其富营养化风险也越高;自然降水对河流水动力的改善,只有在较高强度的流量增加时才能有效的抑制浮游植物生长。
    为了保持河流的生态系统较高的完整性,并有利于污染物质的净化和水体富营养化风险的缓解,河流水利工程建设中,需要避免河床硬化和过度筑坝的水动力弱化,并适当筑坝、控制外源营养物质输入、防止坝内泥沙淤积产生内源污染、提高水生生物多样性。
 
Other Abstract

    With the  continuous advance of  the urbanization process,  more and  more small dams  (e.g.  rubber  dam  and  weir  for  water  impoundment),  together  with  channel hardening  (in  case  channel erosion  and  water  seepage),  are  constructed  in  rivers,especially    in    urban    rivers    for     landscaping    and    flood    discharge.    These damming&hardening rivers  for landscape water  storage have drastically changed  the structure and habitat of river ecosystem. Furthermore, the eutrophication problems are becoming more and more severe  in damming&hardening rivers. However, comparing to  lakes  and  reservoirs, the  eutrophication  problems  and  the  ecological  effects  of damming&hardening rivers have received less attention. In order to efficiently improve ecological environment  of damming&hardening rivers,  we selected 5  river segments with difference levels of damming and hardening as the study area, which are along the main streams  of Qingshui River  and Yang  River in the  upstream of Yongding  River watershed, North China. Among the 5 river segments, the one that has higher degree of damming and hardening reveals weaker hydraulic condition. Thus the 5 river segments are  defined as  high  level, medium  level,  medium-low level,  low level  and  zero of hydraulic weakening,  respectively. This study  was mainly investigated  the effects  of river  hydraulic condition,  which  was  changed  by damming  and  hardening,  on  the transport of the phosphorus and  nitrogen, and on the subsequent water tropic status  in rivers. The main results of this study are as follows:
(1) The river health index (RHI), including five indicators of channel structure, channel substrate, hydraulic condition, aquatic life and water quality, was constructed to analyze the quality conditions  of riverine environment  of the five river  segments. The results showed  that  the health  degree  of  channel  structure  and  channel  substrate showed significant  relationship with  RHI  values  (p <  0.01).  It revealed  that  damming  and hardening  changed  the  physical  structure  of  river  channel,  and  hence  altered  the substrate composition  and hydraulic  condition, which  together deteriorated  the river ecosystem. In addition,  the high pollution of  phosphorus and organic matters  in river water and the low diversity of aquatic lives also  reduced the ecosystem health level of all river segments.
(2)  Based  on  mass  balance method,  we  calculated  the  retention  load  and  rate  of phosphorus and nitrogen  in the river segments. The  lake-like river segment|, with the highest level of damming  and hardening, had a high retention  capacity of phosphorus (42.5%,  7.69 t/yr)  and  nitrogen (48%,  158.1  t/yr)  like reservoirs.  The  phosphorus, particulate  forms dominated,  was mainly  retained  within dams  of  the upmost  river section (the retention  rate was 47.6%,  being significantly higher  than the lower river sections with retention rate of -8.3%~9.2%,p < 0.05), while nitrogen, nitrate account for the largest proportion,  transported longer distance and was  mainly retained within dams of the middle and lower river section (the retention rate was 16.2%~26.3%, when the retention rate in the upper river section was from -2.5% to 8.0%). So the N:P atomic ratio increased from the entrance to the middle of the river, and then decreased, with all the  values   higher  than   16:1,  indicating  a   status  of   phosphorus-limited  primary production.  Due  to  the  biological uptake  and  denitrification,  the  retention  rate  of dissolved  reactive  forms  of  phosphorus  (phosphate,  86.3%)  and  nitrogen  (nitrate,66.3%) was higher than that of particulate forms (40.3% and 30.1% respectively). The retention rate  of nutrients was  highest in summer  time because  of biological effects. However, as the level of damming and hardening  and hydraulic conditions weakening raised, the retention rates of phosphorus and nitrogen increased first and then decreased. The river segments  with moderate dams  and natural bed substrate  were conducive to the riverine  retention of phosphorus  and nitrogen. Even  though the  flow increase by precipitation  could  decrease  the  retention  rate  of  nutrients  in  river  segments,  the decrease tendency  of  nutrients retention  was lower  in river  segments  under weaker hydraulic condition.
(3) The effects of damming on phosphorus transport between sediments and water were studied using sediment phosphorus release potential (EPCsat) and regression method. It revealed that the  riverine physiochemical properties changed  directly or indirectly by
dam  construction indeed  affected  the  phosphorus transport  between  sediments  and overlying water. Therefore, in  the river segment with 30  rubber dams, the EPCsat  was lower at the 4th dam (4#, 67%) than at the entrance of the river segment (76%) because of high deposition of fine suspended sediments before 4# after flow velocity decreasing
from 1 m3/s at BBF to  0.01 m3/s within  dams. While then the EPCsat  increasing from 4#  to  the outlet  of  the  river  segment  (90%)  was  because of  the  decrease  of  fine sediments from the  5   to 30    dams, the decrease of  water phosphorus concentration,and increase of sediment bioavailable phosphorus  and organic materials by increasing macrophyte and phytoplankton growth within dams.
(4) According  to algae  biological index  and regression  method, we  investigated the driving factors for trophic status  of the damming&hardening rivers. It showed that,  in river segment with high level of damming and hardening and hydraulic weakening, the
water trophic status increased from mesotrophic condition (5 ug/L≤ chlorophyll a  <25 ug/L) to eutrophic condition (chlorophyll a > 50 ug/L, phytoplankton cells > 100×10  cells/L) as the dam numbers and water residence time increased. Flow (accounting 6 for the variance of 36.8%) and phosphorus concentration (26.3%) were the main factors
determining  river  eutrophication. Moreover,  the  growth  rate  of phytoplankton  and eutrophication risk in the river segments with weaker hydraulic conditions were higher than that with stronger hydraulic conditions, compared under similar nutrients level, as the growth  rate per kilometer of  phytoplankton was higher  in the river  segment with
high level of hydraulic weakening (18.4 %) than in the river segment with low level of hydraulic weakening (-3.3 %), and higher in the river segment with medium-low level of hydraulic weakening (27.9 %) than in the river segment without hydraulic weakening (14.7 %). The phytoplankton growth could only be efficiently inhibited when the flow
by precipitation was increased large enough.

    To  sum up,  in  order to  maintain  the ecosystem  quality,  to  promote pollutants removal and to reduce the risk of eutrophication in rivers, the managers should set dams properly  but  no  channel  hardening,  reduce  the  external  nutrients  pollution,  avoid sediment blocking  and  increasing riverine  biodiversity when  constructing  hydraulic engineering measures in the river systems.

 
 

Pages170
Language中文
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/42178
Collection城市与区域生态国家重点实验室
Recommended Citation
GB/T 7714
鲍林林. 筑坝与硬化对华北山区河流磷氮迁移的影响研究[D]. 北京. 中国科学院生态环境研究中心,2019.
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