Restoration of Impaired Waters - What are we really trying to do?

Harvey H. Harper, Ph.D., P.E. Environmental Research & Design, Inc.

Florida Stormwater Association 2017 Annual Conference

June 16, 2017

Evolution of Regulatory Approach Federal Water Pollution Control Act (FWPCA) -1948 – 1st laws addressing water pollution

FWPCA amended in 1972 – Became known as Clean Water Act – Goal of “ensuring that surface waters would meet standards necessary

for human sports and recreation by 1983.” – Section 314 - Clean Lakes Program

Provide financial and technical assistance to States in restoring publicly-owned lakes Sections for point sources, non-point sources, and in-lake actions One of the first Federal programs to recognize the significance of watershed loadings to lakes Recognized the lake and watershed as an “ecological unit” Basic approach: assess condition, identify causative agents for any undesirable features, address processes to achieve desired condition Fully recognized the significance of both internal and external loadings Funded ~$145 million of grant activities since 1976 No appropriations for the program since 1994 Re-authorized in 2000, but no funding provided

– Section 402 - NPDES Program 2

Evolution of Regulatory Approach – cont.

Clean Water Act Amendments – 1977 – Goal: "to restore and maintain the chemical, physical, and

biological integrity of the Nation's waters“ – Section 303(d) – Impaired Waters – States must develop TMDLs for every water body/pollutant

combination on the 303(d) list. – Required development of a "Best Management Practices"

Program as part of the state area-wide planning program – Authorized the Fish and Wildlife Service to provide technical

assistance to states in developing "best management practices“ – Exempted various activities from the dredge and fill prohibition

including normal farming, silviculture, and ranching activities

3

Evolution of Regulatory Approach – cont.

Clean Water Act Amendments – 1987 – Section 319 authorized Nonpoint Source Management Program – Significant studies released which highlighted significance of

runoff in pollutant loadings to surface waters NURP – 1979 to 1983, 28 urban watersheds across U.S.

– Continued shift toward watershed focus – De-emphasis of in-lake measures by neglect

Resistance to in-lake funding based on “not addressing root causes” – Funds may be used for in-lake work when all external sources

have been treated – Phased out the construction grants under the Clean Lakes

Program

4

TMDLs

TMDLs – The TMDL allocates loadings to point sources and nonpoint

sources “which include both anthropogenic and natural background sources of the pollutant”

– Loading calculations rarely include internal processes – Only cursory mention of internal loadings in EPA guidance

documents – Often referred to as “Watershed TMDLs” – EPA – “water quality standards set a goal for restoring and

protecting a watershed over the long term.”

5

TMDL Approach

Surface water restoration has morphed from an “ecosystem approach” to a watershed approach – Assumes that “impaired waters” will be restored through

stormwater management The current TMDL process ignores many significant sources of nutrient loadings to waterbodies – Internal recycling – Groundwater seepage – Baseflow

Over-emphasizes the significance of runoff loadings – Many models overestimate runoff loadings – Models are often calibrated by increasing runoff to account for

missing components

6

Stormwater Management as a Cure-All

Managing and treating stormwater has become institutionalized and a large stormwater industry has developed Since stormwater caused the problems, then the approach assumes that runoff must be treated to restore waters – Example

Narrow focus on reducing runoff loadings – Almost a punitive approach

Focus more on process than outcomes

Loose sight of the primary objective : restore water quality

7

Typical Nutrient Inputs/Losses to Waterbodies

Bulk Precipitation

Water Fowl Runoff/ Baseflow

Groundwater Seepage

Lake/Tributary Inflow

Outflow

Deep Recharge

Sedimentation

Sediment

Release

8

Typical Nutrient Inputs Included in TMDL Evaluations

Bulk Precipitation

Water Fowl Runoff/ Baseflow

Groundwater Seepage

Lake/Tributary Inflow

Outflow

Deep Recharge

Sediment Release

Septic Tank Impacts Only

9

Models assume that a direct predictable relationship exists between nutrient loading and water quality: Annual loadings required to generate existing water quality are calculated and used to calibrate the loading model Since several significant sources are omitted, the calibration process often leads to over-estimation of the evaluated parameters This omission threatens the success of the TMDL program in restoring waters

