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 seeding by native plants. The various habitats on the restoration site include open-water sub-tidal, mudflats, emergent marsh, grassland, and upland transition zone. San Francisco Bay is contaminated with legacy mercury (Hg) from historic use in mining areas throughout the watershed, as well as from contemporary atmospheric and point-source inputs. Since wetlands are known to be particularly effective zones for the production of toxic methylmercury (MeHg) from inorganic Hg(II), the National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA) documentation associated with the HWRP restoration identified MeHg production as a potentially significant impact of restoring the site to wetland habitat. As part of the USACE Monitoring and Adaptive Management plan (MAMP) for the restoration, the USACE was directed by the Regional Water Quality Control Board (RWQCB) and the San Francisco Bay Conservation and Development Commission (BCDC) to assess MeHg concentrations at the HWRP site. To fulfill this requirement, the USACE entered into an agreement with the U.S. Geological Survey (USGS) to conduct a multi-year and multi-phase investigation of mercury in biota (fish), water, and sediment at the HWRP site. The Sample and Analysis Plan (SAP) covers a period of 13 years and is divided into three phases. Phase 1 included the monitoring of sediment and water pre-breach [2013] and post-breach [2014], and the monitoring of fish pre-breach [2013 only]. Phase 2 covers the three-year period 2014-2016 (near-term post-breach). Phase 3 covers the nine-year period from 2017-2025 (long-term post-breach). Field sampling occurred once per year during a two-week window from mid to late June. A reference site, (Sonoma Baylands) managed by the U.S. Fish and Wildlife Service, was similarly sampled coincident with the HWRP site throughout the study. During the first year of study (2013, pre-breach), an additional reference site was sampled (China Camp) but was subsequently dropped. This data release summarizes the result to date for surface water and bed sediment. Fish data are not included. The list of surface water constituents include: filter-passing total mercury (THg) and methylmercury (MeHg); particulate THg, MeHg and divalent reactive mercury (RHg, operationally defined); particulate organic carbon (POC) along with the carbon-13 isotopic composition (δ 13C-POC); particulate nitrogen (PN) along with the nitrogen-15 isotopic composition (δ 15N-PN); total suspended solids (TSS); chlorophyll_a (Chl_a); specific conductance (SpC); dissolved oxygen (DO); pH; oxidation reduction potential (Eh); and temperature. The list of bed sediment constituents include: THg, MeHg, RHg, iron speciation [ferrous iron (Fe(ll)), crystalline and amorphous ferric iron (Fe(lll))]; total reduced sulfur (TRS); Eh; organic content as percent loss on ignition (%LOI); grain size; porosity; bulk density; and temperature. This data release includes five data tables given both as

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 seeding by native plants. The various habitats on the restoration site include open-water sub-tidal, mudflats, emergent marsh, grassland, and upland transition zone. San Francisco Bay is contaminated with legacy mercury (Hg) from historic use in mining areas throughout the watershed, as well as from contemporary atmospheric and point-source inputs. Since wetlands are known to be particularly effective zones for the production of toxic methylmercury (MeHg) from inorganic Hg(II), the National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA) documentation associated with the HWRP restoration identified MeHg production as a potentially significant impact of restoring the site to wetland habitat. As part of the USACE Monitoring and Adaptive Management plan (MAMP) for the restoration, the USACE was directed by the Regional Water Quality Control Board (RWQCB) and the San Francisco Bay Conservation and Development Commission (BCDC) to assess MeHg concentrations at the HWRP site. To fulfill this requirement, the USACE entered into an agreement with the U.S. Geological Survey (USGS) to conduct a multi-year and multi-phase investigation of mercury in biota (fish), water, and sediment at the HWRP site. The Sample and Analysis Plan (SAP) covers a period of 13 years and is divided into three phases. Phase 1 included the monitoring of sediment and water pre-breach [2013] and post-breach [2014], and the monitoring of fish pre-breach [2013 only]. Phase 2 covers the three-year period 2014-2016 (near-term post-breach). Phase 3 covers the nine-year period from 2017-2025 (long-term post-breach). Field sampling occurred once per year during a two-week window from mid to late June. A reference site, (Sonoma Baylands) managed by the U.S. Fish and Wildlife Service, was similarly sampled coincident with the HWRP site throughout the study. During the first year of study (2013, pre-breach), an additional reference site was sampled (China Camp) but was subsequently dropped. This data release summarizes the result to date for surface water and bed sediment. Fish data are not included. The list of surface water constituents include: filter-passing total mercury (THg) and methylmercury (MeHg); particulate THg, MeHg and divalent reactive mercury (RHg, operationally defined); particulate organic carbon (POC) along with the carbon-13 isotopic composition (δ 13C-POC); particulate nitrogen (PN) along with the nitrogen-15 isotopic composition (δ 15N-PN); total suspended solids (TSS); chlorophyll_a (Chl_a); specific conductance (SpC); dissolved oxygen (DO); pH; oxidation reduction potential (Eh); and temperature. The list of bed sediment constituents include: THg, MeHg, RHg, iron speciation [ferrous iron (Fe(ll)), crystalline and amorphous ferric iron (Fe(lll))]; total reduced sulfur (TRS); Eh; organic content as percent loss on ignition (%LOI); grain size; porosity; bulk density; and temperature. This data release includes five data tables given both as

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 seeding by native plants. The various habitats on the restoration site include open-water sub-tidal, mudflats, emergent marsh, grassland, and upland transition zone. San Francisco Bay is contaminated with legacy mercury (Hg) from historic use in mining areas throughout the watershed, as well as from contemporary atmospheric and point-source inputs. Since wetlands are known to be particularly effective zones for the production of toxic methylmercury (MeHg) from inorganic Hg(II), the National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA) documentation associated with the HWRP restoration identified MeHg production as a potentially significant impact of restoring the site to wetland habitat. As part of the USACE Monitoring and Adaptive Management plan (MAMP) for the restoration, the USACE was directed by the Regional Water Quality Control Board (RWQCB) and the San Francisco Bay Conservation and Development Commission (BCDC) to assess MeHg concentrations at the HWRP site. To fulfill this requirement, the USACE entered into an agreement with the U.S. Geological Survey (USGS) to conduct a multi-year and multi-phase investigation of mercury in biota (fish), water, and sediment at the HWRP site. The Sample and Analysis Plan (SAP) covers a period of 13 years and is divided into three phases. Phase 1 included the monitoring of sediment and water pre-breach [2013] and post-breach [2014], and the monitoring of fish pre-breach [2013 only]. Phase 2 covers the three-year period 2014-2016 (near-term post-breach). Phase 3 covers the nine-year period from 2017-2025 (long-term post-breach). Field sampling occurred once per year during a two-week window from mid to late June. A reference site, (Sonoma Baylands) managed by the U.S. Fish and Wildlife Service, was similarly sampled coincident with the HWRP site throughout the study. During the first year of study (2013, pre-breach), an additional reference site was sampled (China Camp) but was subsequently dropped. This data release summarizes the results to date for surface water and bed sediment. Fish data are not included. The list of surface water constituents include: filter-passing total mercury (THg) and methylmercury (MeHg); particulate THg, MeHg and divalent reactive mercury (RHg, operationally defined); particulate organic carbon (POC) along with the carbon-13 isotopic composition (δ 13C-POC); particulate nitrogen (PN) along with the nitrogen-15 isotopic composition (δ 15N-PN); total suspended solids (TSS); chlorophyll_a (Chl_a); specific conductance (SpC); dissolved oxygen (DO); pH; oxidation reduction potential (Eh); and temperature. The list of bed sediment constituents include: THg, MeHg, RHg, iron speciation [ferrous iron (Fe2+), crystalline and amorphous ferric iron (Fe3+)]; total reduced sulfur (TRS); Eh; organic content as percent loss on ignition (%LOI); grain size; porosity; wet bulk density; and temperature. This data release includes five data tables given both as

