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- 38 Physico-chemical and biological variables of San José Creek, Otún river drainage/upper Cauca, Colombia Variables físicoquímicas y biológicas de la quebrada San José, afluente del río Otún, Alto Cauca, Colombia

Carlos A. García-Alzate*, Cesar Román-Valencia*, Diana X. Lopera*, Melissa I. González* & Maja Šimunović**
Recibido: Agosto 13 de 2008 Aceptado: Noviembre 4 de 2008

RESUMEN Se realizó un análisis bimodal y nictemeral en la quebrada San José, afluente del río Otún, Alto Cauca. Se evaluaron variables fisicoquímicas y biológicas; se aplico índices de diversidad alfa Shannon-Wiener, Simpson, Margalef y Pielou. El ANDEVA mostró que existen diferencias significativas, entre los periodos de lluvias y sequía, para la temperatura superficial del agua, la temperatura máxima, el pH y la conductividad. Se registraron 1571 ejemplares de macroinvertebrados: 1010 en lluvias y 561 en sequía; Ephemeroptera fue el más abundante en ambos periodos. El fitoplancton presentó 3977 individuos en lluvias y 25093 en sequía, Ankistrodesmus fue el más abundante en lluvias (39,02 % AR) y Cladophora en sequía (35,16% AR); mientras Vorticella fue el más abundante en ambas épocas (82,72% AR en lluvias y 45,10% AR en sequía). Los peces Hemibrycon rafaelense y Bryconamericus caucanus fueron abundantes y dominantes. Los resultados son consistentes a drenajes oligotróficos en sequía con tendencia a la eutroficación en lluvias. Palabras claves: bimodal, nictemeral, plancton, invertebrados, peces. ABSTRACT A bimodal, nictemeral analysis of San José Creek, a tributary of the Otún River, Upper Cauca was studied. We evaluated physico-chemical and biological variables and applied Shannon-Wiener, Simpson, Margalef and Pielou's biological diversity indices. ANOVA showed that there are significant differences between wet and dry seasons, in surface water temperature, maximum air temperature, pH and conductivity. A total of 1571 macroinvertebrates were collected: 1010 from the rainy season and 561 from the dry. Ephemeroptera was the most abundant taxon in both periods. For phytoplankton we collected 3977 individuals during the wet season and 25093 from the dry. Species of the genus Ankistrodesmus were most abundant during the rainy season (39.02% RA) and Cladophora during the dry (35.16% RA). Vorticella was the most abundant specie of zooplankton in both seasons (82.72% RA wet, 45.10% RA dry). Hemibrycon rafaelense and Bryconamericus caucanus, fishes of the family Characidae, were the most abundant and dominant. Our results indicate that the drainage was oligotrophic in the dry season, but eutrophic during the wet. Key Words: bimodal, plankton, invertebrates, fishes.

INTRODUCTION ater is directly connected with every part of life; it forms aquatic ecosystems where series of live communities develop that depend on water properties (pH, conductivity, temperature, specific heat, superficial tension, among others) for survival (Posada et al. 2000; Román-Valencia et al. 2005). One of the most important properties of water is its capacity to maintain many elements, both solid and gas in solution (oxygen, carbon dioxide, phosphates, nitrates, etc.), that are fundamental for organisms that live there (Roldán, 1992). In the Neotropics,

W

dramatic variations of physical and chemical variables are present in continental waters (rivers, streams, lakes) because of strong rains, electrical storms, prolonged droughts, etc. that alter biotic communities (Sierra et al. 2004). But anthropogenic activity influences freshwater ecosystems more than any of these. Geomorphological, hydrological and biological interactions determine baseline parameters present in river communities (Bernal et al. 2006). Two major elements of biotic communities that develop in continental waters are the aquatic macroinvertebrates and fishes (Roldán, 1992). In

