Digital Object.pdf

Overview:

Urban
runoff is surface runoff of rainwater created by urbanization. Impervious
surfaces are constructed during land development. Rainwater generally doesn’t
have problems soaking into porous ground, like vegetation. However, impervious
surfaces like driveways, paved roads, sidewalks, and streets prevent the ground
from soaking in the water. When it rains, the water passes through the streets and
can carry with it dirt, bacteria, chemicals from pesticides and fertilizers,
highway runoff, and other potentially dangerous pollutants. This water gets
carried into a storm sewer system or dumps right into our watersheds. Although
nitrogen is found naturally in the environment, it is also introduced through
sewage and fertilizers. The overabundance of Nitrogen can cause a number of
adverse health and ecological effects. The object of this study is to see if
there is a relationship between the amount of vegetative coverage and the water
quality parameters of nitrogen and dissolved oxygen (DO) on Shoal Creek. The
results will show how nitrogen and DO levels in Shoal Creek are affected by the
amount of vegetative coverage that surrounds it.

Shoal
Creek is an area shared by runners, nature watchers, dog walkers, commuters,
and other Austin residents. Despite its importance to Austin’s community, Shoal
Creek has been identified as having elevated levels of bacteria and is no
longer deemed safe for contact recreation. 50 different locations along the
creek will be investigated and the explanatory variable levels of nitrogen and response
variable DO will be measured. Each location will be assessed for the
categorical explanatory variable of vegetative coverage (sparsely or densely
vegetative). Vegetative coverage is an indicator of human activity and pervious
cover, thus a negative correlation coefficient is expected between vegetative
coverage and nitrogen levels. Sparsely vegetative coverage will have higher nitrogen
content and lower DO levels, and densely vegetative coverage will have lower nitrogen
content and higher DO levels. DO levels are expected to decrease with
increasing levels of nitrogen, because nitrogen fluxes cause algal blooms
(hypoxia) and warm water surface runoff reduce DO content in stream water.

Nitrogen
and DO content will be measured using a YSI water quality meter. The meter is
sensitive to disturbances in the water samples, so the water will not be
disturbed before the location is tested. The distance in-between every sampling
location will be 366 meters, this is obtained by dividing the distance of Shoal
Creek (approximately 11.4 miles) by 50 different locations. This will ensure the individual locations are
representative of the entire creek, and eliminate potential bias in simply choosing
locations along the creek to test. At every
location a 15x3 meter area on both the right and left side of the creek will be
marked off with cones and the vegetative coverage (sparsely or densely
vegetative) in this area will be observed. All buildings, sidewalks, pavement,
concrete and walls will be considered impervious surfaces and will not be
considered vegetation. Areas less than 40% vegetation will be categorized as
sparsely vegetative and areas greater than 40% vegetation will be categorized
as densely vegetative. Because DO is also an indicator of temperature, data
will be collected on days that are very similar in temperature/weather patterns
to reduce the sampling error.

Objective:
The object of this study is to see if there is a relationship between the amount of vegetative cover and the water quality parameters of nitrogen and dissolved oxygen on Shoal Creek. The results will show how DO is affected by the nitrogen content and vegetative cover surrounding Shoal Creek.
Results:
While controlling for vegetative cover, nitrogen is a significant predictor of DO (p-value < alpha). For ever 1mg/L increase in nitrogen, DO will increase by 9.833 mg/L, on average. 
While controlling for nitrogen, vegetative cover is a significant predictor of DO (p-value < alpha). Sparsely vegetative cover will have a DO content of 7.6269 (mg/L) more, on average than densely vegetative cover. 
There is an interaction between the effects of vegetative cover and nitrogen content on the amount of DO found in the creek (p-value < alpha). This is confirmed by the interaction plot.