Removal of pesticide mixtures in a stormwater wetland collecting runoff from a vineyard catchment

Wetlands can collect contaminated runoff from agricultural catchments and retain dissolved and particle-laden pesticides. However, knowledge about the capacity and functioning of wetland systems with respect to the removal of pesticides is very limited. Here we show that stormwater wetlands can efficiently remove pesticides in runoff from vineyard catchments during the period of pesticide application, although flow and hydrochemical conditions of the wetland largely vary over time. During the entire agricultural season, the inflowing load of nine fungicides, six herbicides, one insecticide and four degradation products was 8.039 g whereas the outflowing load was 2.181 g. Removal rates of dissolved loads by the wetland ranged from 39% (simazine) to 100% (cymoxanil, gluphosinate, kresoxim methyl and terbuthylazine). Dimethomorph, diuron, glyphosate, metalaxyl and tetraconazole were more efficiently removed in spring than in summer. More than 88% of the input mass of suspended solids was retained, underscoring the capability of the wetland to trap pesticide-laden particles via sedimentation. Only the insecticide flufenoxuron was frequently detected in the wetland sediments. Our results demonstrate that stormwater wetlands can efficiently remove pesticide mixtures in agricultural runoff during critical periods of pesticide application, although fluctuations in the runoff regime and hydrochemical characteristics can affect the removal rates of individual pesticides.     

Comparing the partitioning behavior of Giardia and Cryptosporidium with that of indicator organisms in stormwater runoff

Microbial association with particles can significantly affect the fate and transport characteristics of microbes in aquatic systems as particle-associated organisms will be less mobile in the environment than their free phase (i.e. unattached) counterparts. As such, similarities or dissimilarities in the partitioning behavior of indicator organisms and pathogens may have an impact on the suitability of a particular indicator to act as a surrogate for a pathogen. This research analyzed the partitioning behavior of two pathogens (Cryptosporidium, Giardia) and several common indicator organisms (fecal coliform, Escherichia coli, Enterococci, Clostridium perfringens spores, and coliphage) in natural waters under both dry and wet weather conditions. Samples were taken from several streams in two distinct sampling phases: (i) single grab samples; and (ii) intrastorm samples obtained throughout the duration of four storms. Partitioning behavior varied by microbial type, with 15-30% of bacterial indicators (fecal coliform, E. coli, and Enterococci) associated with settleable particles compared to 50% for C. perfringens spores. Both pathogens exhibited similar levels of particle association during dry weather (roughly 30%), with increased levels observed during wet weather events (Giardia to 60% and Cryptosporidium to 40%). The settling velocities of particle-associated microbes were also estimated, with those of the bacterial indicators (fecal coliform, E. coli, and Enterococci), as well as C. perfringens spores, being similar to that of the Giardia and Cryptosporidium, suggesting these organisms may exhibit similar transport behavior. With respect to intrastorm analysis, the highest microbial concentrations, in both particle-associated and free phase, occurred during the earlier stages of a storm. The total loadings of both indicators and pathogens were also estimated over the course of individual storms.     

Characterizing fecal contamination in stormwater runoff in coastal North Carolina, USA

Microbial contaminants in stormwater runoff have the potential to negatively impact public health. Stormwater runoff to coastal waters is increasing in amount and rate of discharge due to loss of vegetated landscape and increasing coastal development. However, the extent and nature of microbial contamination of stormwater runoff in North Carolina (NC) has not been previously characterized. The aim of this study was to measure a range of fecal indicator bacteria (FIB) and molecular markers at three coastal sites. E. coli and Enterococcus sp. were measured in addition to molecular markers including Bacteroides Human-Specific Marker (HS) and fecal Bacteroides spp. Levels of FIB in stormwater far exceeded recreational water quality guidelines, frequently by several orders of magnitude. High concentrations of fecal Bacteroides spp. and the presence of HS indicated the presence of human fecal contamination in the stormwater runoff, but only during specific storms. Examinations of levels of fecal contamination in stormwater over multiple seasons and a range of storm conditions will allow managers to consider appropriate design of effective mitigation strategies necessary to maintain and restore coastal water quality.     

