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Structure and dynamics of phytoplankton in an Amazon lake, Brazil.

The state of Roraima is located in the Brazilian Amazon and has a hydrographic basin with a large variety of aquatic systems, which are distinguished by their combination of physical, chemical and biological characteristics. Some lakes located in depressions of the Boa Vista Formation are generally small and isolated from large and medium-sized rivers. In these areas, lakes generally have clear waters, which may be either occupied by different species of aquatic macrophytes and filamentous algae or deprived of vegetation (Filho et al. 1997).

Lake systems in the savannas of the state of Roraima are important reservoirs for the residential water supply, fish production, recreational activities and enjoyment of their natural beauty. However, their existence is increasingly compromised by the human influence, such as landfills for real estate purposes and contamination from agriculture runoff. This affects the health status of ecosystems and produces negative effects, such as degradation and the loss of biodiversity.

Environmental changes affect algal structuring. The species best adapted to the new ecological situation become more abundant and there is a reorganization of the structure and dynamics of the community. Phytoplankton is a good indicator of changes in aquatic environments due to its rapid response within short time intervals, especially with regard to reproductive processes. Certain organisms are bioindicators of climatic, physical and chemical conditions as well as trophic state and biological pressure, such as predation (Reynolds 1998, Reynolds et al. 2002). These taxa can help researchers gain a better understanding of current processes and design intervention strategies for improving the health status of ecosystems.

A number of studies have been carried out on the floodplains of hydrographic basins in Argentina, Mexico, the United States, Spain, Japan and Colombia, addressing the structure and dynamics of the phytoplankton community and the main effects of variations in water level on the composition and functioning of these communities (Izaguirre et al. 2001, Takano et al. 2001; Maberly et al. 2002; Komarkova & Tavera 2003; Rodrigo et al. 2003; Domitrovic 2003; Schagerl & Oduor 2003; Kangurt et al. 2003; Roozen et al. 2003; Schemel et al. 2004; Walks & Cyr 2004; Pinilla 2006). The results of these studies demonstrate that cyanobacteria and Chlorophyta are important groups and often dominant groups in such environments.

In the Brazilian Amazon, studies addressing the phytoplankton community began in the 1940s, with the pioneering work of Gronblad (1945), followed by ten studies published in the 1960s, 70s and 80s. Investigations in the region began to intensify in the 1990s with studies by Bittencourt-Oliveira (1993), Menezes et al. (1995), Sophia & Dias (1996), Huszar (1996a), Sophia & Huszar (1996), Keppeler et al. (1999a, 1999b), Lopes & Bicudo (2003), Roland (2000) and Souza et al. (2007). These taxonomic studies demonstrate that Chlorophyta is an important group in the phycological flora, with Desmidiaceae the most representative due to the acidic characteristics of the waters in Amazonian ecosystems.

Subsequent studies were carried out with a focus on phytoplankton ecology with assessments of biomass, density, primary production and hydrological variables (Huszar 1996b; Huszar & Reynolds 1997; Huszar et al. 1998; Ibanez 1998; Kristiansen & Menezes 1998; Huszar 2000; Dellamano-Oliveira et al. 2003). These studies demonstrate that temporal and spatial patterns of the structure of the phytoplankton community may be influenced by hydrological pulses.

The aim of the present study was to analyze the structure and dynamics of a phytoplankton community as a tool for gathering knowledge on the health status of aquatic systems. For this purpose, a natural lake in the Brazilian Amazon was studied during a circadian cycle in two distinct seasonal periods.

MATERIALS AND METHODS

The present study was carried out in Lake Caracarana (03[degrees]50'41" N and 59[degrees]46'52" W), which is located in the depression of the Boa Vista Formation and distributed among savanna areas in the Northeastern region of the State de Roraima (Brazilian Amazon). The lake has a circumference of approximately 3.8km (Filho et al. 1997) and has clear waters, with a seasonal variation in depth ranging from 2.0 to 6.0m in the dry and rainy seasons, respectively. Lake Caracarana is colonized by a dense community of immersed and submersed aquatic macrophytes. Based on the Koppen-Geiger classification, the State of Roraima pertains to the A climatic group (humid tropical). The rainfall pattern is represented by two rather distinct periods: a rainy season (April to September) and a dry season (October to March) (Roraima Environment and Technology Foundation, 1994). Mean monthly rainfall during the study period ranged from 7mm (February) to 643.7mm (June) and temperature ranged from 26.4[degrees]C (July) to 29.4[degrees]C (November) (Brazilian National Meteorology Institute, 2006).

Water samples for nutrient analysis and the investigation of the phytoplankton community (taxonomic and density studies) were collected at the same time and with two repetitions with a vertical van Dorn bottle with a 3L of capacity at a central station in the lake over 24-hour sampling periods from the subsurface, middle of the water column and approximately 30cm above the bottom. Samples (n=2) were taken at four-hour intervals for a total of seven collections per period (Noon, 4 pm, 8 pm, 12 am, 4 am, 8 am and midnight). Sampling was performed once in the rainy season (June 2006) and dry season (November 2006).

Abiotic variables were determined in situ and included water temperature and dissolved oxygen (Schott Glaswerke Mainz, handylab OX1); conductivity and total dissolved solids (TSD) (Schott Glaswerke Mainz, handylab LF1); turbidity (Hanna Instruments, HI 93703); pH (Digimed, DMPH-2) and water transparency (Secchi disc 25cm in diameter). For the determination of dissolved and total nutrients, water aliquots were placed in 300ml polyethylene flasks and kept refrigerated until analysis. Samples were filtered through 47mm AP20 glass multi-pore filters for the determination of dissolved nutrients. Non-filtered aliquots were used for the determination of total nutrients. Analysis to determine concentrations of total nitrogen ([micro]mol.TN/L), nitrite ([micro]mol.N-N[O.sub.2]/L) and nitrate ([micro]mol.N-N[O.sub.3]/L) followed the procedures described by Valderrama (1981), Mackereth et al. (1978) and Golterman et al. (1978), respectively. Total phosphorus ([micro]mol. TP/L) and total dissolved phosphorus ([micro]mol. TDP/L) were determined following Valderrama (1981). Orthophosphate ([micro]mol.P-P[O.sub.4]/L) was determined following Strickland & Parsons (1965).

The Carlson Trophic State Index adapted by Toledo Jr. et al. (1983) for tropical regions was used for the trophic characterization of the ecosystem. Calculations were based on values of chlorophyll a, Secchi depth, total phosphorus and orthophosphate. Ultra-oligotrophic ([less than or equal to] 20). oligotrophic (21 to 40), mesotrophic (41 to 50), eutrophic (51 to 60) and hypertrophic ([greater than or equal to] 61) conditions were then determined (Kratzer & Brezonik 1981).

Samples for taxonomic and density analyzes (n=2) were preserved in acetic Lugol's solution. Morphometric features of the reproductive and vegetative phases were analyzed under a Zeiss microscope (model Axioskop) equipped with a light chamber, photographic camera and ocular with a measurement grid. Those for which identification was not possible were considered phytoflagellates. The samples were added to the collection at the Professor Vasconcelos Sobrinho Herbarium of the Universidade Federal Rural de Pernambuco.

