Papers by Evangelos Kakouros
AGUFM, Dec 1, 2008
Tidal marshes of varying hydrology and salinity have been shown to have high rates of microbial m... more Tidal marshes of varying hydrology and salinity have been shown to have high rates of microbial methylmercury (MeHg) production, especially the periodically flooded, higher elevations which are densely vegetated with shallowly rooted plants. The specific influence of emergent wetland plants and their active rhizosphere (root zone) on mercury (Hg) biogeochemistry, however, is poorly understood. Seasonal and spatial patterns of Hg
AGUFM, Dec 1, 2009
Well-mixed surface water in the restored salt marsh at Crissy Field, Golden Gate National Recreat... more Well-mixed surface water in the restored salt marsh at Crissy Field, Golden Gate National Recreation Area, was found to have high aqueous methylmercury (MeHg) concentrations (>1 ng MeHg / L), despite its sandy substrate and low sediment total mercury (THg) concentrations. We sought to determine a) the extent to which the marsh was a source or a sink of MeHg to San Francisco Bay, b) where and when MeHg is produced within the marsh, and c) the extent to which MeHg concentrations in sediment and water varied with extended multi-week flooding events, impoundments caused by periodic sediment accumulation in the narrow inlet. Because Crissy Marsh is small in size, has a single inlet slough channel, and has a tidally-dominated water budget, we had a unique opportunity to construct a THg and MeHg flux budget for this single well-constrained wetland. A 24-hour sampling event was conducted over a full diurnal tidal cycle during August 2008. Particulate and filter-passing (0.45mum) THg and MeHg concentrations were assessed, in addition to concentrations of chlorophyll-a and total suspended solids. These measurements were coupled to water flux calculations from a USGS-derived hydrodynamic model based on tidal prism relationships at this site. The resulting Hg load calculations demonstrated that for this 24-hour period, the marsh was a net source of dissolved MeHg to the bay and a net sink of particulate THg from the bay. To determine where and when Hg was being methylated within the marsh environment, sediment percent (%) MeHg (a surrogate measure of MeHg production efficiency) was examined for 2 years along 8 transects, seasonally and across three marsh elevations (subtidal, low-intertidal, and high-intertidal). The low-intertidal zone (cordgrass-dominated) had higher sediment %MeHg than the other two elevations. Sediment %MeHg was also higher during summer than during winter, highest at the sediment surface (0-2cm), correlated with sediment organic content, and elevated during closure events at some intertidal sites, suggesting enhanced MeHg production during impoundment. However, aqueous MeHg concentrations (both filtered and unfiltered) fell during inlet closure events. Additional data suggest that increased algal production and decreased suspended solids (increased water clarity) may remove MeHg from the water column during closure events, either through settling of mineral and algal components or via photodemethylation. We conclude that MeHg production is most active in the low intertidal sediments of Crissy Marsh, and that this spatial trend is driven by both wetting/drying cycles and the comparatively elevated organic matter concentrations in this zone. We further conclude that the mercury present in Crissy Marsh, whether due to historic contamination, atmospheric deposition or tidal loads, is subject to methylation and export as MeHg. At only 18 acres, Hg fluxes between Crissy Marsh and the larger Bay may be small, but the flux dynamics demonstrated here may be representative of semi-enclosed salt marshes elsewhere in San Francisco Bay.
AGUSM, May 1, 2009
ABSTRACT The specific controls on the production of highly toxic methylmercury (MeHg) in sediment... more ABSTRACT The specific controls on the production of highly toxic methylmercury (MeHg) in sediments are many, but can largely be grouped into those that control either the activity of bacteria that methylate inorganic divalent mercury (Hg(II)) or the availability of Hg(II) to those bacteria. The San Francisco Bay estuary and its watershed is a region contaminated with mercury from both historic mining sources and contemporary anthropogenic inputs. For more than a decade, the USGS has conducted research into the factors that control benthic MeHg production in a diverse suite of habitats throughout this system, across a range of both salinity and hydrologic gradients. Consistent approaches were used throughout multiple individual regional studies to assess both rates of microbial activity and available Hg(II) concentration, as well as the geochemical constituents that influence each of these two major factors. This presentation will briefly summarize this body of research, the results of which are widely applicable to other diverse freshwater, estuarine, and coastal environments. Key findings include: a) total mercury concentrations are a poor predictor of MeHg concentrations; b) only a small fraction (ca. < 0.1% to 5%) of total Hg(II) is available for microbial methylation, and this fraction decreases as sediment conditions become more chemically reducing; c) the activity of the Hg(II)-methylating microbial community varies more widely across different habitat types than does the availability of Hg(II) to those communities; d) iron-reducing bacteria may play a central role in mediating Hg(II)-methylation in freshwater habitats; and e) seasonal wetlands and other periodically inundated habitats are more important zones of MeHg production than permanently submerged habitats.