TMDL Water Quality Modeling

Nutrient Loadings

Prod

uctiv

ity

10

Deficiencies in TMDL Process

1. Failure to include all sources – Groundwater seepage

2. Nutrient limitation 3. Internal recycling

11

1. Seepage

12

- Shallow groundwater seepage originates as precipitation which infiltrates into the ground

- Other inputs include septic tanks, fertilizers, agriculture, wastewater disposal, and industries

- Water moves vertically to the saturated zone and begins to move laterally down gradient

- Seepage characteristics are impacted by inputs, soil characteristics, travel distance, etc.

13

1. Groundwater Seepage (What is Groundwater Seepage?)

a. TMDL Process Assumptions - Seepage only considered if septic tanks are located within the basin - Seepage impacts are limited to parcels adjacent to the receiving water - Only “failed” systems are considered as an input b. Actual Conditions - Seepage inputs occur into virtually every waterbody whether septic

tanks are present or not - Seepage inflow originates from the entire basin area

Parameter Units No. of Lakes

Range of Values

Mean Value

Lake Area acres 32 25.8-4519 409

Seepage Inputs ft/yr 32 0.89-5.59 2.00

TN – Sewered mg/l 8 0.89-4.26 2.348

TN – Septic mg/l 19 1.0-8.57 3.775

TN - Sewered/Reuse mg/l 1 5.27 5.274

TP – Sewered mg/l 8 0.01-0.14 0.083

TP – Septic mg/l 19 0.2 – 1.82 0.356

TP - Sewered/Reuse mg/l 1 0.254 0.254

Parameter Units Mean Value

TN Load - Sewered g/m2-yr 1.443

TN Load - Septic g/m2-yr 2.057

TN Load - Sewered g/m2-yr 0.082

TN Load - Septic g/m2-yr 0.194

14

1. Groundwater Seepage – cont. (Typical Loadings)

Typical Seepage Meter Installation

Figure 2-15c

Seepage Meter

Float

Water Surface

Floating Marker

Weight

PVC Valve 50 gal. PE Bag

PVC Camlock Fitting

2 ft. diameter aluminum cylinder

w/ open bottom

Seepage Flow

15

1. Groundwater Seepage – cont. (Measurement)

Seepage Monitoring Sites in Bear Gully Lake

10 Sites

D

D

D

D D

D

D

D

D

D

9

8

7

6

5 4

3

2

1

10

500 0 500 1,000 250

Feet

16

Mean Seepage Inflow Isopleths (liters/m2-day) for Bear Gully Lake from March 2008-January 2009

0 300 600 900 150

Feet 17

Isopleths of Total Phosphorus Influx from Groundwater Seepage Into Bear Gully Lake from March 2008-January 2009

0 300 600 900 150

Feet 18

Estimated Mean Annual Mass Loadings of Total Nitrogen and Total Phosphorus Entering

Bear Gully Lake

Source

Total N Total P

kg Percent of Total

kg Percent of Total

Bulk Precipitation 544 14 43.1 21

Bear Gully Creek 966 25 32.9 16

Dodd Road Culvert 929 24 27.0 13

Direct Runoff 541 14 47.3 22

Groundwater Seepage 904 23 30.4 15

Internal Recycling -- 0 27.3 13

Totals: 3,884 100 208.0 100

19

2. Nutrient Limitation

20

Justis von Liebig (1803-1873)

- A pioneer in agricultural chemistry, biochemistry and organic chemistry - Invented fertilizer - In 1840 he developed a theory, later referred to as Liebig’s Law of the Minimum, that states that an organism will continue to grow until an element important for the development of the organism, becomes in short supply, and growth can no longer occur - This element is then referred to as the “limiting nutrient”

