 our next speaker is Muriel Brookner. She is at Utrecht University and also works on estuaries and her talk today will be on bioturbation and mass distribution in estuarine systems. Yes, hello everyone. Thanks Irina for the introduction and thank you for having me at this summer series of CSDMS. I'm very happy to be able to talk about my modeling efforts by combining bioturbation and estuarine morphology and I want to present today to you my model that I developed together with my co-authors which combines bioturbation and a hydromorphodynamic model of an estuary. And we haven't been talking about estuaries yet so I'm very excited to show you how exciting it is to work with estuarine morphology. This is an example of the Dovi estuary and as you can see an estuary is governed by both the river discharge here on the right hand side of the picture and by the tides and the morphology of the estuary is governed by lots of different processes so the channels and the bar pattern are actually governed by not only the tides but also by species that grow in the middle of the estuary and that is actually the topic of my PhD to find out how important they are. So when we look at these eco-engineering species I will talk about bioturbators today and they are very often overlooked because they're really small but they occur in large abundances so they might have a large effect on the morphology of an estuary because they live in the sediment and they move around and by doing so they kind of increase the irrotability of the sediment which will lead to larger erosion rates and the sediment has to go somewhere so I would like to find out where does the sediment go does it deposit somewhere out in the estuary or is it exported so ultimately these species might have a large scale effect on the morphology of estuaries so for my study I look at two contrasting bioturbators which are very abundant in northwestern Europe probably also have something similar even the same species in the states but I don't know very much about that but these two species are quite important because they are quite dominant species in in northwestern estuaries and they cost a contrasting in a way that they prefer different types of habitat so the lack room on the left hand side are nicola marina as usually growing in sandy environments that are quite dynamic while the mushroom corovian volutator prefers muddy sediments and occurs in more calmer regions of the estuary but this is not the only difference they also have a different effect on the bioturbation so our nicola marina has a quite small bioturbation potential compared to corovium that means that if our nicola is present then not so much sediment will be eroded compared to the mushroom which will have also different effects on the morphology and what's also very interesting to know is that these species are actually competitive so when they occur both in the same environment then our nicola will be dominant over corovium and corovium will leave the area where our nicola moves in so to come to my research question I would like to know how large is the effect of each of these species on estuarine morphology and what happens if we combine these species so I look at the mud distribution of an estuary after 50 years of morphological evolution and to do that I use a coupled model of the hydromorphodynamic model in Dolph 3D flow and a bioturbation model that I wrote a mud lab to represent the species and in the top panel you can see my idealized estuarine domain so we have on the left hand side the tides and the ocean and on the right hand side the river and I let the morphology evolve with the sand bars and also quite some extensive mud flats already especially along the river and on the on the tidal bars and then I couple this domain to my species model which means that where the species occur they will change the erodibility of the mud species also have an effect on the sand but usually it's supposed to be a higher effect on the mud erodibility so I only parameterized the effect on the mud which means I change the critical bachelor stress in the erosion parameter which basically is just just means that the erodibility of the mud is increased when the species are present but on the other side of the feedback loop we also have an effect of the hydromorphology on the species distribution so based on literature I parameterized the species distribution based on inundation period flow velocity and mud content and I couple these two models every m2 tide so there's a continuous update of the species and the hydromorphology along with the simulation and then I look at the results after 50 years and this is what it looks like so we see here the species abundance on the bathymetry of the estuary and on the top panel in red you see that our nicola marina is really abundant it grows in large parts of the estuary especially in the mouth and the center why a corofium volatator is restricted to the sides of the estuary where we also previously saw all the mud flats before so this makes sense but interestingly if we combine both species then corofium almost disappears so there are only a few small patches here and on the bars where the species can still survive because of the competition effect with our nicola but what's even more interesting is that our nicola is able to expand to the sides of the estuary where it couldn't occur in the first scenario with only our nicola present so there seems to be like a positive feedback between the species that corofium changes the morphology and then our nicola is able to actually extend and expand its habitat so if we then look at the morphology on the right hand side we have the mud distribution in the estuary and these colors indicate the difference of the mud compared to a reference run that has no species so basically everything that's blue in the area means that there is more erosion when species are present and if it's red then there is more accretion than when there are no species present and everything is blue so there is quite a large effect of the species on the mud fraction in the estuary and especially the the scenarios that include corofium reduce large mud fractions at the sides of the estuary and if we if we compare the middle and the lower panel so the scenarios where corofium actually occurs we we see kind of similarity between the results so apparently the the efficient bio-turbator corofium determines the morphology of the estuary compared to the compared to the lacquerm ironicola so to conclude the mud content reduces unabiturbation and there is an export from the system because we haven't seen any depositional areas CV is the dominant eco-engineer because it governs the morphological development even if there's several species present and then there is the kind of this positive eco-engineering effect between the species that facilitate the occurrence of ironicola when there are several species present and why is this important why should you consider these species well if they have such a large effect on the on the large-scale morphology and we know there's habitat degradation or there are pollutants that threat these species then there might be species shifts and that will lead to a different effect on the morphology that we should consider thank you very much for the for listening to my presentation thank you mario