Mangroves in the Anthropocene 2024 | Lecture 7 | Dissolved and Particulate Carbon Dynamics

Speaker: Dr. Stéphane Mounier | Professor at the Université de Toulon, MIO Laboratory (France)

​Dr. Stéphane Mounier is a researcher at the Mediterranean Institute of Oceanography. He obtained his PhD on the flux and characterization of organic matter in the Amazon River at the University of Paris VI. He works on the spectroscopy of organic matter and its interaction with metals in various environments (soils, lakes, seawater, pore water, sediments, and solids) using PARAFAC decomposition. His latest work focuses on mangrove organic matter and its fluorescence characterization.

welcome everyone um morning afternoon or evening depending on where you are in the world uh glad you could join us and I’m glad that you remembered the change of uh day of the week for the talk um so it gives me great pleasure to introduce our speaker today uh Dr Stefan munier uh who is from the University of tulong and I should just uh start by uh acknowledging that tulong university has recently uh become a member of the I and so we’re very pleased about that and equally pleased to have you speak for with us today Stefan so uh Stefan is a researcher at the Mediterranean Institute of oceanography at the University he obtained his PhD on the flux and characterization of organic matter in the Amazon River at the University of Paris uh six and uh he works on the uh spectroscopy of organic matter and its interaction with Metals in various environments such as soils Lakes seawater po water uh sediments and solids using p a r a f decomposition and I have to confess Stan I’m not sure I know what that is so maybe at some point you’ll let you’ll let me know um and his latest work is focusing on Mangrove organic matter and its F fluorescence characterization so welcome and you can go ahead start sharing your screen okay um let me share up up up so thank you duke for for this introduction um this presentation is about carbon Dynamics and contaminant in mongra ecosystem and more specifically we will focus on what happened in mongra sediment and the role of organic matter in contamination or metallic contamination uh before for me it’s necessary to Define um what about we are talk what what uh we are talking about uh is for metal there is no ambiguity for organic matter SE there is several words we talk about carbon we talk about organic carbon and it’s it is important to remind what compartment we are talking about so um what carbon are we interested in uh in fact uh we we saw in the literature a lot of expression blue carbon stock of car carbon carbon dioxide Etc and also organic matter labile Etc refractory organic matter but what what is this carbon is so carbon it’s just a general point of view carbon is there is two forms there is the inorganic carbon the oxidized form and the most common form are carbon dioxide and carbonates and uh these two forms are in relation between several compartments because the carbon dioxide can associate with water to make Carbonic acids and this make a relation with atmosphere because when you have more pressure of carbon dioxide you have more um acidic carbonic acid in the water and if there is a variation of pH or if you reach some basic pH you can see The Apparition of carbonate and this carbonate can in some condition uh concentration or pressure can precipitate in solids so in fact uh the inorganic carbon is principally gases liquid or in solution and and solids and there is also two other form that are less uh important is graphite and Diamond okay uh but generally we also discuss about organic matter so the organic matter is carbon reduced carbon in fact and uh is uh based on the name that we have a skeleton with carbon okay so it contains organic molecules simples from Ura or some very simple molecules but it can be a little by little more complex like oil or proteines until uh leaning or big proteins that we can call biopolymers uh this part of biopolymer contain is about 20 to 30% of the organic matter uh in the environment and uh all these big molecules or B molecules are uh degraded by biotic or abiotic processes and they give a lot of thousand of molecules that have several structures and we call generally this uh this part uh this undefined pool of organic matter geopolymer uh also we can add in this pool of organic matter all the molecules that we made the human made like Plastics chemicals Etc because they they are in by definition organic matters because their skeleton is made with carbon so when we talk about organic matter or when we talk carbon we talk about one of these compartment or the organic or or the UN inorganic or about organic matter or about carbon but all these pool are linked what is the distribution in fact in the the Earth uh 99% of the carbon on the earth is in the rocks in fact you can see that U most of the carbon is in the sediments in the crystal Earth and uh there is uh if we take apart this sediment we have a small part that is in the water sea water and oan but even in this compartment oan we have most most of the carbon I don’t know if you see my my mouse but most of the carbon is inorganic one carbonate and a little part is organic and this part of organic carbon is more or less the same than the biomass biomass that can be in river on air on soils so only finally 1% or less than 1% of the carbon on the earth is organic matter uh why it is important finally to to to care