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 seeding by native plants. The various habitats on the restoration site include open-water sub-tidal, mudflats, emergent marsh, grassland, and upland transition zone. San Francisco Bay is contaminated with legacy mercury (Hg) from historic use in mining areas throughout the watershed, as well as from contemporary atmospheric and point-source inputs. Since wetlands are known to be particularly effective zones for the production of toxic methylmercury (MeHg) from inorganic Hg(II), the National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA) documentation associated with the HWRP restoration identified MeHg production as a potentially significant impact of restoring the site to wetland habitat. As part of the USACE Monitoring and Adaptive Management plan (MAMP) for the restoration, the USACE was directed by the Regional Water Quality Control Board (RWQCB) and the San Francisco Bay Conservation and Development Commission (BCDC) to assess MeHg concentrations at the HWRP site. To fulfill this requirement, the USACE entered into an agreement with the U.S. Geological Survey (USGS) to conduct a multi-year and multi-phase investigation of mercury in biota (fish), water, and sediment at the HWRP site. The Sample and Analysis Plan (SAP) covers a period of 13 years and is divided into three phases. Phase 1 included the monitoring of sediment and water pre-breach [2013] and post-breach [2014], and the monitoring of fish pre-breach [2013 only]. Phase 2 covers the three-year period 2014-2016 (near-term post-breach). Phase 3 covers the nine-year period from 2017-2025 (long-term post-breach). Field sampling occurred once per year during a two-week window from mid to late June. A reference site, (Sonoma Baylands) managed by the U.S. Fish and Wildlife Service, was similarly sampled coincident with the HWRP site throughout the study. During the first year of study (2013, pre-breach), an additional reference site was sampled (China Camp) but was subsequently dropped. This data release summarizes the results to date for surface water and bed sediment. Fish data are not included. The list of surface water constituents include: filter-passing total mercury (THg) and methylmercury (MeHg); particulate THg, MeHg and divalent reactive mercury (RHg, operationally defined); particulate organic carbon (POC) along with the carbon-13 isotopic composition (δ 13C-POC); particulate nitrogen (PN) along with the nitrogen-15 isotopic composition (δ 15N-PN); total suspended solids (TSS); chlorophyll_a (Chl_a); specific conductance (SpC); dissolved oxygen (DO); pH; oxidation reduction potential (Eh); and temperature. The list of bed sediment constituents include: THg, MeHg, RHg, iron speciation [ferrous iron (Fe2+), crystalline and amorphous ferric iron (Fe3+)]; total reduced sulfur (TRS); Eh; organic content as percent loss on ignition (%LOI); grain size; porosity; wet bulk density; and temperature. This data release includes five data tables given both as

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 seeding by native plants. The various habitats on the restoration site include open-water sub-tidal, mudflats, emergent marsh, grassland, and upland transition zone. San Francisco Bay is contaminated with legacy mercury (Hg) from historic use in mining areas throughout the watershed, as well as from contemporary atmospheric and point-source inputs. Since wetlands are known to be particularly effective zones for the production of toxic methylmercury (MeHg) from inorganic Hg(II), the National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA) documentation associated with the HWRP restoration identified MeHg production as a potentially significant impact of restoring the site to wetland habitat. As part of the USACE Monitoring and Adaptive Management plan (MAMP) for the restoration, the USACE was directed by the Regional Water Quality Control Board (RWQCB) and the San Francisco Bay Conservation and Development Commission (BCDC) to assess MeHg concentrations at the HWRP site. To fulfill this requirement, the USACE entered into an agreement with the U.S. Geological Survey (USGS) to conduct a multi-year and multi-phase investigation of mercury in biota (fish), water, and sediment at the HWRP site. The