Showing papers in "Journal of Environmental Quality in 1998"

The role of phosphorus in the eutrophication of receiving waters: a review

Abstract: Phosphorus (P) is an essential element for all life forms, It is a mineral nutrient Orthophosphate is the only form of P that autotrophs can assimilate Extracellular enzymes hydrolyze organic forms of P to phosphate Eutrophication is the overenrichment of receiving waters with mineral nutrients The results are excessive production of autotrophs, especially algae and cyanobacteria This high productivity leads to high bacterial populations and high respiration rates, leading to hypoxia or anoxia in poorly mixed hottom waters and at night in surface waters during calm, warm conditions Low dissolved oxygen causes the loss of aquatic animals and release of many materials normally hound to hottom sediments including various forms of P This release of P reinforces the eutrophication Excessive concentrations of P is the most common cause of eutrophication in freshwater lakes, reservoirs streams, and headwaters of estuarine systems In the ocean, N becomes the key mineral nutrient controlling primary production Estuaries and continental shelf waters are a transition zone, where excessive P and N create prohlems It is best to measure and regulate total P inputs to whole aquatic ecosystems, but for an easy assay it is hest to measure total P concentrations, induding particulate P, in surface waters or NIP atomic ratios in phytoplankton

Phosphorus loss in agricultural drainage: historical perspective and current research

Abstract: The importance of P originating from agricultural sources to the nonpoint source pollution of surface waters has been an environmental issue for decades because of the well-known role of P in eutrophication. Most previous research and nonpoint source control efforts have emphasized P losses by surface erosion and runoff because of the relative immobility of P in soils. Consequently, P leaching and losses of P via subsurface runoff have rarely heen considered important pathways for the movement of agricultural P to surface waters. However, there are situations where environmentally significant export of P in agricultural drainage has occurred (e.g., deep sandy soils, high organic matter soils, or soils with high soil P concentrations from long-term overfertilization andlor excessive use of organic wastes). In this paper we review research on P leaching and export in subsurface runoff and present overviews of ongoing research in the Atlantic Coastal Plain of the USA (Delaware), the midwestern USA (Indiana), and eastern Canada (Quehec). Our objectives are to illustrate the importance of agricultural drainage to nonpoint source pollution of surface waters and to emphasize the need for soil and water conservation practices that can minimize P losses in suhsurface runoff.

Agricultural Phosphorus and Eutrophication: A Symposium Overview

Abstract: Phosphorus in runoff from agricultural land is an important component of nonpoint-source pollution and can accelerate eutrophication of lakes and streams. Long-term land application of P as fertilizer and animal wastes has resulted in elevated levels of soil P in many locations in the USA. Problems with soils high in P are often aggravated by the proximity of many of these areas to P-sensitive water bodies, such as the Great Lakes, Chesapeake and Delaware Bays, Lake Okeechobee, and the Everglades. This paper provides a brief overview of the issues and options related to management of agricultural P that were discussed at a special symposium titled, “Agricultural Phosphorus and Eutrophication,” held at the November 1996 American Society of Agronomy annual meetings. Topics discussed at the symposium and reviewed here included the role of P in eutrophication; identification of P-sensitive water bodies; P transport mechanisms; chemical forms and fate of P; identification of P source areas; modeling of P transport; water quality criteria; and management of soil and manure P, off-farm P inputs, and P transport processes.

Phytoaccumulation of Trace Elements by Wetland Plants: I. Duckweed

Abstract: There has been much interest recently in the use of constructed wetlands for the removal of toxic trace elements from wastewaters. Wetland plants play an important role in the trace elements removal process. It is not known, however, which wetland plant species absorb specific trace elements at the fastest rates. Such knowledge is essential to maximize the efficiency of trace element removal by wetlands. In this study, we investigated the potential of duckweed (Lemna minor L.) to accumulate Cd, Cr, Cu, Ni, Pb, and Se when supplied individually in a nutrient solution at a series of concentrations ranged from 0.1 to 10 mg L -1 . The results show that under experimental conditions, duckweed proved to be a good accumulator of Cd, Se, and Cu, a moderate accumulator of Cr, and a poor accumulator of Ni and Pb. The highest concentrations of each trace element accumulated in duckweed tissues were 133 g Cd kg -1 , 4.27 g Se kg -1 , 336 g Cu kg -1 , 2.87 g Cr kg -1 , 1.79 g Ni kg -1 , and 0.63 g Pb kg -1 . Duckweed exhibited some symptoms of toxicity (e.g, reduced growth, chlorosis) at higher levels of element supply (except for Cr). The toxicity effect of each trace element on plant growth was, in descending order of damage, Cu > Se > Pb > Cd > Ni > Cr. We conclude that duckweed shows promise for the removal of Cd, Se, and Cu from contaminated wastewater since it accumulates high concentrations of these elements. Further, the growth rates and harvest potential make duckweed a good species for phytoremediation activities.

