Relationships among nitrogen and total phosphorus,algal biomass and zooplankton density in the central Amazonia lakes

The relationship among concentrations of total nitrogen (TN), total phosphorus (TP), algal biomass (Chl) and the density and size of individuals of the zooplankton community were studied for the dry season (November 1999–January 2000) at 20 lakes of the Central Amazonia. The study was conducted along a productivity gradient to identify the existence of resource or predator-dependent patterns on the primary producers of the trophic web. A strong positive relationship was observed between the log Chl and TN (r ² = 0.88, P = 0.000) and to log Chl and log TP (r ² = 0.85, P = 0.000) in a simple linear regression. However, when both variables were running together in a multiple regression, TN alone explained every variation of algal biomass (r ² = 0.89, P _TN = 0.022, P _TP = 0.233). The total density of the zooplankton showed a positive correlation with log Chl (r ² = 0.53, P = 0.000) and the large zooplankton (>0.5 mm) was found to be a more positive function of the phytoplankton (r ² = 0.65) than the density of the small ones (<0.5 mm, r ² = 0.44). Results show that complex food web interactions could be responsible for patterns in tropical systems. We contend that Chl variation in tropical lake systems is controlled by TN and TP, but the predictor power of the TN increase the fit of the model in analysis and can be use alone to access the variability in algae biomass to Amazonian tropical lakes. We also agree that the density of large zooplankton individuals is regulated by the biomass of primary producers. Hence we concluded that the resource-dependent hypothesis is supported in these systems. Handling editor: J. Padisak     

Population responses of Lake Michigan phytoplankton to nitrogen and phosphorus enrichment

A natural phytoplankton assemblage from Grand Traverse Bay, Lake Michigan, was treated with factorial enrichments of nitrate and phosphorus, with maintained nutrient concentrations ranging from 5 to 60 μg total soluble phosphorus liter⁻¹ and 0.225 to 1.12 mg nitrate-nitrogen liter⁻¹.One container was spiked with added vitamins, a chelator, and trace metals. The assemblage response was monitored at the species level. Significant differences in growth rates as a function of nutrient enrichment were detected at both the division and the species levels. Growth rates associated with the various levels of enrichment are reported for several diatom taxa. Many of the diatom taxa exhibited highly significant (P < 0.01) increases in growth rate after phosphorus enrichment, with the largest effects occurring between 5 and 15 μg total soluble phosphorus liter⁻¹. Significant (P < 0.05) N effects were also observed, and the nature of these effects was found to be taxon-specific. Taxa also showed significant changes in percent composition, due both to time and to nutrient enrichment, indicating a substantial heterogeneity in response at the species level. Experimentally induced population changes were qualitatively similar to those observed in regions of the Great Lakes which have undergone anthropogenic eutrophication. Contribution No. 222 of the Great Lakes Research Division, University of Michigan. Work was supported by funds from the Michigan Sea Grant Program and the Environmental Protection Agency. Contribution No. 222 of the Great Lakes Research Division, University of Michigan. Work was supported by funds from the Michigan Sea Grant Program and the Environmental Protection Agency.     

Photoacoustics: a novel tool for the determination of photosynthetic energy storage efficiency in phytoplankton

Photosynthetic energy storage efficiency controls the development and decline of phytoplankton biomass. All abiotic environmental factors such as light intensity; temperature, nutrient availability and pollutants will exert detectable changes in the photosynthetic energy storage efficiency of phytoplankton, and subsequently affect total biomass and composition of phytoplankton assemblages. Since this efficiency is a sensitive amplifier of ambient conditions, it thereby is an excellent reporter of water quality parameter. We demonstrate the applicability of the novel photoacoustic method in easily and directly estimating the energy storage efficiency of phytoplankton in a drinking water reservoir of different nutrient status. Electronic Supplementary Material Supplementary material is available in the online version of this article at and accessible for authorised users Handling editor: J. Padisak     

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     

A model for seasonal phytoplankton blooms

We analyse a generic bottom-up nutrient phytoplankton model to help understand the dynamics of seasonally recurring algae blooms. The deterministic model displays a wide spectrum of dynamical behaviours, from simple cyclical blooms which trigger annually, to irregular chaotic blooms in which both the time between outbreaks and their magnitudes are erratic. Unusually, despite the persistent seasonal forcing, it is extremely difficult to generate blooms that are both annually recurring and also chaotic or irregular (i.e. in amplitude) even though this characterizes many real time-series. Instead the model has a tendency to 'skip' with outbreaks often being suppressed from 1 year to the next. This behaviour is studied in detail and we develop analytical expressions to describe the model's flow in phase space, yielding insights into the mechanism of the bloom recurrence. We also discuss how modifications to the equations through the inclusion of appropriate functional forms can generate more realistic dynamics.     

