Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Relevant sediment processes and water quality interaction at temporary streams

The scientific knowledge for sediment processes and their interaction to water quality in temporary streams provides the scientific basis for developing sustainable environmental flow requirements. The main aim of this result is to quantify the extent to which surface drying and rewetting determine in-stream sediment processes (storage, transformation, and remobilisation of organic matter and pollutants), and how these processes influence downstream water quality.

Partners UDUES (sediment analyses) IRSA (microbial activity), TUC and HCMR (mineralisation, leaching), EAWAG (respiration, upscaling), IMAR and UACEG contributed to the cross-comparison and laboratory experiments.

Across the Southern European catchments four temporary rivers located in different Mediterranean regions and typically characterised by a substantial intermittency of the water flow were studied in depth including Sediment characterisation, Bacterial Carbon Production (BCP), Mineralisation capacity, and Sediment respiration: The River Tagliamento (Italy), the River Krathis (Greece), the Mulargia, and the River Pardiela.

The four rivers differed considerable in their chemical composition. Degebe was the enriched in organic matter (AFDM) and in TOP, while the Tagliamento was the most nurient and organic matter poor river. Related to the Bacteria Carbon production, the results showed that the overall responses to drying of the bacterial community were independent from sediment origin and strictly related to water content. The mineralisation capacity was depended on the organic matter content and to a minor extent on the sediment moisture content.

Increased soil moisture content increased the mineralisation capacity of the sediments. Respiration varied significantly among habitats, over time and incubation temperature. After six hours of inundation respiration rates were highest for the floodplain forest followed by the large wood accumulation and gravel habitat at any incubation temperature. Temperature explained a high proportion of the variation of respiration. We expect that natural temporary streams provide multiple services including the provision of clean drinking water, the self purification of waste water, the recharge of ground water, the provision of habitats for a rich terrestrial and aquatic fauna and flora, as well as cultural and aesthetic values. A natural flowing and drying regime is required to maintain these services.

The results demonstrate that the effect of inundation duration, following a rainfall pulse, controls the process diversity within the channel. Very short pulses, as characteristic for low-order stream segments, leach nutrients, which again increases instream productivity further downstream. The relative extent and the dynamics of the temporary channel network within a catchment may therefore influence the capacity of the rivers to produce, transform, and store nutrients and organic matter.

The major dissemination of the results is made by publishing the synthesis article "Heterogeneity of Ecosystem Processes in Temporary Streams: The Role of Drying and Rewetting" as well as a number of additional specific papers.

The expected benefit is mainly related to a more adequate consideration of dry land ecosystem functionning in the watershed management and the implementation of the Water Framework directive, as well as to the determination of suitable minimum flow conditions for semi-arid streams.

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