Biomass decay rate and influencing factors of four submerged aquatic vegetation in Everglades wetland.

Submerged aquatic vegetation (SAV) enhances assimilation efficiency of nutrients in wetlands, and improves the water quality, but may serve as secondary sources when their litter residues are decomposed. A laboratory incubation was conducted to investigate the biomass decay rate of four common SAV species: Hydrilla (Hydrilla verticillata), Naiad (Najas guadalupensis), Potamogeton (P. illinoensis), and Chara (Chara spp). Plant biomass samples were collected from the stormwater treatment areas in south Florida, USA and incubated in water at 40 °C for 126 days. At the end of incubation, the mixtures were passed through a 1 m sieve, and the plant debris above the screen were rinsed, oven-dried, and weighed. Biomass (dry matter) was measured and the decay rate was calculated, and total concentration of carbon (C), nitrogen (N), phosphorus (P) and other elements (K, Na, Ca, Mg, Al, Fe, and Mn) in the SAV plants were determined. Subsamples (5 mL) of the suspension (representing floc solution) were used for bacteria and fungi colony counting. The relationships between the decay rate and nutrient features or chemical components were analyzed. The results showed that Hydrilla had the highest decay rate (0.007930 d-1), and Chara had the lowest (0.002798 d-1). Concentrations of N, P, C and cations (K, Na, and Mn), and the ratio (K + Na)/(Ca + Al) in the SAVs had positive correlations with the biomass decay rate, whereas concentrations of Ca and Al, and the ratios of C/N and C/P in the plants were negatively correlated with the decay rate. However, the effect of microorganisms in the biomass decay rate of SAVs was not significant. These results suggest that high C concentration and more Ca and Al in the plant tissues can retard SAV biomass decomposition.

Acidic leaching of potentially toxic metals cadmium, cobalt, chromium, copper, nickel, lead, and zinc from two Zn smelting slag materials incubated in an acidic soil.

A column leaching study, coupled with acid deposition simulation, was conducted to investigate the leaching of potentially toxic metals (PTM) from zinc smelting slag materials (SSM) after being incubated in an acid Alfisol for 120 days at room temperature. Two SSMs (SSM-A: acidic, 10 yrs exposure with moderate high PTM concentrations versus SSM-B: alkaline, 2 yrs exposure with extremely high PTM concentrations), were used for the incubation at 0.5, 1, 2.5, 5 wt% amendment ratios in triplicate. Five leaching events were conducted at day 1, 3, 7, 14, and 28, and the leaching of PTMs mainly occurred in the first three leaching events, with the highest PTM concentrations in leachate measured from 5 wt% SSM amendments. After leaching, 2.5, 12, 5.5, 14, 11, and 9 wt% of M3 extractable Pb, Zn, Cd, Co, Cr, and Ni could be released from 5 wt% SSM-A amended soils, being respectively 25, 12, 4, 2, 2, and 2 times more than those from 5 wt% SSM-B amended soils. In the leachates, the concentrations of PTMs were mostly affected by leachant pH and were closely correlated to the concentrations of Fe, Al, Ca, Mg and P with Cd, Pb, and Zn showing the most environmental concern. Visual MINTEQ 3.1 modeling suggested metallic ions and sulfate forms as the common chemical species of PTMs in the leachates; whereas, organic bound species showed importance for Cd, Pb, Cu, and Ni, and CdCl+ was observed for Cd. Aluminum hydroxy, phosphate, and sulfate minerals prevailed as the saturated minerals, followed by chloropyromorphite (Pb5(PO4)3Cl) and plumbogummite (PbAl3(PO4)2(OH)5·H2O) in the leachates. This study suggested that incubation of SSMs in acidic soil for a long term can enhance the release of PTMs as the forms of metallic ions and sulfate when subjected to acid deposition leaching.

Leaching of cadmium, chromium, copper, lead, and zinc from two slag dumps with different environmental exposure periods under dynamic acidic condition.