about this small part it’s because uh as you know it is in relation with several Reservoir we have the atmosphere we have the hydrosphere ocean and river and we have the souls pedosphere and we have the leosphere which are the biggest Reservoir and in fact in this between this Reservoir there is not the same kinetics so when we increase the CO2 in the atmosphere it takes a longer time to go in the hydrosphere and pedosphere and a longer longer time to go in the leosphere and it’s why this link is very important we try to now diminish the production of CO2 and to di to increase also this uh transfer from the atmosphere to the pedosphere are to the hydrosphere in fact we try to trap the carbon or we try we want to trap so uh and this carbon in soils and hydrosphere is not homogeneous uh we can see that if we take in account the biomass distribution uh the productivity is not the same around around the earth and principally depend on the latitudes so in north latitude we have less production at the maximum of biomass production is near the tropical Zone in the South uh this is probably due to the temperature uh most temperature higher um increase of plants but for the soils it’s more or less the contrary because if you look at the distribution of carbon in soils uh we have in the north less uh higher sorry higher uh content of carbon or organic matter in the soils you can see here and lesser in the South this also is due to uh probably the temperature because if you have higher temperature you have higher biological activity in the soils and you have a higher mineralization of organic matter but what about uh mongr because we want to talk about mongr so mongr uh they they are important because uh they represent 0.5% of the costin but 10% of the carbon export to the oan when we talk about carbon export it’s organic carbon export and also this small part of the of the surface they are uh three to five times High efficient to stock carbon in the biomass so it’s why we are interested in mongra and we want to know how it works inside these ecosystems also if we talk about biomass is not really the same thing that if we talk about uh um content in fact because uh if you look at this map we can see that there is a carbon content a difference in carbon content depending on the region the Indonesian and North American region zon seems to be more productive here and here and uh this is a production for the one top meter of soils Mong Groves in fact so the average more or less uh if you take this around the world it’s around 370% 370 megga megagram of carbon by hectar but this evaluation is probably underestimated because there is a lack of study in certain region particularly in Africa and also we take only in this prediction only in account the first one meters of of of sediments of soils but more or less we can see that uh the central Endo Pacific region is uh more more efficient to to bual carbon and uh also more or less Tropical Atlantic uh also it’s difficult to study organic matter in mongra because there is a difference between the morphology of carbon on the same work from Saka we can see that depending on the sorry it’s represent I forget to say that it represent only 1 to 4% of the organic matter carbon stock but uh export sorry uh depending on the typology or morphology of the mongr you have also different variability of carbon bual so depending on the mangrove you can expect some difference and it’s very hard to have a global or general uh point of view of the function in the in the stock of carbon so but more or less we can say that whatever the system we can expect 2,000 to 4,000 uh gram of organic carbon by square meter by year concerning the stocks and also it’s not only the the the morphology or the superficy of the mongra it’s also the the edge of the mongra because we can see on this work that depending on the age of the forest either it’s Forest uh there is a difference in the capture of the carbon in the system so at the beginning of the increasing of the forest is not really efficient the maximum of efficiency is between 10 and 20 and after it decrease and after 40 it’s little bit more complicated to have a a trend okay uh this was a gener introduction for the the organic matter carbon and we we so that we can expect a very large um large structure and large function for organic matter but what is the dynamic of organic matter and metals in mongroo systems so um EST mongr umed in fact it’s know the river inputs from the land okay this uh matter or this organic carbon but also in organic but this carbon is alus and it integrate the contamination and the erosion of all the water sh uh this inputs in counter uh the seawater and surfur to delant and this mixing process modify the geochemistry of of the system salinity temperature oxygen Etc but also the physical system with velocity and density and part of this dissolved organic matter um settles on the surface of the sediments and one part go through directly in the open oan and another part go into floculation and element the the surface of the sediment on this surface there will appear High activity of microorganism and there will have some depletion of oxygen and it will appear some modification in the speciation of the metal in on the of the carbon inside the the sediment some layers will appear and for the metal it’s the same thing dissolve metal go with the organic matter and go to flate part of this metal will associate to the floculation