Backwater Area Research Articles

Occurrence and Characteristics of Microplastic Pollution in Xiangxi Bay of Three Gorges Reservoir, China.

Microplastic pollution in inland waters is receiving growing attentions. Reservoirs are suspected to be particularly vulnerable to microplastic pollution. However, very limited information is currently available on pollution characteristics of microplastics in reservoir ecosystems. This work studied the distribution and characteristics of microplastics in the backwater area of Xiangxi River, a typical tributary of the Three Gorges Reservoir. Microplastics were detected in both surface water and sediment with concentrations ranging from 0.55 × 105 to 342 × 105 items km-2 and 80 to 864 items m-2, respectively. Polyethylene, polypropylene, and polystyrene were identified in surface water, whereas polyethylene, polypropylene, and polyethylene terephthalate, and pigments were observed in sediment. In addition, microplastics were also detected in the digestion tracts of 25.7% of fish samples, and polyethylene and nylon were identified. Redundancy analysis indicates a weak correlation between microplastics and water quality variables but a negative correlation with water level of the reservoir and Secchi depth. Results from this study confirm the presence of high abundance microplastics in reservoir impacted tributaries, and suggest that water level regulated hydrodynamic condition and input of nonpoint sources are important regulators for microplastic accumulation and distribution in the backwater area of reservoir tributaries.

Experimental study on durability of FRP sheets under wet-dry cycles in various solutions

Abstract Fiber-reinforced polymer (FRP) is being extensively used in repair and rehabilitation of concrete structures due to their excellent performance and ease of application. Externally bonded FRP hydraulic structures in fluctuating backwater area are likely being exposed to wet-dry cycles and unavoidably being attacked by chloride ions, sulfate ions in water. Therefore, the long-term durability of FRP composites under wet-dry cycles in various corrosive solutions becomes a major consideration in the selection of these composites. This paper evaluates the durability of three kinds of FRP sheets under four kinds of wet-dry cycles, which represent the hydraulic structures various conditions. Tensile tests of FRP sheets for periods up to one year have been presented. Test results indicate that: (1) Degradation of FRP sheets is primarily observed on the level of tensile strength rather than of elastic modulus; (2) Degradation of FRP sheets under wet-dry cycles in sulfate and chloride solutions is more significant than in alkali and acid solutions; (3) AFRP sheets and CFRP sheets show better resistance against wet-dry cycles in various solutions than BFRP sheets.

Eutrophication status of the Daning River within the Three Gorges Reservoir and its controlling factors before and after experimental impoundment

We evaluated 4-year-old data set to assess the trophic state and the controlling factors of the TGR during different experimental impounding (January 2005 to December 2005, stage I–stage II; January 2007 to December 2007, stage II–stage III; January 2009 to December 2009, stage III–stage IV) and normal operating (January 2011 to December 2011, stage IV) periods. The trophic state indices (TSITP) increased in the study area after TGR impoundment, and the TSISD and TSICHL did not significantly change after TGR impoundment; the values of TSICHL only increased at S1 (upstream sampling sites) after the TGR impoundment. The TSISD values in the Daning River (S1, S2, and S3) and the main stream of the TGR (S4) showed similar seasonal variations, with the highest values observed in the flood seasons, followed by the normal seasons and the dry seasons in descending order. The TSICHL only values varied substantially among the three seasons in the backwater area of the Daning River (S2), with the highest value occurring in the flood seasons, followed by dry seasons and normal seasons. The differences in the trophic state indices became smaller between the three seasons after TGR impoundment. The values of TSITP and TSISD showed similar spatial variances, with the highest value observed at S4, followed by S3, S2, and S1 in descending order. The TSICHL values were higher at S2 than at S3, S1, and S4. The results showed that the phosphorus and nonalgal turbidity limit trophic status of the mainstream of TGR and Daning River before and after experimental impoundment.

Succession of phytoplankton assemblages in response to large-scale reservoir operation: a case study in a tributary of the Three Gorges Reservoir, China.

