Consumption of carbon dioxide, as measured by direct coulometry in light and dark bottles, was used to estimate the rate of natural assemblages of phytoplankton incubated in situ. A total of 30 experiments were made during a 12 mo period in Bedford as&, Nova Scotia.For comparison, simultaneous estimates of primary production were made on each occasion using both the Light-and-darkbottle oxygen method and the I4C method. Primary production values fell in the range < 1 to 50 mm01 C m-3 d-l. Throughout this range, excellent agreement was found between primary production as estimated by the 14C method and gross primary production estimated by change in dissolved carbon dioxide. Release of labelled carbon into solution accounted for 2 to 19 % of total pnmary production as measured by the I4C method, with the lower values occurring in the spring bloom period. When the carbon-based results were compared w t h the oxygen-based ones, they agreed to within a mean apparent photosynthetic quotient of 1.6. High apparent PQ's in ulnter are attnbuted to an overestimation of oxygen primary production and an undereshmation of I4C primary production. Direct coulometry offers considerable promise as a technique for measuring photosynthesis by phytoplankton.
This article discusses a problem at the Hilltown Township (Pennsylvania) Water and Sewer Authority with naturally occurring arsenic in its groundwater. The article describes how the township tested an iron‐based adsorption treatment technology as part of the U.S. Environmental Protection Agency's Environmental Technology Verification Program. The program verifies the performance of innovative technologies that can improve protection of human health and the environment. The article discusses the testing process, along with test results, and the installation of a 300 gpm arsenic removal system at the utility as the solution for the arsenic problem. The system uses three‐stage adsorber vessel treatment technology in which the pretreatment system removes iron and manganese before water enters an adsorber containing ferric‐oxide media for arsenic removal. The pretreatment system allowed the township to address its needs for reducing iron, manganese, and arsenic at the same time. As media capture iron and manganese, system pressure begins to climb, and backwashing is performed based on pressure differential. The system is backwashed every 3‐4 weeks. More frequent backwashing is required when the system operates 24 hr/day in the summer.
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