Evaluation of nitrate nitrogen fluxes from a tile-drained watershed in central Iowa

Nitrate N fluxes from tile-drained watersheds have been implicated in water quality studies of the Mississippi River basin, but actual NO3-N loads from small watersheds during long periods are poorly documented. We evaluated discharge and NO3-N fluxes passing the outlet of an Iowa watershed (5134 ha) and two of its tile-drained subbasins (493 and 863 ha) from mid-1992 through 2000. The cumulative NO3-N load from the catchment was 168 kg ha(-1), and 176 and 229 kg ha(-1) from the subbasins. The outlet had greater total discharge (1831 mm) and smaller flow-weighted mean NO3-N concentration (9.2 mg L(-1)) than the subbasins, while the larger subbasin had greater discharge (1712 vs. 1559 mm) and mean NO3-N concentration (13.4 vs. 11.3 mg L(-1)) than the smaller subbasin. Concentrations exceeding 10 mg L(-1) were common, but least frequent at the outlet. Nitrate N was generally not diluted by large flows, except during 1993 flooding. The outlet showed smaller NO3-N concentrations at low flows. Relationships between discharge and NO3-N flux showed log-log slopes near 1.0 for the subbasins, and 1.2 for the outlet, considering autocorrelation and measurement-error effects. We estimated denitrification of subbasin NO3-N fluxes in a hypothetical wetland using published data. Assuming that temperature and NO3-N supply could limit denitrification, then about 20% of the NO3-N would have been denitrified by a wetland constructed to meet USDA-approved criteria. The low efficiency results from the seasonal timing and NO3-N content of large flows. Therefore, agricultural and wetland best management practices (BMPs) are needed to achieve water quality goals in tile-drained watersheds.     

How well do parents manage young driver crash risks?

Motor vehicle crashes are extremely high among young drivers during at least the first year of licensure. Crash risks decline with increased experience, but the more newly licensed teenagers drive, the greater their risk exposure. Hence, the dilemma facing policy makers and parents is how to provide young drivers with driving experience without unduly increasing their crash risk. Graduated driver licensing policies serve to delay licensure and then limit exposure to the highest risk conditions after licensure, allowing young drivers to gain experience only under less risky driving conditions. A similar strategy is needed to guide parents. Parents do not appear to appreciate just how risky driving is for novice drivers and tend to exert less control over their teenage children's driving than might be expected. Recent research has demonstrated that simple motivational strategies can persuade parents to adopt driving agreements and impose greater restrictions on early teen driving.     

Technical assessment of fuel cell operation on anaerobic digester gas at the Yonkers, NY, wastewater treatment plant

This paper summarizes the results of a 2-year field test to assess the performance of a specially modified commercial phosphoric acid 200-kW fuel cell power plant to recover energy from anaerobic digester gas (ADG) which has been cleansed of contaminants (sulfur and halide compounds) using a patented gas pretreatment unit (GPU). Specific project goals include characterization of the fuel cell power plant emissions and verification of the GPU performance for removing sulfur contaminants. To remove halide contaminants from the ADG, a halide guard, consisting of a vessel with a metal oxide supported on alumina, was incorporated into the fuel cell reactant supply. This first-of-a-kind demonstration was conducted at the Yonkers, NY, wastewater treatment plant, a sewage processing facility owned and operated by Westchester County. Results have demonstrated that the ADG fuel cell power plant can produce electrical output levels close to full power (200 kW) with negligible air emissions of CO, NO(x), and SO(2). The GPU removed virtually 100% of H(2)S and 88% of organic sulfur, bringing the overall sulfur removal efficiency of the GPU to over 99%. The halide guard removed up to 96% of the halides exiting the GPU.     

