Abstract  A critical evaluation of potential chemical interference on a molybdenum-based phosphorus ( P) colorimetric method that is used widely for soil, plant, and water research was conducted. A wide variety of elements and compounds [ aluminum ( Al), manganese ( Mn), iron ( Fe), potassium ( K), calcium ( Ca), magnesium ( Mg), sodium ( Na), nitrate ( NO3), and ethylenediaminetetraacetic acid ( EDTA)] commonly found in these materials or extracting solutions used on them were shown to cause interferences. The interferences were subtle but complex, with changes to the rate at which the color product was formed and its apparent final chemical composition. There were interactions between the type of element or compound involved and the concentration of P in the test solution. The effect of nitrate on the color product could not be distinguished from the effect of the cation ( K versus Na) with the nature of salt used because of the complexity of interacting factors. Increasing the time and temperature allowed the final absorbance for the color product to develop and produce more stable values, but the final absorbance was changed by the interfering element. Significant errors in P by the colorimetric method were observed in soil extracts and plant digests, showing that the resulting values were not accurate. Historic data using values measured by this method need re- evaluation. Alternative methods need examination to select for accurately measuring the P content to refine our knowledge of the role of this important element in soil, plant, and water studies.

Abstract  The suitability of soil-test analyses for fertilizer recommendations for hazelnuts was assessed by detailed examinations of correlations with corresponding leaf-tissue concentrations in an orchard survey study. Correlations were examined only where optimum leaf-tissue nutrient concentrations had previously been established (i.e. N, P, K, S, Mg and Ca). Soil nitrate concentrations tended to increase substantially and relatively consistently in orchards where leaf N concentrations were greater than the optimum range, showing that soil and leaf analyses can be used for fertilizer recommendations for conservation and environmental as well as production considerations. Since most of the trees of the orchards in the study had P that was at or above adequate amounts, only limited conclusions could be made for soil P tests. Data from this survey and other literature showed that hazelnut trees can obtain adequate P from soils that have relatively low Bray-1 extractable P. Ammonium acetate extraction provides a reasonably good estimate of the K and Mg that are available to hazelnuts, and, for both nutrients, K and Mg fertilizer should be recommended for hazelnut (compared with many other crops) when soil-test analyses are relatively high. Ammonium acetate extracted considerable Ca from the soil, and the amount extracted was not correlated with the concentration of Ca measured in the leaves. Calcium chloride (which extracts only unadsorbed sulphate) was a relatively poor extractant for available S because of the occurrence of sulphate adsorption in these soils. A surface 15-cm soil sample was adequate for most of the nutrients measured, but supplementation with subsurface analyses would improve nitrate, and possibly subsurface S should be included in the development of a soil test for S. Soil testing is necessary to determine whether nutrients are building up in the soil. Also, only soil testing can be used for analysis-based recommendations prior to tree planting.

Abstract  Kinetics of cell death and the production of dissolved organic carbon (DOC) were investigated in Anabaena flos-aquae (Lyngb.) Breb grown on three different N sources (N-2, nitrate, and ammonium) in a phosphorus (P)-limited chemostat. The fraction of live cells in the total population increased as growth rate increased with decreasing P limitation. Cell death was less in nitrate and ammonium media than in N-2. The specific death rate (gamma), when calculated as the slope of v(x)(-1) vs. D-1, where v(x) and D are live cell fraction (or cell viability) and dilution rate, respectively, was 0.0082 day(-1) in N-2 and 0.0042 day(-1) in nitrate. The slope of the plot in ammonium culture was not significant; however, the value of the live cell fraction was within the range for the NO3- culture. The fraction of live vegetative cells in N-2 culture was constant at all growth rates and the increase in the overall live cell fraction with growth rate was due entirely to an increase in live heterocysts. Live heterocysts comprised 3.5% of the total cells at a growth rate of 0.25 day(-1) and increased to 6.3% at 0.75 day(-1) with the ratio of live heterocysts to live vegetative cells linearly increasing with growth rate. The fraction of live vegetative cells was invariant in nitrate cultures as in N-2 cultures. The live heterocysts fraction also increased with growth rate in nitrate cultures, along with the live heterocysts : live vegetative cells ratio, but the level was lower than in N-2 cultures. DOC released from dead cells increased inversely with growth rate in N-2 from 36.4% of the total DOC at a growth rate of 0.75 day(-1) to 54.1% at 0.25 day(-1). The contribution of cell death to the total DOC production in nitrate and ammonium media was significantly less than that under N-2. DOC from dead cells consisted mainly of high-molecular-weight compounds, whereas DOC excreted from live cells was largely of low molecular weight.

