Impact Of Water Level Fluctuations Research Articles

Regulating flow to maximize riverine nitrogen removal by riparian zones downstream of reservoirs

Flood waves generated by reservoir discharge play a crucial role in the potential for riparian denitrification downstream. The efficiency of nitrogen (N) removal from river water by riparian zones is typically enhanced with greater wave amplitude (A) and duration (T). However, a knowledge gap exists with respect to the impact of flood waves on N removal when considering a fixed-value integral over time of flood waves (IOFW). This study explored N transport and transformation in the riparian zone downstream of the dammed Inbuk River, Korea under various wave conditions with a fixed IOFW. The results revealed a logarithmic enhancement in solute infiltration into the riverbank with an increasing wave amplitude/duration ratio (A/T ratio). The solute residence time within the riparian zone displays an initial increase followed by a decrease with the increment in the A/T ratio. We identified a threshold for the wave A/T ratio that maximizes riverine N removal by the riparian zone, a phenomenon observed across various dammed rivers. Our findings indicated that riparian denitrification is reaction time-limited when the wave A/T ratio exceeds the threshold; contrarily, it becomes transport capacity-limited. Additionally, we observed a significant relationship between the net nitrate removal and the return/infiltration time ratio of water (r2 = 0.93, p < 0.05). The research results contribute to a better understanding of the impact of water level fluctuations on the N cycle in riparian zones, and provide valuable insights for developing sustainable reservoir operation strategies.

Landscape Pattern Changes of Aquatic Vegetation Communities and Their Response to Hydrological Processes in Poyang Lake, China

Hydrology is an important environmental factor for the evolution of wetland landscape patterns. In the past 20 years, Poyang Lake, the largest freshwater lake in China, has experienced significant inundation shrinkage and water level decrease, posing a significant threat to the local vegetation community. To explore the potential relationship between aquatic vegetation and hydrological processes in the recent hydrological situation, in this study, the landscape patterns of aquatic vegetation communities in Poyang Lake were studied using time-series Landsat remote sensing images and a support vector machine classifier. The stepwise regression analysis method was adopted to analyze the relationship between the vegetation area and hydrological factors. The results indicated that the area of submerged and emergent vegetation in the entire lake decreased significantly from 2001 to 2017, whereas the area of moist vegetation showed a remarkably increasing trend. The average distribution elevation of the submerged vegetation increased by 0.06 m per year. The corresponding landscape patterns showed that the degree of fragmentation of aquatic vegetation communities in Poyang Lake increased. Several hydrological factors were selected to quantify the potential impact of water level fluctuations. The correlation analysis results indicated that hydrological conditions during the rising- and high-water periods may be the key factors affecting the area of aquatic vegetation. This study systematically investigated the evolution of vegetation communities in Poyang Lake wetlands over the past two decades, which contributes to the protection and management of this unique ecosystem.

Methods and algorithms for creating relief models of hydrological modelling for assessing the impact of water level fluctuations on coastal objects and territories

Methods and algorithms for creating relief models of hydrological modelling for assessing the impact of water level fluctuations on coastal objects and territories

Distinct differences of vertical phytoplankton community structure in mainstream and a tributary bay of the Three Gorges Reservoir, China.

The vertical distribution of phytoplankton plays a crucial role in shaping the dynamics and structure of aquatic communities. In highly dynamic reservoir systems, water level fluctuations significantly affect the physiochemical conditions and the phytoplankton community. However, the specific effects on the vertical characteristics of phytoplankton between the mainstream and the tributary bay of the reservoir remain unstudied. This study investigated the vertical aspects of phytoplankton density, biomass, α and β diversity through monthly sampling over two years in the mainstream (Chang Jiang, CJ) and a tributary bay (Xiang Xi, XX) of the Three Gorges Reservoir in China. Phytoplankton density and biomass were significantly higher in XX, indicating an increased risk of algal blooms in the tributary. The phytoplankton community in CJ showed more stable species-environment relationships, a lower Shannon index and a higher evenness index, suggesting a relatively simple structure and a more uniform distribution of phytoplankton among different water layers. Conversely, XX showed greater differences between water layers (higher β diversity), with significant negative correlations with water level and positive correlations with DO difference, dissolved silica (DSi) difference, and stratification. Peak phytoplankton density and biomass, as well as high β diversity in XX, occurred during periods of decreased water levels with strong stratification in spring and summer. A structural equation model complemented by path analysis revealed that a decrease in water level could increase β diversity either directly through internal processes with extended residence time or indirectly by modifying stratification and the vertical distribution of DSi in XX. Therefore, a proposed water quality management strategy for XX was to increase the water level or reduce β diversity by implementing artificial mixing during stratification periods. Overall, this study lies in its comprehensive investigation of the vertical characteristics of the phytoplankton community in both the mainstream and the tributary bay of the Three Gorges Reservoir, elucidating the significant impact of water level fluctuations and providing insights for targeted water quality management strategies in the tributary bay to mitigate potential ecological impacts.

