Effects of phytoplankton on the elemental composition (C,N, P) of suspended particulate material in the lower river Rhine

The spatial and temporal distribution of element concentrations were monitored together with chlorophyll a as an indicator of algal density to assess the effect of phytoplankton on the elemental composition (C, N, P) of suspended materials in the lower Rhine. The high concentrations of particulate C, N and P in the river were found to decrease in the delta and to increase again in the estuarine turbidity zone. Phytoplankton blooms increased the concentrations of particulate C, N, and P significantly in the upstream part of the river. In summer 1989, 15–65% of the particulate C and 20–75% of the particulate N were attributable to phytoplankton. Together with published data these observations indicate that in eutrophic rivers, the input of organic materials from the catchment is strongly modified and supplemented by in situ growth of phytoplankton. During seaward transport the phytoplankton and the particulate elements disappeared from the river water concomitantly with the suspended matter, indicating an increased retention of these elements due to sedimentation. In contrast, soluble ammonia, nitrite and phosphate increased in the tidal reaches of the river because of local input in the harbour and city of Rotterdam and because of mineralization. Therefore the total nutrient load of the Rhine estimated at the German/Dutch border does not reflect the actual input into the sea.     

Seasonal variation in composition and production of planktonic communities in the lower River Rhine

1. The composition and activity of phytoplankton, zooplankton and bacterioplankton in the lower River Rhine were measured in 1990 as part of an international biological inventory of the river. A seasonal study was carried out on two stations: one in the river mouth (km 1019) and one at the German/Dutch border (km 863). 2. High densities of phytoplankton (with up to 140 μg chlorophyll a 1-^?1) and occasional depletion of dissolved silicate were observed at the upstream station. Phosphate concentrations were also lowered during blooms. 3. Phytoplankton blooms, dominated by a few species of centric diatoms, declined one order of magnitude during downstream transport. During non-bloom conditions (low) algal densities were maintained during transport, or increased slightly, indicating the suitability of the river reach for algal growth. 4. Bacterial cell number and production (measured by the ³H-thymidine method) showed a broad summer maximum with activity peaks (0.5 nK < M thymidine h^?1) coincident with declining phytoplankton blooms. Winter values of bacterial production (0.02–0.05 n < Mh^?1) were substantial, probably as a result of allochthonous input of organic matter. 5. Rotifers and crustaceans made up the greater part of the zooplankton biovolume, but at the upstream station the contribution of Dreissena larvae and rhizopods was also substantial. High zooplankton biovolumes, of over 500 × 10⁶μm³1-^?1, were observed only during the phytoplankton spring bloom. 6. Quantitative relationships between the high phytoplankton production (2.1–3.4 gCm^?2 day^?1), the high bacterial substrate uptake (0.5–1gCm^?2 day^?1), and grazing were analysed for the growing season 1990. Algal grazing by metazoan herbivores was substantial only during spring, while the role of phagotrophic microplankton and cell lysis were indicated as major factors responsible for the downstream decline of phytoplankton blooms in the lower Rhine.     

Fixation of dissolved silicate and sedimentation of biogenic silicate in the lower river Rhine during diatom blooms

Concentrations of dissolved silicate and particulate biogenic silicate were measured in three branches of the lower river Rhine in The Netherlands in order to analyse the role of this element in the eutrophication of the river basin. Particulate silicate followed the seasonal development of the phytoplankton, which was dominated by diatoms. The concentration of dissolved silicate fell during blooms (< 0.1 mg.l^–1 ), but the amounts of biogenic silicate measured ( 1 mg.l^–1) were insufficient to explain the seasonal decrease in the dissolved fraction; this indicates retention of silicate upstream. Some particulate biogenic silicate in river water settled in man-made sedimentation areas in the Rhine delta. The observations suggest that changes in silicate fixation in the Rhine may have contributed to the incidence of non-diatom phytoplankton blooms in receiving waters.     

