High Water Level Period Research Articles

Research on Water Level Trends of the Middle Yangtze River Based on Mann-Kendall and ARIMA Model

The middle Yangtze River is the throat and hub zone of the Yangtze golden channel, and the water level is an important limiting factor of the Yangtze River shipping. This paper used Mann-Kendall and ARIMA methods to study the trend of water level changes in the middle Yangtze River. To test the time series of water level in the middle Yangtze River by Mann-Kendall test model, and to analyze the variations of water level changes. Because of the irregular of water level changes, to study the trend of water level changes in the middle Yangtze River by ARIMA model. Model results show that the majority segment of the middle Yangtze River will appear the duration of low water level in 2013-2020, and the period of high water level will have no significant change compared to historical data. This conclusion is made that helps the choice of organizational form the middle Yangtze River shipping, standardization of ship and development research strategies of the Yangtze River shipping logistics systems.

Zooplankton in Lake Sevan during the period of high water level and low fish density

It is shown that, upon the flooding of ephemeral waterbodies in the coastal region and the formation of new warmer sites of the shoals due to the rising water level in Lake Sevan in 2011, species typical for temporary waterbodies and various shoals have been recorded in the zooplankton. Among them, Daphnia (Ctenodaphnia) magna Straus reached mass development, which was favored by the minimal control from “the top” and favorable trophic conditions. Owing to the abovementioned factors, the total lake zooplankton biomass and water transparency increased. The uneven distribution of D. (C.) magna was determined by the density of fish that prefer it as food.

Postglacial history of vegetation, human activity and lake-level changes at Jezioro Linówek in northeast Poland, based on multi-proxy data

We present the postglacial history of vegetation, human activities and changes in lake level in the context of climate change in northeast Poland from ~14,000 cal. b.p. to the present day. The palaeoecological reconstruction is based on the results of high-resolution plant macrofossil analyses as well as records from pollen, Cladocera and radiocarbon dating. Climate fluctuations and human activity have caused many changes in vegetation development in Jezioro Linówek and in the vicinity of this lake. The Early Holocene warming that occurred at ~9500 b.c. caused an increase in Betula and the colonisation of Linówek by Potamogeton lucens, Nymphaea alba and Chara sp. At ~2300 b.c., climate cooling was accompanied by the spread of Picea abies and the appearance of Potamogeton alpinus and Nuphar pumila in the lake. The first traces of farming in the form of Cerealia pollen have been dated back to ~2100 b.c. The cultivation of Triticum began at ~250 b.c., Secale at ~a.d. 550, and Fagopyrum at ~a.d. 1720. The rapid increase in human activity at ~a.d. 1700 and the simultaneous loss of woodland is associated with the establishment of villages in the area and is expressed by the decline of tree curves. In Linówek, which was formed ~14,000 cal. b.p., three periods of high water level occurred (12000–9400, 7000–4000 and 1450 b.c.–a.d. 650), and two periods of low water level (9400–7100 and 3700–1700 b.c.). The changes of water level correspond well with other sites in central and northern Europe.

The residues, distribution, and partition of organochlorine pesticides in the water, suspended solids, and sediments from a large Chinese lake (Lake Chaohu) during the high water level period

The levels of organochlorine pesticides (OCPs) in the water, suspended solids, and sediments from Lake Chaohu during the high water level period were measured by a solid-phase extraction gas chromatograph-electron capture detector. The spatial distributions of the three phases and the water/suspended solids and sediment/water partition coefficients were analyzed. The results showed the following: (1) The mean contents of OCPs in the water, suspended solids, and sediments were 132.4 ± 432.1 ng/L, 188.1 ± 286.7 ng/g dry weight (dw), and 13.7 ± 9.8 ng/g dw, respectively. The dominant OCP components were isodrin (85.1%) for the water, DDTs (64.4%) for the suspended solids, and both isodrin (48.5%) and DDTs (31.8%) for the sediments. (2) β-HCH was the primary isomer of HCHs in the water and sediments, and the proportions were 61.7 and 41.3%; γ-HCH was the primary isomer in the suspended solids, accounting for 49.3%; p,p'-DDT was the dominant content of DDTs in the water and suspended solids, whereas p,p'-DDD was the main metabolite of DDTs in the sediments. (3) The concentrations of contaminants in the water from the western lake were greater than those from the eastern lake, but the concentrations in the suspended solids from the western lake were less than those from the eastern lake. (4) There was no significant correlation between the water-suspended solids partition coefficient Kd and the n-octanol-water partition coefficient Kow, and between the sediment-water organic-C weighted sorption coefficients Koc and Kow.

