Jehangir H. Bhadha

Aluminum water treatment residuals as permeable reactive barrier sorbents to reduce phosphorus losses

Two aluminum water treatment residuals (Al-WTRs) from water treatment plants in Manatee County, FL and Punta Gorda, FL were evaluated as potential permeable reactive barrier (PRB) media to reduce groundwater phosphorus (P) losses. Short-term (<24h) P sorption kinetics and long-term P sorption capacity were determined using batch equilibration studies. Phosphorus desorption was characterized following P loadings of 10, 20, 30, 40 and >70 g kg(-1). Sorption and desorption studies were conducted on the <2.0mm material and three size fractions within the <2.0mm material. The effect of dissolved organic carbon (DOC) on P retention was determined by reacting Al-WTRs with P-spiked groundwater samples of varying initial DOC concentrations. Phosphorus sorption kinetics were rapid for all size fractions of both Al-WTRs (>98% P sorption effectiveness at shaking times ≥2 h). The effect of DOC was minimal at <150 mg DOCL(-1), but modest reductions (<22%) in P sorption effectiveness occurred at 587 mg DOC L(-1). The P sorption capacities of the Manatee and Punta Gorda Al-WTRs (<2.0mm) are ∼44 g kg(-1) and >75 g kg(-1), respectively, and the lifespan of an Al-WTR PRB is likely many decades. Desorption was minimal (<2% of the P sorbed) for cumulative P loadings <40 g kg(-l), but increased (<9% of the P sorbed) at cumulative P loads >70 g kg(-1). The <2.0mm Manatee and Punta Gorda Al-WTRs are regarded as ideal PRB media for P remediation.

Surface and Pore Water Mixing in Estuarine Sediments: Implications for Nutrient and Si Cycling

Abstract Dissolved constituent fluxes from the sediment to the water column are important in estuarine environments. Benthic nutrient source depends on the mechanisms driving advection, the advective transport rate, and the concentration of nutrients in the discharged water, all of which depend on the source of discharged water and water-solid reactions along its flow. Pore water advection has been measured at rates of 3 to 6 cm/d using seepage meters in the Banana River Lagoon, Florida. Diffusion, advection, and reaction modeling of SiO2 profiles in pore water indicate that advection and reactions are more important than diffusion in the upper 1 m of the sediments. Advection results from the recirculation of the overlying water column through the bottom sediments, oxygenating the lagoon water, while pore water lacks oxygen. As lagoon water recirculates through sediments, the subsequent loss of oxygen enhances regeneration of buried organic matter. Using measured seepage rates and average pore water concentrations of nutrients, N and P fluxes from the sediment are estimated to be 33 to 38 µg/cm2/y and 3 to 5 µg/cm2/y, respectively. On the basis of sedimentation rates and the average concentrations of N and P in the sediment, the fluxes of N and P to the sediment are estimated to be 9 to 38 µg/cm2/y and 2 to 6 µg/cm2/y, respectively. These values suggest that 100% more N and 30% more P may discharge with recirculating lagoon water than is deposited in the sediment. Because the source of most pore water is surface water, the excess nutrients appear to originate from organic matter regeneration at or near the sediment-water interface, thereby elevating their concentrations in pore waters and depleting their concentration in the buried sediment. This regeneration of nutrients appears to limit their burial rate in the lagoon.

Effect of Flood Depth on Rice Water Weevil (Coleoptera: Curculionidae) Populations in Florida Rice Fields

Abstract  The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is an important pest of rice (Oryza sativa L.) grown in Florida. Reports on the effect of flood depth on rice water weevil populations have been inconsistent. Our objective was to determine if flood depth has any significant effect on rice water weevil populations and other arthropods in rice grown in Florida. Sampling was conducted using adult foliar damage scars, core samples for larvae, and sweep nets for arthropods above the water. Results showed that shallow flooding reduced rice water weevil populations in Florida. Sweep net data showed that flood depth had little, if any, effect on populations of damselflies (Odonata), leafhoppers (Cicadellidae), spiders (Arachnida), or stink bugs (Oebalus spp.).

Sugarcane by-products used as soil amendments on a sandy soil: Effects on sugarcane crop nutrition and yield

ABSTRACT Agricultural by-products applied as soil amendments have the potential to improve crop production on low organic matter (OM) soils. This two-year study investigated the use of two readily available sugarcane (Saccharum spp.) milling by-products, mill mud, and mill ash, as soil amendments to improve first sugarcane crop (plant cane) and subsequent crop (first ratoon) grown on a sandy Spodosol. Sugarcane was grown in lysimeters receiving mill mud, mill ash, and a 50:50 (v:v) mill mud to mill ash mix. Amendments were applied at low, medium, and high application rates (5, 10, and 15 cm depths, respectively) and then incorporated 30 cm deep. Amendment effects on plant nutrition, soil characteristics, and crop yield were determined. High rate applied mill mud and mill ash had the highest soil OM content for both years and soil OM did not significantly change between crops for all treatments except for high rate mill mud, which increased the second year (ratoon crop). Leaf nutrient levels for nitrogen (N), iron (Fe), and copper (Cu) for all treatments both years were insufficient; nutrient levels for magnesium (Mg), manganese (Mn), and silicon (Si) were within marginal to sufficient range for all treatments both years. All amendments produced significantly higher biomass and sucrose yields for plant cane and first ratoon crops compared to the control. Mill ash treatments produced the greatest increase in sucrose and biomass yields from plant cane to ratoon crops, which corresponded with an increase in potassium (K) in leaf tissue. However, mid and high rates of mix produced the highest sugarcane biomass and sucrose yields for the both the plant cane and ratoon crops.

Capturing Flow-weighted Water and Suspended Particulates from Agricultural Canals During Drainage Events

The purpose of this study is to describe the methods used to capture flow-weighted water and suspended particulates from farm canals during drainage discharge events. Farm canals can be enriched by nutrients such as phosphorus (P) that are susceptible to transport. Phosphorus in the form of suspended particulates can significantly contribute to the overall P loads in drainage water. A settling tank experiment was conducted to capture suspended particulates during discrete drainage events. Farm canal discharge water was collected in a series of two 200 L settling tanks over the entire duration of the drainage event, so as to represent a composite subsample of the water being discharged. Imhoff settling cones are ultimately used to settle out the suspended particulates. This is achieved by siphoning water from the settling tanks via the cones. The particulates are then collected for physico-chemical analyses.