Abstracts

 

Wetland Elevated CO2 Experimental Facility

Dr. Karen L. McKee

Scientist Emeritus, U.S. Geological Survey


Acceleration in sea-level rise (SLR) threatens low-lying coastal areas and the extensive wetland habitat located within these areas.  I am investigating how elevated concentrations of atmospheric CO2 (carbon dioxide) may interact with other factors such as flooding and salinity to alter wetland ecosystems and their capacity to accommodate SLR.  This work is carried out in the Wetland Elevated CO2 Experimental Facility located at the National Wetlands Research Center, Lafayette, LA.  Mesocosms containing intact sections of marsh are exposed to different conditions representing future scenarios of climate, CO2, and sea level.  Complimentary field studies are also carried out to relate experimental findings with how these ecosystems accrete vertically in response to SLR.

 

Mangroves and geomorphological processes

 

Professor Colin David Woodroffe

School of Earth and Environmental Sciences,
University of Wollongong,
Wollongong, NSW 2522,
Tel :  (02) 42213359
Fax : (02) 42214250
Email : Cette adresse email est protégée contre les robots des spammeurs, vous devez activer Javascript pour la voir.

Mangroves occur on low-energy tropical and subtropical shorelines where there is suitable substrate in the upper intertidal zone. Their distribution and shoreline dynamics are therefore a function of coastal geomorphology. Although there are important ecological interactions that influence species distribution, longer-term changes can be viewed across a range of time and space scales. At the smallest scale, the ‘instantaneous’ scale at which physiological and sediment processes operate, mangroves can occur across a broad range of environmental gradients on the shoreline. There can be significant disruptions to mangrove ecosystems as a result of unusual or extreme events, such as individual storm events, and the ‘event’ time scale exerts a particular influence on mangrove ecosystems because the trees have life histories of decades, preserving evidence of such events. By contrast, the longest time scale, termed the ‘geological’ time scale, is concerned with thousands to millions of years. This is the time scale over which coastal plains have prograded, deltas have been built out at river mouths, and mangrove ecosystems have responded to altered boundary conditions, such as changes in sea level. The response of mangroves at this time scale, and the evolutionary history of associated landforms, can be inferred from the stratigraphy and age of sedimentary sequences. Coastal managers, involved with planning need to consider the ‘engineering’ time scale of several decades. This is the scale at which planning decisions need to be made, anticipating behaviour of the shoreline, but it is perhaps the most difficult to understand because it falls between the knowledge based on observations of processes and events over the past few decades, and the long-term behaviour recorded in the sedimentary record. In this review, the geomorphological behaviour of a variety of coastal systems will be examined, with examples from around Australia, and elsewhere in the southeast Asia and Oceania region. The idea of ‘environmental settings’ within which mangroves occur, and the predominant processes in each of these settings will be discussed as a basis for considering what the likely impacts of changes in climate, particularly sea-level rise, may be on mangrove ecosystems.

 

Impacts of climate-induced mangrove expansion on the ecological functions of salt marshes

Dr. Irving A. Mendelssohn

Department of Oceanography & Coastal Sciences
3263 Energy, Coast and Environment Bldg., School of the Coast and Environment
Louisiana State University, Baton Rouge, LA 70803
Tel : 225 578-6425
Fax : 225 578-6423
Email : Cette adresse email est protégée contre les robots des spammeurs, vous devez activer Javascript pour la voir.

