Nutrient Loading Rates from Irrigation with Reclaimed Water

June 16, 2017

Florida Irrigates with Reuse

2015 Reuse Inventory, Water Reuse Program, Florida Department of Environmental Protection, May, 2016

About 738 MGD of reclaimed water

produced in Florida in 2015

We all know inappropriate fertilizer application can lead to eutrophication. But, what about landscape irrigation with reclaimed water?

Asking Good Questions• What is the concentration of nitrogen and

phosphorus in reclaimed water? • How much nitrogen and phosphorus are loaded

to lawns as a result of irrigating with reclaimed water?

• Is supplemental fertilization necessary if I irrigate with reclaimed water?

• Does responsible landscape irrigation with reclaimed water lead to eutrophication of downstream waters?

Study Site

Loxahatchee RiverPhoto © M. Dubiner

Study System

25 days mean residence time

165 MG storage

Study Site

Name TypeArea

Irrigated (acres)

Irrigation Amount (MGD)

Reclaimed Water Application Rate

(gallons/acre/day)Jupiter Country Club Golf Course 260 0.90 3,462Bear’s Club Golf Course 141 0.50 3,546Trump National* Golf Course 130 0.50 3,846Turtle Creek Golf Course 138 0.55 3,986Loxahatchee Club Golf Course 163 0.65 3,988Indian Creek Golf Course 85 0.34 4,000Riverbend Golf Course 100 0.40 4,000Tequesta CC Golf Course 125 0.50 4,000Admiral’s Cove Golf Course 350 1.40 4,000Jonathan’s Landing Golf Course 120 0.48 4,000Jupiter Hills #1 Golf Course 110 0.54 4,909Abacoa Mixed Use† 807 4.10 5,081Jupiter Hills #2 Golf Course 110 0.66 6,000

Total = 2,639 11.52 4,365

Study Site

Study System

Methods

Parameter Analytical MethodTotal Kjeldahl Nitrogen (TKN) EPA 351.2Nitrate + Nitrite (NO2 + NO3) EPA 353.2Ammonia Nitrogen (NH3) SM 4500-NH3 CTotal Phosphorus (TP) SM 4500-P E

NELAC certified laboratory analyzed the followingwater quality parameters using approvedanalytical methods.

0

3

6

9

12

15

18

21

End of Pipe On-SiteStorage

Lake

Off-SiteStorageLakes

SprinklerHeads

DownstreamCanal

Nitr

ogen

(mg-

N/L

)

Organic N Inorganic N

How Much Nitrogen?

Period of Record: 2009-2016; Error bars represent ± 1 standard deviation

77% reduction

44% reduction

N=95

N=93 N=144N=241 N=28

34% reduction

0

1

2

3

End of Pipe On-SiteStorage Lake

Off-SiteStorage Lakes

SprinklerHeads

DownstreamCanal

Phos

phor

us (m

g-P/

L)

Total Phosphorus

How Much Phosphorus?

Period of Record: 2009-2016; Error bars represent ± 1 standard deviation

34% reduction

19% reduction

27% reduction*

N=295 N=94 N=144 N=246 N=28

Estimating Nutrient Loading• Nutrient concentrations

– I’ve shown they decline considerably as reclaimed water moves through the distribution system.

• Irrigation Rate – Abacoa’s actual landscape irrigation rates, on

average, were 2,668 gallons per acre per day (0.52 inches per week), with contractually-defined maximum irrigation rates no more than 4,000gallons per acre per day (1 inch per week).

• Nutrient loading rates were standardized using pounds (of nitrogen or phosphorus) per 1,000 ft2 per year.

