Nutrients and Ecosystems

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

Nutrient Loads to the Land LanduseNitrogen LoadPhosphorus Loads Crops350 kg/ha/yr40 kg/ha/yr Pasture125 kg/ha/yr25 kg/ha/yr Lawn280 kg/ha/yr20 kg/ha/yr Forest25 kg/ha/yr2+ kg/ha/yr

USGS, 2000

Nutrient Loading Calculations

Watershed Export (kg/ha) Flow m 3 Concentration mg/m 3 Understanding of Lab report Representative sample X Requires:

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/m 3

Biven’s Arm TN= 2,700 mg/m 3 TP= 230 mg/m 3 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= 730 mg/m3 TP= 50 mg/m3 chlA=1 mg/m3 Secchi = 50m Trophic State? Intermediate Aquifer TN=1,470 mg/m3 TP=310 mg/m3

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

Example Export - Load Problem: 50 ha watershed 2,000,000 m 3 /yr runoff [TP] in runoff is 20 mg/m 3 Water body is a 5 ha lake. 2,000,000 m 3 x 20 mg/m 3 = 40,000,000 mg P = 40kg 40,000,000 mg P / (5 ha x 10,000m 2 /ha) = 800 mg / m 2 (watershed export= 40 kg / 50 ha = 0.80 kg/ha/yr) Export Load 1,000,000 mg = 1 kg

Example Problem

1. What is the TP export (kg/ha/yr) from the watershed with total forest cover? 500,000 m 3 x 10 mg/m 3 = 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? 500,000m 3 x 10mg/m 3 = 5,000,000 mg 5,000,000mg / (10ha x 10,000m 2 ) = 50mg/m 2 /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 m 2 = 600 mg/m 2 Lake Surface Area

TP (mg/m 3 ) Load (mg/m 2 /yr lake surface) +Mean lake depth (m)Flushing rate (y)Sedimentation ( ) Loads to Lake Concentrations – Using the Das Vollenweider Model = TP L (ρ+σ)(ρ+σ) Z = 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)(ρ+σ) = ( ) TP= TP= 100 mg/m 3

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

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

Calculate Load that will yield desired concentration Set Watershed Export Measure Water Body Concentration Observe the desired condition (elsewhere?) TP<50mg/m 3 What TMDL level?

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 EPA or State (WMDs) set TMDL TMDL reset Load reduction allocation Law Suits

Watershed export is the amount of a substance exported from a watershed usually expressed as: kg / ha watershed / yr Water body load is the amount of a substance delivered to a water body usually expressed as: mg / m 2 water body surface area / yr

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

Recent Developments – Numeric Nutrient Criteria Nov 14 th 2010 – EPA signed into law new rules about nutrient pollution in Florida –Becomes effective March 6 th 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 90 th 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.