Sample and Analysis Plan (SAP) covers a period of 13 years and is divided into three phases. Phase 1 included the monitoring of sediment and water pre-breach [2013] and post-breach [2014], and the monitoring of fish pre-breach [2013 only]. Phase 2 covers the three-year period 2014-2016 (near-term post-breach). Phase 3 covers the nine-year period from 2017-2025 (long-term post-breach). Field sampling occurred once per year during a two-week window from mid to late June. A reference site, (Sonoma Baylands) managed by the U.S. Fish and Wildlife Service, was similarly sampled coincident with the HWRP site throughout the study. During the first year of study (2013, pre-breach), an additional reference site was sampled (China Camp), but was subsequently dropped. This data release summarizes the result to date for surface water and bed sediment. Fish data are not included. The list of surface water constituents include: filter-passing total mercury (THg) and methylmercury (MeHg); particulate THg, MeHg and divalent reactive mercury (RHg, operationally defined); particulate organic carbon (POC) along with the carbon-13 isotopic composition (δ 13C-POC); particulate nitrogen (PN) along with the nitrogen-15 isotopic composition (δ 15N-PN); total suspended solids (TSS); chlorophyll_a (Chl_a); specific conductance (SpC); dissolved oxygen (DO); pH; oxidation reduction potential (Eh); and temperature. The list of bed sediment constituents include: THg, MeHg, RHg, iron speciation [ferrous iron (Fe2+), crystalline and amorphous ferric iron (Fe3+)]; total reduced sulfur (TRS); Eh; organic content as percent loss on ignition (%LOI); grain size; porosity; bulk density; and temperature. This data release includes four data tables given both as Excel

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 seeding by native plants. The various habitats on the restoration site include open-water sub-tidal, mudflats, emergent marsh, grassland, and upland transition zone. San Francisco Bay is contaminated with legacy mercury (Hg) from historic use in mining areas throughout the watershed, as well as from contemporary atmospheric and point-source inputs. Since wetlands are known to be particularly effective zones for the production of toxic methylmercury (MeHg) from inorganic Hg(II), the National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA) documentation associated with the HWRP restoration identified MeHg production as a potentially significant impact of restoring the site to wetland habitat. As part of the USACE Monitoring and Adaptive Management plan (MAMP) for the restoration, the USACE was directed by the Regional Water Quality Control Board (RWQCB) and the San Francisco Bay Conservation and Development Commission (BCDC) to assess MeHg concentrations at the HWRP site. To fulfill this requirement, the USACE entered into an agreement with the U.S. Geological Survey (USGS) to conduct a multi-year and multi-phase investigation of mercury in biota (fish), water, and sediment at the HWRP site. The Sample and Analysis Plan (SAP) covers a period of 13 years and is divided into three phases. Phase 1 included the monitoring of sediment and water pre-breach [2013] and post-breach [2014], and the monitoring of fish pre-breach [2013 only]. Phase 2 covers the three-year period 2014-2016 (near-term post-breach). Phase 3 covers the nine-year period from 2017-2025 (long-term post-breach). Field sampling occurred once per year during a two-week window from mid to late June. A reference site, (Sonoma Baylands) managed by the U.S. Fish and Wildlife Service, was similarly sampled coincident with the HWRP site throughout the study. During the first year of study (2013, pre-breach), an additional reference site was sampled (China Camp), but was subsequently dropped. This data release summarizes the result to date for surface water and bed sediment. Fish data are not included. The list of surface water constituents include: filter-passing total mercury (THg) and methylmercury (MeHg); particulate THg, MeHg and divalent reactive mercury (RHg, operationally defined); particulate organic carbon (POC) along with the carbon-13 isotopic composition (δ 13C-POC); particulate nitrogen (PN) along with the nitrogen-15 isotopic composition (δ 15N-PN); total suspended solids (TSS); chlorophyll_a (Chl_a); specific conductance (SpC); dissolved oxygen (DO); pH; oxidation reduction potential (Eh); and temperature. The list of bed sediment constituents include: THg, MeHg, RHg, iron speciation [ferrous iron (Fe2+), crystalline and amorphous ferric iron (Fe3+)]; total reduced sulfur (TRS); Eh; organic content as percent loss on ignition (%LOI); grain size; porosity; bulk density; and temperature. This data release includes four data tables given both as Excel

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 seeding by native plants. The various habitats on the restoration site include open-water sub-tidal, mudflats, emergent marsh, grassland, and upland transition zone. San Francisco Bay is contaminated with legacy mercury (Hg) from historic use in mining areas throughout the watershed, as well as from contemporary atmospheric and point-source inputs. Since wetlands are known to be particularly effective zones for the production of toxic methylmercury (MeHg) from inorganic Hg(II), the National Environmental Policy Act (NEPA) and California Environmental Quality Act (CEQA) documentation associated with the HWRP restoration identified MeHg production as a potentially significant impact of restoring the site to wetland habitat. As part of the USACE Monitoring and Adaptive Management plan (MAMP) for the restoration, the USACE was directed by the Regional Water Quality Control Board (RWQCB) and the San Francisco Bay Conservation and Development Commission (BCDC) to assess MeHg concentrations at the HWRP site. To fulfill this requirement, the USACE entered into an agreement with the U.S. Geological Survey (USGS) to conduct a multi-year and multi-phase investigation of mercury in biota (fish), water, and sediment at the HWRP site. The Sample and Analysis Plan (SAP) covers a period of 13 years and is divided into three phases. Phase 1 included the monitoring of sediment and water pre-breach [2013] and post-breach [2014], and the monitoring of fish pre-breach [2013 only]. Phase 2 covers the three-year period 2014-2016 (near-term post-breach). Phase 3 covers the nine-year period from 2017-2025 (long-term post-breach). Field sampling occurred once per year during a two-week window from mid to late June. A reference site, (Sonoma Baylands) managed by the U.S. Fish and Wildlife Service, was similarly sampled coincident with the HWRP site throughout the study. During the first year of study (2013, pre-breach), an additional reference site was sampled (China Camp), but was subsequently dropped. This data release summarizes the result to date for surface water and bed sediment. Fish data are not included. The list of surface water constituents include: filter-passing total mercury (THg) and methylmercury (MeHg); particulate THg, MeHg and divalent reactive mercury (RHg, operationally defined); particulate organic carbon (POC) along with the carbon-13 isotopic composition (δ 13C-POC); particulate nitrogen (PN) along with the nitrogen-15 isotopic composition (δ 15N-PN); total suspended solids (TSS); chlorophyll_a (Chl_a); specific conductance (SpC); dissolved oxygen (DO); pH; oxidation reduction potential (Eh); and temperature. The list of bed sediment constituents include: THg, MeHg, RHg, iron speciation [ferrous iron (Fe2+), crystalline and amorphous ferric iron (Fe3+)]; total reduced sulfur (TRS); Eh; organic content as percent loss on ignition (%LOI); grain size; porosity; bulk density; and temperature. This data release includes four data tables given both as Excel

This dataset includes mercury and other constituent concentration and physical properties data for surface sediment, pore water and surface water collected as part of the South San Francisco Bay Salt Pond Restoration Phase 1 (2010 to 2018) studies. The overarching focus of these studies was to monitor mercury (Hg) biogeochemistry in both sediment and water in response to management actions associated with the conversion of former salt producing ponds to contemporary wetland habitat. The two primary management actions included the breaching of Pond A6 during December 2010, and the construction and operation of an adjustable tidal control structure (TCS) associated with the Pond A5/A7/A8 Complex beginning in June 2011. The TSC that reconnects the Complex to Alviso Slough (specifically referred to as the A8-TCS), a historically Hg contaminated waterway that represents the terminus of watershed drainage that includes the New Almaden mercury mining district. The A8-TCS consists of eight gates, each five feet wide. During the initial testing period (starting in June 