Comparison of plant families in a greenhouse phytoremediation study on an aged polycyclic aromatic hydrocarbon-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous, recalcitrant, and potentially carcinogenic pollutants. Plants and their associated rhizosphere microbes can promote PAH dissipation, offering an economic and ecologically attractive remediation technique. This study focused on the effects of different types of vegetation on PAH removal and on the interaction between the plants and their associated microorganisms. Aged PAH-polluted soil with a total PAH level of 753 mg kg(-1) soil dry weight was planted with 18 plant species representing eight families. The levels of 17 soil PAHs were monitored over 14 mo. The size of soil microbial populations of PAH degraders was also monitored. Planting significantly enhanced the dissipation rates of all PAHs within the first 7 mo, but this effect was not significant after 14 mo. Although the extent of removal of lower-molecular-weight PAHs was similar for planted and unplanted control soils after 14 mo, the total mass of five- and six-ring PAHs removed was significantly greater in planted soils at the 7- and 14-mo sampling points. Poaceae (grasses) were the most effective of the families tested, and perennial ryegrass was the most effective species; after 14 mo, soils planted with perennial ryegrass contained 30% of the initial total PAH concentration (compared with 51% of the initial concentrations in unplanted control soil). Although the presence of some plant species led to higher populations of PAH degraders, there was no correlation across plant species between PAH dissipation and the size of the PAH-degrading population. Research is needed to understand differences among plant families for stimulating PAH dissipation.     

Effect of root death and decay on dissipation of polycyclic aromatic hydrocarbons in the rhizosphere of yellow sweet clover and tall fescue

A 12-mo greenhouse study was conducted to evaluate the contribution of root death and decay on the dissipation of polycyclic aromatic hydrocarbons (PAHs) in rhizosphere soil. The contaminated soil was previously treated by land-farming, but residual PAHs remained after treatment. Tall fescue (Festuca arundinacea Schreb.) and yellow sweet clover (Melilotus officinalis Lam.) were the target plants. To specifically evaluate the effect of root decay on contaminant dissipation, plants were treated with glyphosate, a broad spectrum herbicide, to induce root decay. Although tall fescue treatments had the highest root and shoot biomass and root surface area, this plant did not result in the highest contaminant degradation rates. Significant differences were noted between treatments for seven PAHs, with the active yellow sweet clover resulting in 60 to 75% degradation of these compounds. Induced root death and decay did not produce a significant enhancement of PAH degradation. The PAH microbial degrader populations in the vegetated treatments were more than 100 times greater than those in the unvegetated control. The phospholipid fatty acid (PLFA) structural group profile shifted over the growing period, indicating a change in the community structure. In conclusion, phytoremediation was shown to be an effective polishing tool for PAH-affected soil previously subjected to biological treatment.     

Dissipation of pentachlorophenol in the aerobic-anaerobic interfaces established by the rhizosphere of rice ( Oryza sativa L.) root

Phytoremediation is an emerging technology for the detoxification and remediation of organic pollutants such as pentachlorophenol (PCP). To investigate the dissipation behavior of PCP in the aerobic-anaerobic interfaces established by the rhizosphere of rice ( L.) root, a glasshouse experiment was conducted using a specially designed rhizobox. The possible biogeochemical mechanisms were also studied through illustration of the dynamic behavior of important electron acceptors and donors that are potentially involved in the reductive dechlorination and aerobic catabolism processes of PCP. The soil was spiked with 20 ± 0.25 and 45 ± 0.25 mg of PCP kg soil. Soil in the rhizobox was divided into five different compartments at various distances from the root surface. Maximum dissipation of PCP in planted soil was observed at 3-mm distance from the root zone as well as rapid changes in concentrations of sulfate, chloride, nitrate, and ammonium at the same distance from the root. In contrast, in the unplanted soil, no difference was observed in the PCP concentration with increasing distance. After 45 d, a significantly higher concentration of PCP was degraded in planted soil compared with unplanted soil. In the unplanted microcosms, about 45% of the initial PCP was lost at both low and high added rates, respectively. This was, proportionately, a significantly smaller percentage compared with the planted rhizosphere (an average of 66 and 64.5%, respectively). Moreover, the correlations of PCP dissipation with SO, NO, and Fe were significantly negative, while the correlations of PCP dissipation with NH, Fe, and Cl were significantly positive. This suggested the oxidization of soil constituents can inhibit aerobic catabolism of PCP by consuming O, and the reduction of soil constituents can inhibit anaerobic reductive dechlorination of PCP. Therefore, the significance of the rhizosphere in phytoremediation of chlorinated compounds such as PCP differs significantly between wetland and rainfed systems.     

