Watershed and water quality assessment of the Allen’s Creek watershed

David A. Tomasko, Ph.D.

Cheryl Propst, M.S.

May 16, 2012

Allen’s Creek Water Quality Stations

Marine stations predominate – example station locations

Station 19-02Belcher RoadSaltwater Site

Station 19-04St. Paul’s DriveSaltwater Site

Station 19-06Bellair Road

Saltwater Site

Station 19-03Longbow Lane

Freshwater Site

Station 19-05Bellair Road

Freshwater Site

Shelf under Bellair Road bridge prevents brackish water from flowing upstream

during incoming tide

Red mangroves and horses downstream

of Bellair Road culverts. Lift station

on upstream side.

Station 19-10Kent Place

Freshwater Site

Black mangroves appear in tidal area downstream where tributary meets

Allen’s Creek

Outside* of WBIDSample upstream of culvert

How is water quality at these sites?

• Rather than WBID as a whole, data looked at station by station

• Water quality data compared to IWR criteria• Number of “exceedances” compared to

verified list criteria

FDEP Screening Criteria Station Summary

Station* Marine/FreshwaterChl a

Corrected BOD DOFecal

Coliforms

21FLPDEM19-01 Marine 54/15 59/17 34/15 18/16

21FLPDEM19-02 Marine 68/14 82/21 34/15 16/16

21FLPDEM19-03 Freshwater ID ID 64/21 ID

21FLPDEM19-04 Marine 78/19 ID 58/21 ID

21FLPDEM19-06 Marine 71/21 ID 50/21 ID

21FLTPA27554138244454 Marine ID ID 52/22 ID

21FLPDEM19-10 Freshwater ID 69/16 76/18

*Stations with N≥25 at a depth of ≤ 0.5m

ID = Insufficient Data

Mean Value Above Target and Meets Verified List Criteria

Mean Value Below Target but Verified Impaired due to % Exceedance

<10% Exceedance

0% Exceedance

Percent exceedance criteria vary with sample size. Numbers within cells represent – Actual % Exceedance / % Exceedance Criteria.

Findings

• Most marine sites had levels of Chl-a in excess of IWR guidance (11 ug / liter) and would also exceed criteria for Old Tampa Bay

• Stations 1 and 2 exceed for Chl-a, BOD, DO and fecal colifom bacteria

• DO criteria is being revised by FDEP– Allens Creek not a trout stream

• Bacteria impairments the basis for existing TMDL

Does fecal coliform bacteria exceedance mean sewage leaks?

• Perhaps leaks are involved, but…• Impacts of birds are well documented in literature

– Estimates in prior TMDLs of 200 to 400 million fecal coliform bacteria per bird per day– humans about 2 billion per day

• Using low end estimate, one bird could cause 13,000 gallons of water to exceed 400 CFU / 100 ml

• Experiment in Clam Bay (Collier County) - – Source ID work found no evidence of human impacts (nor did sewage collection

system operators)– Variety of bird fecal “events” sampled– Highest range was > 200,000 fecal coliform bacteria from one bird (white ibis) from

one event• It is within the realm of possibilities that birds are an important source of

bacteria in Allens Creek– Additional source identification efforts could be warranted

Photo from Estero Bay, Lee County

Does exceedance of Chl-a mean nutrient enrichment is to blame?

• Data from marine and freshwater stations were compared to screening criteria used by FDEP and EPA for TMDL loading models

• Additional screening criteria used– FDEP’s recently adopted NNC criteria– EMC values for residential stormwater runoff– EMC values for forested uplands (for comparison)– Locally-derived TN and TP from regression equations

vs. Chl-a and appropriate targets (11 and 20 ug / liter)

Freshwater Screening Level Criteria

Forested Uplands

EMC value Single Family Residential EMC Value FDEP NNC Criteria

TMDL

TargetsSarasota Bay (Heyl 1992)

1993 TBEP Loading Model

Sarasota Bay (Heyl 1992)

62-302 F.A.C.(regional streams)

TN (mg/l) 1.60 1.02 1.90 1.87 1.54

TP (mg/l) 0.22 0.16 0.31 0.39 0.12

Marine Screening Level Criteria

Forested Uplands

EMC value Single Family Residential EMC Value FDEP NNC Criteria

TMDL

TargetsSarasota Bay (Heyl 1992)

1993 TBEP Loading Model

Sarasota Bay (Heyl 1992)

62-302 F.A.C. (Old Tampa Bay)

TN (mg/l) 1.00 1.02 1.9 1.87 1.08

TP (mg/l) 0.19 0.16 0.31 0.39 0.23

FDEP Screening Criteria Station Summary

Station* Marine/FreshwaterChl a

Corrected TN TP BOD DOFecal

Coliforms

21FLPDEM19-01 Marine 54/15 26/15 83/15 59/17 34/15 18/16

21FLPDEM19-02 Marine 68/14 22/15 56/15 82/21 34/15 16/16

21FLPDEM19-03 Freshwater ID 6/19 36/21 ID 64/21 ID

21FLPDEM19-04 Marine 78/19 77/19 91/21 ID 58/21 ID

21FLPDEM19-06 Marine 71/21 82/21 48/21 ID 50/21 ID

21FLTPA27554138244454 Marine ID ID ID ID 52/22 ID

21FLPDEM19-10 Freshwater 3/16 43/16 ID 69/16 76/18

*Stations with N≥25 at a depth of ≤ 0.5m

ID = Insufficient Data

Mean Value Above Target and Meets Verified List Criteria

Mean Value Below Target but Verified Impaired due to % Exceedance

<10% Exceedance

0% Exceedance

Percent exceedance criteria vary with sample size. Numbers within cells represent - Actual % Exceedance / % Exceedance Criteria.

