Interim Update: Preliminary Analyses of Excursions in the A.R.M. Loxahatchee National
Wildlife Refuge
August 18, 2009
Prepared by SFWMD and FDEP as part of a Working Group of the Technical Oversight
Committee
Data Analyses
• Analyses of the environmental conditions leading up to the November 2008 and June 2009 sample collections included: TP concentrations and loads Rainfall Stage Water depths
Loxahatchee National Wildlife Refuge TP and Stage Data presented at June 30, 2009 TOC Meeting
Additional TP and Stage Data
MonthGeometric Mean TP Concentration
(ppb)
Long-term Level (ppb)
Difference (ppb)
Average Stage (ft NGVD 1929)
Number of TP Samples
Jun-08 8.9 14.9 -6.0 15.68 8Jul-08 9.2 10.3 -1.1 16.37 14Aug-08 8.6 10.2 -1.6 16.39 14Sep-08 7.7 8.3 -0.6 16.81 14Oct-08 7.2 7.2 0.0 17.42 14Nov-08 7.4 7.2 0.2 17.22 14Dec-08 6.3 7.8 -1.5 16.95 14Jan-09 7.0 8.8 -1.8 16.68 14Feb-09 4.7 10.4 -5.7 16.35 12Mar-09 7.5 13.5 -6.0 15.86 9Apr-09 9.7 14.9 -5.2 15.69 8May-09 11.0 N/A N/A 15.01 1
1st sample collection in June 2009
13.2 12.1 1.1 16.05 12
MonthGeometric Mean TP Concentration
(ppb)
Long-term Level (ppb)
Difference (ppb)
Average Stage (ft NGVD 1929)
Number of TP Samples
2nd sample collection in June 2009
9.7 12.8 -3.1 15.96 14
Jul-09 7.4 9.8 -2.4 16.47 14
Estimates of stage were available at all three gauges during all sample collections
Analysis of Rainfall DataAnalysis of Rainfall Data
Analysis of daily rainfall from S-5A, S-6 and S-39: 6-month period prior to May 2009 was driest in 45 years of record
November - April Rainfall Amounts: 1963-2009
The 6-month period preceding May 2009 was the driest on record
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 5 10 15 20 25 30 35 40Rainfall (inches)
Fre
quen
cy o
f L
ower
Rai
nfal
l
1963-2009 Period
1978-1983 Base Period
November 2008 - April 2009 4.99 inches
Analysis of daily rainfall from S-5A, S-6 and S-39: May 2009 was 4th wettest on record; last 2 weeks was 2nd wettest on record
May Rainfall Amounts: 1963-2009May 2009 was the 4th wettest on record; greater than 42 other years
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0Rainfall (inches)
Fre
qu
ency
of
Low
er R
ain
fall
1963-2009 period
1979-1983 base period
May 2009
Analysis of Stage DataAnalysis of Stage Data
Analysis of daily stages from 1-7, 1-8C and 1-9: Rapid fluctuation in stage; lowest 3-gauge average stage was 14.86 ft on May 12, 2009
Refuge Stage: May and June 2009
14.5
15.0
15.5
16.0
16.5
17.0
5/1/
2009
5/8/
2009
5/15
/200
9
5/22
/200
9
5/29
/200
9
6/5/
2009
6/12
/200
9
6/19
/200
9
6/26
/200
9
3-G
auge
Ave
rage
(ft
NG
VD
)
June 1 & 2 2009 Sampling: 16.05 ft
May 2009 Sampling: 15.01 ft
Lowest Stage: 14.86 ft on May 12 2009
June 17 & 19 2009 Sampling: 15.96 ft
Analysis of daily stages from 1-7, 1-8C and 1-9: The monthly change in stage was 3rd highest in 200 months that TP samples
were collected (June 1979-June 2009).