Phytoremediation of polycyclic aromatic hydrocarbons in manufactured gas plant-impacted soil

Contamination of soil by hazardous substances poses a significant threat to human, environmental, and ecological health. Cleanup of the contaminants using destructive, invasive technologies has proven to be expensive and more importantly, often damaging to the natural resource properties of the soil, sediment, or aquifer. Phytoremediation is defined as the cleanup of contaminated sites using plants. There has been evidence of enhanced polycyclic aromatic hydrocarbons (PAHs) degradation in rhizosphere soils for a limited number of plants. However, research focusing on the degradation of PAHs in the rhizosphere of trees is lacking. The objective of this study was to assess the potential use of trees to enhance degradation of PAHs located in manufactured gas plant-impacted soils. In greenhouse studies with intact soil cores, acenaphthene, anthracene, fluoranthene, naphthalene, and phenanthrene decreased significantly (p < 0.05) in green ash (Fraxinus pennsylvanica Marshall) and hybrid poplar (Populus deltoides x P. nigra DN 34) phytoremediation treatments when compared to the unplanted soil control. Increases in PAH microbial degraders in rhizosphere soil were observed when compared to unvegetated soil controls. In addition, the rate of degradation or biotransformation of PAHs was greatest for soils with black willow (Salix nigra Marshall), followed by poplar, ash, and the unvegetated controls. These results support the hypothesis that a variety of plants can enhance the degradation of target PAHs in soil.     

Hycrest crested wheatgrass accelerates the degradation of pentachlorophenol in soil

We investigated the effects of vegetation on the fate of pentachlorophenol (PCP) in soil using a novel high-flow sealed test system. Pentachlorophenol has been widely used as a wood preservative, and this highly toxic biocide contaminates soil and ground water at many sites. Although plants are known to accelerate the rates of degradation of certain soil contaminants, this approach has not been thoroughly investigated for PCP. The fate of [14C]PCP, added to soil at a concentration of 100 mg/kg, was compared in three unplanted and three planted systems. The plant used was Hycrest, a perennial, drought-tolerant cultivar of crested wheatgrass [Agropyron desertorum (Fischer ex Link) Schultes]. The flow-through test system allowed us to maintain a budget for 14C-label as well as monitor mineralization (breakdown to 14CO2) and volatilization of the test compound in a 155-d trial. In the unplanted systems, an average of 88% of the total radiolabel remained in the soil and leachate and only 6% was mineralized. In the planted system, 33% of the radiolabel remained in the soil plus leachate, 22% was mineralized, and 36% was associated with plant tissue (21% with the root fraction and 15% with shoots). Mineralization rates were 23.1 mg PCP mineralized kg-1 soil in 20 wk in the planted system, and for the unplanted system 6.6 mg PCP kg-1 soil for the same time period. Similar amounts of volatile organic material were generated in the two systems (1.5%). Results indicated that establishing crested wheatgrass on PCP-contaminated surface soils may accelerate the removal of the contaminant.     