Nutrient-related “exceedances”

• Highest exceedance rates are at marine sites at St. Paul’s Drive and Bellair Road (19-04 and 19-06)

• Other marine sites exceeded criteria thresholds, but mean value below target criteria

• Neither freshwater sites had TN exceedance– This is where nutrients come from

• TP exceedance was widespread– But is TP the likely limiting nutrient?

21FLPDEM19-01

21FLPDEM19-02

21FLPDEM19-03

21FLPDEM19-04

21FLPDEM19-06

21FLPDEM19-10

21FLTPA 275541382444540.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0Mean TN:TP by Station

Station

Mea

n TN

:TP

21FLPDEM19-01

21FLPDEM19-02

21FLPDEM19-04

21FLPDEM19-060.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

Marine Stations(Total Nitrogen)

TMDL TN Target Forested Uplands TN Target TBEP Model TN TargetSarasota Bay TN Target 62-302 F.A.C. (OTB) TN Target Regression Analysis TN Target

Mea

n TN

(mg/

l)

Targets determined using regression analysis were based on chlorophyll a criteria of 11 µg/l

21FLPDEM19-01

21FLPDEM19-02

21FLPDEM19-04

21FLPDEM19-060.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

Marine Stations(Total Phosphorus)

TMDL TP Target Forested Uplands TP Target TBEP Model TP TargetSarasota Bay TP Target 62-302 F.A.C. (OTB) TP Target Regression Analysis TP Target

Mea

n TP

(mg/

l)

Targets determined using regression analysis were based on chlorophyll a criteria of 11 µg/l

21FLPDEM19-03

21FLPDEM19-100.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

Freshwater Stations(Total Nitrogen)

TMDL TN Target Forested Uplands TN Target TBEP Model TN TargetSarasota Bay TN Target 62-302 F.A.C. TN Target

Mea

n TN

(mg/

l)

Targets determined using regression analysis were based on chlorophyll a criteria of 20 µg/l

21FLPDEM19-03

21FLPDEM19-100.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

Freshwater Stations(Total Phosphorus)

TMDL TP Target Forested Uplands TP Target TBEP Model TP Target Sarasota Bay TP Target62-302 F.A.C. TP Target

Mea

n TP

(mg/

l)

Targets determined using regression analysis were based on chlorophyll a criteria of 20 µg/l

Is there a relationship between nutrients and corrected chlorophyll a levels?

StationMean TN:TP

TN Correlatio

n

TN Regression

R2

TP Correlatio

n

TP Regression

R2

21FLPDEM19-01 3.26 X 0.144 X 0.151

21FLPDEM19-02 3.86 X* 0.181 X 0.137

21FLPDEM19-03 5.50        

21FLPDEM19-04 4.78     X* 0.231

21FLPDEM19-06 6.81     X* 0.233

21FLPDEM19-10 4.59        21FLTPA 27554138244454 4.89 X* 0.315 X* 0.649

All Freshwater Stations   X* 0.516    

All Saltwater Stations 0.869 X* 0.15

 

Significant correlation defined at p<0.05         

*Not normal distribution         

Is there a relationship between nutrients and salinity levels?

StationMarine or

Freshwater

TN Correlati

on

TN Regression

R2

TP Correlati

on

TP Regression

R2

21FLPDEM19-01 Marine X 0.843    

21FLPDEM19-02 Marine X* 0.750    

21FLPDEM19-04 Marine        

21FLPDEM19-06 Marine     X* 0.165

All Stations Mixed X* 0.442 X* 0.159

Significant correlation defined at p<0.05      

*Not normal distribution      

**N<20          

Recommendations moving forward

• Source identification efforts and focused efforts to document potential role of birds on bacteria within Allen's Creek

• Work with FDEP to ensure reasonableness of proposed alternative DO criteria for freshwater and marine waters

Recommendations moving forward

• Based on TN:TP ratios, phosphorus not a nutrient of concern for eutrophication– Exceedances may have more to do with regional geology than

eutrophication• Work with FDEP to develop site-specific alternative criteria

for TN (and maybe TP)– Regression analysis to develop TN for 11 and 20 ug /liter for

marine and freshwater stations– Develop salinity-normalized TN and TP targets for regular

reporting (e.g., Clam Bay’s SSAC in 62-302)• Ensure that loading model used is appropriate for

developing load reduction targets for various stations

Questions or comments?