21

2. Nutrient Limitation (Liebig’s Law of the Minimum)

During the 1970s , Schindler conducted whole lake enrichment and nutrient limitation studies in the experimental lake region of Canada Artificially fertilized lakes with N and P and monitored results Quantified impacts of nutrient loadings both visually and chemically Fertilized

Non-Fertilized

22

2. Nutrient Limitation – cont. (Whole Lake Nutrient Enrichment Studies)

Nutrient limitation has been evaluated in a variety of ways: 1. Comparing relative quantities of major nutrients, such as N:P

ratios TN:TP ratio DIN:SRP – (Dissolved Inorganic N:SRP) Most common method

2. Algal bioassys – provide direct quantification of nutrient additions on water quality

Extrapolation of data to in-situ conditions is difficult Algae are separated from nutrient re-supply from internal sources

3. Physiological assays of phytoplankton health

23

2. Nutrient Limitation – cont. (Defining Nutrient Limitation)

Nutrient limitation is most commonly evaluated using TN:TP ratios - Nutrient limitation is defined using the following ratios (weight

basis):

- Method implies that TN and TP provide a reliable estimate of the amount of N and P available for growth

TN:TP Ratio Nutrient Limitation

<10 N Limited

10-30 (20) Nutrient Balanced

>30 (20) P Limited

24

2. Nutrient Limitation – cont. (Nutrient Ratios)

Reference N:P Ratio Phytoplankton Nutrient Condition

Bulgakov & Levich

2-5 5-20 >20

Cyanobacteria Diatoms

Chlorophyta

N limited Balanced P limited

McQueen & Lean (1987) >5 Cyano not observed -

Michard, et.al (1996) <5 Microcystis became

domonant P limited

20-50 5-10

Chlorococcales Cyanobacteria

P limited N limited

>25 Unfavorable for Cyano P limited

- Phytoplankton assemblage is often regulated by nutrient ratios rather than by absolute nutrient concentrations

- Seasonal changes in N:P ratios may be a significant factor in seasonal changes in algal species

25

d. Nutrient Limitation (Algal Responses to TN:TP Ratios)

TN:TP Ratio0 50 100 150 200

TSI (C

hlya

)

0

20

40

60

80

100

120

N li

miti

ng

P lim

iting

Bala

nced

N = 1092 lakes

Eutrophic Mesotrophic

Oligotrophic

Hyper-eutrophic

26

2. Nutrient Limitation – cont. (Relationships Between TSI & TN:TP Ratios) (LAKEWATCH Data 1980-2008)

10 30

Most N limited lakes are either eutrophic or hyper-eutrophic with a high rate of internal recycling of P – Elevated water column nutrient concentrations – Phytoplankton are dominated by non N2 fixing cyanobacteria, such as

Lyngbya, Oscillatoria, and Microsystis The low N:P ratio suggests that N reduction is necessary to improve water quality However, as N is lowered, given adequate P, N2 fixers can make up for virtually any N deficit – N limitation never occurs and growth will continue until P is exhausted – Biomass yield is dependent on P even under N limiting conditions

Well established link between elevated P and cyanobacteria which are favored at N:P ratios <5 N reduction may actually be counterproductive: – Under existing conditions N:P = 2100 µg/l:300 µg/l = 7:1 – After N reduction project N:P = 900 µg/l:300 µg/l = 3:1 which would

favor cyanobacteria formation

27

2. Nutrient Limitation – cont. (Nitrogen Limitation)

Normal algal growth

– Process repeated until water column N

concentrations become too low for uptake

Algal growth with N fixation – N is constantly replenished – N never becomes limiting – Growth will continue until P is exhausted

16 N ● ● ● ● ● ●

1 P ● ● ● ● ● ●

Abundant Limited Amount

● ● ● ● ● ●

28

2. Nutrient Limitation – cont. (Theory of Nitrogen Limitation)

Schindler, et. al (2008) published a paper which summarized 37 years of whole lake experiments on Lake 227 in the Experimental Lakes Region (ELR) in Alberta titled:

