Bioremediation of residual fertilizer nitrate: I. Laboratory demonstration of an on-farm in situ pollution control system

This exploratory laboratory study was undertaken to develop and test an in situ bioremediation system intended to point the way toward a possible field application. The proposed method uses a water table management (WTM) system to deliver nutrients or other amendments to subsoil microorganisms for biostimulation and subsequent biodegradation of pollutants in the saturated and unsaturated zones of the soil. The study was carried out on packed soil columns and bioremediation of residual fertilizer nitrate was attempted. Different levels of organic carbon supplement (glucose C) were introduced into these columns via subirrigation in order to supplement the readily available organic carbon levels in the soil. The study was carried out in two experimental setups. The first setup investigated (i) the effect of addition of a high (970 mg L(-1)) and a low (120 mg L(-1)) glucose C level and (ii) the efficacy of using the subirrigation system as a method for nutrient delivery in bioremediation of leached nitrate. This setup was monitored with time, depth, and with reference to the nitrate residue in the soil solution. Leached nitrate was denitrified to less than 10 mg L(-1) nitrate N at both glucose levels. The second setup investigated the effect of a range of low levels of glucose C on nitrate decontamination, soil pH, and total microbial count in order to find out an optimal glucose C level that reduced the most nitrate and maintained the pH homeostasis of soil.     

Interactions between soil texture and placement of dairy slurry application: II. Leaching of phosphorus forms

Managing phosphorus (P) losses in soil leachate folllowing land application of manure is key to curbing eutrophication in many regions. We compared P leaching from columns of variably textured, intact soils (20 cm diam., 20 cm high) subjected to surface application or injection of dairy cattle (Bos taurus L.) manure slurry. Surface application of slurry increased P leaching losses relative to baseline losses, but losses declined with increasing active flow volume. After elution of one pore volume, leaching averaged 0.54 kg P ha(-1) from the loam, 0.38 kg P ha(-1) from the sandy loam, and 0.22 kg P ha(-1) from the loamy sand following surface application. Injection decreased leaching of all P forms compared with surface application by an average of 0.26 kg P ha(-1) in loam and 0.23 kg P ha(-1) in sandy loam, but only by 0.03 kg P ha(-1) in loamy sand. Lower leaching losses were attributed to physical retention of particulate P and dissolved organic P, caused by placing slurry away from active flow paths in the fine-textured soil columns, as well as to chemical retention of dissolved inorganic P, caused by better contact between slurry P and soil adsorption sites. Dissolved organic P was less retained in soil after slurry application than other P forms. On these soils with low to intermediate P status, slurry injection lowered P leaching losses from clay-rich soil, but not from the sandy soils, highlighting the importance of soil texture in manageing P losses following slurry application.     

Environmental impact of irrigation in La Violada District (Spain): II. Nitrogen fertilization and nitrate export patterns in drainage water

Fertilizer leaching affects farm profitability and contributes to nonpoint-source pollution of receiving waters. This work aimed to establish nitrate nitrogen export from La Violada Gully in relation to nitrogen fertilization practices in its basin (La Violada Gully watershed, VGW, 19,637 ha) and especially in La Violada Irrigation District (VID, 5282 ha). Nitrogen (N) fertilization in VID (and VGW) was determined through interviews with local farmers for the hydrologic years 1995 and 1996 and NO3-N load in the gully was monitored from 1995 to 1998. The N fertilizer applied in VGW was 2175 Mg in 1995 and 2795 Mg in 1996. About 43% was applied in VID (945 Mg in 1995 and 1161 Mg in 1996). The most fertilized crop was corn: 398 kg N ha-1 (665 Mg) in 1995 and 453 kg N ha-1 (911 Mg) in 1996. Nitrogen fertilization was higher than N uptake for irrigated crops, especially for corn and rice. Nitrate N load in La Violada Gully averaged 427.4 Mg yr-1. Seventy-five percent of the exports took place during the irrigation season (321.8 Mg). During the non-irrigation season maximum NO3-N loads (3.1 Mg NO3-N d-1) were found after heavy rains following the N side-dressing of wheat in the rain-fed area of VGW (February). During the irrigation season NO3-N load was determined by outflow from the district (caused by irrigation) and to a lesser extent by changes in NO3 concentration (caused by fertilization), showing peaks in April (pre-sowing corn N fertilization and first irrigations) and June to August (highest irrigation months and corn side-dress N applications, maximum 6.3 Mg NO3-N d-1 in July). Adjusting N fertilization to crops' needs, improving irrigation efficiencies, and better scheduling N fertilization and irrigation in corn could reduce N export from VID.     

Developing a sustainable energy strategy for a water utility. Part II: A review of potential technologies and approaches

Environmental legislation is increasing the amounts of bought-in electricity required for sewage treatment, and generating larger volumes of sewage sludge to be treated and disposed of. Concurrently, concerns over global warming and food safety from sewage sludge recycling on agricultural land is augmenting the costs of conventional sewage and sludge treatment technologies and practices. This paper reviews some emerging technologies and practices that may assist in mitigating these problems in the future. In addition, a number of potential renewable energy technologies available to water companies are reviewed. Results suggest that through the take-up of new technologies, current and future water quality standards could be delivered in a more sustainable way. However, this series of papers also highlights that institutional and political conflicts may have inadvertently failed to recognise the wider effects of improving water quality and lessened the financial support necessary for their widespread take-up. It is also suggested that through the use of a Strategic Environmental Assessment (SEA) approach, stakeholders could gain a better understanding of the broader environmental effects of achieving certain water quality standards and develop policy and long-term investment strategies accordingly. However, to fulfill the information requirements of an SEA, an appropriate appraisal tool that considers many of these factors in unison is required, and a possible technique is suggested.     

Monitoring of Gin Drinkers' Bay landfill,Hong Kong: II. Gas contents,soil properties,and vegetation performance on the side slope

This second part of the study concerned the plant cover, gas contents, and soil properties of the side slope area of the landfill, which is not protected against gas infiltration. Five different sites on the slope and a control site outside the landfill were chosen, and pipes were installed in the region. Gas contents were tested, and plant cover recorded by quadrat analysis Over 20 species of grasses, herbs, and vines were present on the slope The relative adaptabilities of the species were ranked according to the abundance of the plants Plant cover was found to be negatively correlated with landfill gas contents. The landfill soil had elevated contents of nitrogen, organic carbon, and extractable metals Total nitrogen, ammonia nitrogen, and extractable lead were further identified to be negatively correlated while available phosphate was positively correlated with plant cover