117 research outputs found
Carbon Sequestration in a Pacific Northwest Eelgrass (Zostera marina) Meadow
No full textCoastal wetlands are known to be efficient carbon sinks due to high rates of primary productivity, carbon burial by mineral sediments, and low rates of sediment organic matter decomposition. Of the three coastal wetland types: tidal marshes, tidal forests, and seagrass meadows, carbon burial by seagrasses is relatively under-studied, and reported rates range widely from 45 to 190 g C m-2 yr-1. Additionally, most of these seagrass rates are biased toward tropical and subtropical species, particularly Posidonia oceanica, with few focused on Zostera marina, the most widespread species in the northern hemisphere. We measured sediment organic content, carbon content, and long-term accretion rates to estimate organic carbon stocks and sequestration rates for a Z. marina meadow in Padilla Bay, a National Estuarine Research Reserve in Washington. We found rates of carbon sequestration to be quite low relative to commonly reported values, averaging 9 to 11 g C m-2 yr-1. We attribute this to both low sediment organic content and low rates of accretion. We postulate here that Padilla Bay\u27s low carbon sequestration capacity may be representative of healthy Z. marinameadows rather than an anomaly, and that Z. marina meadows have an inherently low carbon sequestration capacity because of the species\u27 low tolerance for suspended sediment (which limits light availability) and sediment organic content (which leads to toxic sulfide levels). Further research should focus on measuring carbon sequestration rates from other Z. marina meadows, particularly from sites that exhibit, a priori, the potential for higher rates of carbon sequestration
The Use of Secondarily Treated Wastewater Effluent for Forested Wetland Restoration in a Subsiding Coastal Zone.
No full textInsufficient sedimentation, coupled with high rates of relative sea-level rise (RSLR), are two important factors contributing to wetland loss in coastal Louisiana. I hypothesized that adding nutrient rich, secondarily treated, wastewater effluent to subsiding coastal wetlands in Louisiana could promote vertical accretion in these systems through increased organic matter production and subsequent deposition, and allow accretion to keep pace with estimated rates of RSLR (subsidence plus eustatic sea-level rise). To test this hypothesis, I measured processes affecting wetland elevation including, organic matter decomposition, sediment accretion, aboveground primary production, and, plant tissue nutrient (N, P, K, Ca, Mg, Fe) concentrations, in a coastal forested wetland receiving wastewater effluent, and in an adjacent control site, both before and after effluent applications began. A Before-After-Control-Impact statistical analysis revealed that neither aboveground tree production nor annual rates of decomposition were affected by wastewater effluent. However, because of increased floating aquatic vegetation production in the treatment site, rates of sediment accretion increased significantly after wastewater applications began (from 7.8 to 11.4 mm/yr), and approached the estimated rate of RSLR (12.0 mm/yr). No corresponding increase was observed in the control site. In general, N, P and K green leaf concentrations increased in the treatment site, with respect to the control, after effluent applications began. A wetland elevation ecosystem model, that incorporated elevation feedback mechanisms and simulated above and belowground primary production, sediment dynamics (decomposition, compaction and accretion) and mineral inputs over decades, was developed to examine the long term response of wetlands to increasing rates of RSLR, and to predict the effect of effluent additions on elevation. Model-generated sediment height was balanced with eustatic sea-level rise and deep subsidence, both forcing functions, to determine wetland elevation relative to sea-level. Data gathered as part of the field study were used for calibration and validation. Simulations revealed that wetland elevation was more sensitive to the uncertainty surrounding estimates of eustatic sea-level rise and deep subsidence than in possible effluent-related changes in autogenic processes, such as decomposition and primary production
Eelgrass (Zostera marina) meadows provide many ecosystem goods and services but high rates of carbon sequestration may not be one of them
