On the annual variation of phytoplankton biomass in Finnish inland waters

Annual variations in phytoplankton biomass in 63 lakes in Southern and Central Finland are discussed. Biomass is rather small during winter (January–April), usually <0.05 mg l^–1 (fresh weight) and there are no differences between oligotrophic and eutrophic lakes. In early spring and in autumn biomass varies widely, depending mainly on water temperature. Phytoplankton biomass is smaller in July than in June and August in oligotrophic lakes (biomass <0.20 mg l^–1 fresh weight) and mesotrophic (biomass 1.0–2.5 mg l^–1) lakes, but greater in eutrophic (biomass 2.5–10.0 mg l^–1) and hypereutrophic (biomass >10.0 mg l^–1) lakes. The standard deviation of phytoplankton biomass in Finnish inland waters is usually smallest in July, which facilitates the comparison of phytoplankton between different kinds of lakes.     

Spring phytoplankton of 54 small lakes in southern Finland

The abundance and species composition of phytoplankton communities were studied rapidly following the spring ice-melt in 54 small Finnish lakes that form a unique mosaic of water bodies. Phytoplankton biomass and cell density varied among the study lakes with a factor 100 between the lowest and highest values. Highest biomass and densities of phytoplankton characterized small ( < 0.05 km²) lakes with moderate or high water colour (> 80 mg Pt l^–1). In contrast, biomass was low in clear-water lakes and lakes where water throughflow was strong. Typically one species dominated most phytoplankton communities, and usually comprised up to about 45% of the total phytoplankton biomass. Two-thirds of the 103 taxa observed were Chrysophyceans and Chlorophyceans. The most common taxa wereChlamydomonas spp. (Chlorophyceae) andCryptomonas ovata (Cryptophyceae).     

A survey of toxicity of cyanobacterial blooms in Lake Ladoga and adjacent water bodies

Twentyfive cyanobacterial blooms in Lake Ladoga and adjacent water bodies were studied in the summer of 1990–1992. Toxicity of the water bloom material for mice was detected in 9 cases. The maximal tolerable doses (MTD) of the material extracted from biomass varied within 3–30 mg kg^–1 mouse body weight; 50% lethal doses (LD₅₀) were within 45–125 mg kg^–1. Toxic water blooms were registered in Karelian lakes and in the Neva Bay, Gulf of Finland. Cyanobacterial samples collected on the eastern coast of Lake Ladoga proved to be non-toxic. The species identified in toxic bloom material included Anabaena circinalis, A. flos-aquae, A. lemmermannii, Anabaena sp., Aphanizomenonflos-aquae, Gloeotrichia echinulata, G. pisum, Microcystis aeruginosa and Oscillatoria sp. These data suggest that toxic forms of cyanobacteria are widespread in Karelian lakes belonging to the drainage basin of Lake Ladoga.     

Phytoplankton periodicity of the Waitaki Lakes,New Zealand

The Waitaki River system in the South Island of New Zealand includes three large glacially-formed headwater lakes, Tekapo, Pukaki and Ohau, which drain into the manmade Lake Benmore. Phytoplankton periodicity was followed from December 1975 to January 1980 as part of a study investigating possible changes in these lakes as a consequence of hydroelectric development. The phytoplankton was highly dominated by diatoms, e.g., Diatoma elongatum, Cyclotella stelligera, Asterionella formosa, and Synedra acus, but in lakes Ohau and Benmore populations of green algae occasionally developed. In all four lakes seasonal phytoplankton periodicity was observed with maximum biomass in spring and summer. In Lake Tekapo, the first lake in the chain, maximum biomass did not exceed 300 mg m^–3, but in the very turbid Lake Pukaki the maximum summer biomass ranged between 300 and 800 mg m^–3. In Lake Ohau, the least turbid lake, maximum biomass was around 1 000 mg m^–3. In the newly created Lake Benmore periodicity was less evident and summer maxima reached over 1 500 mg m^–3. The phytoplankton periodicity in these lakes is greatly influenced by seasonal patterns of turbidity from inflowing glacial silt.     

