Julia A. Cherry

Elevated CO2 stimulates marsh elevation gain, counterbalancing sea-level rise

Tidal wetlands experiencing increased rates of sea-level rise (SLR) must increase rates of soil elevation gain to avoid permanent conversion to open water. The maximal rate of SLR that these ecosystems can tolerate depends partly on mineral sediment deposition, but the accumulation of organic matter is equally important for many wetlands. Plant productivity drives organic matter dynamics and is sensitive to global change factors, such as rising atmospheric CO2 concentration. It remains unknown how global change will influence organic mechanisms that determine future tidal wetland viability. Here, we present experimental evidence that plant response to elevated atmospheric [CO2] stimulates biogenic mechanisms of elevation gain in a brackish marsh. Elevated CO2 (ambient + 340 ppm) accelerated soil elevation gain by 3.9 mm yr−1 in this 2-year field study, an effect mediated by stimulation of below-ground plant productivity. Further, a companion greenhouse experiment revealed that the CO2 effect was enhanced under salinity and flooding conditions likely to accompany future SLR. Our results indicate that by stimulating biogenic contributions to marsh elevation, increases in the greenhouse gas, CO2, may paradoxically aid some coastal wetlands in counterbalancing rising seas.

Hurricane Katrina sediment slowed elevation loss in subsiding brackish marshes of the Mississippi River delta

Although hurricanes can damage or destroy coastal wetlands, they may play a beneficial role in reinvigorating marshes by delivering sediments that raise soil elevations and stimulate organic matter production. Hurricane Katrina altered elevation dynamics of two subsiding brackish marshes in the Mississippi River deltaic plain by adding 3 to 8 cm of sediment to the soil surface in August 2005. Soil elevations at both sites subsequently declined due to continued subsidence, but net elevation gain was still positive at both Pearl River (+1.7 cm) and Big Branch (+0.7 cm) marshes two years after the hurricane. At Big Branch where storm sediments had higher organic matter and water contents, post-storm elevation loss was more rapid due to initial compaction of the storm layer in combination with root-zone collapse. In contrast, elevation loss was slower at Pearl River where the storm deposit (high sand content) did not compact and the root zone did not collapse. Vegetation at both sites fully recovered within one year, and accumulation of root matter at Big Branch increased 10-fold from 2005 to 2006, suggesting that the hurricane stimulated belowground productivity. Results of this study imply that hurricane sediment may benefit subsiding marshes by slowing elevation loss. However, long-term effects of hurricane sediment on elevation dynamics will depend not only on the amount of sediment deposited, but on sediment texture and resistance to compaction as well as on changes in organic matter accumulation in the years following the hurricane.

FLORAL AND FAUNAL DIFFERENCES BETWEEN FRAGMENTED AND UNFRAGMENTED BAHAMIAN TIDAL CREEKS

We characterized biota in two unfragmented and two fragmented mangrove-lined tidal creeks on Andros Island, Bahamas, in May 2003, to examine particular effects of tidal creek fragmentation by road blockage. Total number of plant and fish species was significantly different between fragmented and unfragmented creeks, and species composition was significantly different both between unfragmented and fragmented creeks, and between downstream and upstream areas within fragmented creeks. More reef-associated, economically important and ecologically critical plant, macroinvertebrate, and fish species were observed in unfragmented tidal creeks, while fragmented creeks contained: 1) plant species typical of higher elevation estuarine habitat, 2) terrestrial and aquatic macroinvertebrate species typical of upland habitats, 3) macroinvertebrate species adapted to low flow, and 4) temperature- and salinetolerant macroinvertebrate and fish species. Furthermore, fragmented tidal creeks had different size distributions of common organisms, e.g., smaller sizes of two economically important fish species (Lutjanidae). This study suggests that fragmentation of tidal creeks and the subsequent loss of hydrologic connectivity influences the diversity and composition of aquatic flora and fauna, and may considerably inhibit nursery function and other ecosystem services provided by these coastal systems. These data also provide a baseline with which community- and ecosystem-level responses to restoration of hydrologic connectivity in fragmented tidal creeks will be assessed.

Understanding the Potential Impacts of Global Climate Change on Marsh Birds in the Gulf of Mexico Region

Global climate change is expected to significantly affect coastal ecosystems worldwide. For tidal marsh birds of the Gulf of Mexico, the extent of these impacts on future population dynamics is unknown. Here, we present information on our current understanding of marsh bird responses to climate change, identify gaps in that understanding, and propose ways of improving our ability to predict impacts on avian populations. Our understanding of how Gulf Coast avian populations will respond to environmental drivers such as sea-level rise, precipitation patterns, and hurricanes is limited, and detailed local and regional studies linking avian biology to wetland processes are needed. Impacts of wetland change on marsh bird species will be optimally assessed and forecasted within an adaptive framework, making use of process-driven studies that include models designed to elucidate patterns in avian biology and wetland dynamics. Further, because management and conservation efforts are implemented at local or site-specific scales, we recommend that process-driven studies incorporate hierarchical structures, nesting local efforts within a regional context. Implementing this research program will prove fundamental in furthering our understanding of avian population dynamics within the changing Gulf of Mexico environment.

