Pigment signatures reveal temporal and regional differences in taxonomic phytoplankton composition off the west coast of Ireland

The composition of phytoplankton assemblages in April, 1998in Galway Bay and during a summer phytoplankton bloom occurringsouthwest of Ireland in August, 1998, was characterized by pigmentsmeasured by high-performance liquid chromatography. Pigmentdata reflecting phytoplankton assemblages dominated by diatomsin Galway Bay and dinoflagellates in the southwest of Irelandwere compared to phytoplankton cell counts. Significant relationshipswere found between the fucoxanthin concentrations and the diatomcell numbers (P < 0.0002 r² 0.63) during April, and betweenfucoxanthin (P < 0.0001 r² 0.79), 19'hexanoyloxyfucoxanthin(P < 0.0001 r² 0.77) concentrations and Gyrodinium aureolumcell numbers during the summer bloom.     

Effects of resuspension and eutrophication level on summer phytoplankton dynamics in two hypertrophic areas of Lake Taihu,China

The composition of summer phytoplankton communities in two highly eutrophic areas of Lake Taihu, a large, shallow water body in China (area 2,338 km²; mean depth 2.0 m), was studied in relation to selected environmental variables. Both areas have multiple uses, including drinking water supply, fisheries, and recreation. The first area, Meiliang Bay, is much closer to central lake and subjected to wind-driven sediment resuspension, while the second, at Wuli Lake, is less affected by wave action but is considered more nutrient-rich due to its proximity to human inhabitation. By comparing two lake areas, we attempt to advance the understanding and management of different regions of shallow lakes, mainly differing in resuspension levels and eutrophication levels. A comparison of these two lake areas indicated a higher standing crop of phytoplankton in Wuli Lake than in Meiliang Bay. Canonic Correspondence Analysis indicated that nutrient status and sediment resuspension were the principal factors influencing phytoplankton composition in both areas. The dominant algal group in Meiliang Bay comprised immobile R-type strategists (Reynolds in Growth and reproductive strategies of freshwater phytoplankton, 1988), including filamentous diatoms and green algae (Aulacoseira granulate and Planctonema lauterbornii), and recruitment-beneficial RS-type strategists, mainly the colonial cyanobacteria (Microcystis spp.). The community of Wuli Lake was dominated by S-strategists, principally motile flagellates (Cryptomonas spp.) and C-strategists including small nonmotile centric diatoms and chlorococcal green algae.     

基于VGPM模型和MODIS数据估算梅梁湾浮游植物初级生产力

基于MODIS影像数据反演的2009年2月份至12月份太湖梅梁湾水域表面叶绿素a、悬浮物浓度以及水温数据,结合初级生产力垂向归纳模型(Vertically Generalized Production Model:VGPM)估算获得梅梁湾2009年逐月平均日初级生产力时空分布。结果表明,梅梁湾2009年年平均日初级生产力及逐月平均日初级生产力空间分布差异显著,呈现从湾内向湾口逐渐递减的趋势。时间序列分析显示,梅梁湾初级生产力季节差异显著,夏季>秋季>春季>冬季,全年初级生产力主要集中在夏季,占47.4%。通过分析VGPM模型中几个输入参数对初级生产力的影响,发现悬浮物浓度与标准化初级生产力存在显著负冥函数关系,反映沉积物再悬浮引起的悬浮物浓度增加能降低水体初级生产力。温度对初级生产力也有一定的调控与制约,与初级生产力呈现正相关趋势,在低于21℃的温度范围内与最大光合作用速率呈现正相关。     

