A view on coastal and estuarine systems

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(1)1. A VIEW ON COASTAL AND ESTUARINE GEO-INFORMATION SCIENCE SYSTEMS ERVATION. E FOR GLOBAL LOPMENT. PROF. DR. DAPHNE VAN DER WAL.

(2) 2. PROF. DR. DAPHNE VAN DER WAL.

(3) 3. A VIEW ON COASTAL AND ESTUARINE SYSTEMS INAUGURAL LECTURE GIVEN (IN A SHORTENED FORM) TO MARK THE ASSUMPTION OF THE POSITION AS PROFESSOR OF SPATIAL WATER QUALITY AND AQUATIC SYSTEMS AT THE FACULTY OF GEO-INFORMATION SCIENCE AND EARTH OBSERVATION (ITC) AT THE UNIVERSITY OF TWENTE ON THURSDAY 6 DECEMBER 2018. DAPHNE VAN DER WAL.

(4) 4. COLOPHON Prof. dr. Daphne van der Wal © Prof. dr. Daphne van der Wal, 2018 All rights reserved. No parts of this publication may be reproduced by print, photocopy, stored in a retrieval system or transmitted by any means without the written permission of the author..

(5) 5. PREAMBULE Dear Rector of the University of Twente, Dean of the Faculty of Geo-Information Science and Earth Observation ITC, colleagues, family and friends, thank you for being here today.. CONNECTED TO THE SEA Let me start with sun, sea and sand! I grew up in Bergen, a place near the coast (Figure 1a), and I have always felt attracted to the coast. And I am not alone in this. More than 40% of the world’s population lives within 100 kilometres of the coast (IOC/UNESCO et al. 2011). And this percentage is rising. What’s the attraction? Many people live in coastal urban agglomerations and coastal megacities, such as Tokyo, Mumbai, New York and Shanghai (von Glasow et al., 2013), that often developed from ports that connect land and sea, facilitating trade. Coastal waters provide sea-food. The nature of coasts and estuaries is an attraction and an inspiration.. Figure 1 (a) An aerial view of the coast of Bergen aan Zee, North Holland (Source: Rijkswaterstaat, https://beeldbank.rws.nl) and (b) a cliffed dune at Bergen aan Zee (Photo D. van der Wal).. But… living at the edge comes with a risk. Soft-sediment coasts are typically low-lying and flat, vulnerable to the destruction by waves during storms (e.g., Figure 1b). Low-lying flat coasts are also vulnerable to flooding from the sea and from the rivers - think of Bangladesh, for example. The risk of flooding will increase, as global mean sea level is rising (Church et al., 2004)..

(6) 6. As more and more people live near the sea, the pressures on these systems increase (Lotze et al., 2006; Newton et al., 2012). Fairways to ports are dredged to accommodate large ships. Diversion of rivers, dams and land use changes affect the load of sediment transported downstream. Levees are built to keep out the water, but they also prevent sedimentation on land. Urbanisation and industrialization cause loss of natural habitat and a loss of accommodation space for water, and may also lead to a reduction of the quality of surface waters and sediments. To achieve a better future for all, the United Nations (2015) agreed on Sustainable Development Goals. These include the sustainable use and conservation of marine and coastal ecosystems. To see how these systems are doing and to manage these systems in a sustainable way, there is a need for observations and a need for knowledge. I will address this today.. A FUNCTIONAL VIEW The title of my chair is Spatial Water Quality and Aquatic Systems. I focus on the soft-sediment marine and coastal aquatic systems, including the coast – where land meets sea -, and river mouths, such as estuaries and deltas - where the river meets the sea. I identify four important components in these systems (Figure 2).. Figure 2 A functional view on coastal and estuarine systems..

(7) 7. First, the shape or morphology of these coasts and estuaries, and their sediments, such as sands and muds. Secondly, the biota, including the algae, plants and animals living in and on the sediment bed and in the water. Then, water quality, describing the substances in the water and the properties of the water. And finally, water quantity and hydrodynamics, including the water level and the flow of the tides, waves and river discharge. My prime focus is on the functioning of the coasts and estuaries, the processes, regulated by the interactions between these four components. From a human perspective, these systems come with hazards, such as flooding, and risks, and they offer us services, such as providing seafood. We also play a role in shaping these systems, either directly or indirectly, for example by engineering the coast, and by changing the climate. I investigate these interactions using another key element in my chair name: the spatial aspect. For this, I use geo-information and remote sensing. There are many different remote sensing techniques available for observing the earth. Sensors can be operated from satellites, airplanes, drones or mounted on towers or aquatic platforms. These sensors include optical imaging systems that provide snapshots of the earth, like a camera (Figure 3a). We can go beyond the visible, and detect other spectral ranges, such as the near-infrared or infrared (Figure 3b), providing us extra information on, for example, vegetation and water. And we can detect even further in the spectral domain, in the microwave (radar) range. Synthetic Aperture Radar (SAR) sends microwave pulses to the earth that are scattered back depending on the properties of the surface (Figure 3c; 3d). This allows us to detect different surface characteristics, particularly soil moisture and surface roughness (and hence, e.g., vegetation structure, shell-fish reefs and flooded areas). Different polarisations and wavelengths of these microwaves provide complementary information on such surface characteristics. And with pairs of such radar images, the phase difference of the returning waves can be used to derive (changes in) surface height; a technique called radar interferometry. We also use sensors such as (airborne or terrestrial) laser altimetry or LIDAR that send pulses of laser light to the earth, and derive height of the terrain from the time it takes for the pulses to return. Radar altimeters, often operated from satellites, follow the same principle, but with microwave pulses, providing information on, e.g., global sea level..