* Laboratorio de ictiología. Universidad del Quindío A.A. 2639. Armenia, Colombia. [email protected] & [email protected] ** Division of Biology, Faculty of Science, University of Zagreb Rooseveltov trg 6, Zagreb, Croatia. E-mail: [email protected]

rev. invest. univ. quindio (18): 38-48. Armenia - Colombia

Physico-chemical and biological variables of the otun river - 39 past years, rapid evaluation procedures to assess biological communities as well as physical and chemical properties of aquatic systems have been used to characterize and restore ecosystems affected by contaminants (Marqués et al. 2001). Macroinvertebrate communities have been used as biological indicators of aquatic ecosystems affected by contamination (Alba-Tercedor, 1996). The objective of this article is to present the results of a nictemeral and bimodal analysis of some physicochemical and biological variables, to determine and record the current condition of San Jose Creek, a tributary of the Otún River, Upper Cauca drainage, of northwest Colombia. MATERIALS AND METHODS Samples were taken from San José Creek, Otún River drainage, Upper Cauca, located in municipality Dos Quebradas, Risaralda, Colombia (04° 47' 087''N, 075° 38' 072''W) at 1575 m.a.s.l. Stream bottom is covered principally by rocks, bank vegetation consists of Guadua angustifolia, and Araceae, (Pteridophyta and some Graminaceae). Samples were collected between 3rd and 4th March and 28th and 29th April 2007; work includes both climatic seasons of this area (Fig. 1). Physico-chemical variables: The following equipment was used: oxymeter OXI196Microprocessor to measure dissolved oxygen and superficial temperature of water; mercury thermometer for air temperature; maximum and minimum thermometer air temperature; conductivity with HANNA HI98842 conductimeter; water pH with potentiometer PIN POINT-BNC and relative humidity with thermohygrometer; that was recorded every hour during 24 hours. Physical variables width and depth were measured with decameter and flexometer respectively; current velocity was calculated by timing a floating ball as it travelled one meter. To determine chemical variables, water samples were collected in sample jars for measuring: Chemical Demand of Oxygen (C.D.O.), hardness (calcium and magnesium), alkalinity, acidity, turbidity, pH and chlorine, moreover, Biochemical Demand of Oxygen (B.D.O 5 ) was measured according to methodology recommended by APHA (1998) and Wetzel & Likens (2000). We also measured total and fecal coliform concentrations. Samples were analyzed in the water lab of the University of Quindío, Armenia, Colombia. The concept of trophic state was described according to Dodds (2007). Biological variables. Phy toplankton and zooplankton identification was carried out for specimens from water samples jars, preserved with 4% formalin and colored with lugol. They were determinated with the help of taxonomic keys: Lackey (1956), Kudo (1966), Bicudo & Bicudo (1970), Uhlerkovich & Schmidt (1974) and Needham & Needham (1978). Macroinvertebrates were collected near shore in areas with flow with nets and entomological forceps and later conserved in vials of 70%-alcohol, in a quantitative analysis. Samples were taken to the Biology Laboratory of the University of Quindío, Armenia, for identification with the use of taxonomic keys (Needham & Needham, 1978; Correa et al., 1981; Roldán, 1996; Wetzel & Likens, 2000; Posada-Garcia & RoldánPérez, 2003). Fishes were collected with different kinds of nets, held by two people, and making passes both up and downstream, and from one bank to the other, to cover all stream biotypes. Identifications were made in-situ, and some specimens were conserved in 10%-formalin and transferred to the Ichthyology laboratory of University of Quindío, Armenia, Colombia (IUQ), to confirm identifications using taxonomic keys and comparative specimens (Román-Valencia 1993, 1995, 2003; Román-Valencia & Ruiz-C. 2005, 2007; Román-Valencia et al. 2003, 2005; Ruiz-Calderón & Román-Valencia 2006 a, b; García-Alzate et al, 2007; García-Álzate & Román-Valencia, 2008a, b). Statistical analysis. Average was used to indicate central tendency and the coefficient of variation by Pearson (CV) for relative dispersion. Analysis of variance (ANOVA α = 0.05) was used to evaluate significance of average variation for physicochemical variables with biological importance between sampling sites. The program STATISTIC 7.0 for Windows was used. Diversity Indices. Shannon-Weiner (1949), Simpson dominance (1945), Margalef richness (1951) and Pielou equity (1966) indices were calculated to evaluate numeric structure of plankton, fish and aquatic macroinvertebrate communities. The index of contamination for organic matter (ICOMO) was also calculated using the formula of Ramirez & Viña (1998):