with the absorption and for this the principal drivers are the solubility of some elements for example chloride or some species for chloride or carbonate but also the adsorption on Surface and this surface can be oh sorry the the this surface can be a mineral surface with clay and silt Etc but also the new formed Surface by the organic matter that suffer floculation uh or yes floculation concerning the particulate uh inputs is the same thing we have the same systems and but we can add in the particulate some autous inputs from biomass and from uh atmospheric depositions um they uh add this on the surface and uh we have some fresh organic matter and this will uh suffer a diagenesis process and intertidal exchange with seawater um what is diagenesis in fact uh oh no sorry it’s not what is um what what is the stock of metallic of metals and carbon in the in the mongra we can uh separate two more or less we have the over over surface overground carbon and the underground carbon in the biomass and in the sediment even if uh we can consider that the roots of the mov inside the sediments are make parts of the biomass compartment so this comparments we can see here that metals are not distributed in compartment in the biomass this is a work from Ramos uh we can see that for example for iron uh we have most iron below ground roots and for zinc nickel and chromium it’s in trunk and for uh um for sorry aluminium and copper and for zinc nickel and I miss I miss the the line but uh it is in trunk and in oh sorry it is in the B ground it is in in roots for the nickel aluminum and and copper and it is in trunk for zinc nickel and chromium and for Dink it’s more or less same distribution between branches and and belr uh what see what it makes this difference probably due to the difference of chemical species that are present in the sediments and uh we will see that these species come from the speciation of metals and the interaction probably with organic matter and some mineral lians in the in the in the sediment on this work uh Ramos tried to make some balance in biomass uh so he estimated that uh from the liter fall there is some flu of metals here that come on the reservoir of biomass and one part is exported by the biomass and we can see that uh uh except for uh canum and zinc the balance is negative it means that uh the mongr are um sync of metals and the stock of metals in biomass should probably increase but in sediments there is another story in sediments uh there is a story between clay organic matter and metals uh at the surface there is fine fine partic that settled on the surface and these fine particles offer a very high specific surface and this ey very this very ey specific surface um allow the association of this clay with or the clay with organic matter we can see here that if we take um profile of sediments we have at the surface more clay and more carbons they are in fact Associated and this Association of clay and organic matter also induced association with Metals if you look as this work uh we can see that uh when there is it’s the same s but when there is less clay there is less metals and when there is high content of clay or organic matter there is higher concentration of metals it means that between clay organic matter and metals there is Association and generally we can say that we have a concentration that go increasing from SE toland and U the more the site is exposed to high energy like wave and perturbation uh the less we have Clay and the less we have metals and carbon so metals and carbon are associated in this type of consideration and uh if we have some protection we have higher fine particles and we having higher um higher fine particles we have higher Association to Metals uh this mean that the sediments of Mong Groves can be used and they are used uh to uh measure the activity of the of the Basin uh this can be seen on this work from asan here we have the metal content into uh sediment surface and they are measured between 2008 and 2015 and uh we can see that for the guandong province between uh 2008 and 2015 we have an increase of um chromium Arsenic and leads concerning the guanzi province we have a decrease of uh lead and zinc and a little increase little increase in chromium this mean that the sediments are uh register the activity because on the gandon province between these two dates it it was an increase of economic activity so when the economic activity arrives there is an increase of contents and for the GUI it’s a change of activity it means that they pass from industrial to tourism and uh there was a registration of What’s Happen in the waterers shed it mean also that the sediment of mongr are very reactive so they they change in very few uh time and they integrate the contamination and they keep this memory in inside their metal contents anyway it’s not only the the the total concentration of metal that is important in sediment uh it’s also what’s happened in the spaces in the sediment and to understand what’s happened uh to Metals inside sediment we need to to go a little bit more in the diagenesis process so on the left graph uh we have sediment and on the right it’s another but on the left we can see that there is some uh heterogenity in the in the sediment and the brown the brown Mark are in fact oxidate one and the oxygen was bring by The Roots here and it means that on this part there is oxygen and The Roots bring the oxygen to this uh Zone but when you see at the black