(8) 8. Figure 3 Saltmarsh and mudflats near Tillingham, southwest England, United Kingdom, observed from (a) a Copernicus Sentinel-2 MSI True Colour (visible light) satellite image of 23 July 2016 and (b) the same Sentinel-2 MSI image of 23 July 2016, showing VNIR (visible and near-infrared) information, (c) a Sentinel-1 SAR VV-polarised satellite image of 3 July 2016 and (d) the same Sentinel-1 SAR image of 3 July 2016, but VH-polarised.. Remote sensing techniques are used for mapping and for monitoring. Moreover, these maps and time-series can help to understand how coastal and estuarine systems work. In this address, I show examples of the use of remote sensing to investigate each of the four components drawn in Figure 2 in the coastal and estuarine system, highlight the interactions, and identify opportunities for further research.. MORPHOLOGY, LAND SUBSIDENCE AND SEDIMENT DYNAMICS I start with an example of the shape of the landscape, the morphology or elevation. In the year 2000, the Shuttle Radar Topography Mission (SRTM) flew on board the Space Shuttle Endeavour and collected 3D data of the largest part of the earth in a consistent way, with a uniform accuracy (Farr et al., 2007). The 3D data show us directly where the low-lying areas in the world are, here displayed in dark green (Figure 4). Elevation is not static. For example, land subsidence may occur. In some coastal cities, such as Shanghai and Jakarta, land is sinking fast, centimeters to even a few decimetres per year, due to natural compaction of the (soft) soil, locally exacerbated by the withdrawal of groundwater for industry and agriculture, gas extraction and the load of buildings (Syvitski et al., 2007; Chaussard et al., 2013). Radar interferometry, or InSAR, informs us where land subsidence is most severe (e.g., Chaussard et al., 2013). Relative sea level rise increases the risk of tidal flooding, especially in poorly protected areas. Such tidal flooding can be detected with SAR and optical images (Figure 5) (e.g., Dewi et al., 2016). Apart from relative.

(9) 9. sea level rise, there are factors that make these areas more prone to tidal flooding, such as the conversion of mangrove areas into aquaculture ponds in the area shown in Figure 5 (e.g., Van Wesenbeeck et al., 2015), as we will see later.. Figure 4 Shaded and coloured SRTM elevation model of the world, with data acquired in February 2000. Colour coding is directly related to topographic height: green at the lower elevations, then yellow and tan, to white at the highest elevations. Image courtesy SRTM Team NASA/JPL/NIMA.. Figure 5 Copernicus Sentinel-2 MSI satellite image of 7 Oct 2015, central Java, Semarang, Indonesia, showing coastal settlements vulnerable to tidal flooding..

(10) 10. The sediments also move. Take the Westerschelde estuary, in the southwest of the Netherlands (Figure 6). The estuary is an intricate network of tidal flats (that fall dry during low tides and are submerged during high tides), subtidal shoals and channels, constantly changing shape by the tides, waves and the river. The Westerschelde estuary also serves as access to the port of Antwerp for large container ships, and the navigation channel is therefore maintained by dredging, and occasional deepening is carried out to accommodate still larger ships. The challenge is to do this in a way that safety levels are guaranteed, ships can pass without problems and nature does not suffer (ProSes, 2005): finding a balance in safety, economic activities and nature, that is faced by many coasts and estuaries across the world.. Figure 6 Elevation of the Westerschelde estuary, Netherlands, from airborne laser altimetry and shipborne (multibeam) echo sounding (source: Rijkswaterstaat), in 1996 and in 2016. Blue-yellow colours indicate shallow subtidal shoals, yellow and yellow-brown colours indicate intertidal areas (falling dry at low tides) and supratidal areas, while blue colours indicate deeper subtidal areas (up to ca 60 m below NAP).. LIFE ON THE SEDIMENT Environmental changes, ecological consequences Let’s take a look at a tidal flat in the Westerschelde estuary (Figure 7) and the habitat it provides. A tidal flat, here seen during low tide, looks bare, but it is teeming with life. To start with, there are the microscopic algae (microphytobenthos). They need a quiet place to live, and they need light to grow. Typically, the higher on the tidal flat, the calmer the hydrodynamic conditions, and the more sunlight for photosynthesis they receive during low tide, thus the better these micro-algae grow, until.

(11) 11. a point where they are limited, e.g., by desiccation; at high elevations saltmarsh may take over. Many invertebrate animals living in and on the sediments (benthic macrofauna) of these tidal flats are feeding on these micro-algae (Christianen et al., 2017). These animals too need a good place to live, depending on abiotic conditions, such as sediment grainsize (e.g., mud or sand) and hydrodynamics - each species with their own preferences (Van der Wal et al., 2008). In general, places with high biomasses of micro-algae relate to high total biomasses of these benthic animals, as we found out with hyperspectral airborne surveys and ample field sampling (Van der Wal et al., 2008). Wader birds are feeding on these small animals, and some bird and fish species directly feed on the micro-algae. The tidal flats thus have an important function for the food web. Management of the Westerschelde estuary aims to maintain the dynamic multiple channel system with these rich shoals and tidal flats, by dredging the navigation channel and disposing of dredged materials in smart ways (ProSes, 2005).. Figure 7 Airborne hyperspectral image (acquired in collaboration with VITO, 2006), sampling for benthic animals, and spectral measurements on the tidal flat Walsoorden, Westerschelde estuary, Netherlands. The bright green colour on the tidal flat indicates algae living on the sediment, the dark green patches are saltmarshes (Van der Wal et al., 2008).. The structuring of life in and on the sediment applies to this tidal flat, but it also applies to other tidal flats in the Westerschelde, and to other estuaries and coasts (Figure 8). Even small changes in abiotic conditions, such as in relative elevation, be it due to natural causes, direct human activities or sea level rise, can potentially lead to changes in the food web..

