Home About us Contact
|
Home About us Contact | ||
|
|
||
Phytoplankton Biomass (phytoplankton + biomass)
Selected AbstractsA fish kill event, hypoxia and other limnological impacts associated with early wet season flow into a lake on the Mary River floodplain, tropical northern AustraliaLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 3-4 2003Simon A. Townsend Abstract The Mary River, in the Australian wet/dry tropics, flows seasonally to inundate a coastal floodplain. In the dry season, the river reduces to a series of disconnected lakes located along the main river channel. This paper examines the impact of riverine inflow, at the beginning of the wet season, on the limnology of Shady Camp Lake, and addresses broader water quality management issues. The first wet season flow of Mary River carried a high biological oxygen demand that reduced the lake's oxygen concentration. The resulting hypoxic conditions prompted fish avoidance behaviour and caused the death of at least 200 fish. There is no evidence of any direct anthropogenic pollution causing the event. After reaching near anoxic conditions, dissolved oxygen concentrations recovered several weeks later, although they remained low. The water quality of the Mary River was characterized by an initial pulse of water with high concentrations of organic carbon, suspended particulate material, colour, total nitrogen and total phosphorus. Phytoplankton biomass, measured as chlorophyll a, did not increase because of nitrogen limitation attributed to low nitrate and ammonia concentrations in the inflow waters. The low concentrations of available nitrogen were probably a result of denitrification, which would have been enhanced by the warm temperatures and low oxygen concentrations. The oxygen sag in Shady Camp Lake caused by the inflow of the Mary River exemplifies the vulnerability of floodplain channel lakes to riverine waters and underscores the need to manage catchment practices to minimize the concentration of labile organic material in the river and its associated oxygen demand. [source] Low reproductive success for copepods during a bloom of the non-aldehyde-producing diatom Cerataulina pelagica in the North Adriatic SeaMARINE ECOLOGY, Issue 3 2008Adrianna Ianora Abstract Egg production rates and/or hatching success in the copepods Acartia clausi, Calanus helgolandicus and Temora longicornis were negatively affected by a late spring (May,June 2003) phytoplankton bloom in the North Adriatic Sea, dominated mainly by the large diatom Cerataulina pelagica. Highest total concentrations of 3.3·104 cells·ml,1 were located in the vicinity of the Po River, which also corresponded to the area where the highest numbers of phaeophorbides were measured (0.779, 0.528 and 0.419 ,g·l,1, respectively, compared to an average of the remaining stations of 0.183 ± 0.049 SD), suggesting some grazing on the bloom. Phytoplankton biomass in terms of carbon was dominated by diatoms, representing on average 42% of total phytoplankton carbon and more than 80% at several stations. Cerataulina pelagica, Cyclotella spp., Chaetoceros spp. and small unidentified centric diatoms dominated the diatom community numerically but C. pelagica was by far the dominant diatom in terms of carbon due to its large cell size. This species represented more than 60% of the diatom biomass at nine of the 14 stations sampled, and was absent only at one station, which was the most offshore station sampled during the cruise. Although polyunsaturated aldehydes (PUAs) were not detected, other oxylipins which are hydroxy and keto derivatives of eicosapentaenoic and docosahexaenoic acids that affect copepod reproduction were found in these samples. Hence, we can attribute the negative impact of diatoms not only to PUAs, as previously believed, but also to these compounds. This is the first direct evidence of the presence of oxylipins other than PUAs in marine blooms dominated by diatoms. [source] Contrasting bacterioplankton community composition and seasonal dynamics in two neighbouring hypertrophic freshwater lakesENVIRONMENTAL MICROBIOLOGY, Issue 11 2001K. Van der Gucht We characterized the bacterioplankton community and its seasonal dynamics in two neighbouring hypertrophic lakes by denaturing gradient gel electrophoresis (DGGE) analysis of short (193 bp) 16S ribosomal DNA polymerase chain reaction (PCR) products obtained with primers specific for the domain Bacteria. Lake Blankaart is turbid and has a high phytoplankton biomass and episodic cyanobacterial blooms, whereas biomanipulated Lake Visvijver is characterized by clearwater conditions and the establishment of a dense charophyte vegetation. Both lakes were dominated by bacterial groups commonly found in freshwater habitats (e.g. ACK4 cluster of Actinomycetes; ACK stands for clones isolated from the Adirondack mountain lakes). Yet, cluster analysis and principal components analysis (PCA) revealed that taxon composition of the bacterioplankton community of the two lakes differs substantially and consistently throughout the season. During the study year (1998), the bacterioplankton community of both lakes showed a distinct seasonal pattern. Lake Blankaart showed a clear differentiation between winter, spring, summer and autumn. In Lake Visvijver, summer samples differed greatly from spring, autumn and winter samples. We hypothesize that the contrasting bacterioplankton in the two neighbouring shallow lakes is determined largely by the presence or absence of macrophytes. [source] The role of macroinvertebrates and fish in regulating the provision by macrophytes of refugia for zooplankton in a warm temperate shallow lakeFRESHWATER BIOLOGY, Issue 10 2010MARÍA de los ÁNGELES GONZÁLEZ SAGRARIO Summary 1.,The zooplankton often undergoes diel horizontal migration (DHM) from the open water to the littoral of shallow lakes, thus avoiding predators in the former. This behaviour has functional impacts within the lake, as it enhances zooplankton survival, increases their control of phytoplankton and tends to stabilise the clear water state. However, most of the evidence supporting this migration pattern comes from cold north temperate lakes, and more evidence from tropical and subtropical areas, as well as from southern temperate areas, is needed. 2.,We conducted a field study of the diel horizontal and vertical migration of zooplankton, and the horizontal distribution of potential predatory macroinvertebrates and fish, over two consecutive days in the summer in a temperate lake in the southern hemisphere. We took zooplankton samples at two depths, at three sampling stations (inside beds of aquatic macrophytes, at their edge and in open water) along three transects running from the centre of a bed of Ceratophyllum demersum to open water. At each sampling station, we also took samples of macroinvertebrates and fish and measured physical and chemical environmental variables. 