Potential phytoplankton indicator species for monitoring Baltic coastal waters in the summer period

There are very few time series documenting clear trends of change in the biomass of total phytoplankton or single taxa that coincide with trends of increasing nutrient concentrations. Weekly or biweekly monitoring since 1997 on a cross section of the central Gulf of Finland (NE Baltic Sea) with similar climatic and hydrographic conditions, but different nutrient levels, provided a uniform dataset. In order to evaluate seasonal (June–September) patterns of phytoplankton succession, more than 1,200 samples were statistically analyzed by selecting 12 dominant taxa using wet weight biomass values. In addition, the continuously measured hydrographic parameters on board the ships of opportunity, and simultaneous nutrient analyses gave high frequency information on the water masses. The objective of this study was to identify the taxa that may prove indicative in the assessment of eutrophication in the appropriate monitoring time periods. None of the most common bloom-forming species (Aphanizomenon sp., Nodularia spumigena, and Heterocapsa triquetra) showed reliable correlations with enhanced nutrient concentrations. The species we suggest as reliable eutrophication indicators—oscillatorialean cyanobacteria and the diatoms Cyclotella choctawhatcheeana and Cylindrotheca closterium—showed the best relationships with total phosphorus concentrations. Their maxima appear toward the end of July or in August–September when phytoplankton community structure is more stable, and less frequent observations may give adequate results. Another diatom, Skeletonema costatum, exhibited stronger correlations with dissolved inorganic and total nitrogen in June, during the period of the summer phytoplankton minimum. Guest editors: J. H. Andersen & D. J. Conley Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark     

Temporal organization of phytoplankton communities linked to physical forcing

The performance of individual phytoplankton species is strongly governed by the thermal stratification’s impact on vertical mixing within the water column, which alters the position of phytoplankton relative to nutrients and light. The present study documents shifts in phytoplankton structure and vertical positioning that have accompanied intensified long-term stratification in a natural ecosystem. Ordination analysis is used to extract gradients in phytoplankton composition in Lake Tahoe, an extremely nutrient-poor lake, over a 23-year period of records. Community structure in the 1980s was associated most strongly with resource availability (low nitrogen to phosphorus ratios, deeper euphotic zone depth), while intensified stratification dominated the phytoplankton structure since the late 1990s. Within diatoms, small-sized cells increased with reduced mixing, suggesting that suppressed turbulence provides them with a competitive advantage over large-sized cells. Among the morphologically diverse chlorophytes, filamentous and coenobial forms were favored under intensified stratification. The selection for small-sized diatoms is accompanied by a shoaling trend in their vertical position in the water column. In contrast, the motile flagellates displayed a deeper vertical positioning in recent years, indicating that optimal growth conditions shifted likely due to reduced upwelling of nutrients. As the thermal stratification of lakes and oceans is strongly linked to climate variables, the present study confirms that climate warming will alter phytoplankton structure and dynamics largely through effects on nutrient availability and sinking velocities. Intensified stratification should favor the expansion of small-sized species and species with the capability of buoyancy regulation, which may alter primary productivity, nutrient recycling, and higher trophic productivity. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

大型枝角类蚤状溞对小型热带湖泊浮游植物群落影响的研究

2006年4月10日至2006年4月22日,采用原位吊瓶实验的方法,在暨南大学校园明湖中进行了大型枝角类蚤状溞(Daphnia pulex)对浮游植物种群变化和群落结构影响的实验。实验初期,明湖浮游植物群落的组成是以飞燕角甲藻(Ceratium hirundinella)和单角盘星藻(Pediastrum simplex)为优势种。在室内将蚤状溞培养至体长2mm以上,将蚤状溞加入到装满湖水的4.5L的透明瓶中,设置4个梯度:0ind(A,对照),10ind.(B),20ind(C)和30ind(D),每个梯度有3个平行,将实验瓶置于水表层50cm处。12d后实验结束,不同处理之间的浮游植物种群数量和组成有了明显的差异。与对照组相比,飞燕角甲藻和颗粒直链藻(Meclosira granulata)密度在实验组B、C和D中下降明显;小环藻(Cyclotella)和栅藻(Scenedesmus)等小型浮游植物在牧食压力比较大的C和D瓶中密度低于对照组,而在牧食压力相对较低的B瓶中,它们的密度高于对照组,这可能是由于蚤状溞加速了水体的营养盐循环反过来促进这些小型浮游植物的生长。处理组中绿藻门的盘星藻数量没有明显的下降,这与盘星藻不能被浮游动物直接滤食有关。实验结果表明蚤状溞对浮游植物的群落数量和组成的影响程度与其自身的种群密度密切相关,也与浮游植物群落结构有关。由于飞燕角甲藻是一种细胞较大的种类,蚤状溞对它的抑制作用主要是通过机械伤害作用实现的。     

赤潮过程浮游植物与营养物质时间变化率研究

利用2000年大亚湾澳头海域赤潮定点连续调查资料及其多年现场调查资料,采用灰色回归模型,综合分析赤潮发生过程水体中浮游植物细胞密度与营养物质(NO3-、NH4+、PO4^3-、SiO3^2-、Fe)的时间变化率关系,分析了叶绿素a含量与浮游植物细胞密度相互关系．结果表明,预测值与实测基值本一致,复相关系数范围在0．51～0．83．当水体叶绿素浓度为5．8μg·dm-3,预示可能发生赤潮,通过采样分析水体叶绿素a含量或利用水色卫星遥感资料反演水体叶绿素浓度,计算浮游植物细胞密度,为赤潮的预测预报提供简便有效的方法．此外．本水域初级生产力由磷控制．     

Nutrients and phytoplankton in Lake Peipsi during two periods that differed in water level and temperature

Data for the vegetation periods (May–November) of 1985–2003 were used to collate the nutrient content and biomass of the most important phytoplankton groups in Lake Peipsi (Estonia). Two periods differing in external nutrient load and water level were compared by analysis of variance. The years 1985–1988 were characterized by the highest loads of nitrogen and phosphorus, high water level and cool summers. The years 2000–2003 were distinguished by low or medium water levels and warm summers. The first period showed statistically significantly higher values of total nitrogen (N_tot) and a higher N_tot:P_tot mass ratio. The second period showed a higher content of total phosphorus (P_tot), a higher ratio of dissolved inorganic compounds N to P and higher phytoplankton and cyanobacterial biomasses. Comparison between parts of the lake demonstrated that the differences between the two periods were more evident in the shallower and strongly eutrophic parts, Lake Pihkva and Lake Lämmijärv, than in the largest and deepest part, the moderately eutrophic Lake Peipsi s.s. Temperature and water level acted synergistically and evidently influenced phytoplankton via nutrients, promoting internal loading when the water level was low and the temperature high. The effect of water level was stronger in the shallowest part, Lake Pihkva. The difference in P_tot content between the southern and northern parts was twofold; the N_tot:P_tot mass ratio was significantly lower in the southern parts, and phytoplankton biomass (particularly the biomass of cyanobacteria) was significantly higher for Lake Pihkva and Lake Lämmijärv than for Lake Peipsi s.s.     

Periodic response to periodic forcing of the Droop equations for phytoplankton growth

The dynamics of a phytoplankton population growing in a chemostat under a periodic supply of nutrients is investigated with the model proposed by Droop. This model differs from the well-known Monod equations by incorporating nutrient storage by the cells. In spite of its nonlinearity and the time delays introduced by an internal nutrient pool, the model predicts a simple response to a periodic nutrient supply. The population is shown to oscillate with the same frequency as the forcing. To prove the existence of a periodic solution local and global bifurcation results are used. This work establishes a basis on which to evaluate experimental data against the model as a representation of the nutrient-phytoplankton interaction when nutrients fluctuate.     

Effects of phosphorus and nitrogen enrichment on the phytoplankton in a tropical reservoir (Lobo Reservoir,Brazil)

The effects of enrichment with phosphate (0–500 µg. 1^–1) and forms of nitrogen (nitrate, nitrite, ammonia an and urea) (0–3500 µgg. ^–1) on the phytoplankton growth of Lobo Reservoir (Brazil) were studied in July, 1979. Suspended matter, chlorophyll a, cell concentrations and the carotenoid:cchlorophyll ratio were estimated following 14 days of in situ incubation. Phosphate alone caused no significant effects, but enrichment with nitrogen caused a substantial increase on the growth of phytoplankton. Comparison between the different forms of nitrogen showed insignificant effects after their additions with 350 µg. ^–1 and in combination with phosphate. However, when nitrogen was added in large quantities (3 500 µg. ^–1), significant differences between the nitrogeneous forms were found, with urea causing the strongest effect. In July, nitrogen is mhe main limiting nutrient to phytoplankton growth of Lobo Reservoir.Supported by CNPq and FAPESP.     

