Ecosystem Service Assessment of TIDE Estuaries

5b. Determining conservation objectives with ES

Mostly, benefit transfer methods based on reviews of monetary values are applied to demonstrate the societal value of ecosystems in monetary terms. These values are not linked to local ecological and socio-economic realities and do not have the order of detail required to base local decisions upon. However, they are relevant for discussion as they provide us with the order of magnitude of societal benefits which are at stake.
In the recent review of de Groot et al (2012), a monetary value is compiled for different biomes, based on a compilation of existing local valuation studies around the world. Although these monetary values are based on an extensive and up to date literature study, they do not offer adequate data to analyze separate, local ecosystem services. Every ecosystem has its specificities, and in order to address ecosystem services, the local demand and supply of ecosystem services should be addressed on the appropriate scale.

Such an approach was taken in the Scheldt estuary. With a length of 160 km, flowing from Gent in Flanders to Vlissingen in the Netherlands, it is one the largest European estuaries with a complete gradient from marine over brackish to fresh water tidal habitats, the latter being very rare on a European scale. The Scheldt catchment is one of the most densely populated in Europe and heavily impacted by human activities. Changes in land use and water management altered the hydrology and lead to a larger variability of fresh water discharges to the estuary. Buffering of peak flows is reduced, while extensive water abstraction strongly reduces the flows during dryer periods, both changing the water residence time, a crucial parameter determining ecological functioning. Large inputs of nutrients, pollutants and suspended solids resulted in serious problems of water and sediment pollution. The geomorphology changed due to land reclamation for agricultural and industrial development, infrastructural works to improve and maintain the fairway to the harbours and sea level rise, causing coastal squeeze, the trapping of tidal marshes and mudflats between the sea walls and the rising sea. This reduced the capacity to absorb tidal energy and as a result the tidal range in Antwerp increased by nearly one meter over the last century, causing serious safety problems.

The loss of habitats (along with pollution of the remaining ones) not only reduced biodiversity, but also ES such as the nursery function, fisheries, nutrient retention and flood protection. The capacity to absorb the increasing loads of nutrients has declined, resulting in bigger loads towards the coastal sea, increasing the risks of eutrophication. During this century, the magnitude and frequency of floods are likely to increase due to climate change induced high rainfall and rising sea levels, increasing the risk on flooding. This means the amount of areas at risk of flooding will further increase. There has also been a rise in the vulnerability to flooding due to the increase in the number of people and economic assets located in flood risk zones.

While little experience exists with defining conservation objectives (CO’s) in compliance with the Habitat Directive, its importance became clear after the Court of Justice’s case on the Cockle fisheries in the Wadden Sea: the CO’s should be the main reference point to judge whether an effect is significant or not. This point of view places CO’s at the centre of the appropriate assessment in terms of article 6.3 of the Habitat Directive. CO’s have to describe the desirable state of the ecosystem and can be formulated qualitatively or quantitatively e.g. a desired population size or habitat area. These objectives are mostly formulated from a structural point of view and do not really suit the ecosystem approach that was put forward by IUCN and adopted by the Convention on Biodiversity as a strategy for the integrated management of land, water and living resources that promotes conservation and sustainable use in an equitable way. It is based on the application of appropriate scientific methodologies focused on different levels of biological organization which encompass the essential processes, functions and interactions among organisms and their environment. It also recognises that humans are an integral component of ecosystems.

This approach is essential in economically important areas such as estuaries. Major infrastructural works were planned in the Scheldt: the deepening of the fairway to the harbour of Antwerp and the Sigmaplan to protect the land from storm floods coming from the North Sea. As the whole estuary, both in the Netherlands and Flanders, is protected by the EU habitat directive, infrastructural works should not have a significantly negative impact on the conservation objectives (CO’s). However, these objectives were not yet accurately defined for the Scheldt estuary.

In the Scheldt, therefore, a methodology was developed to define CO’s that allow a more strategic, integrated and sustainable approach to objectives settings and decision making.

The analysis of the Scheldt measures in view of Natura 2000 is based on the contents of the Long Term Vision for the Scheldt estuary for 2030 (LTV) and Development plan 2010 (Ontwikkelingsschets – OS). These bilateral agreements fit in the long term cooperation between both neighbor states. The overall target of the long term vision is about the conservation of the physical characteristics of the estuary and the optimal balance between safety, accessibility and environmentally. Regarding the environmental aspect, this means specifically the sustainable preservation in 2030 of a large diversity of habitats with associated species communities. Therefore, ecological objectives were developed regarding the naturalness aim from the Long Term Vision:

• A large diversity in estuarine habitat (marshes, mudflats, shallow water and sandbars in fresh, brackish and saline water) with sustainable associated life communities;
• Space for natural dynamical physical, chemical and ecological processes. Maintenance of the multiple-channel system in the Westerschelde;
• The water quality may not be a limiting factor anymore.

