Bill Simpkins Research
My research in hydrogeology is focused in five major areas:
- the hydrogeology and geochemistry of till and glacial sediments
- the hydrogeology and geochemistry of restored, multi-species riparian
buffers in agricultural watersheds;
- processes controlling nutrient transport via groundwater to lakes
in Iowa
- application of groundwater modeling to predict the hydrologic effects
of conservation practices in agricultural watersheds
- application of field investigations, groundwater dating, and groundwater
models to evaluate the water supply potential in alluvial and buried
channel aquifers in central Iowa.
Research Area 1
Our research group has completed a study on groundwater flow
and transport of three conservative tracers and fertilizer-derived nitrate
and atrazine (a common corn herbicide) in fractured till in Iowa. Former
Ph.D. student Martin Helmke, now teaching at West Chester University,
excavated large, 0.5-m-high by 0.45-m-diameter cores of till from deep
(4 m) pits for use in laboratory column tracer experiments. Breakthrough-curve
data were analyzed using 1-D (CXTFIT), 2-D (FRACTRAN), and 3-D stochastic
(FRACMAN-MAFIC) models. His results, published in 2004 and 2005 in the
Vadose Zone Journal (Paper),
Journal of Environmental Quality (Paper),
and Ground Water (Paper),
indicate that rapid transport of common agricultural chemicals and nutrients
is controlled by fractures in the till and that aquifers underlying
thin, fractured till are vulnerable to contamination. Martin's research
is also one of the first to provide a comparative analysis of these
models for fracture transport in till and to address the importance
of time scale in laboratory column experiments.
Research area 2
This involves investigating the effect of restored, multi-species riparian
zones on water quality (buffer
research and Dr.
Simpkins' work on buffers). The study site on Bear Creek in central
Iowa (about 20 minutes north of Ames) contains 88 piezometers, 72 tensiometers,
and 3 dataloggers that have allowed for investigation of nitrate transport
in groundwater through alluvial sediments of Holocene age. Research
by M.S. students Diane Johnston-Pals, Rob Andress (Paper),
and Tim Wineland, has shown most reaches are gaining and that denitrification
is the predominant mechanism of nitrate removal as water moves from
the field edge through the buffer and to the creek. Former graduate
student Colleen Fowle used an analytic element model to simulate groundwater
flow in the Bear Creek watershed and to identify optimal areas for riparian
restoration. A similar study is underway in northeastern Missouri by
graduate student Chu-lin Cheng. Former graduate student Cheng Cheng
used MODFLOW and MODPATH to simulate groundwater flow and advective
transport in buffers in 9 generic geologic settings. He found that residence
time in buffers is highly dependent on the geology, and that buffers
underlain by loamy material may have the best chance of removing nitrate
prior to the stream. M.S. student Jenny Abrahamson (B.A., Beloit College)
is using geophysics to further investigate the hydrogeology in the buffers.
Research Area 3
We are continuing our study of groundwater/lake interaction and nutrient
transport at Clear Lake (about 1.5 hours north of Ames). Using background
research published recently in Ground Water (Paper),
ISU senior Jonathon Carter (now at the University of Wisconsin-Madison),
along with Dr. Michael Thompson in Agronomy and Dr. Tim Parkin in the
National Soil Tilth Laboratory, investigated the origin of high phosphorus
(P) concentrations and transport of phosphorus in groundwater at Clear
Lake during the 2004-05. Jonathon found consistently high concentrations
of CH4 and H2S in association with high total P concentrations in groundwater
adjacent to the lake and speculated that the reducing conditions maintain
mobility of P. In cooperation with Dr. Jiasong Fang of our department,
we are analyzing the phospholipid fatty acid profiles and C isotopic
composition of groundwater to identify the bacterial communities. We
continue to monitor groundwater quality at Clear lake with the help
of David Knoll and the CLEAR project, with the goal of refining groundwater
and geochemical models to better understand P transport to and from
the lake.
Research Area 4
This project is new and came about through a grant from the USDA Conservation
Effects Assessment Program (CEAP
description). The overall project goal is to model the effects of
conservation practices in 3 watersheds in Iowa. The project is interdisciplinary
and is housed in the Center for Agricultural and Rural Development (CARD)
at ISU. M.S. student Lucie Macalister (B.S., Colorado School of Mines)
is comparing the water table and streamflow solutions generated by GFLOW
to those generated by the Soil Water Assessment Tool (SWAT) in 2 of
the 3 watersheds. SWAT is the de facto standard for modeling nonpoint
source pollution in watersheds and is used widely for making policy
decisions related to agriculture. As part of this effort, we cooperated
with the USGS District office in Iowa City in 2005 to install 24 nested
piezometers in the South Fork watershed - a till-dominated watershed
containing multiple moraines about one hour northeast of Ames. The piezometers
will be used for rigorous GFLOW model calibration prior to comparison
with SWAT output. Similar data from existing piezometers will be used
for modeling the Walnut Creek and Squaw Creek watersheds in Jasper County,
in cooperation with staff of the Iowa Geological Survey in Iowa City.
Research Area 5
In 2005, we entered into a funded agreement with the City of Ames to
re-evaluate the future potential of the Ames aquifer to supply water
to Ames and surrounding communities. This begins with an investigation
of the hydrogeology of a combined alluvial and buried channel aquifer
- the most common aquifer type in Iowa. The study includes an examination
of groundwater flow and nutrient transport to the lakes at Ada Hayden
Heritage Park, a 3-D MODFLOW simulation of the aquifer, groundwater
dating using 3H/3He, an assessment of the geochemistry of the aquifer,
and a MODFLOW optimization for pumping the aquifer (using MODOFC). New
M.S. student Evan Christianson (B.A., Gustavus Adolphus College) is
investigating groundwater flow, groundwater quality, and groundwater/lake
interaction at Ada Hayden Heritage Park - the backup water supply for
the city. This study should provide great insights into the water supply
potential of these systems and into the interaction of bedrock and alluvial
aquifers in Iowa.