(12) 12. Figure 8 Long-term average biomass of benthic algae (algae living on the bottom sediment) derived during emergence of the tidal flats, in selected estuaries and basins in the Netherlands and the United Kingdom, derived from time-series of MODIS Aqua satellite images, 2002-2008 (Van der Wal et al., 2010). The colours relate to benthic algae biomass, scaling from low biomass (light yellow) to high biomass (dark green) of benthic algae, while blue depicts subtidal area (water).. Where abiotic conditions such as elevation largely explain the spatial distribution of these algae in space, the temporal variations in algal biomass are driven mainly by weather conditions (Van der Wal et al., 2010). By comparing time-series of sites across different coasts and estuaries using thousands of optical images, we understand these variations better. The temporal (year-to-year) variations in biomass of algae act over large distances: when biomasses of algae are higher than normal in the Westerschelde, they are also higher than normal in the Wadden Sea and Oosterschelde. In the Eems-Dollard in particular, year-to-year variations in algal biomass are negatively affected by wind/waves. In the basins in the north of the United Kingdom, days with air frost appear important in restricting algal biomass (Van der Wal et al, 2010). By investigating such comparisons, we get an understanding of the sensitivities of these coastal and estuarine systems to climate change – but there’s still many unknowns about interactions and feedbacks.. Saltmarshes, mangroves and coral reefs: habitats and coastal protection Let’s look at another important habitat in coastal areas and estuaries: saltmarshes (Figure 9). I study the mechanisms of saltmarsh development.

(13) 13. in the field, and by analysing aerial photographs and images taken by drones. Moreover, the 30-year archive of satellite images allows us to detect the changes in the extent of these saltmarshes around the world; that is: where these saltmarshes are lost or expand. PhD student Marieke Laengner is investigating how saltmarshes worldwide are affected over the past decades by changes in global and local conditions. For example, in the Mississippi delta (US), saltmarshes have eroded rapidly, because of, among other factors, limited sediment supply due to river conversions and construction of levees, land subsidence and sea level rise (Blum and Roberts, 2009). But saltmarshes themselves are also able to influence their environment and improve their own conditions. The plants protect the soil from eroding. The mudflats and saltmarshes slow down the water and reduce the waves (Bouma et al., 2014). By doing so, the plants trap fine sediments. This positive feedback between the plants, the water and the sediment allows the saltmarsh to grow vertically; they can, to some extent, keep up with a rising sea level, when there is enough supply of sediment (Kirwan and Megonigal, 2013). This process also affects the resilience of saltmarshes (Van de Koppel et al., 2005; Van Belzen et al., 2017). Moreover, (especially the organic) saltmarshes can store water. For all these reasons, saltmarshes are regarded as nature’s solution for flood management, limiting flooding of the hinterland.. Figure 9 Saltmarsh Zuidgors, Westerschelde, southwest Netherlands. Photo Jeroen van Dalen, NIOZ..

(14) 14. Figure 10 Map of Leaf Area Index (LAI) of the saltmarsh vegetation near Tillingham, southwest England, United Kingdom, derived from a Copernicus Sentinel-2 MSI satellite image of 23 July 2016.. Figure 11 Example from the Copernicus downstream service MI SAFE (https://fast.openearth.eu), showing elevation along a cross-section of a saltmarsh near Tillingham, United Kingdom (see Figure 3). Topography is shown from mudflat (elevation displayed in brown, left-hand axis) to saltmarsh and land (elevation displayed in green, left-hand axis). Vegetation presence (displayed in green) and elevation are derived from many satellite images. The solid light blue line shows predicted wave height (scale at the right-hand axis), while the dashed dark blue line shows predicted wave height in case there would not have been vegetation (scale at the right-hand axis). See De Vries et al. (2018) for further information. Graph: Deltares..

(15) 15. Deltares fed maps of the vegetation presence and type from the satellite into their hydrodynamic models, together with information on the height of the foreshore, also from satellite remote sensing as provided by the University of Cadiz (De Vries et al., 2018). This results in predictions of waves over the mudflats and saltmarsh (Figure 11). It predicts how high the waves are, that reach the hinterland, what water levels we can expect during extreme storms and if this would lead to flooding. We made a Copernicus downstream service called MI SAFE, a tool open for anyone to make first predictions for flood risk and safety anywhere in the world.. Figure 12 Copernicus Sentinel-2 MSI satellite image of 9 Oct 2017, Belize with mangroves, subtidal seagrass fields and coral reefs.. While saltmarshes are important for coastal protection in temperate areas, in many (sub)tropical systems, coral reefs, seagrass and mangroves contribute to coastal protection (Guannel et al., 2016), see also Figure 12; when co-occuring these ecosystems even facilitate each other by attenuating waves (Gillis et al., 2017). The other way around, sediments and nutrients from rivers are filtered by mangroves, and are subsequently trapped by the seagrasses, and eventually clearer water is reaching the coral reefs (Gillis et al., 2017). Satellites not only allow us to map and monitor the extent of these systems, but also the fluxes from one.

(16) 16. ecosystem to the other (Gillis et al., 2017). When these ecosystems are being degraded, waves are less attenuated, less sediment is trapped and vulnerability of the hinterland to flooding increases, while water quality will also be affected. The loss of mangrove areas in central Java due to particularly aquaculture (Figure 5), and the erosion and drowning of wetlands in the Mississippi delta are examples of how this may increase flood risks.. Shellfish reefs: extended footprints Let’s have a look at other biota: shellfish. Mussels and oysters are harvested for consumption worldwide, and birds, such as the oyster catcher, like them too. The shellfish clump together on the sediment bed and form reefs. In his PhD research, Sil Nieuwhof developed a method to detect the presence of the beds during low tides using dual-polarised Synthetic Aperture Radar or SAR. As this sensor is sensitive to the roughness of the surface, it allows us to distinguish the mudflats and sandflat, from the rougher shellfish beds. Hence, we can rapidly map where these shellfish beds are (Nieuwhof et al., 2015). Further studies are needed to distinguish mussels from oysters, for example by using different wavelengths of SAR, or different combinations of sensors.. but no or just a few slum dwellers, as classified by the Indian census.. Figure 13 Schematic interactions between the sediment and the water column (benthic-pelagic coupling) on a tidal flat with an oyster reef (Nieuwhof, 2018).. Like the saltmarshes, mangroves, seagrasses and corals, the mussels and oysters also take part in coastal processes. They influence their.

(17) 17. environment; they engineer it (Figure 13). They filter algae from the water column to feed on, produce bio-deposits and trap the fine particles, making the water clearer and the bottom muddy. Indeed, satellite data analyses by Nieuwhof (2018) show that these shellfish influence their surroundings at a scale that extends their own footprint, as this muddy, nutrient-rich sediment allows algae to grow, which in turns provides food for animals. A recent large-scale experiment in oyster reefs carried out by the University of Nantes (Echappé et al., 2018) at the mudflats in Brittany shows that this is mainly related to filtering of the water by the oysters. In this case too, there are thus close interactions between the organisms and the substances in the water.. WATER QUALITY This brings me to the water quality in Figure 2, including salinity and temperature. From optical satellite images, we can detect the coloured substances in the water that interact with the light by absorption, scattering, emission or fluorescence, as well as the fate (attenuation) of light in the underwater landscape. Examples of such optically active substances in the water are chlorophyll (that links back to biota) and Suspended Particulate Matter (that links back to sediment dynamics). Biooptical models are used to retrieve the concentrations of these opticallyactive substances and characterise the underwater light climate from our satellite images. Retrieval of the water constituents in turbid coastal and estuarine waters has always been a challenge. In the literature, these waters are referred to as optically complex waters (IOCCG, 2000), and for good reason. Moreover, the signal that the satellite sensor receives from the water is small. The satellite sensor should have both sufficient spectral resolution and radiometric sensitivity. European medium resolution ocean colour sensors such as MERIS and OLCI can do this, and since 2015, the Sentinel-2 Multi-Spectral Imager enables us to derive these water variables at a high spatial resolution of ca 10 m (Giardini et al., 2018). This has created opportunities for new applications in coastal waters. I will illustrate this for the Dutch Delta, at the interface of the North Sea and the rivers Rhine, Meuse and Scheldt, using such a Sentinel-2 image (Figure 14). This area has been influenced by humans over centuries. We built dikes to live here and keep our feet dry. Still, in 1953, a devastating storm surge occurred. To increase the safety level, while assuring fresh water supply, and taking into account accessibility for shipping, the delta works were implemented, with dams, storm surge barriers and reinforced dikes. It has kept us safe since. But it has had consequences for these aquatic systems..

(18) 18. The minuscule drifting algae in the water, phytoplankton, are the primary producers that support the aquatic food web; they determine the carrying capacity of the system and sequester carbon. Problems can occur if the phytoplankton concentrations are high as a result of accumulation, or as a result of an excess of nutrients, a problem named eutrophication. When such a bloom dies, bacterial decomposition can lead to oxygen depletion. Additionally certain species of cyanobacteria for example, may produce toxins. The green chlorophyll-a (CHL) pigment in phytoplankton absorbs light for photosynthesis, particularly the blue part of the light spectrum, but also in a narrow red absorption peak. The satellite image and derived concentrations of chlorophyll (Figure 14) show a bloom in the Markiezaatsmeer. As a result of the Delta works, this basin changed from tidal saline waters to stagnant brackish and even freshwater. This makes good conditions for blooms of cyanobacteria. In many of the other basins in the Dutch delta the water quality also changed in response to changes in the hydrodynamic regime associated with the Delta works. In the satellite image, we observe the differences in colour between the basins in the delta. The Westerschelde estuary looks bright brownyellow due to scattering of light by the mineral particles; it has high concentrations of Suspended Particulate Matter (SPM). This basin kept the connection with both the sea and the river, allowing access to the port of Antwerp. In the enclosed basins, we see dark water bodies, as incoming light is mostly absorbed by the deep water, and there are few particles in the water that scatter the light. In the Oosterschelde, the open storm surge barrier still lets most of the tides in and out, but there is no supply of sediment from the rivers anymore.. Figure 14 (a) Copernicus Sentinel-2 MSI satellite image of the Dutch Delta on 12 March 2016, and retrieved (unvalidated) concentrations of (b) Suspended Particulate Matter (SPM) and (c) Chlorophyll (CHL)..