Modeling continuous cultures of microalgae colimited by nitrogen and phosphorus

It is well documented that the combination of low nitrogen and phosphorus resources can lead to situations where colimitation of phytoplankton growth arises, yet the underlying mechanisms are not fully understood. Here, we propose a Droop-based model built on the idea that colimitation by nitrogen and phosphorus arises from the uptake of nitrogen. Indeed, since N-porters are active systems, they require energy that could be related to the phosphorus status of the cell. Therefore, we assumed that N uptake is enhanced by the P quota. Our model also accounts for the biological observations that uptake of a nutrient can be down-regulated by its own internal quota, and succeeds in describing the strong contrast for the non-limiting quotas under N-limited and P-limited conditions that was observed on continuous cultures with Selenastrum minutum and with Isochrysis affinis galbana. Our analysis suggests that, regarding the colimitation concept, N and P would be better considered as biochemically dependent rather than biochemically independent nutrients.     

Response of Salvinia molesta to insect damage: changes in nitrogen,phosphorus and potassium content

Summary When adults and larvae of the weevil Cyrtobagous salviniae destroyed buds and tunnelled through rhizomes of Salvinia molesta, the plant responded by producting new growth which contained higher concentrations of nitrogen than in undamaged plants or in the older parent tissue of the same plant. Damage to leaves by the moth, Samea multiplicalis did not induce the same response. C. salviniae fed on the new growth and the higher nitrogen intake would have increased its reproductive capacity and enhanced its action as a biological control agent.Damage by both insects resulted in potassium leaching from the plant but no change in concentrations of phosphorus. The results support earlier suggestions that damage by C. salviniae might improve the qualtity of the host plant for this herbivore.     

Factors controlling the seasonal development and distribution of the phytoplankton community in the lowland course of a large river in Northern Italy (River Adige)

The principal environmental factors influencing the seasonal dynamics of phytoplankton were examined from September 1997 to July 1998 in three stations along a 26-km stretch of the lowland course of River Adige (northeast Italy). Nutrient concentrations did not appear to be limiting for the phytoplankton growth. Annual minimum concentrations of reactive and total phosphorus, and dissolved inorganic nitrogen were 22 μg P l⁻¹, 63 μg P l⁻¹ and 0.9 mg N l⁻¹, respectively. The most critical forcing factors were physical variables, mainly water discharge and other variables related to hydrology, i.e. suspended solids and turbidity, which acted negatively and synchronously by diluting phytoplankton cells and decreasing light availability. Higher algal biomass was recorded in early spring, in conditions of lower flow velocity and increasing water temperature. In late spring and summer, higher water discharge caused a decrease in phytoplankton biomass. Conversely, low algal biomass in late autumn and winter, during low discharge, was mainly related to low water temperatures and shorter photoperiod. Physical constraints had a significant and measurable effect not only on the development of total biomass, but also on the temporal dynamics of the phytoplankton community. Abiotic and biotic variables showed a comparable temporal development in the three sampling stations. The small number of instances of spatial differences in phytoplankton abundance during the period of lower flow velocity were related to the increasing importance of biological processes and accumulation of phytoplankton biomass.     

Interaction of nitrogen status and UVB sensitivity in a temperate phytoplankton assemblage

The influence of nitrate supplementation and ultraviolet-B (UVB; 280–320 nm) enhancement was tested on a coastal phytoplankton assemblage from eastern Canada exposed to ambient or supplemental UVB irradiance, equivalent to a local 60% ozone depletion. During a 10 d-long mesocosm experiment, 24-h surface bag incubations were repeated three times with half the bags supplemented with nitrate, phosphate and silicate while the other half received only phosphate and silicate. At beginning and the end of these 24-h surface incubations, chlorophyll fluorescence measurements were performed and the abundance of photoprotective pigments diadinoxanthin and diatoxanhtin, of the PSII reaction center D1 protein and of the large subunit of the ribulose-1,5-biphosphate carboxylase/oxygenase enzyme (RuBisCO LSU) was determined. Results showed that as long as nutrients were abundant inside the mesocosms, phytoplankton exposed to supplemental UVB at the surface were able to maintain their maximal quantum yield of PSII fluorescence. As nutrients became limiting inside the mesosocoms, however, phytoplankton showed an increased sensitivity to supplemental UVB and suffered more net photodamage to the PSII reaction centers (seen as decreases in D1 protein abundance). Supplemental UVB also resulted in low abundance of RuBisCO LSU and exacerbated photoinhibition compared to the phytoplankton exposed to surface ambient irradiance. Supplementing nitrate during this nutrient deficient period limited the inactivation of the PSII reaction centers and lowered photoinhibition. Nitrate supplementation had no clear effect on the abundance of the D1 protein but it helped the community to maintain a greater abundance of RuBisCO LSU. Overall, results from this study suggest that the sensitivity of the RuBisCO enzyme to the combined effects of supplemental UVB and nitrate limitation can influence the tolerance of PSII to UVB stress.     

