Category:  Group Project
Participants:  Millie Chamblee, Rebecca Marks, April McCrae, Stacy Weaver, Jherimechee Womack
Site:  Las Cruces

Key Words: Macroinvertebrates, turbidity, pH, flow rate, tributary

Summary:

The Wilson Botanical Garden located in the Las Cruces biological reserve of Costa Rica is situated in direct proximity to three tributaries of the Rio Jaba.  The three tributaries include Quebrada Culvert, Quebrada Wilson and Quebrada Lutite.  It was this group’s hypothesis that the impact on water quality as it related to the Wilson Botanical Garden was proportional to the tributary’s distance from the affecting area.
 
 

Introduction:

The Las Cruces Biological Station (LCBS) and its associated botanical garden is located at mid-elevation and is surrounded by various natural and agricultural landscapes (LCAC 1998).  Among the natural resources within the reserve are four small tributaries that feed into the Rio Jaba.  The four tributaries from closest to farthest proximity to the garden include Quebrada Culvert, Quebrada Culebra, Quebrada Wilson and Quebrada Lutite.

The Robert and Catherine Wilson Botanical Garden is maintained by LCBS and provides an educational resource by sharing conservation and research facilities.  While it is understood that the facility’s use of agrochemicals to control plant disease and pests are at a minimum (LCAC 1998), our group was concerned that impact on these tributaries may be significant and would likely be proportional to distance from the garden.   Physical, chemical and biological properties of aquatic systems can be examined to determine both water quality and any long-term effects of pollutants on its biotic communities (Fishman et al. 1995).  In an attempt to measure the water quality of each of these tributaries, the pH, temperature, flow rate, depth, turbidity and macroinvertebrate surveys were done before and after rain.
 
 

Methods:

We first examined the water quality of the four Rio Jaba tributaries nearest the botanical gardens by conducting biological, chemical and physical surveys on 31, July 1999.  Before rain surveys were done between 8:00 and 11:00 a.m. while after rain data was collected between ______________ and _______________ p.m.

Four sites were chosen along the ____________________trail.  Each tributary was surveyed within 50 feet from the trail crossings to minimize the affects of human traffic on biota.  Macroinvertebrate samples were taken from each area using basic kick net procedures.  At each site, pH was measured with pHydrion paper.  Temperature was measured in the area of greatest depth.  Maximum depth nearest the sampling area was measured using a measuring tape, and turbidity was determined using visual observations.  To measure basic water velocity, a vial cap was timed as it traveled approximately four meters downstream at each site.  Using conversions, these measurements were put into units of meters/second.  All tests, excluding the macroinvertebrate survey were repeated shortly after the afternoon rain.
 

Results:
 
After completing our research, we discovered that the botanical garden had no significant effect on tributaries of close proximity.  In testing water acidity, pH levels before rain were as follows: Quebrada Lutite = 8, Quebrada Wilson = 7.5, Quebrada Culebra = 7.5 and Quebrada Culvert = 7.5.  After it rained, pH levels were 8, 7.5, 8.5 and 8.5 respectively.  Temperature at sites 1,2 and 4 measured 68 degrees Fahrenheit both before and after rain.  Site #3 measured 70 degrees Fahrenheit at both times.
 
In measuring turbidity, we noted that water clarity remained clear both before and after rain.  However, as would be expected, depth at each site increased slightly after rain with the exception of site four.  The actual measurements can be seen in figure 1-1.  Rate of flow, as measured on general terms, did not vary significantly in measurements before and after rainfall (see fig. 1-2).

Macroinvertebrate inventory from each site revealed a general trend toward species that indicate moderate to poor water quality.  A listed inventory can be seen in figure 1-3.
 

Discussion:
 
In studying our results it was found that the pH levels of Quebrada Culvert and Quebrada Culebra illustrated the greatest change before and after the rain.  These tributaries are closest in proximity to the botanical gardens and the pH measurements could be and indicator of some runoff contamination.  However, more precise testing must be done before any conclusions can be met.

Looking at macroinvertebrate populations showed that, as expected, the greatest number of organisms were found to be in the slowest moving waters while the lesser number of organisms was found  in waters of greater velocity.  All tributaries had a number of organisms indicative of poor water quality. However, each tributary also exhibited small populations of more sensitive organisms.  This information may be slightly skewed due to small sampling sizes prescribed by the amount and type of equipment available.  A more extensive survey would lead to more accurate conclusions.
 
Temperature and turbidity measurements were relatively constant before and after rain.  This led us to believe that these indicators are not highly affected by runoff created by rainfall.  While our observations show little difference in temperature and turbidity, these factors should not be ignored in future studies.
 
After studying pH, temperature, rate of flow, turbidity and macroinvertebrate populations, our group has decided that further investigation is required before any conclusions can be made.  The original hypothesis held that the closer the tributary was in proximity to the garden, the greater the impact on water quality.  It was our observation that distance from the garden was not a true indicator based on several unknowns.  These unknowns include contamination of head waters, cross contamination outside of the reserve area, and/or direct runoff from the garden.  Further investigation into surrounding environmental practices may lead to a more complete picture of runoff characteristics.
 

References:

Fishmen, M.,E. Franklin and C. Siebert. 1995.  The Effect of Pollution and Runoff on Water Quality and Biotic Communities.  UCEAP Coto Brus, Costa Rica.

http://www.people.virginia.edu/~sos-iwla/Stream-Study/Key/MacroKeyIntro.HTML
 
 

Classroom Application

To incorporate this type of activity in the classroom would be relatively easy.  Students can use measurement, graphing, language arts, mathematical and modeling skills to complete a similar study on water quality within the general vicinity of their school.  If there were no natural waterways in the area, students could still follow an inquiry based lesson