浅水草型湖泊除草技术的实验

滆湖位于江苏南部,面积为164km~2,是一个典型的草型湖泊,其中80X以上的面积为黄丝草(Pataraogeton maackianus)所覆盖。针对该湖水生植被中草食性鱼类喜食性水草资源逐渐衰竭,非喜食性水草群落逐渐扩张的状况,1988—1990年,进行了湖泊水草群落的定向改良试验和抑制相关水草发生和蔓延的试验。结果表明,采用生物防治,以鱼除草,无论是网拦放牧式除草技术,还是网围养殖式除草技术,对各种沉水植物都可彻底清除,而且直接将水草转化为鱼产品,并且有利于湖泊水域生态环境的改善。     

两小型浅水湖泊水体叶绿素a浓度的季节变化及与理化因子和生物因子的关系

为探讨非生物因子和生物因子对水体叶绿素a(Chl.a)浓度变动的相对重要性,对芜湖市内的汀棠湖(每半月1次)和镜湖(每4天或7天1次)进行高频采样,分析理化因子及浮游动物密度与Chl.a浓度间的关系.结果表明,从全年来看,2个湖泊的Chl.a浓度均与水温和透明度间分别呈现显著的正相关性和负相关性,与浮游动物密度均无显著相关性;镜湖Chl.a浓度随着总磷浓度和氮磷比的增加分别呈上升和降低趋势.从季节来看,冬季两湖中的Chl.a浓度最低,轮虫密度与此阶段镜湖中藻类Chl.a总浓度和小型藻类的Chl.a浓度间均呈显著负相关,且其对上述两类Chl.a浓度变动的影响程度最大,表明轮虫对藻类的牧食效应降低了冬季镜湖中的Chl.a浓度.从各环境因子对Chl.a浓度变动影响的相对权重来看,除了冬季的镜湖外,2个湖泊中的两类Chl.a浓度均与透明度的关系最密切,且均随着透明度的上升而降低,暗示了透明度可作为预测小型封闭性浅水湖泊中Chl.a浓度的简便指标.     

Sediment characteristics and wind-induced sediment dynamics in shallow Lake Markermeer, the Netherlands

In 2007/08, a study was undertaken on the sediment dynamics in shallow Lake Markermeer (the Netherlands). Firstly, sediment characteristics were determined at 49 sites in the lake. Parameters such as median grain size and loss on ignition showed a spatial as well as water depth related pattern, indicating wind-induced sediment transport. Highly significant correlations were found between all sediment parameters. Lake Markermeer sediment dynamics were investigated in a sediment trap field survey at two permanent stations in the lake. Sediment yields, virtually all coming from sediment resuspension, were significantly correlated with average wind speeds, though periods of extreme winds also played a role. Sediment resuspension rates for Lake Markermeer were high, viz. on average ca. 1,000 g m⁻² day⁻¹. The highly dynamic nature of Lake Markermeer sediments must be due to the overall shallowness of the lake, together with its large surface area (dynamic ratio = [√(area)]/[average depth] = 7.5); wind-induced waves and currents will impact most of the lake’s sediment bed. Indeed, near-bed currents can easily reach values >10 cm/s. Measurements of the thickness of the settled “mud” layer, as well as ¹³⁷Cs dating, showed that long-term deposition only takes place in the deeper SE area of the lake. Finally, lake sediment dynamics were investigated in preliminary laboratory experiments in a small “micro-flume”, applying increasing water currents onto five Lake Markermeer sediments. Sediment resuspension started off at 0.5–0.7 cm/s and showed a strongly exponential behaviour with respect to these currents.     

