Fertilizers, soil analysis and plant nutrition /

C36

Fertilizers, soil analysis and plant nutrition /

C367 rev 194

Freshwater Community Responses to Mixtures of Agricultural Pesticides: Synergistic Effects of Atrazine and Bifenthrin

This study was an investigation of the effects of the herbicide atrazine and the insecticide bifenthrin on lake communities. The study was conducted in two phases: in phase one, we examined the effects of environmentally realistic levels of atrazine and bifenthrin, based on published data of concentrations measured in fresh waters; in phase two, the impacts of higher levels of atrazine and bifenthrin were investigated, based on concentrations used in previous studies. The factorial designed experiment included three levels of bifenthrin (0, 1/39, and 1/287 ngL in phase one and 0, 1/125, and 1/3150 ngL in phase two) cross-classified with three levels of atrazine (0, 1/15, and 1/153 ugL in phase one and 0, 1/385, and 1/2167 ugL in phase two), with duplicate replication of each treatment combination. Pesticides were added to 5,500 L fiberglass tanks containing natural plankton assemblages and bluegill. Tanks were sampled 7 and 14 d following the first pesticide treatment and 7 d after the second pesticide addition. In phase one of the study, atrazine significantly reduced chlorophyll concentrations and turbidity on day 7 Wand had no significant impact on primary productivity or algal cell densities. Atrazine also had a significant negative effect on copepod nauplii and rotifers (days 7 and 14) and on Bosmina and particulate phosphorus in the 20-200 um size fraction (day 14). Bifenthrin significantly reduced Bosmina (days 7 and 14), cyclopoid copepodids (days 7 and 14), and copepod nauplii (day 14), however bifenthrin increased rotifers at day 7. Bifenthrin addition also increased colonial green algae and decreased particulate phosphorus in the 20-200 um size fraction on day 7 and decreased turbidity and particulate phosphorus in the >200 um size fraction on days 7 and 14. Only one fish mortality (in the high bifenthrin, no atrazine treatment combination) occurred during phase one of the study. Significant interaction effects were found only for Bosmina (day 14), rotifers (day 7), and turbidity (days 7 and 14), indicating that at the concentrations used in phase one of this study, these agricultural pesticides did not act synergistically. In phase two, higher levels of atrazine resulted in significant reductions in primary productivity, chlorophyll, green colonies, Bosmina, rotifers, and particulate phosphorus (>200 um and 20-200 um) on day 7. Bifenthrin had a negative impact on Bosmina, copepod nauplii, rotifers, primary productivity, chlorophyll, green colonies, and all particulate phosphorus fractions. In addition, 33% bluegill mortality was observed in treatment combinations with an average maximum concentration of 1/3150 ngL bifenthrin. The interaction effects found indicated that when either compound was introduced at ecologically realistic levels, its effects were essentially masked if the other toxicant was present at high concentrations

Risk averse choices of managed beach widths under environmental uncertainty

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Jin, D., Hoagland, P., & Ashton, A. D. Risk averse choices of managed beach widths under environmental uncertainty. Natural Resource Modeling, (2021): e12324, https://doi.org/10.1111/nrm.12324.Applying a theoretical geo-economic approach, we examined key factors affecting decisions about the choice of beach width when eroded coastal beaches are being nourished (i.e., when fill is placed to widen a beach). Within this geo-economic framework, optimal beach width is positively related to its values for hazard protection and recreation and negatively related to nourishment costs and the discount rate. Using a dynamic modeling framework, we investigated the time paths of beach width and nourishment that maximized net present value under an accelerating sea level. We then analyzed how environmental uncertainty about expected future beach width, arising from natural shoreline dynamics, intermittent large storms, or sea-level rise, leads to economic choices favoring narrower beaches. Risk aversion can affect a coastal property owner's choice of beach width in contradictory ways: the expected benefits of hazard protection must be balanced against the expected costs of repeated nourishment actions.Support for this study was provided by NSF Grant No. ARG 1518503, WHOI Sea Grant (NOAA Award Number: NA18OAR4170104), and the J. Seward Johnson Fund in Support of the Marine Policy Center