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 Estimates of stage were available at all three gauges during all sample collections

Analysis 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

Analysis of daily rainfall from S-5A, S-6 and S-39: May 2009 was 4 th wettest on record; last 2 weeks was 2 nd wettest on record

Analysis 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 ft on May 12, 2009

Analysis of daily stages from 1-7, 1-8C and 1-9: The monthly change in stage was 3 rd highest in 200 months that TP samples were collected (June 1979-June 2009).

Analysis of hydraulic gradient: East rim canal stage - minimal opportunity for movement of canal water into interior marsh

Analysis of Hydraulic Gradient: West rim canal stage - minimal opportunity for movement of canal water into interior marsh

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 Data

Monthly Trend Analysis of TP concentrations at 14 Refuge stations: Statistically significant trend of reductions in TP concentrations

Other Evidence TP Concentrations Have Improved TP concentrations in the interior of the Refuge compare favorably with the Base Year and the extended 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 Calibration Period

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 Base Year and during the extended period. The November 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 Base Year, and lower than the 10 ppb annual average of the individual geometric means for the Clean 3 sites during the Base Year. The 3-gauge average stage for the November sample collection was ft which is above the highest stage that occurred in the Base Year, and above the highest stage that occurred in the extended 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

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 Historical median increase in TP following rewetting was 2 ppb

Analysis of TP concentrations at 14 Refuge stations: Short-term spike observed in initial June sampling had subsided 2½ weeks later

Analysis of 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)

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 2 nd 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 2 nd sample collection in June 2009 was 3.5 ppb lower than geometric mean of 1 st 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 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 Analyses are continuing