Phytoplankton Activity Research Articles

Extracellular phosphatase activity of freshwater phytoplankton exposed to different in situ phosphorus concentrations

Extracellular phosphatase production and biomass change were investigated in phytoplankton species transplanted from the phosphorus-limited dam area of a eutrophic reservoir and exposed to the phosphorus-sufficient inflow part and vice versa. Extracellular phosphatase activity was studied using the enzyme-labelled fluorescence (ELF) technique, allowing for direct microscopic detection of enzyme activity and, moreover, its quantification using image cytometry. Several phytoplankton species (e.g. Anabaena planctonica, Microcystis aeruginosa, Fragilaria crotonensis, Ankyra ancora and Planktosphaeria gelatinosa) regulated phosphatase activity according to external phosphorus concentration. On the contrary, picocyanobacteria and several green algae (Coelastrum microporum, Crucigeniella sp., Pediastrum tetras, and Staurastrum planctonicum) did not produce extracellular phosphatases at all. The species-specific extracellular phosphatase activity of F. crotonensis, A. ancora, and P. gelatinosa ranged between 0.02 and 3.5 fmol μm−2 h−1.

Late glacial to Holocene climate and sedimentation history in the NW Black Sea

Gravity cores from the continental slope in the northwestern Black Sea were studied using high-resolution stable isotope, grain size and XRF-scanning data. The measurements provide a 30 000 years AMS 14C-dated record of variations in the hydrological regime of the Black Sea and give insight into changing paleoenvironments in the surrounding areas. Stable climatic conditions during the Last Glacial Maximum were followed by a series of meltwater pulses most likely originating from the Scandinavian ice sheet between 18 000 and 15 500 yr BP. 1 1 All dates are calibrated to calendar years B.P. (yr BP). This meltwater input rose the level of the Caspian Sea to a point that Caspian water could spill into the Black Sea via the Manych-depression north of the Caucasian mountains. High-frequency oscillations in the XRF-data during this period suggest a probable link to the arctic climate regime. Later, during the Bølling/Allerød and the early Holocene, prevailing high temperatures led to authigenic calcite precipitation through increased phytoplankton activity, interrupted by the Younger Dryas and the “8200 yr BP cold event” with dominant clastic sedimentation.

Availability of iron and major nutrients for phytoplankton in the northeast Atlantic Ocean

Because of recent findings that Fe is a limiting factor for phytoplankton activity even at relatively high dissolved iron (DFe) concentrations, the potential importance of Fe limitation was revisited in the northeast Atlantic Ocean (39−45°N, 17−21°W). We report data gathered during deck incubation experiments performed at three stations in February‐March 2001 with surface seawater containing DFe concentrations of ~0.40 nmol L−1. At all stations, Fe addition enhanced phytoplankton growth. Fe limitation was moderate and occurred simultaneously with limitation by major nutrients. This was clearly demonstrated for diatoms that were colimited by orthosilicic acid. Micro‐, nano‐, and picoplankton benefited from Fe enrichment. Experiments performed with the trihydroxamate siderophore desferrioxamine mesylate B (DFOB) indicated that Fe reserves exist within the cells, especially within the larger cells. This reserve could result from luxurious storage of Fe by colimited cells during episodic atmospheric deposition of Saharan dust. Simulating concentrations of dust resulting from aerosol deposition in well‐stratified surface waters, we determined that the solubility of Saharan dust was very low (<0.1% w/w) but the amount of DFe released in seawater was sufficient to relieve the Fe limitation of the ambient phytoplankton community.

