Calibrating an ultra-low expansion cavity for high precision spectroscopy from 630 THz to 685 THz using molecular tellurium lines.

We report on the calibration of a temperature stabilized ultra-low expansion (ULE) cavity using previously measured molecular tellurium and atomic cesium lines. By means of a dual frequency modulation technique, the frequency dependence of the free spectral range of the ULE cavity is measured and was found to vary by less than 60 Hz over the ∼55 THz range of the calibration. This method of calibration enables the ULE cavity to measure absolute frequencies to better than 1.5 MHz.

Transfers and transformations of zinc in flow-through wetland microcosms.

Two microcosm-scale wetlands (570-liter containers) were integratively designed and constructed to investigate transfers and transformations of zinc associated with an aqueous matrix, and to provide future design parameters for pilot-scale constructed wetlands. The fundamental design of these wetland microcosms was based on biogeochemical principles regulating fate and transformations of zinc (pH, redox, etc.). Each wetland consisted of a 45-cm hydrosoil depth inundated with 25 cm of water, and planted with Scirpus californicus. Zinc ( approximately 2 mg/liter) as ZnCl2 was amended to each wetland for 62 days. Individual wetland hydraulic retention times (HRT) were approximately 24 h. Total recoverable zinc was measured daily in microcosm inflow and outflows, and zinc concentrations in hydrosoil and S. californicus tissue were measured pre- and post-treatment. Ceriodaphnia dubia and Pimephales promelas7-day aqueous toxicity tests were performed on wetland inflows and outflows, and Hyalella azteca whole sediment toxicity tests (10-day) were performed pre- and post-treatment. Approximately 75% of total recoverable zinc was transferred from the water column. Toxicity decreased from inflow to outflow based on 7-day C. dubia tests, and survival of H. azteca in hydrosoil was >80%. Data illustrate the ability of integratively designed wetlands to transfer and sequester zinc from the water column while concomitantly decreasing associated toxicity.

Design and construction of wetlands for aqueous transfers and transformations of selected metals.

Two pilot-scale wetland cells (6.1 x 30.5 m) were integratively designed and constructed to emphasize and enhance transfers and transformations of selected metals (Cu, Pb, and Zn) in an aqueous matrix. A series of preliminary experiments and analyses were conducted to select macrofeatures (hydroperiod, hydrosoil, and vegetation) of the constructed wetland system. These wetland cells were designed to operate in series or parallel with nominal hydraulic retention times of 24-48 hr, respectively. With water at a depth of 30 cm, both wetland cells had hydrosoil (45 cm) planted with Scirpus californicus. After 250 days of wetland operation, average hydrosoil redox potentials in each wetland cell decreased from +90 mV to -165 mV, and average plant height increased from 0.3 to 2.7 m. Aqueous samples were collected over a 4.5-month period at the inflow and outflow sites of the wetland cells. Average inflow concentrations of total recoverable Cu, Pb, and Zn were 22.4, 10.5, and 565.9 micrograms/L, respectively. After a 46-hr HRT, average outflow concentrations of total recoverable Cu, Pb, and Zn were 15, 2.2, and 85.9 micrograms/L, resulting in removals of 33, 79, and 85%, respectively. Initial results suggest that these constructed wetlands can be designed to remove targeted metals in wastewater.