Preferential bromide and pesticide movement to tile drains under different cropping practices

Subsurface drainage systems are useful tools to study chemical leaching in soils. Our objective was to compare the breakthrough behavior of bromide, atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamid] to tile drains under two fall tillage practices (conventional tillage [CT] with a moldboard plow, and reduced tillage [RT] with a chisel plow) in field plots cultivated with corn (Zea mays L.). Leachate volume were greater in RT than in CT, with no statistical differences. Soil analysis showed that bromide migrated deeper in the soil profile than both herbicides, with little tillage effect. All chemicals were detected in drainage water at the same time and followed an event-driven behavior. Tillage had no effect on atrazine and metolachlor found in drainage water, while bromide concentration peaks were higher in RT than in CT in 1999. Concentration peaks were recorded earlier for atrazine and metolachlor than for bromide. Plots of cumulative relative chemical mass (cumulative mass divided by total mass measured in drainage) as a function of cumulative drainage were mostly linear for bromide, while they were S-shaped for both herbicides. Drainage that corresponded to 50% of relative cumulative mass ranged from 40 to 55% for bromide and from 5 to 28% for both herbicides. Rapid chemical movement to tile drains suggested that preferential flow was important in both CT and RT, and that these tillage practices had little influence on this phenomena.     

Ion cycling in hemlock-northern hardwood forests of the southern Lake Superior region: a preliminary study

Upland forests of the southern Lake Superior region are diverse and contain a shifting mosaic of eastern hemlock [Tsuga canadensis (L.) Carr.] and northern hardwood forests dominated by sugar maple (Acer saccharum Marsh.). In this study, we survey the relative effects of management practice (old growth vs. managed), forest cover type (hemlock vs. northern hardwood), and soil great group (Entic Haplorthod vs. Alfic Oxyaquic Fragiorthod) on ion cycling as a precursor to a longer-term, more detailed study. Bulk precipitation, throughfall, and soil leachates at three depths were collected for two growing seasons in eight stands on the Ottawa National Forest in the Upper Peninsula of Michigan. A total of 1210 solutions were analyzed for pH, Na, K, Mg, Ca, Cl, NO3, and SO4. Losses of base cations (Ca, Mg, K) and SO4 from the bottom of the rooting zone generally were greater in old-growth than in managed northern hardwoods on both fragic and nonfragic soils. Leaching losses of base cations and NO3 usually were greater beneath old-growth northern hardwoods than beneath old-growth hemlock on both soil types and for both forest cover types and management practices on fragic than nonfragic soils. Management practice, forest cover type, and soil type all appear to affect ion cycling within these forests. All of the stands featured striking losses of base cations that probably are influenced strongly by NO3 and SO4 in atmospheric deposition.     

Soil testing to predict phosphorus leaching

Subsurface pathways can play an important role in agricultural phosphorus (P) losses that can decrease surface water quality. This study evaluated agronomic and environmental soil tests for predicting P losses in water leaching from undisturbed soils. Intact soil columns were collected for five soil types that a wide range in soil test P. The columns were leached with deionized water, the leachate analyzed for dissolved reactive phosphorus (DRP), and the soils analyzed for water-soluble phosphorus (WSP), 0.01 M CaCl2 P (CaCl2-P), iron-strip phosphorus (FeO-P), and Mehlich-1 and Mehlich-3 extractable P, Al, and Fe. The Mehlich-3 P saturation ratio (M3-PSR) was calculated as the molar ratio of Mehlich-3 extractable P/[Al + Fe]. Leachate DRP was frequently above concentrations associated with eutrophication. For the relationship between DRP in leachate and all of the soil tests used, a change point was determined, below which leachate DRP increased slowly per unit increase in soil test P, and above which leachate DRP increased rapidly. Environmental soil tests (WSP, CaCl2-P, and FeO-P) were slightly better at predicting leachate DRP than agronomic soil tests (Mehlich-1 P, Mehlich-3 P, and the M3-PSR), although the M3-PSR was as good as the environmental soil tests if two outliers were omitted. Our results support the development of Mehlich-3 P and M3-PSR categories for profitable agriculture and environmental protection; however, to most accurately characterize the risk of P loss from soil to water by leaching, soil P testing must be fully integrated with other site properties and P management practices.     