The Effects of Periphyton, Fish and Fertilizer Dose on Biological Processes Affecting Water Quality in Earthen Fish Ponds

The potential of periphyton-based aquaculture in South Asia is under investigation in an extensive research program. This paper is a further analysis of data from four experiments carried out in that framework, to explore periphyton, fish and fertilizer dose effects on water quality. Factor analysis and ANOVA models applied to a data matrix of water quality parameters in ponds with and without artificial substrates (bamboo poles and kanchi sticks), with and without fish (filter feeders catla and rohu, with and without bottom feeder kalbaush), and with a standard or 50% increased fertilizer dose, allowed us to identify the underlying ecological processes governing this novel periphyton-based pond system, and construct conceptual graphic models of the periphyton–environment relationships observed. We clearly established that the phosphorus flow is mainly linked to phytoplankton activity in the water column and decomposition on the pond bottom, while nitrogen flow is mainly linked to autotrophic (photosynthesis) and heterotrophic (decomposition and nitrification) processes that take place in the periphyton in addition to the water column and pond bottom. Consequently, disruption of the pond bottom by bottom feeding fish primarily promoted phosphate cycling and phytoplankton, while periphyton development on the supplied substrates and fertilization mainly improved oxygen balance and nitrogen related processes developing in the water column. The use of bamboo poles led to better results than kanchi sticks, related to the greater autotrophic periphyton development on bamboo and to the larger surface of bamboo poles that facilitate fish grazing and periphyton dislodgment that in turn have a renewal effect on periphyton. Stocking bottom feeding fish produces a fertilizing effect through the food web that benefits the filter-feeding fish and that makes it unnecessary to increase the dose of inorganic and organic fertilizers applied to the ponds. Thus, the output of this analysis will help the fish farmers in resource constrained countries to improve their production in periphyton-based ponds just by choosing bamboo substrates, stocking a bottom feeder fish together with the filter feeders, and saving money on fertilizers.

Processing watershed‐derived nitrogen in a well‐flushed New England estuary

Isotopically labeled nitrate (15NO3−) was added continuously to the Rowley estuary, Massachusetts, for 22 d to assess the transport, uptake, and cycling of terrestrially derived nitrogen during a period of high river discharge and low phytoplankton activity. Isotopic enrichment of the 3.5‐km tidal prism (150,000 m3) was achieved for the 3 weeks and allowed us to construct a nitrogen mass balance model for the upper estuary. Mean δ15NO3− in the estuary ranged from 300‰ to 600‰, and approximately 75%–80% of the 15N was exported conservatively as 15NO3− to the coastal ocean. Essentially all of the 20%–25% of the 15N processed in the estuary occurred in the benthos and was evenly split between direct denitrification and autotrophic assimilation. The lack of water‐column 15N uptake was attributed to low phytoplankton stocks and short water residence times (1.2–1.4 d). Uptake of watercolumn NO3− by benthic autotrophs (enriched in excess of 100‰) was a function of NO3− concentration and satisfied up to 15% and 25% of the total nitrogen demand for benthic microalgae and macroalgae, respectively. Approximately 10% of tracer assimilated by benthic autotrophs was mineralized and released back to the water column as 15NH4+. By the end of the study, 15N storage in sediments and marsh macrophytes accounted for 50%–70% of the 15N assimilated in the estuary. These compartments may sequester watershed‐derived nitrogen in the estuary for time scales of months to years.

Characterization of proteolytic enzyme activities in macroalgae

Proteases are essential components of cells and participate in processes ranging from photoacclimation and nutrient acquisition to development and stress responses. Virtually nothing is known about this diverse group of enzymes in macroalgae. Methods to measure proteases developed for phytoplankton (caseinolysis, leucine aminopeptidase (LAP) activity and casein zymograms) have been modified to allow use with spectrophotometers as well as spectrofluorometers, so making them accessible to a wider number of users. Applying the methods to a wide range of macroalgae from intertidal zones in south-western Spain and Northern Ireland detected proteases in all species examined. Protease activities differed among species but there was little systematic variation with taxonomic group. Moreover, similar species in Spain and Northern Ireland often showed differences. With the exception of LAP activities in brown algae, protease activities were one to two orders of magnitude greater in macroalgae than those previously measured in phytoplankton, when expressed per unit protein. However, scaling of activities to protein was complicated by significant interferences. Copper-based protein assays gave erroneously high results when applied to the brown algae, and partial purification of proteins by trichloroacetic acid precipitation did not overcome the problem. The higher levels of protease activity suggest that proteolysis plays a more significant role in multicellular than in unicellular algae. Proteases were characterized in terms of activities at different pH and the effect of protease inhibitors. In common with microalgae but in contrast to findings for animals and higher plants, proteases tended to show higher activities in the neutral and alkaline ranges. Many commonly used protease inhibitors (e.g. leupeptin and phenylmethylsulphonyl fluoride) had relatively little effect, which may explain why biochemical work with macroalgal species has traditionally been difficult. Our results suggest that macroalgal proteases are easily measurable but highly variable. A major source of variability that has not been assessed is differing environmental conditions. If this is correct, measurements of proteolytic enzymes may provide a valuable tool for examining biologically relevant changes in environments. Controlled laboratory experiments and seasonal monitoring are the next logical steps towards this goal.

