Introduction
The InVEST Nutrient Retention is a series of three models. The first, Water Yield, requires 6 “biophysical” raster datasets:
precipitation, potential evapotranspiration, soil depth, plant available water fraction, land use/land cover, and watersheds. In
addition, it requires a biophysical table that references each land use/land cover category and assigns the corresponding
evapotranspiration expected for that type of land cover, the root depth of any plant life that might be at that location, the amount
of nitrogen loaded to the environment by the land cover/land use type, and lastly the efficiency of the land cover to remove the
nutrient of choice. After gathering the data from the appropriate sources (see Figure 1), the model was able to produce a new
raster, water yield per cell. This is the amount of water available at each cell where nutrients of interest (NOI) can be loaded.
Source/Process
The first model, Water Yield, required various data points. All cells corresponding to water or urban in our land cover data were
assigned a soil depth of 0. The plant available water content (PAWC) values were loaded into ArcMap using the Soil Data Viewer.
Null data points were determined using neighborhood geospatial statistics. For root depth, each land cover was determined
based on most dominant species. For the Forest Land Cover, the U.S. Forestry service was referenced to determine the most
abundant species in the area (Oak, Pine, and Hickory.) The documented root depths for each genus were cumulatively averaged
to determine average root depth for Forest Land Cover. For Agriculture, the NC agricultural census provided the most dominant
crops in the Upper Neuse (Sweet potato, potato, soybean, corn, oat, barley, rye, tobacco, and wheat.) The root depths were
averaged and applied to the Agriculture Land Cover. For Wetlands, two dominant NC wetland species were used (Sweetgum and
Loblolly Pine). Nutrient loading values were obtained from the North Carolina DENR/DWQ WARMF Report and then divided by
the number of hectares provided in the Upper Neuse Watershed. ETK and EFF_N provided by WWF were used to determine
evapotranspiration and nitrogen removal efficiency by land cover.
The next model, Nutrient Retention, requires 4 raster datasets: digital elevation model (DEM), water yield per cell, land use/land
cover, a sub-watershed raster, and a watershed raster. In addition, two database files are needed: the Biophysical Table as
described above and a Water Purification Table. The Water Purification Table requires watersheds to be delineated, a calibration
unit based on validated reading at any point of interest, the cost of removing the NOI, the maximum allowable amount of NOI that
can be loaded to the watershed, the time span for the cost of removing the NOI (i.e. how long it will be at that cost), and a
discount rate used in net present value calculations. See Figure 1 for each value applied. The Nutrient Retention model produces
a raster dataset and a database file necessary for the final model, Valuation. The raster dataset reveals where the NOI is
immobilized. Where the NOI is immobilized is determined based on the relative elevation of the land cover, the NOI loading
values at higher elevations, and the efficiency of the land cover to absorb the NOI. These values were normalized by dividing all
cells by the largest possible cell value using Raster Calculator.
The last model, Valuation, requires 3 raster datasets and 2 database file. The raster datasets include the DEM, nutrient retained
(produced by the second model), and watershed raster file. The cost for the valuation model was adopted from the NC
DENR/DWQ WARMF Report. The report estimates a future Ecosystem Enhancement Program (EEF) nitrogen offset rate of
$44/lb of nitrogen. The rate was converted to $/kg of nitrogen. Based on proposed 2 stage Nutrient Strategy Rules from the NC
Environmental Management Commission, the cost value is applied through the completion of the first stage of action. A
standardized 5% discount rate was applied. Maximum annual allowable nitrogen loading for our single point of interest (Falls
Lake Dam) was determined from NCAC 15A Rule .0234 and .0279. Rule .0234 (6) (A) is aimed at those dischargers greater
than/equal to .05 MGD. It estimates that 15% of the annual discharge limit in section (6)(A) should be allowed through the dam.
15% of the Stage 1 annual discharge limit provided in proposed rule NCAC 15A .0279 (19,303 lbs/yr) was adopted as the
maximum annual allowable nitrogen loading value at our point of interest. This value was then converted from lbs/yr to kg/yr.
Figure 1: Data and Associated Citations.
Data Name
Maximum
Allowable
Nitrogen Loading
(Entire Upper
Neuse Watershed)
Nitrogen Loading
(At point of
interest – Falls
Dam)
Cost
Value
58,370.99
8,756.00
97.00
Unit
kg N/yr
kgN/yr
$/kg/yr
Citation
North Carolina Department of Environment and Natural Resources & Division of Water
Quality. (2010) 15A NCAC 2B .0279 (4)(a); Proposed Falls Water Supply Nutrient Strategy:
Wastewater Discharge. November, 2, 2010, Retrieved at:
http://portal.ncdenr.org/c/document_library/get_file?folderId=209700&name=DLFE19076.pdf.
North Carolina Department of Environment and Natural Resources & Division of Water
Quality. (2010) 15A NCAC 2B .0234 (6)(a); Neuse River Basin – Nutrient Sensitive Waters
Management Strategies: Wastewater Discharge Requirements. November, 4, 2010, Retrieved
at: http://h2o.enr.state.nc.us/nos/2b-0234.pdf.