Phytoremediation of aged petroleum sludge: effect of irrigation techniques and scheduling

The use of higher plants to accelerate the remediation of petroleum contaminants in soil is limited by, among other factors, rooting depth and the delivery of nutrients to the microsites at which remediation occurs. The objective of this study was to test methods of enhancing root growth and remediation in the subsurface of a contaminated petroleum sludge. The phytoremediation of highly contaminated petroleum sludge (total petroleum hydrocarbons >35 g kg(-1) was tested in the greenhouse as a function of the frequency and the depth of irrigation and fertilization. Water and dissolved plant nutrients were added to the soil surface or at a depth of 30 cm, either daily or weekly. Equivalent quantities of water and nutrients were added in all cases. Daily irrigation at a depth of 30 cm invoked greater root growth and enhanced contaminant degradation relative to all other treatments. In the absence of plants, residual concentrations of petroleum hydrocarbons after 7 mo were higher than with plants. The presence of plant roots clearly improved the physical structure of the soil and increased microbial populations. Thus, the plant roots in conjunction with daily additions of soluble N and P appeared to enhance oxygen transport to greater depths in the soil, stimulate petroleum-degrading microorganisms, and provide microbial access to soil micropores. Subsurface irrigation with frequent, small amounts of water and nutrients could significantly accelerate phytoremediation of field soils contaminated with petroleum hydrocarbons.     

Phytoremediation of aged petroleum sludge: effect of inorganic fertilizer

Phytoremediation is a promising new technology that uses higher plants to enhance biodegradation. Nutrient availability is an important factor governing the success of phytoremediation and can be regulated through the addition of fertilizer. A greenhouse study was conducted to assess the importance of nitrogen and phosphorus for the phytoremediation of petroleum sludge. Degradation of total petroleum hydrocarbons (TPH) was quantified for six fertilization rates and three vegetation treatments: bermuda grass [Cynodon dactylon (L.) Pers.], tall fescue (Festuca arundinacea Schreb.), and an unvegetated control. During the first 6 mo of the experiment, TPH declined by an average of 49% with no significant differences between treatments. After 1 yr, TPH degradation was significantly greater in both vegetated treatments with a mean TPH reduction of 68% for bermuda, 62% for fescue, and 57% for the unvegetated control. Degradation of TPH in the fescue and bermuda treatments was significantly lower in the treatments in which no fertilizer was added or N and P were added simply to maintain plant growth compared with the higher rates of fertilization. For this short-term, greenhouse experiment, optimal remediation was obtained by fertilization that produced a C to N to P ratio of 100:2:0.2.     

Soil-to-root transfer and translocation of polycyclic aromatic hydrocarbons by vegetables grown on industrial contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) are possible contaminants in some former industrial sites, representing a potential risk to human health if these sites are converted to residential areas. This work was conducted to determine whether PAHs present in contaminated soils are transferred to edible parts of selected vegetables. Soils were sampled from a former gasworks and a private garden, exhibiting a range of PAH concentrations (4 to 53 to 172 to 1263 and 2526 mg PAHs kg-1 of dry soil), and pot experiments were conducted in a greenhouse with lettuce (Lactuca sativa L. var. Reine de Mai), potato (Solanum tuberosum L. var. Belle de Fontenay), and carrot (Daucus carota L. var. Nantaise). At harvest, above- and below ground biomass were determined and the PAH concentrations in soil were measured. In parallel, plates were placed in the greenhouse to estimate the average PAH-dust deposition. Results showed that the presence of PAHs in soils had no detrimental effect on plant growth. Polycyclic aromatic hydrocarbons were detected in all plants grown in contaminated soils. However, their concentration was low compared with the initial soil concentration, and the bioconcentration factors were low (i.e., ranging from 13.4 x 10(-4) in potato and carrot pulp to 2 x 10(-2) in potato and carrot leaves). Except in peeled potatoes, the PAH concentration in vegetables increased with the PAH concentration in soils. The PAH distribution profiles in plant tissues and in soils suggested that root uptake was the main pathway for high molecular weight PAHs. On the opposite, lower molecular weight PAHs were probably taken up from the atmosphere through the leaves as well as by roots.     