Monitoring Yanwan deep-seated toppling deformation with the impact of water-level fluctuation by SAR observations

Monitoring Yanwan deep-seated toppling deformation with the impact of water-level fluctuation by SAR observations

Impact of Water Level Fluctuation on Microplastic Transportation and Redistribution in a Floodplain Lake System

Microplastic contamination is a challenge in aquatic systems. Among these, floodplains exhibit their cyclical hydrological patterns with substantial fluctuations in water levels caused by annual floods or discharges from rivers into lakes. The influence of water level fluctuation on microplastics within complex floodplain systems has received limited attention in existing studies. This study employs hydrological data and a physics-based hydrodynamic model to assess the effects of water level fluctuations on the transport and redistribution of microplastics within Poyang Lake from 2018 to 2025. High spatiotemporal distribution variability in microplastic concentrations was found within the flood and drought periods. Furthermore, the residence rate of microplastics was assessed based on the microplastic concentration variations in the computational time. A gradual drop in the average discharge rate of microplastics was assessed at the outlet of Poyang Lake. The microplastics are more likely to drain into the Yangtze River in the high water-level period. Meanwhile, under the influence of hydrodynamics, local topography, and water level fluctuation, an accumulation of microplastics appears on the shallow shoals of the western and eastern regions of Poyang Lake, especially in the Gan River. Overall, by means of numerical simulation, the aim of our study is to serve as a reference and advance our understanding of the transportation patterns of microplastics at the aquatic–terrestrial interface.

InSAR-based method for monitoring the long-time evolutions and spatial-temporal distributions of unstable slopes with the impact of water-level fluctuation: A case study in the Xiluodu reservoir

Slope instability in reservoir areas is one of the greatest concerns for public and governments worldwide. The long-time evolution of the unstable slopes in reservoir areas after the impoundments remain poorly understood. Among the technologies applied to detecting and monitoring unstable slopes, interferometry synthetic aperture radar (InSAR) technology is one of the most effective. However, owing to the slopes in a reservoir suffering from periodic water-level fluctuations, InSAR technology has shortcomings for monitoring unstable slopes with large displacement for a long time. In this study, a post-processing method of InSAR and a practical strategy were proposed to monitor the long-time evolution of the unstable slopes in reservoir areas both spatially and temporally. The strategy can capture the evolution trends of the unstable slopes based on the variations in their deformation areas with reservoir water-level fluctuations for a long time. The case study was carried out in the Xiluodu reservoir area of China. The monitoring data of the unstable slopes before and after reservoir impoundment were extracted from multi-source SAR data, including those from ALOS-1, ENVISAT ASAR, and Sentinel-1. It was found that there were 40 unstable slopes before the reservoir impoundment and 152 unstable slopes after the reservoir impoundment. Of the 152 slopes, 142 slopes (94%) began deforming in the first 3 years after reservoir impoundment, 15 slopes have been experiencing continuous deformation, and 137 slopes underwent intermittent deformation. The areas of 79 slopes (52%) increased during the water-level drawdown periods and decreased during the rising periods. The areas of 22 slopes (14%) demonstrated the opposite trend, and the areas of 51 slopes (34%) increased independently of the water-level fluctuations. In terms of evolution trends in the deformation area, 30% of slopes experienced a decreasing trend, 15% were under a constant deformation trend, and 55% showed an increasing trend. The distribution of the unstable slopes varied from the dam site to the end of the reservoir, and most of them favorited the areas where slope angle and height were 20–35° and 30–300 m, respectively. The soil slopes composed of the previous landslide deposits were prone to deformation, followed by the dip to overdip layered rock slopes.