Meteorological influences on algal bloom potential in a nutrient-rich blackwater river

1. The effect of variability in rainfall on the potential for algal blooms was examined for the St Johns River in northeast Florida. Water chemistry and phytoplankton data were collected at selected sites monthly from 1993 through 2003. Information on rainfall and estimates of water turnover rates were used in the analyses of trends in phytoplankton biomass.
2. Major trends in rainfall and runoff within the lower St Johns River catchment over the 10-year study period were marked by both significant drought and flood periods. Autumn and winter rainfall patterns were strongly correlated with the range of Pacific sea surface temperature anomalies associated with El Niño events and La Niña periods. The effect of these major shifts in rainfall was evident in the strong relationship to replacement rates for water within the lower St Johns River.
3. The eutrophic status of the river was reflected in the high concentrations of nitrogen and phosphorus observed at all sampling sites, with total nitrogen concentrations up to 3100  μ g L⁻¹ and total phosphorus concentrations up to 180  μ g L⁻¹.
4. While it is clear that the high phytoplankton biomass and frequent blooms that characterize the freshwater portions of the lower St Johns River are fundamentally based on nutrient status, the expression of that potential was strongly correlated to water replacement rates, as revealed by the inverse relationship between phytoplankton biovolume increase and water turnover rate, with an R ² of 0.80 for the major bloom season. The sensitivity of algal blooms to rainfall patterns over the 10-year study period suggest that longer-term temporal and spatial shifts in rainfall, such as multi-decadal cycles and the global-warming phenomenon, will also influence the frequency and intensity of algal blooms.     

Impact of eutrophication on the silicate cycle of man-made basins in the Rhine delta

The impact of eutrophication on the biogeochemical cycle of silicate in the Rhine delta was analysed by 1) comparing the seasonal variation in river water, stagnant fresh water and coastal seawater and 2) observations in well-controlled experimental reservois subjected to different regimes of phosphate precipitation. The high input of dissolved sliciate from Rhine water was rapidly depleted in receiving waater systems through vigorous phytoplankton (datom) growth. In reservoirsca. 50% of the silicate input was retained over a seven years' observation period. Regeneration of silicate immobilized by diatoms was accelerated by very dense blooms of phytoplankton in reservoirs and in Lake IJssel that increased the pH value over 9.The prevailling lowratios of Si/N and Si/P in Rhine water entall the risk of massive blooms of flagellates or cyanobacteria in receiving waters. The 50% reduction in nitrogen and phosphate emission agreed upon in the Rhine Action Plan may reduce butnot eliminate this risk.     

Response of the Dutch Wadden Sea ecosystem to phosphorus discharges from the River Rhine

The primary production in the western part of the Dutch Wadden Sea (Marsdiep tidal basin) has been reported to have increased by a factor of two since the late 1970s. This doubling of the phytoplankton and the microphytobenthos production has been ascribed to the eutrophication of that area: mean annual phosphate concentrations have increased, whereas the nitrogen concentrations have not. Analysis of the available production data indicates a more than tenfold increase of the production of the phytoplankton in the Marsdiep tidal channel since the early 1950s. The increase in the phytoplankton production in the inner area seems to be of the same order of magnitude. The primary production of the phytobenthos and the secondary production of the macrozoobenthos seems to have increased proportionally to that of the phytoplankton. It is known that the nutrients in the Marsdiep tidal basin originate from the River Rhine. However, there are two possible routes for nutrients to reach that area. One is via the River IJssel and Lake IJssel (varying amounts of fresh water are sluiced out from the latter into the Wadden Sea). The other is along the coast of the North Sea, where the water transport is driven northeastwards by the residual current. Analysis of available data shows that the annual primary production in the Marsdiep tidal basin is mainly determined by the phosphate discharge from Lake IJssel which directly reach that part of the Wadden Sea, rather than from the River Rhine of which the water must run northward along the coast before reaching the western Dutch Wadden Sea. The close relation between fluctations in annual phosphate discharges and fluctations in annual phytoplankton primary production up to more than ten times the 1950 values indicates that primary production in the Marsdiep tidal channel and probably even in the main part of the whole basin, was and is phosphate limited.The mineralization of North Sea particulate organic matter inside the Wadden Sea, previously thought to be the main phosphate source, is questioned. The repercussions of this finding for management are discussed.     