Hydrologic Controls on Phosphorus Loss from Upland Agricultural Watersheds

Abstract: Development of strategies for controlling P loss from upland agricultural watersheds requires an ability to identify specific source areas of P at field and farm scales, and to predict their resultant effects at the watershed scale. Key to identification of P source areas is defining the interaction between P availability over the landscape and its potential for movement to the watershed outlet by runoff and erosion. A current weakness in quantifying this interaction is determining specific zones of runoff and erosion within a watershed, that is, source areas for the P transport mechanisms. Research results from a series of studies within a small, upland agricultural watershed in east-central Pennsylvania show that the zones of runoff production, and consequently the areas ultimately controlling most P transport, are often a limited and identifiable portion of the landscape. Quantifying the hydrologic controls on P transport within and from a watershed in this way allows us to focus management options on small and definable portions of the total watershed that contribute most P export.

The Science of Composting

Abstract: If moist food scraps are placed in a container and left to sit for a week or two, the end product is likely to be a smelly \" slop \" that attracts flies. Given the proper conditions, these same food scraps can be composted to produce a material that looks and smells like rich soil and can be used to enhance soil texture and productivity. So, what are these conditions that promote composting? The physical and chemical conditions that should be maintained in a compost heap seem logical if you think about what compost really is — a big pile of food for billions of minute organisms. These microorganisms have certain chemical requirements, primarily carbon for energy, nitrogen to build proteins, and oxygen for respiration. Interacting with these are physical requirements, such as aeration to maintain optimal oxygen levels while not depleting the moisture necessary for microbial growth. This chapter begins with an overview of the chemical, physical, and biological changes that occur during thermophilic composting, thereby providing an example of how several sciences can be integrated in the study of composting. This overview is followed by more detailed, separate sections on compost chemistry, physics, and biology. Much of the information in the chemistry and physics sections focuses on thermophilic composting. The biology section includes a discussion of the microbes that are present in all types of composting, and of the diversity of invertebrates that live in outdoor and some worm composting systems. The information presented here reflects the current body of scientific knowledge regarding composting. Much remains unknown, leaving a variety of intriguing questions for future research. Some of these questions are identified as Research Possibilities, sprinkled in italics throughout the text. We hope they will provide the inspiration for students to ask a much wider range of questions, and to design their own original research.

Regulation of Organic Matter Decomposition and Nutrient Release in a Wetland Soil

Abstract: In wetland soils, the supply of O 2 to soil is greatly reduced; thus, alternate electron acceptors must be utilized by the microbial populations during decomposition of organic matter. These changes in the supply of electron acceptors affect the size of microbial populations, enzyme production, and decomposition of organic matter. A laboratory study was conducted to determine the role of redox potential (Eh) and availability of electron acceptors on selected microbial processes regulating organic matter decomposition and nutrient release. Soil Eh was maintained approximately at 620, 310, -100, and -220 mV, with the addition of O 2 , NO 3 , SO 2- 4 , and HCO 3 , respectively. The soil microbial biomass, as determined by fumigation-extraction methods, gradually decreased as soils became more reduced. Microbial biomass C ranged from 354 to 10 100 mg C kg 1 soil (dw), while microbial biomass N and P ranged from 140 to 439 mg N kg -1 soil (dw), and 64 to 180 mg P kg -1 soil (dw), respectively, Organic C, N, and P mineralization rates decreased as soils became more reduced. Organic C mineralization rates measured by CO 2 production ranged from 51 to 400 mg C kg -1 (dw) d -1 . Corresponding values of organic N and P mineralization rates ranged from 21 to 150 mg N kg -1 (dw) d ', and 6 to 107 mg P kg ' (dw) d - ', respectively. Significant relationships (P < 0.01) were observed among the soil enzyme activities, microbial biomass, and the mineralization rates of C, N, and P.

Preferential transport of phosphorus in drained grassland soils

Abstract: Phosphorus is the limiting factor for primary production in most freshwater ecosystems. In many areas, diffuse P losses from intensively cultivated land cause severe eutrophication of surface waters. We investigated the P export from two drainage systems under intensively used grassland in a catchment of the Swiss Plateau. Flow rate and nutrient concentrations were measured with a high temporal resolution during discharge events. During most flow peaks, P concentrations strongly increased with increasing flow rates. Concentrations of soluble-reactive P (SRP) reached up to 155 μmol L -1 . Phosphorus was mainly transported as soluble-reactive and particulate P. Organic P compounds, as well as P associated with colloids between 0.05 and 0.45 μm in effective diameter, were of minor importance. Estimated P loads from the drainage systems were 227 g SRP ha -1 within a period of 2.5 mo at site I and 1290 g ha -1 during 6 mo at site II. Estimation uncertainty was large (±21 and ±36% for the two sites, respectively) due to the weak correlation between discharge and concentration for all data from a given site. Water-extractable P in the soil was concentrated in the uppermost layer of the profiles or, for short periods after spreading of manure, deposited on the vegetation. The discharge-concentration relationship indicated that P was transported through preferential flow paths extending from close to the surface to the drains. Sprinkling experiments with a blue dye confirmed this conclusion. At one site, we observed preferential flow in a downhill direction within the saturated zone.