one in fact there is a depletion of oxygen this this mean that uh depending on the biot turbas and the zone and the sediment it could be very difficult to have something homogeneous uh on the on the left picture you can see that it’s very hard to make something Global because there is small small zone of different environment or chemical environment but on the left it’s more uh homogeneous and you have I don’t know if it is well defined on my picture but on the bottom of the sediment there is a black uh black color here and it is the the reductive zones so uh what is the diagen this process in fact so uh I told you that uh surface of sediment are alimented by uh fresh we say fresh organic matter from inputs of river particulate dissolve that flate and also some biomass that arrived uh on this surface uh rapidly on the top of the sediment the the oxygen is consumed and cause some depletion turning the the the environment anoxic but if there is no more oxygen um bacteria will use other oxidant is not the same bacteria there is a change in the bacteria between the Surface to the bottom but some bacteria are able to take oxygen from nitrates and so you you will have the use of the nitrates on these sediments and they will uh consume these nitrates after the cons consume of the nitrate you will they will use the manganes oxide and the iron oxides until the sulfat and uh the sulfate oxy the the use of sulfate for respiration in fact cause some precipitation or by the help of some bacteria cause The Apparition of PID that is solids and this pide can co-precipitate some metals and at the end uh at the bottom of the sediment and not always but it can occurs uh you can have some methanogenesis the production of methan it is the organic matter that dismute and one part is used for respiration and one part is used for uh for biomass production so all the this uh layer are in equilibrium normally uh I suppress some some slides that show that uh uh this equilibrium is very rapid in fact and can move in the hour depending on the condition of fresh organic matter of fresh oxygen of tal frequency this layer will move um uh rapidly if there is no change uh the only production of or the only exportation of metals or the only exportation will be the adjective Transportation or adjective transfer from the bottom to the surface but in mongra it’s always modified and there is always a modification but once we talk about this organic matter as a fuel for diagenesis uh what is in fact the uh interaction between organic matter and metals we only discuss about reduction oxic but we didn’t talk about uh interaction so of course the organic matter is not only the fuel for diagenesis uh it is observed in most of mongr in the world that Metals exportation is associated to organic matter exportation in this for in this for from L we can see that uh they associate the organic matter export to the or to the metallic export here it’s for manganes and Cobalt and generally in the uh literature there is no uh study of the mechanism it’s only there is a correlation and this correlation and just some complexation of metal but it’s not clear because it’s not because there is correlation that there is uh relation so we need to investigate a little bit more what is the speciation of metal and what is complexation in term of chemistry so uh if we take this this schem uh it is the schem of metal uh speciation when there is a metal a Kon in solution we have several uh compartments we can have several compartment in equilibrium one part is the solid part in fact what we call solid part is not include in Mineral ltis but it just complexation or adsortion absorption on Surface solids so this part is called more or less solid or inorganic or particulate uh metals and can be associated with function that are organic or that are inorganic is difficult to make the difference another part of the speciation is the complex one so this part is the association by complexation of metals with several lians most of the lians could be inorganic like chlorate like sulfate etc etc or hydroxide and one part is organic it could be simple molecules like exudates or it can be organic matter and what is organic matter is comp complicated to to say so we can talk about yic substance for the moment but this organic matter are organic lians and there is several forms of metals and the most little part is the free ion the free the free ion of metals is in fact uh the smallest part of the system generally when you make some modelization it represents less than 1% of the total metal concentration and what is interesting here is that generally this free uh metal or this free ion is considered as the toxic species because this is the species that can enter in the cell wall and make some damage in the uh in the Bap but it’s not always the case it depend on the metals if we took for if take for example Mercury or arenite is not really the free metal the free ions that is toxic but the complex form so we have to take into account that most of the metals are toxic in or yes are toxic in the free um in a free ion form but Subs are uh at the contrary uh non- toxics so uh what when we talk about um this uh toxicity is uh the free ion but we can also uh talk about uh Metals for translocation because the metal that is in Roots and leaf Etc is not really a speciation but one part is related to this uh avable metal and the exportation of metal uh is uh related to the several forms in fact