(19) 19. With our archive of satellite imagery, we have a time machine! It is clear that the Oosterschelde looks different now than it looked in 1979 (Figure 15), before construction of the Oosterschelde storm surge barrier and the Oesterdam. Note that when observing changes, it is important to take into account the many scales of spatiotemporal variations, e.g., by analysing many snapshots in time. Concentrations of suspended sediments, for example, also change with the seasons and the tides (Eleveld et al., 2014).. Figure 15 NASA Landsat 2 MSS VNIR (visible and near-infrared) satellite image of 8 Oct 1978, Dutch Delta.. In a number of these basins, modifications are implemented or planned, e.g., to improve water quality or (in the Oosterschelde) to compensate for sediment deficits by sand nourishments. We will likely need to make further changes in future to these works, to cope with sea level rise, intrusion of salt water and changing river discharge. This shows the need for science to understand these systems, and it shows the need to look at coastal and estuarine systems from multiple perspectives.. Pelagic primary production The water quality parameters retrieved from remote sensing enable us to investigate the base of the food web. In her MSc thesis, Robyn Gwee.

(20) 20. mapped the patterns of primary production in the North Sea (Figure 16), based on information on chlorophyll and the light climate from thousands of satellite images from the Envisat MERIS sensor, validated by measurements from ships at fixed monitoring stations. Results are shown binned by month, to detect the seasonal variation in primary production. We work on improvements of estimates of primary production, to get a grip on (changes in) the carrying capacity of the North Sea.. Figure 16 Primary production in the North Sea, monthly averages over the period 2002-2012 modelled with input derived from Envisat MERIS satellite images (Gwee, 2018).. WATER QUANTITY AND HYDRODYNAMICS The fourth and final component in Figure 2 has been the crucial force throughout this lecture: water quantity and hydrodynamics. Getting this information directly from remote sensing in the coastal zone (rather than from hydrodynamic models or field measurements) is still a challenge. Here, coastal science can learn from oceanography. For oceans, (operational) remote sensing techniques are available to detect sea level, surface ocean currents and circulation, wind fields and wave heights, derived from (combinations of) altimeters, scatterometers and other observations (e.g., Klemas, 2012). Additionally, information from sea surface salinity is available (from, e.g., the SMOS satellite mission)..

(21) 21. But in coastal and estuarine areas, oceanographic data, with their spatial resolution of 100s of metres to kilometres, typically will not do. We need a better spatial resolution, and we need to deal with the complexity of these shallow waters to obtain reliable retrievals of hydrodynamics. Efforts are already made in this direction. Fine-scale radar images are being used to retrieve the local wind field (e.g. Lehner et al., 2012; Plaskachevsky et al., 2016). Geostationary satellites, such as GOCE observing the Yellow Sea, are suitable to simultaneously obtain information on sediment in the water and current velocities (Choi et al., 2012; Yang et al., 2014). Anticipated satellite missions, such as the SWOT mission, also attempt to fill this gap by providing hydraulic information of nearshore, coastal and estuarine waters (e.g., Chevalier et al., 2018). Such developments help to investigate the interfaces, including land-sea interactions, sea-river interactions, and the coupling between the water and the sediment bed, and thus how and at what time-scales coastal and estuarine systems respond to sea level variations, changes in river flow and extreme events, such as storms and droughts. At the NIOZ Sea Level Centre, we are aiming to bridge the gap between the oceans and the coast with respect to sea level, predicting what sea level change we can expect at our coast (e.g., Vermeersen et al., 2018). I contribute by investigating what that would mean for the functioning of our coasts and estuaries, and how it will affect sediment dynamics, coastal safety, water quality and production, through the interactions I sketched in this lecture.. CHALLENGES AND OPPORTUNITIES OF REMOTE SENSING What you see is what you get? Can we measure everything with remote sensing? Considering that most sun-synchronous satellites are between 600 and 800 km above us, we can detect a lot. But even for optical satellite images, what you see is not what you get, as there is an atmosphere in between the sensor and the ground. Good atmospheric correction of the satellite remote sensing signal is essential to enable mass satellite processing; this applies notably to water bodies, as water-leaving radiance is small. Radiative transfer models are required to obtain the relationships between radiation from the sensor and the properties of the surface. The Department of Water Resources at ITC has a great tradition of developing.

(22) 22. such models. More than 35 years ago, now Em. Prof. Wout Verhoef developed the SAIL model (Verhoef, 1984), to model these relationships for vegetation, and this work is expanded in the SCOPE model, by Christiaan van der Tol. Likewise, the 2SeaColor model, developed by Suhyb Salama and Wout Verhoef (Salama and Verhoef, 2015) allows to retrieve spatial water quality in optically complex waters. In the microwave domain, we have already shown the potential of backscatter models to link to properties of the coast (e.g., Van der Wal et al., 2005; Nieuwhof et al., 2015), and I would like to expand this work. I see many applications in coasts and estuaries. For some variables, the signal from our sensors may not directly link to what we want to retrieve, and we have to rely on proxies and empirical relationships based on field or laboratory data. This applies for example, to nutrients in the water, and to the grain-size of the sediment on the mudflats and sandflats. In other cases, we cannot rely on satellites or drones. For example, we need complementary models, field data or in-water sensors to obtain water quality information for the entire water column, rather than for the surface waters where light can penetrate. The power here is in the combination of approaches. In all cases, though, field measurements remain needed for validation.. Big data This is the era of big data: petabytes (Ramapriyan et al., 2013) when it comes to satellite data. Weather satellites (such as AVHHR) and land satellites (such as Landsat and SPOT) have now been collecting earth observations for well over 30 years. We now start to be able to address climate change using satellite data. A number of initiatives, such as the ESA Climate Change Initiative, already bring these climate data records from satellite missions together in a consistent way. Analysing this wealth of data is also made easier, using cloud computing and platforms, rather than processing data on a local computer. These developments facilitate a detailed, global approach and a consistent comparison of systems worldwide. However, with this potential, there is still the need for careful retrieval, analysis and error assessments: the domain of ITC..

