FATE OF DISSOLVED ORGANIC MATTER IN BAY Stephen Kelly, David Rudnick, Christopher Madden, Robin Bennett, Teresa Coley, Joshua Creasser and Amanda McDonald Coastal Ecosystems’ Division (2004) Introduction Decomposition of Everglades’ DOM in Florida Bay Hydrologic restoration of the Everglades system will result in increased fresh water flow toward Florida Bay. Nutrients, especially dissolved organic nitrogen 14 Day Decomposition Experiment Once again, DO uptake (and therefore DOM consumption) was higher with Pond associated with this increased flow, may impact the Florida Bay ecosystem. 5 water than water, and more pronounced in the sediment plus P Little is known of the fate and effects of Everglades dissolved organic matter An experiment was run for 14 days in duplicate 300 ml BOD bottles in the dark. treatments. There was little P effect on water column DO consumption, and only a (DOM) in Florida Bay. This is a key uncertainty regarding the effect of Duplicate bottles were sacrificed at each time point. Source waters were Duck Key slight effect on the sediment treatments (1.3 fold higher). The loss of DOC and Comprehensive Everglades Restoration Plan (CERP) implementation on the (8 mg/l DOC) and Pond 5 (10 mg/l DOC). Water was filtered (0.2 µm) to exclude TDKN confirm these trends. Florida Bay ecosystem. ambient microbes. Salinity in Pond 5 water was increased to that of Duck water, Duck Pond 5 Duck Pond 5 using NaCl. An inoculum of Duck Key bacterioplankton (5 mls/l of GF/F filtrate) or DOC Loss TDKN Loss Conceptual Model of DOM processing (N steps in blue): benthic microbes (2 g/l of Duck Key sediment slurry) was added to each bottle. 4 0.4 Experiments were run with or without nutrient amendments (5 uM phosphate plus 3 0.3 Everglades 500 uM glucose final concentration) that were intended to ensure N limitation. )

) l

l DOM import /

/ 2 0.2

Results are presented as the cumulative DO uptake per bottle in mg O /l. g 2 g

m

m ( 0.1 ( 1 Refractory Cumulative Oxygen Uptake per Liter, August 2003 POM humification 0 0.0 Labile DOM DOM Duck:No Nutrient Addition Pond 5: No Nutrient Addition NO P NO P PLUS P PLUS P NO P NO P PLUS P PLUS P photodegradation NO SED PLUS SED NO SED PLUS SED NO SED PLUS SED NO SED PLUS SED Primary Duck:Nutrient Addition Pond 5: Nutrient Addition producers biodegradation net No Sediment With Sediment Gulf of export 25 25 Mexico P Heterotrophic We calculated the minimum bioavailable carbon pool and the decay constants for P net import microbes 20 20 this pool using linear regressions of LN transformed oxygen uptake rates. The

