Water quality in stormwater detention ponds and the impacts of pond discharges on ecosystem processes

within tidal creek receiving waters:

Erik M. Smith North Inlet - Winyah Bay National Estuarine Research Reserve University of South Carolina, Baruch Marine Field Laboratory

Funding provided by:

Collaborators: Amy Willman, Amber Stojak, Ashley Riggs, Tracy Buck,

Ben Lakish, Susan Denham, Angie Defore

Myrtle Beach

Charleston

Hilton Head

Created ponds have become a major feature of the coastal landscape

Pond delineation: 2006 Color IR DOQs; ground resolution of 1m Digitally delineated at a screen resolution of 1:3000

Total number = 14,446 Total area

= 8,659 hectares = 21,397 acres

= 86.6 km2

Geospatial inventory of ponds in coastal SC

Most stormwater ponds are detention ponds §  Designed to capture “first flush” (typically 1st 0.5” of runoff) §  Outlet structure discharges to adjacent surface water §  Ultimately drain to coastal receiving waters.

How do water quality impacts in these (freshwater) ponds affect water quality conditions and ecosystem function in (marine) tidal receiving water?

Myrtle Beach

Surfside Beach

Pawleys Island

North Inlet

A.I.W. All Ponds

Study Ponds

Murrells Inlet

26 residential ponds 2 Undeveloped 7 Low density development 10 Medium density development 10 High density development

Pond size mean

Pond depth mean

All sampled ponds are freshwater.

: 0.25 – 13.6 acre = 4.3 acre

: 1.0 – 5.0 m = 2.0 m

Comparative study of 26 stormwater ponds spanning a range of development density

Comparative study of 26 stormwater ponds spanning a range of development density

Myrtle Beach

Surfside Beach

Pawleys Island

North Inlet

A.I.W. All Ponds

Study Ponds

Murrells Inlet

26 residential ponds 2 Undeveloped 7 Low density development 10 Medium density development 10 High density development

Sampling (8 times from June – September): •  Nutrients (N & P in all forms, particulate & dissolved) •  Organic carbon (particulate & dissolved, % labile) •  Chlorophyll a •  Diurnal O2 dynamics in surface & bottom waters à Net Ecosystem Production •  Pond vertical structure and light attenuation

Mixing experiments: Effects of pond discharges on coastal marine waters

Total nutrient concentration variability across all ponds: To

tal N

itrog

en

(µg

L-1 )

No develop. Low Medium High max mean

min 10

100

1000

10000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Low: x = 466 Medium: x = 766 High: x = 1011

Tota

l Pho

spho

rus

(µg

L-1 )

1

10

100

1000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Low: x = 14 Medium: x = 62 High: x = 95

SCECAP “fair” and “poor” levels for coastal waters:

SCECAP “fair” and “poor” levels for coastal waters:

10

100

1000

10000

1.0 10.0 100.0 1000.0

Tota

l Nitr

ogen

(µg

L-1 )

Total Phosphorus (µg L-1)

Strong Relationship Between Total Nitrogen and Total Phosphorus

(all ponds, all sampling events)

“Redfield” Ratio 16N:1P (molar) ~7N:1P (mass)

Region of P deficiency

Region of N deficiency

y = 190x0.35 r2 = 0.60

p < 0.0001

Total phosphorus is a strong predictor of Chlorophyll across all ponds

0.1

1.0

10.0

100.0

1000.0

1.0 10.0 100.0 1000.0

Chl

orop

hyll

(µg

L-1 )

Total Phosphorus (µg L-1)

y = 0.4x1.02 r2 = 0.65

p < 0.0001

Nutrient Distributions: Particulate vs. Dissolved & Organic vs. Inorganic

0

20

40

60

80

100

Perc

ent

TN as Dissolved

TP as Dissolved

0

20

40

60

80

100

Ø  TN dominated by DISSOLVED N.

Ø  TP dominated by PARTICULATE P.

TN Dissolved as Inorganic

0

20

40

60

80

100

TP Dissolved as Inorganic

0

20

40

60

80

100

Ø  TNdissolved dominated by DON.

Ø  TPdissolved much more variable.

Nutrient Distributions: Particulate vs. Dissolved & Organic vs. Inorganic

0

20

40

60

80

100

0 40 80 120 160

% T

P D

isso

lved

as

Inor

gani

c

Total phosphorus (µg L-1)

LN(%DIP) = 1.5 – 0.6*LN(TP) r2 = 0.55; p < 0.0001

TP Dissolved as Inorganic

0

20

40

60

80

100

PON

POP

DON*

Recycling (excretion, grazing, etc.)

