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1.
The problem of the vertical distribution of phytoplankton is considered in the presence of gravitational settling, turbulent
mixing, population growth due to cell division and a constant rate of loss due to predation and natural death. Nutrients are
assumed to be plentiful so that the production rate depends only on the light available for photosynthesis. The non-linear
saturation of plankton growth is modeled by allowing the attenuation rate of light to be a linear function of the plankton
density. The turbulent diffusivity is assumed constant which corresponds to a mixed layer depth very much greater than the
depth of light penetration (euphotic depth). It is shown that an exact analytical solution of this non-linear problem is possible
for an idealized model in which the functional dependence of production on light intensity is assumed to be a step function.
Non-zero solutions are shown to exist only if the parameters characterizing the system are above a certain critical curve
in a two dimensional parameter space. Numerical simulations using functional forms of the production curve that resemble the
measured photosynthetic response of plankton, show, that the qualitative behavior of the system is similar to that of the
idealized model presented. Comparisons are made with other analytical approaches to the problem.
Received: 14 March 2002 / Revised version: 27 September 2002 / Published online: 28 February 2003
Key words or phrases: Self-shading – Plankton – Nonlinear – Turbulence 相似文献
2.
Consideration of nitrogen fixation adds a positive nonlinear feedback to plankton ecosystem models. We investigate the consequences
of this feedback for secondary phytoplankton blooms and the response of phytoplankton dynamics to physical forcing. The dynamics
of phytoplankton, Trichodesmium (the nitrogen fixer), and nutrients is modeled with a system of three differential equations. The model includes two types
of nonlinear interactions: the competition of phytoplankton and Trichodesmium for light, and the positive feedback resulting from Trichodesmium recycling. A typical simulation of the model in time, with forcing by a varying mixed-layer depth, reveals a clear successional
sequence including a secondary or ‘echo’ bloom of the phytoplankton. We explain this sequence of events through the stability
analysis of three different steady states of the model. Our analysis shows the existence of a critical biological parameter,
the ratio of normalized growth rates, determining the occurrence of ‘echo’ blooms and the specific sequence of events following
a physical perturbation. The interplay of positive and negative feedbacks appears essential to the timing and the type of
events following such a perturbation. 相似文献
3.
Klára Řeháková Eliška Zapomělová Ondřej Prášil Jana Veselá Hana Medová Aharon Oren 《Hydrobiologia》2009,636(1):77-88
There are several conflicting hypothesis that deal with the influence of flooding in the natural river–floodplain systems.
According to the Flood Pulse Concept, the flood pulses are not considered to be a disturbance, while some recent studies have
proven that floods can be a disturbance factor of phytoplankton development. In order to test whether flooding acts as a disturbance
factor in the shallow Danubian floodplain lake (Lake Sakadaš), phytoplankton dynamics was investigated during two different
hydrological years—extremely dry (2003) without flooding and usually flooded (2004). A total of 18 phytoplankton functional
groups were established. The sequence of phytoplankton seasonality can be summarized P/D → E (W1, W2) → C/P (only in potamophase) → S2/H1/SN/S1 → W1/W2 → P/D. The canonical correspondence analysis (CCA) demonstrated that the water level was a significant environmental
variable in 2004. Due to the higher total biomass of Bacillariophyceae established under potamophase conditions, floodings
in the early spring seem to be a stimulating factor for phytoplankton development. On the other hand, the flood pulses in
May and June had dilution effects on nutrients, so that a significantly lower phytoplankton biomass was established indicating
that flooding pulses can be regarded as a disturbance event. Such conditions supported diatom development (D, P, C species)
and prolonged its dominance in the total phytoplankton biomass. A long-lasting Cyanoprokaryota bloom (various filamentous
species—S1, S2, SN and H1 representatives) with very high biomass characterized the limnophase (dry conditions) in summer and autumn of both
years. In-lake variables (lake morphology, internal loadings of nutrients from sediments, light conditions) seem to be important
for the appearance of Cyanoprokaryota bloom. The equilibrium phase was found during the Cyanoprokaryota bloom only in the
extremely dry year. This study showed that depending on the time scale occurrence, flood pulses can be a stimulating or a
disturbance factor for phytoplankton development in Lake Sakadaš.
Handling editor: J. Padisak 相似文献
4.