A Predominance of Lyngbya Contorta Lemm. and the Photosynthetic Activity of Phytoplankton in Brackishwater Meromictic Lake Shira

A Predominance of Lyngbya Contorta Lemm. and the Photosynthetic Activity of Phytoplankton in Brackishwater Meromictic Lake Shira

Growth and potential photosynthesis of cyanobacteria are stimulated by viable gut passage in crucian carp

Growth and potential photosynthetic activity of phytoplankton passed through intestine of crucian carp (Carassius auratus) from a small Siberian reservoir were compared with those of phytoplankton taken the directly from the reservoir. The dominant phytoplankton species in the reservoir, Microcystis aeruginosa, showed a significant increase of growth after the passage. Subdominant Planktothrix agardhii also showed an increase in growth rate, while subdominants Anabaena flos-aquae and Aphanizomenon flos-aquae were not stimulated by the gut passage.

Effects of viral infection on photosynthetic processes in the bloom-forming alga Heterosigma akashiwo

Pulse-amplitude-modulated (PAM) fluorescence is a technique that allows rapid assess- ment of photosynthetic activity of phytoplankton. This approach was used to evaluate the effect of viral infection on the photosynthesis of Heterosigma akashiwo, a toxic bloom-forming raphidophyte found in coastal waters of Japan and Canada. We found that viral infection caused by a single strand RNA virus (HaRNAV Strain 263) and 2 uncharacterised DNA viruses (Strains WBs1 and OIs1) gradually impaired photosynthetic activity during the lytic cycle and that photosynthetic electron transport was directly affected by viral infection. Photosystem (PS) II quantum yield of the active reaction centre was much less affected than the overall PSII-PSI electron transport. The decrease in the photosynthetic activity of the infected algae promoted the non-photochemical energy dissipation (heat). Furthermore, the lytic cycle of the viruses was of similar duration in darkness as in the light (ca. 100 h), and therefore it was not dependent on photophosphorylation. Our study demonstrates that the sensitivity of PAM fluorometry makes it a useful tool for studying viral infection in phyto- plankton populations. Moreover, the results have implications for understanding the role of viral infection on the bloom dynamics of H. akashiwo by showing that viral replication is not light- dependent. Hence, viral production can occur below the photic zone.

Iron speciation in eutrophic and oligotrophic Mediterranean coastal waters; impact of phytoplankton and protozoan blooms on iron distribution

Speciation, distribution and temporal differences in iron chemistry are important for understanding the biological roles of iron in marine systems. This paper presents a study of iron species in different coastal systems of the northeastern Mediterranean and the observed consequences of enrichments of coastal water by major nutrients and iron. Iron species were detected by using a serial chromatographic column method in the eutrophic inner and middle, transient and oligotrophic outer section of İzmir Bay, western Turkey. In order to understand the impact of biological activity on the distribution of Fe species in coastal systems, phytoplankton densities and POC were also measured along with other relevant biological, physical and chemical variables in surface waters at different stations and seasons in İzmir Bay. A significant decrease in iron concentration was observed in the outer bay despite of a very high iron input particularly from the sediment in shallow waters of the inner and middle bay. Average colloidal iron (ColFe) was 14±7% of the total iron that could pass a filter (<0.4 μm) (TFFe) throughout the bay water, however, Chelex column-labile Fe (ClxLFe) was significantly higher (42±25% of TFFe) and reached up to 80% of TFFe, especially in the shallow inner and middle bay. A dramatic decrease in ClxLFe was observed during the phytoplankton bloom in early April in the inner and middle bay. Hydrophobic organically complexed iron (HpOFe) and ClxLFe increased with increasing protozoan activity and collapse of phytoplankton.