Abstract  Submarine groundwater discharge (SOD) and its role in marine nutrient cycling are well known since the last decade. The freshwater equivalent, lacustrine groundwater discharge (LGD), is often still disregarded, although first reports of LGD are more than 50 years old. We identify nine different reasons why groundwater has long been disregarded in both freshwater and marine environments such as invisibility of groundwater discharge, the size of the interface and its difficult accessibility. Although there are some fundamental differences in the hydrology of SGD and LGD, caused primarily by seawater recirculation that occurs only in cases of SOD, there are also a lot of similarities such as a focusing of discharge to near-shore areas. Nutrient concentrations in groundwater near the groundwater surface water interface might be anthropogenically enriched. Due to spatial heterogeneity of aquifer characteristics and biogeochemical processes, the quantification of groundwater-borne nutrient loads is challenging. Both nitrogen and phosphoras might be mobile in near-shore aquifers and in a lot of case studies large groundwater-borne nutrient loads have been reported.

Abstract  The impact that nitrogen (N), phosphor-us (P), and potassium (K) application rates on the sulfur (S) fractions in leaves and fruits of greenhouse-grown cucumbers plants (Cucumis sativus L. cv. Brunex) are presented. The treatments were as follows: N (N1=5g NO3NH4/m(2), N2=10g NO3NH4/m(2), N3=20g NO3NH4/m(2), N4=40 g NO3NH4/m(2)), two levels of P(P1=8 g H3PO4/m(2) and P2=16g H3PO4/m(2)), and two levels of K (K1 = 20g K2SO4/m(2) and K2 = 40 g K2SO4/m(2)). The foliar and fruit contents were determined for total S, organic S and sulfate. The influence of the N treatments on the total S (St: organic S + sulfate) concentration, proved significant, showing a progressive increase in the leaf and fruit concentrations. In the leaves, the P slightly diminished the St concentration but values in the fruits did not appreciably differ from control. The K dosage did not cause the St concentration to differ from that of P, although in the fruit a slightly lower St concentration appeared in the K2 treatment. The response of the organic-S concentration in the leaves resembled that of St, and thus organic S should not be used as a diagnostic method for S status. In the relationship SO42-/St, the SO42- concentration proved more influential than did the St form, providing a more accurate representation of the potential status of this nutrient in the plant.

Abstract  Multi-soil-layering (MSL) system can be applied to wastewater treatment. The component of an MSL system can be varied as a function of site-specific availability of materials. This study investigates the comparative efficiency of five MSL systems as a function of alternative organic materials (Japanese sawdust, Thai sawdust, rice straw, kenaf, and corncob). The MSL systems were set up in 15 X 50 X 100 cm boxes consisting of "soil mixture blocks" alternated with a zeolite layer. The February-May 1999 results indicated that all the MSL systems under a non-aeration regime effectively reduced the biochemical oxygen demand (BOD5) and removed soluble reactive phosphorus (SRP) with percentages ranging from 88.0-99.8 and 92.5-100, respectively. From January to September 2000 when an on-off aeration regime was adopted, the MSL treatments comprising rice straw, kenaf, and corncob continued to effectively reduce BOD5 and remove SRP. On the other hand, the efficiency of Japanese sawdust and Thai sawdust MSL treatments in reducing BOD5 and removing SRP gradually decreased. Fine particles and slowly decomposable characteristics of Thai sawdust and Japanese sawdust induced compaction and subsequent clogging. Therefore, rice straw, kenaf, and corncob were found to be more appropriate than Thai sawdust and Japanese sawdust for use as components of the MSL systems. Aeration at a rate of 64,000 L m(-3) d(-1) for 1 week enhanced BOD5 reduction and SRP removal, especially, when clogging was observed. However, aeration at this rate reduced the TN removal efficiency of the MSL system due to the inhibition of denitrification, excessive nitrification as well as the discharge of stored NH4+-N.