Fluxes of Carbon Dioxide, Nitrous Oxide, and Methane in Grass Sod and Winter Wheat‐Fallow Tillage Management

Abstract: Cropping and tillage management can increase atmospheric CO{sub 2}, N{sub 2}O, and CH{sub 4} concentrations, and contribute to global warming and destruction of the ozone layer. Fluxes of these gases in vented surface chambers, and water-filled pore space (WFPS) and temperature of surface soil were measured weekly from a long-term winter wheat (Triticum aestivum L.)-fallow rotation system under chemical and mechanical tillage follow management and compared with those from native grass sod at Sidney, NE, from March 1993 to July 1995. Cropping, tillage, within-field location, time of year, soil temperature, and WFPS influenced net greenhouse gas fluxes. Mean annual interrow CO{sub 2} emissions from wheat-fallow ranged from 6.0 to 20.1 kg C ha{sup {minus}1} d{sup {minus}1} and generally increased with intensity and degree of tillage. Nitrous oxide flux averaged autumn > winter. Winter periods accounted for 4 to 10% and 3 to 47% of the annual CO{sub 2} and N{sub 2}O flux, respectively, and 12 to 21% of the annual CH{sub 4} uptake. Fluxes of CO{sub 2} and N{sub 2}O, and CH{sub 4} uptake increased linearly with soil temperature. No-till fallow exhibited the least threat to deterioration of atmospheric or soil quality as reflected by greater CH{sub 4} uptake, decreased N{sub 2}O and CO{sub w} emissions, and less loss of soil organic C than tilled soils. However, potential for increased C sequestration in this wheat-fallow system is limited due to reduced C input from intermittent cropping.« less

Constrained Optimization of Spatial Sampling using Continuous Simulated Annealing

Abstract: Spatial sampling is an important issue in environmental studies because the sample configuration influences both costs and effectiveness of a survey. Practical sampling constraints and available pre-information can help to optimize the sampling scheme. In this paper, spatial simulated annealing (SSA) is presented as a method to optimize spatial environmental sampling schemes. Sampling schemes are optimized at the point-level, taking into account sampling constraints and preliminary observations. Two optimization criteria have been used. The first optimizes even spreading of the points over a region, whereas the second optimizes variogram estimation using a proposed criterion from the literature. For several examples it is shown that SSA is superior to conventional methods of designing sampling schemes. Improvements up to 30% occur for the first criterion, and an almost complete solution is found for the second criterion. Spatial simulated annealing is especially useful in studies with many sampling constraints. It is flexible in implementing additional, quantitative criteria.

Decreasing Metal Runoff from Poultry Litter with Aluminum Sulfate

Abstract: Aluminum sulfate [Al 2 (SO 4 ) 3 - 14H 2 O] applications to poultry litter can greatly reduce P concentrations in runoff from fields fertilized with poultry litter, as well as decrease NH 3 volatilization. The objective of this study was to evaluate metal runoff from plots fertilized with varying rates of alum-treated and untreated (normal) poultry litter. Alum-treated (10% alum by weight) and untreated litter was broadcast applied to small plots in tall fescue (Festuca arundinacea Schreb.). Litter application rates were 0, 2.24, 4.49, 6.73, and 8.98 Mg ha -1 (0, 1, 2, 3, and 4 tons acre -1 ). Rainfall simulators were used to produce two runoff events, immediately after litter application and 7 d later. Both concentrations and loads of water-soluble metals increased linearly with litter application rates, regardless of litter type. Alum treatment reduced concentrations of As, Cu, Fe, and Zn, relative to untreated litter, whereas it increased Ca and Mg. Copper concentrations in runoff water from untreated litter were extremely high (up to 1 mg Cu L), indicating a potential water quality problem. Soluble Al, K, and Na concentrations were not significantly affected by the type of litter. Reductions in trace metal runoff due to alum appeared to be related to the concentration of soluble organic C (SOC), as well as the affinity of SOC for trace metals. Metal runoff from alum-treated litter is less likely to cause environmental problems than untreated litter, since threats to the aquatic environment by Ca and Mg are far less than those posed by As, Cu, and Zn.

Agricultural phosphorus and water quality: a U.S. Environmental Protection Agency perspective

Abstract: Pollution of lakes, rivers, and estuaries from agricultural sources of P is a major water quality problem in the USA. This paper explains the regulatory and nonregulatory programs developed by the U.S. Environmental Protection Agency (USEPA) to implement its legal mandate to control water pollution from these sources. The Clean Water Act defines concentrated animal feeding operations as point sources of pollution that are required to obtain permits to discharge into waters of the USA. All other agricultural sources are considered nonpoint and are not regulated under federal law. The USEPA provides grant money to the states to develop and implement nonpoint source programs. The Coastal Zone Act Reauthorization Amendments of 1990 requires coastal states to adopt nonpoint management measures that are backed by enforceable policies and mechanisms. For water bodies that continue to be impaired despite the basic implementation of these laws and other programs, states are required to develop a total maximum daily load (TMDL). The TMDL process is the quantitative basis for reaching water quality standards. The USEPA is putting a new emphasis on controlling nutrient pollution sources to meet the goal of the Clean Water Act.

