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What
is the Quality of the Water in a River Bordering a Costa Rican Banana
Plantation?
Bob
Burch, Annmarie Merager, Pam Norton, Matt Hays, Sim Huang, Robert Simmons
Introduction: Costa Rica, with an area of 51,000 km2 , is Central
America’s second smallest country, with more than 100 major watersheds, most
having a moderately high water quality.
Producing about 20% of the world’s premium bananas, these fruits are
Costa Rica’s largest single export.
Banana production in Costa Rica is intensive and mono-cultural. It requires large amounts of land, vigorous
control over the amount of groundwater, shallow systems of canals and drainage
ditches, and high levels of agrochemicals.
Agrochemicals, including fungicides, fertilizers, insecticides, and
herbicides are applied 22 times on the ground during the growth cycle (9
months) and fungicides 45 times (per growth cycle) from airplanes. Of the applied amount, 15% is lost to wind,
40% to the soil, and 35% is washed off by the rain (Hernandez and Witter,
1996).
Environmental and social
concerns regarding banana production are significant and profound. They include: changes in soil use, deforestation, displacement of communities
in order to extend areas of cultivation, loss of tropical flora and fauna,
sedimentation and erosion, and contamination of the soil, atmosphere, ground
and surface waters. Costa Ricans
working in banana plantations have shown 10% higher instances of sterility and
damage to major organs, and the overall immune system, than people who did not
work in banana plantations (Hernandez & Witter, 1996).
Our study is concerned
with determining the quality of the water above and below a banana plantation
bordering the Rio Sarapiqui. Our
hypothesis is that the water below the plantation will show higher levels of
pollutants from agrochemical runoff.
Methods
and Materials: We used
the LaMotte Water Pollution Detection Outfit, Model AM-21 (LaMotte Company,
Chestertown, Maryland) to test for the presence of various ions. The kit employs two typical quantitative
chemical test methods: colorimetric comparison
with standards of known value or titration of the sample with solutions of
known value. The ions we tested for
using colorimetic comparison were chlorine, nitrate, iron, ammonia nitrogen,
phosphate, copper and pH. We used
titration to test for the presence of calcium, magnesium, total hardness,
chloride, and total dissolved solids.
Study
Area--- Figure 1
We collected water samples
at four sites along a banana plantation bordering the Rio Sarapiqui. (See Fig 1). The samples were collected in one liter, plastic bottles. The samples were gathered by placing the
bottle at least 10 centimeters below the surface. The samples were gathered after a long period of heavy rain. These heavy rains, near the banana plantation,
caused the rivers to swell 2 meters above normal. The additional rain increased the amount of water in the drainage
ditches as well. Both sites 1 and 2
(see Fig 1) were plantation drainage ditches.
Site 3 was a tributary of the Rio Sarapiqui, and site 4 was on the Rio
Sarapiqui (see Fig 1).
Data Table
The data table reflects
the results of testing the agrochemical composition of drainage ditches and
local rivers near a banana plantation.
According to the World Health Organization (WHO) ,water quality
standards, the water locations that were tested had significantly high iron,
copper, and phosphate. The other
agrochemicals in the test sites were within WHO standards.
|
|
Water
Quality Standards |
Site 1 Trial A |
Site 1 Trial B |
Site 1
Average |
Site 2
Trial A |
Site 2
Trial B |
Site 2
Average |
Site 3
Trial A |
Site 3
Trial B |
Site 3
Average |
Site 4
Trial A |
Site 4
Trial B |
Site 4
Average |
|
Ammonia |
|
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
Calcium |
200 |
16 |
16 |
16 |
8 |
8 |
8 |
12 |
|
12 |
8 |
|
8 |
|
Chloride |
250 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
|
Chlorine |
0.2 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Copper |
0.03 |
0.225 |
0.325 |
0.275 |
0.225 |
0.275 |
0.25 |
0.35 |
0.325 |
0.3375 |
0.325 |
0.31 |
0.3175 |
|
Hardness |
350 |
16 |
16 |
16 |
25 |
25 |
25 |
32 |
|
32 |
20 |
|
20 |
|
Iron |
0.3 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
2 |
0.5 |
0.5 |
0.5 |
|
Magnesium |
150 |
0 |
0 |
0 |
4 |
4 |
4 |
20 |
|
20 |
12 |
|
12 |
|
Nitrate |
10 |
1 |
|
1 |
0 |
|
0 |
1 |
|
1 |
0 |
|
0 |
|
pH |
7 |
7 |
7 |
7 |
6.5 |
6.5 |
6.5 |
6 |
6 |
6 |
7 |
7 |
7 |
|
Phosphate |
0.1 |
0.5 |
0.5 |
0.5 |
1 |
0.5 |
0.75 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Total Dissolved Solids |
500 |
95 |
110 |
102.5 |
120 |
110 |
115 |
85 |
80 |
82.5 |
80 |
70 |
75 |
|
|
|||
|
|
|||
|
|
Discussion: We investigated the water quality of rivers and drainage ditches in and around a banana plantation. Our primary focus was on how the water quality in the Rio Sarapiqui is impacted by banana plantations, primarily agrochemical pollution. We found that the levels of phosphates at sites 1 and 2 exceeded WHO standards (see Fig 2). Iron levels exceeded WHO standards at all 4 sites (see Fig 3). Possible explanations for high iron levels at sites 1, 2, and 3 may be soil leaching. Site 4 iron levels were ¼ of the other sites, possibly due to dilution factors in the larger river. Reasons for high phosphate levels at sites 1 and 2 could be due to drainage of chemicals from the banana plantation. Interestingly, sites 3 and 4 had zero levels of phosphates possibly due to dilution in the Rio Sarapiqui. The most alarming results were the test on the copper levels (Figure 4). The WHO standard for copper is .03 ppm. The copper levels at the sites ranged from .275 ppm to .337ppm. The high levels of copper could be the result of copper sulfide usage on the banana stems or residuals from past usage on the plantation. The usage of copper sulfate has been banned by the Costa Rican government. However, the high levels reflected in the sites tested, merit further investigation. The implementation of copper sulfide into banana production has been shown to cause sterility in the soil. All other ions tested within WHO standards at all sites (see Figs 2, 4, and 6-13).
The area had received 2 ¼ inches of rainfall during the prior 24 hour period. We recommend retesting the area during times of less rain. Another indicator of water quality may be the diversity and quantity of macroinvertebrates. Studies have suggested negative impacts on human and ecosystem health due to the presence of agrochemicals. Careful and frequent monitoring of water quality is suggested.
Classroom Applications: Water quality analysis is easily used in most science classrooms. It can be used 6-12 with commercial kits currently available and with a minimum amount of teacher knowledge or training. The LaMotte Water Pollution Outfit comes with a procedural guide as well as easy to read booklets on the basics of water quality testing.
Water quality testing is an excellent open-ended inquiry
based learning activity. The teacher
serves as a facilitator, guiding students toward relevant research and testing
procedures. It generally requires more
time to accomplish, however, the experiences do generally reflect the
scientific process.
The impact of agrochemicals will touch us all. The students of the new millennium must not be given the hands on experience of water testing without understanding the long-term process. The students should be allowed to study some communities close to them that have experienced a decrease in water quality due to agricultural advances.
References:
Hernandez and Witter (1996)
http://www/lead/org/lead/traininginternational/costarica/96/ch2.htm
LaMotte Water Pollution Detection Outfit, Model AM-21,
LaMotte Company, Chestertown, MD
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