Over the past few decades, zinc smelting activities in Guizhou, China have produced numerous slag dumps, which are often dispersed on roadsides and hill slopes throughout the region. During periods of acid rain, these exposed slags release heavy metals into surface water bodies. A column leaching study was designed to test the potential release of the heavy metals cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) under simulated acid rain events. Two slags with varying environmental exposure periods were packed in columns and subjected to leaching solutions of pH 3.5, 5.5, or DI H2O at intervals of 1, 7, 14, 28, 56d. Pulse concentrations of Cd in leachate were found above 5µg/L, Cr, Pb, and Zn >10µg/L, whereas, Cu reached 10µg/L. After five leaching events, the leachability (percentage of cumulative heavy metal leached after five leaching events as in its respective total concentration in slags) of Cd was 0.05 percent and 0.035 percent from the old and young slag, respectively. Cr (0.035 percent and 0.05 percent) was greater than Cu (0.002 percent and 0.005 percent) and Zn (0.006 percent and 0.003 percent), while the lowest leachability was observed for Pb (0.0005 percent and 0.0002 percent) from the old and young slags, respectively. Reaction rates (release amount of heavy metals in certain period of leaching) of heavy metals in the leachates demonstrated the sequence of Zn>Cr>Cd, Cu>Pb. Leaching release of heavy metals was jointly affected by the pH of leaching solution and mineral composition of slags (including chemical forms of Cd, Cr, Cu, Pb, and Zn). Environmental exposure period of slags, resulting in the alteration of minerals, could affect the release process of heavy metals in leaching as well.

Impact of mixed land-use practices on the microbial water quality in a subtropical coastal watershed.

Surface runoff water is an important non-point source of fecal pollution to downstream water; however, there is a lack of systematic studies on the microbial quality of surface runoff water from watersheds with mixed land uses. In this study water samples from 12 surface runoff holding water bodies (SRW), which collected runoff from various patterns of land use within the St. Lucie watershed along the southeastern coastline of Florida, were collected monthly for 22 months. The concentration of fecal indicator bacteria (FIB) and frequency of detection of Salmonella and host specific markers (HF183, CF128, CF193, and HS-esp) were determined, and their associations with land use, rainfall, and water physico-chemical parameters were investigated. Higher FIB concentrations were observed from urban land and cattle ranch sites. Within the same primary land use pattern, different sub-patterns did not have the same level of FIB: golf communities contributed less to fecal pollution than residential areas, and plant nursery sites contained relative higher FIB concentrations than other agricultural sites. Salmonella, CF128, and CF193 markers were more frequently detected from the cattle ranch sites. In contrast the frequency of detecting human specific markers (HF183 and HS-esp) was much higher in residential sites. Rainfall positively affected the concentration of FIB and occurrence of Salmonella, possibly by providing more inputs or mobilizing the sources from sediments. Water temperature, dissolved organic carbon (DOC), and nutrient levels were positively correlated with FIB concentrations and occurrence in SRW, possibly by promoting their growth and survival. This study indicated the need for site specific mitigation strategies to improve SRW and downstream water quality.

Dolomite phosphate rock (DPR) application in acidic sandy soil in reducing leaching of phosphorus and heavy metals-a column leaching study.

A column leaching study was designed to investigate the leaching potential of phosphorus (P) and heavy metals from acidic sandy soils applied with dolomite phosphate rock (DPR) fertilizers containing varying amounts of DPR material and N-Viro soils. DPR fertilizers were made from DPR materials mixing with N-Viro soils at the ratios of 30, 40, 50, 60, and 70 %, and applied in acidic sandy soils at the level of 100 mg available P per kilogram soil. A control and a soluble P chemical fertilizer were also included. The amended soils were incubated at room temperature with 70 % field water holding capacity for 21 days before packed into a soil column and subjected to leaching. Seven leaching events were conducted at days 1, 3, 7, 14, 28, 56, and 70, respectively, and 258.9 mL of deionized water was applied at each leaching events. The leachate was collected for the analyses of pH, electrical conductivity (EC), dissolved organic carbon (DOC), major elements, and heavy metals. DPR fertilizer application resulted in elevations up to 1 unit in pH, 7-10 times in EC, and 20-40 times in K and Ca concentrations, but 3-10 times reduction in P concentration in the leachate as compared with the chemical fertilizer or the control. After seven leaching events, DPR fertilizers with adequate DPR materials significantly reduced cumulative leaching losses of Fe, P, Mn, Cu, and Zn by 20, 55, 3.7, 2.7, and 2.5 times than chemical fertilizer or control. Even though higher cumulative losses of Pb, Co, and Ni were observed after DPR fertilizer application, the loss of Pb, Co, and Ni in leachate was <0.10 mg (in total 1,812 mL leachate). Significant correlations of pH (negative) and DOC (positive) with Cu, Pb, and Zn (P<0.01) in leachate were observed. The results indicated that DPR fertilizers had a great advantage over the soluble chemical fertilizer in reducing P loss from the acidic sandy soil with minimal likelihood of heavy metal risk to the water environment. pH elevation and high dissolved organic carbon concentration in soils after DPR fertilizer application are two influential factors.

