Eleven sites have been selected to develop workpackages 1, 2, and 3 (the packages involving field work). Study streams were selected to have low water quality due to either point sources (wastewater treatment plant effluents) or diffuse nutrient sources. To cover a broad range of possible scenarios of the causes and consequences of this low water quality, we have considered several study templates (or problem scenarios) based on the combination of the following physical and chemical descriptors:

1. Dominant direction of surface-subsurface water interaction. In the Mediterranean region, stream surface water usually recharges subsurface zones, and stream reaches tend to be "loosing reaches", especially during summer. In contrast, in mesic regions, groundwater continuously recharges the surface stream, and in terms of hydrologic balance, stream reaches tend to be "gaining reaches".
    

2. Relative importance of point versus non-point nutrient sources. The amount as well as the forms of nutrients entering the stream depends on the type of land-use practices developed on each catchment. The degree to which stream nutrient inputs from the catchment can be controlled depends on the types of land-use practices. Point sources are associated with urban and industrial activities (e.g., inputs from sewage treatment plant effluents) and are relatively easy to control, whereas non-point sources are mostly related to agricultural activities and their control is more complex.
    

3. Magnitude of point nutrient sources relative to stream baseflow. The effect of point nutrient sources on stream water quality will depend on their input rates relative to the stream flow and nutrient concentration upstream from the source. One extreme situation is found in temporary streams during the dry season, when most of the stream flow is supported by point sources.
    

4. Whether mechanisms of nutrient removal from point sources prior to discharge into the stream are implemented. These mechanisms diminish nutrient loads into the stream, reducing the effect of human activity on stream water quality. Moreover, the chemical composition (especially in terms of nitrogen forms) of sewage effluents from treatment plants with mechanisms of nutrient removal tends to be more constant and result in a more stable "environment" for the stream communities than is the case when treatment plants lack those mechanisms.

The descriptors are arranged according to the degree of difficulty with which they can be controlled by management strategies. Among the descriptors, only one encompasses physical aspects of the catchment; the other three express different degrees of human control on the stream nutrient loads.

Streams have been selected following the suggestions from the water managers participating in this project. Streams selection was based on: a) the existence of background data and information, b) the fact that they are representatives of common water quality problems, c) most of the study sites are of special interest because either the stream water is used for human consumption in cities located downstream from the study site, or they are considered sensitive areas according to the EC Directives.

 

STUDY SITE SELECTION TREE Click on the name of a stream to learn about the site