Acknowledgements

1
LATITUDINAL AND TEMPORAL CHANGES IN DISCHARGE AND
NITROGEN FLUXES FROM LARGE WATERSHEDS IN THE
NORTHEASTERN UNITED STATES AN APPLICATION OF
RENUMA
D. P. Swaney1, R. W. Howarth1 , A. E.. Galford1,
R.M. Marino1,and E.W. Boyer2 1Cornell
University, Ithaca, NY USA, 2University of
California at Berkeley, Berkeley, CA USA
ReNuMa Hydrological Dynamics
 ABSTRACT Nitrogen load to the coastal zone
drives estuarine ecosystem dynamics, and, in
cases of extreme loading, can result in ecosystem
catastrophes like the anoxic zone in the
Mississippi plume. Riverine nitrogen fluxes
depend on interactions between input loading
rates within the watershed, climate, and
landscape processes. Direct relationships between
average Net Anthropogenic Nitrogen Inputs (NANI)
and riverine fluxes have been shown with a
relatively simple nitrogen accounting methodology
for 16 large watersheds in the northeastern US
(Boyer et al., 2002). More recently, statistical
models have shown that the average response of
these watersheds per unit nitrogen load is
strongly related to precipitation or hydrology
(Howarth et al., in press). To examine the
temporal response of these systems in response to
climate and land use change, we are developing a
simple Regional Nutrient Management model
(ReNuMa) based on watershed-scale water balances
and statistical relationships between N loads and
responses. For the 6-year period examined so far,
interannual discharge is well predicted over a
range of watersheds. Nitrogen fluxes vary
latitudinally across watersheds in response to
the balance of anthropogenic sources, including
atmospheric deposition and fertilizer use.
Daily Temperature
Daily Precipitation
Snowpack
Evapotranspiration
Snowmelt
Urban
Annual DIN flux in 16 large Northeastern US
watersheds
Streamflow
Shallow flow/runoff
SCS runoff equation for each cover type
Unsaturated zone
Baseflow
Saturated zone
Human waste contributes N through sewers and
septic system effluent. N deposition traverses
lakes and wetlands without retention, but
exhibits a threshold landscape response in
forests. Agricultural N sources (fertilizer,
manure and fixation) also exhibit a threshold
response due to retention (ie landscape
denitrification, etc). The proportions of
in-river denitrification are based on estimates
in Van Breemen et al., 2002)
(1st order linear reservoir)
Annual streamflow in 16 large Northeastern US
watersheds
16 watersheds in the Northeastern USA in which
Net Anthropogenic Nitrogen Inputs (NANI) have
been related to average riverine N fluxes
over the period 1988-93 (Boyer et al., 2002).
We are extending the analysis to
simulate seasonal and annual streamflow
and nitrogen fluxes using the ReNuMa model.
Examples of threshold responses in agricultural
and forest systems in the literature. Left
response of NO3 to fertilizer loads in
agricultural leachate (Billen Garnier, 2000)
Right response of NO3 to N deposition in
forest leachate (Aber, et al., 2003). We use a
similar parameterization to estimate landscape
response from these land cover types.
The 2928 weather stations in the National Climate
Data Center network for Northeastern states were
identified (http//www.ncdc.noaa.gov/oa/ncdc.html)
To select candidate stations for each
watershed, Thiessen polygons for the network were
generated using ArcView 3.2. Stations with
polygons intersecting a watershed and with gt95
complete records (daily temperature and
precipitation) were averaged to obtain
representative weather data for each watershed.
Missing temperature data for each station were
replaced with averages of the records preceding
and following the missing interval missing
precipitation values were replaced with zero.
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)471-478. A spreadsheet-based version of
the model can be found on the web at
http//cfe.cornell.edu/biogeo/USGSWRI.htm.
Other references
Aber, J. D., C. L. Goodale, S. V. Ollinger, M.-L.
Smith, A. H. Magill, M. E. Martin, R. A. Hallett,
and J. L. Stoddard. 2003. Is Nitrogen Deposition
Altering the Nitrogen Status of Northeastern
Forests? Bioscience 54(4)375-389. Billen, G.
and J. Garnier. 2000. Nitrogen transfers through
the Seine drainage network a budget based on the
application of the Riverstrahler model.
Hydrobiologia. 410 139150. 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 57/58137-169.
Howarth, R.W., D.P. Swaney, E.W. Boyer, R.M.
Marino, N. Jaworski and C.L. Goodale. The
influence of climate on average nitrogen export
from large watersheds in the Northeastern United
States. Accepted for publication in
Biogeochemistry. Mayer, B., E.W. Boyer, C.L.
Goodale, N.A. Jaworski, N. Van Breemen, R.W.
Howarth, S.P. Seitzinger, G. Billen K. Lajtha,
K.J. Nadelhoffer, D. Van Dam, L.J. Hetling, M.
Nosal, and K. Paustian,. 2002. Sources of
nitrate in rivers draining sixteen watersheds in
the northeastern U.S. Isotopic constraints.
Biogeochemistry 57/58 171197. Van Breemen, N.,
E.W. Boyer, C.L. Goodale, N.A. Jaworski, K.
Paustian, S.P. Seitzinger, K. Lajtha, B. Mayer,
D. Van Dam, R.W. Howarth, K.J. Nadelhoffer, M.
Eve, and G. Billen. 2002. Where did all the
nitrogen go? Fate of nitrogen inputs to large
watersheds in the northeastern U.S.A.
Biogeochemistry 57/58 267293.
Ongoing work and future directions

• Our work to date has focused on developing
  parameterizations of biogeochemical responses
  related to landuse/landcover
• Atmospheric deposition
• Landscape level N retention of agricultural N
  sources (fertilizer, manure, N-fixation)
• Nitrogen retention and losses (DIN) from forests
• In-stream and landscape denitrification
• We are currently working on refining the model
  parameters for individual watersheds to reduce
  bias at this scale, as well as developing
  alternative parameterizations of processes which
  incorporate results from smaller-scale models.
  Additional processes to be considered will
  include
• Processing and transport of total N in addition
  to dissolved N
• Phosphorus losses from P-saturated soils
• Soil erosion and sediment transport

Minor adjustments to evaporative cover factor for
the Androscoggin and Susquehanna rivers were the
only changes made to baseline parameter values
for the watersheds. While individual watersheds
may exhibit some bias above or below observations
(ie USGS annual streamflows http//waterdata.usgs.
gov/nwis/ ), agreement over all years and across
all watersheds was generally good.
Acknowledgements This work has been supported by
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, EPA Grant Number
R830882, R.W. Howarth, P.I. For more
information, email dps1_at_cornell.edu