Influences of the lowland river Spree on phytoplankton dynamics in the flow-through Lake Müggelsee (Germany)

The influences of imports of nutrients and planktonic algae from the River Spree on the dynamics of phytoplankton were examined in the shallow, eutrophic Müggelsee, which has a retention time of only 42 days. Phytoplankton biomass and nutrient concentrations were measured in both the lake and its inflow from 1980–1990. On a long-term average, mean biomass as well as vitality of most dominant phytoplankton populations in the lake were not significantly different from those in the river. Nevertheless, during distinct periods the external rates of biomass change of single lake populations (due to dilution or enrichment) were as high as the lake internal ones. The import of inocula populations from the river probably induced the formation of the typical community structure in the lake. Growth and decay of phytoplankton populations in the river strongly influenced the load of dissolved nutrients and thus indirectly the dynamics of planktonic algae in the downstream lake. For example, intensive assimilation of phosphorus by riverine algae in spring intensified the P-shortage and supported possible P-limitation of algal growth in the lake at that time. In years with high vernal biomass of centric diatoms in the river, and thus diminished import of dissolved silicon, the growth of diatoms was suppressed and that of cyanobacteria was favoured in the lake during summer.     

Typology of shallow lakes of the Salado River basin (Argentina), based on phytoplankton communities

The phytoplankton communities of eleven shallow lakes from Buenos Aires Province, Argentina, were studied seasonally from 1987 to 1989. Several physical and chemical properties were measured in each lake (pH, temperature, dissolved oxygen, transparency, nutrients), in order to interpret the structural and dynamic traits of the phytoplankton community.Important differences between the lakes studied were put in evidence by means of multivariate techniques (Cluster Analysis and PCA). The shallow lakes densely populated by macrophytes hosted lowest phytoplanktonic densities, with average values ranging from 690 to 16500 algae ml^–1. High species diversities were observed in these lakes (4.0–4.8). Lakes less colonized by macrophytes had higher phytoplankton densities. In some of them important blooms of Cyanophyceae were recorded, with between 60 000 and 179 000 algae ml^–1, and concomitant low diversities.The results of this investigation support the hypothesis that the phytoplankton community is strongly influenced by the macrophytes, by direct competition and/or by competition from periphytic algae associated with higher plants.     

Phytoplankton strategies and time scales in a eutrophic reservoir

Phytoplankton species groups were studied in a eutrophic reservoir at different time scales (daily, weekly, monthly and yearly). Four strategic groups along the r-K continuum were defined and their seasonal time courses were followed. Their temporal distribution of relative biomass reflected resource partitioning because each strategic group dominated the phytoplankton community at different times in the year. However, the relationships between strategic groups changed with the time scale involved. At the daily scale an inverse relationship between r- and K-groups occurred whereas at supradaily scales such relationships did not hold. Species groups reflected strategic groups. No relationship between population growth and losses was found, suggesting that both were not counterbalanced. In the long term (supraannual) the phytoplankton community changed very much in this reservoir, its ecological memory being small as compared with that of lakes.     

Different responses to changes in phosphorus,P, among lakes. A study of slopes in chl-a = f(P) graphs

