Interspecific competition delays recovery of Daphnia spp. populations from pesticide stress

Xenobiotics alter the balance of competition between species and induce shifts in community composition. However, little is known about how these alterations affect the recovery of sensitive taxa. We exposed zooplankton communities to esfenvalerate (0.03, 0.3, and 3 μg/L) in outdoor microcosms and investigated the long-term effects on populations of Daphnia spp. To cover a broad and realistic range of environmental conditions, we established 96 microcosms with different treatments of shading and periodic harvesting. Populations of Daphnia spp. decreased in abundance for more than 8 weeks after contamination at 0.3 and 3 μg/L esfenvalerate. The period required for recovery at 0.3 and 3 μg/L was more than eight and three times longer, respectively, than the recovery period that was predicted on the basis of the life cycle of Daphnia spp. without considering the environmental context. We found that the recovery of sensitive Daphnia spp. populations depended on the initial pesticide survival and the related increase of less sensitive, competing taxa. We assert that this increase in the abundance of competing species, as well as sub-lethal effects of esfenvalerate, caused the unexpectedly prolonged effects of esfenvalerate on populations of Daphnia spp. We conclude that assessing biotic interactions is essential to understand and hence predict the effects and recovery from toxicant stress in communities

The influence of competition on effect and recovery from pesticides in freshwater zooplankton communities

Intra- and interspecific competition play an important role in natural communities. In addition, toxicants are reported to alter biotic interactions. However, little is known about the influence of competition on toxicant effects within the aquatic community context. The present PhD thesis contributes to the understanding of how competition alters effect and recovery from pesticides of sensitive taxa under natural conditions. Two microcosm experiments with zooplankton communities were conducted in 2008 and 2009 over a period of 4 and 5 months, respectively. In both experiments, communities were exposed to a pulse of the pyrethroid insecticide esfenvalerate (0.03, 0.3 and 3 µg/L). In the first experiment, the influence of competition on pesticide effects was investigated under an increased range of biotic interactions. For this purpose abiotic and biotic conditions were varied by shading and regular harvesting of the communities. In the second experiment, the combined effect of warming periods and exposure to esfenvalerate on the zooplankton communities was analysed. Following the general introduction in Chapter 1, the results on the interaction of competition and pesticide exposure are described within the first experiment (Chapters 2 and 3) as well as the second experiment (Chapters 3 and 4), focused on the sensitive genus Daphnia. The results of Chapter 2 show that the pesticide-related survival of Daphnia spp. strongly depended on their densities before contamination, independent of the treatments of shading and harvesting. High densities before contamination were assumed to increase intraspecific competition for food and space and thus to affect the fitness of the organisms at the individual level. Consequently, high intraspecific competition enhanced the pesticide sensitivity of Daphnia spp. by a factor of up to 100 within the community context. The recovery of Daphnia spp. from the effect of esfenvalerate is described in Chapter 3 (Experiment 1). The time needed for the recovery of populations was up to eight times longer than predicted by models using the population growth rates under optimal single species conditions. Interspecific competition with closely related but less sensitive Daphniidae was detected as the underlying process. Following a pesticide-related reduction of sensitive Daphnia spp., less sensitive Daphniidae benefitted from the resources released and increased in abundance. This indirect increase in less sensitive taxa in turn delayed the recovery of Daphnia spp. from esfenvalerate, especially at concentrations leading to partial mortality of the populations (0.03 and 0.3 µg/ L). The findings described in Chapters 2 and 3 were enabled by the exceptionally high number of replicates compared to similar experimental outdoor systems (n = 24 per concentration level). Chapter 4 is based on the second experiment, showing that the presence of short warming periods alone altered the community structure and thus the long-term biotic interactions. As a result, interspecific competition was prolonged under warming conditions, causing a delay in recovery of Daphnia spp. from 3 µg/L esfenvalerate that exceeded the recovery under ambient conditions by a factor of two. This study highlights that changing environmental conditions may further increase the influence of competition on the recovery of populations from toxicant stress. In conclusion, the thesis identifies and quantifies the role of intraspecific competition in increasing pesticide sensitivity, and interspecific competition in delaying the recovery of populations from pesticides in the community context. The outcomes can be used to reduce uncertainty and improve the predictive quality of the current risk assessment framework

