Using stable isotope analysis in stream mesocosms to study potential effects of environmental chemicals on aquatic-terrestrial subsidies

Abstract

While recent research has provided evidence that the emergence of merolimnic insects (species with an aquatic larval stage) provides a considerable energy subsidy to riparian food webs, it has also shown that merolimnic insects may serve as a vector for contaminants. Therefore, riparian food webs may be at risk from either an aquatic-terrestrial transfer of contaminants or from the contaminant-driven reductions of emerging merolimnic insects. The objective of the present study was to develop an integrated stream mesocosms test design capable of identifying these inter-ecosystem boundary effects and to provide a comprehensive approach as a basis for ecotoxicological testing. We chose the widely distributed web-building spider Tetragnatha extensa as a representative species for riparian predators. Trophic aspects of riparian food webs were investigated by stable isotope analysis of carbon (δ(13)C) and nitrogen (δ(15)N). Utilization of stable isotope ratios provided detailed information on the riparian food web structure and the dietary composition of T. extensa. Merolimnic invertebrates (mainly Cloeon spp. and Chironomidae) were found to contribute up to 71 % of T. extensa's diet, demonstrating their importance in riparian food webs in ecotoxicological mesocosm testing. This study provides a conceptual and methodological basis for assessing aquatic insect emergence-related pollutant transfer or effect translation from aquatic to adjacent terrestrial systems.

Fungicides: An Overlooked Pesticide Class?

“…Despite their potential to propagate to the functional level, indirect fungicide effects have received little attention compared to direct effects, which might be partly attributable to the difficulties to detect them and discriminate them from the latter. − Recent progress in proteomics and metabolomics, however, enables the clear identification of toxic effects, and in turn the identification and quantification of indirect implications. , Moreover, stable isotope analysis might support the identification of indirect effects through reconstructing food webs within test systems, , while potential shifts in isotope signatures due to toxicity need to be considered . Given their sensitivity and the important roles they play in food webs, toxic effects in fungi seem prone to trigger indirect effects via both vertical (e.g., control of algae populations by chytrid fungi) and horizontal (e.g., tolerant species benefiting from a release from fungicide-sensitive competitors; see “Indirect Effects” section) interactions.…”

Response and recovery of the macrophytes Elodea canadensis and Myriophyllum spicatum following a pulse exposure to the herbicide iofensulfuron‐sodium in outdoor stream mesocosms

“…The present study was conducted at the stream mesocosm facility of the University of Koblenz-Landau, Campus Landau, Germany [24,25]. The study design comprised 16 independent stream mesocosms (Figure 1) consisting of concrete channels (length ¼ 45 m; width ¼ 0.4 m; average water depth ¼ 0.26 m).…”

Aquatic‐Terrestrial Insecticide Fluxes: Midges as Neonicotinoid Vectors

“…This may be relevant for a wide range of predators, including birds, bats, lizards, and spiders, which obtain a large proportion of their energy requirements through consumption of emerging aquatic insects (Baxter et al, 2005). Furthermore, this may be especially relevant for predators which specialize on emerging aquatic insects as a food source, for example some species of riparian spiders (Wieczorek et al, 2015). In addition, the emerging adult insects themselves may be negatively impacted by retained neonicotinoid insecticides.…”