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1.
We analyzed cladoceran remains in dated sediment cores from four lakes in Nova Scotia, Canada, to assess the potential effects of climate warming, acidic deposition, and a major fish kill caused by copper sulphate poisoning on assemblage composition and Bosmina size structure. In three of the four lakes, we observed a decline in Daphnia in the early 20th century that might be indicative of limnological changes in response to acidic deposition or increased fish predation. The appearance of the softwater zooplankter Holopedium glacialis in Hirtle Lake ~1995 might be linked to declining aqueous [Ca], a consequence of acidic deposition. No shifts in subfossil Cladocera were identified in this study that could be linked to climate warming. The application of copper sulphate as a fish poison to Trefry Lake (the lake was later re-stocked with trout fry) in 1938 resulted in dramatic and persistent changes in the cladoceran assemblage, where littoral Cladocera declined in relative abundance and small, pelagic Bosmina increased. In addition, we observed a reduction in the mean body size of Bosmina in post-1938 sediments, suggesting that planktivorous fish abundance increased and/or predatory copepods and other invertebrate predators decreased. No recovery of Cladocera to pre-disturbance conditions was observed. Overall, our data suggest that acidic deposition and calcium decline may have had a modest impact on the cladoceran communities in these lakes, but the effects of copper sulphate poisoning on the food web in Trefry Lake were widespread, and still persist over 70?years following this intervention. 相似文献
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《Limnologica》2021
We measured lipid biomarkers (n-alkanes [n-ALKs] and n-alkanoic acids [n-FAs]) and other components of organic matter (total organic carbon [TOC] and total nitrogen [TN]) in a sediment core from Lake Issyk-Kul, Central Asia, to infer environmental changes in and around the lake during the last ∼300 years. Stratigraphic shifts in lipid biomarkers, TOC and TN, indicate three distinct environmental stages in the lake over the past three centuries: (1) Stage I (1670s–1790s, 51–36 cm sediment depth) corresponds to a period of stable hydrology in the lake, reflected by relatively constant concentrations of n-ALKs and n-FAs and values of related indexes. The interval was a period of relatively low trophic state. Natural factors were the main controls on environmental changes in and around the lake. (2) Stage II (1800s–1970s, 35–15 cm sediment depth) was a period when human activities began to exert influence on the environment in and around the lake. Enhanced agricultural exploitation and greater regional rainfall resulted in delivery to the lake of more land-derived lipids. Logging activity around the lake altered the vegetation, as revealed by shifts in C27/C33 ratios and the average chain length (ACL27−33). A significant decline in lake level caused by excessive water consumption impacted aquatic macrophytes, as revealed by a reduction in macrophyte indicators. Lower nutrient concentrations were inferred for this period. (3) Stage III (1980s–present, 14–0 cm sediment depth) corresponds to a period of accelerating eutrophication. Before year 2000, lake level declined steadily as a result of low rainfall (drought) and high evaporation, which exerted a strong influence on the lake condition. In addition, anthropogenic activities contributed to lake eutrophication. After 2000, the lake experienced a dramatic increase in trophic state, characterized by high algal productivity, as indicated by greater TN, short-chain n-ALKs and short-chain n-FAs. The change was probably caused by flourishing tourism around the lake. In summary, environmental changes in and around Lake Issyk-Kul during the past ∼300 years were originally driven largely by natural factors such as shifts in regional precipitation amount. Human activities (e.g. logging, agriculture, water extraction, and more recently, tourism) took on increasingly important roles during the last two centuries, affecting watershed vegetation, the lake primary producer community and lake trophic status. Changes recorded in the lake sediments over the last ∼300 years are in good agreement with historical records. 相似文献