Responses of Soil Respiration to Clipping and Grazing in a Tallgrass Prairie

Abstract: Soil-surface CO 2 flux (F,) is an important component in prairie C budgets. Although grazing is common in grasslands, its effects on F s have not been well documented. Three clipping treatments: (i) early-season clipping (EC); (ii) full-season clipping (FC); and (iii) no clipping (NC); which represented two grazing strategies and a control, were applied to plots in a tallgrass prairie in northeastern Kansas, USA. Measurements of F s were made with a portable gas-exchange system at weekly to monthly intervals for 1 yr. Concurrent measurements of soil temperature and volumetric soil water content at 0.1 m were obtained with dual-probe heat-capacity sensors. Measurements of F, also were obtained in grazed pastures. F, ranged annually from 8.8 x 10 -3 mg m -2 s -1 during the winter to 0.51 mg m -2 s -1 during the summer, following the patterns of soil temperature and canopy growth and phenology. Clipping typically reduced F s 21 to 49% by the second day after clipping despite higher soil temperatures in clipped plots. Cumulative annual F s were 4.94, 4.04, and 4.11 kg m -2 yr - 1 in NC, EC, and FC treatments, respectively; thus, dipping reduced annual F s by 17.5%. Differences in F s between EC and FC were minimal, suggesting that different grazing strategies had little additional impact on annual F,. Daily F s in grazed pastures was 20 to 37% less than F, in ungrazed pastures. Results suggest that grazing moderates F, during the growing season by reducing canopy photosynthesis and slowing translocation of carbon to the rhizosphere.

Nitrous oxide emission in three years as affected by tillage, corn-soybean-alfalfa rotations, and nitrogen fertilization

Abstract: Nitrous oxide (N 2 O) produced from agricultural activities must be determined if management procedures to reduce emissions are to be established. From 1994 to 1996, N 2 O emissions were determined using a closed chamber technique. Continuous corn (Zea mays L.) at four N rates of 0, 170, 285, and 400 kg of N ha -1 was used on a Ste. Rosalie heavy clay (a very-fine-silty, mixed, nonacid, frigid Typic Humaquept) and a Chicot sandy loam (a fine-loamy, frigid, Typic Hapludalf). On two additional sites, a Ste. Rosalie clay and an Ormstown silty clay loam (a fine-silty, mixed, nonacid, frigid Humaquept) no-till (NT) and conventional tillage (CT); monocultural corn (CCC), monocultural soybean (Glycine max L.) (SSS); corn-soybean (SSC, CCS); and soybean-corn-alfalfa (Medicago sativa L.) phased rotations (SAC, CSA, and ACS) were used. Nitrogen rates of 0, 90, and 180 kg of N ha ' for corn and 0, 20, and 40 kg of N ha -1 for SSS were used. Rates of N 2 O emission were measured from April to November in 1994 and 1995, and from mid-March to mid-November in 1996. Maximum N 2 O emissions reached from 120 to 450 ng of N m -2 s -1 at the Ormstown site to 50 to 240 ng of N m -2 s -1 at the Ste. Rosalie soil. Generally, N 2 O emissions were higher in the NT systems, with corn, and increased linearly with increasing N rates, and amounted to 1.0 to 1.6% of fertilizer N applied. The N 2 O emission rates were significantly related to soil denitrification rates, water-filled pore space, and soil NH 4 and NO 3 concentrations, A corn system using conventional tillage, legumes in rotation, and reduced N fertilizer would decrease N 2 O emission from agricultural fields.

Greenhouse evaluation of agronomic and crude oil-phytoremediation potential among Alfalfa genotypes

Abstract: Phytoremediation is an effective, non-intrusive, and inexpensive means of remediating soils contaminated with organic chemicals. Different plant species have different remediation capabilities, so intra-species variation may also exist. If intraspecific variation exists and is heritable, population improvement for performance in and phytoremediation of contaminated soils should be possible. The objectives of this study were (i) to determine if variability exists among alfalfa (Medicago sativa L.) genotypes for agronomic performance in and phytoremediation of crude oil-contaminated soil and (ii) to determine the effect of contaminated soil on the agronomic performance of alfalfa. In one greenhouse experiment, 20 genotypic clones were transplanted into 20 g kg -1 crude oil-contaminated soil. After 1 yr, differences existed among genotypes for total forage yield (P < 0.05), maturity at harvest (P < 0.001), plant height (P < 0.01), and phytoremediation potential (P < 0.001). Degradation rates ranged from 33 to 56% among genotypes with 46% for the unvegetated control. Two genotypes had significantly greater degradation rates than that of the unvegetated control. In a second greenhouse experiment, eight genotypes from the previous experiment were compared with their clones in uncontaminated soil. After 1 yr, mean total forage yield in contaminated soil was 32% of the yield of the same clones in uncontaminated soil. Plants in contaminated soil also matured later and were shorter. Genotype variability was present for all traits but not on all evaluation dates. The results indicate that overall agronomic performance is reduced in contaminated soil, but variability exists among genotypes for growth in and phytoremediation of contaminated soils.

