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Our study was located in a part of one Reserve, but saltwater intrusion into agricultural fields occurs in several low-lying coastal counties of eastern North Carolina.
Farmers have been observing a phenomenon where patches of their agricultural fields
display stressed/unhealthy crops, or in extreme cases, where patches of bare ground
take over vegetated swaths of cropland. The phenomenon has been observed on farms
with corn, soybeans, wheat and other cash crops. Tests of the soils in these farmlands
have indicated that the soils have high concentrations of salts that inhibit the healthy
growth of plants. The burning questions on the farmers’ minds are where are these
salts coming from, will the problem become bigger with time, and what can be done
to solve this problem? These are important considerations because the answers to
these questions will help us determine the future impact of saltwater intrusion on
farmers’ livelihoods.
Working in collaboration with farmers, and state and county agricultural agents,
my research team has deployed different types of instruments in several fields to try
and provide answers to the farmers’ questions. Our suite of instruments is focused on
recording the weather, water quality, and quantity. Thus, we have deployed a weather
station to record air temperature, precipitation, wind direction, and wind speed at each
field site. We have installed clusters of shallow groundwater monitoring wells to help
us measure and record water levels and salinity in the groundwater system. And we
are using automated water level and salinity loggers to record water quantity and quality measurements every 10 min. We have also deployed water level and salinity loggers to record water levels and salinity in creeks, canals and the Albemarle Sound.
In addition to recording water quality and quantity in groundwater/surface water,
we are monitoring soil moisture content, soil temperature and soil conductivity to
investigate processes that may lead to soil salinization. We have also applied noninvasive techniques to image the subsurface through the use of geophysical techniques on impacted field sites. The geophysical techniques, that include direct
current electrical resistivity, capacitively coupled resistivity, and ground penetrating
radar, are useful for characterizing subsurface features and properties, as well as
delineating the extent of saltwater plume in the subsurface. It is envisioned that the
use of these techniques will help to show where the saltwater is coming from and
how it is moving from the surface to the subsurface.
It is likely that a combination of several of the possible processes that I described
earlier are responsible for aquifer and soil salinization in eastern North Carolina.
Perhaps the combination varies from place to place. Further, since some processes
may have a larger influence than others, any adaptation or mitigation strategies that
may be devised would have to align with the major driver of saltwater intrusion. For
example, if the major driver is intermittent overwash and storm surge, then applying
gypsum to agricultural fields followed by flooding with freshwater could lessen the
magnitude and extent of aquifer/soil salinization. However, this process is expensive and may be impracticable if a source of freshwater is unavailable. If, however,
the major driver is sea-level rise, then farmers may have to abandon their fields, or
they may have to plant other crops that are more tolerant to salty soils. Our continuing project will help farmers understand the environmental changes occurring in the
region so that they can better plan for their futures.
A. K. Manda
Our study was located in a part of one Reserve, but saltwater intrusion into agricultural fields occurs in several low-lying coastal counties of eastern North Carolina.
Farmers have been observing a phenomenon where patches of their agricultural fields
display stressed/unhealthy crops, or in extreme cases, where patches of bare ground
take over vegetated swaths of cropland. The phenomenon has been observed on farms
with corn, soybeans, wheat and other cash crops. Tests of the soils in these farmlands
have indicated that the soils have high concentrations of salts that inhibit the healthy
growth of plants. The burning questions on the farmers’ minds are where are these
salts coming from, will the problem become bigger with time, and what can be done
to solve this problem? These are important considerations because the answers to
these questions will help us determine the future impact of saltwater intrusion on
farmers’ livelihoods.
Working in collaboration with farmers, and state and county agricultural agents,
my research team has deployed different types of instruments in several fields to try
and provide answers to the farmers’ questions. Our suite of instruments is focused on
recording the weather, water quality, and quantity. Thus, we have deployed a weather
station to record air temperature, precipitation, wind direction, and wind speed at each
field site. We have installed clusters of shallow groundwater monitoring wells to help
us measure and record water levels and salinity in the groundwater system. And we
are using automated water level and salinity loggers to record water quantity and quality measurements every 10 min. We have also deployed water level and salinity loggers to record water levels and salinity in creeks, canals and the Albemarle Sound.
In addition to recording water quality and quantity in groundwater/surface water,
we are monitoring soil moisture content, soil temperature and soil conductivity to
investigate processes that may lead to soil salinization. We have also applied noninvasive techniques to image the subsurface through the use of geophysical techniques on impacted field sites. The geophysical techniques, that include direct
current electrical resistivity, capacitively coupled resistivity, and ground penetrating
radar, are useful for characterizing subsurface features and properties, as well as
delineating the extent of saltwater plume in the subsurface. It is envisioned that the
use of these techniques will help to show where the saltwater is coming from and
how it is moving from the surface to the subsurface.
It is likely that a combination of several of the possible processes that I described
earlier are responsible for aquifer and soil salinization in eastern North Carolina.
Perhaps the combination varies from place to place. Further, since some processes
may have a larger influence than others, any adaptation or mitigation strategies that
may be devised would have to align with the major driver of saltwater intrusion. For
example, if the major driver is intermittent overwash and storm surge, then applying
gypsum to agricultural fields followed by flooding with freshwater could lessen the
magnitude and extent of aquifer/soil salinization. However, this process is expensive and may be impracticable if a source of freshwater is unavailable. If, however,
the major driver is sea-level rise, then farmers may have to abandon their fields, or
they may have to plant other crops that are more tolerant to salty soils. Our continuing project will help farmers understand the environmental changes occurring in the
region so that they can better plan for their futures.
A. K. Manda