Henderson Paul B.

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Paul B.
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Author: Dulaiova, Henrieta ×

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  • Preprint
    Geochemical and physical sources of radon variation in a subterranean estuary — implications for groundwater radon activities in submarine groundwater discharge studies
    ( 2007-12-13) Dulaiova, Henrieta ; Gonneea, Meagan E. ; Henderson, Paul B. ; Charette, Matthew A.
    Submarine groundwater discharge (SGD), in form of springs and diffuse seepage, has long been recognized as a source of chemical constituents to the coastal ocean. Because groundwater is two to four orders of magnitude richer in radon than surface water, it has been used as both a qualitative and a quantitative tracer of groundwater discharge. Besides this large activity gradient, the other perceived advantage of radon stems from its classification as noble gas; that is, its chemical behavior is expected not to be influenced by salinity, redox, and diagenetic conditions present in aquatic environments. During our three-year monthly sampling of the subterranean estuary (STE) in Waquoit Bay, MA, we found highly variable radon activities (50-1600 dpm L-1) across the fresh-saline interface of the aquifer. We monitored pore water chemistry and radon activity at 8 fixed depths spanning from 2 to 5.6 m across the STE, and found seasonal fluctuations in activity at depths where elevated radon was observed. We postulate that most of pore water 222Rn is produced from particle-surface bound 226Ra, and that the accumulation of this radium is likely regulated by the presence of manganese (hydr)oxides. Layers of manganese (hydr)oxides form at the salinity transition zone (STZ), where water with high salinity, high manganese, and low redox potential mixes with fresh water. Responding to the seasonality of aquifer recharge, the location of the STZ and the layers with radium enriched manganese (hydr)oxide follows the seasonal land- or bay-ward movement of the freshwater lens. This results in seasonal changes in the depth where elevated radon activities are observed. The conclusion of our study is that the freshwater part of the STE has a radon signature that is completely different from the STZ or recirculated sea water. Therefore, the radon activity in SGD will depend on the ratio of fresh and recirculated seawater in the discharging groundwater.
  • Article
    GEOTRACES radium isotopes interlaboratory comparison experiment
    (Association for the Sciences of Limnology and Oceanography, 2012-06) Charette, Matthew A. ; Dulaiova, Henrieta ; Gonneea, Meagan E. ; Henderson, Paul B. ; Moore, Willard S. ; Scholten, Jan C. ; Pham, Mai Khanh
    In anticipation of the international GEOTRACES program, which will study the global marine biogeochemistry of trace elements and isotopes, we conducted a multi-lab intercomparison for radium isotopes. The intercomparison was in two parts involving the distribution of: (1) samples collected from four marine environments (open ocean, continental slope, shelf, and estuary) and (2) a suite of four reference materials prepared with isotopic standards (circulated to participants as 'unknowns'). Most labs performed well with 228Ra and 224Ra determination, however, there were a number of participants that reported 226Ra, 223Ra, and 228Th (supported 224Ra) well outside the 95% confidence interval. Many outliers were suspected to be a result of poorly calibrated detectors, though other method specific factors likely played a role (e.g., detector leakage, insufficient equilibration). Most methods for radium analysis in seawater involve a MnO2 fiber column preconcentration step; as such, we evaluated the extraction efficiency of this procedure and found that it ranged from an average of 87% to 94% for the four stations. Hence, nonquantitative radium recovery from seawater samples may also have played a role in lab-to-lab variability.
  • Preprint
    Coupled radon, methane and nitrate sensors for large-scale assessment of groundwater discharge and non-point source pollution to coastal waters
    ( 2009-12-09) Dulaiova, Henrieta ; Camilli, Richard ; Henderson, Paul B. ; Charette, Matthew A.
    We constructed a survey system of radon/methane/nitrate/salinity to find sites of submarine groundwater discharge (SGD) and groundwater nitrate input. We deployed the system in Waquoit Bay and Boston Harbor, MA where we derived SGD rates using a mass balance of radon with methane serving as a fine resolution qualitative indicator of groundwater. In Waquoit Bay we identified several locations of enhanced groundwater discharge, out of which two (Childs and Quashnet Rivers) were studied in more detail. The Childs River was characterized by high nitrate input via groundwater discharge, while the Quashnet River SGD was notable but not a significant source of nitrate. Our radon survey of Boston Harbor revealed several sites with significant SGD, out of these Inner Harbor and parts of Dorchester Bay and Quincy Bay had groundwater fluxes accompanied by significant water column nitrogen concentrations. The survey system has proven effective in revealing areas of SGD and non-point source pollution.
  • Article
    Erratum : GEOTRACES radium isotopes interlaboratory comparison experiment
    (Association for the Sciences of Limnology and Oceanography, 2012-06) Charette, Matthew A. ; Dulaiova, Henrieta ; Gonneea, Meagan E. ; Henderson, Paul B. ; Moore, Willard S. ; Scholten, Jan C. ; Pham, Mai Khanh
    In our original paper, Charette, M. A., H. Dulaiova, M. E. Gonneea, P. B. Henderson, W. S. Moore, J. C. Scholten, and M. K. Pham. 2012. GEOTRACES radium isotopes interlaboratory comparison experiment. Limonol. Oceanogr.: Methods 10:451, the incorrect headers were used for Table 9.
  • Article
    Shelf-derived iron inputs drive biological productivity in the southern Drake Passage
    (American Geophysical Union, 2009-10-27) Dulaiova, Henrieta ; Ardelan, M. V. ; Henderson, Paul B. ; Charette, Matthew A.
    In the Southern Ocean near the Antarctic Peninsula, Antarctic Circumpolar Current (ACC) fronts interact with shelf waters facilitating lateral transport of shelf-derived components such as iron into high-nutrient offshore regions. To trace these shelf-derived components and estimate lateral mixing rates of shelf water, we used naturally occurring radium isotopes. Short-lived radium isotopes were used to quantify the rates of shelf water entrainment while Fe/228Ra ratios were used to calculate the Fe flux. In the summer of 2006 we found rapid mixing and significant lateral iron export, namely, a dissolved iron flux of 1.1 × 105 mol d−1 and total acid leachable iron flux of 1.1 × 106 mol d−1 all of which is transported in the mixed layer from the shelf region offshore. This dissolved iron flux is significant, especially considering that the bloom observed in the offshore region (0.5–2 mg chl a m−3) had an iron demand of 1.1 to 4 × 105 mol Fe. Net vertical export fluxes of particulate Fe derived from 234Th/238U disequilibrium and Fe/234Th ratios accounted for only about 25% of the dissolved iron flux. On the other hand, vertical upward mixing of iron rich deeper waters provided only 7% of the lateral dissolved iron flux. We found that similarly to other studies in iron-fertilized regions of the Southern Ocean, lateral fluxes overwhelm vertical inputs and vertical export from the water column and support significant phytoplankton blooms in the offshore regions of the Drake Passage.