Forms and concentration of phosphorus in drainage water of twenty-seven tile-drained soils

Abstract: In most mineral soils, P leaching is rarely viewed as an important environmental issue. However, P accumulation and decreased P sorption capacities in surface horizons of long-term fertilized soils may increase downward P movement. The objective of this study was to measure the concentration and characterize the P forms in drainage waters from nine soil series widely differing in clay content. Twenty-seven sites were sampled in 1994 and 1995 from an intensively cropped area of the province of Quebec, Canada. Drainage waters were characterized for their total P (TP), dissolved reactive P (DRP), dissolved organic P (DOP), and total particulate P (TPP) contents. The Quebec surface water quality standard of 0.03 mg TP L¹ was exceeded in 14 out of 27 sites in 1994 but only in 6 out of 25 sites in 1995. Of the 14 sites exceeding 0.03 mg TP L⁻¹ in 1994, 10 were clayey soils. Under these circumstances, more than 50% of the TP was as TPP whereas DOP forms represented <30%. In 1995, TPP forms accounted for, on average, <50% of TP and DOP accounted for more than 40% of the TP concentrations. This study suggests that flat clayey soils of medium to rich P status may be particularly at risk of exceeding water quality standards in subsurface runoff. Phosphorus losses in particulate form may be important in subsurface runoff from clayey soils when weather conditions favor rapid flow through cracks or macropores. Contribution of the Soils and Crops Research Centre no. 565.

Comparison of Four USEPA Digestion Methods for Trace Metal Analysis Using Certified and Florida Soils

Abstract: It is critical to compare existing sample digestion methods for evaluating soil contamination and remediation. USEPA Methods 3050, 3051, 3051a, and 3052 were used to digest standard reference materials and representative Florida surface soils. Fifteen trace metals (Ag, As, Ba, Be, Cd, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se, and Za), and six macro elements (Al, Ca, Fe, K, Mg, and P) were analyzed. Precise analysis was achieved for all elements except for Cd, Mo, Se, and Sb in NIST SRMs 2704 and 2709 by USEPA Methods 3050 and 3051, and for all elements except for As, Mo, Sb, and Se in NIST SRM 2711 by USEPA Method 3052. No significant differences were observed for the three NIST SRMs between the microwave-assisted USEPA Methods 3051 and 3051A and the conventional USEPA Method 3050 Methods 3051 and 3051a and the conventional USEPA Method 3050 except for Hg, Sb, and Se. USEPA Method 3051a provided comparable values for NIST SRMs certified using USEPA Method 3050. However, for method correlation coefficients and elemental recoveries in 40 Florida surface soils, USEPA Method 3051a was an overall better alternative for Method 3050 than was Method 3051. Among the four digestion methods, the microwave-assistedmore » USEPA Method 3052 achieved satisfactory recoveries for all elements except As and Mg using NIST SRM 2711. This total-total digestion method provided greater recoveries for 12 elements Ag, Be, Cr, Fe, K, Mn, Mo, Ni, Pb, Sb, Se, and Zn, but lower recoveries for Mg in Florida soils than did the total-recoverable digestion methods.« less

Phosphorus Flux between Sediment and Overlying Water in Lake Okeechobee, Florida: Spatial and Temporal Variations

Abstract: Total P is increasing over time in the waters of Lake Okeechobee, Florida, but the concentrations do not correlate with external loads. The objectives of this study were to determine: (i) the P flux from various sediment types within the lake, (ii) the factors that control direction and magnitude of P flux, and (iii) the amount of P associated with various inorganic P phases within the sediment. Phosphorus flux was measured from intact sediment cores taken from eight sites that represent major sediment types and major inflows of Lake Okeechobee at four time periods in 1989–1990. At the same location-times, dissolved reactive phosphorus (DRP) in porewater was determined using porewater equilibrators and/or sediment cores. Results indicate that P flux from sediments is very sensitive to changes in O₂ status of the overlying water, with anaerobic conditions promoting large P fluxes. Despite steep porewater DRP gradients in sediments (varying from 0.1 mg P L⁻¹ at the sediment/water interface to more than 1 mg P L⁻¹ at lower depths), P flux was not regulated by such gradients. Such lack of dependence of P flux on DRP gradients highlights the role redox reactions (involving Fe) can play in P chemistry in the top few centimeters of the sediment. Internal P loads (i.e., flux from bottom sediments) were found to be approximately equivalent to external P loads (≈1 mg P m⁻² d⁻¹). Contribution from the Univ. of Florida.