Prospects for Minimizing the Potential Environmental Impacts of the Hydro-Agricultural Dam of M’Bahiakro (Côte d’Ivoire)

This study aims at characterizing the physical environment and suggesting solutions for a better management of the hydro-agricultural dam of M’Bahiakro which is being constructed over the N’Zi River and is the first inflatable dam in Cote d’Ivoire. In this survey, data related to hydrology, characteristics of the dam and the irrigated rice production area were obtained with the Water Resources Agency and the National Office of Rice Development of Cote d’Ivoire. Physicochemical parameters of the N’Zi River were collected seasonally at three monitoring stations. Results showed that the N’Zi River is characterized by a high water level period from April to November and a low water level period from November to April. The gap between the low flows and the high flows is important (about 206 m3/s on average). The annual average flow is 40 m3/s with a standard deviation of 32.52 m3/s and a variation coefficient of 0.88. The SAR average value (1.63) and the average conductivity (78.44 μS/cm) showed that waters of the N’Zi River are of high quality to be used for irrigation. Suspended sediment concentrations do not present significant difference along the river. But the seasonal variations are important; they are higher during the rainy seasons (45.8 mg/L on average) than in the dry seasons (17.7 mg/L on average). The annual solid flux of the N’Zi River is 41897 tons, i.e. 15810 m3 of sediments. The annual sediment flux is important and can lead to high depositions in the line-shaped reservoir of the dam and that calls for attention to control the silting up of the reservoir. Great efforts concerning interdisciplinary approaches, as well as extensive and intensive field work are needed in order to better manage the hydro-agricultural dam of M’Bahiakro.

Paleoenvironmental settings of the Sofia lignite basin: Insights from coal petrography and molecular indicators

Compositions of Balsha lignite, Sofia coal-bearing basin, Bulgaria and carbonaceous shales are studied by petrological and geochemical proxies. The macropetrographic characteristic of profiles is relatively constant. The lignite is generally composed of dull matrix coal containing significant amounts of xylite fragments. The typical microscopic constituents of the lignite are the ulminite, and less frequently textinite lenses, scattered within attrinitic groundmass. The maceral composition of the organic matter in carbonaceous shales does not differ significantly from that of the lignite samples.Biomarker assemblages of the extractable portions are determined by gas chromatography–mass spectrometry. Additional information for the compositions of residues after extractions is obtained by TMAH thermally assisted hydrolysis/methylation.Petrographic contents, lipid assemblage and TMAH thermally assisted hydrolysis/methylation data imply that the original peat bog is formed in fresh-water forest swamp preferably composed by gymnosperms. Polar diterpenoids argue for Cupressaceae s.l., Taxodiaceae as the most probable vegetation. For one of the profiles appreciable angiosperm rich herbaceous-type flora contribution is assumed. Polar oleanane triterepenoids and their aromatized derivatives argue for angiosperm input. The relevance of A-norfriedel-8-en-10-one/friedelin ratio for groundwater level appraisal is discussed. It admits long period of high water level in the paleomire.High content of vanillyl structures and subordinated presence of syringyl units in products of TMAH thermally assisted hydrolysis/methylation are hint for Gymnospermae input in the paleoswamp and Angiospermae contribution to one of the profiles. Cinnamyl phenolic units, indicating non-woody angiosperm vegetation presence, are registered as well. Flavonoids in products are considered as taxonomic markers of Cupressaceae plants in the paleoswamp.

Effects of water levels on distribution patterns of the Yangtze finless porpoises in Poyang and Dongting Lakes, China

Two large freshwater lakes in China (Poyang and Dongting Lakes) are crucial habitats of the Yangtze finless porpoises. The lakes are confronted with threatens from low water levels. For evaluating possible impacts of low water levels on the porpoises in the lakes, the distribution patterns of the animals in the lakes were monitored in different seasons by using a boat-towing A-tag array from 2009 through 2011. The survey routes were almost same among different seasons. The acoustical detection number (i.e. encounter number) of porpoise in every 3-km section was calculated by counting the bearing angle traces of the sonar sources recorded by the array. The numbers in the same section were compared between high and low water level periods. Results indicated that porpoises appeared to congregate in deep water areas in low water level periods, while they tended to disperse toward the near shore waters in high water level periods. The results suggest concentration of individuals during low water level period. The variations of distribution patterns in different water level periods remind us that protection efforts should be focused on different areas according to the changes of water levels in different seasons.

