f/EPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30613
Research and Development
EPA-600/S3-80-087 July 1981
Project Summary
Effect of Agricultural Land
Development on Drainage
Waters in the North Carolina
Tidewater Region
R. W. Skaggs, J. W. Gilliam, T. J. Sheets, and J. S. Barnes
In a three-year study, the effect of
agricultural drainage and develop-
ment on hydrology and the effect of
runoff water quality on high organic
soils were examined in the North
Carolina Tidewater Region. A small
but significant increase was found in
organic nitrogen in drainage water as a
result of agricultural development.
True organic soils lost considerably
more phosphorus to drainage waters.
Development caused a decrease in
evapotranspiration with a consequent
small increase in annual outflow even
during years when droughts occurred.
Dissolved oxygen, biochemical oxygen
demand, temperature, pH, and other
water quality parameters exhibited
relatively small changes as a result of
development. A significant increase in
the loss of fecal and total coliform
bacteria from pasture land was ob-
served, which represents a potential
water quality problem. Studies of the
herbicide alachlor showed that it
disappeared rapidly from soil after
application but also showed that low,
nonphytotoxic concentrations per-
sisted from one season to the next.
High concentrations in drainage waters
appeared to be caused by direct spray-
ing or by spray drift. Soil subsidence
was greatest immediately after devel-
opment.
This Project Summary was devel-
US EPA Headquarters Library
401MSI..SW (3404)
Washington, DC 20460
oped by EPA's Environmental Research
Laboratory, Athens, GA, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
Land in the Tidewater Reg ion of North
Carolina is flat, with surface elevations
of only a few meters above sea level.
The water table is close to surface and,
under natural conditions, large areas of
the region are swampy. Many of the
soils are organic or have high organic
surface layers. These soils, which are
referred to cumulatively as the Black-
lands, present several specific and
unique agricultural problems. Drainage,
which is essential for agricultural pro-
duction in the region, was first initiated
in the late 1600s. Since that time,
periods of clearing and development
have been followed by longer periods of
inactivity.
The latest period of increased drainage
activity began in the early 1970s when
several large corporations became
involved in clearing and developing
thousands of hectares of land in eastern
North Carolina. This developmental
activity coincided with the algae bloom
problems in the Chowan River and the
general awareness that development of
any type results in some environmental
-------
changes. Consequently, it is natural and
appropriate that questions were raised
by the scientific community, by various
state and federal agencies and by the
general public, about the effect that
massive land changes would have upon
the environment.
One specific concern was the effect of
land development on the rate and time
distribution of runoff with some appre-
hensions that greatly increased peak
rates would surpass the capacity of
existing outlet canals and rivers. The
land under development lies between
the Albemarle and Pamlico estuaries,
which are important for both commercial
and sport fishing. State agencies were
concerned that these estuaries might be
damaged through increased sedimenta-
tion from the developing lands, increased
nutrient flux into the estuaries causing
algal blooms, a change in organic matter
entry into estuaries, pesticide move-
ment into the water, increased input of
fecal organisms from pasture lands,
increased heavy-metal concentrations,
and a change in the freshwater distribu-
tion resulting in detrimental effects on
salt water organisms because of de-
creased salinity. Others expressed con-
cern that clearing and drainage would
cause a large increase in oxidation of
the organic matter in the soils resulting
in a general subsidence of the land
surface.
In attempting to address potential
problems and to assess the environ-
mental impact of the planned activities,
it was recognized that there was a void
in basic scientific information concern-
ing the effects of clearing and develop-
ment on the hydrology and quality of the
drainage waters from organic and high
organic mineral soils. A research project
was developed to study those effects.
The project was sponsored by the U.S.
Environmental Protection Agency, the
North Carolina Water Resource Research
Institute through the matching grants
program with the Office of Water Re-
search and Technology, and the North
Carolina Agricultural Research Service.
Procedure
Experiments were conducted on paired
developed and undeveloped sites of
three different soils that span the range
of soils being developed in the Tidewater
Region (Blacklands).
