RESUMO
We describe the development and features of a program called IGMPlot, which is based on the independent gradient model (IGM) and its local descriptor δ g . The IGM approach analyzes the gradient of the electron density (ED) in a molecular system to identify regions of space where chemical interactions take place. IGMPlot is intended for use by both experimental scientists and theoretical chemists. It is standalone software written in C++, with versions available for multiple platforms. Some key features are: probing and quantifying interactions between two given molecular fragments, determining bond strength (IBSI), estimating the atomic contributions to an intermolecular interaction and preparing data to build 2D and 3D representations of interaction regions. The software has been updated to include new features: critical point analysis of the ED, assessing ED asymmetry of a given bond (PDA) and a new descriptor called q g designed to enhance the IGM- δ g analysis. The program can be found at: http://igmplot.univ-reims.fr.
RESUMO
Aquatic ecosystems could be enriched with inorganic and organic matters after road runoff discharge. In this context, we studied the effects of road runoff on river biofilms (periphyton). To operate under controlled conditions the experiments were carried out in two indoor experimental streams. Glass slides were used as artificial substrates for the periphyton colonisation in the experimental streams. Current velocity was maintained at 12 cms(-1) (slow) in the first experimental stream and at 50 cms(-1) (fast) in the second one. The periphyton communities were periodically exposed to road runoff over 30 days. For this experiment, the road runoff was collected in settling basins of a motorway during rainfall events. The runoff was then characterised according to physical and chemical parameters. We tested two exposure durations (1 and 4 h) and two runoff dilutions (10% and 50%). Two laboratory experiments carried out during this study revealed that the biomass (AFDW: 0.92-2.83 g m(-2)), the chlorophyll a content (6.8-78.9 mg m(-2)) and the metabolic activity (net primary production: 61-334 m gO(2) m(-2)h(-1) and respiration: 17.2-68.3 mg O(2) m(-2) h(-1)) of the biofilms increased (p < 0.05). However, this was a function of current velocity, the runoff exposure duration, and the content in organic and inorganic elements present in the tested rainwater. Experimental streams constituted a simplified natural system, which did not allow the reproduction of all the environmental conditions. Thus, these experiments should be performed on natural sites.