Influence of nitrogen enrichment on size-fractionated in vitro carboxylase activities of phytoplankton from Thau Lagoon (Coastal Mediterranean Lagoon, France)

The influence of dissolved inorganic and organic nitrogen (DIN and DON) enrichments on pools of enzymes responsible for CO 2 fixation by the Calvin–Benson (Rubisco) and β-carboxylation pathways (β-carboxylases) were studied in a natural plankton assemblage. The plankton community from a coastal Mediterranean lagoon were incubated in situ for 24 h with initially ammonium, nitrate and DON (taurine) enrichments and compared to a control without any enrichment. An increase of small picophytoplankton and diatom biomass was observed in the enriched inorganic nitrogen treatments 7–10 h after the initial enrichment. Phytoplankton biomass decreased in the control and under taurine enrichment suggesting an inorganic nitrogen limitation of phytoplankton growth. Nevertheless, the ratio of particulate carbon (C) versus chlorophyll a concentrations decreased throughout the experiment, pointing out the increasing importance of the autotroph community in all the carboys. The pool of Rubisco enzyme per biomass generally decreased in all the incubation carboys. In contrast, an increase in the pool of β-carboxylase enzymes normalised to the particulate carbon, chlorophyll and cell concentrations was observed at the end of the experiment under inorganic N-deficient conditions, in the control and with the addition of taurine. Under these latter conditions, the anaplerotic carbon fixation by β-carboxylation may potentially exceed photosynthetic carbon fixation by Rubisco in phytoplankton cells. A shift towards heterotrophy for natural phytoplankton cells using organic sources of nitrogen is proposed to explain the increase of the enzymatic pool of the β-carboxylation pathway.

Fatty acid and phytoplankton compositions of different types of mucilaginous aggregates in thenorthern Adriatic

The biomarkers (fatty acid proportions and ratios characteristic of phytoplankton and bacteria) and phytoplankton species in small (0.5‐2.0 cm) and large (0.5‐5 m) marine aggregates were determined in samples collected in the northern Adriatic Sea, during a mucilage event in 1997, as well as in 1993, 1994 and 1998, when events were not observed. Types of aggregates were identified according to various biomarker relationships, particularly those related to bacterial and phytoplankton activities and changes in the diatom species composition. Aged mucilaginous aggregates (in summer 1997) showed fatty acid proportions (16P/18P, 3.9‐7.7) characteristic of the highest phytoplankton activities, and also showed the highest bacterial fatty acid proportions (13.3‐17.1%) and ratios (C15:br/C15:0, 4.4‐6.0). They showed an different diatom community (dominated by Cylindrotheca closterium) from that in surrounding waters. These characteristics suggest a continuous renewal of the aggregate organic matter, supporting the hypothesis that aggregate is a ‘selfsustaining’ community. In contrast, both freshly formed marine snow, dominant during periods without mucilage events, and freshly formed mucilaginous aggregates presented biomarker proportions and ratios similar to those of suspended matter (bacterial fatty acids 3‐6.7%, C15:br/C15:0 1.2‐4.6, 16P/18P 0.4‐4.0), and diatom composition similar to that of the ambient water. This indicates that marine snow sinks more rapidly than large aggregates, before significant changes can occur in its plankton composition. Other aging aggregate types showed intermediate characteristics, suggesting that their residence times in the water column were still sufficient to develop organic production‐decomposition cycles that modified to various extents their biochemical composition.

