References of "Kristensen, Erik"
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See detailEmission of CO2 and CH4 to the atmosphere by sediments and open waters in two Tanzanian mangrove forests
Kristensen, Erik; Flindt, Mogens R.; Ulomi, Shadrack et al

in Marine Ecology. Progress Series (2008)

Carbon gas balance was evaluated in an anthropogenically impacted (Mtoni) and a pristine (Ras Dege) mangrove forest in Tanzania. Exchange of carbon dioxide (CO2) was measured for inundated and air-exposed ... [more ▼]

Carbon gas balance was evaluated in an anthropogenically impacted (Mtoni) and a pristine (Ras Dege) mangrove forest in Tanzania. Exchange of carbon dioxide (CO2) was measured for inundated and air-exposed sediments during day and night using in situ and laboratory incubations. In situ methane (CH4) emissions were measured in the dark during air exposure only. Emission of CO2 and CH4 from open waters (e.g. creeks) was estimated from diurnal measurements of CO2, partial pressure (pCO2) and CH4 concentrations. CO2 emission from darkened sediments devoid of biogenic structures was comparable during inundation and air exposure (28 to 115 mmol m–2 d–1) with no differences between mangrove forests. Benthic primary production was low with only occasional net uptake of CO2 by the sediments. Emissions of CH4 from air-exposed sediment were generally 3 orders of magnitude lower than for CO2. Presence of pneumatophores and crab burrows increased low tide emissions several fold. Emissions from open waters were dependent on tidal level and wind speed. Lowest emission occurred during high tide (1 to 6 mmol CO2 m–2 d–1; 10 to 80 μmol CH4 m–2 d–1) and highest during low tide (30 to 80 mmol CO2 m–2 d–1; 100 to 350 μmol CH4 m–2 d–1) when supersaturated runoff from the forest floor and porewater seepage reached the creek water. Based on global average primary production and measured gas emissions, the carbon gas balance of the 2 mangrove forests was estimated. The densely vegetated Ras Dege forest appears to be an efficient sink of greenhouse carbon gases, while extensive clear-cutting at the Mtoni forest apparently has reduced its capacity to absorb CO2, although it is seemingly still a net sink for atmospheric CO2. [less ▲]

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See detailMangrove production and carbon sinks: a revision of global budget estimates
Bouillon, Steven; Borges, Alberto ULg; Castañeda-Moya, Edward et al

in Global Biogeochemical Cycles (2008), 22(GB2013),

Mangrove forests are highly productive but globally threatened coastal ecosystems, whose role in the carbon budget of the coastal zone has long been debated. Here we provide a comprehensive synthesis of ... [more ▼]

Mangrove forests are highly productive but globally threatened coastal ecosystems, whose role in the carbon budget of the coastal zone has long been debated. Here we provide a comprehensive synthesis of the available data on carbon fluxes in mangrove ecosystems. A reassessment of global mangrove primary production from the literature results in a conservative estimate of 218 ± 72 Tg C a 1. When using the best available estimates of various carbon sinks (organic carbon export, sediment burial, and mineralization), it appears that >50% of the carbon fixed by mangrove vegetation is unaccounted for. This unaccounted carbon sink is conservatively estimated at 112 ± 85 Tg C a 1, equivalent in magnitude to 30–40% of the global riverine organic carbon input to the coastal zone. Our analysis suggests that mineralization is severely underestimated, and that the majority of carbon export from mangroves to adjacent waters occurs as dissolved inorganic carbon (DIC). CO2 efflux from sediments and creek waters and tidal export of DIC appear to be the major sinks. These processes are quantitatively comparable in magnitude to the unaccounted carbon sink in current budgets, but are not yet adequately constrained with the limited published data available so far. [less ▲]

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See detailImportance of intertidal sediment processes and porewater exchange on the water column biogeochemistry in a pristine mangrove creek (Ras Dege, Tanzania)
Bouillon, Steven; Middelburg, Jack J.; Dehairs, Frank et al

in Biogeosciences (2007), 4

We sampled a tidal creek (Ras Dege, Tanzania) during a 24-h cycle to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and ... [more ▼]

We sampled a tidal creek (Ras Dege, Tanzania) during a 24-h cycle to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and biological driving forces. Since the creek has no upstream freshwater inputs, highest salinity was observed at low tide, due to evaporation effects and porewater seepage. Total suspended matter (TSM) and particulate organic carbon (POC) showed distinct maxima at periods of highest water flow, indicating that erosion of surface sediments and/or resuspension of bottom sediments were an important source of particulate material. Dissolved organic carbon (DOC), in contrast, varied in phase with water height and was highest at low tide. Stable isotope data of POC and DOC displayed large variations in both pools, and similarly followed the variations in water height. Although the variation of 13CDOC (−23.8 to −13.8‰) was higher than that of 13CPOC (−26.2 to −20.5‰), due to the different endmember pool sizes, the 13C signatures of both pools differed only slightly at low tide, but up to 9‰ at high tide. Thus, at low tide both DOC and POC originated from mangrove production. At high tide, however, the DOC pool had signatures consistent with a high contribution of seagrass-derived material, whereas the POC pool was dominated by marine phytoplankton. Daily variations in CH4, and partial pressure of CO2 (pCO2) were similarly governed by tidal influence and were up to 7- and 10-fold higher at low tide, which stresses the importance of exchange of porewater and diffusive fluxes to the water column. When assuming that the high dissolved inorganic carbon (DIC) levels in the upper parts of the creek (i.e. at low tide) are due to inputs from mineralization, 13C data on DIC indicate that the organic matter source for mineralization had a signature of −22.4‰. Hence, imported POC and DOC from the marine environment contributes strongly to overall mineralization within the mangrove system. Our data demonstrate how biogeochemical processes in the intertidal zone appear to be prominent drivers of element concentrations and isotope signatures in the water column, and how pathways of dissolved and particulate matter transport are fundamentally different. [less ▲]

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