The advancement of species poleward, presumably due to global climate warming, has recently been documented in several regions of the world. In coastal ecosystems, one unique distributional shift is the movement of Avicennia germinans (black mangrove) northward into temperate Spartina alterniflora salt marshes.  In the Mississippi River Delta Complex of the northern Gulf of Mexico, black mangroves were historically restricted to the southernmost barrier islands and beaches by winter freeze events; however, in recent years a noticeable expansion has been observed.  Given the sparse documentation of the ecosystem-level effects of black mangroves expansion within coastal salt marshes, our goal was to quantify the impacts of this expansion on ecological processes including surface sediment accretion, organic matter production, organic matter decomposition, and carbon assimilation, as well as several edaphic characteristics.  Our results indicate that presently black mangrove expansion has had no major impacts on the ecosystem processes we measured.  Sediment accretion rates, belowground production, decomposition rates, and carbon assimilation were similar between Avicennia and Spartina stands located within the same hydrologic setting.  While decomposition rates were similar between habitats, mangrove leaves and roots decomposed more quickly than Spartina leaves and roots.  Some differences were documented in edaphic parameters between habitats.  Elevation, redox potential, bulk density, and soil ammonium were slightly higher, while soil moisture and porewater salinity were somewhat lower, where black mangroves had expanded into the surrounding salt marsh.  Other researchers working in different regions of the northern Gulf of Mexico have reported similar findings, which will be reviewed. Even tropical cyclone-generated sedimentation did not significantly differ between mangrove and salt marsh habitats located over large geographic distances. Because the expanding black mangrove stands are small in stature as well as areal coverage, significant effects on ecosystem processes may presently be muted.  However, if stands continue to grow in vertical and horizontal extent, effects on ecosystem processes may occur in the future.  This research provides a baseline from which future ecosystem responses may be evaluated as mangrove populations continue to develop.

Keywords

Climate change, ecotone, function, structure

 

 

Mangrove forests and sea level rise

Professor Catherine Ellen Lovelock

School of Biological Sciences,
The University of Queensland, St Lucia, QLD 4072.
Tel :    07 3356 2304
Fax :       07 3365 5755
Email :    Cette adresse email est protégée contre les robots des spammeurs, vous devez activer Javascript pour la voir.

Increases in sea level pose a threat to mangrove forests and other coastal ecosystems. Rising sea levels may result in losses of mangroves on seaward fringes. On seaward fringes they occur low in the intertidal zone and their tolerance of inundation may be exceeded. Additionally, with increasing tidal inundation of adjoining ecosystems, expansion of forests into adjacent ecosystems (e.g. salt marshes) is also anticipated. Barriers to migration, both human and natural, will result in coastal “squeeze” where the area of forest is reduced. Although the projections for losses of mangroves with sea level rise are often high, mangrove ecosystems may “keep pace” with rising sea levels through increasing soil volume. The rate of sea level rise, coastal geomophology, sediment availability, plant productivity and human management of the coast all have critical roles in determining the fate of mangroves with sea level rise.

 

Measuring the stability of coastal wetlands: The surface elevation table – marker horizon method

Professor Catherine Ellen Lovelock

School of Biological Sciences,
The University of Queensland, St Lucia, QLD 4072.
Tel :    07 3356 2304
Fax :       07 3365 5755
Email :    Cette adresse email est protégée contre les robots des spammeurs, vous devez activer Javascript pour la voir.

 

The surface elevation table – marker horizon method (SET-MH or Rod SET-MH) is used globally to provide a measure of the stability of coastal wetlands. The SET-MH method uses a benchmark or baseline that is anchored deep in the soil profile (a rod pounded to resistance) from which increases or decreases in the elevation of the soil surface can be measured using a set of pins on a ”table” or measuring arm that is situated on top of the benchmark rod. Changes in elevation over time can be measured to mm accuracy. Coastal wetlands that keep pace with local rates of sea level rise can be distinguished from those that are failing to keep pace. The concurrent use of marker horizons (MH), which allow detection of soil surface accretion (e.g. sediment deposition) allow changes in soil elevation to be attributed to surface or subsurface processes. The method enhances understanding of the processes important for “keeping pace” with sea level rise in coastal wetlands which informs management for sustainable wetlands.