“Eutrophication of lakes cannot be controlled by reducing nitrogen input: Results of a 37-year whole-ecosystem experiment” Lake 227 was fertilized for 37 years with constant annual inputs of P and steadily reducing inputs of N

– Test the hypothesis that controlling N can control algal growth Reducing nitrogen inputs favored N2 fixing

cyanobacteria as a response to N limitation N fixation was sufficient to maintain eutrophic

conditions in spite of lack of external N loads N reductions without P reduction increased

algal growth

Year N (kg/yr) P (kg/yr) N:P

1969 249 20.7 12.1

1970-74 308 24.8 12.4

1975-82 110 23.6 4.7

1983 110 19.8 5.5

1984-89 110 23.6 4.7

1990-97 0 23.6 0

1998 0 31.9 0

1999-05 0 24.5 0

Concluded that to reduce eutrophication, the focus of must be on

decreasing inputs of P 29

2. Nutrient Limitation – cont. (Impacts of Nitrogen Reduction)

How does nutrient limitation relate to water quality restoration? – Nutrient limitation relates to factors necessary to increase algal growth – Water quality restoration evaluates factors required to reduce algal

growth – Two very different objectives

Eutrophic lakes cannot be restored by reducing nitrogen – No valid scientific account of a eutrophic lake ever being restored by

controlling nitrogen – Nutrient ratios may have diagnostic value for the lake – Only P reduction can restore a eutrophic lake since any nitrogen

deficiency can be easily satisfied by cyano-bacteria

The N:P ratio cannot be used to determine the nutrient that must be reduced to restore water quality The N:P ratio can be useful for regulating algal species composition

30

2. Nutrient Limitation (Restoration Strategies)

At a minimum restoration strategy should be to maximize the N:P ratio to create favorable conditions for desirable plankton species – Maximize N:P ratio by reducing P inputs to the lake

Restoration strategy should maximize P removal – However, most BMPs which remove P also remove N as well – P is easier and much less expensive to remove with more predictable

outcomes than N

P removal must be applied to all P sources, not just external sources – Internal recycling of P is significant in most eutrophic lakes and must be

addressed as a nutrient source

31

2. Nutrient Limitation (Restoration Strategies – cont.)

3. Internal Recycling

32

P retention ~ 80-95%

N retention ~ 40-50%

Oligotrophic Lake - few nutrients - low productivity - little sediment - P limited - N:P ratio >30

Mesotrophic Lake - increasing nutrients - moderate prod. - increasing sediment - decreasing depth - N:P ratio ~ 10-30

Eutrophic Lake - high nutrients - high productivity - deep sediments - plant invasions - N:P ratio <10 33

3. Internal Recycling (Nutrient Retention During Lake Aging)

Lakes are sinks for nutrients – accumulated nutrients can be recycled – internal loading of P can be the dominant source in a lake

Internal loading supports algal blooms and favors cyano- bacteria by low N:P ratio

Watershed management cannot eliminate internal loading

34

3. Internal Recycling – cont. (Internal Loading)

Hypolimnion -Poor circulation

- Anoxic

Epilimnion - Photic zone

~1% of surface light

Photosynthesis > Respiration

Respiration > Photosynthesis

Pelagic Zone (Open water) Littoral Zone

Littoral Zone

- P inputs to lakes accumulate in the sediments over time -Bacteria in sediments decompose organic matter and release soluble P

-Iron is an abundant element in many sediments, and forms precipitate with P -When sediments are anoxic, the Fe-P bond is unstable, and P is released

-P diffuses from sediments into water column -Zone of potential P release extends to at least 10 cm into sediments 35

3. Internal Recycling – cont. (Typical Zonation in a Lake)

If a lake has high external loading, then it also has a high internal loading

Nürnberg & LaZerte 2001

10 100 1000 10000 External load (mg/m2-yr)

1

10

100

1000

10000 In

tern

al L

oad

(mg/

m2 -

yr)