太湖浮游植物优势种长期演化与富营养化进程的关系

利用1991年至2002年每月一次的监测资料,系统分析了浮游植物优势种和生物量的周年变化情况。同时,总氮、总磷和浮游植物叶绿素a含量等相关资料也被用于解释太湖富营养化演化与浮游植物的关系。结果显示,太湖总氮、总磷、叶绿素a和生物量均呈自梅梁湾底至湖心的逐步递减趋势。在20世纪80年代末太湖刚开始富营养化时,浮游植物优势种群从硅藻转变为蓝藻。之后,浮游植物优势种群一直是蓝藻,但各年的浮游植物总生物量有变化。总氮、总磷、叶绿素a和生物量的年均值持续增长至1996年,其后有逐步下降的趋势,究其原因可能和当地政府在太湖流域的控制排污行动有关。微囊藻在太湖的占优是太湖富营养化的标志之一。研究结果说明浮游植物在大型浅水湖泊中可以作为反映富营养化进程的生态指标。     

Temporal-spatial variations of chlorophyll a and primary production in Meiliang Bay, Lake Taihu, China from 1995 to 2003

There are few long-term data sets on primary production in alake, which can be used to validate the output from a productionmodel. To address this need, we determined the temporal–spatialvariations of chlorophyll a (Chl a) and primary production (PP_eu),based on the vertically generalized production model (VGPM)by using 742 samplings at seven sites in Meiliang Bay in LakeTaihu from 1995 to 2003. An empirical model estimating primaryproduction (PP_in) was used to validate VGPM PP_eu and the dominantfactors controlling PP were determined. Markedly higher Chla and PP_eu values were recorded in Meiliang Bay in 1996 and1997 than in other years and a marked decrease in Chl a andPP_eu was found between 2001 and 2003. Peaks of Chl a typicallyappeared in summer (June–August) and minima occurred inwinter (January). The highest daily mean PP_eu usually occurredin summer (June); the exception was at site 1, where peak dailymean PP_eu occurred in spring (April). The lowest daily meanPP_eu was recorded in winter (January). In Meiliang Bay, 43.0%of annual PP occurred in only 3 months, from June to August.The relative difference of maximum and minimum PP_eu was markedlylarger than the corresponding difference in Chl a. Levels ofboth Chl a and PP_eu were markedly decreased from the inner tothe outer areas of Meiliang Bay; the highest annual integratedPP_eu was found at site 1, close to the inflow of the River Liangxiand this level was 1.85 and 2.14 times higher than at sites3 and 6, respectively, that were located in outer Meiliang Bay.The estimated daily mean PP_eu variation closely matched withthat of the Chl a concentration, implying that Chl a concentrationcan account for the considerable variation of PP. The annualintegrated PP_eu of the euphotic zone in Meiliang Bay rangedfrom 3.44 x 10⁴ tC year^-1 to 8.59 x 10⁴ tC year^-1 with an overallmean of 5.65 x 10⁴ tC year^-1. A significant positive linearrelationship was found between VGPM PP_eu and empirical modelPP_in [PP_in = 0.826 (±0.015)PP_eu + 272.0 (±25.0),r² = 0.80, n = 742, P < 0.0001]. By considering the effectof water temperature, photosynthetically active radiation andphotoperiod on PP, the VGPM- generated PP_eu more accuratelycaptured monthly variations than did the empirical model thatonly included Chl a concentration.     

Temporal variation in plankton assemblages and physicochemistry of Devils Lake, North Dakota

