Short term spatial and temporal variation of phytoplankton in a shallow tropical oligotrophic reservoir,southeast Brazil

Locally called IAG pond, system is a small, oligotrophic, shallow, urban reservoir located in the Parque Estadual das Fontes do Ipiranga Biological Reserve, south of São Paulo municipality, southeastern Brazil. Study was carried out in two phases to cover the two climatic periods (dry and rainy) that characterize the area. Daily samples were collected on seven consecutive days (dry = 20–26 August 1996; rainy = 22–28 January 1997), three times a day (07:00 h, 13:00 h, and 19:00 h), following the water column vertical profile at reservoir’s deepest site (Z _max = 4.7 m). The phytoplankton’s community structure’s diurnal variation was compared with environmental variables (thermal structure of the water column, pH, CO₂, dissolved oxygen, total phosphorus, and NH₄). Analysis of variance (ANOVA) showed significant variation among sampling hours and days but not among depths for most species, thus revealing a tendency towards a homogeneous vertical distribution of phytoplankton in the reservoir. Canonical Correspondence Analysis (CCA) showed a significant relationship between distribution of phytoplankton species and environmental variables used for ordination. Water temperature was the environmental variable that best explained distribution of sample units. Atelomixis was the only possible explanation for how a non-motile alga as, for example, the chlorococcal Oocystis lacustris Chodat and the diatom Cyclotella stelligera Cleve &; Grunow, can be so widespread and abundant in the IAG pond during the stratified period.     

Effects of different fish species and biomass on plankton interactions in a shallow lake

Thirty-six enclosures, surface area 4 m², were placed in Little Mere, a shallow fertile lake in Cheshire, U.K. The effects of different fish species (common carp, common bream, tench and roach) of zooplanktivorous size, and their biomass (0, 200 and 700 kg ha^–1) on water chemistry, zooplankton and phytoplankton communities were investigated. Fish biomass had a strong effect on mean zooplankton size and abundance. When fish biomass rose, larger zooplankters were replaced by more numerous smaller zooplankters. Consequently phytoplankton abundance rose in the presence of higher densities of zooplanktivorous fish, as zooplankton grazing was reduced. Fish species were also significant in determining zooplankton community size structure. In enclosures with bream there were significantly greater densities of small zooplankters than in enclosures stocked with either carp, tench and, in part, roach. When carp or roach were present, the phytoplankton had a greater abundance of Cyanophyta than when bream or tench were present. Whilst top-down effects of fish predation controlled the size partitioning of the zooplankton community, this, in turn apparently controlled the bottom-up regeneration of nutrients for the phytoplankton community. At the zooplankton–phytoplankton interface, both top-down and bottom-up processes were entwined in a reciprocal feedback mechanism with the extent and direction of that relationship altered by changes in fish species. This has consequences for the way that top-down and bottom-up processes are generalised.     

Distribution of filter-feeding caddisflies (Trichoptera) and plankton drift in a Swedish lake-outlet stream

The objectives of this investigation were to relate the longitudinal distribution of filter-feeding caddisflies to quality and quantity of seston, and to document factors facilitating coexistence among filter-feeding species, in a 4th-order lake-outlet stream in central Sweden. A sharp decline in abundance and biomass of filtering caddisflies was evident within 1 km from the lake outlet following negative power functions. In contrast to particulate organic carbon, significant reductions of both phytoplankton and zooplankton biomass, especially some large species, were recorded between the lake-outlet and 1.9 km downstream. Differences in longitudinal and temporal distribution provide evidence of resource partitioning between filtering species included.     

Effect of young-of-the-year walleye (Percidae: Stizostedion vitreum) on plankton dynamics and water quality in ponds

To understand the impact of young-of-the-year (YOY) fish on food web dynamics and water quality, we stocked larval walleye (9 mm TL) (Stizostedion vitreum) in six experimental ponds using two fish densities (10 and 50 fish m^–3) with three replicates. At high fish density, the average abundances of cladocerans and copepods and the Secchi depth were lower whereas abundances of rotifers and algae, gross primary productivity (GPP), pH and total phosphorus concentration were higher than at low fish density. Fish impact on bacterial abundance, dissolved oxygen, nitrogen and phosphorus concentrations, however, was not significant. The within treatment measurements of all variables except GPP were significantly different over time. Our results indicate that YOY walleye predation at high density can affect plankton community by reducing large zooplankton biomass and water clarity, and increasing phytoplankton abundance. The impact of YOY piscivorous fish on plankton should be considered when biomanipulation is applied for improvement of water quality.     

