Limitations of instantaneous water quality sampling in surface-water catchments: Comparison with near-continuous phosphorus time-series data.

The validity of load estimates from intermittent, instantaneous grab sampling is dependent on adequate spatial coverage by monitoring networks and a sampling frequency that re?ects the variability in the system under study. Catchments with a ?ashy hydrology due to surface runoff pose a particular challenge as intense short duration rainfall events may account for a signi?cant portion of the total diffuse transfer of pollution from soil to water in any hydrological year. This can also be exacerbated by the presence of strong background pollution signals from point sources during low flows. In this paper, a range of sampling methodologies and load estimation techniques are applied to phosphorus data from such a surface water dominated river system, instrumented at three sub-catchments (ranging from 3 to 5 km2 in area) with near-continuous monitoring stations. Systematic and Monte Carlo approaches were applied to simulate grab sampling using multiple strategies and to calculate an estimated load, Le based on established load estimation methods. Comparison with the actual load, Lt, revealed signi?cant average underestimation, of up to 60%, and high variability for all feasible sampling approaches. Further analysis of the time series provides an insight into these observations; revealing peak frequencies and power-law scaling in the distributions of P concentration, discharge and load associated with surface runoff and background transfers. Results indicate that only near-continuous monitoring that re?ects the rapid temporal changes in these river systems is adequate for comparative monitoring and evaluation purposes. While the implications of this analysis may be more tenable to small scale ?ashy systems, this represents an appropriate scale in terms of evaluating catchment mitigation strategies such as agri-environmental policies for managing diffuse P transfers in complex landscapes.

Investigating the of Water treatment residuals on Phosphorus mobility derived from biosolid application to Willow coppice

Short rotation willow coppice (SRWC) treatment of biosolids is limited by the oversupply of biosolid derived phosphorus; this can lead to eventual losses of phosphorus to water. Water treatment residuals (WTR), a by-product of potable water treatment, have been identified as a viable soil amendment for mitigation of phosphorus loss. WTR exploit the capacity of internally held aluminium oxide-hydroxide complexes to immobilise labile phosphorus. However indiscriminate additions to plots can result in inadequate control or excessive immobilization of soluble P, leading to crop deficiencies. Four commercially grown common willow (Salix) genotypes (Terra Nova, Endeavour, Resolution and Tora) were grown in soil amended with WTR at five different application rates (0, 10, 25, 50 and 100 tonne ha-1 air-dry basis) in a glasshouse pot experiment. The effects of application rates on plant yields, tissue P concentrations, P uptake and soil labile P availability were measured. Results indicate labile P was reduced with increasing WTR application rates, without any negative agronomic impacts.

Influences of phosphorus starvation on OsACR2.1 expression and arsenic metabolism in rice seedlings

The effects of phosphorus (P) status on arsenate reductase gene (OsACR2.1) expression, arsenate reductase activity, hydrogen peroxide (H(2)O(2)) content, and arsenic (As) species in rice seedlings which were exposed to arsenate after -P or +P pretreatments were investigated in a series of hydroponic experiments. OsACR2.1 expression increased significantly with decreasing internal P concentrations; more than 2-fold and 10-fold increases were found after P starvation for 30 h and 14 days, respectively. OsACR2.1 expression exhibited a significant positive correlation with internal root H(2)O(2) accumulation, which increased upon P starvation or exposure to H(2)O(2) without P starvation. Characterization of internal and effluxed As species showed the predominant form of As was arsenate in P-starved rice root, which contrasted with the +P pretreated plants. Additionally, more As was effluxed from P-starved rice roots than from non-starved roots. In summary, an interesting relationship was observed between P-starvation induced H(2)O(2) and OsACR2.1 gene expression. However, the up-regulation of OsACR2.1 did not increase arsenate reduction in P-starved rice seedlings when exposed to arsenate.

