Carbon dioxide concentration and flux in an urban residential area in Seoul,Korea

The carbon dioxide （CO2） concentrations and fluxes measured at a height of 17.5 m above the ground by a sonic anemometer and an open-path gas analyzer at an urban residential site in Seoul, Korea from February 2011 to January 2012 were analyzed. The annual mean CO2 concentration was found to be 750 mg m-3, with a maximum monthly mean concentration of 827 mg m-3 in January and a minimum value of 679 mg m-3 in August. Meanwhile, the annual mean CO2 flux was found to be 0.45 mg m-2 s-1, with a maximum monthly mean flux of 0.91 mg m-2 s-1 in January and a minimum value of 0.19 mg m-2 s-1 in June. The hourly mean CO2 concentration was found to show a significant diurnal variation; a maximum at 0700-0900 LST and a minimum at 1400-1600 LST, with a large diurnal range in winter and a small one in summer, mainly caused by diurnal changes in mixing height, CO2 flux, and surface complexity. The hourly mean CO2 flux was also found to show a significant diurnal variation, but it showed two maxima at 0700-0900 LST and 2100-2400 LST, and two minima at 1100-1500 LST and 0300-0500 LST, mainly caused by a diurnal pattern in CO2 emissions and sinks from road traffic, domestic heating and cooking by liquefied natural gas use, and the different horizontal distribution of CO2 sources and sinks near the site. Differential advection with respect to wind direction was also found to be a cause of diurnal variations in both the CO2 concentration and flux.     

Toxicological impact assessment of heavy metal contamination on macrobenthic communities in southern coastal sediments of Korea

In the heavily industrialized Masan Bay of southern coast, Korea, the potential harmful effects of heavy metals (Cd, Co, Cu, Ni, Pb, Sn, Zn, and Hg) were evaluated in terms of the pollution load index (PLI) and ecological risk assessment index (ERI) methods, and the results obtained were considered alongside the health of the macrobenthic fauna communities. The results revealed that the bay sediments, especially in the inner bay and the outfall area of a sewage treatment plant, are exposed to moderate to serious levels of metal pollution. Hg and Cd contributed the most to the potential toxicity response indices in sediments recently deposited in the bay. The potential ecological risk assessment of heavy metals in the bay was highlighted by the use of the benthic biological pollution index (BPI), suggesting that the ERI is a useful toxicity response index, which can quantify the overall ecological risk level to a target environment.     

Projections of hydrology in the Tocantins-Araguaia Basin,Brazil: uncertainty assessment using the CMIP5 ensemble

ABSTRACT

A semi-distributed hydrological model is developed, calibrated and validated against unregulated river discharge from the Tocantins-Araguaia River Basin, northern Brazil. Climate change impacts are simulated using projections from the 41 Coupled Model Intercomparison Project Phase 5 climate models for the period 2071–2100 under the RCP4.5 scenario. Scenario results are compared to a 1971–2000 base line. Most climate models suggest declines in mean annual discharge although some predict increases. A large proportion suggest that the dry season experiences large declines in discharge, especially during the transition to the rising water period. Most models (>75%) suggest declines in annual minimum flows. This may have major implications for both current and planned hydropower schemes. There is greater uncertainty in projected changes in wet season and annual maximum discharges. Two techniques are investigated to reduce uncertainty in projections, but neither is able to provide more confidence in the simulated changes in discharge.

Editor D. Koutsoyiannis Associate editor F. Hattermann     

Influences of spatial distribution of soil thickness on shallow landslide prediction

Shallow landslides usually occur during hevy rainfall and result in casualties and property losses. Thus, the possible locations where landslides are likely to occur must be identified in advance in order to avoid or reduce the harm they cause. When performing a slope-instability analysis, soil thickness is an important factor; however, soil thickness information from landslide-prone areas is rarely obtained. The objective of this study is to realize the influences of spatial distribution of soil thickness on shallow landslide prediction. Three different spatial soil-thickness distributions were applied to perform a slope-instability analysis, and uniform-distributed soil thicknesses from 0.4 m to 2.0 m were also applied for comparison. Geomorphologic information and hydrological records from a landslide-prone area in southern Taiwan were collected. Results show that the spatial distribution of soil thickness related to wetness index provides a reasonable estimation in order to avoid an over-prediction for landslide-prone areas or an under-prediction for stable areas. The analytical procedure used in this study is a simple way for assessing hillslope instability for shallow landslide prediction.     