Responses of phytoplankton diversity to physical disturbance under manual operation in a large reservoir, China

In aquatic ecosystems, physical disturbances have been suggested to be one of the main factors influencing phytoplankton structure and diversity. To elucidate whether large-scale artificial operation of a hydroelectric reservoir has potential impacts on phytoplankton diversity, the impact on phytoplankton biodiversity of physical disturbances under artificial operation from May 2007 to April 2008 in tributaries of the Three Gorges Reservoir (TGR), China, was analysed. Two disturbance parameters, i.e. the absolute incremental rates of discharge (Rd,i) and precipitation (Rp,i), were created in this study for evaluating physical disturbance intensities during low and high water level periods of the TGR. Results showed that river discharge seemed to be the main factor controlling the phytoplankton diversity in low water level periods (≤151 m), and that precipitation was a potential promoter of the physical disturbance. During the 156-m impoundment process, the species diversity clearly decreased due to the high dilution effect on the phytoplankton communities. At high water level periods (>151 m), the low levels of disturbance eventually allowed the phytoplankton community to approach competitive exclusion in late February 2008. Sharply declining diversity values appeared when the Dinophyta blooms occurred in late March and late April 2008 (Peridinium and Ceratium, respectively).

Grain-size characteristics and sedimentary environment change of JZ-2010 section in Jianghan Plain, Hubei Province

通过对江汉平原JZ-2010湖相沉积剖面AMS¹⁴C年代的精确测定与校正,以及代用指标粒度、磁化率的分析和研究,重建了研究区12.76 cal ka BP以来的环境演变过程:1)12.76-6.70 cal ka BP,区域环境处于偏干的晚冰期向湿润的早全新世发展阶段.2)6.70-4.47 cal ka BP,区域环境湿润,为湿度配置最佳的全新世适宜期,这是大溪文化向屈家岭文化转变时期自然背景.3)4.47-3.67 cal ka BP,区域气候环境偏干,其中经历了明显的4.2 cal ka BP干旱事件.4)3.67-1.22 cal ka BP时期,环境向湿润发展;在2.5 cal ka BP左右水动力条件明显变强,此时正对应于古云梦泽扩张时期.5)1.22 cal ka BP后,研究区处于湖泊面积减小的干旱时期;人类活动带来的影响达到高峰,围湖造田等农业活动也是江汉平原湖群趋于衰退的重要原因之一.;Based on the precise measurement and correction of AMS ¹⁴C dating ages combined with the analysis and research of environmental proxies such as grain-size, magnetic susceptibility from the lake sedimentary records of JZ-2010 section in the Jianghan Plain of Hubei Province, this paper reconstructs the sedimentary paleoenvironment of the study area during last 12.76 cal ka BP:1) 12.76-6.70 cal ka BP. All the proxies show that sedimentary grain size gradually turned fine, which reflects a period of high water level and extended lake area. The regional environment turned from dry Late Glacial to fairly wet Early Holocene, characterized with transition and fluctuation. 2) 6.70-4.47 cal ka BP. The regional environment is moist in the whole phase, which is the Holocene Optimum with optimal moist. The regional environment is the natural background of Daxi Culture transitioning to Qujialing Culture, moreover human settling into the heart area of Jianghan Plain. 3) 4.47-3.67 cal ka BP. The regional environment is in dry conditions. Among this stage, all the proxies distinctively figured out the global 4.2 cal ka BP dry event in the Jianghan Plain. 4) 3.67-1.22 cal ka BP. Regional environment became wet again and hydrodynamic conditions obviously stronger around 2.5 cal ka BP which correspondence to the ancient Yunmeng Marsh expansion recorded in Pre-Qin historical documents. 5) Since 1.22 cal ka BP, lakes in Jianghan Plain have shrunk showing relatively dry environment conditions. These environmental changes appeared to be largely caused by anthropogenic factor and reached its peak during the Tang and Song Dynasty. Settlement development and agricultural activities such as reclaiming farmland has also been one of the important reasons reduced the lakes area of Jianghan Plain.

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.

