The influence of seagrass beds on carbonate sediments in the Bahamas

Borges

Estuarine, Coastal and Shelf Science

2009

The partial pressure of CO 2 (pCO 2 ) and dissolved inorganic carbon (DIC) were monitored in shallow coastal waters located inside and outside giant kelp beds (Macrocystis pyrifera) located in the Kerguelen Archipelago (Southern Ocean).Photosynthesis and respiration by microplankton and kelp lead to marked pCO 2 and DIC diel cycles. Daily variations of pCO 2 and DIC are significant in the spring and summer, but absent in the winter, reflecting the seasonal cycle of biological activity in the kelp beds. If the kelp beds seem to favour the onset of phytoplankton blooms, most of the primary production inside the kelp beds is due to the kelp itself. The primary production of Macrocystis kelp beds in the Sub-Antarctic high-nutrient, lowchlorophyll (HNLC) waters off the Kerguelen Archipelago is elevated and closely linked to light availability. This production is significant from October to March and reaches its climax in December at the solar radiation maximum.

Section: Introductionsupporting

confidence: 82%

Influence of giant kelp beds (Macrocystis pyrifera) on diel cycles of pCO2 and DIC in the Sub-Antarctic coastal area

Borges

Estuarine, Coastal and Shelf Science

2009

“…) found model-predicted F-mobilization rates to range between 170 and 770 pm01 rnp2 d-l in a carbonate sediment located some distance from a seagrass bed in Florida Bay. Given an IP : F-l ratio of 0.09 in their sediment, the concurrent rate of IP mobilization would be 15.5-70 pm01 m 2 d-l. Because overall sediment metabolism seems generally higher in seagrass beds than on bare sediment (Morse et al 1987), we consider it possible that carbonate dissolution could occur with a similar rate in the Bermuda seagrass beds. If so, carbonate dissolution would contribute significantly to the daily P requirement for T. testudinum (see be- low).…”

Section: Resultsmentioning

confidence: 99%

“…phosphate) onto CaCO, particles. This mechanism of P immobilization is inferred from adsorption experiments where excess DIP disappears rapidly from solution when added to sediment slurries (deKane1 and Morse 1978; Morse et al 1987; Short et al 1990; McGlathery et al 1994), and from stoichiometric nutrient regeneration models that indicate a depletion of DIP relative to ammonium in sediment pore 'Present address: …”

mentioning

confidence: 99%

Forms and availability of sediment phosphorus in carbonate sand of Bermuda seagrass beds

Jensen¹,

et al. 1998

Primary production by seagrasscs in tropical and subtropical carbonate sediments often appears to be phosphorus (P) limited, and several studies have sought to identify the possible sources of P for long-term growth. Here, we quantify concentrations of particulate and dissolved P and fluoride (F-) in carbonate sediments, sediment-water P exchange, and leaf-tissue P concentrations in three seagrass beds in Bermuda. We also present data on the sequential extraction of P and F-from the sediments at each site. Total sediment P (TP,,,) in the upper 20 cm ranged from 650 to 1,250 mmol P m-2 and was some 500-fold larger than the pool of P dissolved in pore waters. Loosely adsorbed inorganic P comprised 2% of TPsed, while a surface-bound inorganic P pool extracted by dithionite buffer constituted 15-20%. Most of the remaining P and nearly all of the Ca and F-present in the sediment was recovered when the remaing sediment was dissolved in an acetic acid buffer solution. This pool includes calcium-fluoroapatite (CFA), which is considered the primary diagenetic sink for P in carbonate sands. Dissolved inorganic P and Fwere both elevated in the rhizosphere pore waters from the three seagrass beds. In combination with our analysis of sediments by sequential extraction, this result indicates that the carbonate matrix of the sediment is being dissolved in the rhizosphere, with a resulting release of P to the pore water and hence to the seagrass roots. We suggest that this is important in the P economy of these subtropical seagrass (Thalussia testudinum) beds and note that the carbonate-bound P pool is large enough to sustain seagrass P requirements for decades. Nonetheless, primary production in such seagrass systems can remain P limited if the rate of P release from sediment dissolution is too slow to support maximum seagrass growth rates. Analysis of seagrass leaf tissues revealed that P availability was highest at the site with the highest anthropogenic influences: This site was also characterized by the highest sediment P release, indicating that high P availability may also be partly due to higher release of P as sediments are dissolved. Phosphorus was released from the sediment mainly as dissolved organic P causing a net efflux of dissolved P at all sites in April and at two sites in August.Carbonate sediments of tropical and subtropical coastal waters are thought to trap phosphorus (P) efficiently by strong adsorption of dissolved inorganic P (DIP) (i.e. phosphate) onto CaCO, particles. This mechanism of P immobilization is inferred from adsorption experiments where excess DIP disappears rapidly from solution when added to sediment slurries (deKane1 and Morse 1978; Morse et al. 1987; Short et al. 1990; McGlathery et al. 1994), and from stoichiometric nutrient regeneration models that indicate a depletion of DIP relative to ammonium in sediment pore 'Present address:

