Temporal and spatial distributions of sediment total organic carbon in an estuary river

Understanding temporal and spatial distributions of naturally occurring total organic carbon (TOC) in sediments is critical because TOC is an important feature of surface water quality. This study investigated temporal and spatial distributions of sediment TOC and its relationships to sediment contaminants in the Cedar and Ortega Rivers, Florida, USA, using three-dimensional kriging analysis and field measurement. Analysis of field data showed that large temporal changes in sediment TOC concentrations occurred in the rivers, which reflected changes in the characteristics and magnitude of inputs into the rivers during approximately the last 100 yr. The average concentration of TOC in sediments from the Cedar and Ortega Rivers was 12.7% with a maximum of 22.6% and a minimum of 2.3%. In general, more TOC accumulated at the upper 1.0 m of the sediment in the southern part of the Ortega River although the TOC sedimentation varied with locations and depths. In contrast, high concentrations of sediment contaminants, that is, total polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), were found in sediments from the Cedar River. There was no correlation between TOC and PAHs or PCBs in these river sediments. This finding is in contradiction to some other studies which reported that the sorption of hydrocarbons is highly related to the organic matter content of sediments. This discrepancy occurred because of the differences in TOC and hydrocarbon source input locations. It was found that more TOC loaded into the southern part of the Ortega River, while almost all of the hydrocarbons entered into the Cedar River. This study suggested that the locations of their input sources as well as the land use patterns should also be considered when relating hydrocarbons to sediment TOC.     

Impacts of Changes in Precipitation Amount and Distribution on Water Resources Studied Using a Model Rainwater Harvesting System

Water supply reliability is expected to be affected by both precipitation amount and distribution changes under recent and future climate change. We compare historical (1951‐2010) changes in annual‐mean and annual‐maximum daily precipitation in the global set of station observations from Global Historical Climatology Network and climate models from the Inter‐Sectoral Impact Model Intercomparison Project (ISI‐MIP), and develop the study to 2011‐2099 for model projections under high radiative forcing scenario (RCP8.5). We develop a simple rainwater harvesting system (RWHS) model and drive it with observational and modeled precipitation. We study the changes in mean and maximum precipitation along with changes in the reliability of the model RWHS as tools to assess the impact of changes in precipitation amount and distribution on reliability of precipitation‐fed water supplies. Results show faster increase in observed maximum precipitation (10.14% per K global warming) than mean precipitation (7.64% per K), and increased reliability of the model RWHS driven by observed precipitation by an average of 0.2% per decade. The ISI‐MIP models show even faster increase in maximum precipitation compared to mean precipitation. However, they imply decreases in mean reliability, for an average 0.15% per decade. Compared to observations, climate models underestimate the increasing trends in mean and maximum precipitation and show the opposite direction of change in reliability of a model water supply system.     

A numerical study on the effects of EGR and spark timing to combustion characteristics and NOx emission of a GDI engine

EGR is one of the most significant strategies for reducing especially nitrogen oxides (NO_x) emissions from internal combustion engines. The thermal efficiency of spark ignition engines is lower than compression ignition engines because of its lower compression ratio. If the compression ratio is increased to obtain higher thermal efficiency, there may be a knocking tendency in spark ignition engines. EGR can be used in order to reduce NO_x emissions and avoid knocking phenomena at higher compression ratios. In-cylinder temperature at the end of combustion is decreased and heat capacity of fresh charge is increased when EGR applied. Besides EGR, spark timing is another significant parameter for reducing exhaust emissions such as nitrogen oxides, and unburned hydrocarbon (UHC). In this study the effects of EGR and spark timing on spark ignition engine were investigated numerically. KIVA codes were used in order to model combustion process. The combustion process has been modeled for a single cylinder, four stroke and gasoline direct injection (GDI) spark ignition engine. The results showed that in-cylinder pressure and heat release rate decrease as EGR ratio increase. In-cylinder pressure increases with the advancing of spark timing. Advancing spark timing increases the heat release rate and in-cylinder temperature. The simulation results also showed that EGR reduced exhaust gas temperature and NO_x emissions.     

A new approach to quantify the degradation kinetics of linuron with UV, ozonation and UV/O3 processes

The degradation of linuron, one of phenylurea herbicides, was investigated for its reaction kinetics by different treatment processes including ultraviolet irradiation (UV), ozonation (O₃), and UV/O₃. The decay rate of linuron by UV/O₃ process was found to be around 3.5 times and 2.5 times faster than sole-UV and ozone-alone, respectively. Experimental results also indicate overall rate constants increased exponentially with pH above 9.0 while the increase of rate constants with pH below 9 is insignificant in O₃ system. All dominant parameters involved in the three processes were determined in the assistant of proposed linear models in this study. The approach was found useful in predicting the process performances through the quantification of quantum yield (rate constant for the formation of free radical HOO⁻ from ozone decomposition at high pH), rate constant of linuron with ozone (k_O3,LNR), rate constant of linuron with hydroxyl radical (k_OH,LNR), and α (the ratio of the production rate of OH and the decay rate of ozone in UV/O₃ system).     