The least squares estimator of a linear regression coefficient _L will give an overall expression for the change in with x. In fresh water ecology, however, subgroups, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiuaSGaci% 4Aaaaa!37BE!\[P\operatorname{k}\], of a parent population may have slopes which differ from the overall slope, _L. By constructing frequency histograms for the set of angles: Arctang % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaci4uaSGaam% yAaiaadQgaaaa!38AE!\[\operatorname{S} ij\],% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaci4uaSGaam% yAaiaadQgaaaa!38AE!\[\operatorname{S} ij\]= para sa y and x% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiikaiaadM% faliaadMgakiabgkHiTiaadMfaliaadQgakiaacMcacaGGVaGaaiik% aiaadIhaliaadMgakiabgkHiTiaadIhaliaadQgakiaacMcaaaa!42F0!\[(Yi - Yj)/(xi - xj)\], i < j, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiEaSGaam% yAaOGaeyiyIKRaamiEaSGaamOAaaaa!3BAB!\[xi \ne xj\], peaks in the distribution may be identified and related to ecological phenomenon. To identify peaks we fit Gaussian distributions to the frequency histograms. For a set consisting of 142 observations of chlorophyll-a and total phosphorus (nutrient) concentrations (TP) from 16 lakes we found four Gaussian peaks corresponding to four subgroups, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamiuaSGaci% 4Aaaaa!37BE!\[P\operatorname{k}\]k = 1,4. One group identified a response of chl-a to changes in TP which correspond approximately to the average slope found by least square regression (the slope was 0.49). The second group consisted of steeper response than the average (1.28). A third group showed that there is an enhanced proportion of cases where chl-a does not respond to TP (zero slope, all the three deep lakes > 10 m, included in the date set contributed to this group). The size of the last group, spanning a wide range of slopes, suggested that about 30% of the inter annual changes in chl-a is unrelated to TP. The results are compared to result obtained by simple least squares regression and to the Theil non-parametric slope estimator.     

Regulation of phytoplankton dynamics in a Laurentian Great Lakes estuary

The composition and dynamics of phytoplankton populations were examined in Old Woman Creek estuary, Lake Erie (USA). The centric bacillariophytes,Cyclotella atomus Hust.,Cyclotella meneghiniana Kütz., andAulacoseira alpigena (Grun.) Krammer, and the cryptophytes,Cryptomonas erosa Ehren. andRhodomonas minuta var. nannoplanctonica Skuja, dominated the phytoplankton most of the year. Chlorophytes, euglenophytes, and cyanophytes were observed less frequently. Estuarine and Lake Erie phytoplankton were considered distinct populations; lake taxa were largely confined to the estuary mouth and present only in low biomass. Maxima and minima of estuarine phytoplankton coincided with meteorological and hydrological forcing in the form of rainfall and subsequent storm-water inflows, respectively. Distinct population dynamics between the upper and lower estuary following storm events were attributed to the presence/absence of refugia serving as a source for repopulation by opportunistic taxa, fluctuating light conditions in the water column resulting from influx of particulate matter and resuspension of bottom sediments, and nutrient inputs associated with surface runoff and sub-surface interflow. Additionally, agricultural herbicides introduced by storm-water inflows potentially may affect and/or control the growth and physiological responses of individual taxa.     

Non-photochemical fluorescence quenching and the diadinoxanthin cycle in a marine diatom