Effect of larval fish and nutrient enrichment on plankton dynamics in experimental ponds

The hypotheses that larval fish density may potentially affect phytoplankton abundance through regulating zooplankton community structure, and that fish effect may also depend on nutrient levels were tested experimentally in ponds with three densities of larval walleye, Stizostedion vitreum (0, 25, and 50 fish m^–3), and two fertilizer types (inorganic vs organic fertilizer). A significant negative relationship between larval fish density and large zooplankton abundance was observed despite fertilizer types. Larval walleye significantly reduced the abundances of Daphnia, Bosmina, and Diaptomus but enhanced the abundance of various rotifer species (Brachionus, Polyarthra, and Keratella). When fish predation was excluded, Daphnia became dominant, but Daphnia grazing did not significantly suppress blue-green algae. Clearly, larval fish can be an important regulator for zooplankton community. Algal composition and abundance were affected more by fertilizer type than by fish density. Inorganic fertilizer with a high N:P ratio (20:1) enhanced blue-green algal blooms, while organic fertilizer with a lower N:P ratio (10:1) suppressed the abundance of blue-green algae. This result may be attributed to the high density of blue-green algae at the beginning of the experiment and the fertilizer type. Our data suggest that continuous release of nutrients from suspended organic fertilizer at a low rate may discourage the development of blue-green algae. Nutrient inputs at a low N:P ratio do not necessarily result in the dominance of blue-green algae.     

Predictability and possible mechanisms of plankton response to reduction of planktivorous fish

The predictability of plankton response to reductions of planktivorous fish was investigated by comparing the plankton community in three biomanipulated lakes and ten unmanipulated lakes differing in intensity of fish predation. Data collected on total phosphorus, phytoplankton and zooplankton biomass and share of cyanobacteria and large grazers, as well as specific growth rate of phytoplankton, were further used to test some of the proposed underlying response-mechanisms. In the biomanipulated lakes the algal biomass and share of cyanobacteria decreased, specific growth rate of phytoplankton increased, and zooplankton biomass and share of large grazers increased or remained unchanged. This pattern was largely reflected in the differences in food-chain structure between the unmanipulated lakes with highversus those with low fish predation. The qualitative response to planktivorous fish reduction thus seems largely predictable. The biomanipulated lakes differed, however, in magnitude of response: the smallest hypertrophic, rotenone-treated lake (Helgetjern) showed the most dramatic response, whereas the large, deep mesotrophic lake (Gjersjøen), which was stocked with piscivorous fish, showed more moderate response, probably approaching a new steady state. These differences in response magnitude may be related to different perturbation intensity (rotenone-treatmentversus stocking with piscivores), food-chain complexity and trophic state. Both decreased phosphorus concentration and increased zooplankton grazing are probably important mechanisms underlying plankton response to biomanipulation in many lakes. The results provide tentative support to the hypothesis that under conditions of phosphorus limitation, increased zooplankton grazing can decrease algal biomassvia two separate mechanisms: reduction of the phosphorus pool in the phytoplankton, and reduction of the internal C:P-ratio in the phytoplankton cells.

