The role of rice (Oryza sativa L.) in sequestering phosphorus compounds and trace elements: Speciation and dynamics.

In southern Florida, the sequestering of nutrients through the cultivation of rice (Oryza sativa L.) in alternation with sugarcane (Saccharum spp.) crops is an essential step in minimizing downstream eutrophication of the Florida Everglades. Phosphorus (P) is known to be the leading cause of this eutrophication; however, the cultivation/harvesting of rice effectively reduces P and additional macro and micro-nutrients from agrarian soil and runoff through plant uptake. In this study, soil, water, sugarcane, and rice plants at two different stages (flooded and vegetative) were analyzed for twelve different elements (Al, As, Co, Cr, Cu, Fe, Ni, Zn, Ca, Mn, Mg, and P) by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). 31P Nuclear Magnetic Resonance (NMR) spectra of the rice plants confirmed ten different P compounds being transported and/or transformed throughout the entirety of the sugarcane and rice plants. On average, dried rice plants contained 1677 ± 14 mg-P, of which 1277 ± 3.0 mg-P was in the panicle at the vegetative stage. Harvesting of the rice panicle has the potential to remove about 14.7 kg-P/ha for the top 10 cm of the soil. This present study demonstrates that in rotations with sugarcane crops and with no added P fertilizer, rice cultivation can reduce considerable amounts of P that would otherwise leach into the Greater Everglades from the Everglades Agricultural Area.

The rain-watered lawn: Informing effective lawn watering behavior.

Water restrictions are a common municipal water conservation strategy to manage outdoor water demand, which generally represents more than 50% of total urban-suburban water use. Although water restrictions are designed to limit the frequency of lawn watering, they do not always result in actual water savings. The project described here tested a weather-based add-on water conservation strategy in a South Florida suburban community to determine if it promoted more effective lawn watering behavior than mandatory water restrictions alone. The "rain-watered lawn" pilot program was designed to inform people of recent rainfall and how that contributed to naturally watering their lawns and offset the need to irrigate as often, or in some cases, at all. The goal of the study was to determine if homeowners would water more conservatively than with water restrictions alone if they were also informed of recent rainfall totals. The results show that households in neighborhoods where the add-on rain watered lawn strategy was implemented watered up to 61% less frequently than the control neighborhoods with water restrictions alone. This study demonstrates that weather-based information strategies can be effective for conservation and suggests that a program that focuses on coupling lawn watering behavior with actual climate variables such as rainfall can yield significant water savings. This study holds significance for municipal areas with water restrictions and provides a model to help improve outdoor water conservation.

Evaluating the effectiveness of water restrictions: a case study from Southeast Florida.

One of the most commonly employed water conservation strategies is to restrict lawn watering to limited times on specified days. Water managers typically assume that limiting the frequency and duration of lawn watering will reduce water use. Consequently, the effectiveness of water restrictions is often evaluated based on observed compliance to the specified schedule, whether or not actual reductions in water use are achieved. This assessment approach is more practical than quantifying the reduction in water use brought about by restrictions because quantification of lawn water use is hampered by difficulties in disaggregating the various components of residential water use. Dual meters to separately meter the portion of public supply devoted to lawn water use are rare, and for households that withdraw water from private wells, canals, or ponds for lawn watering, there is no record of such water use at all. As a consequence of this gap in water use data, compliance to a prescribed frequency of watering is often equated with effectiveness. In this paper we develop an alternative metric for evaluating the effectiveness of water restrictions and present a case study in a suburban area in Southeast Florida that illustrates some of the challenges of quantifying lawn water use and explores some of the limitations of day of the week water restrictions as a conservation strategy.

Arsenic geochemistry and hydrostratigraphy in midwestern U.S. glacial deposits.

Arsenic concentrations exceeding the U.S. EPA's 10 µg/L standard are common in glacial aquifers in the midwestern United States. Previous studies have indicated that arsenic occurs naturally in these aquifers in association with metal-(hydr)oxides and is released to groundwater under reducing conditions generated by microbial oxidation of organic matter. Despite this delineation of the arsenic source and mechanism of arsenic mobilization, identification of arsenic-impacted aquifers is hindered by the heterogeneous and discontinuous nature of glacial sediments. In much of the Midwest, the hydrostratigraphy of glacial deposits is not sufficiently characterized to predict where elevated arsenic concentrations are likely to occur. This case study from southeast Wisconsin presents a detailed characterization of local stratigraphy, hydrostratigraphy, and geochemistry of the Pleistocene glacial deposits and underlying Silurian dolomite. Analyses of a single core, water chemistry data, and well construction reports enabled identification of two aquifers separated by an organic-rich aquitard. The upper, unconfined aquifer provides potable water, whereas arsenic generally exceeds 10 µg/L in the deeper aquifer. Although coring and detailed hydrostratigraphic characterization are often considered impractical, our results demonstrate that a single core improved interpretation of the complex lithology and hydrostratigraphy. This detailed characterization of hydrostratigraphy facilitated development of well construction guidelines and lays the ground work for further studies of the complex interactions among aquifer sediments, hydrogeology, water chemistry, and microbiology that lead to elevated arsenic in groundwater.