“…Much higher CaCO 3 cycling both in terms of production and dissolution was observed in P. oceanica meadows compared to unvegetated sediments. Enhanced CaCO 3 dissolution in seagrass vegetated sediments compared to adjacent unvegetated sediments has been documented in Thalassia testudium meadows of the Bahamas (Morse et al 1987;Burdige and Zimmerman 2002) and in mixed meadows of Florida Bay (Ku et al 1999;Halley 2003, 2006). The enhanced CaCO 3 dissolution in seagrass meadows is attributed to intensified sediment metabolic activity related to higher organic carbon availability, O 2 diffusion from rhizomes to pore waters (Ku et al 1999;Burdige and Zimmerman 2002), or sulfate reduction (Ku et al 1999;Yates and Halley 2006).…”

Section: Discussionmentioning

confidence: 99%

“…The high production and input of organic carbon make seagrass meadows sites of elevated microbial activity, as well as enhanced animal abundance, which result in high heterotrophic activity (Hemminga and Duarte 2000;Middelburg et al 2005). In addition to their important metabolic activity, seagrass meadows also support high calcium carbonate (CaCO 3 ) production (cf., Canals and Ballesteros 1997;Gattuso et al 1998;Gacia et al 2003) and dissolution (Morse et al 1987;Ku et al 1999;Burdige and Zimmerman 2002). Seagrass meadows are sites of intense organic and inorganic carbon fluxes.…”

Section: Introductionmentioning

confidence: 99%

Organic carbon metabolism and carbonate dynamics in a Mediterranean seagrass (Posidonia oceanica), meadow

Barrón

Duarte

Frankignoulle

et al. 2006

Estuaries and Coasts

117

We measured monthly dissolved oxygen (DO) changes in situ benthic incubations from March 2001 to October 2002 in a Posidonia oceanica meadow and unvegetated sediments of Magalluf Bay (Mallorca Island, Spain) to determine gross primary production (GPP), community respiration (R), and net community production (NCP). From June 2001 to October 2002, we also measured fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TAlk). The yearly integrated metabolic rates based on DO changes show that the P. oceanica communities are net autotrophic while the metabolic rates in the unvegetated benthic communities are nearly balanced. Higher calcium carbonate (CaCO 3 ) cycling, both in terms of production and dissolution, was observed in P. oceanica communities than in unvegetated benthic communities. In the P. oceanica meadow, the annual release of CO 2 from net CaCO 3 production corresponds to almost half of the CO 2 uptake by NCP based on DIC incubations. In unvegetated benthic communities, the annual uptake of CO 2 from net CaCO 3 dissolution almost fully compensates the CO 2 release by NCP based on DIC incubations. CaCO 3 dynamics is potentially a major factor in CO 2 benthic fluxes in seagrass and carbonate-rich temperate coastal ecosystems.