Relations between production and biomass of phytoplankton in four Swedish lakes of different trophic status and humic content

Production and biomass values from phytoplankton populations in four different Swedish lakes were analysed. The production in all lakes was directly proportional to biomass during homothermal periods. When the lakes were stratified there was a strong negative relation between specific growth rate and biomass. The data fitted to a logistic density dependent growth equation of the form: dB/ dt = µ_mB(1-B · K^–1) where B is the biomass, µ_m the maximum specific growth rate and K the carrying capacity. The equation was used to derive the parameters µ · µ_m ^–1 and carrying capacity (the maximum possible biomass). These parameters were then discussed in relation to light climate, phosphorus concentration and humic content.     

Distribution and production ofChironomus salinarius (Diptera: Chironomidae) in a shallow coastal lagoon in the Bay of Cádiz

The abundance, generation time and production ofChironomus salinarius larvae in a lagoon fish-pond system in the Bay of Cádiz were studied by taking monthly samples at 3 sites during 1991 and 1992. Numerical abundance and biomass of larvae showed considerable spatial, seasonal and interannual variation (ANCOVAs,P<0.001). The maximum mean annual density was 7048 larvae m^–2, and corresponded to a biomass of 3.08 g dry weight (DW) m^–2. It was recorded at the site with the lowest rate of water renewal. Seasonal patterns were similar at all sites, with main annual peaks of abundance and biomass in autumn-early winter. Chironomid density was positively related to the biomass of benthic macroalgae (P<0.001). The population studied was multivoltine with a probable average of five generations per year, with overlapping cohorts and a predominance of third- and fourth-instar larvae. Estimates of annual production ranged between 72.2 g DW m^–2 yr^–1 at the site with the lowest rate of water renewal in 1991 and 0.1 g DW m^–2 yr^–1 at the site with the highest rate of water renewal in 1992. Mean annual production and the production/biomass ratio for the system was estimated to be 16.8 g DW m^–2 yr^–1 and 12.7, respectively. Possible factors leading to the observed density fluctuations are discussed, as well as possible sources of error in production estimates.     

Interactions between sediment and water in a shallow and hypertrophic lake: a study on phytoplankton collapses in Lake Søbygård,Denmark

Short-term changes in phytoplankton and zooplankton biomass have occurred 1–3 times every summer for the past 5 years in the shallow and hypertrophic Lake Søbygård, Denmark. These changes markedly affected lake water characteristics as well as the sediment/water interaction. Thus during a collapse of the phytoplankton biomass in 1985, lasting for about 2 weeks, the lake water became almost anoxic, followed by rapid increase in nitrogen and phosphorus at rates of 100–400 mg N M^–2 day^–1 and 100–200 mg P m^–1 day^–1. Average external loading during this period was about 350 mg N m^–2 day^–1 and 5 mg P m^–2 day^–1, respectively.Due to high phytoplankton biomass and subsequently a high sedimentation and recycling of nutrients, gross release rates of phosphorus and nitrogen were several times higher than net release rates. The net summer sediment release of phosphorus was usually about 40 mg P m^–2 day^–1, corresponding to a 2–3 fold increase in the net phosphorus release during the collapse. The nitrogen and phosphorus increase during the collapse is considered to be due primarily to a decreased sedimentation because of low algal biomass. The nutrient interactions between sediment and lake water during phytoplankton collapse, therefore, were changed from being dominated by both a large input and a large sedimentation of nutrients to a dominance of only a large input. Nitrogen was derived from both the inlet and sediment, whereas phosphorus was preferentially derived from the sediment. Different temperature levels may be a main reason for the different release rates from year to year.     

Bacterial productivity in ponds used for culture of penaeid prawns

The quantitative role of bacteria in the carbon cycle of ponds used for culture of penaeid prawns has been studied. Bacterial biomass was measured using epifluorescence microscopy and muramic acid determinations. Bacterial growth rates were estimated from the rate of tritiated thymidine incorporation into DNA. In the water column, bacterial numbers ranged from 8.3×10⁹ 1^–1 to 2.57×10¹⁰ 1^–1 and production ranged from 0.43 to 2.10 mg Cl^–1 d^–1. In the 0–10 mm zone in sediments, bacterial biomass was 1.4 to 5.8 g C m^–2 and production was 250 to 500 mg C m^–2 d^–1. The results suggested that most organic matter being supplied to the ponds as feed for the prawns was actually being utilized by the bacteria. When the density of meiofauna increased after chicken manure was added, bacterial biomass decreased and growth rates increased.     