1:1

36

3. Internal Recycling – cont. (Signs of Internal Recycling)

Mesotrophic Lakes

Figure 2-15c

Seepage Meter

Float

If your lake looks like this, you probably don’t have significant internal recycling

If your lake looks like this, you probably do have significant internal recycling 37

3. Internal Recycling – cont. (Signs of Internal Recycling)

Precipitation6%

Runoff51%

Direct Overland Flow5%

Groundwater Seepage

<1%

Lake Inwood<1%

Recycling37%

Pumped Discharge to Little Lake

Conway9%

Sediments91%

Precipitation6%

Runoff51%

Direct Overland Flow5%

Groundwater Seepage

<1%

Lake Inwood<1%

Recycling37%

Pumped Discharge to Little Lake

Conway9%

Sediments91%

TP Inputs

TP Losses

Lake Anderson

- 12.7 acre urban lake - mean depth = 13 ft.

- mesotrophic/eutrophic

38

Lake Killarney

- 240 acre urban lake - mean depth = 15 ft.

- mesotrophic/eutrophic - significant BMPs installed

TP Inputs

TP Losses

Precipitation8%

Runoff17%

Direct Overland Flow1%

Lake Bell Inflow1%

Lake Mendsen Inflow

2%

Seepage8%

Recycling63%

Drainage Wells4%

Sediments96%

39

Lake Holden (266 ac.)

Watershed Boundary

(769 ac. total)

Watershed/Lake Area Ratio = 2.9

40

Total P

Year

1970 1975 1980 1985 1990 1995

Tota

l Pho

spho

rus

(mg/

l)

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

Trend Line: R-square = 0.6646

3. Internal Recycling – cont. (Total Phosphorus in Lake Holden from 1972-1991)

Trophic State Index

Year

1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992

Trop

hic

Stat

e In

dex

50

55

60

65

70

75

80Trend Line: R-square = 0.6646

Hypereutrophic

Eutrophic

MesotrophicHydrilla

Infestations

-During the period from 1985-1991, Lake

Holden ranked second only to Lake Apopka

for highest mean annual TSI value in

Orange County

-Aeration systems installed in 1981 but removed in 1984 due

to declining water quality

Aeration Installed

Aeration Discontinued

3. Internal Recycling – cont. (TSI Values in Lake Holden from 1972-1991)

Sub-basins Retrofitted with Alum Stormwater Treatment Systems

43

Sub-basin 12 (26.3 ac.)

Wet Detention

Pond

The installed BMPs (alum + wet detention) included: - 64% of the annual runoff volume - 80% of annual runoff P loadings

In addition, the MSTU funded:

- Constructed 2 dry detention ponds

- Initiated weekly vacuum street sweeping

- Installed 120 inlet baskets, maintained monthly

- Installed CDS unit - Extensive SAV planting

44

3. Internal Recycling – cont. (Sub-Basin 13 Wet Detention Pond)

Lake Holden

Roadway Areas with Current Street Sweeping

Activities in all Unincorporated Areas

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 2 7 12 13 21

Sub-Basin

To

tal

Ph

os

ph

oru

s (

µg

/l)

19922004

46

Changes in Runoff Characteristics: 1992-2004

AST

AST

AST

WP

WP

WP

AST – Alum Treatment System WP – Wet Pond/Retention

Year

1985

19

86

1987

19

88

1989

19

90

1991

19

92

1993

19

94

1995

19

96

1997

19

98

1999

20

00

2001

20

02

2003

20

04

2005

20

06

2007

20

08

2009

20

10

2011

20

12

2013

Tota

l Nitro

gen

(µg/l

)

0

500

1000

1500

2000

2500

Year

1985

19

86

1987

19

88

1989

19

90

1991

19

92

1993

19

94

1995

19

96

1997

19

98

1999

20

00

2001

20

02

2003

20

04

2005

20

06

2007

20

08

2009

20

10

2011

20

12

2013

Tota

l Pho

spho

rus (

µg/l)

0

10

20

30

40

50

60

70

AlumAdditions

AlumAdditions

Alum

SW

Trea

t.Al

um S

W Tr

eat.