Cumulative Frequency Distribution of Stage ChangeSample Collections from June 1978 to June 2009
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
-1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Monthly Change in Stage (ft/month)
Fre
quen
cy o
f L
ower
Cha
nge
in S
tage
1994-2009
1978-1983 Base Period
June 1 & 2 2009
June 1 & 2 2009: Stage change was greater than
98% of all months
Analysis of hydraulic gradient: East rim canal stage - minimal opportunity for movement of canal water into interior marsh
Comparison of East Canal Stage to Marsh StageAnd Potential Load from STA-1E (assuming 0.1 ft threshold to sustain flow)
13.0
13.5
14.0
14.5
15.0
15.5
16.0
16.5
17.0
17.5
18.0
6/1/
2008
6/15
/200
8
6/29
/200
8
7/13
/200
8
7/27
/200
8
8/10
/200
8
8/24
/200
8
9/7/
2008
9/21
/200
8
10/5
/200
8
10/1
9/20
08
11/2
/200
8
11/1
6/20
08
11/3
0/20
08
12/1
4/20
08
12/2
8/20
08
1/11
/200
9
1/25
/200
9
2/8/
2009
2/22
/200
9
3/8/
2009
3/22
/200
9
4/5/
2009
4/19
/200
9
5/3/
2009
5/17
/200
9
5/31
/200
9
Stag
e (f
t N
GV
D)
0
200
400
600
800
1,000
STA
-1E
Loa
d (k
g)
Marsh
East Canal
Potential STA-1E Load
November 2008June 2009
Analysis of Hydraulic Gradient: West rim canal stage - minimal opportunity for movement of canal water into interior marsh
Comparison of West Canal Stage to Marsh StageAnd Potential Load from STA-1W (assuming 0.1 ft threshold to sustain flow)
13.0
13.5
14.0
14.5
15.0
15.5
16.0
16.5
17.0
17.5
18.0
6/1/
2008
6/15
/200
8
6/29
/200
8
7/13
/200
8
7/27
/200
8
8/10
/200
8
8/24
/200
8
9/7/
2008
9/21
/200
8
10/5
/200
8
10/1
9/20
08
11/2
/200
8
11/1
6/20
08
11/3
0/20
08
12/1
4/20
08
12/2
8/20
08
1/11
/200
9
1/25
/200
9
2/8/
2009
2/22
/200
9
3/8/
2009
3/22
/200
9
4/5/
2009
4/19
/200
9
5/3/
2009
5/17
/200
9
5/31
/200
9
Stag
e (f
t N
GV
D)
0
100
200
300
400
500
600
700
800
900
1,000
STA
-1W
Loa
d (k
g)
Marsh
West Canal
Potential STA-1W Load
November 2008June 2009
Interim Preliminary Finding #1
• An unprecedented sequence of meteorological and hydrological events preceded the June 2009 sample collection.
• A lack of sustainable hydraulic gradient between the rim canal and marsh minimized the opportunity for canal water penetration.
• Environmental conditions (rainfall and stage increase) were outside the range of conditions that were observed during the calibration period used for deriving the compliance equation.
Analysis of TP DataAnalysis of TP Data
Monthly Trend Analysis of TP concentrations at 14 Refuge stations: Statistically significant trend of reductions in TP concentrations
Compliance Period February 1999 Through June 2009
NA
NA
NA
NANA
NA
NA
NA
NA
NA
NA
NA
?
?
0
5
10
15
20
25
30
35
40
45
50
TP
Ge
om
etr
ic M
ea
n (
pp
b)
0
5
10
15
20
25
30
35
40
45
50 Concentration Below Long-term Level
Concentration Exceeding Long-term Level
NA Concentration at Mean Stage <15.42 feet ? Questionable Data
Seasonal Kendall Trend LineGeometric Mean = 9.20 - 0.20 (Year)Tau Statistic = -0.33 p <= 0.001 (p = 0.03 when adjusted for serial dependency)Trend is significant
Long-term Level Effective
Other Evidence TP Concentrations Have Improved
• TP concentrations in the interior of the Refuge compare favorably with the 1978-1979 Base Year and the extended 1978-1983 period used to calibrate the compliance equation.
The average TP concentration of the 14-station network during the June 1978 – May 1979 Base Year was 9.7 ppb, compared with the most recent June – May year average of 7.6 ppb.
The average TP concentration of the Clean 3 sites during the June 1978 – May 1979 Base Year was 7.7 ppb, compared with the most recent June – May year average of 7.5 ppb.
No adjustment in stage was made for these comparisons since extensive monthly data collected over the last fifteen years across a wide range of water levels indicate that stage is not well correlated with variations in TP concentrations in that data set.
Relationship between Stage and TP has Changed since 1978-1983 Calibration Period
Relationship Between Clean 3 Geometric Mean and Average Stage Using Data from 2/1999-7/2009
0
10
20
30
15.0 15.5 16.0 16.5 17.0 17.5 18.0
3-gauge Average Stage (ft NGVD)
Geo
met
ric
Mea
n (p
pb)
1999-2009 Data
1999-2009 Relationship
Base Period Relationship
Factors other than stage account for 80% of
variations in TP concentrations for 1999-
2009 data
Factors other than stage account for 75% of
variations in TP concentrations for 1978-
1983 data
Other Evidence TP Concentrations Have Improved
• In February 2009, the geometric mean of the 14-station network was 4.7 ppb:
the lowest concentration recorded from the 14-station network since compliance began in February 1999, and
was lower than all of the geometric mean concentrations from the Clean 3 sites during the 1978-1979 Base Year and during the extended 1978-1983 period.