The diadinoxanthin cycle (DD-cycle) in chromophyte algae involves the interconversion of two carotenoids, diadinoxanthin (DD) and diatoxanthin (DT). We investigated the kinetics of light-induced DD-cycling in the marine diatom Phaeodactylum tricornutum and its role in dissipating excess excitation energy in PS II. Within 15 min following an increase in irradiance, DT increased and was accompanied by a stoichiometric decrease in DD. This reaction was completely blocked by dithiothreitol (DTT). A second, time-dependent, increase in DT was detected 20 min after the light shift without a concomitant decrease in DD. DT accumulation from both processes was correlated with increases in non-photochemical quenching of chlorophyll fluorescence. Stern-Volmer analyses suggests that changes in non-photochemical quenching resulted from changes in thermal dissipation in the PS II antenna and in the reaction center. The increase in non-photochemical quenching was correlated with a small decrease in the effective absorption cross section of PS II. Model calculations suggest however that the changes in cross section are not sufficiently large to significantly reduce multiple excitation of the reaction center within the turnover time of steady-state photosynthetic electron transport at light saturation. In DTT poisoned cells, the change in non-photochemical quenching appears to result from energy dissipation in the reaction center and was associated with decreased photochemical efficiency. D1 protein degradation was slightly higher in samples poisoned with DTT than in control samples. These results suggest that while DD-cycling may dynamically alter the photosynthesis-irradiance response curve, it offers limited protection against photodamage of PS II reaction centers at irradiance levels sufficient to saturate steady-state photosynthesis.Abbreviations CAP chloramphenicol - D1 PS II reaction center protein - DD diadinoxanthin - DD cycle-diadinoxanthin cycle - DT diatoxanthin - DTT dithiothreitol - FCP fucoxanthin chlorophyll a-c protein - F_m maximum fluorescence yield in the dark-adapted state - F_o minimum fluorescence yield in the dark-adapted state - F_m and F_o maximum and minimum fluorescence yields respectively in some light adapted state - F_v maximum variable fluorescence yield in the dark-adapted state - I_k Irradiance at the intercept of the initial slope of the photosynthesis-irradiance curve and the maximum photosynthetic rate - k_D first order rate constant for nonradiative de-excitation of excitions in the PS II antenna - k_d first order rate constant for non-radiative de-excitation of excitons in the PS II reaction center - k_F first order rate constant for fluorescence - k_T first order rate constant for exciton transfer to the reaction center - k_t first order rate constant for exciton transfer from the reaction center to the antenna - Rubisco ribulose bisphosphate carboxylase - SV_m Stern-Volmer quenching coefficient of the maximum fluorescence yield - SV_o Stern-Volmer quenching coefficient of the miniximum fluorescence yield - _{PS II} apparent absorption cross-section of PS II - _arr average interval between exciton arrival to the PS II reaction center (ms) - _rem average interval between electron turnover during photosynthesis in the PS II reaction center (ms) - _d the probability that an exciton is non-radiatively dissipated in the reaction center - _T the probability that an exciton in the antenna is transferred to the reaction center - _t the probability that an exciton is transferred back from the reaction center to the antenna     

ACTIVE GROWTH OF THE OCEANIC DINOFLAGELLATE CERATIUM TERES IN THE CARIBBEAN AND SARGASSO SEAS ESTIMATED BY CELL CYCLE ANALYSIS1

The growth rate of an oceanic dinoflagellate, Ceratium teres Kofoid, was investigated in the Sargasso and Caribbean Seas from September 1989 to July 1990 using the cell cycle analysis method. Estimated growth rates ranged from 0.29 to 0.58 day^?1 and were 1.5–7.2 times higher than generally accepted rates for oceanic dinoflagellates. The higher rates in this report were mainly due to an improvement in techniques that determine the duration of a terminal cell cycle phase in situ. The day-to-day variation in growth rates was surprisingly small, but, from long-term measurements, a weak correlation was found among temperature, daily irradiance, and seasonal growth rate. The calculated species-specific primary production ranged from 0.5 to 1.8 mg C·m^?2·day^?1, about 1% of the estimated total production. Ceratium teres may be an important carbon source at the base of the grazing food chain.     

A comparison of phytoplankton assemblages in the Chesapeake and Delaware estuaries (USA), with emphasis on diatoms

The Delaware Bay is characterized as having greater nutrient and turbidity levels than the Chesapeake Bay. In reference to these differences, a one year study was conducted to identify any similarities and differences in the phytoplankton populations in these estuaries. The results indicated patterns of similarity in the diatom composition, with the total phytoplankton assemblage forming two site groups along a salinity gradient in each bay. These site groups were associated with stations located in the tidal fresh-oligohaline and meso-polyhaline regions of both estuaries. The seasonal concentrations of diatoms and total phytoplankton in both of these regions were higher in the Chesapeake Bay.Subtle differences between the two estuaries include a more diversified and abundant assemblage of neritic phytoplankters (including dinoflagellates) are present in the lower Chesapeake Bay. In contrast, a diatom dominated community is more characteristic of Delaware Bay. It is suggested the entry of neritic species into lower regions of the estuaries was enhanced by the reduced amount of rainfall and flow rates that occurred during the study period. The greater success of neritic species in the Chesapeake Bay is attributed to the lower turbidity of that estuary compared to Delaware Bay.     