Sediment delivery,resuspension, and transport in two contrasting canyon environments in the southwest Gulf of Lions

Multiple canyons incise the continental slope at the seaward edge of the continental shelf in the Gulf of Lions and are actively involved in the transfer of sediment from shelf to deep sea. Two canyons in the southwest region of the Gulf of Lions, Lacaze-Duthiers Canyon and Cap de Creus Canyon, were instrumented with bottom-boundary-layer tripods in their heads to evaluate the processes involved in sediment delivery, resuspension and transport. In both canyons, intense cold, dense-water flows carry sediment across the slope. In the Lacaze-Duthiers canyon head (located ∼35 km from the shoreline), dense-water cascading into the canyon was episodic. Currents were highly variable in the canyon head, and responded to interactions between the along-slope Northern Current and the sharp walls of the canyon. Inertial and other high-frequency fluctuations were associated with suspended-sediment concentrations of ∼5 mg/l. In Cap de Creus canyon head (located ∼14 km from the shoreline), downslope currents were higher in magnitude and more persistent than in Lacaze-Duthiers canyon head. Greater suspended-sediment concentrations (peaks up to 20 mg/l) were observed in Cap de Creus Canyon due to resuspension of the canyon seabed during dense-water cascading events. The similarities and contrasts between processes in these two canyon heads emphasize the importance of the interaction of currents with sharp canyon bathymetry. The data also suggest that cold, dense-water flows have more potential to carry sediment to the slope on narrow shelves, and may more efficiently transfer that sediment to the deep sea where a smooth transition between shelf and slope exists.     

Morphological and molecular analysis of bloom-forming Cyanobacteria in two eutrophic, shallow Mediterranean lakes

We investigated the diversity of Cyanobacteria by microscopic observation and sequencing of cyanobacterial-specific amplified 16S rRNA genes in the water column of two shallow, eutrophic lakes (Doirani and Kastoria, northern Greece) during summer blooms. Previous phytoplankton studies in these lakes have shown that prolonged cyanobacterial blooms can occur, which are dominated by known toxic species, as well as other less known, co-occurring species. A total of 118 clones were sequenced which were grouped in 23 Cyanobacteria and 11 chloroplast-like phylotypes. Phylogenetic analysis revealed that each library included several unique phylotypes, as well as members of all common bloom-forming Cyanobacteria. Most of the phylotypes belonged to the genera Microcystis, Anabaena, Aphanizomenon, Cylindrospermopsis-Raphidiopsis group, Limnothrix and Planktothrix, comprising most of the diversity previously recognized by morphological observations in cyanobacterial morphospecies in these lakes. In addition, novel phylotypes belonging to the Chroococcales were recognized in both lakes. The structure of the cyanobacterial communities of the lakes were very similar, as revealed by the diversity index H (2.06 and 2.01 for L. Doirani and Kastoria, respectively) and LIBSHUFF analysis (XY₁₂P-value = 0.122 and YX₁₂P-value = 0.536), due to occurrence of groups of common phylotypes. This study gives an example for successful cyanobacterial bloom analysis by the combination of morphological and phylogenetic methods useful for monitoring cyanobacteria and water quality in freshwaters.     

Sediment yield variability in central Tunisia: a quantitative analysis of its controlling factors

Abstract

This paper refers to the quantification and prediction of the sedimentation rate of 26 hillside-dam reservoirs in Central Tunisia. The objectives of the study are to develop a simple and practical methodology to identify controlling factors of sedimentation, and to propose a regionalization from the study sites. Principal component analysis (PCA) and complementary multi-dimensional statistical methods are used to relate highly variable area-specific sediment yield to hydro-morphometric, lithological, geomorphological and anthropogenic characteristics of catchments. It appears that catchment area is not the main controlling factor of sedimentation in the studied area. The overall slope index, drainage network characteristics and runoff parameters are also important in characterizing sediment yield. Applied to the annual sedimentation rate series, PCA resulted in retaining the first three principal axes, explaining 65% of the total variance. Statistical methods showed that the overall slope index, the total drainage length, the compacity index and the runoff parameters are as important for the sedimentation quantification. This allowed a graphical clustering of the study zone into three distinct groups having similar behaviours: (i) watersheds characterized by high sediment transport rates and high runoff coefficients, (ii) basins distinguished by relatively low values of both flow discharge and sediment transport rates, and (iii) watersheds with an intermediate sediment yield, especially characterized by relatively high relief. In a second step, a multiple regression model including the four characteristic catchment properties was developed, presenting a valuable tool to predict area-specific sediment yield from catchments in central Tunisia. This model shows reasonable efficiency with an absolute prediction error of 81%.

