Sorption dynamics of organic and inorganic phosphorus compounds in soil

Phosphorus retention in soils is influenced by the form of P added. The potential impact of one P compound on the sorption of other P compounds in soils has not been widely reported. Sorption isotherms were utilized to quantify P retention by benchmark soils from Indiana, Missouri, and North Carolina when P was added as inorganic P (Pi) or organic P (beta-D-glucose-6-phosphate, G6P; adenosine 5'-triphosphate, ATP; and myoinositol hexaphosphate, IP6) and to determine whether soil P sorption by these organic P compounds and Pi was competitive. Isotherm supernatants were analyzed for pH and total P using standard protocols, while Pi and organic P compounds were assayed using ion chromatography. Under the controlled conditions of this study, the affinity of all soils for P sources followed the order IP6 > G6P > ATP > Pi. Each organic P source had a different potential to desorb Pi from soils, and the order of greatest to least Pi desorption was G6P > ATP > IP6. Glucose-6-phosphate and ATP competed more directly with Pi for sorption sites than IP6 at greater rates of P addition, but at the lesser rates of P addition, IP6 actually desorbed more Pi. Inositol hexaphosphate was strongly sorbed by all three soils and was relatively unaffected by the presence of other P sources. Decreased total P sorption due to desorption of Pi can be caused by relatively small additions of organic P, which may help explain vertical P movement in manured soils. Sorption isotherms performed using Pi alone did not accurately predict total P sorption in soils.     

Use of beryllium-7 to document soil redistribution following forest harvest operations

Rapid and reliable methods for documenting soil erosion associated with forest harvest operations are needed to support the development of best management practices for soil and water conservation. To address this need, the potential for using 7Be measurements to estimate patterns and amounts of soil redistribution associated with individual post-harvest events was explored. The 7Be technique, which was originally developed for use on agricultural land, was employed to estimate soil redistribution associated with a period of heavy rainfall within a harvested forest area located in the Lake Region of Chile (39 degrees 44'7' S, 73 degrees 10'39' W; 22% slope; and mean annual rainfall 2300 mm yr(-1)). The results provided by the 7Be technique were validated against direct measurements of soil gain or loss during the same period obtained using erosion pins. The information produced by the two approaches was similar. The results of this study demonstrate the potential for using 7Be measurements to document event-based erosion in recently harvested forest areas.     

Effects of elevated atmospheric carbon dioxide on biomass and carbon accumulation in a model regenerating longleaf pine community

Plant species vary in response to atmospheric CO2 concentration due to differences in physiology, morphology, phenology, and symbiotic relationships. These differences make it very difficult to predict how plant communities will respond to elevated CO2. Such information is critical to furthering our understanding of community and ecosystem responses to global climate change. To determine how a simple plant community might respond to elevated CO2, a model regenerating longleaf pine community composed of five species was exposed to two CO2 regimes (ambient, 365 micromol mol(-1) and elevated, 720 micromol mol(-1)) for 3 yr. Total above- and belowground biomass was 70 and 49% greater, respectively, in CO2-enriched plots. Carbon (C) content followed a response pattern similar to biomass, resulting in a significant increase of 13.8 Mg C ha(-1) under elevated CO2. Responses of individual species, however, varied. Longleaf pine (Pinus palustris Mill.) was primarily responsible for the positive response to CO2 enrichment. Wiregrass (Aristida stricta Michx.), rattlebox (Crotalaria rotundifolia Walt. Ex Gmel.), and butterfly weed (Asclepias tuberosa L.) exhibited negative above- and belowground biomass responses to elevated CO2, while sand post oak (Quercus margaretta Ashe) did not differ significantly between CO2 treatments. As with pine, C content followed patterns similar to biomass. Elevated CO2 resulted in alterations in community structure. Longleaf pine comprised 88% of total biomass in CO2-enriched plots, but only 76% in ambient plots. In contrast, wiregrass, rattlebox, and butterfly weed comprised 19% in ambient CO2 plots, but only 8% under high CO2. Therefore, while longleaf pine may perform well in a high CO2 world, other members of this community may not compete as well, which could alter community function. Effects of elevated CO2 on plant communities are complex, dynamic, and difficult to predict, clearly demonstrating the need for more research in this important area of global change science.     