Effect of peroxide on neutralization-potential values of siderite and other carbonate minerals

To assess quantitatively the effect of peroxide addition to standard static tests of the neutralization potential (NP) of mine wastes, 10 specimens of carbonate minerals, including five of siderite (FeCO3) and two of rhodochrosite (MnCO3), were analyzed by electron microprobe. The compositions of the siderite span a range from 60 to 86 mol % Fe. Tests of NP for the siderite diluted with 80% (w/w) kaolinite gave values of 647 to 737 kg CaCO3 equivalent per Mg for determinations by the standard Sobek method. However, if it is assumed that the ferrous carbonate component of the mineral does not contribute to NP in field situations because oxidation of Fe(II) to Fe(III) and the subsequent hydrolysis of Fe(III) leads to the release of an equivalent amount of acid, then the calculated NP for the samples ranges from 110 to 390 kg CaCO3 equivalent per Mg. Two different methods involving the addition of peroxide to the test solutions were successful in bringing the measured NP values closer to the theoretical ones. By contrast, the tests with rhodochrosite indicated the Mn(II) to be stable. For long-term environmental planning, especially for wastes from metalliferous sulfide-poor deposits in which gradual dissolution of silicate and aluminosilicate minerals may be involved in attenuating the acidity, consideration in the overall NP budget needs to be given to the ferrous iron content of those minerals. The presence of Fe2+-bearing minerals, especially carbonates, in tested mine-waste materials may lead to overestimated Sobek NP values, thus increasing the risk of poor-quality drainage and the need for costly remediation.     

Intra-storm study of solute chemical composition of overland flow water in two agricultural fields

Few studies have assessed the transport of dissolved nutrients at the field scale under natural rainfall conditions. Hysteresis between dissolved nutrients and discharge behavior can complicate such assessments and this effect has only been examined qualitatively. In this study, we investigated factors contributing to short-term variations of dissolved cation (Ca, Mg, Na, and K) and anion (soluble reactive phosphorus [SRP], NO3, and SO4) concentrations in runoff water and developed a quantitative method to study their hysteretic behavior. Within-storm variations of dissolved nutrient concentrations were determined in two agricultural fields during four natural rainfall events along with discharge, sediment, antecedent soil water conditions, and nutrient contents. For each event, nutrient loads were plotted against discharge during the rising and falling limb of the runoff hydrograph. The resulting hysteresis curves were characterized by an index H, which is the ratio between the integrated areas under the rising and falling curves of the hydrograph. Results showed that nutrient concentrations increased with time during each event. Counterclockwise (H < 1) hysteresis, occurring when the falling limb had larger loads, was found when soils were initially dry whereas clockwise hysteresis (H > 1) was associated with prior wet soil conditions. Two hypotheses are suggested to explain these variations. First, suspended sediments could have acted as a sink for dissolved nutrients and the sensitivity of nutrients to hydrological conditions was determined by their preferential sorption on these sediments. Second, movement of nutrients into runoff occurred more readily as soils became wetter during an event.     

Effects of gallium on common carp (Cyprinus carpio): acute test, serum biochemistry, and erythrocyte morphology

Gallium (Ga) is one of the intermetallic elements that are increasingly being used in making high-speed semiconductors such as gallium arsenide. The purposes of this study were to investigate the effects of gallium on acute toxicity, on serum biochemical variables as well as on erythrocyte morphological changes in the blood stream of common carp (Cyprinus carpio). Median lethal concentrations were determined in acute tests. The 96-h LC50 value was 19.78 (18.49-21.16) mgl(-1). Common carp were exposed to different gallium concentrations (2.0, 4.0, and 8.0 mgl(-1)) for 28 days in laboratory toxicity tests. Means of the measured serum biochemistry parameters (including glucose, blood urea nitrogen, creatinine, cholesterol, and triglyceride) of these exposed groups significantly differed from those of the untreated group. Deformation of erythrocytes suggest disturbance of respiration as an additional indicator of Ga exposure. Our results suggest that 2.0 mgl(-1) is proposed as a biologically safe concentration which can be used for establishing tentative water quality criteria concerning of same size common carp. In addition, serum biochemical parameters as well as erythrocyte morphological changes are promising clinical diagnostic tools for assessing the effects of gallium compounds on common carp.     