Bermudagrass fertilized with slow-release nitrogen sources. I. Nitrogen uptake and potential leaching losses

With the objectives of analyzing N recovery and potential N losses in the warm-season hybrid bermudagrass 'Tifgreen' [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy], two greenhouse studies were conducted. Plugs were planted in PVC cylinders filled with a modified sandy growing medium. Urea (URE), sulfur-coated urea (SCU), and Hydroform (HYD) (Hydro Agri San Francisco, Redwood City, CA) were broadcast at rates of 100 and 200 kg N ha-1 every 20 and 40 d. The grass was clipped three times every 10 d and analyzed for N concentration and N yield. In addition, leachates were analyzed for NO3-N. Use of the least soluble source, HYD, resulted in the lowest average clipping N concentration and N yield, as compared with SCU and URE. Clipping N concentration and N yield showed a cyclic pattern through time, particularly under long-day (> 12 h) conditions. When the photoperiod decreased below 12 h, leachate NO3-N concentration exceeded the standard limit for drinking water (10 mg L-1) by 10 to 19 times with the high SCU and URE application rate and frequency. However, leaching N losses represented a minimal fraction (< 1%) of the total applied N. More applied N was recovered in plant tissues using SCU and URE (89.5%) than using HYD (64.1%), with more than 52% of applied N accumulating in clipping. Highly insoluble N sources such as HYD decrease N leaching losses but may limit bermudagrass growth and quality. Risks of NO3-N losses in bermudagrass can be avoided by proper fertilization and irrigation programs, even when a highly soluble N source is used.     

Polycyclic aromatic hydrocarbon storage in a typical Cerrado of the Brazilian savanna

There may be important biological sources of polycyclic aromatic hydrocarbons (PAHs) to the global environment, particularly of naphthalene, phenanthrene, and perylene, that originate in the tropics. We (i) studied the distribution of PAHs among different compartments of a typical Cerrado to locate their sources and (ii) quantified the PAH storage of this ecosystem. The sum of 20 PAH (sigma20PAHs) concentrations ranged from 25 to 666 microg kg(-1) in plant tissue, 7.4 to 32 microg kg(-1) in litterfall, 206 to 287 microg kg(-1) in organic soil, and 10 to 79 microg kg(-1) in mineral soil. Among the living biomass compartments, the bark had the highest mean PAH concentrations and coarse roots the lowest, indicating that PAHs in the plants originated mainly from aboveground sources. Naphthalene and phenanthrene were the most abundant individual PAHs, together contributing 33 to 96% to the sigma20PAHs concentrations. The total storage of the X20PAHs in Cerrado was 7.5 mg m(-2) to a 0.15-m soil depth and 49 mg m(-2) to a 2-m soil depth. If extrapolated to the entire Brazilian Cerrado region, roughly estimated storages of naphthalene and phenanthrene correspond to 7300 and 400 yr of the published annual emissions in the United Kingdom, respectively. The storage of benzo[a]pyrene, a typical marker for fossil fuel combustion, in the Cerrado only corresponds to 0.19 yr of UK emissions. These results indicate that the Brazilian savanna comprises a huge reservoir of naphthalene and phenanthrene originating most likely from the aboveground parts of the vegetation or associated organisms. Thus, the Cerrado might be a globally important source of these PAHs.     

Nutrient removal in tropical subsurface flow constructed wetlands under batch and continuous flow conditions

