PUB00070

• Year: 1998
• Title: Ground Water and Surface Water A Single Resource U.S. Geological Survey Circular 1139
• CWCB Section: Interstate & Federal
• Author: T.C. Winter, J.W. Harvey, O.L. Franke, W.M. Alley
• Description: Overview of current understandimg of interaction of ground water and surface water in terms of quality and quantity
• Publications - Doc Type: Historical

./
.-
.-

A

EXPLANATION

.." ../"".
"----

I
/

D Cropland
D Forest
D Wetland
D Subtidal
mudflats

1.

/
)

J

..r-

.~

"\ 1 .-/"_
,-,' To
Chesapeake
Bay

0.5 1 MILE

8

NITROGEN BUDGET

Precipitation
31%
Cropland I Forest
fertilizer 46% I >52% uptake
I \ I and I
, I denitrification I
harvest: t :
I I

Q~I
'0(...') 53%
"'..
<1t&rIIO"""

Wetland
and
Mudflats

Rhode
River
Estuary

Streamflow <1%
::--i-.

Tidal exchange
-+- <1%

c

PHOSPHORUS BUDGET

Precipitation
7%
Cropland I Forest
fertilizer 45% I Sediment I
j I I transport I
--+-- 55% ---+-
harvest I I
I I
I I
I
I

Wetland
and
Mudflats

Sedi ment
deposition
48%

I
I
I
I
I
I
I Tidal
I excha nge
--+-- <7%

Rhode
River
Estuary

Ffgure J-2. Forests and wetfands separate cropland from
streams in the Rhode River watershed in Maryland (A). More
than half of the nitrogen applied to cropland is transported by
ground water toward riparian forests and wetfands (B). More
than half of the total phosphorus applied to cropland is trans-
ported by streams to wetlands and mudffats. where most is
deposited in sediments (C). (Modified from Correll, D.L.,
Jordan, TE, and Weller, DE, 1992, Nutrient ffux in a
landscape-Effects of coastal land use and terrestrial commu-
nity mosaic on nutrient transport to coastal waters: Estuaries,
v. 15, no. 4, p. 431-442.) (Reprinted by permission of the
Estuarine Research Federation.)

The gentle relief and sandy, well-drained soils of
coastal terrain are ideal for agriculture. Movement of excess
nutrients to estuaries are a particular problem in coastal areas
because the slow rate of flushing of coastal bays and estu-
aries can cause them to retain nutrients. At high concentra-
tions, nutrients can cause increased algal production, which
results in overabundance of organic matter. This, in turn, can
lead to reduction of dissolved oxygen in surface water to the
extent that organisms are killed throughout large areas of
estuaries and coastal bays.
Movement of nutrients from agricultural fields has
been documented for the Rhode River watershed in Maryland
(Figure J-2). Application of fertilizer accounts for 69 percent
of nitrogen and 93 percent of phosphorus input to this water-
shed (Figure J-2B and J-2C). Almost all of the nitrogen
that is not removed by harvested crops is transported in
ground water and is taken up by trees in riparian forests
and wetlands or is de nitrified to nitrogen gas in ground water
before it reaches streams. On the other hand, most of the
phosphorus not removed by harvested crops is attached to
soil particles and is transported only during heavy precipitation
when sediment from fields is transported into streams and
deposited in wetlands and subtidal mudflats at the head of the
Rhode River estuary. Whether phosphorus is retained in sedi-
ments or is released to the water column depends in part on
whether sediments are exposed to oxygen. Thus, the uptake
of nutrients and their storage in riparian forests, wetlands, and
subtidal mudflats in the Rhode River watershed has helped
maintain relatively good water quality in the Rhode River
estuary.
In other areas, however, agricultural runoff and input
of nutrients have overwhelmed coastal systems, such as in
the northern Gulf of Mexico near the mouth of the Mississippi
River. The 1993 flood in the Mississippi River system deliv-
ered an enormous amount of nutrients to the Gulf of Mexico.
Following the flood, oxygen-deficient sediments created areas
of black sediment devoid of animal life in parts of the northern
Gulf of Mexico.

i.-
Rhode River, Maryland. (Photograph by David Correll.)

45