     

Effects of fertiliser and crayfish on plankton and nutrient dynamics in hardwater ponds

Although phosphorus fertilisation can improve productivity in most freshwater ponds, phosphate may become limiting in extremely hard water due to rapid precipitation with calcium. Hence we studied the characteristics of plankton and nutrient dynamics in water containing >400 mg CaCO₃ l^–1in pond and microcosm systems. The field experiment was conducted in eight earthen ponds involving two nutrient ratios (N:P = 1:1 and 20:1) with or without crayfish. Fertilisation significantly increased concentrations of NO₂–N and NO₃–N, but soluble reactive phosphorus was depleted to the level prior to fertilisation within 24 h. The laboratory test showed that after 6 h of fertilisation, 45% phosphorus was precipitated by calcium, 30% phosphorus was assimilated by phytoplankton and only 25% phosphorus remained in water column. The phytoplankton abundance in hardwater ponds was regulated by the abundance of zooplankton population rather than by either crayfish or fertilisation. The presence of crayfish only increased the concentration of total phosphorus. This study suggests that when phytoplankton production is required in crayfish ponds the maintenance of phytoplankton abundance will depend on the effective control of zooplankton rather than fertilisation. Due to the rapid precipitation of phosphorus by calcium in hard water ponds, more frequent phosphorus fertilisation is needed to enhance primary productivity.     

Abundance and Community Structure of Limnetic Zooplankters in Kumaun Lakes,India

The zooplankton compositions in the limnetic zones of two subtropical lakes, the Nainital and the Bhimtal (U.P., India) were more or less similar in terms of species composition. Numerically, zooplankters were abundant during the thermal stratification (summer-autumn) period and scarce during the over-turn (winter). The density of the zooplankton population reported from the eutrophic Lake Nainital was higher than in the oligotrophic Lake Bhimtal. Among the three groups studied copepods dominated over cladocerans and rotifers in both the lakes. The Shannon Weaver diversity was higher for Lake Bhimtal than for Lake Nainital. The community structure has also been discussed on the basis of crustacean species.     

Response of fish and plankton to nutrient loading reduction in eight shallow Danish lakes with special emphasis on seasonal dynamics

1. For 13 years the response of the plankton and fish community to a decline in external phosphorus loading was studied in eight lakes with a mean depth <5 m. We conducted chi‐square analyses of sign of slope (positive or negative) of bimonthly averages of plankton variables for the eight lakes versus time. For fish, we compared results from two periods, i.e. 1989–1994 versus 1994–2001 as less data were available. 2. Fish community structure tended to respond to the lowered concentration of total phosphorus (TP), although not all changes were significant. While catch per unit effort (multi‐mesh sized gill nets) of cyprinids (especially bream, Abramis brama and roach, Rutilus rutilus) was highest in the first 5‐year period, the quantitative importance particularly of perch (Perca fluviatilis), pike (Esox lucius) and rudd (Scardinius erythropthalmus), a littoral species, increased significantly after 1994. 3. No changes occurred in zooplankton biomass, except for an increase in November and December. Biomass of small cladocerans, however, declined during summer and autumn, and the proportion of Daphnia to cladoceran biomass also increased. Average body weight of Daphnia and that of all cladocerans increased. The proportion of calanoids among copepods decreased in summer and the average body weight of cyclopoids and calanoids decreased during summer and autumn/early winter. 4. Total biovolume of phytoplankton declined significantly in March to June and tended to decline in November and December as well, while no significant changes were observed during summer and autumn. Non‐heterocystous cyanobacteria showed a decreasing trend during summer and autumn, while heterocystous cyanobacteria increased significantly in late summer. An increase in late summer was also evident for cryptophytes and chrysophytes, while diatoms tended to decline during most seasons. 5. We conclude that phytoplankton, and probably also fish, responded rapidly to reduced loading, whereas the effect on zooplankton was less pronounced. However, increases in body weight of cladocerans and the zooplankton to phytoplankton biomass ratio during summer indicate reduced top‐down control on zooplankton and enhanced grazing on phytoplankton. This conclusion is supported by a tendency for fish biomass to decline and a shift towards greater dominance by piscivores and, thus, an increased likelihood of predator control of zooplanktivorous cyprinids.     

The physical-chemical limnology of a desert reservoir

The physical-chemical limnology of a desert lake in central Arizona was investigated from February 1971–July 1973. The reservoir was found to be a warm-monomictic, eutrophic lake which exhibited pronounced thermal stratification during the summer months. Surface water temperatures ranged from a minimum of ca. 9 C in January to a maximum near 30 C in July–August. Chemically the lake may be described as a hard water lake of moderately high alkalinity and salinity. The concentration of the principal ions was affected significantly by precipitation run-off. The primary nutrients N and P were subject to considerable seasonal variability, being influenced most by precipitation and phytoplankton abundance. Trace element concentrations were low and showed comparatively little fluctuation during the study.     

