西安城市河流浮游植物群落结构及其与环境因子的关系

为探究西安市城市河流浮游植物群落结构特征及其与环境因子的关系,分别于2020年10月和2021年6月对灞河、浐河、沣河及黑河共计24个采样点进行了浮游植物群落组成、细胞密度和生物量的调查研究,并利用冗余分析(RDA)研究环境因子对浮游植物群落结构的影响。调查结果显示,枯水期共鉴定出浮游植物6门115种,主要包括蓝藻门(11.30%)、硅藻门(54.78%)及绿藻门(26.96%),浮游植物细胞密度均值为(3.36±3.50)×106 cells/L,生物量均值为(1.79±3.59) mg/L。丰水期共鉴定出浮游植物7门168种,主要包括蓝藻门(7.74%)、硅藻门(51.79%)及绿藻门(29.76%),浮游植物细胞密度均值为(9.17±9.73)×10⁶ cells/L,生物量均值为(6.54±11.57) mg/L。与枯水期相比,丰水期在物种数量、细胞密度和生物量都大于枯水期。聚类分析结果表明,西安城市河流大部分采样点之间浮游植物群落结构及水环境状况具有相似性,而人类活动可能是导致其余点位具有空间差异性的主要原因。冗余分析(RNA)结果表明影响西安市城市河流...     

松花江哈尔滨段浮游植物群落格局及其与环境因子的相关性

松花江是黑龙江在我国境内的最大支流,流经吉林、黑龙江两省。松花江哈尔滨段是哈尔滨市工农业生产与生活用水的重要水资源,近年来由于人类活动的频繁影响,水体质量有所下降。鉴于此,于2018年春、夏、秋三季(4月、8月和10月),在松花江哈尔滨段设置14个采样点,对电导率、总氮和总磷等理化指标进行测定,同时对其浮游植物群落结构及环境因子相关性进行研究。利用群落相似性分析(ANOSIM)探讨浮游植物群落时空分布差异;通过SIMPER分析筛选出影响群落时空格局的关键物种。基于优势种和10项理化指标的冗余分析(RDA)揭示了浮游植物群落生态分布特征并对关键影响因子进行识别。研究结果表明,调查期间共鉴定浮游植物136种,其中优势种15种,群落结构主要以硅藻门和绿藻门的物种构成。松花江哈尔滨段浮游植物群落结构与过去10余年间相比较为稳定。ANOSIM和SIMPER分析表明,季节变化和人为活动干扰对浮游植物群落时空格局具有一定驱动作用,蓝藻门物种的空间分布活动干扰影响明显。RDA分析表明,浮游植物分布特征与水环境时空异质性关系密切,驱动松花江哈尔滨段浮游植物群落时空分布的主要水环境因子为电导率、总磷、浊度和pH。     

鹤地水库浮游植物群落的结构与动态

鹤地水库位于雷州半岛北部(21°42'～22°22'N,109°54'～110°25'E),是一座中营养化的大型水库.为了研究其浮游植物群落的结构与变化特点,在水库设置5个采样点,并于2003年2、7、9、12月对其采样.鹤地水库浮游植物生物量变化为O.156～2.548 mg L~(-1),主要由蓝藻和硅藻组成.5个采样点的浮游植物生物量具有明显的季节变化,且变化趋势相同,即丰水期的生物量高于枯水期,主要是由于丰水期水温较高以及入库河水带入的营养盐.5个采样点的浮游植物生物量从主要入库河流至大坝区呈下降趋势,与磷浓度的降低直接相关.浮游植物优势种主要以热带代表性种类为主,且有明显的季节变化,枯水期主要为硅藻的根管藻(Rhizosolenia sp.)、小环藻(Cyclotella sp.)、颗粒直链藻(Melosira granulata)以及模糊直链藻(Melosira ambigua)等.丰水期为蓝藻的拟柱孢藻(Cylindrospermopsis raciborskii)、湖泊假鱼腥藻(Pseudanabaena limnetica)等,浮游植物优势种类的变化主要受磷浓度的影响.浮游植物前8个优势种的生物量占浮游植物群落生物量的850%～92%,显著低于温带地区浮游植物群落结构稳定的湖泊.     