The impacts of water level fluctuations from paddy fields and aquaculture ponds on wetland habitats for wintering waterbirds: Implications for wetland management

The distribution and composition of wetland habitats for wintering waterbirds are heavily influenced by water level fluctuations. Through polder construction and aquaculture activities, paddy fields and aquaculture ponds have decreased the lateral connectivity of water level fluctuations in the lake. However, the impacts of water level fluctuations on habitat suitability, which can be seen using high-resolution images analysis, often cannot separate disturbances caused by the paddy fields and aquaculture ponds, and it is difficult to capture the actual impact of water level fluctuations on wetland habitats. Based on remote sensing image data and hydrological data, we selected Caizi Lake as a study site and comparatively analyzed the changes in wintering waterbird habitats in a water level sequence under the two scenarios. Our work showed that paddy fields and aquaculture ponds should be considered as potential options for creating more suitable habitats for migratory waterbirds if combined with reasonable and effective management of the water level within the paddy fields and aquaculture ponds. The present study results could facilitate the management and sustainable utilization of Caizi Lake wetlands and provide support for creating small habitats by managing the water levels of paddy fields and aquaculture ponds.

Impact of Water Level Fluctuations on Landslide Deformation at Longyangxia Reservoir, Qinghai Province, China

The construction of Longyangxia Reservoir has altered the hydrogeological conditions of its banks. Infiltration and erosion caused by the periodic rise and fall of the water level leads to collapse of the reservoir banks and local deformation of the landslide. Due to heterogeneous topographic characteristics across the region, water level also varies between different location. Previous research on the influence of fluctuations in reservoir water level on landslide deformation has focused on single-point monitoring of specific slopes, and single-point water level monitoring data have often been used instead of water level data for the entire reservoir region. In addition, integrated remote sensing methods have seldom been used for regional analysis. In this study, the freely-available Landsat8 OLI and Sentinel-2 data were used to extract the water level of Longyangxia Reservoir using the NDWI method, and Sentinel-1A data were used to obtain landslide deformation time series using SBAS-InSAR technology. Taking the Chana, Chaxi, and Mangla River Estuary landslides (each having different reservoir water level depths) as typical examples, the influence of changes in reservoir water level on the deformation of three wading landslides was analyzed. Our main conclusions are as follows: First, the change in water level is the primary external factor controlling the deformation velocity and trend of landslides in the Longyangxia Reservoir, with falling water levels having the greatest influence. Second, the displacement of the Longyangxia Reservoir landslides lags water level changes by 0 to 62 days. Finally, this study provides a new method applicable other areas without water level monitoring data.

Impacts of water level fluctuations on mercury concentrations in hydropower reservoirs: A microcosm experiment

Hydropower generation, a renewable source of electricity, has been linked to elevated methylmercury (MeHg) concentrations in impoundments and aquatic biota. This study investigates the impact of water level fluctuations (WLF) on MeHg concentrations in water, sediment, and fish. Using a set of controlled microcosm experiments emulating the drawdown/refill dynamics and subsequent sediment exposure to air experienced in reservoirs, we demonstrate that less frequent WLFs, and/or increased exposure of sediment to air, can lead to elevated MeHg concentrations in sediment, and total mercury (THg) and MeHg concentrations in water. In examining the effects of WLF frequency (two-day, weekly, and monthly), the monthly treatment displayed the highest THg and MeHg water levels, while the weekly treatment was characterized by the highest MeHg levels in the sediment. Our work supports emerging evidence that longer duration between WLF creates a larger surface area of sediment exposed to air leading to conditions conducive to higher MeHg concentrations in sediments and water. In contrast, THg, MeHg, and fatty acid trends in fish were largely inconclusive characterized by similar among-treatment effects and minimal temporal variability over the course of our experiment. This result could partly be attributed to overall low mercury levels and simple “worm-forage fish” food web in our experiment. To elucidate the broader impacts of water fluctuations on aquatic chemistry and biota, other factors (e.g., longer WLF cycles, dissolved organic matter, temperature, more complex food webs) which modulate both methylation rates and food web dynamics must be considered.

