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.     

Acrylamide monomer leaching from polyacrylamide-treated irrigation furrows

Water-soluble anionic polyacrylamide (WSPAM), which is used to reduce erosion in furrow irrigated fields and other agriculture applications, contains less than 0.05% acrylamide monomer (AMD). Acrylamide monomer, a potent neurotoxicant and suspected carcinogen, is readily dissolved and transported in flowing water. The study quantified AMD leaching losses from a WSPAM-treated corn (Zea mays L.) field using continuous extraction-walled percolation samplers buried at 1.2 m depth. The samplers were placed 30 and 150 m from the inflow source along a 180-m-long corn field. The field was furrow irrigated using WSPAM at the rate of 10 mg L(-1) during furrow advance. Percolation water and furrow inflows were monitored for AMD during and after three furrow irrigations. The samples were analyzed for AMD using a gas chromatograph equipped with an electron-capture detector. Furrow inflows contained an average AMD concentration of 5.5 microg L(-1). The AMD in percolation water samples never exceeded the minimum detection limit and the de facto potable water standard of 0.5 microg L(-1). The risk that ground water beneath these WSPAM-treated furrow irrigated soils will be contaminated with AMD appears minimal.     

Biochar and manure affect calcareous soil and corn silage nutrient concentrations and uptake

Carbon-rich biochar derived from the pyrolysis of biomass can sequester atmospheric CO, mitigate climate change, and potentially increase crop productivity. However, research is needed to confirm the suitability and sustainability of biochar application to different soils. To an irrigated calcareous soil, we applied stockpiled dairy manure (42 Mg ha dry wt) and hardwood-derived biochar (22.4 Mg ha), singly and in combination with manure, along with a control, yielding four treatments. Nitrogen fertilizer was applied when needed (based on preseason soil test N and crop requirements) in all plots and years, with N mineralized from added manure included in this determination. Available soil nutrients (NH-N; NO-N; Olsen P; and diethylenetriaminepentaacetic acid-extractable K, Mg, Na, Cu, Mn, Zn, and Fe), total C (TC), total N (TN), total organic C (TOC), and pH were evaluated annually, and silage corn nutrient concentration, yield, and uptake were measured over two growing seasons. Biochar treatment resulted in a 1.5-fold increase in available soil Mn and a 1.4-fold increase in TC and TOC, whereas manure produced a 1.2- to 1.7-fold increase in available nutrients (except Fe), compared with controls. In 2009 biochar increased corn silage B concentration but produced no yield increase; in 2010 biochar decreased corn silage TN (33%), S (7%) concentrations, and yield (36%) relative to controls. Manure produced a 1.3-fold increase in corn silage Cu, Mn, S, Mg, K, and TN concentrations and yield compared with the control in 2010. The combined biochar-manure effects were not synergistic except in the case of available soil Mn. In these calcareous soils, biochar did not alter pH or availability of P and cations, as is typically observed for acidic soils. If the second year results are representative, they suggest that biochar applications to calcareous soils may lead to reduced N availability, requiring additional soil N inputs to maintain yield targets.     

Solute response to changing nutrient loads in soil and walled ceramic cup samplers under continuous extraction

This report evaluates a vacuum-assisted walled percolation sampler preconditioned in soil, and examines the dynamic response of leachate solutes. The 20-cm walled percolation sampler extracted soil water under continuous tension via a ceramic cup collector embedded in a silica flour layer, whose upper surface interfaced with field soil. In the laboratory, alternating solutions with high and low NO3-N (232 or 3.6 mg L(-1)), molybdate-reactive P (MRP) (1.75 or 0.0 mg L(-1)), K+ (568 or 3.6 mg L(-1)), and Br- (9.6 or 0.0 mg L(-1)) concentrations were delivered directly to the (i) sampler ceramic cup; (ii) silica flour bed surface, or (iii) 12-mm soil layer placed over the silica flour bed. For alternating input solutions delivered to the silica-flour bed surface, (i) solute breakthrough (95% equivalency) occurred in 4 pore volumes and was the same for both the high and low concentration input phases of the application, and (ii) concentrations of NO3-N, Br-, and MRP in cumulative extracted water volumes were within 5% of those in corresponding input volumes. Alternating nutrient loads from high to low levels in the fixed flow rate input waters caused excess MRP (1.6 times that in the high concentration MRP solution) to leach from the calcareous soil. The dynamic character of P transport in K-fertilized soils deserves further study and may have important environmental implications.     