1. A phytoplankton community model [Phytoplankton RespOnses To Environmental CHange (PROTECH)] was used to examine the effect of a wide range of varied light intensities and mixed depths upon simulated phytoplankton populations. Two different column lengths of the simulated water body were examined (the upper 5 m and the whole 14.5 m water column) for each scenario.
2. The hypotheses tested were that: (i) under low light intensity and/or deep mixing the simulated community will be dominated by a phytoplankter with a low critical light intensity; (ii) at high light intensity and shallow mixing the simulated community will be dominated by small, fast-growing phytoplankters; (iii) under all conditions, except deep mixing, the largest proportion of phytoplankton biomass will be found near the surface.
3. It was found under most conditions that, although there was a bloom in the upper column (dominated by algae such as Chlorella , Ceratium or Rhodomonas ), the largest phytoplankton biomass in the water column was located 9 m below the surface and consisted of solely Asterionella . This bloom was missed by the 5-m samples. Thus, using the whole column sample lengths, hypothesis (i) was not rejected but hypotheses (ii) and (iii) were refuted.
4. The inclusion of specific movement characteristics of phytoplankton in the model allowed the possibility of the dominance of multiple spaces within the water column and should be included in any model-based investigation of this topic. Further, the results from the model suggest that a reduced depth of mixing creates greater environmental heterogeneity, allowing more species to persist. 相似文献
2. The hypotheses tested were that: (i) under low light intensity and/or deep mixing the simulated community will be dominated by a phytoplankter with a low critical light intensity; (ii) at high light intensity and shallow mixing the simulated community will be dominated by small, fast-growing phytoplankters; (iii) under all conditions, except deep mixing, the largest proportion of phytoplankton biomass will be found near the surface.
3. It was found under most conditions that, although there was a bloom in the upper column (dominated by algae such as Chlorella , Ceratium or Rhodomonas ), the largest phytoplankton biomass in the water column was located 9 m below the surface and consisted of solely Asterionella . This bloom was missed by the 5-m samples. Thus, using the whole column sample lengths, hypothesis (i) was not rejected but hypotheses (ii) and (iii) were refuted.
4. The inclusion of specific movement characteristics of phytoplankton in the model allowed the possibility of the dominance of multiple spaces within the water column and should be included in any model-based investigation of this topic. Further, the results from the model suggest that a reduced depth of mixing creates greater environmental heterogeneity, allowing more species to persist. 相似文献
5.
Seasonal variation of mixing depth and its influence on phytoplankton dynamics in the Zeya reservoir, China 总被引:2,自引:0,他引:2
Xuechu Chen Xiaodong Wang Deyi Wu Shengbing He Hainan Kong Zen’ichiro Kawabata 《Limnology》2009,10(3):159-165
In reservoirs or lakes, mixing depth affects growth and loss rates of phytoplankton populations. Based on 1-year data from
the Zeya reservoir, China, we scaled the mixing depth throughout a whole year by utilizing cluster analysis, and then investigated
its influence on phytoplankton dynamics and other physical and chemical parameters. Over the whole year, all physical and
chemical parameters except TN and temperature had significant correlations with mixing depth, indicating that mixing depth
is one of the important driving factors influencing water environment. According to mixing depth, a year can be divided into
three different periods, including the thermally stratified period, isothermally mixed period, and transition period between
them. When considering the former two different periods separately, mixing depth had no correlation with the phytoplankton
biovolume. However, over the whole year a significant correlation was observed, which indicated that the influence of mixing
depth on phytoplankton growth in the Zeya reservoir still followed Diehl’s theory. Furthermore, according to the steady-state
assumption, a unimodal curve (mixing depth—phytoplankton biovolume) with a significant peak appearing at a mixing depth of
2 m was observed, closely agreeing with Diehl’ prediction. 相似文献
6.
Phytoplankton require light for photosynthesis. Yet, most phytoplankton species are heavier than water and therefore sink. How can these sinking species persist? Somehow, the answer should lie in the turbulent motion that redisperses sinking phytoplankton over the vertical water column. Here, we show, using a reaction-advection-diffusion equation of light-limited phytoplankton, that there is a turbulence window sustaining sinking phytoplankton species in deep waters. If turbulent diffusion is too high, phytoplankton are mixed to great depths, and the depth-averaged light conditions are too low to allow net positive population growth. Conversely, if turbulent diffusion is too low, sinking phytoplankton populations end up at the ocean floor and succumb in the dark. At intermediate levels of turbulent diffusion, however, phytoplankton populations can outgrow both mixing rates and sinking rates. In this way, the reproducing population as a whole can maintain a position in the well-lit zone near the top of the water column, even if all individuals within the population have a tendency to sink. This theory unites earlier classic results by Sverdrup and Riley as well as our own recent findings and provides a new conceptual framework for the understanding of phytoplankton dynamics under the influence of mixing processes. 相似文献
7.