No full textCoastal wetlands are known to be efficient carbon sinks due to carbon burial by mineral sediments, high rates of primary productivity, and low rates of decomposition. Of the three coastal wetland types: tidal marshes, tidal forests, and seagrass meadows, carbon burial by seagrasses is relatively under-studied, with reported rates ranging widely from 45 to 190 g C m-2 yr-1. Additionally, most of these seagrass data are from the species Posidonia oceanica and not from Zostera marina, the species common to the Pacific Northwest. In this study, we measured sediment organic matter and long-term accretion rates to estimate carbon stocks and sequestration rates for a Z. marina meadow in Padilla Bay, a U.S. National Estuarine Research Reserve in the Salish Sea. We found rates of carbon sequestration to be quite low, averaging 20 g C m-2 yr-1, due to both low sediment organic content and low rates of accretion. We postulate here that Padilla Bay’s low carbon sequestration capacity may be representative of most Z. marina meadows rather than an outlier, and that Z. marina meadows have an inherently low carbon sequestration capacity due to the species’ low tolerance for suspended sediment (which limits light availability) and sediment organic content (which leads to toxic sulfide levels). We note here that we are reporting only on the rates of carbon sequestration and not the standing stock, which can still be quite high despite low rates of sequestration. As a next step, research should focus on measuring carbon sequestration rates from other Z. marina meadows, particularly from sites that exhibit, a-priory, a potential for higher rates of carbon sequestration (i.e., existing beds in active depositional zones, if such a thing exists)
Numerical models of salt marsch evolution: Ecological, geomorphic, and climatic factors
No full textSalt marshes are delicate landforms at the boundary between the sea and land. These ecosystems support a diverse biota that modifies the erosive characteristics of the substrate and mediates sediment transport processes. Here we present a broad overview of recent numerical models that quantify the formation and evolution of salt marshes under different physical and ecological drivers. In particular, we focus on the coupling between geomorphological and ecological processes and on how these feedbacks are included in predictive models of landform evolution. We describe in detail models that simulate fluxes of water, organic matter, and sediments in salt marshes. The interplay between biological and morphological processes often produces a distinct scarp between salt marshes and tidal flats. Numerical models can capture the dynamics of this boundary and the progradation or regression of the marsh in time. Tidal channels are also key features of the marsh landscape, flooding and draining the marsh platform and providing a source of sediments and nutrients to the marsh ecosystem. In recent years, several numerical models have been developed to describe the morphogenesis and long-term dynamics of salt marsh channels. Finally, salt marshes are highly sensitive to the effects of long-term climatic change. We therefore discuss in detail how numerical models have been used to determine salt marsh survival under different scenarios of sea level rise.
Global Change Impacts on the Future of Coastal Systems: Perverse Interactions Among Climate Change, Ecosystem Degradation, Energy Scarcity, and Population
No full textLevee and dike breaching as a restoration tool in coastal wetlands for long-term resiliency to sea level rise
No full textAs sea levels rise, a “resilient” coastal wetland can respond in two ways; it can migrate upslope to escape rising water levels (the horizontal solution) or it can trap and accrete sediments to keep pace with the rate of sea level rise (the vertical solution). The two solutions are not necessarily mutually exclusive. The current practice of removing or breaching dikes and levees to restore historic coastal wetlands allows for both solutions; creating a pathway for landward escape and providing for the reintroduction of sediment laden waters, be they tidal, riverine or both, to the restored wetlands. Over the past two decades, using marker horizons, surface elevation tables and Pb210 dating, we’ve measured rates of accretion and elevation change in numerous coastal wetlands of the Salish Sea. From this, we present here two lines of evidence that point towards the potential and efficacy of dike removal as a restoration tool in the face of rising seas. First, in relatively unmodified, un-leveed natural coastal wetlands, open to the subsidizing energies of tides and sediment-rich river water, we consistently measure rates of sediment accretion equal to or in excess of the current rate of local sea level rise, indicating an adequate sediment supply for marsh maintenance. Second, our measurements in coastal wetland sites restored by levee breaching reveal high rates of accretion and elevation gain, far exceeding current and predicted rates of sea level rise. For example, in a recent restoration site in the Stillaguamish River estuary, we measured a mean rate of elevation gain of +3.1 cm yr-1 since levee removal in 2012. In summary, the many active deltaic distributaries of the Salish Sea provide a source of sediments that coastal wetlands, unencumbered by levees and dikes, can and do use to maintain a dynamic equilibrium with sea level rise