The Three Gorges Dam (TGD) has greatly altered ecological and environmental conditions within the reservoir region, but it is not known how these changes affect phytoplankton structure and dynamics. Here, a bimonthly monitoring program was implemented from 2007 to 2009 to study the impact of damming on phytoplankton assemblages in the backwater area of the Pengxi River (PBA). By application of the phytoplankton functional group (C strategists, competitive species; S strategists, stress-tolerant species; R strategists, rapid propagation species), seasonal changes in phytoplankton relative to environmental variations were evaluated using ordination analysis. Seasonal patterns of phytoplankton dynamics were detected during this study, with CS/S strategists causing algal blooms from mid-spring to early summer, CS/CR strategists often observed during flood season, and CS strategists dominant during mid-autumn. CR/R groups dominated during winter and caused algal blooms in February. Our results indicated that phytoplankton assemblages were directly related to reservoir operation effects. Generally, the TGD had a low water level during flood season, resulting in a relatively short hydraulic retention time and intensive variability, which supported the cooccurrence of CS and CR species. During the winter drought season, water storage in the TGD increased the water level and the hydraulic retention time in the PBA, enabling R/CR strategists to overcome the sedimentation effect and to out-compete S/CS species in winter. As expected, these diversity patterns were significantly correlated with the hydraulic retention time and nutrient limitation pattern in the PBA. This study provides strategic insight for evaluating the impacts of reservoir operations on phytoplankton adaptation.

Spatial and temporal relation rule acquisition of eutrophication in Da’ning River based on rough set theory

Since the mechanisms of eutrophication are complicated and many other factors affect these mechanisms, methods such as quantitative statistics and numerical simulation, have their limitations in analyzing the spatiotemporal relations of eutrophication. The rough set theory (RST) was used to describe the spatiotemporal relations of eutrophication in Da’ning River without any of other prior knowledge. Rules of relations in time and space affecting eutrophication in the Da’ning River backwater area were extracted by taking representation of relations in time and space among eutrophication at a long river section of Da’ning River backwater area, by taking nine sets of encrypted monitoring data in 2003 as example, and by making season, area and eutrophication level as the decision attributes, respectively, to represent specific features of the eutrophication phenomenon in the Da’ning River backwater area from the points of view of time, space, and level by analysis of spatiotemporal relationship rules. This study result shows that the temporal and spatial differences between eutrophication phenomena in the long river section of the Da’ning River backwater area are significant. Eutrophication for each section is less serious in autumn, more in spring and most in summer. Eutrophication degree gradually decreases from estuary to upstream, which is in conformity with reality. The RST of eutrophication in Da’ning River may inform environmental decision-makers and assist them in making more cost-effective decisions.

Cyanobacteria in a tributary backwater area in the Three Gorges Reservoir, China

The ecological processes leading to cyanobacterial dominance in reservoirs differ somewhat from those in lakes and rivers. To explore the development of cyanobacteria in response to large-scale reservoir operation, a 2-year, biweekly monitoring program was implemented from 2007 to 2009 in the Pengxi River Backwater Area, a typical tributary of the Yangtze River in the Three Gorges Reservoir. The data were divided into 3 subsets based on the seasonal operations of the reservoir. During the low-water operation period, temperature stratified in the water column, and intensive rainfall brought suspended solids and nutrients into the Pengxi River Backwater Area. These drivers led to relatively high levels of total particulate matter and low levels of euphotic depth in the water column compared with both the high-water operation period and reservoir discharge period. During these 2 periods, increases in water temperature stimulated the growth of most cyanobacteria. We concluded that the large-scale operation caused structurally different habitats in the Pengxi River Backwater Area, related to water depth, reservoir volume, and nutrient dynamics. These impacts were closely linked to seasonal effects, such as rainfall, river flow, and water temperature, which resulted in differences in habitat among reservoir operation stages.