Climate change and the timing, magnitude, and composition of the phytoplankton spring bloom 总被引:2,自引:0,他引:2
In this article, we show by mesocosm experiments that winter and spring warming will lead to substantial changes in the spring bloom of phytoplankton. The timing of the spring bloom shows only little response to warming as such, while light appears to play a more important role in its initiation. The daily light dose needed for the start of the phytoplankton spring bloom in our experiments agrees well with a recently published critical light intensity found in a field survey of the North Atlantic (around 1.3 mol photons m?2 day?1). Experimental temperature elevation had a strong effect on phytoplankton peak biomass (decreasing with temperature), mean cell size (decreasing with temperature) and on the share of microplankton diatoms (decreasing with temperature). All these changes will lead to poorer feeding conditions for copepod zooplankton and, thus, to a less efficient energy transfer from primary to fish production under a warmer climate. 相似文献
8.
We consider a simple phytoplankton model introduced by Shigesada and Okubo which incorporates the sinking and self-shading
effect of the phytoplankton. The amount of light the phytoplankton receives is assumed to be controlled by the density of
the phytoplankton population above the given depth. We show the existence of non-homogeneous solutions for any water depth
and study their profiles and stability. Depending on the sinking rate of the phytoplankton, light intensity and water depth,
the plankton can concentrate either near the surface, at the bottom of the water column, or both, resulting in a “double-peak”
profile. As the buoyancy passes a certain critical threshold, a sudden change in the phytoplankton profile occurs. We quantify
this transition using asymptotic techniques. In all cases we show that the profile is locally stable. This generalizes the
results of Shigesada and Okubo where infinite depth was considered.
相似文献
9.
We have utilized data from a recently developed three-dimensionalvelocity fluctuation meter to compute the dissipation of turbulentkinetic energies (TKE) and the intensity of turbulent mixingin horizontal and vertical planes in the pelagic, epilimnicwater of Lake Kinneret, Israel. These characteristics of wind-inducedturbulent movement have been monitored from January 1992 throughDecember 1996. The turbulence parameters were strongly correlatedto wind energy inputs, calculated daily as 5 day cumulativeinputs. There have been dramatic changes in the annual and seasonaldevelopment of phytoplankton, together with unusually high levelsof primary production in this lake since 1994. We observed differentpatterns of vertical and horizontal turbulent movement and ofTKE dissipation rates during the years when unusualphytoplankton development occurred (19941996) comparedto normal years (1992, 1993). The first appearanceof the filamentous cyanobacterium Aphanizomenon in this lakein AugustSeptember 1994 coincided with a period of markedlylower rates of TKE dispersion and a shift from vertical to horizontaldominance of the turbulent eddy spins. The absence of a regularwinter-spring bloom of the dinoflagellate, Peridinium, in 1996occurred when dissipation rates of TKE were extremely high,while record high amounts of dinoflagellates (1994, 1995) appearedwhen dissipation rates were very low. Correlations were shownbetween phytoplankton parameters (chlorophyll, primary productionand the ratio of primary production to chlorophyll) and boththe dissipation rate of TKE and the intensity of water turbulentmixing in the vertical plane. We suggest that the changes inthe turbulence climate of Lake Kinneret were animportant factor in determining shifts in phytoplankton successionand the population composition of the algal assemblage. 相似文献
10.