The zooplankton-phytoplankton interface in lakes of contrasting trophic status: an experimental comparison

We report here the results of an experimental study designed to compare algal responses to short-term manipulations of zooplankton in three California lakes which encompass a broad range of productivity (ultra-oligotrophic Lake Tahoe, mesotrophic Castle Lake, and strongly eutrophic Clear Lake). To assess the potential strength of grazing in each lake, we evaluated algal responses to a 16-fold range of zooplankton biomass. To better compare algal responses among lakes, we determined algal responses to grazing by a common grazer (Daphnia sp.) over a range ofDaphnia densities from 1 to 16 animals per liter. Effects of both ambient grazers andDaphnia were strong in Castle Lake. However, neither ambient zooplankton norDaphnia had much impact on phytoplankton in Clear Lake. In Lake Tahoe, no grazing impacts could be demonstrated for the ambient zooplankton butDaphnia grazing had dramatic effects. These results indicate weak coupling between phytoplankton and zooplankton in Clear Lake and Lake Tahoe, two lakes which lie near opposite extremes of lake trophic status for most lakes. These observations, along with work reported by other researchers, suggest that linkages between zooplankton and phytoplankton may be weak in lakes with either extremely low or high productivity. Biomanipulation approaches to recover hypereutrophic lakes which aim only to alter zooplankton size structure may be less effective if algal communities are dominated by large, inedible phytoplankton taxa.     

Physical and chemical limnology of a wind-swept tropical highland reservoir

Valle de Bravo (VB) is a tropical reservoir located (19°21′30″ N, 100°11′00″ W) in the highlands of Mexico. The reservoir is daily swept by strong (7.4 m s⁻¹ mean speed) diurnal (12:00–19:00 h) winds that blow along its two main arms. As expected from its fetch (6.9 km) and its depth (21.1 m mean), the reservoir behaves as a warm monomictic water body. During 2001, VB was stratified from February to October, and well mixed from November to January. Its mean temperature was 19.9°C; the maximum found was 23.8°C in the epilimnion, while a minimum of 17.8°C was registered during mixing. VB exhibited a thermal regime similar to other water bodies of the Mexican tropical highlands, except for a steady increase of its hypolimnetic temperature during stratification, which is attributed to entrainment of epilimnetic water into the hypolimnion. During stratification, the hypolimnion was anoxic, while the whole water column remained under-saturated (60%) during mixing. The flushing time is 2.2 years. Mineralization and total alkalinity are low, which allows strong changes in pH. Ammonia remained low (2.4 μmol l⁻¹ mean) in the epilimnion, but reached up to 60 μmol l⁻¹ in the hypolimnion. Soluble reactive phosphorous had a mean of 0.28 μmol l⁻¹ in the epilimnion and a mean of 1.25 μmol l⁻¹ in the hypolimnion. Nitrate exhibited maxima (up to 21 μmol l⁻¹) during mixing, and also in the metalimnion (2 μmol l⁻¹) during stratification. Low dissolved inorganic nitrogen indicated nitrogen limitation during stratification. Eutrophication is an emerging problem in VB, where cyanobacteria dominate during stratification. At VB chlorophyll a is low during mixing (mean of 9 μg l⁻¹), and high during stratification (mean 21 μg l⁻¹), when blooms (up to 88 μg l⁻¹) are frequent. This pattern is similar to that found in other eutrophic tropical water bodies. We propose that in VB the wind regime causes vertical displacements of the thermocline (0.58–1.10 m hr⁻¹) and boundary mixing, enhancing the productivity during the stratification period in this tropical reservoir.     