Artificial tide generation and its effects on the water environment in the backwater of Three Gorges Reservoir

Since the water impounding of the Three Gorges Reservoir (TGR) in 2003, the water stage in the backwater region increased from 65 m before water impounding to 145 m, and the velocity of the stream flow decreased significantly. The outflows of the tributaries that flow into TGR were also obstructed by the backwater. Stopping the stream flow prevented the pollutants from diffusing and transporting themselves into the water body, hence polluting the water in several tributaries. The authors proposed an artificial tide generation approach to solve this problem. The man-made flood peak in the downstream and the waves of the water stage in the upstream of the TGR can be produced by operating hydropower generators daily to deal with peak-and-bottom variations in the electricity demand. These waves will propagate upwards and form artificial tides in the backwater area. The water stage variation will intensify the flow exchange between the main stem and the tributaries as well as enhance the diffusion of pollutants, which will subsequently decrease the eutrophication of the water body in the outlet of branches as well as relieve the algal bloom problem in the region. The daily operations in the reservoir were simulated and tested by using the proposed hydrodynamic model of TGR. The hydropower operation for the peak load of electricity demand will produce artificial tides in the backwater area of TGR as well as increase the water stage variation from 0.30 m to 0.50 m within a day. This periodic fluctuation of water stage waves will intensify the water exchange between the main reach of Changjiang (Yangtze River) and its tributaries with an additional inflow or outflow of up to 300-500 m(3)/s, which is equivalent to the average discharge of these tributaries during the summer. The artificial tide generation can enhance the internal exchange of backwater as well as improve the water environment condition in the backwater area. This operation approach provides a new technology for controlling the water quality in reservoirs as well as enhances environmental protection and resource utility. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.

Application of 2-D sediment model to fluctuating backwater area of Yangtze River

Based on the characteristics of backflow, a two-dimensional mathematical model of sediment movement was established. The complexity of the watercourse boundary at the confluence of the main stream and the tributary was dealt with using a boundary-fitting orthogonal coordinate system. The basic equation of the two-dimensional total sediment load model, the numerical calculation format, and key problems associated with using the orthogonal curvilinear coordinate system were discussed. Water and sediment flow in the Chongqing reach of the Yangtze River were simulated. The calculated water level, flow velocity distribution, amount of silting and scouring, and alluvial distribution are found to be in agreement with the measured data, which indicates that the numerical model and calculation method are reasonable. The model can be used for calculation of flow in a relatively complicated river network.

Effects of flow speed on the change of <i>in situ</i> growth rates of algae in Pengxi River backwater zone, Three Gorges Reservoir

To understand the influence of flow speed on algae growth rates in reservoirs,in situ experiment using stirring experimental tank was carried out in different water level periods( low water level and high water level) in Pengxi River backwater area,a tributary of the Three Gorges Reservoir. Four different treatments,i. e. flow speeds of 0,0. 1,0. 2 and 0. 3 m / s,were selected in the experiment. In summer low water level period,light and temperature conditions were feasible for the growth of algae. Increase in flow speed( 0. 2 m / s) would have significant impacts on the growth of algae. In general,relationships between algal growth rates and flow speeds were in accordance with logarithmic function. In winter,a high water level period,increasing in flow speed would increase in turbulence in water column,preventing sedimentation of algae. In this period,regulating flow speed and discharge to control algal growth might be difficult.

Alkaline phosphatase activity and its kinetics in Lake Gaoyang, Pengxi River during high water level of the Three Gorges Reservoir