安徽沱湖夏季浮游植物群落结构特征与环境因子关系

为了揭示沱湖浮游植物群落结构特征及其与水环境因子的关系,于2016年7月(夏季),对沱湖流域上游至下游11个采样点浮游植物种类组成、细胞丰度、生物量等进行调查研究。结果显示,沱湖共有浮游植物96种(含变种),隶属8门48属,其中绿藻门(Chlorophyta)和硅藻门(Bacillariophyta)种类最多,绿藻门有23属39种,占总种数的40.63%,硅藻门有7属20种,占总种数的20.83%;其次为裸藻门(Euglenophyta),有5属17种,占总种数的17.71%,蓝藻门(Cyanophyta) 8属14种,占14.58%;甲藻门(Pyrrophyta) 2属2种,隐藻门(Cryptophyta) 1属2种,各占总种数的2.08%,黄藻门(Xanthophyta)与金藻门(Chrysophyta)均有1属1种,均占总种数的1.04%。绿藻和硅藻类物种在沱湖浮游植物群落结构中处于优势地位,沱湖夏季浮游植物种类组成表现为绿藻-硅藻型。沱湖夏季浮游植物细胞丰度与生物量从上游到下游呈逐渐增加趋势,细胞丰度与生物量平均值分别为4.022×106cells/L与3.046 mg/L,蓝藻门和绿藻门类群为沱湖浮游植物细胞丰度主体,硅藻门和裸藻门类群为沱湖浮游植物生物量的主体;上游浮游植物多样性指数与均匀度指数均略高于下游采样点,沱湖水质呈β中污型-无污染型,上游水质优于下游水质。浮游植物群落结构与水环境因子的典型对应分析(CCA)结果表明,电导率、透明度、水深及pH值等环境因子与沱湖夏季浮游植物群落结构有较强的相关性。     

抚仙湖夏季热分层时期浮游植物空间分布特征

抚仙湖是云贵高原典型的深水贫营养湖泊。为了研究其浮游植物群落的空间分布特征和影响因子,于2014年7月在抚仙湖设置了3个采样点进行分层采样。结果表明:共检出浮游植物37种,隶属于6门18科27属;全湖浮游植物的平均生物量为0.41mg·L~(-1),其中绿藻门的比例超过70%;绿藻门中的转板藻(Mougeotia sp.)是夏季抚仙湖浮游植物中的绝对优势种,平均生物量为0.18 mg·L~(-1);在水平分布上,浮游植物生物量在北部湖区大于中部和南部;在垂直分布上,浮游植物主要分布在湖体的表层和温跃层,最大值出现在水面以下10 m,深水层的生物量显著降低。线性相关性分析表明,表层和温跃层浮游植物生物量主要受水深变化引起的一系列环境变量如水温、光照等变化的影响,而影响深水层浮游植物生物量的主要因子是溶解氧和pH。冗余分析显示,环境变量较好地解释了浮游植物群落组成的空间变化,水温、电导率和pH是最关键的几个影响因子,氮、磷营养盐的作用并不显著。本研究对探究亚热带高原深水湖泊浮游植物群落的分布特征具有积极意义。     

太湖金墅湾水源地浮游植物群落结构及其与环境因子的关系

利用典范相关分析方法(CCA),对太湖金墅湾水源地水体浮游植物群落结构及其与环境因子之间的关系进行了研究.共鉴定浮游植物7门58属,群落组成以蓝藻、硅藻和绿藻为主;夏季浮游植物的种类和数量均较多,平均密度为250×104ind.L-1,略高于春季(238×104ind.L-1).春、夏2季浮游植物群落结构差异较大,春季以蓝藻为最优势门类、鱼腥藻为最优势类群;夏季以绿藻为最优势门类,无最优势类群,但平裂面藻和栅藻在数量上较占优势.除受季节温度影响外,春季影响浮游植物分布的主要环境因子依次为铵态氮、总磷、总氮和磷酸盐,而总氮、铵态氮、磷酸盐、悬浮物、高等水生植物、总磷和透明度对夏季浮游植物分布的影响较大.     