rev. invest. univ. quindio (18): 38-48. Armenia - Colombia

- 40 - García-Alzate, C. A. et al. ICOMO= 1/3 (I. BDO + I. Total coliform + I. Oxygen %) Where: I. BDO= -0.05 + 0.70 Log. BDO (mg/l) I. Tot. Col. = -1.44 + 0.56 Log. Total Col.(NMP/100ml) I. Oxygen %= 1- 0.01 oxygen % (Oxygen (%) > 100% have I. Oxygen %= 1) Range Concentration Indicator 0 – 0,2 Very Low Very Good 0,2 - 0,4 Low Good 0,4 - 0,6 Media Medium 0,6 - 0,8 High Bad 0,8 – 1 Very High Very Bad BMWP/col. For bioindicator analysis Biological Monitoring Working Party (BMWP/col) modified for Colombia by Roldan (2003) was used, this method uses degree of tolerance of macroinvertebrate families to contamination.
21 20 19

mm

18 17 16 15 14

Jan Feb Mar Apr May Jun

Jul

Aug Sep Oct Nov Dec

Month

Figure 1. Monthly pluviometric multi-annual data, Bosque station, Dos Quebradas (Risaralda), Colombia, 1980-2004.

RESULTS Physico-chemical variables. At the study area it rains from September to November and from March to May; and is dry from June to August and January to February (Fig. 1). Samples were taken from wet and dry seasons calculated from existing rainfall records. Nictemeral oscillations as indicated by coefficient of variation of physicochemical variables were low, except ambient temperature and re l at i ve h u m i d i t y ( Ta b . 1 ) . Wate r temperature varied from 17.4º to 22.3 °C in the dry season and 15º-19.6°C in the rainy season (Fig. 2a; Tab. 1.), coefficient of variation was higher in dry (7.9%) than in rainy (4.56%). ANOVA showed significant differences between climatic seasons for water temperature (F= 9.84, p= 0.0029). Ambient and minimal temperature did not show statistically significant variations between seasons. Ambient temperature varied with the nictemeral cycle in both seasons (11.82% CV in dry and 20.18% CV in rainy). Minimum temperature varied little between seasons. Maximum ambient temperature and water temperature did vary significantly (F=358.25; P=0.000), coefficients of variance were generally low in both seasons (2.67% in rainy and 4.93% in rainy). Maximum and minimum showed similar patterns, with lowest values at dawn and the first morning hours, and highest registered values in afternoon hour (Fig. 2b).

Dissolved oxygen showed low diel variation in the dry season (1.96% C.V) but high variation in the rainy season (24.91% C.V) Figure 2. Diel and seasonal patterns of variation for physico-chemical (Tab. 1). ANOVA indicated that there were variables of San José Creek, Otún River, Upper Cauca, Colombia. no significant differences between seasons A: Surface water and air temperature. B: Maximum and minimum
temperature. C: Dissolved oxygen. rev. invest. univ. quindio (18): 38-48. Armenia - Colombia