Lake age and water level affect the turbidity of floodplain lakes along the lower Rhine

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.     

Plankton in the River Rhine: structural and functional changes observed during downstream transport

The growth dynamics of phytoplankton, zooplankton and bacterioplanktonin the River Rhine were analysed simultaneously with a numberof environmental factors in order to identify environmentalsteering factors and to describe some of their interrelations.Observations on the metabolic activity (for algae and bacteria)and density (for all organisms) were carried Out three timesin 1990 using successive sampling of the same water parcel duringits transport in the lower 660 km reach of the river. High algaldensities (up to 170.5 µg chlorophyll a l^–1), rotifers(up to 1728 l^–1), crustaceans (up to 65 l^–1) andbacteria (up to 16x10⁹ l^–1) were found. Algae and rotifersshowed a rapid successive development during transport, whilecrustaceans were only abundant in the tidal reach of the river.In May, a vigorous growth of phytoplankton, zooplankton andbacteria was found. The diatom-dominated phytoplankton depletedthe dissolved silicate in the river water and this led to acollapse of the populations, indicated by a decreased specificrate of photosynthesis (measured by the ¹⁴C method) and vigorousbacterial growth (measured by [³H]thymidine incorporation).Subsequently, the remaining phytoplankton diminished to verylow levels near the river mouth. In July and September, it seemedthat biological interactions within the plankton populationsor between plankton and benthos balance the population densitiesso that separate developmental stages, as in spring, were lessprominent. Estimates of the growth rates and loss rates of thephytoplankton were made. Phytoplankton exerted a substantialinfluence on the partitioning of nutrients (nitrogen, phosphorus,silicate) over water and suspended matter (as analysed by elementanalysis). It seems likely that only the reduction of phosphate,as planned under the Rhine Action Programme, and not that ofnitrogen, may restrict the peaks of plankton growth describedhere.     

Exoenzyme activity associated with lotic epilithon

SUMMARY. 1. Epilithic communities were developed on glass slides under four regimes of relative current velocity and light exposure, designated as slow-light, slow-dark, fast-light and fast-dark, in a fourth-order boreal stream. Ten samples were collected over an 8-month period and analysed for biomass, chlorophyll and exoenzyme activity. Fourteen assays were used to monitor the activity of eleven types of exoenzymes involved in the degradation of cellulose, lignin, chitin, xylan, protein, glycogen, organic phosphates and organic sulphates.
2. The communities that developed under each current and light regime were distinct in structure and species composition, but had similar patterns of exoenzyme activity. Overall, exoenzyme activity was closely correlated with biomass. The most readily detected enzymes were phenol oxidase, phosphatase, alpha-1, 4-glucosidase, beta-1, 4-N-acetylglucosamidase, and beta-1, 4-glucosidase.
3. Calculating exoenzyme activities per unit biomass eliminated the covariance between biomass and enzyme activity, revealing quantitative differences in exoenzyme activity among communities. The highest exoenzyme activity was associated with the slow-dark epilithon and the least with the slow-light. Fast-light and fast-dark were intermediate.
4. Biomass, chlorophyll and exoenzyme activity showed marked seasonal variations. In general, carbohydrases and the phenol oxidases had different seasonal activity patterns with carbohydrase activity peaking in the summer and phenol oxidase activity increasing markedly in the autumn.
5. Differences among epithilic communities could not be readily accounted for by single factors. Community development was determined by the interactions among current, light, macroinvertebrates and season.     