Ecological Significance of Nitrogen Cycling by Tubificid Communities in Shallow Eutrophic Lakes of the Danube Delta

Importance of tubificid populations on nitrogen cycle in two categories of shallow eutrophic lakes in the Danube Delta was quantitatively assessed for the 1992-1993 period. The structure of the primary producers in the studied lakes was used to discriminate between the two categories:(i) lakes dominated by macrophytes (A₁) and (ii) lakes dominated by phytoplankton (A₂). In both categories tubificid worms represented important fraction of the entire benthic community (35 and 32%, respectively, as number of individuals). They influence the sediment-water exchange of nutrients. The main processes involved are excretion of nutrients and their continuous release from sediments by molecular diffusion or through channels created by bioturbation. Inorganic nitrogen released from bottom sediments may regulate nitrogen load in the water body and thus, phytoplankton production. In 1992-1993, nitrogen stocks in tubificid biomass accounted for 5.3% in A₁ lakes and 15.6% in A₂ lakes of the amount stocked in phytoplankton, and only for 1.2 and 2.9% respectively, of the nitrogen load in water body. Nitrogen excretion rates ranged between 60.52 and 153.74 mg N m^–2 year^–1, and release rates from sediments between 378.26 and 960.87 mg N m^–2 year^–1, the lowest values being recorded for A₂ category. Differences are related to tubificid biomass, structure and abundance of primary producers and to nutrient load in different ecosystems. Ratios between release rate of inorganic nitrogen by tubificid worms and sedimentation rate of organic nitrogen in the two categories of lakes were 8.3 and 6.4% respectively. Contribution of nitrogen released daily from sediments to the dissolved inorganic nitrogen load in the water column was less than 0.5%. However, in A₁ and A₂ lakes, the released nitrogen had a potential to sustain 24.74 and 8.01%, respectively, of the annual phytoplankton production. These values suggest the significance of tubificids in keeping the eutrophication process at a high level, especially during the periods when nitrogen is the main limiting factor for phytoplankton production.     

Contemporary state of the zooplankton in Lake Peipsi

L. Peipsi is one of the richest fish lakes in Europe. Planktivorous smelt dominates in the fish fauna. The abundance of zooplankton fluctuates between 43 600–2241 500 ind m^–3, with the average 974 000 ind m^–3, biomass ranges from 0,09–3,69 g m^–3, with the average 1,86 g m^–3. Since the 1960s the abundance of rotifers has risen considerably while the mean zooplankter weight (B/N) has decreased from 0.005 mg to 0.004 mg. Zooplankton production (herbivores 20.6, predators 1.8, whole zooplankton community 22.4 g C m^–2 per period between May and October) can be considered high. Predatory zooplankton eats on an average 50% of the production of herbivorous zooplankton; about 50% of the whole zooplankton production (P_{Filt + Pred}) reaches fishes. The production of herbivorous zooplankton constitutes 10.1% of primary production. This ratio indicates a direct relationship between zoo- and phytoplankton in the food chain; the detrital food chain seems of little importance. About 6% of phytoplankton energy reaches fishes. The transformation of energy in the food web is efficient. On the basis of zooplankton L. Peipsi can be considered a moderately eutrophic or meso-eutrophic lake.     

Macro- and megabenthic communities in the high Arctic Canada Basin: initial findings

We investigated the macro- and megabenthos of the Canada Basin, one of the biologically least known areas of the Arctic deep sea. Macro-infauna was collected with 11 box cores at six stations ranging from 640 to 3,250 m water depth. Total abundance ranged from 3 to 265 individuals 0.04 m^–2 (75–6,625 individuals m^–2) and decreased with increasing depth. Biomass ranged from 0.04 to 228 mg wet weight 0.04 m^–2 (1–5,700 mg wet weight m^–2) and followed the same trend. Polychaetes, crustaceans and bivalves dominated the faunal densities, biomass and species numbers. At Northwind Ridge (800 and 1,800 m), apparently historic (~5,000 years BP) fish otolith deposits were abundant. The invertebrate epi-megafauna was qualitatively analyzed from 9.2 h of video and 853 still images collected at four remotely operated vehicle stations. The epifauna was dominated by polychaetes, crustaceans, echinoderms, cnidarians and fish, with most suspension-feeders occurring in the Northwind Ridge area. A total of 90 benthic invertebrate species/taxa from four biogeographic affinities were identified, including at least three new species of Isopoda. The evident low abundances and biomass are in agreement with findings from the Eurasian Arctic deep sea.     

Primary production and phytoplankton in two small,polyhumic forest lakes in southern Finland

Primary production and phytoplankton in polyhumic lakes showed a very distinct seasonal succession. A vigorous spring maximum produced by Chlamydomonas green algae at the beginning of the growing season and two summer maxima composed mainly of Mallomonas caudata Iwanoff were typical. The annual primary production was ca. 6 g org. C · m^–2 in both lakes. The mean epilimnetic biomass was 1.1 in the first lake and 2.2 g · m^–2 (ww) in the second one. The maximum phytoplankton biomass, 14 g · m^–2, was observed during the vernal peak in May.     

Biomass and litter dynamics in a Melaleuca forest on a seasonally inundated floodplain in tropical,northern Australia

Litterfall from a Melaleuca forest was investigated as part of chemical cycling studies on the Magela Creek floodplain in tropical, northern Australia. The forest contained two species of tree, Melaleuca cajaputi and Melaleuca viridiflora, with a combined average density of 294 trees ha^–1. The M. viridiflora trees had diameter breast height measurements ranging from 11.8 to 62.0 cm, median class 25.1–30.0cm and a mean value of 29.2±1.0 cm, compared to 13.0 to 66.3 cm, 30.1–35.0cm and 33.5±1.0cm for M. cajaputi trees. A regression model between tree height, diameter breast height and fresh weight was determined and used to calculate average tree weights of 775±1.6kg for M. viridiflora and 1009±1.6kg for M. cajaputi, and a total above-ground fresh weight of 263±0.3t ha^–1. The weight of litter recorded each month on the ground beneath the tree canopy ranged from 582±103 to 2176±376 g m^–2 with a monthly mean value of 1105±51 g m^–2. The coefficient of variation of 52% on this mean indicates the large spatial and temporal variability in litter distribution over the study site. This variability was greatly affected by the pattern of water flow and litter transport during the Wet season. Litterfall from the trees was evaluated using two techniques - nets and trays. The results from these techniques were not significantly different with annual litterfall collected in the nets being 705 ± 25 g m^–2 and in the trays 716±49 g m^–2. The maximum monthly amount of litterfall, 108 ±55g m^–2, occurred during the Dry season months of June–July. Leaf material comprised 70% of the total annual weight of litter, 480±29 g m^–2 in the nets and 495 ± 21 g m^–2 in the trays. The tree density and weight of litter suggest that the Melaleuca forests are highly productive and contribute a large amount of material to the detrital/debris turnover cycle on the floodplain.     

Trophic structure and productivity of the lagoonal communities of Tikehau atoll (Tuamotu Archipelago,French Polynesia)

Carbon standing stocks and fluxes were studied in the lagoon of Tikehau atoll (Tuamotu archipelago, French Polynesia), from 1983 to 1988.The average POC concentration (0.7–2000 µm) was 203 mg C m^–3. The suspended living carbon (31.6 mg C m^–3) was made up of bacteria (53%), phytoplankton < 5 µm (14.2%), phytoplankton > 5 µm (14.2%), nanozooplankton 5–35 µm (5.7%), microzooplankton 35–200 µm (4.7%) and mesozooplankton 200–2000 µm (7.9%). The microphytobenthos biomass was 480 mg C m^–2.Suspended detritus (84.4% of the total POC) did not originate from the reef flat but from lagoonal primary productions. Their sedimentation exceeded phytobenthos production.It was estimated that 50% of bacterial biomass was adsorbed on particles. the bacterial biomass dominance was explained by the utilisation of 1) DOC excreted by phytoplankton (44–175 mg C m^–2 day ^–1) and zooplankton (50 mg Cm^–2 day^–1)2) organic compounds produced by solar-induced photochemical reactions 3) coral mucus.50% of the phytoplankton biomass belongs to the < 5 µm fraction. This production (440 mg C m^–2 day^–1) exceeded phytobenthos production (250 mg C m^–2 day^–1) when the whole lagoon was considered.The zooplankton > 35 µm ingested 315 mg C m^–2 day^–1, made up of phytoplankton, nanozooplankton and detritus. Its production was 132 mg C m^–2 day^–1.     

