A comparison of vegetation indices and conventional ecotoxicological plant growth metrics to assess the lethal and sublethal effects of atrazine in smooth cordgrass, Spartina alterniflora

This study assessed the use of vegetation indices (PRI, NDVI and Carter Indices) and conventional ecotoxicology end points for survival, growth and biomass in Spartina alterniflora chronically exposed to atrazine for 21 days at ambient light, photoperiod, and temperature during both the summer and the fall.;Results of this study have indicated that chronic atrazine exposure adversely affected growth and survival in Spartina alterniflora and that the sublethal plant growth stress can be detected using hyperspectral imagery techniques. Specific results indicated that chronic atrazine exposure adversely affected including water quality including pH, dissolved oxygen and % oxygen saturation in both chronic 21 day atrazine tests (summer and fall),were significantly (p < 0.05 - 0.001) reduced in a general dose dependant manner (e.g. increasing reductions with increasing atrazine concentrations). While there were also significant differences in water temperature and salinity, these differences were only 1.1 oC for temperature and 1.5 ppt in comparisons between controls and atrazine exposure.;PRI Indices measurements revealed differing responses between Tests 1 and 2. PRI Indices measurements in Test 1 were not significantly (p > 0.05) different in comparison among atrazine treatments and control at days 7 and 14 of exposure; however, at day 21, reflectance was significantly (p < 0.004 - 0.0001) increased in most atrazine treatments (10 - 10,000 ug/L) when compared to controls. This was indicative of increased chlorosis observed in Spartina alterniflora, following repeated, chronic atrazine exposure. In Test 2, there were no significant ( p > 0.05) differences in PRI Indices measurements in comparisons among atrazine treatments and control at days 7, 14 and 21 of exposure. This suggests that PRI measurements may be more sensitive during the peak summer growing season (during peak temperatures, photoperiod and light intensity) than in the fall during cooler temperatures and declining photoperiod and light intensity.;NDVI measurements also revealed differing responses between Tests 1 and 2. NDVI measurements in Test 1 were not significantly (p > 0.05) different in comparisons among atrazine treatments and control at days 7 and 14 of exposure; however, at day 21, reflectance was significantly (p < 0.004 - 0.0001) increased in the two highest atrazine treatments (1,000 and 10,000 ug/L) when compared to controls. This was indicative of increased chlorosis observed in Spartina alterniflora, following repeated, chronic atrazine exposure but only at very high atrazine exposure levels. In Test 2, there were no significant ( p > 0.05) differences in NDVI measurements in comparisons among atrazine treatments and control at days 7 and 21 of exposure.; however at day 14 reflectance was significantly (p < 0.01 - 0.07) increased in the two atrazine treatments (1 and 10,000 ug/L) when compared to controls. This suggests that NDVI measurements were not as sensitive as PRI measurements, although both indices did discern evidence of plant stress following chronic atrazine exposure (days 14-21). In addition the PRI appeared to discern stress at a wider range of atrazine exposure (10 - 10,000 ug/L PRI versus 1,000 -10,000 ug/L) during Test 1. In Test 2, the NDVI Indices was somewhat more sensitive than the PRI, suggesting that the NDVI was better able to discern stress during lower temperature, light intensity and photoperiods. Carter Index revealed differing responses between Tests 1 and 2. Carter Indices measurements in Test 1 were not significantly (p > 0.05) different in comparisons among atrazine treatments and control at days 7 and 14 of exposure; however, at day 21, reflectance was significantly (p < 0.004 - 0.0001) increased only in the highest atrazine treatments (10,000 ug/L) when compared to controls. In Test 2, there were no significant ( p > 0.05) differences in Carter Indices measurements in comparisons among atrazine treatments and control at days 7, 14, and 21 of exposure.;Comparison of atrazine exposure levels in agricultural row crops in TX, South FL, and SC with the LOEC for biomass (1 ug/L) and Hyperspectral PRI (10 ug/L) in Spartina alaterniflora, indicated that only atrazine exposure levels from agriculture in row crops and vegetable crops exceeded the LOEC for biomass (1 ug/L), primarily in widespread areas in TX (locations adjoining agricultural production, as well as second order streams and bay sites). Atrazine exposure in SC urban areas only approached or occasionally (<33% of the time) exceeded the LOEC for biomass (1 ug/l). Comparisons with the LOEC for Hyperspectral PRI (10 ug/L) indicated that only atrazine exposure from row crops, exceeded levels that would discern sublethal stress (chorosis) in Spartina alterniflora. (Abstract shortened by UMI.)...