Einführung einer Abgabe auf Pflanzenschutzmittel in Deutschland

2013 wurden in Deutschland rund 100.000 Tonnen an Pflanzenschutzmitteln abgesetzt, Tendenz steigend. Herbizide, Fungizide, Insektizide und Wachstumsregler sind wichtige Hilfsmittel in der Land- und Forstwirtschaft sowie bei Siedlungs- und Verkehrsflächen, um Schädlinge und unerwünschte Pflanzen zu unterdrücken. Die Mittel verursachen zugleich unerwünschte Auswirkungen für Umwelt und menschliche Gesundheit. Die vorliegende Studie zeigt konkret für Deutschland auf, wie der Mitteleinsatz durch Einführung einer steuerlichen oder nicht-steuerlichen Abgabe risikoorientiert gezielt verringert und Anwender an den externen Kosten beteiligt werden können. Entsprechende Pflanzenschutzmittelabgaben erheben in der EU mit Erfolg schon Dänemark, Frankreich und Schweden. Die Studie schlägt ein einfaches, gleichwohl wirkungsorientiertes Modell vor und untersucht anhand von 66 ausgewählten Produkten dessen ökologische und ökonomische Auswirkungen. Zugleich klärt sie alle notwendigen politischen und rechtlichen Fragen zur Einführung einer solchen Lenkungsabgabe.»Introduction of a Regulatory Charge on Plant Protection Products in Germany«Chemical plant protection products (PPPs) are an important resource in modern intensive agriculture. However, they are also used in forestry, leisure gardening and in municipal areas and thoroughfares. Their effects take immediate action in the environment, commonly resulting in adverse consequences for non-target organisms, water bodies and soil, as well as residents, in addition to affecting the target organisms. A charge levied on PPPs would mean manufacturers, dealers and users would be making a contribution towards the ecological and health-related costs of the use of PPPs, funding for protective measures and research, and provide an economic incentive for reducing the use of PPPs. This book outlines a simple model for levying a risk-based regulatory charge for Germany and investigates its assumed consequences

Seasonal changes in the functional diversity of bacterioplankton in contrasting coastal environments of the NW mediterranean

10 pages, 4 figures, 1 tableTo understand the seasonal and intersite variations in the functional diversity of coastal bacterioplankton assemblages, their utilization of 31 different carbon sources was analyzed with Biolog-Ecoplates™ in waters from 3 harbours and 2 oligotrophic coastal environments of the NW Mediterranean. Polymers (α-cyclodextrin and glycogen) and carbohydrates (d-cellobiose and N-acetyl-d-glucosamine) were most utilized in the harbours, while carboxylic acids were mainly used in the coastal areas. Seasonal differences in the patterns of carbon source utilization (the so-called ‘functional diversity’) were investigated in 2 spatially close, but contrasting, coastal stations: the oligotrophic coastal site of Blanes Bay, and the Barcelona inner harbour. The existence of a possible seasonal trend in functional diversity of bacterioplankton in the oligotrophic coastal station, but not in the harbour, suggests that the bacterial assemblage of oligotrophic environments can adapt to changing inputs of nutrients and DOC. In contrast, the low water exchange in the harbour provides a pool of DOC of relatively stable composition throughout the year which could allow few potential bacterial metabolisms to persist. We considered the quantity of substrates used (of all those provided in the Biolog plate) as an index of potential functional diversity. The index calculated for the harbour and the coastal station samples was negatively correlated with chlorophyll a concentration, suggesting that the bacterial assemblages of oligotrophic systems have a higher number of metabolic pathways in order to be able to exploit a wide variety of DOC molecules present at low concentrationsThis work was supported by the projects BIOHAB (EVK3-CT99-00015), BASICS (EVK3-CT2002- 00078) and PROCAVIR (CTM 2004-04404-C02-01/MAR) and by a CSIC-I3P post-doctoral contract funded by the Fondo Social Europeo to M.M.S.Peer reviewe