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从1950s开始, 云南地区部分湖泊受到了水文调控(如筑坝)和鱼类引入等流域开发活动的直接影响, 湖泊水环境与生态系统结构已出现明显改变. 开展浮游动物群落的长期生态响应评价有助于认识气候波动和人为胁迫的影响模式. 本文选取云龙天池进行了沉积物记录分析, 在重建过去100年环境变化历史的基础上开展了枝角类群落的多指标分析(物种组成、个体大小、生物量等), 进一步结合多变量分析识别了枝角类群落构建的关键驱动因子. 结果显示, 云龙天池在过去100年间经历了明显的水位波动, 约1962年以前水位较低, 1950s起的水文调控(筑坝)导致湖泊水位波动上升, 2006年以来略有下降. 枝角类群落随水位波动呈现由底栖种向浮游种占优转变的模式, 并在2006年以来底栖种略有增加. 总体上, 低水位时期底栖枝角类占优, 高水位时期浮游枝角类占优. 水体营养水平也对枝角类群落产生了较为显著的影响. 在沉积物总氮和有机质通量上升时, 长额象鼻溞(Bosmina longirostris)相对丰度和枝角类浓度都明显上升. 枝角类象鼻溞个体大小表明, 1969年鱼类引入后象鼻溞的壳长、壳刺长度、触角长度显著减小, 反映了鱼类捕食压力上升的影响. 本研究进一步揭示了水文调控和鱼类引入对湖泊环境和生物群落结构的驱动影响. 其中, 1960s以前云龙天池处于自然波动的状态, 湖泊环境和枝角类群落变化主要受气候(如降水、气温)的影响; 1960s以来人类活动的影响强度已经掩盖了气候变化的信号, 成为影响湖泊生态演化轨迹的主要因素. 为了开展有效的湖泊保护与生态治理, 有必要综合评估水文调控、鱼类引入等人类活动对湖泊生态健康的长期影响. 相似文献
4.
Characterisation of hydroclimatological trends and variability in the Lake Naivasha basin,Kenya 
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下载免费PDF全文 Vincent Omondi Odongo Christiaan van der Tol Pieter R. van Oel Frank M. Meins Robert Becht Japheth Onyando Zhongbo Su 《水文研究》2015,29(15):3276-3293
Recent hydro‐climatological trends and variability characteristics were investigated for the Lake Naivasha basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using a Bayesian change point analysis and modified Mann–Kendall tests, time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes, were analysed for the period 1960–2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35 × 106 m3 year?1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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6.
Inter‐annual variability in the effects of riparian woodland on micro‐climate,energy exchanges and water temperature of an upland Scottish stream 下载免费PDF全文
下载免费PDF全文 Grace Garner Iain A. Malcolm Jonathan P. Sadler Colin P. Millar David M. Hannah 《水文研究》2015,29(6):1080-1095
The influence of riparian woodland on stream temperature, micro‐climate and energy exchange was investigated over seven calendar years. Continuous data were collected from two reaches of the Girnock Burn (a tributary of the Aberdeenshire Dee, Scotland) with contrasting land use characteristics: (1) semi‐natural riparian forest and (2) open moorland. In the moorland reach, wind speed and energy fluxes (especially net radiation, latent heat and sensible heat) varied considerably between years because of variable riparian micro‐climate coupled strongly to prevailing meteorological conditions. In the forested reach, riparian vegetation sheltered the stream from meteorological conditions that produced a moderated micro‐climate and thus energy exchange conditions, which were relatively stable between years. Net energy gains (losses) in spring and summer (autumn and winter) were typically greater in the moorland than the forest. However, when particularly high latent heat loss or low net radiation gain occurred in the moorland, net energy gain (loss) was less than that in the forest during the spring and summer (autumn and winter) months. Spring and summer water temperature was typically cooler in the forest and characterised by less inter‐annual variability due to reduced, more inter‐annually stable energy gain in the forested reach. The effect of riparian vegetation on autumn and winter water temperature dynamics was less clear because of the confounding effects of reach‐scale inflows of thermally stable groundwater in the moorland reach, which strongly influenced the local heat budget. These findings provide new insights as to the hydrometeorological conditions under which semi‐natural riparian forest may be effective in mitigating river thermal variability, notably peaks, under present and future climates. © 2014 The Authors. Hydrological Processes published by John Wiley & Sons Ltd. 相似文献
7.
