Nitrogen and phosphorus content of flow from drains fertilized with cow manure slurry

Summary The rate of flow and nitrate and phosphorus content of the water from four drained sandy and clayey plots of size 12×60 m cropped to continuous corn were determined following two annual applications of different rates (0, 260, 390 and 520 kg N/ha) of cow manure slurry. The drain flow was directly related to the rainfall and was greatly influenced by soil texture. The N losses were greater in 1972 (7.8 to 19.1 kg N/ha) than in 1971 (0.4 to 7.8 kg N/ha) because of more summer rainfall. Nitrogen and phosphorus losses were larger from the sandy plots than from the clayey plots. The manure application rates had no apparent effect on nitrogen losses in the drain water.     

Anaerobic biotransformations of pollutant chemicals in aquifers

Summary Anaerobic microbial communities sampled from either a methanogenic or sulfate-reducing aquifer site have been tested for their ability to degrade a variety of groundwater pollutants, including halogenated aromatic compounds, simple alkyl phenols and tetrachloroethylene. The haloaromatic chemicals were biodegraded in methanogenic incubations but not under sulfate-reducing conditions. The primary degradative event was typically the reductive removal of the aryl halides. Complete dehalogenation of the aromatic moiety was required before substrate mineralization was observed. The lack of dehalogenation activity in sulfatereducing incubations was due, at least in part, to the high levels of sulfate rather than a lack of metabolic potential. In contrast, the degradation of cresol isomers occurred in both types of incubations but proved faster under sulfate-reducing conditions. The requisite microorganisms were enriched and the degradation pathway forp-cresol under the latter conditions involved the anaerobic oxidation of the aryl methyl group. Tetrachloroethylene was also degraded by reductive dehalogenation but under both incubation conditions. The initial conversion of this substrate to trichloroethylene was generally faster under methanogenic conditions. However, the transformation pathway slowed when dichloroethylene was produced and only trace concentrations of vinyl chloride were detected. These results illustrate that pollutant compounds can be biodegraded under anoxic conditions and a knowledge of the predominant ecological conditions is essential for accurate predictions of the transport and fate of such materials in aquifers.     

The distribution and interconversion of ammonium and nitrate in the Skallingen salt marsh (Denmark) and their exchange with the adjacent coastal water

The potential nitrogen sources for the primary production in the intertidal area are nitrogen compounds obtained from mineralization in the sediment and the water column, nitrogen fixation, outflow from rivers and groundwater seeping from the mainland. The available inorganic nitrogen in the adjacent coastal waters decreases from 50–80 μmol NO₃ ^-/l and 6–15 μmol NH₄ ⁺/l in early spring to ca one tenth during the growing season. In the sediment of the tidal flats available ammonia and nitrate vary between 50 and 100 μmol/1 pw. In the salt marsh available ammonia increases from 200–300 nmol NH₄ ⁺/g fwt to approximately double the amount, and the available nitrate varies from 100–300 nmol NO₃ ^-/g fwt (250–750 μmol NO₃ ^-/l pw) to ca one third during the growing season. The exchange of NH₄ ⁺, NO₂ ^- and NO₃ ^- across the sediment water interface has been estimated during tidal cycles under light and dark conditions on the tidal flats. The flux of nitrogen was dependent on the flora and fauna as well as the time of the year. The tidal activity, frequency and length of inundation are considered the driving force in a two-way process between salt marshes and adjacent coastal waters. The role of marsh sediment, tidal water and sediments of the tidal flats as sites of accumulation, consumption and remineralization of organic matter is emphasized. The possible exchange of ammonia and nitrate between the salt marsh and the different compartments of the tidal water is discussed.     

