Modelling sulphate-enhanced cadmium uptake by Zea mays from nutrient solution under conditions of constant free Cd2+ ion activity

A controlled hydroponic experiment was undertaken to investigate Cd uptake in relation to the activity of Cd species in solution other than the free ion (Cd²⁺) by maintaining a constant Cd²⁺ activity under variable SO₄₂⁻ and Cl⁻ concentrations exposed to maize (Zea mays var. Cameron) plants. The objectives of these experiments were: (1) to distinguish and quantify the different uptake rates of free and inorganic-complexed Cd from nutrient solution, and (2) to model the uptake of Cd by maize with a Biotic Ligand Model (BLM) in a system which facilitates the close examination of root characteristics. Results of the current experiments suggest that, in addition to the free ion, CdSO₄⁰ complexes are important factors in determining Cd uptake in nutrient solution by maize plants. Higher nominal SO₄²⁻ concentrations in solution generally resulted in a greater Cd accumulation by maize plants than predicted by the Cd²⁺ activity. A better integration of the complete dataset for the 3 harvest times (6, 9 and 11 days after treatment) was achieved by including consideration of both the duration of Cd exposure and especially the root surface area to express Cd uptake. Similarly, the fit of the BLM was also improved when taking into account exposure time and expressing uptake in terms of root morphological parameters.     

Assessment of soil erosion under rainfed sugarcane in KwaZulu‐Natal,South Africa

Soil erosion from agricultural land use runoff is a major threat to the sustainability of soil composition and water resource integrity. Sugarcane is an important cash and food security crop in South Africa, subjected to an intensive soil erosion, and consequently, severe land degradation. This study aimed to investigate soil erosion and associated soil and cover factors under rainfed sugarcane, in a small catchment, KwaZulu‐Natal, South Africa. Three replicated runoff plots were installed at different slope positions (down, mid and upslope) within cultivated sugarcane fields to monitor soil erosion during the 2016–2017 rainy season. On average, annual runoff (RF) was significantly greater from 10 m² plots with 1163.77 ± 2.63 l/m/year compared to 1 m² plots. However, sediment concentration (SC) was significantly lower in 10 m² (0.34 ± 0.04 g/l) compared to 1 m² (6.94 ± 0.24 g/l) plots. The annual soil losses (SL) calculated from 12 rainfall events was 58.36 ± 0.77 and 8.84 ± 0.20 t/ha from 1 m² and 10 m² plots, respectively. The 1 m² plot, SL (2.4 ± 1.41 ton/ha/year) in the upslope experienced 33% more loss than the midslope and 50% more loss than the downslope position. SL was relatively lower from the 10 m² plots than the 1 m² plots, which is explained by high sediment deposition at the greater plot scale. SL was negatively correlated with the soil organic carbon stocks (r = ?0.82) and soil surface cover (r = ?0.55). RF decreased with the increase of slope gradient (r = ?0.88) and soil infiltration rate (r = ?0.87). There were considerable soil losses from cultivated sugarcane fields with low organic matter. These findings suggest that to mitigate soil erosion, soil organic carbon stocks and vegetation cover needs to be increased through appropriate land management practices, particularly in cultivated areas with steep gradients.     

A Rapid Response Survey to Characterize the Impacts of the 2017 High Water Event on Lake Ontario

In the spring and summer of 2017, communities along the Lake Ontario shoreline suffered from the worst flood event on record. In late May, daily water levels reached their highest point in over 100 years, and flooding continued throughout much of the summer as lake levels slowly declined, with inundation and erosion significantly impacting shoreline homes and businesses. In this work, we present results from a rapid response online survey of property owners along the New York Lake Ontario shoreline to quantify the perceived flood impacts of the 2017 extended high water event. The survey focused on the degree and spatial distribution of inundation and erosion; the duration and drivers of inundation; the associated damages to different property features, with an emphasis on shoreline protection; and the degree of disruption to business and other activities and services. Photographic documentation of inundation extent and property damage also was provided by survey respondents. We demonstrate the potential utility of this dataset by characterizing key features of inundation and erosion impacts across the shoreline, and by using classification and regression trees to explore the predictability of inundation and erosion based on property characteristics. This work is part of a larger effort to develop models of inundation and erosion that can support flood impact assessments across the shoreline and help communities better prepare for future extended high water events.     

