Can we predict community-wide effects of herbicides from toxicity tests on macrophyte species?

Macrophyte communities play an essential role in the way freshwater ecosystems function. It is thus of great concern to understand how environmental factors, especially anthropogenic ones, influence their composition and diversity. The aim of this study was to examine whether the effects of a herbicide mixture (50% atrazine, 35% isoproturon, 15% alachlor) on single macrophyte species can be used to predict its impact at a community level. In a first experiment we tested the sensitivity of six species (Azolla filiculoides, Ceratophyllum demersum, Elodea canadensis, Lemna minor, Myriophyllum spicatum and Vallisneria spiralis) grown separately and exposed to 0.6–600 gL−1 of the herbicide mixture. In a second experiment, conducted in microcosms, we tested the effects of herbicides on macrophyte assemblages composed of the same six species exposed to 0, 6 or 60 gL−1 of the herbicide mixture. Species grown separately exhibited growth inhibition at 60 and 600 gL−1. At 600 gL−1 the sensitivity differed significantly between species. V. spiralis was the most resistant species, C. demersum, M. spicatum and E. canadensis exhibited intermediate sensitivities, and A. filiculoides and L. minor were the most sensitive species. In microcosms, community biomass and Shannon evenness index were reduced after 8 weeks at 60 gL−1. Communities also exhibited changes in their composition: the relative and absolute abundance of C. demersum increased at 6 gL−1, while the relative abundance of V. spiralis increased at 60 gL−1. These results are in agreement with the individual responses of these species to the herbicides. It is therefore concluded that short-term effects of herbicides on simple macrophyte communities can be predicted from the sensitivity of individual species. However, further investigations are required to examine whether longer term effects can be predicted as well, especially in more complex communities

ASSESSING ECONOMIC AND TECHNICAL IMPACTS OF NON EXPECTED WEATHER EVENTS ON FRENCH SUCKLER COW FARMS DYNAMICS: A DYNAMIC RECURSIVE FARM MODEL

Weather variability can threaten French suckler cow farms which rely on rather extensive forage production. However, flexibility of the production system can help farmer to face crop production shocks. This study aims at assessing how crop yield shocks impact on farms outcomes when adaptive capacity is taken into account. Our objectives are to develop a dynamic model which enables us 1) to predict the optimal mix of production adjustments to face crop yield shocks, 2) to quantify how far the system moves from the equilibrium and how long it takes to return and 3) to measure impact of shocks on economic results when adaptive capacity is taken into account. An original dynamic recursive bio-economic farm model integrating detailed technical and biological constraints and coupled with biological sub-models has been built and calibrated to represent an average farm producing charolais finished animals. Crop yield shocks of intensities ranging between -60% and +60% of their average values are simulated in between average years. A preference for maintaining animal sales and animal live weight at the expense of crop products trade balance is found. Thought, when intensities of shocks get higher, forced sales and important variations of the area of pasture cut are observed. Essential of loss (or gain) of net profit is felt the year of the shock but can be remnant for several years. In addition, gains for good years do not totally compensate loss of symmetric bad ones. Consequently, farms capacity to face risk could be weaken over time. Minimum consumption needs, probability distribution of shocks and successions or combinations of shocks would have thought to be taken into account to assess real capacity of farms to maintain over time.livestock farm model, dynamic recursive model, crop yield variability, Livestock Production/Industries,

On-farm weather risk management in suckler cow farms: A recursive discrete stochastic programming approach

Currently France wants to introduce a weather risk management framework into its agricultural policy for livestock farming. The aim of this paper is to better understand how on-farm risk reducing strategies modify the production system and profit distribution of French suckler cow enterprises. We present in this paper an original bioeconomic model that takes into account both risk anticipation and risk adjustments and that details biotechnical relationships between the different components of the beef cattle production system and their dynamics. On-farm risk management strategies are endogeneized under weather uncertainty and tested on real observed weather sequences. We simulate four scenarios characterized by different risk aversions and feed prices. Results emphasized that production adjustments, particularly the adjustments of area of grassland harvested and the possibility to purchase substitutes to on-farm forage production, improve farmers profit under weather variability. However, limiting the amplitude of these adjustments helps decreasing profit variability. All simulated long term decisions associated to risk reducing strategies encompass a reduction of long term stocking rate and the constitution of feed stocks. The impact of hay feed price on the market has similar effects on the long term strategy.Livestock Production/Industries, Risk and Uncertainty,

Estimating a production function under production and price risks: An application to the suckler cow farms in the French charolais production area