Vegetation stress detection through chlorophyll a + b estimation and fluorescence effects on hyperspectral imagery

Physical principles applied to remote sensing data are key to successfully quantifying vegetation physiological condition from the study of the light interaction with the canopy under observation. We used the fluorescence-reflectance-transmittance (FRT) and PROSPECT leaf models to simulate reflectance as a function of leaf biochemical and fluorescence variables. A series of laboratory measurements of spectral reflectance at leaf and canopy levels and a modeling study were conducted, demonstrating that effects of chlorophyll fluorescence (CF) can be detected by remote sensing. The coupled FRT and PROSPECT model enabled CF and chlorophyll a + b (Ca + b) content to be estimated by inversion. Laboratory measurements of leaf reflectance (r) and transmittance (t) from leaves with constant Ca + b allowed the study of CF effects on specific fluorescence-sensitive indices calculated in the Photosystem I (PS-I) and Photosystem II (PS-II) optical region, such as the curvature index [CUR; (R675.R690)/R2(683)]. Dark-adapted and steady-state fluorescence measurements, such as the ratio of variable to maximal fluorescence (Fv/Fm), steady state maximal fluorescence (F'm), steady state fluorescence (Ft), and the effective quantum yield (delta F/F'm) are accurately estimated by inverting the FRT-PROSPECT model. A double peak in the derivative reflectance (DR) was related to increased CF and Ca + b concentration. These results were consistent with imagery collected with a compact airborne spectrographic imager (CASI) sensor from sites of sugar maple (Acer saccharum Marshall) of high and low stress conditions, showing a double peak on canopy derivative reflectance in the red-edge spectral region. We developed a derivative chlorophyll index (DCI; calculated as D705/D722), a function of the combined effects of CF and Ca + b content, and used it to detect vegetation stress.     

Picloram and napropamide sorption as affected by polymer addition and salt concentration

Polymer application to soil is a growing practice to improve soil physical properties and reduce soil erosion. Polymer addition can potentially influence herbicide and pesticide sorption in soil. The one-point distribution coefficient Kd values of two herbicides in the absence and presence of each of 10 polymers (7 polyacrylamides and 3 polysaccharides) were determined by the batch equilibrium method. The results showed that nonionic napropamide [2-(alpha-naphthoxy)-N,N-diethyl propionamide] sorption was essentially unaffected by the presence of any of the polymers. The influence of polymers on anionic picloram (4-amino-3,5,6-trichloropicolinic acid) sorption depends on the charge characteristics of polymers and salt concentrations in the solution. Electrostatic interaction and competition for sorption sites are two primary underlying mechanisms for the polymer influence. At low salt concentration, the increased picloram sorption in the presence of both cationic and anionic polymers was attributed to different electrostatic interactions and polymer partitioning between soil and solution phases. At high salt levels, the presence of polymers had either no influence or a slightly negative influence on the picloram sorption, which was attributed to competition for sorption sites. In field conditions, it is more likely that polymers have no or a slightly negative influence on herbicide sorption due to the presence of salts.     

Modeling the fate of benzo[a]pyrene in the wastewater-irrigated areas of Tianjin with a fugacity model

A Level III fugacity model was applied to characterize the transfer processes and environmental fate of benzo[a]pyrene in wastewater-irrigated areas of Tianjin, China. The physical-chemical properties and transfer parameters of benzo[a]pyrene were used in the model and the concentration distribution of benzo[a]pyrene in sediment, soil, water, air, fish, and crop compartments, as well as transfer fluxes across the compartments, were then derived under steady-state assumptions. The calculated results were compared with monitoring data for air, soil, water, and sediment collected from the literature. The results indicate that there was generally good agreement and the differences were within an order of magnitude for air, soil, and sediment. The concentration of benzo[a]pyrene in the ambient air in the area was very low with a majority present sorbed to aerosol. In the water compartment, approximately 70% of benzo[a]pyrene dissolved in water phase. Relatively high concentrations of the compound were found in the soil and sediment, with the soil serving as the dominant sink in the area. Benzo[a]pyrene, with a slow metabolic rate, was found to accumulate in fish in the area.     

Fate and efficacy of polyacrylamide applied in furrow irrigation: full-advance and continuous treatments

Polyacrylamide (PAM) is applied to 400000 irrigated hectares annually in the USA to control irrigation-induced erosion, yet the fate of dissolved PAM applied in irrigation water is not well documented. We determined the fate of PAM added to furrow streams under two treatments: Initial-10, 10 mg L(-1) PAM product applied only during the initial hours of the irrigation, and Cont-1, 1.0 mg L(-1) PAM product applied continuously during the entire irrigation. The study measured PAM concentrations in 167-m-long PAM-treated furrow streams and along a 530-m tail ditch that received this runoff. Soil was Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid) with 1.5% slope. Samples were taken at three times during the irrigations, both during and after PAM application. Polyacrylamide was adsorbed to soil and removed from solution as the streams traversed the soil-lined channels. The removal rate increased with stream sediment concentration. Stream sediment concentrations were higher when PAM concentrations were <2 mg L(-1) a.i., for early irrigations, and when untreated tributary flows combined with the stream. In these cases, PAM concentration decreased to undetectable levels over the flow lengths used in this study. When inflows contained >6 mg L(-1) PAM a.i., stream sediment concentrations were minimal and PAM concentrations did not change down the furrow, though they decreased to undetectable levels within 0.5 h after application ceased. One percent of applied PAM was lost in tail-ditch runoff. This loss could have been eliminated by treating only the furrow advance or not treating the last two irrigations.     