Seasonal and annual variation in biomass and structure of algal assemblages of hyposaline Devils Lake were examined in relation to turbidity, ambient concentrations of major ions, trace elements and nutrients, and the standing crop of herbivores. Lake level declined during the early years of study, but rose markedly in subsequent years as historically large volumes of water flowed into this hydrologically-closed basin. Winter algal assemblages were dominated (in biomass) most years by small, non-motile chlorophytes ( Choricystis minor, Kirchneriella lunaris or Dunaliella sp.), or Euglena sp. in the most saline sub-basin. Spring assemblages were dominated by diatoms (Stephanodiscus cf. minutulus, Surirella peisonis, Cyclotella meneghiniana and Entomoneis paludosa were especially prominent) or chlorophytes ( C. minor) until the lake level rose. C. minor abundances then declined in spring assemblages and diatoms ( Stephanodiscus cf. agassizensis and S. niagarae; E. paludosa in the more saline sub-basins) dominated. The potential for nitrogen-deficient conditions for phytoplankton growth was evidenced most summers and early autumns by consistently high concentrations of reactive-P relative to inorganic-N and blooms of the N-fixing cyanophyte Aphanizomenon flos-aquae; Microcystis aeruginosa typically was a co-dominant (>30% of biomass) in these assemblages. Pulses of diatoms ( S. cf. agassizensis and C. meneghiniana) occurred in summers following unusually prolonged periods of calm weather or large water inflows. Physical (irradiance, turbulence) and chemical (major nutrients) variables were the primary factors associated with phytoplankton growth. Transparency and major nutrient concentrations accounted for more of the annual variation in phytoplankton structure than did salinity. Seasonal abundance patterns of the dominant zooplankton (the copepod Diaptomus sicilis; the cladocerans Ceriodaphnia quadrangula, Chydorus sphaericus, Daphnia pulex and Diaphanosoma birgei; and the rotifers Brachionus spp., Filinia longiseta, Keratella cochlearis and K. quadrata) also indicated variation in algal populations related to grazing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phytoplankton population dynamics of a small reservoir: effect of intermittent mixing on phytoplankton succession and the growth of blue-green algae

The seasonal succession of the phytoplankton of a small reservoir(Guelph Lake, Ontario) in the spring-summer of 1982 was comparedto that in 1981. Mixing of the deeper waters occurred severaltimes throughout the summer in 1982 but not in 1981. The waterat 10 m became anoxic for only 2 weeks in late July in 1982.In contrast, in 1981, the water at 10 m became anoxic at thebeginning of July and remained so until mid-September. The phytoplanktondynamics observed in 1982 did not follow the typical progressionfrom spring diatoms to summer species adapted to survive understratified conditions, as in 1981. Diatoms were present throughoutthe summer in higher amounts in 1982 than in 1981. The mostobvious difference in the two summers was the much greater abundanceof Aphanizomenon flow-aquae in 1982. Other blue-green algaeincluding Microcystis aeruginosa, Gomphosphasria lacustris,and Lyngbya birgei appeared earlier on in 1982, but did notimmediately increase in abundance as in 1981. In 1982, ratesof phytoplankton community change were low in May and June andincreases were observed in mid-July, early August, late Augustand late September. In contrast, in 1981, the rate of communitychange increased in late May, mid-June, early July and lateJuly and remained low throughout August and September. ¹Present address: Department of Zoology, University of Alberta,Edmonton, Alberta T6G 2E1, Canada. ²Present address: CSIRO Division of Fisheries Research, G.P.O.Box 1538, Hobart, Tasmania 7001, Australia     

Effects of low concentrations of heavy metals on plankton community dynamics in a small, shallow, fertile lake

Significant differences in phytoplankton abundance developedamong identical, untreated 2.3-m³ enclosures, maintained ina shallow, fertile lake in northern Italy for 14 days in June1981. Differences in soluble reactive phosphorus concentrationwere significant after 7 days and developed more rapidly ifthe water columns were isolated from the sediment. Three replicateenclosures were used per treatment in experiments carried outbetween November 1981 and June 1983 to investigate heavy metaltoxicity. This enabled between-treatment variation caused bythe heavy metal additions to be distinguished from within-treatmentvariation caused by containing the water column within enclosures.For plankton abundance and physico-chemical variables, the within-treatmentcoefficient of variation exceeded ±50% if experimentswere >3 weeks. Containment within enclosures affected theecosystem differently in different seasons but, in general,planktonic populations resembled those in the lake. Cadmium,copper and mercury additions of between 10 and 100 µgl^–1 had little immediate effect upon phytoplankton biomassin summer. In winter, marked reductions occurred in the first2 days of the experiment. Zooplankton was more sensitive thanphytoplankton to the heavy metals in summer, cladoceran androtifer populations declining precipitously, shortly after heavymetal addition in each experiment. Copepods were the most heavy-metal-tolerantzooplankters. As the direct toxicity of the heavy metals subsided,there was disruption of zooplankton predation and nutrient regeneration.In summer, reduced grazing by heavy-metal-sensitive zooplanktoncaused algae to proliferate, whereas in winter, inorganic nutrients,which accumulated in the treatments due to heavy-metal-induceddecreases in plankton biomass, later supported larger populationsof algae than would otherwise have occurred. Low nutrient concentrationsin summer probably reflected rapid uptake in productive conditions.Mercury persisted in the water for a shorter period than dideither cadmium or copper, and accumulated more rapidly in periphyton.Copper remained longest in the water column and was largelyassociated with suspended particulate material. Cadmium alsopersisted in the water column but remained largely in solution.Heavy metal accumulation in sediment was not evident, but mayhave been masked by high background concentrations.     