Citation Ayadi, I., Abida, H., Djebbar, Y. & Mahjoub, M. R. (2010) Sediment yield variability in central Tunisia: a quantitative analysis of its controlling factors. Hydrol. Sci. J. 55(3), 446–458.     

南京市两个小型富营养湖泊浮游硅藻的季节性变化

为研究浅水富营养湖泊硅藻季节演替的规律,选择南京两个城市湖泊(前湖和月牙湖)作为对象,对水体硅藻和水质进行逐月采样和实验分析,结合数理统计分析手段,对2006年硅藻浓度、种群组合变化及其与环境因子的关系进行了讨论,结果表明:两湖硅藻都呈现较明显的季节演替特点,冬季浮游硅藻组合主要由Cyclostephanos的种类为主,代表了冷水富营养种组合类型:夏季和秋季以Cyclotella atomus和C.meneghiniana暖水耐营养种优势组合为主,硅藻和环境指标月富营养湖泊,春季硅藻丰度增加对初级生产量的贡献很小;随着营养程度的不断提高,温度对浮游硅藻的限制更为突出.     

Effect of sediment resuspension on underwater light field in shallow lakes in the middle and lower reaches of the Yangtze River: A case study in Longgan Lake and Taihu Lake

Based on three continuous in situ underwater light field measurement under different wind waves conditions in Longgan Lake, Meiliang Bay of Taihu Lake in July 2003 and littoral zone near TLLER in July 2004, respectively, the effects of sediment resuspension caused by wind waves on PAR diffuse attenuation, absorption coefficients and euphotic depths are analyzed. In Longgan Lake, PAR diffuse attenuation coefficients during small, middle and large wind waves were 1.74, 2.02 and 2.45 m-1, respectively, and the corresponding PAR spectral diffuse attenuations ranged from 0.98 to 2.97, 1.34 to 3.95 and 1.80 to 5.40 m-1, respectively. In Meiliang Bay, PAR diffuse attenuation coefficients were 2.63, 3.72, 4.37 m-1 during small, middle and large wind waves. PAR diffuse attenuation coefficients increased by 41% and 66% from small to middle, large wind waves, respectively. Absorption coefficients integrated over the range of PAR of CDOM, phytoplankton were 0.26, 0.28 m-1; 0.76, 0.49 m-1, respectively during middle and large wind waves. Absorption coefficients integrated over the range of PAR of non-algal particulate matter and total suspended particulate matter increased from 0.94 to 1.73 m-1, and from 1.70 to 2.22 m-1, respectively during middle and large wind waves. Relative contributions of absorption coefficients of non-algal particulate matter to total absorption coefficient integrated over the range of PAR were 44.14%, 65.05%, respectively, during middle and large wind waves. PAR euphotic depths decreased by 0.40, 0.19, 0.20 m from middle to large wind waves in Longganhu Lake, Meliang Bay and littoral zone near TLLER. Significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and total suspended paniculate matter, wind velocity, wave height. Most significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and inorganic suspended paniculate matter but low correlations for chlorophyll a, dissolved organic carbon. Increase of total suspended paniculate matter, especially inorganic suspended paniculate matter caused by wind waves was the dominant factor affecting underwater light field in shallow lakes in the middle and lower reaches of the Yangtze River based on observations at three stations.     

Effect of sediment resuspension on underwater light field in shallow lakes in the middle and lower reaches of the Yangtze River: A case study in Longgan Lake and Taihu Lake

