# Status Review and Key Issues for the Nutrient Criteria to Protect Florida’s Lakes Ken Weaver Standards and Assessment Section Florida Department of Environmental Protection 

# June 3, 2009 1

# Lakes Nutrient Criteria Development Overview  

# DEP has demonstrated significant and strong nutrient relationships with chlorophyll a  

# DEP proposes using chlorophyll a relationships as primary line of evidence  

# LVI response provides additional support for criteria development in clear lakes

2

# Chlorophyll a Thresholds  

## To decide on appropriate chlorophyll a thresholds, first looked at Trophic State Index  

## Carlson (Kent State University) created an interpretation scheme for the TSI based on nutrient/chlorophyll a responses in northern lakes

 

### TSI 30 – 40: Exhibit classical oligotrophy, but some shallower lakes will become anoxic in the hypolimnion during the summer
 

### TSI 40 – 50 : Mesotrophic conditions, Water moderately clear, but increasing probability of anoxia in hypolimnion during summer.
 

### TSI 50 – 60: Lower boundary of classical eutrophy  

## Florida lakes do not have certain attributes of northern lakes, including the presence of cold - water or cool -water fisheries and fully oxygenated hypolimnetic (bottom) areas 3

# Chlorophyll a Thresholds (continued)  

## Salas and Martino (1991) proposed an alternate TSI categorization based on their work in phosphorus limited warm- water tropical lakes

 

## TSI in mesotropic warm- water lakes range from 50 to 60  

## TSI of 60 is equivalent to a chlorophyll a of 20 μg/L  

## Eutrophy occurs at a TSI ≥70  

## Oligotrophy occurs at TSI ≤ 40
4 

# TSI Category TP (ug/L) Chlorophyll a

40 Oligotrophic 21.3 5 50 Mesotrophic 39.6 10 70 Eutrophic 118.7 40

# Chlorophyll a Thresholds (continued)  

# IWR TAC recommended TSI threshold of 60 for most Florida Lakes  

# However, TAC realized that this may not be protective of oligotrophic lakes

 

# PCA analysis classified TSI and related parameters by color  

# Lakes with Color ≤ 40 PCU had significantly lower TSI (oligotrophic lakes)  

# DEP recommended and TAC agreed to a TSI threshold of 40 for clear lakes ( ≤ 40 PCU )  

# These TSIs equate to chlorophyll a of 20 and 5 μg/L for colored and clear lakes, respectively 5

# Lines of Evidence Supporting Protective Chl - a Thresholds

6 

### Line of Evidence Chlorophyll a target State Paleolimnological studies 14 to 20 μg/L and higher for some lakes (Average condition) Florida Expert opinion 20
- 33 μg/L ( Annual or summertime averages ) Virginia, Iowa, West Virginia, Maryland Fisheries responses (warmwater) 35
- 60 μg/L (Summer average) Virginia Lake user perceptions 20
- 25, up to 30 μg/L in colored lakes (Instantaneous) Texas and Florida Existing levels approach 5
- 27 μg/L (Average condition) Alabama Reference lake approach 9
- 18 μg/L in colored lakes (Average condition) Florida, using 75 th percentile

# Relationships between Chlorophyll a and Cyanobacteria  

# Cyanobacteria blooms can be toxic and present a health risk to people recreating in and on the water  

# World Health Organization  

## A chlorophyll a level of 10 μg/L in which cyanobacteria are dominant presents a relatively low probability of mild effects  

## 50 μg chl - a/L in which cyanobacteria are dominant presents a moderate risk of adverse health effects  

# Cyanobacteria are usually an unfavorable food source to zooplankton and many other aquatic animals 7

# Relationship between chlorophyll a percent Cyanobacteria

8 April 2000 July 2006

5 50 500 -20

0 20 40 60 80 100 120 Dominated by HAB Not Dominated by HAB



### Chlorophyll a (μg/L)CyanobacteriaPercent

• 1,364 phytoplankton samples from small and large lakes sampled between 2000 and 2006 in Florida’s probabilistic sampling network • A small sub - set of individual lakes with repeat visits did show relationships

# Chlorophyll a Thresholds  

# Based on multiple lines of evidence , an annual average chlorophyll a of 20 μg/L in colored lakes is protective of designated uses  

# 5- 10 μg/L in clear lakes
 

## “Maintain existing condition approach”  

## IWR TSI of 40 primarily targeted at a specific geographic region of Florida (the panhandle)  

## Coldwater fishery: 3 - 5 μg/L  

## TetraTech reference lake: 8 μg/L  

## Salas and Martino TSI 50 (mesotrophic): 10 μg/L  

## Seeking TAC feedback 9

# Response Seasonality

Clear Lakes Colored Lakes

10 Jan.-April, Oct.-Dec. May-Sept.Chlorophyll**a**(μg/L)

0.01 0.1

1 10 100 1000

Jan.-April, Oct.-Dec. May-Sept.Chlorophyll**a**(μg/L)

0.1 1 10 100 1000 10000 

## • Similar chlorophyll a levels in summer as in spring, fall, and winter • Chlorophyll a nutrient responses were not significantly different by season • Recommend that the chlorophyll a response be evaluated as an annual average

# Do we Need both N and P?  

# Great deal of recent scientific debate (Schindler et al., 2008)  

# Emphasis on controlling eutrophication in freshwater lakes has been focused heavily on decreasing inputs of phosphorus  

# Many studies in lakes and estuaries still conclude that nitrogen must be controlled as well as, or instead of, phosphorus to reduce eutrophication (Schindler et al., 2008; Howarth & Marino, 2006). 11