Griselda Chaparro María Cristina Marinone Ruben J. Lombardo María Romina Schiaffino Alice de Souza Guimarães Inés O’Farrell 《Limnologica》2011,41(4):371-381
We examined the zooplankton abundance and composition of Laguna Grande, a floodplain wetland of the Lower Paraná Basin (Argentina), during an extraordinary drought–flood cycle that affected both the environment and the biological conditions of the lake. Low waters were characterised by remarkably high conductivities and pH values, and high phytoplankton and bacterioplankton abundances with cyanobacterial blooms, while high waters showed opposite features. In relation to zooplankton, the mean abundances of all the taxonomic groups (rotifers, cladocerans, copepods, ciliates, and heterotrophic nanoflagellates) were slightly higher at low waters. Major changes were observed in the specific composition of metazooplankton: the euryhaline species assemblage that dominated in the dry warm period was replaced by several oligohaline littoral and planktonic species characteristic of the Paraná River Basin, when the water level rose. Mean species richness values at high waters doubled those of low waters and were directly correlated to water depth. Most of the rotifers of the genus Brachionus and the cladoceran Moina micrura switched from parthenogenetic to sexual reproduction during low waters, as a response to a harsh environment and crowding. We suggest that the main changes in the environmental conditions in this eutrophic floodplain lake are driven by the hydrology, which regulates the zooplankton succession. The herein described shifts in the zooplankton structure and dynamics of Laguna Grande over an extraordinary drought–flood cycle contribute to the understanding of the processes that might occur under the scenarios predicted by climate change models. 相似文献
8.
Mediterranean lake–wetland systems are threatened by climate change and intensive human impacts. Individual lake responses to these threats are poorly known but urgently required to steer preservation strategies. The dramatic water-level fall (~8 m since 1987) of Lake Megali Prespa endangers this global biodiversity hotspot and the wider catchment’s water resources. Annual lake fluctuations are found to be strongly related to wet-season (Oct.–Apr.) precipitation variability, which is linked to the North Atlantic Oscillation. The lake primarily adjusts to sustained inflow changes through amending surface evaporation. Cumulative water abstraction since 1951 (~19 × 106 m3/year: ~0.006% of lake volume) explains ~70% of the long-term decrease in surface evaporation; climate variability explains the remainder. Persistent low lake levels after 1995 are caused by water abstraction. Compared to 1952/53–1977/78, the period 1978/79–2003/04 experienced significant decreases in wet-season precipitation, snowfall and discharge; the number of very dry years increased.
EDITOR A. Castellarin; ASSOCIATE EDITOR D. Gerten 相似文献
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《Limnologica》2020
The freshwater microalgal species, Gonyostomum semen, has increased in abundance and distribution in boreal lakes during the past few decades, concerning ecologists and water managers. Due to its rapid spread, G. semen has often been referred to as an invasive species, although it was first described in the 1800s. We hypothesized that G. semen is not an invasive species in Norwegian lakes, and that the increasing success is due to beneficial changes in environmental conditions for this species during the past century. We tested these hypotheses by performing a paleolimnological study of a Norwegian Lake, Skjeklesjøen, with known mass occurrence of G. semen. A specific G. semen pigment biomarker, heteroxanthin, was used to detect this species in layers of a sediment core with known age determinations. Environmental factors in both lake and catchment were further investigated and the relationships with the amounts of G. semen was tested. Our results suggested that G. semen was in fact not an invasive species in this lake the past decades. Several factors were identified as plausible drivers for G. semen in this boreal lake. Between 1874–2016, the increasing levels of G. semen in Lake Skjeklesjøen was most closely correlated with Carbon (C), lake color (measured as absorbance of sediment extracts), Nitrogen (N) and spring temperature. Our results suggest that the rapid increase in G. semen population in this boreal lake over the past 70 years was probably due to a combination of climate change and local anthropogenic activities in the catchment, causing increased browning and increased inputs of organic matter and nutrients. 相似文献
10.