uh mostly complex and free ion because it is water that go through the the the mongr but also part of the particles because it depend on the strength of erosion of the particles and also in biomass because we can have biomass that can be export by into the mongr how we can measure this U this uh this several compartment it’s very hard in fact uh the most used is the acidly fraction uh and this uh way of measure the metal in sediments uh take into account the three ions the complex ions and one part of the absor of the of the of the metals on solids and this method uh have some drawback the advantage is that it’s easy and Rapid but the drawback is that you make some desorption or decomplexation by using this extraction uh mostly you have some destruction or dis the yes some destruction of the carbonates and it’s difficult to predict what happen if you change the condition it’s only parameter that you can correlate to biological effect and Di like uh low effect range that can be used what content of metal in a sediment before to have a damage in the biota as an example we have here the content for copper and nickels in uh uh in sediment okay it’s not really the the good way to investigate the uh relation between organic matter and metals another uh technique is to use the DT uh dgt are very interesting because uh technically it’s the technique that allow to measure only the three metal ions uh I don’t know if you know this technique but in fact fact it’s a thin diffusive film uh yes thin thin diffus thin diffusive film you have a resin and you have a gel here and the filter and only the free metal can reach the resin so technically is the nearest technique from the biodisponibility so because we can consider that the gel gel and filter Act as the cell wall it’s high sensitive uh technique but also it’s sensitive to temperature and defusion so uh you need to measure on the same time in C2 the temperature and the diffusion and make some calculus to uh extrapolate the concentration of metal that were seen by the dgt and also in sediment of from mongr it’s perhaps not the uh most appropriate techniques because uh you need a long time of exposition so generally it’s around one week and uh it’s not able to take into account all the change that can occurs during a tal variation so you have something average or something integrated but it’s difficult to uh uh deduce what can happen inside the sediment the last uh way to to have the the speciation between organic matter and metals is the model in fact modeling the the system you need to have a lot of information it’s very hard hard work to have but in fact if you have all the association constant and the concentration You can predict as on the right graph You can predict the speciation of your metal and also you can PR predict this speciation under change temperature pH or Redux the only problem of this is if all the inorganic liant are generally well known even the adsorption on solid etc etc the um less known parameters in this system is the interaction with uh organic matter generally uh it is assumed by researcher that we have two pool of organic matter geopolymers they don’t take into account biopolymers generally and these two pools are tuned to uh fit with the experiment there is no reality in fact it just parameter that you fit to have the good results but there is some uh way to obtain some information about the organic matter pool property of complexation and it’s why I will talk about to you now I took an example from um an experiment we done in new calonia we measure or we samples during 24 hours uh water that come out from the sediments okay just on the the output of the sediment uh you can see here the the salinity in red and the pH on the on the system and from these uh samples we made some uh experiment of quenching uh what is quenching in fact it’s a way to uh investigate the interaction of metal with organic matter the principle is this organic matter has um fluorescent property and the quantum yeld of fluoresence and when this organic matter associate with Associates with Metals uh the Quantum of fluoresence is decreasing so if you uh consider that there is an equilibrium between organic matter and metals this is the constants or quasi Thom thermodynamic constant here and that there is a number of site of complexation you can uh um deduce or you can fit the these two parameters number of sides and uh constant of complexation you made it by adding little by little the the metal and by add the metal you have a decrease of fluoresence and by using the model you have an equation in fact and this equation once it’s fitted give you the constant and the uh uh capacity of complexation which is the number of site by gram of carbon so we made this on the 24 uh samples we model this before modeling we separate the signal signal uh we obtain uh on the 24 samples two type of fluoresence this fluoresence was Yumi like fluoresence representing more or less organic matter from or geopolymers and another here which is uh protein like uh during the tidal uh event we have here um the the variation of this concentration or contribution you can see that for the protein in red there is no variation or little but for the uh organic matter the yic like uh systems we had some very high variation of concentration in fact and we investigate these uh samples by fluorescent quenching so some events occurs generally when there is a variation or just before just after the