Physico-chemical and biological variables of the otun river - 41 (F= 2.27, P=0.1388). Nevertheless, this variable had lower oscillation in the dry vs. rainy seasons (Fig. 3), describing this water body as autotrophic in dry (8.3mg/l) and heterotrophic in rain (4.24 mg/l). Conductivity was on average during the rainy season than in the dry season (44.46 µs/cm and 71 µs/cm respectively), probably as a consequence of flushing out of dissolved and suspended solids in water. It showed little oscillation during the day (Fig. 3), and larger fluctuation in the rainy season. ANOVA revealed significant differences in conductivity between seasons (F= 406.78, P=0.000). pH was near neutral, with little variation between seasons (4.45% dry and 3.4% rain), mean was 7.79 mg/l in dry and 7.46 mg/l in rainy season (Tab. 1); during the first hours of the day the largest variation was observed (Fig. 3); this pattern was similar in both seasons; it was determined that pH had significant variation between seasons (F= 10.55, P=0.0022). Total alkalinity was high (47.5 mg/l in dry and 37.2 mg/l in rainy season) compared to acidity that presented low values (8.94 mg/l in dry and 15.82 mg/l in rainy). Total hardness was very similar in both seasons, but lower in the rainy (40 mg/l CaCO3 and 42 mg/l CaCO3 respectively), with permanent hardness higher than temporary hardness in both seasons (32 mg/l CaCO3
A
80 70 60 µs 50 40 30 20 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 1 Time (hour) 2 3 4 5 6 7 8 9

in rainy and 24 mg/l CaCO3 in dry). Biochemical demand for oxygen (BDO) was low for both seasons (0.55 mg/l in dry and 1.88 mg/l in rainy). Chemical demand for oxygen (CDO) had low values in dry (40.4 mg/l O2) and high in the rainy season (425.8 mg/l O2). Chlorine didn't show marked seasonal differences, generally it was low (31.03 mg/l CaCO3 in dry and 38.041 mg/l CaCO3 rainy). Biological variables: Phytoplankton. A total of 29074 individuals were recorded, 3977 from the rainy season and 25077 during the dry season (Tab. 2). Seven families were identified: Desmidiacea, Chroccocales, Chlorophyceae, Chrysophyceae, Bacillariophyceae, Xanthophyceae and Cyanophyceae, and 45 genera (Tab. 2). Ankistrodesmus was the most abundant during the rainy season (39.02% RA), followed by Melosira (15.06% RA). In the dry season Cladophora (35.16%), Ankistrodesmus (29.82%), Closterium (11.98%) and Tetrapedia (11.62%) were most abundant. Shannon-Wiener diversity was low for both seasons (1.98 bits/ind. in dry and 1.76 bits/ind. in rainy) (Tab. 6), Simpson dominance was high (0.24 in dry and 0.22 in rainy), revealing dominance of various genera like: Closterium, Ankistrodesmus, Cladophora and Tetrapedia (Tab. 2). Margalef index showed that richness was high (3.62 for both seasons) and lastly, values of Pielou's index (0.57 for rainy and 0.51 for dry) showed that there are genera that have same relative abundance, such as Microspora and Navicula in rainy and Phormidium and Tabellaria in dry season (Tab. 6). Zooplankton. 158 individuals were collected; 107 from the rainy season, and 51 from the dry (Tab. 3). Two divisions of zooplankton were identified: Protozoa and Rotifera; eight genera of protozoa and three genera of rotifera. Vorticella was most abundant in both seasons (89.72 % RA in rainy and 45.10 % RA in dry). Shannon–Wiener index had lower values for the rainy (0.46 bits/ind.) than the dry (1.81 bits/ind.), while Simpson dominance had higher values in the dry season (0.81) vs. the rainy (0.24). The Pielou index had low values during the rainy season (0.33), since in this season a marked dominance of the genus Vorticella was observed. In contrast, the Margalef index had lower values during the rainy season vs. the dry (0.64 and 2.014 respectively) (Tab. 6).

Rainy Season Dry season

B
9 8,5 8 7,5 7 6,5 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 1 Time (hour) 2 3 4 5 6 7 8 9

Rainy Season Dry season

pH

Figure 3. Diel and seasonal patterns of physicochemical variables in San José Creek, Otún River, Upper Cauca, Colombia. A: Conductivity. B: pH.

