Enrique Reyes

Numerical models of salt marsh evolution: ecological, geomorphic, and climatic factors

Salt 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.

Understanding the Coastal Ecosystem-Based Management Approach in the Gulf of Mexico

ABSTRACT Yáñez-Arancibia, A.; Day, J.W., and Reyes, E., 2013. Understanding the coastal ecosystem-based management approach in the Gulf of Mexico. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 244–262, Coconut Creek (Florida), ISSN 0749–0208. The Gulf of Mexico (GOM) is a shared ecosystem in which problems and solutions are a common responsibility among governments, primarily the United States and Mexico. Concepts about management of coastal systems suggest that GOM ecosystem-based management approaches should be coupled with ecological risk assessment and that quantitative modeling is a valuable tool for ecosystem-based management, which results in sound sustainable management. Sustainable management requires the consideration of a number of processes and issues. These include definition of ecological regions, description of processes controlling primary productivity, wetland restoration and coastal fisheries, and an understanding that pulsing is a fundamental characteristic of coastal systems, that climate change must be taken into consideration in management, and that environmental sustainability and socioeconomic development are strongly related. Throughout the 6,134 km of coastline stretching from Florida to Quintana Roo, there are several major geographic regions that include the warm-temperate GOM, the tropical GOM, and the Caribbean coast connected to the GOM. Within each geographic region, discrete complex systems can be defined as geographic/hydrological subregions, characterized by the interactions of geology, geomorphology, oceanography, climate, freshwater input, biogeochemistry, coastal vegetation, wildlife, estuary-shelf interactions, and human factors. We conclude: (a) system functioning should serve as a basis for sustainable coastal management; and (b) to sustain environmental and socioeconomic conditions, the GOM must be maintained as a healthy, productive, and resilient ecosystem. The challenge for future coastal management in the GOM should be towards an integration of coastal management with large marine ecosystem management.

Assessment of Carbon Sequestration Potential in Coastal Wetlands

This paper describes model (Marsh Equilibrium Model) simulations of the unit area carbon sequestration potential of contemporary coastal wetlands before and following a projected 1 m rise in sea level over the next century. Unit rates ranged typically from 0.2 to 0.3 Mg C ha−1 year−1 depending primarily on the rate of sea-level rise, tidal amplitude, and the concentration of suspended sediment (TSS). Rising sea level will have a significant effect on the carbon sequestration of existing wetlands, and there is an optimum tide range and TSS that maximize sequestration. In general, the results show that carbon sequestration and inventories are greatest in mesotidal estuaries. Marshes with tidal amplitudes <50 cm and TSS < 20 mg l−1 are unlikely to survive a 1 m rise in sea level during the next century. The majority of the United States coastline is dominated by tidal amplitude less than 1 m. The areal extent of coastal wetlands will decrease following a 1 m rise in sea level if existing wetland surfaces <1 m fail to maintain elevation relative to mean sea level, i.e. expansion by transgression will be limited by topography. On the other hand, if the existing vegetated surfaces survive, coastal wetland area could expand by 71%, provided there are no anthropogenic barriers to migration. The model-derived contemporary rate of carbon sequestration for the conterminous United States was estimated to be 0.44 Tg C year−1, which is at the low end of earlier accounts. Following a 1 m rise in sea level, with 100% survival of existing wetland surfaces, rates of carbon sequestration rise to 0.58 and 0.73 Tg C year−1 at TSS = 20 and 80 mg l−1, respectively, or 32–66% higher than the contemporary rate. Globally, carbon sequestration by coastal wetlands accounts for probably less than 0.2% of the annual fossil fuel emission. Thus, coastal wetlands sequester a small fraction of global carbon fluxes, though they take on more significance over long time scales. The deposits of carbon in wetland soils are large. There have been large losses of coastal wetlands due to their conversion to other land uses, which creates opportunities for restoration that are locally significant.

In situ measurements of wind-driven salt fluxes through constructed channels in a coastal wetland ecosystem

Department of Geological Sciences, East Carolina University, Graham 101, East 5th Street, Greenville, NC 27858, USA 2 Institute for Coastal Science and Policy, East Carolina University, Flanagan 387, East 5th Street, Greenville, NC 27858, USA Department of Biology, East Carolina University, N108 Howell Science Complex, East 5th Street, Greenville, NC 27858, USA 4 Institute for Coastal Science and Policy, East Carolina University, Howell S211, East 5th Street, Greenville, NC 27858, USA Correspondence Alex K. Manda, Department of Geological Sciences, East Carolina University, Graham 101, East 5th Street, Greenville, NC 27858, USA. Email: mandaa@ecu.edu Funding information East Carolina University Intramural Award

Modeling Management Options for Controlling the Invasive Zebra Mussel in a Mediterranean Reservoir

Abstract The zebra mussel, Dreissena polymorpha , is among the most invasive organisms worldwide, with well-documented economic and ecological impacts. In Spain, it was first detected in the Riba-roja Reservoir (Ebro River) in the summer of 2001. Although it has been suggested that mussel density determines its invasiveness and impact, there are few studies on what factors are responsible for population dynamics (i.e., variations over space and time). The model used here was able to reproduce all population dynamics previously described in the literature; therefore, it was used to predict future mussel population trends within the Riba-roja Reservoir and test the usefulness of water-level fluctuations as a mussel management tool. Carrying capacity was based on total phosphorus concentration and was found to control peak density. Consequently, if the decrease in phosphorus observed in the basin remains at its present level, an increase in mussel density is not expected. A decrease in the water level (simulated through an increment in mortality rates) had a significant effect on mussel dynamics. Population response was related to mussel density, age-class composition, and its reproductive cycle. Population response capability was reduced outside of the spawning season and effects were higher when two water releases were combined, one before the spawning season and a second after the next spawning season. Model predictions at a local scale may be helpful in developing adequate control plans by both predicting future species trends and forecasting management effects.