Transport of bromide in an entisol and its dissipation in a surficial aquifer

Contamination of groundwater by nitrate is an important environmental conce rn in some parts of the citrus growing region in Florida. Although some of the test wells with high levels of nitrate in the surficial aquifer are in close proximity to citrus groves, there is no evidence to substantiate that the nitrate contamination of groundwater with the help of an alternate tra cer i.e., "Bromide". A field experiment was conducted in two large blocks o f a citrus grove of "Valencia" orange trees [Citrus sinensis (L.) Obs.] on rough lemon rootstock [Citrus sinensis (L.)] planted in an Astatula fine sa nd (Hyperthermic, uncoated Typic Quartzipsamments) to determine the transpo rt of Bromide (Br-.) in the vadose zone and its lateral movement in the sur ficial aquifer. Time required for Bromide (112 kg Br-1 ha(-1) on treated ar ea basis) applied on the soil surface to be detected in the surficial aquif er was evaluated by analysis of groundwater samples collected from monitori ng wells (MWS) installed within the area of application. In addition, Br- w as monitored in multi-level samplers (MLS), located 7.6 and 164.9 m and in another set of MWS, 172.5 m away along the down gradient from the center of the application band in the direction of groundwater flow. Within the area of application, Bi was detected in the surficial aquifer (approximately 2. 4 m below land surface), 17 d after application, which demonstrates rapid l eaching of Br- in the vadose zone of this soil. Therefore, the leaching pot ential is quite high for soil applied NO3- if significant rainfall occurs a nd before it is taken up by the trees. This study also provides evidence of a moderate rate of lateral movement of groundwater as shown from detection of Br- in the MWS 172.5 m down gradient point of Br- application within 65 0 d of application. Over the two years period, vertical transport of Br- wi thin the Surficial aquifer was down to the entire depth of sampling i.e., 6 m.