三峡水库汛末蓄水后易出现支流回水区磷累积现象,并在冬季末期常出现硅藻水华现象.为研究汛末蓄水的磷积累与冬季末期硅藻水华的相互关系,分析2013年13月三峡澎溪河高阳平湖库湾水体中碱性磷酸酶活性、磷形态的转化和藻类生长的协同过程.结果表明,总碱性磷酸酶活性(TAPA)及其最大反应速率(V_max)、特异性碱性磷酸酶活性(PAPA/Chl.a)及PAPA与TAPA的比值(PAPA/TAPA)随着时间推移总体呈先增加后减小而后再增加减小的双峰趋势,分别在2月中旬和3月中旬达到峰值.根据冬季末期水华暴发程的特点将其分为Ⅰ、Ⅱ、Ⅲ、Ⅳ4个阶段.Ⅰ阶段为诱导期,水体活性磷主要来自藻类碱性磷酸酶分解的有机磷,藻类对磷过度摄取.Ⅱ阶段为过渡期,温度低,水体碱性磷酸酶活性相对较低.Ⅲ阶段为水华时期,水中碱性磷酸酶主要来源于细菌,叶绿素a浓度达到最大,溶解态反应性磷浓度达到最低;Ⅳ阶段为水华末期,水体叶绿素a浓度逐渐下降,溶解态反应性磷浓度回升,水中碱性磷酸酶主要来源于细菌.;In the tributary backwater area, the Three Gorges Reservoir, impoundment after flooding season often results in phosphorus accumulation. Meanwhile, algal blooms occur almost every year in late winter. To find their relationship, we studied the activity of alkaline phosphatase(alkaline phosphatase activity of phytoplankton-PAPA and total alkaline phosphatase activity-TAPA) and different phosphorus forms during January and March 2013. Results showed that TAPA, maximum reaction rate for total alkaline phosphatase V_max, PAPA/TAPA and PAPA/Chl.a flunctuated greatly, reaching the first and second peak at the middle of February and March respectively. According to the characteristics of the algal blooms, we divided it into four periods Ⅰ, Ⅱ, Ⅲ and Ⅳ. The first is induction period, during which SPR was mainly from the decomposition of organic phosphorus by alkaline phosphatase of phytoplankton and meanwhile, algae presented excessive intake of phosphate. The second is transition period, when water temperature and alkaline phosphatase activity was relatively low. The third is bloom stage, during which the alkaline phosphatase was mainly from the germs, chlorophyll-a concentration reached the maximum and SPR the minimum. The last is the ending period of the algal bloom, the alkaline phosphatase was also mainly from the germs, chlorophyll-a concentration decreased and soluble reactive phosphorus concentration increased gradually.

Landslide susceptibility analysis based on ArcGIS and Artificial Neural Network for a large catchment in Three Gorges region, China

A landslide susceptibility map is very important and necessary to efficiently prevent and mitigate the losses brought by natural hazard for a large area. For the purpose of landslide susceptibility analysis for the whole Xiangxi catchment (3,209 km2), Artificial Neural Network (ANN) analysis was applied as the main method. The whole catchment was divided into two parts: the training area and the implementation area. The backwater area (559 km2) of Xiangxi catchment was used as the training area for the ANN method. In the training area the correlations between the landslide distribution and its causative factors, which includes lithology, slope angle, slope curvature and river network, have been analyzed based on the geological map and digital elevation model (DEM). The back-propagation training algorithm in ANN was selected to train the sample data from the training area, which were composed of input data (causative factors) and target output data (landslide occurrence), in order to find the correlations between them. Based on these correlations and input data in the implementation area (causative factors), the network output data were obtained for the implementation area. In the end, a map of landslide susceptibility, which was established by network output data, was presented for Xiangxi catchment. ArcGIS was applied to extract and quantify input information from a DEM for susceptibility analysis and also to present the result visually. As a result, a landslide susceptibility map, in which 70 % of all landslides are rightly classified in the training area (backwater area), was created for Xiangxi catchment.

Spatio-temporal variations of carbon dioxide and its gross emission regulated by artificial operation in a typical hydropower reservoir in China