Dashboard riser structures with weirs
were installed at the drainage outlets of
each of the six experimental sites. The
triangular weirs were calibrated in
place, and outflow rates were measured
continuously by recording the stage
upstream from the weirs. A flow-pro-
portional automatic water sampler was
located at each site for collection of
water samples. The stage recorders
were serviced weekly and water samples
were collected at the same time for
laboratory analyses. Rainfall was con-
tinuously recorded at each site. Water
tables were also continuously recorded
on each site at points midway between
field drains. Field measurements of
conductivity, salinity, dissolved oxygen,
temperature, and pH were made on grab
samples taken at the weekly sampling
times. Laboratory measurements of
total P, total N, nitrate-nitrogen, total
organic carbon, filterable solids, and
turbidity were run on the weekly samples.
Analyses for Ca, Mg, Na, Cu, Fe, Mn, Cd
and Zn were run on composite samples
at monthly intervals. Fecal and total
coliforms were run on grab samples
taken every two weeks.
Pesticide application during the study
consisted almost entirely of alachlor [2-
chloro-2, 6-diethyl-N-(methoxymethyl)
acetanilide]. Samples of soil were taken
for the first four weeks after application.
Runoff samples were collected during
and after two to five rainfall events
following pesticide application. The
water samples were field processed
with a XAD-2 macroreticular resin and
transorted to the laboratory for analyses.
Results
Peak runoff rates occur earlier and
are three to four times higher on devel-
oped as on similar undeveloped lands.
As presently designed, the drainage
canal network, with pump-assisted
outlets in some cases, does not have the
capacity to remove the water at the rate
that it can drain from developed fields.
As a result there may be little difference
between runoff rates from developed
and undeveloped lands during the
largest runoff events.
Total annual outflows from the devel-
oped sites were somewhat higher than
from undeveloped sites during certain
years of the study, but about the same in
others. In general, however, develop-
ment will cause a decrease in evapo-
transpiration (ET) with a consequent
increase in annual runoff during years
in which drought periods occur. The
increase in total runoff will usually be
small but will depend on the number of
droughts that are followed by runoff-
producing rainfalls.
Drainage systems currently installed
in the organic and high organic mineral
soils provide mostly surface rather thaw
subsurface drainage. Water tables are
usually close to the surface during the
winter and change continuously with ET
and rainfall during the growing season.
Average water table depths were about
22-cm deeper on the developed than on
the undeveloped deep organic soil.
Because of the influence of the root mat,
water tables were actually deeper on
ditched, but undeveloped, mineral and
shallow organic soils.
The composition of drainage water
from agricultural fields in the organic
and high organic soils of the Blacklands
is somewhat different from other agri-
cultural areas of North Carolina. Conse-
quently, the effect of development of
natural areas for agricultural production
is different. Much less inorganic nitrogen
is found in drainage water from devel-
oped fields in the Blacklands'as com-
pared to most fields further inland. This
is a result of the very low nitrate levels in
drainage waters from these organic rich
soils. The inorganic nitrogen losses to
drainage water from developed areas
are greater than from natural areas, but
the increase in nitrogen concentration
is not as large as might be predicted
based on data from other agricultural
areas.
The largest potential eutrophication
hazard resulting from development may
be the increase in phosphorus in drain-
age waters. The effect of development
upon phosphorus losses in drainage
waters is dependent upon soil type.
Inorganic soils react with fertilizer
phosphorus to prevent its loss. The
solubility of phosphorus in shallow and
deep organic soils is much greater than
in inorganic soils, so much of the added
phosphorus can be lost to drainage
water. The weighted average concen-
tration in drainage waters from the two
developed organic soils was 1 to 2.5
mg/l for a total phosphorus efflux of 7 to
10 kg ha"1 yr"1. The amount of this
phosphorus reaching major streams or
estuaries will depend on the distance
the water must travel to reach the
outlet, the type of sediment in the
collector ditches, and the soil material in
the banks. If the sediments are from
inorganic soils or the canals are cut into
mineral layers, much of the inorganic
orthophosphate may be removed from
sol ution by these sediments. Fortu nately,
much of the current agricultural devel-
opment is on mineral soils where P
losses are small. It should be recognized
however, that agricultural developmerl
of organic soils that are low in mineral
-------
iontent and immediately adjacent to
estuaries or major streams will signifi-
cantly increase the entry of phosphorus
into these waters.
