Tasks

Task A1. Sample preparation: Sediment, water and MPB

Surface intertidal sediment (top 5 cm) will be collected from the Suances Estuary, in order to do the tests with the characteristic granulometry of the study area. Sediment samples will be autoclaved (sterilised) before being used to destroy any remaining meiobenthos and microbiota. Additionally, all sediment will be sieved to 2 cm to remove macrobenthos and homogenised.

Due to the high Zn concentrations in water at the Suances estuary, the freshwater and saltwater samples for the experimental tests will be obtained from sites with low Zn concentrations to allow the preparation of different solutions (salinity percentages and Zn concentrations). The freshwater will be taken from the Asón River, located 50 km east of the estuary and the saltwater provided by the Spanish Oceanography Institute from El Bocal, a coastal area located 17 km east of the estuary mouth. In both cases, the water will be previously filtered and treated with UV to avoid the proliferation of microorganisms.

MPB will be cultivated in test trays with surface intertidal sediment (2 cm thick) and freshwater-saltwater solution (salinity according to test case). Test trays will be in a room with controlled temperature and light (photoperiod) conditions. During the culturing period (different depending on the test case), the nutrients will be supplied homogenously in all the test trays.

Task A2. Rheological analysis of estuarine sediments colonized/not colonized by MPB

Task A2 will consist in the analysis of the effects generated by the presence of MPB on the estuarine cohesive sediments according to their rheological properties. Rheological properties will be measured using a rheometer in test trays with three different salinities (minimum, average and maximum values according to typical estuary ranges obtained in NEMESIS project) over four different moments of the growth curve of MPB (first time without MPB and the last one at its maximum maturity).

The results of these tests will enable the parameterisation of rheological properties of estuarine sediments with and without the presence of MPB taking into account the average salt concentration of each estuarine area during tides.

Task A3. Calculation of sedimentation and deposition critical shear stresses in estuaries colonized/not colonized by MPB

Task A3 will consist in the calculation of sedimentation and deposition critical shear stresses in estuaries with/without MPB. Critical shear stresses will be calculated with an artificial channel constructed ad hoc for this project. A sediment plate with/without MPB (depending on the test) will be located at the centre of the channel.

A time variable flow will be used in every test. The flow channel will be increased until generating a suspended solids concentration. Once erosion is started, the relationship between the currents along the channel and the suspended solids concentration will allow obtaining the critical shear stress for erosion. Next, channel flow will be diminished until the suspended solids concentration in the water column disappears to obtain the critical shear stress for deposition by means of the aforementioned relationship between currents and suspended solids concentration. Suspended solids concentration in the water column during tests will be monitored along the sediment plate (at the beginning, at the middle and at the end of the plate) located at the centre of the channel. Current velocity along the channel will be monitored at the beginning, middle place and at the end of the channel. Every test will be performed by triplicate in order to minimise the measurement uncertainties.

Task A4. Development of biostabilisation submodel in the presence of MPB

Task A4 will be consist in the development of a biostabilisation submodel that will be implemented in Delft3D suite. This model will include the rheological variations of estuarine sediment colonized by MPB, as well as the variations on the critical sedimentation and deposition shear stresses due to its maturity (stabilization) and the salinity influence.

The submodel validation will be performed with the results of three physical tests (one for each considered salinity of Task A2 and A3) using the artificial channel constructed in Task A3. Physical tests will be used to determine the erosion-sedimentation patterns along the channel using an enough flow to break critical erosion shear stress values. Every test will use a plate with sediment colonized by MPB with its rheological properties stabilized (plates with sediments will be the same as Task A3).

A Laser Scanner will be passed over the channel before and after tests in order to evaluate the obtained erosion-sedimentation pattern by means of its difference. Tests results will be compared with those obtained by the numerical submodel developed and included in Delft3D using statistical techniques.

The result of this task will be an extension of the existing numerical morphodynamic models for estuaries, including in a shallow water model the capacity to replicate the dynamics of the estuarine sediment colonized by MPB.

Task B1. Sample preparation: Sediment, water and MPB

Surface intertidal sediment, freshwater-saltwater solutions and MPB cultivation will be prepared following the steps described in Task A1. In this case, deeper containers are necessary for MPB cultivation, due to the Zn concentration will be measured in the surface sediment layer with MPB, and in the lower layer (more compacted and without MPB). Therefore, the test trays will be replaced by test crystallizers.

Task B2. Characterization of the Zn diffusion and partitioning in the presence of MPB

Task B2 will consist in carrying out Zn adsorption-desorption tests in the estuarine sediment to determine the parameters that govern the process in the presence of the MPB (partition coefficient and kinetic constants), representing an advance with respect to the results of the VERTIZE project. These tests will be developed in a mesocosm to be able to evaluate the processes in conditions similar to those of the estuaries. Several test crystallizers (see Tasks A1 and B1) will be arranged in a room with controlled conditions, allowing to obtain the variation induced in the adsorption-desorption parameters, in a period sufficient to reach the equilibrium (which will be previously defined), due to the combination of the following variables: temperature, salinity, and initial Zn concentration in water and sediment.

