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Long Pine Key

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Sisal Pond

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Water source utilization and nutrient status in upland plant communities in Everglades National Park (ENP)Amartya K Saha1 (asaha@bio.miami.edu), Leonel O da S L Sternberg1 (leo@bio.miami.edu),Fernando Miralles-Wilhelm2

1Department of Biology, University of Miami, Coral Gables, FL 33124, USA2 Department of Civil and Environmental Engineering, Florida International University, Miami, FL, USA

average soil depth hammock and pineland, Long Pine Key

-10

010

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3040

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7080

90

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transect points

so

il d

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th t

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Fig 2: average soil depth in hammock (left) and pineland (right) in cm. Long Pine Key, ENP.

Hammocks and Pinelands highest elevations in the Evergladesonly areas above water in the wet season); only 4 % of park area; habitat for terrestrial life,; high floral species diversity, several endemics, northernmost range of evergreen tropical species from the Neotropics

Fig 1: Hammocks and Pinelands occur on the Miami Rock Ridge on eastern edge of the park. Study sites shown. Photo shows hammock on the left and pineland on the right.

Hammock Pineland

Closed canopy, higher photosynthetic biomass per unit area

Open canopy

Humid microclimate stops fires

Natural fires burn off organic matter

Organic soil layer present

Soil only in cracks and sinkholes

• This organic soil layer in hammocks caused by litter accumulation . So how may this litter layer influence this difference between hammocks and adjacent pinelands ?

• Litter layer traps rain in wet season. This water solubilizes nutrients present in decomposing litter/leachates from leaves.

H y p o t h e s e s

A: Water sourcesIn the wet season, hammock plants use mostly soilwaterwhile pinelands use mainly groundwaterIn dry season, litter layer dries, so both hammocks and pinelands use groundwaterB: Foliar nutrient statusHammock plants attain higher foliar concentrations of N and Pby virtue of access to nutrient-rich soil litter water.

Fig 3: hammocks (left) have a soil layer (that traps rain) while pinelands (right) so not. Blue shows water table (groundwater). Wet season.

The Study (March 2005 – March 2006)1. Three hammock/pineland pair sites 2. Rain and GW sampled every 2 weeks in each site3. Plant stems (water) and leaves (nutrients) sampled every 2 months (species in adjacent table)4. 5 individuals of 5 species per hammock or pineland 25 for hammock + 25 pineland 50 plants per site. 3 sites.

R e s u l t s1.Isotopic composition (δ18O, δ2H) of rain, groundwater and soilwaterare different, thus enabling determination of plant water sources

Nutrients

Results (continued)

Nutrient Hammock soil (ppm)

Groundwater (ppm)

Available P 2.1 - 44.5 0.03 - 0.05

nitrate 5.5 – 126 0.01 –0.15

ammonium 6.52 – 150 0.09 - 0.15

C o n c l u s i o n Water trapped in the organic litter layer is a significant source for hammock plants,

especially in the wet season. The litter layer provides a vadose zone for the roots of flood intolerant hammock trees.

In the dry season hammock trees utilize more groundwater while the litter layer dries out. However, if water levels fall very low, then hammock plants may encounter difficulty in sending roots through the limestone bedrock to access the lowered groundwater table.

This has implications for hydrological management upstream of the Everglades, for

maintaining water levels within the above bounds for preserving upland ecosystems.

Pineland plants also depend upon both sources, however depending upon the species, they are more tolerant of some flooding. They can share a similar susceptibility to low water levels in the dry season.

Acknowledgements Funding: NSF Biocomplexity GrantFieldwork and labwork: Help from Maria Camila Pinzon, Yiming Lin, Patrick Ellsworth, Frans Juola, Diego Melgarejo, Pab Pandit, Saha family, Angela Garcia, Bruno Rosado, Cassandra, Shu Ju.

Table 2: Hammock soil and groundwater nutrients. Data from Long Pine Key,ENP

Our main questions

1.What are the water sources for upland plant communities (hammocks and pinelands) in the ENP and how they vary with season.

2. Are foliar nutrient concentrations indicative of higher nutrient levels in hammock soils ?

Hammock/Pineland sites

Tree island sites

Fig 4: δ18O values of rain (○), groundwater (●) and soilwater (hammock (▲) and pineland (∆)). Upper panel shows rainwater being isotopically diluted in the wet season, a trend also reflected in groundwater, which however displays lower amplitude owing to its larger volume. The lower panel depicts soil water showing the same trend. However soilwaters are also enriched evaporatively in the heavier isotopies of water, especially evident in the dry season.

wet season

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dry season

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‰18O

‰2H

‰18O

Fig 5: Plot of δ 18O vs δ2H for rain (○), groundwater (●) and soilwater (hammock (▲) and pineland (∆)). The global meteoric water line is also included. Both rain and groundwater cluster around the meteoric water line year round. In the dry season, soilwater veers to the right of the meteoric water line, a trajectory typical of evaporatively enriched water.

Fig 6: Left plot: correlation of average hammock plant δ18O with groundwater δ18O. The right hand plot = correlation of pineland plant δ18O with groundwater δ18O. Pineland plants have a higher correlation with groundwater on average (R2 = 0.75) as compared to hammock plants (R2 = 0.57), signifying a greater usage of groundwater.

2. Pineland plant stemwater δ18O better correlated with groundwater. Hammock plants not correlated with groundwater in wet season.

Fig 7A: monthly rainfall over 2005-2006

Fig 7B: hammock and pineland plant average % groundwater utilized through a year. Vertical dotted lines in plot 3 indicate thewet season.In the wet season (June – September end), hammocks (filled circles) use less groundwater than pinelands (empty circles) (25% in comparison to 40%). As the dry season progresses, the difference between hammocksand pinelands reduces until in mid May (late dry season) both communities have approximately 90% of their water coming from groundwater.

Fig 7C: Daily groundwater level at station NP72 (ENP)Dashed horizontal line indicates level of 50% groundwater usage, with increasing usage at lower levels.

Hammock plants (●) have significantly higher foliar N and P than pineland plants (●). However there is a strong species effect.

%P (mg P/mg dry leaf)

0.00 0.01 0.02 0.03 0.04 0.05 0.06

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