Karl Appuhn . A Forest on the Sea: Environmental Expertise in Renaissance Venice . Baltimore: Johns Hopkins University Press. 2009. Pp. xi, 361. $60.00.

Karl Appuhn has written a brilliant piece of environmental history, focusing on a set of forestry studies commissioned by Venetian officials between the fourteenth and eighteenth centuries. Ruling elites in Venice continually asserted that the forests they relied on for ship building and repairs to the lagoon were dwindling at a rate that endangered the republic. This impelled them not only to gain mainland holdings that had timber reserves, but also to claim and manage the most useful forests as state assets. They acquired forests for the state by documenting local failures to maintain them, and managed their holdings with laws and a bureaucracy charged with periodic reviews and systematic uses of Venetian forests. Appuhn is particularly attentive to the knowledge gap that developed between elites in Venice who experienced shortages of timber and firewood, and forestry officials who studied mainland reserves. Patricians in Venice understood forests as static repositories of resources depleted by human action, not dynamic systems of growth in need of ongoing maintenance. Over the centuries, both forests full of healthy trees and rhetoric about their decline could coexist because of this gap. Forestry officials who tried to bridge it pointed to logistical bottlenecks in the supply system that led to shortages, such as the short period of high river water levels for floating timber and limited peasant labor for felling trees. Venetian elites nonetheless perceived shortages as a threat caused by peasant abuse of their forests. Even studies that demonstrated that communal forests managed by peasants were healthier than either state or private forests had little political purchase.

Estimation of nitrate removal by riparian wetlands and streams in agricultural catchments: effect of discharge and stream order

Summary1. Assessment of the role of landscape structures such as buffers is a necessary prerequisite for the sustainable management of water resources in an agricultural setting.2. We monitored nitrate concentrations during interstorm periods at the outlet of 16 subcatchments of different orders within a catchment of 378 km2. We characterised stream network, wetlands, agricultural practices and land cover and identified their relationships with nitrate fluxes and concentrations.3. Two main factors controlled annual nitrate fluxes: the agricultural nitrogen surplus and the nature of the system comprising the wetland zone and adjoining watercourses. In the latter case, nitrate fluxes were reduced in proportion to the surface area of the riparian wetland and the flowpath distance of fluxes in the stream network. At the scale of the order‐6 stream, 53% of annual nitrate flux during interstorm periods was removed during transfer via the wetland and the river, corresponding to 21.1 kg N ha−1 per year.4. The influence of the riparian wetland zone/watercourse system increased during periods of low water level, explaining up to 64% of nitrate concentration variation among locations within the river network, but only 9% during periods of high water level.5. The buffering role was stronger at higher stream orders, and the dependence on stream order was more apparent at low water level, when we observed mean nitrate concentrations in the order‐6 stream that were 47% lower than observed in order‐2 or order‐3 streams.

Wetlands of the Lake Innes - Cathie catchment

The Innes-Cathie catchment is located on the mid-north coast of New South Wales, south of Port Macquarie, Lake Innes is a shallow 464 hectare lake surrounded by 1471 hectares of wetlands. The Lake Cathie system is composed of Lake Cathie (32 hectares of open water and 180 hectares of wetlands) and Cathie Channel (45 hectares of open tidal water and 406 hectares of wetlands). Innes Swamp (620 hectares) drains into Cathie Channel (map 1). Lake Cathie and Cathie Channel display a series of attributes similar to other ephemeral entrance coastal lagoons of the New South Wales coast (Roy, 1982). Lake Innes was isolated from tidal flows until a channel was dug connecting Lake Innes to Cathie Channel in 1933. Prior to 1933 interconnection of the two lake systems only occurred during periods of high water level when the ocean entrance was closed.

Impact of Water Level Fluctuation on Water Quality and Trophic State of Lake Nasser and its Khors, Egypt.