3.,Zooplankton (pelagic cladocerans, calanoid copepods and rotifers) avoided the shore, probably because of the greater risk from predators there. Larger and more vulnerable cladocerans, such as Diaphanosoma brachyurum and Moina micrura, were two to four times more abundant in open water than at the edge of or inside beds of macrophytes, respectively, by both day and night. Less vulnerable zooplankton [i.e. of medium body size (Ceriodaphnia dubia) or with the ability to swim fast (calanoid copepods)] were distributed evenly between open water and the edge of the plant beds. Small zooplankton, Bosmina huaronensis and pelagic rotifers, showed an even distribution among the three sampling stations. Accordingly, no DHM of zooplankton occurred, although larger organisms migrated vertically inside C. demersum stands. 4.,Macrophytes contained high densities of predatory macroinvertebrates and fish. The predator assemblage, composed of large-bodied macroinvertebrates (including odonates and shrimps) and small littoral fish, was permanently associated with submerged macrophytes. None of these groups moved outside the plant beds or changed their population structure (fish) over the diel cycle. 5.,Submerged macrophyte beds do not represent a refuge for zooplankton in lakes where predators are numerous among the plants, implying a weaker top-down control of phytoplankton biomass by zooplankton and, consequently, a more turbid lake. The effectiveness of macrophytes as a refuge for zooplankton depends on the associated assemblage of predatory macroinvertebrates and fish among the plants. [source] Impact of the fish Garra on the ecology of reservoirs and the occurrence of Microcystis blooms in semi-arid tropical highlands: an experimental assessment using enclosuresFRESHWATER BIOLOGY, Issue 8 2009TADESSE DEJENIE Summary 1.,Many man-made reservoirs in the semi-arid highlands of Northern Ethiopia (Tigray) are characterised by the occurrence of intensive blooms of cyanobacteria and a dominance of small riverine fishes belonging to the genus Garra. 2.,We carried out enclosure experiments to test for the effect of these small fish on abiotic characteristics, phytoplankton biomass and zooplankton community structure in the pelagic of two reservoirs (Gereb Awso and Tsinkanet). Two experiments were carried out in each of the reservoirs, one at the end of the rainy season (highest water level) and one at the end of the dry season (lowest water level). 3.,The presence of Garra in general increased the amount of suspended matter, nutrient concentrations (total nitrogen and total phosphorus), phytoplankton and Microcystis biomass (including the proportion of Microcystis in the phytoplankton community), and reduced water transparency. The positive effect of the presence of Garra on nutrient concentrations and phytoplankton productivity indicate that Garra has the potential to affect food web functioning indirectly through bottom-up effects, by enhancing nutrient concentrations through sediment resuspension and excretion of nutrients. Indeed, population densities of the cladoceran zooplankton taxa Ceriodaphnia and Diaphanosoma also showed an overall increase in enclosures with Garra. 4.,However, our data also provide some evidence for a potential of Garra to exert top-down control on large bodied daphnids (Daphnia carinata, D. barbata), although such effect varied among experiments. The limited capability of Garra to control zooplankton communities mainly reflects the low efficiency of these small, riverine and benthos-oriented fish in foraging on zooplankton and suggests the existence of an unoccupied niche for zooplanktivorous fish in the majority of the reservoirs. 5.,Although the main effects of Garra on the pelagic food web seemed to be mediated by bottom-up mechanisms, our results also indicate that one of the key variables, the relative abundance of Microcystis, was impacted by Daphnia -mediated trophic cascade effects. [source] The role of light for fish,zooplankton,phytoplankton interactions during winter in shallow lakes , a climate change perspectiveFRESHWATER BIOLOGY, Issue 5 2009METTE ELISABETH BRAMM Summary 1.,Variations in the light regime can affect the availability and quality of food for zooplankton grazers as well as their exposure to fish predation. In northern lakes light is particularly low in winter and, with increasing warming, the northern limit of some present-day plankton communities may move further north and the plankton will thus receive less winter light. 2.,We followed the changes in the biomass and community structure of zooplankton and phytoplankton in a clear and a turbid shallow lake during winter (November,March) in enclosures both with and without fish and with four different light treatments (100%, 55%, 7% and <1% of incoming light). 3.,In both lakes total zooplankton biomass and chlorophyll- a were influenced by light availability and the presence of fish. Presence of fish irrespective of the light level led to low crustacean biomass, high rotifer biomass and changes in the life history of copepods. The strength of the fish effect on zooplankton biomass diminished with declining light and the effect of light was strongest in the presence of fish. 4.,When fish were present, reduced light led to a shift from rotifers to calanoid copepods in the clear lake and from rotifers to cyclopoid copepods in the turbid lake. Light affected the phytoplankton biomass and, to a lesser extent, the phytoplankton community composition and size. However, the fish effect on phytoplankton was overall weak. 5.,Our results from typical Danish shallow eutrophic lakes suggest that major changes in winter light conditions are needed in order to have a significant effect on the plankton community. The change in light occurring when such plankton communities move northwards in response to global warming will mostly be of modest importance for this lake type, at least for the rest of this century in an IPCC A2 scenario, while stronger effects may be observed in deep lakes. [source] Size-fractionated phytoplankton biomass and its implications for the dynamics of an oligotrophic tropical lakeFRESHWATER BIOLOGY, Issue 1 2008MARÍA FERNANDA ADAME Summary 1. Size-fractionated phytoplankton biomass was examined in relation to the hydrodynamics of tropical Lake Alchichica from 1999 to 2002. 