Validation of empirical SeaWiFS algorithms for chlorophyll-a retrieval in the Mediterranean Sea

The major aim of this paper is the validation of SeaWiFS-derived chlorophyll-a concentration in the Mediterranean Sea. A data set containing in situ chlorophyll-a profiles and optical measurements of in-water and above-water radiances was used to evaluate the performances of several ocean color algorithms in the Mediterranean Sea. The analysis revealed a systematic overestimation of chlorophyll-a concentration by National Aeronautics and Space Administration (NASA) global algorithms (OC2v4 and OC4v4). The error appears to be correlated with chlorophyll-a concentration, by exhibiting marked differences at low values (C<0.15 mg/m 3 ). In particular at low concentration, the bias observed for OC2v4 is about twice that observed for OC4v4. The same analysis made using the Gitelson et al. [J. Mar. Syst. 9 (1996) 283.] Coastal Zone Color Scanner (CZCS) regional algorithm (GIT) revealed that this model underestimates the pigments concentration but it does not exhibit a correlation between the error and the measures. On the other hand, when the NASA standard algorithms are applied to remotely sensed data, the behavior appears reversed: the OC2v4 algorithm exhibits better estimates than OC4v4, which is probably more affected by atmospheric correction problems. When applied to satellite data, the GIT algorithm performs better than the NASA global algorithms, although the estimates are very poor in the high chlorophyll-a range. Two new Mediterranean algorithms are then proposed by fitting our Mediterranean bio-optical data set with linear and OC2-like functional forms. The new algorithms perform well when applied either to the bio-optical measurements or to satellite data. The different behavior of the same algorithm when applied to biooptical measurements or to remotely sensed data demonstrates that the atmospheric correction is still the main source of error in ocean color data. Due to the relatively small number of available in situ data, the algorithms that we generated have to be considered very preliminary. Discussion was carried out on the reasons of the global algorithm misfit, providing possible explanations and some preliminary result. The influence of coccolithophores and of the yellow substance on the optical response of the Mediterranean waters is investigated, showing that they can at least partially explain the systematic misfit. All the above shows that a region like the Mediterranean Sea requires an independent treatment of the atmospheric and of the in-water bio-optical term to obtain reliable estimates of phytoplankton activity. D 2002 Elsevier

Bacterial growth and primary production along a north-south transect of the Atlantic Ocean.

The oceanic carbon cycle is mainly determined by the combined activities of bacteria and phytoplankton, but the interdependence of climate, the carbon cycle and the microbes is not well understood. To elucidate this interdependence, we performed high-frequency sampling of sea water along a north-south transect of the Atlantic Ocean. Here we report that the interaction of bacteria and phytoplankton is closely related to the meridional profile of water temperature, a variable directly dependent on climate. Water temperature was positively correlated with the ratio of bacterial production to primary production, and, more strongly, with the ratio of bacterial carbon demand to primary production. In warm latitudes (25 degrees N to 30 degrees S), we observed alternating patches of predominantly heterotrophic and autotrophic community metabolism. The calculated regression lines (for data north and south of the Equator) between temperature and the ratio of bacterial production to primary production give a maximum value for this ratio of 40% in the oligotrophic equatorial regions. Taking into account a bacterial growth efficiency of 30%, the resulting area of net heterotrophy (where the bacterial carbon demand for growth plus respiration exceeds phytoplankton carbon fixation) expands from 8 degrees N (27 degrees C) to 20 degrees S (23 degrees C). This suggests an output of CO2 from parts of the ocean to the atmosphere.

Partitioning of phytoplanktonic organic carbon production and bacterial production along a coastal-offshore gradient in the NE Atlantic during different hydrographic regimes