Densities (individuals per microliter) were estimated based on the method described by Utermohl (1958), using an inverted microscope (Zeiss, Axiovert). Organism counts were carried out with two repetitions for each depth sampled; the values are presented as the mean of the repetitions. The calculations were carried out based on the method described by Villafaine & Reid (1995). Dominant and abundant species were determined based on the concepts described by Lobo & Leighton (1986), for which a dominant species is that which surpasses 50% of the total phytoplankton density and an abundant species is that with a density value greater than the mean value of the community. The values are presented as the mean of the repetitions.

Analysis of variance (ANOVA) was used with a 5% level of significance to determine the degree of temporal variation (time of day and season), seasonal period and spatial variation (depth). Tukey's multiple comparison tests was used to identify where differences were expressed in time and space. Analyses were performed using the Statistica 2004 software program (StatSoft, Inc., Tulsa, OK, USA). The Shannon-Wiener diversity index (H', bits/ind) was calculated (Shannon & Weaver 1963); Evenness was assessed based on the H' of the Shannon-Wiener index. Canonical correspondence analysis (CCA) was used to determine correlations between biotic and abiotic variables. Only abundant and dominant species were considered for the analysis. The PC-ORD version 4.14 for Windows was used for the statistical analysis (McCune & Mefford 1999).

RESULTS

Lake Caracarana has high light availability, with transparency values of 2.90m in the rainy season and 2.00m in the dry season. High water temperatures occurred in both seasons. Thermal stratification occurred in the rainy season and there was no stratification in the dry season. Dissolved oxygen exhibited a clinograde pattern in the rainy season and high oxygenation in the hypolimnion in the dry season. Vertical variations were also recorded for pH, turbidity and total phosphorus in the rainy season, with the water near the sediment more acidic, turbid and with a greater concentration of phosphorus (Table 1). The other parameters did not exhibit statistically significant vertical differences (p>0.05) (Table 2). Based on physiochemical characteristics, Lake Caracarana is classified as an ultra-oligotrophic to oligotrophic system (Table 1).

Dissolved oxygen, conductivity, pH, nitrite, total phosphorus and total dissolved phosphorus exhibited significant diel variations in the rainy season, whereas water temperature, dissolved oxygen, total nitrogen and total dissolved phosphorus exhibited significant differences between times of the day in the dry season (p<0.05) (Table 2).

Significant seasonal differences were found for the abiotic variables, except water temperature and orthophosphate (p>0.05) (Table 2). Conductivity, turbidity, total nitrogen, nitrite and total dissolved phosphorus values were greater in the rainy season, whereas dissolved oxygen, pH, nitrate and total phosphorus were greater in the dry season (Table 1).

The phytoplankton comprised 39 taxa (Table 3), with five identified on the genus level, 33 species and one group of phytoflagellates. Chlorophyta contributed the greatest species richness, totaling 25 taxa. Among the Chlorophyta, the desmids were the most diverse, accounting for 52% of the taxa of this division. The genus with the greatest number of species was Staurastrum (six species). Bacillariophyta was the second most diverse division, with nine species. Cyanophyta was represented by just three species.

Low phytoplankton densities were encountered throughout the study, with densities ranging from 202 individuals/mL (at the bottom, at 8 am in both seasons) to 1 135 ind/mL (in the middle of the water column at 8 pm in the rainy season) (Table 3). No significant variations in phytoplankton density were found between times in either the dry or the rainy season (p>0.05). Total density exhibited significant vertical differences (p<0.001) in both seasons (F=17.063 in the dry season; F=18.531 in the rainy season), with significantly lower values at the subsurface (p<0.01).

Cyanophyta were dominant (73.41% of the total density) in the rainy season, whereas Chlorophyta were dominant (73.08%) in the dry season (Figure 1A and 1B). Cyanophyta was abundant in 100% of the samples; Chlorophyta in 95.24%; Bacillariophyta in 42.86%; and phytoflagellates were abundant in just 2.38%. Thirteen taxa were classified as abundant, with the predominance of: Merismopedia tenuissima Lemmermann (50.66%), Monoraphidium griffithii (Berkeley) Komarkova-Legnerova (12.97%), Botryococcus terribilis J. Komarek & P. Marvan (9.23%) and Sphaerocystis schroeteri Chodat (5.65%), (Table 3).

Diel variations in the Shannon-Wiener diversity index ranged from 1.05 to 2.91 in the rainy season and 2.66 to 3.57 in the dry season. The phytoplankton community exhibited low evenness (0.35 to 0.75) in the rainy season and high evenness (0.70 to 0.87) in the dry season.

Low evenness was associated with the predominance of Merismopedia tenuissima, which had higher density in the rainy season than the dry season.

The results of the canonical correspondence analysis (CCA) are displayed in Table 4 and Figure 2. The Monte Carlo test demonstrated that Axes 1 and 2 achieved statistical significance (p<0.05), indicating correlations between the environmental variables and the phytoplankton community. The values of Axes 1 and 2 explained 54.2% of the variability in the data. Pearson's correlation coefficient for the axes indicated a strong correlation between species and environmental variables.

On Axis 1, there was a separation of the sample units between the rainy and dry seasons. An analysis of the intra-set correlation coefficient reveals that conductivity, turbidity and total dissolved phosphorus were associated with the rainy season, whereas dissolved oxygen, pH, nitrate and total phosphorus were associated with the dry season. Merismopedia tenuissima and phytoflagellates were the most important taxa on this axis and associated with the rainy season. The following species were associated with the dry season: Botryococcus terribilis, Cosmarium contractum, Monoraphidium grijfithii, Sphaerocystis schroeteri, Staurastrum nudibrachiatum and Tabellaria sp.

On Axis 2, there was vertical separation of the samples in both seasons. This axis revealed diel variation in the rainy season. Based on the canonical coefficient, the most important variables were dissolved oxygen and total phosphorus. The following species were associated with this axis: Aulacoseira ambigua, Cylindrospermopsis raciborskii, Pinnularia maior and Surirella sp.

DISCUSSION

Studies carried out in the Amazon have demonstrated that thermal behavior is a determinant factor in the daily variety of a number of limnological variables, whether in the reduction of dissolved oxygen or in the accumulation of nutrients at greater depths (Tundisi et al. 1984, Esteves et al. 1994). Pivato et al. (2006) found chemical stratification accompanied by thermal stratification in the Corumba reservoir in Central-Western Brazil, with lower dissolved oxygen values at greater depths. In Lake Caracarana, thermal stratification occurred in the rainy season, whereas the water column was homogeneous in the dry season. The clinograde profile in this lake may likewise be associated with thermal stratification.

The low pH values recorded in Lake Caracarana corroborate findings on waters in ecosystems in the state of Roraima (Menezes, unpublished data), other areas of the Amazon (Sioli 1991, Panosso & Kubrusly 2000) and other regions of the country (Espindola et al. 1996, Dellamano-Oliveira et al. 2003). These values are associated with the acidic characteristics of the soils in savanna areas, decomposition of aquatic macrophytes (which release organic acids) and geochemical characteristics of the region.

