Drift Propensity Research Articles

AERIAL SPRAY DRIFT FROM DIFFERENT FORMULATIONS OF GLYPHOSATE

Glyphosate and similar herbicides have facilitated low and no-till production systems through more effective management of winter weeds before planting spring-seeded crops. Crop cultivars tolerant to specific herbicides are also more readily available. Increased use of these systems and their requirements for timely herbicide applications have increased the acreage of herbicides applied by aircraft. Manufacturers of glyphosate have also made some changes in the product formulations in an effort to provide improved efficacy and convenience. A combination of these and other factors have increased the incidence and raised awareness of spray drift from aerial applications of glyphosate. This study was conducted to provide information in response to those concerns. Four spray mixes of glyphosate from three different formulations were included in an extensive field study to determine relative drift propensity of the spray mixes from the different formulations. There were no meaningful differences in spray deposition, spray drift, and atomization in a wind tunnel between the glyphosate formulations of Roundup® and Roundup Ultra®.

Effects of drift- and benthic-foraging fish on the drift dispersal of three species of mayfly nymphs in a Japanese stream

Differences in the effects of two common predatory fishes, rainbow trout (Oncorhynchus mykiss) and freshwater sculpin (Cottus nozawae), on drift dispersal of the nymphs of three mayfly species, Baetis thermicus, Cinygmula sp., and Paraleptophlebia chocorata, were examined by manipulative field experiments using stream enclosures in a northern Japanese stream. The diel periodicity of prey consumption rate differed considerably between the two fishes; the prey consumption of the drift-foraging trout was greater at both dawn and dusk, whereas the benthic-foraging sculpin showed a higher consumption rate at night. The drift propensity at night was much greater than during the day for all the mayfly species in each of the trout, sculpin and fishless treatments, as well as under natural conditions with both fishes present. The nighttime drift propensities of the epibenthic grazers, B. thermicus and Cinygmula sp., were greater in the sculpin treatment than in trout and fishless treatments, and they did not differ between the trout and fishless treatments. By contrast, the nighttime drift propensity of P. chocorata, an infaunal collector-gatherer, did not differ among the treatments. The daytime drift propensity did not differ among the treatments for any of the mayfly species. Thus differences in drift response to the predatory fishes could be related to the characteristic microhabitats of the mayfly species. Moreover, the experiments demonstrated that benthic-foraging sculpin had greater overall effects on prey drift than drift-foraging trout.

A functional classification of the drift: traits that influence invertebrate availability to salmonids

Twelve categories/traits were used to classify and rank aquatic invertebrates based on their propensity to drift and importance as a food resource for salmonids. Invertebrate availability was based on their (i) propensity to intentionally drift, (ii) likelihood of being accidentally dislodged by the current, (iii) drift distance, (iv) adult drift, (v) benthic exposure, (vi) body size, and (vii) abundance. This study represents the first attempt to characterize the intentional drift propensity of stream invertebrates. A ranking procedure separated invertebrates into Baetis and three groups decreasing in availability. Predicted ranks were significantly correlated with the actual rank of invertebrates in trout guts taken in three separate studies conducted in the central Rocky Mountains, suggesting that this procedure can effectively rank invertebrates based on their availability as a food resource for salmonids. A cluster analysis separated the 95 taxa into four drift guilds and six availability groups. This study provides criteria for determining when alterations in invertebrate community composition will affect food resources for higher trophic levels by causing a decline in the most available taxa. This research also supports previous findings that floods are important in maintaining invertebrates that represent an important food resource for salmonids.

Positioning on substrates, positioning changes, and diel drift periodicities in mayflies

Diel changes in the positioning of several mayflies (Ephemeroptera) on the top and bottom surfaces of artificial substrates were examined. Stream drift samples were taken in conjunction with substrate samples. No significant diel changes in positioning were observed while all taxa exhibited nocturnal increases in drift. All taxa had apparent surface preferences. Baetis species occurred largely on top surfaces while Ephemerella spp., Paraleptophlebia mollis, and Heptageniidae largely occupied bottom surfaces. Diel positioning changes did not appear to be an important mechanism producing diel drift periodicities. Drift propensity showed large variation between taxa and was positively correlated with the proportion of individuals on top surfaces. For most taxa, drift probability varied markedly between dates and was correlated with high growth rates.