Abstract  Hydrosedimentological conditions of floodplain rivers can affect nutrient delivery processes. This study evaluated the effects of sedimentological and hydrological regimes on nitrogen (N) speciation and transport in the floodplain-river system of the Middle Parana. Relations of sedimentological and hydrological regimes, assessed through turbidity and hydrometric level, with N speciation and concentration were analyzed. Simple linear regressions were performed to assess whether N load changed within the main channel in response to hydrological and sedimentological regimes. From the main channel to the floodplain, dissolved inorganic N decreased; however, the most isolated lake had the highest N concentration, almost totally in organic form. Turbidity was negatively associated with concentrations of nitrate-N (NO3-N), nitrite-N (NO2-N), and dissolved organic N (DON), and relative contributions of these N forms to total N (TN) but was positively correlated to particulate N (PN) and ammonium-N (NH4-N). The hydrometric level was positively associated with DON concentration and its relative contribution at the main channel but negatively associated with DON, PN, and TN concentrations in the most isolated lake. Simple linear regressions showed that the sedimentological regime significantly explained all N forms but not TN load. Flooding increased TN and mainly DON load. The results show that the hydrosedimentological regime largely affects N transport and speciation. The sediment peak incorporates PN to the system and affects dissolved N speciation, probably through effects of suspended particles on redox reactions. The increase of N inputs to the fluvial system during the flood could be caused by DON exportation from the floodplain.

Abstract  At-grade distribution systems for wastewater treatment represent potential sources of nutrient input to the environment. The efficacy of nutrient treatment in the vadose zone below an at-grade distribution system receiving secondary treated municipal wastewater effluent was studied on silt loam soil at a site in Calgary, Alberta, Canada, where there are large seasonal temperature fluctuations and cold winter conditions. In addition to wastewater effluent characterization, field monitoring of pore water chemistry, soil temperature, and interstitial soil gas concentrations was conducted at five different depths (up to 150 cm below surface) over the 47-week effluent dosing period. Results showed that ammonium-N from the applied effluent was effectively nitrified in the top 30 cm of the soil profile. While there was evidence for subsequent nitrate removal by denitrification in this same zone, it was limited to the warm summer months and did not appear to result in significant nitrogen mass removal (5-15%) at greater depths in the soil profile. Phosphate was rapidly attenuated in the top 60 cm of the soil profile. This study demonstrated the importance of climatic conditions on biochemical nitrogen transformations in the shallow subsurface and suggested a greater potential for nitrate leaching to groundwater in the winter. DOI: 10.1061/(ASCE)EE.1943-7870.0000560. (C) 2012 American Society of Civil Engineers.

Abstract  Through a completely randomized design and five repetitions, the content of macrominerals, microminerals, ash, and nitrates was studied in four varieties of Pennisetum purpureum (King grass, Taiwan 146, Cuba CT-115 and Cuba CT-169). There were significant differences between varieties, for the indicators studied in leaves and stems. The nitrates varied from 0.023 up to 1 07 The stem had the highest values In the macrominerals, phosphorous ranged between 0.08 and 0.21 %, potassium between 0.62 and 3.25 calcium between 0.25 and 0 76 %, magnesium between 0 29 and 0 85 %, and silica between 0 57 and 4 21 %. In all of them, the highest value was always for the leaves In the microminerals, copper varied between 6.03 and 20 09 ppm, and zinc between 17 42 and 38 32 ppm. The steins recorded the highest value, while the leaves had the highest values for manganese andiron It is concluded that there was variability in the varieties of Pennisetum for the minerals under view, as well as between their leaves, steins and seasonal periods These data may be a guide for the efficient management through the correct application of mineral or organic fertilizers or for the calculation of the mineral needs of ruminants New studies are recommended to widen and complement the information obtained