Enchytraeid worms retard polycyclic aromatic hydrocarbon degradation in a coniferous forest soil

In this study the fate of naphthalene, fluorene and pyrene were investigated in the presence and absence of enchytraeid worms. Microcosms were used, which enabled the full fate of ¹⁴C-labelled PAHs to be followed. Between 60 and 70% of naphthalene was either mineralised or volatilised, whereas over 90% of the fluorene and pyrene was retained within the soil. Mineralisation and volatilisation of naphthalene was lower in the presence of enchytraeid worms. The hypothesis that microbial mineralisation of naphthalene was limited by enchytraeids because they reduce nutrient availability, and hence limit microbial carbon turnover in these nutrient poor soils, was tested. Ammonia concentrations increased and phosphorus concentrations decreased in all microcosms over the 56 d experimental period. The soil nutrient chemistry was only altered slightly by enchytraeid worms, and did not appear to be the cause of retardation of naphthalene mineralisation. The results suggest that microbial availability and volatilisation of naphthalene is altered as it passes through enchytraeid worms due to organic material encapsulation. © 2004 Elsevier Ltd. All rights reserved.

Relationship between plant phosphorus status and the kinetics of arsenate influx in clones of deschampsia cespitosa (L.) beauv. that differ in their tolerance to arsenate

Uptake kinetics of arsenate were determined in arsenate tolerant and non-tolerant clones of the grass Deschampsia cespitosa under differing root phosphorus status to investigate the mechanism controlling the suppression of arsenate influx observed in tolerant clones. Influx was always lower in tolerants compared to non-tolerants. Short term influx of arsenate by the high affinity uptake system in both tolerant clones was relatively insensitive to root phosphorus status. This was in contrast to the literature where the regulation of the phosphate (arsenate) uptake system is normally much more responsive to plant phosphorus status. The low affinity uptake system in both tolerant and non-tolerant clones, unlike the high affinity uptake system, was more closely regulated by root phosphate status and was repressed to a much greater degree under increasing root phosphorus levels than the high affinity system. © 1994 Kluwer Academic Publishers.

Biomass allocation, phosphorus nutrition and vesicular-arbuscular mycorrhizal infection in clones of Yorkshire Fog, Holcus lanatus L. (Poaceae) that differ in their phosphate uptake kinetics and tolerance to arsenate

Biomass and phosphorus allocation were determined in arsenate tolerant and non-tolerant clones of the grass Holcus lanatus L. in both solution culture and in soil. Arsenate is a phosphate analogue and is taken up by the phosphate uptake system. Tolerance to arsenate in this grass is achieved by suppression of arsenate (and phosphate) influx. When clones differing in their arsenate tolerance were grown in solution culture with a range of phosphate levels, a tolerant clone did not fare as well as a non-tolerant at low levels of phosphate nutrition in that it had reduced shoot biomass production, increased biomass allocation to the roots and lower shoot phosphorus concentration. At a higher level of phosphate nutrition there was little or no difference in these parameters, suggesting that differences at lower levels of phosphate nutrition were due solely to differences in the rates of phosphate accumulation. In experiments in sterile soil (potting compost) the situation was more complicated with tolerant plants having lower growth rates but higher phosphorus concentrations. The gene for arsenate tolerance is polymorphic in arsenate uncontaminated populations. When phosphorus concentration of tolerant phenotypes was determined in one such population, again tolerants had a higher phosphorus status than non-tolerants. Tolerants also had higher rates of vesicular-arbuscular mycorrhizal (VAM) infection. The ecological implications of these results are that it appears that suppression of the high affinity uptake system, is at least in part, compensated by increased mycorrhizal infection. © 1994 Kluwer Academic Publishers.

Phosphorus nutrition of arsenate-tolerant and nontolerant phenotypes of velvetgrass