he morophometric configuration of lakes or reservoirs plays an important role in their water quality variations. The morophometry of Lake Nasser is characterized by the presence of many dendritic side extensions known as side channels or Khors. The surface area, depth and shape of these Khors depend upon the water level upstream the Aswan High Dam (AHD). In the last decade, the water level upstream the Dam fluctuated from about 181m ASL during year 2001 to about 174 m ASL during year 2005.This Fluctuation of water level from year to year affects water quality status of the Lake and its Khors due to the change of their morophometric configuration. To study the effect of water level fluctuation, four main important Khors characterized by gentle slope and sandy bottom with different size were selected. These Khors are Kalabsha, El-Alaki, Toushka, and Sara at Km, 41, 91, 247, and 325 from AHD respectively. The main goal for the present study is to assess the quality of water in the main Khors of Lake Nasser and its main channel during periods of low and high water levels (years 2001 and 2005 respectively). This assessment explores the potential pollution hazards coming from these Khors to the whole Lake. To achieve this goal water quality data generated from the analysis of water samples collected from the Khors and main channel during high and low water levels were used to calculate the water quality and trophic state indices as well as determination of the limiting nutrient factor of the lake. The abundances of Phytoplankton were also considered. The results of the water quality index (WQI) calculations during this study showed that the drop in Lake water levels led to a decline in the water quality of the Lake and Khors from the order of good to medium. Also, the trophic state index (TSI) values revealed that the productivity of the Lake changed from mesotrophic during high water level to eutrophic during low water level. These results are consistent with high phytoplankton counts recorded during low water level period. The values of N/P ratios indicated that phosphorus controls the phytoplankton growth during high water level, while during low water level either phosphorus (P) or nitrogen (N) could be limiting phytoplankton growth. Based on the obtained results of the present study, it could be concluded that the drop in water level upstream the dam may have negative impact on the water Quality of the Khors. This impact may in turn influence the whole Lake due to water rebounce from the Khors to the main channel. Therefore, it is further concluded that khors could be considered as potential pollution sources during low water levels of the lake.

Influence and modelling of urban runoff on the peak flows in rivers

Surface waters and urban drainage systems are usually studied separately. However there are important interactions between both systems. Urban drainage systems can have an important impact on the surface waters, mainly at combined sewer overflows. On the other hand during periods of high water levels in a river, the runoff from the urban drainage system can be significantly influenced by backwater, which increases the probability of flooding in is not obvious, because the modelling tools for both systems are often hard to combine properly. To properly assess the probability of flooding for this kind of integrated water systems, different submodels are needed for both subsystems. In practice often one single model is used to describe the runoff to rivers despite the presence of urban catchments. The main objective of this study is to show the limits of this simplified approach. Furthermore, it is necessary to use continuous long term simulations, because of the differences in runoff behaviour. Detailed hydrodynamic models do not really fit for this purpose because of long simulation times and high demands in memory and disk space. Therefore simplified conceptual models are more useful.

Diatom assemblage variations in the Aral Sea core C2/2004 over the past two millennia.

This study assesses changes in the environmental conditions in Chernyshov Bay (northern part of Aral Sea Western Basin) during the last ~2 ky from geochemical and diatom analyses of sediment core C2/2004. Comparison of fossil assemblages with the contemporary distribution of diatoms in the Aral Sea suggests that considerable changes occurred in water level as well as salinity. Deposits with high diatom concentrations and dominance of the marine species Actinocyclus octonarius EHRENBERG are interpreted as periods of high water level, whereas replacement by Tryblionella compressa (BAILEY) BOYER is considered to indicate lake level fall. On the other hand sediments with low diatom concentration represent higher freshwater input and therefore salinity decrease. This interpretation is supported by estimates of siliciclastic and chemogenic sediment components. A chronology of major lake stages is derived and roughly agrees with recent findings from other studies.

Adipocere withstands 1600 years of fluctuating groundwater levels in soil

An extraordinarily well-preserved skeleton of a child, interred in a stone sarcophagus in the Late-Roman era, was discovered in the city of Mainz (Germany) in 1998, covered with a puff pastry-like substance assumed to be adipocere. It is the first time that this substance, which is derived from fat under oxygen-deficient conditions and prevents corpses from decaying, has been discovered on corpses buried under conditions described in the present paper. The body was buried at groundwater level (2.9 m below surface) in a moist zone close to the Rhine that was affected by seasonally fluctuating groundwater levels. The fluctuating groundwater levels would appear to have had an effect on the degradation of the interred body. The discovery of the skeleton gave us an excellent opportunity to examine fatty acid material which had been subjected to prolonged fluctuating aerobic and anaerobic conditions in a moderate environment. The body's fatty acid composition and 13C abundance were determined and compared with modern adipocere values. Element analysis of the stone sarcophagus in which the child was buried provided information on the burial environment. Our findings indicate that fatty material must have been converted into adipocere under anaerobic conditions in periods of high water levels, leaving the material open to decay during periods of low water levels. The fact that the excavated body was still covered with adipocere 1600 years after the burial clearly shows the robustness of the material against decay.