Actual Irrigation Rate Relative to Actual Rainfall Rate

0

2

4

6

8

10

12

14

16

18

Jan-

09Ju

l-09

Jan-

10Ju

l-10

Jan-

11Ju

l-11

Jan-

12Ju

l-12

Jan-

13Ju

l-13

Jan-

14Ju

l-14

Jan-

15Ju

l-15

Jan-

16Ju

l-16

Rain

fall

& Ir

rigat

ion

Rate

(in

ches

per

mon

th)

Irrigation Rainfall

Nitrogen Loading based on actual reclaimed water irrigation rate

Period of Record = 2009-2016

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

End of Pipe On-Site StorageLake

Off-Site StorageLake

Sprinkler Head

Nitro

gen

Appl

icatio

n Ra

te

(lbs/

1,00

0 ft2

/yr)

Total Nitrogen Inorganic Nitrogen

0%

20%

40%

60%

80%

100%

120%

140%

End of Pipe On-SiteStorage Lake

Off-SiteStorage Lake

Sprinkler Head

Nitr

ogen

App

licat

ion

Rat

e (%

of T

arge

t)

Total Nitrogen Inorganic Nitrogen

Nitrogen Loadingbased on actual reclaimed water irrigation rate

3 lbs/1,000 ft2/yr; Knox et al. 2002. Fertilizer Recommendations for Landscape Plants.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

End of Pipe On-Site StorageLake

Off-Site StorageLake

Sprinkler Head

Phos

phor

us A

pplic

atio

n Ra

te

(lbs/

1,00

0 ft2

/yr)

Total Phosphorus

Phosphorus Loading based on actual reclaimed water irrigation rate

Period of Record = 2009-2015

Findings by EW Consultants, Inc• Quantitative and qualitative assessment of

turf grass health in Abacoa across 0%, 50%, 75%, and 100% of ‘normal’ fertilizer application rates.

• “nutrients delivered with the reclaimed irrigation water when combined with 75% of the recommended fertilization can achieve nearly identical turfgrass quality.”

Abacoa Reclaimed Water Fertilization Study Fertilization Guidelines. June, 2015. EW Consultants, Inc.

Questions Answered• How much nitrogen and phosphorus are in

reclaimed water? – Depends where you are in the transmission system, but

a lot less than was expected.• How much nitrogen and phosphorus are loaded to

lawns as a result of irrigating with reclaimed water? – Not nearly as much as has been suggested.

• Is supplemental fertilization necessary if I irrigate with reclaimed water? – Yes, in this study system; nonetheless, fertilizer

application rates should be offset based on nutrient loading from reclaimed water irrigation.

Questions Answered• Does responsible landscape irrigation with

reclaimed water lead to eutrophication of downstream waters?– No. – Downstream canal samples showed TN and

TP concentrations were both lower than pending DEP/EPA numeric nutrient criteria for streams in the Peninsula Region (i.e., TN < 1.54 mg/l and TP < 0.12 mg/L).

What did we Learn?Significant ‘treatment’ occurs within

reclaimed water storage lakes. Inorganic nitrogen appears to be assimilated. Moving reclaimed water through the

existing storage and transmission system appears to be a cost & energy efficient option to achieve significant nutrient reduction. (AWT for free!)

Treatment Plant

Treatment Plants

Regulatory ConsiderationsEnd of pipe concentrations are irrelevant.Estimated nutrient loading rates are

significantly over estimated when end of pipe nutrient concentrations are used.

Permits should be structured so nutrient limits are measured at a relevant point of discharge (i.e., sprinkler heads).

Regulations should consider actual nutrient loading rates and provide offsets when fertilizer use is proportionately reduced.

Additional ResearchWe need to better characterize water

quality throughout reuse distribution systems, especially at sprinkler heads. We need to better understand variability of

nutrient concentrations within and across reuse distribution systems.We need to understand the

mechanisms driving reduced nutrient concentrations.

Thank you

Nitrogen Loading based on MAXIMUM reclaimed water irrigation rate

Period of Record = 2009-2016

0%

50%

100%

150%

200%

End of Pipe On-SiteStorage Lake

Off-SiteStorage Lake

Sprinkler HeadNitr

ogen

App

licat

ion

Rat

e (%

of T

arge

t)

Total Nitrogen