Document ID: EPA-HQ-OW-2003-0074-0378
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2003-12-24T05:00Z

National
Water
Quality
Assessment
Program
(
NAWQA)­­
Analysis
of
Nutrients
March
3,
2003
The
first
synthesis
of
NAWQA
data
(
and
the
only
one
currently
available)
is
for
Nutrients
and
Pesticides.
It
is
contained
in
"
The
Quality
of
Our
Nation's
Waters
 
Nutrients
and
Pesticides".
The
following
summarizes
the
information
available
for
nutrients.

Purpose:
The
purpose
of
the
NAWQA
program
is
to
develop
long­
term,
consistent
and
comparable
information
on
streams,
ground
water,
and
aquatic
ecosystems
to
support
sound
management
and
policy
decisions.
The
NAWQA
program
tries
to
answer
the
following
questions
relating
to
nutrients:
1.
Which
nutrients
are
found
in
streams
and
ground
water
across
the
nation?
At
what
concentrations?
2.
Are
elevated
concentrations
more
prevalent
in
certain
geographic
regions
and
environmental
settings?
3.
How
do
differences
in
land
use,
chemical
use,
land­
management
practices,
and
natural
processes
help
explain
differences
in
vulnerability
to
contamination
of
streams
and
ground
water?
4.
Are
nutrient
concentrations
elevated
only
at
certain
times
of
the
year?
Are
concentrations
changing
over
time?
5.
What
are
the
implications
to
human
health
and
the
environment?
6.
How
is
this
information
useful
for
guiding
future
research,
monitoring,
and
watermanagement
and
protection
strategies
related
to
nutrients?

Chemicals:
The
program
includes
500
chemical
constituents.

Sample
Locations:
The
NAWQA
program
focuses
on
water
quality
in
more
than
50
major
river
basins
and
aquifer
systems,
referred
to
as
"
Study
Units".
Together,
these
include
water
resources
available
to
more
than
60
percent
of
the
population
in
watersheds
that
cover
about
one­
half
of
the
land
area
of
the
conterminous
U.
S.
The
report
on
nutrients
uses
the
information
from
the
first
20
study
units.
Attachment
I
shows
the
location
of
these
study
units.

Sample
Design:
Streams
and
shallow
ground
water
in
agricultural,
urban,
and
some
undeveloped
(
mostly
forested)
settings
were
studies
in
the
first
20
study
units.
The
agricultural
areas
are
diverse
in
climate
and
geography,
and
they
span
coastal,
desert,
and
temperate
environmental
settings.
They
include
areas
of
corn
and
soybean
production
in
the
Midwest;
areas
of
production
of
wheat
and
other
grains
in
the
Great
Plains;
areas
of
mixed
row
crop
and
poultry
production
in
the
East;;
rangeland
grazing
and
cattle
feeding
operations
in
the
arid
Southwest;
and
areas
of
intensive
production
of
grain,
fruits
and
nuts,
vegetables,
and
specialty
crops
in
California
and
the
Pacific
Northwest.
Sampling
of
streams
and
shallow
ground
water
in
urban
areas
represented
primarily
residential
land
use,
typically
with
low
to
medium
population
density.
In
general,
the
urban
assessments
focused
on
non­
point
sources
of
contaminants,
although
some
sampling
or
rivers
was
done
downstream
from
major
metropolitan
areas
which
have
point
discharges
from
municipal
wastewater
treatment
plants.
Nutrients
also
were
assessed
in
major
rivers
and
in
aquifers
commonly
used
for
drinking
water.
These
samples
represent
integrated
water­
quality
effects
from
multiple
land
uses
and
environmental
settings
that
occur
within
relatively
large
contributing
areas.
The
following
table
summarizes
the
sites
sampled
in
the
study.

SUMMARY
OF
SAMPLE
SITES
Type
of
Sample
Number
of
Samples
Relatively
Undeveloped
Forest
or
Rangeland
Streams
28
Shallow
ground­
water
studies
4
Agricultural
Land
Streams
75
Shallow
ground­
water
studies
36
Urban
Land
Streams
22
Shallow
ground­
water
studies
13
Mixed
Land
Use
Streams
87
Major
aquifers
33
Study
Duration:
NAWQA
began
investigations
in
20
study
units
in1991
and
phased
in
work
in
more
than
30
additional
basins
by
1997.
The
report
on
nutrients
uses
the
information
from
the
first
20
study
units.