variation of salinity so we think that it’s because we have a change of uh condition in the sediment and there is some activation of biota or protein not protein but bacteria and there is production of organic matters we will investigate uh what is the property of complexation of this organic matter here it is the results uh on the left you have the constant thermodynamic constant which is the strength of complexation of this organic matter in blue it is the uh yic like no it’s not we consider that there is two sites in fact we we obtain this there is two site of complexation on the organic matter one in blue and one in red and it correspond to two pool of fluorescent organic matter that react with Metals for the constant we observe that during the middle of the experiment which is high tide during the night we have a higher complexation strength it’s not uh linear it’s logarithmic it means that during this period we have organic matter that is 100 times more complexant than the uh ual organic matter and concerning the number of sites meaning that the number of function function of complexation there is also an increase here in the middle and a little bit in the when there is a low tight but what we can uh use is that for each samples we can predict or we can measure What’s happen for the metals so on the same sample we also measure the total dissolved nickel so we have the variation of nickels during the tidal event and we used this complexation data and the concentration of all major calcium ction anion Etc in the water the pH and we calculate the speciation of nickel in the water in this water this is the results of the this calculus you can see on the left the percentage of organic nickel meaning the quantity of nickels that is associated to organic matter we don’t know which organic matter we know only its fluorescent property and its of carbon we don’t know if it is yic substance we don’t know if it is biopolymers but in fact it means that uh this pool of organic matter complex the nickels and you can observe that during the high TI there is uh until 70% of nickel that is complex and it correspond to the lower quantity of nickel in the water so uh this mean that that during this high tide we have the production or Apparition of organic matter that that complex more the nickel in the system and the rest of the time it’s 0 to 10% so there is a reaction of the mongr to the to the system and say when there is less nickel it complex more nickel and this type of Ro was also done by Tada for example and they use uh more Works to calculate also the Flux Of exportation of metals Associated to organic matter uh on the graph on the on the right you have here in the Blue Zone the mongr nips and Prim and you have the exportation uh balance of uh copper and Arsenic and also uh chromium I think yeah here yes so um what we observe is that on this work there is an association of the exportation of metal and exportation of organic matter in fact okay so as we can as we saw before the organic matter can be highly Associated to the metals by complexing property and if you look at this uh value it means that concerning the inorganic sediment or the sediment compartment there is an exportation of metals so the mangrove in the point of view of sediments and organic matter and dissolved Metals act as a source of metals and I Tred to to make some well it’s not the same work but I tried to make a comparison between the exportation of biomass uh for the copper because the similar metal for the copper we have a ret retention of small amount of copper 0.2 mole byct by year but for the um water and the tal in and out we have we have in fact more copper that go out it’s about 0.115 Mo byct my and if we consider this exportation it mean that considering sediments and biomass there is an exportation of copper if we look at the stock of metals inside these sediments it means that by hectar we have a very large amount of copper and we have time we have time to eliminate the copper in the in the mongr because it would take most that 30,000 years for this but what I WR about this small comparison is that uh mongra perhaps don’t don’t act as only syn of metallic contamination but can also act as a reactor that transform the metals and allow them to be exported in another form and particularly complex one and uh okay the organic matter is associated to metals and we have some complexing property and this complexing property are associated to organic matter pH etc etc What’s happen when I I will finish my presentation on the the change that suffer mongr you can see Urban one there is you see from Gabon some um deforestation and we have here some consequence of the shm production uh so uh what we know is that Urban impact inputs more labile organic matter uh these uh nutrients active the bacteria the surface and even if it is shrimp inputs or Urban water inputs this organic matter with increase the transformation or the mineralization of organic matter and there will be yes less carbon in soils but also less organic matter that can um complex or stabilize the metals uh this can be seen here for the two Mong Groves in Brazil one it’s the mongr of Rio Coco and the other is from the pacotti the first is an urban and the other is quite pristine or less impacted and this is the constant made on the Zone during six months and we can see that more or less it is the same strength of complexation between organic matter and metals here the metals is copper