Relationships between phytoplankton and periphyton communities in a central Iowa stream

Relationships between phytoplankton and periphyton communities were investigated in a central Iowa stream. Results generally support the hypothesis that the phytoplankton community arises from the epipelic periphyton community. A high correlation existed between the proportion of benthic diatoms composing the epipelon and phytoplankton. One dominant epipelic species (Nitzschia acicularis) showed a greater tendency to become planktonic than the grouped remainder of Nitzschia spp. There was a significant inverse relationship between the proportion of centric diatoms in the plankton and volume of flow. Centric diatoms were important members of the plankton only when volume of flow was less than 60 ft³ / sec (2.1 m³ / sec). Possible mechanisms explaining these phenomena are discussed.This study represents a portion of a dissertation submitted to the Graduate College, Iowa State University in partial fulfillment of requirements for the degree Doctor of Philosophy.     

Nitrogen versus phosphorus limitation of phytoplankton growth in Ten Mile Creek, Florida, USA

Ten Mile Creek (TMC) is a major tributary of the Indian River Lagoon (IRL), one of the largest and most ecologically diverse estuaries of the east coast of Florida. Recent algal blooms within the IRL have focused attention on the role of different watersheds playing in the supply of growth-limiting nutrients. The goal of this study was to determine the nutrient-limiting status of the TMC outflow, which is influenced by both agricultural input and urban development. Four laboratory experiments were conducted with water samples from TMC, adding different concentrations of phosphorus (P) and nitrogen (N) under controlled conditions. The results showed that turbidity and phytoplankton biomass (in terms of chlorophyll a concentration) in TMC water samples were responsive to N additions. Turbidity and phytoplankton biomass increased with addition of available N, but were not affected by addition of reactive P. The results indicate that available N is the limiting nutrient for the growth of phytoplankton in the TMC. Handling editor: L. Naselli-Flores     

鄱阳湖湿地两种优势植物叶片C、N、P动态特征

2011年2—6月在鄱阳湖南矶湿地国家级自然保护区逐月测定了灰化苔草(Carex cinerascens)、南荻(Triarrhena lutarioriparia)叶片C、N、P含量及其地上生物量,以阐明鄱阳湖湿地优势植物C、N、P含量及化学计量比动态特征与控制因子,探讨湿地养分利用与限制状况。结果表明：1）两种优势植物叶有机碳含量变化范围分别为365.3—386.6 mg/g和352.6—393.2 mg/g,平均值(?标准差)分别为(375.5?17.4) mg/g和(371.7?12.5) mg/g;叶N含量分别为6.96—17.59 mg/g和5.50—20.68 mg/g,平均值分别为(11.35?1.40) mg/g和(11.54?0.84) mg/g;叶P含量变化范围为0.65—2.14 mg/g和0.57—2.25 mg/g,平均含量为(1.56?0.69) mg/g和(1.55?0.68) mg/g。两种植物C:N、C:P、N:P平均值分别为37.65、413.60、9.62和41.05、410.29、9.57,C、N、P及其化学计量比种间差异不显著(P>0.05)。2）气温与地上生物量是N、P及其化学计量比季节变化的主要控制因子,气温和生物量对两种优势植物叶片氮、磷含量的影响要高于对叶有机碳含量的影响。3）植物C:N、C:P与地上生物量变化趋势基本一致,显示N、P养分利用效率随植物的快速生长而提高;根据两种优势植物及土壤N、P含量与化学计量比来判断,研究区植物更多地受氮限制。     

Dominance of phosphorus over nitrogen as the limiter to phytoplankton growth rate

Laboratory experiments with natural phytoplankton assemblages from three lakes (two mesotrophic and one oligotrophic) showed that added PO₄ predictably affected growth rate (μ, determined as P : B) while NO₃ had little effect even when the N P ratio approached one. The response to PO₄ followed the typical Monod-type function. The lack of effect of NO₃ on μ at such low N : P ratios is in striking contrast to the added effect of NO₃ Plus PO₄ on maximum biomass produced versus only PO₄ alone. Contribution No. 193 to the IBP-Coniferous Forest Biome. The work was supported in part by National Science Foundation Grant No. GB-20963 (IBP-Coniferous Forest Biome), and in part by Environmental Protection Agency Training Grant T900313-W P293-03,04. Contribution No. 193 to the IBP-Coniferous Forest Biome. The work was supported in part by National Science Foundation Grant No. GB-20963 (IBP-Coniferous Forest Biome), and in part by Environmental Protection Agency Training Grant T900313-W P293-03,04.