Abstract  A simple, expeditious procedure for confirming the presence of N-nitrosamines in previously screened positive water samples was proposed. Water samples were continuously aspirated into a photometric flow system for screening. Positive samples were then confirmed and N-nitrosamines were identified by gas chromatography using different detectors (mass spectrometry, flame ionization and nitrogen-phosphorus). The system for the screening purpose was based on the preconcentration of the analytes onto a sorbent column, elution, and derivatization to form nitrite, then formation of a coloured product (Griess reaction) and photometric detection. The detection limits of the gas chromatographic method for 100 ml of sample were 2.0-3.5 microg/l, 20-80 and 3-13 ng/l for flame ionization, nitrogen-phosphorus and mass spectrometric detectors, respectively. The precision as RSD was similar for all detectors (3.0-6.5%). The screening of different types of water showed that wastewaters contain levels of N-nitrosamines that can be detected only using MS as a detector.

Abstract  Nanocrystalline Ni-substituted Zn ferrites with compositions of NixZn1-xFe2O4 (x = 0-1.0) were synthesized by sol-gel auto-combustion method using metal nitrate as the reactants. Diethanolamine was selected as the fuel instead of conventional fuels such as urea, citric acid, tartaric acid or glycine. Characterization of after-calcined ferrite samples were conducted in terms of crystal structure, molecular vibrations, morphology and magnetic properties through X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope and vibrating sample magnetometer analysis, respectively. The photocatalytic activities of these ferrites were studied in term of degradation of Rhodamine B under daylight-irradiation. The corresponding results indicate that nickel loading content has significant effect on physical, magnetic, optical and photocatalytic properties of the ferrite. Comparing to the undoped Zn ferrite, Ni0.6Zn0.4Fe2O4 shows the enhancement in photocatalytic activity accompanying the degradation of Rhodamine B aqueous solution up to 77 % within 4 h. The result suggests the feasibility of this material as potential sunlight-activated photocatalyst in wastewater treatment and environment cleaning applications.

Abstract  Transparent and high preferential c-axis-oriented ZnO thin films doped with SiO(2) have been prepared by sol-gel method using zinc nitrate and tetraethylorthosilicate as precursors, absolute ethanol as solvent, and diethanolamine as sol stabilizer. Thin film deposition was performed by spin coating technique at a spinning speed of 2000 rpm/sec on glass substrate followed by calcinations at 500 degrees C. The structural characteristics of the samples were analyzed by x-ray diffractometer and atomic force microscope. The optical properties were studied by an ultraviolet-visible spectrophotometer. The results show that all the prepared ZnO thin films have a compact hexagonal wurtzite structure. With the change in the amount of SiO(2) dopants, the intensity of (002) peak, particle size, surface root mean square roughness, thickness, transmittance, absorbance, and the optical band gap of the ZnO-SiO(2) thin films were changed as well.

Abstract  In this paper, the anticorrosive effects of two types of corrosion inhibitors (anodic inhibitors and cathodic inhibitors) on rebars immersed in the simulated concrete pore solution with 3.5%( wt) NaCl were studied by the static weight loss method. The results are as following: firstly, all of the inhibitors had an anticorrosive effect on the rebars and sodium nitrite performed best. Besides, the higher the concentration, the more obvious effect.Secondly, diethanolamine had the best performance in the cathodic inhibitors. Thirdly, sodium nitrite had a good coordination effect with diethanolamine instead of being used alone. In this way, it can exist synergy and reduce the activity of cathode and anode by the formation of consecutively protective film on the surface of the rebars.

Abstract  The novel chain coordination polymer {[Cu-2(Piv)(4)(H(3)tBuDea)](Piv)}(n) (1) has been prepared through the self-assembly reaction of copper(II) nitrate with pivalic acid (HPiv) and N-tert-butyldiethanolamine (H(2)tBuDea) in acetonitrile solution. Crystallographic analysis revealed the extremely rare non-chelating bridging coordination mode of diethanolamine ligand in 1, observed for the first time in transition metal complexes, as well as in complexes of diethanolamine having a non-coordinating aliphatic group at the N atom. Possible reasons for such a coordination and analysis of the main coordination modes of diethanolamine-based ligands are discussed. Variable-temperature (1.8-300 K) magnetic susceptibility measurements showed that 1 represents a rare example of dicopper(II) tetracarboxylate that is a diamagnetic solid at room temperature. This behaviour is compared with literature examples and discussed on the basis of DFT calculations. Furthermore, 1 acts as an efficient catalyst for the mild hydrocarboxylation of linear and cyclic C-5-C-8 alkanes into the corresponding carboxylic acids.