Mercury measurement and control in a CO2-enriched flue gas

Oxycombustion is being considered as a promising solution to carbon capture and sequestration. Standard sampling and measurement methods may or may not be valid under oxycombustion conditions because the flue gas differs significantly from that of conventional air-blown coal combustion.Bench-scale tests were conducted to evaluate the measurement validity of continuous mercury monitors (CMMs), with and without a flue gas preconditioning unit, in a simulated oxycombustion flue gas with varied CO₂ concentrations. Tests also included mercury capture with activated carbon in typical oxyfuel combustion flue gas. Research data indicated that highly concentrated CO₂ streams affect the accuracy of the mass flow rate and the subsequent gaseous mercury measurement, although this is specific to the type of CMM. Concentrated CO₂ streams also induced solid precipitation in the wet-chemistry conversion unit and resulted in a biased measurement of the gas-phase mercury. Flue gas dilution appeared to provide accurate measurement of total gas-phase mercury and be applicable to mercury measurement in highly concentrated CO₂ streams, although mercury speciation appeared to be problematic and will require additional modification and validation. Mercury capture with activated carbon under CO₂-enriched conditions showed similar performance to typical high-acid coal combustion flue gas.     

Water Quality Trading with Lumpy Investments,Credit Stacking,and Ancillary Benefits

This paper studies the economics of a water quality trading market in a predominantly agricultural watershed, and explores the effects of credit stacking in such a market when buyers and sellers of pollution credits can only reduce pollution with large, discrete investments that yield discontinuous supply and demand. The research simulates hypothetical water quality trading markets in the corn‐belt area of Illinois, where wastewater treatment plants (WWTPs) can pay farmers to reduce nutrients by installing wetlands and farmers may or may not be allowed to earn payments for multiple services from one wetland. We find that wetlands are a more cost‐effective way to mitigate nitrogen pollution than abatement by WWTPs. Stacking credits may improve social welfare while providing more ecosystem services if there is enough demand for the primary credit in the market (nitrogen) to cover most of the cost of installing the wetland but the supply of nitrogen credits is not exhausted. However, in the presence of lumpy pollution reduction activities, the effects of allowing stacked credit sales are idiosyncratic and not necessarily positive; stacked payments may or may not satisfy additionality. The results imply that credit trading for nitrogen is likely to make society better off, but the effects of allowing farmers to receive multiple payments from a single wetland depend on details of the situation.     

Biochar: a synthesis of its agronomic impact beyond carbon sequestration

Biochar has been heralded as an amendment to revitalize degraded soils, improve soil carbon sequestration, increase agronomic productivity, and enter into future carbon trading markets. However, scientific and economic technicalties may limit the ability of biochar to consistently deliver on these expectations. Past research has demonstrated that biochar is part of the black carbon continuum with variable properties due to the net result of production (e.g., feedstock and pyrolysis conditions) and postproduction factors (storage or activation). Therefore, biochar is not a single entity but rather spans a wide range of black carbon forms. Biochar is black carbon, but not all black carbon is biochar. Agronomic benefits arising from biochar additions to degraded soils have been emphasized, but negligible and negative agronomic effects have also been reported. Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences. Hardwood biochar (black carbon) produced by traditional methods (kilns or soil pits) possessed the most consistent yield increases when added to soils. The universality of this conclusion requires further evaluation due to the highly skewed feedstock preferences within existing studies. With global population expanding while the amount of arable land remains limited, restoring soil quality to nonproductive soils could be key to meeting future global food production, food security, and energy supplies; biochar may play a role in this endeavor. Biochar economics are often marginally viable and are tightly tied to the assumed duration of agronomic benefits. Further research is needed to determine the conditions under which biochar can provide economic and agronomic benefits and to elucidate the fundamental mechanisms responsible for these benefits.     

Role of cold resistance and burial for winter survival and spring initiation of an Ulva spp. (Chlorophyta) bloom in a eutrophic lagoon (Veerse Meer lagoon, The Netherlands)

In the eutrophic Veerse Meer lagoon (The Netherlands) large amounts of free-floating thalli from Ulva spp. are present from May to October. In winter however, no algae seem to occur in the lagoon. Sexual reproduction appears to be negligible, as spore formation and germling growth are observed only sporadically. Results of a field survey showed that in winter, viable Ulva biomass is present buried in the sediment of the shallow parts of the lagoon. Freezing experiments demonstrated that the algae are able to survive temperatures of −5 °C for 2 weeks when kept in darkness. In spring, the buried Ulva thalli are liberated out of the sediment to initiate a bloom. A field experiment indicates that bioturbation by the lugworm Arenicola marina does not stimulate the release of the thalli. Burial and winter survival can explain the rapid increase in Ulva biomass in spring and suggest that the initial spring biomass is one of the major factors determining the maximal biomass in summer. Received: 28 October 1997 / Accepted: 20 January 1998