Rainwater and the resulting runoff chemistry in Shiraz city,southwest Iran

Samples were collected from rainwater, the resulting runoff in urban drainage channels and the Khoshk River (a seasonal river which passes through the city and receives urban drainage channels runoff). Major elements and selected heavy metals (Cu, Pb and Zn) concentrations were investigated for rainwater samples. Marine and non-marine sources of the elements in rainwater were investigated by calculation of Sea salt fraction, Non sea salt fraction and application of factor analysis. pH and mean concentrations of major ions and heavy metals (Cu, Pb and Zn) were compared to the results of similar studies in other countries. GIS interpolation maps indicated the impact of traffic pollution and Shiraz industrial complex on spatial distribution of Cu, Pb and Zn in rainwater. Major ions and Cu, Pb and Zn mean concentrations in runoff samples were also studied and compared to the rainwater results. Since the Khoshk River is the main runoff drainage channel in the city and is used for irrigation, its water quality was also examined.     

Short-term algal toxicity test based on phosphate uptake

In order to develop a short-term algal toxicity test, the growth of and the phosphate uptake by the green alga Selenastrum capricornutum during batch culture were observed. In the control medium, S. capricornutum took up phosphate earlier than it grew. It was also observed that the phosphate uptake was inhibited by the presence of a toxicant. From these results, phosphate uptake was considered as one of the useful effect parameters for a short-term algal toxicity test. As the removal rate of phosphate from the medium is a function of the amount of algal cell initially inoculated, the test period is variable. The relationship between the amount of inoculation and phosphate uptake was examined and the test conditions suitable for a 3-h toxicity test were established as one example. According to this test procedure, the inhibitory effect of some toxicants on the phosphate uptake was determined. For comparison, a conventional algal assay based on algal growth was also performed. The EC50s for both tests were close. This indicated that the algal toxicity test method proposed in this paper would be useful for the uses where rapidity is required.     

Comparison between the short-term and the long-term toxicity of six triazine herbicides on photobacteria Q67

The bioluminescence inhibition of six triazine herbicides including desmetryne (DES), simetryn (SIM), velpar (VEL), prometon (PRO), metribuzin (MET), and aminotriazine (AMI) on Vibrio qinghaiensis sp.-Q67 (Q67) was determined to investigate the effects of exposure duration on the ecotoxicological relevance of triazine herbicides. Based on the short-term microplate toxicity analysis (MTA), a long-term MTA was established to assess the impact of exposure time on the toxicities of the herbicides. The results show that the long-term toxicities of DES and SIM are similar to their short-term toxicities, and the long-term toxicities of VEL, PRO, and MET are higher than their short-term toxicities, while AMI without short-term toxicity has a high long-term toxicity. In addition, a parabolic relationship was found between the pEC₅₀ (the negative logarithm of the EC₅₀, log 1/EC₅₀) and the logarithm of octanol-water partition coefficient (logK_ow). To better understand their toxicity process, the time-dependent toxicities of the six herbicides on Q67 were determined over a period of 12 h during which measurements were taken every 30 min to generate an integral effect surface related to both concentration and duration.     

A study on pesticide runoff from paddy fields to a river in rural region--1: field survey of pesticide runoff in the Kozakura River, Japan

Runoff characteristics of nine kinds of herbicides from paddy fields were surveyed in the Kozakura River, that is one of the tributaries flowing into the Lake of Kasumigaura, over a period of 23 April to 30 June (before and after rice transplantation) of year. The flow rates of river water and the concentrations of herbicides in the river water were measured every day in May and every 2 days in April and June at six survey sites along the river. The runoff characteristics of herbicides were elucidated by taking account of the rainfall data, the detailed application data (application date and quantities of herbicides applied to each paddy field in a region), and their physico-chemical properties. The runoff rates (the runoff/application amounts ratio) were calculated for each herbicide, resulting in the range of 8.2-22.4%. The runoff rates were correlated fairly well with octanol-water partition coefficient, logP(ow), rather than with water solubility of herbicides.     