Abstract  Silver nanoparticles (AgNPs) are commonly used in consumer products for their antibacterial activity. Silver nanoparticles may adversely influence organisms when released into the environment. The present study investigated the effect of AgNPs on the growth, morphology, and physiology of the aquatic plant duckweed (Spirodela polyrhiza). The toxicity of AgNPs and AgNO(3) was also compared. The results showed that silver content in plant tissue increased significantly with higher concentrations of AgNPs and AgNO(3) . Silver nanoparticles and AgNO(3) significantly decreased plant biomass, caused colonies of S. polyrhiza to disintegrate, and also resulted in root abscission. Physiological analysis showed that AgNPs and AgNO(3) significantly decreased plant tissue nitrate-nitrogen content, chlorophyll a (Chl a) content, chlorophyll a/b (Chl a/b), and chlorophyll fluorescence (Fv/Fm). Changes in soluble carbohydrate and proline content were also detected after both AgNO(3) and AgNPs treatment. However, after 192 h of recovery, total chlorophyll content increased, and Fv/Fm returned to control level. Median effective concentration (EC50) values for Chl a and phosphate content showed that AgNO(3) was more toxic than AgNPs (EC50 values: 16.10 ± 0.75 vs 7.96 ± 0.81 and 17.33 ± 4.47 vs 9.14 ± 2.89 mg Ag L(-1) , respectively), whereas dry-weight EC50 values showed that AgNPs were more toxic than AgNO(3) (13.39 ± 1.06 vs 17.67 ± 1.16 mg Ag L(-1) ).

Abstract  The present investigation describes a facile and rapid approach of conductive nanocomposites production and assesses the opportunity of their use as electro-mechanical sensors. Hybrid materials containing silver and polyaniline nanopartides reinforcing a thermoplastic elastomeric matrix were studied. The approach developed includes ultrasonically assisted in situ inverse emulsion polymerization of aniline oxidized by a weak oxidant and silver nitrate, and supported with a strong oxidant, ammonia peroxydisulfate. Aniline was doped with dodecylbenzene sulfonic acid in the presence of dissolved styrene-isoprene-styrene thermoplastic elastomer. While conventional polymerization of aniline with silver nitrate takes 2 weeks, by utilization of inverse emulsion polymerization, the reaction time reduces to 5 days. The assistance of a strong oxidant dramatically shortens the reaction time to 30 min. The technique developed results in uniform distribution of polyaniline/silver (PANI/Ag) conductive nanoparticles in the elastomeric matrix. The morphological studies of the films reveal spherically shaped 45 nm Ag particles. The presence of PAN I/Ag in the styrene-isoprene-styrene elastomeric matrix enhances the electrical, thermal, and mechanical properties of the nanocomposites. The approach described provides an opportunity of the development of tunable structures and a remarkably distinctive architecture. A rapid electrical resistance response to an applied strain makes the nanocomposites developed useful as sensitive strain sensors. Copyright (c) 2014 John Wiley & Sons, Ltd.

Abstract  The sediments of Haidong bay and Macun bay in Dianchi Lakes' experimental area were studied. The sediment column was cut in every 3cm, and the following items are tested, such as total phosphorus, phosphorus species, which include labile phosphate, Fe, Al-P, Ca-P and residual-P, total nitrogen, nitrate nitrogen, nitrite nitrogen, ammonium nitrogen. The results showed that the loads of nitrogen and phosphorus of these two bays increased quickly in recent years. The Fe, Al-P was the largest component in all the P-forms and the content of ammonium nitrogen in these two bays less than that of other lakes. The layer of 9 to 12 centimeters of the two bays was polluted less than the rests. It indicated that these years more and more wastewater was inflow in these two bays. At the same time, the distribution of each testing items showed another low value between 24 to 39 centimeters. So considering feasibility and economic restriction, we can set the 24 similar to 39 centimeters depth as a dredging layer.

