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INTRODUCTION
Hydrological and physical-chemical characteristics, as well as disturbances, spatial and temporal heterogeneity in rivers, define distribution, dispersion, colonization and the response of organisms to the environment 1, factors such as light, flow velocity, flow rate, weather, riparian vegetation, the direct intervention of man in extracting materials and changing the course of the river, govern the physical and morphological processes of rivers 2. Phytoperifiton dynamics are also controlled by factors such as light, current velocity, as well as substrate type, chemical composition of water, herbivores and temperature; As all these factors interact with each other, it is difficult to say which is the limiting factor for their growth 3.
Phytoperifiton has a better development in substrates that provide stability and with minimal current activity. Furthermore, the limiting factor in the production of this community is the type of substrate rather than light intensity or nutrients 2. These algae are among of the dominant primary producers of aquatic ecosystems and are the main source of energy that guides production at the highest trophic levels 1.
Rivers and bodies of water in general are crucial in the development of human settlements, and in order to understand how this complex system works, it is necessary to know the composition and structure of its environment. These ecosystems foster the development of aquatic communities such as phytoperifiton, where species appear with varied biological strategies; Such as resistance to environmental changes and fluctuations, explosive type reproduction, short life cycles among others 4. However, in order for development to be optimal, water conditions must have the characteristics required by these communities.
Scant protection at riverbanks which leads to tree and vegetation losses is among the main problems observed in the Cesar River, where better conditions can contribute to soil conservation; indiscriminate deforestation with no awareness of natural dynamics itakes place as an economic activity (artisanal fishing), which is a crucial resource for the inhabitants and neighboring villages. Therefore, the Ministry made a declaration of calamity regarding the Cesar iver in 2014
Therefore, it was necessary to determine phytoperifiton composition and structure in the middle and lower basins of the Caesar River and how it relates with the physical and chemical variables; thus, this study will serve as a basis for numerous studies in the areas of taxonomy, ecology and bioindication.
MATERIALS AND METHODS
Area studied. The Cesar River is born in the snowy peaks of the Sierra Nevada de Santa Marta, at an altitude of approximately 1800 meters above sea level, in the Department of La Guajira, it runs for approximately 380km until it flows into the Zapatosa swamps and on to the Magdalena river. The drainage area of the basin covers about 22931km2 (Figure 1).
Figure 1 Map of the Cesar Department, representing the course of the Cesar River and the location of the sampling stations in the middle and low basin.
Eight sampling stations with their respective coordinates (Table 1) were placed, covering the middle and lower basins of the Cesar River, with heights ranging from 163 m above sea level to 31 meters above sea level. The type of vegetation where the stations were placed were areas of cultivation, livestock grazing, where we found species in the early stages of succession in the form of shrub and herbaceous growth. The following were found among the tree species: Crataeva tapia (toco), Enterolobium cyclocarpum (carito), Guazuma ulmifolia (guácimo), Cassia grandis, Samanea saman, Crescentia cujete (totumo), Samanea riparia (mulatto), elements of advanced stages of succession were found in the riparian vegetation, where tree is greater and with a lower amount of sunlight reaching the soil, given the flood characteristics of some areas of the river.
Table 1 Sampling stations coordinates.
| Stations | characteristics | Coordinates | Height (masm) | |
|---|---|---|---|---|
| Middle Basin | ||||
| E1 | Veracruz | San Juan del Cesar | Lat 10° 38’ 14.2” N: Lat 73° 04’ 55.4” N: | 163 |
| E2 | Rio Badillo | Valledupar Cesar | Lat 10° 31’ 58.6” N: Lon 73° 08’ 23.1’’ O | 146 |
| E3 | Guacochito | Valledupar Cesar | Lat 10° 32’ 52.0” N: Lon 73° 0.7’ 29.3’’ O | 142 |
| E4 | Puente Salguero | Valledupar Cesar | Lat 10° 26’ 23.8” N: Lon 73° 12’ 02.4’’ O | 125 |
| E5 | Las Pitillas | San Diego Cesar | Lat 10° 23’ 05.4” N: Lon 73° 14’ 01.7’’ O | 112 |
| Lower Basin | ||||
| E6 | Puente Canoas | El Paso - Cesar | Lat 10° 19’ 57, 6’’N: Lon 73° 14’ 57, 6’’O. | 103 |
| E7 | Rabo Largo | La Paz - Cesar | Lat 09° 48’ 24,3’’N : Lon 73° 37’ 37.8’’ O | 51 |
| E8 | El Paso | El Paso - Cesar | Lat 09° 48’ 2,785’’N : Lon 73 ° 48’13.749 “W | 38 |
Organism collection and identification. Sampling was carried out between February and September 2011 during the drought and rain events on the site, samples were collected on available natural substrates (rocks, sediments and plant debris) 5, scaling with 2x2 grids was carried out randomly 10 times for a total area of 40cm 2, a thin bristle brush was used to protect phytoperifiton structures, the samples were fixed with 4% formalin and lugol solution in order to prevent altering the internal or external structures of organisms 3, and were labeled with field specifications (date, time, substrate and sampling point).