Reproductive toxicity of nitroaromatics to the cricket, Acheta domesticus

The effect of TNT (2,4,6-trinitrotoluene) and its metabolites, 2,4-dinitrotoluene (2,4-DNT), 2-amino-4,6-dinitrotoluene (2A-DNT), and 4-amino-2,6-dinitrotoluene (4A-DNT) on cricket (Acheta domesticus) reproduction was evaluated. We previously used crickets to assess the toxicity of a nitramine explosive (RDX) and its metabolites. It is common to find that while much information on the environmental impact of the parent compound is available in the literature, such is often not the case for the degradation metabolites of the parent compound. In some instances, these metabolites are as toxic (or more so) as the parent compound and we hypothesized that this might be the case for TNT. The presence of TNT and its metabolites in sand (10 µg/g) did not adversely affect cricket egg production, but adversely affected hatching of cricket eggs as compared to controls. However, there were no differences in hatching success among TNT and metabolite treatment groups. Hatching success of cricket eggs in soil or following topical exposure decreased as concentrations of TNT and its metabolites increased. The relative toxicity of TNT and its metabolites in soil generally followed the trend of TNT < 2A-DNT < 4A-DNT < 2,4-DNT. In addition, toxicity appeared to be higher in sand than in sandy loam soil or in the topical exposure test. After 45 days of exposure in sandy loam soil, the EC₂₀ (20% effect concentration), EC₅₀ (50% effect concentration), and EC₉₅ (95% effect concentration) were 14, 116, and 10,837 µg/g for TNT: 1.7, 32, and 16,711 µg/g for 2A-DNT: 1.9, 9, and 296 µg/g for 4A-DNT: and 0.4, 5.7, and 1437 µg/g for 2,4-DNT. Overall, results suggest that parent TNT and metabolites are toxic to cricket eggs at relatively high concentrations and these toxic effects are manifested as a decrease in hatching success.     

Complexation and toxicity of copper and the free metal bioassay technique

The concentrations of free and total copper toxic to Daphnia and guppies were determined in inorganic media with and without addition of various concentrations of β-alanine, glycine, glutamic acid or Tris. Free copper concentrations were determined using a cupric ion electrode. Stability constants calculated for each of the detected complexes compared favourably with previously published values, with the possible exception of the Cu(OH)₂ complex. Free copper concentrations in solutions equally toxic to Daphnia were observed to vary greatly, primarily because of the toxicity of copper amino acid complexes to this organism. The copper/amino acid complexes were, nevertheless, less toxic than the free copper ions. The copper/β-alanine complex was observed to be less toxic to guppies than to Daphnia, indicating a difference in sensitivity to different copper complexes in different organisms. Copper/Tris complexes were found to be only slightly toxic to both Daphnia and guppies. A bioassay technique for determining free copper concentrations by comparing copper toxicity before and after addition of Tris was tested and verified. Although free metal concentrations can be determined from properly conducted bioassays, the variation in free metal concentration in equally toxic solutions demonstrates that free metal concentrations cannot be calculated by simply comparing metal toxicity in a test solution with toxicity of the same metal in a standard solution with known free metal concentration, unless it is known that no complexes are present in the test solution which can form toxic complexes with the metal.     

Toxicity of the 13 priority pollutant metals to Vibrio fisheri in the Microtox chronic toxicity test

The Microtox Acute Toxicity Test has been successfully used to measure the toxicity of metals and other pollutants at high concentrations (ppm) in selected environmental samples. However, metals and other toxicants are often found in much lower concentrations (ppb) in many municipal wastewaters and receiving waters. In order to assess the toxicity of these pollutants in these samples, a more sensitive toxicity assay is needed. The Microtox chronic toxicity test has been developed to measure the sublethal effect of toxicants over multiple generations of the test species, Vibrio fisheri. In this study, the toxicity of the 13 priority pollutant metals [i.e. As, Se, Cd, Cr (III and VI), Cu, Pb, Sb, Ag, Tl, Zn, Be, Hg and Ni] to V. fisheri was evaluated using the Microtox chronic toxicity test. In this test, the inhibitory concentration (IC), lowest observable effect concentration (LOEC), and no observable effect concentration (NOEC) were obtained after 22-h of incubation at 27+/-1 degrees C, by comparing the light output of the control to that of the test sample. Among the 13 priority pollutant metals, beryllium (Be) was found to be the most toxic in the test (LOEC=0.742-1.49 microg/l) while thallium (Tl) was the least toxic (LOEC=3840-15300 microg/l). The LOECs for copper (as Cu) and lead (Pb) in reagent (ASTM Type I) water were 6.78-13.6 microg/l and 626-1251 microg/l, respectively. The toxicity of copper sulfate (as Cu) in reagent water was shown and significantly reduced with the addition of natural organic matter (fulvic acid) or EDTA to the sample. The LOEC values for the 13 priority pollutant metals in this test were comparable to or lower than those reported for commonly used aquatic toxicity tests, such as the Ceriodaphnia dubia assay.     

