Hongbing Sun

A two-dimensional analytical solution of groundwater response to tidal loading in an estuary

A two-dimensional transient groundwater flow equation for a confined nonleaky aquifer is solved analytically with an estuary tidal-loading boundary condition. The amplitude and phase of the tide varies with position and time, respectively. These variations, called the “damping coefficient,” for amplitude, and “separation constant,” for phase along the coastline, are considered in the analysis. The solution presented is more advanced than the traditional one-dimensional analytical solution with a one-dimensional tidal-loading boundary condition. The damping coefficient and separation constant in the application study are obtained from the harmonic analysis of the observed tidal level in Apalachicola Bay, Florida. The analytical solution is compared to a two-dimensional finite difference solution. A numerical simulation illustrates the response of piezometric head to tidal loading. The piezometric head and phase from both solutions match closely. The analytical and numerical solutions show that a piezometric head along both sides of the estuary can be predicted given a tidal elevation at the entry of an estuary. The fluctuation of piezometric head in response to tidal loading diminishes rapidly inland and diminishes slowly along the coastline of an estuary. There are also obvious phase shifts associated with spatial variations as the wave propagates.

Annual precipitation and river discharges in Florida in response to El Niño- and La Niña-sea surface temperature anomalies

Abstract Statistical analysis proves that El Nino and La Nina are responsible for up to 40% of annual precipitation variations and up to 30% of river discharge variations in Florida. The analysis is based on 44-year records of precipitation from more than 30 gauge stations and stream discharge from 20 gauge stations distributed all across Florida Peninsula. The cross-correlation coefficients for both the sea surface temperature (SST) and precipitation data series, the SST and river data series are calculated after the SST data series, precipitation and river data series are prewhitened by an autoregressive moving average (ARMA) model (0, 1). The cross-correlations between the SST anomalies and both the precipitation and river discharge are positively significant. The conclusion is that a higher annual precipitation amount (a ‘wet’ year) is expected from an El Nino year, and a lower precipitation amount (a ‘dry’ year) is expected from a La Nina year. Large amounts of fresh water recharge into the estuary in an El Nino year and less fresh water recharges into an estuary in a La Nina year. Also a higher groundwater table is expected in an El Nino year, and a lower ground-water table is expected in a La Nina year. Assuming that SST anomalies are the input signals for a time-series analysis, the impulse response weights of both precipitation and river discharge to SST signals can be calculated due to their positive correlations. The impulse response weights can be used to build the linear transfer functions of precipitation, river discharge and SST signals. The annual precipitation and stream discharge amount therefore can be predicted from the SST anomalies. This can provide some guidance for the water management policy and planning.

Mobilization of thorium, radium and radon radionuclides in ground water by successive alpha-recoils

Abstract Alpha-recoil is an important way for the mobilization of α-decay daughters in ground water. The processes of decay and recoil from 238 U to 222 Rn and from 232 Th to 220 Rn are successive. The release rates of successive recoils in this study are quantitatively estimated under two extreme conditions: complete absorption; and no adsorption of recoil elements by the porous medium. The recoil probability, recoil embedding and effective surface area are considered during the analysis. The result of this study shows that the recoil supply rates in the porous medium decrease down the decay chains. For the isotopes within the same decay chains, recoil emanation ratios of daugthers to parent are usually greater than 1 under both end-member conditions. This is consistent with the higher daughter to parent ratios observed in the field measurements. It is also found that the emanation ratios of Th, Ra and Rn show little change with the change of porosity in general. Radon emanation is most efficient at 15–20% porosity under the condition of complete adsorption. The calculated radioactivity ratios of daughters to parents from this study can provide a partial explanation for the disequilibrium of radioactivity of daughters relative to parents observed in natural water. Because of the low solubility of thorium, radium and radon, the emanation rates calculated under the condition of complete adsorption are closer to the natural conditions.

Soil mineral structural water loss during loss on ignition analyses

Water loss from soil minerals has been known to cause errors in the determination of soil organic matter when the loss on ignition (LOI) method is used. Unfortunately, no known published studies reliably quantify the range of structural water in the soil. To do this, 15 common reference minerals were analyzed by LOI to obtain their individual water loss. In addition, 14 upland, loamy soil samples and 3 wetland/hydric soil samples with varied mineral contents were analyzed to collect their X-ray powder diffraction spectra. Based upon X-ray spectra peak intensities, the modal abundance of minerals in each soil sample was determined using the RockJock computer program. The resultant modal weight percentages of all identified minerals in each soil sample were then multiplied by the LOI value for each mineral to obtain the mineral structural water loss (SWL) of that soil sample. For the 17 soil samples analyzed, the range of mineral water loss is 0.56 to 2.45%. Depending on the LOI values of the soil samples, ...