Natural and anthropogenic lead in soils and vegetables around Guiyang city, southwest China: a Pb isotopic approach.

Soils, vegetables and rainwaters from three vegetable production bases in the Guiyang area, southwest China, were analyzed for Pb concentrations and isotope compositions to trace its sources in the vegetables and soils. Lead isotopic compositions were not distinguishable between yellow soils and calcareous soils, but distinguishable among sampling sites. The highest (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios were found for rainwaters (0.8547-0.8593 and 2.098-2.109, respectively), and the lowest for soils (0.7173-0.8246 and 1.766-2.048, respectively). The (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios increased in vegetables in the order of roots

High diversity and differential persistence of fecal Bacteroidales population spiked into freshwater microcosm.

Bacteroidales markers are promising indicators of fecal pollution and are now widely used in microbial source tracking (MST) studies. However, a thorough understanding of the persistence of Bacteroidales population after being released into environmental waters is lacking. We investigated the persistence of two host specific markers (HF183 and CF193) and temporal change of Bacteroidales population over 14 days in freshwater microcosms seeded with human or bovine feces. The concentrations of HF183/CF193 and Escherichia coli were determined using quantitative polymerase chain reaction (qPCR) and standard cultivation method, respectively. Shifts in the Bacteroidales population structure were fingerprinted using PCR-denaturing gradient gel electrophoresis (DGGE) and subsequent sequencing analysis targeting both 16S rDNA and rRNA-transcribed cDNA. Both HF183 and CF193 decayed significantly faster than E. coli but the decay curves fit poorly with first-order model. High diversity of Bacteroidales population was observed for both microcosms, and persistence of different species in the population varied. Sequence analysis indicated that most of the bovine Bacteroidales populations in our study are unexplored. DGGE and decay curve indicated that RNA decayed faster than DNA, further supporting the use of rRNA as indicator of metabolically active Bacteroidales population. Evaluations with more realistic scenarios are warranted prior to extending the results of this study to real field settings.

Lead, zinc, and cadmium in vegetable/crops in a zinc smelting region and its potential human toxicity.

Lead, Zn, and Cd in vegetables/crops were investigated in a zinc smelting region in China, and their daily dietary intake by local residents was estimated. It is observed that Pb, Zn, and Cd were in 34.7-91.1, 242-575, and 0.199-2.23 µg g(-1) dry weight in vegetables/crops with their greatest concentrations in leafy vegetable. The daily dietary intake of Pb, Zn, and Cd by adult residents reached 3, 646, 59,295, and 186 µg day, respectively, and lettuce and cabbage together contributed 75% of the Pb, 50% of the Zn, and 70% of the Cd.

Immobilization of copper in contaminated sandy soils using calcium water treatment residue.

Chemical remediation has attracted increasing attention for heavy metal contaminated soils because of its relatively low cost and high efficiency. In this study laboratory incubation and column leaching experiments were conducted to understand the mechanisms of copper (Cu) immobilization by calcium water treatment residue (Ca-WTR) and to estimate the optimal rate for remediating Cu-contaminated soils. The results showed that Ca-WTR amendment significantly raised soil pH and decreased water soluble and exchangeable Cu by 62-90% in the contaminated soils. Most of the bioavailable Cu was converted into more stable Cu fractions, i.e. oxides-bound and residual Cu. The cumulative amount of Cu in the leachate after 10 leaching events was reduced by 80% and 73%, respectively for the two tested soils at the Ca-WTR rate of 20 g kg(-1) for Alfisol and 100 g kg(-1) for Spodosol. These results indicate that Ca-WTR is effective in raising soil pH and converting labile Cu to more stable forms in the contaminated soils. A pH value of 6.5 was found to be critical for lowering Cu availability in the soils. Based on this criterion and pH response curve to Ca-WTR application, the optimal rates of Ca-WTR can be estimated for different Cu-contaminated soils.