• The November 2008 14-station geometric mean that was determined to be an excursion was 7.4 ppb
This concentration was lower than four of the five geometric means at the Clean 3 sites during the 1978-1979 Base Year, and
lower than the 10 ppb annual average of the individual geometric means for the Clean 3 sites during the 1978-1979 Base Year.
The 3-gauge average stage for the November sample collection was 17.22 ft which is above the highest stage that occurred in the 1978-1979 Base Year, and above the highest stage that occurred in the extended 1978-1983 period used to calibrate the compliance equation.
Monthly Analysis of TP concentrations at 14 Refuge stations and external loading: Excursions occurred despite significant reductions
in controllable external TP loading
0
25
50
75
100
125
150
175
200
09/21/04 03/07/05 09/21/05 03/07/06 09/19/06 03/05/07 09/17/07 03/05/08 09/17/08 03/09/09
TP
Lo
ad
(M
etr
ic T
on
s/y
ea
r)
0
25
50
75
100
125
150
175
200
TP
Co
nc
en
tra
tio
n (
pp
b)
Inflow TP Load
Inflow TP Conc
Interior TP Conc
2009 data are preliminary and subject to revisionSince September 2004, the excursion frequency has been 6%, well below the compliance method limit
Jun-2009
Excursion: November 200812-month inf low = 406,000 AF
12-month load = 14.5 metric tons12-month concentration = 29 ppb
Excursion: June 2, 200912-month inf low (through May) = 379,100 AF
12-month load (through May) = 15.2 metric tons12-month concentration (through May) = 32 ppb
June 2, 2009 interior TP = 13.2 ppb
Approximate TP Load From Atmospheric Deposition:
20.3 metric tonsExcursion: October 200712-month inflow = 159,300 AF
12-month load = 9.0 metric tons12-month concentration = 46 ppb
Analysis of TP concentrations and water depths at 14 Refuge stations: Short-term spike in June 2009 (median=4 ppb) may likely
be the result of dryout and rewetting of organic sediment
Increase in TP Concentration Following DryoutMay 1999 - 1st data collection in June 2009
-10
0
10
20
30
40
50
Cha
nge
in T
P (
ppb)
Maximum Increase
Median Increase
June 2009 Increase
Maximum Increase 6.0 47.0 13.0 5.0 18.0 10.0 15.0 9.0 7.0 5.0 7.0 7.0 4.0 10.0
Median Increase 1.0 2.0 0.0 3.0 -1.0 5.0 3.0 2.5 2.5 0.0 2.0 4.5 2.0 1.0
June 2009 Increase 0.0 20 0 -8 -8 2 4 9 7 5 4 3 0
LOX3 LOX4 LOX5 LOX6 LOX7 LOX8 LOX9 LOX10 LOX11 LOX12 LOX13 LOX14 LOX15 LOX16
NCNC
NC = No sample collected due to dry conditions
Historical median increase in TP following rewetting was 2 ppb
Comparison of TP Concentrations in June 2009June 1 & 2: Geometric mean=13.2 ppb; average stage=16.05 ft
June 17 & 19: Geometric mean=9.7 ppb; average stage=15.96 ftCombined geometric mean = 11.5 ppb; average stage of 16.01 ft
0
5
10
15
20
25
30
TP
Con
cent
rati
on (
ppb)
June 1 & 2
June 17 & 19
June 1 & 2 25 10 20 8 15 14 14 14 12 12 11 11
June 17 & 19 11 12 13 9 14 9 9 10 11 6 7 11 7 10
LOX3 LOX4 LOX5 LOX7 LOX8 LOX9 LOX10 LOX6 LOX11 LOX12 LOX13 LOX14 LOX15 LOX16
Analysis of TP concentrations at 14 Refuge stations: Short-term spike observed in initial June sampling had subsided 2½ weeks later
Analysis of 2003-2004 soil TP concentrations in 0-10 cm depth at 14 Refuge stations: With 1-2 exceptions, the areas in the vicinity of the 14 stations are not “Impacted” as defined by Florida’s TP Water Quality
Standard for the Everglades (500 mg/kg)
StationRadius
(km)Ave. TP in the Area Near
Station (mg/kg)
Standard Deviation (mg/kg)
Value Nearest Station (ppb)
Radius to Nearest Site
(km)LOX3 2.0 300 37 270 1.0LOX4 1.5 350 Single site 350 1.5LOX5 2.0 260 34 290 1.0LOX6LOX7 2.0 200 Single site 200 2.0LOX8 2.0 300 Single site 300 2.0LOX9 1.0 450 Single site 450 1.0
LOX10 2.0 510 161 360 1.0LOX11 2.0 320 93 390 1.5
LOX12 1.0 490 67 490 1.0
LOX13
LOX14 2.0 520 84 520 2.0
LOX15 2.0 340 77 340 2.0LOX16 1.0 380 41 380 1.0
No data within 2 km
No data within 2 km
G 3 0 0G 3 0 1
A C M E 1 D SG 3 1 0
G 9 4 DG -2 5 1
L O X 1 0 7L O X A 1 3 0
X 1
L O X 1 0
L O X 1 1
L O X 1 2 L O X 1 3
L O X 1 4
L O X 1 5L O X 1 6
L O X 3 L O X 4
L O X 5
L O X 6L O X 7
L O X 8L O X 9
X 3
Z 2