2. Alchichica is a warm monomictic lake, in which mixing takes place from late December to early March. The lake is oligotrophic (mean total chlorophyll- a concentration 4.2 ± 4.2 ,g L,1) and its phytoplankton biomass is dominated (72.3 ± 16.4%) by large individuals (>2 ,m). The degree of dominance of the large size class (nano- and microplankton) over the small size class (picoplankton) throughout the year is mainly determined by the availability of silicate and the Si/N ratio in the hypolimnion prior to the mixing period. 3. This is the first record of an oligotrophic tropical lake dominated by large size fractions of phytoplankton. Because of this dominance, the fate of most primary productivity is rapid sedimentation to the bottom followed by decomposition that promotes an anoxic hypolimnion. 4. Our findings in tropical Lake Alchichica challenge the idea that oligotrophic waters are dominated by small phytoplankton, as has been well established for the oligotrophic ocean and temperate lakes. [source] Allelopathic effect of the aquatic macrophyte, Stratiotes aloides, on natural phytoplanktonFRESHWATER BIOLOGY, Issue 3 2006GABI MULDERIJ Summary 1. A survey of different Dutch Stratiotes stands showed that the density of phytoplankton (except cyanobacteria) was always higher outside S. aloides than between the rosettes of S. aloides. Analyses of water samples revealed that nutrient limitation was unlikely to have caused the lower phytoplankton biomass in the vicinity of S. aloides. 2. An in situ incubation experiment in the Danube Delta, Romania, indicated allelopathic activity against phytoplankton in S. aloides stands. The growth rate of natural phytoplankton populations exposed to water from S. aloides stands was significantly lower than that of populations that had not been in contact with S. aloides exudates. 3. A laboratory microcosm experiment showed a significantly lower phytoplankton biomass in treatments with S. aloides exudates. Nutrient concentrations and the light intensity were high enough that the lower phytoplankton biomass could not be explained by nutrient or light limitation. [source] Phosphorus decrease and climate variability: mediators of synchrony in phytoplankton changes among European peri-alpine lakesFRESHWATER BIOLOGY, Issue 10 2005ORLANE ANNEVILLE Summary 1. In an attempt to discern long-term regional patterns in phytoplankton community composition we analysed data from five deep peri-alpine lake basins that have been included in long-term monitoring programmes since the beginning of the 1970s. Local management measures have led to synchronous declines in phosphorus concentrations by more than 50% in all four lakes. Their trophic state now ranges from mesotrophic to oligotrophic. 2. No coherence in phytoplankton biomass was observed among lakes, or any significant decrease in response to phosphorus (P)-reduction (oligotrophication), except in Lakes Constance and Walen. 3. Multivariate analyses identified long-term changes in phytoplankton composition, which occurred coherently in all lakes despite the differing absolute phosphorus concentrations. 4. In all lakes, the phytoplankton species benefiting from oligotrophication included mixotrophic species and/or species indicative of oligo-mesotrophic conditions. 5. A major change in community composition occurred in all lakes at the end of the 1980s. During this period there was also a major shift in climatic conditions during winter and early spring, suggesting an impact of climatic factors. 6. Our results provide evidence that synchronous long-term changes in geographically separated phytoplankton communities may occur even when overall biomass changes are not synchronous. [source] Lake responses to reduced nutrient loading , an analysis of contemporary long-term data from 35 case studiesFRESHWATER BIOLOGY, Issue 10 2005ERIK JEPPESEN Summary 1. This synthesis examines 35 long-term (5,35 years, mean: 16 years) lake re-oligotrophication studies. It covers lakes ranging from shallow (mean depth <5 m and/or polymictic) to deep (mean depth up to 177 m), oligotrophic to hypertrophic (summer mean total phosphorus concentration from 7.5 to 3500 ,g L,1 before loading reduction), subtropical to temperate (latitude: 28,65°), and lowland to upland (altitude: 0,481 m). Shallow north-temperate lakes were most abundant. 2. Reduction of external total phosphorus (TP) loading resulted in lower in-lake TP concentration, lower chlorophyll a (chl a) concentration and higher Secchi depth in most lakes. Internal loading delayed the recovery, but in most lakes a new equilibrium for TP was reached after 10,15 years, which was only marginally influenced by the hydraulic retention time of the lakes. With decreasing TP concentration, the concentration of soluble reactive phosphorus (SRP) also declined substantially. 3. Decreases (if any) in total nitrogen (TN) loading were lower than for TP in most lakes. As a result, the TN : TP ratio in lake water increased in 80% of the lakes. In lakes where the TN loading was reduced, the annual mean in-lake TN concentration responded rapidly. Concentrations largely followed predictions derived from an empirical model developed earlier for Danish lakes, which includes external TN loading, hydraulic retention time and mean depth as explanatory variables. 4. Phytoplankton clearly responded to reduced nutrient loading, mainly reflecting declining TP concentrations. Declines in phytoplankton biomass were accompanied by shifts in community structure. In deep lakes, chrysophytes and dinophytes assumed greater importance at the expense of cyanobacteria. Diatoms, cryptophytes and chrysophytes became more dominant in shallow lakes, while no significant change was seen for cyanobacteria. 5. The observed declines in phytoplankton biomass and chl a may have been further augmented by enhanced zooplankton grazing, as indicated by increases in the zooplankton : phytoplankton biomass ratio and declines in the chl a : TP ratio at a summer mean TP concentration of <100,150 ,g L,1. This effect was strongest in shallow lakes. This implies potentially higher rates of zooplankton grazing and may be ascribed to the observed large changes in fish community structure and biomass with decreasing TP contribution. In 82% of the lakes for which data on fish are available, fish biomass declined with TP. The percentage of piscivores increased in 80% of those lakes and often a shift occurred towards dominance by fish species characteristic of less eutrophic waters. 6. Data on macrophytes were available only for a small subsample of lakes. In several of those lakes, abundance, coverage, plant volume inhabited or depth distribution of submerged macrophytes increased during oligotrophication, but in others no changes were observed despite greater water clarity. 