The low conductivity values associated with low turbidity indicate that the waters of Lake Caracarana have good quality. These results are similar to those described by other authors for different ecosystems in the Amazon and a savannah region in Brazil (Panosso & Kubrusly 2000, Pivato et al. 2006).

Lake Caracarana has low nutrient values due to the fact that it drains relatively nutrient-poor terrains, particularly tertiary sediments from the Boa Vista Formation that make up the drainage basin of this lake (Filho et al. 1997). The low concentration of nutrients was confirmed by the Trophic State Index calculated for the two circadian cycles.

The composition of species found in Lake Caracarana and the greater number of taxa from the Chlorophyta division are similar to findings reported in previous studies on Brazilian lakes (Huszar 1996a; Nogueira & Leandro-Rodrigues 1999; Oliveira & Calheiros 2000; Nabout et al. 2006). All of these surveys found have a high diversity of Chlorophyta. In Amazon waters, desmids are considered an important group due to the acidic conditions of the waters (Huszar 1996b, 2000, Keppeler et al. 1999a, 1999b).

Nabout et al. (2006) identified 292 species of algae in 21 lakes on the flood plains of the Araguaia River, with Chlorophyceae as the dominant group. Melo et al. (2004) recorded 108 phytoplankton taxa for the Batata and Mussura Lakes of the Brazilian Amazon. In Lake Caracarana, the number of phytoplankton taxa was lower than that described in the studies cited above, but comparable to values described by Espindola et al. (1996) in the Pantanal wetlands of Brazil (83 taxa) as well as values described by Diaz et al. (1998) in Argentine lakes (40 taxa); in these studies, sampling efforts were greater, carried out over a period of one year and 11 months, respectively. The number of taxa was also similar to that described by Pivato et al. (2006) in an aquatic environment in a savanna region in Brazil (58 taxa), with nicthemeral collections in two seasonal periods, as in the present study.

The low densities of phytoplankton, homogeneity in the distribution of algae among the time of the day and a vertical and seasonal variations observed in Lake Caracarana are the results of the oligotrophic condition of the system. Melo et al. (2004) report low phytoplankton densities for Amazon lakes. Occasional, limited blooms occurred, with densities of Botryococcus terribilis, Cylindrospermopsis raciborskii, Merismopedia tenuissima and Monoraphidium griffithii had densities greater than 100 ind/mL in at least one sampling unit. Based on CCA, the high density of Chlorophyta was attributed to higher pH values and concentrations of dissolved oxygen, total phosphorus and nitrate. The greater density of M. tenuissima is explained by higher conductivity and turbidity values as well as concentrations of total dissolved phosphorus, whereas the occurrence of C. raciborskii was associated with oxygenated layers of water in the rainy season.

[FIGURE 1 OMITTED]

Lake Caracarana is a typical oligotrophic Amazonian lake, with low species richness and low algae densities. Knowledge on the phytoplankton in this lake contributes toward knowledge on algal diversity in a lake located on an indigenous reservation in the Brazilian Amazon. The occurrence of potentially toxic algae, such as C. raciborskii, does not indicate that the lake is undergoing a process of eutrophication, but monitoring is necessary in order to avoid future blooms. The occurrence of this species is the result of the shallow depth of Lake Caracarana as well as its high temperatures and availability of light. Despite the occurrence of taxa that indicate organic pollution, the biomass and frequency of these taxa indicate that the system is not currently threatened.

[FIGURE 2 OMITTED]

ACKNOWLEDGMENTS

The authors are grateful to the Brazilian fostering agency Coordenacao de Aperfeicoamento de Pessoal do Ensino Superior (CAPES - PQI 42).

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Ise de Goreth Silva (1), Ariadne do Nascimento Moura (2) *, Enio Wocyli Dantas (3) & Maria do Carmo Bittencourt-Oliveira (4)

(1.) Universidade Federal de Roraima, Departamento de Biologia, Av. Ene Garcez, 2413, Aeroporto, 69304-000, Boa Vista, RR, Brazil.

(2.) Universidade Federal Rural de Pernambuco, Departamento de Biologia, Area de Botanica, R. Dom Manoel de Medeiros, s/n, Dois Irmaos, 52171-030, Recife, PE, Brazil; ariadne@db.ufrpe.br

(3.) Universidade Estadual da Paraiba, Centro de Ciencias Biologicas e Sociais Aplicadas, Rua Monsenhor Walfredo Leal, 487, Tambia, 58020-540, Joao Pessoa, PB, Brazil.

(4.) Escola Superior de Agricultura Luiz de Queiroz, Departamento de Ciencias Biologicas, Av. Padua Dias, 11, C. Postal 9, 13418-900, Piracicaba, SP, Brazil.

* Corresponding author.

Received 04-VIII-2009. Corrected 20-III-2010. Accepted 26-IV-2010.
TABLE 1
Physicochemical variables and trophic Index State, over 24-hour
sampling periods, at the subsurface, middle and bottom in the
Caracarand lake, state of Roraima, Brazil, during dry and rainy
seasons of 2006

                           Hours            Noon            04 pm

Variables              Depths/periods   Rainy    Dry    Rainy    Dry

Water temperature      Subsurface       32.00   29.30   30.30   29.50
  ([degrees]C)         Middle           29.10   29.30   29.10   29.50
                       Bottom           28.20   29.30   28.30   29.40

Dissolved oxygen       Subsurface       4.10    5.90    4.20    5.20
  (mg/L)               Middle           3.50    7.20    3.60    5.50
                       Bottom           0.00    7.00    0.06    6.70

Electric               Subsurface       19.40   8.60    16.20   10.70
  conductivity         Middle           20.60   9.50    16.40   8.00
  ([micro]S/cm)        Bottom           21.00   8.80    16.40   9.70

pH                     Subsurface       6.40    7.60    6.50    7.60
                       Middle           6.30    7.60    6.20    7.70
                       Bottom           5.80    6.00    5.80    7.70

Turbidity (UNT)        Subsurface       31.82   1.96    31.62   1.96
                       Middle           31.10   2.75    38.55   2.36
                       Bottom           53.00   2.75    47.20   2.75

Total nitrogen         Subsurface       1.29    0.42    1.84    0.84
  ([micro]mol/L)       Middle           3.13    1.26    1.11    0.84
                       Bottom           5.34    0.84    2.76    0.42

Nitrate                Subsurface       0.00    0.04    0.01    0.02
  ([micro]mol/L)       Middle           0.01    0.01    0.01    0.04
                       Bottom           0.01    0.04    0.01    0.04

Nitrite                Subsurface       0.02    0.04    0.01    0.01
  ([micro]mol/L)       Middle           0.01    0.02    0.04    0.04
                       Bottom           0.04    0.05    0.04    0.03

Total phosphorus       Subsurface       0.26    0.32    0.37    0.46
  ([micro]mol/L)       Middle           0.11    0.37    0.24    0.46
                       Bottom           0.35    0.32    0.28    0.37