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- 42 - García-Alzate, C. A. et al.
Table 1. Physicochemical variables in San José Creek, Otún River, Upper Cauca, Colombia. C.V. = Coefficient of Variation, average in parentheses.
VARIABLES Water temperature °C Ambient temperature °C Maximal temperature °C Minimal temperature °C Dissolved oxygen (mg/l) Relative humidity % pH Conductivity (µS/cm) Turbidity Total alkalinity (mg/l CaCO 3) Total acidity (mg/l CaCO 3) Total hardness (mg/l CaCO 3) Calcium hardness (mg/l CaCO 3) Magnesium hardness (mg/l CaCO 3) Chlorine (mg/l CaCO 3) CDO (mg/l O 2) BDO (mg/l O 2) Total coliform (UFC/100ml) Fecal coliform (UFC/100ml) Depth (m) Width (m) Color Substrate Velocity of current (m/s) DRY 19.22 (17.4 -22.3) 20.68 (16 -28) 26.96 (25 -28) 19.28 (15 -24) 3.33 (3.2 -3.4) 76.46 (42 -91) 7.79 (7.43 -8.62) 71 (64 -76) 25 43.5 8.94 42 24 18 31.0 3 40.4 0.55 361 117 0.75 8.93 Crystal Stony 0.38 C.V. % 7.9 20.18 2.67 17.76 1.96 22.06 4.45 3.92 RAINY 17.7 (15 -19.6) 19 (16-23) 21.42 (20 -24) 17.88 (11 -23) 3.06 (2-4.2) 7.46 (7.03 -8.11) 44.46 (25 -49) 37.2 15.82 40 32 8 38 425.8 1.88 1200 1000 1.5 12.5 Brown Stony 0.85 C.V. % 4.56 11.82 4.93 14.7 24.9 3.4 12.74 -

Table 2. Phytoplankton community of San José Creek, Otún River, Upper Cauca, Colombia.
Division Chlorophyta Family Desmidiacea Genus Gonatozygon Microspora Navicula Closterium Docidium Cosmarium Mesotaenium Genicularia Pleurotaenium Netrium Penium Protococus Ankistrodesmus Chroococcus Cladophora Oedogonium Ophiocytium Tribonema Ulothrix Mougeotia Chaetophora Spirogyra Crucigenia Zygnema Rainy 185 27 27 23 2 5 4 19 1 3 1552 507 12 1 2 2 454 3 34 1 3 3 8 5 599 2 47 2 325 1 1 14 30 73 3977 Dry 244 76 62 3004 120 5 7 511 211 101 7477 302 8818 4 2 454 4 2 23 73 33 1 37 3 4 2 12 537 1 22 7 1 4 2913 25077 Rainy 4.65 0.68 0.68 0.58 0.05 0.13 0.10 0.48 0.03 0.08 39.02 12.75 0.30 0.03 0.05 0.05 11.42 0.08 0.85 0.03 0.08 0.08 0.20 0.13 15.06 0.05 1.18 0.05 8.17 0.03 0.03 0.35 0.75 1.84 100 Dry 0.97 0.3 0.25 11.98 0.48 0.02 0.03 2.04 0.84 0.4 29.82 1.2 35.16 0.02 0.01 1.81 0.02 0.01 0.09 0.29 0.13 0.004 0.15 0.012 0.02 0.01 0.05 2.14 0.004 0.09 0.03 0.004 0.02 11.62 100

Chroccocales

Chlorophyceae

Chrysophyta

Chrysophyceae Bacillarophyceae Tabellaria Nitzschia Gomphonema Melosira Stauroneis Cymbella Synedra Amphora Gyrosigma Xanthophyceae Ophoctium Melosira Tribonema Phormodium Cyanophy ceae Rivularia(colonies) Coelosphaerium Polycistis Spirulina Anabaena Phormidium Nostoc Tetrapedia

TOTAL

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Physico-chemical and biological variables of the otun river - 43 Table 3. Zooplankton community of San José Creek, Otún River, Upper Cauca, Colombia. R. A: Relative Abundance.
Division Protozoa Family Taxon Vorticella Urostyla Stentor Centropyxis Oxytricha Eudorina Naegleria Pithothorax rotondus Conochlius Philodina Chromogastes Cladocera TOTAL # of individuals Dry Rainy 23 96 5 10 4 1 3 3 1 1 3 1 1 1 1 4 51 107 R. A. % Dry 45,10 9,80 19,61 1,96 1,96 1,96 5,88 1,96 1,96 1,96 7,84 100 Rainy 89,72 3,74 2,80 2,80 0,93 100