Phosphatase activity in relation to phytoplankton composition and pH in Swedish lakes

SUMMARY. 1. Potential phosphatase activity and phytoplankton from several lakes of different character were compared in order to evaluate the importance of lake water pH and phytoplankton composition for the activity and pH optimum of lake water phosphatases.
2. In oligotrophic lakes, in which phytoplankton biomass was most often dominated by Ochromonadaceae spp., optimum phosphate activity was found at pH values <6. In eutrophic lakes, where species of Cyanophyceae and Bacillariophyceae dominated the phytoplankton biomass, optimum phosphatase activity was found at pH 7.5 or 8.5.
3. The pH optimum of phosphatase activity often differed from the corresponding lake water pH.
4. Experimental variation in phosphorus availability resulted in predictable changes in phosphatase activity. However, specific phosphatase activity, calculated per biomass of phytoplankton, was dependent on plankton species composition.     

Development and ecological importance of phytoplankton in a large lowland river (River Meuse,Belgium)

The ecological importance of the River Meuse phytoplankton with regard to carbon and nutrient transport has been examined in two reaches of the Belgian course of the river.Field measurements of total particulate organic carbon (POC), particulate organic nitrogen (PON) and particulate phosphorus (PP) show that the large autochtonous production of organic matter strongly affects the carbon and nutrient budget of the aquatic system. During the growing season, phytoplankton accounts for nearly 60% of the POC and dominates the PON. Calculations of the carbon and oxygen budget in the upper reach of the Belgian Meuse demonstrates that the ecosystem is autotrophic, i.e. that autochtonous FPOM (fine particulate organic matter) production is the major carbon input. This suggests that in large lowland rivers, primary production (P) may exceed community respiration (R), i.e. P:R>1, whereas they are assumed to be heterotrophic (P:R<1) in the River Continuum concept.The question of maintenance of phytoplankton in turbid mixed water columns is also addressed, and the case of the River Meuse is treated on the basis of studies of photosynthesis and respiration (ETS measurements). The results suggest that the potamoplankton may show some low-light acclimation, through an increase of chlorophyll a relative to biomass, when it comes to deep downstream reaches, and that algal respiration rate may be reduced. A simulation of the longitudinal development of the algal biomass shows the different phases of algal growth and decline along the river and brings support to the importation hypothesis for explaining maintenance of potamoplankton in the downstream reaches.     

Phytoplankton and bacterial alkaline phosphatase activities in relation to phosphate and DOP availability within the Gironde plume waters (Bay of Biscay)

Previous studies conducted on the continental shelf in the Southeast Bay of Biscay influenced by Gironde waters (one of the two largest rivers on the French Atlantic coast) showed the occurrence of late winter phytoplankton blooms and phosphorus limitation of algal growth thereafter. In this context, the importance of dissolved organic phosphorus (DOP) for both algae and bacteria was investigated in 1998 and 1999 in terms of stocks and fluxes. Within the mixed layer, although phosphate decreased until exhaustion from winter to spring, DOP remained high and phosphate monoesters made up between 11 to 65% of this pool. Total alkaline phosphatase activity (APA, V_max) rose gradually from winter (2-8 nM h⁻¹) to late spring (100-400 nM h⁻¹), which was mainly due to an increase in specific phytoplankton (from 0.02 to 3.0 nmol μgC⁻¹ h⁻¹) and bacterial APA (from 0.04 to 4.0 nmol μgC⁻¹ h⁻¹), a strategy to compensate for the lack of phosphate. At each season, both communities had equal competitive abilities to exploit DOP but, taking into account biomass, the phytoplankton community activity always dominated (57-63% of total APA) that of bacterial community (9-11%). The dissolved APA represented a significant contribution. In situ regulation of phytoplanktonic APA by phosphate (induction or inversely repression of enzyme synthesis) was confirmed by simultaneously conducted phosphate-enrichment bioassays. Such changes recorded at a time scale of a few days could partly explain the seasonal response of phytoplankton communities to phosphate depletion.     