Total dissolved        Subsurface       0.43    0.30    0.65    0.35
  phosphorus           Middle           0.60    0.26    0.74    0.35
  ([micro]mol/L)       Bottom           0.54    0.39    0.54    0.35

Ortophosphate          Subsurface       0.01    0.01    0.01    0.01
  ([micro]mol/L)       Middle           0.01    0.01    0.01    0.01
                       Bottom           0.01    0.01    0.02    0.01

Trophic Index State    Subsurface       23.81   26.46   24.00   26.95
                       Middle           15.81   27.95   25.11   29.80
                       Bottom           21.33   25.20   21.42   28.15

                           Hours            08 pm          Midnight

Variables              Depths/periods   Rainy     Dry    Rainy    Dry

Water temperature      Subsurface       31.30    29.30   30.40   29.10
  ([degrees]C)         Middle           29.10    29.30   29.20   29.10
                       Bottom           28.30    29.20   28.30   29.10

Dissolved oxygen       Subsurface        4.00    5.70    3.80    6.00
  (mg/L)               Middle            3.50    6.10    3.20    6.10
                       Bottom            0.06    7.10    0.05    7.00

Electric               Subsurface       15.40    8.60    15.60   10.10
  conductivity         Middle           15.20    9.20    15.60   10.10
  ([micro]S/cm)        Bottom           16.40    9.60    15.80   9.80

pH                     Subsurface        6.60    6.90    6.70    7.60
                       Middle            6.50    6.80    6.30    7.30
                       Bottom            6.10    7.10    5.90    7.60

Turbidity (UNT)        Subsurface       33.36    2.75    36.36   1.57
                       Middle           36.37    3.14    37.11   2.36
                       Bottom           122.00   3.14    43.67   1.96

Total nitrogen         Subsurface        1.65    0.84    1.84    0.42
  ([micro]mol/L)       Middle            3.02    0.42    2.21    0.42
                       Bottom            0.98    0.42    2.58    0.42

Nitrate                Subsurface        0.01    0.04    0.01    0.01
  ([micro]mol/L)       Middle            0.01    0.02    0.01    0.01
                       Bottom            0.00    0.02    0.00    0.05

Nitrite                Subsurface        0.02    0.02    0.02    0.01
  ([micro]mol/L)       Middle            0.03    0.03    0.04    0.01
                       Bottom            0.04    0.01    0.04    0.07

Total phosphorus       Subsurface        0.26    0.32    0.24    0.41
  ([micro]mol/L)       Middle            0.24    0.46    0.24    0.41
                       Bottom            0.35    0.41    0.26    0.18

Total dissolved        Subsurface        0.70    0.35    0.86    0.26
  phosphorus           Middle            0.74    0.39    0.86    0.22
  ([micro]mol/L)       Bottom            0.91    0.35    0.75    0.26

Ortophosphate          Subsurface        0.01    0.01    0.01    0.00
  ([micro]mol/L)       Middle            0.01    0.01    0.02    0.01
                       Bottom            0.01    0.01    0.01    0.01

Trophic Index State    Subsurface       25.19    25.60   25.75   25.22
                       Middle           22.21    26.67   25.34   29.74
                       Bottom           15.78    26.38   24.99   27.19

                           Hours            04 am           08 am

Variables              Depths/periods   Rainy    Dry    Rainy    Dry

Water temperature      Subsurface       29.70   28.90   29.60   28.80
  ([degrees]C)         Middle           29.40   28.90   29.30   28.70
                       Bottom           28.40   28.80   28.30   28.70

Dissolved oxygen       Subsurface       4.10    6.00    4.10    6.20
  (mg/L)               Middle           3.80    7.10    3.90    6.30
                       Bottom           0.10    7.00    0.15    7.20

Electric               Subsurface       15.00   10.50   20.80   9.00
  conductivity         Middle           15.00   8.80    18.50   10.00
  ([micro]S/cm)        Bottom           15.00   10.20   20.50   9.60

pH                     Subsurface       6.10    7.20    6.40    6.00
                       Middle           6.10    7.00    6.20    6.90
                       Bottom           5.30    7.30    5.90    6.90

Turbidity (UNT)        Subsurface       42.21   1.96    39.14   1.18
                       Middle           38.81   2.36    42.40   2.36
                       Bottom           85.00   1.96    83.00   10.60

Total nitrogen         Subsurface       1.29    2.94    1.84    1.68
  ([micro]mol/L)       Middle           0.37    2.94    0.74    2.52
                       Bottom           0.74    2.94    0.74    0.84

Nitrate                Subsurface       0.01    0.01    0.00    0.01
  ([micro]mol/L)       Middle           0.01    0.05    0.00    0.04
                       Bottom           0.00    0.04    0.01    0.21

Nitrite                Subsurface       0.10    0.06    0.08    0.01
  ([micro]mol/L)       Middle           0.08    0.04    0.05    0.02
                       Bottom           0.08    0.05    0.08    0.01

Total phosphorus       Subsurface       0.11    0.23    0.07    0.27
  ([micro]mol/L)       Middle           0.11    0.32    0.07    0.32
                       Bottom           0.26    0.32    0.28    0.41

Total dissolved        Subsurface       0.43    0.30    0.48    0.09
  phosphorus           Middle           0.54    0.13    0.43    0.13
  ([micro]mol/L)       Bottom           0.48    0.43    0.54    0.30

Ortophosphate          Subsurface       0.01    0.02    0.00    0.02
  ([micro]mol/L)       Middle           0.01    0.00    0.01    0.01
                       Bottom           0.00    0.01    0.01    0.01

Trophic Index State    Subsurface       17.77   29.93   14.12   32.61
                       Middle           16.54   23.21   13.99   26.73
                       Bottom           18.85   28.46   20.04   29.52

                           Hours             Noon

Variables              Depths/periods   Rainy     Dry

Water temperature      Subsurface       29.80    29.30
  ([degrees]C)         Middle           29.10    29.30
                       Bottom           28.50    29.20

Dissolved oxygen       Subsurface        4.00    6.30
  (mg/L)               Middle            3.30    7.20
                       Bottom            0.04    7.20

Electric               Subsurface       21.80    8.50
  conductivity         Middle           23.40    10.10
  ([micro]S/cm)        Bottom           27.40    8.70

pH                     Subsurface        6.80    7.00
                       Middle            6.80    6.00
                       Bottom            6.80    7.00

Turbidity (UNT)        Subsurface       36.05    2.75
                       Middle           40.51    2.36
                       Bottom           135.00   1.96

Total nitrogen         Subsurface        1.66    0.42
  ([micro]mol/L)       Middle            0.55    0.84
                       Bottom            2.58    1.68

Nitrate                Subsurface        0.01    0.01
  ([micro]mol/L)       Middle            0.01    0.05
                       Bottom            0.00    0.00

Nitrite                Subsurface        0.06    0.01
  ([micro]mol/L)       Middle            0.04    0.02
                       Bottom            0.06    0.07