Cilophora Rotifera

Macroinvertebrates. There were 31 families and eight orders recorded: Ephemeroptera, Odonata, Coleoptera, Diptera, Trichoptera, Neuroptera, Plecoptera and Hemiptera. A total of 1571 individuals were identified; 1010 from rainy season collections and 561 from the dry (Tab. 4). During the rainy season the orders with most diversity were Ephemeroptera, Trichoptera and Diptera, with five families each. Baetidae (Ephemeroptera) was the most diverse with four genera (Baetodes, Baetis, Dactylobaetis and Moribaetis), the same as Libellulidae (Odonata) with genera Erythemis, Dythemis, Sympertrumillotum and Macrothemis (Tab. 4). In the dry season, the most abundant genus was Thraulodes (Leptophlebiidae, Ephemeroptera), (relative abundance 16.58%), followed by Baetodes (Baetidae, Ephemeroptera with 12.83%) and Leptonema (Hydropsychidae, Trichoptera with 12,48%). During the rainy season Baetodes (Baetidae, Ephemeroptera) had high relative abundance (40.22%), followed by Leptohyphes (Ephemeroptera) (9.98%) and the genus Mortoniella (Glosoomatiidae, Trichoptera with 8.70%) (Tab. 4). Generally diversity indices were low due to the dominance of Baetodes in the rainy and Thraulodes in the dry seasons (Tab. 4). The Margalef index showed that there were more genera with high values (5.95) during the dry season. Fishes. 214 individuals were collected; 136 in the rainy season and 78 in the dry (Tab. 5). The dominant species was Hemibrycon rafaelense for both seasons (77.2% in dry and 50% in raint), followed by

Bryconamericus caucanus (11% in dry) and Astroblepus cyclopus (32.05% in rainy) (Tab. 5). Shannon–Weiner index had low values for both seasons (rainy 1.17 bits and dry 0.8 bits) (Tab. 6), as did the Margalef index (0.92 rainy and 0.81 dry) and the Simpson index because of differences species abundances. Water Quality Index ICOMO. In the rainy season ICOMO was 0.4, indicating low concentrations of coliform bacteria. In the dry season values were even lower, 0.11, indicating that the water had good quality during the rainy season, and very good quality in the dry, although it showed an abrupt increase of total and fecal coliform bacteria at the onset of the rainy season (Tab. 1). B.M.W.P/col. In the rainy season the total value for macroinvertebrates was 89 (Clase II), which indicates that water had acceptable quality but showed some effects of contamination. In the dry season, the value was 113 (Class I), indicating that water had good quality and that no contaminants were present. DISCUSSION In the Neotropics there are evident variations of physical and chemical variables in continental waters, due to influence of climatic seasons (dry and rainy). For this reason, ANOVA of water temperatures revealed variation between seasons with higher values during the dry season, and lower during the rainy. Maximum temperature varied more than minimum temperature, probably due to deterioration of riverine vegetation or no existing barrier sufficient to prevent light penetration; a