Impact of Water Level Fluctuation on Sediment and Phosphorous Dynamics in Tonle Sap Lake, Cambodia

Water level variation substantially affects the trophic levels in a lake. The primary objective of this research is to investigate the impact of water level fluctuation on sediment and phosphorous (P) dynamics in Tonle Sap Lake (TSL), Cambodia. Water samples were collected from eight cross sections in a lake at 3-month intervals for 3 years, during the low-water period (March and June) and high-water period (September and December) from December 2016 to June 2019. Water quality parameters—temperature, conductivity, salinity, dissolved oxygen, pH, oxidation reduction potential, chlorophyll-a (Chl-a), and blue green algae—were measured using an EXO(R) sensor. The sedimentation and resuspension rates of the sediment were measured using a sediment trap. Sediments were collected during the low-water period of March 2017. The sediment resuspension condition was simulated via centrifugation (150 rpm, end-to-end mechanical shaker, room temperature 25 °C for 24 h) to assess phosphorous dynamics. The P content in the bed sediment was fractionated to obtain loosely bound, metal oxide bound, apatite bound, and organic bound P. Sediment resuspension was greater during the low-water period ( 4.8 m). The sites exhibited significant variation (p < 0.05) in terms of dissolved oxygen, pH, oxidation–reduction potential, Chl-a, and depth during low- and high-water periods. In general, the Chl-a concentration throughout the sampling campaigns ranged between 1.7 and 9.0 μg/L, suggesting the existence of a mesotrophic state in the TSL. The zero equilibrium P concentration of sediment in TSL was greater when the sediment was under the resuspension condition (18.9 ± 3.0 μg/L) than under the static condition (7.7 ± 1.1 μg/L). In TSL, during resuspension (low-water) conditions, sediments act as a source and release P (apatite bound, loosely bound, metal oxide bound, and soluble reactive P). However, in static (high-water) conditions, sediments act as a sink by adsorbing P from the overlying water.

Impact of water level fluctuations with different amplitudes and frequencies on biomass and morphological traits of &lt;i&gt;Vallisneria spinulosa&lt;/i&gt;

沉水植物是维持浅水湖泊清水稳态以及湖泊生态系统结构与功能的关键生物类群.近年来，气候变化和人类活动的双重作用造成湖泊水文情势的明显改变，对沉水植物的生长、繁殖和演替有着较大的影响.本文选取2个水位波动幅度与2个波动频率（逐渐改变水位），以恒定水位作为对照，研究湿地中具有重要生态功能的沉水植物刺苦草（Vallisneria spinulosa）的生物量及地上和地下营养器官形态结构对水位波动的响应.结果表明，相对于恒定水位，波动水位（低幅度低频率、低幅度高频率、高幅度低频率、高幅度高频率）对刺苦草的总生物量和获取限制资源相关器官有显著影响.相比于对照组，水位波动能够显著降低刺苦草分株数、叶片数、根数、根长、匍匐茎数、总匍匐茎长以及叶、根、地上和地下生物量，但会显著增加其株高和比叶面积.不同波动频率（低频率和高频率）和幅度（低幅度和高幅度）对光合器官的形态特征都没有显著影响，但叶和地上部分的生物量积累均受到波动幅度的显著影响.水位波动幅度显著改变了刺苦草的根数和根长，而波动频率的影响不显著.因此，对浅水湖泊受损刺苦草群落进行重建时，应避免较大幅度的水位波动，从而有利于增强植株快速恢复的能力.

Impacts of Water Level Fluctuations on Soil Aggregate Stability in the Three Gorges Reservoir, China

Aggregate is the basic unit of soil structure, which is crucial to the sustainability of soil system functions such as structural stability and Fertility Maintenance. Three Gorges Dam (TGD) has extensively led to a dramatic hydrological regime alteration, which may consequently affect various soil physical properties. The aim of this study was to investigate the long-run temporal variation of soil aggregate stability as induced by water-level fluctuations in the riparian zone of the Three Gorges Reservoir (TGR). Sampling plots were established along different elevations considering the interval of 5 m, starting from 150 m to 175 m. A Laser Diffraction based analysis that allows the measurement of soil aggregate stability after the removal of soil organic matter helped to particularly study the effect of external factors on soil aggregate stability of the study area. In addition, wet-sieving method considering the effect of chemical binding agents was used to quantify aggregate stability. The present results indicated a significant increase of Mean Volume Diameter, MVD (p &lt; 0.05) within the study period. Continuous drying-wetting cycles mended soil aggregate stability with a 14.25% increase of the MVD from 2012 to 2016. In the Water-Level Fluctuation Zone (WLFZ), the lower land has predominantly contributed to the increase of soil aggregate stability compared to upper land, with an increase of 62.19% and 37.81% for MVD, 60.88% and 39.12% for D10, 95.34% and 4.66% for D90 at lower and upper elevations, respectively. Sediment deposition below 165 m has precluded a direct effect of water stress on soil aggregates, which certainly declined soil disaggregation. The removal of SOM while analyzing aggregate stability by LD may explain the contradiction between the resulted MVD, and the MWD and GMD. The increase of MWD and GMD was mainly attributed to the increase of SOM with r2 = 0.89 (p &lt; 0.01) and r2 = 0.90 (p &lt; 0.01), while the increase of MVD was highly predicted by the decrease of SOM with r2 = 0.88 (p &lt; 0.01). Since this study presents a remarkable change of soil in the riparian area due to dry-wet cycles, our results may help to deeply understand the soil ecology and environmental changes in the WLFZ.