Suckler cow production in France relies mainly on a relatively extensive management of forage, implying that production risk may be enhanced by the sensitivity of those crops to weather variability. However risk exposure is supposed to be mitigated either through ex-ante decisions concerning pasture area management or through ex-post decisions concerning the purchase of feeds. This paper aims at assessing weather impacts on cattle production level decisions. Since farmers' decisions depend on farmers' behaviour regarding risks, which are namely production and price risks, we test constant absolute risk aversion, constant relative risk aversion and risk neutrality assumptions. We develop an econometric model encompassing an auto-regressive price function and a production function which allow inputs to affect independently mean and variance of the production. Weather indicators embodied by average regional forage production for current and past years are explicitely introduced as non controllable inputs. The estimation framework consist in conditions on the first and second moment of output production, output price and profit. Following, ISIK (2003), additional condition on each of both allocable inputs enable us to take into account risk aversion and both price and production risks in parameters estimation. We use the Generalized Method of Moments in order to make minimum assumptions regarding variable exogeneity and error distribution. We apply the model to an original panel dataset containing 65 individual yearly observations recorded over the period 1987-2005 on French suckler cow farms of the north of Massif Central. Because of the difficulties to find a relevant set of instruments, these preliminary results do not analyse weather impact on production mean. However we can advance that production decisions depend on price and production risks as farmers are found to be risk averse. Weather variability of the current year increase production risk whereas fertilizer level application slightly increased it. However we did not highlight that weather impact depend on production level.Production function estimation, GMM, weather impact, price and production risks, risk aversion, suckler cow farms, French charolais production area, Livestock Production/Industries, Production Economics,

Les commis voyageurs, acteurs et témoins de la grande transformation

Tout consommateur d’aujourd’hui a probablement déjà expérimenté le doute de celui qui conclut un achat en ligne, d’un bien ou d’une prestation d’une valeur significative, auprès d’une entreprise inconnue et plus ou moins totalement dématérialisée. Connue uniquement à travers son interface, cette entreprise à laquelle on vient de fournir un titre de paiement existe-t-elle réellement ? Est-elle fiable ? Tiendra-t-elle ses engagements et quels sont les recours possibles en cas de malversation ? Force est cependant de constater que de telles incertitudes n’ont pas empêché l’essor spectaculaire du commerce en ligne au cours de la dernière décennie, auprès des consommateurs comme des entreprises. [Premier paragraphe

Les commis voyageurs, acteurs et témoins de la grande transformation

Tout consommateur d’aujourd’hui a probablement déjà expérimenté le doute de celui qui conclut un achat en ligne, d’un bien ou d’une prestation d’une valeur significative, auprès d’une entreprise inconnue et plus ou moins totalement dématérialisée. Connue uniquement à travers son interface, cette entreprise à laquelle on vient de fournir un titre de paiement existe-t-elle réellement ? Est-elle fiable ? Tiendra-t-elle ses engagements et quels sont les recours possibles en cas de malversation ? Force est cependant de constater que de telles incertitudes n’ont pas empêché l’essor spectaculaire du commerce en ligne au cours de la dernière décennie, auprès des consommateurs comme des entreprises. [Premier paragraphe

Comparisons of degradation kinetics of chloroethenes in groundwater between microcosms and field scale

International audienceGroundwater pollution by chlorinated solvents is a major concern since several years. It has been demonstrated that in specific physicochemical conditions, microbial processes like direct reductive dechlorination allow contamination reduction at several sites. Therefore, determination of biodegradation kinetics of chloroethenes is crucial in applying Natural Attenuation protocols on contaminated sites and assessing the potential risks for human health and natural media Biodegradation of chlorinated solvents is effective in highly reduced conditions, which rarely concerns the whole contaminant plume. In this study, direct reductive dechlorination of chloroethenes was studied on two different scales, on microcosms in the laboratory and at the real scale that corresponds to the contaminated site Microcosms studies were conducted in three different ways. (1) sediments sampled from the site and mixed with groundwater modified or not by a synthetic electron donor (Na propionate, Na lactate, toluene), (2) composite sediments coming from several places of the site mixed with groundwater modified or not by a synthetic electron donor; (3) autoclaved sediments and groundwater modified or not by synthetic organic matter. Studies on the real scale were conducted by the achievement of a synthesis of historical data (hydrogeological, geological and physicochemical data) of a polluted site. The synthesis of physicochemical data and then modelling the real site revealed the presence of degradation products of chloroethenes in the plume : cis-1,2-DCE and VC The results of comparisons of degradation kinetics obtained on the laboratory and the field under the same physicochemical conditions showed significant differences. Indeed, biodegradation of chlorinated solvents were faster in lab studies than in the field at the global scale. The existence of chlorinated ethenes biotransformation in microcosms confirmed the presence of a bacterial population able to catalyse reductive dechlorination reaction until CV. It is also likely that the bacterial consortium permitted to degrade other species like electron acceptors; detection of sulphide ions and Fe(II) and the presence of a black precipitate of FeS are proofs of sulphate reducing, ferro reducing and dechlorinating activities. The clear difference that there is between kinetics of degradation on microcosms and field scale could be explained by differences in chemical conditions that are not optimal everywhere in the plume of pollutants. The differences of chemical conditions (electron acceptors, type of natural organic matter, pH, redox potential...) are investigated in details to explain the differences in kinetic constant