RENUMA: A REGIONAL SCALE NUTRIENT LOADING MODEL FOR MANAGEMENT
1
Dennis P. Swaney *, Robert W. Howarth1 and Beth Boyer2
Basic Configuration
In uncertainty analysis, the
user selects which variables
Should be random in the
“stochastic worksheet”, and
specifies their probability
distribution and the desired
number of runs…random
values are generated…
1Cornell
University, Ithaca, NY USA
2SUNY College of Environmental Science and Forestry, Syracuse, NY USA
The pulldown menu
*(email: dps1@cornell.edu)
permits the user to
choose between
alternate simulation
or other options
Model outputs can be
viewed in the output
worksheets
Parameters can be
changed in the
parameter worksheets
(yellow)
ABSTRACT
We are developing ReNuMA, an event-based, regional watershed-scale nutrient loading model with biogeochemical
dynamics that is readily accessible to watershed and coastal zone managers. The model, written in Visual Basic,
uses Microsoft Excel as a platform. The spreadsheet format facilitates model dissemination to users, and
visualization of model output of simulations of water, N and P dynamics. The modeling package is based on
hydrologic dynamics of the GWLF model (Haith and Shoemaker, 1987), and quantifies solid-phase as well as
dissolved nutrient transport processes; when complete, the model will incorporate new biogeochemical dynamics,
including explicit consideration of atmospheric deposition, denitrification, and phosphorus saturation. Novel aspects
of the analysis include consideration of the effect of alternative land-use ‘trajectories’, i.e. categories of land use
change over the period of the simulation, rather than fixed ‘snapshots’ of landuse, and model parameter fitting using
the Excel solver feature. Maximum event loads, of particular significance to the coastal zone, can be estimated as
well as seasonal and annual loads.
The user next chooses the
type of simulation, and the
model is run repeatedly for
each random value of the
combination of parameters
selected…As this takes
some time, the current
iteration number is
displayed in a worksheet
along with a message that
the analysis is in progress…
Standard Simulation Mode – Simulating effects of hypothetical changes
in land use and climate change
ReNuMA is a VBA application which runs in MS Excel. It is structured as
a collection of worksheets, including parameter worksheets (yellow tabs),
output worksheets (blue tabs) and special function worksheets, which
include options for calibration and uncertainty analysis (red tabs).
User selects whether to fit streamflow, sediment or nutrient
data. Objective function is sum of squares of deviations
from monthly values.
Uncertainty/Sensitivity Analysis Mode
A standard mode of using the model
is to evaluate the response of a
watershed to hypothetical scenarios
of landuse or climate change…In this
case, an increase of 2 degrees C and
20% increase in precipitation over 10
years are considered, together with a
doubling of area of urban and
agricultural landuses…
Model Calibration Mode
When the simulation is
complete, the user can
observe the results in the
“uncertainty” worksheet, in
which the mean and
standard deviations of all
model variables are
reported for each year
simulated…
The calibration mode uses the
standard Excel addin package,
Solver, to determine best-fit values
of user-selected parameters to
user-specified monthly data.
User enters time series of data to
calibrate the model.
Current list of available
parameters to fit
Climatic change appeared to be more
important than landuse change to ET
and streamflow in this simulation…
…But both landuse
and climatic change
affected nitrogen
flux…
Ongoing work and future directions
Our work to date has focused on porting an established model to the Excel platform,
performing preliminary testing, and expanding its functionality to include some of the
features reported here, especially parameter estimation and uncertainty analysis. Our
current emphasis is to add representations of additional biogeochemical processes,
including:
•Atmospheric deposition
•landscape level denitrification
•in-stream denitrification
•Phosphorus losses from P-saturated soils
Solver iterates the selected parameters until
it finds the best solution,
then displays a message
And reports the best-fit value
•Nitrogen losses (DON+DIN) from forests
References
The predecessor of ReNuMa is the Generalized Watershed Loading Function Model (GWLF):
Haith, D. A., Shoemaker, L. L. 1987. Generalized watershed loading functions for stream flow nutrients. Water
Resources Bulletin 23(3):471478. A spreadsheet-based version of the model can be found on the web at:
http://cfe.cornell.edu/biogeo/USGSWRI.htm.
Other references cited in the poster:
Boyer, E.W., C. L. Goodale, N. A. Jaworski and R. W. Howarth. 2002. Anthropogenic nitrogen sources and relationships
to riverine nitrogen export in the northeastern U.S.A. Biogeochemistry 57/58:137-169.
Sheldon, J.E. and M. Alber. 2002. A Comparison of residence time calculations using simple compartment models of
the Altamaha River estuary, Georgia. Estuaries 25:1304-1317.
•Agricultural N-fixation
•More detailed treatment of management practices
Within the next year, we expect to test our representations of these processes against
datasets collected on watersheds in the NE United States (Boyer et al., 2002) and, with
colleagues at Stockholm University, in several major drainages of the Baltic Sea. We also
plan to add linkages to models of estuarine dynamics, including SqueezeBox (Sheldon and
Alber, 2002)
Acknowledgements
Software development has been funded in part by a USGS/NWRI project, “A Watershed-Scale Biogeochemical
Loading Model for Nitrogen and Phosphorus”, R.W. Howarth, P.I. Project # G-12. Development is currently continuing
with funding from an EPA STAR grant, “Developing regional-scale stressor models for managing eutrophication in
coastal marine ecosystems, including interactions of nutrients, sediments, land-use change, and climate variability
and change.”