Distribution of plasmids in groundwater bacteria

Summary Bacteria isolated from groundwater aquifer core materials of pristine aquifers at Lula and Pickett, OK, and from a site with a history of aromatic hydrocarbon contamination and natural renovation located at Conroe, TX, were screened for the presence of plasmid DNA by alkaline or enzyme lysis and agarose gel techniques. Some of the isolates were also subjected to taxonomic tests in addition to screening for resistance to antibiotics, tolerance to heavy metal salts, and bacteriocin production. There was no significant difference in the distribution of the traits usually associated with plasmid occurrence in isolates from the three sites. These traits, which occurred at low frequencies, were not restricted to plasmid-bearing strains of the communities. Plasmids were found in isolates from all three sites, but on the average there was a significantly higher percentage of isolates containing plasmids in the samples from Conroe (19.4%) than from either Lula (1.8%) or Pickett (7.7%). The sizes of the plasmids found ranged between 3.5 and 202 kilobases but, for the Conroe samples, many more isolates (67%) contained smaller plasmids (<10 kb) rather than larger ones. No plasmids were found in bacteria recovered from naturally renovated aquifer material at the Conroe site.     

Responses of restored grassland ditch vegetation to hydrological changes, 1989–1992

The impact of hydrological manipulation of an unfertilised, Dutch peat grassland area on plant species composition on ditch banks and in ditchwater was studied. The hydrological manipulation involved raising the groundwater level by admitting nutrient-poor, Ca-rich groundwater in one compartment, and by retaining precipitation in another compartment. A third compartment served as control.The plant species composition showed significant correlations with the following hydrochemical parameters: in bank vegetation with K⁺ concentration, and winter and summer groundwater levels, water depth and elevation; in aquatic vegetation with pH, the concentrations of Cl^- organic-C and NH₄ ⁺ water temperature and elevation.The number of terrestrial plant species increased after compartmentation from 97 to 122; 16 submerged and floating species were found. Most new terrestrial species probably emerged in response to cessation of fertilization and biomass removal, since they showed no preference for any compartment. Five species showed preference for the groundwater compartment and two for the rainwater compartment. Of the new terrestrial plants, seven were relatively rare: Carex panicea, C. oederi, C. pallescens, C. vesicaria, Galium uliginosum, Juncus acutiflorus and Stellaria uliginosa. Of the aquatic plants, eight were relatively rare: Chara globularis, two Callitriche spp., four potamogetonaceae and Ranunculus circinatus.This study indicates that hydrological manipulation of grassland systems in which fertilisation has ceased has profound effects on the vegetation in the ditches of these systems. Bank vegetation responds more slowly and to other hydrochemical factors than aquatic vegetation. Short-term responses in terms of increase in diversity of vegetation pattern and species richness are promising. Long-term responses are not yet known.     

The extracellular nuclease of Serratia marcescens: studies on the activity in vitro and effect on transforming DNA in a groundwater aquifer microcosm

A quantitative endonuclease assay, which relies on the introduction of single and double strand breaks into supercoiled plasmid DNA, was used to study the activity of the extracellular nuclease of Serratia marcescens SM6 in buffer and in groundwater. The parallel enzyme concentration-dependent production of relaxed and linear plasmid molecules suggests that the nuclease produces single and double strand breaks in duplex DNA. Bovine serum albumin stimulated the nuclease activity towards DNA and RNA and increased the stability of the enzyme against thermal inactivation. The DNase activity at 4 °C and 50 °C was almost half of that at the optimum temperature (37 °C). The nuclease was active in groundwater, although the specific activity was lower than in buffer. In a groundwater aquifer microcosm, mineral-adsorbed transforming DNA was substantially less accessible to the nuclease than was dissolved DNA. The data suggest that the extracellular nuclease of Serratia marcescens may contribute to DNA turnover in the environment and that adsorption of DNA to minerals provides protection against the nuclease.Abbreviations GW groundwater GWA groundwater aquifer     

Nitrous oxide and methane fluxes of a pristine slope mire in the German National Park Harz Mountains

