Figure 1' The study area in

1
Estimating Critical Phosphorous Loading Areas in
Six Mile Creek Watershed Megan Molique, Art
Lembo, Stephen DeGloria
Introduction
Contributing Area/Dispersal Area Export
Coefficient Model (CADA-ECM)
N LN S (EiNTIiNBIi)Ai S W
P i1 Equation 2
In order to manage NPS pollution, areas likely to
produce NPS pollution runoff from a watersheds
critical loading areas must be identified to
determine the source of pollution potential. The
targeted critical area management approach
enables agencies to be more efficient in
determining areas that have the potential for
contributing to nonpoint source pollution
downstream. The Export Coefficient Model (ECM)
scoping model is useful to manage a watersheds
NPS pollution in foreseeing how land use will
effect water quality throughout a variety
watersheds. The ECM has been utilized by the
USEPA who has distributed it nationally as a NPS
tool. It is a simple model that requires land
cover data. The ECM is limited in that it
provides lumped basin loads and is not designed
to estimate spatial distributions of loading
intensity. Adding weighted export coefficient
values to the ECM scoping model spatially
distributes the pollution according to its
location within the watershed according to the
slope gradient and presence of a
buffer. (Endreny and Wood 2003)
Where, LN weighted basin nutrient load
(kg/yr), Ei export coefficient (kg/ha/yr)
for land class i, NTIi Normalized Topographic
Index NBIi Normalized Buffer Index Ai area
of the watershed in land class i S septic
systems W wastewater treatment plants P
precipitation (Endreny Wood, 2003)
  Equation 2 is the full CADA-ECM model equation
where the ECVs are weighted and therefore
spatially distributed by incorporating the
influence of the Topography and presence of
vegetated buffers as represented by the
Topographic Index (NTI) and Buffer Index (NBI),
respectively. The combined effect of the NTI and
NBI represents the CADA weighting function, and
can be used to map a watersheds hydrologically
sensitive areas, by modifying ECM predictions.
Figure 4. The output of the CADA-ECM weighted
model for Six Mile Creek Watershed showing darker
values as critical areas of phosphorous loading.
Figure 2. This is the land cover map for Six Mile
Creek watershed. Areas that are dark brown are
cropland which has one of the highest export
coefficient values.
Comparing the ECM model output to the CADA
Weighted ECM Model
Export Coefficient Values (ECVs) for Each Land
Cover Class
Objective
  The objective of this study is to use the
Contributing Area/Dispersal Area Export
Coefficient Model (CADA-ECM) to estimate critical
non-point source phosphorous loading areas in
Six Mile Creek watershed in Tompkins County,
NY.
Study Area

• Area 340 km2
• Feeds into Cayuga Lake
• Primarily forest land and agriculture
• NPS pollution assumed to come from agricultural
  and urban areas
• Forested land serves as exceptional buffers
• Development, agricultural runoff, erosion, and
  silt loading are all
• major threats to Cayuga Lake.

