Comparison of nutrient and contaminant fluxes in two areas with different hydrological regimes (Empordà Wetlands, NE Spain).

Nutrient (N and P), heavy metal (Ni, Cd, Cr, Cu and Pb) and pesticide (DDT, DDD, DDE, lindane, aldrin, endrin, dieldrin, permethrin, atrazine and simazine) concentrations in water and sediment were analysed in the Empordà Wetlands, a Mediterranean wetland area in NE Spain. Mean nutrient and contaminant concentrations and input and output loads via tributaries were compared in two marshes with different water turnover: a freshwater marsh (FWM), with a high water turnover rate due to continuous surface water inputs and outputs, and a brackish water marsh (BWM), with lower turnover and no continuous surface output, where water remains confined during dry periods. Mean concentrations of most heavy metals exceeded the maximum permissible concentration (MPC) in BWM, whilst only some pesticides reached MPC in FWM. The confined waters of BWM showed higher sensitivity to contaminant input loadings than FWM due to the lack of continuous water outputs. Non-point source pollution inputs during runoff (mainly in FWM) and concentration during confinement (mainly in BWM) showed as the main environmental problems related to nutrients and contaminants in these ecosystems. Thus, the importance of confinement and its effect on pollutant concentrations must be borne in mind to achieve correct management of Mediterranean wetlands.

Seasonal development of a turbid hydrothermal lake plume and the effects on the fish distribution.

Measurements of the suspended particle concentration in a lake demonstrate the presence of a turbid hydrothermal plume. The plume, generated from a warm source develops upward carrying a suspension of particles from the bottom. It is found that the vertical structure of the plume depends on the stratification of the water column, which in turn depends on the seasonal meteorological conditions. During the stratified period of the lake, the plume is constricted to the hypolimnion zone. At the beginning of the summer season, the plume reaches the bottom of the metalimnion meanwhile at the end of this season the plume does not. In the mixed period of the lake, the plume develops in the whole water column and reaches the surface of the lake, where particles accumulate and spread around the center. Measurements of the vertical fish distribution in the stratified period show that the plume can constrict the fish habitat due to an increase of suspended particles transported by the plume.