The Use of Secondarily Treated Wastewater Effluent for Forested Wetland Restoration in a Subsiding Coastal Zone.

Insufficient 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

Carbon Sequestration in a Pacific Northwest Eelgrass (Zostera marina) Meadow

Coastal 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

Hurricane Mitch: Impacts on Mangrove Sediment Elevation Dynamics and Long-term Mangrove Sustainability

Hurricane Mitch left three very different impacts on mangroves in the coastal zone of Central America. First, in the Caribbean, direct wind and flood-induced mangrove mortality was seen in the Bay Islands. Second, wave-induced erosion of beaches and subsequent sediment deposition buried mangrove forests of Punta de Manabique, Guatemala. Finally, along the Pacific coast, some mangroves of the Gulf of Fonseca were buried under up to 100 cm of sediments eroded from uplands and carried down slope by river flooding. Each of these three impacts left a different footprint on the mangrove communities, and these communities are expected to follow different recovery trajectories. These time-dependent responses will lead to different rates of success at reaching prehurricane conditions and imply differences in mangrove forest sustainability in face of a constantly changing environment. Rising sea level, for example, might make Caribbean mangroves more susceptible to hurricane-induced elevation deficits

Variable marsh resilience to stress offers clues to climate change adaptive management

In Puget Sound’s Stillaguamish estuary, tidal marshes exhibit evidence of multiple stressors that affect their vulnerability and provide insight into adaptive management opportunities to enhance their resilience. Despite high accretion rates, some marsh areas have receded by 10m/yr since 1964. Sources of stress include overgrazing by snow geese, high soil salinities, insect attacks, and changes in flow and inundation patterns. These interact with winter vegetation structure, sediment composition, and wave exposure to result in spatially variable marsh resilience. Some marshes are receding quickly, some slowly, and others are minimally affected. In the context of climate change, with potentially substantial near-term salinity changes due to summer low flow projections, and likely changes in sediment dynamics, it is critical to identify how marshes will respond, and develop adaptive management actions to increase resilience. Geese consume the rhizomes of four dominant bulrushes, and loosen the soil during winter storm season. Each bulrush species has different winter structural characteristics that affect grazing vulnerability, and the ability to trap sediment and attenuate erosive wave energy. Coarser sediments affect grazing intensity, being more difficult for geese bills to probe. Sediment and soil salinity affect plant density and height. During summer 2015, a harbinger for coming decades, twice-normal soil salinities resulted in stunted marsh that failed to flower. Finally, small differences in winter wave exposure affect marsh susceptibility to erosion after heavy grazing. With spatially variable marsh resilience to stress, potential adaptive management responses should similarly vary. Responses could include, among others, restoration to improve freshwater connectivity, sediment addition in restored areas to shift them above erosion thresholds or to target grazing-resistant bulrush species, snow goose population management or behavior modification, manipulation of soil particle size with sediment addition, and strategic use of logjams and sediment addition to reduce wave energy

Three birds with one stone: Tidal wetland restoration, carbon sequestration, and enhancing resilience to rising sea levels in the Snohomish River Estuary, Washington

Recent attention has focused on exploring the carbon storage and sequestration values of tidal wetlands to mitigate greenhouse gas emissions. Efforts are now underway to develop the tools and refine the science needed to bring carbon markets to bear on tidal wetland restoration activities. Effective restoration not only maximizes carbon storage in former tidal wetlands but also, through the accumulation of organic and mineral matter, enhances these systems’ resilience to rising sea levels. To this end, this project focuses on the Snohomish River estuary of the Puget Sound, Washington, which offers a continuum of diked and un-diked wetlands including seasonal floodplains, open mudflats, mature and tidal forests, and salt marsh habitats. In addition, there is strong restoration potential in a suite of ongoing and proposed projects. We report here on the carbon storage pools, long-term sediment accretion rates (100 years), and estimated rates of carbon storage, derived from sediment cores collected at representative sites within the Snohomish estuary during the spring and summer of 2013. We found that natural wetlands (open to tidal exchange and riverine inputs) were accreting at rates that equaled or exceeded current rates of eustatic sea level rise, while formerly, or currently diked wetlands (closed to such exchanges and inputs) revealed marked evidence of subsidence. Restored sites showed evidence of both high rates of sediment accretion (1.61 cm/year) and carbon storage (352 g C/m2/year)

Mangrove Peat Collapse Following Mass Tree Mortality: Implications for Forest Recovery from Hurricane Mitch

