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The role of buffering capacities in stabilising coastal lagoon ecosystems.


1. To identify, describe and define the biotic and abiotic components of internal processes and their interrelationships in coastal lagoon systems which act as buffers against environmental change induced by external forcing.
2. Once described and defined, to quantify the "buffering capacity" and, consequently, to determine the threshold levels of external forcing processes, above which have a major impact on community structure and biogeochemical flows.
3. To study the potential and occurrence of mechanisms that represent natural recycling and restoration of "buffering capacities" on different time scale's (including studies of diel and tidal cycles as well as seasonal variations).
4. to perform mechanistic studies to elucidate interactions among organisms, which belong to different taxonomic and ecological functional groups, and their abiotic environment, in order to achieve understanding of buffering capacities that occur at the community level.
"Buffer capacities" has been defined in ecology as a holistic concept (e.g. Jørgensen, 1992), but we show that it can also be worked out in mechanistic studies. Hence, the concept is powerful to create a dialogue between holistically and mechanistically oriented researchers, and is particularly useful to study non-linear changes in coastal lagoon ecosystems (compare to importance of non-linear changes in ELOISE Science Plan).
We have applied this concept to understand "local stability" in sea grass ecosystems and their vulnerability towards structural changes into macro-algal dominated communities.

We present evidence and quantitative data in support of the following mechanistic hypothesis:
i- plant assimilation provide a buffer against water column nitrate loading;
ii- the balance between nitrogen fixation and denitrification can be modified in favour of nitrogen loss upon N-loading, but this phenomenon is quantitatively of minor importance compared to nitrogen assimilation by the plants;
iii- during degradation of eelgrass biomass, the nitrogen demand of organotrophic bacteria in the sediment results in nitrogen retention of N in the sediment and hence a buffer against release of nitrogen compounds from sediments;
iv- habitat diversification in sea grass meadows provides shelter for meiofauna and hence buffering against adverse conditions;
v- sedimentary iron provides a buffer against noxious sulphide (note: bacterial sulphide production is enhanced in anoxic sediment niches by increased organic matter loading).
On the other hand, in the coastal system we studied, sedimentary iron appears insignificant as a redox-coupled buffer system against phosphate loading. This is because most inorganic phosphate is bound to calcium rather than to iron. In addition, our studies have highlighted the importance of plant-microbe interactions in the sea grass meadows.
The project focuses on identifying, describing and defining the biotic and abiotic processes in coastal lagoons that act as buffers against environmental change induced by external forcing. These mechanisms provide stability and reobustness, but when their capacities are exceeded they give rise to non-linear responses. Non-linear behaviour of coastal ecosystems has been recognised as a major reason why such changes are difficult to predict. Buffering capacities needs to be restored on an appropriate timescale in order to provide the long-term sustainability and economic, social and scientific value of these unique ecosystems.
The project involves mechanistic studies and requires a multi-disciplinary approach involving microbiologists, marine biologists (algologists and zoologists), biogeochemists and system ecologists. It will focus on the following processes that are related to buffering capacities: 1) role of sediment oxygenation in rooted phanerogam communities and microbial processes in the rhizosphere; 2) primary production of plant and algal biomass as a mechanism for countering the effects of nutrient load; 3) the iron redox system in the sediment and its role as trap for toxic hydrogen sulphide and sequestering phosphate; 4) the rates and pathways fo benthic mineralisation of organic carbon, nitrogen and phosphorus compounds, and how they are regluated by the quality, quantity, availability and sedimentary depth distribution of organic matter inputs as well as how they determine nutrient fluxes across the sediment water-interface.
The work content is organized in four work packages: 1) field measurements on annual time-scales, 2) detailed and intensive field measurements during joint field campaigns in the Bassin d'Archacon to study processes that occur on short time scales, 3) mesocosm experiments to evaluate the effect of forcing factors, and 4) laboratory experimentation to study the ecophysiology of individual microbial species and the interactions occurring amongst physiologically dissimilar populations.


Université de Bordeaux I
2,Rue Du Professeur Jolyet
33120 Arcachon

Participants (6)

28,Vierstraat 28
4401 EA Yerseke
540,Ny Munkegade 540
8000 Aarhus C
United Kingdom
DD1 4HN Dundee
Viale Delle Scienze 11/A
43100 Parma
Universidad de Alicante
S/n,crta. De Valencia
03071 San Juan De Alicante
Università degli Studi di Ferrara
Via L. Borsari 46
44100 Ferrara