Denise J. Reed

Coastal Ecosystem-Based Management with Nonlinear Ecological Functions and Values

A common assumption is that ecosystem services respond linearly to changes in habitat size. This assumption leads frequently to an “all or none” choice of either preserving coastal habitats or converting them to human use. However, our survey of wave attenuation data from field studies of mangroves, salt marshes, seagrass beds, nearshore coral reefs, and sand dunes reveals that these relationships are rarely linear. By incorporating nonlinear wave attenuation in estimating coastal protection values of mangroves in Thailand, we show that the optimal land use option may instead be the integration of development and conservation consistent with ecosystem-based management goals. This result suggests that reconciling competing demands on coastal habitats should not always result in stark preservation-versus-conversion choices.

Climate Change Impacts on U.S. Coastal and Marine Ecosystems

Increases in concentrations of greenhouse gases projected for the 21st century are expected to lead to increased mean global air and ocean temperatures. The National Assessment of Potential Consequences of Climate Variability and Change (NAST 2001) was based on a series of regional and sector assessments. This paper is a summary of the coastal and marine resources sector review of potential impacts on shorelines, estuaries, coastal wetlands, coral reefs, and ocean margin ecosystems. The assessment considered the impacts of several key drivers of climate change: sea level change; alterations in precipitation patterns and subsequent delivery of freshwater, nutrients, and sediment; increased ocean temperature; alterations in circulation patterns; changes in frequency and intensity of coastal storms; and increased levels of atmospheric CO2. Increasing rates of sea-level rise and intensity and frequency of coastal storms and hurricanes over the next decades will increase threats to shorelines, wetlands, and coastal development. Estuarine productivity will change in response to alteration in the timing and amount of freshwater, nutrients, and sediment delivery. Higher water temperatures and changes in freshwater delivery will alter estuarine stratification, residence time, and eutrophication. Increased ocean temperatures are expected to increase coral bleaching and higher CO2 levels may reduce coral calcification, making it more difficult for corals to recover from other disturbances, and inhibiting poleward shifts. Ocean warming is expected to cause poleward shifts in the ranges of many other organisms, including commercial species, and these shifts may have secondary effects on their predators and prey. Although these potential impacts of climate change and variability will vary from system to system, it is important to recognize that they will be superimposed upon, and in many cases intensify, other ecosystem stresses (pollution, harvesting, habitat destruction, invasive species, land and resource use, extreme natural events), which may lead to more significant consequences.

Restoration of the Mississippi Delta: Lessons from Hurricanes Katrina and Rita

Hurricanes Katrina and Rita showed the vulnerability of coastal communities and how human activities that caused deterioration of the Mississippi Deltaic Plain (MDP) exacerbated this vulnerability. The MDP formed by dynamic interactions between river and coast at various temporal and spatial scales, and human activity has reduced these interactions at all scales. Restoration efforts aim to re-establish this dynamic interaction, with emphasis on reconnecting the river to the deltaic plain. Science must guide MDP restoration, which will provide insights into delta restoration elsewhere and generally into coasts facing climate change in times of resource scarcity.

Non‐linearity in ecosystem services: temporal and spatial variability in coastal protection

Natural processes tend to vary over time and space, as well as between species. The ecosystem services these natural processes provide are therefore also highly variable. It is often assumed that ecosystem services are provided linearly (unvaryingly, at a steady rate), but natural processes are characterized by thresholds and limiting functions. In this paper, we describe the variability observed in wave attenuation provided by marshes, mangroves, seagrasses, and coral reefs and therefore also in coastal protection. We calculate the economic consequences of assuming coastal protection to be linear. We suggest that, in order to refine ecosystem-based management practices, it is essential that natural variability and cumulative effects be considered in the valuation of ecosystem services.

Pattern and Process of Land Loss in the Mississippi Delta: A Spatial and Temporal Analysis of Wetland Habitat Change

An earlier investigation (Turner 1997) concluded that most of the coastal wetland loss in Louisiana was caused by the effects of canal dredging, that loss was near zero in the absence of canals, and that land loss had decreased to near zero by the late 1990s. This analysis was based on a 15-min quadrangle (approximately 68,000 ha) scale that is too large to isolate processes responsible for small-scale wetland loss and too small to capture those responsible for large-scale loss. We conducted a further evaluation of the relationship between direct loss due to canal dredging and all other loss from 1933–1990 using a spatial scale of 4,100 ha that accurately captures local land-loss processes. Regressions of other wetland loss on canal area (i.e., direct loss) for the Birdfoot, Terrebonne, and Calcasieu basins were not significant. Positive relationships were found for the Breton (r2=0.675), Barataria (r2=0.47), and Mermentau (r2=0.35) basins, indicating that the extent of canals is significantly related to wetland loss in these basins. A significant negative relationship (r2=0.36) was found for the Atchafalaya coastal basin which had statistically lower loss rates than the other basins as a whole. The Atchafalaya area receives direct inflow of about one third of the Mississippi discharge. When the data were combined for all basins, 9.2% of the variation in other wetland loss was attributable to canals. All significant regressions intercepted the y-axis at positive loss values indicating that some loss occurred in the absence of canals. Wetland loss did not differ significantly from the coast inland or between marsh type. We agree with Turner that canals are an important agent in causing wetland loss in coastal Louisiana, but strongly disagree that they are responsible for the vast majority of this loss. We conclude that wetland loss in the Mississippi delta is an ongoing complex process involving several interacting factors and that efforts to create and restore Louisiana’s coastal wetlands must emphasize riverine inputs of freshwater and sediments.