Assessing Padilla Bay’s response to sea level rise with a hybrid ecogeomorphic model
No full textEstuaries worldwide are facing the possibility of conversion to open water if accretion cannot keep pace with increasing rates of eustatic sea level rise (ESLR). Recent research into sediment elevation dynamics in Padilla Bay, a National Estuarine Research Reserve in Puget Sound, has revealed a mean bay-wide elevation deficit of -0.39 cm/year since 2002. However, a more mechanistic prediction of the estuary’s response to future ESLR should also incorporate non-linear feedback mechanisms between water depth, plant biomass, and sediment deposition. Therefore, we used the field data collected as part of this research (measurements of sediment accretion rates, suspended sediment concentrations, eelgrass stem density, and above- and belowground eelgrass biomass) to build and calibrate a marsh equilibrium model (MEM), developed elsewhere but applied here for the first time to this eelgrass-dominated intertidal habitat. We then coupled the MEM with a relative elevation model (REM) which has previously been applied here, to create a hybrid model that combines each model’s strengths in mechanistically simulating above- and belowground processes, respectively. The model predicts elevation change under various ESLR and suspended sediment scenarios. We used an 11-year elevation change dataset obtained from an extensive surface elevation table (SET) network in Padilla Bay for model validation. Here we present preliminary results suggesting sediment accretion rates to be primarily determined by stem density instead of plant biomass or water depth. Because the non-native eelgrass, Zostera japonica, grows in higher densities than the native Z. marina, Z. japonica may provide a disproportionate contribution toward maintaining elevation in the face of sea level rise in this sediment-starved estuary
An economic analysis of using wetlands for treatment of shrimp processing wastewater — a case study in Dulac, LA
No full textBlue Carbon and Climate Mitigation Capacity of Central Salish Sea Eelgrass Meadows
No full textBLUE CARBON IN CENTRAL SALISH SEA EELGRASS MEADOWS
AUTHORS: Mira Lutz* (Western Washington University Masters Candidate, [email protected]), John Rybczyk ([email protected]), Katrina Poppe ([email protected]) Chelsea Johnson (Western Washington University Undergraduate Intern, [email protected] ), Mason Lanphier (Western Washington University Undergraduate Intern, [email protected] ), Meriel Kaminsky (Western Washington University Undergraduate Intern, [email protected])
ABSTRACT: Seagrass meadows provide more than habitat, biodiversity support, storm surge and wave abatement, and water quality improvement; they help mitigate climate change by taking up and storing (sequestering) carbon (C), reportedly at rates only surpassed worldwide by salt marsh and mangrove ecosystems. Global average sediment C stock and sequestration rate values are currently being used in allotting carbon finance funding to restoration projects. However, little data exists for eelgrass meadows in the Pacific Northwest. The intent of our study is to quantify carbon stocks and sequestration rates over three bays in the central Salish Sea. Preliminary results from our study show lower estimated Corg concentration (mean=0.42%, range=0.098%-5.28%), Corg stock (mean=24.69 Mg ha-1, range=13.80-56.70), and C sequestration rates (means=82.17, 26.42, and 22.00 g m-2 yr-1 in Samish, Padilla, and Skagit Bays, respectively, based on preliminary analysis of 210Pb activity levels) than those reported in published studies from most other locations. These data have implications for carbon finance policy that determines the amount of eelgrass meadow area required for restoration to offset a given amount of emissions from parties releasing greenhouse gases or disturbing eelgrass habitat.
KEYWORDS: Eelgrass, blue carbon, C-sequestration
FORMAT: Poste
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