Phosphate Budget and Mineralogy in Lake Ballard

heehawultraMécanique

22 févr. 2014 (il y a 3 années et 1 mois)

38 vue(s)

Phosphate Budget and Mineralogy in Lake Ballard

Introduction
:

Phosphate

is

often

the

limiting

nutrient

in

freshwater

bodies

(EPA

2012
)
.

As

phosphate

cycles,

it

is

used

by

plants

and

bacteria

or

can

be

incorporated

into

the

sediments

(Gunnars

1996
)
.

The

amount

of

phosphate

stored

in

the

sediment

is

dependent

on

a

variety

of

factors

such

as

amount

of

oxygen

in

the

water,

percent

organic

matter,

mineralogy,

and

salinity

(
Bostrom

1988
,

Wang

2006
)
.

If

the

sediment

is

a

source

of

phosphate

for

the

lake,

it

will

be

released

into

the

water

column
.

We

are

studying

the

total

phosphate

cycling

at

Lake

Ballard

(Portsmouth,

VA)
.

From

that

we

will

determine

the

phosphate

budget

for

the

lake
.

Methods
:

Water

Column
:

-
Water

samples

collected

at

1

meter

intervals

(
0
-
12

m)

-
Samples

filtered

with

hand

pump

and

GF/F

filters
.

-
Strickland

and

Parsons

(
1985
)

method

used

to

find

the

soluble

phosphate

concentration

-
Particulate

phosphate

obtained

from

filters

was

converted

to

soluble

and

tested

for

phosphate

concentration


Acknowledgments
:


We

would

like

to

thank

the

professors

Dr
.

Fred

Dobbs,

Dr
.

Rodger

Harvey,

Dr
.

Rich

Whittecar

and

the

T
.
A’s

Patrick

Tennis

and

Tanya

Muniak

as

well

as

the

staff

of

Hoffler

Creek
.

We

would

also

like

to

thank

Dr
.

Cutter‘s

Lab

for

their

assistance

and

Tony

Spicher
,

Ben

Hiza
,

Robert

Murray,

Erik

Hovland
,

and

Matthew

Kelley

for

the

use

of

their

samples

and

data
.


Discussion

and

Conclusion
:

In the water column, there are low phosphate concentrations in the
epilimnion

because of
photosynthetic uptake. In
hypolimnion

we observed an increase in phosphate concentrations. After
analyzing the benthic lake sediment, the phosphate in the shallow region was mainly bonded to the
sediment; in the deep region, the phosphate was stored in the organic material that had not been
decomposed. After testing mineralogy, over eighty percent of the phosphate binding was found in
organic minerals and clays. By combining this information as well as phosphate information from other
classmates, we created a phosphate budget for Lake Ballard. The source of phosphate was through the
groundwater and was higher than the calculated phosphate sedimentation rate. Based on our
calculations there is a larger sink of phosphate in the lake; we theorize the sediment is the most likely
sink location.

Amanda
Antosh
, Dan Christian, Rick Goshen,
Jessi

Strand, Regan Thomas

Ocean, Earth and Atmospheric Science, Old Dominion University,
Nofolk
, VA

Methods

(cont)
:

Water

Column

(cont)
:


-
Darcy’s

Law

and

well

data

used

to

calculate

groundwater

flow

of

the

Lake

Ballard

area


-
Soluble

phosphate

concentration

calculated

in

wells

surrounding

Lake

Ballard



-
Mass

balance

equation

was

used

to

determine

the

movement

of

phosphate

in

and

out

of

Lake


Anoxic

and

Onxic

Benthic

sediments
:

-
Took

grabs
;

separated

into

two

portions


-
first

portion

just

organic

surface

layer


-
second

portion

organic

layer

and

sediment


-
Dried

and

weighed

-
Strickland

and

Parsons

(
1965
)

total

digestion

-
Samples

were

reacted

with

a

modified

molybdate

solution

(Cutter,

1985
)

-
Read

absorbency

in

a

Milton

Roy

Spectronic

601

spectrophotometer

at

885
nm


-
Converted

absorbance

numbers

to

phosphate

concentrations

(
Clesceri

et

al
.

1989
)


Mineralogy:

-
Samples sieved through 250um
seive

-
1
g

of

sediment

mixed

with

0
.
250
g

of

corundum,

ground

to

0
.
03

mm

with

4
mL

of

ethanol

in

a

McCrone

micronizing

mill

for

5

mins

-
Mixture

dried

overnight

at

80
C

-
Sample

placed

in

plastic

scintillation

vial

with

3

10
mm

plastic

balls

and

hexane

(
0
.
5
mL),

shaken

for

10
mins

using

Retsch

MM
2000

shaker

-
Resieved

through

250
um

sieve

and

loaded

in

XRD

-
XRD

data

output

ran

through

RockJock

11

excel

workbook
.

Sources:


Bostrom
, B., J. M. Andersen, S. Fleischer, and M.
Jansson
. 1988. Gunnars, A., and S.
Blomqvist
. 1996.


Environmental Protection Agency (EPA). 2012. Water Monitoring: Phosphorus. Wang, S., X. Jin, H.
Zhoa
, X. Zhou, F. Wu. 2006.



Figure 1. Lake Ballard sampling sites and well locations.

Figure 4. Total phosphate concentration in water column
at “deep spot”.

Figure 5. Standard addition curve used to convert absorbance values
to phosphate concentrations. The * indicates the same absorbance
values.

Figure

3
.

Mineralogy

of

Lake

Ballard

benthic

sediment
.

Insert

shows

minerals

that

bond

to

Phosphate
.

Figure 6.
Total phosphate budget for Lake Ballard. Data collected between
Jan 28 and Mar 20 of 2013.

*

Results:

`

Sediment
ation Out

𝑆
𝑜
=
5
.
20

8
𝜇𝑜 𝑃

𝐺
𝑖

(
𝐴
𝑜
+
𝑆
𝑜
)
=
2
.
56

8
𝜇
𝑜 𝑃

5
𝟏

𝐃𝐚𝐲



𝟒

Budget

Adsorpti
on Out

𝐴
𝑜
=
6
.
35
𝑒
9
𝜇𝑜 𝑃

Figure 2. Collecting deep water samples.

Binding