Simulating interactive effects of symbiotic nitrogen fixation, carbon dioxide elevation, and climatic change on legume growth

The underlying mechanisms of interaction between the symbiotic nitrogen-fixation process and main physiological processes, such as assimilation, nutrient allocation, and structural growth, as well as effects of nitrogen fixation on plant responses to global change, are important and still open to more investigation. Appropriate models have not been adequately developed. A dynamic ecophysiological model was developed in this study for a legume plant [Glycine max (L.) Merr.] growing in northern China. The model synthesized symbiotic nitrogen fixation and the main physiological processes under variable atmospheric CO2 concentration and climatic conditions, and emphasized the interactive effects of these processes on seasonal biomass dynamics of the plant. Experimental measurements of ecophysiological quantities obtained in a CO2 enrichment experiment on soybean plants, were used to parameterize and validate the model. The results indicated that the model simulated the experiments with reasonable accuracy. The R2 values between simulations and observations are 0.94, 0.95, and 0.86 for total biomass, green biomass, and nodule biomass, respectively. The simulations for various combinations of atmospheric CO2 concentration, precipitation, and temperature, with or without nitrogen fixation, showed that increasing atmospheric CO2 concentration, precipitation, and efficiency of nitrogen fixation all have positive effects on biomass accumulation. On the other hand, an increased temperature induced lower rates of biomass accumulation under semi-arid conditions. In general, factors with positive effects on plant growth tended to promote each other in the simulation range, except the relationship between CO2 concentration and climatic factors. Because of the enhanced water use efficiency with a higher CO2 concentration, more significant effects of CO2 concentration were associated with a worse (dryer and warmer in this study) climate.     

Real-time, high-resolution quantitative measurement of multiple soil gas emissions: selected ion flow tube mass spectrometry

A new technique is presented for the rapid, high-resolution identification and quantification of multiple trace gases above soils, at concentrations down to 0.01 microL L(-1) (10 ppb). The technique, selected ion flow tube mass spectrometry (SIFT-MS), utilizes chemical ionization reagent ions that react with trace gases but not with the major air components (N2, O2, Ar, CO2). This allows the real-time measurement of multiple trace gases without the need for preconcentration, trapping, or chromatographic separation. The technique is demonstrated by monitoring the emission of ammonia and nitric oxide, and the search for volatile organics, above containerized soil samples treated with synthetic cattle urine. In this model system, NH3 emissions peaked after 24 h at 2000 nmol m(-2) s(-1) and integrated to approximately 7% of the urea N applied, while NO emissions peaked about 25 d after urine addition at approximately 140 nmol m(-2) s(-1) and integrated to approximately 10% of the applied urea N. The monitoring of organics along with NH3 and NO was demonstrated in soils treated with synthetic urine, pyridine, and dimethylamine. No emission of volatile nitrogen organics from the urine treatments was observed at levels >0.01% of the applied nitrogen. The SIFT method allows the simultaneous in situ measurement of multiple gas components with a high spatial resolution of < 10 cm and time resolution <20 s. These capabilities allow, for example, identification of emission hotspots, and measurement of localized and rapid variations above agricultural and contaminated soils, as well as integrated emissions over longer periods.     

Three-dimensional nickel ion transport through porous media using magnetic resonance imaging

The transport of Ni2+ ions in a column, filled with porous media, was observed in three dimensions and time by magnetic resonance imaging (MRI) in a clinical scanner. For porous media we used glass beads or quartz sand in a saturated continuous flow mode. The magnetic moment of Ni2+ decreased the T1 relaxation time of 1H in aqueous solution. This concentration-dependent effect was used by a fast low angle shot (FLASH) MRI sequence for imaging the concentration of the dissolved ions. Since Ni2+ behaves as a conservative tracer under the chosen conditions, the tracer motion was representative for the water flow in the porous medium. Currently, we can achieve an isotropic spatial resolution of 1.5 mm and a temporal resolution of 170 s. The transport observation gives direct access to hydraulic flow properties of the porous media. The fluid flow velocity field was calculated by a fronttracking method and the statistical properties of the velocities were investigated. We also compared the experimental data with the three-dimensional particle tracking model PARTRACE, which uses the experimental flow field as input.