Earth Science Frontiers, 2006
Selenium (Se) is a biologically essential element, but can become a potent toxicant even at low c... more Selenium (Se) is a biologically essential element, but can become a potent toxicant even at low concentrations. Toxic concentrations of Se are present in irrigation drainage water from large areas in western USA, including Stewart Lake Waterfowl Management Area located in the middle Green River basin, Utah. As part of a major investigation of Se geochemistry and remediation for this site, undisturbed cores were collected to determine the form, concentration, and mobility of Se. Wet digestion analysis of soil and weathered Mancos Shale samples gave high total Se concentrations (up to 3 ppm) and sequential extractions showed that Se was present mainly in association with organic matter (19%～79%) and in the elemental form (17%～67%). Column experiments indicated that Se could be leached rapidly from the deeper soil, where soluble Se is high (up to 292 ppb). The Se leaching rate for the surface soil was initially lower, but was more stable and eventually exceeded that of the deeper soil. The leaching rate of both surface and deeper soils increased when the cores were sterilized by irradiation. Calculations indicate that the quantity of water required to remediate these Se-rich soils by leaching would be large (～ 500 L/kg of soil).
AGU Fall Meeting Abstracts, Dec 5, 2005
Environmental Geosciences, Jun 1, 2005
Journal of Geochemical Exploration, Apr 1, 2006
AGU Fall Meeting Abstracts, Dec 1, 2007
... Authors: Marvin-Dipasquale, MC; Windham-Myers, L.; Alpers, CN; Agee, JL; Cox, MH; Kakouros, E... more ... Authors: Marvin-Dipasquale, MC; Windham-Myers, L.; Alpers, CN; Agee, JL; Cox, MH; Kakouros, E.; Wren, SL. ... YBWA) is part of the larger Yolo Bypass floodwater protection zone associated with the Sacramento River and the Sacramento&150;San Joaquin Delta, California. ...
Restoration Ecology, Dec 14, 2011
Page 1. 1 INTRODUCTION Oil and natural gas currently are the main sources of primary energy in th... more Page 1. 1 INTRODUCTION Oil and natural gas currently are the main sources of primary energy in the USA, supplying about 63% of the energy consumption, and forecasts indicate that by 2025 their consumption will increase by 48 and 50%, respectively (EIA 2003). ...
Limnology and Oceanography-methods, Feb 11, 2017
Science of The Total Environment, Jun 1, 2014
Geochimica et Cosmochimica Acta Supplement, Jun 1, 2009
Scientific Investigations Report, 2018
Applied Geochemistry, Oct 1, 2007
... Yousif K. Kharaka a , Corresponding Author Contact Information , E-mail The Corresponding Aut... more ... Yousif K. Kharaka a , Corresponding Author Contact Information , E-mail The Corresponding Author , Evangelos Kakouros a , James J. Thordsen a , Gil Ambats a and Marvin M. Abbott b. a US Geological Survey, Menlo Park, CA 94025, USA. ...
The Hamilton Wetland Restoration Project (HWRP) is a joint venture between the US Army Corps of E... more The Hamilton Wetland Restoration Project (HWRP) is a joint venture between the US Army Corps of Engineers (USACE; San Francisco District) and the California State Coastal Conservancy. The site is located on the property of the former Hamilton Army Airfield in Novato, California, along the western edge of San Pablo Bay, which is part of northern San Francisco Bay. The initial stages of wetland restoration, which included dredged sediment reuse, took place during 2009-2011. From 2011 until April 2014, the site was maintained as partially flooded through a temporary one-way culvert that allowed bay water onto the site. On April 25th, 2014, the outboard levee towards the north-eastern corner of the site was breached to restore tidal connectivity from the bay to the restoration area. The anticipated period for complete site restoration and marsh evolution is 10-15 years. During this period an active wetland vegetation replanting program was established by the USACE to augment the natural...
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Papers by Evangelos Kakouros