Comparative analysis of nutrients,chlorophyll and transparency in two large shallow lakes (Lake Taihu,P.R. China and Lake Okeechobee,USA) 总被引:5,自引:0,他引:5
This article compares limnological attributes of two of the world’s largest shallow lakes—Lake Okeechobee in Florida, USA
and Lake Taihu in P.R. China. Both the systems support an array of ecological and societal values including fish and wildlife
habitat, public water supply, flood protection, and recreation. Both have extensive research programs, largely because of
concern regarding the lakes’ frequent cyanobacterial blooms. By evaluating these systems together, we compare and contrast
properties that can generally advance the understanding and management of large shallow lowland lakes. Because of shallow
depth, long fetch, and unconsolidated mud sediments, water chemistry, and transparency in both the lakes are strongly influenced
by resuspended sediments that affect light and nutrient conditions. In the central region of both the lakes, where depth is
the greatest, evaluation of limiting factors by a trophic state index approach indicates that light most often limits phytoplankton
biomass. In contrast, the more sheltered shoreline areas of both the lakes display evidence of nitrogen (N) limitation, which
also has been confirmed in nutrient assays conducted in earlier studies. This N limitation most likely is a result of excessive
levels of phosphorus (P) that have developed in the lakes due to high external loads over recent decades and the currently
high internal P recycling. Comparisons of these lakes show that Lake Taihu has higher N than, similar total phosphorus (TP)
and similar light conditions to that of Lake Okeechobee, but less chlorophyll a (CHL). The latter may be as a result of lower winter temperatures in Lake Taihu (around 5°C) compared to Lake Okeechobee
(around 15°C), which could reduce phytoplankton growth and abundance through the other seasons of the year. In these systems,
the important role of light, temperature, and nutrients in algal bloom dynamics must be considered, especially due to possible
adverse and unintended effects that might occur with projects such as sediment removal, and in the long term, in regard to
buffering lake responses to external load reduction.
Handling editor: D. Hamilton 相似文献
11.
Based on a 1D model considering phytoplankton and nutrients in a vertical water column, we investigate the consequences of temporal and spatial variations in turbulent mixing for phytoplankton production and biomass. We show that in seasonally mixed systems, the processes controlling phytoplankton production and the sensitivity of phytoplankton abundance to ambient light, trophic state and mixed-layer depth differ substantially from those at steady state in systems with time-constant diffusivities. In seasonally mixed systems, the annually replenished nutrient pool in the euphotic zone is an important factor for phytoplankton production supporting bloom development, whereas without winter mixing, production mainly depends on the diffusive nutrient flux during stratified conditions. Seasonal changes in water column production are predominantly determined by seasonal changes in phytoplankton abundance, but also by seasonal changes in specific production resulting from the transport of nutrients, the exploitation of the nutrient pool and the increase in light shading associated with phytoplankton growth. The interplay between seasonal mixing and the vertical distribution of mixing intensities is a key factor determining the relative importance of the processes controlling phytoplankton production and the sensitivity of the size and timing of the annual maximum phytoplankton abundance to the abiotic conditions. 相似文献
12.
A simple model that describes the dynamics of nutrient-driven phytoplankton blooms is presented. Apart from complicated simulation studies, very few models reported in the literature have taken this "bottom-up" approach. Yet, as discussed and justified from a theoretical standpoint, many blooms are strongly controlled by nutrients rather than by higher trophic levels. The analysis identifies an important threshold effect: a bloom will only be triggered when nutrients exceed a certain defined level. This threshold effect should be generic to both natural blooms and most simulation models. Furthermore, predictions are given as to how the peak of the bloom Pmax is determined by initial conditions. A number of counterintuitive results are found. In particular, it is shown that increasing initial nutrient or phytoplankton levels can act to decrease Pmax. Correct predictions require an understanding of such factors as the timing of the bloom and the period of nutrient buildup before the bloom. 相似文献
13.
Spring bloom dynamics in Kongsfjorden,Svalbard: nutrients,phytoplankton, protozoans and primary production 总被引:1,自引:0,他引:1
The marine ecosystem in Kongsfjorden (79°N), a glacial fjord in Svalbard, is to a large extent well known with regard to hydrography,
mesozooplankton and higher trophic levels. Research on primary production and lower trophic levels is still scare and especially
investigations from winter and spring periods. The spring bloom dynamics in Kongsfjorden were investigated in 2002. The development
in nutrient conditions, phytoplankton, protozoans and primary production were followed from 15 April until 22 May. The winter/spring
in 2002 was categorized as a cold year with sea ice cover and water masses dominated by local winter-cooled water. The spring
bloom started around 18 April and lasted until the middle of May. The bloom probably peaked in late April, but break-up of
sea ice made it impossible to sample frequently in this period. Diatoms dominated the phytoplankton assemblage. We estimated
the total primary production during the spring bloom in 2002 to range 27–35 g C m−2. There was a mismatch situation between the mesozooplankton and the phytoplankton spring bloom in 2002. 相似文献
14.
