Presentation on theme: "Water source utilization and nutrient status in upland plant communities in Everglades National Park (ENP) Amartya K Saha 1 Leonel."— Presentation transcript:
Water source utilization and nutrient status in upland plant communities in Everglades National Park (ENP) Amartya K Saha 1 Leonel O da S L Sternberg 1 Miralles-Wilhelm 2 1 Department of Biology, University of Miami, Coral Gables, FL 33124, USA 2 Department of Civil and Environmental Engineering, Florida International University, Miami, FL, USA Fig 2 : average soil depth in hammock (left) and pineland (right) in cm. Long Pine Key, ENP. Hammocks and Pinelands highest elevations in the Everglades only 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. HammockPineland 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 sources In the wet season, hammock plants use mostly soilwater while pinelands use mainly groundwater In dry season, litter layer dries, so both hammocks and pinelands use groundwater B: Foliar nutrient status Hammock plants attain higher foliar concentrations of N and P by 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 site 3. 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 s 1.Isotopic composition (δ 18 O, δ 2 H) of rain, groundwater and soilwater are different, thus enabling determination of plant water sources Nutrients Results ( continued ) NutrientHammock soil (ppm) Groundwater (ppm) Available P nitrate5.5 – –0.15 ammonium6.52 – 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 Grant Fieldwork 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 ? 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. 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 δ 18 O with groundwater δ 18 O. The right hand plot = correlation of pineland plant δ 18 O with groundwater δ 18 O. Pineland plants have a higher correlation with groundwater on average (R 2 = 0.75) as compared to hammock plants (R 2 = 0.57), signifying a greater usage of groundwater. 2. Pineland plant stemwater δ 18 O better correlated with groundwater. Hammock plants not correlated with groundwater in wet season. Fig 7A: monthly rainfall over Fig 7B: hammock and pineland plant average % groundwater utilized through a year. Vertical dotted lines in plot 3 indicate the wet 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 hammocks and 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.