Phytoplankton community growth-rate response to nutrient pulses in a shallow turbid estuary, Galveston Bay, Texas

Phytoplankton growth is a physiological process often limitedby temperature, nutrients or light, while biomass accumulationis a function of growth rates, grazing and deposition. Althoughprimary productivity measurements are usually used to assessresponses to limiting factors, the rates are proportional tobiomass and inversely related to grazing pressure during experimentalincubations. Alternatively, carbon-specific growth-rate determinationsprovide insights into physiological responses without the confoundingeffects of biomass and grazing. The objective of this studywas to quantify the growth-rate responses of phytoplankton toenhanced nutrient availability (nitrate and phosphate) overa range of in situ irradiances. Growth rates were determinedbased on chlorophyll a-specific ¹⁴C-uptake rates by phytoplankton.Phytoplankton demonstrated high (24 h) growth rates when exposedto increased concentrations of limiting nutrients, independentof the surface irradiances (12–41%). Growth-rate responseswere also compared with the biomass (chlorophyll a) responsesand community composition. Observed and estimated phytoplanktonbiomass changes during the incubations differed, emphasizingthe structural role of grazers on the phytoplankton community.The phytoplankton community in Galveston Bay has the potentialto instantaneously respond to nutrient pulses, facilitatingdiatom biomass accumulations in spring and summer and small,flagellated species and cyanobacteria during periods of lownutrient inputs. Thus, Galveston Bay phytoplankton biomass andcommunity composition reflect a dynamic balance between thefrequency of nutrient pulsing and grazing intensity.     

太湖梅梁湾湖岸带浮游植物群落演替及其与水华形成的关系

利用2009～2010年周年观测数据,结合江苏太湖湖泊生态系统研究站15年监测数据,分析了太湖梅梁湾湖岸带浮游植物群落演替及其与蓝藻水华形成的关系.50次周监测结果表明:蓝藻门(Cyanophyta)、绿藻门(Chlorophyta)、硅藻门(Bacillariophyta)分别占浮游植物总生物量的60%、16%和22%.冬春季绿藻、硅藻为主要优势种,夏秋季蓝藻门的微囊藻占绝对优势.4月下旬～6月初,平均温度低于20℃,蓝藻没有大规模生长,硅藻门、绿藻门生物量急剧降低,总生物量小于1mg·L^-1;随后温度超过25℃,蓝藻迅速增长并很快成为绝对优势,蓝藻增加滞后于绿藻、硅藻的减少.在营养盐充足、物理因素合适的条件下,浮游植物群落结构自然演替是蓝藻水华形成的主要原因之一.     

Characterization of a small eutrophic Antarctic lake (Otero Lake, Cierva Point) on the basis of algal assemblages and water chemistry

Otero Lake is the main water body of Cierva Point, Danco Coast (SSSI No. 15). During the 1992/1993 and 1994/1995 seasons, abiotic parameters and the structure and dynamics of the phytoplankton were studied. Algal assemblages from the phytoplankton, from algal clumps encased in the lake ice and from the benthic algal felt were compared. Low Jaccard similarity indices between these three assemblages suggest different survival strategies. The higher species richness of phytoplankton when studied during the whole summer also suggests that external propagule inputs can heavily influence the structure of this community. High levels of phosphate, nitrate and ammonium throughout the study periods indicate that they do not limit summer growth of the phytoplankton community. Blooms of Chlamydomonas subcaudata Wille are apparently characteristic. This group of features define Otero Lake as a highly eutrophic water body, in which outflow seems to be the main cause of phytoplankton loss during summer. Received: 23 December 1996 / Accepted: 29 August 1997     

Phytoplankton Cell Lysis after Water Bloom in a Eutrophic Freshwater Lake Taihu (China)

The phytoplankton lysis rates in the different eutrophic regions of Lake Taihu were determined based on the activities of particle and dissolved esterase, as well as the decay rate of the latter, from August 2009 to March 2010. Two peaks were observed for the chlorophyll a concentration, one in September 2009 and another in January 2010. The highest phytoplankton lysis rates observed in October were associated with the decay of the summer bloom, whereas the minimum lysis rates observed in January were associated with the winter bloom. The highest cell lysis rates in Meiliang Bay, Lake centre, and Gonghu Bay were 0.67, 0.77, and 0.68 d^–1, respectively, whereas the lowest lysis rates in these regions were 0.03, 0.01, and 0.05 d^–1, respectively. Water temperature showed an apparent indirect effect on lysis rate. In addition, a significant inverse relationship was observed between lysis rates and nitrate concentration in the three lake regions, which suggests that phytoplankton cell lysis is associated with changes in nitrate concentration. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The structure and dynamics of the phytoplankton assemblages in Lake Kinneret, Israel

The phytoplankton of Lake Kinneret, a warm monomictic lake,is dominated by a Pyrrhophyta-Chlorophyta assemblage. Four stagesof succession of planktonic algae occur in the lake, startingwith thermal and chemical destratification and ending with stratification. The index of diversity of the phytoplankton communities is highduring the destratification and mixed periods. The index reachesminimal values during late summer, when the ecosystem is subjectto strong physical, chemical and biological stresses. The diversityin Lake Kinneret increases with the increase in nutrients andnot with the increase in temperature. During most of the year, the nanoplanktonic forms are in greaternumbers than the netplankton species. This fact is correlatedwith the amounts of available nutrients in the lake. The annual averages of the wet autotrophic biomass in Lake Kinneretare very high in comparison with other warm lakes. The contributionof the nanoplanktonic species to the total algal biomass isvery small during the Peridinium bloom, but represents approximatelyhalf of the total algal biomass during the rest of the year. The concentration of nutrients in the water, together with theadverse competitive effect of Peridinium on other algae, areto a large extent responsible for the composition, successionand abundance of the phytoplankton assemblages in Lake Kinneret.     

太湖梅梁湾浮游植物叶绿素a和初级生产力

1998年5月～1999年8月对太湖梅梁湾4站点进行了每季1次、为期1年的初级生产力及相关因子研究,分析了梅梁湾叶绿素a含量和初级生产力的时空分布特征．结果表明,梅梁湾的叶绿素a含量、初级生产力均存在明显的季节变化和空间差异,春、夏季浮游植物叶绿索a含量和初级生产力要比秋、冬季高,空间上位于污染严重的直湖港口6#点叶绿索a含量和初级生产力要高,并大致呈现从湾内向湾口递减的趋势;在春、夏、秋季光照较强时,初级生产力最大指值出现在水下20～50cm处。到冬季垂直差异不明显;10～30℃之间初级生产力基本上随温度的上升而呈指数增加趋势．浮游植物生物现存量与初级生产力存在显著的正相关．营养盐与初级生产力相关性变化很大．光照显著地影响初级生产力的日变化。春、夏季强光作用下表面光抑制现象比较明显．     

Phytoplankton periodicity in a subtropical lake (Lake Kinneret,Israel)