 

Mangrove carbon dynamics in a human-impacted world

Professor Shing Yip (Joe) LEE

Australian Rivers Institute and School of Environment
Griffith University Gold Coast campus,Qld 4222, Australia


Tropical estuaries are the most heavily populated areas of the world. Coastal urbanisation, a global phenomenon, has and will continue to alter the structure of estuarine habitats and influence their capacity for beneficial ecosystem services such as nearshore fishery production. One of the central paradigms of tropical estuarine ecology is the role of mangroves in coastal carbon dynamics. Early studies of coastal wetlands emphasised their role of net exporters of carbon, whereas recent findings suggest that mangroves could serve as important long-term carbon storages. While many biophysical factors (e.g. the tidal regime, activity of key biota) influence the behaviour of tropical mangroves along this export-storage continuum, intense urbanisation and other human activities also significantly modify the actual role of mangroves in the organic matter dynamics of modern tropical estuaries. In this presentation, I will propose a conceptual model on carbon dynamics of tropical urban estuaries, discuss an example of how human activities and urbanisation in the catchment may shape estuarine and nearshore nutrient dynamics, and propose options and opportunities of managing tropical mangrove-dominated estuaries to maximise their services in a sustainable way.

 

 

Mangroves in a Changing World

Dr. Karen L. McKee

Scientist Emeritus, U.S. Geological Survey


Mangrove ecosystems are subject to a range of climate change factors, including atmospheric CO2, air and sea temperatures, precipitation, and sea-level. Although rising concentrations of atmospheric CO2 may have direct effects on mangrove vegetation, CO2 may interact with other factors such as nutrient availability, flooding or salinity stress, and competition, to alter mangrove structure and function. Mangroves respond to higher CO2 with increased growth, but some studies suggest that other factors such as competition and herbivory may limit the beneficial effects.  Although findings indicate that biological interactions could modify the direct effects of higher CO2, predictions are difficult to make at a global scale due to limited data on mangrove species. Global changes in temperature and rainfall may also modify mangrove distribution patterns, leading to range expansion at their latitudinal limits. Such climate changes, however, may be facilitated by negative effects on competing, temperate vegetation in sub-tropical regions, e.g., the Mississippi River Delta where the black mangrove, Avicennia germinans, has expanded into areas where the temperate salt marsh grass, Spartina alterniflora has succumbed to periodic dieback associated with drought. One of the most important global change factors affecting mangroves is sea-level rise. Recent work has shown how both physical and biological processes influence vertical land building in mangrove forests and how factors affecting organic matter accumulation may lead to changes in elevation trajectories. Analysis of a global dataset revealed that high rates of sedimentation do not guarantee accommodation of sea-level rise because of high rates of subsidence; peat-forming areas are able to keep up because of subsurface expansion driven by root matter accumulation.  Carbon sequestration rates estimated from surface accretion of organic carbon, however, were similar in organic (216 g C m-2 yr-1) and mineral (145 g C m-2 yr-1) soil types, but varied across geographic locations (41 to 591 g C m-2 yr-1), suggesting spatial variation in controls on C deposition.  Subsurface inputs of carbon, which were estimated using measured rates of root matter accumulation and root carbon content, averaged 121 g m-2 yr-1, but exceeded 400 g m-2 yr-1 at several sites.  In summary, changes in atmospheric CO2 concentration, climate, and sea level will lead to complex interactions affecting the structure and function of mangroves.  Predicting the outcome of such interactions will be aided by multivariate approaches that allow simultaneous examination of multiple drivers of change along with internal feedback pathways and linkages among physical and biological components.

 

 

Towards National Coastal Health Archive and Monitoring Programs (CHAMPs) for assessing change, and identifying drivers of change, in tidal wetlands and coastal margins.