Figure 5. An upclose look at the comparison of
the ECM unweighted model output to the CADA
weighted model output. The CADA weighted model
takes topography and vegetated buffers into
consideration where the ECM alone does not.
Darker areas indicate a greater value of the
export coefficient indicating there is more nps
pollution present. The Six Mile Creek Watershed
Land Cover of the area of comparison is shown
here to show how forest land acts as good buffers
when they are located downslope from critical
areas where they can trap runoff. The total basin
load for Six Mile Creek Watershed is 28,802 kg/yr
as determined by the ECM, and 23,632 kg/yr as
determined by the CADA-ECM.
Source Endreny and Wood 2003 Table3. Export
Coefficients were assigned to each land cover
type based on values from the literature. Table
3 shows that Agriculture-Cropland has one of the
highest Export Coefficient Values at 9.80
kg/ha/yr, indicating that cropland has a high
potential to be one of the main contributing
factors for the source of Phosphorous runoff into
Six Mile Creek.
Results and Discussion
Export Coefficient Model (ECM)To estimate the
unweighted NPS pollution potential at the
watershed scale
The ECM alone assumes all areas with the same
land use have the same potential for exporting
phosphorus nonpoint source pollution. The ECM
including CADA considers the topography, presence
of vegetative buffers. Processing the CADA-ECM
for Six Mile Creek Watershed determined that
Agricultural lands without buffers have higher
load values, forested land does not have high
load values and are therefore good buffers if
they are located strategically in the watershed,
agriculture surrounded by forest land have a low
nutrient load value, and brush and grassland
dont trap nutrients as well as forestland.
Cayuga Lake
M LN S Ei Ai S W P
i1 Equation 1
Where, LN basin nutrient load (kg/yr), Ei
export coefficient (kg/ha/yr) for land class
i, Ai area of the watershed in land class i
S septic systems W wastewater
treatment plants P precipitation
(Endreny Wood, 2003)
Conclusions
Six Mile Creek Watershed
The CADA-ECM is beneficial in watershed
management because it can be used when the
availability of data is scarce and there is
limited information available to manage a
watershed, especially where a more complex model
may be utilized if data requirements are too
great.   This research on Six Mile Creek
Watershed demonstrates how CADA weighting can be
used to forecast spatial arrangements of
Phosphorous loading in a NPS scoping model. CADA
encompasses the theory of Phosphorous runoff
hydrology to assist watershed managers to locate
and further quantify significant areas with NPS
pollution. Adjustments to the ECVs can assist in
predicting how improvements to the watershed can
be made.   Further Study Despite the fact that
there was no validation data, the normalized maps
effectively stratify the watershed to serve as a
basis for social scientists to survey. Model
output will help guide a socio-economic survey of
watershed stakeholders to determine which areas
represent the greatest risk of nonpoint source
pollution. Social Scientists will survey land
owners to validate the critical areas and
evaluate their attitudes and behavior when they
are confronted about their involvement in the
mitigation of nps pollution.
Figure 1. The study area in Tompkins County, NY.
Methods
  Six Mile Creek Land Cover data was multiplied
by assigned export coefficient values for each
land cover type to calculate the
unweighted lumped basin nutrient load the ECM
portion of the model.
Figure 3. The basin nutrient load was solved for
the Maximum ECV load. Cropland is shown as being
a higher load than most other areas.
Six Mile Creek Watershed Land Cover
Data Source
References
Land Use Land Cover Data Tompkins
County http//owasco.co.tompkins.ny.us/gis/ DEM
USGS through CUGIR http//cugir.mannlib.cornell.e
du/browse_lis/drg_list.html Export Coefficient
Values modified from Endreny Wood JAWRA Feb
2003 HydrologyTompkins County http//owasco.co.t
ompkins.ny.us/gis/
  Reckhow, K. H., M. N. Beaulac, and J. R.
Simpson. 1980. Modeling Phosphorous Loading and
Lake Response Under Uncertainty A Manual and
Compilation of Export Coefficients.
EPA-440/5-8-011, U.S. Environmental Protection
Agency, Washington, D.C.   Endreny, T.A., and
E.F. Wood. 2003.Watershed Weighting of Export
Coefficients to Map Critical Phosphorous Loading
Areas. Journal of the American Water Resources
Association, 39(1) 165-181.   Heller, S., and G.
Potter. 1999. Tompkins County Land Use and Land
Cover Mapping Project Methodology Report
Version 3. Tompkins County Information Technology
Services, GIS Division.   Watershed and Clean
Water Grants Program. 2001. Six Mile Creek
Riparian Restoration Project. Northeastern Area
and the Northeastern Area Association of State
Foresters (December).
ECM Limitations The ECM is limited in that it
only provides lumped basin loads and is not
designed to estimate spatial distributions of
loading intensity (Endreny and Wood 2003).
Incorporating CADA to the ECM Adding weighted
export coefficient values to the ECM scoping
model spatially estimates pollution potential.
The model does so according to the location of
pollution potential within the watershed as the
pollution relates to the slope gradient and
presence of a vegetated buffer (Endreny and Wood
2003).
Acknowledgements
Table 1 shows that Six Mile Creek is dominated by
deciduous forests at 61 which will act as a
vegetated buffer against phosphorous runoff from
agriculture and urban areas if positioned
down-slope from high potential runoff areas.
The following individuals were supportive of this
study and their contributions are gratefully
acknowledged Theodore A. Endreny and Eric F. Wood
April 2004