The aim of this investigation was to evaluate the influence of batch versus continuous flow on the removal efficiencies of chemical oxygen demand (COD), nitrogen (N) and total phosphorus (TP) in tropical subsurface flow constructed wetlands (SSF CW). The quantitative role of the higher aquatic plants in nutrient removal in these two operational modes was also investigated. Results indicated no significant difference (p > 0.05) in COD removal between batch and continuous flow modes for either the planted or unplanted treatments. Furthermore, the batch-loaded planted wetlands showed significantly (p < 0.05) higher ammonium removal efficiencies (95.2%) compared with the continuously fed systems (80.4%), most probably because the drain and fill batch mode presented systematically more oxidized environmental conditions. With respect to TP removal, for both planted and unplanted beds, there was significant enhancement (p < 0.05) in batch flow operation (69.6% for planted beds; 39.1% for unplanted beds) as compared to continuous flow operation (46.8% for planted beds; 25.5% for unplanted beds). In addition, at a 4-day hydraulic retention time (HRT), the presence of plants significantly enhanced both ammonia oxidation and TP removal in both batch and continuous modes of operation as compared to that for unplanted beds. An estimation of the quantitative role of aeration from drain and fill operation at a 4-day HRT, as compared to rhizosphere aeration by the higher aquatic plant, indicated that drain and fill operation might account for only less than half of the higher aquatic plant's quantitative contribution of oxygen (1.55 g O2 per m2 per day for batch flow versus 1.13 g O2 per m2 per day for continuous flow).     

Polycyclic aromatic hydrocarbon removal from soil by surfactant solubilization and Phanerochaete chrysosporium oxidation

Surfactant soil washing can remove polycyclic aromatic hydrocarbons (PAHs) from contaminated soil, and the white rot fungus, Phanerochaete chrysosporium Burdsall in Burdsall & Eslyn, can oxidize PAHs. The objective of this study was to develop a novel bioremediation technology using a combination of abiological surfactant soil washing followed by PAH biological oxidation in soil washwater using P. chrysosporium in a rotating biological contactor (RBC) reactor. Soil used for experimentation was an 11-month aged contaminated soil spiked with a total of nine PAHs: acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, benzo(a)pyrene, dibenz(a-h)anthracene, and benzo(ghi)perylene. After 11 months of aging, recovery percentages of high molecular weight PAHs [i.e., from chrysene to benzo(ghi)perylene] were greater than 86%, while those of low molecular weight PAHs (i.e., from acenaphthene to pyrene) were less than 19%. Total removal efficiency for any of the nine PAHs was greater than 90% using a combination of surfactant soil washing and P. chrysosporium oxidation of soil washwater in the RBC reactor when used in batch operation, and greater than 76% when used in continuous operation. The treatment of PAH-contaminated soil using a combination of surfactant soil washing and subsequent PAH removal from the resultant washwater in an RBC reactor, in the presence of immobilized P. chrysosporium, permits (i) a rapid abiological cleanup of soil for compliance with relevant soil quality standards and (ii) PAH biological removal in soil washwater for compliance with aqueous discharge standards.     

Analysis of transgenic Indian mustard plants for phytoremediation of metal-contaminated mine tailings

Transgenic Indian mustard [Brassica juncea (L.) Czern.] plants overproducing the enzymes gamma-glutamylcysteine synthetase (ECS) or glutathione synthetase (GS) were shown previously to have increased levels of the metal-binding thiol peptides phytochelatins and glutathione, and enhanced Cd tolerance and accumulation. Furthermore, transgenic Indian mustard plants overexpressing adenosine triphosphate sulfurylase (APS) were shown to have higher levels of glutathione and total thiols. These results were obtained with a solution culture. To better examine the phytoremediation potential of these transgenics, a greenhouse experiment was performed in which the transgenics were grown on metal-contaminated soil collected from a USEPA Superfund site near Leadville, Colorado. A grass mixture used for revegetation of the site was included for comparison. The ECS and GS transgenics accumulated significantly (P < 0.05) more metal in their shoot than wild-type (WT) Indian mustard, while the APS plants did not. Of the six metals tested, the ECS and GS transgenics accumulated 1.5-fold more Cd, and 1.5- to 2-fold more Zn, compared with wild-type Indian mustard. Furthermore, the ECS transgenics accumulated 2.4- to 3-fold more Cr, Cu, and Pb, relative to WT. The grass mixture accumulated significantly less metal than Indian mustard: approximately 2-fold less Cd, Cu, Mn, and Zn, and 5.7-fold less Pb than WT Indian mustard. All transgenics removed significantly more metal from the soil compared with WT Indian mustard or an unplanted control. While WT did not remove more metal than the unplanted control for any of the metals tested, all three types of transgenics significantly reduced the soil metal concentration, and removed between 6% (Zn) and 25% (Cd) of the soil metal. This study is the first to demonstrate enhanced phytoextraction potential of transgenic plants using polluted environmental soil. The results confirm the importance of metal-binding peptides for plant metal accumulation and show that results from hydroponic systems have value as an indicator for phytoremediation potential.     

Polycyclic aromatic hydrocarbon release from a soil matrix in the in vitro gastrointestinal tract

Soil ingestion is an important exposure route by which immobile soil contaminants enter the human body. We assessed polycyclic aromatic hydrocarbon (PAH) release from a contaminated soil, containing 49 mg PAH kg(-1), using a SHIME (Simulator of the Human Intestinal Microbial Ecosystem) reactor comprising the stomach, duodenal, and colon compartments. Polycyclic aromatic hydrocarbon release was defined as that fraction remaining in the digest supernatant after centrifugation for 5 min at 1500 x g. The PAH release in the stomach digest was only 0.44% of the total PAH present in soil, resulting in PAH concentrations of 23 micrograms PAH L(-1) chyme. The lower PAH releases in duodenum (0.13%) and colon (0.30%) digests, compared with the stomach digest, were thought to be attributed to combined complexation and precipitation with bile salts, dissolved organic matter, or colon microbiota. We studied these complexation processes in an intestinal suspension more in depth by preparing mixtures of 9-anthracenepropionic acid, a Bacillus subtilis culture, and cholin as model compounds for PAHs, organic matter, and bile salts, respectively. Bile salts or organic matter in the aqueous phase initially enhance PAH desorption from soil. However, desorbed PAHs may form large aggregates with bile and organic matter, lowering the freely dissolved PAH fraction in the supernatant. Using the model compounds, mathematical equations were developed and validated to predict PAH complexation processes in the gastrointestinal tract. Contaminant release and subsequent complexation in the gut is an important prerequisite to intestinal absorption and thus bioavailability of that contaminant. The data from this research may help in understanding the processes to which PAHs are subjected in the gastrointestinal tract, before intestinal absorption.     

Phytoremediation and long-term site management of soil contaminated with pentachlorophenol (PCP) and heavy metals

Pentachlorophenol (PCP) is a persistent organic pollutant (POP) previously used as a timber treatment chemical to prevent sap stain and wood rot. Commonly used in wood treatment industries for the last 50 years, there are now many sites worldwide that are contaminated with PCP. Although persistent, PCP is a mobile contaminant and therefore has a propensity to leach and contaminate surrounding environments. Both willow (Salix sp., 'Tangoio') and poplar (Populus sp. 'Kawa') growing in an open-ended plastic greenhouse were found to tolerate soil PCP concentrations of 250 mg kg(-1) or less and both species stimulated a significant increase in soil microbial activity when compared to unplanted controls. Both poplar and willow could not survive PCP concentrations above 250 mg kg(-1) in soil. Pentachlorophenol degradation occurred in both planted and unplanted pots, but a higher rate of degradation was observed in the planted pots. Soil contaminated by wood-treatment activities often contains co-contaminants such as B, Cr, Cu and As, that are also used as timber preservatives. An additional column leaching experiment, done along side the potted trial, found that PCP, B, Cr, Cu and As were all present in the column leachate. This indicates that although Cu, Cr and As are generally considered immobile in the soil, they were mobilised under our column conditions. If a contaminated site were to be hydraulically 'sealed' using plants, a reticulation irrigation system should be installed to capture any contaminant leachate resulting from heavy rains. This captured leachate can either be independently treated, or reapplied to the site. Our data demonstrate a reduction in soil hydraulic conductivity with repeated application of leachate containing PCP and metal compounds but the soil did not become anaerobic. This would need to be considered in site remediation design.     

Long-term effects of clipping and nitrogen management in turfgrass on soil organic carbon and nitrogen dynamics: the CENTURY model simulation

Experiments to document the long-term effects of clipping management on N requirements, soil organic carbon (SOC), and soil organic nitrogen (SON) are difficult and costly and therefore few. The CENTURY ecosystem model offers an opportunity to study long-term effects of turfgrass clipping management on biomass production, N requirements, SOC and SON, and N leaching through computer simulation. In this study, the model was verified by comparing CENTURY-predicted Kentucky bluegrass (Poa pratensis L.) clipping yields with field-measured clipping yields. Long-term simulations were run for Kentucky bluegrass grown under home lawn conditions on a clay loam soil in Colorado. The model predicted that compared with clipping-removed management, returning clippings for 10 to 50 yr would increase soil C sequestration by 11 to 25% and nitrogen sequestration by 12 to 28% under a high (150 kg N ha(-1) yr(-1) nitrogen (N) fertilization regime, and increase soil carbon sequestration by 11 to 59% and N sequestration by 14 to 78% under a low (75 kg N ha(-1) yr(-1)) N fertilization regime. The CENTURY model was further used as a management supporting system to generate optimal N fertilization rates as a function of turfgrass age. Returning grass clippings to the turf-soil ecosystem can reduce N requirements by 25% from 1 to 10 yr after turf establishment, by 33% 11 to 25 yr after establishment, by 50% 25 to 50 yr after establishment, and by 60% thereafter. The CENTURY model shows potential for use as a decision-supporting tool for maintaining turf quality and minimizing negative environmental impacts.     

Biomass of Speckled Alder on an Air-Polluted Mountain Site and its Response to Fertilization

The article summarizes outcomes of a biomass study conducted in a young speckled alder plantation on a cold mountain site. At this location, the previously existing old forest was clear felled because of damage from air pollution, and present-day surface humus is in need of restoration. The intention of this study was to quantify the biomass and nutrients accumulated by alders and their components and assess whether the initial fertilization resulted in increased biomass production and nutrient accumulation in the biomass. Besides the control, two fertilized treatments were installed. In the surface treatment (SUT), the amendment was applied as a base dressing in small circles around trees. In the planting-hole treatment (PHT), the amendment was incorporated into soil inside the planting holes. Five growth seasons after planting and fertilization, six alders from each treatment were harvested including roots. Their biomass was quantified and analyzed for macroelements. The greatest pool of dry mass (DM) was branches in the control and stem wood in the fertilized treatments. The greatest pools of macroelements were leaves and branches. The most pronounced effects of fertilization were recorded in the DM and consequently in the absolute quantities of nutrients. The DM of an average tree in the control, SUT, and PHT was 85, 226, and 231 g, respectively. The absolute contents of nutrients per tree in the fertilized treatments showed the following increases, as compared with the control: (N) 2.5–2.6 times; (P) 1.6–2.4 times; (K) 1.8–2.1 times; and (Mg) 1.8–2.0 times, respectively. Speckled alder responded positively to fertilization.     

PERFORMANCE VARIATIONS OF COD AND NITROGEN REMOVAL BY VEGETATED SUBMERGED BED WETLANDS1

ABSTRACT: Vegetated submerged bed wetlands can supplement treatment of onsite wastewater systems. This study evaluated vegetation, media, and seasonal impacts on system performance in six meso scale rock plant filters with and without narrow leaf cattails (Typha augustifolia). Daily chemical oxygen demand (COD) reductions in planted cells averaged 85 percent and weekly total nitrogen (TN) reductions averaged 50 percent. Planted cells had 17 percent greater COD reduction and 76 percent greater TN reduction than unplanted cells, both significant differences. Media type affected COD reduction, particularly in unplanted cells. COD treatment in planted cells was highest for fine crushed limestone (87±13 percent) and least variable for coarse river gravel (85±11 percent). No significant difference in TN reduction was observed for different media types (48 to 51 percent range). Seasonal influences on treatment included a significant decrease during late fall and early spring and a significant increase with temperature. After a step increase in organic loading, treatment efficiency decreased sharply but returned to prior levels after an adaptation period of about one month. Planted cells not only exhibited higher treatment efficiency but also had a retarded organic matter breakthrough, appearing after three to seven times the period for a bromide tracer. This supports a hypothesis that retardation of contaminant movement through the treatment cells results in enhanced removal. These results support the use of rock plant filters, but demonstrate the need to account for performance variations in system design. (KEY TERMS: constructed wetlands; seasonal effects; subsurface flow; Typha augustifolia; onsite wastewater treatment; water quality.)     