Alexei B. Ryabov 《Theoretical Ecology》2012,5(3):373-385
Resource competition in heterogeneous environments is still an unresolved problem of theoretical ecology. In this article, I analyze competition between two phytoplankton species in a deep water column, where the distributions of main resources (light and a limiting nutrient) have opposing gradients and co-limitation by both resources causes a deep biomass maximum. Assuming that the species have a trade-off in resource requirements and the water column is weakly mixed, I apply the invasion threshold analysis (Ryabov and Blasius, Ecol Lett 14:220–228, 2011) to determine relations between environmental conditions and phytoplankton composition. Although species deplete resources in the interior of the water column, the resource levels at the bottom and surface remain high. As a result, the slope of resources gradients becomes a new crucial factor which, rather than the local resource values, determines the outcome of competition. The value of resource gradients nonlinearly depend on the density of consumers. This leads to complex relationships between environmental parameters and species composition. In particular, it is shown that an increase of both the incident light intensity or bottom nutrient concentrations favors the best light competitors, while an increase of the turbulent mixing or background turbidity favors the best nutrient competitors. These results might be important for prediction of species composition in deep ocean. 相似文献
15.
Picoeukaryotes dominate the phytoplankton of Lake Balaton—the largest shallow lake in Central Europe—in the winter period.
We examined the annual dynamics of picoplankton abundance and composition in the lake in order to establish if the picoeukaryotes
merely survive the harsher winter conditions or they are able to grow in the ice-covered lake when the entire phytoplankton
is limited by low light and temperature. Lake Balaton has an annual temperature range of 1–29°C, and it is usually frozen
between December and February for 30–60 days. In the spring-autumn period phycocyanin and phycoerythrin rich Cyanobacteria
are the dominant picoplankters, and picoeukaryotes are negligible. Our five-year study shows the presence of three types of
picophytoplankton assemblages in Lake Balaton: (1) Phycoerythrin-rich Cyanobacteria—the dominant summer picoplankters in the
mesotrophic lake area; (2) Phycocyanin-rich Cyanobacteria—the most abundant summer picoplankters in the eutrophic lake area
and; (3) Picoeukaryotes—the dominant winter picoplankters in the whole lake. The observed winter abundance of picoeukaryotes
was high (up to 3 × 105 cells ml−1), their highest biomass (520 μg l−1) exceeded the maximum summer biomass of picocyanobacteria (500 μg l−1). Our results indicate that the winter predominance of picoeukaryotes is a regular phenomenon in Lake Balaton, irrespective
of the absence or presence of the ice cover. Picoeukaryotes are able to grow at as low as 1–2°C water temperature, while the
total phytoplankton biomass show the lowest annual values in the winter period. In agreement with earlier findings, the contribution
of picocyanobacteria to the total phytoplankton biomass in Lake Balaton is inversely related to the total phytoplankton biomass,
whereas no such relationship was observable in the case of picoeukaryotes. 相似文献
16.
The relationship between specific environmental factors as independent variables and temporal changes in phytoplankton community
structure in the Vaal River (a turbid system) during 1984 was investigated by employing different diversity indices. Temporal
changes in community structure reflected temporal changes in certain environmental factors. Phytoplankton diversity, measured
with Shannon-Wie H' and Hurlbert PIE indices, was related firstly to discharge and discharge derived variables (such as SO4, Si, N and P loading) and secondly to turbidity derived variables (such as euphotic zone depth). Discharge appears to be
of prime importance in affecting diversity. Observations were made that shed new light on conditions contributing to the development
of an August peak (dominated by Stephanodiscus hantzschii fo. tenuis and Micractinium pusillum) in phytoplankton concentration. Increased environmental stress may reduce the number of sensitive species, thus reducing
interspecific competition between tolerant species which could then exploit the — for them — more favourable conditions resulting
in an increase in their numbers to peak concentrations. 相似文献
17.