(23) 23. OUTLOOK The focus of my work is on the following three themes: (1) sediment dynamics, and applications of sediment management in coastal areas (2) bio-physical interactions in the intertidal zone, and applications to coastal safety and resilience of coasts (3) benthic (bottom sediment) and pelagic (water column) primary production. I will further develop earth observation algorithms, and combine remote sensing data from satellites, airplanes and drones with models and field data for hypotheses testing and scenario evaluation to study these coastal and estuarine processes. In short, my work is on remote sensing of coasts and estuaries. With both an appointment at ITC and NIOZ Royal Netherlands Institute for Sea Research, I aim to do this in collaboration with both institutes. My work at the Estuarine and Delta Systems department of NIOZ is focusing on ecosystem functioning of coasts and estuaries. At ITC, I focus on remote sensing of coasts and estuaries in a broader sense, including water quality aspects and hydrological aspects. I will investigate the coastal and estuarine processes in a generic way, but with applications in coastal and estuarine systems worldwide. This fits well within ITC, with its strength in geo-information science and earth observation, a global view on the world, and a mission for sustainable development. It also fits well within the Water Resources department of ITC, with the focus both on water quantity and quality, impacted by human activities and climate change. It also links to other ITC departments, particularly regarding flood risk, natural resources and ecosystem services. Moreover, I see ample opportunities for collaboration both within UT, especially with the Water Engineering and Management department, and outside.. EDUCATION At ITC, I look forward to guide MSc students and PhD students on their thesis work related to coastal and estuarine systems. But education starts earlier. For me, this became clear when I gave a workshop for high school students at the Pre-UT seminar earlier this year..

(24) 24. It is good to see high school students concerned about coastal flooding, even though Enschede is relatively safe from the sea. This academic year, we will start the common course “Global challenges, local action”, which brings together MSc students from different disciplines, ranging from urban planners, ecologists and water management engineers, to tackle wicked problems. One of the focal points of this course is the coastal zone. I’m looking forward to see MSc students from many countries bringing in their point of view and cultural perspective. I think this approach is essential to address the problems the coastal zone is facing, and I am enjoying coordinating this coastal project within the course. Collaboration between ITC and NIOZ will also lead to mutual benefits in education and capacity building, including hands-on training in the Dutch delta, at the doorstep of NIOZ in Yerseke. I would like to mention the NCK Summer School here, organised on Texel every two years by the Netherlands Centre for Coastal Research. It brings together and educates PhD students from different disciplines related to the coastal zone. The atmosphere is relaxed; indeed, sun, sea and sand, with a little mud. I am looking forward to a new edition..

(25) 25. WORDS OF THANKS The diagram I have drawn here in Figure 2 very much reflects my journey through science over the years, starting with my PhD on aeolian sediment transport on beaches and dunes at the University of Amsterdam, longterm estuarine morphology at the University of London, estuarine ecology at the Netherlands Institute of Ecology, bio-physical interactions at NIOZ, and recently water quality at NIOZ and ITC. Along that journey, I went from sandy coasts to muddy estuaries, from land to water, and from the Netherlands to the world, always from a spatial perspective. With this chair, I aim to bring this work together. I would like to thank a number of people that have supported me during this journey. First of all, I would like to express my gratitude to the Rector of the University of Twente, the Dean of ITC and the appointment advisory committee to enable my appointment at ITC. I have appreciated the warm welcome at ITC, and the welcome and good spirits at the Water Resources Department in particular. Thank you Bob Su, heading the Water Resources department; thank you for your full support! And thanks to all colleagues at Water Resources and other ITC departments! I would like to thank Klaas Timmermans, head of department Estuarine and Delta Systems of NIOZ, and Henk Brinkhuis, director of NIOZ, for support. Thanks also to other colleagues at NIOZ, including PhD students and postdocs, (field) technicians, and Annette Wielemaker for support with GIS. Thank you especially Peter Herman, Tjeerd Bouma, Johan van de Koppel and Tom Ysebaert for solid collaborations and in depth discussions. Thanks to my promotor Pim Jungerius and co-promotor John van Boxel at the University of Amsterdam, and to Ken Pye, then at University of London. I would like to thank everyone for being here today. And I would like to thank three more people that have contributed to where I am today: my parents, and last but not at all least Marieke Eleveld. Ik heb gezegd..