1 We measured sediment elevation and accretion dynamics in mangrove forests on the islands of Guanaja and Roatan, Honduras, impacted by Hurricane Mitch in 1998 to determine if collapse of underlying peat was occurring as a result of mass tree mortality. Little is known about the balance between production and decomposition of soil organic matter in the maintenance of sediment elevation of mangrove forests with biogenic soils. 2 Sediment elevation change measured with the rod surface elevation table from 18 months to 33 months after the storm differed significantly among low, medium and high wind impact sites. Mangrove forests suffering minimal to partial mortality gained elevation at a rate (5 mm year−1) greater than vertical accretion (2 mm year−1) measured from artificial soil marker horizons, suggesting that root production contributed to sediment elevation. Basin forests that suffered mass tree mortality experienced peat collapse of about 11 mm year−1 as a result of decomposition of dead root material and sediment compaction. Low soil shear strength and lack of root growth accompanied elevation decreases. 3 Model simulations using the Relative Elevation Model indicate that peat collapse in the high impact basin mangrove forest would be 37 mm year−1 for the 2 years immediately after the storm, as root material decomposed. In the absence of renewed root growth, the model predicts that peat collapse will continue for at least 8 more years at a rate (7 mm year−1) similar to that measured (11 mm year−1). 4 Mass tree mortality caused rapid elevation loss. Few trees survived and recovery of the high impact forest will thus depend primarily on seedling recruitment. Because seedling establishment is controlled in large part by sediment elevation in relation to tide height, continued peat collapse could further impair recovery rates

Conserving Coastal Wetlands Despite Sea Level Rise

Coastal wetlands provide valuable services such as flood protection and fisheries production to a global population that is increasingly concentrated near the coast and dependent on its resources. Many of the world\u27s coastal wetlands suffered significant losses during this century, and the creation of new wetland areas is not keeping pace with recent losses. Some destruction of wetland areas can be expected as a consequence of the continual reworking of the coastal zone by dynamic geologic processes. Yet human activities also play a role, both directly by encroaching on coastal wetlands and indirectly by influencing the hydrologic and geologic processes in the coastal zone

Immunization with Cocktail of HIV-Derived Peptides in Montanide ISA-51 Is Immunogenic, but Causes Sterile Abscesses and Unacceptable Reactogenicity

BACKGROUND: A peptide vaccine was produced containing B and T cell epitopes from the V3 and C4 Envelope domains of 4 subtype B HIV-1 isolates (MN, RF, CanO, & Ev91). The peptide mixture was formulated as an emulsion in incomplete Freund's adjuvant (IFA). METHODS: Low-risk, healthy adult subjects were enrolled in a randomized, placebo-controlled dose-escalation study, and selected using criteria specifying that 50% in each study group would be HLA-B7+. Immunizations were scheduled at 0, 1, and 6 months using a total peptide dose of 1 or 4 mg. Adaptive immune responses in16 vaccine recipients and two placebo recipients after the 2nd immunization were evaluated using neutralization assays of sera, as well as ELISpot and ICS assays of cryopreserved PBMCs to assess CD4 and CD8 T-cell responses. In addition, (51)Cr release assays were performed on fresh PBMCs following 14-day stimulation with individual vaccine peptide antigens. RESULTS: 24 subjects were enrolled; 18 completed 2 injections. The study was prematurely terminated because 4 vaccinees developed prolonged pain and sterile abscess formation at the injection site-2 after dose 1, and 2 after dose 2. Two other subjects experienced severe systemic reactions consisting of headache, chills, nausea, and myalgia. Both reactions occurred after the second 4 mg dose. The immunogenicity assessments showed that 6/8 vaccinees at each dose level had detectable MN-specific neutralizing (NT) activity, and 2/7 HLA-B7+ vaccinees had classical CD8 CTL activity detected. However, using both ELISpot and ICS, 8/16 vaccinees (5/7 HLA-B7+) and 0/2 controls had detectable vaccine-specific CD8 T-cell responses. Subjects with moderate or severe systemic or local reactions tended to have more frequent T cell responses and higher antibody responses than those with mild or no reactions. CONCLUSIONS: The severity of local responses related to the formulation of these four peptides in IFA is clinically unacceptable for continued development. Both HIV-specific antibody and T cell responses were induced and the magnitude of response correlated with the severity of local and systemic reactions. If potent adjuvants are necessary for subunit vaccines to induce broad and durable immune responses, careful, incremental clinical evaluation is warranted to minimize the risk of adverse events. TRIAL REGISTRATION: ClinicalTrials.gov NCT00000886

Levee and dike breaching as a restoration tool in coastal wetlands for long-term resiliency to sea level rise

As 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

Eelgrass (Zostera marina) meadows provide many ecosystem goods and services but high rates of carbon sequestration may not be one of them

Coastal 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)