Multi-proxy evidence for late Holocene anthropogenic environmental changes at Bongpo marsh on the east coast of Korea

We present a multi-proxy record (pollen, microscopic charcoal, magnetic susceptibility, carbon-isotopic composition, total organic carbon [TOC], carbon/nitrogen [C/N] ratios, and particle size) of the late Holocene environmental change and human activities from Bongpo marsh on the east coast of Korea. Mutual interaction between the environment and humans during the late Holocene has not been properly investigated in Korea due to the lack of undisturbed samples with high sedimentation rates. In this study, the history of human responses to late Holocene environmental changes is clearly reconstructed using a multi-proxy paleoenvironmental approach that has not previously been applied in Korea. The evidence from Bongpo marsh indicates that 1) Bongpo marsh began to develop ca. 650 BC as a coastal lagoon was rapidly filled with organic matter, 2) agricultural disturbance around the study site remained slight until ca. AD 600, 3) full-scale intensive agriculture prevailed and the area of deforestation increased between ca. AD 600 and ca. AD 1870, and 4) the land use changed from lowland rice agriculture to upland cultivation when agricultural productivity declined after AD 1870, probably due to severe deforestation and the consequent heavy influx of clastic sediment on rice fields, as described in various historical documents.     

Method for the determination of residual carbon dioxide saturation using reactive ester tracers

The mechanisms for storage of CO₂ in rock formations include structural/stratigraphic, mineral, solubility and residual trapping. Residual trapping is very important in terms of both containment security and storage capacity. However, to date, the contribution from residual trapping (i.e. immobilisation of supercritical fluid via capillarity in pore spaces) is still relatively difficult to quantify accurately. Using a laboratory-based testing program, this study demonstrates the feasibility of using reactive ester tracers (i.e. triacetin, propylene glycol diacetate and tripropionin), which partition between a mobile water phase and a stationary supercritical CO₂ phase, to quantify the residual CO₂ saturation, S_gr, of a rock formation. The proposed single-well test involves injecting these tracers into the subsurface, followed by CO₂ saturated water, where the ester tracers slowly hydrolyse to form products with differing partition coefficients. After a suitable period of time, allowing for partial hydrolysis, water containing the tracer mixture is produced from the subsurface and analysed using gas chromatography mass spectrometry (GCMS). A numerical simulator of the tracer behaviour in a reservoir is used to explain the differential breakthrough of these tracer compounds during water production to estimate S_gr. Computer modelling suggests that the use of esters tracers to determine CO₂ residual saturation is a potentially robust method. The supercritical CO₂/water partition coefficients directly dictate the amount of time that each tracer spends in the CO₂ and water phases. As such for modelling of tracer behaviour and estimating S_gr, knowing the tracer partition coefficient is essential; in this paper, the first laboratory study to determine the partition coefficients of these reactive ester tracers is described.     

Influence of non-feedback variations of radiation on the determination of climate feedback

Recent studies have estimated the magnitude of climate feedback based on the correlation between time variations in outgoing radiation flux and sea surface temperature (SST). This study investigates the influence of the natural non-feedback variation (noise) of the flux occurring independently of SST on the determination of climate feedback. The observed global monthly radiation flux is used from the Clouds and the Earth's Radiant Energy System (CERES) for the period 2000–2008. In the observations, the time lag correlation of radiation and SST shows a distorted curve with low statistical significance for shortwave radiation while a significant maximum at zero lag for longwave radiation over the tropics. This observational feature is explained by simulations with an idealized energy balance model where we see that the non-feedback variation plays the most significant role in distorting the curve in the lagged correlation graph, thus obscuring the exact value of climate feedback. We also demonstrate that the climate feedback from the tropical longwave radiation in the CERES data is not significantly affected by the noise. We further estimate the standard deviation of radiative forcings (mainly from the noise) relative to that of the non-radiative forcings, i.e., the noise level from the observations and atmosphere–ocean coupled climate model simulations in the framework of the simple model. The estimated noise levels in both CERES (>13 %) and climate models (11–28 %) are found to be far above the critical level (~5 %) that begins to misrepresent climate feedback.     