Supersaturation and excess emission of greenhouse gases in freshwater reservoirs have received a great deal of attention in recent years. Although impoundment of reservoirs has been shown to contribute to the net emission of greenhouse gases, reservoir age, geographical distribution, submerged soil type and artificial regulation also have a great impact on their emissions. To examine how large scale reservoir operation impact the water column CO2 and its air-water interface flux, a field study was conducted in 2010 to evaluate potential ecological processes that regulate the partial pressure of CO2 (pCO2) in the water column in the Pengxi River backwater area (PBA), a typical tributary in the Three Gorges Reservoir, China. Measurements of total alkalinity (TA), pH and water temperature were applied to compute the pCO2. And this approach was also validated by calculation of pCO2 from the dissolved inorganic carbon data of samples. Partial least squares (PLS) regression was used to determine how the dynamics of the water pCO2 were related to the available variables. The estimated pCO2 in our sample ranged from 26 to 4,087 μatm in the surface water. During low water operation from July to early September, there was an obvious pCO2 stratification, and pCO2 in the surface was almost unsaturated. This phenomenon was also observed in the spring bloom during discharge period. Conversely, there was no significant pCO2 stratification and the entire water column was supersaturated during high water operation from November to the following February. Significant correlation was observed between the magnitude of pCO2, DO and chlorophyll a, suggesting that phytoplankton dynamics regulate pCO2 in the PBA. The average areal rate of CO2 emissions from the Pengxi River ranged from 18.06 to 48.09 mmol m(-2) day(-1), with an estimated gross CO2 emission from the water surface of 14-37 t day(-1) in this area in 2010. Photosynthesis and respiration rates by phytoplankton might be the dominant processes that regulated pCO2 in the water column. We conclude that pCO2 values in the surface water of Pengxi River could be regarded as potential sources of CO2 to the atmosphere were smaller or similar to those that have been reported for many other reservoirs to date.

Use of main channel and two backwater habitats by larval fishes in the Detroit River

Recent investigations in the Detroit River have revealed renewed spawning activity by several important fishes, but little is known about their early life history requirements. We surveyed two main channel and two backwater areas in the lower Detroit River weekly from May to July 2007 to assess habitat use by larval fishes. Backwater areas included a soft-sediment embayment (FI) and a hard-sediment area (HIW). Main channel sites were located adjacent to each backwater area. Water temperature, velocity and clarity measurements and zooplankton samples were collected weekly. A macrophyte assessment was conducted in July. Growth and diet of larval yellow perch (Perca flavescens), bluegill (Lepomis macrochirus) and round goby (Neogobius melanostomus) were used to assess habitat quality. Macrophyte diversity and percent cover were higher and velocity lower at FI than HIW. Although larval fish diversity was highest in the main channel, yellow perch and bluegill larvae only grew beyond the yolk stage at FI, where they preferentially selected copepods, while Daphnia were selected in the main channel. Round goby ate harpacticoid copepods and Daphnia and grew at similar rates in HIW and the main channel. These data indicate that FI was a valuable nursery area for yellow perch and bluegill, whereas HIW was better suited to round goby. We only assessed two backwater areas, thus a complete census of wetland areas in the Detroit River is needed to identify valuable habitats. Restoration of shallow backwater areas is essential for rehabilitating fish populations and should be a priority in the Detroit River.

Clostridium perfringens Is Not Suitable for the Indication of Fecal Pollution from Ruminant Wildlife but Is Associated with Excreta from Nonherbivorous Animals and Human Sewage

During a 3-year study, Clostridium perfringens was investigated in defined fecal sources from a temperate alluvial backwater area of a large river system. The results reveal that using C. perfringens as a conservative water quality indicator for total fecal pollution monitoring is no longer justified but suggest that it can be used as a tracer for excreta from nonherbivorous wildlife and human sewage.

Phytoplankton diversity and water quality in the main stream and tributaries of Three Gorges Reservoir region of Yangtze River during dry seasons

