All tidal wetlands are blue carbon ecosystems.

Managing coastal wetlands is one of the most promising activities to reduce atmospheric greenhouse gases, and it also contributes to meeting the United Nations Sustainable Development Goals. One of the options is through blue carbon projects, in which mangroves, saltmarshes, and seagrass are managed to increase carbon sequestration and reduce greenhouse gas emissions. However, other tidal wetlands align with the characteristics of blue carbon. These wetlands are called tidal freshwater wetlands in the United States, supratidal wetlands in Australia, transitional forests in Southeast Asia, and estuarine forests in South Africa. They have similar or larger potential for atmospheric carbon sequestration and emission reductions than the currently considered blue carbon ecosystems and have been highly exploited. In the present article, we suggest that all wetlands directly or indirectly influenced by tides should be considered blue carbon. Their protection and restoration through carbon offsets could reduce emissions while providing multiple cobenefits, including biodiversity.

Total ecosystem carbon stocks at the marine-terrestrial interface: Blue carbon of the Pacific Northwest Coast, United States.

The coastal ecosystems of temperate North America provide a variety of ecosystem services including high rates of carbon sequestration. Yet, little data exist for the carbon stocks of major tidal wetland types in the Pacific Northwest, United States. We quantified the total ecosystem carbon stocks (TECS) in seagrass, emergent marshes, and forested tidal wetlands, occurring along increasing elevation and decreasing salinity gradients. The TECS included the total aboveground carbon stocks and the entire soil profile (to as deep as 3 m). TECS significantly increased along the elevation and salinity gradients: 217 ± 60 Mg C/ha for seagrass (low elevation/high salinity), 417 ± 70 Mg C/ha for low marsh, 551 ± 47 Mg C/ha for high marsh, and 1,064 ± 38 Mg C/ha for tidal forest (high elevation/low salinity). Soil carbon stocks accounted for >98% of TECS in the seagrass and marsh communities and 78% in the tidal forest. Soils in the 0-100 cm portion of the profile accounted for only 48%-53% of the TECS in seagrasses and marshes and 34% of the TECS in tidal forests. Thus, the commonly applied limit defining TECS to a 100 cm depth would greatly underestimate both carbon stocks and potential greenhouse gas emissions from land-use conversion. The large carbon stocks coupled with other ecosystem services suggest value in the conservation and restoration of temperate zone tidal wetlands through climate change mitigation strategies. However, the findings suggest that long-term sea-level rise effects such as tidal inundation and increased porewater salinity will likely decrease ecosystem carbon stocks in the absence of upslope wetland migration buffer zones.

The use of sterol profiles, supported with other faecal source tracking methods, to apportion septic tanks contamination in rural catchments.

Identifying the origin of faecal pollution in water is needed for effective water management decisions to protect both human health and aquatic ecosystems. Traditionally used indicators of faecal contamination, such as E. coli, only indicate pollution from warm-blooded animals and not the specific source of contamination; hence, more source specific tracers are required. The study has focussed on separating the two main sources of contaminants within rural catchments in Ireland, agriculture and on-site wastewater treatment systems (predominantly septic tanks). While human-specific effluent tracers may assist in identifying potential pathways from individual septic tanks to surface waters, it is difficult to quantify the cumulative impact of such systems at a catchment scale. This study has investigated faecal sterols as a method to quantify such an impact on four small catchments in areas of low subsoil permeability with high densities of septic tanks. The results demonstrate the usefulness of faecal sterols which provide a quantitative evaluation of the respective impact between agricultural pasture inputs and on-site effluent showing differences between the four catchments. The study also highlights the need to derive more specific local reference sterol profile databases for specific countries or regions, using local source material of animal faeces and effluent. Two intensive sampling campaigns on the four catchments then used faecal sterols in parallel to fluorescent whitening compounds (FWCs), caffeine, artificial sweeteners and selected pharmaceuticals to gain further insights and confirmation about contamination hotspots as well as providing comparison between the different parameters. The combination of sterols, FWCs, caffeine, acesulfame and cyclamate has proven suitable to provide an estimate of the extent of human contamination in these rural catchments and has yielded additional information about potential pollution pathways and proximity of contamination. Overall, this methodology can help to facilitate a targeted and effective water management in such catchments.

Insights into estuary habitat loss in the western United States using a new method for mapping maximum extent of tidal wetlands.

Effective conservation and restoration of estuarine wetlands require accurate maps of their historical and current extent, as well as estimated losses of these valued habitats. Existing coast-wide tidal wetland mapping does not explicitly map historical tidal wetlands that are now disconnected from the tides, which represent restoration opportunities; nor does it use water level models or high-resolution elevation data (e.g. lidar) to accurately identify current tidal wetlands. To better inform estuarine conservation and restoration, we generated new maps of current and historical tidal wetlands for the entire contiguous U.S. West Coast (Washington, Oregon, and California). The new maps are based on an Elevation-Based Estuary Extent Model (EBEEM) that combines lidar digital elevation models (DEMs) and water level models to establish the maximum historical extent of tidal wetlands, representing a major step forward in mapping accuracy for restoration planning and analysis of wetland loss. Building from this new base, we also developed an indirect method for mapping tidal wetland losses, and created maps of these losses for 55 estuaries on the West Coast (representing about 97% of historical West Coast vegetated tidal wetland area). Based on these new maps, we estimated that total historical estuary area for the West Coast is approximately 735,000 hectares (including vegetated and nonvegetated areas), and that about 85% of vegetated tidal wetlands have been lost from West Coast estuaries. Losses were highest for major river deltas. The new maps will help interested groups improve action plans for estuarine wetland habitat restoration and conservation, and will also provide a better baseline for understanding and predicting future changes with projected sea level rise.