# Colored Lake Chl - a Response to Total Phosphorus

12 

### Annual Geometric Mean TP (mg/L) 0.01 0.1 1Annual Geometric Mean Chl-a (μg/L)

1 10 100 Ln (y) = 1.128 Ln(x) + 5.729 R2 = 0.581 Regression Line 50% Prediction Interval


### Chl - a typically > 20 Chl - a typically < 20 Range of Uncertainty

0.05 0.157

# Colored Lake Chl - a Response to Total Nitrogen

13 

### 0.05 0.157 Annual Geometric Mean TN (mg/L) 0.1 1 10Annual Geometric Mean Chl-a (μg/L)

0.1 1 10 100 1000 Ln (y) = 1.965 Ln(x) + 1.995 R2 = 0.645 Regression Line 50% Prediction Interval



### 1.23 2.25

# Colored Lake Chl - a Response to Nutrients (based on lakes with color >40 - 140 PCU) Total Phosphorus

Annual Geometric Mean TN (mg/L) 0.1 1 10Annual Geometric Mean Chl-a (μg/L)

0.1 1 10 100 1000 Ln (y) = 1.965 Ln(x) + 1.995 R2 = 0.645 Regression Line 50% Prediction Interval 

## Total Nitrogen

Annual Geometric Mean TP (mg/L) 0.01 0.1 1Annual Geometric Mean Chl-a (μg/L)

1 10 100 Ln (y) = 1.128 Ln(x) + 5.729 R2 = 0.581 Regression Line 50% Prediction Interval

14

# Florida Colored Lake LVI Response to Nutrients LVI Paired to 1 - year Annual Average N and P (n=52) Phosphorus Response Nitrogen Response

15 One Year Geometric Mean TP (mg/L) 0.01 0.1 1LVI

0 10 20 30 40 50 60 70 80 90 100 y = -7.819 Ln(x) + 35.02 R 2 = 0.198

p =0.001

One Year Geometric Mean TN (mg/L) 0.1 1 10LVI

10 20 30 40 50 60 70 80 90 100 y = -11.5 Ln(x) + 60.02 R 2 = 0.124 p = 0.011

# Draft Colored Lake TP and TN Criteria Stressor Variables Response Variable  

## Chlorophyll a ≤ 20 μg/L as annual geometric mean  

## Potential acute threshold: >40 μg/L in less than 10% of samples on annual basis

 

### Additional IWR threshold  

### 62 - 302?

16 

### 50% Prediction Interval Stressor Lower Threshold Upper Threshold TP (mg/L) 0.05 0.157 TN (mg/L) 1.23 2.25

# Clear Lake Chlorophyll a Response to Total Phosphorus (n=195 lakes, 504 Lake - years)

Annual Geometric Mean TP (mg/L) 0.001 0.01 0.1 1Annual Geometric Mean Chl-a (μg/L)

0.1 1 10 100 1000 Ln (y) = 1.136 Ln(x) + 6.370 R2 = 0.677

Regression Line 50% Prediction Interval

17

# Clear Lake Chlorophyll a Response to Total Nitrogen (n=195 lakes, 509 Lake - years)

Annual Geometric Mean TN (mg/L) 0.1 1 10Annual Geometric MeanChl-a (μg/L)

0.1 1 10 100 1000 Ln (y) = 1.729 Ln (x) + 2.482 R2 = 0.769 Regression Line 50% Prediction Interval

18

# Florida Clear Lake LVI Response to Nutrients LVI Paired to 1 - year Annual Average N and P (n=91)

Annual Geometric Mean TP (mg/L) 0.001 0.01 0.1 1LVI

0 10 20 30 40 50 60 70 80 90 100 y = -12.6 Ln(x) + 0.3 R2 = 0.441

Annual Geometric Mean TN (mg/L) 0.1 1 10LVI

10 20 30 40 50 60 70 80 90 100 y = -15.74 Ln(x) + 43.16 R 2 = 0.287 

# Phosphorus Response Nitrogen Response

1920 

# Alternative Analysis: Algal Bloom Frequency

# Conditional Probability Analysis Probability that a TP Concentration will result in a 10% Exceedance of 40 μg chl - a/L

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### Annual Geometric Mean Total Phosphorus (mg/L) 0.0 0.2 0.4 0.6 0.8 1.0 1.2Probability of >40 μg/ Chl-a inat least 10% of samples

0.0 0.1 0.2 0.3 0.4 0.5 0.6 

### Fitted Logisitc Curve Probability 95% C.I. 0.061 0.107

# Conditional Probability Analysis Probability that a TN Concentration will result in a 10% Exceedance of 40 μg chl - a/L

22 

### Annual Geomteric Mean TN (mg/L) 0 2 4 6 8 10 12Probability of >40 μg/ Chl-a inat least 10% of Samples

0.0 0.1 0.2 0.3 0.4 0.5 0.6
Fitted Logistic Curve Probability 95% C.I. 1.23 2.09

# Lines of Evidence Comparison (Colored Lakes)

23 Annual Geometric Mean Total Phosphorus (mg/L) 0.0 0.2 0.4 0.6 0.8 1.0 1.2Probability of >40 μg/ Chl-a inat least 10% of samples

0.0 0.1 0.2 0.3 0.4 0.5 0.6 Fitted Logisitc Curve Probability 95% C.I. 0.061

0.107

Annual Geomteric Mean TN (mg/L) 0 2 4 6 8 10 12Probability of >40 μg/ Chl-a inat least 10% of Samples

0.0 0.1 0.2 0.3 0.4 0.5 0.6
Fitted Logistic Curve Probability 95% C.I. 1.23 2.09 

### 50% Prediction Interval Stressor Lower Threshold Upper Threshold TP (mg/L) 0.05 0.157 TN (mg/L) 1.23 2.25 

### Bloom Frequency Conditional Probability Annual Average Condition Regression