Nitrate Removal from Groundwater Using a Denitrification Wall Amended with Sawdust: Field Trial

Abstract: Nitrate (NO 3 ) contamination of groundwater can cause pollution of receiving waters. We examined the mechanisms by which a denitrification wall removed NO 3 from shallow groundwater. The denitrification wall was constructed by digging a trench (35 m long, 1.5 m deep, and 1.5 m wide) that intercepted groundwater. The excavated soil was mixed with sawdust (30% v/v) as a C source then returned to the trench. We assessed NO 3 removal and denitrification in the wall for 1 yr. Incoming concentrations of NO 3 in groundwater ranged from 5 to 16 mg of N L -1 but these decreased to <2 mg N L -1 in the denitrification wall. Total N in the wall declined during the year demonstrating that N immobilization was not a large sink for NO 3 . Denitrifying enzyme activity (DEA) reached a maximum of 906 ng of N g -1 h -1 after 6 mo of operation, indicating that denitrification was an important mechanism for NO 3 removal. We calculated a maximum rate of NO 3 removal by denitrification of 3.6 g N m -3 d -1 . Substrate-amendment experiments showed that denitrification in the wall was primarily limited by NO 3 concentration and not C. During the study there was no significant decrease (P < 0.05) in total C but the availability of the remaining C declined. Despite this decrease, the DEA and microbial biomass were stable during the last 6 mo. This study demonstrated that denitrification walls can effectively remove NO 3 from groundwater thereby protecting receiving waters.

Phosphorus sorption capacities of wetland soils and stream sediments impacted by dairy effluent

Abstract: The ability of stream sediments and adjacent wetlands to retain added P depends on the P sorption capacity and physico-chemical properties of sediments or wetland soils. The objectives of this study were to: (i) determine the potential P sorption capacities of wetland soils and stream sediments in systems with distinctly different P loadings. and (ii) establish the relationship between P sorption capacity and selected physico-chemical properties. Batch sorption isotherms were measured under aerobic and anaerobic conditions for sediments and wetland soils along a stream-wetland-upland continuum at two sites in the Lower Kissimmee River Basin and Taylor Creek/Nubbin slough of the Okeechobee Basin, Florida. Soluble P and equilibrium P concentrations (EPC) of stream sediments generally decreased along the wetland-upland continuum. The EPC values were about twofold greater under anaerobic conditions than aerobic conditions; however, P sorption capacities decreased by about 35% under anaerobic conditions compared with aerobic conditions. The P sorption maxima, estimated by a single point isotherm measured at an added P level of 1000 mg P kg ', correlated well with Langmuir adsorptive maxima. Phosphorus retention by stream sediments and wetland soils was strongly correlated with contents of amorphous and poorly crystalline forms of Fe and Al, which explained 87% of the variability in P retention maximum. Addition of total organic C to predictive equations improved the predictability by only 5%.

Plant Genetic Approaches to Phosphorus Management in Agricultural Production

Abstract: Much of the P in corn (Zea mays I,.) grain is present in the form of phytic acid. Phytic acid P is unavailable to monogastric animals with most heing excreted in the waste. As a result, the substantial P stores in grain are essentially wasted and may contribute to water pollution rather than animal productivity. The initial goal of this research was to isolate chemically induced mutants with reduced levels of phytic acid P in corn. Such mutants, referred to as low phytic acid or lpa, were isolated and were found to have little or no other effect on kernel composition including no effect on total grain P content. The first mutant characterized, lpal-1, contains a 65% reduction in phytic acid and is accompanied hy a molar-equivalent increase in inorganic P. This mutant was backcrossed into elite corn inbred lines and resulting hybrids were evaluated for yield and other important agronomic traits. Preliminary field trials indicated germination, stalk strength, grain moisture at harvest, and flowering date were not affected by lpal-1. Some, but not all. lpa1-1 hyhrids had yield reductions. In a preliminary chick feeding trial, the low phytic acid grain resulted in greater P availability and reduced P content in the waste. Altering the phytic acid content genetically in corn is possible and may have the potential to improve feeding efficiencies and reduce P released to the environment.

Fractionation and Distribution of Arsenic in Soils Contaminated by Cattle Dip

Abstract: Soils surrounding cattle dips in Australia are known to be highly contaminated with As and are potentially of major concern to the environment and human health. A study of 11 dip sites in northern New South Wales (NSW) has revealed considerable surface soil (0-10 cm) contamination with As (37-3542 mg As kg -1 soil). In addition it was shown that considerable movement of As down through the soils had occurred with concentrations at 20 to 40 cm ranging from 57 to 2282 mg As kg -1 soil. At one particular site, an As concentration of above 14 000 mg As kg -1 soil was determined at a depth of 40 to 45 cm. A sequential fractionation scheme, based on a soil P fractionation, was developed to assess the chemical nature, and thus the potential bioavailability and mobility of As at the sites. Soil As is separated into six fractions with (i) anion exchange resin, (ii) NaHCO 3 , (iii) NaOH, (iv) NaOH following sonication, (v) HCl, and (vi) HCl/HNO 3 . Although substantial differences between sites and soil depths were present, some general trends were apparent. Most sites contained substantial concentrations of As in the two most labile fractions, indicating high potential for phytotoxicity and leaching. The bulk of the contaminant As at the sites seemed to be associated with soil amorphous Fe and Al minerals.

Phytoremediation of a Radiocesium-Contaminated Soil: Evaluation of Cesium-137 Bioaccumulation in the Shoots of Three Plant Species

Abstract: A field study was conducted to investigate the potential of three plant species for phytoremediation of a 137 Cs-contaminated site. Approximately 40-fold more 137 Cs was removed from the contaminated soil in shoots of red root pigweed (Amaranthus retroflexus L.) than in those of Indian mustard [Brassica juncea (L.) Czern] and tepary bean (Phaseolus acutifolius A. Gray). The greater potential for 137 Cs removal from the soil by A. retroflexus was associated with both high concentration of 137 Cs in shoots and high shoot biomass production. Approximately 3% of the total 137 Cs was removed from the top 15 cm of the soil (which contained most of the soil radiocesium) in shoots of 3-mo-old A. retroflexus plants. Soil leaching tests conducted with 0.1 and 0.5 M NH 4 NO 3 solutions eluted as much as 15 and 19%, respectively, of the soil 137 Cs. Addition of NH 4 NO 3 to the soil, however, had no positive effect on 137 Cs accumulation in shoots in any of the species investigated. It is proposed that either NH 4 NO 3 solution quickly percolated through the soil before interacting at specific 137 Cs binding sites or radiocesium mobilized by NH 4 NO 3 application moved below the rhizosphere, becoming unavailable for root uptake. Further research is required to optimize the phytotransfer of the NH 4 NO 3 -mobilized 137 Cs. With two croppings of A. retroflexus per year and a sustained rate of extraction, phytoremediation of this 137 Cs-contaminated soil appears feasible in <15 yr.

Effect of soil solution chloride on cadmium availability to Swiss chard

Abstract: Potted soil experiments were conducted to analyze how higher Cl concentrations in soil enhance Cd uptake by plants. Two soils (W,L) were moistened with complete nutrient solution containing either NaCI or NaNO 3 at concentrations ranging from 0 to 120 mmol L -1 . Swiss chard (Beta vulgaris L., cv. Fordhook Giant) was grown in the soils until the 4th leaf appeared (15 d on soil W, 20 d on soil L). Plant dry weights generally decreased with increasing salt concentration, but were not significantly affected by the type of Na salt. For both soils, shoot Cd concentrations in the 120 mmol L -1 NaCl treatment almost doubled those in the zero salt treatments. In contrast, increasing NaNO 3 concentrations either reduced shoot Cd concentration (soil L) or had no effect (soil W). Increasing concentrations of NaCI in the soil solution significantly increased the Cd concentration in solution from 65 to 400 nmol L ' (soil W) and from 64 to 300 nmol L ' (soil L). Increasing concentrations of NaNO 3 in solution had no effect on Cd concentrations in solution. Speciation calculations predicted that the solution concentration of the free metal ion Cd 2+ was not significantly affected by the NaCl (both soils) or NaNO 3 (soil L) treatments. In soil W, the predicted Cd 2+ concentrations in soil solution slightly decreased with increasing NaNO, rate. It is concluded that the enhancing effect of NaCl on Cd uptake is due to chloride complexation of Cd.

Patchiness in Microbial Nitrogen Transformations in Groundwater in a Riparian Forest

Abstract: We measured microbial N transformations in 15 cm diam. by 40 cm intact horizontal sections of aquifer material (mesocosms), taken from a riparian forest in Rhode Island, USA, incubated under ambient conditions. The mesocosms allowed us to measure these transformations on the same scale as hydrologic tracer methods (Br - /NO 3 - ratios) that measure net NO 3 - removal. Our objective was to reconcile discrepancies between hydrologic tracer and microbial measurements in previous studies where laboratory-based microbial NO 3 - consumption measurements were much lower than in situ hydrologic measurements of net NO 3 - removal. We hypothesized that small patches of organic matter in the aquifer matrix, which are easily missed when sampling for microbial measurements, are hotspots of NO 3 - removal and are responsible for these discrepancies. Mesocosms were subjected to three treatments [Br - only, Br - + 15 NO 3 - , Br - + 15 NO 3 - + dissolved organic carbon (DOC)]. Solution (NH 4 + , NO 3 - , dissolved organic N) and gaseous (N 2 O, 15 N 2 O, and 15 N 2 ) inputs and outputs to the mesocosms were measured over a 132-d incubation, followed by destructive sampling for the presence of patches and residual 15 N in aquifer matrix and patch material. Total (gross) NO 3 - consumption by denitrification and immobilization was greater than net removal of NO 3 - measured by Br/NO 3 - ratios. Net NO 3 - , consumption was only observed in mesocosms that contained patches of organic matter and was not increased by addition of DOC, suggesting that these patches, which represent <1% of aquifer weight, are critical to groundwater NO 3 - removal in riparian forests.