The aim of this study was to present quantitative data on the population dynamics of Chlorella-bearing ciliates (Stentor, Ophrydium) compared to the total zooplankton community in a deep, oligotrophic North Patagonian lake. Mixotrophic and heterotrophic ciliates, rotifers and microcrustaceans, and important ecological parameters were sampled during a 1-year study. The results showed a low biodiversity with only a few dominant species in every zooplankton group. Three mixotrophic ciliates - Stentor araucanus, S. amethystinus and Ophrydium naumanni - were found. They peaked in summer and autumn with maximum values of 152-313 Ind L−1 (Stentor) and 1880 Ind L−1 (Ophrydium). Their contribution to the total ciliate abundance was 16±17% (annual average). Both Stentor species displayed a distinct vertical zonation during the stratification period with peak depth between 10 and 15 m (metalimnion). The contribution to total zooplankton biomass was 59.4% on an annual average (Stentor: 41%, O. naumanni: 18.4%) and 83% during the stratification period. Both abundance and biomass of mixotrophic ciliates correlated strongly with temperature and to a lesser degree with copepods, rotifers and small cladocerans. According to this study mixotrophic ciliates were by far the dominant zooplankton group in Lake Caburgua. We report for the first time the importance of O. naumanni in a deep Chilean North Patagonian lake. 相似文献
11.
《Continental Shelf Research》2008,28(18):2601-2613
From July 2001 to May 2005, seawater samples were collected once a week at a fixed station in Lisbon bay (38°41′N, 09°24′W) in order to describe the ecological dynamics of the coccolithophore community. The seasonal and interannual distribution patterns of the different species and their relationships with environmental parameters are addressed. The present work aimed to identify potential proxies for different local water bodies and environmental conditions. Throughout the period of study, the upwelling events were weak and progressively more persistent. High sea surface temperatures (SST) were observed earlier in the year; summers and winters were gradually warmer and colder, respectively. Salinity variations reflected the different weather conditions as they are strongly influenced by rainfall and thus by the Tagus river flow. The extended periods of weak upwelling and the overall increase in SST resulted in the development of phytoplankton populations as measured by chlorophyll a. However, the persistence of the upwelling, and thus shorter convergence periods, favoured other phytoplankton groups than coccolithophore populations as these decreased towards the end of the sampling period. The annual structure of the coccolithophore assemblage showed a pronounced and recurrent seasonal variability, mainly related with the intensity and persistence of upwelling. The highest cell densities were recorded from spring to autumn. An overall preference by most species for mature upwelled waters and low turbulent conditions was observed associated with high temperatures and salinities, although the species develop in different windows with mismatching maxima. The coccolithophores observed were capable of withstanding coastal processes such as turbulence and were well adapted to an environment rich in nutrients provided by both continental runoff and upwelling.The consistency of the results enabled local oceanographic tracers to be defined. Emiliania huxleyi and Gephyrocapsa species can be used as proxies of surface productivity waters during spring and summer while Coccolithus pelagicus indicates the presence of upwelling fronts. Calcidiscus leptoporus is a tracer of the convergence of subtropical oceanic waters onto the shelf, during winter while Coronosphaera mediterranea, Syracosphaera pulchra, Helicosphaera carteri and Rhabdosphaera clavigera revealed the presence of those waters during the short period that characterized the transition from upwelling to downwelling seasons. 相似文献
12.
Using lumped conceptual rainfall-runoff models to simulate daily isotope variability with fractionation in a nested mesoscale catchment 总被引：1，自引：0，他引：1
Christian Birkel Doerthe Tetzlaff Sarah M. Dunn Chris Soulsby 《Advances in water resources》2011,34(3):383-394
This paper presents 19 months of stable isotope (δ2H and δ18O) data to enhance understanding of water and solute transport at two spatial scales (2.3 km2 and 122 km2) in the agricultural Lunan catchment, Scotland. Daily precipitation and stream isotope data, weekly lake and spring isotope data and monthly groundwater isotope data revealed important insights into flow pathways and mixing of water at both scales. In particular, a deeper groundwater flow path significantly contributes to total streamflow (25-50%). Upstream lake isotope dynamics, susceptible to evaporative fractionation, also appeared to have an important influence on the downstream isotope composition. This unique tracer data set facilitated the conceptualization of a lumped catchment-scale flow-tracer model. The incorporation of hydrological, mixing and fractionation processes based on these data improved simulations of the stream δ2H isotope response at the catchment outlet from 0.37 to 0.56 for the Nash-Sutcliffe statistic. The stable isotope data successfully aided model conceptualization and calibration in the quest for a simple water and solute transport model with improved representation of process dynamics. 相似文献
13.
