Shiqin Wang

Stable isotopic compositions in Australian precipitation

Stable deuterium (delta D) and oxygen-18 (delta O-18) isotopes in 1962 to 2002 precipitation from the seven Australian stations of the Global Network of Isotopes in Precipitation (GNIP) were used to investigate isotope characteristics including temporal and spatial distributions across different regions of Australia. On the basis of 1534 samples, the local meteoric water line (LMWL) was established as delta D = 7.10 delta O-18 + 8.21. delta O-18 showed a depletion trend from north and south to central Australia (a continental effect) and from west to east. Precipitation amount effects were generally greater than temperature effects, with quadratic or logarithmic correlations describing delta/T and delta/P better than linear relationships. Nonlinear stepwise regression was used to determine the significant meteorological control factors for each station, explaining about 50% or more of the delta O-18 variations. Geographical control factors for delta O-18 were given by the relationship delta O-18 (parts per thousand) = -0.005 longitude (degrees) - 0.034 latitude (degrees)-0.003 altitude (m) - 4.753. Four different types of d-excess patterns demonstrated particular precipitation formation conditions for four major seasonal rainfall zones. Finally, wavelet coherence (WTC) between delta O-18 and SOI confirmed that the influence of ENSO decreased from east and north to west Australia.

The impacts of a linear wastewater reservoir on groundwater recharge and geochemical evolution in a semi-arid area of the Lake Baiyangdian watershed, North China Plain

Sewage leakage has become an important source of groundwater recharge in urban areas. Large linear wastewater ponds that lack anti-seepage measures can act as river channels that cause the deterioration of groundwater quality. This study investigated the groundwater recharge by leakage of the Tanghe Wastewater Reservoir, which is the largest industrial wastewater channel on the North China Plain. Additionally, water quality evolution was investigated using a combination of multivariate statistical methods, multi-tracers and geochemical methods. Stable isotopes of hydrogen and oxygen indicated high levels of wastewater evaporation. Based on the assumption that the wastewater was under an open system and fully mixed, an evaporation model was established to estimate the evaporation of the wastewater based on isotope enrichments of the Rayleigh distillation theory using the average isotope values for dry and rainy seasons. Using an average evaporation loss of 26.5% for the input wastewater, the estimated recharge fraction of wastewater leakage and irrigation was 73.5% of the total input of wastewater. The lateral regional groundwater inflow was considered to be another recharge source. Combing the two end-members mix model and cluster analysis revealed that the mixture percentage of the wastewater decreased from the Highly Affected Zone (76%) to the Transition Zone (5%). Ion exchange and redox reaction were the dominant geochemical processes when wastewater entered the aquifer. Carbonate precipitation was also a major process affecting evolution of groundwater quality along groundwater flow paths.

Vehicle Design of Tethered Hexaroters for Heavy Payload Applications

This research addresses the vehicle design problem for industry class tethered hexa rotor development project. Hexarotors are unmanned aerial vehicles of resent research interest due to their capability of vertical take offs, landings and hovering at specific locations. Tethered vehicles has the advantage over battery operated flights for not having the flight time restrictions. In existing tethered hexarotors the payloads are lower than 20kg due to the design and the weight of power conversion devices. This paper presents vehicle design and automated cable winding structure of new prototype of heavy payload type tethered hexarotor which is capable of carrying user specified data acquisition device mounted on vehicle weighing more than 30kgs and has capability to provide about extra 1kw power to operate in field operations where reliability is the key factor. The proposed vehicle design is compact, light weighted, aerodynamically and mechanically optimum to proceed to the actual vehicle assembly. The proposed automated cable winding structure makes the tethered system efficient and safe.

Delineation of contaminant sources and denitrification using isotopes of nitrate near a wastewater treatment plant in peri-urban settings