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- 44 - García-Alzate, C. A. et al.
Table 4. Aquatic macroinvertebrate community of San José Creek, Otún River, Upper Cauca, Colombia.
# of individuals Order Ephemeroptera Family Baetidae Genus Baetodes sp. Baetis sp. Dactylobaetis sp. Moribaetis sp Tricorythidae Leptophlebiidae Thraulodes Terpides Travellera Oligoneuriidae Heptageniidae Psephenidae Coleoptera Elmidae Psephenops Psephenus Cyllopus Heterelmis Macrelmis Lutrochidae Ptilodactylidae Hydropsychidae Trichoptera Hydrobiosidae Glossomatidae Polycentropodidae Polycentropus Hidroptilidae Helicopsychidae Larvas Odonata Calopterygidae Libellulidae Hetaerina Erythemis Dythemis Sympetrumillotum Brechmorhoga Libelulido Macrothemis Gomphidae Simuliidae Diptera Chironomidae Blepharoceridae Caraptepogonidae Tipulidae Veliidae Hemiptera Naucoridae Saldidae Hidracarido Corydalidae Neuroptera Plecoptera TOTAL Pupas Perlolidae Perlodes Corydalus Progomphus Phylogomphoides Simulium Chironominae Lemonicola Psycodidae Stilobezzia Atherix Rhagovelia Limnocoris Ochrotichia Helicopsiche Leptonema Smicridea Atopsyche Mortoniella Lutrochus Anchytarsus Lachlania Homoeoneuria Stonema Precloen Tricorythodes Leptohyphes sp. Rainy 407 58 5 6 18 101 33 30 3 7 15 1 2 3 1 4 2 37 68 5 88 2 1 51 2 2 2 1 1 46 1 1 1 1 1 1 3 1 1012 Dry 72 10 11 2 1 12 11 93 3 2 4 47 3 1 7 11 1 5 5 2 70 35 4 7 15 2 14 2 6 3 1 7 1 14 13 7 4 4 2 15 12 16 4 561 R. A. % Rainy 40.22 5.73 0.49 0.59 1.78 9.98 3.26 2.96 0.30 0.69 1.48 0.10 0.20 0.30 0.10 0.40 0.20 3.66 6.72 0.49 8.70 0.20 0.10 5.04 0.20 0.20 0.20 0.10 0.10 4.55 0.10 0.10 0.10 0.10 0.10 0.10 0.30 0.10 100 Dry 12.83 1.78 1.96 0.36 0.18 2.14 1.96 16.58 0.53 0.36 0.71 8.38 0.53 0.18 1.25 1.96 0.18 0.89 0.89 0.36 12.48 6.24 0.71 1.25 2.67 0.36 2.50 0.36 1.07 0.53 0.18 1.25 0.18 2.50 2.32 1.25 0.71 0.71 0.36 2.67 2.14 2.85 0.71 100

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Physico-chemical and biological variables of the otun river - 45 Table 5. Fish community of San José Creek, Otún River, Upper Cauca, Colombia.
Species
Dry Number of Individuals Rainy Dry Relative Abundance % Rainy

Hemibrycon rafaelense Bryconamericus caucanus Astroblepus cyclopus Lasciancistrus caucanus Chaetostoma fischeri Brycon henni Total

105 15 9 2 5 0 136

39 25 8 0 5 1 78

77.2 11 6.62 1.47 3.68 0 100

50 10.26 32.05 1.28 6.41 0 100

Table 6. Diversity indices for biological variables in San José Creek, Otún River, Upper Cauca, Colombia.
Index / Seasons Zooplankton rainy dry Phytoplankton rainy dry Macroinvertebrates rainy dry Fishes rainy dry

Shannon-Weiner Margalef Simpson Pielou

0.46 0.64 0.81 0.33

1.81 2.01 0.24 0.83

1.98 3.62 0.21 0.57

1.75 3.62 0.24 0.51

0.95 4.62 0.37 0.27

1.47 5.95 0.06 0.4

1.17 0.92 0.37 0.73

0.8 0.814 0.61 0.49

similar situation was described Bojsen & Barriga (2002). Temperature is a biotic factor that regulates vital processes for living organisms, and also affects physicochemical properties of other parameter of the aquatic ecosystem such as: nutrient solubility, gas solubility, physical state of nutrients, grade of xenobiotics toxicity and physicochemical properties: pH, redox potential, gas solubility, density, physical state and substrate viscosity (Roldan, 1992). These variations in temperature in general, could be considered as decisive factors that cause strong season changes in tropical aquatic ecosystems (Roldan et al., 1984) such as San José Creek. Other variables useful to determine the trophic state of water bodies is the dissolved oxygen. In this study dissolved oxygen varied little during the dry season but more during the rainy, indicating autotrophy in the dry, and a tendency to heterotrophy during the rainy season. According to Dodds (2007) this is probably due to the mixing of allochthonous material and flushing out of pesticides and fertilizers used in village cultures close to the stream, and expressed in the abrupt increase of CDO in the rainy season of more than 390 ppm. In general, patterns of variation among physicochemical variables established that this water body is oligotrophic in the dry season with a tendency to eutrophication in the rainy season.