7. Recovery of lakes after nutrient loading reduction may be confounded by concomitant environmental changes such as global warming. However, effects of global change are likely to run counter to reductions in nutrient loading rather than reinforcing re-oligotrophication. [source] Timing of predation by rainbow trout controls Daphnia demography and the trophic status of a Minnesota lakeFRESHWATER BIOLOGY, Issue 6 2005LEIF K. HEMBRE Summary 1. Stocking of lakes with rainbow trout is a common practice that presents a potential conflict for lake managers who must balance the interests of anglers with those concerned that zooplanktivory by trout may trigger a trophic cascade and result in decreased water clarity. 2. This study examined how the timing of trout stocking (autumn versus spring) in a Minnesota (U.S.A.) lake affected (i) the population dynamics of their zooplankton food supply (Daphnia pulicaria), (ii) phytoplankton biomass and water clarity and (iii) trout survival. Sizes of both Daphnia and trout populations were estimated acoustically with high-frequency (192 kHz) sonar. 3. Daphnia were nearly eliminated from the lake during winters after trout were stocked in autumn. In both of these years (1996 and 1997), the Daphnia population was small in the spring, and grew during the summer and into the autumn as the trout population diminished. 4. The lake was then stocked in spring for 2 years (1998 and 1999). This fisheries manipulation alleviated predation over the winter, but increased predation on D. pulicaria during the spring, summer and autumn. However, the high mortality caused by the spring-stocked trout was offset by even higher rates of reproduction by the relatively large populations of fecund Daphnia that survived the winter in 1998 and 1999. 5. Grazing by these dense populations of Daphnia produced clear-water phases during May and June that were inhibited in autumn stocking years. In addition, the large Daphnia populations present during the spring and early summer of 1998 and 1999 provided abundant forage for trout. 6. This fisheries manipulation achieved seemingly mutually exclusive management objectives: a robust planktivorous sport fishery, and clear water for other forms of recreation. [source] Do cyanobacteria dominate in eutrophic lakes because they fix atmospheric nitrogen?FRESHWATER BIOLOGY, Issue 6 2004L. R. Ferber Summary 1. The sources of nitrogen for phytoplankton were determined for a bloom-prone lake as a means of assessing the hypothesis that cyanobacteria dominate in eutrophic lakes because of their ability to fix nitrogen when the nitrogen : phosphorous (N : P) supply ratio is low and nitrogen a limiting resource. 2. Nitrogen fixation rates, estimated through acetylene reduction with 15N calibration, were compared with 15N-tracer estimates of ammonium and nitrate uptake monthly during the ice-free season of 1999. In addition, the natural N stable isotope composition of phytoplankton, nitrate and ammonium were measured biweekly and the contribution of N2 to the phytoplankton signature estimated with a mixing model. 3. Although cyanobacteria made up 81,98% of phytoplankton biomass during summer and autumn, both assays suggested minimal N acquisition through fixation (<9% for the in-situ incubations; <2% for stable isotope analysis). Phytoplankton acquired N primarily as ammonium (82,98%), and secondarily as nitrate (15,18% in spring and autumn, but <5% in summer). Heterocyst densities of <3 per 100 fixer cells confirmed low reliance on fixation. 4. The lake showed symptoms of both light and nitrogen limitation. Cyanobacteria may have dominated by monopolizing benthic sources of ammonium, or by forming surface scums that shaded other algae. [source] Lake age and water level affect the turbidity of floodplain lakes along the lower RhineFRESHWATER BIOLOGY, Issue 3 2003F. C. J. M. Roozen SUMMARY 1. We sampled a set of 93 lakes situated in the floodplains of the lower River Rhine in search for morphometric and other factors that explain their variation in clarity. 2. Lakes with a drop in summer water level were less turbid at the time of sampling, mainly because of a lower concentration of inorganic suspended solids (ISS). 3. We also found that older lakes were more turbid than younger lakes and that this was largely because of an increase in phytoplankton. 4. Water clarity was positively related to lake depth and the presence of vegetation. 5. Model calculations indicated that the underwater light climate was strongly affected by chlorophyll and ISS, the latter being the dominant factor affecting Secchi depth. Dissolved organic carbon (DOC) was less important. 6. The high concentration of ISS suggests that intensive resuspension occurs in most of the lakes. Using a simple wave model, and assuming that vegetation protects sediments against resuspension, we could eliminate wind resuspension as an important process in 90% of the lakes, leaving resuspension by benthivorous fish as probably the most important factor determining transparency. 7. Chlorophyll a concentration showed a strong positive correlation to ISS concentration, suggesting that resuspension may also have a positive effect on phytoplankton biomass in these lakes. 8. In conclusion, in-lake processes, rather than river dynamics, seem to be driving the turbidity of floodplain lakes along the lower River Rhine. [source] Effects of experimentally induced cyanobacterial blooms on crustacean zooplankton communitiesFRESHWATER BIOLOGY, Issue 2 2003Anas Ghadouani SUMMARY 1.,Large in situ enclosures were used to study the effects of experimentally induced cyanobacterial blooms on zooplankton communities. A combination of N and P was added to shallow (2 m) and deep enclosures (5 m) with the goal of reducing the TN : TP ratio to a low level (,5 : 1) to promote cyanobacterial growth. After nutrient additions, high biomass of cyanobacteria developed rapidly in shallow enclosures reaching levels only observed during bloom events in eutrophic lakes. 2.,In the shallow enclosures, particulate phosphorus (PP) was on average 35% higher in comparison with deep enclosures, suggesting that depth plays a key role in P uptake by algae. Phytoplankton communities in both deep and shallow enclosures were dominated by three cyanobacteria species ,Aphanizomenon flos-aquae, Anabaena flos-aquae and Microcystis aeruginosa, which accounted for up to 70% of total phytoplankton biomass. However, the absolute biomass of the three species was much higher in shallow enclosures, especially Aphanizomenon flos-aquae. The three cyanobacteria species responded in contrasting ways to nutrient manipulation because of their different physiology. 3.,Standardised concentrations of the hepatotoxic microcystin-LR increased as a result of nutrient manipulations by a factor of four in the treated enclosures. Increased biomass of inedible and toxin producing cyanobacteria was associated with a decline in Daphnia pulicaria biomass caused by a reduction in the number of individuals with a body length of >1 mm. Zooplankton biomass did not decline at moderate cyanobacteria biomass, but when cyanobacteria reached high biomass large cladocerans were reduced. 4.,Our results demonstrate that zooplankton communities can be negatively affected by cyanobacterial blooms and therefore the potential to use herbivory to reduce algal blooms in such eutrophic lakes appears limited. [source] The potential significance of microbial Fe(III) reduction during deposition of Precambrian banded iron formationsGEOBIOLOGY, Issue 3 2005K. O. KONHAUSER ABSTRACT During deposition of late Archean,early Palaeoproterozoic Precambrian banded iron formations (BIFs) the downward flux of ferric hydroxide (Fe(OH)3) and phytoplankton biomass should have facilitated microbial Fe(III) reduction. However, quantifying the significance of such a metabolic pathway in the Precambrian is extremely difficult, considering the post-depositional alteration of the rocks and the lack of ideal modern analogues. Consequently, we have very few constraints on the Fe cycle at that time, namely (i) the concentration of dissolved Fe(II) in the ocean waters; (ii) by what mechanisms Fe(II) was oxidized (chemical, photochemical or biological, the latter using either O2 or light); (iii) where the ferric hydroxide was precipitated (over the shelf vs. open ocean); (iv) the amount of phytoplankton biomass, which relates to the nutrient status of the surface waters; (v) the relative importance of Fe(III) reduction vs. the other types of metabolic pathways utilized by sea floor microbial communities; and (vi) the proportion of primary vs. diagenetic Fe(II) in BIF. Furthermore, although estimates can be made regarding the quantity of reducing equivalents necessary to account for the diagenetic Fe(II) component in Fe-rich BIF layers, those same estimates do not offer any insights into the magnitude of Fe(III) actually generated within the water column, and hence, the efficiency of Fe and C recycling prior to burial. Accordingly, in this study, we have attempted to model the ancient Fe cycle, based simply on conservative experimental rates of photosynthetic Fe(II) oxidation in the euphotic zone. We estimate here that under ideal growth conditions, as much as 70% of the biologically formed Fe(III) could have been recycled back into the water column via fermentation and organic carbon oxidation coupled to microbial Fe(III) reduction. By comparing the potential amount of biomass generated phototrophically with the reducing equivalents required for Fe(III) reduction and magnetite formation, we also hypothesize that another anaerobic metabolic pathway might have been utilized in the surface sediment to oxidize the fermentation by-products. Based on the premise that the deep ocean waters were anoxic, this role could have been fulfilled by methanogens, and maybe even methanotrophs that employed Fe(III) reduction. [source] Large-scale climatic signatures in lakes across Europe: a meta-analysisGLOBAL CHANGE BIOLOGY, Issue 7 2007THORSTEN BLENCKNER Abstract Recent studies have highlighted the impact of the winter North Atlantic Oscillation (NAO) on water temperature, ice conditions, and spring plankton phenology in specific lakes and regions in Europe. Here, we use meta-analysis techniques to test whether 18 lakes in northern, western, and central Europe respond coherently to winter climate forcing, and to assess the persistence of the winter climate signal in physical, chemical, and biological variables during the year. A meta-analysis approach was chosen because we wished to emphasize the overall coherence pattern rather than individual lake responses. A particular strength of our approach is that time-series from each of the 18 lakes were subjected to the same robust statistical analysis covering the same 23-year period. Although the strongest overall coherence in response to the winter NAO was exhibited by lake water temperatures, a strong, coherent response was also exhibited by concentrations of soluble reactive phosphorus and soluble reactive silicate, most likely as a result of the coherent response exhibited by the spring phytoplankton bloom. Lake nitrate concentrations showed significant coherence in winter. With the exception of the cyanobacterial biomass in summer, phytoplankton biomass in all seasons was unrelated to the winter NAO. A strong coherence in the abundance of daphnids during spring can most likely be attributed to coherence in daphnid phenology. A strong coherence in the summer abundance of the cyclopoid copepods may have been related to a coherent change in their emergence from resting stages. We discuss the complex nature of the potential mechanisms that drive the observed changes. [source] Atmospheric nitrogen deposition has caused nitrogen enrichment and eutrophication of lakes in the northern hemisphereGLOBAL CHANGE BIOLOGY, Issue 4 2006ANN-KRISTIN BERGSTRÖM Abstract We compiled chemical data and phytoplankton biomass (PB) data (chlorophyll a) from unproductive lakes in 42 different regions in Europe and North America, and compared these data to inorganic nitrogen (N) deposition over these regions. We demonstrate that increased deposition of inorganic N over large areas of Europe and North America has caused elevated concentrations of inorganic N in lakes. In addition, the unproductive lakes in high N deposition areas had clearly higher PB relative to the total phosphorus (P) concentrations illustrating that the elevated inorganic N concentrations has resulted in eutrophication and increased biomass of phytoplankton. The eutrophication caused by inorganic N deposition indicates that PB yield in a majority of lakes in the northern hemisphere is (was) limited by N in their natural state. We, therefore, suggest that P limitation largely concerns lakes where the balance between N and P has been changed because of increased anthropogenic input of N. [source] Temporal variability of phytoplankton in a salt wedge estuary, the Swan,Canning Estuary, Western AustraliaHYDROLOGICAL PROCESSES, Issue 13 2001Peter A. Thompson Abstract The temporal cycles of variation in salinity, temperature and river flow in the Swan,Canning Estuary plus rainfall in the vicinity are examined. A ,normal' pattern is defined for rainfall and river flow based on long-term median monthly values from available historical data. Long-term monthly median rainfall and median monthly river flow were highly correlated. Deviations from the ,normal' patterns of rainfall and river flow are documented. Three years of detailed data on the temporal distribution