Bed load transport and incipient motion below a large gravel bed river bend

A new data set of bed load measurements in a cross-section at the exit of a river bend is presented. Data are analyzed to identify processes that contribute to the morphodynamic stability of gravel bed meanders. It is shown that boundary shear stress and bed material texture are strongly coupled, resulting in an almost equal mobility at incipient motion over the bend point bar in relation to channel flow stage. Conversely, for conditions above bankfull an excess of fine sediment towards the inner-bank, likely related to more intense crosswise flux and grain size sorting, results in size selective transport in relation to the local bed material. We suggest that bed armoring and structuring, as well as crosswise sediment flux, add stability to the outer-bank pool, while the point bar is eroded by large floods and restored by moderate flows. Results reveal the strong feedback of processes at different scales promoting stability at bends of gravel bed rivers.info:eu-repo/semantics/acceptedVersio

New tools to analyse the ecological status of mediterranean wetlands and shallow lakes

The efforts done in Catalonia (Spain) to assess the ecological status of Mediterranean wetlands and shallow lakes are described. The term wetland includes all shallow lentic waterbodies, temporary or permanent, where light reaches the bottom allowing the development of primary producers at the maximum water depth. Two water quality indexes and one habitat condition rapid assessment were developed. The first quality index (QAELSe 2010) is based on the sensitivity of microcrustaceans (cladocerans, copepods and ostracods) and the richness of crustaceans and insects found in these habitats; the second one (EQAT) uses the composition of Chironomidae pupal exuviae. Rapid assessment of habitat condition (ECELS index) considers wetland hydromorphological aspects, the presence of human pressures in the surroundings and the conservation status of the wetland vegetation. Some data of the current ecological status of Mediterranean wetlands in Catalonia are also provided.TECNIOspring Program - (Grant agreement no. 600388 of REA

Environmental filtering determines metacommunity structure in wetland microcrustaceans.

Metacommunity approaches are becoming popular when analyzing factors driving species distribution at the regional scale. However, until the popularization of the variation partitioning technique it was difficult to assess the main drivers of the observed patterns (spatial or environmental). Here we propose a new framework linking the emergence of different metacommunity structures (e.g., nested, Gleasonian, Clementsian) to spatial and environmental filters. This is a novel approach that provides a more profound analysis of how both drivers could lead to similar metacommunity structures. We tested this framework on 110 sites covering a strong environmental gradient (i.e., microcrustacean assemblages organized along a salinity gradient, from freshwater to brackish water wetlands). First we identified the metacommunity structure that better fitted these microcrustacean assemblages. Then, we used hierarchical variation partitioning to quantify the relative influences of environmental filters and the distance among wetlands on the identified structure. Our results showed that under strong environmental filtering metacommunity structures were non-random. We also noted that even passive dispersers, that are supposed to be poorly spatially filtered, showed spatial signals at a large geographical scale. However, some difficulties arose when inferring biotic interactions at finer-scale spatial signals. Overall, our study shows the potential of elements of metacommunity structure combined with variation partition techniques to detect environmental drivers and broadscale patterns of metacommunity structure, and that some caution is needed when interpreting finer-scale spatial signals