Polycyclic aromatic hydrocarbons (PAHs) in soils of the Moscow Region--concentrations, temporal trends, and small-scale distribution

The knowledge of the environmental fate of polycyclic aromatic hydrocarbons (PAHs) is restricted to few climatic regions of the world almost excluding the Taiga. Our objectives were to (i) separate anthropogenic from background contributions to PAH concentrations and (ii) determine temporal trends in PAH concentrations during the last century including the change in distribution of PAHs in interior and exterior portions of aggregates in soils of the Moscow region. Along a southeast-bound transect from Moscow (windward in winter) and at a background location northeast of Moscow (leeward in winter), seven topsoil samples were collected in 1910-1954 and 35 in 1998-2003. We fractionated the soils in interior and exterior portions of aggregates > 10 mm and remaining soil without aggregates. The sum of 21 PAHs (sigma21PAHs) concentrations in recent bulk soil ranged from 59 to 1350 ng g(-1). The concentrations of all PAHs were lower outside than in Moscow. The range of the concentrations of the sigma21PAHs in archived soil samples (159-1280 ng g(-1)) was similar as in recent soils. In most recent and archived samples, naphthalene and phenanthrene, were most abundant. The concentrations of low-molecular-weight PAHs decreased during the last century at most sites; those of high-molecular-weight compounds increased. The sigma21PAHs concentrations were accumulated in the exterior of aggregates (109%) and depleted in the interior (95%) relative to the concentration in bulk soil (defined as 100%), which was similar to that in the soil without aggregates (99%). The differences between aggregate interior and exterior did not change during the last century. The dominance of naphthalene and phenanthrene is typical of remote regions. The urban influence on PAH concentrations in the last century was small.     

Sequential supercritical fluid extraction (SSFE) for estimating the availability of high molecular weight polycyclic aromatic hydrocarbons in historically polluted soils

Sequential supercritical fluid (CO2) extraction (SSFE) was applied to eight historically contaminated soils from diverse sources with the aim to elucidate the sorption-desorption behavior of high molecular weight polycyclic aromatic hydrocarbons (PAHs). The method involved five extraction phases applying successively harsher conditions by increasing fluid temperature and density mobilizing target compounds from different soil particle sites. Two groups of soils were identified based on readily desorbing (available) PAH fractions obtained under mildest extraction conditions (e.g., readily desorbing fractions of fluoranthene and pyrene significantly varied between the soils ranging from <10 to >90%). Moreover, extraction behavior strongly correlated with molecular weight revealing decreasing available PAH fractions with increasing weight. Physicochemical soil parameters such as particle size distribution and organic dry mass were found to have no distinct effect on the sorption-desorption behavior of PAHs in the different soils. However, PAH profiles significantly correlated with readily available pollutant fractions; soils with relatively less mobile PAHs had higher proportions of five- and six-ring PAHs and vice versa. Eventually, biodegradability corresponded well with PAH recoveries under the two mildest extraction phases. However, a quantitative relationship was only established for soils with biodegradable PAHs. Out of eight soils, five showed no biodegradation including the four soils with the lowest fraction of readily desorbing PAHs. Only one soil (which was found to be highly toxic to Vibrio fischeri) did not match the overall pattern showing no PAH biodegradability but large fractions of highly mobile PAHs, concluding that mass transfer limitations may only be one of many factors governing biodegradability of PAHs.