Total Alkalinity and Dissolved Inorganic Carbon Production in Groundwaters Discharging through a Sandy Beach

Temporal and spatial fluctuations of groundwater-derived alkalinity fluxes to a semiarid coastal embayment

We conducted a comprehensive analysis of a variety of geochemical data including total alkalinity (TA), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), major ions, stable isotopes, and submarine groundwater discharge, to understand biogeochemical and hydrologic processes driving the seasonal to annual estuarine buffering capacity in Nueces Bay, Texas. These measurements, together with statistical analysis and geochemical modeling, show large variability of freshwater influence. TA consumption, common to spring seasons, was mainly driven by CaCO₃ precipitation and, to some extent, by aerobic respiration. TA production occurred in some parts of the bay during summer, fall and winter, likely driven by denitrification. CaCO₃ dissolution is stimulated by input of undersaturated river waters following significant flooding events. Since consumption and production of TA was not necessarily associated with different salinity zones, SGD, identified to be significant year-round, likely offsets the effects of salinity changes. Net DIC and TA fluxes exceeded dissolved organic carbon flux by an order of magnitude, except for winter 2014 when it was in the same order of magnitude. In addition to generally larger SGD rates when compared to other studies, production of TA (DIC and DOC) in the bottom sediments, as observed in this study, leads to larger fluxes, especially for the driest season (winter 2014), in the mid-bay area (6.27·10⁶μMm^-2d^-1). Consistently larger inputs occur along the shoreline stations (6.14·10⁶μMm^-2d^-1) following the flood recession, when compared to mid-bay (1.26·10⁶μMm^-2d^-1) and are associated with lower SGD following the summer 2015 flooding. This study demonstrates that the carbonate chemistry of estuaries in semiarid areas is affected by non-conservative processes because of seasonal variability of hydroclimatic conditions.

Treating organic cyanide-containing groundwater by immobilization of a nitrile-degrading bacterium with a biofilm-forming bacterium using fluidized bed reactors

Organic cyanide are widely used as an ingredient in the production of plastics, synthetic rubbers, polymers, pharmaceuticals and pesticides or used in laboratories and industries as solvents. Although nitrile-containing wastewater is subjected to primary and secondary treatments, residual nitriles may slowly seep and further migrate through groundwater, resulting in the micropollution of groundwater by organic pollutants. In this study, water samples were collected from different study areas in North China during a period of 3y (from 2013 to 2015) and analyzed to evaluate organic cyanide (CN^-) contamination in groundwater. Three parallel lab-scale fluidized bed reactors (FBRs) were tested for their ability to remove organic cyanide from groundwater. The organic cyanide concentration in groundwater increased significantly (P < 0.05) from 2013 to 2015. With an optimal hydraulic residence time (HRT) of 54 min, reactor R3 (inoculated with a nitrile-degrading bacterium, BX2, and a biofilm-forming bacterium, M1) effectively removed 99.8% of CN^- under steady operation, which was better than that of other reactors. Short-term shutdowns of FBRs had no serious effects on the efficiency of treating organic cyanide. This work demonstrated that the biofilm-forming bacterium could facilitate the fixation of nitrile-degrading bacterium and enhance the efficiency of removing organic cyanide from groundwater.