The impact of lateral flow contraction on the rock plucking process under sub-critical flow conditions

Rock plucking is the vertical removal of chunks of rock along intersection joint planes by flowing water. The plucking of durable jointed rock in a natural stream alters stream morphology and potentially damages a bridge substructure situated on a rock foundation by local erosion. Despite its importance, the mechanics of bedrock erosion by plucking are not well understood. In this study, we conduct laboratory experiments to investigate the threshold of block entrainment through plucking near a flow obstruction under sub-critical conditions. In a laboratory flume, we reproduce a wide range of typical lateral flow contraction scenarios that occur around a large rock or bridge substructure and investigate the process of the vertical entrainment of blocks near the obstruction. Two different modes of block removal process (impulsive plucking and accumulative plucking) are observed near the bluff structure. We find that under severe flow contraction, blocks are more likely to escape quickly via impulsive plucking because higher flow contraction and the resulting strong local turbulence around the structure generate large instantaneous uplift force that removes the block within a short period of time; however, we observe accumulative plucking under weaker flow contraction near the bluff structure. From the experimental results, we develop a formula for the threshold point of block dislocation caused by plucking with respect to the degree of lateral flow contraction. The results indicate that increasing the flow contraction ratio reduces block stability because of higher flow acceleration and the increased turbulence effect near the upstream edge of the obstruction. The results of this study should be useful to those who estimate the rate of rock erosion by plucking in natural open channels around a bluff structure.     

Removal of ammonia toxicity in marine sediment TIEs: a comparison of Ulva lactuca,zeolite and aeration methods

Toxicity Identification Evaluations (TIEs) can be used to determine the specific toxicant(s), including ammonia, causing toxicity observed in marine sediments. Two primary TIE manipulations are available for characterizing and identifying ammonia in marine sediments: Ulva lactuca addition and zeolite addition. In this study, we compared the efficacy of these methods to (1) remove NH(x) and NH(3) from overlying and interstitial waters and (2) reduce toxicity to the amphipod Ampelisca abdita and mysid Americamysis bahia using both spiked and environmentally contaminated sediments. The utility of aeration for removing NH(x) and NH(3) during a marine sediment TIE was also evaluated preliminarily. In general, the U. lactuca and zeolite addition methods performed similarly well at removing spiked NH(x) and NH(3) from overlying and interstitial waters compared to an unmanipulated sediment. Toxicity to the amphipod was reduced approximately the same by both methods. However, toxicity to the mysid was most effectively reduced by the U. lactuca addition indicating this method functions best with epibenthic species exposed to ammonia in the water column. Aeration removed NH(x) and NH(3) from seawater when the pH was adjusted to 10; however, very little ammonia was removed at ambient pHs ( approximately 8.0). This comparison demonstrates both U. lactuca and zeolite addition methods are effective TIE tools for reducing the concentrations and toxicity of ammonia in whole sediment toxicity tests.     

Estimates of Tsunami Risk Zones on the Coasts Adjacent to the East (Japan) Sea based on the Synthetic Catalogue

Prognostic characteristics of tsunamis in the East (Japan) Sea based on numerical simulations are investigated by using linear long wave theory. Due to the lack of observed data, the concept of the synthetic catalogue is applied to generate possible tsunami scenarios. It includes four real events that occurred in the East (Japan) Sea during the 20th century, 24 hypothetical tsunamigenic earthquakes located in the gap zones of the seismic map, and 76 idealized model ‘hydrodynamic’ sources covering the eastern part of the East (Japan) Sea uniformly. The tsunami wave height distributions along the East (Japan) Sea coastline due to these hypothetical events are computed. From the geographical distributions of tsunami wave height for all possible events, it is found that there exist several coastal locations where the tsunami risk is relatively lower than in other zones. The relation between the maximal value of the tsunami height and its average value is analyzed. It is found that the maximal tsunami height does not exceed the mean wave height times a constant. The uniform bounded curve for all areas can be obtained if the mean wave height is replaced by the modified mean wave height (1/3 of largest waves). The problem of quantitative definition of the prognostic tsunami wave height for each location based on the data from the synthetic catalogue is discussed. The results of tsunami wave height analysis based on the synthetic catalogue can be used as a tool for coastal disaster mitigation planning.