Frequency Of Water Exchange Research Articles

Desenvolvimento "in vitro" de larvas e juvenis de Emerita brasiliensis Schmitt (Crustacea, Decapoda, Hippidae) sob diferentes condições de temperatura, salinidade e regime alimentar

Hatched larvae and field sampled juveniles of the sand crab Emerita brasiliensis were reared at different temperatures and food diet in order to evaluate the best conditions for laboratory maintenance. The effects of frequency of changing the aquarium seawater on larval development was also studied evaluating the survival, growth and duration of larval stages. The duration of larval stage and growth of the last three zoes phases correlate positively with temperature. Temperatures between 18 and 26oC did not influence the larval survival. The kind of food and frequency of water exchange did not influence the development, growth, and survival of larvae, as well as the development, and survival of juveniles.

Hydrodynamics is a major determinant of streambed biofilm activity: From the sediment to the reach scale

The effects of hydrodynamics and organic matter on sediment biofilm esterase activity and [3H]thymidine incorporation were investigated at several depths in the streambed and riparian zone of the alpine stream Oberer Seebach (Austria). On the sediment scale, microbial activity increased with both upwelling and downwelling Darcian velocities of interstitial water and was minimal when the surface/subsurface water exchange decreased. As revealed by stepwise multiple regression analyses, sediment carbohydrates and chlorophyll a explained a considerable percentage (up to 97% in summer) of the variance of biofilm esterase activity and [3H]thymidine incorporation, whereas pore‐water temperature and concentrations of dissolved organic carbon (DOC) and dissolved oxygen (DO) were poor predictors of biofilm activity. DOC and DO fluxes, however, accounted for a considerable percentage of the variance in [3H]thymidine incorporation, which points toward the importance of flow in biofilm functioning. On the reach scale, the ratio of surface water travel length to the subsurface travel length, which is an index of the surface/subsurface water exchange frequency, determined average reach biofilm activity. Downstream routing along predominantly subsurface flow paths increased streambed esterase activity, whereas elevated surface travel lengths reduced esterase activity. Esterase activity and [3H]thymidine incorporation were also positively related to the streambed DOC retention efficiency, which underscores the role of biofilms in solute retention. These results highlight the coupling between streambed hydrodynamics and microbial activity and link sediment‐scale and reach‐scale processes.