Biological Connectivity of Seasonally Ponded Wetlands across Spatial and Temporal Scales

Many species that inhabit seasonally ponded wetlands also rely on surrounding upland habitats and nearby aquatic ecosystems for resources to support life stages and to maintain viable populations. Understanding biological connectivity among these habitats is critical to ensure that landscapes are protected at appropriate scales to conserve species and ecosystem function. Biological connectivity occurs across a range of spatial and temporal scales. For example, at annual time scales many organisms move between seasonal wetlands and adjacent terrestrial habitats as they undergo life‐stage transitions; at generational time scales, individuals may disperse among nearby wetlands; and at multigenerational scales, there can be gene flow across large portions of a species’ range. The scale of biological connectivity may also vary among species. Larger bodied or more vagile species can connect a matrix of seasonally ponded wetlands, streams, lakes, and surrounding terrestrial habitats on a seasonal or annual basis. Measuring biological connectivity at different spatial and temporal scales remains a challenge. Here we review environmental and biological factors that drive biological connectivity, discuss implications of biological connectivity for animal populations and ecosystem processes, and provide examples illustrating the range of spatial and temporal scales across which biological connectivity occurs in seasonal wetlands.     

Application of Pesticide Sprays to Fresh Produce: A Risk Assessment for Hepatitis A and <Emphasis Type="Italic">Salmonella</Emphasis>

The purpose of this study was to quantify the transfer of viral and bacterial pathogens in water used to dilute pesticides sprayed onto the surfaces of cantaloupe, iceberg lettuce, and bell peppers. The average percent transfer of bacteria was estimated to range from 0.00021 to 9.4%, while average viral transfer ranged from 0.055 to 4.2%, depending on the type of produce. Based on these values the concentrations of hepatitis A virus (HAV) and Salmonella in water necessary to achieve a 1:10,000 annual risk of infection were calculated. Under worst case scenario assumptions, in which a pesticide is applied on the same day that the produce is harvested and when maximum transfer values are used, concentrations of 1.5 × 10⁻³ CFU Salmonella or 2.7 × 10⁻⁷ MPN HAV per 100 ml of the water used for application would result in 1:10,000 annual infection risk to anyone who consumes the fresh produce. If harvesting does not occur until at least 14 days after the application, to produce the same risk of infection, the numbers of Salmonella in 100 ml of water used to dilute the pesticides will be greater by up to five orders of magnitude, while the HAV numbers will have increased by up to two orders of magnitude. Based on the reported concentrations of enteric viruses in surface and ground waters in the United States, a 1:10,000 annual risk of infection could easily be exceeded with some groundwater sources used in the United States. To reduce the risks associated with the consumption of fresh produce, water used to prepare pesticides in spray applications should be evaluated for its microbiological quality.     

Urban Stream Rehabilitation: A Design and Construction Case Study

/ This paper describes the fundamental design features, and construction methods and sequence, of a rehabilitation project on a small suburban creek in Moscow, Idaho, USA. A meandering channel pattern was reestablished for approximately 280 m of straightened, dredged channel, a new floodplain was excavated, and the new riparian zone was replanted. The new stream channel was sized to accommodate an estimated natural bankfull discharge ( approximately 5.6 cms), and floodplain design attempted to match the conveyance of the old enlarged channel (14-20 cms). The project was coordinated by a local nonprofit environmental organization, and the design and construction were tailored to donated materials and a largely volunteer labor force. A high-magnitude flood event (ca. 50-year recurrence interval) six months after construction had no significant impact on the newly constructed channel and revetments, but underscored the need for important detailing of the structures. The use of volunteer labor, while entailing certain benefits, complicates project planning and construction. The most general lesson learned from this project is that sponsoring agencies and clients need to be informed of the many steps and sequencing of properly constructed, complex stream rehabilitation projects as well as the high time and cost requirements for these tasks. KEY WORDS: Stream corridor restoration; Channel design; Streambank revetments     

Aphids are unaffected by the elemental defence of the nickel hyperaccumulator Streptanthus polygaloides (Brassicaceae)

Summary. Nickel hyperaccumulation, resulting in plant Ni contents of >1000 mg kg^у dry mass, has been shown to defend plants against folivorous herbivores. We determined whether this elemental defence tactic protected hyperaccumulating plants from attack by a phloem-feeding herbivore. We used the pea aphid, Acyrthosiphon pisum, and the Ni-hyperaccumulating plant Streptanthus polygaloides. Aphids were allowed to colonize mixed arrays of S. polygaloides in which plants either were hyperaccumulating Ni, not hyperaccumulating Ni and treated with a systemic insecticide, or not hyperaccumulating Ni. Aphid numbers g^у dry mass of plant biomass were lowest for the insecticide treatment, intermediate for low-Ni plants, and highest for plants hyperaccumulating Ni. Artificial liquid aphid diet, amended with varying levels of Ni, resulted in decreased aphid survival at 2500 mg kg^у Ni dry mass (or 5.03 mM Ni). We concluded that Ni levels in the phloem of hyperaccumulating plants of S. polygaloides were < 5.03 mM and, as a result, were not effective in defending plants against aphid attack.     

