1. Nutrients and Ecosystems

3. Fertilizer Application Rates
Lawns: kg N/ha/yr
Athletic Fields: kg N/ha/yr
Pastures (Dairy): kg N/ha/yr
Vegetables: kg N/ha/yr
Corn: kg N/ha/yr
Citrus: kg N/ha/yr
Forests: kg N/ha/20+ yrs

4. Nutrient Loads to the Land
Landuse Nitrogen Load Phosphorus Loads
Crops 350 kg/ha/yr 40 kg/ha/yr
Pasture 125 kg/ha/yr 25 kg/ha/yr
Lawn kg/ha/yr 20 kg/ha/yr
Forest 25 kg/ha/yr 2+ kg/ha/yr

6. USGS, 2000

7. Nutrient Loading Calculations

8. Estimating Biological Response from Concentration
Recall that TP is strongly correlated with chlorophyll a production in shallow lakes
Use measured or predicted TP to estimate lake response

9. 5. Gator Lake TP concentration with a totally forested watershed is 6 mg/m3. What is the predicted Secchi depth?
What is the predicted Secchi for the lake if 10 ha of the watershed are converted to urban land use?
TP= 100 mg/m3

11. Biven’s Arm TN= 2,700 mg/m3 TP= 230 mg/m3 chlA= 130 Secchi ~0.5m
Hypereutrophic

12. Lake Sheeler
TN= 70 mg/m3
TP= 4 mg/m3
chlA=1 mg/m3
Secchi = 8m
Oligotrophic

13. Silver Springs
TN= 1400 mg/m3
TP= 50 mg/m3
chlA=1 mg/m3
Secchi = 50 m
Trophic State?

14. TN= 730 mg/m3
TP= 50 mg/m3
chlA=1 mg/m3
Secchi = 50m
Trophic State?

15. Lake Santa Fe
TN = 450 mg/m3
TP= 15 mg/m3
chlA = 8
Secchi = 1.5m
Mesotrophic

16. TN = 450 mg/m3
TP= 15 mg/m3
chlA = 8
Secchi = 1.5m

17. Lake Alice
TN = 500
TP = 550
chlA = 10
Secchi = 1.7

18. TN = 500
TP= 550
chlA= 10
Secchi 1.7m

19. mg / m2water body surface area / yr
Watershed export is the amount of a substance exported from a watershed usually expressed as:
kg / hawatershed / yr
Water body load is the amount of a substance delivered to a water body usually expressed as:
mg / m2water body surface area / yr

20. Watershed Export (Flux)
Export is a MASS (kg)
Index time (per year) and area (per hectare)
Typical units: kg/ha/yr
To get mass: flow volume x concentration
Flow (m3/yr) x Conc. (mg/m3) = mass (mg/yr)
To get mass per hectare, divide by area

21. Lake Loading
Mass export from the watershed impacts a lake (or estuary) in proportion to the area of that aquatic system
Lake loading is mass (kg/yr) per lake area (m2)
Units: kg/m2/yr
We work on what happens to that load later

22. 1,000,000 mg = 1 kg Example Export - Load Problem: 50 ha watershed
2,000,000 m3/yr runoff
[TP] in runoff is 20 mg/m3
Water body is a 5 ha lake.
Export
1,000,000 mg = 1 kg
2,000,000 m3 x 20 mg/m3 = 40,000,000 mg P = 40kg
(watershed export= 40 kg / 50 ha = 0.80 kg/ha/yr)
Load
40,000,000 mg P / (5 ha x 10,000m2/ha) = 800 mg / m2

23. Example Problem

24. 1. What is the TP export (kg/ha/yr) from the watershed with total forest cover?
500,000 m3 x 10 mg/m3 = 5,000,000 mg = 5 kg
5 kg / 100 ha = 0.05 kg/ha/yr

25. 2. What is the TP load to the Gator Lake with total forest cover?
500,000m3 x 10mg/m3 = 5,000,000 mg
5,000,000mg / (10ha x 10,000m2) = 50mg/m2/yr

