Joris Eekhout

Placement of wood in streams has become a common method to increase ecological values in river and stream restoration and is widely used in natural environments. Water managers, however, are often hesitant to introduce wood in channels that drain agricultural and urban areas because of backwater concerns. This study aims to understand and predict wood-induced backwater in lowland streams in different natural conditions. Water levels upstream and downstream of wood patches were hourly gauged and collected for four streams in the Netherlands. Directly after wood insertion, the water level drop over the wood patch increased significantly by 0.1 m relative to a water depth of 0.5 m before wood insertion. The water level drop was found to increase with discharge, up to a certain maximum. If the discharge increased beyond this maximum, the water level drop reduced to the value that may represent the situation without wood. This reduction predominately depends on the obstruction ratio, calculated as the area covered by wood in the channel cross-section divided by the total cross-section area. In addition, morphologic adjustments in the stream and reorientation of the woody material reduced the water level drop over the patches in time. A newly developed, one-dimensional stationary model demonstrates that backwater effects can be reduced by optimizing the location where wood patches are placed, and by manipulating the obstruction ratio. The model can therefore function as a generic tool to achieve a stream design with wood that optimizes the hydrological and ecological potential of streams.

The Mediterranean region has been identified as one of the most affected global hot-spots for climate change, which is already manifested by faster increasing temperatures than the global mean and significant decreases in annual precipitation. Besides, over the past decades, important land cover changes have occurred, such as reforestation, agricultural intensification, urban expansion and the construction of many reservoirs. Here we study the impacts of these changes in a typical large Mediterranean catchment and focus on relevant ecosystem services, i.e. primary production, water supply, food production, water regulation, flood and erosion control, and cultural ecosystem services. We applied a hydrological model, coupled with a soil erosion and sediment transport model, for the period 1971-2010 to the entire catchment, and for an extended period (1952-2018), with more pronounced land use changes, to one of its subcatchments that plays a crucial role for regional drinking water provision. Climate change in the evaluated period is characterized by a decrease in precipitation and an increase in temperature. Land use changes included an increase in natural vegetation in the headwaters, agricultural intensification and reservoir construction in the central part, and urban expansion in the downstream part of the catchment. The positive impacts on ecosystem services were quantified by a decrease in hillslope erosion, sediment yield, sediment concentration and flood discharge, which are mainly attributed to climate change and reservoir construction. The negative impacts were quantified by an increase in plant water stress and a decrease in reservoir storage, for which the latter is mainly attributed to reforestation in the headwater catchments. While grey infrastructures like reservoir construction showed important positive impacts on some ecosystem services, such as water regulation and flood control, they also potentially induce negative impacts, such as an increase of water demand and ecological integrity. We argue that a shift is needed to green infrastructures and nature based solutions, such as reforestation and sustainable land management, which may lead to similar benefits on ecosystem services, but without the negative impacts caused by grey infrastructures. This supports the need for integrated land-use management to sustainably protect ecosystem services, considering the expected climate change impacts on Mediterranean environments and societies.

The use of check-dams in mountain environments to regulate fluxes of water and sediments is widely applied across Mediterranean mountains. Besides the use of “grey infrastructures” such as check-dams, other restoration and hydrological control measures rely more on the use of “green infrastructures” or “nature-based solutions” (e.g. reforestation, buffer lines) or a combination of both types of measures. It is widely accepted that both are complementary, and that prioritization should be based on economic, ecological and cultural criteria. This paper brings together all the knowledge generated during more than one decade concerning the impact of land use changes, reforestation, and hydrological control works on several ecosystem services in a representative Mediterranean catchment. The work evaluates different management scenarios aiming to optimize provision of ecosystem services in the area. The study area is a medium-sized catchment (∼300 km2) in Southeast Spain, representative of Mediterranean mountains that experienced agricultural land abandonment, greening up, and restoration works in the second half of the twentieth century. The methods combined: (i) previous research results for the area that were organized in an ecosystem services framework, providing data for three representative scenarios of catchment management; (ii) the use of value content analysis of the existing management plans for the area to understand the view of the managers; and (iii) a multicriteria analysis of the management scenarios to determine the most sustainable scenario to optimize different ecosystem services. The results of the evaluation were later validated with the stakeholders (technicians and managers involved in the management plans) through interviews. Our results show that solutions that respect landscape and ecological dynamics are more sustainable and cheaper in the medium and long term than scenarios based on “grey infrastructures”, although the latter could have more desirable short-term impacts. The value analysis reflects how there are some concepts, such as ecosystem services, that could easily be further incorporated into several management plans. When choosing a management scenario, this needs to be adapted to the local environmental conditions and to the specific objectives of the restoration works. Tailor-made management scenarios taking into account two factors (local conditions and specific management objectives) can optimize resources and achieve medium to long-term sustainability.