of the algal biomass and phytoplankton community composition from the Swan,Canning Estuary are presented and discussed. Significant interannual variability in the phytoplankton biomass was observed with 1996 having a significantly lower median chlorophyll a concentration than 1995 or 1997. Different years also had pronounced differences in the timing, persistence and occurrence of algal blooms. Links with, and between, rainfall, river flow, nutrient concentrations and phytoplankton biomass are made by careful examination of the temporal patterns. Deviations from the proposed ,normal' temporal pattern of physical and chemical environmental factors relevant to the growth of phytoplankton biomass are assessed. Deviations from ,normal' rainfall and river flow, depending upon their timing and intensity, appear to be associated with occurrence of algal blooms. For example, the lack of a dinoflagellate bloom in December 1996 or January 1997 appears to be associated with a wetter than normal spring. Based upon the observed data, published reports and basic principles of algal ecology a set of predicted responses to variation in the major environmental variables (rainfall and river flow) are tabulated. The tabulated predictions are proposed as a useful tool for resource managers. Copyright © 2001 John Wiley & Sons, Ltd. [source] Effects of Nutrients, Fish, Charophytes and Algal Sediment Recruitment on the Phytoplankton Ecology of a Shallow LakeINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 6 2007María-José Villena Abstract The influence of nutrient levels, fish density and charophytes on the phytoplankton ecology of a shallow Mediterranean lake was studied by means of an in situ mesocosm experiment. Different levels of nutrients and fish were added over the course of an eight-week experiment, during which charophytes were removed towards the end. After submerged plants were removed, phytoplankton biomass increased significantly in all the mesocosms, with a reduction of algal diversity and species richness and dominance of cyanobacteria. Cyanobacteria recruited from the sediment played an important role in sustaining planktonic populations of the dominant species. Oscillatorial species (Pseudanabaena galeata, Planktolyngbya limnetica) dominated at higher nutrient levels (0.5,1 mg L,1 P and 5,10 mg L,1 N) and chroococcal cyanobacteria (Merismopedia tenuissima) at lower nutrient levels. Density of planktivorous fish had little effect on the algal recruitment from the sediment and phytoplankton biomass and diversity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Picophytoplankton contribution to phytoplankton community structure in the Gulf of Venice (NW Adriatic Sea)INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2006Fabrizio Bernardi Aubry Abstract The size distribution of the phytoplankton community has been analyzed on a monthly basis in the Gulf of Venice (NW Adriatic Sea), with the aim to assess the seasonal variation of the contribution of autotrophic picoplankton (APP) to total phytoplankton. The investigation was carried out in two stations characterized by different influences of fluvial inputs. APP was mainly made up of Synechococcus , the larger fraction (Utermöhl Fraction Phytoplankton, UFP: µm as maximum linear dimension) of diatoms and nanoflagellates. The average APP abundance (46 × 103 cells ml,1) and biomass (8.1 µg C dm,3) indicate that APP was a persistent and significant component of the NW Adriatic phytoplankton. The highest APP abundance (up to 270 × 103 cells ml,1) and biomass (up to 49 µg C dm,3) were recorded from summer to autumn, UFP peaked from late winter to late spring. The mean APP contribution to total phytoplankton abundance and biomass was 98% and 31% respectively. The seasonal variation of total phytoplankton biomass was mainly driven by the UFP fraction; however, a seasonal shift in the relative importance of UFP and APP occurred from spring to summer. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Autotrophic and Heterotrophic Picoplankton in Wetlands: Differences with Lake PatternsINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 5 2003María A. Rodrigo Abstract This study describes the occurrence, importance and seasonal patterns of picoplankton in two wetlands (TDNP and La Safor), and compares them to a system of fifteen interconnected lakes (Ruidera). In TDNP we performed a six-year monthly study in three sites of the wetland. Bacterial abundance increased throughout time and the autotrophic picoplankton (APP) range was wide (up to 33 × 106 cells/ml). The annual averaged APP contribution to total picoplankton and phytoplankton biovolumes was 0.5,22% and 0.03,6% respectively. There were large differences among sites in terms of APP absolute and relative abundance and seasonal patterns. In La Safor, the APP relative contribution to picoplankton and phytoplankton biovolumes was 0,25% and 0,40%, respectively, while in the Ruidera lakes was 0,47% and 0,5%, respectively. In the three systems there was a significant correlation between bacterial abundance and chlorophyll a but the slopes of the linear regressions were different. No significant relationships were found of APP abundance and trophic status in the wetlands, but were noted in the lake system. There was no clear relationship of APP contribution to total phytoplankton biomass to the trophic gradient in wetlands. In the lakes, the higher contribution of APP was found in those with higher trophic levels. [source] 30,Seasonal control of phytoplankton biomass and productivity in coastal british columbia lakes and reservoirsJOURNAL OF PHYCOLOGY, Issue 2003J. M. Davies Factors controlling algal abundance and carbon fixation form a cornerstone of aquatic ecology. Central among these are light, nutrients, and grazers. We measured 14C fixation over one year in six coastal BC lakes that differed in trophic status and grazer community structure. The lakes in our study were never covered with ice, so mixing due to wind energy was more similar to summer months and light levels were higher during winter than comparable ice-covered lakes. Our study, therefore, offered a unique opportunity to examine how seasonal changes in light and temperature affects the functioning of these lakes. While many of our study lakes had higher chlorophyll concentrations during winter months, only the lake with a community dominated by small grazers maintained moderate nutrient deficiency throughout the year and increased 14C-fixation during the winter (Jan,Feb). [source] DO PHYSICAL FACTORS REGULATE PHYTOPLANKTON DISTRIBUTION PATTERNS IN LARGE, SHALLOW LAKES?JOURNAL OF PHYCOLOGY, Issue 2000H.J. Carrick Factors that regulate phytoplankton dynamics in shallow, productive