Monitoring the morphological and biological developments of intertidal areas is crucial to understand the functioning of the biogeomorphological system and effectively manage this system. This applies to both short- and long-term management (months to years vs. years to decades) to assess the direct impacts of interventions (eg. nourishments, structures), as well as to assess coastal safety and comply with regulations (eg. EU Bird/ and Habitats Directive) over time. The ArgusBio monitoring stations provide the possibility for remote and continuous monitoring in form of geo-referenced JPEG-images taken by different types of cameras. Traditionally, monitoring requires regular visits of project sites in order to assess e.g. changes in bed level, the number of birds, or the (re)colonisation by benthic animals and vegetation. Most tidal flats however, are difficult to access and therefore expensive to visit, especially in averse weather conditions. Consequently, the monitoring frequency may be too low to capture the relevant dynamics of the system. Additionally, field monitoring methods tend to focus on one system component at a time, i.e. birds are counted at a different time than benthos is sampled or the bathymetry is measured. This makes it more difficult to interpret the data in terms of relations between these components. As an alternative, remotely controlled and continuously operating monitoring systems can provide valuable, comprehensive and high-resolution information about the development of intertidal areas.
The ArgusBio monitoring station uses multiple geo-referenced cameras to observe the environment. Listed below are the layout and settings as used to observe the dynamics of the Tidal flat nourishment - Galgeplaat, NL in the Eastern Scheldt, the Netherlands (note: station removed 2012 at the end of the Galgeplaat project). Note that the system was built early 2009; nowadays cameras with better specifications are available at the same cost. Also note that different locations and/or different interests might ask for different equipment.
All these cameras are fixed in waterproof housings on a 15 m high platform mounted on a steel pile of 1 m diameter, which was drilled 12 m into the sand. The station is also equipped with solar panels and batteries for power supply, a water level sensor, a lightning conductor, a thermometer, a computer for data acquisition and equipment for data storage and communication. The data produced by ArgusBio are essentially geo-referenced JPEG-pictures (or movies), saved in the Argus-database together with information on time and camera settings. Interpretation of this data requires a substantial amount of human labour or algorithms for automated recognition. Tools have been developed for the automated recognition of shorelines, the detection of wet, dry or moist areas, birds and microphytobenthos (diatoms). See 'practical applications' for more information.
An ArgusBio monitoring station can be used at various locations: coasts, bays, estuaries and rivers. The area that can be monitored by one station depends on the quality of the cameras, the required level of detail (i.e. the features under observation) and the height of the observation post. An ArgusBio station can be used for monitoring before, during and after construction activities, or for long-term monitoring.
Before a station is fully functional, the following steps need to be taken:
After the desired operational period, which can range from several months to (possibly tens of) years, the station can be removed and be re-used at another location. Since ArgusBio is a modular system, specific components can be upgraded or added, depending on the requirements for the new location. As new equipment may cause a discontinuity in the dataset and is likely to require new calibration measurements, upgrades can best be combined with relocation, unless there is an urgent need. The life span of an ArgusBio station strongly depends on the quality and durability of its components, as well as the local weather conditions. With good protection against rain, salt spray, lightning and bird excreta, most electronic components will last several years. Heat, cold, moisture and sudden power shortages likely shorten the life span of these components as compared to regular indoor use.
The data produced by ArgusBio are essentially geo-referenced JPEG-pictures (or movies). Interpretation of this data requires substantial human effort, or algorithms for automated recognition. Algorithms for automated data processing and analysis existed for bathymetric monitoring, but not for monitoring birds, macrofauna or algae. Therefore, the following tools were developed:
Use and evaluation of results
The ArgusBio monitoring station has been used to monitor the morphological and biological development of the ). More experimental applications were the use of the system to assess the presence of macroalgae and diatoms over time using a multi-spectral camera (van der Wal et al., 2011, subm., Rammos, 2012) and to count birds (Baldi, 2010 and Rammos, 2012) using the pan/tilt/zoom camera. These experiments were predominantly performed to further develop the possibilities of ArgusBio, and were not directly linked to other projects.. The monitoring of morphological developments showed very little changes in morphology, which was confirmed by visual inspection and accurate RTK-DGPS topographic surveys. The novel application of the monitoring system to detect which areas were wet, moist or dry during low tide, and how this pattern developed over the years proved to be very useful for linking micro-topography to the re-colonisation of benthos (see
Most algorithms are part of the Matlab-shell around the Argus database located at Deltares, which is under license from Oregon State University and therefore not readily available to others (for more information on use and licensing options: contact Deltares). The tools that aid manual identification of bed moisture levels and birds are easy to use and require no other specific knowledge than basic ornithology. The automated recognition algorithms require more expert knowledge to set all parameters that enable identification correctly.
Due to the complexity of the ArgusBio monitoring station (many components, limited power to supply all components simultaneously) and the natural system under observation, installation is a task for experts: the cameras need to be geo-referenced, the sequence of image acquisition needs to be tuned to the expected dynamics of the environment (light, tide, occurrence of relevant features) and the available power supply or communication bandwidth. Experience shows that this is an iterative process that can take considerable time and resources: analysis of a series of images, sometimes spanning a spring-neap cycle can be necessary to see whether the settings are right. As ArgusBio is a monitoring system based on visual observations, the availability and quality of its data strongly depend on the light conditions, i.e. weather and the day/night rhythm. Since this day/night rhythm differs from the tidal rhythm and changes through the seasons, it is not always easy to gather a consistent and well-structured data set.
The ArgusBio monitoring station can be a useful tool in situations where high-resolution data in space and/or time are required, or for projects where simultaneous data on several biological features and their environment are needed. These can be research projects about the functioning of the natural intertidal system (e.g. foodweb studies, salt marsh development) or projects that closely study the process and effects of altering the system (e.g. and other Building with Nature pilots). Another advantage of ArgusBio is its possible application at remote locations. Due to the effort related to installation, their application is more economic in long-term projects than in short-term projects. The high time-resolution means that ArgusBio gives more detailed information about e.g. the dynamics of bird occurrence than traditional counts. How this high-resolution data compares to the traditional low-resolution data is yet unknown. Moreover, the high frequency is not compatible with current environmental regulations and management practices.
Application provides the most valuable information if the station is operational well in advance of the execution of a project, such that a representative baseline or reference is obtained. Depending on the dynamics of the natural or altered system, the station should remain operational for several years; macrofauna on the nourishment on the Galgeplaat had not yet fully recovered after three years. The ArgusBio monitoring system can also be applied in a customized 'light' version, i.e. only a pan/tilt/zoom camera if birds are of main interest, or only a multi-spectral camera for algae. The images from ArgusBio are very suitable to explain what is happening to the general public.
The application of the ArgusBio monitoring station near the Galgeplaat nourishment had the goal to monitor morphological changes and the presence of algae, macrofauna and birds. Several lessons were learned, e.g.: