Both eutrophication and SO₄ pollution can lead to higher availability of nutrients and potentially toxic compounds in wetlands. To unravel the interaction between the level of eutrophication and toxicity at species and community level, effects of SO₄ were tested in nutrient-poor and nutrient-rich fen mesocosms. Biomass production of aquatic and semi-aquatic macrophytes and colonization of the water layer increased after fertilization, leading to dominance of highly competitive species. SO₄ addition increased alkalinity and sulphide concentrations, leading to decomposition and additional eutrophication. SO₄ pollution and concomitant sulphide production considerably reduced biomass production and colonization, but macrophytes were less vulnerable in fertilized conditions. The experiment shows that competition between species, vegetation succession and terrestrialization are not only influenced by nutrient availability, but also by toxicity, which strongly interacts with the level of eutrophication. This implies that previously neutralized toxicity effects in eutrophied fens may appear after nutrient reduction measures have been taken. Interspecific competition, vegetation succession and terrestrialization in fens depend on the interacting effects of SO₄ pollution, sulphide toxicity and nutrient availability.

Reactive filter materials used for phosphorus (P) removal from wastewater can be disposed of as soil amendments after treatment, thus recycling P and other macro- and micro-nutrients to plants. In addition, materials with a high pH and Ca content, such as Polonite, are potential soil conditioners, which can be particularly beneficial for acid soils. Polonite previously used for on-site wastewater treatment was applied as a soil amendment to a mountain meadow. The amendment significantly increased soil pH and decreased the hydrolytic acidity, thus reducing Al toxicity risks. The effects were comparable to those of liming. No difference in yield and P uptake by meadow plants was observed. The uptake of metals was lower for amended soils, especially the uptake of Mn. Using Polonite after wastewater treatment as a soil amendment is thus a viable disposal alternative that can replace liming, when necessary, being capable of recycling P and other nutrients to meadow plants. Filter substrate Polonite can benefit acid soils after wastewater treatment.

Nitrous oxide (N₂O) emissions from a typical greenhouse vegetable system in Northern China were measured from February 2004 to January 2006 using a close chamber method. Four nitrogen management levels (NN, MN, CN, and SN) were used. N₂O emissions occurred intermittently in the growing season, strongly correlating with N fertilization and irrigation. No peak emissions were observed after fertilization in the late Autumn season due to low soil temperature. 57-94% of the seasonal N₂O emissions came from the initial growth stage, corresponding to the rewetting process in the soil. The annual N₂O emissions ranged from 2.6 to 8.8 kg N ha⁻¹ yr⁻¹, accounting for 0.27-0.30% of the annual nitrogen input. Compared with conventional N management, site-specific N management reduced N fertilization rate by 69% in 2004 and by 76% in 2005, and consequently reduced N₂O emissions by 51% in 2004 and 27% in 2005, respectively. High N₂O emissions coming from the initial growth stage can be attributed to the rewetting process in the greenhouse soil.

Soluble phosphate is a common ingredient of fertilizer used in agriculture production all over the world. This chemical mixed with soil is transported into the water and marine environment via rainfall causing a range of environmental problems such as toxic algae bloom. Kaolin clay is a common material found in soil and is used as a model system to understand the effects of phosphate adsorption on the flocculation/dispersion of the clay slurries. In the topics, torrential downpours are common. The large water flow will easily disperse the unflocculated or weakly flocculated sediments over a wide area including river and marine environments. Phosphate adsorption was found to weaken the interparticle forces between clay platelets in the slurries. At high enough concentration, it will completely deflocculate the clay slurries, i.e. the net interparticle force is repulsive. A deflocculated slurry is characterised by a low viscosity and no yield stress. As a result, it is much easier to disperse this slurry over a wide area possible even in a small downpour. This study will present the flow and yield stress behaviour of kaolin clay slurries under the influence of adsorbed phosphate.

A study was conducted to determine nitrogen budget and ammonia volatilization in Japanese paddy fields supplemented with liquid cattle waste (LCW). A series of four, 2 x 10 m experimental plots was established in a paddy field with silty clay soil planted with forage rice (Oryza sativa L.). In addition to 195 kg N ha⁻¹ of chemical or compost-based basal fertilizer, LCW was applied as an additional fertilizer at total nitrogen rates of 0, 255, 255, and 405 kg N ha⁻¹ to the four plots C195, T450-1, T450-2, and T600, respectively. The mass balance showed that after application of LCW, 32-39% of total input nitrogen was assimilated into aboveground parts of rice plants, 11-15% leached downward, 2.5-4.0% was lost via ammonia volatilization, 1.6-5.1% was retained in roots or was adsorbed onto soil, and approximately 30-40% was lost via denitrification. Compared to animal waste slurries applied to unsaturated soils, nitrogen loss via ammonia volatilization was relatively lower, probably due to the dilution effect of floodwater. Nitrogen loss via denitrification was markedly higher in areas where LCW was applied compared to areas without LCW application. On the other hand, nitrogen leaching downwards represented a substantial loss and may be an environmental concern. However, after LCW application only, the ammonium ion was detected, at a maximum nitrogen concentration of 11.4 mg L⁻¹. In this system, therefore, nitrogen has a different fate to that in animal waste slurries applied to unsaturated soil. In that situation, the major nitrogen form in leaching water is nitrate nitrogen, which moves readily into groundwater.

We assessed the potential of nitrate-nitrogen (NO₃-N) and fluoride (F) contamination in drinking groundwater of an intensively cultivated district in India as a function of its agricultural activities. Three hundred and forty two groundwater samples were collected from different types of wells with varying depths and analyzed for pH, EC, NO₃-N load and F content. Database on predominant cropping system, fertilizer and pesticide uses were also recorded for the district. The NO₃-N load in groundwater samples were low ranging from 0.01 to 5.97 mg L⁻¹ with only 6.7% of them contained greater than 3.0 mg L⁻¹. Samples from the habitational areas showed higher NO₃-N content over the agricultural fields. But all the samples contained NO₃-N below the 10 mg L⁻¹, the threshold limit fixed by WHO for drinking purpose. The content decreased with increasing depth of wells (r = -0.297, P <= 0.01) and increased with increasing rate of nitrogenous fertilizer application (r = 0.931, P <= 0.01) and was higher in areas where shallow-rather than deep-rooted crops are grown. Fluoride content in groundwater was also low (0.02 to 1.19 mg L⁻¹) with only 2.4% of them exceeding 1.0 mg L⁻¹ posing a potential threat of fluorosis in some locality. On average, its content varied little spatially and along depth of sampling aquifers indicating homogeneity in lithology of the district. The content showed a significant positive correlation (r = 0.237, P <= 0.01) with the amount of phosphatic fertilizer (single super phosphate) used for agriculture. Results thus indicated that the groundwater of the study area is presently safe for drinking purpose but some anthropogenic activities associated with intensive cultivation had a positive influence on its loading with NO₃-N and F.

This study examines the relationship between dissolved inorganic nitrogen (DIN: NH₄ ⁺ + NO₂ ⁻ + NO₃ ⁻) and dissolved organic nitrogen (DON) in river water and groundwater in an agriculturally-dominated catchment in south-east Spain, and estimates the contribution of DON to the total dissolved nitrogen (TDN) concentrations. The studied aquifer-dependent river system consists of Quaternary alluvial sediments deposited by the Guadalquivir River and its tributaries, with both river water and groundwater in the catchment being aerobic. DON is the predominant form of nitrogen in river water (72-97% of the TDN), whereas its proportion to TDN varies considerably in groundwater (<1-99%). A seasonal pattern in the concentration of dissolved nitrate in river water was observed, whereas DON concentrations showed no significant change during the study period. The export of DON from the Guadalquivir River is approximately 2 kg N ha⁻¹ year⁻¹ and is an order of magnitude higher than the export of DON from pristine catchments. Dissolved nitrate concentrations in groundwater were slightly higher in winter and DON concentrations were significantly lower (p < 0.05) in summer. It is found that agricultural soils constitute the main storage of organic nitrogen in the catchment with a steady leaching of high DON concentrations into the alluvial aquifer system (mean value 19.1 mg N L⁻¹), and so indicating that DON should not be overlooked in the nitrogen budgets of agriculturally-dominated catchments.

In this study we have investigated the uptake and distribution of arsenic (As) and phosphate (Pi) in roots, shoots, and grain of wheat grown in an uncontaminated soil irrigated with solutions containing As at three different concentrations (0.5, 1 and 2 mg l⁻¹) and in the presence or in the absence of P fertilization. Arsenic in irrigation water reduced plants growth and decreased grain yield. When Pi was not added (P-), plants were more greatly impacted compared to the plus Pi (P+) treatments. The differences in mean biomass between P- and P+ treatments at the higher As concentrations demonstrated the role of Pi in preventing As toxicity and growth inhibition. Arsenic concentrations in root, shoot and grain increased with increasing As concentration in irrigation water. It appears that P fertilization minimizes the translocation of As to the shoots and grain whilst enhancing P status of plant. The observation that P fertilization minimises the translocation of arsenic to the shoots and grain is interesting and may be useful for certain regions of the world that has high levels of As in groundwater or soils.

Background, aim, and scope Tobacco, Nicotiana tabacum, is a widely used model plant for growth on heavy-metal-contaminated sites. Its high biomass and deep rooting system make it interesting for phytoextraction. In the present study, we investigated the antioxidative activities and glutathione-dependent enzymes of different tobacco clones optimized for better Cd and Zn accumulation in order to characterize their performance in the field. Main features The improved heavy metal resistance also makes the investigated tobacco clones interesting for understanding the plant defense enzyme system in general. Freshly harvested plant material (N. tabacum leaves) was used to investigate the antioxidative cascade in plants grown on heavy metal contaminated sites with and without amendments of different ammonium nitrate and ammonium sulfate fertilizers. Materials and methods Plants were grown on heavily polluted soils in north-east Switzerland. Leaves were harvested at the field site and directly deep frozen in liquid N₂. Studies were concentrated on the antioxidative enzymes of the Halliwell-Asada cycle, and spectrophotometric measurements of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), superoxide dismutase (SOD, EC 1.15.1.1), glutathione peroxidase (GPX, EC 1.11.1.9), glutathione reductase (GR, EC 1.6.4.2), glutathione S-transferase (GST, EC 2.5.1.18) were performed. Results and discussion We tried to explain the relationship between fertilizer amendments and the activity of the enzymatic defense systems. When tobacco (N. tabacum) plants originating from different mutants were grown under field conditions with varying fertilizer application, the uptake of cadmium and zinc from soil increased with increasing biomass. Depending on Cd and Zn uptake, several antioxidant enzymes showed significantly different activities. Whereas SOD and CAT were usually elevated, several other enzymes, and isoforms of GST were strongly inhibited. Conclusions Heavy metal uptake represents severe stress to plants, and specific antioxidative enzymes are induced at the cost of more general reactions of the Halliwell-Asada cycle. In well-supplied plants, the glutathione level remains more or less unchanged. The lack of certain glutathione S-transferases upon exposure to heavy metals might be problematic in cases when organic pollutants coincide with heavy metal pollution. When planning phytoremediation of sites, mixed pollution scenarios have to be foreseen and plants should be selected according to both, their stress resistance and hyperaccumulative capacity.