仙女湖及入湖河流浮游植物功能类群与环境因子的相互关系

文章分析了仙女湖及入湖河流浮游植物群落结构和功能类群的时空分布特征, 探讨了影响其时空分布规律的关键环境因子。调查期间共鉴定表层水体中浮游植物82种(属), 包括蓝藻15种(属), 绿藻33种(属), 硅藻23种(属), 甲藻3种(属), 裸藻5种(属), 隐藻2种(属), 金藻1种(属)。各季节平均密度和生物量分别在7.95×106—2.19×109 cells/L和10.52—792.91 mg/L变化。群落功能类群的结果表明, 冬、春河流生境中具硅质结构的无鞭毛个体浮游植物(硅藻门)占据主导地位(Ⅵ功能群), 而湖区生境中具鞭毛、中等到大型的单细胞或群体浮游植物(如隐藻和甲藻)具有明显优势(Ⅴ功能群); 而夏秋季节不同生境中虽然Ⅵ型浮游植物数量仍然相对较高, 但是具伪空胞的、较大表面积/体积比的丝状个体浮游植物(Ⅲ型)以及具胶质鞘、小的表面积/体积比的群体类的浮游植物(如蓝藻, Ⅶ功能群)在某些河流和湖泊生境中的比重有显著增长。功能类群与环境因子的相关分析表明: 冬、春季Ⅴ与Ⅵ功能群浮游植物生物量主要受到总氮和总磷水平影响; 而夏、秋季节Ⅲ与Ⅶ功能群浮游植物受到水温、浊度、总氮和总磷水平的多重影响。     

云南中部和南部湖泊夏季浮游植物空间分布及其影响因子

高原湖泊是云南地区重要的淡水资源储库,目前面临富营养化、重金属污染等环境问题,持续的流域开发明显改变水生生物群落的结构特征与分布模式。浮游植物作为初级生产者,是湖泊食物网的重要基础。本研究以云南中部(8个)和南部(5个)的13个湖泊为对象,于2016年夏季进行浮游植物采样,结合水质数据和湖泊基础资料,对区域尺度上浮游植物的空间分布特征及其影响因子进行识别。结果表明:13个湖泊中浮游植物共有7门72属161种;浮游植物群落结构除抚仙湖、差黑海和石林长湖外,其他湖泊均以蓝藻门为主; Jaccard相异性指数显示,滇池浮游植物群落组成与差黑海、长湖、月湖、阳宗海、长桥海和杞麓湖差异性最大(0.98),长桥海和大屯海浮游植物群落组成最相似(0.19); ANOSIM分析显示,云南中部和南部湖泊浮游植物群落结构差异性显著(R=0.27,P0.05);南部湖泊生物量总体高于中部湖泊(南部和北部平均生物量分别为105.87和29.27 mg·L-1; t检验:P0.05); Pearson相关分析表明,浮游植物生物量与温度、总磷(TP)、总氮(TN)、砷和电导率呈显著正相关,与海拔和透明度显著负相关(P 0.05,n=13)。典型对应分析(CCA)结果显示,总磷、氮磷比、锰、钙和空间变量(PCNM1)是影响云南中部和南部湖泊夏季浮游植物空间分布的主要因子;方差分解显示,营养水平(TN、TP)、空间变量(PCNM5)和湖泊类型(水体面积)共同影响了云南中部和南部湖泊夏季浮游植物的空间分布,分别单独解释了群落变化的30.35%、4.90%和3.44%,人类活动与空间变量和湖泊类型分别共同解释了群落变化的6.52%和4.27%;在流域开发日益加强的背景下,水体富营养化已经成为影响该地区浮游植物群落构建的主控因子,而湖泊类型、空间分布等自然环境特征的驱动作用明显降低。因此,养分控制是云南富营养化湖泊环境治理和生态修复的关键内容,是高原湖泊藻类爆发防控和生物多样性保护的重要基础。     

浙南大罗山天河水库浮游植物群落结构的季节变化及对水质的指示作用

为了探究浙南地区山区水库浮游植物群落结构的季节变化及水质状况,于2019年2月-2020年1月对位于温州大罗山天河水库的浮游植物群落结构和水体理化因子进行了调查分析.结果 表明:天河水库浮游植物隶属于7门60属89种,全年浮游植物平均丰度为2.02×105 cells·L-1,年均生物量为0.26 mg·L-1.硅藻门...     