47

Mean Annual Concentrations of Total Phosphorus in Lake Holden from 1985-2012

Collection of Core Samples

Incubation Set-Up

Large diameter sediment core samples collected at various areas and depths Core samples incubated in dark under aerobic and anoxic conditions 20 ml water samples collected daily for 30 days and analyzed for SRP and TP P release rate defined as slope of ΔP over time

Estimation of Internal Recycling

48

Lake Holden Total P Budget

Total Phosphorus Inputs

Internal Recyling, 265 kg/yr

Stormwater Runoff,

201 kg/yr

Bulk Precipitation,

31.4 kg/yrGroundwater Seepage, 11.1 kg/yr

49

Summary of Alum Additions to Lake Holden

Dates Alum

(gallons) Water Column Dose

(mg Al/liter)

4/4/05 – 4/8/05 77,794 4.4

9/7/05 - 9/22/05 112,012 6.3

2/22/06 – 3/1/06 94,500 5.3

1/8/10 – 1/14/10 47,701 2.7

6/1/10 – 7/2/10 47,824 2.7

1/24/12 – 2/1/12 47,546 2.6

Total: 427,377 24.0

50

3. Internal Recycling – cont. (Alum Application Techniques)

Application Equipment

Lake Killarney During Application

Year

1985

19

86

1987

19

88

1989

19

90

1991

19

92

1993

19

94

1995

19

96

1997

19

98

1999

20

00

2001

20

02

2003

20

04

2005

20

06

2007

20

08

2009

20

10

2011

20

12

2013

Tota

l Nitr

ogen

(µg/

l)

0

500

1000

1500

2000

2500

Year

1985

19

86

1987

19

88

1989

19

90

1991

19

92

1993

19

94

1995

19

96

1997

19

98

1999

20

00

2001

20

02

2003

20

04

2005

20

06

2007

20

08

2009

20

10

2011

20

12

2013

Tota

l Pho

spho

rus

(µg/

l)

0

10

20

30

40

50

60

70

AlumAdditions

AlumAdditions

Alum

SW

Tre

at.

Alum

SW

Tre

at.

52

Mean Annual Concentrations of Total Phosphorus in Lake Holden from 1985-2012

Aerial photo of Lake Holden

during January 2010

- Growth of vegetation visible over much of lake

bottom

53

Overview of Lake Yale Figure 1-3

Overview of Lake Yale

LakeYale

(4,012 ac.)

Umatilla

- Prior to 1985, Lake Yale was an oligotrophic lake with submerged

vegetation over the entire lake bottom

- Excellent fishing resource

Water Depth Contours for Lake Yale

Trends in Total Phosphorus and

Chlorophyll-a in Lake Yale from

1982-2016

- statistically significant increases in both TP and Chlorophyll-a

over time

- impairment status caused by improper vegetation

management, not runoff

Total Nitrogen

Year

82 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12 14 16 18

TN (µ

g/l)

0

1000

2000

3000

4000

LakeWatchLake Co. - CenterLake Co. - North CenterLake Co. - South CenterSJRWMD - 20020371SJRWMD - LYCAnnual Average

Total Phosphorus

Year

82 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12 14 16 18

TP (µ

g/l)

0

10

20

30

40

50

60

p = <0.0001slope = 0.53 / year

p = <0.0001slope = 44.1 / year

Chlorophyl - a

Year

82 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12 14 16 18

Cho

loro

phyl

- a

(mg/

m3 )

0

20

40

60

80

100

120

140

LakeWatchLake Co. - CenterLake Co. - North CenterLake Co. - South CenterSJRWMD - 20020371SJRWMD - LYCAnnual Average

Secchi Depth

Year

82 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12 14 16 18

Secc

hi D

epth

(m)