Pristine peatlands covered by Histosols (bogs and fens) with high water table and a restricted oxygen (O₂) availability are known to have low emissions of nitrous oxide (N₂O) but may be a significant source for atmospheric methane (CH₄) which are both important greenhouse gases. For the first time N₂O and CH₄ fluxes of a pristine slope mire in the German Harz Mountains have been monitored. Previously reported peatlands are characterised by anaerobic conditions due to high water table levels. Slope mires monitored here receive O₂ through slope water inflow. Gas fluxes have been monitored deploying closed chamber method on a central non-forested area and a forested area at the periphery of the slope mire. By means of groundwater piezometers water table levels, ammonium and nitrate contents as well as hydro-chemical variables like oxygen content and redox potential of the mire pore water have been concurrently measured with trace gas fluxes at both monitoring sites of the slope mire. The slope mire took up small amounts of atmospheric methane at a rate of −0.02 ± 0.01 kg C ha⁻¹ year⁻¹ revealing no significant difference between the forested and non-forested site. Higher uptake rates were observed during low water table level. In contrast to pristine peatlands influx of oxygen containing pore water into slope mire does limit reduction processes and resultant CH₄ emission. N₂O fluxes of the forested and non-forested sites of the slope mire did not differ and amounted to 0.25 ± 0.44 kg N ha⁻¹ year⁻¹. Higher emissions were observed at low water table levels and during thawing periods. In spite of favourable conditions N₂O fluxes of the slope mire have been comparable to those of pristine peatlands.     

固相反硝化技术同时去除地下水中的硝酸盐与农药进展

概述了固相反硝化技术及其特点,综述了固相反硝化技术在去除地下水中硝酸盐与农药的研究现状,分析了反应机理及当前研究中存在的问题,并在此基础上对固相反硝化的未来核心研究方向进行了展望。     

Kinetics of Sulfate Reduction in a Coastal Aquifer Contaminated with Petroleum Hydrocarbons

An integrated field and laboratory study was conducted to quantify the effect of environmental determinants on the activity of sulfate reducers in a freshwater aquifer contaminated with petroleum hydrocarbons (PHC). Within the contaminated zone, PHC-supported in␣situ sulfate reduction rates varied from 11.58±3.12 to 636±53 nmol cm⁻³ d⁻¹ and a linear increase (R ²=0.98) in reduction rate was observed with increasing in situ sulfate concentrations suggesting sulfate limitation. Half-saturation concentration (K _s) for sulfate reduction coupled to PHC mineralization was determined for the first time. At two different sites within the␣aquifer, maximum sulfate reduction rate under␣non-limiting conditions (R _max) was 5,000 nmol cm⁻³ d⁻¹, whereas the retrieved K _s values were 3.5 and 7.5 mM, respectively. The K _s values are the highest ever reported from a natural environment. Furthermore, the K _s values were significantly higher than in situ sulfate concentrations confirming sulfate limited growth. On addition of lactate and formate, sulfate reduction rate increased indicating that reactivity and bioavailability of organic substrate may also have played a role in rate inhibition in certain parts of the aquifer. Experiments with sulfide amendments show statistically minor decrease in sulfate reduction rates on addition of sulfide and analogous increase in sulfide toxicity with increasing sulfide concentrations (0.5–10 mM) was not apparent.     

Water utilization of tropical hardwood hammocks of the Lower Florida Keys

Summary Predawn water potential of representative plant species, together with stable isotope composition of stem water and potential water sources were investigated in four low-elevation tropical hardwood hammocks in the Lower Florida Keys, during a one year period. Hammock species had the lowest water potentials when soil water content was low and/or soil salinity was high, but differences in groundwater salinity had no effect on the water potential. Comparison of D/H ratio of plant stem water with soil and ground water corroborates the conclusion that they are primarily utilizing soil water and not groundwater. Thus, tropical hardwood hammocks are buffered from saline groundwater, and are able to thrive in areas where groundwater salinity is as high as 25. The effect of sea level rise on these forests may depend more on changes in the frequency of tidal inundation of the soil surface than on changes in groundwater salinity.