by Abelardo Correa, Evelyn Erickson and Steven Zbaida
 

INTRODUCTION:

Abundance and biodiversity of macroinvertebrates in a stream can be used as an indicator for water quality.  Biodiversity scales have been developed to determine an ecosystem's health.  "An organism is considered an indicator of water quality when it is found invariably in an ecosystem of well defined characteristics and when its population is, percentage wise, superior or slightly above other organisms in its shared habitat" (Alba-Tercedor 1996).  Prior studies indicate that the presence of Mayfly (Ephemeroptera) is an indicator of non-polluted freshwater.  In the present study we selected two sites to research biodiversity in the Jaba River, located near Las Cruces Biological Station in the Puntarenas province of Costa Rica.  The river runs through  forested and agricultural areas, this land has been  used as pasture land as well. Our hypothesis is that water flowing within a forested area will have a greater variety  than water running beside an agricultural area.  This study is important because it tests the impact of farm land/pastures on the water quality supplied to the city of San Vito.
 
 

METHODOLOGY:

We established two sites to collect samples.  Samples were collected at the same time on both days, using the same method.  Temperatures for both sites were recorded. On day one, we collected five biodiversity samples from site 1 (pasture area).  On day two, we collected five samples from site 2 (undisturbed primary forest). The kick method was used to collect samples.  "Kick sampling involves dislodging invertebrates in the stream bed by kicking and disturbing the substrate and catching the dislodged invertebrates in a net held a short distance downstream." (Sutherland, 1996)  The samples were brought back to the lab for analysis.  Then, the macroinvertebrates were tallied and identified by using a dichotomous key (Cummins et al, 1985).
 
 

RESULTS:

We observed 8 species of invertebrates among both streams.  Biodiversity was higher in  the agricultural area (6) than in the forested area (4).  However,  abundance of Mayfly Nymphs, indicators of water purity, was much higher in the forested area (23) than in the agricultural area (4).  The abundance of Caddis fly Nymphs, Aquatic worms, and Tamanini was higher (12, 1, 9) in the forested area.  In agricultural fields these species totaled 3, 0, 0 respectively. Temperature in the agricultural area averaged 71oF and 68oF in the forested area.
 
 

DISCUSSION:

The results falsified the original hypothesis that water flowing within a forested area will have a greater variety  than water running beside an agricultural area.  Biodiversity in the agricultural site was higher (6) than in the forested area (4).  These results were also inconsistent with the results stated in a prior study by Vargas Clemente.  Despite the differences in the level of Biodiversity between the two sites, abundance of Mayfly Nymphs in the forested area indicates a better quality of water.  Discrepancies between this study and the prior one may be attributed to the methodology used.
 One plausible explanation for increased biodiversity in site 1 may be caused by the higher attraction of some insects to vegetation that thrives in disturbed areas.  This may impact the biodiversity of insect predators within the Jaba River.
 The temperature difference between the two different sites in the Jaba River is due to a higher level of ambient light in the pasture areas.  Water purity may also be affected by chemicals found in the runoff of the agricultural areas.  We recommend additional studies to solidify or negate our findings.
 

APPLICATIONS:

This activity may be done in the classroom using local rivers, streams, ponds or lakes.  It emphasizes inquiry, critical thinking, and the use of laboratory instrumentation and technology.
 
 

LITERATURE CITED:

Cummins, Kenneth W., and Wilzbach, Margaret A. (1985).  Field  Procedures for Analysis of  Functional Feeding Groups of Stream Macroinvertebrates.  Bonnie B. Hall, Maryland.

Sutherland, William J., editor (1996).  Ecological Census Techniques: A Handbook.  Cambridge University Press, United Kingdom.

Vargas Clemente, Itavclerh (1998).  An‡lisis de Indices que Indican las Caracter’sticas Biol—gicas del Agua en la Cuenca del Rio Jaba, San Vito-Costa Rica.
 
 

ACKNOWLEDGMENTS:

We want to thank James Cole and Tom Langen for their assistance, support and expertise.