Temporal changes in food web structure in semiarid waterholes

ABSTRACT High seasonality of semiarid aquatic ecosystems may be due to large-amplitude water level fluctuations. The resulting habitat changes impact aquatic communities and food web structures as a result of species replacement or loss. To study the impact of water level fluctuations on planktonic food web structure, we compared food web descriptors in contrasting seasons. We examined the planktonic food webs associated with semiarid natural and artificial waterholes sampled in Hwange National Pak, Zimbabwe, during the hot dry (HDS), wet (WS), and cold dry seasons (CDS). Natural waterholes are filled by rainwater, while underground water is pumped into artificial waterholes to provide drinking water to wildlife during the dry season. We computed the descriptors of 66 food webs. WS food webs tended to be more complex than those of HDS and CDS; the percentage of basal species was lower, whereas the food web connectance, percentage of intermediate species, omnivory index, mean trophic level, and maximum trophic height of species were higher. Pumping water to maintain pans in the dry season had no effect on food web properties. The drying up of waterholes in semiarid environments simplifies planktonic food webs. The dominance of small rotifers may explain the observed low omnivory index and food web connectance in HDS compared to those observed in other studies.

Spatial and Temporal Dynamics of Water Hyacinth and Its Linkage with Lake-Level Fluctuation: Lake Tana, a Sub-Humid Region of the Ethiopian Highlands

Water hyacinth originated from the Amazon Basin and has expanded to other parts of the world since the 1800s. In Ethiopia, the weed is affecting the socio-economic activities of the people whose livelihood is directly or indirectly dependent on Lake Tana. Still, the area covered by water hyacinth and the impact of water level fluctuation on the expansion of water hyacinth has not been known clearly. Therefore, the main objective of this study was to determine the spatiotemporal distribution of water hyacinth and relation with lake-level fluctuation. The area covered by water hyacinth was determined using monthly Sentinel-2 images, which were collected from November 2015 to December 2019. The impact of water level fluctuation on the expansion of water hyacinth was evaluated using hourly water level data converted to a monthly average to correlate with the area covered by the water hyacinth. In addition, MOD13Q1.006 data was used to evaluate the trend of the Normalized Difference Vegetation Index (NDVI) and its linkage with the weed. The maximum areas covered by water hyacinth were 278.3, 613.6, 1108.7, 2036.5, and 2504.5 ha in Feb 2015, October 2016, September 2017, December 2018, and in December 2019, respectively. Its areal coverage was declining from the northern corridors and increasing in eastern shores of the lake. The lake-level fluctuation was observed in the range of 1.5 to 3.98 m in this study. The annual mean maximum spatial values of the NDVI were in the range of 0.27 and 0.47. The area covered by water hyacinth was increasing significantly (P &lt; 0.05) and positively correlated with the seasonal lake-level fluctuation. High water level enabled the expansion of the weed by extending its suitable habitat of shallow water to the flood plain. Based on the results of this study, lake-level fluctuations can have an adverse impact on the expansion of the weed.

Temporal Scaling of Water Level Fluctuations in Shallow Lakes and Its Impacts on the Lake Eco-Environments