The samples were taken to the Universidad of Atlántico UARC-135 Biological Collections Museum. Individual counting was carried out using the aliquot counting method, which consists in taking an aliquot with a known volume, placing it between the slide and coverslip, for which precision pipettes (Stempel, Eppendorf) were used, they were taxonomically identified through direct observation using an optical microscope (Leica, DIMIN) with a maximum magnification of 100X 6, the taxonomic keys proposed by 7-14 were used with the help of iconographic material from recognized bibliographies such as 15-17, the taxonomic categories of The Species 2000, Algabase and ITIS Catalog of Life webpages were taken into account, the qualification of individuals was achieved using the formula:
N°/ cm 2 = (C*TA) / (A*S*V)*(total area sampled in the field)
Where:
TA = coverslip area in mm2
TA = A = area of 1 row in mm 2
C = number of organisms counted.
S = number of rows counted.
V = sample volume under coverslip
Characterization of physical and chemical variables. The following variables where measured on-site: pH, surface water temperature, conductivity, oxygen saturation percentage, dissolved oxygen, flow, Total Suspended Solids and flowrate (Table 2), water samples were collected in 250 mL plastic capable of measuring nutrients (NO 2 -N, NO 3 -N, N 2 , PO 4 -P and BOD 5 ), which were analyzed in vivo in the Universidad del Atlántico laboratory, following the techniques set forth in the standard method 18.
Table 2 Physical and chemical variables measured at each of the sampling stations.
| VARIABLE | DEVICE / BRAND / REFERENCE |
|---|---|
| PH | PH meter-WTW-3210 |
| Temperature (° C) | PH meter - WTW -3210 |
| Conductivity (μs / cm) | Conductometer -WTW-3110 |
| Oxygen (mg /L) | Oximeter -WTW- 3205 |
| Saturation (%) | Oximeter -WTW- -3205 |
| SST (mg /L) | Vacuum Pump - Filter ... pores |
| Turbidity (NTU) | Turbidimeter - HACH-2100 Q |
| Nitrites (μg / L) | Spectrophotometer - Genesis-5 |
| Nitrates (μg / L) | Spectrophotometer - Genesis-5 |
| Nitrogen (μg /L) | Spectrophotometer - Genesis-5 |
| Phosphates (μg / L) | Spectrophotometer - Genesis-5 |
| DBOƽ | Incubation for 5 days at 25º C |
| Flowrate (m³/s) | Flow meter |
Data analysis. The richness and the number of species was determined by sampling, and density as the number of individuals per area. This analysis is coupled with the Shannon-Weaver (1949), Equity of Pielou (1984) and Simpson Dominance (1949) indexes. Statistical techniques were applied to establish central tendency measurements and data dispersion (descriptive statistics), which are required for characterization. The Kolmogorov-Smirnov normality test (N>30) was conducted, which showed that the data do not have a normal distribution (p=≥0.05). The Jaccard Similarity analysis (CLUSTER) was performed to compare Phytoperiton estructure on the stations. Linear regressions were performed to see the relationship and the function that best explains each of the independent variables (physical and chemical variables) with dependent phytoperifiton variables (density and richness). The physical and chemical characterization used in sampling (temporal) and stations (spatial) was carried out using Principal Component Analysis (PCA). A Canonical Correspondence analysis (CCA) was conducted with the two most representative classes during the trial period (Bacillariophyceae and Cyanophyceae) to study their relationship with abiotic components. Analisis was carried out using the PAST 3.0 Statistical Software.
