PM08 Sediment Quality Assessment
Exhibit Hall
8:00 AM - Monday
(PM118) Molybdenum enrichment as an indicator of hypoxic water conditions.
Boothman, W1, Coiro, L1, 9, S., Rego1, 1 U.S. Environmental Protection Agency, Narragansett, RI, USA9
ABSTRACT- Most programs examining the extent of low dissolved oxygen (DO) conditions in marine systems require in-situ sensors to be deployed during periods of low DO. This limits the ability to monitor hypoxia over larger spatial and/or temporal scales. Determination of authigenic molybdenum (Mo) in marine sediments may provide an alternative procedure to monitor local or wide-scale investigations of low DO. Molybdenum is enriched in surficial sediments when overlying waters become sufficiently hypoxic for surficial interstitial waters to become sulfidic, causing Mo to precipitate from interstitial waters. The magnitude of Mo accumulation is related to the length of time the overlying waters remain hypoxic. We present work exploring the distribution of Mo in marine sediments and relate field data with laboratory experiments. Accumulation of Mo in sediments from Narragansett Bay (RI, USA) with differing organic carbon and grain size distributions, maintained under controlled DO conditions in laboratory experiments, is compared against concentrations found in field sediments from those same sites. Bottom water DO concentrations were continuously monitored at the field sites and ranged from highly oxygenated to completely anoxic, both spatially and temporally. Effects of reversal of DO exposure, such as oxidative remobilization, are also shown. The relationship between concentrations of Mo in surficial sediments and extent of hypoxic water column conditions could form the basis for determining spatial and temporal extent of hypoxia due to anthropogenic eutrophication. Profiles of Mo in sediment cores can also provide indications about trends in the occurrence of hypoxic conditions over relatively long periods of time.
Key words: dissolved oxygen , : molybdenum , hypoxia , sediments