Temporal and spatial variations of copper, cadmium, lead, and zinc in Ten Mile Creek in South Florida, USA.

Lead (Pb), zinc (Zn), copper (Cu), and cadmium (Cd) often seriously deteriorate water quality. Spatial and temporal fluctuations of the metal concentrations in the Ten Mile Creek (Florida) (TMC) were monitored on a weekly basis at 7 sampling sites, from June 2005 to September 2007. River sediment samples were also collected from these sites in April, June, and October 2006 and January 2007, and analyzed for water, Mehlich 1 (M1), and Mehlich 3 (M3)-extractable metals (Mehlich, 1953, 1984), to examine the role of sediments as sources or sinks of the metals. The concentrations of lead, zinc, copper, and cadmium in the water samples were

Allocation and source attribution of lead and cadmium in maize (Zea mays L.) impacted by smelting emissions.

Plants grown in contaminated areas may accumulate trace metals to a toxic level via their roots and/or leaves. In the present study, we investigated the distribution and sources of Pb and Cd in maize plants (Zea mays L.) grown in a typical zinc smelting impacted area of southwestern China. Results showed that the smelting activities caused significantly elevated concentrations of Pb and Cd in the surrounding soils and maize plants. Pb isotope data revealed that the foliar uptake of atmospheric Pb was the dominant pathway for Pb to the leaf and grain tissues of maize, while Pb in the stalk and root tissues was mainly derived from root uptake. The ratio of Pb to Cd concentrations in the plants indicated that Cd had a different behavior from Pb, with most Cd in the maize plants coming from the soil via root uptake.

Temporal and spatial variations of nutrients in the Ten Mile Creek of South Florida, USA and effects on phytoplankton biomass.

Water quality throughout south Florida has been a major concern for many years. Nutrient enrichment in the Indian River Lagoon (IRL) is a major surface water issue and is suggested as a possible cause of symptoms of ecological degradation. In 2005-06, water samples were collected weekly from seven sites along Ten Mile Creek (TMC), which drains into the Indian River Lagoon, to investigate and analyze spatial and temporal fluctuations of nutrients nitrogen (N) and phosphorus (P). The objective of this study was to understand the relationships among chlorophyll a concentration, nutrient enrichment and hydrological parameters in the surface water body. High median concentrations of total P (TP, 0.272 mg L(-1)), PO4-P (0.122 mg L(-1)), and dissolved total P (DTP, 0.179 mg L(-1)); and total N (TN, 0.988 mg L(-1)), NO3(-)-N (0.104 mg L(-1)), NH4+-N (0.103 mg L(-1)), and total Kjeldahl N (TKN, 0.829 mg L(-1)), were measured in TMC. The concentrations of TP, PO4-P, DTP, TN, NO3(-)-N, NH4+-N, and TKN were higher in summer and fall than in winter and spring. However, chlorophyll a and pheophytin concentrations during this period in TMC varied in the range of 0.000-60.7 and 0.000-17.4 microg L(-1), with their median values of 3.54 and 3.02 microg L(-1), respectively. The greatest mean chlorophyll a (10.3 microg L(-1)) and pheophytin (5.71 microg L(-1)) concentrations occurred in spring, while the lowest chlorophyll a (1.49 microg L(-1)) and pheophytin (1.97 mug L(-1)) in fall. High concentrations of PO4-P (>0.16 mg L(-1)), DTP (>0.24 mg L(-1)), NO3(-)-N (>0.15 mg L(-1)), NH4+-N (>0.12 mg L(-1)), and TKN (>0.96 mg L(-1)), occurred in the upstream of TMC, while high concentrations of chlorophyll a (>6.8 mug L(-l)) and pheophytin (>3.9 microg L(-l)) were detected in the downstream of TMC. The highest chlorophyll a (11.8 mug L(-l)) and pheophytin (6.06 microg L(-l)) concentrations, however, were associated with static and open water conditions. Hydrological parameters (total dissolved solid, electrical conductivity, salinity, pH, and water temperature) were positively correlated with chlorophyll a and pheophytin concentrations (P < 0.01) and these factors overshadowed the relationships between N and P concentrations and chlorophyll a under field conditions. Principal component analysis and the ratios of DIN/DP and TN/TP in the water suggest that N is the limiting nutrient factor for phytoplankton growth in the TMC and elevated N relative to P is beneficial to the growth of phytoplankton, which is supported by laboratory culture experiments under controlled conditions.