Abstract    Pelleted wood ash (A) or crushed dolomite lime with added potassium and phosphorous (CaMgPK) was applied to plots in a 60-yr-old Norway spruce stand in Southwest Sweden. Eight years later, we measured the effect of these treatments on a number of root parameters, including root biomass and distribution (in different diameter classes), root length density (cm cm^sup -3^ soil), specific root length (SRL, m g^sup -1^ DM), and number of mycorrhizal root tips. Layers sampled included the humus layer and the upper 30 cm of the mineral soil. The total fine root (0-1 mm) biomass in the mineral soil layer was lower in the A plots than the control plots, and the fine root (1-2 mm) systems were shallower in the A plots compared to both the control and CaMgPK plots. SRL was higher in the humus layer in both the CaMgPK and A plots than in the controls, and higher in the CaMgPK than in the A plots. The number of mycorrhizal root tips was also higher in the treated plots than in the controls, with the highest numbers being found in CaMgPK plots. Based on our results, we conclude that both the CaMgPK and ash treatments resulted in changes in root morphology and, therefore, presumably increased the capacity for nutrient uptake. FOR. SCI. 50(6):802-809. [PUBLICATION ABSTRACT] Key Words: Fine roots, liming, root length, Norway spruce, wood-ash recycling.

Abstract  A bench scale reactor using a sequencing batch reactor process was used to evaluate the applicability of biosensors for the process optimization of biological carbon and nitrogen removal. A commercial biochemical oxygen demand (BOD) biosensor with a novel microbial membrane was used to determine the duration of each phase by measuring samples in real time in an SBR cycle with filling/anoxic-anaerobic/aerobic/sludge wasting/settling/withdrawal periods. Possible strategies to increase the efficiency for the biological removal of carbon and nitrogen from synthetic wastewater have been developed. The results show that application of a BOD biosensor enables estimation of organic carbon, in real time, allowing the optimization or reduction the SBR cycle time. Some typical consumption patterns for organic carbon in the non-aeration phase of a typical SBR operation were identified. The rate of decrease of BOD measured using a sensor BOD, was the highest in the initial glucose breakdown period and during denitrification. It then slowed down until a 'quiescent period' was observed, which may be considered as the commencement of the aeration period. Monitoring the BOD curve with a BOD biosensor allowed the reduction of the SBR cycle time, which leads to an increase in the removal efficiency. By reducing the cycle time from 8 to 4 h cycle, the removal efficiencies of nitrate, glucose, and phosphorus in a given time interval, were increased to nearly double, while the removal of nitrogen ammonium was increased by one-third.

Abstract  At two experimental coniferous forest sites in south-central Sweden, soil chemistry was examined following the application of different doses of self-hardened and crushed wood ash and a pelleted wood ash. One site was covered by a mixed Picea abies/Pinus sylvestris stand growing on a podzolized soil, and the other was dominated by P. sylvestris growing on a podzolized soil. Wood ash was applied in September 1995 at rates of 3, 6, and 9 ton/ha. Results are presented in terms of pH, calcium, magnesium, potassium, phosphorus, nitrogen, and carbon contents. Ash-induced increases in pH and extractable amounts of Ca and Mg in the humus layer were observed following ash application. Large differences in the recovery of applied nutrients were observed between the two sites, however. No effects on total N and C contents were noted, but there was a significant ash dose effect for ammonium in the humus layer at the pine site but not at the mixed site. When compared at the same ash dose, the effects on soil chemistry of the two different ash formations did not differ significantly.