Uptake

Re- mineralization DOP

DIN DIP

Biomass

Dissolved Organics

Nutrient Input

(Substantially inorganic)

Box sizes indicate relative partitioning

of either N or P

Fate?

Conceptual Model of Nutrient Dynamics in Ponds

*DON as high C:N ratio DOM

§  Chlorophyll concentration §  Phytoplankton primary production rate (14C method) §  Bacterioplankton production rate (3H-Leucine method)

Quantify over 3 days of incubation under natural sunlight

Approach: Mix: 20 % filtered pond water with 80 % North Inlet water

Response Variables:

Filtered Pond Water

Coastal Water

20%

80%

3 day incubation in natural sunlight

Each day measure:

1.  Chl (µg L-1) 2.  PP (µg C L-1 h-1) 3.  BP (µg C L-1 h-1)

What happens when this DON enters (N-limited) coastal marine waters?

Treatments (triplicate incubations): Ø  0.2 µm filtered pond water Ø  D.I. water (control for dilution effects) Ø  D.I. water with equivalent concentration of N as DIN (50:50 NH4:NO3)

What happens when this DON enters (N-limited) coastal marine waters?

Approach: Mix: 20 % filtered pond water with 80 % North Inlet water

Time (h) Time (h)

Chl

a (µ

g L-

1 )

0

5

10

15

20

25

30

35

0 20 40 60 80

Control

0 2 4 6 8 10 12 14 16 18 20

0 20 40 60 80

Control Pond  Water Pond  Water Inorganic  N Inorganic  N

Alg

al P

rodu

ctio

n (µ

g C

L-1

h-1

)

Max Phytoplankton Production Rate

Phytoplankton Biomass

Autotrophic response:

Bac

teria

l Pro

duct

ion

(µg

C L

-1 h

-1)

0

1

2

3

4

5

0 20 40 60 80

Control Pond  Water Inorganic  N

Time (h)

0

5

10

15

20

25

30

35

0 20 40 60 80

Control Pond  Water Inorganic  N

Alg

al P

rodu

ctio

n (µ

g C

L-1

h-1

)

Time (h)

Max Phytoplankton Production Rate

Bacterioplankton Production Rate

Autotrophic vs. heterotrophic responses:

Pond discharge effects relative to those from other sources

Hutchins PR, EM Smith, ET Koepfler, RF Viso, RN Peterson (2013) Metabolic responses of estuarine microbial communities to discharge of surface runoff and groundwater from contrasting landscapes. Estuaries and Coasts, in press.

Forest drainage Urban stormwater runoff

Pond discharge effects relative to those from other sources

0.0

0.5

1.0

1.5

2.0

2.5

24 72 24 72

Trea

tmen

t Res

pons

e C

ontr

ol

Phytoplankton Production

Bacterioplankton Production

Pond discharge

Forest runoff

Pond = Forest =

0.13 µM DIN 5.40 µM DIN

Pond = Forest =

668 µM DOC 1636 µM DOC

Time point Time point

0.0

5.0

10.0

15.0

20.0

25.0 Pond discharge

Forest runoff

Urban runoff

Trea

tmen

t Res

pons

e C

ontr

ol

Phytoplankton Production

Bacterioplankton Production

Pond = Forest = Urban =

0.13 µM DIN 5.40 µM DIN

203.22 µM DIN

Pond = Forest = Urban =

668 µM DOC 1636 µM DOC 2628 µM DOC

24 72 24 72 Time point Time point

Pond discharge effects relative to those from other sources

Summary Ø Stormwater detention ponds have become a major feature of the landscape

in coastal South Carolina. ~ 14,000 ponds within coastal zone, covering ~ 85 Km2 (~ 21,000 acres)

Ø Ponds exhibit a large range in nutrient and chlorophyll concentrations. §  Development appears to increase TP more so than TN concentrations

•  Relatively little variation in nitrogen within and across ponds •  Substantial variation in phosphorus within and across ponds

Ø  Chl concentrations more a function of TP variability, than TN variability

Ø Pond organic matter dominated by dissolved materials & ponds effectively convert DIN inputs to DON, which accumulates as high C:N DOM.

Ø Pond exports have little to no direct effect on marine autotrophic processes, but significantly stimulate heterotrophic processes. à Responses to pond discharges much smaller than response to direct

urban stormwater runoff