On the taxonomy of the genus Megadiaptomus Kiefer,including the description of a new species (Copepoda,Calanoida) from India

The insecticide permethrin (a synthetic pyrethroid) was applied into enclosures (1 m diameter and 3.5 m deep) placed in a pond. The chemical was rapidly removed from the water to the sediments. Daphnia rosea and its predator, Chaoborus flavicans were seriously affected by this application and disappeared from the enclosure. Acanthodiaptomus pacificus increased as Chaoborus decreased. Two species of Cladocera which had not been observed before the treatment, established their populations after 10 days, when Chaoborus had not recovered. Whereas Tropocyclops pracinus declined when permethrin was applied at 10 µg 1^–1, the number of rotifer Keratella valga increased, suggesting a close relationship between these two species.Photosynthesis and phytoplankton were not significantly affected by permethrin, except for Ceratium hirundinella. The dominance of Dinobryon divergens continued in the treated enclosures, whereas other flagellate species, Scenedesmus and Nitzschia occurred during the second half of the experiments in the control enclosure and pond.     

Early responses of plankton and turbidity to biomanipulation in a shallow prairie lake

We evaluated the effect of a fish removal from a shallow, turbid, eutrophic lake. By late May (following an October fish removal), the cladoceran community shifted from small-bodiedBosmina andChydorus (less than 100 l⁻¹) to largerDaphnia (over 100 l⁻¹). During the periods of peak daphnid abundance (late May–June) chlorophyll-a concentrations and edible diatoms were reduced and water transparency improved dramatically. Total phosphorus was not significantly lowered during this period. Although this clear-water phase was short-lived (May, June and early July), it corresponded to the critical period of plant growth and allowed dramatic increases in submergent macrophytes.     

飞来峡水库蓄水初期浮游植物组成与数量的变化

于2000~2002年的丰水期和枯水期对飞来峡水新建后库的营养状态和浮游植物进行监测。结果表明,水库中氮盐的浓度无显著变化,总磷浓度下降显著。浮游植物优势种类和丰度有较大差异。2000年浮游植物种类为29种,2001和2002年增加到99种;其中以绿藻和硅藻增加的种类数最多,分别增加34和27种。浮游植物丰度为13.4×104~41.6×104cells.L-1,2000年最高,2001年最低。2000年丰水期优势种较为单一,主要以假鱼腥藻(Pseudoanbeanaspp.)为主,枯水期主要是硅藻中的颗粒直链藻(Melosira granulata)丰度较高;2001和2002年丰水期蓝藻、绿藻和硅藻共同占优势,浮游植物无绝对的优势种,蓝藻的相对丰度较高的为假鱼腥藻、蓝纤维藻(Dactylococcopsis acicularis)和粘球藻(Gloeocapsa magma),绿藻的优势种为衣藻(Chlamydomonassp.)和美丽胶网藻(Dictyospharium pul-chellum);硅藻的优势种为梅尼小环藻(Cyclotella menighiniana)和针杆藻(Synedraspp.),枯水期主要是硅藻占优势,优势种为颗粒直链藻、变异直链藻(Melosira varians)等。     

Phytoplankton and Zooplankton Associations in a Set of Alpine High Altitude Lakes: Geographic Distribution and Ecology

Species composition and interactions, biomass dominance, geographic distribution and driving variables were investigated for two key elements of the pelagic food web of Alpine lakes, the phytoplankton and the zooplankton, based on a single sampling campaign during summer 2000. Altogether, 70 lakes were surveyed, 49 of which located in three different lake districts of the west and eastern Italian Alps and 21 in the central Austrian Alps (within the uppermost Danube catchment). In addition to the analysis of environmental variables affecting distribution and species structure of the two planktonic compartments, a brief review of the main research lines and hypotheses adopted in the past for the study of phytoplankton and zooplankton in high Alpine lakes is given. The lakes, investigated partly within the European project EMERGE (EVK1-CT-1999-00032) and partly within a regional project in the eastern Alps, comprise a wide range of morphological, chemical and trophic conditions. The phytoplankton communities were found to be diverse and mostly dominated by flagellates (chrysophytes, cryptophytes and dinoflagellates), and only to a lesser extent by non-motile green algae, desmids and centric diatoms. The zooplankton communities were mainly dominated by Alpine cladocerans and copepod species, while rotifers were abundant within one group of Italian lakes (sampled in early summer). The multivariate statistical analyses (CCA) showed that catchment features (i.e. percentage of vegetation cover and geochemical composition) and nitrate concentration are essential drivers for the phytoplankton, whereas for zooplankton also trophic status of the lakes and phytoplankton structure are important. The combined variance analysis of the lake clusters outlined by the multivariate analyses on phytoplankton and zooplankton data, respectively, allowed the identification of four principal lake types (three located on siliceous and one on carbonaceous bedrock), each one characterised by a certain combination of habitat features, which in their turn influence trophic state, and phytoplankton and zooplankton species composition and functionality.     