Norman C Duke*, Jock Mackenzie, Damien Burrows


Norman Clive DUKE

Mangrove Hub, TropWATER
Centre for Tropical Water and Aquatic Ecosystem Research

James Cook University (JCU), Townsville Qld 4811 AUSTRALIA
Tel : (07) 5534 7082 (office)
Email : Cette adresse email est protégée contre les robots des spammeurs, vous devez activer Javascript pour la voir.
Web Sites : www-public.jcu.edu.au/actfr/staff/JCU_081848, www.mangrovewatch.org.au

Regional Coastal Health Archive and Monitoring Program (CHAMP) projects offer significant socio-economic and conservation benefits providing world-class, national, living archives of interactive online maps and oblique imagery showing the extent, condition, impacts, change, and health of valuable, but always threatened, natural habitats, as well as man-made infrastructure, for full coastlines of each region.

The chief outputs proposed will be highly visible and easily accessible, on public-access websites featuring sponsor recognition and links along with complete assessments of risk and vulnerability of entire regional shorelines - including estuaries, beaches, channels and islands. The conservation benefits are tangible and without precedent, where the proposed resource of such interactive knowledge that is both current and historically relevant will become a key base reference resource for all future conservation, assessment and management of regional coastlines. Furthermore, this innovative program establishes a new standard for best-practice environmental management for coastal regions around each country, and worldwide.

 

Suivi de la mangrove en contexte minier

Dr Cyril Marchand

Le projet que nous avons présenté au CNRT intègre une démarche qui vise à déterminer le rôle de la mangrove dans les processus globaux de transfert continent-océan en milieu tropical, et notamment son rôle de filtre vis-à-vis des effluents miniers.

En Nouvelle-Calédonie, la superficie couverte par les mangroves est particulièrement étendue et la richesse floristique de ces dernières est très significative. Cependant, la mangrove calédonienne est une zone tampon entre un lagon de plus de 20 000 km2, délimité par la plus longue barrière récifale continue au monde, et les massifs ultrabasiques et leurs couvertures d'altération, couvrant 1/3 du territoire calédonien et caractérisés par leur grande richesse en un certain nombre d’éléments traces métalliques (ETM) (Fe, Mn, Ni, Cr et Co). En effet, la Nouvelle-Calédonie, 3ème producteur mondial de nickel (30 % des réserves mondiales) connaît une activité minière particulièrement intense depuis la fin du 19ème siècle. Depuis le début de cette activité, environ 300 millions de m3 de stériles latéritiques riches en Fe, Mn, Ni, Cr et Co ont été remaniés. Une partie significative de ces stériles a été transportée par érosion vers les zones littorales à la faveur d’épisodes climatiques violents qui interviennent régulièrement dans cette région. En période de crue cyclonique, les processus naturels d’érosion et de sédimentation sont fortement accentués par l’exploitation minière, et représentent la plus importante source de dégradation du littoral, de la mangrove, des récifs frangeants et du lagon.

Dans le cadre du présent projet, nous mettons en place un dispositif de suivi du milieu en combinant l’outil télédétection (images optiques et radars haute résolution), et une instrumentation in-situ visant à déterminer la quantité des apports en particules sédimentant dans la mangrove ainsi que la durée d’inondation de chaque zone de mangrove. La combinaison de ces deux approches nous permettra de déterminer l’impact de ces apports sur cet écosystème. L’objectif du présent projet de recherche est de délivrer un dispositif de suivi de la mangrove, qui permettra d’évaluer son évolution en fonction des apports sédimentaires, et des modifications du réseau hydrographique liées aux apports. Dans ce contexte, nous nous sommes focalisés sur une mangrove située en aval d’un bassin versant caractérisé par une activité minière, et présentant une structuration de l’écosystème typique, à savoir la mangrove située en fond de baie de Vavouto.

Le caractère ambitieux et innovant de ce projet réside, d’une part, dans le fait qu’il n’existe actuellement aucun appareil de mesure in situ permettant de suivre la durée d’immersion et le taux de sédimentation dans la mangrove, et d’autre part, qu’il s’agira d’une première application de la télédétection très haute résolution à l’étude de la mangrove, et à son suivi dans un contexte d’exploitation minière.

