Perchlorate accumulation in forage and edible vegetation

The accumulation of perchlorate in vegetation is becoming a concern, with increasing numbers of sites reporting the presence of perchlorate in groundwater and surface water. This study investigated potential perchlorate uptake and distribution by a variety of forage and edible crops in both the laboratory and the field. Perchlorate concentrations in soybean leaves grown in the greenhouse were significantly higher than perchlorate concentrations in soybean seeds and pods. Perchlorate concentrations in alfalfa grown in sand were significantly lower than those in alfalfa grown in soil. The concentration of perchlorate in tomato was lower in the fruit than the leaves. Commercially grown wheat and alfalfa samples all contained perchlorate, 0.72-8.6 mg/kg of fresh weight (FW) in the wheat stems, 0.71-4.4 mg/kg of FW in the wheat heads, and 2.9 mg/kg of FW in alfalfa. All field garden samples tested (including cucumber, cantaloupe, and tomato) that were irrigated with perchlorate-tainted water contained perchlorate at various concentrations ranging from 0.040 to 1.65 mg/kg of FW. Bioconcentration factors (BCF), ratios of plant fresh weight concentrations to estimated or measured groundwater concentrations [(microg/kg of FW)/microg/L], were all in the same order of magnitude ranging from 215 +/- 126 for wheat stems to 233 +/- 264 for wheat heads and to 380 +/- 89 for alfalfa. BCF for garden fruit samples were much lower (0.5-20). Results from this study highlight the potential for perchlorate exposure by routes other than drinking water.     

Recycling of water for irrigation: Persistence of enteroviruses in sewage effluent and natural waters receiving the effluent

A virological analyses of a sewage treatment plant which provided chlorinated, activated sludge treated sewage effluent to irrigate a complete two-year crop of sugarcane was made. The raw, the activated sludge treated and the chlorinated sewage effluent, as well as streams and a harbor receiving sewage effluents were concentrated by either the polymer two-phase, PE-60, Al(OH)₃, protamine sulfate, or cellulose membrane method and assayed for human enteric viruses. Viruses were recovered from 100% (11/11) of the raw sewages tested at concentrations ranging from 27 to 19 000 PFU l^?1 while 76% (13/17) of the activated sludge treated effluent was positive at concentrations ranging from 7 to 5222 PFU l^?1. After chlorination, 58% (31/53) of the samples was positive for virus at concentrations ranging from 2 to 750 PFU l^?1. Human enteroviruses were also isolated from shallow flowing streams at distances up to 3 mi (5 km) from the closest known sewage effluent discharge point and from a harbor approximately 0.5 mi (0.8 km) from the point of sewage discharge entering the harbor. The viruses most often isolated were echovirus 7, coxsackievirus B-4, B-5 and poliovirus 1, 2, and 3. These results indicate that although activated sludge treatment plus chlorination remove approximately 90% of the virus from the raw sewage, the final treated sewage effluent, which is normally discharged into a stream and in this experimental study to irrigate sugarcane, still contains a significant concentration of infectious viruses. Furthermore, the recovery of enteroviruses from waterways at points distant from the sewage treatment plants indicates that sewage-borne viruses persist in natural water environment. The significance of enteric viruses in waters accessible to the public and used for irrigation purposes remains to be determined.     

Effects of charcoal production on maize yield,chemical properties and texture of soil

The effects of charcoal production on soil textural and chemical properties were investigated in Ejura, Ghana. The aim was to study the effects of heating and charcoal residue on maize yield, soil texture and soil chemical properties. Composite samples were taken from the 0–10 cm layer of soil at charcoal-making sites and from adjacent fields (control). Twelve sites were randomly selected for the study across the range of the Kotokosu watershed. Maize was planted in four selected locations on charcoal site soils (CSS) and adjacent field soils (AFS) to assess the impact of charcoal production on crop yield. There was a significant increase in soil pH, base saturation, electrical conductivity, exchangeable Ca, Mg, K, Na and available P in the soil at the kiln sites as compared to the adjacent soils. A relative change of up to 329% was observed in K while organic C and total N decreased by 9.8% and 12.8%, respectively. Organic C and total N were highly correlated ( P <0.01) and both parameters significantly ( P <0.05) depended on clay minerals in the soils. Soil texture was also modified with a significantly higher sand content and lower clay fraction in the CSS. The grain and biomass yield of maize increased by 91% and 44%, respectively, on CSS as compared to AFS. Further research to ascertain the long-term effects of charcoal production on the soil environment and the fertility of tropical soils is needed.     

The impacts of individual plant species on rhizosphere microbial communities in soils of different fertility

To investigate the effects of individual plant species on microbial community properties in soils of differing fertility, a microcosm experiment was carried out using plant species representative of the dominant flora in semi-fertile temperate grasslands of northern England. Soil microbial biomass and activity were found to be significantly greater in the more fertile, agriculturally improved soil than in the less productive unimproved meadow soil. Differences in microbial community structure were also evident between the two soils, with fungal abundance being greater in the unimproved soil type. Individual plant species effects significantly differed between the two soils. Holcus lanatus and Anthoxanthum odoratum stimulated microbial biomass in the improved soil type, but negatively affected this measure in the unimproved soil. In both soil types, herb species generally had negative effects on microbial biomass. Patterns for microbial activity were less consistent, but as with microbial biomass, A. odoratum and H. lanatus promoted respiration, whereas the herbs negatively affected this measure. All plant species grown in the improved soil increased the abundance of fatty acids synthesised by bacteria (bacterial phospholipid fatty acid analysis) relative to bare soil, but they negatively impacted on this group of fatty acids in unimproved soil. Similarly, the abundance of the fungal fatty acid 18:26 was increased by all plants in the more fertile improved soil only, albeit non-significantly. Our data indicate that effects of plant species on microbial properties differ markedly in soils of differing fertility, making general predictions about how individual plants impact on soil properties difficult to make.     

On the cause of the 1930s Dust Bowl

During the 1930s, the United States experienced one of the most devastating droughts of the past century. The drought affected almost two-thirds of the country and parts of Mexico and Canada and was infamous for the numerous dust storms that occurred in the southern Great Plains. In this study, we present model results that indicate that the drought was caused by anomalous tropical sea surface temperatures during that decade and that interactions between the atmosphere and the land surface increased its severity. We also contrast the 1930s drought with other North American droughts of the 20th century.