Sediment samples were collected from mercury-contaminated streams and lakes in Texas, Virginia, and Tennessee and were analyzed for total carbon (TC) and total nitrogen (TN). A portion of the sample was combusted at 550 degrees C for 2 hours prior to analysis to remove the organic carbon and nitrogen, thus giving total inorganic carbon (TIC) and total inorganic nitrogen (TIN). Total organic carbon (TOC) and total organic nitrogen (TON) were calculated from these values.

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 (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 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 (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

The Cache Creek Settling Basin (CCSB) is a 13.3 km2 leveed basin located at the terminal drainage of the Cache Creek watershed, immediately NE of the town of Woodland (Yolo County), California and approximately 18 km NW of Sacramento, California. The basin was constructed by the U.S. Army Corps of Engineers (completed in 1937 and modified in 1993) for the purpose of trapping suspended sediment transported from the upper Cache Creek watershed during high-flow events, thus preventing sediment from entering the Yolo Bypass, a larger downstream floodwater conveyance and agricultural zone. In addition to trapping suspended sediment, the CCSB also traps sediment-associated mercury (Hg), which is particularly elevated in the upper watershed, owing to natural Hg deposits and associated historic Hg mining areas. The CCSB is a multi-use area containing a number of habitat types that are typical of the California Central Valley region, including: open-water (stream, canal), riparian, floodplain (woody, non-woody), and agriculture (row crop fields) habitats. This dataset includes shallow surface sediment (top 0–2 cm interval) constituent concentration data (primarily) and microbial methylmercury production potential rate data (limited) collected between April 2010 and July 2019 from the above-noted habitats to assess spatial and temporal variations in sediment geochemistry and mercury speciation within the CCSB. The dataset is presented in two sections (child pages): one has the constituent concentration and microbial rate data, and the other includes results of habitat mapping that was conducted within the CCSB for the purpose of data analysis. First posted – October 16, 2018 (available from author) Revised – July, 2021 (version 2.0)