AbstractModelling long-term pesticide transfer to rivers at the catchment scale is still difficult due to a lack of knowledge of agricultural practices and poorly adapted field observation. The Orgeval experimental catchment was first investigated to validate a modelling approach. In addition to pesticide practices investigated over 20 years, directly collected from farmers, monthly integrated river samples were analysed for 10 years. To explicitly integrate agricultural practices and crop rotation, the STICS crop model was adapted to simulate pesticide transfer in soil. Annual load simulations were compared to observed pesticide fluxes in rivers. To simulate the contamination of groundwater, the STICS-Pest model was coupled to the MODCOU hydrogeological model. The results are discussed at the subbasin scale in relation to available data. To upscale the approach at the Seine River basin scale, other strategies need to be developed.

The Orgeval watershed (104 km(2)) is a long-term experimental observatory and research site, representative of rural areas with intensive cereal farming of the temperate world. Since the past few years, we have been carrying out several studies on nitrate source, transformation and transfer of both surface and groundwaters in relation with land use and agriculture practices in order to assess nitrate (NO3(-)) leaching, contamination of aquifers, denitrification processes and associated nitrous oxide (N2O) emissions. A synthesis of these studies is presented to establish a quantitative diagnosis of nitrate contamination and N2O emissions at the watershed scale. Taking this watershed as a practical example, we compare curative management measures, such as pond introduction, and preventive measures, namely conversion to organic farming practices, using model simulations. It is concluded that only preventive measures are able to reduce the NO3(-) contamination level without further increasing N2O emissions, a result providing new insights for future management bringing together water-agro-ecosystems.

Les pratiques intensives de l’agriculture conventionnelle (AC) des annees 70, ont entraine une contamination nitrique importante des aquiferes, des eaux de surface et de l’atmosphere, due aux engrais de synthese. En effet, les essais de longues durees de l’Institut National de Recherche Agronomique (INRA) des annees 90, qui ont etudie les concentrations sous-racinaires sur grandes cultures AC dans le nord de la France, conduisent a une moyenne de 25 mg N-NO3.L-1 avec ± 4 mg N-NO3.L-1 selon differents types de sols, de cultures et de conditions climatiques, sachant que la norme de potabilite est de 11 mg N-NO3.L-1. Depuis, la directive « nitrates » (1991) qui a mis en oeuvre un code de « bonnes pratiques agricoles » et la directive cadre europeenne sur l’eau (2000) qui impose le « bon etat » chimique des eaux souterraines d’ici decembre 2015, la question de l’agriculture biologique (AB), qui utilise uniquement des engrais organiques, se pose comme alternative pour limiter les contaminations nitriques. Toutefois les donnees concernant les reelles contaminations en AB manquent. Pour y pallier, le projet ABAC (DIM ASTREA-AESN) en lien avec le PIREN-Seine s’est donne pour objectif d’equiper des exploitations agricoles et des sites experimentaux de grandes cultures dans plusieurs poles pedoclimatiques du bassin de la Seine, afin de pouvoir quantifier les concentrations et flux sous-racinaires dans des systemes AB du nord de la France. Les poles pedoclimatiques se situent a ce stade de l’etude a l’est de Paris (Brie, Seine-et-Marne) ; au nord (plateau Picard, Oise) ; au nord-ouest (essai de la Motte, ferme de Villarceaux, Val d’Oise et essai de la Cage, INRA Versailles) ; au sud, dans l’Yonne et l’Essonne. Depuis 2011/2012, deux exploitations ont ete suivies en Seine-et-Marne (77) et dans l’Oise (60). Aujourd’hui, ces deux poles comprennent deux exploitations AB, converties depuis 3 et 10 ans, ainsi qu’une exploitation en AC. Les rotations AB ont une moyenne de huit ans [1.luzerne ; 2.luzerne ; 3.ble ; 4.cereales secondaires ; 5.cereales secondaires ; 6.feverole ; 7.ble ; 8.cereales secondaires] et en AC de 3 ans [1.Ble ; 2. Mais ; 3.Colza]. Dans chaque exploitation, tous les termes de la rotation sont equipes de six bougies poreuses verticales a une profondeur de 90cm. Les bougies poreuses permettent d’aspirer l’eau sous-racinaire, via une mise-sous vide prealable du dispositif. Les prelevements sont effectues une fois par semaine des le debut de la saison hydrologique puis tous les quinze jours selon les episodes pluvieux. Nos premiers resultats (2011-2012) montrent que les concentrations sous-racinaires en AB sont maximales lors des premieres pluies drainantes, avec un minimum de 0,6 mg N-NO3.L-1 pour la luzerne de premiere annee et un maximum de 45,5 mgN-NO3.L-1 pour le ble de luzerne. De plus, les deux exploitations presentent des concentrations sous-racinaires similaires selon le type de cultures, soit de 14 mg N-NO3.L-1 pour les bles post 2 ans de luzerne ; 7 mg N-NO3.L-1 pour les cereales post-legumineuses et de 3 mg N-NO3.L-1 pour les legumineuses (luzerne, feverole). Ces resultats sont encore preliminaires mais seront completes en 2013 pour prendre en compte la variabilite liee aux annees climatiques, aux itineraires techniques AB/AC et aux differents types de sol. L’equipement ainsi que le suivi des differents poles seront prolonges avec l’aide des agriculteurs et des organismes de recherches (INRA-Laon, INRA-Versailles-Grignon, INRA-Mirecourt, Irstea Antony) et agricoles (FNAB, GAB, Chambre d’Agriculture de Seine-et-Marne, Arvalis) afin de consolider et de multiplier nos premiers resultats.

The transportation of triazines (atrazine, simazine, ametryne and cyanazine) was investigated in an experimental catchment basin situated in an agricultural area. It focused on the surface and groundwaters from March 1991 to December 1993. In addition, the phenylureas (isoproturon, linuron, diuron and chlortoluron) were studied in the surface waters from January 1992 to December 1993. So as to assess the evolution of water contamination by triazines and phenylureas during the survey period, the herbicide concentrations were considered together with the characteristic parameters of the catchment basin: types of cultivations, flows and precipitations. The main herbicides found in the stream of Fossé Rognon during our study were the atrazine (30–2450 ng/l), the simazine (10–1880 ng/l) and the isoproturon (10–1800 ng/l). The results, obtained from the stream, show that the contamination overstepped the application periods. The precipitations play a major part in the herbicide leaching after their application. In the groundwaters, the atrazine concentration (5–1700 ng/l) and the simazine concentration (5–1120 ng/l) were higher than those found in 1977, despite a reduction of the corn cultivated areas. The only degradation product of atrazine found in both the surface and the groundwaters was desethylatrazine (10–850 ng/l). It appears that the groundwaters were the main incoming sources of desethylatrazine to surface waters. The exportation balances by the stream of Fossé Rognon, expressed as a percentage of the applied amounts, were for atrazine, simazine and isoproturon, in 1992: 0.085, 0.18 and 0.035, and in 1993: 0.28, 0.3 and 0.083, respectively.