2011) only one gate was opened, and the structure was closed again during the winter-spring months (from December until the following June). Over the subsequent seven years, the number of gates open was increased to three (15 feet, June 2012), to five (25 feet, September 2014), and eventually to all eight (40 feet, June 2017). Beginning in 2014 the A8-TCS was opened year-round. Field sampling occurred in both ponds and sloughs. In addition to sampling within the Complex ponds, two control ponds (A3N and A16) were also sampled. Similarly, in addition to sampling within Alviso Slough, two nearby control sloughs (Mallard Slough a.k.a Artesian Slough and Guadalupe Slough) were sampled (beginning in 2014 for Guadalupe Slough). Sediment sampling was conducted for the period of May 2010 through August 2011, which represents the period immediately prior to and immediately after the two above mentioned management actions. Additional sediment sampling was conducted in Mallard Slough exclusively during the August- September period 2011-2013, 2015, and 2017. Surface water sampling was conducted during three periods. The first period was in conjunction with the sediment sampling (May 2010 through August 2011). The second period involved a unique series of high temporal resolution sampling events conducted at a single site in mid-Alviso Slough, when water samples were collected hourly over a 25-hour period to capture the Hg dynamics associated with two full tidal cycles. A total of five such high-resolution ‘diel’ sampling events were conducted between May 2012 and February 2013, which included each of the four seasons and the annual ‘first flush’ event associated with the initiation of the 2012-13 rainy season. The third period, from February 2014 through February 2018, represents when all ponds and sloughs were again sampled (akin to the first period). This third period also represents when the A8-TCS was sequentially opened from 15 feet (3 gates open) to 40 feet (all 8 gates open), and when the A8-TCS management transitioned from being closed during the winter months to being opened year-round, beginning in 2014. This data release includes five data tables given both as Excel (*.xlxs) and machine readable 'comma-separated values' format (*.csv): 1) ‘SBSP.Data.Dictionary_2010-18’, the Data Dictionary, which provides definitions and details related to the other four data tables and includes analytical methods citations; 2) ‘SBSP.SED_2010-17’, the surface sediment analytical dataset; 3) ‘SBSP.SW_2010-18’, the primary surface water analytical dataset; 4) ‘SBSP.SW_Diel_2012-13’, the surface water diel sampling dataset; 5) ‘SBSP.QA_2010-18’, quality assurance data summary for the sediment and water datasets.

Habitat biogeochemistry was assessed by measuring 31 variables in sediments, porewater, and surface waters related to mercury content, organic matter, sediment characteristics, and microbial rates of sulfate reduction, iron reduction, and methanogenesis. Fifty-six composite surface (0-2 cm) sediment cores and 32 surface water samples were collected in three wetlands in the spring and summer of 2005 and 2006.

Under the Great Lakes Restoration Initiative, the U.S. Geological Survey Mercury Research Lab (USGS MRL) conducted a multiyear assessment of mercury across the Laurentian Great Lakes. Biannual sampling was conducted across all five lakes onboard the U.S. Environmental Protection Agency (US EPA) research vessel Lake Guardian (in years 2010–2014, 2018) at pelagic sampling locations established by the long-term US EPA Great Lakes monitoring program. In addition to the regularly scheduled biannual sampling, in September 2013 and 2014 Lake Michigan and Lake Erie (respectively) were sampled with increased focus on shallow nearshore locations. Throughout these sampling efforts, sediments, mussels, surface water, and plankton were collected from open-water locations within all five of the Great Lakes. Additionally, surface water from Great Lake tributaries were sampled by the USGS MRL and preceded (2005 or 2006) or overlapped (2010-2015) with the open lake sampling efforts. All surface water samples were analyzed for methylmercury, total mercury, and dissolved organic carbon. Plankton and mussel tissue were analyzed for methylmercury, total mercury, and carbon/nitrogen stable isotopes and concentrations (plankton only). Sediments were analyzed for methylmercury, total mercury, and carbon content.