Defining Chlorophyll-a Reference Conditions in European Lakes

The concept of “reference conditions” describes the benchmark against which current conditions are compared when assessing the status of water bodies. In this paper we focus on the establishment of reference conditions for European lakes according to a phytoplankton biomass indicator—the concentration of chlorophyll-a. A mostly spatial approach (selection of existing lakes with no or minor human impact) was used to set the reference conditions for chlorophyll-a values, supplemented by historical data, paleolimnological investigations and modelling. The work resulted in definition of reference conditions and the boundary between “high” and “good” status for 15 main lake types and five ecoregions of Europe: Alpine, Atlantic, Central/Baltic, Mediterranean, and Northern. Additionally, empirical models were developed for estimating site-specific reference chlorophyll-a concentrations from a set of potential predictor variables. The results were recently formulated into the EU legislation, marking the first attempt in international water policy to move from chemical quality standards to ecological quality targets

Adsorption calorimetric study of the organization of sodium n-decyl sulfate at the graphite/solution interface

The material and enthalpy balances of the adsorption of sodium n-decyl sulfate from aqueous solutions onto graphitized carbon black were determined between 288 and 318 K by using an automated flow sorption/microcalorimeter system. At low concentrations, the surfactant molecules form a flat monomolecular film on the graphite plane, in consequence of surface-directed ordering. A mechanism is proposed in which two adsorbed phases coexist during the formation of this surfactant monolayer. The enthalpy of adsorption in the monolayer region is ca. -42 kJ mol(-1), which does not depend appreciably on the temperature or on the surface coverage. At higher concentrations, the ordered monolayer induces surface aggregation to produce half-cylindrical hemimicelles as the critical micelle concentration is approached. The enthalpies of surface aggregation at 288, 298, and 318 K are -10, -16, and -26 kJ mol(-1), respectively. As the temperature is increased from 288 to 318 K, the average number of surfactant molecules in the cross section of a half-cylinder drops from ca. 5.4 to 3.4. Calorimetric evidence is provided that cationic and anionic surfactant adsorption on graphite follow the same mechanism in the low-density and high-density adsorbate regions