2010年4月对长江干流和26条支流未淹没区与回水区的浮游植物进行调查.结果表明,硅藻、绿藻和蓝藻共占浮游植物种类的93.33%~93.88%.干流优势种类有1门1种、未淹没区有3门6种、回水区有5门6种,出现率分别为15.38%、9.23%和25.00%.回水区现存量平均值最高、未淹没区其次、干流最低.现存量组成在干流、未淹没区和回水区之间有差异,绿藻所占比例干流最高,硅藻所占比例未淹没区最高,隐藻、蓝藻和甲藻所占比例均在回水区最高.Shannon-Wiener多样性指数(H')和Pielou均匀性指数(J),未淹没区最高、干流次之、回水区最低.17条支流回水区H'和8条支流回水区J均低于未淹没区.水质评价显示,轻或无污染断面(采样点)的比例,干流为76.92%,未淹没区为84.62%,回水区为47.06%.19条(73.08%)支流回水区出现中污染或重污染,7条(26.92%)支流未淹没区出现中污染或重污染.三峡工程蓄水对回水区浮游植物与水质影响比长江干流更大.;A survey on phytoplankton was carried out along the main stream of the Yangtze River and inundated and backwater areas of 26 tributaries in April,2010.Species of diatoms,green algae and cyanobacteria accounted for 93.33%-93.88% of the total phytoplankton.Dominant species in the main stream,inundated area,and backwater area were 1 species in 1 phylum,six species in 3 phyla and 6 species in 5 phyla,respectively.The occurrence rates of dominant species in the main stream,inundated area, and backwater area were 15.38%,9.23% and 25.00%,respectively.The average value of phytoplankton standing stock was the highest in backwater area,followed by inundated area and the lowest in the main stream.Compositions of phytoplankton standing stock were different among the main stream,inundated area and backwater area.The proportions of green algae and diatom were the highest in the main stream and inundated area,while the proportions of cryptophyta,cyanophyta and pyrrophyta were all the highest in backwater area.Shannon-Wiener diversity indexes and Pielou evenness indexes were the highest in inundated area,followed by the main stream,and the lowest in backwater area.Shannon-Wiener diversity indexes of backwater area of 17 tributaries and Pielou evenness of backwater area of 8 tributaries were both lower than those inundated area.Water quality assessment indicated that the proportions of slightly polluted or not polluted monitoring sections in the main stream,inundated area and backwater area were 76.92%,84.62% and 47.06%,respectively.Moderate polluted or seriously polluted were found in backwater area of 19 tributaries (73.08%) and inundated area of 7 tributaries (26.92%).The influence of the Three Gorges Dam Project on phytoplankton and water quality in backwater area is greater than that in the main stream of Yangtze River.

The Riverbed Evolution and its Influence on Channel in Tunaozi Reach after Three Gorges Water Storage

Tunaozi reach is one of the three famous sediment depositing reach on the Sichuan section of Yangtze River. It’s on the fluctuation backwater area when the Three Gorges Project is operated at the level of 135 m. According to the measured data before and after impoundment, this paper analyzes and calculates the sediment of the reach, and discusses the variation of silting and scouring of the reach after impoundment. Thus, this paper will have a study on the reason that silting and scouring lead to channel condition change. The result as follow: after impoundment, the bank-up water level of the reach has been head up 2 m during the flood season, sediment deposition becomes heavier than before impoundment; in post-flood season, the water level is 139m in November, it has been head up 7 m, compared with low water level in natural, current slowly flow further, the silt lack of enough scour in flood season, it leads to cumulative deposition. Until December 2005, thalweg plane position move left 200 m after impoundment. The maximum silting height of the thalweg longitudinal section is 30 m. The prime channel has been basically silted flat, year. Since the Three Gorges reservoir began to store water for three years, in low water level periods, ship tank is out of shallow, some timely dredging measure should be taken and make sure the smooth channel.

Test Studyed of Yangjiawan Grand Bridge in the Project of Lanyu Railway by Movable Bed Model

Yangjiawan grand bridge is located in Lanzhou section of the Yellow River. In order to study the change laws near the bridge site of flow direction, velocity distribution, water surface slope, backwater area, river bed topography change and the effect of flood control on Lanzhou city after the bridge-built when the river gets through the average discharge, 20-year discharge, and 100-year discharge before and after the bridge-built. Based on the similar principle of model, the river near the bridge site was simulated by the hydraulic model experiment of movable bed. The result of experiment showed that the design data adopted in bridge project of Yangjiawan grand bridge were reasonable and fulfilled the requirements of city flood control. It was also suggested to excavate and dredge river near the piers of 6# ~11# and strengthen embankment near the riverbank and protection of constructions after the bridge-built.