Abstract  The possibility of short-term nutrient removal from wastewater with microalgae was evaluated with semicontinuous cultures of Scenedesmus sp. in artificial wastewater, with 30, 40 and 50% renewal of the medium every 24 h and a simulated day-night cycle. Organic biomass production ranged from 33.8 to 39.5 mg times l super(-1), with protein contents of 52-54%. Nitrate removal was high (69 to 79%), but the initial concentration of ammonia decreased only by 8 to 13%. The total inorganic nitrogen removed in 24 h varied from 17 to 22%, and 42 to 44% of the amount removed was recycled into new organic biomass. The concentration of phosphorus decreased by between 29 and 43%, with an estimated efficiency of recycling of 35 to 45%. As with nitrogen, removal was related to the availability of light, which favours active uptake and causes photosynthesis - related changes in water chemistry due to the high pH of the medium, with fast ammonia stripping and phosphate precipitation. Given that in outdoor cultures light is discontinuous, short-term nutrient removal does not seem feasible with the solar technology available for tertiary biological treatment.

Abstract  Since the late 1980s, the use of commercial fertilisers in most Eastern European countries has decreased at an unprecedented rate. We examined the impact of this dramatic reduction in agricultural inputs on concentrations of nutrients in four rivers in Eastern Europe: the Emajogi and Ohnejogi (Estonia), the Daugava (Latvia), and the Tisza (Hungary). Time series of nitrate (NO3-N) and phosphate (PO4-P) concentrations and data on runoff were selected to represent catchments with substantial areas of agricultural land and available time series of sufficient length and frequency. The study period was 1987-1998. We detected downward trends in nitrate-N and phosphate-P in only two of the four rivers. Our results imply that the response to the extensive decrease in agricultural intensity since the late 1980s has been slow and limited in many rivers. Corresponding results in the literature are inconclusive and comprise several examples of both decreasing and non-decreasing nutrient concentrations. Our findings, along with similar data from other studies, indicate that large cuts in nutrient inputs do not necessarily induce an immediate response, particularly in medium-sized and large catchment areas. Moreover, the difference we noted between nitrogen and phosphorus suggests that factors other than reduced fertiliser application influenced the inertia of the water quality response.

Abstract  A lettuce crop (Lactuca sativa L. cv. 'Sitonia') was grown hydroponically using the Nutrient Film Technique (NFT) in greenhouse experiments designed to investigate the effects on growth and elemental accumulation of reduced concentrations of nitrogen (N), phosphorus (P), and/or potassium (K) in the nutrient supply. The concentration of these elements was varied ever a 100-fold range, either separately or simultaneously; the highest concentration (Control) being that used by local commercial hydroponic lettuce growers. Reductions in the external concentrations of these elements (below Control) had no adverse effect on growth, rates of uptake, and accumulation of N, P, and K, and hence, utilization efficiency of these elements. External concentrations of N, P, and K may, therefore, safely be reduced to 1/10th of the Control in a recirculating hydroponic system; in non-recirculating systems, they may be reduced to 1/100th of the control.

Abstract  Phosphorus loss from soil can play an important role in eutrophication of aquatic bodies. The seasonal variation of available phosphorus in soil profiles of three major paddy soils (Bai soil, Huangni soil and Wushan soil) during wheat and rice growth seasons was studied in the Taihu Lake region of China. The results were as follows: the available phosphorus contents differed in the three paddy soils. Available phosphorus content in Bai soil was the lowest in these soils. The available phosphorus content decreases rapidly with depth from the soil surface and reach the minimum value at approximately 45?cm before increasing slightly near the groundwater. The contents of available phosphorus were higher in February (tillering and shooting period of wheat) and in September (full heading time of rice) than in other months. The total phosphorus content strongly affects available phosphorus content in the studied soils. During the period of wheat cultivation, they show a typical power function relationship with correlation coefficient r?=?0.6492** (n?=?13), a significant positive linear correlation. In addition, available phosphorus content has a remarkable positive linear correlation with organic matter content, r?=?0.9111** (n?=?13), and a remarkable negative linear correlation with pH value, r?=?-0.5945* (n?=?13). In Wushan soil, there is a negative linear correlation between clay content and available phosphorus content, r?=?-0.9289* (n?=?4). Therefore, total phosphorus content, organic matter content and pH value are major impact factors on available phosphorus content in these soils.