Characteristics of Spikes Delivered to Mesocosms

Direct and indirect ecological effects of the widely used insecticide bifenthrin on stream ecosystems are largely unknown. To investigate such effects, a manipulative experiment was conducted in stream mesocosms that were colonized by aquatic insect communities and exposed to bifenthrin-contaminated sediment; implications for natural streams were interpreted through comparison of mesocosm results to a survey of 100 Midwestern streams, USA. In the mesocosm experiment, direct effects of bifenthrin exposure included reduced larval macroinvertebrate abundance, richness, and biomass at concentrations (EC50s ranged 197.6 – 233.5 ng bifenthrin/ g organic carbon) previously thought safe for aquatic life. Indirect effects included a trophic cascade in which periphyton abundance increased after macroinvertebrate scrapers decreased. Adult emergence dynamics and corresponding terrestrial subsidies were altered at all bifenthrin concentrations tested. Extrapolating these results to the Midwestern stream assessment suggests pervasive ecological effects, with altered emergence dynamics likely in 40% of streams and a trophic cascade in 7% of streams. This study provides new evidence that a common pyrethroid might alter aquatic and terrestrial ecosystem function at the regional scale.广泛使用的杀虫剂联苯菊酯（bifenthrin）对溪流生态系统造成的直接与间接生态效应，目前在很大程度上尚不明确。为探究此类效应，研究人员在定殖了水生昆虫群落且暴露于联苯菊酯污染沉积物的溪流中宇宙（stream mesocosms）中开展了操控性实验，并通过将中宇宙实验结果与美国中西部100条溪流的调查数据进行对比，阐释了该杀虫剂对自然溪流的潜在影响。在本次中宇宙操控实验中，联苯菊酯暴露的直接效应包括：在此前被认为对水生生物安全的浓度（半效应浓度EC50范围为197.6~233.5 ng 联苯菊酯/克有机碳）下，大型无脊椎动物幼虫的丰度、物种丰富度及生物量均显著下降。间接效应则表现为营养级联反应：当大型无脊椎动物刮食者种群数量减少后，周丛生物（periphyton）的丰度出现上升。所有受试联苯菊酯浓度下，成虫羽化动态及对应的陆地源性营养补给均发生改变。将上述研究结果外推至中西部溪流调查数据后发现，联苯菊酯会产生广泛的生态效应：约40%的溪流可能出现羽化动态改变，7%的溪流则可能发生营养级联反应。本研究提供了新的实证证据，表明一种常见的拟除虫菊酯类（pyrethroid）杀虫剂，可能在区域尺度上改变水生与陆地生态系统的功能。