Based on three continuous in situ underwater light field measurement under different wind waves conditions in Longgan Lake, Meiliang Bay of Taihu Lake in July 2003 and littoral zone near TLLER in July 2004, respectively, the effects of sediment resuspension caused by wind waves on PAR diffuse attenuation, absorption coefficients and euphotic depths are analyzed. In Longgan Lake, PAR diffuse attenuation coefficients during small, middle and large wind waves were 1.74, 2.02 and 2.45 m^?1, respectively, and the corresponding PAR spectral diffuse attenuations ranged from 0.98 to 2.97, 1.34 to 3.95 and 1.80 to 5.40 m^?1, respectively. In Meiliang Bay, PAR diffuse attenuation coefficients were 2.63, 3.72, 4.37 m^?1 during small, middle and large wind waves. PAR diffuse attenuation coefficients increased by 41% and 66% from small to middle, large wind waves, respectively. Absorption coefficients integrated over the range of PAR of CDOM, phytoplankton were 0.26, 0.28 m^?1; 0.76, 0.49 m^?1, respectively during middle and large wind waves. Absorption coefficients integrated over the range of PAR of non-algal particulate matter and total suspended particulate matter increased from 0.94 to 1.73 m^?1, and from 1.70 to 2.22 m^?1, respectively during middle and large wind waves. Relative contributions of absorption coefficients of non-algal particulate matter to total absorption coefficient integrated over the range of PAR were 44.14%, 65.05%, respectively, during middle and large wind waves. PAR euphotic depths decreased by 0.40, 0.19, 0.20 m from middle to large wind waves in Longganhu Lake, Meliang Bay and littoral zone near TLLER. Significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and total suspended particulate matter, wind velocity, wave height. Most significant correlations were found between transparency, PAR diffuse attenuation coefficients, euphotic depths and inorganic suspended particulate matter but low correlations for chlorophyll a, dissolved organic carbon. Increase of total suspended particulate matter, especially inorganic suspended particulate matter caused by wind waves was the dominant factor affecting underwater light field in shallow lakes in the middle and lower reaches of the Yangtze River based on observations at three stations.     

Sediment and nutrient transport dynamics in two tributaries of Lake Erie: A numerical model

The objective of this research is to investigate spatial and temporal variation in the transport of phosphate by grain size fractions of suspended sediment in two Lake Erie tributaries. A sediment-phosphate transport model is proposed to evaluate and quantify the kinetic control of dissolved phosphate by fluvial sediment. A first-order assessment of the sediment-phosphate export from Big Otter Creek and Big Creek to Lake Erie is presented. Output from this model was calculated using historical discharge and sediment data collected by Environment Canada in combination with adsorption coefficients derived from laboratory experiments for a range of sediment grain size fractions. Results of these calculations provide a quantitative interpretation of the influence of suspended sediment on phosphate dynamics in tributaries and the potential impact on water quality of receiving waters.     

An evaluation of the role of daphnids in controlling phytoplankton biomass in clear water versus turbid shallow lakes

Phytoplankton and zooplankton were monitored during 2 years in four eutrophic shallow lakes (two turbid and two clear water) from two wetland reserves in Belgium. In each wetland, phytoplankton biomass was significantly higher in the turbid lake than in the clear water lake. Although total macrozooplankton biomass and the contribution of daphnids to total zooplankton biomass was comparable in the clear water and the turbid lakes, the grazing pressure of macrozooplankton on phytoplankton as estimated from zooplankton to phytoplankton biomass ratios was higher in the clear water lakes. Estimated grazing by daphnids in the clear water lakes was always high in spring. In summer, however, daphnid biomass was low or daphnids were even absent during prolonged periods. During those periods phytoplankton was probably controlled by smaller macrozooplankton or by submerged macrophytes through nutrient competition, allelopathic effects or increased sedimentation rates in the macrophyte vegetation.     

苏州平原河网区浅水湖泊叶绿素a与环境因子的相关关系

运用回归统计方法,研究苏州平原河网区60个浅水湖泊水体叶绿素a与水温、pH、Do、CODMn、TN、TP等环境因子的相关性,建立相应的同归方程,同时分析了湖泊水体叶绿素a的时空分布特征.研究表明,平原河网区浅水湖泊水体叶绿素a含量具有一定的时空差异性,冬季叶绿索a平均含量比夏季低,但冬、夏季叶绿素a含量空间分布具有一定相似性,整个区域呈现较明显的东高两低的分布趋势;湖泊水体叶绿素a含量与理化环境因子水温、pH、DO、CODMn呈显著正相关,水温可能是平原河网区浅水湖泊浮游植物生长的限制性因子:叶绿素a与NO2-N呈显著正相关,与NH4 -N无明显负相关,与NO3-N无显著正相关,与TN无显著相关,而叶绿素a的对数与TP的对数呈一定的正相关,与TN/TP的对数呈显著负相关.平原河网区浅水湖泊可能是一定程度的磷限制性湖泊.     