刘家峡水库浮游植物群落结构与环境因子的关系

研究分析刘家峡水库浮游植物群落结构的变化, 探讨西北地区河道型水库环境因素对浮游植物群落结构的影响, 为刘家峡水库增殖渔业提供科学依据。2020年3—10月, 在刘家峡水库设置11个采样点, 每月对浮游植物进行定性和定量采集, 同时采集水样监测总氮、总磷和高锰酸盐指数等水环境指标, 分析水质变化规律, 及浮游植物的优势种、多样性和群落结构的季节变化特征。结果表明: 刘家峡水库共检测到浮游植物7门35属63种, 其中硅藻门种类最多, 共17属40种; 其次为绿藻门8属12种; 蓝藻门4属4种, 裸藻门1属2种, 黄藻门2属2种, 甲藻门2属2种, 金藻门1属1种。浮游植物密度在(3.17—59.09)×104个/L, 平均密度为13.54×104个/L。浮游植物生物量在0.0370—0.5004 mg/L, 平均生物量为0.2137 mg/L。浮游植物密度和生物量均有在4、5月份上升和6月份骤然下降的趋势, 最高值均出现在5月份。多样性指数H′值在1.16—2.43, 平均值为1.84; 丰富度指数D值在1.22—1.57, 平均值为1.42; 均匀度指数J值在0.23—0.51, 平均值为0.38。丰富度指数D值变化趋势与均匀度指数J值刚好相反。RDA分析显示, 对浮游植物影响最强的环境因子是总氮和透明度, 其次为溶解氧和水温。综合浮游植物和水质指标评价刘家峡水库处于Ⅰ或Ⅱ类水, 是极贫营养至贫营养类型。研究可为刘家峡水库水生态保护和渔业资源的可持续利用提供科学依据。     

巢湖双桥河底泥疏浚过程中浮游植物功能群分类研究

浮游植物功能群分类分析可以精确地反映水体环境变化对水生生物群落的影响。为探究巢湖双桥河底泥疏浚工程对浮游植物群落及水生生态系统的影响,对2017年6月—2018年3月双桥河底泥疏浚期间的水体理化因子、浮游植物群落结构和功能群划分开展了研究。研究发现,底泥疏浚工程能够大量削减双桥河水体中的氮、磷营养盐,但疏浚后的双桥河仍处于中-富营养状态;双桥河浮游植物群落依据其生态功能可划分为M、H1、H2、MP、S1、L_O、X2、X1、J、F、N、G、X3、C、D、Y、W1、L_M、E、T、S_N、K、P等23个功能群,绝对优势功能群为以微囊藻为主的M功能群和以硅藻为主的MP、P功能群。底泥疏浚工程对双桥河浮游植物种类的影响不大,但藻类密度和生物量在疏浚后有显著地下降,浮游植物多样性指数也有提升。将浮游植物功能群生物量与环境因子进行冗余分析(RDA)和Pearson分析发现,水环境因子变化对双桥河浮游植物功能群产生了较大影响,双桥河浮游藻类优势功能群由底泥疏浚前的M、MP、P、W1、Y类转变为底泥疏浚后的C、F、J、M、MP、P、Y类。其中,底泥疏浚工程造成的氮营养盐削减可以对双桥河浮游植物功能群产生较大影响。研究认为双桥河底泥疏浚工程在改善河流浮游植物生态功能,减轻水体污染程度上有积极的作用。     

Downstream changes in phytoplankton composition and biomass in a lowland river–lake system (Warnow River, Germany)

To determine longitudinal changes in phytoplankton composition and biomass in the Warnow River (Germany), single water parcels were followed during their downstream transport in August and October 1996 and April 1997. In summer, the phytoplankton assemblage was dominated by centric diatom and cyanobacteria species. Stephanodiscus hantzschii, Pseudanabaena limnetica, Planktothrix agardhii and Aulacoseira granulata var. angustissima were the most frequent species. In autumn, small centric diatoms dominated the whole river course. Irrespective of the season, in the fluvial lakes of the upper river, a substantial increase of phytoplankton biomass was observed. Shallow upstream river stretches were associated with large biomass losses. In the deep, slow flowing lower regions, total biomass remained constant. Longitudinal changes in biomass reflected downstream variations in flow velocity and river morphology. Cyanobacteria, cryptophytes and diatom species were subjected to large biomass losses along fast flowing, shallow river sections, whereas chlorophytes were favoured. Diatoms and cryptophytes benefited from low flow velocity and increased water depth in the downstream river. Changes in water depth and flow velocity have been found as key factors that cause the longitudinal differences in phytoplankton composition and biomass in small rivers.     