Total phosphorus       Subsurface        0.11    0.27
  ([micro]mol/L)       Middle            0.04    0.18
                       Bottom            0.28    0.41

Total dissolved        Subsurface        0.32    0.26
  phosphorus           Middle            0.27    0.13
  ([micro]mol/L)       Bottom            0.54    0.22

Ortophosphate          Subsurface        0.02    0.02
  ([micro]mol/L)       Middle            0.01    0.01
                       Bottom            0.00    0.01

Trophic Index State    Subsurface       21.79    31.44
                       Middle           10.34    2717
                       Bottom           17.18    29.95

TABLE 2
Variance values between depths, hours and seasons (dry and
rainy-2006) for abiotic variables studied at the Caracarand
lake-Roraima, Brazil. Significant values in bold type (p<0.05)

                                                     Depths

Variables                              Season      F          p

Water temperature ([degrees]C)         Rainy     24.818#    <0.001
                                       Dry       9.000#     0.004

Dissolved oxygen (mg/L)                Rainy    2038.037#   <0.001
                                       Dry       20.452#    <0.001

Electric conductivity ([micro]S/cm)    Rainy     2.344      0.137
                                       Dry       0.025      0.976

pH                                     Rainy     22.257#    <0.001
                                       Dry       0.051      0.951

Turbity (UNT)                          Rainy     10.951#    0.002
                                       Dry       1.191      0.338

Total nitrogen ([micro]mol/L)          Rainy     0.845      0.543
                                       Dry       0.632      0.553

Nitrate ([micro]mol/L)                 Rainy     1.200      0.336
                                       Dry       1.341      0.298

Nitrite ([micro]mol/L)                 Rainy     1.887      0.193
                                       Dry       1.881      0.194

Total phosphorus ([micro]mol/L)        Rainy     9.802#     0.003
                                       Dry       0.275      0.767

Total dissolved phosphorus             Rainy     0.787      0.519
  ([micro]mol/L)                       Dry       3.677      0.056

Ortophosphate ([micro]mol/L)           Rainy     0.391      0.689
                                       Dry       1.200      0.336

                                                     Hours

Variables                              Season      F         p

Water temperature ([degrees]C)         Rainy     0.613     0.718
                                       Dry      182.714#   <0.001

Dissolved oxygen (mg/L)                Rainy     3.044#    0.048
                                       Dry       3.612#    0.028

Electric conductivity ([micro]S/cm)    Rainy    26.549#    <0.001
                                       Dry       0.653     0.690

pH                                     Rainy    10.037#    0.001
                                       Dry       1.872     0.167

Turbity (UNT)                          Rainy     1.204     0.368
                                       Dry       0.708     0.651

Total nitrogen ([micro]mol/L)          Rainy     1.704     0.203
                                       Dry      11.026#    0 .001

Nitrate ([micro]mol/L)                 Rainy     0.400     0.865
                                       Dry       0.826     0.572

Nitrite ([micro]mol/L)                 Rainy    10.254#    0.001
                                       Dry       1.134     0.400

Total phosphorus ([micro]mol/L)        Rainy     3.515#    0.030
                                       Dry       1.103     0.415

Total dissolved phosphorus             Rainy     9.367#    0.001
  ([micro]mol/L)                       Dry       3.392#    0.034

Ortophosphate ([micro]mol/L)           Rainy     0.609     0.721
                                       Dry       0.571     0.747

                                                    Seasons

Variables                              Season      F         p

Water temperature ([degrees]C)         Rainy     0.590     0.547
                                       Dry

Dissolved oxygen (mg/L)                Rainy    30.832#    <0.001
                                       Dry

Electric conductivity ([micro]S/cm)    Rainy    131.415#   <0.001
                                       Dry

pH                                     Rainy    31.829#    <0.001
                                       Dry

Turbity (UNT)                          Rainy     0.031#    <0.001
                                       Dry

Total nitrogen ([micro]mol/L)          Rainy     4.568#    0.033
                                       Dry

Nitrate ([micro]mol/L)                 Rainy    18.492#    <0.001
                                       Dry

Nitrite ([micro]mol/L)                 Rainy     5.435#    0.023
                                       Dry

Total phosphorus ([micro]mol/L)        Rainy    19.963#    <0.001
                                       Dry

Total dissolved phosphorus             Rainy
  ([micro]mol/L)                       Dry      50.263#    <0.001

Ortophosphate ([micro]mol/L)           Rainy     0.086     0.769
                                       Dry

Note: Significant value are indicated with #.

TABLE 3

Mean density (ind/mL) of phytoplankton species in Caracarand lake,
State of Roraima, Brazilian Amazon, during a nictemeral cycle in a
rainy and dry seasons of 2006

                                          Noon              04 pm

                            Season    S     M     B     S     M     B

CYANOPHYTA

Chroococcus turgidus        Rainy    --    --    --     3    --     3
  (Kiitzing) Ndgeli         Dry      --     9    --     3     3     3

Cylindrospermopsis          Rainy    --    --    --    --    --    --
  raciborskii (Wok.)        Dry      --    --    --    --    --    --
  Seenayya et Subba-Raju

Merismopedia tenuissima     Rainy    413   569   139   595   760   211
  Lemmermann                Dry      28    94    40    31    40    34

CHLOROPHYTA

Ankistrodesmus spiralis     Rainy    --    --     3    --    --    --
  (W.B. Turner)             Dry       9    --    --     3    --    --
  Lemmermann

Botryococcus terribilis     Rainy    14    20    11    37    17    14
  J. Komarek & P. Marvan    Dry      97    57    83    80    54    60

Chlorococcum sp.            Rainy     6     3    --     3     3     3
                            Dry      --    --    --     3     6     3

Closterium navicula         Rainy    --    --    --    --    --    --
  (Brebisson)               Dry       3    --    --    --     9    --
  Lutkemtfller

Coelastrum reticulatum      Rainy    20    11    23    20     9    28
  (Dangeard) Senn.          Dry       9    14     3    17    --     6

Cosmarium contractum        Rainy    --    --     6    --    --    --
  0. Kirchner               Dry      14    46    28    17    31    28

Crucigenia fenestrata       Rainy    --    --    --    --    --    --
  (Schmidle) Schmidle       Dry      --    --    --    --    --    --

Dictyosphaerium             Rainy    --    --    --    --    --    --
  pulchellum H.C. Wood      Dry      --    --    --    --    --     9

Euastrum sp.                Rainy    --    --     3    --    --    --
                            Dry      --     3     3     6     3    --

Kirchneriella lunaris       Rainy    --    --    --    --    --    --
  (Kirchner) K. M6bius      Dry      --    --    --    --    --    --

Micrasterias furcata        Rainy    --     3    --     3    --    --
  C. Agardh ex Ralfs        Dry      --    --    --     6     3     3

Monoraphidium griffithii    Rainy    83    142   11    74    117   48
  (Berkeley)                Dry      85    80    11    74    54    20
  Komarkova-Legnerova

Nephrocytium agardhianum    Rainy    --    --    --    --    --    --
  Ndgeli                    Dry      --    --    --    --    --     3