Aquatic vegetation dynamics in two pit lakes related to interannual water level fluctuation

Water regime characteristics have been recognized as critical factors for aquatic vegetation. In this study, we examined changes in aquatic vegetation coverage area in two shallow sub-lakes of Poyang Lake (Bang Lake and Cuoji Lake) during the dry season from 1987 to 2017. The relationships between eight water regime components (annual average water level, annual maximum water level, annual minimum water level, and flooded days at five water levels [11, 13, 15, 17, and 19 m]) and aquatic vegetation coverage area were determined. The most critical water regimes were identified and results demonstrated that aquatic vegetation coverage area in Bang Lake and Cuoji Lake peaked in drier years (2005 and 2009, respectively) with no obvious up or down trend. Water regimes indicating high flow events such as annual maximum water level, flooded days at water level 19 m, and annual average water level were found to be more important for predicting aquatic vegetation. High-flow events appear to be essential for understanding aquatic vegetation dynamics in pit lakes, yet overall the influences of water level fluctuation on aquatic vegetation varied among wetland units of Poyang Lake. This study helps to understand the hydroecological dynamics in connected lakes further and provide a reference for the lake management and protection.     

Differences in stable isotope compositions of freshwater snails from surface sediments of two Polish shallow lakes

The study reports and discusses the differences in δ¹³C and δ¹⁸O values of shells between several species of freshwater snails. Shells were derived from sediment samples collected from depths of 0.5, 1, 2 and 3 m along transects in two shallow eutrophic lakes located in mid-western Poland. Mean δ¹³C values of the shells ranged between −7.5 and −3.8‰ in Lake Jarosławieckie and between −8.1 and −5.2‰ in Lake Rosnowskie Duże, whereas mean δ¹⁸O values ranged between −2.2 and −0.2‰ and between −2.2 and 0.4‰ respectively in the studied lakes. A similar order of species in terms of shell isotope values, from least to most ¹³C and ¹⁸O-depleted was observed in both lakes and seems to indicate constancy of the factors controlling the stable isotope compositions of snail shells. We postulate that the nearly 4‰ difference in the mean carbon stable isotope values between the species was primarily controlled by the amount of metabolic carbon incorporated into the shells and the δ¹³C values of the snail food. Different growth cessation temperatures and microhabitats of the species studied result in temporally and spatially varied DIC δ¹³C values, water δ¹⁸O values and water temperature of shell precipitation, and may thus differentiate the δ¹³C and δ¹⁸O values of shells. The range of δ¹³C and δ¹⁸O values of individual shells from a sediment sample (mean 2.35 and 2.15‰, respectively) is interpreted as reflecting an intraspecific variability of isotope compositions in shells from a population and changes of the ambient conditions during the accumulation of the sediment layer. The species-specificity and intraspecific variability in C and O isotopic compositions of shells allow concluding that in palaeolimnological studies, stable isotope analyses should be performed on a set of mono-specific shells representing mean isotope compositions of the species for the interval studied rather than single shells or multispecific bulk shell material.     

Geologic framework as a factor controlling coastal morphometry and dynamics.Curonian Spit,Lithuania

The geologic framework is an important factor worth consideration when analyzing the development of seacoasts. The different coastal responses to hydrometeorological and anthropogenic factors depend on the composition and amount of original coast-forming sediments. The impact of sediment composition on morphometric parameters is best observed in areas where sand unrepresentative of the adjacent coastal sectors appears on beaches with a relatively uniform lithological composition. These areas are referred to as lithological anomalies. Large amounts of coarse-grained sand, uncharacteristic of the adjacent coastal sectors of the Curonian spit, accumulated in the area of the strait that existed in the Post-Littorina Late Subboreal(3.7-2.5 ka BP) time south of the Juodkrante settlement. Due to accumulation of coarse sand, the beach in this sector is narrow and has a higher slope, and the ridge is lower and with a smaller volume of sand than in the adjacent coastal sectors. The specific sand composition and morphology of this coastal sector are responsible for different coastal dynamics during storms. During extreme storms, beach erosion in this coastal sector is minimal(sometimes even accretion takes place)compared with other sectors where beach erosion is rather substantial. Meanwhile, during periods of relatively calm weather, i.e. times of expected regeneration of the cross profile, this sector stands out for active erosion processes.     