RESULTS
Biological variables. It was established that among 110 species, with a total density of 1911.70 Cel/cm2, the Bacillariophyceae species was the most representative at 48% (913.40 Cel/cm2), followed Cyanophyceae with 35% (663.40 Cel/cm2), Fragilariophyceae with 7% (128.80 Cel/cm2), Zygnemaphyceae with 4% (78.80 Cel/cm2), Euglenophyceae and Chlorophyceae with 2% (39.60 and 30.30 Cel/cm2), Trebouxiophyceae, Coscinodiscophyceae with 1% (29.90 and 27.40 Cel/cm2 respectively) and lastly Ulvophyceae with 0.00005% (0.10 Cel/cm2). The greatest richness was observed in Bacillariophyceae with 45 species, followed by Cyanophyceae with 18 species, Zygnemaphyceae with 14 species, Chlorophyceae with 11 species, Fragilariophyceae with 9 species, Coscinodiscophyceae, Trebouxiophyceae with 4 and 3 species, respectively, and with just one Ulvophyceae species (Table 3).
The spatial and temporal distribution of Phytoperifiton richness showed that the Badillo station (E2) registered a greater number of species (59) in August, and the Rabo Largo (E7) station had the lowest number of species, which was 13. Navicula and Nitzschia (9 species each), Cosmarium (7 species), Oscillatoria and Fragilaria (6 species each) were among the genera that had the highest number of species. The highest densities were reported in July and August, the dominance of the Bacillariophyceae species was observed, and the most abundant species were Pinnularia viridis, Navicula sp.1, Navicula sp.2, Nitzschia dissipata, Navicula platalea and Stauroneis anceps.
The Cosmarium, Scenedesmus and Pediastrum Chlorophyceae genera were the ones that contributed to phytoperifiton density. Although Cyanophyceae did not have ahigh density, they are part of the composition of this community, the most representative genera were Oscillatoria, Nostoc and Mycrocystis. The lowest densities were seen in April presented when compared to other sampling months. The highest diversity was found in the Rabo Largo station (E7) in the month of February (H’= 3.64) and the lowest value was recorded at the Puente Canoas station in August (H’=1.13). Dominance showed low values at all sites (D=0.031).
The Jaccard similarity index, considering an arbitrary value with a similarity of over 76%, showed that the final sector of the middle area (Guachito-E3) and the beginning of the lower area (Puente Salguero-E4, Las Pitilla -E5 and Rabo Largo-E7) are a conglomerate (Figure 2), this result is associated with the hydraulic characteristics of these sites; however, the Las Pitillas (E5) and Rabo Largo (E7) stations were more closely related and had a greater degree of similarity. This situation coincides with the use of the resource that is present in this sector, where the affected downstream stations with the largest wastewater discharge volumes, corresponding to the sewage system of the city of Valledupar, at the station located in Salguero Bridge, this may be corroborated with the physical and chemical water variables and the hydrological conditions measured.
Figure 2 Station Jaccard Similarity Dendrogram Gua=Guacochito; LP= Las Pitillas; RL=Rabo Largo; EP=El Paso; Ver=Veracruz; PC=Puente Canoa y Bad=Badillo.
Characterization of physical and chemical variables. The study area had a surface temperature of 25.5 to 31.7°C, the pH was neutral as can expected from a tropical system, and had a positive correlation with abundance (r=0.41: p≥0.05), oxygen showed significant differences between the months of February-April (p≥0.05) and June-August (p≥0.05). The maximum oxygen values (8.3 mg / L; CV = 41.1) were reported in February at the Badillo station (E2) and minimum values (1.3 mg/L; CV=41.1) were reported at Las Pitillas station (E5). The oxygen saturation percentage did not show significant differences between sampling months, the dissolved oxygen and oxygen saturation percentages had a negative correlation with BOD5, (r=-0.3549; p≥0.05 and r=-0.3764; p≥0.05 respectively). Conductivity showed significant temporary (p≥0.05) and spatial (p≥0.05) differences.
On nutrients. Total Suspended Solids showed significant differences between samples and stations (p≥0.05), the highest values were recorded in the month of April during the low rainfall season, turbidity showed significant differences between months and seasons (p≥0.05). The maximum Biochemical Demand values Of Oxygen were reported at the Puente Salguero station in February and April (60 mg/L; CV=128.4). Nitrates reached their highest levels in February at the Puente Salguero station (723.44 mg.l-1), as nitrites in the month of April (44.13 mg.l-1). The maximum phosphates value was reported at the Puente Salguero station in February (756.21 mg.l -1), the hydrological variable (flow) showed significant differences in the months of February and August (p≥0.05) and maximum values were observed in stations placed at the lower segment.
The CPA (Figure 3), shows a sectorization of some stations at the Cesar River, which records a group of variables associated with these sites such as turbidity, Total Suspended Solids and oxygen saturation percentage. Salguero Bridge (E4) was seen as a completely different station characterized only by organic phosphorus concentrations (where the the Star Salguero discharge is located), which were used as indicator of spill contamination caused by the effect of wastewater inflow with high organic material content.