Population growth of Euchlanis dilatata (Rotifera): combined effects of methyl parathion and food (Chlorella vulgaris)

In the present work, the combined impact of four concentrations (0, 0.0625, 0.125, and 0.25 mg/L) of methyl parathion and three densities (0.5 x 10(6), 1.0 x 10(6), and 2.0 x 10(6) cells/mL) of the green alga Chlorella vulgaris on the population growth of Euchlanis dilatata was studied. In general, regardless of the food level, an increase in the concentration of methyl parathion resulted in a significant reduction of the maximal population density and rate of population increase. The population growth rate in the controls ranged from 0.248 to 0.298; rates were lower in the presence of the pesticide. At any toxicant concentration, rotifers fed higher algal density showed significantly higher population growth compared with those at lower food levels. An interaction between toxicant and food level was evident on the population growth of E. dilatata. Results have been discussed in light of the protective role of algal density on the toxic effects of insecticides on rotifers and the differences in susceptibility to toxicants between planktonic and littoral rotifers.     

Adsorption of cadmium on biosolids-amended soils

Debate exists over the biosolid phase (organic or inorganic) responsible for the reduction in phytoavailable Cd in soils amended with biosolids as compared with soils amended with inorganic salts. To test the importance of these two phases, adsorption isotherms were developed for soil samples (nine biosolids-amended soils and their five companion controls) and two biosolids samples from five experimental sites with documented histories of biosolids application. Subsamples were treated with 0.7 M NaClO to remove organic carbon. Cadmium nitrate was added to both moist soil samples and their soil inorganic fractions (SIF) in a 0.01 M Ca(NO3)2 solution at three pH levels (6.5, 5.5, and 4.5), and equilibrated at 22 +/- 1 degrees C for at least 48 h. Isotherms of Cd adsorption for biosolids-amended soil were intermediate to the control soil and biosolids. Decreasing pH did not remove the difference between these isotherms, although adsorption of Cd decreased with decreasing pH level. Organic matter removal reduced Cd adsorption on all soils but had little influence on the observed difference between biosolids-amended and control soils. Thus, increased adsorption associated with biosolids application was not limited to the organic matter addition from biosolids; rather, the biosolids application also altered the adsorptive properties of the SIF. The greater affinity of the inorganic fraction of biosolids-amended soils to adsorb Cd suggests that the increased retention of Cd on biosolids-amended soils is independent of the added organic matter and of a persistent nature.     

Functional classification of swine manure management systems based on effluent and gas emission characteristics

Gaseous emissions from swine (Sus scrofa) manure storage systems represent a concern to air quality due to the potential effects of hydrogen sulfide, ammonia, methane, and volatile organic compounds on environmental quality and human health. The lack of knowledge concerning functional aspects of swine manure management systems has been a major obstacle in the development and optimization of emission abatement technologies for these point sources. In this study, a classification system based on gas emission characteristics and effluent concentrations of total phosphorus (P) and total sulfur (S) was devised and tested on 29 swine manure management systems in Iowa, Oklahoma, and North Carolina in an effort to elucidate functional characteristics of these systems. Four swine manure management system classes were identified that differed in effluent concentrations of P and S, methane (CH4) emission rate, odor intensity, and air concentration of volatile organic compounds (VOCs). Odor intensity and the concentration of VOCs in air emitted from swine manure management systems were strongly correlated (r2 = 0.88). The concentration of VOC in air samples was highest with outdoor swine manure management systems that received a high input of volatile solids (Type 2). These systems were also shown to have the highest odor intensity levels. The emission rate for VOCs and the odor intensity associated with swine manure management systems were inversely correlated with CH4 and ammonia (NH3) emission rates. The emission rates of CH4, NH3, and VOCs were found to be dependent upon manure loading rate and were indirectly influenced by animal numbers.