(26) 26. References Blum, M.D., H.H. Roberts (2009). Drowning of the Mississippi Delta due to insufficient sediment supply and global sea-level rise. Nature Geoscience 2: 488-491. Bouma, T.J., J. van Belzen, T. Balke, Z. Zhu, L. Airoldi, A.J. Blight, A.J. Davies, C. Galvan, S.J. Hawkins, S.P.G. Hoggart, J.L. Lara, I.J. Losada, M. Maza, B. Ondiviela, M.W. Skov, E.M. Strain, R.C. Thompson, S. Yang, B. Zanuttigh, L. Zhang, P.M.J. Herman (2014). Identifying knowledge gaps hampering application of intertidal habitats in coastal protection: opportunities & steps to take. Coastal Engineering 87: 147-157. Chaussard, E., F. Amelung, H. Abidin, S.-H. Hong (2013). Sinking cities in Indonesia: ALOS PALSAR detects rapid subsidence due to groundwater and gas extraction. Remote Sensing of Environment 128: 150-161. Chevalier, L., B. Laignel, I. Turki, F. Lyard, C. Lion (2018). Time variability of hydrodynamics and potential use of surface water and ocean topography mission in estuarine macrotidal system: example of Seine estuary. Journal of Applied Remote Sensing 12, 036008. DOI: 10.1117/1.JRS.12.036008 Choi, J.K., Y.J. Park, J.H. Ahn, H.S. Lim, J. Eom, J.H. Ryu (2012). GOCI, the world’s first geostationary ocean color observation satellite, for the monitoring of temporal variability in coastal water turbidity. Journal of Geophysical Research 117, C9. Christianen, M. J. A., J.J. Middelburg, S.J.Holthuijsen, J. Jouta, T.J. Compton, T. van der Heide, T. Piersma, J.S.Sinninghe Damste, H.W. van der Veer, S. Schouten, H. Olff (2017). Benthic primary producers are key to sustain the Wadden Sea food web: stable carbon isotope analysis at landscape scale. Ecology 98, 1498: 1512. Church, J.A., N.J. White, R. Coleman, K. Lambeck, J.X. Mitrovica (2004). Estimates of the regional distribution of sea level rise over the 19502000 period. Journal of Climate 17: 2609-2625. Echappé, C., P. Gernez, V. Méléder, B. Jesus, B. Cognie, P. Decottignies, K. Sabbe, L. Barillé. (2018). Satellite remote sensing reveals a positive impact of living oyster reefs on microalgal biofilm development. Biogeosciences 15: 905-918. Eleveld, M.A., D. van der Wal, T. van Kessel (2014). Estuarine suspended particulate matter concentrations from sun-synchronous satellite remote sensing: Tidal and meteorological effects and biases. Remote Sensing of Environment 143: 204-215..

(27) 27. de Vries, M., I. Möller, G. Peralta, D. van der Wal, B. van Wesenbeeck, A. Stanica (Ed.) (2018). Earth Observation and the Coastal Zone: from global images to local information. FAST FP7 Project synthesis. GeoEcoMar: Bucuresti. ISBN 978-606-94282-5-2, 66 pp. Dewi, R. S., Bijker, W., Stein, A. & Marfai, M. A. (2016). Fuzzy Classification for shorelines change monitoring in a part of the Northern coastal area of Java, Indonesia. Remote Sensing 8: 190. Giardino, C., V.E. Brando, P. Gege, N. Pinnel, E. Hochberg, E. Knaeps, I. Reusen, R. Doerffer, M. Bresciani, F. Braga, S. Foerster, N. Champollion, A. Dekker (2018). Imaging spectrometry of inland and coastal waters: state of the art, achievements and perspectives. Surveys in Geophysics, doi: 10.1007/s10712-018-9476-0. Gillis, L.G., C.G. Jones, A.D. Ziegler, D. van der Wal, A. Breckwoldt and T.J. Bouma (2017). Opportunities for protecting and restoring tropical coastal ecosystems by utilising a physical connectivity approach. Frontiers in Marine Science, doi: 10.3389/fmars.2017.00374. Guannel, G., K. Arkema, P. Ruggiero, G. Verutes (2016). The power of three: coral reefs, seagrasses and mangroves protect coastal regions and increase their resilience. PLOS ONE, doi: 10.1371/journal. pone.0158094. Gwee, R. (2018). Modelling primary production in the North Sea: Applying a light-dependent model on MERIS images between 2002-2012. MSc thesis. NIOZ and University of Utrecht, 67 pp. IOC/UNESCO, IMO, FAO, UNDP (2011). A blueprint for ocean and coastal sustainability. Paris, IOC/UNESCO. http://www.unesco.org/new/ fileadmin/MULTIMEDIA/HQ/SC/pdf/interagency_blue_paper_ocean_ rioPlus20.pdf. Last accessed 19 Nov 2018. IOCCG (2000). Remote sensing of ocean colour in coastal, and other opticallycomplex, waters (ed. S. Sathyendranath). Dartmouth, NS, Canada, International Ocean-Colour Coordinating Group (IOCCG), 140pp. (Reports of the International Ocean-Colour Coordinating Group, No. 3), DOI: http://dx.doi.org/10.25607/OBP-95. Farr, T. G., P.A. Rosen, E. Caro, R. Crippen, R. Duren, S. Hensley, M. Kobrick, M. Paller, E. Rodriguez, L. Roth, D. Seal, S. Shaffer, J. Shimada, J. Umland (2007). The Shuttle Radar Topography Mission, Reviews of Geophysics 45, RG2004, doi:10.1029/2005RG000183. Lotze, H.K., H.S. Lenihan, B.J. Bourque, R.H. Bradbury, R.G. Cooke, M.C. Kay, S.M. Kidwell, M.X. Kirby, C.H. Peterson, J.B.C. Jackson (2006). Depletion, degradation, and recovery potential of estuaries and coastal seas. Science 312: 1806-1809. Kirwan, M.L., J.P. Megonigal (2013). Tidal wetland stability in the face of human impacts and sea-level rise. Nature 504: 53–60..

