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(19-38) Novel test methods for assessing herbicide effects on aquatic plants using Glyceria maxima . Davies, Joanna*,1, Newman, Jonathan2, 1 IACR-Long Ashton Research Station, Bristol, UK2 IACR-Centre for Aquatic Plant Management, Reading, Berkshire, UK ABSTRACT- Herbicides entering the aquatic environment by spray drift, run-off and leaching to field drains may cause adverse effects on non-target aquatic vegetation. The potential for such effects is initially evaluated using the floating plant, Lemna, in laboratory tests where the herbicide is introduced into the culture medium, thus simulating exposure via run-off or drain-flow. This approach does not allow for spray drift interception by emergent vegetation or root uptake from sediment and may not reflect the activity of foliar-acting herbicides, or those that partition into sediment. Consequently, alternative procedures were developed using the emergent, rooted macrophyte, Glyceria maxima (reed-sweet grass). This monocotyledonous species grows in permanently, or seasonally flooded habitats where it spreads by means of extensive rhizome networks. Glyceria plants, collected from natural habitats, were established under glasshouse conditions and methods were developed to enable year-round, vegetative propagation of uniform plants in a soil-based system. This system was used to test for the effects of herbicides, applied either by direct foliar over-spray, to simulate spray-drift, by soil surface drench, to simulate partitioning to sediment, or by introduction into the water column to simulate drain-flow. Assessments made after 28 days showed that shoot and leaf number counts were useful indicators for compounds with growth regulating properties, although shoot height and fresh and dry weight measurements provided more sensitive and consistent data for estimation of EC50 and NOEC parameters. Data will be presented to show the response of Glyceria maxima to 6 herbicides and the effect of growth stage and exposure route on plant sensitivity. Examples are also given which demonstrate that the test system can be readily adapted for a range of environmental conditions and to incorporate a recovery phase for monitoring the ability of plants to recover from any adverse effects of exposure. Key words: non-target aquatic plants, herbicides, toxicity test, Glyceria maxima |
