High-frequency greenhouse gas flux measurement system detects winter storm surge effects on salt marsh.

The physical controlling factors on coastal plant communities are among the most dynamic of known ecosystems, but climate change alters coastal surface and subsurface hydrologic regimes, which makes rapid measurement of greenhouse gas fluxes critical. Greenhouse gas exchange rates in these terrestrial-aquatic ecosystems are highly variable worldwide with climate, soil type, plant community, and weather. Therefore, increasing data collection and availability should be a priority. Here, we demonstrate and validate physical and analytical modifications to automated soil-flux chamber measurement methods for unattended use in tidally driven wetlands, allowing the high-frequency capture of storm surge and day/night dynamics. Winter CO2 flux from Sarcocornia perennis marsh to the atmosphere was significantly greater during the day (2.8 mmol m-2  hr-1 ) than the night (2.2 mmol m-2  hr-1 ; p < 0.001), while CH4 was significantly greater during the night (0.16 µmol m-2  hr-1 ) than the day (-0.13 µmol m-2  hr-1 ; p = 0.04). The magnitude of CO2 flux during the day and the frequency of CH4 flux were reduced during a surge (p < 0.001). Surge did not significantly affect N2 O flux, which without non-detects was normally distributed around -24.2 nmol m-2  hr-1 . Analysis with sustained-flux global potentials and increased storm surge frequency scenarios, 2020 to 2100, suggested that the marsh in winter remains an atmospheric CO2 source. The modeled results showed an increased flux of CO2 to the atmosphere, while in soil, the uptake of CH4 increased and N2 O uptake decreased. We present analytical routines to correctly capture gas flux curves in dynamic overland flooding conditions and to flag data that are below detection limits or from unobserved chamber-malfunction situations. Storm surge is an important phenomenon globally, but event-driven, episodic factors can be poorly estimated by infrequent sampling. Wider deployment of this system would permit inclusion of surge events in greenhouse gas estimates.

Storm-driven particulate organic matter flux connects a tidal tributary floodplain wetland, mainstem river, and estuary.

The transport of terrestrial plant matter into coastal waters is important to regional and global biogeochemical cycles, and methods for assessing and predicting fluxes in such dynamic environments are needed. We investigated the hypothesis that upon reconnection of a floodplain wetland to its mainstem river, organic matter produced in the wetland would reach other parts of the ecosystem. If so, we can infer that the organic matter would ultimately become a source for the food web in the mainstem river and estuary. To accomplish this, we adapted numerical hydrodynamic and transport modeling methods to estimate the mass of particulate organic matter (POM) derived from the annually senescent aboveground parts of herbaceous marsh plants (H-POM). The Finite-Volume Community Ocean Model (FVCOM), parameterized with flow, tide, and aboveground biomass data, simulated H-POM mobilization from fluid shear stress during tidal exchange, flooding, and variable river flow; entrainment into the water column; transport via channel and overland flow; and entrapment when wetted surfaces dry. We examined export from a recently reconnected, restoring tidal emergent marsh on the Grays River, a tributary to the Columbia River estuary. Modeling indicated that hydrologically reconnecting 65 ha at the site resulted in export of about 96 × 103  kg of H-POM, primarily during pulsed storm flooding events in autumn and early winter. This exported mass amounted to about 19% of the summer peak aboveground biomass measured at the site. Of that 19%, about 48% (47 × 103  kg) was deposited downstream in the Grays River and floodplain wetlands, and the remaining 52% (50 × 103  kg) passed the confluence of the Grays River and the mainstem estuary located about 7 km from the study site. The colonization of the restoring study site largely by nonnative Phalaris arundinacea (reed canarygrass) may have resulted in 18-28% lower H-POM mobilization than typical marsh plant communities on this floodplain, based on estimates from regional studies of marshes dominated by less recalcitrant species. We concluded that restored floodplain wetlands can contribute significant amounts of organic matter to the estuarine ecosystem and thereby contribute to the restoration of historical trophic structure.

Effects of river infrastructure, dredged material placement, and altered hydrogeomorphic processes: The stress ecology of floodplain wetlands and associated fish communities.

Recognition of the habitat values of coastal and floodplain wetlands has inspired research and engineering to restore biological functions after widespread species declines. However, the restoration and management of tidal river floodplains requires a more complete understanding of anthropogenic stressors on hydrogeomorphology and ecological processes. River floodplains near the ocean are affected by localized diking and dredging as well as basin-wide stressors such as dams. We evaluated the effects of stressors versus spatial position, both longitudinal and lateral to the mainstem, using physical and biological response variables in river floodplain wetlands. We categorized historical and modern stressors on the hydrogeomorphic regime of the lower Columbia River and estuary, northeast Pacific coast, including basin-scale management and local impacts. Using this categorization, we analyzed 44 attributes using field-collected data from 50 floodplain wetlands. Attributes represent channels, floods, plant communities, and fish communities. Here we show that plant and fish communities are stratified by position along the estuarine-riverine gradient, in contrast to physical habitat characteristics, which are stratified by stressors on hydrogeomorphic regimes and in some cases the lateral distance from the mainstem river on tributaries. Spatial position relative to water-level dynamics and salinity more strongly affect the biota than does stressor history. Stressor effects were greatest on the geomorphology observed in formerly diked, now reconnected wetlands and in wetlands with a history of dredged material placement; historically diked sites had anomalously deep channels with larger cross-sectional areas while sites with dredged material had shallow channels and lower levels of organic carbon in sediment. In wetlands subject only to landscape-scale stressors such as flow alterations by dams, organic carbon levels were higher. These findings provide natural resource managers with opportunities to enhance similarity to natural conditions and better understand future wetland evolution from different baselines of stressor history and river position.

Identifying priority ecosystem services in tidal wetland restoration.

Classification systems can be an important tool for identifying and quantifying the importance of relationships, assessing spatial patterns in a standardized way, and forecasting alternative decision scenarios to characterize the potential benefits (e.g., ecosystem services) from ecosystem restoration that improve human health and well-being. We present a top-down approach that systematically leverages ecosystem services classification systems to identify potential services relevant for ecosystem restoration decisions. We demonstrate this approach using the U.S. Environmental Protection Agency's National Ecosystem Service Classification System Plus (NESCS Plus) to identify those ecosystem services that are relevant to restoration of tidal wetlands. We selected tidal wetland management documents from federal agencies, state agencies, wetland conservation organizations, and land stewards across three regions of the continental United States (northern Gulf of Mexico, Mid-Atlantic, and Pacific Northwest) to examine regional and organizational differences in identified potential benefits of tidal wetland restoration activities and the potential user groups who may benefit. We used an automated document analysis to quantify the frequencies at which different wetland types were mentioned in the management documents along with their associated beneficiary groups and the ecological end products (EEPs) those beneficiaries care about, as defined by NESCS Plus. Results showed that a top combination across all three regions, all four organizations, and all four tidal wetland types was the EEP naturalness paired with the beneficiary people who care (existence). Overall, the Mid-Atlantic region and the land steward organizations mentioned ecosystem services more than the others, and EEPs were mentioned in combination with tidal wetlands as a high-level, more general category than the other more specific tidal wetland types. Certain regional and organizations differences were statistically significant. Those results may be useful in identifying ecosystem services-related goals for tidal wetland restoration. This approach for identifying and comparing ecosystem service priorities is broadly transferrable to other ecosystems or decision-making contexts.

Multiscale analysis of restoration priorities for marine shoreline planning.

Planners are being called on to prioritize marine shorelines for conservation status and restoration action. This study documents an approach to determining the management strategy most likely to succeed based on current conditions at local and landscape scales. The conceptual framework based in restoration ecology pairs appropriate restoration strategies with sites based on the likelihood of producing long-term resilience given the condition of ecosystem structures and processes at three scales: the shorezone unit (site), the drift cell reach (nearshore marine landscape), and the watershed (terrestrial landscape). The analysis is structured by a conceptual ecosystem model that identifies anthropogenic impacts on targeted ecosystem functions. A scoring system, weighted by geomorphic class, is applied to available spatial data for indicators of stress and function using geographic information systems. This planning tool augments other approaches to prioritizing restoration, including historical conditions and change analysis and ecosystem valuation.