26. 3. What is the load to Gator Lake when 10ha of the watershed is converted to urban land use?
90 x 0.05 kg/ha x 1,000,000 mg/kg= 4,500,000 mg
10 x 5.55 kg/ha x 1,000,000 mg/kg= 55,500,000 mg
60,000,000 mg
60,000,000 mg / 100,000 m2 = 600 mg/m2
Lake Surface Area

27. Loads to Lake Concentrations – Using the Das Vollenweider Model
Load (mg/m2/yr lake surface)
TP (mg/m3) = +
Mean lake depth (m)
Flushing rate (y)
Sedimentation ( ) L TP = Z
(ρ+σ)
Models used by WMDs are similar. Estimating sedimentation (σ) in Florida Lakes can be problematic because many are shallow and winds can easily re-suspend bottom sediments (internal load).

28. 4. What is the predicted TP concentration of Gator Lake if 10 ha of the watershed are converted to urban land use? TP L Z
(ρ+σ) =
600
TP=
2 ( )
TP= 100 mg/m3

29. Regulations and Restoration

30. So…what’s an OK Pollution level?
Depends on what you want it for
Designated Use
Potable (Drinking Water)
Fishable/Swimmable
Agricultural/Industrial
When water fails to meet its designated use, government intervenes
Sets Total Maximum Daily Loads (TMDL) to try to clean up the watershed via equitable apportionment of responsibility

31. Water Quality and Designated Use
The Clean Water Act (1972) mandates protection of the nations water for “designated uses”
Water Supply (Class I), Shellfish Harvest (Class II), Fishable (Class III), Industrial (Class V)
Current FDEP move to add “splashable” and “boatable”
Water quality standards are set based on designated use
Numeric criteria (pollutant thresholds based on conc.)
Narrative criteria (ecosystem measures based on effects)

32. Oversight of Designated Uses
Regulation of point source permits (NPDES)
Enforcement of “presumed compliant” activities
BMPs
If water body consistently fails to meet designated use, process of attainment starts
Total Maximum Daily Load (TMDL)
Pollutant/Water Body Specific (establish pollutant load reduction goals based on models and/or historical data)
Equitable apportionment of responsibility
Headed by FDEP in Florida; FDACS/DoF have compliance tasks

33. TMDL Implementation Reduce Watershed Exports Water Body Load
(convert total export to mg and divide by lake surface area)
Water Body Load
(Models: concentration function of load, flushing out puts, sediment outputs & dilution factor)
Water Body Concentration
(Regressions, models, wishful thinking)
Improvements in Use/ Appearance / Biology

34. What TMDL level? Set Watershed Export
Calculate Load that will yield desired concentration
Set Watershed Export
Measure Water Body Concentration
Observe the desired condition
(elsewhere?)
TP<50mg/m3

35. Section 305 (b) of the CWA (fishable, swimmable)
Sample water and/or biology to determine if water meets use for that class (5 classes in Florida)
305 (b) report
Meets use
Partially meets or fails to meet use
303 (d) list of impaired waters
Law Suits
EPA or State (WMDs) set TMDL
Law Suits
TMDL reset
Load reduction allocation
Law Suits

36. Criteria Based on Geography
47 Lake Ecoregions in Florida
3 Level III Ecoregions in Florida

37. Recent Developments – Numeric Nutrient Criteria
Nov 14th 2010 – EPA signed into law new rules about nutrient pollution in Florida
Becomes effective March 6th 2012
Result of lawsuit against EPA by Earthjustice arguing that existing rules were under-protective
Why?
8% of assessed river miles, 26% of assessed lake acres
Increased 3% in extent between 2008 and 2010

38. Narrative vs. Numeric
Narrative – “shall not cause an imbalance in the native flora and fauna”
Intrinsically reactive
Numeric – a single number for all systems
Intrinsically over-general

39. Stressor – Response for Streams
No association in the data between indices of ecological condition and nutrient levels
Elected to use a reference standard whereby the 90th percentile of unimpacted streams is adopted as the criteria

40. What’s Happened? In a word…lawyers Procedural challenges to EPA rules
Arbitrary and capricious standard of review
Excess of authority (state’s rights)
Reference conditions in spite of no cause and effect relationship in streams
Insufficient recognition of natural variation
Florida’s Attorney General, Counties, Municipalities, Florida Farm Bureau, etc.