The Blackland soils are flat so erosion
is not a problem, but development does
cause a small increase in sediment load
of drainage waters. This increase is
particularly apparent during the devel-
opmental phase. Turbidity of the drain-
age water is increased during clearing
and land shaping. Once initial develop-
ment is completed, erosion and turbidity
during normal agricultural production is
not likely to cause a water quality
problem.
Several water quality parameters are
measurably affected by development,
but the change is relatively small. For
example, dissolved oxygen, biochemical
oxygen demand, and pH are all slightly
higher in drainage water from developed
areas. Other parameters that change
upon development but are not generally
considered critical in evaluation of
water quality in this region are Ca, Mg,
Cl, Na, and K. Development has little
effect upon efflux of Cu, Zn, Mn, andFe.
One potential problem with develop-
ment of the organic soils for pastures
Rear shell fishing waters is the loss of
veal organisms in drainage waters. The
counts of fecal and total coliform bacteria
in drainage water from the pastured site
were considerably greater than from
natural areas. This increase in coliform
bacteria from grazed lands is common
throughout the United States and ap-
parently causes few problems. Problems
could result, however, if grazed land is
located immediately adjacent to shell-
fish waters. Development also caused
an increase in coliform bacteria from
the cropped shallow organic soil even
though no domestic animals were ever
kept on this site.
Comparison of elemental deposition
from the atmosphere, as compared to
losses in drainage waters from the
natural areas, showed that three to four
times as much N and P were deposited
as was lost in drainage waters. The
deposition of Na, Cl, K, Ca, Mg, Cu, Mn,
and Zn was approximately the same as
removal in drainage waters. There was
a net loss of Fe from the natural areas.
The high organic matter content soils
in eastern North Carolina require special
sampling techniques to provide reliable
estimates of the amount of pesticides
applied. The most effective method of
fnfirming the rate of deposition of the
rbicide alachlor was the use of filter
per discs laid on the soil surface
during application.
Alachlor residues among individual
soil samples taken after herbicide appli-
cation were highly variable, but an
average of seven or more samples
within a plot or analysis of a composite
sample from seven sites within a plot
appeared to provide a reliable estimate
of the residue level.
Residues of alachlor (parent com-
pound) disappeared rapidly after appli-
cation to the organic soil; however, low
levels of "apparent" alachlor persisted
from one season to the next in a biologi-
cally inactive form. There was no signifi-
cant accumulation of alachlor residue
above the detectable, but very low con-
centrations, that carried over. Transport
of alachlor, and probably other pesticides
as well in surface runoff from the high-
organic soils of the Tidewater Region of
eastern North Carolina and similar
areas elsewhere, does not appear to
pose a significant hazard to aquatic life.
Concentrations of alachlor in drainage
water after application suggested that
some applicators were careful to avoid
spraying the V-ditches draining the
fields but that some may have sprayed
directly over them, or so close that
heavy drift of sprays occurred, causing
excessively high concentrations of
herbicide in drainage water during the
first few days after some applications.
More diligence and care during applica-
tion of all pesticides used on many
farms in the Tidewater Region of North
Carolina, where ecologically sensitive
areas exist in close proximity to large
agricultural areas, would reduce or
even eliminate significant hazards
caused by direct spraying of, or drift
onto, water in drainage canals.
The major effects of agricultural
development on soil properties involved
the surface horizon. Development re-
moved the root mat and decreased the
surface elevation. The bulk density of
the surface horizon increased and the
porosity decreased. Both hydraulic
conductivity and drainable porosity are
decreased during the developmental
process. The effects of development on
all soil properties increased with the
depth of the organic layer.
Subsidence of the organic soils is
greatest directly after development
because of irreversible drying and
shrinkage of soil in the root zone. After
this initial period, subsidence on the
deep organic pasture site was less than
1 mm/year for a three-year period.
R. W. Skaggs, J. W. Gilliam, and T. J. Sheets are with North Carolina State
University. Raleigh. NC 27650; J. S. Barnes is with First Colony Farms,
Creswell. NC 27928.
C. N. Smith is the EPA Project Officer (see below).
The complete report, entitled "Effect of Agricultural Land Development on
Drainage Waters in the North Carolina Tidewater Region." (Order No.
PB 81-105 959; Cost: $21.50. subject to change! wilt be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
Athens, GA 30613
» US. GOVERNMENT PRINTING OFFICE: tWl -757-012/7206
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business-
Penalty for Private Use $300
------- |