Within-tree variation in transpiration in isolated evergreen oak trees: evidence in support of the pipe model theory.

Within-tree variation in sap flow density (SFD) was measured in two isolated evergreen oak (Quercus ilex L.) trees growing in an oak savannah (dehesa) in southwest Spain. Sap flow was estimated by the constant heating method. Three sensors were installed in the trunk of each tree in three orientations: northeast (NE), northwest (NW) and south (S). Sap flow density was monitored continuously from May 18 to September 27, 1993. Daily values of SFD ranged between 500 and 4500 mm3 mm-2 day-1. There were significant differences in SFD between orientations; SFD was higher in the NE and NW orientations than in the S orientation. These differences were noted on both a daily and seasonal time scale, and were less pronounced on cloudy days and at the end of the drought period, when SFD was relatively low. Our results support the idea that branches of trees can be viewed as a collection of small independent plants.

Design and performance of experimental constructed wetlands treating coke plant effluents.

Reed beds were chosen to treat effluents from a coke plant in France (Usinor-Sollac, Fos/mer). The pilot is composed by a two-stage gravel bed with subsurface flow and Phragmites australis as plant. This experimental constructed wetland was monitored for one year at steady-state conditions. The composition of influent shows high concentrations of organic compounds. The hydraulic residence time was close to 10-12 days with a plug flow with longitudinal dispersion. Results show that global removal of nitrogen ranged from 54 to 94% of load removal efficiency, but corresponds easily to the regulation recommendations. Because of wintertime, the denitrification process was inhibited by aerobic conditions observed in the gravel bed with oxygen concentrations higher than 2-3 mg/L, and by small amounts of biodegradable carbon. The fate of mineral pollutants are linked to the complex ferric hydroxides balance and a lack of phosphorus was observed for reed plants, as this nutrient is dependent on iron compounds. Some necrosis was observed on plant tissues corresponding with anthocyanic pigments accumulation caused by phosphorus absorption deficiency due to its co-precipitation with iron.