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Easy identification of chemical signatures characteristic of water systems has become a major issue in the field of environmental protection and management. We propose an exploratory method, exclusively based on the statistical analysis of river water composition, capable of characterizing river waters in a given watershed through their chemical composition, as well as of detecting modifications, even when not related to pollution sources. Although the method is based on well-known statistic techniques (Principal Component Analysis and Linear Discriminant Analysis), and therefore is very simple and straightforward to apply, it goes far beyond the common data reduction use of these techniques. Its capabilities are illustrated through its application to rivers in Canton Geneva, Switzerland, a hydrographical network consisting of 310 km of waterways with 250 streams and rivers. The procedure results in a very satisfactory classification of watersheds, in our case by using only two geochemical indicators: U and Ba concentrations. The method also makes it possible to follow the seasonal evolution of river regimes or the effect of wetlands on river water composition., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Some of the problems involved in quantifying operationally-defined parameters in natural waters are generally overlooked. In particular, the implications of the fact that standards have an effect on the results obtained that differs from usual analytical determinations are often ignored. On the basis of a revision of published data and personal experience, the case of natural organic matter types is discussed here for four different categories: carbohydrates, thiols, TEP (transparent exopolymers), and humic substances in freshwaters. In all cases, the results obtained are noticeably dependent on the standard, though the type of dependency varies. Key aspects are discussed in detail and advice is given about the procedure to follow when reporting data. Conclusions are applicable to other aquatic systems and natural organic matter fractions., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

To quantify the effect of the filter feeder Daphnia on the aggregation of mineral particles, temporal changes in the particle size distribution of inorganic colloids were experimentally determined both in the presence and in the absence of Daphnia in water samples of Lake Brienz, Switzerland, an oligotrophic lake rich in suspended inorganic colloids. The results obtained show that daphnids favour the aggregation of mineral colloids, but only for particle sizes above the Daphnia filter mesh size. However, the number concentration of particles smaller than the Daphnia filter mesh size simultaneously increases in the presence of the filter feeder, suggesting either the break-down of existing aggregates or the aggregation of particles with initial sizes below the measured size range. The density of daphnids in this lake is currently too low to have any significant effect on the fate of inorganic colloidal particles as compared with aggregation due to physical processes of particle collision. However, in more productive water bodies where Daphnia is more abundant, they may play a significant role.

Colloidal-size particles play an important, yet not very well understood, role in the speciation of phosphate in freshwaters. This study assesses the size distribution of molybdate reactive phosphorous in various 1.2 microm-filtered freshwaters using cross-flow filtration. Concurrently, colloid size was determined by a single particle counter technique, and mineralogical composition by a combination of transmission electronic microscopy coupled with energy dispersive spectroscopy and selected area electron diffraction. The percentage of colloidal molybdate reactive phosphorous varied a great deal in the samples studied: it ranged from 26% down to only 3%. A direct comparison of the percentages of colloidal-P can be misleading. The simultaneous determination of the amount, size distribution and mineralogical composition of the colloids present in the water bodies proved to be essential for interpreting the results. The causes of the observed variation were numerous and were site-dependent.