Development of Dynamic Tube Blocking Test Method to Study Halite Scale Deposition and Inhibition

Halite scaling has been observed in the oil/gas field with high TDS and low water cut. Due to its higher solubility, slight changes in temperature (T) and pressure (P) and evaporative effect could yield a large amount of scale, causing significant operational problems. Accurate prediction and control of halite scaling in the oil and gas production system have been a challenge. Therefore, this study aims to shed light on the prediction of halite scale formation, deposition behavior, and inhibition at close to oil field conditions. We have designed and developed a dynamic scale loop (DSL) test methodology that can be used at various T and P. The test method utilizes a change in temperature (ΔT) as a driving force to create halite supersaturation and follow with the scale precipitation/deposition. The tube blocking experiments suggest that the tube blockage can be caused by bulk precipitation and or deposition of halite precipitate. SEM analysis of the tube cross-sections indicated that tube blockage, presumably by bulk precipitation, could be seen at the beginning of the reaction tube, but deposition was observed towards the exit end of the tube. Similarly, various experimentation to simulate the water dilution at constant pressure and ΔT were conducted. The effect of the addition of water to prevent halite deposition was analyzed computationally by using ScaleSoftPitzer (SSP) software. Brine compatibility of several inhibitors were tested via bottle tests and autoclave tests and qualified inhibitors were tested in the tube blocking experiments to identify the performance of the inhibitor to treat the halite precipitation at high temperature and pressure. Overall, a robust test method was designed and developed for halite scaling under high temperature and pressure that can simulate the oil and gas production in the field.

Hydrochemical Fluxes in Bulk Precipitation, Throughfall, and Stemflow in a Mixed Evergreen and Deciduous Broadleaved Forest

Rainfall is one of the primary sources of chemical inputs in forest ecosystems, and the basis of forest nutrient cycling. Mixed evergreen and deciduous broadleaved forests are currently one of the most threatened ecosystems due to their sensitivity to anthropogenic climate change. As such, understanding the hydrochemical fluxes of these systems is critical for managing their dynamics in the future. We investigate the chemistry of bulk precipitation, stemflow and throughfall in a mixed evergreen and deciduous broadleaved forest in the Shennongjia region of Central China. Mean nutrient concentrations in throughfall and stemflow were higher than in bulk precipitation. Stemflow ion fluxes from deciduous tree species were greater than those for evergreen tree species because of the differences in bark morphology and branch architecture. Throughfall and stemflow chemistry fluctuated dramatically over the growing season. Nitrate nitrogen and ammonium nitrogen were retained, while other elements and compounds were washed off or leached via throughfall and stemflow pathways. Our findings will facilitate a greater understanding of nutrient balance in canopy water fluxes.

Long-term study of atmospheric mercury deposition at monitoring stations in Lithuania

The results of the long-term study of atmospheric mercury concentrations in the rain water carried out at the Aukštaitija and Žemaitija integrated monitoring stations are presented in this work. The bulk precipitation samples at both stations were collected every week during the 2007–2017 period. The mercury measurement method is based on the absorption of radiation by mercury vapour at the 253.7 nm line. The monthly samples of precipitation after preparation were analysed using a mercury analyzer ‘Gardis’ developed at our institution. The average annual concentrations, deposition amounts and trends of mercury in the precipitation over the period of 2007–2017 were analysed. The tendency of average monthly mercury concentrations in the precipitation at the Žemaitija station was continuously increasing before 2011, however, after 2012 it has a decreasing tendency which was contrary to that at the Aukštaitija station. At the same time, the tendencies of average monthly amounts of mercury deposited with precipitation showed decreasing amounts, especially at the Žemaitija station. Explanation of the above-mentioned phenomenon is complicated and the main reason is very changeable air mass trajectories and irregularity of precipitation.

Input-Output Budgets of Nutrients in Adjacent Norway Spruce and European Beech Monocultures Recovering from Acidification

Soil acidification has constituted an important ecological threat to forests in Central Europe since the 1950s. In areas that are sensitive to acid pollution, where the soil buffering capacity is naturally low, tree species can significantly modulate the extent of soil acidification by affecting throughfall deposition and the composition of litter. A principal difference can be expected between coniferous and broadleaf tree species. The aim of our study was to compare long-term trends in element cycling in two stands representing the main types of forest ecosystem in the region (Picea abies vs. Fagus sylvatica). In the period of 2005–2017, we continually measured element concentrations and fluxes in bulk precipitation, throughfall precipitation, and soil leachates. A continuous decline of acid deposition was detected in both bulk precipitation and throughfall. Declining deposition of S and N in both forests has led to the recovery of soil solution chemistry in the mineral soil, manifested by rising pH from 4.25 to 4.47 under spruce and from 4.42 to 4.69 in the beech stand. However, soil water in the spruce stand was more acidic, with higher concentrations of SO42− and Al when compared to the beech stand. While the acidity of soil leachates from organic horizons was driven mainly by organic anions, in lower mineral horizons it was controlled by inorganic acid anions. NO3− concentrations in deeper horizons of the spruce stand have diminished since 2006; however, in the beech plot, episodically elevated NO3− concentrations in mineral horizons are a sign of seasonal processes and of nearby perturbations. Higher output of S when compared to the input of the same element indicates slow S resorption, delaying the recovery of soil chemistry. Our results indicate that, although forest ecosystems are recovering from acidification, soil S retention and the ability to immobilize N is affected by the dominant tree species.

Imbalanced phosphorus and nitrogen deposition in China’s forests

Acceleration of anthropogenic emissions in China has substantially increased nitrogen (N) deposition during last three decades and may result in an imbalance of atmospheric N and phosphorus (P) inputs in terrestrial ecosystems. However, the status of P deposition in China is poorly understood. This study synthesized data on total P and total N concentrations in bulk precipitation and throughfall from published literature to assess the characteristics of P deposition, N deposition and N : P deposition ratio in China’s forests. Our results show relatively high mean rates of atmospheric P inputs by bulk precipitation (0.38 kg P ha-1 yr-1) and throughfall (0.84 kg P ha-1 yr-1), but they were accompanied by even much higher N inputs by bulk precipitation (16.5 kg N ha-1 yr-1) and throughfall (26.2 kg N ha-1 yr-1), resulting in high N : P ratios in bulk precipitation (44.4) and throughfall (32.8), respectively. Total P and N concentrations both were significantly enriched in throughfall versus bulk precipitation, leading to an estimate of canopy captured dry deposition of 0.46 kg P ha-1 yr-1 and at least 9.7 kg N ha-1 yr-1, respectively. We found significantly higher P deposition and lower N : P ratios nearby than far from semiarid regions. Moreover, fluxes of total P and total N in bulk precipitation and throughfall both showed a significant power-law increase with closer distance to the nearest large cities. Our results suggest an anthropogenic alternation of regional P and N cycling, which might shift large areas of China’s forests towards human-induced P limitation especially in southern China.