Artificial destratification of a small tropical reservoir: effects upon the phytoplankton

Seasonal changes in the phytoplankton community of a small tropical reservoir were monitored over a four year period comprising of an initial two seasonal cycles during which the water column stratified strongly for extended periods each year, and two further seasonal cycles after installation of a mechanical aeration system to induce artificial destratification. In the unmanaged reservoir, the concentration of chlorophyll a at 0.5 m reached maximum values (on one occasion > 90 mg m⁻³) when the water column was stratified and the epilimnion was very shallow (ca 2 m depth). The hypolimnion at this time was anoxic (less than 2% oxygen saturation) and had a high concentration of bacteriochlorophyll (100–200 mg m⁻³). The phytoplankton community of the unmanaged reservoir was generally dominated by cyanobacteria (Cylindrospermopsis raciborskii, Anabaena tenericaulis) during the warmer months of the year (November–March) (but replaced by chlorophyta, dinophyceae and euglenophyceae after periods of intense rain) and by bacillariophyceae (Synedra ulna var. chaseana, S. tenera) during the cooler, dry months. In the artificially destratified reservoir (8 h aeration day⁻¹), the phytoplankton community was largely dominated by diatoms except after depletion of the silica content of the water column which caused diatoms to be replaced by cyanobacteria (dominated by A. tenericaulis) and a range of chlorophytes. The changing pattern of stratification and circulation of the water column in the unmanaged reservoir caused repeated disruption of the established phytoplankton assemblage with peaks of high biomass associated with transient cyanobacterial blooms. Continuous aeration and the consequent increase in the ratio mixed: euphotic depth provided conditions suitable for dominance of the phytoplankton by diatoms, as long as silica was available, and resulted in average chlorophyll levels higher than in the unmanaged reservoir (120 ± 10 v. 64 ± 9 mg m⁻²). Hierarchical fusion analysis based on the biomass of species differentiated the phytoplankton samples into cluster groups that could be related primarily to stratification or mixing of the water column.     

PHYSIOLOGICAL ACCLIMATION OF MARINE PHYTOPLANKTON TO DIFFERENT NITROGEN SOURCES1

We examined the energetic dependency of the biochemical and physiological responses of Thalassiosira pseudonana Hasle and Heimdal. Chaetoceros gracilis Schütt, Dunaliella tertiolecta Butcher, and Gymnodinium sanguineum Hirasaka to NH₄⁺, NO₃^?, and urea by growing them at subsaturating and saturating photon flux (PF). At subsaturating PF, when energy was limiting, NO₃^? and NH₄⁺ grown cells had similar growth rates and C and X quotas. Therefore, NO₃^? grown cells used up to 48% more energy than NH₄⁺ grown cells to assimilate carbon and nitrogen. Based on our measurements of pigments, chlorophyll-a-specific in vivo absorption cross-section, and fluorescence-chlorophyll a^?1, we suggest that NO₃^?, grown cells do not compensate for the greater energy requirements of NO₃^? reduction by trapping more light energy. At saturating PF, when energy is not limiting, the utilization of NO₃^?, compared to NH₄⁺ resulted in lower growth rates and N quotas in Thalassiosira pseudonana and lower N quotas in Chaetoceros gracilis, suggesting enzymatic rather than energetic limitations to growth. The utilization of urea compared to Nh₄⁺ resulted in lower growth rates in Chaetoceros gracilis and Gymnodinium sanguineum (saturating PF) and in lower N quotas in all species tested at both subsaturating and saturating PF. The high C:N ratios observed in all urea-grown species suggest that nitrogen assimilation may be limited by urea uptake or deamination and that symptoms of N limitation in microalgae may be induced by the nature of the N source in addition to the N supply rate. Our results provide new eridence that the maximum growth rates of microalgae may be limited by enzymatic processes associated with the assimilation of NO₃^?, or urea.