Soil nitrate nitrogen dynamics after biosolids application in a tobosagrass desert grassland

Dormant-season application of biosolids increases desert grass production more than growing season application in the first growing season after application. Differential patterns of NO3-N (plant available N) release following seasonal biosolids application may explain this response. Experiments were conducted to determine soil nitrate nitrogen dynamics following application of biosolids during two seasons in a tobosagrass [Hilaria mutica (Buckl.) Benth.] Chihuahuan Desert grassland. Biosolids were applied either in the dormant (early April) or growing (early July) season at 0, 18, or 34 dry Mg ha(-1). A polyester-nylon mulch was also applied to serve as a control that approximated the same physical effects on the soil surface as the biosolids but without any chemical effects. Supplemental irrigation was applied to half of the plots. Soil NO3-N was measured at two depths (0-5 and 5-15 cm) underneath biosolids (or mulch) and in interspace positions relative to surface location of biosolids (or mulch). Dormant-season biosolids application significantly increased soil NO3-N during the first growing season, and also increased soil NO3-N throughout the first growing season compared to growing-season biosolids application in a year of higher-than-average spring precipitation. In a year of lower-than-average spring precipitation, season of application did not affect soil NO3-N. Soil NO3-N was higher at both biosolids rates for both seasons of application than in the control treatment. Biosolids increased soil NO3-N compared to the inert mulch. Irrigation did not significantly affect soil NO3-N. Soil NO3-N was not significantly different underneath biosolids and in interspace positions. Surface soil NO3-N was higher during the first year of biosolids application, and subsurface soil NO3-N increased during the second year. Results showed that biosolids rate and season of application affected soil NO3-N measured during the growing season. Under dry spring-normal summer precipitation conditions, season of application did not affect soil NO3-N; in contrast, dormant season application increased soil NO3-N more than growing season application under wet spring-dry summer conditions.     

Effects of calibration on L-THIA GIS runoff and pollutant estimation

Urbanization can result in alteration of a watershed's hydrologic response and water quality. To simulate hydrologic and water quality impacts of land use changes, the Long-Term Hydrologic Impact Assessment (L-THIA) system has been used. The L-THIA system estimates pollutant loading based on direct runoff quantity and land use based pollutant coefficients. The accurate estimation of direct runoff is important in assessing water quality impacts of land use changes. An automated program was developed to calibrate the L-THIA model using the millions of curve number (CN) combinations associated with land uses and hydrologic soil groups. L-THIA calibration for the Little Eagle Creek (LEC) watershed near Indianapolis, Indiana was performed using land use data for 1991 and daily rainfall data for six months of 1991 (January 1-June 30) to minimize errors associated with use of different temporal land use data and rainfall data. For the calibration period, the Nash-Sutcliffe coefficient was 0.60 for estimated and observed direct runoff. The calibrated CN values were used for validation of the model for the same year (July 1-December 31), and the Nash-Sutcliffe coefficient was 0.60 for estimated and observed direct runoff. The Nash-Sutcliffe coefficient was 0.52 for January 1, 1991 to December 31, 1991 using uncalibrated CN values. As shown in this study, the use of better input parameters for the L-THIA model can improve accuracy. The effects on direct runoff and pollutant estimation of the calibrated CN values in the L-THIA model were investigated for the LEC. Following calibration, the estimated average annual direct runoff for the LEC watershed increased by 34%, total nitrogen by 24%, total phosphorus by 22%, and total lead by 43%. This study demonstrates that the L-THIA model should be calibrated and validated prior to application in a particular watershed to more accurately assess the effects of land use changes on hydrology and water quality.     

Ultrasound and enzyme assisted biodegradation of distillery wastewater

Irradiation with ultrasound (US) and use of an enzyme (E) as pretreatment techniques were carried out to treat a complex effluent (distillery wastewater). These two techniques have been used alone as well as in combination and the efficacy of these techniques was tested by subjecting the effluent to subsequent aerobic biological oxidation (AO). When used alone, US exposure for 30 min and 2 h yielded the best COD reduction during the aerobic oxidation step (US+AO). For the enzyme when used alone, a pH value of 4.8 (corresponding to the optimum pH of the enzyme), a dose of 50 U and a pretreatment time of 24 h yielded better COD removal efficiency as compared to untreated effluent (aerobic oxidation alone). When used in combination, ultrasound followed by enzymatic pretreatment (US+E+AO) yielded the best COD removal efficiencies during aerobic oxidation as compared to the other combinations tested for the treatment of the distillery wastewater. A 4-fold increase in the initial oxidation rate was observed over the untreated batch for the integrated technique (US+E+AO). On the basis of the variation in the values of the biokinetic parameters it can be concluded that the type of pretreatment scheme affects the subsequent rate of the aerobic oxidation significantly.     