Heavy metals in an impacted wetland system: a typical case from southwestern China.

Historical zinc smelting in Hezhang, southwestern China, has resulted in significant heavy metal contamination of the surrounding ecosystems. The Caohai wetland system, which is an important national nature reserve close to the Hezhang zinc smelting area, was investigated in the present study. Results showed that sediments from the Caohai wetland system have been seriously contaminated by Cd, Pb and Zn with the highest concentrations in the surface sediments being up to 71, 160 and 1,200 microg g(-1), respectively. The heavy metals in the sediments were strongly associated with the organic/sulphide and residual fractions. A more oxidized condition induced by aquatic plants tended to cause the Cd, Pb and Zn bound to the Fe-Mn oxide fraction to become more dominant. Pb isotopic compositions in the sediments indicated that the inventories of Pb in the Caohai wetland sediments were mainly derived from the historical zinc smelting in the Hezhang area, although other anthropogenic sources, such as the gasoline Pb, also made a substantial contribution to the Pb in the sediments. Heavy metal contamination in aquatic plants was also studied and the results indicated that heavy metals accumulated by plants may pose a potential threat to the higher trophic-level organisms, including humans.

Use of amendments to reduce leaching loss of phosphorus and other nutrients from a sandy soil in Florida.

GOAL, SCOPE AND BACKGROUND: Transport of P from agricultural land contributes to the eutrophication of surface waters. Soil amendment is considered one of the best management practices (BMPs) to reduce P loss from sandy soils. Laboratory column leaching experiments were conducted to evaluate the effectiveness of different soil amendments in reducing P leaching from a typical sandy soil in Florida. METHODS: The tested amendments were CaCl2, CaCO3, Al(OH)3, cellulose, and mill mud, and applied at the rate of 15 g/kg for a single amendment and each 7.5 g/kg if two amendments were combined. Leaching was conducted every four days for 32 days, 250 mL of deionized water being leached for each column per leaching event. Leachates were collected from each leaching event and analyzed for reactive P, PO4-P, and macro and micro-elements. RESULTS AND DISCUSSION: Except for the soils amended with CaCl2, or CaCl2+CaCO3, reactive P and PO4-P leaching losses mainly occurred in the first three leaching events. Phosphorus leaching from the soils amended with CaCl2 or CaCl2+CaCO3 was less but more persistent than that of other amendments. Reactive P leaching loss was reduced by 36.0% and 40.4% for the amendments of CaCl2, and CaCl2+CaCO3, respectively, as compared with chemical fertilizer alone, and the corresponding values for PO4-P were 70.8% and 71.9%. The concentrations of K, Mg, Cu, and Fe in leachate were also decreased by CaCl2 or CaCl2+CaCO3 amendment. Among the seven amendments, CaCl2, CaCO3, or their combination were most effective in reducing P leaching from the sandy soil, followed by cellulose and Al(OH)3, the effects of mill mud and mill mud + Al(OH)3 were marginal. CONCLUSIONS: These results indicate that the use of CaCl2, CaCO3, or their combination can significantly reduce P leaching from sandy soil, and should be considered in the development of BMPs for the sandy soil regions. Recommendations and Outlook. Most agricultural soils in south Florida are very sandy with minimal holding capacities for moisture and nutrients. Repeated application of fertilizer is necessary to sustain desired yield of crops on these soils. However, eutrophication of fresh water systems in this area has been increasingly concerned by the public. Losses of P from agricultural fields by means of leaching and surface runoff are suspected as one of the important non-point contamination sources. The benefits and effectiveness of soil amendment in reducing P losses from cropping production systems while sustaining desired crop yield need to be demonstrated. Calcium chloride, CaCO3, or their combination significantly reduce P leaching from sandy soil, and should be considered in the development of BMPs for the sandy soil regions.