L O X A 1 0 5
L O X A 1 2 4
L O X A 1 3 6
L O X 1 7
L O X A 1 4 0
Interim Preliminary Finding #2• TP concentrations in the Refuge continue to improve.• Elevated TP readings in June 2009 were short-term and
are likely not indicative of chronic water quality problem.• The primary source of TP causing the short-term spike
may be natural and not due to long-term controllable external TP loading such as the STA discharges.
Additional evidence that external loading may not be the primary factor in the June and November sample collections is provided by comparing the concentrations at LOX8 with adjacent LOX7 and LOX9 sites. In both instances, the latter sites, although closer to the rim canals, and thereby closer to potential sources of external surface loading, reported lower concentrations than LOX8.
Question for working group:• How should the 2nd set of TP concentrations
collected in June 2009 be factored into compliance assessment?
• Precedence: During May 2000, multiple samples were collected and averaged. Both the composite geometric mean (11.0 ppb) and the individual geometric mean (9.3 ppb) were below compliance levels. Initial reports presented both values; later reports only presented composite geometric mean.
Analysis of Monthly TP Concentrations: The 14 stations in the Refuge demonstrate highly variable TP concentrations.
• Geometric mean TP concentration of 2nd sample collection in June 2009 was 3.5 ppb lower than geometric mean of 1st sample collection – yet stage and external loading were almost identical.
• In the 186 months of sample collections since January 1994 there have been seventeen instances of TP concentrations above the levels computed by the equations of Appendix B, and
• five of those occurred before compliance assessments began in February 1999.
• the geometric mean TP concentration in the month following thirteen of those was as good as or better than the computed levels.
• Since January 2000, the month following each excursion was better than the computed levels.
Interim Preliminary Finding #3
• The TP data collected at the 14 interior stations exhibit a high degree of short-term variability which are likely associated with natural marsh conditions.
• These variations can occur when factors such as stage and external loading remain fairly constant.
Summary of Interim Preliminary Analyses• Analyses of the environmental conditions leading up to
the November 2008 and June 2009 sample collections suggest that the following factors should be considered in evaluating the excursions:
fluctuations in rainfall, resulting in an rapid increase in stage prior to the June 1st and 2nd 2009 sample collection, with a potential associated flux of TP from the marsh soil upon rewetting;
natural high variability of TP concentrations in the Refuge marsh, which may be due to local factors, rather than controllable external factors; and
application of the compliance equation outside the range of environmental conditions that existed at the time of sample collections used in deriving the compliance equation.
• Analyses are continuing
Summary of Interim Preliminary Analyses
Summary of Preliminary Analyses – Matrix of Potential Contributing Factors Potential Contributing Factor Data Evaluated Finding
Data collection error Sample collection records No evidence of error Laboratory analysis error Sample analyses records No evidence of error
Unprecedented low rainfall in the six months prior to the June sample collection, followed by extremely high rainfall in the last two weeks of May preceding sample collection, resulting in an extreme rapid rise in Refuge stage following extensive
soil dry out
Daily rainfall records between 1963 and 2009; stage records
between 1978 and 2009
May be a significant contributing factor
External phosphorus loading
Daily structure flows and TP levels between 1994 and 2009; STA-1E treatment cell water
levels, flow and TP data.
Analysis suggests that external loading was
not a significant contributing factor.
• Analyses are continuing
Top Related