New investigation findings on the 2006 Danvers,MA explosion

On November 22, 2006 the largest explosion in the history of Massachusetts occurred in Danvers, MA at approximately 2:46 am. This paper presents a detailed analysis into the potential causes and lessons learned from the Danvers explosion. Other investigative groups concluded that the cause of the explosion was an overheated production tank. However, the analyses presented here demonstrate that their proposed scenario could not have occurred and that other potential causes are more likely.Using the computational fluid dynamics tool FLACS, it was possible to investigate the chain of events leading to the explosion, including: (1) evaluating various leak scenarios by modeling the dispersion and mixing of gases and vapors within the facility, (2) evaluating potential ignition sources within the facility of the flammable fuel–air mixture, and (3) evaluating the explosion itself by comparing the resulting overpressures of the exploding fuel–air cloud with the structural response of the facility and the observed near-field and far-field blast damage. These results, along with key witness statements and other analyses, provide valuable insight into the likely cause of this incident. Based on the results of our detailed analysis, lessons learned regarding the investigative procedure and methods for mitigating this and future explosions are discussed.     

Using computational fluid dynamics (CFD) for blast wave predictions

Explosions will, in most cases, generate blast waves. While simple models (e.g., Multi Energy Method) are useful for simple explosion geometries, most practical explosions are far from trivial and require detailed analyses. For a reliable estimate of the blast from a gas explosion it is necessary to know the explosion strength. The source explosion may not be symmetric; the pressure waves will be reflected or deflected when hitting objects, or even worse, the blast waves may propagate inside buildings or tunnels with a very low rate of decay. The use of computational fluid dynamics (CFD) explosion models for near and far field blast wave predictions has many advantages. These include more precise estimates of the energy and resulting pressure of the blast wave, as well as the ability to evaluate non-symmetrical effects caused by realistic geometries, gas cloud variations and ignition locations. This is essential when evaluating the likelihood of a given leak source as cause of an explosion or equally when evaluating the potential risk associated with a given leak source for a consequence analysis.In addition, unlike simple methods, CFD explosion models can also evaluate detailed dynamic effects in the near and far field, which include time dependent pressure loads as well as reflection and focusing of the blast waves. This is particularly valuable when assessing actual near-field blast damage during an explosion investigation or potential near-field damage during a risk analysis for a facility. One main challenge in applying CFD, however, is that these models require more information about the actual facility, including geometry details and process information. Collecting the necessary geometry and process data may be quite time consuming. This paper will show some blast prediction validation examples for the CFD model FLACS. It will also provide examples of how directional effects or interaction with objects can significantly influence the dynamics of the blast wave. Finally, the challenge of obtaining useful predictions with insufficient details regarding the geometry will also be addressed.     

Wetland Flowpaths Mediate Nitrogen and Phosphorus Concentrations across the Upper Mississippi River Basin

Eutrophication, harmful algal blooms, and human health impacts are critical environmental challenges resulting from excess nitrogen and phosphorus in surface waters. Yet we have limited information regarding how wetland characteristics mediate water quality across watershed scales. We developed a large, novel set of spatial variables characterizing hydrological flowpaths from wetlands to streams, that is, “wetland hydrological transport variables,” to explore how wetlands statistically explain the variability in total nitrogen (TN) and total phosphorus (TP) concentrations across the Upper Mississippi River Basin (UMRB) in the United States. We found that wetland flowpath variables improved landscape-to-aquatic nutrient multilinear regression models (from R² = 0.89 to 0.91 for TN; R² = 0.53 to 0.84 for TP) and provided insights into potential processes governing how wetlands influence watershed-scale TN and TP concentrations. Specifically, flowpath variables describing flow-attenuating environments, for example, subsurface transport compared to overland flowpaths, were related to lower TN and TP concentrations. Frequent hydrological connections from wetlands to streams were also linked to low TP concentrations, which likely suggests a nutrient source limitation in some areas of the UMRB. Consideration of wetland flowpaths could inform management and conservation activities designed to reduce nutrient export to downstream waters.