Rapid infiltration basins (RIBs) are effective tools for wastewater treatment and groundwater recharge, but continuous application of wastewater can increase soil P concentrations and subsequently impact groundwater quality. The objectives of this study were to (1) investigate the effects of reclaimed water infiltration rate and “age” of RIBs on soil P concentrations at various depths, and (2) estimate the degree (percentage) of sorption equilibrium reached between effluent P and soil attained during reclaimed water application to different RIBs. The study was conducted in four contrasting cells of a RIB system with up to a 25 year history of secondary wastewater application. Soil samples were collected from 0 to 300 cm depth at 30 cm intervals and analyzed for water extractable phosphorus (WEP) and oxalate extractable P, Al, and Fe concentrations. Water extractable P and P saturation ratio (PSR) values were generally greater in the cells receiving reclaimed water compared to control soils, suggesting that reclaimed water P application can increase soil P concentrations and the risk of P movement to greater depths. Differences between treatment and control samples were more evident in cells with longer histories of reclaimed water application due to greater P loading. Data also indicated considerable spatial variability in WEP concentrations and PSR values, especially within cells from RIBs characterized by fast infiltration rates. This occurs because wastewater-P flows through surface soils much faster than the minimum time required for sorption equilibrium to occur. Studies should be conducted to investigate soil P saturation at deeper depths to assess possible groundwater contamination.
Artigo completo: www.ncbi.nlm.nih.gov
Moura DR, Silveira ML, O’Connor GA, Wise WR.
Contamination of soils and groundwater by chlorobenzene and benzene is a common problem at industrial sites worldwide. Since chemical remediation techniques are rarely completely effective, remnants of these contaminants often persist at levels that can still influence ecosystem health. We evaluated the potential of Pinus taeda and Eucalyptus urograndis to accelerate the removal of these compounds from sand/water systems using a completely randomized block greenhouse experiment with a no-plant control. At 2-day intervals, we added a solution containing both chlorobenzene and benzene with the same concentration of 50 mg L−1 (25 mg pot−1), and we monitored leachate concentrations daily. The planted treatments showed greater decrease of contaminants over time. In the absence of plants, the contaminant mass decreased 50–60% during each 2-day cycle; whereas, in the planted treatments the contaminant mass decreased 91–98%. At the end of the experiment the plant roots, leaves, and the sand-substrate each contained less than 1 mg kg−1 of contaminants, which is ∼1% of the total contaminant mass added. In addition, we observed no tree mortality even at concentrations exceeding the aqueous solubility limit of both compounds. Our results suggest both trees are good candidates for remediating chlorobenzene and benzene in soils and groundwater.
Artigo completo: www.tandfonline.com
Diego Barcellos, Lawrence A. Morris, Valentine Nzengung, Tiago Moura, Nehru Mantripragada & Aaron Thompson.
Mechanical site preparation has been considered essential to southern pine plantation establishment since the 1950s. Although survival and early growth responses to site preparation are well documented, several factors often contribute to these responses, and the specific contribution of soil tillage is not well established. Soil moisture content, soil resistance to penetration, and loblolly pine (Pinus taeda L.) growth were measured on eight sites in the Upper Coastal Plain (UCP) and Piedmont in tilled (T) and nontilled (NT) rows under three conditions: operational site preparation with initial vegetation control (O), operational plus annual fertilization (O+F), and operational plus annual fertilization and complete vegetation control (O+F+V). Tillage reduced average soil resistance to penetration by 9 to 51% across cultural treatments. Soil tillage also reduced volumetric water content. On the most affected site, T rows contained 68% of the water of NT rows in the 0.15- to 0.30-m interval and 53% of the water in the 0.30- to 0.60-m interval. Tillage resulted in positive growth responses on seven of the eight sites, and growth increases occurred across all cultural treatments. After two growing seasons, the largest trees were on a Lucy series soil where the O+F+V treatment resulted in an average stem volume index (SVI) of 8932 cm3. The smallest trees were on a clayey Faceville series soil where the NT rows in the O treatment had an average SVI of 101 cm3. Growth responses were poorly correlated with measured differences in average resistance or differences in resistance between T and NT rows in any depth increment (0–0.15, 0.15–0.30, or 0.30–0.60 m); however, soil resistance in the 0- to 0.15-m depth increment demarcated an upper bound for growth. A tillage effect on the volume of soil below a critical soil resistance was helpful for explaining some of the observed responses.
Artigo completo: www.dl.sciencesocieties.org
Bruno F. Furtado, Lawrence A. Morris *b and Daniel Markewitzb