2

2

O O 15 15

bioavailable pool is a minimum because the day 1 data rates were dropped due

g g 10 10 m Inorganic N m to experimental errors. The magnitude of this negative bias in our estimate is 5 5 unknown. The decay rates refer to the bioavailable carbon pool, not the total 0 0 carbon pool. Data are reported as mean + standard deviation. Study Area 0 100 200 300 0 100 200 300 Elapsed Time (hrs) Elapsed Time (hrs) Duck Key Duck Key Pond 5 Pond 5 Decay Constant Minimum Decay Constant Minimum Everglades Results show strong nutrient effects - DO consumption was stimulated by k (d-1) Bioavailable k (d-1) Bioavailable National nutrient additions. This effect was relatively greater in water column (mg C /l) (mg C /l) Park N experiments than sediment experiments (12 fold increase in DO consumption No P, No Sed 0.028 +0.006 1.54 + 0.13 0.021 +0.007 2.04 + 0.30 vs. 4 -10 fold increase). DO consumption was higher with microbial No P, Plus Sed 0.037 +0.007 1.64 + 0.19 0.023 +0.009 2.68 + 0.57 Area of mapping decomposition of Pond 5 DOM than Duck Key DOM when nutrients were Plus P, No Sed 0.031 +0.004 1.58 + 0.23 0.024 +0.005 2.06 + 0.33 added. This difference was most pronounced in bottles with sediments, with below Pond 5 Plus P, Plus Sed 0.018 +0.004 2.95 + 0.40 0.013 +0.002 4.83 + 0.66 DO demand with Pond 5 water nearly 2 fold that with Duck Key water. Duck Key Multifactor ANOVA’s were run to examine how decay rates (k d-1) were affected by the main factors (site, P, sediment) and interactions among these factors. These 2 Month Decomposition Experiment analyses suggests there was a significant difference between sites (Duck k > Florida Bay Pond 5 k) and a sediment by P interaction effect (p< 0.01, df=24). No other A two month experiment (April-May, 2004) was run with modifications to the significant differences were noted. In addition, the sediment plus P treatments at Florida original design. Incubations were done in quadruplicate 2.5 liter polycarbonate Keys bottles, with sub-samples removed to triplicate 60 ml BOD bottles for DO both sites had lower decay constants, but a larger bioavailable carbon pool, 10 km suggesting that P may enhance microbial decay of less labile DOM. uptake rate measurements. Duck Key (5.5 mg/l DOC) and Pond 5 (15 mg/l DOC) water, along with a sediment control in artificial seawater (ASW), were Conclusions incubated with and without phosphorus (P) amendments. Rates from ASW • DOM is transported from the Everglades to Florida Bay with fresh water. Shipboard Mapping of Everglades’ Outflows controls were subtracted from the sediment addition treatments. Linear regressions of LN transformed oxygen uptake rates were modeled to yield the • CDOM in Florida Bay decreases rapidly with distance from the shore line. Inflow Inflow cumulative oxygen uptake in mg/l. Dark rectangles along X-axis represent • During two week experiments, microbial respiration increased with Everglades Inflow 4 Inflow 1 June 2003 5 June 2003 DOM additions when P and C were readily available.

2 5 time and duration of BOD incubations.

2 30 • During two month experiments, microbial respiration once again increased with 1 5 4 2 Cumulative Oxygen Uptake per Liter, April-May 2004 Everglades DOM additions and enhanced further with sediment additions. 0 1 5 3 Duck:No Nutrient Addition • Increased P levels may allow the microbial decomposition of less labile DOM. 2 20 Pond 5: No Nutrient Addition

8 • At least 14% of the DOM from Pond 5 and 28% of the DOM from Duck Key 0 Duck:Nutrient Addition Pond 5: Nutrient Addition 5 2 2 appears to be bioavailable. Bioavailable DOM concentrations are similar in this

6 With Sediment 0 No Sediment 5 10 1 pond and eastern Florida Bay and have similar decay rates that are surprisingly 2 7 7 4 4 6 0 8 6 0 8 8 2 2 4 4 4 4 4 3 3 3 3 3 2506 2508 2510 2512 2514 2506 2508 2510 2512 2514 2 fast (~2% / day). 0 0 0 0 0 0 0 0 0 0 0 6 8 8 8 8 8 8 8 8 8 8 Salinity8 (psu) 0 6

Dissolved Organic Matter (rfu)

2 5 • These results indicate that Everglades DOM decomposition may be more rapid at 2 5 8048 8046 8044 8042 8040 8038 8036 8034 8032 8030 8028 8048 8046 8044 8042 8040 8038 8036 8034 8032 8030 8028

O

0 O 4 4 g the sediment-water interface and during resuspension events than in clear Florida

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3 m 3 Map above shows coverage area with boat tracts m 2 Bay waters, especially in central and western parts of the Bay where P levels are • Areas with high fresh water flow have low salinity and high 2 1 1 relatively high. concentrations of colored DOM (CDOM, measured by fluorescence) 0 0 • The effects of changing fresh water flow on the Florida Bay ecosystem depend • Fate and effect of this CDOM in the Bay is unknown 0 20 40 60 0 20 40 60 upon changes in DOM inputs, bioavailability, decay rates and water residence Elapsed Time (days) • DOM may be degraded via microbial and photochemical processes Elapsed Time (days) times in different regions of Florida Bay