Modelling phytoplankton productivity in turbid waters with small euphotic to mixing depth ratios 总被引:4,自引:0,他引:4
A model which was developed and calibrated for predicting algalgrowth in mass cultures, was modified for natural systems. Inturbid systems the ratio of euphotic to aphotic depth is usuallysmall and mixing may exceed the compensation depth. In orderto compensate for the various light regimes to which the phytoplanktonwould be subjected, the losses due to dark respiration weremodified so that the effective light history would determinethe actual rate. The efficiency of light utilization also changesunder different light regimes and the model was modified totake these variations into account. Both these modificationsresulted in different production profiles being generated forthe same surface conditions, but with different mixing depths,where the phytoplankton become more efficient as the light regimedeteriorates (i.e. less respiration and greater light utilizationefficiency). A further consequence is that the criticalmixing depth is {small tilde}2.5 times greater than thatwhich was previously accepted, being {small tilde}20 times theeuphotic depth. The model predicted productivities to within90% of observed rates. It was also suggested how the predictionscould be used to determine the extent of nutrient limitation.The predictions also have biomanipulatory consequences, as alterationsof the light regime through the addition of non-photosynthesizingmaterials, under certain conditions, may even result in a stimulationof phytoplankton productivity. 相似文献
18.
This study aimed at simulating different degrees of winter warming and at assessing its potential effects on ciliate succession
and grazing-related patterns. By using indoor mesocosms filled with unfiltered water from Kiel Bight, natural light and four
different temperature regimes, phytoplankton spring blooms were induced and the thermal responses of ciliates were quantified.
Two distinct ciliate assemblages, a pre-spring and a spring bloom assemblage, could be detected, while their formation was
strongly temperature-dependent. Both assemblages were dominated by Strobilidiids; the pre-spring bloom phase was dominated
by the small Strobilidiids Lohmaniella oviformis, and the spring bloom was mainly dominated by large Strobilidiids of the genus Strobilidium. The numerical response of ciliates to increasing food concentrations showed a strong acceleration by temperature. Grazing
rates of ciliates and copepods were low during the pre-spring bloom period and high during the bloom ranging from 0.06 (Δ0°C)
to 0.23 day−1 (Δ4°C) for ciliates and 0.09 (Δ0°C) to 1.62 day−1 (Δ4°C) for copepods. During the spring bloom ciliates and copepods showed a strong dietary overlap characterized by a wide
food spectrum consisting mainly of Chrysochromulina sp., diatom chains and large, single-celled diatoms.
Priority programme of the German Research Foundation—contribution 4. 相似文献
19.
Phytoplankton response to a changing climate 总被引:5,自引:0,他引:5
Phytoplankton are at the base of aquatic food webs and of global importance for ecosystem functioning and services. The dynamics of these photosynthetic cells are linked to annual fluctuations of temperature, water column mixing, resource availability, and consumption. Climate can modify these environmental factors and alter phytoplankton structure, seasonal dynamics, and taxonomic composition. Here, we review mechanistic links between climate alterations and factors limiting primary production, and highlight studies where climate change has had a clear impact on phytoplankton processes. Climate affects phytoplankton both directly through physiology and indirectly by changing water column stratification and resource availability, mainly nutrients and light, or intensified grazing by heterotrophs. These modifications affect various phytoplankton processes, and a widespread advance in phytoplankton spring bloom timing and changing bloom magnitudes have both been observed. Climate warming also affects phytoplankton species composition and size structure, and favors species traits best adapted to changing conditions associated with climate change. Shifts in phytoplankton can have far-reaching consequences for ecosystem structure and functioning. An improved understanding of the mechanistic links between climate and phytoplankton dynamics is important for predicting climate change impacts on aquatic ecosystems. 相似文献
20.
Sedimentation loss of phytoplankton cells from the mixed layer: effects of turbulence levels 总被引:2,自引:0,他引:2
In this paper, we describe a study of the role of turbulencein the loss by sedimentation of phytoplankton cells from themixed layer. The approach presented allows the quantificationof the sedimentation rate of phytoplankton in the whole rangeof turbulence levels of this layer. Two types of phytoplanktercan be distinguished according to the effect that turbulencecan exert on their sedimentation rate. The rate of those cellswhose settling velocity is lower than 1 m day1will not be modified by turbulence. The sedimentation rate ofcells with higher settling velocities can, however, be modifiedby the level of turbulence. A set of dimensionless numbers isgiven to delimit several processes that are important in thedynamics of phytoplankton sedimentation in a turbulent regime.The use of these dimensionless numbers suggests that an increasein the turbulence level in the mixed layer does not always implya decrease in the sedimentation rate of phytoplankton cells. 相似文献