Seasonal changes in composition and biomass of epilithic algal floras of a chalk stream and a soft water stream with estimates of production

Microscopic epilithic algae in the River Itchen at Otterbourne near Southampton and in the Ober Water in the New Forest were studied during 1984 and 1985. The River Itchen rises from chalk springs and has a steady pH near 8.2 and a mean alkalinity of 236 mg HCO₃ 1^–1; at the study site the river is about 16 m wide and 20 cm deep, with a mean flow rate of 0.33 m s^–1 and a discharge ranging through the year between 0.34 and 2.46 m³ s^–1. The Ober Water, which drains sands and gravels, has a pH between 6.9 and 7.2 and a mean alkalinity of about 50 mg HCO₃ 1^–1; at the study site it is about 6 m wide, with a mean flow rate of 0.27 m s^–1 and a discharge ranging through the year between 0.08 and 1.0 m³ s^–1.Epilithic algae removed from the pebbles that form the major part of the beds of both streams show seasonal changes in abundance and composition. Diatoms peaked in April/May and dominate the epilithic flora in both streams, comprising 70–95% of all algal cells; highest numbers of chlorophytes occurred in summer and cyanophytes increased in autumn. The species composition of the epilithic flora in the two streams was different, as was the population density; algal cell numbers ranged between 500 and 7000 cells mm^–2 of stream floor in the River Itchen and between 8 and 320 cells mm^–2 of stream floor in the Ober Water. The chlorophyll a content of epilithic algae in the River Itchen ranged between 115 and 415 mg m^–2 of stream floor, representing an annual mean biomass of about 8 g m^–2, whereas in the Ober Water a chlorophyll a content of 2.2 to 44 mg m^–2 of stream floor was found, representing an annual mean biomass of about 1 g m^–2. Cautious estimates of the annual production of epilithic algae in these streams suggest a value of about 600 g organic dry weight m^–2 in the River Itchen and about 75 g m^–2 in the Ober Water.     

Crustacean plankton in Høylandet

Crustacean plankton was studied in 12 lakes in theHøylandet area in 1986–87. Basic lake characteristicsare elevation 134–415 m, surface area 9–530 ha, pH 5.9–7.1,conductivity (25 °C) 12–40 µS cm^-1 andSecchi depth 4–9 m. Number ofspecies present varied between 3 and 11. Populationnumbers between 4000 and 400 000 per m² andbiomasses were within the range 30 to1800 mg m^-2 dry weight. Cladocera dominated overCopepoda in lakes with allopatric brown trout (Salmo trutta L.), on the contrary to lakes also populatedby Arctic charr (Salvelinus alpinus (L.)). Thesevariations are caused by differences in elevation,lake morphometry, water quality, fish predation andthe general distribution of the species. The largestlakes at lowest elevation were richest in species. Theacid sensitive genus Daphnia was represented by 3species. The lakes Storgrønningen (530 ha) andRøyrtjønna (27 ha) were sampled monthly in theice-free seasons of 1986–89, and Storgrønningen moreintensively from June to November in 1987 and 1988. The same6 species of Cladocera and 5 of Copepoda were presentin both lakes. Their life cycles were traditional orknown from several other Scandinavian lakes. Meanseasonal biomasses were of the range600–750 mg m^-2. At the species level, there wereconsiderable variations between years inStorgrønningen and particularly in Røyrtjønna. Noeffects of human impacts on the crustacean planktonwere found. The Høylandet lakes are representative forScandinavian oligotrophic to almost ultra-oligotrophiclakes. Storgrønningen is well qualified as a referencesystem. The between year variations in Røyrtjønna areso extreme, that any human impact could only be traced at alevel causing the extinction of species.     

