Geoscience Reference
In-Depth Information
to apply GWR in this area, and this study can become a valuable pilot study for
spreading GWR techniques to water resources research.
9.3 Data Sources and Methods
9.3.1 Water Quality Indicators
Water quality data during the period of 1990-2005 were extracted on-line
from the USGS National Water Information System Web (NWISWeb; URL
http://waterdata.usgs.gov/nwis
/). The NWISWeb is a very important and widely
used public water quality and streamflow data source for research, education, and
administration in the US. It contains water quality data collected by various projects.
The accuracy of the water quality data provided to the public is insured by the
USGS. Based on data availability, 129 water quality sampling sites were selected,
excluding the sites with part of upstream drainage area extending outside of the
study area (Fig.
9.1
). The mean values of 14 water quality parameters during the
period of 1990-2005 were calculated. The water quality parameters are specific
conductance (SC), dissolved solid (residue on evaporation, DS), calcium (Ca), mag-
nesium (Mg), sodium (Na), potassium (K), chloride (Cl), sulfate (SO
4
), ammonia
nitrogen (NH
3
-N), nitrite nitrogen (NO
2
-N), ammonia plus organic nitrogen (also
known as kjeldahl nitrogen, KN), nitrate plus nitrite nitrogen (NO
3
-N + NO
2
-N),
phosphorus (P), and orthophosphate phosphorus (PO
4
-P). SC is a measure of the
ability of water to conduct electrical current and reflects the concentrations of dis-
solved ions or solids in water. Dissolved ions, solid, and nutrients are the pollutants
that affect aquatic ecosystem and can be contributed by human activities associ-
ated with urbanization. Anthropogenic sources of dissolved ions and solid include
runoff from roads treated by deicers, discharges of residential, municipal, and indus-
trial sewage, and mining. High concentrations of dissolved ions and solid are toxic
to freshwater organisms and cause death of aquatic life. Dissolved nutrients might
come from fertilizer and pesticide use in urban and residential lawns, dumping of
raw and treated sewage and industrial discharges, and phosphate detergents. High
concentrations of dissolved nutrients can cause algal blooms, death of fish, and
reduction of diversity and growth of aquatic life (Enger and Smith
2010
). Therefore,
all the above water quality parameters are good indicators to assess water quality
degradation affected by urbanization.
9.3.2 Urbanization Indicators
Percentage of developed land (PDLU) and population density (PD) were used
as urbanization indicators. Developed land consists of residential, commercial,
industrial, transportation, and recreational lands. The land use data for 1999 and
population data by census block for 2000 were obtained from the website of the
