Back to the Classroom
1 Bibiliography Appendix
Smith Terry High School, Terry, MS
Gordon Applied Learning Academy, Fort Worth, TX
|July 28, 2001
|Introduction: There is degradation of water quality associated with habitat destruction and
increasing human development. This degradation may be manifested in increased levels of
nitrates, nitrites, phosphates, metals such as copper, or sediment levels due to
fertilizer and/or pesticide use, irrigation, and changes in land use. (LaMotte 1999). An
increase in temperature or changes in pH in an area are also indicators of pollution,
particularly in association with changes in presence or abundance of indicator organisms
(Cook,1999). In addition many of mans activities increase the turbidity of the
water. Rice field irrigation, flooding, and application of fertilizers and pesticides
create an artificial wetland with a chemical soup (Allen, 1999). Rice farmers cultivate
their fields by replacing the back wheels of their tractors with large angle iron paddle
wheels, effectively crushing vegetation into the mud (McCoy, 1994). Changes would be
expected in water chemistry parameters as well as loss of biodiversity of organisms at
every level, including microorganisms.
Cattle grazing was eliminated in the fresh water marsh at Palo Verde
in 1980 when it became a wildlife refuge. Almost immediately cattail (Typha dominguensis)
invaded and covered the marsh, eliminating much of the habitat for the sixty plus species
of resident and migratory waterfowl, which used the marsh (McCoy, 1994). Since 1987,
limited grazing of cattle combined with burning, digging, and crushing of cattails has
been instituted in an attempt to restore the marsh. There are now more open areas in the
marsh populated by floating vegetation. Small areas were fenced to exclude cattle to
provide control areas in the marsh. In addition 10-meter square plots of cattails were
left standing in the cattle areas to provide biodiversity, edge effect, and to protect the
delicate sedges, which dont recover after crushing.
We theorized that there would be differences in water chemistry and
species richness of microorganisms (mainly protists and algae) between cultivated rice
fields, cattail marshes, and marsh areas with mainly floating vegetation, even though each
environment is a product of mans activities.
Since each of these sites has been subjected to environmental degradation, evidence of
compromised water quality should be evident. (lower pH, higher temperature, higher
conductivity, presence of nitrates, and lower dissolved oxygen). Rice fields, because they
are cultivated and subjected to chemical treatment, were expected to be worse than the
marsh areas. In addition, the monoculture of the rice field was expected to depress
biodiversity. T. dominguensis areas of the marsh, because of its quality of invasiveness
(quick growing, prolific, etc.) should be more productive and show higher dissolved oxygen
values (Windham, 1996). Cattle exclusionary areas should show some improvement in
dissolved oxygen values compared to cattle grazing areas.
CBL with probes for DO, Temperature, & Conductivity
Collecting vials Nitrate test strips
PH test strips
- Sites for testing were determined.
thumbnail to see enlarged image
||a. Cultivated Rice Field
4 replicate samples were taken at each site
||b. Drainage Ditch next to
rice field 4 replicate samples were taken at each site.
||c. Cattle grazing area
dominated by cattails (Typha dominguensis)
||d. Cattle grazing area dominated by water
lilies (Nymphaea spp.)
||e. Cattle exclusionary area dominated by
cattails (T. dominguensis)
||f. Cattle exclusionary area dominated by water
lilies (Nymphaea spp.)
Results: Air temperature (Figure 1) was measured in order to calculate % saturation of
dissolved oxygen. No difference between water temperature and air temperature were found.
Water depth and water temperature were not significantly different from site to site. (see
figure 2 & Figure 3).
pH was consistently 7.5 in the rice field and environs, which is within the normal range.
In the marsh, a pH of 9 was consistent across all sites, indicating very basic (alkaline)
water conditions (see figure 4) Nitrates and Nitrites
values were negligible (see Data Table Appendix A). Dissolved Oxygen values showed
differences between the rice plantations & marsh sites, above normal values of oxygen
saturation in the rice plantation and very low values for all marsh areas (see figure 5). Conductivity values were within normal range
(250mg/l for lakes and streams) at the rice plantation and very high for the marsh areas (see figure 6). A microorganism species richness was
greater in the marsh, as were their relative numbers (See Table 1).
- CBL equipment including Dissolved Oxygen (DO), conductivity, and
temperature probes were collected and calibrated.
- Researchers traveled to rice field site and to the marsh for data
- CBL probes for DO, conductivity, and temperature were used as well as pH
and nitrate/nitrite dip sticks.
- Researchers collected water samples for later investigation at the lab.
- Observational data were recorded.
- Researchers examined samples with a microscope for protists and algae.
- Data recorded and analyzed.
quality values in the rice fields and environs were different from the marsh areas in
terms of pH, dissolved oxygen values and total dissolved solids TDS (conductivity). Yet,
the rice field values are more inline to the accepted normal values for U.S. streambeds
(LaMotte, 1999). The marsh pH was very high (out of range) for many fresh water organisms
to live in. The accepted pH range should be between 6.5-8.2 (LaMotte, 1999). The
conductivity was very high due to the mixture of the salty Tempisque Rivers tide. In
irrigation crops total values of dissolved solids lie between 175-500. A reading above
1500 is considered to be high (LaMotte, 1999) the marshes dissolved oxygen values were
extremely low, even though the marsh vegetation was photosynthesizing. Minimum oxygen
levels for fish and frogs are considered to be greater than 5 ppm DO. In fact, we did not
see any minnows or frogs in the marsh water, as we did in the irrigation ditch. In the
marsh the DO was low which was probably influenced by the rotting vegetation or the
floating animal fecal material, which uses oxygen in the decomposition process. However,
there was no foul odor in the water. Only one of the rice sites had a nitrogen reading
while the other tested areas had a zero value for nitrate/ nitrite values. We expected
this value to be high in the rice fields and run of ditch because of fertilizer
application and high in the marsh because of cattle waste defecation. Due to the fact that
the rice had already been harvested , may explain why the nitrogen levels were lower than
expected. Nitrogen fertilizers are added at the beginning of the growing season or in
pulses throughout. Expected differences between cattail areas (T. dominguensis) and
floating aquatic vegetation (Nymphaea spp.) were not evident, which may reflect
sampling size or the overwhelming oxygen demand of decomposition. Biodiversity in the
marsh areas as measured by species richness and relative numbers in microorganisms was
greater than the rice fields. However, macro organism indicators were not studied. Besides
the lack of fish and frogs, a far greater number of waterfowl, many which eat the macro
invertebrates, were observed at the rice plantation. High diversity could have been
influenced by the nitrites presence in the water. Overall the rice plantation is a managed
enterprise seen in this limited sampling to be a healthier environment for aquatic
organisms rather than the marsh area.
|Figure1: Air Temperature
||Figure 2: Water Temperature
||Figure 3: Water Depth
|Figure 4: average pH
||Figure 5: %Oxygen Saturation
||Figure 6: Conductivity