Lake kinneret is a subtropical monomictic lake characterized by a Pyrrhophyta-Chlorophyta assemblage, supplemented by Cyanophyta in some years. Concerning their abundance and seasonal occurrence, the phytoplanktonic algae belong to two groups: algae appearing in quantity at a definite annual period and algae present throughout the year. Four stages of algal succession occur in the lake. There is a marked periodicity in the phytoplankton composition with a high standing stock in winter-spring, due to the dinoflagellate water-bloom, and a low one during the summer months, related to the high stability of summer stratification. The annual succession at the species level has been an almost constant event in the lake for many years.The increase in nutrient concentrations in 1973 and 1974 increased the diversity and abundance of algae (except Peridinium) but did not lead to significant changes in algal succession. Conversely, the decrease of the zooplankton grazing pressure in 1975 and 1976 facilitated the development of algal maxima during summer-fall. They were caused by nanoplanktonic forms, and they developed without additional enrichment of nutrients. The algal abundance and diversity decreased. The years 1981 and 1982 were characterized by both an increase in phosphorus and a decrease in zooplankton. These conditions favored the concomitant abundance of many species and an increase of non-Pyrrhophyta biomass.     

Role of atelomixis in replacement of phytoplankton assemblages in Dom Helvécio Lake, South-East Brazil

Scale and frequency of changes in a lake’s physical structure, light dynamics, and availability of nutrients are closely related to phytoplankton ecology. Since phytoplankton assemblages were first described, phytoplankton ecologists concluded that these assemblages provide insight into phytoplankton responses to environmental changes. Objectives of this study were to investigate ecology of phytoplankton during a complete hydrological cycle in the deepest natural lake in Brazil, Dom Helvécio, and to sort species into the list of assemblages, checking its accordance with environmental changes in a tropical system within the middle Rio Doce Lake district, South-East Brazil. Canonical Correspondence Analysis, t-test, Mann–Whitney U-test, and Kruskal–Wallis test were used to analyze climatological, environmental, and plankton data, which were obtained monthly in 2002. A new phytoplankton assemblage, N_A (atelomixis-dependent desmids), is suggested because atelomixis (robust movement of water occurring once a day) contributed to replacement of species in Dom Helvécio Lake. Stability of stratification, water chemistry, and composition of phytoplankton assemblages characterized two periods. The first period occurred in six rainy months (Jan–Mar and Oct–Dec) when the lake was stratified and phytoplankton was dominated by two assemblages: N_A and F. The second period occurred in six dry months (Apr–Sep) when the lake was nonstratified and phytoplankton was dominated by four assemblages: S2, X1, A, and L_O. Results suggest that phytoplankton in Dom Helvécio Lake was shaped by seasonal and daily changes of water temperature, even with its lower amplitude of variation within 2002 (El Niño year). These changes promoted water column stratification or mixing, reduced light, and increased nutrient availability. Temperature, therefore, is similarly important to phytoplankton ecology in tropical regions as it is in temperate ones. Sorting phytoplankton species into assemblages matched well with environmental changes and periods identified so it is also suggested that this can be further used as an appropriate tool to manage water quality when evaluating tropical lakes.     

Phytoplankton community structure derived from HPLC analysis of pigments in the Faroe-Shetland Channel during summer 1999: the distribution of taxonomic groups in relation to physical/chemical conditions in the photic zone