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 29:239-252 (2002) - doi:10.3354/ame029239 Partitioning of phytoplanktonic organic carbon production and bacterial production along a coastal-offshore gradient in the NE Atlantic during different hydrographic regimes Xosé Anxelu G. Morán1,*, Josep M. Gasol2, Carlos Pedrós-Alió2, Marta Estrada2 1Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Camín de L¹Arbeyal s/n, 33212 Xixón, Spain 2Departament de Biologia Marina i Oceanografia, Institut de Ciències del Mar, CMIMA-CSIC, Passeig Marítim 37-49, 08003 Barcelona, Spain *E-mail: xelu.moran@gi.ieo.es ABSTRACT: The rates of primary production of particulate (POC-pr) and dissolved organic carbon (DOC-pr), production of heterotrophic bacteria (BHP), and the abundance of autotrophic and heterotrophic picoplankton were estimated on 2 cruises in NE Atlantic coastal waters off the Iberian peninsula. Downwelling conditions prevailed during the spring cruise (1997), while a sequence of marked upwelling-relaxation-weak upwelling was found in late summer (1998). The standing stocks and activities of phytoplankton and bacteria displayed coastal-offshore gradients in both sampling periods. Whereas DOC-pr was similar on both cruises, POC-pr was generally higher in late summer, yielding lower values of percent extracellular release (PER): 6 ± 5% versus 9 ± 4% (mean ± SD) in spring. Short-term changes in hydrographic conditions strongly affected the relative release of photosynthate in late summer. PER tended to decrease with increasing production, with values below 5% at rates higher than 3 mg C m-3 h-1. Chlorophyll a (chl a) normalized DOC-pr (DOCB-pr) also increased significantly the higher the contribution of picoplankton (<3 μm) to total chl a concentration, confirming the importance of the size distribution of algae in the relative rates of extracellular release. Although BHP was significantly correlated with chl a, it bore no relationship to primary production rates, either dissolved or particulate, and released DOC was insufficient to meet estimates of bacterial demand of labile carbon, indicating that the activities of bacterioplankton and phytoplankton were uncoupled during the surveys. These results suggest that bacteria were mostly independent of algal DOC for growth in this coastal system. KEY WORDS: Primary production · Percent extracellular release · Bacterial production · Phytoplankton-bacterioplankton coupling · Upwelling · Short-term changes Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 29, No. 3. Online publication date: October 23, 2002 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2002 Inter-Research.

Phytoplankton drives nitrite dynamics in the Gulf of Aqaba, Red Sea

This study focuses on the seasonal changes in the Gulf of Aquaba, Red Sea, in nitrite concentration and their relationship with phytoplankton activity, which is mainly controlled by an alternation of water-column stratification with vertical mixing. Within the euphotic zone, during ther- mal summer stratification, nutrient depletion was severe, and no nitrite could be detected in the upper 70 m. However, during stratification, nitrite was always associated with the nutriclines and formed a deep maximum at the bottom of the euphotic zone. In contrast, nitrite accumulated in the mixed water column during winter, closely paralleling the development of phytoplankton biomass. In the Gulf of Aqaba, maximum nitrite accumulation occurred when winter mixing reached its greatest depth, which in turn was coincident with the height of the phytoplankton spring bloom. Thus, our field data suggest that accumulation of nitrite is associated with nutrient-stimulated phytoplankton growth. This hypothesis was supported by nutrient-enrichment bioassays performed concomitantly: only when phytoplankton growth was stimulated by nutrient additions, did nitrite accumulate in the water. In the bioassays, the time-course of nitrite accumulation closely paralleled the development of phytoplankton biomass during the incubation period. We therefore suggest that the accumulation of nitrite in the mixed water column during winter is due to excretion by algal cells. Our field and exper- imental data show that between 10 and 15% of the total amount of nitrogen entering the mixed-water column is released as nitrite by phytoplankton. Further, our field and experimental data support the hypothesis that nitrite excretion by phytoplankton has a significant role in the formation of the deep nitrite maximum (DNM) during stratification in summer. In the bioassays, phytoplankton cells excreted nitrite even when ammonia was the nitrogen source. This indicates a so far unrecognised physiological pathway involved in nitrite excretion by phytoplankton cells.

Partial recovery of a eutrophic reservoir through managed phosphorus limitation and unmanaged macrophyte growth