Pediastrum tetras           Rainy    --    --    --    --    --    --
  (Ehrenberg) Ralfs         Dry      --    --    --    --    --    --

Quadrigula lacustris        Rainy    --    --    --    --    --    --
  (Chodat) G.M. Smith       Dry      --     3    --    --     6    --

Scenedesmus quadricauda     Rainy    --    --    --    --    --     3
  (Turpin) Br6bisson ex     Dry      --    --    --    --    --    --
  Ralfs

Sphaerocystis schroeteri    Rainy    31    17    43    26    14    34
  Chodat                    Dry      20    40     9    37    48    28

Staurastrum boergesenii     Rainy    --    --    --     3     3     9
  Raciborski                Dry       3    --     3     3     3    --

Staurastrum grallatorium    Rainy    --    --    --    --    --    --
  C.F.O. Nordstedt          Dry       6    --     3     6     6    --

Staurastrum leptocladum     Rainy    --    --    --    --    --     3
  L.N. Johnson              Dry      --     3    --    --    --    --

Staurastrum minnesotense    Rainy    --    --    --    --    --    --
  F. Wolle                  Dry      --    --    --    --    --    --

Staurastrum                 Rainy    --    --    --    --    --    --
  novae-caesareae F.        Dry      --    --    --    --    --    --
  Wolle

Staurastrum                 Rainy    --    --     3    --    --    --
  nudibrachiatum            Dry       3     3     3     3     6     3
  O.F. Borge

Staurodesmus                Rainy    --    --    --    --    --    --
  triangularis              Dry       9    --     3     3    --     3
  (Lagerheim) Teiling

Xanthidium antilopaeum      Rainy    --    --    --    --    --    --
  (Brebisson) Kutzing       Dry      --    --    --    --    --    --

BACILLARIOPHYTA                      413   569   139   595   760   211

Aulocoseira ambigua         Rainy    --    --    23    --    --    23
  (Grunow) Simonsen         Dry      --    --    --    --    --    --

Aulocoseira granulata       Rainy    --    --     3    --    --    --
  (Ehrenberg) Simonsen      Dry      --    --    --    --    --    --

Encyonema minutum           Rainy    --    --    --    --    --     3
  (Hilse) D.G. Mann         Dry      --    --     3     3    --     3

Frustulia rhomboides        Rainy     3    --     3     3    --    --
  (Ehrenberg) De Toni       Dry       3     6    --     6    --    --

Gomphonema parvulum         Rainy    --    --    --    --    --    --
  (Kutzing) Grunow          Dry      --    --    --    --    --    --

Pinnularia maior            Rainy    --    --    14    --    --     3
  (Kutzing) Cleve           Dry      --    --    --    --    --    --

Surirella sp.               Rainy    --    --    26    --    --    --
                            Dry      --    --    --    --    --    --

Tabellaria sp.              Rainy    --     3    --    --    --    --
                            Dry      20    37    14    20    11    11

Urosolenia eriensis         Rainy    --    --    --    --    --    --
  (H.L.) Round & Crawf      Dry      --    --    --    --    --    --

DINOPHYTA                            413   569   139   595   760   211

Peridinium sp.              Rainy    --    --     3    --    --    --
                            Dry      --    --    --    --    --    --

PHYTOFLAGELLATES            Rainy    40    28    11    46    34    26
                            Dry       3     3     9     9    --     9

                                          08 pm           Midnight

                            Season    S     M     B     S     M     B

CYANOPHYTA

Chroococcus turgidus        Rainy    --     3    --    --    --    --
  (Kiitzing) Ndgeli         Dry       6    --    --     9     9    --

Cylindrospermopsis          Rainy    --    --    --    --    --    --
  raciborskii (Wok.)        Dry      --    --    --    --    --    --
  Seenayya et Subba-Raju

Merismopedia tenuissima     Rainy    760   845   265   720   637   202
  Lemmermann                Dry      48    60    46    23    37    17

CHLOROPHYTA

Ankistrodesmus spiralis     Rainy    --    --    --    --    --    --
  (W.B. Turner)             Dry      --     3     3    --     3     3
  Lemmermann

Botryococcus terribilis     Rainy    14    20    31    20    23     3
  J. Komarek & P. Marvan    Dry      105   48    83    71    71    65

Chlorococcum sp.            Rainy     6    11    11    --     6    --
                            Dry       3     3     9     3     3    --

Closterium navicula         Rainy    --    --    --    --    --    --
  (Brebisson)               Dry      --     6    --    --     6    --
  Lutkemtfller

Coelastrum reticulatum      Rainy    20    20    26    23     6     9
  (Dangeard) Senn.          Dry      28     6     9    11     9     9

Cosmarium contractum        Rainy    --    --    --    --    --    --
  0. Kirchner               Dry      37    57    37    31    17    37

Crucigenia fenestrata       Rainy    --    --    --    --    --    --
  (Schmidle) Schmidle       Dry      --    --    --    --    --    --

Dictyosphaerium             Rainy    --    --    --    --    --    --
  pulchellum H.C. Wood      Dry       3    --     6    --    --    --

Euastrum sp.                Rainy    --    --    --    --    --    --
                            Dry      --     3    --     3     3    --

Kirchneriella lunaris       Rainy    --    --    --     9    --    --
  (Kirchner) K. M6bius      Dry       3    --    --    --     6    --

Micrasterias furcata        Rainy     3    --    --    --    --     6
  C. Agardh ex Ralfs        Dry      --    --    --     6     3     9

Monoraphidium griffithii    Rainy    117   131   40    108   108   54
  (Berkeley)                Dry      91    97    28    23    65    17
  Komarkova-Legnerova

Nephrocytium agardhianum    Rainy    --    --    --    --    --    --
  Ndgeli                    Dry      --    --     3    --    --    --

Pediastrum tetras           Rainy    --    --    --    --    --    --
  (Ehrenberg) Ralfs         Dry      --    --    --    --    --    --

Quadrigula lacustris        Rainy    --    --    --    --    --    --
  (Chodat) G.M. Smith       Dry      --    --    --     3    --     3

Scenedesmus quadricauda     Rainy    --     3     3    --    --    --
  (Turpin) Br6bisson ex     Dry      --    --    --    --    --    --
  Ralfs

Sphaerocystis schroeteri    Rainy    17    23    28    23    11    17
  Chodat                    Dry      65    46    43    23    57    20

Staurastrum boergesenii     Rainy    --    --    --     3    --    --
  Raciborski                Dry       6     3    --    --    --    --

Staurastrum grallatorium    Rainy    --    --    --    --    --    --
  C.F.O. Nordstedt          Dry      --    --    --    --    --    --

Staurastrum leptocladum     Rainy    --    --    --    --    --    --
  L.N. Johnson              Dry      --    --    --    --    --     3

Staurastrum minnesotense    Rainy    --    --    --    --    --    --
  F. Wolle                  Dry      --    --    --    --    --     3