lakes are poorly understood, due to their predisposition for frequent algal blooms and sediment resuspension events. In Lake Apopka, greatest phytoplankton biomass reflects wind-induced resuspension of algae (meroplankton) that exists on the aphotic lake bottom in a layer approximately 5 cm thick; this assemblage is dominated by diatoms (>60% of total biomass) that can occur in resting stages. Once exposed to moderate light, meroplankton are capable of growth and photosynthetic rates comparable with surface populations. In Lake Okeechobee, remote sensing was used to assess the basin-wide distribution of suspended particles. Satellite reflectance values agreed well with in situ particle densities at 20 in-lake stations (average r2; LANDSAT = 0.81, AVHRR = 0.53), and maps of algal blooms (r2 = 0.79, p , 0.01). The greatest chlorophyll concentrations occurred in the vicinity of tributary nutrient inputs at the lake's perimeter, while turbidity increased towards the center of the lake reflecting predominant water circulation patterns. These results underscore the importance of physical-biological interactions in lakes. [source] The effects of water retention time and watershed features on the limnology of two tropical reservoirs in BrazilLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 4 2008Maria Carolina S. Soares Abstract Although reservoirs are similar to natural lakes in many respects, such driving forces as water retention time and watershed features can play important roles in the limnology of manmade lakes. With the goal of investigating how these factors influence the limnology of tropical reservoirs, physical and chemical variables were measured at four sampling sites in two reservoirs in southern Brazil, from June 2002 to June 2003. Funil Reservoir is located in one of the most-populated areas in the country, in the Paraíba do Sul river basin, which drains and drastically influences the water quality of the reservoir. In contrast, Lajes Reservoir is located in a well-preserved area, with its water retention time varying from six to 30 times longer than for Funil Reservoir. Funil Reservoir is a turbid (median euphotic zone = 4.3 m), eutrophic reservoir (median total phosphorus (TP) = 3.1 µm), with a high phytoplankton biomass (median chlorophyll- a concentration = 10.0 µg L,1). In contrast, Lajes Reservoir is a transparent (median euphotic zone = 9.2 m), mesotrophic water system (median TP = 1.0 µm), with a low phytoplankton biomass (median chlorophyll- a = 1.9 µg L,1). Both reservoirs were stratified during the summer months, but isothermy was only observed in Funil Reservoir. Because of its short water retention time, Funil Reservoir is a much more dynamic system than Lajes Reservoir, with a pronounced temporal pattern related to changes in its water column and its phytoplankton biomass. Spatial heterogeneity is more evident in Lajes Reservoir, mainly as a consequence of its location in a preserved area, long water retention time and the presence of net cages for fish culture in the waterbody. The typical spatial zonation found in reservoirs, related to nutrient sedimentation and light availability, however, is more evident in Funil Reservoir than in Lajes Reservoir. Despite the similarities between these two water systems, which are in the same geographical region with similar climate, and are comparable in size, the distinct watershed features and water retention time are responsible for marked differences between these reservoirs. [source] Bacterioplankton heterotrophic activity in relation to the phytoplankton compartment in a recently formed reservoirLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2008Louis-B. Abstract Seasonal and spatial variations in bacterial abundance, biomass and potential heterotrophic activity in a recently flooded reservoir were measured for two consecutive years, in conjunction with phytoplankton biomass (chlorophyll- a concentration) and activity (primary production). The mean value of primary production remained constant between the two study years, while those of the chlorophyll- a concentrations, bacterial abundance, bacterial biomass and bacterial heterotrophic activity decreased. The observed trends in the bacterial variables were linked to changes in the relative importance of allochthonous dissolved organic matter, in addition to selective grazing activity on bacterioplankton. Multivariate regression analyses identified bacterial abundance (29%) and temperature (17%) as dominant correlates of the bacterial potential heterotrophic activity. We concluded that, in a new reservoir, organic matter, other than that from phytoplankton, might be of great importance for bacterioplankton metabolism. Furthermore, grazing activity on bacteria by metazoa in a new reservoir represents, on occasion, an important trophic link between the top consumer and otherwise unavailable dissolved organic carbon sources. Finally, even if little energy is transferred to larger consumers, the microbial route is still important in re-mineralizing organic matter in Sep Reservoir. [source] Prediction of Lake Baikal ecosystem behaviour using an ecosystem disturbance model,LAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2001Eugene A. Silow Abstract This paper combines predictions of the effects of anthropogenic impacts on the plankton of Lake Baikal with models of ecosystem disturbance. Increases in mineralization, non-toxic organic matter, nutrients, phenolic compounds, oil products and heavy metals were simulated. Significantly higher sensitivity of the community below the ice to external influences was demonstrated compared to the summer,autumn community, when there was no ice layer. Models of the distribution of aquatic pollutants demonstrate the occurrence of deviations from ecosystem state parameters in the bottom layer under the influence of pollutant input with precipitation and the distribution of perturbations over greater (up to 500 km) distances. Simulation of pollutant input at present levels shows that Lake Baikal is already perturbed. This is indicated by increases in bacterial and summer phytoplankton biomass and nutrient concentration, and by fluctuations in the zooplankton biomass. [source] Nutrients, Chlorophyll a and Phytoplankton in the ,skenderun Bay (Northeastern Mediterranean)MARINE ECOLOGY, Issue 2 2002Sevim Polat Abstract. The monthly changes in chlorophyll a, phytoplankton abundance and nutrient concentrations at two stations, one at the inshore and the other at the deep waters of the northern part of ,skenderun Bay, were investigated between 1994,,,1995. The vertical distribution of nutrients and phytoplankton biomass were also studied at the deep station. The concentrations of