Ecosystem – What? Public Understanding and Trust in Conservation Science and Ecosystem Services

In this mixed-methods study, we replicate a national Nature Conservancy survey on a regional scale to understand what local audiences know and believe about ecosystem services and conservation science. After the Deepwater Horizon oil spill in 2010, the Gulf Coast Ecosystem Restoration Council was created and charged with administering a large portion of the

Assessing coastal wetland vulnerability to sea-level rise along the northern Gulf of Mexico coast: Gaps and opportunities for developing a coordinated regional sampling network

13.7 billion in penalties (via the Gulf Coast Restoration Fund) for ecosystem restoration research and implementation programs. Almost as quickly as oil gushed into the Gulf, conservation organizations (local, state, federal and NGO) along the coast drafted proposals and requests for a piece of the funding. In December 2014, the State of Alabama submitted five proposed restoration projects with an estimated total cost of

The dynamic nature of land-water interfaces: changes in structure and productivity along a water depth gradient in the Talladega Wetland Ecosystem

54.2 million. Many of the projects use the language of ecosystem science, restoration and services to promote efforts to restore the ecosystem and economy of the Gulf Coast region. These phrases, once disciplinary jargon, are now heard in soundbites on the evening news and seen in the headlines of popular news sources (e.g. AL.com, Gulf Coast News Today, WKRG-Mobile and WPMI-Mobile). As this phraseology becomes more pervasive in this region, our specific goal is to investigate what the public knows and believes about one of the key concepts, ecosystem services, and identify who they trust to inform them about ecosystem services. This study confirms previous evidence that the public trusts scientists, but they do not always understand the language of science.

Elevated CO2 enhances biological contributions to elevation change in coastal wetlands by offsetting stressors associated with sea-level rise.

Coastal wetland responses to sea-level rise are greatly influenced by biogeomorphic processes that affect wetland surface elevation. Small changes in elevation relative to sea level can lead to comparatively large changes in ecosystem structure, function, and stability. The surface elevation table-marker horizon (SET-MH) approach is being used globally to quantify the relative contributions of processes affecting wetland elevation change. Historically, SET-MH measurements have been obtained at local scales to address site-specific research questions. However, in the face of accelerated sea-level rise, there is an increasing need for elevation change network data that can be incorporated into regional ecological models and vulnerability assessments. In particular, there is a need for long-term, high-temporal resolution data that are strategically distributed across ecologically-relevant abiotic gradients. Here, we quantify the distribution of SET-MH stations along the northern Gulf of Mexico coast (USA) across political boundaries (states), wetland habitats, and ecologically-relevant abiotic gradients (i.e., gradients in temperature, precipitation, elevation, and relative sea-level rise). Our analyses identify areas with high SET-MH station densities as well as areas with notable gaps. Salt marshes, intermediate elevations, and colder areas with high rainfall have a high number of stations, while salt flat ecosystems, certain elevation zones, the mangrove-marsh ecotone, and hypersaline coastal areas with low rainfall have fewer stations. Due to rapid rates of wetland loss and relative sea-level rise, the state of Louisiana has the most extensive SET-MH station network in the region, and we provide several recent examples where data from Louisiana’s network have been used to assess and compare wetland vulnerability to sea-level rise. Our findings represent the first attempt to examine spatial gaps in SET-MH coverage across abiotic gradients. Our analyses can be used to transform a broadly disseminated and unplanned collection of SET-MH stations into a coordinated and strategic regional network. This regional network would provide data for predicting and preparing for the responses of coastal wetlands to accelerated sea-level rise and other aspects of global change.

Temporary floating island formation maintains wetland plant species richness: The role of the seed bank

Hydrologic factors sueh as water depth, hydroperiod, and residenee time largely deterrnine the strueture and funetion of wetlands by modifying physieoehemistry and influeneing speeies eomposition and riehness (MrrscH & GossELINK 2007). Generally, produetivity is depressed by stagnant, flooded eonditions but enhaneed by flow and pulsing hydroperiods. When wetlands are impounded, flooding leads to anaerobiosis, low soil redox potential, redueed nutrient availability, deereased species riehness, and eonsequently, redueed primary produetion (MrrscH et al. 1991 ). Conversely, flood pulsing eontributes to higher primary produetivity by providing adequate water, subsidizing nutrients, oxygenating the rhizosphere, and flushing waste produets (JUNK et al. 1989). Variation in water depth ereates a diversity o f mierohabitats for plants that support different mierobial and invertebrate eommunities. Wetlands, and in partieular beaver impounded wetlands, are not permanent features ofthe landseape. Extent and volume of these wetland habitats vary as a funetion o f hydrologie change as beavers maintained impoundrnents are created and lost. During 15 years of study at the Talladega Wetland Eeosystem, pond habitats were ereated by new impoundrnents and lost when beavers failed to maintain or repair breaehed dams at existing ponds. Seeondary sueeession following a dam breaeh in a 50+ year-old pond provided an interesting seientifie perspeetive on habitat permanenee and the dynarnism ofwetland landseapes. We deseribe differenees in the strueture and funetion of different zones of a beaver-impounded wetland in the southeastem United States as a site for understanding how wetlands respond following the loss of a beaver dam.