so it means that from Coco and from there is the same strength of complexation but if we look at the capacity of complexation meaning that the number of sites we can see that in the Coco there is less than in pacotti comparing to the uh global system here is the before the mongr and after mongr this mean that during the mongr of European mongr you have destruction or uh dimin of the capacity of the or matter to complex metals and urban mongr are the Zone where there is more Metals so there is a vicious circles because you have more input this inputs destroy the organic matter and this destruction of organic matter release the metals and uh also uh when the with the global change global climate change we have also more uh oxic anoxic Al alternance and with this alternance we have more erosion and more oxygen and so there is again uh transformation of the solid Spades and also well for the pite you have the liberation of acids but you have also for the organic matter this destruction and this destruction uh leads to liberation of metals because the metal was Associated to organic matter and these metals can go back on the ne solids but most of it Go by the by Way by because it can be free or uh Associated to organic matter and this can be SE on another work made by goal uh after uh after Extreme events uh the exportation of metals uh is in front of the mongr this is the concentration of cobalt and nickels in front in front of on the surface sediments in front of mongr so there is uh uh the extreme event or the the alter the yes the extreme events cause in fact the liberation of metallic contamination and also to finish uh you can have the increase of temperature we can imagine that increasing the temperature we can have increase of plants and increase of plants is increase of organic matter and increasing organic matter is more exudate more complexation but in fact no it was shown that increasing organic matter or increasing biomass increas the laile organic matter and this enhance in fact the mineralization at the surface and it liberates more Metals than uh trap so increasing CO2 in temperature is not good also it’s a c Vicious Circle it will liberate more contamination in metals so to finish uh because it’s time um for me the the organic matter in mongra uh so we show that there is a big Affinity with clay and refractory it is refactory in depth but fresh organic matter that arrived in the mongra enhance the respiration and has a bad effect on the carbon stock and enhance the production of the mineralization and production of CO2 and also uh it reduce the capacity of mongr to to stop or to complex the metals in fact because it expose the refractory organic matter or the complexing oranic matter to degradation or to mineralization so what we can conclude on this is that mongr are very sensitive to climate change and human use because of modifying the organic matter in the in the system that is linked to the speciation of metals and for uh we have to constrain bit a little bit more the the the the the reservoir because uh if you consider only biomass it’s a thing but uh if you consider also the flux and reflux of water in the mongra it’s not really clear that it is a sink it can be a source also and this behavior of mongr is highly correlated to the property of organic matter to complex Metals uh as we can see so that there is is can be uh it can be 70% of organic matter Metals Associated to organic matter and once again uh depending on the relation of this organic matter and metals you can have release due to the disparition or to the degradation of the uh retention by complexation uh as a perspective I think that we need more investigation on the lability or resilience of organic matter uh in mongra and it is a it is really important for me to uh to know how many amounts of organic matter will resist to the oxidation uh and the effect of this oxidation on metal release because uh this destruction of organic matter or this mineralization organic matter make the mongr lose the their buffer property toward metals and also in metal stocks because I tried to find some data in stocks of metals in mongra and it’s not so easy to have but if we consider that 1 to 7% of mongr is lost by year uh it means that all these uh metals and carbon that are in the sediment will be released but uh they are not be released in the form in sediment they will be oxidate and what is the behavior of the organic matter that would be transformed or mineralized toward the metals we saw that is not really uh good news because the organic matter will release the m so I think that uh it’s better or in perspective we need to understand understanding the the real impact of the global climate change on the MRA okay I hope that I was uh not too spread in my in my presentation but uh uh thank you for for your attention and uh I’m ready for any question or any remarks that you can have thank you very much Stefan that was an excellent uh and thorough overview of the geochemistry of Mangrove systems so um as always we open it now to questions uh and uh you can either use the chat function uh to type out a question or please feel free to open your mind mic and your your camera and ask question in person whichever you prefer what is the chat I try to find the chat okay so far we have no questions there but uh I I’ll read them out if we do get questions there maybe while people are thinking of questions uh I could ask you one and this is about