Use of partition coefficients to predict mixture toxicity

By using the C(18)-Empore disks/water partition coefficient (K(MD)) to describe the toxicity of 50 mixed halogenated benzenes to Photobacterium phosphoreum, an approach is proposed in this study. Application of the approach to the 15 other related mixtures prove the predictive capability of this K(MD)-based approach, due to the consistency between the predicted toxicity and the observed ones with r(2)=0.929, SE=0.104, F=169.513 at P<0.001. Further analysis of this approach finds that, for the mixtures, although the toxicity is highly correlated with their hydrophobicity, this correlation is free from the range difference of the hydrophobicity, the ratio or the number of the individual chemicals. These analysis results suggest that this K(MD)-based approach is able to predict the toxicity of mixture pollutants in wastewater.     

A study on pesticide runoff from paddy fields to a river in rural region--2: development and application of a mathematical model

A mathematical model was developed to predict the runoff of pesticides from paddy fields to a river in a rural region. The model comprises three submodels: (1) submodel for river flow, (2) submodel for pesticide behavior in paddy fields, (3) submodel for pesticide behavior in a river. The tank model was applied to predict the river flow and the paddy water. In order to reproduce the actual behavior of pesticides in paddy fields, the kinetics of the transport and reaction mechanisms of pesticides applied to paddy fields were considered in the model. The model was applied to the Kozakura River Basin where the detailed field survey was conducted. The model reflected well the runoff characteristics of pesticides obtained from the detailed field survey.     

Temporal flux and spatial dynamics of nutrients, fecal indicators, and zoonotic pathogens in anaerobic swine manure lagoon water

Confined animal feeding operations (CAFOs) often use anaerobic lagoons for manure treatment. In the USA, swine CAFO lagoon water is used for crop irrigation that is regulated by farm-specific nutrient management plans (NMPs). Implementation of stricter US environmental regulations in 2013 will set soil P limits; impacting land applications of manure and requiring revision of NMPs. Precise knowledge of lagoon water quality is needed for formulating NMPs, for understanding losses of N and C in ammonia and greenhouse gas emissions, and for understanding risks of environmental contamination by fecal bacteria, including zoonotic pathogens. In this study we determined year-round levels of nutrients and bacteria from swine CAFO lagoon water. Statistical analysis of data for pH, electrical conductivity (EC), inorganic and organic C, total N, water-soluble and total minerals (Ca, Cu, Fe, K, Mg, Mn, P, and Zn) and bacteria (Escherichia coli, enterococci, Clostridium perfringens, Campylobacter spp., Listeria spp., Salmonella spp., and staphylococci) showed that all differed significantly by dates of collection. During the irrigation season, levels of total N decreased by half and the N:P ratio changed from 9.7 to 2.8. Some seasonal differences were correlated with temperature. Total N and inorganic C increased below 19 °C, and decreased above 19 °C, consistent with summer increases in ammonia and greenhouse gas emissions. Water-soluble Cu, Fe, and Zn increased with higher summer temperatures while enterococci and zoonotic pathogens (Campylobacter, Listeria, and Salmonella) decreased. Although their populations changed seasonally, the zoonotic pathogens were present year-round. Increasing levels of E. coli were statistically correlated with increasing pH. Differences between depths were also found. Organic C, total nutrients (C, Ca, Cu, Fe, Mg, Mn, N, P, and Zn) and C. perfringens were higher in deeper samples, indicating stratification of these parameters. No statistical interactions were found between collection dates and depths.     

Novel homologs of the multiple resistance regulator marA in antibiotic-contaminated environments

Antibiotics are commonly detected in the environment as contaminants. Exposure to antibiotics may induce antimicrobial-resistance, as well as the horizontal transfer of resistance genes in bacterial populations. We selected the resistance gene marA, mediating resistance to multiple antibiotics, and explored its distribution in sediment and water samples from surface and sewage treatment waters. Ciprofloxacin and ofloxacin (fluoroquinolones), sulphamethoxazole (sulphonamide), erythromycin, clarythromycin, and spiramycin (macrolides), lincomycin (lincosamide), and oxytetracycline (tetracycline) were measured in the same samples to determine antibiotic contamination. Bacterial populations from environmental samples were challenged with antibiotics to identify resistant isolates. The gene marA was found in almost all environmental samples and was confirmed by PCR amplification in antibiotic-resistant colonies. 16S rDNA sequencing revealed that the majority of resistant isolates belonged to the Gram-positive genus Bacillus, not previously known to possess the regulator marA. We assayed the incidence of marA in environmental bacterial populations of Escherichia coli and Bacillus by quantitative real-time PCR in correlation with the levels of antibiotics. Phylogenetic analysis indicated the possible lateral acquisition of marA by Bacillus from Gram-negative Enterobacteriaceae revealing a novel marA homolog in Bacillus. Quantitative PCR assays indicate that the frequency of this gene in antropised environments seems to be related to bacterial exposure to water-borne antibiotics.     