Firstly, based upon data on presence and trends in the numbers of different characteristic and relevant species and based on knowledge of habitat selection, densities etc., population targets were defined and translated to a surface of habitats necessary. Next a required amount of ES desired or needed from the system was defined. To protect the land against flooding a certain amount of water must be stored during storm tides. Based on hydrodynamic models this volume was translated in the surface of flood control area needed, given a politically agreed level of safety. To reduce the nutrient load towards the coastal sea, the surface of tidal marshes needed to provide a significant nitrogen sink was calculated using an ecological model. Basic research proved that tidal marshes are essential in delivering dissolved silica to the estuary and in this way play a crucial role in sustaining pelagic primary production. Based on this knowledge the surface of tidal marshes necessary to prevent a shift towards blooms of blue-green toxic algae was derived. Similar calculations were done for the various relevant ES. However, the delivery of ES is not only dependent on the surface of habitats but also on habitat quality. Therefore, objectives were set for several environmental parameters (e.g. water and soil quality). All of this information was finally compiled in CO’s for the estuary described both in terms of population sizes and in terms of the amount of ecosystem services required for a sustainable development. ES in turn were translated in the necessary surface of habitats and required environmental quality.

From a biodiversity point of view, objectives are set primarily as a number of individuals. For instance we can argue that a CO is to have a population of 10.000 Oystercatchers in the estuary during winter. Based on basic knowledge of feeding ecology we know that the average density of Oystercatchers on the tidal flats is about 5/ha, given an average biomass of cockles present. This can then easily be translated into a required surface of tidal flats needed, being 10.000/5 = 2000 ha. This can be done for all species for which we make CO’s.

Much more interesting it become however if we define also CO for ES. This can be done in many different ways. A CO can be for instance the safety level. The objective is that an area is only flooded with a storm occurring only once in 500 years. We know from such a storm that the high water levels are 8 m and that such a volume of water must be accommodated at that time. If we know that we need to store x million m³ we can again translate this into a surface of habitat. Another example is the reduction of pollutants. A certain load of a pollutant, let’s say N, is entering the estuary. Because we want to reduce the eutrophication of the North Sea, we can allow only a certain load leaving the estuary towards the North Sea. The difference between input in the estuary and output to the estuary is the amount that should be stored/transformed in the estuary. As we know that tidal marshes are a sink for N and we know how much N can be stored/transformed per ha marsh we can calculate how much surface of marshes we need to remove this load. In this way we are making very functional conservation objectives.

The advantages of defining the CO’s in such a comprehensive and systemic manner are huge. Not only does it put the emphasis on protecting and restoring species and habitats, but to a very large extent it also emphasizes the fundamental problems of the system (such as increasing tidal energy) that negatively affects both the ecology and economy of the system. The ES-approach is also an opportunity to link the various environmental legislations (Bird and Habitat-, Water Framework-, flood directive etc.). This enables a truly integrated approach and makes it much easier to negotiate with all of the different stakeholders.

A cost benefit analysis, taking into account the ES, clearly proved the overall economic benefits of the integrated plan versus sectorial plans. In view of the increasing risk of flooding complementary measures are needed along the Scheldt River to achieve an acceptable protection level. A technological option (storm barrier) was compared with dike heightening and controlled inundation areas.

AS such, a concrete application of considering multiple ES in estuarine management combining conservation goals, safety, recreation and biogeochemical functioning took place. An innovative site restoration technique of controlled reduced tides was elaborated and tested in a pilot project and is now being implemented along the entire estuary, Involving the building of over 1500 hectares of flooding area.

In the cost benefit analysis including ecosystem services, two kinds of floodplains were taken into account: a system where the existing land use is maintained (mostly agriculture) and a tidal system that delivers multiple ES.

• Regulating services were quantified through the OMES-model. This ecosystem model was developed for the Scheldt estuary in order to study the possible impact of different water management strategies on the ecosystem. This model was based on a monitoring program for all major groups (plankton, benthos, avifauna, fish, and littoral vegetation), carried out by different universities and institutes, and simulated major ecosystem processes, such as the C, N and P cycles. The OMES-model makes distinctions between the impact of riverine wetlands in the fresh water, brackish and salt zone of the river.
• The flood control service was quantified by a large hydrodynamic model. Based on land use data, damage factors and replacement values for houses, household furniture, roads, industry, crops and other damage categories the flood damages in the inundated area were estimated.
• A Contingent Valuation study was performed to value the recreational value of new floodplains.

Results of the cost benefit analysis show that an intelligent combination of dikes and floodplains can offer higher net benefits (596 Million Euros) at lower costs (132 Mio.Eur, payback period 14 years) compared to more drastic measures as a storm surge barrier near Antwerp (net benefits 339 Mio.Eur, Costs 387 Mio.Eur, payback period 41 years).

The hydrodynamic modelling also indicated that floodplains are necessary to ensure safety levels in the longer term in the Scheldt basin. Dike heightening only would cause a shift in flooded areas but does not suffice to importantly reduce flood risk. Additionally results showed that the benefits of the controlled reduced tidal areas (RTA) exceeded benefits of the controlled inundation area (CIA) with agricultural use. Based on these results, the Dutch and Flemish governments approved the integrated management plan consisting of the restoration of approximately 2500 ha of intertidal and 3000 ha of non-tidal areas, the reinforcements of dikes and the necessary dredging to improve the fairway to Antwerp.

This example demonstrates that ecosystem services can form the basis of an approach to obtain an integrated management including industry and port development, agriculture, conservation goals, recreation etc. Currently, a guidance document is developed to describe a methodology for monetary valuation of ecosystem services in estuaries which is based on best available data and state-of-the-art insights (Liekens et al 2013)