BIOSEDIMENTOLOGICAL CASCADES: THE EFFECTS OF WADING BIRDS ON THE EROSION, PROPERTIES AND ECOSYSTEM SERVICES OF INTERTIDAL MUDDY SEDIMENTS
Lead Research Organisation:
University of East Anglia
Department Name: Environmental Sciences
Abstract
Coastal habitats, including intertidal mudflats, are one of the planets most imperiled ecosystems, disappearing 4-10 ten times faster than tropical rainforest and declining in the UK 10 times faster than they are being created. Mudflats are at the forefront of climate driven changes such as sea level rise. They provide numerous ecosystem services, including coastal protection and primary productivity, supporting a diverse and important biota.
Muddy intertidal sediments are intrinsically linked with their fauna and flora and are therefore biologically-mediated systems. The biota strongly influence sediment processes (e.g. erosion/accretion dynamics), and changes to sediments influence the biota that live in the sediment (e.g. productivity). Previous studies have highlighted the importance of biota to sediment dynamics and vice versa; in particular, the ability of benthic microalgae to stabilise sediments. Sediment stability responds to temporal and spatial variability in biota and sediment properties, often in an apparently idiosyncratic fashion. There is increasing recognition that this is caused by a complex interaction of direct and indirect processes. Advancing our knowledge of how biotic and abiotic processes interact to mediate sediment erosion is vital for predicting and mitigating the effects of climate change on these important habitats.
One understudied, but potentially highly significant impact is how wading birds and their changing migration patterns will affect the ecosystem services of biostabilisation, nutrient flux and productivity by microphytobenthos. Previous research has shown that the presence of wading birds causes significant changes in benthic macrofauna behaviour, driving knock-on effects on microalgae, which causes significant changes to ecosystem services such as the erosion threshold and productivity. However, these remain poorly understood, thus the impacts of future changes in bird migration are difficult to predict.
OBJECTIVES
This project will experimentally manipulate the density and species composition of wading birds in the field using size selective exclusion cages, to investigate how changing wading bird density and species composition alters biostabilisation, processes of erosion and deposition, sediment biogeochemical properties, nutrient flux and benthic microalgae productivity (either directly or indirectly). Experiments will be done on muddy intertidal sites along the Norfolk and Essex coastline.
This will improve our understanding of the biological/physical interactions that drive these properties and processes. Teasing apart such interactions is essential to advancing our knowledge of how biotic and abiotic components mediate sedimentary processes and alter delivery of vital ecosystem services in coastal habitats.
The project will use advanced techniques, such as PAM fluorometry, erosion devices (FloWave, Cohesive Strength Meter) and cryogenic coring techniques. Sediment cores will be used to measure a suite of sediment properties, including: the water content, grain size, bulk density, organic matter, carbohydrates, exopolymeric substances creating sediment cohesion, pigments and nutrients. This will be the first time such a suite of techniques has been combined to investigate the effects of wading birds on intertidal sediments. This will provide essential data for improving models of near-shore sediment dynamics, informing decision making around coastal adaptive management strategies and mitigating climate change.
Muddy intertidal sediments are intrinsically linked with their fauna and flora and are therefore biologically-mediated systems. The biota strongly influence sediment processes (e.g. erosion/accretion dynamics), and changes to sediments influence the biota that live in the sediment (e.g. productivity). Previous studies have highlighted the importance of biota to sediment dynamics and vice versa; in particular, the ability of benthic microalgae to stabilise sediments. Sediment stability responds to temporal and spatial variability in biota and sediment properties, often in an apparently idiosyncratic fashion. There is increasing recognition that this is caused by a complex interaction of direct and indirect processes. Advancing our knowledge of how biotic and abiotic processes interact to mediate sediment erosion is vital for predicting and mitigating the effects of climate change on these important habitats.
One understudied, but potentially highly significant impact is how wading birds and their changing migration patterns will affect the ecosystem services of biostabilisation, nutrient flux and productivity by microphytobenthos. Previous research has shown that the presence of wading birds causes significant changes in benthic macrofauna behaviour, driving knock-on effects on microalgae, which causes significant changes to ecosystem services such as the erosion threshold and productivity. However, these remain poorly understood, thus the impacts of future changes in bird migration are difficult to predict.
OBJECTIVES
This project will experimentally manipulate the density and species composition of wading birds in the field using size selective exclusion cages, to investigate how changing wading bird density and species composition alters biostabilisation, processes of erosion and deposition, sediment biogeochemical properties, nutrient flux and benthic microalgae productivity (either directly or indirectly). Experiments will be done on muddy intertidal sites along the Norfolk and Essex coastline.
This will improve our understanding of the biological/physical interactions that drive these properties and processes. Teasing apart such interactions is essential to advancing our knowledge of how biotic and abiotic components mediate sedimentary processes and alter delivery of vital ecosystem services in coastal habitats.
The project will use advanced techniques, such as PAM fluorometry, erosion devices (FloWave, Cohesive Strength Meter) and cryogenic coring techniques. Sediment cores will be used to measure a suite of sediment properties, including: the water content, grain size, bulk density, organic matter, carbohydrates, exopolymeric substances creating sediment cohesion, pigments and nutrients. This will be the first time such a suite of techniques has been combined to investigate the effects of wading birds on intertidal sediments. This will provide essential data for improving models of near-shore sediment dynamics, informing decision making around coastal adaptive management strategies and mitigating climate change.
Organisations
People |
ORCID iD |
| Trevor Tolhurst (Primary Supervisor) | |
| James Booty (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| NE/S007334/1 | 30/09/2019 | 29/09/2028 | |||
| 1652027 | Studentship | NE/S007334/1 | 30/09/2015 | 30/03/2023 | James Booty |
| Description | Wading bird densities were manipulated on an estuarine mudflat in Essex, England. Chlorophyll a fluorescence (Fo), a proxy for biofilm coverage, was significantly lower where waders were present (p=0.04). This was the opposite result to that expected, and may have resulted from bioturbation by the birds, causing physical removal and disturbance of the biofilm, or the direct biofilm-feeding by small sandpipers such as Dunlin (Calidris alpina). If confirmed, to our knowledge, this biofilm feeding would be the first documented observation of this behaviour in the UK. The erosion threshold of the sediment was lower where waders were present, though not significantly, possibly due to large spatial variability on the mudflat surface and the lower number of sample replicates masking differences. Measurement of nutrient fluxes under lit conditions, between the sediment surface and water column, showed significant differences in four nutrients between areas with and without waders: nitrate (uptake by the sediment was lower where waders were present, p=0.001), phosphate (uptake by the sediment was lower where waders were present, p=0.02), ammonia (release from the sediment was inhibited where waders were present, p=0.05) and nitrite (uptake was inhibited where waders were present, p=0.04). Under dark conditions, nitrate uptake was lower (p=0.05) and ammonia release from the sediment was higher where waders were present (p=0.04).These data suggest that wading birds have a significant effect upon the biofilm coverage of a mudflat, although the process by which this occurred during the experiment was not identified. The biogeochemical cycling of nutrients between the benthic and pelagic zones within an estuarine environment are also significantly altered. |
| Exploitation Route | These results are likely to be interesting to those involved in actively managing estuarine mudflats which hold high numbers of migratory or overwintering waders. The engineering sector may also find uses for this type of data, where works within such areas are required. This work may also, in time, feed into the management of coastal realignment schemes by helping to inform how ecosystem services such as flood defence might alter depending upon the pressures on estuarine habitats and how these are managed. |
| Sectors | Construction Environment |