Contribution of treated wastewater to the microbiological quality of Seine River in Paris

Urban part of Seine River serving as drinking water supply in Paris can be heavily contaminated by Cryptosporidium spp. and Giardia duodenalis. In the absence of agricultural practice in this highly urbanized area, we investigated herein the contribution of treated wastewater to the microbiological quality of this river focusing on these two parasites. Other microorganisms such as faecal bacterial indicators, enteroviruses and oocysts of Toxoplasma gondii were assessed concurrently. Raw wastewaters were heavily contaminated by Cryptosporidium and Giardia (oo)cysts, whereas concentrations of both protozoa in treated wastewater were lower. Treated wastewater, flowed into Seine River, had a parasite concentration closed to the one found along the river, in particular at the entry of a drinking water plant (DWP). Even if faecal bacteria were reliable indicators of a reduction in parasite concentrations during the wastewater treatment, they were not correlated to protozoal contamination of wastewater and river water. Oocysts of T. gondii were not found in both raw and treated wastewater, or in Seine River. Parasitic contamination was shown to be constant in the Seine River up to 40 km upstream Paris. Altogether, these results strongly suggest that treated wastewater does not contribute to the main parasitic contamination of the Seine River usually observed in this urbanized area.     

Comparison of toxicity and release rates of Cu and Zn from anti-fouling paints leached in natural and artificial brackish seawater

Biocide-containing anti-fouling paints are regulated and approved according to the added active ingredients, such as Cu. Biocide-free paints are considered to be less environmentally damaging and do not need an approval. Zn, a common ingredient in paints with the potential of causing adverse effects has received only minor attention. Laboratory experiments were conducted in artificial brackish seawater (ASW) and natural brackish seawater (NSW) to quantify release rates of Cu and Zn from biocide-containing and biocide-free labeled eroding anti-fouling paints used on commercial vessels as well as leisure boats. In addition, organisms from three trophic levels, the crustacean Nitocra spinipes, the macroalga Ceramium tenuicorne and the bacteria Vibrio fischeri, were exposed to Cu and Zn to determine the toxicity of these metals. The release rate of Cu in NSW was higher from the paints for professional use (3.2-3.6 µg cm⁻² d^− 1) than from the biocide leaching leisure boat paint (1.1 µg cm⁻² d^− 1). Biocide-free paints did leach considerably more Zn (4.4-8.2 µg cm⁻² d^− 1) than biocide-containing leisure boat paint (3.0 µg cm⁻² d^− 1) and ship paints (0.7-2.0 µg cm⁻² d^− 1). In ASW the release rates of both metals were notably higher than in NSW for most tested paints. The macroalga was the most sensitive species to both Cu (EC₅₀ = 6.4 µg l^− 1) and Zn (EC₅₀ = 25 µg l^− 1) compared to the crustacean (Cu, LC₅₀ = 2000 µg l^− 1 Zn, LC₅₀ = 890 µg l^− 1), and the bacteria (Cu, EC₅₀ = 800 µg l^− 1 and Zn, EC₅₀ = 2000 µg l^− 1). The results suggest that the amounts of Zn and Cu leached from anti-fouling paints may attain toxic concentrations in areas with high boat density. To fully account for potential ecological risk associated with anti-fouling paints, Zn as well as active ingredients should be considered in the regulatory process.     

A cross comparison of QPCR to agar-based or defined substrate test methods for the determination of Escherichia coli and enterococci in municipal water quality monitoring programs

Molecular methods such as quantitative, real-time polymerase chain reaction (QPCR) are intended to shorten the period between sampling and publicly available results. Cross comparison studies in Racine, WI, USA evaluated QPCR against agar-based (US EPA Method 1600) and defined substrate (IDEXX Colilert-18^®) methods for the detection and quantification of Escherichia coli and enterococci in a variety of aqueous environments (wastewater, stormwater, and surface water). Regulatory outcomes were also compared based on choice of indicator and method. Positive correlation was seen between QPCR cell equivalents and viable cells through the wastewater treatment process and in all surface water samples (river or freshwater bathing beach) but not in direct stormwater discharge. For surface water samples, correlation improved with the application of a site-specific corrective factor, with regulatory action correctly predicted 98% of the time at bathing beaches. This study suggests the potential utility of QPCR for certain water quality monitoring applications.     

