Nutrients and Ecosystems

Fertilizer Application Rates Lawns: 80-240 kg N/ha/yr Athletic Fields: 200-280 kg N/ha/yr Pastures (Dairy): 240-360 kg N/ha/yr Vegetables: 180-200 kg N/ha/yr Corn: 150-210 kg N/ha/yr Citrus: 140-200 kg N/ha/yr Forests: 160-220 kg N/ha/20+ yrs

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 280 kg/ha/yr 20 kg/ha/yr Forest 25 kg/ha/yr 2+ kg/ha/yr

USGS, 2000

Nutrient Loading Calculations

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Example Problem

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

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

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

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).

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 (2.5 +0.5) TP= 100 mg/m3

Regulations and Restoration

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

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)

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

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

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

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

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

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

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

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

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.