(28) 28. Klemas, V. (2012). Remote sensing of coastal and ocean currents: an overview. Journal of Coastal Research 28: 576-586. DOI: 10.2112/ JCOASTRES-D-11-00197.1. Lehner, S., A. Pleskachevsky, M. Bruck (2012). High-resolution satellite measurements of coastal wind field and sea state. International Journal of Remote Sensing 33, 7337-7360. Morris, E.P., J. Gomez-Enri, J., D. van der Wal (2015). Copernicus Downstream Service supports nature-based flood defense; use of Sentinel earth observation satellites for coastal needs. Sea Technology 56: 23-26. hdl.handle.net/10498/17409. Newton, A., T.J.B. Carruthers, J. Icely (2012). The coastal syndromes and hotspots on the coast. Estuarine, Coastal and Shelf Science 96, 39-47. Nieuwhof, S.; Herman, P.M.J.; Dankers, N.; Troost, K.; van der Wal, D. (2015). Remote Sensing of Epibenthic Shellfish Using Synthetic Aperture Radar Satellite Imagery. Remote Sensing 7: 3710-3734. Nieuwhof, S. (2018). The use of remote sensing to reveal landscape-scale ecosystems engineering by shellfish reefs. PhD thesis. University of Twente, Faculty of Geo-Information Science and Earth Observation (ITC). ISBNs 978-90-365-4542-6. Pleskachevsky, A.L., W. Rosenthal, S. Lehner (2016). Meteo-marine parameters for highly variable environment in coastal regions from satellite radar images. ISPRS Journal of Photogrammetry and Remote Sensing 119: 464-484. 10.1016/j.isprsjprs.2016.02.001 ProSes (2005). Ontwikkelingsschets 2010 Schelde-estuarium. Besluiten van de Nederlandse en Vlaamse regering. ProSes (Projectdirectie ontwikkelingsschets Schelde-estuarium). Brussel / Den Haag, in Dutch, 84 pp. Ramapriyan, H., J. Brennan, J. Walter, J. Behnke (2013). Managing big data. Earth Imaging Journal, http://eijournal.com/2013/managing-big-data. Salama, M.S., W. Verhoef (2015).Two-stream remote sensing model for water quality mapping: 2SeaColor. Remote sensing of Environment 157: 111-122. Syvitski, J.P.M., A.J. Kettner, I. Overeem, E.W.H. Hutton, M.T.Hannon, G.R. Brakenridge, J. Day, C. Vörösmarty, Y. Saito, L. Giosan, R.J. Nicholls (2009). Sinking deltas due to human activities. Nature Geoscience, doi: 10.1038/NGEO629. van Belzen, J. van de Koppel, M.L. Kirwan, D. van der Wal, P.M.J. Herman, V. Dakos, S. Kéfi, M. Scheffer, G.R. Guntenspergen & T.J. Bouma (2017). Direct evidence for critical slowing down when approaching tipping points in tidal marshes. Nature Communications 8: 15811, doi: 10.1038/ncomms15811..

(29) 29. van de Koppel, J., D. van der Wal, J.P. Bakker, P.M.J. Herman (2005). Self-organization and vegetation collapse in salt marsh ecosystems. American Naturalist 165 (1): E1-E12. van der Wal, D., P.M.J. Herman, A. Wielemaker-van den Dool (2005). Characterisation of surface roughness and sediment texture of intertidal flats using ERS SAR imagery. Remote Sensing of Environment 98: 96-109. van der Wal, D., P.M.J. Herman, R.M. Forster, T. Ysebaert, F. Rossi, S. Ides, Y.M.G. Plancke (2008). Distribution and dynamics of intertidal macrobenthos predicted from remote sensing: response to microphytobenthos and environment. Marine Ecology Progress Series 367: 57-72. van der Wal, D., A. Wielemaker-van den Dool, P.M.J. Herman (2010). Spatial synchrony in intertidal benthic algal biomass in temperate coastal and estuarine ecosystems. Ecosystems 13: 338-351. von Glasow, R., T.D. Jickells, A. Baklanov, G.R. Carmichael, T.M. Church, L. Gallardo, C. Hughes, M. Kanakidou, P.S. Liss, L. Mee, R. Raine, P. Ramachandran, R. Ramesh, K. Sundseth, U.Tsunogai, M. Uematsu, T. Zhu (2013). Megacities and large urban agglomerations in the coastal zone: interactions between atmosphere, land, and marine ecosystems. Ambio 42: 13–28. van Wesenbeeck, B.K., T. Balke, P. van Eijk, F. Tonneijck, M. Sirye, M.E. Rudiantoe, J.C. Winterwerp (2015). Aquaculture induced erosion of tropical coastlines throws coastal communities back into poverty. Ocean & Coastal Management 116: 466-469. Verhoef, W. (1984). Light scattering by leaf layers with application to canopy reflectance modeling: the SAIL model. Remote Sensing of Environment 16:125–141. Vermeersen, B. L. A., A.B.A. Slangen, T. Gerkema, F. Baart, K.M. Cohen, S. Dangendorf, M. Duran-Matute, T. Frederikse, A. Grinsted, M.P. Hijma, S. Jevrejeva, P. Kiden, M. Kleinherenbrink, E.W. Meijles, M.D. Palmer, R. Rietbroek, R.E.M. Riva, E. Schulz, D.C. Slobbe, M.J.R. Simpson, P. Sterlini, P. Stocchi, R.S.W. van de Wal, M. van der Wegen (2018). Sea-level change in the Dutch Wadden Sea. Netherlands Journal of Geosciences - Geologie en Mijnbouw 97, 3: 79-127. United Nations (2015). Transforming our world: the 2030 agenda for sustainable development. A/RES/70/1. United Nations, sustainabledevelopment.un.org, 41 pp. Yang, H., J.-K. Choi, Y.-J. Park, H.-J. Han, J.-H. Ryu (2014). Application of the Geostationary Ocean Color Imager (GOCI) to estimates of ocean surface currents. Journal of Geophysical Research 119, 3988-4000..

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(31) 31.

(32) 32. WWW.UTWENTE.NL.

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