Effect of river water, sediment and time on the toxicity and bioavailability of molinate to the marine bacterium Vibrio fischeri (Microtox)

The toxicity and bioavailability of molinate to Vibrio fischeri (Microtox((R))) were determined in both laboratory and river water in the absence and presence of sediment after 0, 24, 48, 72 and 96-h exposure. The bioavailability of molinate, expressed as 5min EC50s (bioluminescence) and their fiducial limits calculated using initial measured concentrations, to V. fischeri in laboratory water in the absence and presence of sediment ranged from 1.8 (1.7-2.1) to 3.6 (3.5-3.7) mgL(-1) and 1.3 (1.2-1.4) to 4.2 (3.5-4.5) mgL(-1), respectively. The corresponding values in river water and river water plus sediment were 1.7 (1.6-1.8) to 3.8 (3.6-4.1) and 1.3 (1.3-1.4) to 4.6 (4.2-4.9) mgL(-1), respectively. River water did not significantly (P>0.05) reduce the bioavailability of molinate to V. fischeri compared to that of laboratory water. However, the presence of sediment significantly (P<0.05) reduced the bioavailability of molinate to V. fischeri in both waters. The exposure time also significantly (P<0.05) reduced the bioavailability of molinate to V. fischeri in both waters in the presence and absence of sediment. The type of water did not significantly (P>0.05) affect the loss of molinate during the 96-h exposure period. However, the presence of sediment significantly (P<0.01) increased the loss of molinate from the test solutions, probably by binding to the sediment particles. Exposure period and concentration levels significantly (P<0.05) affected the loss of the herbicides over the 96h.     

Release of copper from sintered tungsten-bronze shot under different pH conditions and its potential toxicity to aquatic organisms

Sintered tungsten-bronze is a new substitute for lead shot, and is about to be deposited in and around the wetlands of North America. This material contains copper in the alloyed form of bronze. This in vitro study was performed according to U.S. Fish and Wildlife Service criteria to determine the dissolution rate of copper from the shot, and to assess the toxic risk that it may present to aquatic organisms. The dissolution of copper from tungsten-bronze shot, pure copper shot, and glass beads was measured in a buffered, moderately hard, synthetic water of pH 5.5, 6.6, and 7.8 over a 28-day period. The dissolution of copper from both the control copper shot and the tungsten-bronze shot was affected significantly by the pH of the water and the duration of dissolution (all p values<0.000). The rate of copper release from tungsten bronze shot was 30 to 50 times lower than that from the copper shot, depending on pH (p<0.0000). The observed expected environmental concentration of copper released from tungsten-bronze shot after 28 days was 0.02 microg/L at pH 7.8, and 0.4 microg/L at pH 5.6, using a loading and exposure scenario specific in a U.S. Fish and Wildlife Service protocol. Ratio Quotient values derived from the highest EEC observed in this study (0.4 microg/L), and the copper toxic effect levels for all aquatic species listed in the U.S. Environmental Protection Agency ambient water quality criteria database, were all far less than the 0.1 criterion value. Given the conditions stipulated by the U.S. Fish and Wildlife Service and the U.S. Environmental Protection Agency, heavy loading from discharged tungsten-bronze shot would not pose a toxic risk to potable water, or to soil. Consequently, it would appear that no toxic risks to aquatic organisms will attend the use of tungsten-bronze shot of the approved composition. Given the likelihood that sintered tungsten-bronze of the same formula will be used for fishing weights, bullets, and wheel balance weights, it is expected that the use of this new material in these applications will not be associated with toxic risks to aquatic life.     

Tree-ring hydrologic reconstructions for the Heihe River watershed, western China since AD 1430

Based on the tree-ring-width analysis, the total precipitation from previous July to current June of the Qilian Mountains from 1634 to 2000 AD and the average runoff from previous September to current June in the middle section of the Heihe River from 1430 to 2007 have been reconstructed. This allowed detailed examination of the hydrologic history of the watershed of the Heihe River in western China. Precipitation, runoff and groundwater level were found to be significantly correlated with each other on the decadal scale. The three curves display quite synchronous trends of natural variation before AD 1940 to present before the onset of man-made disturbances. A remarkable period is AD 1925-1940 when the precipitation is low in the upper section, the runoff decreases in the middle section, and the groundwater level declines in the downstream section. After 1940, the groundwater level shows a lag effect, which may be a result of high water consumption in the middle and downstream sections. All three tree-ring based hydrologic indices commonly display the most significant periodicities around 80 (78-82), 50 (49-58) and 2 year. These cycles correspond to large-scale oscillation found in the climate system and appear mainly related to ocean-atmosphere interaction.