A study of the phytoplankton community in the Faroe-ShetlandChannel was conducted in July 1999. Samples were collected atvarious depths in the photic zone along three transects (thenorthern entrance, the center and the southern entrance). Exceptfor a few easterly stations where nitrate and silicate werebelow 1 µM, all nutrients (phosphate, silicate, ammonium,nitrite and nitrate) were non-limiting for phytoplankton growth.HPLC pigment analysis revealed a pronounced (>50%) dominanceof Prymnesiophyceae at all stations. Their pigment ratio ofdiatoxanthin + diadinoxanthin/Chl a (DDX/Chl a) indicated thatthe phytoplankton community was controlled by light. Primaryproduction in the delayed spring bloom varied from 1.2 to 1.8g C m^–2 day^–1 along the northern transect. Alongthe other two transects, primary production ranged from 1.6to 3.8 g C m^–2 day^–1. Associated with the characteristicsindicating the establishment of a bloom, the relative contributionof diatoms and Prymnesiophyceae increased, whereas that of Prasinophyceae,Cryptophyceae, Chrysophyceae and Cyanobacteriaceae decreased.With respect to their vertical distribution, Cyanobacteriaceae,Chrysophyceae and Dinophyceae tended to have a higher abundance,relative to other taxonomic groups, in the surface layers. Therelative abundance of diatoms and Chlorophyceae increased withdepth. The DDX/Chl a ratio of the Prymnesiophyceae decreasedwith depth, indicating that vertical mixing in the upper 30m of the photic zone occurred less frequently than the timespan of physiological acclimation of cellular pigment composition.     

Effects of nutrients and dissolved organic matter on the response of phytoplankton to ultraviolet radiation: experimental comparison in spring versus summer

The effects of nutrients and dissolved organic matter (DOM) on the response of phytoplankton community structure to ultraviolet radiation (UVR) was studied using natural phytoplankton assemblages from Lake Giles (Northeastern Pennsylvania), a temperate, oligotrophic, highly UVR-transparent lake. Microcosm experiments were conducted in 1-l bags in the spring and summer. A factorial design was used, with two UVR treatments (ambient and reduced), two nutrient treatments (control with no nutrients added, and nitrogen and phosphorus addition together), and two DOM treatments (control of 1 mg l⁻¹ and doubled). In April, UVR affected the overall phytoplankton community structure, causing a shift in the dominant species. Significant interactive effects of UVR × nutrients and UVR × DOM were found on total phytoplankton biovolumes. In July, all taxa responded positively to the N + P addition, and were affected differentially by the UVR treatments. The initial communities varied in April and July, but Synura sp. and Chroomonas sp. were present in both seasons. Synura sp. responded positively to the addition of DOM in April and the reduction of UVR in July. Chroomonas sp. responded positively to the reduction of UVR in April and the addition of nutrients in July. The differential sensitivity of these two species suggests that changing environmental factors between spring and summer promoted differences in the relative importance of UVR in changing phytoplankton community structure. Handling editor: Luigi Naselli-Flores     

太湖梅梁湾沿岸带水体生物学与光学特性

基于 1998～ 1999年周年 4季原位水下光场观测资料及中国科学院太湖湖泊生态系统研究站 1992～ 2 0 0 1年悬浮物、叶绿素 a、透明度长期历史观测资料分析了太湖梅梁湾沿岸带第 2号站点水体的生物学与光学特性 ,探讨了水下光合有效辐射(PAR)总量的日变化、垂直分布 ;光衰减系数的季节变化及光谱分布 ;影响光衰减系数的主要水色因子。结果表明 ,无论是 PAR还是光谱衰减系数其值都很高 ,其中 PAR衰减系数在 1.4 0～ 5 .30 / m间变化 ,均值为 2 .4 3± 0 .5 5 / m,秋季最大、夏季最小 ,真光层深度在 0 .87～ 3.2 9m间变化 ,均值为 1.98± 0 .4 1m;水下光谱在蓝光波段衰减最强烈 ,其次是红光、绿光 ,随着深度增加光谱成分出现绿移和红移现象 ,绿红光占得比例越来越大 ;光谱衰减系数随着波长的增加大致呈下降趋势 ,但在 6 70 nm附近有个峰值 ;基于线性相关分析发现在混浊的沿岸带水体中影响光衰减主要因子为水体中的悬浮物和有色可溶性有机物 ,叶绿素 a对 PAR衰减系数的贡献率只占到 1.5 9%～ 14 .2 1%。