Na/Cl molar ratio changes during a salting cycle and its application to the estimation of sodium retention in salted watersheds.

Using soil column experiments and data from natural watersheds, this paper analyzes the changes in Na/Cl molar ratios during a salting cycle of aqueous-soil systems. The soil column experiments involved introducing NaCl salt at various initial concentrations into multiple soil columns. At the start of a salting cycle in the column experiments, sodium was adsorbed more than chloride due to cation exchange processes. As a result, the initial Na/Cl molar ratio in column effluent was lower than 1, but increased thereafter. One-dimensional PHREEQC geochemical transport simulations also were conducted to further quantify these trends under more diverse scenarios. The experimentally determined Na/Cl molar ratio pattern was compared to observations in the annual salting cycle of four natural watersheds where NaCl is the dominant applied road deicing salt. Typically, Na/Cl molar ratios were low from mid-winter to early spring and increased after the bulk of the salt was flushed out of the watersheds during the summer, fall and early winter. The established relationship between the Na/Cl molar ratios and the amount of sodium retention derived from the column experiments and computer simulations present an alternative approach to the traditional budget analysis method for estimating sodium retention when the experimental and natural watershed patterns of Na/Cl molar ratio change are similar. Findings from this study enhance the understanding of sodium retention and help improve the scientific basis for future environmental policies intended to suppress the increase of sodium concentrations in salted watersheds.

Mobilization of arsenic, lead, and mercury under conditions of sea water intrusion and road deicing salt application.

Water geochemistry data from complexly designed salt-solution injection experiments in the laboratory, coastal aquifers of Bangladesh and Italy, taken from the literature, and two salted watersheds of New Jersey, US were collected and analyzed to study the geochemical mechanisms that mobilize As, Pb, and Hg under varied salting conditions. Overall, increased NaCl-concentrations in aquifers and soil are found to increase the release of Pb and Hg into the water. Reducing environments and possible soil dispersion by hydrated Na(+) are found to lead to an increase of As-concentration in water. However, the application of a pure NaCl salt solution in the column injection experiment was found to release less As, Pb, and Hg initially from the soil and delay their concentration increase, when compared to the application of CaCl2 and NaCl mixed salts (at 6:4 weight ratio). The concentration correlation dendrogram statistical analyses of the experimental and field data suggest that the release of As, Hg, and Pb into groundwater and the soil solution depends not only on the salt level and content, but also on the redox condition, dissolved organic matter contents, competitiveness of other ions for exchange sites, and source minerals. With the ongoing over-exploration of coastal aquifers from increased pumping, continued sea-level rise, and increased winter deicing salt applications in salted watersheds of many inland regions, the results of this study will help understand the complex relation between the concentrations of As, Pb, and Hg and increased salt level in a coastal aquifer and in soils of a salted watershed.

Temperature dependence of multiple sclerosis mortality rates in the United States

Background: It is well known that multiple sclerosis (MS) patients are very sensitive to heat events. However, how MS patients respond to the significant temperature difference between the high- and low-latitude regions is not understood. Objective: The goal is to identify the primary factor responsible for the fact that MS mortality rates of the United States is more than three times higher in the northern states than in the southern states. Methods: Correlation coefficients between the age-adjusted mortality rate of MS as the underlying cause of death and the state average temperature, altitude, latitude, duration of sunshine hours, and solar radiation in the 48 contiguous states were compared. Results: MS mortality rates correlate significantly and inversely with temperatures in the 48 states (correlation coefficient r = −0.812 and significance p = 0.00). Durations of sunshine hours and solar radiation do not correlate significantly with MS mortality rates (r = −0.245, −0.14, and p = 0.101, 0.342, respectively). Conclusion: High environmental temperature is the primary reason for the low MS mortality rates and likely the low MS prevalence in low-latitude regions. Implication of the study result is that benefits of long-term heat acclimation through gradual and prolonged exposure to environmental heat for MS patients may be greatly underappreciated.