Influence of Suspended Clay Minerals and Humic Matter on the Solid Phase Extraction Efficiency of Selected Pesticides from Water

The purpose of this investigation was to determine the influence of humic acids (HA) and Ca-montmorillonite (CaM) on the solid-phase extraction (SPE) efficiency of atrazine, alachlor and α-cypermethrin from water samples at various pH-values. The nature and intensity of binding of the studied pesticides to CaM were determined by X-ray diffraction analysis and termogravimetric analysis (TGA) test. The studied pesticides eluted from discs were analysed by thin-layer chromatography (TLC). The effects of CaM and humic acid were generally pH-dependent and acted independently in extraction efficiency influence. Lower recovery of pesticides was observed at higher pH values when CaM was ≥0.1 g and was attributed to greater dispersion of clay, increased surface area and subsequent adsorption. Concentrations of dissolved organic carbon (DOC) in humic acid had less effect on the extraction efficiency when water was at pH 8 compared to water at pH 2, which was probably due to greater nonpolar interactions of the pesticides to the charge-neutralized humic acid molecule.     

Using Aerial Photography to Estimate Riparian Zone Impacts in a Rapidly Developing River Corridor

Riparian zones are critical for protecting water quality and wildlife, but are often impacted by human activities. Ongoing threats and uncertainty about the effectiveness of buffer regulations emphasize the importance of monitoring riparian buffers through time. We developed a method to rapidly categorize buffer width and landuse attributes using 2007 leaf-on aerial photography and applied it to a 65 km section of the Toccoa River in north Georgia. We repeated our protocol using 1999 leaf-off aerial photographs to assess the utility of our approach for monitoring. Almost half (45%) of the length of the Toccoa River was bordered by buffers less than 50 ft wide in 2007, with agricultural and built-up lands having the smallest buffers. The percentage of river length in each buffer width category changed little between 1999 and 2007, but we did detect a 5% decrease in agricultural land use, a corresponding increase in built-up land use, and an additional 149 buildings within 100 ft of the river. Field verification indicated that our method overestimated buffer widths and forested land use and underestimated built-up land use and the number of buildings within 100 ft of the river. Our methodology can be used to rapidly assess the status of riparian buffers. Including supplemental data (e.g., leaf-off imagery, road layers) will allow detection of the fine-scale impacts underestimated in our study. Our results on the Toccoa River reflect historic impacts, exemptions and variances to regulations, and the ongoing threat of vacation home development. We recommend additional monitoring, improvements in policy, and efforts to increase voluntary protection and restoration of stream buffers.