Wavelet-based characterization of water level behaviors in the Pearl River estuary, China

In this paper, we analyzed the high/low water levels of eight stations along the Pearl River estuary and the high/low tidal levels of Sanzao station, and streamflow series of Sanshui and Makou stations using wavelet transform technique and correlation analysis method. The behaviors of high/low water levels of the Pearl River estuary, possible impacts of hydrological processes of the upper Pearl River Delta and astronomical tidal fluctuations were investigated. The results indicate that: (1) the streamflow variability of Sanshui and Makou stations is characterized by 1-year period; 1-, 0.5- and 0.25-year periods can be detected in the high tidal level series of Sanzao station, which reflect the fluctuations of astronomical tidal levels. The low tidal level series of Sanzao station has two periodicity elements, i.e. 0.5- and 0.25-year periods; (2) different periodicity properties have been revealed: the periods of high water levels of the Pearl River estuary are characterized by 1-, 0.5- and 0.25-year periods; and 1-year period is the major period in the low water levels of the Pearl River estuary; (3) periodicity properties indicate that behaviors of low water levels are mainly influenced by hydrological processes of the upper Pearl River Delta. High water levels of the Pearl River estuary seem to be affected by both hydrological processes and fluctuations of astronomical tidal levels represented by tidal level changes of Sanzao station. Correlation analysis results further corroborate this conclusion; (4) slight differences can be observed in wavelet transform patterns and properties of relationships between high/low water levels and streamflow changes. This can be formulated by altered hydrodynamic and morphodynamic processes due to intensifying human activities such as construction of engineering infrastructures and land reclamation.

Changes in thaw lake drainage in the Western Canadian Arctic from 1950 to 2000

AbstractThe permafrost of the Western Canadian Arctic has a very high ground ice content. As a result, the vast number of thaw lakes in this area are very sensitive to a changing climate. With thaw lakes prone to either increases in area due to thermokarst processes, or complete drainage in less than one day due to melting of channels through ice‐rich permafrost. After a lake drains, it leaves a topographic basin that is often termed a Drained Thaw Lake Basin (DTLB). An analysis of aerial photographs and topographic maps showed that 41 lakes drained in the study area between 1950 and 2000, for a rate of slightly less than one lake per year. The rate of drainage over three time periods (1950–1973, 1973–1985, 1985–2000), decreased from over 1 lake/year to approximately 0·3 lake/year. The reason for this decrease is not known, but it is hypothesized that it is related to the effect of a warming climate. There is a large spatial variation in DTLBs, with higher number of drained lakes in physiographic areas with poor drainage. It is likely that this variation is related to variations in ground ice. Although previous studies have suggested that lakes drain during periods of high water level, it is likely that a combination of a warm summer, a resulting deep active layer, and a moderately high lake level were responsible for the drainage of a lake in the study area during the summer of 1989. Although this study has documented changes in the rate of lake drainage over a 50‐year period, there is a need for further research to better understand the complex interactions between climate, geomorphology, and hydrology responsible for this change, and to further consider the potential hazard rapid lake drainage poses to future industrial or resource development in the area. Copyright © 2008 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada. The contributions of P. Marsh, M. Russell, H. Haywood and C. Onclin belong to the Crown in right of Canada and are reproduced with the permission of Environment Canada.

Turbidity in the Amazon Floodplain Assessed Through a Spatial Regression Model Applied to Fraction Images Derived From MODIS/Terra

The objective of this paper was to estimate turbidity in the Curuai floodplain during the high water level period. Spatial regression models were developed by using fraction images derived from a linear spectral mixture model applied to a Moderate Resolution Imaging Spectroradiometer/Terra image and turbidity <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">situ</i> data. As the turbidity in situ data showed spatial autocorrelation, they were divided into four spatial regimes (clusters). Thus, a spatial regression model was developed for each spatial regime. Through the Akaike information criterion, it was verified which spatial regime showed the best fit in the spatial regression model. The best fit was presented by the spatial regime 4 ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.80,p < 0.05). Then, the spatial regression model developed for the spatial regime 4 was applied to all floodplain lakes. The spatial regression models show potential for assessing the water turbidity in aquatic systems by considering a spatial dependence between samples.