Environmental contamination of heavy metals from zinc smelting areas in Hezhang County, western Guizhou, China.

Total heavy metal (Cd, Cr, Cu, Pb and Zn) concentrations were evaluated in smelting waste, soil, crop and moss samples collected from the Hezhang artisanal zinc smelting areas, Guizhou, China. Soil samples from the cornfield near the smelting sites contained extremely high Cd (5.8-74 mg kg(-1)), Pb (60-14,000 mg kg(-1)) and Zn (260-16,000 mg kg(-1)) concentrations. Elevated heavy metal concentrations were also found in corn plants and total Pb (0.80-1.5 mg kg(-1)) and Cd (0.05-0.76 mg kg(-1)) concentrations in corn grain have totally or partially exceeded the national guidance limits for foodstuff. Thus, the soil-to-crop transfer of heavy metals might pose a potential health risk to the local residents. Similar to the high heavy metal levels in soil and corn, Cd, Cr, Cu, Pb and Zn concentrations in moss samples collected from the smelting sites ranged from 10 to 110, 10 to 55, 26 to 51, 400 to 1200 and 330 to 1100 mg kg(-1), respectively, exhibiting a local spatial pattern of metals deposition from the atmosphere. Based on examination of Zn/Cd and Pb/Cd ratios of the analyzed samples, we have distinguished between the flue gas dust derived and smelting waste derived metals in different environmental compartments.

[Evaluation of phytoavailability of zinc and cadmium in contaminated soils by a short sequential extraction procedure].

Cultivated soils and maize samples from heavy metal contaminated locations affected by zinc smelting activities were collected in Hezhang County, Guizhou Province. Chemical fractions of zinc and cadmium (extracted by 0.01 mol x L(-1) CaCl2 and 0.005 mol x L(-1) DTPA) were evaluated by using a short three-step sequential extraction procedure. Results showed that Zn and Cd in soil were dominated by residual fraction, while the CaCl2 extractable and DTPA extractable fraction are only accounted for 0.63%, 3.91% for Zn, and 10.94%, 10.13% for Cd, respectively. Correlation analyses demonstrated that soil CaCl2 extractable metals were not correlated with maize metal concentrations, whereas the DTPA extractable fraction, residual fraction and total Zn and Cd concentrations were correlated significantly with the metal concentrations in maize roots, stems and leaves. These results indicated that CaCl2 extractable fraction may not pay important role on metal phytoavailability in the studied soils. While DTPA extractable fraction and total metal concentrations can be employed to evaluate metals phytoavailability.

Microbial indicators of heavy metal contamination in urban and rural soils.

Urban soils and especially their microbiology have been a neglected area of study. In this paper, we report on microbial properties of urban soils compared to rural soils of similar lithogenic origin in the vicinity of Aberdeen city. Significant differences in basal respiration rates, microbial biomass and ecophysiological parameters were found in urban soils compared to rural soils. Analysis of community level physiological profiles (CLPP) of micro-organisms showed they consumed C sources faster in urban soils to maintain the same level activity as those in rural soils. Cu, Pb, Zn and Ni were the principal elements that had accumulated in urban soils compared with their rural counterparts with Pb being the most significant metal to distinguish urban soils from rural soils. Sequential extraction showed the final residue after extraction was normally the highest proportion except for Pb, for which the hydroxylamine-hydrochloride extractable Pb was the largest part. Acetic acid extractable fraction of Cd, Cu, Ni, Pb and Zn were higher in urban soils and aqua regia extractable fraction were lower suggesting an elevated availability of heavy metals in urban soils. Correlation analyses between different microbial indicators (basal respiration, biomass-C, and sole C source tests) and heavy metal fractions indicated that basal respiration was negatively correlated with soil Cd, Cu, Ni and Zn inputs while soil microbial biomass was only significantly correlated with Pb. However, both exchangeable and iron- and manganese-bound Ni fractions were mostly responsible for shift of the soil microbial community level physiological profiles (sole C source tests). These data suggest soil microbial indicators can be useful indicators of pollutant heavy metal stress on the health of urban soils.