Staurastrum                 Rainy    --    --    --    --    --    --
  novae-caesareae F.        Dry      --    --    --    --    --    --
  Wolle

Staurastrum                 Rainy    --    --    --    --    --    --
  nudibrachiatum            Dry       9     3     3     9    20    14
  O.F. Borge

Staurodesmus                Rainy    --    --    --    --    --    --
  triangularis              Dry      --     6    --    --    --    11
  (Lagerheim) Teiling

Xanthidium antilopaeum      Rainy    --    --    --    --    --    --
  (Brebisson) Kutzing       Dry      --    --    --    --     6    --

BACILLARIOPHYTA                      760   845   265   720   637   202

Aulocoseira ambigua         Rainy    --    --    11    --    --    --
  (Grunow) Simonsen         Dry      --    --    --    --    --     3

Aulocoseira granulata       Rainy    --    --    --    --    --    --
  (Ehrenberg) Simonsen      Dry      --    --    --    --    --    --

Encyonema minutum           Rainy    --    --     3    --    --    --
  (Hilse) D.G. Mann         Dry      --    --    --    --    --    --

Frustulia rhomboides        Rainy    --    --     3    --    --     3
  (Ehrenberg) De Toni       Dry       3    --     6    14    --     6

Gomphonema parvulum         Rainy    --    --    --    --    --    --
  (Kutzing) Grunow          Dry      --    --    --    --    --    --

Pinnularia maior            Rainy    --    --    11    --    --    --
  (Kutzing) Cleve           Dry       9    --     6    --    --     3

Surirella sp.               Rainy    --    --    23    --    --    --
                            Dry      --    --    --    --    --    --

Tabellaria sp.              Rainy    --    --    --    --    --     6
                            Dry      26    28    20    17    26    14

Urosolenia eriensis         Rainy    --    --    --    --    --    --
  (H.L.) Round & Crawf      Dry      --    --    --    --    --    --

DINOPHYTA                            760   845   265   720   637   202

Peridinium sp.              Rainy    --    --    --    --    --    --
                            Dry      --     3    --    --    --    --

PHYTOFLAGELLATES            Rainy    26    77    17    37    71    40
                            Dry       3    --     6    --     3     6

                                          04 am             08 am

                            Season    S     M     B     S     M     B

CYANOPHYTA

Chroococcus turgidus        Rainy    --    --     3    --    --    --
  (Kiitzing) Ndgeli         Dry       6     6     3     6    --     3

Cylindrospermopsis          Rainy    313   --    --    193   324   --
  raciborskii (Wok.)        Dry      --    --    --    --    --    --
  Seenayya et Subba-Raju

Merismopedia tenuissima     Rainy    600   575   188   415   236   80
  Lemmermann                Dry      57    83    31    31    71    17

CHLOROPHYTA

Ankistrodesmus spiralis     Rainy    --    --    --    --    --    --
  (W.B. Turner)             Dry       6    --     3     3     3    --
  Lemmermann

Botryococcus terribilis     Rainy    20    20    11    23     3     9
  J. Komarek & P. Marvan    Dry      122   85    46    91    57    48

Chlorococcum sp.            Rainy    --    --    --    --    --    --
                            Dry      --     6    --    --    --    --

Closterium navicula         Rainy    --    --    --    --    --    --
  (Brebisson)               Dry       6     3    --     6    --    --
  Lutkemtfller

Coelastrum reticulatum      Rainy    17    23    28    14    14     3
  (Dangeard) Senn.          Dry       3     6     3     9     6    --

Cosmarium contractum        Rainy    --     3    --    --    --     3
  0. Kirchner               Dry      20    48    20    23    17    28

Crucigenia fenestrata       Rainy    --    --    --    --    --    --
  (Schmidle) Schmidle       Dry      --    --    --    --    --    --

Dictyosphaerium             Rainy    --    --    --    --    --    --
  pulchellum H.C. Wood      Dry      --    --    --    --    --    --

Euastrum sp.                Rainy    --    --    --    --    --    --
                            Dry      --    --    --    --    --     3

Kirchneriella lunaris       Rainy    --    --    --    --    --    --
  (Kirchner) K. M6bius      Dry       3    --    --    --    --    --

Micrasterias furcata        Rainy    --    --    --    --    --     3
  C. Agardh ex Ralfs        Dry       6     3     3     3    --    11

Monoraphidium griffithii    Rainy    71    94    71    60    26    31
  (Berkeley)                Dry      63    80    31    37    125   11
  Komarkova-Legnerova

Nephrocytium agardhianum    Rainy    --    --    --    --    --     3
  Ndgeli                    Dry      --    --    --    --     3    --

Pediastrum tetras           Rainy    --    --    --    --    --    --
  (Ehrenberg) Ralfs         Dry      --    --    --    --    --    --

Quadrigula lacustris        Rainy    --    --    --    --    --    --
  (Chodat) G.M. Smith       Dry      --    --    --    --     3     3

Scenedesmus quadricauda     Rainy    --    --    --    --    --    --
  (Turpin) Br6bisson ex     Dry      --    --    --    --    --    --
  Ralfs

Sphaerocystis schroeteri    Rainy    14    37    23    11    --    26
  Chodat                    Dry      28    14    54    14    31    23

Staurastrum boergesenii     Rainy    --     3    --    --    --     3
  Raciborski                Dry      --     6     3    --     6    --

Staurastrum grallatorium    Rainy    --    --    --    --    --    --
  C.F.O. Nordstedt          Dry       3    --    --    --    --    --

Staurastrum leptocladum     Rainy    --    --    --    --    --    --
  L.N. Johnson              Dry      --    --    --     3     3    --

Staurastrum minnesotense    Rainy    --    --    --    --    --    --
  F. Wolle                  Dry      --    --    --    --    --    --

Staurastrum                 Rainy    --    --    --    --    --    --
  novae-caesareae F.        Dry      --     3    --    --    --    --
  Wolle

Staurastrum                 Rainy    --    --    --    --    --    --
  nudibrachiatum            Dry      14     3     6     9     6     9
  O.F. Borge

Staurodesmus                Rainy    --    --    --    --    --    --
  triangularis              Dry      --    --    --    --    --    --
  (Lagerheim) Teiling

Xanthidium antilopaeum      Rainy    --    --    --    --    --    --
  (Brebisson) Kutzing       Dry      --    --    --    --    --    --

BACILLARIOPHYTA                      600

Aulocoseira ambigua         Rainy    --    --     3    --    --    11
  (Grunow) Simonsen         Dry      --    --    --    --    --    --

Aulocoseira granulata       Rainy    --    --    --    --    --    --
  (Ehrenberg) Simonsen      Dry      --    --    --    --    --    --

Encyonema minutum           Rainy    --    --     3    --    --    --
  (Hilse) D.G. Mann         Dry      --    --    --    --    --    --

Frustulia rhomboides        Rainy    --    --    --    --    --    --
  (Ehrenberg) De Toni       Dry       6     3     9     3     3     9

Gomphonema parvulum         Rainy    --    --    --    --    --    --
  (Kutzing) Grunow          Dry      --    --    --    --    --    --