The distribution of dissolved DNA in an oligotrophic and a eutrophic river of Southwest Florida

The distribution of dissolved DNA concentrations and some microbial variables were compared in an oligo-mesotrophic river (the Crystal River) and a phosphate-rich eutrophic river (the Alafia River) in Southwest Florida over a 15 month period. Concentrations of phosphate and nitrate in the Alafia River averaged 135 and 18.2 times the respective phosphate and nitrate concentrations of the oligo-mesotrophic Crystal River. The seasonal average dissolved DNA concentration for the Alafia River exceeded that of the Crystal River by a factor of 1.8 (8.2 g 1^–1 compared to 4.6 g 1^–1, respectively). The greatest concentrations of dissolved DNA in the Alafia River were found in areas that contained the largest populations of phytoplankton and bacteria (a reservoir formed from an abandoned phosphate mining pit and two downstream stations near the mouth of the river). Differences in dissolved DNA concentrations between these environments and more pristine environments (i.e. all Crystal River Stations and upstream Alafia River stations) were of the same order of magnitude (1.8 to 2.2-fold) as the differences in bacterial abundance and activity, but considerably less than differences in phytoplankton abundance and activity between such environments. Seasonal variations in dissolved DNA concentrations in the Crystal River corresponded to seasonal variations in microbial populations, with minimal values in January and greater values in July. In the Alafia River, lowest concentrations for dissolved DNA occurred in July during the wet season, when seasonal flooding of area of leaf litter yielded high levels of dissolved organic carbon (DOC) which were low in dissolved DNA. These results suggest that: 1) in situ planktonic activity is a greater source of dissolved DNA than allochthonous or terrestrial sources of DOC; 2) factors that control the magnitude of heterotrophic bacterial populations are more likely to control dissolved DNA levels than factors regulating autotrophic population activity and abundance; 3) differences in dissolved DNA between eutrophic and oligo-mesotrophic environments are often much smaller than the differences in nutrient concentration between such environments.     

Phytoplankton growth in relation to network topology: time‐averaged catchment‐scale modelling in a large lowland river

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Effects of Mississippi River water on phytoplankton growth and composition in the upper Barataria estuary,Louisiana

Diversion of river waters to adjacent estuaries may occur during wetland restoration, navigation channel development, or storms. We proposed that diversions of nitrogen- and phosphorus-enriched waters from the river to estuarine waters would result in increased phytoplankton biomass and shifts to noxious or harmful algal blooms. We tested this hypothesis by conducting four seasonal microcosm experiments in which Mississippi River water was mixed at different volume ratios with ambient estuarine waters of three lakes in the upper Barataria Basin, Louisiana, USA. These lakes included two brackish lakes that were in the path of diverted Mississippi River water, and a freshwater lake that was not. The results from the 3- to 8-day experiments yielded a predictable increase in phytoplankton biomass related to nutrient additions from Mississippi River water. The subsequent decreases in the dissolved nitrate + nitrite, soluble reactive phosphorus, and silicate concentrations explained 76 to 86% of the increase in chlorophyll a concentrations in the microcosms. Our experiments showed that cyanobacteria can successfully compete with diatoms for N and P resources even under non-limiting Si conditions and that toxic cyanobacteria densities can increase to bloom levels with increased Mississippi River water inputs to ambient waters in the microcosms. Diversions of Mississippi River into adjacent estuarine waters should be considered in relation to expected and, possibly, unexpected changes in phytoplankton communities to the receiving waters and coastal ecosystems.