Managing lake water levels from an ecological perspective has become an urgent issue in recent years in efforts to protect, conserve, and restore lake eco-environments. In this study, we considered the actual situation of Ebinur Lake basin to develop a lake water balance model using a System Dynamics (SD) method. The objective of this study is based on the lake water balance model to sufficiently understand the variation and relationship between the lake depth–area–volume. We combined field investigations and hydrological data analysis to expose the major factors affecting lake water level fluctuations (WLFs), as well as the impact of WLFs on lake eco-environments. All with the aim of providing a theoretical basis to manage Ebinur Lake ecosystems for conservation and restoration. The main findings of this study include: (I) The model’s calculation results agree with the observation value, as the monthly lake surface area was used to validate the model. (II) The factors influencing the dynamic changes in the water level of the lake are ranked in ascending order (from the lowest to the highest) as follows: Precipitation, groundwater recharge, evaporation, river inflow. (III) Fluctuations in water level play a significant role in lake shoreline displacement variation, and when the lake’s water level drops below 1 m, the surface area of the water body decreases to approximately 106 km2. (IV) The magnitude and frequency of WLFs drive major differences in the ecology of lake littoral zones, influencing not only the structure and functioning of benthic assemblages but also littoral habitat structure. These results established a quantitative linkage between hydrological variables and ecosystem health for the Ebinur Lake wetlands. These findings could be widely used in managing the Ebinur Lake basin as well as other similar water bodies, and could provide a useful tool for managing lake ecosystems for conservation and restoration.

鄱阳湖丰水期水位波动对浮游动物群落演替的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 鄱阳湖丰水期水位波动对浮游动物群落演替的影响 DOI: 10.5846/stxb201812142730 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31560133） Impact of water level fluctuations on the succession of zooplankton in Poyang lake Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了解鄱阳湖夏季丰水期水位剧烈波动过程中浮游动物的群落演替特征，2012年夏季鄱阳湖水位剧烈波动期间，于6月24日、7月7日和8月27日当水位下降且接近17.6 m时，在江西鄱阳湖国家级自然保护区内的1个浅水碟形湖泊设置4个采样点进行采样调查。共发现浮游动物65种，其中轮虫52种，枝角类7种，桡足类6种，多为营浮游生活的广温性和嗜温性种类。单因子方差分析（one-way ANOVA）显示3个月之间浮游动物的密度和生物量均具有显著差异（P<0.05），7月份浮游动物密度（1030.17±68.18个/L）显著高于6月份（325.16±41.60个/L）和8月份（203.79±24.91个/L）；6月份浮游动物的生物量（0.56±0.04 mg/L）显著低于7月份（1.22±0.11 mg/L）和8月份（0.99±0.11 mg/L）。基于浮游动物多度的聚类分析和自组织映射神经网络图均揭示夏季3个月份的浮游动物可区分为明显的3个群落：6月群落、7月群落和8月群落。蒙特卡罗检验发现水温、电导率、浊度和溶氧与浮游动物群落结构变化显著相关（P<0.05）。典型相关分析显示，6月份浮游动物群落与叶绿素a含量呈显著正相关关系，7月份浮游动物群落与水体温度呈显著正相关关系，8月份浮游动物群落与水深和电导率、浊度和溶氧呈显著正相关关系（P<0.05）。在3个月均为优势物种的盖氏精囊轮虫与叶绿素a含量呈正相关关系（P<0.05），与水温、pH、溶氧呈负相关（P<0.05）。夏季水位波动过程中浮游动物的群落结构在时间上（月份之间）发生明显演替，呈现轮虫密度逐渐降低，枝角类和桡足类密度逐渐增加的变化规律。水位波动引起环境因子的改变，从而对浮游动物的群落演替产生了重要影响。 Abstract:This study aims to understand the succession characteristics of zooplankton communities during dramatic water level fluctuations in Poyang Lake. During the drastic fluctuations in water levels of Poyang Lake in the summer, and on June 24, July 7 and August 27, 2012 when the water level dropped and approached 17.6 meters, four sampling points were established in a shallow dished sub-lake in Poyang Lake National Nature Reserve for the survey of zooplankton. A total of 65 species of zooplankton, including 52 species of rotifers, seven species of cladocerans and six species of copepods, were found during the study period. The zooplanktons were mostly the wide-temperature and mesophilic species of the planktonic type. The one-way analysis of variance revealed significant differences in zooplankton density and biomass within the three-month period (P<0.05). The density of zooplankton in July (1030.17 ±68.18 ind./L) was significantly higher, when compared to that in June (325.16 ±41.60 ind./L) and August (203.79 ±24.91 ind./L). Furthermore, the biomass of zooplankton in June (0.56 ±0.04 mg/L) was significantly lower than that in July (1.22 ±0.11 mg/L) and August (0.99 ±0.11 mg/L). The clustering of zooplankton communities by Bray-Curtis similarity measure and self-organizing maps revealed that the zooplankton was clearly divided into three communities:June community, July community, and August community. The Monte Carlo test revealed that water temperature, conductivity, turbidity and dissolved oxygen were significantly correlated with zooplankton community structure changes (P<0.05). The typical correlation analysis revealed that there was significantly positive correlation between zooplankton community and chlorophyll-a content in June. The water temperature and zooplankton community had a significant positive correlation in July. Furthermore, there were significant positive correlations between the zooplankton community and water depth, conductivity, turbidity and dissolved oxygen in August (P<0.05). Asplanchna girodi, which was the dominant species in the three-month period, was positively correlated with the chlorophyll-a content (P<0.05), but was negatively correlated with water temperature, pH and dissolved oxygen (P<0.05). The present study revealed that the zooplankton community structure exhibited a significant succession between months. Furthermore, the density of rotifers gradually decreased, and the density of cladocerans and copepods gradually increased. Moreover, the water level fluctuations caused changes in environmental factors, which had an important impact on the community succession of zooplankton. 参考文献 相似文献 引证文献