Recovery from an algal to a macrophyte-dominated state in a freshwater system can require both nutrient reduction and a switch to initiate the change. Despite ferric dosing of pumped inputs since 1983 to reduce external phosphorus loading and forced mixing of the main basin by helices since 1985, Alton Water reservoir, Suffolk, UK suffered from increasing planktonic chlorophyll aconcentrations in the main basin, from construction in 1981 until 1992. From 1987 blooms of cyanobacteria were increasingly frequent, with a major bloom of Woronichinia(originally Coelosphaerium) in 1992, resulting in water supply problems. Since 1993 a partial recovery from a eutrophic to mesotrophic state occurred. Studies of chlorophyll a, orthophosphate (OP), total phosphorus (TP), Alkaline Phosphatase Activity (APA) and response of phytoplankton to in situ phosphate addition experiments between 1995 and 1997, revealed gradients indicative of increasing phosphorus limitation of phytoplankton along the length of the reservoir, away from the pumped input. From 1993 to 1997 no algal blooms occurred in the main basin of the reservoir and extensive macrophyte growth was observed around the reservoir periphery, principally Elodea spp. This corresponded with an increase in weed-eating birds, such as coot (Fulica atra) and tufted duck (Aythya fuligula). The partial recovery of the main basin was attributed to bottom-up control through phosphorus limitation as a result of management in the form of ferric dosing, as well as competition for nutrients and light by the extensive macrophyte beds. Increased macrophyte growth was probably induced by changes in the reservoir ecology following the cyanobacterial bloom and associated fish kill in 1992.

Rapid evaluation of photosynthetic activity of phytoplankton by pulse amplitude modulated (PAM) fluorescence in coastal waters

Rapid evaluation of photosynthetic activity of phytoplankton by pulse amplitude modulated (PAM) fluorescence in coastal waters

Water transparency and health of coastal salt marshes: simple enclosure experiments on nutrient dynamics

Abstract1. In many coastal salt marshes, water transparency is decreased by the resuspension of sediments. We analyse the influence of suspended not‐photosynthetic matter on the regulation of phosphorus (P) dynamics in the water column, compared with the role of phytoplankton and sediments.2. Field surveys and manipulative experiments of P enrichment in light and dark enclosures, open and closed at their bottom, were performed in the brackish Lake Alimini Grande (Otranto, LE, Italy).3. Water transparency in Alimini Grande was inversely related to seston organic mass, 98.8% of which was composed of dead organic matter and heterotrophic organisms.4. P enrichment experiments showed an increase of the phytoplankton biomass with time from the beginning of the manipulation (4.9 times) in the light enclosures, but also an exponential decrease of P concentration in all the enclosures, even in the dark one closed at the bottom.5. The rate of P removal from the water column was not significantly affected by phytoplankton activity, even though P concentration was always lower in light than in dark enclosures, or by the activity of sediments.6. Dead suspended organic matter with associated micro‐organisms seemed to remove nutrients very efficiently from the water column in Lake Alimini Grande, contributing significantly to control the potential risk of lake eutrophication. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Effects of Ice Melting on Cu, Cd and Pb Profiles in Ross Sea Waters (Antarctica)

In the framework of the Italian Research Programme in Antarctica, evolution of dissolved and particulate Cu, Cd and Pb profiles in the coastal waters of Gerlache Inlet (Terra Nova Bay, Western Ross Sea) was studied during the Austral Summer 1997/98. In order to relate the distributions of trace metals with the physical and biological processes, a series of temperature and salinity measures were made, and water samples were collected to determine nutrients and chlorophyll. Samples of pack ice and marine microlayer (50–150 μm) were also collected and analysed. Concerning the surface layer, it was found that metal concentrations are mainly affected by the dynamic of the pack ice melting and phytoplankton activity. The first process influences both the input of metals from meltwaters and the covering of the seawater surface, allowing atmospheric dust input only when all ice has been melt or removed. Direct release of particulate Cu from ice was clearly shown by surface maxima and by the high concentrations of suspended particulate matter and particulate metals found in the ice core section interfaced with the seawater. Differently, the high amount of Cd in the particulate included in the pack ice seems not to affect the concentration in surface particulate; on the contrary, the corresponding increase of dissolved Cd indicates that it isreleased in dissolved form when the pack ice melts. Surface distribution is further complicated by the effect of phytoplankton activity, which removes Cu and Cd from water, incorporating them into organic particulate. Finally, in absence of pack ice, there is evidence of inputs of Pb and Cu due to atmospheric dust brought into the column water through marine microlayer. In intermediate and deep waters, the vertical distribution of Pb and Cd was characterised by substantially constant profiles, while Cu shown, during the end of the summer and in absence of a well-defined water column stratification, a “scavenging-type” distribution which overlaps its “nutrient-type” behaviour.