     

Differing growth responses of major phylogenetic groups of marine bacteria to natural phytoplankton blooms in the western North Pacific Ocean

Growth and productivity of phytoplankton substantially change organic matter characteristics, which affect bacterial abundance, productivity, and community structure in aquatic ecosystems. We analyzed bacterial community structures and measured activities inside and outside phytoplankton blooms in the western North Pacific Ocean by using bromodeoxyuridine immunocytochemistry and fluorescence in situ hybridization (BIC-FISH). Roseobacter/Rhodobacter, SAR11, Betaproteobacteria, Alteromonas, SAR86, and Bacteroidetes responded differently to changes in organic matter supply. Roseobacter/Rhodobacter bacteria remained widespread, active, and proliferating despite large fluctuations in organic matter and chlorophyll a (Chl-a) concentrations. The relative contribution of Bacteroidetes to total bacterial production was consistently high. Furthermore, we documented the unexpectedly large contribution of Alteromonas to total bacterial production in the bloom. Bacterial abundance, productivity, and growth potential (the proportion of growing cells in a population) were significantly correlated with Chl-a and particulate organic carbon concentrations. Canonical correspondence analysis showed that organic matter supply was critical for determining bacterial community structures. The growth potential of each bacterial group as a function of Chl-a concentration showed a bell-shaped distribution, indicating an optimal organic matter concentration to promote growth. The growth of Alteromonas and Betaproteobacteria was especially strongly correlated with organic matter supply. These data elucidate the distinctive ecological role of major bacterial taxa in organic matter cycling during open ocean phytoplankton blooms.     

Seasonal changes in particulate and dissolved lipids in a eutrophic prairie lake

1. Critical periods of lipid energy transfer from phyto- to zooplankton were inferred by comparing seasonal patterns of particulate and dissolved lipid fractions in lake water with temporal changes in lipid energy reserves of the zooplankton in a hypereutrophic lake.
2. The midsummer phytoplankton community was dominated by the bloom-forming cyanobacterium Aphanizomenon flos-aquae. The collapse of the bloom was accompanied by a 2-week period of severe nitrogen deficiency after which there was a marked increase in the concentration of lipid energy reserves in the particulate (algal) fraction.
3. Areal lipid energy reserves of the dominant herbivorous zooplankton responded positively to changes in the tri-and diacylglycerol content of the particulate fraction of lake water in a species-specific manner.
4. Bacterial numbers also peaked in September concomitant with a large increase in free fatty acids in the dissolved lipid fraction probably produced by the decay of the
A. flos-aquae bloom.
5. The association between periods of nitrogen deficiency and increased energy reserve lipids in the particulate fraction supports observations made with laboratory algal cultures that periods of nutrient deficiency may intensify lipid synthesis in some algal species, thereby enhancing the rate of lipid energy transfer from phytoplankton to zooplankton.     

着生藻类和浮游藻类在三峡库区河流健康评价中的适宜性比较研究

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Growth, production and losses of phytoplankton in the lowland River Spree: carbon balance

1. Phytoplankton carbon assimilation and losses (exudation, dark carbon losses) as well as oxygen release and dark community respiration were measured regularly for 2 years at four stations along the lower Spree (Germany). Carbon balance of river phytoplankton was estimated using measured assimilation, metabolic losses and variations in algal carbon along a stretch of river. 2. The light/dark bottle method was modified to simulate vertical mixing. 3. Waxing and waning of phytoplankton populations dominated the load of particulate organic carbon as well as the oxygen budget of the river. 4. Phytoplankton assimilated 310–358 g C m^?2 yr^?1. A mean value of 586 mg C m^?3 day^?1 was fixed in photosynthesis, with 16.7 mg C being exuded during the day and 20.1 mg lost at night. The measured dark respiration was equivalent to only 28% of the daily gross oxygen production of the plankton community. Phytoplankton washed from upstream lakes and reservoirs was not measurably damaged by turbulent transport. 5. In spring, 18–22% of assimilated carbon was used for net biosynthesis of phytoplankton along the river course. At this time, the carbon balance of this part of the Spree was dominated by autochthonous net production. During summer, however, total carbon losses exceeded the intensive carbon assimilation. The decline of algal biomass along the river course in summer was not explicable by measurable physiological losses. The importance of sedimentation and grazing losses is discussed.