Community Oxygen and Nutrient Fluxes in Seagrass Beds of Florida Bay, USA

Abstract

We used clear, acrylic chambers to measure in situ community oxygen and nutrient fluxes under day and night conditions in seagrass beds at five sites across Florida Bay five times between September 1997 and March 1999. Underlying sediments are biogenic carbonate with porosities of 0.7-0.9 and with low organic content (<1.6%). The seagrass communities always removed oxygen from the water column during the night and produced oxygen during daylight, and sampling date and site significantly affected both night and daytime oxygen fluxes. Net daily average fluxes of oxygen (−4.9 to 49 mmol m −2 day −1 ) ranged from net autotrophy to heterotrophy across the bay and during the 18-month sampling period. However, the Rabbit Key Basin site, located in the west-central bay and covered with a dense Thalassia testudinum bed, was always autotrophic with net average oxygen production ranging from 4.8 to 49 mmol m −2 day −1 . In November 1998, three of the five sites were strongly heterotrophic and oxygen production was least at Rabbit, suggesting the possibility of hypoxic conditions in fall. Average ammonium (NH 4 ) concentrations in the water column varied widely across the bay, ranging from a mean of 6.9 μmol l −1 at Calusa in the eastern bay to a mean of 0.6 μmol l −1 at Rabbit Key for the period of study. However, average NH 4 fluxes by site and date (−240 to 110 μmol m −2 h −1 ) were not correlated with water column concentrations and did not vary in a consistent diel, seasonal, or spatial pattern. Concentrations of dissolved organic nitrogen (DON) in the water column, averaged by site (15-25 μmol l −1 ), were greater than mean NH 4 concentrations, and the range of day and night DON fluxes (−920 to 1,300 μmol m −2 h −1 ), averaged by site and date, was greater than the range of mean NH 4 fluxes. Average DON fluxes did not vary consistently from day to night, seasonally or spatially. Mean silicate fluxes ranged from −590 to 860 μmol m −2 h −1 across all sites and dates, but mean net daily fluxes were less variable and most of the time contributed small amounts of silicate to the water column. Mean concentrations of filterable reactive phosphorus (FRP) in the water column across the bay were very low (0.021-0.075 μmol l −1 ); but site average concentrations of dissolved organic phosphorus (DOP) were higher (0.04-0.15 μmol l −1 ) and showed a gradient of increasing concentration from east to west in the bay. A pronounced gradient in average surficial sediment total phosphorus (1.1-12 μmol g DW −1 ) along an east-to-west gradient was not reflected in fluxes of phosphorus. FRP fluxes, averaged by site and date, were low (−5.2 to 52 μmol m −2 h −1 ), highly variable, and did not vary consistently from day to night or across season or location. Mean DOP fluxes varied over a smaller range (−8.7 to 7.4 μmol m −2 h −1 ), but also showed no consistent spatial or temporal patterns. These small DOP fluxes were in sharp contrast to the predominately organic phosphorus pool in surficial sediments (site means=0.66-7.4 μmol g DW −1 ). Sign...

Comparing Productivity and Biogeochemistry of Native and Transplanted Thalassia testudinum and Halodule beaudettei in Big Lagoon, Florida, USA

“…Rates in Big Lagoon were comparable to measurements from other beds of H. beaudettei (Cotner et al, 2004;Yarbro and …”

Dissolved oxygen fluxes and ecosystem metabolism in an eelgrass (Zostera marina) meadow measured with the eddy correlation technique

“…As seagrass biomass increases with colonization time, it is expected that respiration rates would also increase , in part because of the high rates of bacterial metabolism fueled by increased organic matter (detritus, phytoplankton) deposition and decreased particle resuspension (Koch 1999;Gacia and Duarte 2001;Gacia et al 2002). Some previous studies and literature reviews have suggested that seagrass meadows are generally net autotrophic (Gattuso et al 1998;Hemminga and Duarte 2000;Gazeau et al 2005); however, it is also common for seagrass meadows to be either in metabolic balance as we found or net heterotrophic (Hemminga and Duarte 2000;Barron et al 2004;Yarbro and Carlson 2008). This variation is likely related to differences in environmental factors (light, nutrients, hydrodynamics), organic matter inputs, and self-shading within the seagrass canopy, and it is clearly important to capture these natural variations in order to understand patterns in trophic status correctly.…”

Degrading seagrass (Posidonia oceanica) ecosystems: a source of dissolved matter in the Mediterranean

“…The excretion of dissolved organic carbon (DOC), for instance, has been found to be slightly higher from the complex Zostera marina leaves-epiphytes than from the clean Z. marina leaves (Penhale & Smith, 1977). The balance also varies depending on season (Ziegler et al, 2004;Yarbro & Carlson, 2008;Barron & Duarte, 2009;Apostolaki et al, 2010) and time of the day. In the light, oxygen production through photosynthesis of seagrass leaves, epiphytes and algae usually counterbalances oxygen consumption through respiration and mineralization, resulting in carbon dioxide and nutrient uptake during daytime (Yarbro & Carlson, 2008).…”