Water quality, geomorphology, and aquatic life assessments for the Olentangy River TMDL evaluation
In the second chapter a customized version of the Soil and Water Assessment
Tool (SWAT) model was used to predict hydrology and water chemistry constituent fate
and transport for the Olentangy River watershed for the time period 1985-2002. The
customized version of SWAT simulates a restrictive layer of material in the soil profile
and its impact of subsurface drainage, watershed hydrology, and nutrient and sediment
transport. Model parameterization and calibration are presented. Predictions of stream
discharge were evaluated at three locations with stream discharge records, however only
one location (USGS gage at Claridon, Ohio) was not impacted by Delaware Dam which
controls discharge. Regression results for annual and monthly observed and predicted
discharge at the Claridon gage provided coefficient of determination values of 0.84 and
0.81, respectively. A similar analysis of annual and monthly discharges with the Nash-
Sutcliffe statistic provided coefficient of efficiency values of 0.81 and 0.77, respectively.
SWAT predictions for water chemistry constituents for the Olentangy River at Claridon
and Worthington, Ohio ranged from 0.32-0.37 mg/l, 3.6-3.8 mg/l, and 114-172 mg/l for
total phosphorus, nitrate-nitrogen, and total suspended sediment, respectively. Measured
water quality from two studies conducted on the Olentangy and Scioto Rivers provided
ranges of 0.23-0.49 mg/l, 3.4-4.4 mg/l, and 47-170 mg/l for total phosphorus, nitratenitrogen,
and total suspended sediment, respectively. Following calibration of the model
all land use in the watershed was changed to forest, prairie, or wetlands to predict the
potential water quality of pre-European conditions in the watershed. The results show
that delivery of sediment, total phosphorus, and nitrate-nitrogen to the stream system has
increased by factors of approximately 50, 20, and 3, respectively, for most subwatersheds
in the Olentangy River watershed.
In chapter 3 the calibrated SWAT model was used to predict the potential water
quality benefits of alternative management scenarios and conservation practices in the
Olentangy River watershed. Alternative management scenarios and conservation
practices that were evaluated include: 1) alternative crop rotations, 2) alternative fertilizer
application rates, 3) alternative types of tillage, 4) timing of tillage operations, and 5)
buffer strips of various widths. A 33-meter buffer strip was predicted to provide the
largest water quality benefits when compared to other alternative management scenarios.
Inclusion of winter wheat into corn-soybean crop rotations also provided significant
water quality benefits.
Another study was conducted to develop a geomorphology assessment index to
evaluate dynamic equilibrium at study sites in the Olentangy River watershed. Regional
curves were developed using geomorphology data from study sites impacted by a variety
of disturbances. The geomorphology assessment index was developed to provide a
logical and minimally biased framework to assess dynamic equilibrium at study sites in
the Olentangy River watershed. A diagnostic approach that integrated multiple lines of
evidence was used to develop the index. Thirty-six sites in the watershed were assessed
with the geomorphology index. The geomorphology index indicated that many streams
in the watershed are incised and further land use change could pose significant threat to
the geomorphology of the stream system.
In chapter 5 a statistical analysis was conducted to examine the relationships
between stream biology and environmental variables such as water quality, habitat, and
geomorphology. The spatial location of a study site within the drainage network and its
impact on the structure of the biological community was also evaluated. Correlation
analyses were performed to develop a parsimonious set of explanatory variables.
Regression analysis was used to confirm the significance of the reduced dataset.
Canonical correspondence analysis (CCA) was used to elucidate relationships between
biology and environmental variability. Partial CCA techniques were used to partition
variation among the groups of environmental variables.
Results of the correlation analysis identified nine significant environmental
variables. The significance of those variables was confirmed with regression analysis.
The CCA identified stream gradient, pool quality, stream order, and width to depth ratio
as the most important environmental variables that explained the structure of biological
communities. Environmental variables were grouped into three categories including
geomorphology variables, habitat variables, and spatial location variables. The partial
CCA technique was used to partition variation between each of the variable groups.
Respectively, 37%, 19%, and 24% of the variation was attributed to geomorphology
variables, spatial location variables, and habitat variables. The remaining variation was
not explained by the measured variables.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:water quality geomorphology watershed management olentangy river ohio
Date of Publication: