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Mobility, bioavailability, and fate of metals in environmental systems depend on the chemical forms (speciation) of the metal in the solid phase. Aware of the inherent limitations of wet chemical extraction methods for speciation determination, D'Amore et al. (1707–1745) provide a broad survey of the potential physical instrumental methods of analysis derived from the fields of analytical chemistry, materials science, geology, and physics. We have examined the literature from the perspective of applications that have already been applied to soils, geologic materials, or complex solids, both organic and inorganic (with emphasis on the latter). Lastly, we have included information derived from studies of several techniques and give both broad and specific recommendations for further study of those techniques that offer the greatest promise. We note that since our interest involved determining lead species in soils, results presented will seem overly biased toward it. This emphasis on lead has no other implication.
Plants Respond to Dominant Factor
Additive or multiplicative models of crop response on which salinity management theory rely may cause errors in the compensative interaction among salinity and other growth factors. Shani et al. (1455–1460) present results from studies of biomass production and transpiration of corn, melon, tomato, onion, and date palms under salinity combined with water or nitrate (growth promoters) or with boron (growth inhibitor). In our measurements, the crops responded to the more severe stress rather than to combinations of various stresses. Shifting management of saline water to a dominant factor approach would reduce environmental contamination and conserve water resources.
Can Hog Diet Affect Manure Emissions?
Control of emissions such as odor and greenhouse gas from swine manure is of environmental and economic importance to the pig industry. Emissions control can often be achieved by altering the pigs' diet, because the feed directly affects the chemistry of the excreted manure. Clark et al. (1461–1466) measured emissions from manure excreted by pigs fed diets with different levels of protein and various kinds of nonstarch polysaccharides, compounds that pass relatively intact through a pig's digestive tract. Manure odor was found not to be affected by the different diets. Manure emissions of carbon dioxide and methane increased when the pigs were fed less protein, a surprising result that invites further investigation. The other feed additives also had varied effects on manure greenhouse gas emissions.
Tillage–Fertilizer Interactions Control Greenhouse Gases
Some studies have suggested that practicing reduced-tillage agriculture could have a favorable impact on atmospheric concentrations of greenhouse gases by promoting the storage of soil carbon and reducing soil CO2 emissions. However, the effects of reduced tillage on soil emissions of the potent greenhouse gases nitrous oxide (N2O) and methane (CH4) must also be considered. Venterea et al. (1467–1477) found that reduced tillage practiced over 12 yr resulted in either increased or decreased N2O + CH4 emissions, depending on fertilizer practices. Using gas flux chambers in corn–soybean rotations in Minnesota, they also found that emissions of these non-CO2 greenhouse gases represented a sizable component of the total ecosystem greenhouse gas budget. This study demonstrates that changes in soil carbon alone do not necessarily represent the net impact of reduced-tillage agriculture on greenhouse gases in the atmosphere.
Plants That Take Up Radioactivity
Quantifying the differences between plant species in radionuclide uptake is useful for predicting food chain contamination and for selecting plants for remediation or monitoring of radionuclides. Willey et al. (1478–1489) show that, after differences in soil availability have been taken into account, a new classification scheme for flowering plants can be used to make predictions of cesium uptake by plants. Of the 273 plant taxa in their dataset, plants in the Caryophyllales (which include the beets, buckwheat, rhubarb, and carnations) tended to have the highest cesium uptake while plants in the Poales (which include cereals, grasses, sedges, and rushes) tended to have the lowest Cs uptake.
Phytoremediation of TNT-Contaminated Soil
TNT (2,4,6-trinitrotoluene) is a toxic and persistent chemical in the environment. Ouyang et al. (1490–1496) applied the CTSPAC model to investigate removing TNT from soil using a poplar tree by simulating temporal variations of xylem water potential, root water uptake, and soil TNT bioavailability. No TNT was found in the stem and leaves, and only about 1% of total TNT mass was observed in the roots because the TNT biodegraded rapidly and transformed into its daughter products. Soil TNT bioavailability decreased with time and approached a constant of 3.1 x 10–6 in 14 d. This study suggests that CTSPAC is a useful model to simulate phytoremediation of TNT-contaminated sites.
Biogeochemistry of Benzothiazole
Benzothiazole (BT) is a natural and industrial chemical found in water and sediments. The transformation of BT was examined in fine, intermediate, and coarse-grained estuarine sediments maintained in micro- and mesocosms un-der simulated environmental conditions: drained (oxidized), flooded (reduced), and tidal (alternately oxidized and reduced). Catallo and Junk (1746–1754) found that BT was transformed in all sediments under all conditions, yielding mixtures of degradation products (phenol, aniline, N-methylaniline) and suites of higher molecular weight compounds (anilo-BT, bis-BT). Benzothiazole degradation was fastest in stirred microcosms under oxidized conditions, intermediate in drained and tidal mesocosms, and slowest under reduced conditions in all sediments. Benzothiazole degradation apparently is surface-enhanced, with increased rates of transformation observed as total particle surface area increased. Physical turbation (stirring and tidal pulsing) was the most significant variable affecting BT transformation rate. Another important variable was sediment grain size (inversely proportional to surface area), which affected BT transformation most significantly under oxidized conditions, with transformation rates increasing with increasing surface area.
Plants Remediate Polycyclic Aromatic Hydrocarbons
Contamination of soil by hazardous substances poses a significant threat to human, environmental, and ecological health. Phytoremediation is defined as using plants to clean up contaminated sites. Spriggs et al. (1755–1762) report that in greenhouse studies with intact soil cores, acenaphthene, anthracene, fluoranthene, naphthalene, and phenanthrene decreased significantly in ash and poplar phytoremediation treatments compared to unplanted soil. Increases in PAH microbial degraders in rhizosphere soil were observed in treated soils but not unvegetated soil. These results support the hypothesis that a variety of plants can enhance the degradation of target PAHs in soil.
Iron(II) Inhibits Uranium Remobilization
Microbial reduction of U(VI) into sparingly soluble U(IV) precipitates has been proposed as a technique to immobilize U(VI) in ground water. The oxidative remobilization of biogenic U(IV) precipitates is a major concern of such immobilization technology when ground water returns to oxic conditions. Zhong et al. (1763–1771) demonstrated that the rate and extent of oxidative remobilization of biogenic U(IV) precipitates in presence of O2 could be inhibited by manipulating Fe(II) concentration and pH. The formation of Fe(III) oxides from oxidative precipitation of Fe(II) provided a barrier that strongly sorbed U(VI) and retarded U(VI) release to aqueous phase after U(IV) oxidation.
Radioactive Nickel and Cadmium Migrated into Vegetables after Wet Aerial Contamination
Sprinkling vegetable beds with contaminated water can introduce contaminants into the human food chain through radionuclide retention and translocation to vegetables. Fismes et al. (1497–1507) report that the chemical–physical characteristics of 63Ni and 109Cd seemed to be the most important factors affecting their fate in plants, while plant species and method of contamination played a secondary role in radionuclide retention and distribution. Nickel-63, an essential micronutrient, can be transported away from the point of contamination, mainly to developing organs (young leaves, fruits, and sink organs) after leaf contamination, whereas 109Cd translocation declined strongly with distance from the contamination source. No radioactivity was found in fruits following foliar contamination. When contamination was chronic, corresponding to both early and late contamination, radionuclide translocation declined, underlining the importance of plant metabolism in translocation processes.
Transgenic Maize Has Higher Lignin Contents than Corresponding Near-Isogenic Lines
Lignin patterns in stems and leaves of two genetically modified Bt maize varieties (Novelis T and Valmont T) were studied along with their non-Bt near-isolines (Nobilis and Prelude, respectively) by molecular-level based thermochemolysis using tetramethylammonium hydroxide (TMAH) in combination with gas chromatography–mass spectroscopy (GC–MS). Poerschmann et al. (1508–1518) found that the stems of the transgenic lines had higher concentrations of total lignin than the respective isogenic lines. The guaiacyl units accounted chiefly for the higher total lignin contents in the transgenic lines. Further work should explain if higher lignin content in transgenic crops is beneficial due to improved structure and (lignin mediated) higher recalcitrance of soil or harmful due to the lignin-mediated preservation of the toxin in soil.
Nitrate Leaching after Bark Beetle Attack
During the past decade, bark beetles killed nearly all of the Norway spruce stands in the unmanaged zone in the highlands of the Bavarian Forest National Park, Germany. Huber (1772–1779) reports that NO–3 concentrations in seepage water in these stands were significantly elevated in the first 5 yr after the dieback compared to intact stands. Nitrate concentrations increased from 27 µmolc L–1 (intact stand) to 579 µmolc L–1 (fifth year after die-back). The high rates of precipitation caused dilution of NO–3, and concentrations remained mostly below the critical level for drinking water (Europe). Part of the observed heterogeneity in NO–3 concentrations could be attributed to different patterns of ground vegetation coverage.
Herbicides Monitored by Photosynthetic Biosensor
For several decades, the contamination of water resources by herbicides has been of general concern since it affects drinking water quality and impacts nontarget organisms and crop safety. Because a large amount of herbicides are applied to agricultural land, their behavior in the soil is of critical importance. Mal
et al. (1780–1788) examined the persistence and movement of a urea-type herbicide, isoproturon, in soil using a new herbicide-monitoring device, the prototype of a portable electrochemical biosensor. Detection is based on inhibiting electron transport activity through the Photosystem II complex by the herbicide under illumination. This assay was effective in determining isoproturon concentration to as low as 10–7 M. The biosensor can give preliminary information about the biological activity of isoproturon in hours, which is an advantage over analytical methods determining the content of compounds.
Microbial Response to Heavy Metal Pollution
Heavy metal pollution of soil, for which the soil microbial community should be a sensitive indicator, is of concern for human health and ecosystem function. In 1998, a mining acid–metal spill in a watershed in southwestern Spain occurred, and in 2003, microbial communities of polluted, reclaimed, and unpolluted soils were studied at this site. Hinojosa et al. (1789–1800) determined the functional microbial diversity using fatty acid (FA) biomarkers and found that Cu, Cd, and Zn, as well as soil pH, were the most important pollution factors affecting microbial communities. An FA stress marker was significantly lower for reclaimed and polluted soil than for nonpolluted soils, and beneficial fungi were suppressed by heavy metals. Two FA extraction methods were tested, and the ester-linked fatty acids (ELFA) method has potential for routine ecological monitoring and risk assessment because of its simplicity and reproducibility.
North Carolina's Farmers Impacted by Phosphorus Indexing Tool
State and federal laws now require consideration of phosphorus in nutrient management plans. North Carolina has developed a site-specific P indexing system called the Phosphorus Loss Assessment Tool (PLAT) to predict potential P loss from agricultural fields. Johnson et al. (1801–1810) report that approximately 8% of producers in the state will be required to apply animal waste based on phosphorus rather than on nitrogen, with the percentage increasing for farmers applying animal waste (approximately 27%). Predicted loss of P from soluble pathways was higher than other loss pathways, including erosion. Sandy soils of the Coastal Plain region and sites receiving poultry waste had the greatest risk for P loss.
Stress-Tolerant Plants Restore Minelands
Proper selection of plant species is critical for the successful establishment and long-term maintenance of vegetation on reclaimed surface mined soils. Evanylo et al. (1811–1819) found that switchgrass, sericea lespedeza, reed canarygrass, tall fescue, and crownvetch were most suitable for long-term revegetation of mineland amended with biosolids as a source of organic matter and essential plant nutrients. These species shared the physiological and reproductive characteristics of low fertility requirements, drought and moisture tolerance, and propagation by rhizome and/or stolons. Two of these species, tall fescue and sericea lespedeza, are or have been commonly seeded on Appalachian coal surface mines and often dominate abandoned pasture sites. No detrimental effects of the heavy metals in the biosolids on plant growth or quality occurred.
Water Treatment Residuals: Don't Waste This Stuff!
The accumulation of excess soil P concentrations has been linked to increases in dissolved phosphorus concentrations in surface water systems. Novak and Watts (1820–1827) tested an alum-based water treatment residual (WTR) incorporated into three sandy soils with high P concentrations to see if it could significantly reduce deionized water and Mehlich-3 (plant available P) extractable forms. Between 0 and 6% WTR was mixed into the soils and laboratory-incubated for 84 d. Incorporating 6% WTR into the three soils reduced Mehlich 3 and deionized P extractable P concentration by as much as 40 and 91%, respectively. Reductions in deionized water-extractable P were higher than Mehlich 3, suggesting that alum-based WTRs are particularly effective at reducing water-soluble P concentrations. Applying alum-based WTR as part of a manure nutrient management plan is a novel chemical-based best management strategy to reduce off-site P transport into water bodies.
Nitrate Moves from Waste Fields to Surface Water
A rapidly increasing swine population and an associated potential for nitrate pollution of surface waters led the state of North Carolina to adopt stringent waste management regulations in 1993. Movement of nitrate from fields managed under these regulations needed assessment. Israel et al. (1828–1842) conducted a 36-mo ground water monitoring study on a swine farm managed under the strict waste management regulations. Nitrogen-15 natural abundance measurements showed that some nitrate derived from swine effluent applied to fields had reached an adjacent stream within 4 yr of initiating waste application. However, absolute nitrate concentrations in the stream were relatively low, averaging 1.0 mg L–1. Dilution of high nitrate water in shallow horizontal flow paths with low nitrate water from deeper horizontal flow paths at or near the stream and some denitrification as ground water discharges through the stream bottom and in the riparian zone contribute to the low nitrate concentration in the stream. This information can be factored into assessments of the effectiveness of current waste management regulations in protecting surface water quality by state regulatory agencies.
Metals in Tissues of Shrews
Because they have a higher metabolic rate and different diet than rodents, shrews should accumulate higher amounts of toxic metals, especially in contaminated areas. 
wiergosz-Kowalewska et al. (1519–1529) report that accumulation of metals (cadmium, lead, copper, and zinc) by insectivores (Sorex araneus and Sorex minutus) is high; shrews accumulated much higher amounts of cadmium and lead than bank voles from the same areas. Comparisons between species show clearly that insectivores accumulate more of those metals, which are not homeostatically regulated. The expected high tissue accumulation of copper at a copper-contaminated area and zinc at a zinc-contaminated area did not occur. The highest cadmium and lead concentrations were found in the tissues of shrews from zinc-contaminated area. Some significant correlations were found between the tissue concentrations of xenobiotic and essential metals (e.g., between cadmium and zinc and between lead and iron).
Sludge Application Did Not Increase Cadmium Sorption
Trace metals applied to arable land in sludge are of concern because of the potential risks of contaminating the food chain. Hypothetically, solution concentrations of toxic trace metals will not increase to harmful levels because of adsorptive inorganic material such as iron and aluminium oxides that are also supplied with sludge. This protection effect has been observed in many experiments. However, Bergkvist et al. (1530–1538) found that cadmium solubility and sorption in long-term sludge-amended soil was unaltered compared to a control treatment, even though the topsoil concentrations of presumed important adsorptive phases (iron and aluminium oxides, soil organic matter) had significantly increased. The reason for this was not established, but it may have been due to competition for sorption sites with sludge-borne iron or zinc.
Reduction of Copper(II) by Iron(II)
Interactions between iron and copper in soil environments are not clearly understood. Matocha et al. (1539–1546) report that divalent copper was reduced rapidly by ferrous iron in laboratory experiments simulating anoxic soil conditions. One resulting product of the reaction, Cu(I), was stabilized in solution at high chloride levels and precipitated as cuprite (Cu2O) at lower chloride concentrations.
Recovery of Biosolids-Applied Trace Metals
Long-term immobilization of biosolids-derived soil metals has been challenged when mass balance application at a number of sites failed to account for a large portion of the applied metals. Sukkariyah et al. (1843–1850) examined the fate of Cu, Ni, and Zn in a highly weathered Davidson clay loam soil in controlled lateral flow field plots. Seventeen years after a single application of biosolids containing high concentrations of Cu and Zn, the biosolids-applied trace metals were primarily concentrated in the Ap horizon (0–15 cm) with slight enrichment down to 0.3 m. No movement below that depth was detected. Almost 90% of the applied Cu, Ni, and Zn were recovered in the top 25 cm. Biosolids application increased trace metals in all soil fractions with most Cu, Zn, and Ni associated with metal oxides. The authors conclude that most of the applied metals are fixed in the zone of incorporation, and there is a little risk of downward movement and contamination of ground water at this site and for soil with similar conditions and management history.
Agricultural Impacts on Stream Hydrology
Agricultural tillage influences runoff and infiltration, but consequent effects on watershed hydrology are poorly documented. Tomer et al. (1547–1558) evaluated 25-yr (1971–1995) stream records from four first-order watersheds in Iowa's loess hills. Two watersheds were under conventional tillage, and two were under conservation (ridge) tillage, one of which was terraced. Ridge tillage reduced surface runoff by 47% but increased baseflow (fed by ground water) by 36% and amplified its seasonal-ity. Therefore, this conservation practice could increase the amount and the seasonality of subsurface movement of pollutants. However, conservation practices stabilized stream flow: ridge-tilled watersheds had the greatest amount and the least variability in total stream discharge and showed faster recovery of baseflow after drought.
Fire and Grazing Affect Soil
Selective grazing of burned patches may compound the independent effects of fire and grazing on soil characteristics. Vermeire et al. (1559–1565) report that wind erosion was affected by whether and when a site was burned. More wind erosion occurred on autumn-burned sites than nonburned sites during the dormant season. Growing-season erosion of nonburned sites was half that of spring-burned sites both years, but growing-season erosion was similar to autumn-burned site erosion when spring growing conditions were favorable. Soil water content was unaffected by patch burn treatments, but at mid-day, soils of burned sites were 1 to 3°C warmer than nonburned sites. Lower water holding capacity of sandy soils probably moderated effects on soil water content and soil temperature.
Surface Runoff Water Quality in a Managed Three Zone Riparian Buffer
Both grass buffers and forest buffers are increasingly used as in conservation to control nonpoint-source pollution in agriculture. Lowrance and Sheridan (1851–1859) report that nitrogen and phosphorus were consistently removed from surface runoff in a managed riparian buffer in the southeastern Coastal Plain. Cutting the managed forest is possible without negatively affecting water quality as long as the permanent forest along the stream is not cut. All nutrient loads decreased significantly within the average buffer, but not all concentrations decreased. Concentrations of nitrogen did not change significantly within the buffer. Concentrations of phosphorus decreased significantly, and chloride increased significantly. The largest percent reduction of the incoming nutrient load took place in the grass buffer zone because of the large decrease in flow in that buffer. The grass buffer removed most of the incoming load. The managed forest and grass buffer combined was an effective buffer system.
Fumigant Degradation in Forest Soils
Fumigation is a means of controlling weeds and soil-borne plant pathogens, particularly in southern U.S. forest nurseries. Enhanced degradation of agrochemicals with repeated applications has been reported in agricultural soils. Zhang et al. (1566–1572) investigated potential degradation enhancement in forest nursery soils. They found that degradation rates of the tested fumigants were related to nursery fumigation history, application rates, and freshness of tested forest soils. Overall, there was no significant difference in degradation rates of fumigated and nonfumigated forest soils, suggesting that enhanced degradation is not as prevalent as in agricultural soils.
Urease is Unaffected by Diazinon and Imidacloprid
Insecticides and urea N are often co-applied to high-quality turfgrass. How does that affect urease activity in soil? Ingram et al. (1573–1580) found that commercial rates of diazinon and imidacloprid applied to soil and sod had little effect on urease activity. They looked at whether these commercial insecticides inhibited or increased urease activity in pure enzymes, urease-producing bacteria, soil slurries, and creeping bent grass or bluegrass sod. Imidacloprid never affected urease activity. Diazinon briefly reduced urease activity in whole cells and soil slurries, but diazinon only reduced urease activity for about 1 d in sod. Co-applying these insecticides along with urea N in commercial lawn care practice should have no adverse effects on N availability.
Surroundings of Moscow are Not Very Contaminated by PAHs
Little is known of the fate of polycyclic aromatic hydrocarbons (PAHs) in soils outside the western world, such as in the Russian Taiga. Wilcke et al. (1581–1590) found that PAH concentrations along a southeast-bound transect from Moscow (south Taiga) were comparatively low and dominated by the low molecular weight compounds naphthalene and phenanthrene, which indicate background PAH patterns. Moscow was, indeed, a source of PAHs as shown by decreasing PAH concentrations with increasing distance from the city. Comparing archived samples from the early 20th century with recent ones revealed that in the last century, total PAH concentrations in soil increased in urban soils while remaining little changed in soils outside Moscow, although high molecular weight PAHs were higher in recent samples than in archived samples because of traffic emissions. The study confirmed that PAHs accumulate at the surface of soil macroaggregates, where biological activity is elevated in many soils. The PAH concentrations in the exterior as opposed to the interior parts of aggregates also did not change in the last century, suggesting that the ecological impact of PAHs has not greatly changed over the last 100 yr.
Sewage Particles in a Recipient Stream
The implementation of wastewater treatment plants (WWTP) has dramatically increased the quality of surface waters in urbanized areas. Yet WWTPs can still discharge noticeable amounts of solutes and particles to recipient streams. Rauter et al. (1591–1599) showed that sewage-derived organic particles are deposited onto the streambed and are thus retained within a relatively short reach of the recipient stream. Once deposited, sewage-derived organic particles contribute to the streambed metabolism but seemingly do not clog the streambed interface. These results emphasize the capacity of a recipient stream to retain sewage-derived organic particles and to reduce their downstream export.
Mixing Layer Affects Phosphorus Release
Phosphorus concentrations usually are higher near the surface of the soil. Release of phosphorus to runoff water depends on the water flow path and degree of interaction with the surface soil. Sánchez and Boll (1600–1609) report that phosphorus release was highest when water traversed the surface soil in the upward direction and by flow parallel to the surface soil. The release of phosphorus was higher at 25°C than at 6°C. Thus, to determine the phosphorus concentration in runoff and interflow, it is important to know how different water flow paths in and over the soil interact with phosphorus in the soil, and if this interaction occurs during winter or summer.
Heavy Metals in Urban Runoff Primarily Associated with Coarse Silt Particles
Heavy metals and organic pollutants in streams and rivers lead to impairment of aquatic life. Runoff from urban areas can dramatically increase loads of these pollutants. Transport and toxicity of pollutants in rivers is, in part, determined by binding to aquatic particles. Morrison and Benoit (1610–1619) investigated aspects of metal binding to colloids and suspended sediment during a winter storm event in an urban river. Large increases in copper and lead concentrations during the storm event were mostly associated with coarse silt particles. Urban runoff data highlighted the importance of colloids and fine clay particles to the speciation of metals and organic carbon. Results showed the type of information gained by using separation techniques and particle size classes other than conventional 0.45-µm membrane separation into dissolved and particulate fractions.
Residue and Manure Influence Phosphorus Losses
Phosphorus (P) in runoff from agricultural lands contributes to degrading surface water quality. Grande et al. (1620–1631) report the effects of residue cover, achieved by high-cutting silage, and manure application timing on P losses from 3-m2 plots that were subjected to 76 mm h–1 (1 h) of simulated rainfall. Dissolved reactive phosphorus (DRP) and total phosphorus (TP) losses were inversely related to percent residue cover. Recently applied dairy manure significantly increased the DRP concentration in runoff; however, the DRP load was unaffected by manure application. Spring-applied manure reduced TP loads by 77 to 90% over plots with no manure but increased the TP concentration of clay-sized sediments by 79 to 125%. By itself, the higher residue cover was often insufficient to reduce P losses; however, the combination of manure application and higher residue levels significantly reduced P losses from corn fields harvested for silage.
Biosolids Characteristics Impact Phosphorus Pollution
Land application of biosolids on agricultural land is a common practice for improving soil fertility but may also contribute to phosphorus (P) runoff pollution of surface waters. Rainfall simulation studies are used to compare runoff P potential of different biosolids. Elliott et al. (1632–1639) report that surface application of many biosolids contributes little P to runoff because the biosolids have been treated by chemical additions and drying processes that reduce the water solubility of their P. Some biosolids, however, contribute significant P to runoff waters. Accurate prediction of P loss from biosolids-amended soils using site assessment indices should include a weighting factor that reflects the relative solubility of the P in the nutrient source.
Soil Phosphorus Levels Affect Runoff
Phosphorus (P) in runoff from agricultural soils accelerates eutrophication in lakes and streams and degrades surface water quality. Davis et al. (1640–1650) report that concentrations of dissolved P in runoff were highly related to Mehlich-3 P, water-soluble P, and different P saturation indexes for the Richfield, Dennis, and Kirkland soil series. However, significant differences existed between the slopes of these relationships, indicating the relationships are soil specific and phosphorus management decisions should consider soil characteristics.
Managing Buffers Optimizes Nitrogen Sequestration
High levels of soluble N observed leaving vegetative buffers contribute to concern that buffer efficiency may decrease over time and that buffers will ultimately become a source of N (and other nutrients) rather than a sink. Bedard-Haughn et al. (1651–1664) examined the effects of regular cutting on veg-etative buffer uptake of NO–3–15N. Over the irrigation season, cut buffers sequestered 2.3 times the 15N of uncut buffers, corresponding to an increase in aboveground biomass and N uptake following cutting. In contrast, the uncut buffers showed very little change in 15N sequestration or biomass, suggesting senescence and a corresponding decrease in N demand. Overall, cutting significantly improved 15N attenuation from both surface and subsurface water. However, the dominant influence on runoff water quality from irrigated pasture remains irrigation rate. Reducing the typical rate by 75% resulted in a 50% decrease in total runoff losses and a sevenfold decrease in 15N concentration.
Development of Bacteria and Benthic TMDLs
The total maximum daily load (TMDL) program is an integrated watershed management approach required by the Clean Water Act. Benham et al. (1860–1872) describe the procedures used by the Center for TMDL and Watershed Studies at Virginia Polytechnic Institute to develop the Linville Creek TMDLs and discuss the key lessons learned from and the ramifications of the procedures used in these and other similar TMDL studies. Two TMDL studies were performed for Linville Creek in Rockingham County, VA, to address bacterial and benthic impairments. Extreme reductions in multiple sources of bacteria are required to meet Virginia's bacteria water quality standards; these extreme reductions are commonly found in bacteria TMDLs in Virginia. Given that many potential benthic community stressors (e.g., nutrient, toxics, organics) are either transported by or associated with sediment, it is not surprising that sediment was identified as the primary stressor for benthic impairment in Linville Creek. Despite the drawbacks associated with using watershed-scale models like Hydrological Simulation Program—Fortran (HSPF) and Generalized Watershed Loading Function model (GWLF) to develop TMDLs, the detailed watershed and pollutant-source characterization required to use these and similar models creates information that stakeholders need to select appropriate corrective measures to address the cause of the water quality impairment when implementing the TMDL.
Atrazine Losses Differ between Neighboring Catchments
Avoiding application of herbicide to fields prone to runoff is a promising mitigation option for reducing herbicide contamination of surface waters. Leu et al. (1873–1882) quantified the differences in atrazine loads from three neighboring agricultural catchments. Despite similar weather conditions, the atrazine losses from the catchments varied from 0.6 to 3.5% of the applied amounts. The connectivity of the fields to streams and the hydrological soil properties were identified as determinants of herbicide losses, although they could not fully explain the differences. The results suggest that herbicide loading could be substantially reduced by avoiding herbicide application on high-risk areas. The maximum concentrations, however, could be minimized by proper handling of spraying equipment, thus diminishing farmyard losses.
Manure Incorporation Reduces Nutrient Losses
Although incorporation of manure is recommended to minimize nutrient losses, few studies have examined differences among incorporation methods. Little et al. (1883–1895) report that all manure incorporation methods reduced surface losses of nitrogen and phosphorus compared with an unincorporated control, but there was little difference between the most common methods: the heavy-duty cultivator and double-disk. Incorporation method had no effect on subsurface phosphorus concentrations; however, subsurface nitrogen concentrations were highest after the moldboard plow tillage treatment. Overall, tillage with a cultivator or double disk immediately after annual manure application appears to minimize surface and subsurface nutrient losses.
Alternative De-Icer Found
Road salting has adversely affected ground water quality in both Finland and several other countries. Hellstén et al. (1665–1671) report that when potassium formate was applied as an alternative deicer, formate was effectively degraded in the unsaturated zone of a sandy aquifer during cold periods. Its application did not cause major undesirable changes in the quality of the percolating water. During the study period, 99% of the applied potassium was retained in the lysimeter. The ion exchange between the potassium and a variety of monovalent and divalent ions may be responsible for the leaching of barium, calcium, magnesium, and sodium from the soil material. Except for manganese, the concentrations of the studied metals in the percolated water did not exceed the threshold values set for drinking water by the Council of the European Union. Further research at field scale is, however, needed on the biodegradation of potassium formate and on its impact on roadside vegetation.
Environmental Impacts of Manure Application
Concentrating cattle in large feedlots generates large amounts of manure, which can be challenging and expensive to handle and can degrade surface and ground water quality. Feedlots may dispose of manure by applying it to nearby fields at high rates, rather than spreading it over more land for more efficient use of the nutrients that it contains. Ferguson et al. (1672–1681) investigated the impact of annual high rates of manure application to silt loam soil over a decade in irrigated corn silage production. They found that careful monitoring of nutrient accumulations in soil, with manure rates adjusted accordingly, helped minimize nitrate accumulation, as did the use of a winter cover crop. Phosphorus levels, however, tended to increase with high manure rates to the point that water runoff could degrade surface water quality. While several years of applying high rates of manure may be acceptable for this soil–crop combination if carefully monitored, using manure nutrients more efficiently by increasing the land area for application is preferable.
Gypsum Reduced Soluble Soil Phosphorus
Applications of animal manures have increased soil test P values in many parts of the United States, and thus increased the risk that soil P will be transferred to surface water and decrease water quality. To continue farming in these areas, landowners need tools to reduce the risk of P moving off agricultural land. Brauer et al. (1682–1686) found that gypsum applications of 5000 pounds per acre were most effective in reducing soil test values for P, whereas a soil amendment made from waste paper was ineffective. These results indicate that amending soils with gypsum can reduce the likelihood that P from soils with high test values will be transferred to streams and lake and decrease their water quality.
Drilling Fluids Impact Soil Properties
Drilling fluids (mud) are necessary for drilling oil and gas wells. After the well is completed, waste drilling fluid is often applied to cropland. Bauder et al. (1687–1696) found that drilling fluids applied to wheat fields in Colorado can increase soil pH, salinity as measured by electrical conductivity and sodium adsorption ratio, and certain trace metals. However, these parameters did not increase to levels harmful to soil quality or crop production at four sites, where drilling fluid had been applied at rates up to 94 Mg ha–1 per year. These results support land application of water-based bentonitic drilling fluids as an acceptable practice on well-drained soils using controlled rates.
Broiler Litter is a Good Source of Micronutrients
Most of the litter produced by the chicken industry in the United States is land-applied as a fertilizer to meet the nitrogen and phosphorus needs of crops. Tewolde et al. (1697–1706) suggest the value of litter as a source of trace minerals is not as appreciated and investigated as is its value as a source of nitrogen and phosphorus. Poultry litter, which is a mixture of manure, bedding material, and spilled feed and water, contains nearly all trace elements essential for plant growth, but the extent of availability of these elements for plant absorption is not well understood. In this research, tissue analysis of the concentration of iron, copper, zinc, and manganese, all of which are essential plant nutrients, showed that broiler chicken litter supplies adequate amounts of iron, copper, and manganese to cotton plants grown in a greenhouse. However, cotton did not receive enough zinc from litter, probably because zinc was not efficiently absorbed by cotton roots. The results of this research also showed that more than 90% of the micronutrients applied with the litter are not removed by cotton and have the potential to accumulate if litter is used as the primary cotton fertilizer.
Phytase Reduces Broiler Litter Phosphorus
Regions of intensive broiler production have some of the most serious problems with nonpoint phosphorus (P) pollution because farm-gate nutrient surpluses often result in overapplication of broiler litter P to soils. McGrath et al. (1896–1909) report that broiler diet modification using phytase and reduced non-phytate P supplements proved effective in reducing litter P concentrations. Furthermore, efforts to minimize litter moisture content during storage effectively minimized P losses in runoff from litter-amended soil. Sequential chemical fractionation and 31P nuclear magnetic resonance (NMR) confirmed that phytase reduces phytic acid in the litter, while reducing dietary non-phytate P decreased litter orthophosphate concentrations. However, wet storage conditions significantly increased litter orthophosphate concentrations, regardless of diet.
Effluent Caused Soil Water Repellency
Use of treated sewage effluent in irrigated agriculture in semiarid areas with water shortages, or for land disposal in other regions, is on the rise. Wallach et al. (1910–1920) demonstrate that long-term irrigation with effluent in a commercial citrus orchard resulted in persistent and extreme soil water repellency in the 0- to 5-cm soil surface layer. Extent of repellency was highly variable on a small (cm) scale; variability was not related to season, soil moisture content, or soil organic matter content. Non-uniform distribution of soil moisture and fingered flow were observed in the soil profile down to 50 cm, demonstrating that the thin repellent layer influenced water flow in the underlying wettable soil. Soil water repellency can adversely affect agricultural production, lead to contamination of underlying ground water resources, and result in excessive runoff and soil erosion.
Phosphorus Dynamics the Everglades
Nutrition of plants and microbes in wetland ecosystems depends on the turnover of organic compounds, yet information on organic forms of phosphorus in wetlands is scarce. In a study of surface and underlying sediment from several contrasting locations in the Florida Everglades, Turner and Newman (1921–1929) discovered that organic phosphorus was composed almost entirely of phosphate diesters such as DNA and phospholipids. This challenges our understanding of phosphorus cycling in wetlands, because the results are in marked contrast to those obtained so far for most soils.
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