your nickel um um I guess I find it surprising uh the how how like the the rapidity of change or the time frame of change excuse me uh in terms of the complexation um presumably the uh the actual uh organic matter itself is not changing that much over one title cycle um so uh something must be happening to the organic matter itself and do you think it’s just a uh um like changes in the the binding sites because you got all the chloride and whatnot coming in as as the salt from the tidal intrusion comes in um or do you think that something in that cycle is actually changing the confirmation of the organic matter you know some people talk about uh or like a a humic molecule sort of uh folding and unfolding depending on the the chemistry yeah uh I think it’s it’s the two when I made the calculation I take in account all the change in the con concentration of cathon and anion so there is the effect of the of the chlorides but I think that uh the change is not really a change of organic matter but more a different organic matter um it’s interesting to see that when you have the intrusion of seawat into the the sediment by interstitial water uh you have um like a flash of fluoresence of of protein you have a reactivation of the system because it’s not the same water that entering in and uh this uh inside the sediment this front of um of new water in fact active some biological processes and there is for me there is production and as you can see on the perhaps I can share no uh in fact there is also a change in fluoresence and uh so it means that it’s not really the same organic matter what is uh difficult to know is the amount of this uh uh of this new organic matter because if we took fluoresence uh if you have something that flues a lot it will it will take a a big part of the signal but is not really a big amount in quantity so I think that there is a change uh not in the river in the river it’s difficult uh in the canal is difficult to have a change because you have a big pool of organic matter that come from the river and if there is some little change uh it will be dute in the system so it’s difficult or hard to see uh but uh if you take as we have done just at the output of the of the mongr and we have another site where we observed something like um uh what is the term uh um Rel of very saline water it it happens and in this very saline water the organic matter is completely different it’s because uh probably that well in fact mongra reactors so when it come on the river it’s uh difficult to see but if you take the sample just before or just after the the the system you can see this difference and this D Dynamic what it could be interesting it to use um uh I high resolution Mass spectroscopy to see what happened during the cycle in fact because uh obviously there is a there is transformation okay thank you I I agree I think the some uh high resolution characterization would be very interesting on some of those samples but it’s difficult to have because you have to stay in the mongra during the night and also uh we have had the chance to have the the automatic Samplers but um we put them uh really uh near the front of the of the sediment and the and the and the river so we have had the chance to have this part of of sampling but to make it for high resolution M spectroscopy I think that we need more more investigation on more materials to to have it in high frequency because also you need lot of matters this is also the problem uh you need big amount of organic matter for the ey Mass this is a the fluoresence has this advantage that you need a very few very few quantity of organic matter yeah I I can see that um okay other questions for Stefan everybody understand all perfectly or maybe it’s just notate I I saw that there is lot of people from Gabon so thank you for for to be here do not hesitate exactly even in French or in Portuguese well it looks like you’re which I would agree with it was very very clear and uh everyone uh seems to have understood it so uh one more chance for questions for Stefan I would remind you that these um presentations are uh shown on our website you can you can go back and um yeah uh pull it up again uh and I I believe at the the first your email address was on the slide was it Stefan uh yes my address I can put it in on the chat if you want that would be helpful uh in case people have questions they would like to get in touch with you privately be Associated it could be Associated to the video if you want uh yes exactly and uh we know that there are some people who uh were not able to join us today just because of the day change and so uh it’d be good for them to have your address in the in the recorded put it in the chat ah sorry it lost uh it it Miss the Aras this one yeah yes the second one okay great uh well then um if there are last chance as I said for questions but if there are no other questions um I would just uh like to thank you again Stefan for an excellent present I excuse me I want to remind everyone that we have another talk next week on Wednesday back to our regular Wednesdays uh and it will be uh Dr Raymond Ward who will be coming back again uh and he’s going to be talking on uh carbon accumulation and settlement accretion uh blue carbon uh greenhouse gas and uh climate change uh next week so I hope you’ll join us all you will all join us uh at that time next week thanks again Stephan thank you for your for your invitation thank you to all for your attention