Plankton dynamics along a 180 km reach of the Saint Lawrence River from its headwaters in Lake Ontario

We test the hypothesis that phytoplankton biomass decrease upon entry into the St. Lawrence River from headwaters in Lake Ontario is attributable to a range of causal factors including, decreased photosynthetic fitness due to turbulence, cell loss due to increased flocculation and subsequent sedimentation, decreases in nutrients, and loss due to grazing. In order to test this, changes in phytoplankton and crustacean zooplankton concentrations were examined during four transects along the river, from 8 km offshore in Lake Ontario to the hydroelectric power dam 180 km downstream. Both phytoplankton biomass, measured as chlorophyll-a, and zooplankton decreased markedly upon entry of lake water into the river. Phytoplankton community composition and size changed little over the river reach and tended to reflect that in Lake Ontario. Total phosphorus increased with transit of river water downstream despite low tributary inputs of water into this reach of river. Light availability was high, photosynthetic efficiency suggested that phytoplankton were not physiologically stressed during transit in turbulent waters, and there was no direct evidence of flocculation causing sedimentation of phytoplankton. Grazing by the benthic community (filtering insect larvae and dreissenid mussels) is inferred to be a dominant biological factor as is the geomorphology in this reach of the river, which includes large littoral areas, shoals, and reaches of high water velocity that can increase particle contact in the water column with benthic grazers. The findings of this study have a bearing on understanding how changing water levels in a regulated river might alter areas of benthic grazing.     

沱江浮游生物群落时空分布及相关环境因子分析

为研究沱江浮游生物群落结构的时空特征,并探讨影响其形成的环境因子,于2013年对沱江10个采样断面按季节进行采样分析。研究期间共检出浮游甲壳动物13种,以中小型枝角类和剑水蚤为主; 尽管桡足类密度与枝角类接近,但由于体型原因桡足类生物量始终占据优势地位。检出浮游植物7门95种,优势属7个,全年均以硅藻为主。两类生物在上游资阳市区的断面中总生物量最高,中游农村断面最低; 其生物量季节变化也趋于一致,均在丰水季节8月取得最高值,枯水季节2月最低。与历史数据相比,呈现出浮游植物增多,浮游甲壳动物减少的趋势。根据结构方程模型(SEM)和冗余分析(RDA)的结果,浮游甲壳动物生物量在浮游植物生物量和溶氧高的环境中较大,桡足类对溶氧的要求比中小型枝角类高。浮游植物对高温、高营养和高pH较偏好,尤其是一些优势属。尽管受浮游植物生物量影响,浮游动物对浮游植物的控制力却极弱。在流速缓慢且污染较严重的城市江段浮游植物密度已高达2.7107 cells/L,浮游动物尽管能选择性地以部分浮游植物为食,对其控制力却极弱,如不加强污染控制,沱江可能有暴发水华的危险。     

Aquatic macroinvertebrate community structure of aNymphoides peltata-dominated and macrophyte-free site in an oxbow lake

The aquatic macroinvertebrates in two freshwater biotopes,viz. aNymphoides peltata-dominated site and a macrophyte-free site, were studied quantitatively in a shallow alkaline oxbow lake of the river Waal, the main branch of the river Rhine in The Netherlands. The research comprised the analysis of water, sediment and macrophyte samples.In the macrophyte-free site Oligochaeta and Nematocera, particularly of the collector gatherer functional feeding group, dominated the prevailing benthic community. The total macroinvertebrate biomass ranged here from 0.3 to 0.9 g ash-free dry weight per m² of biotope.Species richness, densities, and biomass of macroinvertebrates were considerably higher in the biotope dominated byNymphoides peltata. Many taxa were found associated with the aboveground macrophyte. The sediment compartment, however, contributed most to the total density and biomass of macroinvertebrates. Nematocera and Oligochaeta were the most abundant fauna groups, whereas the largest share in total biomass was provided by clams (Mollusca). The biomass of the total macroinvertebrate community in theNymphoides-dominated site ranged from 6.2 to 7.5 g ash-free dry weight per m² of biotope. The biomass of the aboveground phytophilous fauna ranged from 0.1 to 0.6 g ash-free dry weight per m² of biotope. In September, when theNymphoides peltata vegetation was in its senescent phase, the largest numbers and the highest biomass of phytophilous macroinvertebrates were observed. The contribution of the shredder functional feeding group was high in this period. This, and the overall high abundance of fauna with a detritivorous mode of life, indicates the importance of macrophyte detritus as input to food chains.     

