Proposal for good ecological potential (GEP) definition in heavily modified water bodies (HMWBs) in plain area

INHABIT project

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Home Themes & Results Other regions (D2) GEP proposal for HMWB

Proposal for good ecological potential (GEP) definition in heavily modified water bodies (HMWBs) in plain area

The heavily modified water bodies (HMWBs) are defined according the Directive 2000/60/EC (WFD) as water bodies showing severe and extensive hydro-morphological alterations - considered as permanent and irreversible - and determined by a specific anthropic use. The radical removal of the sources of alteration is considered as unfeasible, since it would have unsustainable consequences from the social and/or economic and, sometimes, the environmental point of view. In general the removal of the alteration could compromise the specified use of the water body (e.g. the removal of a dam related to a reservoir for hydroelectric or drinking water purposes, or hydraulic defenses designed to protect a city). Ecological quality objectives for HMWB are lower than natural ones by virtue of alterations that would compromise in various ways habitats features and river ecosystems. Quality objectives for HMWBs are still under development, also due to the limited understanding of the complex effects of hydro-morphological alterations on biotic communities; such objectives include the implementation, by the competent authorities, of measures to mitigate and compensate the alterations, otherwise irremovable.

During INHABIT project, particularly in the context of Deliverable I3d2, the theme of HMWBs was addressed through an activity carried out in parallel to INHABIT within an agreement stipulated with the ARPA Veneto (Veneto Environment Agency). This activity was aimed to a first definition of the ecological potential to be carried out through the study and characterization of heavily modified water bodies of a lowland catchment with a high environmental interest. HMWB were further analyzed and differentiated to be framed in a sort of systematic groups, based on the specified use - which has been attributed mostly to the land context - and on dominant hydro-morphological alterations. It can be considered that physical alterations effects can overlap and undermine the value of differentiation in natural types.

In the study we applied an analysis approach similar to INHABIT approach, which is the reason why it is presented here. It has been observed that, even in situations so degraded by the physical point of view, the biotic communities respond primarily to changes in aquatic and bank habitats. Habitat features would be then confirmed as guiding elements in understanding the structure of benthic communities. Special attention has been put in the identification of physical and habitats variables (related or not to a specified use) that in such contexts could be most closely correlated with macrobenthic biotic communities.  At the same time, a positive response to such alterations by the biological metrics already in use for natural contexts was verified. The riparian vegetation development, the presence of not artificialized banks, the presence of embankments near to the channel and the land use in the perifluvial buffers have emerged as the most significant variables to be considered for the application of recovery measures aimed at improving the ecological quality.

At the same time, the HMWBs characterization, as it has been set on the specified use and prevalent hydro- morphological alterations, may also provide an important base of information where to configure differentiated management measures. If the dominant alterations that identify the HMWB are normally fixed elements, specified use and local context define instead the plausible margins for interventions on the same disturbing factors or, better yet, on the elements which are not essential to the use. In a lowland context the presence of urban land use near the river bed establishes inevitably the limits of intervention on the banks and on the perifluvial buffers; it is on these constraints that measures and effective alternatives must be calibrated. The agricultural context, vice-versa, has a presumably higher potential for recovery, as it would allow more flexibility and more possibilities for reducing alterations.