North Carolina Department of Environment and Natural Resources. (2010) Fiscal Analysis for
Proposed Nutrient Strategy for Falls of Neuse Reservoir. November, 2, 2010, Retrieved at:
http://portal.ncdenr.org/c/document_library/get_file?uuid=2a29f5a4-3db1-4c63-bd63cad51a5ac385&groupId=38364.
Precipitation
(raster)
mm
Prism Climate Group. (2010). Oregon State University. October, 2010, Retrieved at:
http://www.prism.oregonstate.edu/.
Evapotranspiration
(raster)
mm
Food and Agriculture Organization of the United Nations (2010). October, 2010, Retrieved at:
http://www.fao.org/geonetwork/.
Where used in
Model
Water Purification
Table; Nutrient
Retention Model
Input
Water Purification
Table; Nutrient
Retention Model
Input
Water Purification
Table: Nutrient
Retention Model
Input
Precipitation;
Water Yield Input
Raster
Potential
Evapotranspiration
Person
who
found
data
CC
CC
CC
NW
NW
LULC
Watershed
(raster)
(raster)
n/a
???
n/a
NC OneMap. (2007). Local Watershed Plans –EEP. September, 2010. Retrieved at:
www.lib.unc.edu/reference/gis/datafinder/index.html
DEM
(raster)
n/a
Soil Depth
(raster)
Mm
Plant Available
Water Content
(raster)
%
Evapotranpiration
coefficient
(raster)
???
Soil Survey Staff, Natural Resources Conservation Service, United States Department of
Agriculture. Soil survey of Upper Neuse Watershed, North Carolina [Online WWW]. Available
URL: “http://soildatamart.nrcs.usda.gov/Survey.aspx?State=NC” [Accessed September 2010].
Soil Survey Staff, Natural Resources Conservation Service, United States Department of
Agriculture. Soil survey of Upper Neuse Watershed, North Carolina [Online WWW]. Available
URL: “http://soildatamart.nrcs.usda.gov/Survey.aspx?State=NC” [Accessed September 2010].
The Nature Conservancy. (2010). InVEST 1.005 Beta User’s Guide: Integrated Valuation of
Ecosystem Services and Tradeoffs. November, 2010, Retrieved at:
http://www.naturalcapitalproject.org/ConEX/InVEST_1.005beta_Users_Guide.pdf.
Mayaki, W.C. Teare, I.D., and Stone, L.R. (1976) Top and Root Growth of Irrigated and Nonirrigated Soybeans.Crop Science, Vol 16. January- February 1976.
Mou, P. Jones, R.H., Mitchell, R.J. (1995) Spatial Distribution of Above-Ground Biomass and
Soil Nutrients. Functional Ecology, Vol. 9, No. 4, pp. 689-699.
Root_depth
Multiple
values
mm
Evans, R., Cassel, D.K., and Sneed, R.E. Soil, Water, and Crop Characteristics Important to
Irrigation Scheduling. (1996) North Carolina Cooperative Extension Service. Publication
Number: AG 452-1. November, 6, 2010, Retrieved at:
http://www.bae.ncsu.edu/programs/extension/evans/ag452-1.html
Food and Agriculture Organization of the United Nations (2010). November, 2010, Retrieved
at: http://www.fao.org/nr/water/cropinfo_tobacco.html.
The Nature Conservancy. (2010). InVEST 1.005 Beta User’s Guide: Integrated Valuation of
Ecosystem Services and Tradeoffs. November, 2010, Retrieved at:
http://www.naturalcapitalproject.org/ConEX/InVEST_1.005beta_Users_Guide.pdf.
Palta, J.A., Mingtan, L.T., and Fillery, R.P. (2004). Rooting patterns in wheat differing in vigour
are related to the early uptake of nitrogen in deep sandy soils. Crop science. November, 8,
Water Yield Model
Input
Water Yield Model
Input, Nutrient
Retention Model
Input
Nutrient Retention
Model Input,
Valuation Data
Input
Water yield Model
Input
KB
Water yield model
input
NW/SDS
Water yield model
input
SDS
Biophyical Table
Value; Water Yield
Model Input,
Nutrient Retention
Model Input.
SDS
ML/SDS
KB
NW/SDS
2010, Retrieved at: http://www.cropscience.org.au/icsc2004/poster/2/4/1/473_paltaja.htm.
Nitrogen Loading
(load_n)
Nitrogen Removal
Efficiency
(eff_N)
Multiple
values
Multiple
values
North Carolina Department of Environment and Natural Resources & Division of Water
Quality. (2009). Falls Lake Watershed Analysis Risk Management Framework (WARMF)
Development Draft. November, 2, 2010, Retrieved at:
http://h2o.enr.state.nc.us/tmdl/documents/July09DraftFallsLakeWatershedModelReport.pdf.
Lin, J.P. (2004). Review of Published Export Coefficient and Event Mean Concentration (EMC)
Data. Retrieved at: http://el.erdc.usace.army.mil/elpubs/pdf/tnwrap04-3.pdf.
Biophyical Table
Value; Water Yield
Model Input,
Nutrient Retention
Model Input.
Biophyical Table
Value; Water Yield
Model Input,
Nutrient Retention
Model Input.
SDS
CC