在全球变化的背景下,厘清湖泊生态系统对气候环境以及人类活动的响应机制对制定社会的适应政策非常重要.目前的研究手段如现场观测和围隔实验等可以很好地揭示湖泊生态系统在有观测记录以来的演替和变化过程,但是不能提供历史时期湖泊生态系统的变化及其对气候环境变化和人类活动的响应.古湖沼学可以为探讨湖泊生态系统的长期变化及其对气候环境变化的响应提供重要信息.本文以青藏高原中部无鱼湖泊达则错为研究对象,利用沉积物岩芯西藏拟溞（Daphnia tibetana）残体丰度和总烯酮含量重建该区过去1000年的浮游生物记录;利用总氮、总磷以及总有机碳含量重建过去1000年湖泊营养盐以及有机质变化记录;结合烯酮不饱和度重建的古温度记录,探讨达则错过去1000年生态系统变化及其对气候环境演变的响应机制.研究发现达则错湖泊生态系统尤其是生产力在自然状况和人类活动影响下存在显著变化.在自然状况下,较高的湖泊初级和次级生产力发生在温度较低和湖水营养盐浓度较高时;而在过去150年,达则错湖泊环境受到人类活动影响显著,湖泊生产力发生相应变化,较高的湖泊生产力发生在温度较高时期,其主要受由人类活动带来的营养盐元素浓度控制.研究结果表明达则错湖泊生态系统在人类活动影响下发生了显著的改变. 相似文献
14.
《Limnologica》2017
This study tested the hypothesis that the flood pulse affects the diet composition and the niche breadth of Moenkhausia forestii, a small characid fish inhabiting the littoral zone of lakes. To this end, we compared the diet composition (at the population and individual levels) between hydrological periods (high and low water phases) in a floodplain lake of the Upper Paraná River. PERMANOVA revealed differences in the diet between periods (pseudoF1,38 = 8.5; p < 0.001), with predominant consumption of chironomid larvae and Ephemeroptera (aquatic resources) in the low-water period and an increase in the contribution of terrestrial resources (Hymenoptera, Coleoptera, and Orthoptera) during the high-water period. Based on the PERMDISP results, inter-individual variability in M. forestii diet also differed between periods (F1,38 = 5.80; p = 0.02), with higher values during the high-water period resulting in a dietary niche expansion. During the low-water period, we observed the dominance of chironomid larvae in the diets of most individuals, resulting in lower inter-individual variability and thus narrower niche breadth. The diet of M. forestii was affected by the flood pulse at both the population and individual levels. The most important difference was found in the origin of food items; during the low-water period, the diet consisted mainly of aquatic resources, and during the high-water period, there was a large contribution of terrestrial resources. This variation is related to the increased availability of allochthonous resources in the high period, when terrestrial areas are flooded by the overflow of the river, thereby increasing the input of resources into the aquatic environment. The increased availability of food resources during this period allowed the expansion of the trophic niche of M. forestii, accompanied by the highest richness (19 items) and the highest evenness of food items. Our findings demonstrated that the flood pulse affected the composition of the M. forestii diet at both the population and individual levels. These results support the importance of the flood pulse, which connects aquatic and terrestrial ecosystems, in providing food resources for fish. 相似文献
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Integrated dynamic water and chloride balance models with a catchment‐scale hydrological model (PRMS) are used to investigate the response of a terminal tropical lake, Lake Abiyata, to climate variability and water use practices in its catchment. The hydrological model is used to investigate the response of the catchment to different climate and land‐use change scenarios that are incorporated into the lake model. Lake depth–area–volume relationships were established from lake bathymetries. Missing data in the time series were filled using statistical regression techniques. Based on mean monthly data, the lake water balance model produced a good agreement between the simulated and observed levels of Lake Abiyata for the period 1968–83. From 1984 onwards the simulated lake level is overestimated with respect to the observed one, while the chloride concentration is largely underestimated. This discrepancy is attributed to human use of water from the influent rivers or directly from the lake. The simulated lake level and chloride concentration are in better agreement with observed values (r2 = 0·96) when human water use for irrigation and salt exploitation are included in the model. A comparison of the simulation with and without human consumption indicates that climate variability controls the interannual fluctuations and that the human water use affects the equilibrium of the system by strongly reducing the lake level. Sensitivity analysis based on a mean climatic year showed that, after prolonged mean climatic conditions, Lake Abiyata reacts more rapidly to an abrupt shift to wetter conditions than to dry conditions. This study shows the significant sensitivity of the level and salinity of the terminal Lake Abiyata to small changes in climate or land use, making it a very good ‘recorder’ of environmental changes that may occur in the catchment at different time scales. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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ABSTRACTWater temperature dynamics in a reservoir are affected by its bathymetry, climatic conditions and hydrological processes. Miyun Reservoir in China is a large and deep reservoir that experienced a large water level decline in 1999–2004 due to low rainfall and relatively high water supply to Beijing. To study changes of stratification characteristics in Miyun Reservoir from 1998 to 2011, the one-dimensional year-round lake model MINLAKE2010 was modified by adding a new selective withdraw module and a reservoir hydrological model. Simulation results under three scenarios demonstrated that the new MINLAKE2012 model accurately predicted daily water levels and temperature dynamics during the water level fluctuation period. The water level decline led to 7.6 and 3.8°C increases in the maximum and mean bottom temperatures and about 29 days reduction in the stratification days. These simulation results provide an insight into the thermal evolution of Miyun Reservoir during the planned future water filling process.
Editor D. Koutsoyiannis Associate editor M. Acreman 相似文献
17.
Projecting climate change impacts on stream flow regimes with tracer‐aided runoff models ‐ preliminary assessment of heterogeneity at the mesoscale 下载免费PDF全文
下载免费PDF全文 The northern mid‐high latitudes form a region that is sensitive to climate change, and many areas already have seen – or are projected to see – marked changes in hydroclimatic drivers on catchment hydrological function. In this paper, we use tracer‐aided conceptual runoff models to investigate such impacts in a mesoscale (749 km2) catchment in northern Scotland. The catchment encompasses both sub‐arctic montane sub‐catchments with high precipitation and significant snow influence and drier, warmer lowland sub‐catchments. We used downscaled HadCM3 General Circulation Model outputs through the UKCP09 stochastic weather generator to project the future climate. This was based on synthetic precipitation and temperature time series generated from three climate change scenarios under low, medium and high greenhouse gas emissions. Within an uncertainty framework, we examined the impact of climate change at the monthly, seasonal and annual scales and projected impacts on flow regimes in upland and lowland sub‐catchments using hydrological models with appropriate process conceptualization for each landscape unit. The results reveal landscape‐specific sensitivity to climate change. In the uplands, higher temperatures result in diminishing snow influence which increases winter flows, with a concomitant decline in spring flows as melt reduces. In the lowlands, increases in air temperatures and re‐distribution of precipitation towards autumn and winter lead to strongly reduced summer flows despite increasing annual precipitation. The integration at the catchment outlet moderates these seasonal extremes expected in the headwaters. This highlights the intimate connection between hydrological dynamics and catchment characteristics which reflect landscape evolution. It also indicates that spatial variability of changes in climatic forcing combined with differential landscape sensitivity in large heterogeneous catchments can lead to higher resilience of the integrated runoff response. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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2022年我国长江流域经历了长期的高温干旱,对湖泊水生态环境和湖内藻情态势产生了深远影响。但目前关于干旱环境下湖泊水华的响应特征研究较少。以太湖为例,基于2005—2022年湖体营养盐与叶绿素a浓度的长期监测数据,结合卫星遥感影像反演的蓝藻水华面积变化,探讨了2022年高温干旱对太湖蓝藻的影响特征及驱动机制。结果表明,2022年蓝藻水华高发季节(5—9月),太湖蓝藻水华的平均面积和最大面积均明显下降,其中5月的水华面积仅为近5年同期平均面积的20%;水样采集分析获得的水体叶绿素a浓度和微囊藻生物量在春季也明显下降。营养盐方面,2022年太湖的总氮和总磷均值分别为1.41和0.084 mg/L,较近5年均值分别下降了30.6%和27.3%,均为2005年以来的最低值。氮磷浓度空间分布的克里金插值显示,除西北湖区(竺山湾)受河流入湖影响外,大部分湖区的溶解态氮磷也都处于较低状态,冬季溶解性总磷浓度小于0.02 mg/L的水域面积占全湖面积的79%。随机森林分析表明,总磷、水温和风速是影响春季微囊藻和藻类生物量的关键因子。冬季湖体磷水平低,加上春季外源负荷较少,致使2022年春季太湖大范围湖... 相似文献
19.
The tropical Indian Ocean(TIO) displays a uniform basin-wide warming or cooling in sea surface temperature(SST) during the decay year of El Niδo-Southern Oscillation(ENSO) events. This warming or cooling is called the tropical Indian Ocean Basin Mode(IOBM). Recent studies showed that the IOBM dominates the interannual variability of the TIO SST and has impacts on the tropical climate from the TIO to the western Pacific. Analyses on a 148-year-long monthly coral δ 18 O record from the Seychelles Islands demonstrate that the Seychelles coral δ 18 O not only is associated with the local SST but also indicates the interannul variability of the basin-wide SST in the TIO. Moreover, the Seychelles coral δ 18 O shows a dominant period of 3–7 years that well represents the variability of the IOBM, which in return is modulated by the inter-decadal climate variability. The correlation between the Seychelles coral δ 18 O and the SST reveals that the coral δ 18 O lags the SST in the eastern equatorial Pacific by five months and reaches its peak in the spring following the mature phase of ENSO. The spatial pattern of the first EOF mode indicates that the Seychelles Islands are located at the crucial place of the IOBM. Thus, the Seychelles coral δ 18 O could be used as a proxy of the IOBM to investigate the ENSO teleconnection on the TIO in terms of long-time climate variability. 相似文献
20.
《Limnologica》2021
Ciliated protozoans are important constituents of periphytic communities in aquatic habitats, including river-floodplain ecosystems. As the knowledge about the diversity and ecological importance of periphytic ciliates in floodplain habitats is still limited, the main objectives of this study were to analyse the temporal variations in the community structure and functional role and reveal the main environmental factors controlling community dynamics. The study was conducted in one of the Danube's largest conserved floodplains – Kopački Rit in Croatia. In situ research included two experimental series in a lake, the first from spring till winter and the second from summer till winter. Samples were collected biweekly using glass slides as artificial substrates for periphyton development. During the study, two hydrological (low-water and high-water) periods interchanged. High-water periods were characterized by greater water transparency and nutrient concentrations, while electrical conductivity, chlorophyll a concentration, total suspended solids and particulate organic matter in water were higher during low-water periods. Furthermore, hydrological changes greatly affected the periphytic ciliate communities and the highest abundances were registered during low water levels. We identified a total of 133 ciliate taxa, among which the peritrichs, sessile filter feeders, were the dominant representatives in the periphyton, with the highest densities registered in the absence of floods. During extremely high water levels, the composition of the ciliate community in periphyton changed, with mobile ciliates, predators and filter feeders, becoming dominant. This study indicates that the main food source for periphytic ciliates in a floodplain lake are bacteria and algae, confirming the important role of these microorganisms in the lake food web, by making the carbon fixed in bacteria and algae available for the organisms of higher trophic levels. Additionally, periphytic ciliates have a considerable effect on planktonic organisms in the lake, thus connecting benthic and pelagic food webs, especially during low-water periods. 相似文献