Presentation by Dr. Wendy Graham,
Director of the University of Florida Water Institute
UF Student Chapter AWRA Meeting, November
12, 2014
We were delighted to host the Director of the University
of Florida Water Institute, Dr. Wendy Graham, at our third monthly meeting of
the fall semester. Earlier this semester, we hosted author and journalist
Cynthia Barnett and water resource manager Kevin Morris of the Peace River
Manasota Regional Water Supply for our September and October meetings,
respectively. Dr. Graham joined us for our November meeting to tell us about
her work on water modeling in the nearby Santa Fe River Basin and share her
extensive knowledge of local hydrology and current springs research.
The Santa Fe River basin is an “interesting and
vulnerable place to study” according to Graham. The upper basin is confined
while the lower basin is unconfined, so they are governed by different
hydrologic processes. This allows researchers to compare how water and nutrient
transport processes differ in the two regions.
 |
| Study area in the Santa Fe River Basin. The upper basin is confined (green area) while the lower basin is unconfined (orange). For a more in-depth description of confined vs unconfined, see this USGS site. |
Graham’s research, as well as that of the UF Water
Institute, focuses on incorporating humans into the equation. “We can draw
springsheds on a map, but they’re dynamic systems,” she said, and adding humans
to the complex array of causes and solutions to Florida’s water issues is tricky.
For example, the proposed minimum flows and levels (MFLs) are being challenged
by environmentalists on one side and utilities on the other. Water managers are
walking a fine line as fingers are pointed in many different directions, from placing
blame for water woes on agriculture and climate to watering lawns in
Jacksonville and users in southern Georgia.
Numeric nutrient criteria for springs is 0.35 mg/L, and
according to Graham, few springs currently meet this requirement. She and her
team are trying to better understand the hydrologic, ecologic, and economic
tradeoffs required to meet these numeric nitrate requirements. Their specific
goals are to “improve predictive understanding of hydrologic flow paths and
travel times; nutrient sources, transport and transformation; and karst
evolution within an eogenic karst basin.” Basically, they’re trying to better
understand how water and nutrients move within our watersheds.
The source of nitrate in the Santa Fe Springs and river
is predominantly from groundwater, and isotope signatures indicate that most of
this nitrate is from synthetic fertilizers. Nitrate concentrations in the Santa
Fe River depend on several factors, one of which is flow. In the unconfined
portion of the basin, the lower the flow rate, the higher the nitrate
concentration. In this unconfined region, there is also a high correlation
between nitrate and specific conductivity (which depends on the amount of
dissolved solids in the water). She said this is helpful because nitrate
sensors are over $20,000, whereas measuring specific conductivity is much
cheaper and can be done with a less expensive instrument. Researchers use
specific conductivity measurements taken in the river to separate contributions
of groundwater and surface water and to test model predictions.
The hydrologic model they are working on uses climate
data, along with information regarding land cover, soils, and geology to
predict evapotranspiration (ET), stream flow, groundwater elevation, temporal
dynamics of surface/groundwater interactions, and surface/groundwater travel
time distributions in the Santa Fe River. It can predict these variables on
different timescales, i.e. for a specific event (i.e. hurricane or rain event),
for an entire season, or over decades.
The researchers are trying to use the model to evaluate
their current understanding of how the system works and gain a more
comprehensive understanding of the impacts of future water, land use, and
climate scenarios.
The current model does a good job predicting stream flow
characteristics in the confined region, but the model has some problems in the
unconfined region, which she and other researchers are working to address. While
the predictions of the timing of stream flow are good, the rate of recession of
streamflow after storm events is too fast in the unconfined region. Using
specific conductivity data, they determined that the “missing” flow is from
groundwater, especially after wet periods.
To understand where the streamflow originates, they use
“particle tracking.” This means that they release 100,000 particles into the
river (via the model) and run the model backwards, which basically tracks the
particles until they leave the system.
Researchers use this “particle tracking” to estimate the
age of the water (i.e. how long it takes individual particles of water to exit
the system into the atmosphere when the model is run backwards) and figure out
which areas to target in order to most efficiently reduce loading of nitrates
into the aquifer. According to Graham, areas near conduit regions have been
identified by the model as high priority areas.
The model predicts that the age of water in the
unconfined part of the Santa Fe River ranges from less than one month to more
than 500 years, with a median age of 17 years. This median age matches well
with spring flow age measurements made by Dr. Brian Katz (Florida Department of
Environmental Protection).
But what does this mean in terms of management? “People
have to understand how long it may take to reduce nitrate concentrations in
springs,” Graham said, “it could be decades.” Seeing and making these changes
will require “patience and believing in the restoration program until we can
see the benefits,” according to Graham. And meeting the nitrate limits is not
going to be easy: “it will require large-scale changes in how we use land and
water,” she said.
After Graham’s presentation, curious students followed
up with many questions. From the discussion after her talk, it became clear
that a more comprehensive understanding of springs ecology, as well as other
factors, will also play large roles in solving Florida’s springs and water
issues - it’s going to require a truly interdisciplinary effort to come up with
solutions for our springs. The next question is whether or not we’re up for it.