Plankton dynamics under different climate conditions in tropical freshwater systems (a reply to the comment by Sarmento,Amado & Descy, )

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Spatial patterns and relationships between phytoplankton, zooplankton and water quality in the Saimaa lake system, Finland

The interactions between phytoplankton and zooplankton were studied in two large lakes in the Saimaa lake system, Finland. Both are subjected to substantial waste water loading, and exhibit a clear trophic gradient between the loaded and unloaded areas. The phytoplankton and zooplankton were compared in terms of composition, abundance and biomass at 34–39 stations located in different parts of the lakes. At least four mechanisms were thought to affect the composition of plankton communities: (1) the amount of nutrients (trophic gradient), (2) grazing of algae by herbivores, (3) the effect of the algal species composition on feeding by zooplankters (large, colonial algae in the more loaded parts of the lakes) and (4) the regeneration and reorganization of nutrients.     

Comparative limnology of nine lakes of Jammu and Kashmir Himalayas

Two lakes in the lower Siwalik Himalayas, five in the Kashmir valley and two situated in the high mountains of the Kashmir Himalayas were investigated for their physico-chemical and biological features. The lakes, differing significantly in their morphology and in thermal behaviour, rank from the subtropical monomictic to the dimictic type. The lakes at high altitudes (> 3000 m) have very low electric conductivity which increases with the decrease in altitude. The most dominant ions in water are calcium and bicarbonate. The macrophytic vegetation of the lakes does not show any definite relationship either with altitude or with physico-chemical milieu. In the lakes with low fertility the phytoplankton is dominated by diatoms and Chlorophyceae but in eutrophic lakes Cyanophyceae predominate. The zooplankton population of the lakes is mainly comprised of rotifera. On the basis of general limnological features and the rates of phytoplankton production most of the lakes may be categorized either as eutrophic or in the process of rapid evolution. Only one lake is oligotrophic.     

Experimental study of the impacts of silver carp on plankton communities of eutrophic Villerest reservoir (France)

We examined the impact of five silver carp biomass levels (0, 8, 16, 20, and 32 g m⁻³) on plankton communities and water quality of Villerest eutrophic reservoir (France). We realized the experiments using outdoor mesocosms. The presence of silver carp led to changes in zooplankton and phytoplankton assemblages. High fish biomass strongly reduced cladoceran abundance (through predation). Silver carp inefficiently grazed down particles < 20 μm. More importantly, however, the suppression of herbivorous cladocerans resulted in the increase of small size algae which were relieved from grazing and benefit from high nutrient concentrations. In contrast, in mesocosms without fish, the dominance of cladocerans (mainly Daphnia) controlled small size algae and probably also larger size algae (colonial chlorophytes, cyanobacteria). Thus, the Secchi disc transparency increased markedly. Through cascade effects, the modification of grazers communities led to changes in the utilization patterns of the added nutrients by phytoplankton communities. In high fish biomass treatments, nutrients were more efficiently accumulated into particulate fractions compared with no-fish and low-fish biomass treatments that were characterized by higher dissolved nutrients concentrations. Zooplankton was an essential source of food for silver carp. The productivity of zooplankton sustained a moderate silver carp biomass (up to 16 g m⁻³). In the presence of the highest fish biomass, the productivity of zooplankton was not large enough and silver carps fed on additional phytoplankton. Although mesocosms with high fish biomass were characterized by a slight cyanobacteria development compared with other fish mesocosms, silver carp was not effective in reducing cyanobacteria dominance. This revised version was published online in August 2006 with corrections to the Cover Date.