Task B3. Biomobilisation submodel formulation and calibration

Task B3 will be consist in the development of a biomobilisation submodel capable to take into account the influence of MPB. This model will include the Zn partition coefficient and kinetic constants between the water column, the sediment layer and the interstitial water, known as Zn biomobilisation. The submodel validation will be performed with the results of the Task B2 tests.

The result of this task will be implemented in the Delf3D numerical model (D-Water Quality), being an extension of the existing numerical water quality models for estuaries that includes, in a shallow water model, the capacity to replicate the metal dynamics in estuarine sediments colonized by MPB.

Task C1. Field survey at the study site

Task C1 will obtain the information to calibrate and validate the transport model at the study site. For this, a field campaign will be carried out in a transect (5 points) of one of the intertidal zones and in two points of the main channel located at the entrance and exit of the intertidal zone at the Suances estuary. In all the monitoring points, georeferenced by GPS, the following oceanographic variables will be measured: current speed, sea level variation, water temperature and salinity. Moreover, physicochemical variables will be also measured such as solar irradiance, suspended solids, turbidity, pH, redox potential, type of substrate (% silts, sands, gravels and organic matter), concentration of chlorophyll “a” in sediment and Zn concentration in water (total and dissolved), interstitial water (total and dissolved) and sediment (total).

Task C2. Model implementation, calibration and validation at the study site

Task C2 will consist in the implementation of the processes associated with the MPB (biostabilisation and biomobilisation) as well as the inclusion of the MPB potential habitat at the study site.

This implemented model will be calibrated and validated through its application to the Suances estuary and comparison with the field campaign performed in Task C1. In this way, the effect of the inclusion in the global mathematical model of the aforementioned MPB submodels will be validated.

Task D1. Model scenarios to assess the implications of mean hydrological conditions

The calibrated and validated model (Task C3) will be used to assess the morphodynamics evolution of the Suances estuary taking into account the MPB colonization during a year period using mean hydrological conditions. The model will also consider the Zn flow between the bottom and the water column, studying the repercussion of the concentrations released in the aquatic environment on the environmental regulations. The impact of MPB on both morphodynamics and Zn concentrations will be analysed by comparison with the same time period taking into account an estuarine area not colonized by MPB.

Task D2. Model scenarios to assess the implications of extreme weather conditions

MPB populations are located in intertidal zones, sensitive areas to environmental currents and water level variation. Therefore, similar to the Task D1 (both with and without MPB presence), implications on water quality due to releasing and uptaking (from the bottom) of Zn will be analysed for extreme events such as droughts and flood periods, corresponding to 10 and 20 year-return period.

The result of this task will be the difference in the released concentration of Zn into the environment and uptaken from the sea bottom due to the presence/absence of MPB in the estuarine area.

Task D3. Model scenarios to assess the climate change implications

The potential consequences of climate change on the MPB and its impact on the morphodynamics conditions of the estuarine sediment and released Zn concentration in the water column will be evaluated through numerical modelling. Firstly, the modification of MPB habitat suitability due to climate change will be evaluated. Next, this effect will be analysed using the comparison between the current/future MPB distributions in the estuarine area. Furthermore, the climate change effect will be assessed regarding the analysis of the RCP4.5 and RCP8.5 scenarios collected in the Intergovernmental Panel on Climate Change (IPCC) in order to analyse the climate change for mid-century. In these scenarios, the associated changes with sea level rise, temperature and precipitation will be taken into account. Extreme events of floods and droughts with recurrence periods of 10 and 20 years will be analysed for the RCP4.5 and RCP8.5 scenarios.

Analogously to the Tasks D1 and D2, the scenarios will be assessed for a mean hydrological year and extreme weather conditions subject to climate change variations in order to compare the current situation with the possible modifications.

The transfer and dissemination of the scientific technological advances achieved throughout the investigation will be carried out in this workpackage. Firstly, the main milestones achieved in the research and the project results will be displayed in an executive memory. Moreover, the result transference will be performed by means of the following communication channels: (1) Direct transference of the obtained results to the Observer Entities and to the authorities determined by the Ministry of Science, Innovation and Universities of the Government of Spain; and (2) Indirect transfer of results and tools to national and international R+D+i projects and technological development projects.

Regarding the dissemination of the project results, this will be conducted by (1) Publication of the results in journals of national and international scope of scientific; (2) Presentation in national and international congresses; (3) Publication of results.