Numerical simulation of an array of fences in Saemangeum reclaimed land

This paper discusses about the quantitative effect of windbreak fences on wind velocity in the reclaimed land at Saemangeum in South Korea. Windbreak fences were constructed in the reclaimed land to reduce the wind velocity to prevent the generation and diffusion of dust. However, up to this time, no in-depth studies were conducted to quantitatively measure the effect of the windbreak fences on wind velocity thus an optimum windbreak structure is not yet determined. Using CFD simulations, the effects of fence porosity, fence height, and the distance between the adjacent fences were investigated. A wind tunnel experiment was initially conducted and data gathered were used to develop the CFD models. From the experiments and CFD simulations, the overall percentage difference of the measured velocities was 7.20% which is generally acceptable to establishing the reliability of the CFD models. The reduction effect on wind velocity was measured in between the adjacent fences up to a height of 0.6 m from the ground surface. In terms of porosity ( = 0, 0.2, 0.4, 0.6), 0.2 was found to be the optimum value. Conversely, the effect of fence height (0.6, 0.8 and 1.0 m) showed no significant difference; therefore, 0.6 m height is recommended. In addition, the reduction effect of distance between the adjacent fences (2, 4 and 6 m) on wind velocity having a 0.2 porosity has decreased to about 75% regardless of the distance. In the case of the reclaimed land in Saemangeum, a decrease of 75% can prevent the generation and diffusion of dusts. However, the source of dusts is very large. Therefore, constructing an array of windbreak with 6 m distance between them is deemed necessary.     

Mercury bioaccumulation and risk to three waterbird foraging guilds is influenced by foraging ecology and breeding stage

We evaluated mercury (Hg) in five waterbird species representing three foraging guilds in San Francisco Bay, CA. Fish-eating birds (Forster's and Caspian terns) had the highest Hg concentrations in thier tissues, but concentrations in an invertebrate-foraging shorebird (black-necked stilt) were also elevated. Foraging habitat was important for Hg exposure as illustrated by within-guild differences, where species more associated with marshes and salt ponds had higher concentrations than those more associated with open-bay and tidal mudflats. Importantly, Hg concentrations increased with time spent in the estuary. Surf scoter concentrations tripled over six months, whereas Forster's terns showed an up to 5-fold increase between estuary arrival and breeding. Breeding waterbirds were at elevated risk of Hg-induced reproductive impairment, particularly Forster's terns, in which 48% of breeding birds were at high risk due to their Hg levels. Our results highlight the importance of habitat and exposure timing, in addition to trophic position, on waterbird Hg bioaccumulation and risk.     

Arsenic species in ecosystems affected by arsenic-rich spring water near an abandoned mine in Korea

The objectives of this study were to quantitatively estimate the distribution of arsenic with its speciation and to identify potential pathways for transformation of arsenic species from samples of water, sediments, and plants in the ecosystem affected by the Cheongog Spring, where As(V) concentration reached levels up to 0.270 mg L⁻¹. After flowing about 100 m downstream, the arsenic level showed a marked reduction to 0.044 mg L⁻¹ (about 84% removal) without noticeable changes in major water chemistry. The field study and laboratory hydroponic experiments with the dominant emergent plants along the creek (water dropwort and thunbergian smartweed) indicated that arsenic distribution, reduction, and speciation appear to be controlled by, (i) sorption onto stream sediments in exchangeable fractions, (ii) bioaccumulation by and possible release from emergent plants, and (iii) transformation of As(V) to As(III) and organic species through biological activities.     

Characterization of aluminium-based water treatment residual for potential phosphorus removal in engineered wetlands

Aluminium-based water treatment residual (Al-WTR) is the most widely generated residual from water treatment facilities worldwide. It is regarded as a by-product of no reuse potential and landfilled. This study assessed Al-WTR as potential phosphate-removing substrate in engineered wetlands. Results indicate specific surface area ranged from 28.0 m² g⁻¹ to 41.4 m² g⁻¹. X-ray Diffraction, Fourier transform infrared and energy-dispersive X-ray spectroscopes all indicate Al-WTR is mainly composed of amorphous aluminium which influences its phosphorus (P) adsorption capacity. The pH and electrical conductivity ranged from 5.9 to 6.0 and 0.104 dS m⁻¹ to 0.140 dS m⁻¹ respectively, showing that it should support plant growth. Batch tests showed adsorption maxima of 31.9 mg P g⁻¹ and significant P removal was achieved in column tests. Overall, results showed that Al-WTR can be used for P removal in engineered wetlands and it carries the benefits of reuse of a by-product that promotes sustainability.