Evaluation
Method:
Nutrient
levels
are
summarized
on
U.
S.
maps
to
facilitate
analysis
and
comparison
of
regional
and
national
patterns.
Concentrations
or
detection
frequencies
are
ranked
according
to
three
categories:
lowest
for
the
lowest
25%;
medium
for
the
middle
50%;;;
and
highest
for
the
highest
25%
of
concentrations
or
detection
frequencies
among
all
stream
sites
or
ground­
water
studies.
For
nutrients
in
streams,
flow­
weighted
total
nitrogen
and
total
phosphorus
concentrations
were
determined
for
each
stream
site
for
1994
and
1995
and
were
averaged.
For
shallow
ground
water,
median
nitrate
concentration
was
determined
for
each
ground­
water
study.

The
maps
of
national
results
also
show
patterns
of
non­
point
inputs
of
nitrogen
and
phosphorus.
Based
on
county
agriculture
statistics
for
1987
and
1992,
average
annual
nitrogen
and
phosphorus
inputs
to
agricultural
and
urban
land
were
estimated
from
commercial
fertilizer
sales
(
1991­
94)
and
manure
from
animals
(
1992).
Average
annual
input
of
nitrogen
from
the
atmosphere
was
estimated
from
1991­
94
data.

Results
are
reported
as
total
nitrogen
(
nitrate,
nitrite,
ammonia,
and
organic
nitrogen)
and
total
phosphorus
(
phosphates
and
particulate
organic
phosphorus
are
the
main
components).

Results:
Human
activities
 
including
agricultural
and
urban
uses
of
fertilizer,
agricultural
use
of
manure,
and
combustion
of
fossil
fuels
 
have
caused
widespread
increases
of
nitrate
in
shallow
ground
water
and
total
nitrogen
and
total
phosphorus
in
streams
across
the
Nation.

Nitrate
did
not
pose
a
national
health
risk
for
residents
whose
drinking
water
came
from
streams
or
from
major
aquifers
buried
relatively
deep
beneath
the
land
surface.
Some
concerns
were
evident
in
4
of
the
33
major
aquifers
sampled,
where
nitrate
concentrations
in
more
than
15%
of
each
aquifer
exceeded
the
EPA
drinking­
water
standard
(
MCL=
10
mg/
L).
The
most
prevalent
nitrate
contamination
of
ground
water,
however,
was
found
in
relatively
shallow
ground
water
in
rural
areas
where
the
water
commonly
is
used
for
domestic
supply.

In
more
than
one­
half
of
sampled
streams,
concentrations
of
total
nitrogen
and
total
phosphorus
were
above
national
background
concentrations.
Elevated
phosphorus
levels,
in
particular,
can
lead
to
excessive
plant
growth
in
freshwater
environments;
in
more
than
one­
half
of
sampled
streams
and
in
three­
fourths
of
agricultural
and
urban
streams,
average
annual
concentrations
of
total
phosphorus
exceeded
the
EPA
desired
goal
for
prevention
of
nuisance
plant
growth
(
0.1
mg/
L).
The
highest
total
nitrogen
and
total
phosphorus
concentrations
were
found
in
small
streams
draining
watersheds
with
large
proportions
of
agricultural
or
urban
land.
Long­
term
monitoring
of
streams
indicates
that
programs
to
control
point­
source
discharges
of
phosphorus
and
ammonia
have
been
effective,
despite
population
increases
in
most
metropolitan
areas.
Phosphorus
concentrations
have
decreased
as
a
result
of
reductions
in
the
use
of
phosphate
detergents
and
in
the
amount
of
phosphorus
discharged
from
upgraded
wastewater
treatment
plants.
Improved
waste
water
treatment,
which
converts
ammonia
to
nitrate,
generally
has
resulted
in
a
decrease
in
ammonia
concentrations
and
an
increase
in
nitrate
concentrations
in
streams.
Thus,
concentrations
of
total
nitrogen
downstream
from
metropolitan
areas
have
changed
little
during
the
past
20
years,
although
toxicity
to
fish
has
decreased
with
decreasing
ammonia
levels.

Results
from
NAWQA
studies
have
shown
regional
and
seasonal
differences
in
nutrient
concentrations
that
can
be
explained
largely
by
the
amounts
and
timing
of
fertilizer
and
manure
applications
and
by
the
variety
of
soils,
geology,
climate,
and
land­
and
water­
management
practices
across
the
Nation.
Recognition
of
thee
differences
is
important
for
efficient
protection
of
ground
water
needed
for
drinking
and
for
curbing
eutrophication
of
surface
water.

Contact:
http://
water.
usgs.
gov/
lookup/
get?
nawqa
Short­
term
Followup:
None
Long­
term
Followup:
In
more
information
on
nutrients
is
needed,
the
report
contains
detailed
information
that
may
be
useful.