Pinnularia maior            Rainy    --    --     3    --    --    17
  (Kutzing) Cleve           Dry       6    --    --    --    --    14

Surirella sp.               Rainy    --    --     3    --    --     9
                            Dry      --    --    --    --    --    --

Tabellaria sp.              Rainy    --    --    --    --    --     3
                            Dry      17    20    17    11     6    17

Urosolenia eriensis         Rainy    --    --    --    --    --    --
  (H.L.) Round & Crawf      Dry      --    --    --    --    --    --

DINOPHYTA                            600   575   188   415   236   80

Peridinium sp.              Rainy    --    --    --    --    --    --
                            Dry      --     6    --    11    --     3

PHYTOFLAGELLATES            Rainy    11    34    31    31    11     3
                            Dry      11     6     9    17    --     3

                                          Noon

                            Season    S     M     B

CYANOPHYTA

Chroococcus turgidus        Rainy    --    --    --
  (Kiitzing) Ndgeli         Dry      --    --    --

Cylindrospermopsis          Rainy    --    --    --
  raciborskii (Wok.)        Dry      --    --    --
  Seenayya et Subba-Raju

Merismopedia tenuissima     Rainy    489   211   287
  Lemmermann                Dry      77    97    23

CHLOROPHYTA

Ankistrodesmus spiralis     Rainy    --    --    --
  (W.B. Turner)             Dry      --     6     3
  Lemmermann

Botryococcus terribilis     Rainy    11     9    11
  J. Komarek & P. Marvan    Dry      51    80    60

Chlorococcum sp.            Rainy    --     3    --
                            Dry      11    --    --

Closterium navicula         Rainy    --     3    --
  (Brebisson)               Dry      --     9    --
  Lutkemtfller

Coelastrum reticulatum      Rainy    14    17    26
  (Dangeard) Senn.          Dry       6    --    14

Cosmarium contractum        Rainy    --    --    --
  0. Kirchner               Dry      23    28    20

Crucigenia fenestrata       Rainy     3    --    --
  (Schmidle) Schmidle       Dry      --    --    --

Dictyosphaerium             Rainy    --    --    --
  pulchellum H.C. Wood      Dry      --    --    --

Euastrum sp.                Rainy     3    --    --
                            Dry       3     3    --

Kirchneriella lunaris       Rainy    --    --    --
  (Kirchner) K. M6bius      Dry       3    --    --

Micrasterias furcata        Rainy    --    --    --
  C. Agardh ex Ralfs        Dry      --    14    --

Monoraphidium griffithii    Rainy    43    20    31
  (Berkeley)                Dry      57    60    17
  Komarkova-Legnerova

Nephrocytium agardhianum    Rainy    --    --    --
  Ndgeli                    Dry      --    --    --

Pediastrum tetras           Rainy    --    --    --
  (Ehrenberg) Ralfs         Dry       3    --    --

Quadrigula lacustris        Rainy    --    --    --
  (Chodat) G.M. Smith       Dry      --     3    --

Scenedesmus quadricauda     Rainy    --    --     6
  (Turpin) Br6bisson ex     Dry      --    --    --
  Ralfs

Sphaerocystis schroeteri    Rainy    14    23    20
  Chodat                    Dry      26    26    31

Staurastrum boergesenii     Rainy    --    --    --
  Raciborski                Dry      --     9    --

Staurastrum grallatorium    Rainy    --    --    --
  C.F.O. Nordstedt          Dry      --     3    --

Staurastrum leptocladum     Rainy    --    --    --
  L.N. Johnson              Dry      --    -3    --

Staurastrum minnesotense    Rainy    --    --    --
  F. Wolle                  Dry      --    --    --

Staurastrum                 Rainy    --    --    --
  novae-caesareae F.        Dry      --    --    --
  Wolle

Staurastrum                 Rainy    --     3    --
  nudibrachiatum            Dry       6     9     6
  O.F. Borge

Staurodesmus                Rainy    --    --     3
  triangularis              Dry      --    --    --
  (Lagerheim) Teiling

Xanthidium antilopaeum      Rainy    --    --    --
  (Brebisson) Kutzing       Dry      --    --    --

BACILLARIOPHYTA

Aulocoseira ambigua         Rainy    --    --    17
  (Grunow) Simonsen         Dry      --    --    --

Aulocoseira granulata       Rainy    --    --    --
  (Ehrenberg) Simonsen      Dry      --    --    --

Encyonema minutum           Rainy    --    --    --
  (Hilse) D.G. Mann         Dry      --    --    --

Frustulia rhomboides        Rainy    --     3     6
  (Ehrenberg) De Toni       Dry       3     9     6

Gomphonema parvulum         Rainy    --    --     3
  (Kutzing) Grunow          Dry      --    --     6

Pinnularia maior            Rainy    --    --    14
  (Kutzing) Cleve           Dry      --    --    --

Surirella sp.               Rainy    --    --    14
                            Dry      --    --    --

Tabellaria sp.              Rainy    --    --    --
                            Dry      14    14    23

Urosolenia eriensis         Rainy    --    --    --
  (H.L.) Round & Crawf      Dry      --    --    --

DINOPHYTA

Peridinium sp.              Rainy    --    --    --
                            Dry      --    --    --

PHYTOFLAGELLATES            Rainy    11    20     6
                            Dry       3    --    --

Legends: S = Subsurface; M = Middle; B = Bottom.

TABLE 4
Canonical coefficients and intra-set correlation of the environmental
variables of the CCA first two axes performed in the Caracarana
lake-State of Roraima, Brazilian Amazon

                                                       Axis 1   Axis 2

Eigenvalue                                              0.408    0.144
Variance percentage explained                            40.1     14.1
Variance percentage accumulated                          40.1     54.2
Pearson correlation (species-environment)               0.951    0.706
Monte Carlo test
Eigenvalues -p                                           0.01     0.04
Correlation species-environment                          0.01     0.02

                                        Canonical         Intra-set
                                       coefficient       correlation

                                     Axis 1   Axis 2   Axis 1   Axis 2

Water temperature                     0.230   -0.017    0.279    0.145
Dissolved oxygen                     -0.049    0.601   -0.686    0.497
Conductivity                          0.268   -0.194    0.823   -0.153
pH                                   -0.181   -0.101   -0.666    0.033
Turbidity                             0.037   -0.040    0.650   -0.332
Total nitrogen                        0.034   -0.178    0.257   -0.438
Nitrate                              -0.078   -0.205   -0.558   -0.026
Nitrite                               0.066    0.256    0.327    0.519
Total phosphorus                     -0.325   -0.618   -0.685   -0.589
Total dissolved phosphorus            0.355   -0.069    0.677   -0.461
Orthophosphate                       -0.005   -0.237   -0.026   -0.217
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Author:de Goreth Silva, Ise; do Nascimento Moura, Ariadne; Wocyli Dantas, Enio; do Carmo Bittencourt-Olivei
Publication:Revista de Biologia Tropical
Article Type:Clinical report
Date:Dec 1, 2010
Words:8473
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