Geo-temporal estimation and visualization of nitrogen in a mixed-use watershed

sws03-01 ( .pdf )

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00001.txt

SWS-03-01


RSoil and Water Science

Reseaw rcih Bref



GEO-TEMPORAL ESTIMATION AND VISUALIZATION OF NITROGEN IN A
MIXED-USE WATERSHED

S. Grunwald and T.M. Shatar
Co-PIs:
N.B. Comerford, M.W. Clark, D.A. Graetz, R.B. Brown
Soil and Water Science Dept, University of Florida
Collaborators:
R. Srinivasan, Texas A & M
Suwannee River Water Management District (K. Webster)


Increasing nutrient concentrations have
recently been reported in groundwater,
spring water and drinking water wells in the
Suwannee River Basin. Unpolluted
groundwater is important for healthy natural
ecosystems in the Suwannee Basin since it
makes a significant contribution to lakes and
streams. It is also the source of drinking
water and most agricultural and industrial
water in the district.


Suwannee'
.:.,,l ,, n ,


. 1 i


I.


Dixie


Figure 1. The Santa Fe River Watershed (in green).

In particular, elevated nitrate-nitrogen
has been reported within the Santa Fe River
Watershed (part of the Suwannee River
Basin). Nitrate-nitrogen is the most common
groundwater contaminant and can be
harmful to humans. Major sources of nitrate-
nitrogen are believed to be human activities
such as agriculture and silviculture and
urban point sources. The surficial aquifer in
most of the watershed is unconfined or
semi-confined and is thus vulnerable to


soluble contaminants, such as nitrate-
nitrogen.
This brief outlines a recently initiated
project examining nitrate-nitrogen in the
Santa Fe River Watershed. The aim of this
work is to evaluate relationships between
topography, land use, management practices
and soil type and nitrate-nitrogen
concentrations in both soil and water. Soil
nitrate will be predicted at all locations
within the watershed, from soil samples
collected at sites representative of the major
different combinations of soil and land uses
(Potential Factor Combinations PFCs)
found in the basin. Geographic Information
System (GIS) data layers, such as those in
Figure 2, will be used to identify PFCs.
Much of this information is readily
available.
Sampling intensively throughout the
watershed would be an extremely time-
consuming and costly exercise. By using
newly-developed techniques which allow
prediction from data that is already
available, it is possible to save time and
money and still obtain a good representation
of nitrate-nitrogen concentrations over large
areas.
Prediction of soil nitrate will be
achieved using two methods: (1) measured
nitrate-nitrogen values will be transferred to
similar PCFs within the watershed and (2) at









Elevation (m)
0 0-16.7
S16.8 23.6
S 23.7- 30.1
m 30.2 36.9
m 37.0- 42.7
W 42.8- 47.7
m 47.8- 53.5
S53.6- 62.1
62.2 90.9


S _' ,-Data source: USGS National Elevation Dataset

'. .S .-- *J- 1 Land use 1995
Urban
Pa *- ,4 Cropland and pasture land
Streams, Reservoirs, Lakes
"'p ;" ,* r _, ..
S 1 Upland coniferous forest
.. m ,m', Upland hardwood forest
Tree plantations
"' Wetland hardwood forest
." 1 Wetland forest mixed
.: (reduced legend)
S. Santa Fe Watershed boundary
0 10 20 40 60 80 Data source: Suwannee River Water Management
Skm District; St Johns Water Management District

Figure 2. GIS data layers currently available include elevation (top) and land use (bottom).


other unsampled locations stochastic
simulation will be used to predict soil
nitrate-nitrogen concentrations.
Stochastic spatial simulation is a
geostatistical technique which predicts
possible data values at each unsampled
location. The technique uses collected data
to calculate the most likely nitrate-nitrogen
concentrations at unsampled locations.
A single prediction at each location
within the watershed is called a realization.
Multiple realizations will be generated to
provide a better representation of possible
nitrate-nitrogen concentrations within the
watershed than those derived from more
commonly used prediction techniques.
2D and 3D visualization tools will be
used to describe and display the spatial and
temporal distribution of nitrate-nitrogen at


all locations within the Santa Fe River
Watershed, to a depth of 240 cm.
We will be able to identify land uses and
management practices responsible for
elevated nitrogen in surrounding soil and
water. Analysis of interactions between
land use and management practices will
provide a better understanding of the
nitrogen dynamics within this watershed.
Ultimately, this work should help protect
human health and water resources within
and around the Santa Fe River Watershed at
minimal cost.
Authors:
Sabine Grunwald and Tamara Shatar
Soil and Water Science Dept, University of Florida,
2169 McCarty Hall, PO Box 110290,
Gainesville, FL 32611.
SGrunwald@imail.ifas.ufl.edu
http://santafemodvis.ifas.ufl.edu