The phytoavailability of cadmium to lettuce in long-term biosolids-amended soils

Abstract: A field study was conducted to assess the phytoavailability of Cd in long-term biosolids-amended plots managed at high and low pH. The experiment, established 13 to 15 yr prior to the present cropping, on a Christiana fine sandy loam soil (a clayey, kaolinitic, mesic Typic Paleudult) used a variety of biosolids. Two of the biosolids had total Cd concentrations of 13.4 and 210 mg kg 1 . A Cd salt treatment, with Cd added to soil at a rate equivalent to the Cd added by the higher Cd biosolids applied at 100 Mg ha ', was also included. The lettuce (Lactuca saliva var. longifolia) cultivar (Paris Island Cos) used in the initial study was also used in the current study. Lettuce Cd was compared between treatments, and in relation to the soil Cd/soil organic C (OC) ratio. There has been no significant increase in plant Cd since the initial cropping. With 16% of the biosolids added OC remaining, lettuce grown on the soil amended with the more contaminated biosolids was not different than that of the initial cropping. Further, significantly less Cd was taken up by lettuce grown on biosolids-amended soil than lettuce grown on soil amended with equivalent rates of Cd salt. The Cd concentration in lettuce grown in the low Cd biosolids treatment was not different from the control. These results indicate that the potential hazards associated with food chain transfer of biosolids-applied Cd are substantially lower than equivalent Cd salt treatments, and that the hazards do not increase over time.

Effect of Polyaromatic Hydrocarbons in Soil on Arbuscular Mycorrhizal Plants

Abstract: The rhizosphere of plants plays a role in the bioremediation of soils polluted with organic pollutants such as polyaromatic hydrocarbons (PAHs). Arbuscular mycorrhizal (AM) fungi provide a direct link hetween soil and plant roots, but very little is known of the interactions hetween PAHs and AM fungi. We studied the effect of PAHs on mycorrhizal colonization in polluted soil, and the effect of AM fungi on plant growth in these soils. Leek (Allium porrum L.), maize (Zea mays L.), ryegrass (Lolium perenne L.), and clover (Trifolium subterraneum L.) were grown in pots containing a soil artificially contaminated with increasing concentrations of anthracene or mixed with an industrial soil polluted with PAHs. Mycorrhizal colonization by the indigenous AM population of the nonpolluted soil was not significantly affected by the addition of anthracene up to 10 g kg -1 . However, mycorrhizal colonization of clover and leek decreased when the industrial soil was added to the nonpolluted soil, while maize and ryegrass colonization was not affected. The effect of PAHs on plant survival and growth depended on plant species. Inoculation of ryegrass with Glomus mosseae improved plant survival and plant growth in the industrially polluted soil. At 5 g of PAH kg -1 only mycorrhizal plants survived. Mycorrhizal fungi may contribute to the establishment and maintenance of plants in PAH-polluted soils.

Greenhouse gas fluxes following tillage and wetting in a wheat-fallow cropping system

Abstract: Little is known about the relative contributions of episodic tillage and precipitation events to annual greenhouse gas emissions from soil. Consequently, the authors measured carbon dioxide (CO{sub 2}), nitrous oxide (N{sub 2}O), and methane (CH{sub 4}) fluxes from soil in a wheat-fallow cropping system in western Nebraska using vented surface chambers, before and immediately after tillage and wetting with 5.1 cm of water, during the fallow period in 1995/1996. Replicated fallow management treatments included no-tillage, subtillage, and plow representing a wide range in degree of soil disturbance. Soil bulk density, water-filled pore space, electrical conductivity (EC{sub 1:1}), nitrate (NO{sub 3}), and pH within the top 30.5 cm soil, and soil temperature at 0 to 7.6 cm were measured to assess their correlation with variations in gas flux and tillage and wetting. Atmospheric concentrations above the soil (at {approximately} 40 cm) increased by 15% for CO{sub 2} and 9 to 31% for N{sub 2}O and 6 to 16% for CH{sub 4} within 1 min after tillage and returned to background concentrations within 2 h. Except immediately after tillage, net CH{sub 4} flux was negative, from the atmosphere into soil, and is referred to as CH{sub 4} uptake. Overall, increases (1.5--4-fold) inmore » CO{sub 2} and N{sub 2}O losses from soil, and CH{sub 4} uptake by soil were short lived and returned to background levels within 8 to 24 h after tillage. Losses of CO{sub 2} and N{sub 2}O increased to 1.7 and 5 times background emissions, respectively, for 24 h following wetting, while CH{sub 4} uptake declined by about 60% for 3 to 14 d after wetting. Water-filled pore space in the surface soil fell below 60% within 24 h after saturation and exhibited an inverse relationship (R{sup 2} = 0.66) with CH{sub 4} uptake. A significant decline in soil NO{sub 3} and EC{sub 1:1} in the top 7.6 cm occurred following wetting. Under the experimental conditions, and the expected frequency of tillage and wetting events, failure to include these short-lived episodic gas pulses in annual flux estimations may underestimate annual CO{sub 2} and N{sub 2}O loss up to 13 and 24%, respectively, and overestimate CH{sub 4} uptake by up to 18% in this cropping system.« less