Modelling the Distribution and Quality of Sand and Gravel Resources in 3D: a Case Study in the Thames Basin,UK

Three-dimensional (3D) models are often utilised to assess the presence of sand and gravel deposits. Expanding these models to provide a better indication of the suitability of the deposit as aggregate for use in construction would be advantageous. This, however, leads to statistical challenges. To be effective, models must be able to reflect the interdependencies between different criteria (e.g. depth to deposit, thickness of deposit, ratio of mineral to waste, proportion of ‘fines’) as well as the inherent uncertainty introduced because models are derived from a limited set of boreholes in a study region. Using legacy borehole data collected during a systematic survey of sand and gravel deposits in the UK, we have developed a 3D model for a 2400 km² region close to Reading, southern England. In developing the model, we have reassessed the borehole grading data to reflect modern extraction criteria and explored the most suitable statistical modelling technique. The additive log-ratio transform and the linear model of coregionalization have been applied, techniques that have been previously used to map soil texture classes in two dimensions, to assess the quality of sand and gravel deposits in the area. The application of these statistical techniques leads to a model which can be used to generate thousands of plausible realisations of the deposit which fully reflect the extent of model uncertainty. The approach offers potential to improve regional-scale mineral planning by providing an enhanced understanding of sand and gravel deposits and the extent to which they meet current extraction criteria.

     

Potential of microalgae as biopesticides to contribute to sustainable agriculture and environmental development

The loss of yields from agricultural production due to the presence of pests has been treated over the years with synthetic pesticides, but the use of these substances negatively affects the environment and presents health risks for consumers and animals. The development of agroecological systems using biopesticides represents a safe alternative that contributes to the reduction of agrochemical use and sustainable agriculture. Microalgae are able to biosynthesize a number of metabolites with potential biopesticidal action and can be considered potential biological agents for the control of harmful organisms to soils and plants. The present work aims to provide a critical perspective on the consequences of using synthetic pesticides, offering as an alternative the biopesticides obtained from microalgal biomass, which can be used together with the implementation of environmentally friendly agricultural systems.     

Distribution and possible source of trace elements in the sediment cores of a tropical macrotidal estuary and their ecotoxicological significance

The paper presents the first document regarding concentration, distribution and possible sources of selected trace elements (Cu, Fe, Mn, Zn, Cr, Co, Ni, Pb, Al, B and Ba) in core sediments (<63 micro particle size) from the lower stretch of Hugli (Ganges) estuary, northeast coast of Bay of Bengal by ICP-AES and EDXRF to evaluate geochemical processes influencing their distribution and possible environmental consequences. The levels of elements showed a wide range of variations in different core depths, in upper and lower intertidal zones as well as among three sampling stations. The most interesting feature of the study is the downward increase of concentrations of majority of the elements reaching overall maximum values at a depth of 20-28 cm in upper littoral zone of the site located in the extreme downstream stretch of the estuary. Values of organic carbon showed very strong positive correlations with most of the elements as revealed by correlation matrix (r) values. The interelemental relationship revealed the identical behavior of element during its transport in the estuarine environment. The overall variation in concentration can be attributed to differential discharge of untreated effluents originating from industrial, agricultural, and aquacultural sources as well as from domestic sewage along with the fishing and boating activities. The resulting compositional dataset was tested by principal component analyses and cluster analyses. Pollution load index (PLI) and index of Geoaccumulation (Igeo) revealed overall low values but the enrichment factors (EFs) for Pb were typically high for all the stations. The mean concentrations of Zn and to some extent Cu exceeded the Effects Range-Low (ER-L) values in the majority of the cases indicating that there may be some ecotoxicological risk to organisms living in sediments. The concentration of the trace elements reported in this work is useful as baselines for comparison in future sediment quality studies.     

Management of an Agroecosystem

Agroecosystems (AESs) are autotrophic ecosystems managed by man. The goal of the management is to obtain the maximum possible amount of high-quality agricultural products while preserving agricultural resources, primarily the soils and biodiversity. The main components of the management of AES structures and functions, including primary and secondary biological production, the ratio between the energy flows in the plant–man and plant–livestock–man food chains, the efficiency of energy transfer in the plant–livestock link, and conservation of agricultural resources, are considered.