Velvetgrass (Holcus lanatus L.), also known as Yorkshire fog grass, has evolved tolerance to high levels of arsenate, and this adaptation involves reduced accumulation of arsenate through the suppression of the high affinity phosphate-arsenate uptake system. To determine the role of P nutrition in arsenate tolerance, inhibition kinetics of arsenate influx by phosphate were determined. The concentration of inhibitor required to reduce maximum influx (V(max)) by 50%, K₁, of phosphate inhibition of arsenate influx was 0.02 mol m^-3 in both tolerant and nontolerant clones. This was compared with the concentration where influx is 50% of maximum, a K(m), for arsenate influx of 0.6 mol m^-3 for tolerants and 0.025 mol m^-3 for nontolerants and, therefore, phosphate was much more effective at inhibiting arsenate influx in tolerant genotypes. The high affinity phosphate uptake system is inducible under low plant phosphate status, this increasing plant phosphate status should increase tolerance by decreasing arsenate influx. Root extension in arsenate solutions of tolerant and nontolerant tillers grown under differing phosphate nutritional regimes showed that indeed, increased plant P status increased the tolerance to arsenate of both tolerant and nontolerant clones. That plant P status increased tolerance again argues that P nutrition has a critical role in arsenate tolerance. To determine if short term flux and solution culture studies were relevant to As and P accumulation in soils, soil and plant material from a range of As contaminated sites were analyzed. As predicted from the short-term competition studies, P was accumulated preferentially to As in arsenate tolerant clones growing on mine spoil soils even when acid extractable arsenate in the soils was much greater than acid extractable phosphate. Though phosphate was much more efficient at competing with arsenate for uptake, plants growing on arsenate contaminated land still accumulated considerable amounts of As. Plants from the differing habitats showed large variation in plant phosphate status, pasture plants having much higher P levels than plants growing on the most contaminated mine spoil soils. The selectivity of the phosphate-arsenate uptake system for phosphate compared with arsenate, coupled with the suppression of this uptake system enabled tolerant clones of the grass velvetgrass to grow on soils that were highly contaminated with arsenate and deficient in phosphate.

Do leaves of plants on phosphorus-impoverished soils contain high concentrations of phenolic defence compounds?

Prominent theories of plant defence have predicted that plants growing on nutrient-poor soils produce more phenolic defence compounds than those on richer soils. Only recently has the Protein Competition Model (PCM) of phenolic allocation suggested that N and P limitation could have different effects because the nutrients are involved in different cellular metabolic processes. 2. We extend the prediction of the PCM and hypothesize that N will have a greater influence on the production of phenolic defensive compounds than P availability, because N limitation reduces protein production and thus competition for phenylalanine, a precursor of many phenolic compounds. In contrast, P acts as a recyclable cofactor in these reactions, allowing protein and hence phenolic production to continue under low P conditions. 3. We test this hypothesis by comparing the foliar concentrations of phenolic compounds in (i) phenotypes of 21 species growing on P-rich alluvial terraces and P-depleted marine terraces in southern New Zealand, and (ii) 87 species growing under similar climates on comparatively P-rich soils in New Zealand vs. P-depleted soils in Tasmania. 4. Foliar P concentrations of plants from the marine terraces were about half those of plants from alluvial soils, and much lower in Tasmania than in New Zealand. However, foliar concentrations of N and phenolic compounds were similar across sites in both comparisons, supporting the hypothesis that N availability is a more important determinant of plant investment in phenolic defensive compounds than P availability. We found no indication that reduced soil P levels influenced plant concentrations of phenolic compounds. There was wide variation in the foliar N and P concentrations among species, and those with low foliar nutrient concentrations produced more phenolics (including condensed tannins). 5. Our study is the first trait comparison extending beyond standard leaf economics to include secondary metabolites related to defence in forest plants, and emphasizes that N and P have different influences on the production of phenolic defence compounds. © 2009 British Ecological Society.

The hyperaccumulator Sedum plumbizincicola harbors metal-resistant endophytic bacteria that improve its phytoextraction capacity in multi-metal contaminated soil

Endophyte-assisted phytoremediation has recently been suggested as a successful approach for ecological restoration of metal contaminated soils, however little information is available on the influence of endophytic bacteria on the phytoextraction capacity of metal hyperaccumulating plants in multi-metal polluted soils. The aims of our study were to isolate and characterize metal-resistant and 1-aminocyclopropane-1-carboxylate (ACC) utilizing endophytic bacteria from tissues of the newly discovered Zn/Cd hyperaccumulator Sedum plumbizincicola and to examine if these endophytic bacterial strains could improve the efficiency of phytoextraction of multi-metal contaminated soils. Among a collection of 42 metal resistant bacterial strains isolated from the tissues of S. plumbizincicola grown on Pb/Zn mine tailings, five plant growth promoting endophytic bacterial strains (PGPE) were selected due to their ability to promote plant growth and to utilize ACC as the sole nitrogen source. The five isolates were identified as Bacillus pumilus E2S2, Bacillus sp. E1S2, Bacillus sp. E4S1, Achromobacter sp. E4L5 and Stenotrophomonas sp. E1L and subsequent testing revealed that they all exhibited traits associated with plant growth promotion, such as production of indole-3-acetic acid and siderophores and solubilization of phosphorus. These five strains showed high resistance to heavy metals (Cd, Zn and Pb) and various antibiotics. Further, inoculation of these ACC utilizing strains significantly increased the concentrations of water extractable Cd and Zn in soil. Moreover, a pot experiment was conducted to elucidate the effects of inoculating metal-resistant ACC utilizing strains on the growth of S. plumbizincicola and its uptake of Cd, Zn and Pb in multi-metal contaminated soils. Out of the five strains, B. pumilus E2S2 significantly increased root (146%) and shoot (17%) length, fresh (37%) and dry biomass (32%) of S. plumbizincicola as well as plant Cd uptake (43%), whereas Bacillus sp. E1S2 significantly enhanced the accumulation of Zn (18%) in plants compared with non-inoculated controls. The inoculated strains also showed high levels of colonization in rhizosphere and plant tissues. Results demonstrate the potential to improve phytoextraction of soils contaminated with multiple heavy metals by inoculating metal hyperaccumulating plants with their own selected functional endophytic bacterial strains.