Role of plankton in the turnover of organic matter on the Great Barrier Reef,Australia

Number, biomass and production of phytoplankton, bacteria, micro- and mesozooplankton and turnover of labile and stable organic matter were measured in waters over some Capricornia round reefs, and over the reefs of Lizard Island. Primary production was 10 to 40 mg C m^–3 d^–1 but was lower over the living reefs. Microbial wet biomass in reef waters varied from 100 to 500 mg m^–3, and production from 4 to 68 mg C m^–3 d^–1, which was commensurable with primary production. The biomass of microzooplankton (ciliates, zooflagellates and larvae) in waters of Lizard Island reefs reached 100–300 mg m^–3. Mesozooplankton biomass at night in reef waters of Heron Island varied from 200 to 800 mg m^–3. Its composition depended upon the tide phase. PB coefficients in bacterioplankton were 0.3 to 1.2 per day. The food demand of bacterioplankton in waters over the reefs was 5 to 20 times higher than the primary phytoplankton production. Labile organic matter (LOM) doubled in waters after it stayed over living reef for several hours. The turnover time of LOM in reef waters was as short as 1–2 weeks.     

A review of the hydrobiology of Lake Khubsugul (Mongolia)

Lake Khubsugul phytoplankton is dominated by Diatoms and Chlorococcales. Its algal flora is rather peculiar, but lacks Baikalian endemics.Primary production ranges from 2 to 5 mg C m^–3 d^–1. Total bacteria in the open water is 150–200 × 10³ cells ml^–1.Predominant in numbers and biomass throughout the year are two pelagial species of Copepoda — the endemic Mixodiaptomus kozhovi Step., and Cyclops abyssorum Sars.The bottom fauna consists of cold stenothermic invertebrates, mostly Chironomidae. In biomass, they rank only third, however, after Gammaridae and Mollusca. The average zoobenthos biomass of the lake is 5.5g m^–2.     

Some aspects of photosynthetic characteristics in a set of perennial irrigation reservoirs located in five river basins in Sri Lanka

Phytoplankton primary productivity of eleven irrigation reservoirs located in five river basins in Sri Lanka was determined on a single occasion together with light climate and nutrient concentrations. Although area-based gross primary productivity (1.43–11.65 g O₂ m^–2 d^–1) falls within the range already established for tropical water bodies, net daily rate was negative in three water bodies. Light-saturated optimum rates were found in water bodies, with relatively high algal biomass, but photosynthetic efficiency or specific rates were higher in water bodies with low algal biomass, indicating nutrient limitation or physiological adaptation of phytoplankton. Concentrations of micronutrients and algal biomass in the reservoirs are largely altered by high flushing rate resulting from irrigation release. Underwater light climate and nutrient availability control the rate of photosynthesis and subsequent area-based primary production to a great extent. However, morpho-edephic index or euphotic algal biomass in the most productive stratum of the water column is not a good predictor of photosynthetic capacity or daily rate of primary production of these shallow tropical irrigation reservoirs.     

Production,population biology and diet ofNeomysis integer (Leach) in a shallow Frisian lake (The Netherlands)

TheNeomysis integer population of a shallow Frisian freshwater lake, situated in the north of the Netherlands, was studied from May until October 1980. The results were compared with observations on populations in other Frisian lakes, and with the results reported by other authors on brackish-water and marine populations of this species.Three generations were observed: one overwintering generation and two summer generations. Reproduction stopped completely during winter. During 1980 population densities ofN. integer were relatively low in all Frisian lakes. In Slotermeer the maximum population density was only 6 individuals m^–2, production amounted to 10 mg dry wt m^–2 yr^–1. The annual P/B ratio was 4.0. The diet ofN. integer consisted, in terms of biomass, of more than 95% detritus and animal food, the latter mainly consisting ofBosmina and cyclopoid copepods. Feeding intensity reached a maximum at sunset. It was still high during first part of the night and was low in the morning just after sunrise.