 

Dynamique du carbone au sein des mangroves.
Quantification spatio-temporelle des flux de CO2 aux interfaces sol-air et eau-air

Audrey Leopold
Thèse de doctorat (14 décembre 2012)
Université de la Nouvelle Calédonie

Résumé :

Les processus de stockage et de transfert du carbone entre les différents réservoirs de son cycle bio-géochimique jouent un rôle essentiel sur la pression de CO2 dans l'atmosphère, et ont fait l'objet de nombreuses études (voir par exemple les reviews de Berner en 1989 ou de Hedges en 1992). L'augmentation récente de la pression de CO2 dans l'atmosphère résulte de l'utilisation de combustibles fossiles par l'Homme. Son effet aujourd’hui attesté sur un changement climatique à l’échelle du Globe, a attiré l'attention de nombreux chercheurs d’une part sur la quantification des émissions du CO2 dans l’atmosphère et, d’autre part sur des écosystèmes capables de fixer puis de stocker le carbone. Comprendre les facteurs influençant les flux de CO2 entre les différents réservoirs de son cycle est devenu un axe de recherche prioritaire au niveau global.

La mangrove est un écosystème spécifique de la zone intertidale, ayant développé des capacités d'adaptation à des conditions extrêmement sélectives. La mangrove revêt une importance capitale aussi bien au niveau écologique qu’économique, et représente, avec la forêt tropicale humide, un des écosystèmes les plus productifs en domaine terrestre, i.e. 30.0 Tmol C y-1 (Twilley et al., 1992; Jennerjahn et Ittekkot, 2002; Alongi et al., 2005; Kristensen et al., sous presse). Actuellement, elle occupe environ 75 % des littoraux tropicaux sur près de 200 000 km2. Du fait de sa forte productivité, de sa distribution au niveau global, et de sa position à l’interface entre terre et océan, la mangrove est considérée comme un écosystème d’importance dans le cycle du carbone. Elle possède la double compétence de puits pour le CO2 atmosphérique et de source de carbone organique et inorganique pour les zones côtières. Cependant les dernières estimations du bilan de carbone au sein des mangroves font état de nombreuses incertitudes. Lorsque l’on cumule les différents puits de carbone au sein de la mangrove, c'est-à-dire l’export, l’enfouissement et la minéralisation, ces derniers ne représentent que 50 % du carbone fixé par les palétuviers lors de la photosynthèse (Bouillon et al., sous presse). Notre analyse suggère que : i) la minéralisation, c'est-à-dire la transformation du carbone organique en CO2, est fortement sous-estimée, ii) l’export de carbone ne se fait pas seulement sous forme organique mais également sous la forme de carbonate, donc après minéralisation, iii) la néosynthèse de minéraux carbonatés au sein des sédiments doit être prise en compte (Bouillon et al., sous presse ; Marchand et al., sous presse).

Objectif général et questions de recherche traitées :


L’objectif de la thèse sera d’établir un modèle quantifié de la dynamique du carbone au sein des mangroves avec une attention particulière aux différentes formes du carbone minéral, et ce afin de participer à la réflexion internationale sur le rôle des mangroves dans le cycle du carbone le long des littoraux tropicaux.
Les questions spécifiques auxquelles nous souhaitons répondre sont les suivantes :

  • Quels sont les flux de carbone organique apportés par les palétuviers aux sédiments ?
  • Quels sont les flux de CO2 issus des sédiments de mangrove ?
  • Quels sont les facteurs responsables de la variation de ces flux ?
  • Comment varient les concentrations en carbone inorganique dissous au sein des eaux interstitielles ?
  • Quels sont les flux de carbone inorganique dissous à l’interface sédiment-eau ?
  • Quel est le pourcentage du carbone fixé par les palétuviers qui est minéralisé et exporté des sédiments de mangrove (sous forme aqueuse ou gazeuse) ?
  • Dans quelles proportions les mangroves sont-elles un puits pour le CO2 atmosphérique ?
 
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