Figure 3 Principal component analysis of the physical and chemical variables at the sampling stations.
In the Canonical Correspondence (Figure 4) analysis, the way physical and chemical variables behave with biological variables was observed, and whether they influenced Phytoperifiton development and growth. The two most representative groups were analyzed, namely: Cyanophyceae and Bacillariophyceae. Cyanophytes were negatively associated with oxygen and overall oxygen saturation percentage. At the Puente Salguero station, the organic phosphorus and nitrogen variables are the notable conditions at the site; at Las Pitillas (E5), it was observed that nitrite (NO2 -N) and nitrate (NO3 -N) are the notable factors of this station, as are lower flow and conductivity at a lesser degree, the most representative algae of the site were also observed. As for Badillo, it has the highest pH values (basic), Total Suspended Solids and turbidity are the defining variables of this site.
Figure 4 Canonical Correspondence Analysis of the Cyanophyceae and Bacillariophyceae with the physicochemical variables of the Cesar River. OD and SST in mg / L. NO2, NO3, N2 and P in μg / L. Tem in ° C. Sat. O in%. Cond in μS / cm. Turb in NTU and flow in m3/s. Abbreviation of the species see Table 3.
DISCUSSION
Various physical and chemical conditions influence Phytoperifiton structure. When this community is studied in fluctuating (lotic) systems, it is difficult to find find the factors that regulate it. The total density was positively correlated with pH and conductivity and negatively correlated with Total Suspended Solids. Nutrients (NO3 -N, NO2 -N and P) were positively related to abundance and were more available, as were carbonates and bicarbonates, which are the carbon dioxide source source in the water. Rivers are oligotrophic when they are born, but their conductivity and ion concentration increase progressively as they reach the valleys due to channel erosion, sediment trailing and rainfall runoff, maximum conductivity values were found in the month of August where precipitation was present; in many neotropical rivers, these values increase drastically due to agricultural activity and pollution arising from industrial and domestic activities 3).
The highest temperature records were associated with or favored the growth of Chlorophyceae and Cyanophyceae, due to the fat that they have an impact on the photosynthetic metabolism, with a higher cells density. Green algae (Chlorophyceae) grow between 15ºC and 30ºC, and the Cyanophyceae algae at 30ºC 20.
During the trial, diatoms represented a high percentage (41%) of phytoperifiton, due to their ability to develop in benthic habitats; this medium has a variety of microhabitats available for colonization, ain addition to the physical and chemical variables that define the type of organisms that grow on the substrate 21. According to this, two growth strategies were defined, the first consists of small unicellular diatoms adhered to a prostrate substrate which provided greater water flow resistance and flow variations 22; and in the second strategy, species of larger sizes with peduncles or basal adhesion structures found in areas with weaker currents were involved.
The most abundant species at the highest flow rate were Anabaena sp.1, Oscillatoria vaucher, Phormidium sp.1, Chroococcus sp.1, Navicula platalea and Oscillatoria sp.1, and Oscillatoria vaucher, Oscillatoria sp.1, Navicula sp.1 and Navicula platalea in the dry season. These are species that morphologically develop structures that help them endure the changes that take place in the system. The Anabaena sp.1 species is known for its proliferation in polluted waters, and had the highest density in the entire study at 136.70 Cel / cm 2, which was peculiarly recorded at Las Pitillas (E5), a site with a heavy wastewater influence from the neighboring population and located downstream of Puente Salguero, which suggests a plume effect caused by discharges from the sewage system of the city of Valledupar, which does not achieve degradation in its course.
Species density had a positive correlation with conductivity, and therefore high densities were observed in the first stations and during August; however, substrate washing caused by excess flow kept the community in its primary development stages. Thus, species with morphological adaptations such as elongated forms and the presence of raphe have a greater substrate adhesion, as is the case with some Bacillariophyceae and Cyanophyceae 22.
Genres such as Anabaena sp.1; Euglena acus , Trachelomonas and Phacus sp.1; Melosira varians are indicative of water with rich organic matter contents, these organisms were widely distributed throuhout the sampling stations; however, high densities were reported at the Puente Salguero, Las Pitillas and El Paso stations. The species Cymbella gracilis, Nitzschia palea, Surirella elegans and Pinnularia viridis are characteristic of clean water with a low organic matter content (23), these species were found to be more abundant at the Badillo station, in the area where the Badillo River crosses the Cesar River.