Assessment of Infrastructures Assets Induced by Water Level Fluctuation along the Bengawan Solo River

The stability of infrastructure along river channel, such as bridges and embankments, is paramount to continuing service and public safety, and therefore, is essential consideration in the design, construction and maintenance. During the design process, infrastructure stability is often assumed to be static, and considered by implementing a safety factor which is produced by an analysis of extreme condition. However, this has failed to consider the variability of natural factors and importantly, the escalating threat of extreme environmental condition, induced by global climate change. This assumption should, therefore, be revisited for developing a more resilient design and maintenance regime. To demonstrate the changing infrastructure stability, an assessment of safety factor of river embankment and bridge foundation as nearby infrastructures along Bengawan Solo River’s channel and estuary is presented. This was undertaken to determine the impact of water level fluctuation during two extreme conditions during dry and rainy seasons in several critical locations. The river characteristics (i.e. morphology, water fluctuations, velocity, and sub-soil characteristics), embankment conditions and bridge pile foundation were investigated in-situ to assess the change of safety factor. The laboratory investigation focused on river and embankment characteristics including the analysis of the drying-wetting conditions. In-situ and laboratory investigations found an extreme condition which the infrastructures are subjected into, where the water level and flow velocity were 3 m and 0.04 - 0.27 m/s during dry season; and 10 m and 0.46 - 0.84 m/s during rainy season. Furthermore, from the analysis, it can be concluded that certain areas in the river do not meet the minimum requirements for bridge foundation and embankment stability.

Density‐driven water circulation in a typical tributary of the Three Gorges Reservoir, China

AbstractA 2‐D hydrodynamic model was developed for modelling water circulation from 2008 to 2011 in a typical tributary of the Three Gorges Reservoir. The model is capable of describing flow behaviour and mixing mechanisms for different density current patterns and performs well in computing the velocity, the intrusion layer at the plunge point, and the travel distance of the density current. The effects of 10 flow patterns on thermal stratification, hydrodynamics, and algal bloom risk are discussed and classified in terms of algal growth. Patterns (6) and (10) can effectively prevent algal blooms; Patterns (7) and (8) are good for algal blooms. More frequent transformations of flow‐driven patterns, as observed in 2010–2011, could create more eddies and mixing and thus reduce bloom risk. Further studies are necessary and recommended for more accurate predictions, assessing the impact of water level fluctuations on transform flow patterns and water quality.

Drivers and impacts of water level fluctuations in the Mississippi River delta: Implications for delta restoration

This review synthesizes the knowledge regarding the environmental forces affecting water level variability in the coastal waters of the Mississippi River delta and relates these fluctuations to planned river diversions. Water level fluctuations vary significantly across temporal and spatial scales, and are subject to influences from river flow, tides, vegetation, atmospheric forcing, climate change, and anthropogenic activities. Human impacts have strongly affected water level variability in the Mississippi River delta and other deltas worldwide. Collectively, the research reviewed in this article is important for enhancing environmental, economic, and social resilience and sustainability by assessing, mitigating, and adapting to geophysical changes that will cascade to societal systems in the coming decades in the economically and environmentally important Mississippi River delta. Specifically, this information provides a context within which to evaluate the impacts of diversions on the hydrology of the Mississippi delta and creates a benchmark for the evaluation of the impact of water level fluctuations on coastal restoration projects worldwide.