NO3+NO2 -N, PO4 -P and SiO4 -Si of surface water at both stations were 0.31,,,1.63 µg-at · l -1, 0.08,,,0.60 µg-at · l -1 and 0.50,,,2.7 µg-at · l -1, respectively. The highest concentrations were measured at the inshore station and clear differences were found between the inshore and deep-water stations. Chlorophyll a concentrations ranged from 0.17 to 2.78 µg · l -1 and the highest value was measured in March. At the inshore station, which was affected by land run-off, phytoplankton abundance reached the highest value (21,308 cells · l -1) in October 1995, with a marked dominance of Pseudonitzschia pungens (20,200 cells · l -1). The nutrient and chlorophyll a concentrations at the inshore station were higher than those at the deep station. One reason for this is the land-based nutrient input into the coastal area here. In spite of these effects, the bay is not eutrophicated because of circulation events in the northeastern Mediterranean. [source] Temporal Variations of Nutrients, Chlorophyll a and Particulate Matter in Three Coastal Lagoons of Amvrakikos Gulf (Ionian Sea, Greece)MARINE ECOLOGY, Issue 3 2001Konstantinos A. Kormas Abstract. The temporal variations of nutrients, chlorophyll a (chl a), suspended particulate matter (SPM) and particulate organic carbon (POC) were measured over 12 months in three shallow coastal brackish water lagoons of the Amvrakikos Gulf, Ionian Sea. Two of the lagoons, Tsoukalio and Rodia, are interconnected but separated from Logarou by a narrow strip of land. Logarou has a better water exchange with the sea as indicated by the higher salinity and dissolved oxygen concentrations and the smaller variation of the above-mentioned parameters. Nitrate concentrations were largely the same in the three lagoons and higher than in the Amvrakikos Gulf. Phosphate concentrations in Logarou exceeded by far those of Tsoukalio/Rodia; the increased phosphate levels recorded in January caused an extended phytoplankton bloom with chl a concentrations higher than in the other two lagoons. Chl a in Tsoukalio was positively correlated with nitrate whereas in the most shallow lagoon, Logarou, it showed a positive correlation with light winds (force 4 and lower), probably caused by resuspension from the sediment. Increased phytoplankton biomass in Logarou coupled with the better water exchange may be related to the higher fish production in this lagoon. [source] Chlorophyll content and fluorescence responses cannot be used to gauge reliably phytoplankton biomass, nutrient status or growth rateNEW PHYTOLOGIST, Issue 3 2006Mikaela Kruskopf Summary ,,To consider the relationship between chlorophyll a (Chl a) content and phytoplankton growth and nutrient status, four phytoplankton species were grown in nitrogen (N)-limited [and, for one species, phosphorus (P)-limited] culture and measurements were made of CNP biomass, in vivo and in vitro Chl a content, the ratio of variable to maximum fluorescence (FV/FM) and the performance index for photosynthesis, PIABS (a derivative of the O-J-I-P analysis of photosystem II functionality). ,,Interspecies differences plus the development of intraspecies differences during nutrient stress produced c. 10-fold variations in Chl : C. Estimates of C from in vivo Chl content were better than those from extracted Chl content, as the decline in Chl : C during nutrient stress was offset in part by increased Chl fluorescence. ,,FV/FM was not a robust indicator of nutrient status or relative growth rate. Responses of FV/FM in cells re-fed the limiting nutrient showed no consistent pattern with which to gauge nutrient status. PIABS showed some promise as an indicator of nutrient status and relative growth rate. ,,Chl a content and fluorescence parameters do not deserve the unquestioned status they usually enjoy as indicators of biomass and physiological status. [source] Ultraviolet-B Radiation Effects on the Structure and Function of Lower Trophic Levels of the Marine Planktonic Food WebPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2006Gustavo A. Ferreyra ABSTRACT The impact of UV-B radiation (UVBR; 280,320 nm) on lower levels of a natural plankton assemblage (bacteria, phytoplankton and microzooplankton) from the St. Lawrence Estuary was studied during 9 days using several immersed outdoor mesocosms. Two exposure treatments were used in triplicate mesocosms: natural UVBR (N treatment, considered as the control treatment) and lamp-enhanced UVBR (H treatment, simulating 60% depletion of the ozone layer). A phytoplankton bloom developed after day 3, but no significant differences were found between treatments during the entire experiment for phytoplankton biomass (chlorophyll a and cell carbon) nor for phytoplankton cell abundances from flow cytometry and optical microscopy of three phytoplankton size classes (picoplankton, nanoplankton and microplankton). In contrast, bacterial abundances showed significantly higher values in the H treatment, attributed to a decrease in predation pressure due to a dramatic reduction in ciliate biomass (, 70,80%) in the H treatment relative to the N treatment. The most abundant ciliate species were Strombidinium sp., Prorodon ovum and Tintinnopsis sp.; all showed significantly lower abundances under the H treatment. P. ovum was the less-affected species (50% reduction in the H treatment compared with that of the N control), contrasting with ,90% for the other ones. Total specific phytoplanktonic and bacterial production were not affected by enhanced UVBR. However, both the ratio of primary to bacterial biomass and production decreased markedly under the H treatment. In contrast, the ratio of phytoplankton to bacterial plus ciliate carbon biomass showed an opposite trend than the previous results, with higher values in the H treatment at the end of the experiment. These results are explained by the changes in the ciliate biomass and suggest that UVBR can alter the structure of the lower levels of the planktonic community by selectively affecting key species. On the other hand, linearity between particulate organic carbon (POC) and estimated planktonic carbon was lost during the postbloom period in both treatments. On the basis of previous studies, our results can be attributed to the aggregation of carbon released by cells to the water column in the form of transparent exopolymer particles (TEPs) under nutrient limiting conditions. Unexpectedly, POC during such a period was higher in the H treatment than in controls. We hypothesize a decrease in the ingestion of TEPs by ciliates, in coincidence with increased DOC release by phytoplankton cells under enhanced UVBR. The consequences of such results for the carbon cycle in the ocean are discussed. [source] | |||||||||||||