The effects of manipulation of sedimentary iron and organic matter on sediment biogeochemistry and seagrasses in a subtropical carbonate environment
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The microbial metabolism of organic matter (OM) in seagrass beds can create sulfidic conditions detrimental to seagrass growth; iron (Fe) potentially has ameliorating effects through titration of the sulfides and the precipitation of iron-sulfide minerals into the sediment. In this study, the biogeochemical effects of Fe availability and its interplay with sulfur and OM on sulfide toxicity, phosphorous (P) availability, seagrass growth and community structure were tested. The availability of Fe and OM was manipulated in a 2 × 2 factorial experiment arranged in a Latin square, with four replicates per treatment. The treatments included the addition of Fe, the addition of OM, the addition of both Fe and OM as well as no addition. The experiment was conducted in an oligotrophic, iron-deficient seagrass bed. Fe had an 84.5% retention efficiency in the sediments with the concentration of Fe increasing in the seagrass leaves over the course of the experiment. Porewater chemistry was significantly altered with a dramatic decrease in sulfide levels in Fe addition plots while sulfide levels increased in the OM addition treatments. Phosphorus increased in seagrass leaves collected in the Fe addition plots. Decreased sulfide stress was evidenced by heavier δ34S in leaves and rhizomes from plots to which Fe was added. The OM addition negatively affected seagrass growth but increased P availability; the reduced sulfide stress in Fe added plots resulted in elevated productivity. Fe availability may be an important determinant of the impact that OM has on seagrass vitality in carbonate sediments vegetated with seagrasses.
KeywordsFlorida Bay Sediment geochemistry sulfate reduction Sulfide stress Nutrient limitation
We thank Bryan M. Dewsbury and Travis Thyberg for help during field work and collection of samples and Dr R.M. Price for performing the anion concentration analyses. Drs R.M. Chambers and D.L. Childers provided guidance on experimental design, analytical methods and data analyses and read and commented on early drafts of this paper. This material is based upon work supported by the National Science Foundation under the Florida Coastal Everglades Long Term Ecological Research program (Grant No. 9910514). This is contribution number 372 of the Southeast Environmental Research Center at FIU.
- Armitage AR, Frankovich TA, Heck KLJ, Fourqurean JW (2005) Experimental nutrient enrichment causes complex changes in seagrass, microalgae, and macroalgae community structure in Florida Bay. Estuaries 28:422–434Google Scholar
- Carlson PR, Yarbro LA, Barber TR (1994) Relationship of sediment sulfide to mortality of Thalassia testudinum in Florida Bay. Bull Mar Sci 54:733–746Google Scholar
- Cline JD (1969) Spectrophotometric determination of hydrogen sulfide in natural waters. Limnol Oceanogr 14:454–458Google Scholar
- Duarte CM, Merino M, Gallegos M (1995) Evidence of iron deficiency in seagrasses growing above carbonate sediments. Limnol Oceanogr 40:1153–1158Google Scholar
- Fourqurean JW, Zieman JC, Powell GVN (1992b) Relationships between porewater nutrients and seagrasses in a subtropical carbonate environment. Mar Biol 114:57–65Google Scholar
- Frederiksen MS, Holmer M, Borum J, Kennedy H (2006) Temporal and spatial variation of sulfide invasion in eelgrass (Zostera marina) as reflected by its sulfur isotopic composition. Limnol Oceanogr 51:2308–2318Google Scholar
- Kaplan IR, Rittenberg SC (1964) Microbial fractionation of sulphur isotopes. J Gen Microbiol 34:195–212Google Scholar
- Lovley DR, Phillips EJP (1987) Competitive mechanisms for inhibition of sulfate reduction and methane production in the zone of ferric iron reduction in sediments. Appl Environ Microbiol 53:2636–2641Google Scholar
- Rosenfeld JK (1979) Interstitial water and sediment chemistry of two cores from Florida Bay. J Sediment Petrol 49:989–994Google Scholar
- Westrich JT, Berner RA (1984) The role of sedimentary organic matter in bacterial sulfate reduction: the G model tested. Limnol Oceanogr 29:236–249Google Scholar
- Zieman JC, Fourqurean JW, Iverson RL (1989) Distribution, abundance and productivity of seagrasses and macroalgae in Florida Bay. Bull Mar Sci 44:292–311Google Scholar