Picoplankton structure in clear and turbid eutrophic shallow lakes: A seasonal study

The relative abundance of the different picoplankton components (eukaryotic picophytoplankton (Peuk), picocyanobacteria (Pcy) and bacterioplankton), and their relationships with the lake conditions were studied in three types of shallow lakes from the Pampa Plain (Argentina) that differ in their optical properties: clear-vegetated, phytoplankton-turbid and inorganic-turbid. All the selected lakes, but one, are characterized by their different alternative steady state (clear-vegetated and phytoplankton-turbid water phases) following the model proposed by Scheffer et al. (1993).Autotrophic and heterotrophic picoplankton abundances were analyzed seasonally in relation to environmental variables. All the lakes presented high concentrations of total nitrogen (TN) (>229 μg L⁻¹), total phosphorus (TP) (>46 μg L⁻¹) and dissolved organic carbon (DOC) (>13.7 mg L⁻¹). Clear-vegetated lakes were characterized by vertical diffuse PAR (photosynthetic active radiation) attenuation coefficient (kd_PAR) lower than 11 m⁻¹, whereas inorganic-turbid lake always showed values higher than 21.1 m⁻¹. The euphotic zone depth (Z_1%) was wider in clear-vegetated lakes (40–140 cm) and thinner in the inorganic-turbid (10–20 cm). The phytoplankton-turbid lakes presented a wide range in the values of these variables (kd_PAR: 5.2–35.8 m⁻¹; Z_1%: 10–90 cm). Phytoplankton chlorophyll-a (Chl-a) strongly differed, ranging from 1.6 to 334.6 μg L⁻¹. Picophytoplankton was mainly represented by phycocianine-rich (PC-rich) Pcy in all cases, dominating over Peuk algae. The total and relative abundances of eukaryotic picophytoplankton, Pcy and bacterioplankton, as well as the size structure of the phytoplankton community differed among the water bodies. In general, clear-vegetated water bodies exhibited similar abiotic characteristics, picophytoplankton/bacterioplankton ratios, and phytoplankton size structure. Contrarily, no clear trend was identified for the group of turbid lakes. The contrasting results obtained for the importance of the picoplankton components in phytoplankton-turbid shallow lakes evidence that the availability of the energetical and nutrient resources cannot be solely considered to predict their relative importance in this type of shallow lake.     

Tracing contributions to hydro‐isotopic differences between two adjacent lakes in the southern Tibetan Plateau

Hydrological processes of lakes in the Tibetan Plateau are an important indicator of climate change. Due to the high elevation, inaccessibility and limited availability of historical observations, water budget evaluation of typical lake basins has been inadequate. In this study, stable isotopes are used to trace the multiple water sources contributing to two adjacent lakes on the north slope of the Himalayas, Gongmo‐tso and Drem‐tso. The two lakes have nearly the same elevation, lake area and climatic condition. However, the isotopic composition of the two lakes presents significant differences. Qualitative observations attribute the differences to hydrological discrepancies: Gongmo‐tso is a through‐flow lake, whereas Drem‐tso is a terminal lake. Quantitative analyses, including water and isotope mass balance modelling, clarify the fluxes and isotopic compositions among the various hydrological elements. The isotopic composition of input water, calculated as the summation of rainfall and upstream runoff, is estimated using the local meteoric water line (LMWL) combined with the time series of lake water isotope values. The isotopic composition of evaporation is calculated with a linear resistance model using local meteorological data. The results show that Drem‐tso is a closed lake in a hydrological steady state with relatively more enriched lake water isotope values resulting mainly from evaporation. In contrast, through‐flow accounts for more than 88% of the water input into Gongmo‐tso. The large amount of upstream runoff with lower isotopic composition and enrichment due to evaporation are the major contributions to the observed lake water isotope values. Isotopic modelling of the two neighbouring lakes is effective for isotopic and hydrological research in this region with limited in situ observations. Copyright © 2013 John Wiley & Sons, Ltd.