Philippe Vervier

A Perspective on the Permeability of the Surface Freshwater-Groundwater Ecotone

The ecotone concept is used to consider exchanges of matter and energy between groundwater and surface water systems. Ecotones control these exchanges by acting as a combination of three types of filter: the contrast between permanent darkness and day-night alternation produces a photic filter; the matrix of interstitial underground systems creates a mechanical filter which slows down water velocity; biological and chemical processes, which often occur simultaneously, define a biochemical filter. The permeability of these filters changes according to water velocity. Thus, for ecotones between a surface system and a porous aquifer with large substrate pore size, dynamics of permeability are governed by hydrology, whereas between a surface system and a partially clogged aquifer with small substrate pore size, they are governed by aerobic and anaerobic processes. According to the degree of permeability, ecotones can be classified as either permanent or temporary sinks for the two adjacent systems. In the latter case, matter fluxes are retained in the ecotone, often undergoing transformation before being released to one of the ecosystems.

Biodiversity in ground waters

Despite the importance of ground waters in the global water cycle, their ecology and biodiversity have only recently received attention. Three areas are currently being studied: (I ) the origin and colonization ground ground waters, (2) the adaptation of animals to the subterranean environment, and (3) the role of ecotone between surface and ground waters. There are still several gaps in our knowledge of groundwater biodiversity (at the genetic level, the species level, the functional group level and the ecosystem level) to which future research must be directed.

Spatial changes in the modalities of N and P inputs in a rural river network

Abstract Nitrates (NI) and total phosphorus (TP) fluxes were analysed in an agricultural river of southwestern France, the Save River, in order to identify their nonpoint and/or point–source origin. For this purpose, TP and NI concentrations were measured and the fluxes calculated along the whole river at 27 sampling sites during three different seasons; Pearson correlation coefficient and partial correlation were systematically calculated for each sampling period between TP or NI loads and the environmental variables; i.e. number of inhabitants, forest, crop and pasture surfaces. In Spring and Winter, concentrations and fluxes of NI and TP increased from the headwaters to the mouth of the Save River. During the dry season, in Summer, concentrations and fluxes of NI and TP were strongly influenced by instream biological processes and artificial water supply. During wet seasons, i.e. in Winter and Spring, in spite of the same spatial dynamics of TP and NI fluxes, it appears that nitrate fluxes entering the river originated mainly from croplands (i.e. diffuse pollution) whereas phosphorus fluxes were highly related to the number of inhabitants (i.e. point source pollution). During the rainiest season, i.e. in Spring, phosphorus fluxes were also related to forests which are mainly located in the steep slope upstream part of the drainage basin.

Drug residues in urban water: A database for ecotoxicological risk management

Human-use drug residues (DR) are only partially eliminated by waste water treatment plants (WWTPs), so that residual amounts can reach natural waters and cause environmental hazards. In order to properly manage these hazards in the aquatic environment, a database is made available that integrates the concentration ranges for DR, which cause adverse effects for aquatic organisms, and the temporal variations of the ecotoxicological risks. To implement this database for the ecotoxicological risk assessment (ERA database), the required information for each DR is the predicted no effect concentrations (PNECs), along with the predicted environmental concentrations (PECs). The risk assessment is based on the ratio between the PNECs and the PECs. Adverse effect data or PNECs have been found in the publicly available literature for 45 substances. These ecotoxicity test data have been extracted from 125 different sources. This ERA database contains 1157 adverse effect data and 287 PNECs. The efficiency of this ERA database was tested with a data set coming from a simultaneous survey of WWTPs and the natural environment. In this data set, 26 DR were searched for in two WWTPs and in the river. On five sampling dates, concentrations measured in the river for 10 DR could pose environmental problems of which 7 were measured only downstream of WWTP outlets. From scientific literature and measurements, data implementation with unit homogenisation in a single database facilitates the actual ecotoxicological risk assessment, and may be useful for further risk coming from data arising from the future field survey. Moreover, the accumulation of a large ecotoxicity data set in a single database should not only improve knowledge of higher risk molecules but also supply an objective tool to help the rapid and efficient evaluation of the risk.