Distinguishing sources of groundwater contamination in regions with multiple potential sources can be challenging using conventional markers. In this study, isotopes of nitrate (δ15NNO3 and δ18ONO3) were examined in conjunction with other hydrochemical parameters to better distinguish sources of groundwater contamination, where intensive agriculture occurs adjacent to a wastewater treatment plant (WWTP). High nitrate concentrations were found in groundwater both within the WWTP site and surrounding market garden farms (maximum of 99 mg/L and 78 mg/L nitrate as N, respectively). Ranges and median δ15NNO3 values showed clear differences between sample groups. In groundwater close to the WWTP, δ15NNO3 and δ18ONO3 values ranged from 10.4 to 41.2‰ and -0.5to 21.3‰, respectively, indicating predominantly sewage-sourced nitrate, while samples within market gardens showed evidence of mixed fertilizer (manure and synthetic) sourced nitrate, with δ15NNO3 and δ18ONO3 values between 7.2 and 29.8‰ and 0.4 to 15.1‰, respectively. Nitrate interpreted to be derived from the WWTP was also typically associated with elevated ammonia as N (median concentration of 17 mg/L) and SO4 (median concentration of 350 mg/L). These distinctive signatures allowed for clearer delineation of the extent and overlap between different contaminant plumes than otherwise possible. Geochemical conditions in groundwater surrounding the WWTP appear to promote denitrification, evident through enrichment in δ15NNO3 and δ18ONO3 and reduced nitrate concentrations between sampling rounds (locally). However, isotopic signatures in market garden areas showed no evidence of denitrification, and groundwater exhibited conditions likely to preserve nitrate (e.g. dissolved oxygen levels >2 mg/L). There is limited evidence of nitrate contamination currently impacting a nearby groundwater dependent ecosystem (Tootgarook Swamp), located down-gradient from the WWTP. This research demonstrates that a combination of hydrochemical and isotope data can help resolve sources of groundwater contamination and characterise nutrient degradation behaviour in settings with multiple inputs.

Combination of CFCs and stable isotopes to characterize the mechanism of groundwater-surface water interactions in a headwater basin of the North China Plain

Mountainous areas are characterized by steep slopes and rocky landforms, with hydrological conditions varying rapidly from upstream to downstream, creating variable interactions between groundwater and surface water. In this study, mechanisms of groundwatersurface water interactions within a headwater catchment of the North China Plain were assessed along the stream length and during different seasons, using hydrochemical and stable isotope data, and groundwater residence times estimated using chlorofluorocarbons. These tracers indicate that the river is gaining, due to groundwater discharge in the headwater catchment both in the dry and rainy seasons. Residence time estimation of groundwater using chlorofluorocarbons data reveals that groundwater flow in the shallow sedimentary aquifer is dominated by the binary mixing of water approximating a piston flow model along 2 flow paths: old water, carried by a regional flow system along the direction of river flow, along with young water, which enters the river through local flow systems from hilly areas adjacent to the river valley (particularly during the rainy season). The larger mixing ratio of young water from lateral groundwater recharge and return flow of irrigation during the rainy season result in higher ion concentrations in groundwater than in the dry season. The binary mixing model showed that the ratio of young water versus total groundwater ranged from 0.88 to 0.22 and 1.0 to 0.74 in the upper and lower reaches, respectively. In the middle reach, meandering stream morphology allows some loss of river water back into the aquifer, leading to increasing estimates of the ratio of young water (from 0.22 to 1). This is also explained by declining groundwater levels near the river, due to groundwater extraction for agricultural irrigation. The switch from a greater predominance of regional flow in the dry season, to more localized groundwater flow paths in the wet season is an important groundwatersurface water

Renewal rate of groundwater in the Baiyangdian Lake Basin

Human activities, such as water storage in reservoirs and pumping for irrigation, reduce stream flows and deplete unconfined aquifer in the plain area of the Baiyangdian Lake Basin. Without recharges from rivers and groundwater, the Baiyangdian Lake faces the risk of drying up. Considering the impacts of the Baiyangdian Lake on the local environment, biodiversity, and climate, many projects of water transfer for the sustainability of the lake were implemented. However, the result are unsatisfactory due to considerable leakages in the lake. In order to preserve the lake, sustainable groundwater use should be achieved and therefore, it is necessary to study the renewal rate of unconfined groundwater. In this study groundwater was surveyed on the plain area of the Baiyangdian Lake Basin in 2009. thirty six samples from groundwater and surface water were collected for measuring the content of tritium. Tritium content in precipitation since the mid-1950 s was rebuilt by comparing the results from linear interpolation, Wus method and Lians method. Renewal rate of groundwater in the plain area was estimated based on the tritium data and the well- mixed model. Results show that leakage of the lake slightly increased tritium content in the ambient groundwater. Generally, the renewal rate of unconfined groundwater decreased from 15.0 %/a to 4.0 %/a between the mountain area and the lake. Alluvial fans are the main recharge area with an average renewal rate of 9.8 %/a. The renewal rate dropped to 4.4 %/a in the alluvial plain. We recommend that groundwater development should be restricted in the alluvial plain to recover the renewal rate of unconfined groundwater. Although such recovery may take a long time to occur, it is believed that recharging the lake by shallow groundwater is the only way to maintain a sustainable lake.