0

1

2

3

4

5

p = 0.0005slope = 0.69 / year

p = <0.0001slope = -0.05 / year

Trends in Secchi Disk Depth and TSI

in Lake Yale from 1982-2016

- statistically significant decrease

in Secchi Depth and increase in TSI

- decrease in water clarity

prevents submerged vegetation from recovering

Chlorophyl - a

Year

82 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12 14 16 18

Cho

loro

phyl

- a

(mg/

m3 )

0

20

40

60

80

100

120

140

LakeWatchLake Co. - CenterLake Co. - North CenterLake Co. - South CenterSJRWMD - 20020371SJRWMD - LYCAnnual Average

Secchi Depth

Year

82 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12 14 16 18

Secc

hi D

epth

(m)

0

1

2

3

4

5

p = 0.0005slope = 0.69 / year

p = <0.0001slope = -0.05 / year

Trophic State Index

Year

82 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12 14 16 18

TSI

0

10

20

30

40

50

60

70

80

90

TN/TP Ratio

Year

82 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12 14 16 18

TN/T

P R

atio

0

10

20

30

40

50

60

70

80

90

100

110

120

LakeWatchSJRWMD - 20020371SJRWMD - LYC Annual Average

Oligotrophic

Mesotrophic

Eutrophic

Hypereutrophic

Nitrogen Limited

Balanced

Phosphorus Limited

p = <0.0001slope = 0.83 / year

p = 0.8754slope = 0.28 / year

Calculated Mean Annual Loadings of Total Nitrogen and Total Phosphorus Discharging to Lake Yale

Source

Total Nitrogen

Loading

Total Phosphorus

Loading

kg/yr % of Total kg/yr % of Total Bulk Precipitation 15,771 64 1,249 13

Runoff 2,985 12 507 5

Overland Flow 27 < 1 1.6 < 1

Groundwater Seepage 4,341 18 149 2

Internal Recycling 1,429 6 7,981 80

TOTALS: 24,553 100 9,888 100

Comparison of Estimated TMDL and ERD Calculated Loadings of Total Phosphorus to Lake Yale

Source

Annual Total Phosphorus Load

(kg/yr)

TMDL ERD

Bulk Precipitation 14321 (combined)

1249

Runoff + Overland Flow 509

Groundwater Seepage Not Included 149

Internal Recycling Not Included 7,981

TOTAL: 1,432 9,888

1. TMDL requires a 10% reduction in runoff TP = 143 kg/yr = 1.4% of annual ERD load

Sediment P Release as a Function of Trophic State in Central Florida Lakes

60

Phosphorus Release

Aero

bic

rele

ase

(o)

Anox

ic re

leas

e (o

)

Aero

bic

rele

ase

(m)

Anox

ic re

leas

e (m

)

Aero

bic

rele

ase

(e)

Anox

ic re

leas

e (e

)

Phos

phor

us R

elea

se (m

g/m

2 -yr)

0

200

400

600

800

1000

1200

1400

1600

1800

Oligotrophic Lakes (n = 3)

Mesotrophic Lakes (n = 6)

Eutrophic Lakes (n = 4)

Aerobic Anoxic Aerobic Aerobic Anoxic Anoxic

Question

What are we really trying to do?

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Summary

Current TMDL techniques omit significant loading sources to waterbodies

– Baseflow – Seepage – Internal recycling

Omitted parameters are often significant loading sources Process over emphasizes significance of runoff loadings

– Leads to expensive BMP projects with limited water quality improvements

Limiting nutrient concept is incorrectly used – Eutrophic lakes can only be restored by removing P – P removal is less expensive and more reliable than N

Although water quality problems may have been created by runoff, restoration cannot be achieved by treating runoff alone

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Summary – cont.

All eutrophic lakes have significant internal recycling – In many lakes, internal recycling is more significant than runoff inflows – If water quality restoration is the primary objective, then treatment of

stormwater may not provide the best improvement – Control of internal recycling is a highly reliable and low cost method of

reducing P loadings Internal P inactivation - ~ $50/kg TP (20-year PW cost) Stormwater BMPs - ~ $200-10,000+/kg TP (20-year PW cost)

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Questions?

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