Phytoplankton dynamics in the River Meuse as affected by pollution

The temporal and spatial dynamics of phytoplankton in the River Meuse and a number of physical and chemical parameters were analyzed to gain insight into the pollution level in the river affecting the phytoplankton community. During 1993, samples were taken every two months at eight stations along the River Meuse for physical, chemical and biological characterization of the water. In February, water samples were also taken for laboratory incubations of the natural plankton community. The algae showed a rapid successive development with highest densities (up to 77 mg chlorophylla l^–1) in the middle reach of the river in spring and summer. During winter algal biomass remained very low. A substantial input of nutrients (nitrogen, phosphorus) was observed in the middle reach of the river. Concurrently, an increase in temperature and a reduction in pH was observed. Furthermore, the toxicity of polar organic compounds in the Microtox test showed a strong increase up to the city of Liège and the Belgian/Dutch border; the water quality improved further downstream. The relatively high toxicity at the location Liège was reflected in relatively low growth rates of phytoplankton in the laboratory experiments using water from these locations.     

Macroinvertebrate taxa display increased fidelity to preferred biotopes among disturbed sites in a hydrologically variable tropical river

Understanding the biotope requirements of the various aquatic biota is crucial for effective biomonitoring. Yet, the biotope preferences of macroinvertebrates in Afrotropical rivers have been poorly studied. In this study, we investigated the influence of human disturbance and flow-driven biotope changes on the β-diversity and biotope preferences of macroinvertebrates in the Mara River, Kenya. Macroinvertebrates were sampled from various biotopes at seven reference and nine impaired sites in wet and dry seasons. β-Diversity was determined (i) for each biotope and (ii) at the site scale, combining all biotopes sampled, and macroinvertebrate biotope preferences were assessed among biotopes between reference and impaired sites. Minor β-diversity differences were observed between reference and impaired sites based on relative abundance data, but differences were greater when the presence–absence data were used. There were no statistically significant changes in macroinvertebrate biotope preference due to human disturbance, but fidelity to preferred biotopes increased at impaired sites. In fast-flowing waters, Simuliidae, Baetidae, Tricorythidae, and Hydropsychidae dominated stable rocky substrates and were the most sensitive to flow alteration. This study adds valuable information on the effects of biotope reduction/loss and flow alteration on the diversity and biotope preferences of macroinvertebrates in Afrotropical rivers, and contributes to improvement of relevant bioassessment protocols and biodiversity conservation efforts.

     

Downstream variations of phytoplankton in the St.Lawrence River (Québec, Canada)

Longitudinal variations of phytoplankton biomass and composition were assessed in a 250 km-long section of the St.Lawrence River, which alternately runs through narrow (< 2 km) river cross sections and wide (up to 10 km) fluvial lakes. In the main river stem, concentrations of suspended matter and total phosphorus increased with distance downstream, whereas light penetration decreased. Seasonal changes in plankton composition and biomass were more important than those resulting from differences in water mass (tributary) of origin. Sampling at three cross river sections and in two fluvial lakes showed a progressive downstream decrease in phytoplankton biomass and changes in size structure and taxonomic composition. River plankton was primarily composed of small (< 10 µm equivalent spherical diameter), truly planktonic cells belonging to Cryptophyceae and diatoms, with Chlorophyceae in summer. Plankton sampled in summer among rooted macrophytes in fluvial lakes exhibited a higher biomass of resuspended periphytic algae than in the main river stem, which contributed slightly to downstream phytoplankton biomass.Successive river cross sections always shared about 50% of their taxa, indicating a rapid downstream transport of algae within the main water mass. However, the proportion of species common to all cross sections was highest during the spring freshet, and lowest during summer low discharge, likely resulting from the development of a distinct flora in fluvial lakes during summer. Conversely, about 30% of the identified taxa were exclusive to a cross section and were replaced by others occurring downstream. Overall, phytoplankton composition along the St.Lawrence River is primarily controlled by advective forces, which result in a homogeneous flora in the main river stem, with a local contribution of resuspended periphyton from fluvial lakes.