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Jenelle Hopkins, George Goff, Susan Hoffmire
ABSTRACT - Quantitative chemical tests were performed on six small stream tributaries that feed into the Puerto Viejo River located at the La Selva Biological Preserve, Costa Rica. No synergetic affects to the river were noticed for pH, carbon dioxide, phosphate, conductivity or hardness.
INTRODUCTION - The water quality of a river is only as good as the quality of the watershed that feeds into it. The properties of the water itself can be altered by very small amounts of added materials. Surface water, especially, are easily changed. There can be silt brought in by flooding, algae blooms caused by the combination of an increase nutrient supply and sunlight, or the leaching of minerals from soil or decomposing forest litter.
It is also important to remember that water quality changes over time. Sample analysis is only good for the time that the sample was taken. Man’s influence on surface water quality can be seen by deforestation, which can cause an increase in soil erosion, agrochemical pollution, and heavy metal pollution.
There are several easy and simple tests that can quickly asseses the overall abiotic quality of a water sample. The first important preliminary test is measuring pH. Small changes in pH, 0.3 units or less, can be associated with relatively large changes in water quality (Renn, 1970). Metal solubilities and biological processes will then be affected. A change in pH can be the first clue in tracking down a serious water quality problem. Surface water usually has a pH of 6.0 to 8.5.
Carbon dioxide is present in water supplies in the form of a dissolved gas. Surface water normally contains less than 10 parts per million (ppm). Aquatic plant life depends on carbon dioxide for growth. However, a rise in carbon dioxide associated with an increase in the oxygen concentration (usually associated with decomposing organic matter) can make it more difficult for fish to breathe. Such a combination can be associated with waters containing excessive organic waste.
The hardness of water is mainly related to the amount of calcium and magnesium ion concentrations. Because of water’s ability to act as a solvent, water passing through soil and rock, such as limestone or dolomite containing large amounts of calcium and magnesium will leach these elements from the soil and rock and carry it as suspended and/or dissolved material. Waters that pass through rocks that have high acidic content, such as igneous rocks, will pick up acidic ions. Waters in the range of 0-60 ppm total concentration of calcium and magnesium are termed “soft water”. Waters in the range 60-120 ppm are termed “medium hard,”, water in the 120-180 ppm range are termed “hard”, and water above 180 ppm are considered “very hard”.
Water polluted from wastewater sources will contain phosphorus in ranges greater than .1 ppm. Increase in phosphorous concentrations will cause a rapid growth of algae in the water. As the algae dies and decomposes, the oxygen concentration will fall, adversely affecting fish populations.
Conductivity of a water sample can be used to determine the ion concentration in the sample. The ability of a solution to conduct an electric current increases with an increasing concentration of ions. There is a direct relationship between conductivity and total dissolved solids. So a high conductivity reading may indicate an environmental problem. Total dissolved solids usually are regulated at levels below 1100mg/L.
Water samples can easily be analyzed for pH, carbon dioxide, phosphorus concentrations, hardness and conductivity. The analysis can indicate the general “health” of the water system. Streams or rivers whose water samples show spikes in concentrations can then be revisited for the point source pollution. This study will examine six small feeder streams into the Puerto Viejo River for the excessive presence of these six key pollution indicators and compare the concentrations with water samples from the Puerto Viejo River taken upstream and down stream from these feeder streams.
METHODS - Water samples were taken in six different stream tributaries that feed into the Puerto Vierjo River as it runs through the La Selva Biological Preserve, Costa Rica. La Selva is located in the Lowland Carribean Rainforest and receives almost 4000 mm of rainfall annually, Stream tributaries are abundant throughout the park. Our samples were limited to a small area of six tributaries that feed into the Puerto Vierjo River from the south side approximately two kilometers upstream and downstream from the suspension bridge at the La Selva Preserve.
Samples were taken along the marked rain forest trails and places where the trail uses a bridge to cross the stream. These trails were the Sendero Tres Rios (STR), Sendero Sura (SUR) Sendero Oriental (SOC), Camino Circular Cercano (CCC) and the Camino Circular Lejano (CCL). As a bridge over a stream tributary was encountered, a water sample was taken. While standing on the bridge, a large plastic bucket was lowered into the water and tipped so that the bucket lip slid below the surface, but did not drag along the bottom streambed. In this way only the sediment load that was dissolved or in suspension was collected. Two thirty-milliliter plastic containers were filled at each sample location and taken back to the lab for analysis. Observations concerning water color, stream width and depth, smell, stream bank and stream bottom characteristics, stream flow, vegetation and leaf litter were noted at each site. (See Appendix Table 1)
Chemical analysis was done in the lab using the LaMotte Water Pollution Detection Outfit, Model AM-21 and the Vernier conductivity probe. A list of the findings is included in Appendix Table 2. A comparative chart is listed below.
RESULTS - Concentrations of the six key water pollution indicators in water samples taken at STR 850 and STR 450 will influence the concentrations of these same indicators in the river at sample River Downstream Location. STR 850 and STR 450 both showed low conductivity (50 and 80 microseimans, respectively). The conductivity at the downstream river location, however, showed a much higher conductivity. Since this may indicate a higher total dissolved solids concentration, influences from further upstream than STR 850 and STR 450 must be contributing solid material.
Water samples CCL 550, CCC 1000, SUR, and SOR 350 will all influence the concentrations of these same indicators in the river at sample River Upstream Location. High conductivity at CCL 550 and SUR (190 microseimans at both locations) are diluted by the lower readings at the other sites. Overall conductivity in the upstream river location is only 110 microseimans.
pH ranged from 6.0 to 7.5 in all eight water samples. The most acidic water (6.0 reading) was found at STR 450 and SOR 350. The highest pH was found at River Downstream and CCC 1000. These two points were very far from each other. Phosphate levels were none to extremely low in all samples except at STR 450. Phosphate concentrations at this spot were slightly higher, but still less than 5.0 ppm.
Carbon dioxide was slightly higher than the normal 10 ppm in most locations. The highest carbon dioxide reading occurred at SOR 350.
CONCLUSIONS - The LaMotte Water Pollution Detection Outfit gives a quick and easy water sample analysis for many key abiotic water pollution indicators. It would be interesting to compare these results from the many water quality measurements that have been taken here at La Salva. The results from this study show a minor spike in concentrations of carbon dioxide that may have contributed to the lower pH readings at Sendoro Oriental 350. There also appears to be higher dissolved solids in the Camino Circular LeJano 550 and Sura Creek tributaries. These spikes may be a result of past land use practices. There may also be something anthropogenic going on in this area. More water samples could be taken from different places along these two streams to further investigate these spikes.
ACKNOWLEDGEMENTS - The team would like to thank Nancy Vawter, Philippe Hensel and David Silverberg for their invaluable technical assistance and guidance for this project.
REFERENCES CITED
Renn, C. R. 1970. Investigating Water Problems. LaMotte Company, Chestertown, Maryland.