Metals in chosen aquatic plants in a lowland dam reservoir

The research involved S3up Dam Reservoir, which is used as a source of drinking water and for flood prevention. The research material was made up of aquatic plants and water collected in the littoral zone of the reservoir, in which copper, nickel, cadmium, lead and zinc contents were determined. Ceratophyllum demersum L. turned out to be the best accumulator of nickel, cadmium and zinc, Potamogeton crispus L. – copper, and Phragmites communis Trin – zinc. The presence of plants in the backwater area of the dam reservoir definitely improves water quality, not only thanks to their metal accumulation properties but because of their ability to act as a filter of substances carried in the water.

Phytoplankton diversity in backwater area of the Pengxi River in the Three Gorges Reservoir before and after 156 m impoundment

为了解156 m蓄水前后三峡水库次级河流藻类多样性变化特征,对2007年7月至2008年1月澎溪河回水区的藻类种群结构的变化进行连续监测.基于三峡水库水位调度特点,将监测期划分为蓄水前、中、后三个时段,即7-9月、10月、11月至翌年1月,应用Shannon-Weaver多样性指数H'对藻类多样性进行评价,通过Connell中度扰动假说理论结合优势藻种探讨蓄水过程水动力变化及藻类多样性的变化特征.结果表明:2007年7-9月蓄水前H'均值为3.466±0.317,10月蓄水期则降为3.246±0.338,而11月蓄水后高水位阶段H'均值上升为3.431±0.352.蓄水前澎溪河回水区具有河流型特征,流量与降雨作为主要的物理扰动因子影响水体扰动强度,进而引起多样性变化.10月蓄水期间水位突升、流量骤降导致水体扰动强度加剧,较蓄水前藻类多样性下降.自11月蓄水后的高水位阶段,降雨较小、流量趋于稳定,水体扰动降低,多样性回升并维持在相对稳定的状态.;In order to analyze the phytoplankton diversity in the backwater area of Pengxi River before and after the impoundment of the Three Gorges Reservoir (TGR) to the water level of 156 m, the variation of algae community of Pengxi River had been observed from July 2007 to January 2008. According to the water level variation in TGR, the time was divided into three periods:July-September, October and November-January. The algae diversity of five sites in Pengxi River was assessed using Shannon-Weaver diversity index H'. Moreover, the Connell's intermediate disturbance hypothesis was applied to analyze the impact on algae diversity caused by hydrodynamic conditions' variation during the impoundment process. Before 156 m impoundment, the mean H' index was 3.466 ± 0.317, declined to 3.246 ± 0.338 in October and recovered to 3.431 ± 0.352 during the high water level period. Before impounding, the Pengxi River was of riverine-type, with flow and rainfall being the main physical disturbance factors affected the disturbance intensity and algae diversity. As a result of water level suddenly risen and the flow severely droppen, the disturbance intensity increased compared with the impounding period. After 156 m impounding, the Pengxi River was at the high water phase, the less rainfall and stable flow reduced the physical disturbance, so the H' index recovered and maintained at a relatively stable state.

Houseboats in Kerala - Constructional Features and Environmental Issues

Kerala Houseboats (Riceboats) or kettuvallam are country boats that were used in early days for transport of goods from isolated interior villages of Kerala backwater area to the towns like Alleppey, Kollam , Cochin and Kottayam. With the advent of land transport facilities, gradually the kettuvalloms went off the scene. Now they are back again as a major tourist attraction as a modern moving boat house. They form a huge source of revenue and prosperity for the region. It is a well-known fact that only around 100 of the 600-plus houseboats operating in the Vembanad Lake and the surrounding canals and rivers have valid Pollution Control Certificates (PCC) since they have onboard sewage treatment facilities. Houseboats satisfying the essential conditions and adhering to eco-friendly measures will be awarded the Green Palm Certificate, the top classification awarded by the Department of tourism. The sustainability of eco-tourism lays in the four main areas - Environment - Energy - Water - Propulsion. Less fuel/running cost, no oil or diesel contamination into backwaters, no untreated sewage into backwater, reduction in noise pollution are the ways to achieve dream for a green and pleasing future in Kerala backwater and save the same for the next generation.