The acetochlor registration partnership: prospective ground water monitoring program

The Acetochlor Registration Partnership conducted a prospective ground water (PGW) monitoring program to investigate acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)-acetamide] transport to ground water at eight sites. The distribution of soil textures among these sites was weighted toward coarser soil types, while also including finer-textured soils that dominate most corn (Zea mays L.)-growing areas of the United States. Each site consisted of a 1.2-ha test plot adjacent to a 0.2-ha control plot. Suction lysimeters and monitoring wells were installed at multiple depths within each test and control plot to sample soil-pore water and near-surface ground water. Irrigation was applied to each site during the growing season to ensure water input of 110 to 200% of average historical rainfall. Acetochlor dissipated rapidly from surface soils at all sites with a DT(50) (time for 50% of the initial residues to dissipate) of only 3 to 9 d, but leaching was not an important loss mechanism, with only 0.25% of the 15,312 soil-pore water and ground water samples analyzed containing parent acetochlor at or above 0.05 microg L(-1). However, quantifiable residues of a soil degradation product, acetochlor ethanesulfonic acid, were more common, with approximately 16% of water samples containing concentrations at or above 1.0 microg L(-1). A second soil degradation product, acetochlor oxanilic acid, was present at concentrations at or above 1.0 microg L(-1) in only 0.15% of water samples analyzed. The acetochlor PGW program demonstrated that acetochlor lacks the potential to leach to ground water at detectable concentrations, and when applied in accordance with label restrictions, is unlikely to move to ground water at concentrations hazardous to human health.     

Importance of dispersal routes that minimize open‐ocean movement to the genetic structure of island populations

Islands present a unique scenario in conservation biology, offering refuge yet imposing limitations on insular populations. The Kimberley region of northwestern Australia has more than 2500 islands that have recently come into focus as substantial conservation resources. It is therefore of great interest for managers to understand the driving forces of genetic structure of species within these island archipelagos. We used the ubiquitous bar‐shouldered skink (Ctenotus inornatus) as a model species to represent the influence of landscape factors on genetic structure across the Kimberley islands. On 41 islands and 4 mainland locations in a remote area of Australia, we genotyped individuals across 18 nuclear (microsatellite) markers. Measures of genetic differentiation and diversity were used in two complementary analyses. We used circuit theory and Mantel tests to examine the influence of the landscape matrix on population connectivity and linear regression and model selection based on Akaike's information criterion to investigate landscape controls on genetic diversity. Genetic differentiation between islands was best predicted with circuit‐theory models that accounted for the large difference in resistance to dispersal between land and ocean. In contrast, straight‐line distances were unrelated to either resistance distances or genetic differentiation. Instead, connectivity was determined by island‐hopping routes that allow organisms to minimize the distance of difficult ocean passages. Island populations of C. inornatus retained varying degrees of genetic diversity (N_A = 1.83 – 7.39), but it was greatest on islands closer to the mainland, in terms of resistance‐distance units. In contrast, genetic diversity was unrelated to island size. Our results highlight the potential for islands to contribute to both theoretical and applied conservation, provide strong evidence of the driving forces of population structure within undisturbed landscapes, and identify the islands most valuable for conservation based on their contributions to gene flow and genetic diversity.