Electrokinetic treatment of environmental matrices. Contaminants removal and phosphorus recovery

There is a need to develop viable techniques for removal and recovery organic and inorganic compounds from environmental matrices, due to their ecotoxicity, regulatory obligations or potential supplies as secondary materials. In this dissertation, electro –removal and –recovery techniques were applied to five different contaminated environmental matrices aiming phosphorus (P) recovery and/or contaminants removal. In a first phase, the electrokinetic process (EK) was carried out in soils for (i) metalloids and (ii) organic contaminants (OCs) removal. In the case of As and Sb mine contaminated soil, the EK process was additionally coupled with phytotechnologies. In a second phase, the electrodialytic process (ED) was applied to wastes aiming P recovery and simultaneous removal of (iii) toxins from membrane concentrate, (iv) heavy metals from sewage sludge ash (SSA), and (v) OCs from sewage sludge (SS). EK enhanced phytoremediation showed to be viable for the remediation of soils contaminated with metalloids, as although remediation was low, it combines advantages of both technologies while allowing site management. EK also proved to be an effective remediation technology for the removal and degradation of emerging OCs from two types of soil. Aiming P recovery and contaminants removal, different ED cell set-ups were tested. For the membrane concentrates, the best P recovery was achieved in a three compartment (3c) cell, but the highest toxin removal was obtained in a two compartment (2c) cell, placing the matrix in the cathode end. In the case of SSA the best approach for simultaneous P recovery and heavy metals removal was to use a 2c-cell placing the matrix in the anode end. However, for simultaneous P recovery and OCs removal, SS should be placed in the cathode end, in a 2c-cell. Overall, the data support that the selection of the cell design should be done case-by-case.

Root-induced increases in soil pH and nutrient availability to field-grown cereals and legumes on acid sandy soils of Sudano-Sahelian West Africa

A field experiment with millet (Pennisetum glaucum L.), sorghum [Sorghum bicolor (L.) Moench], cowpea (Vigna unguiculata L.) and groundnut (Arachnis hypogeae L.) was conducted on severely P-deficient acid sandy soils of Niger, Mali and Burkina Faso to measure changes in pH and nutrient availability as affected by distance from the root surface and by mineral fertiliser application. Treatments included three rates of phosphorus (P) and four levels of nitrogen (N) application. Bulk, rhizosphere and rhizoplane soils were sampled at 35, 45 and 75 DAS in 1997 and at 55 and 65 DAS in 1998. Regardless of the cropping system and level of mineral fertiliser applied, soil pH consistently increased between 0.7 and two units from the bulk soil to the rhizoplane of millet. Similar pH gradients were observed in cowpea, but pH changes were much smaller in sorghum with a difference of only 0.3 units. Shifts in pH led to large increases in nutrient availability close to the roots. Compared with the bulk soil, available P in the rhizoplane was between 190 and 270% higher for P-Bray and between 360 and 600% higher for P-water. Exchangeable calcium (Ca) and magnesium (Mg) levels were also higher in the millet rhizoplane than in the bulk soil, whereas exchangeable aluminium (Al) levels decreased with increasing pH close to the root surface. The results suggest an important role of root-induced pH increases for crops to cope with acidity-induced nutrient deficiency and Al stress of soils in the Sudano-Sahelian zone of West Africa.