Quantity of ions in water has a great significance in osmotic regulation mechanisms of organisms, where a drastic variation provokes problems in their biological activity. According to Machado & Roldan (1981) normal values are found between 10 and 30 ppm, but values found in this study exceed 30 ppm, possibly due to the mixing of sewage and runoff during the rainy season that affects structure of stream communities (Matthias & Moreno, 1983). This is corroborated by the increase in fecal coliform bacteria present during the rainy season by a factor of more than 900. High pH values for both dry and rainy seasons are withing limits recorded for the neotropics (Alba-Tercedor, 1996). Chlorine concentration is perhaps one of the variables that exert the most influence on aquatic organism distribution, because they have to overcome osmotic pressure (Roldan, 1992). In the rainy season, high values were present due to a higher rate of organic contamination. Low values correlated with high productivity and low species diversity; coinciding with Gómez and Martínez (1998). In the rainy season, the genus Ankistrodesmus was abundant, indicating water with some degree of eutrophication; Bacillariophyceae or diatoms found have diverse physiological characteristics. Some are facultative heterotrophs that can survive in conditions of low light that increase in shallow waters (Aguirre & Palacio, 2005). Presence of this organism in a water

rev. invest. univ. quindio (18): 38-48. Armenia - Colombia

- 46 - García-Alzate, C. A. et al. body possibly indicates that during the rainy season, there was a marked increase of contamination that favors abundance of this group, which is more tolerant to physico-chemical changes. The macroinvertebrate community found was similar to that recorded from other habitats in this area (Rincón, 2002; Londoño et al. 2005, GarciaAlzate et al, 2007). Most abundant were Ephemeroptera, indicators of clear and oligotrophic water (Gallardo-Mayenco, 2003, Caicedo & Palacio, 1998). Nevertheless, the composition of this community was evidently different. Diversity present in San José Creek regarding macro invertebrates was low comparing to other reported studies for tropical streams (Roldán et al. 2001; Rincón, 2002). Diatomeas (Bacillarophyceae) were highly abundant in this stream. They have been used as indicators of water quality, because they can rapidly show changes in physicochemical characteristics: for example the genus Nitzschia was abundant when pH increased (Díaz-Quiroz and Rivera Rondón, 2004). Similar results were found by García-Alzate et al. (2007) in one eutrophic stream in Upper Cauca. The fish community also coincides with previous records for this area (Román-Valencia 1993; 1995). Relative abundance of encountered Characidae species shows that human impacts on this stream were not strong, coinciding with García-Álzate et al. (2007). The eutrophic conditions found during the rainy season are serious because this stream is a home of the endemic species Hemibrycon rafaelense (Román-Valencia & Arcila-Mesa, 2008). BMWP/col coincides in both seasons with ICOMO index that classify this water as very good in dry and good in rain. This change of water quality is possibly a consequence of allochthonous contaminants that influence on macro invertebrate community composition, because some groups don't tolerate certain degrees of contamination, for example, Ephemeroptera and certain families of Plecoptera. In general, the biological quality for both seasons was good according to indices that determine water quality. And in spite of certain indications of contamination, there were no marked visible alterations in physicochemical and biological properties in this water body. Acknowledgments This study was done with support from University of Quindío, Vicerrectoria de Investigaciones (Proyecto 357), academic biology program, International Association for the Exchange of Students for Technical Experience (IAESTE) and students of limnology class I semester 2007 of University of Quindio that collaborated in field work and laboratory. This article benefitted from corrections and suggestions of Donald C. Taphorn, anonymous revisor and editorial committee Revista de investigaciones of University Quindío.

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