Estimating shallow subsidence in microtidal salt marshes of the southeastern United States: Kaye and Barghoorn revisited

Abstract Simultaneous measurements of vertical accretion and change in surface elevation relative to a shallow (3–5 m) subsurface datum were made in selected coastal salt marshes of Louisiana, Florida, and North Carolina to quantitatively test Kaye and Barghoorns contention that vertical accretion is not a good surrogate for surface elevation change because of autocompaction of the substrate. Rates of subsidence of the upper 3–5 m of marsh substrate were calculated for each marsh as the difference between vertical accretion and elevation change measured with feldspar marker horizons and a sedimentation-erosion table. Surface elevation change was significantly lower than vertical accretion at each site after 2 years, indicating a significant amount of shallow subsidence had occurred, ranging from 0.45 to 4.90 cm. The highest rate of shallow subsidence occurred in the Mississippi delta. Results confirm Kaye and Barghoorns contention that vertical accretion is not generally a good surrogate for elevation change because of processes occurring in the upper few meters of the substrate, including not only compaction but also apparently shrink-swell from water storage and/or plant production-decomposition at some sites. Indeed, surface elevation change was completely decoupled from vertical accretion at the Florida site. The assumption of a 1:1 relationship between vertical accretion and surface elevation change is too simplistic a generalization of the complex interactions between accretionary and substrate processes. Consequently, the potential for coastal marsh submergence should be expressed as an elevation deficit based on direct measures of surface elevation change rather than accretion deficits. These findings also indicate the need for greater understanding of the influence of subsurface and small-scale hydrologic processes on marsh surface elevation.

Patterns of sediment deposition in subsiding coastal salt marshes, Terrebonne Bay, Louisiana: the role of winter storms

High rates of wetland loss in the Mississippi deltaic plain have been attributed to a combination of insufficient marsh sedimentation and relative sea-level rise rates of over 1.2 cm yr−1. This study examines contemporary patterns of sediment delivery to the marsh surface by evaluating the contribution of individual marsh flooding events. Strong meteorological effects on water level in Terrebonne Bay often mask the usual microtidal fluctuations in water level and cause flood events to be of unpredictable frequency and duration. Sediment deposited on the marsh surface was collected weekly at two sites. Preliminary results allow the relative contributions of tidal and storm inundations to be calculated. Maximum sedimentation is associated with strong southerly winds both causing increased flooding and mobilizing sediment from open bay areas. Sediment deposition is limited by the availability of suspended sediment and the opportunity for its transport onto the marsh surface.

Coastal Wetland Vulnerability to Relative Sea-Level Rise: Wetland Elevation Trends and Process Controls

The distribution of tidal saline wetlands (e.g., salt marshes and mangroves) is increasingly impacted by global environmental change, including human alteration of the world’s coasts and sea-level rise (Kennedy et al. 2002; Poff et al. 2002). Rates of salt marsh and mangrove loss appear to be accelerating (Nicholls et al. 1999).A better understanding of wetland accretionary dynamics, controls and constraints, and in particular responses to sea-level rise is required to inform the maintenance and restoration of these systems. Differences in wetland form and function result from a range of continentaland regional-scale processes (Mitsch and Gosselink 2000). Local geomorphology, climate regime, and hydrology result in differences in sediment supply, primary production and decomposition, subsidence, and autocompaction, resulting in variations in elevation among both salt marsh and mangrove sites. Combinations of these controls mean that individual wetland sites show different degrees of vulnerability to current and near-future environmental change. Several vulnerability assessment approaches have been developed during the past two decades, including the Global Vulnerability Assessment, first developed by Hoozemans et al. (1993) and recently refined in DINAS_COAST (McFadden et al. 2003), and the Coastal Vulnerability Index (Gornitz 1991; Hammar-Klose and Thieler 2001). These approaches offer valuable planning tools for coastal resource managers at the broad (i.e., global, continental, macro-regional) scale as they allow the identification of both patterns of relative vulnerability and vulnerability ‘hotspots’. However, the numerical scores that they produce cannot be easily assigned a precise physical meaning and

Ecosystem Services as a Common Language for Coastal Ecosystem‐Based Management

Ecosystem-based management is logistically and politically challenging because ecosystems are inherently complex and management decisions affect a multitude of groups. Coastal ecosystems, which lie at the interface between marine and terrestrial ecosystems and provide an array of ecosystem services to different groups, aptly illustrate these challenges. Successful ecosystem-based management of coastal ecosystems requires incorporating scientific information and the knowledge and views of interested parties into the decision-making process. Estimating the provision of ecosystem services under alternative management schemes offers a systematic way to incorporate biogeophysical and socioeconomic information and the views of individuals and groups in the policy and management process. Employing ecosystem services as a common language to improve the process of ecosystem-based management presents both benefits and difficulties. Benefits include a transparent method for assessing trade-offs associated with management alternatives, a common set of facts and common currency on which to base negotiations, and improved communication among groups with competing interests or differing worldviews. Yet challenges to this approach remain, including predicting how human interventions will affect ecosystems, how such changes will affect the provision of ecosystem services, and how changes in service provision will affect the welfare of different groups in society. In a case study from Puget Sound, Washington, we illustrate the potential of applying ecosystem services as a common language for ecosystem-based management.

Sea-level rise and coastal marsh sustainability: geological and ecological factors in the Mississippi delta plain

Chronostratigraphic approaches to coastal geomorphology frequently include consideration of salt marsh deposits as indicators of past sea-level positions. Continuous horizons of such deposits can be used to infer that salt marshes were keeping pace with local rates of relative sea-level rise (RSLR). Rates of past accumulation, estimated using dating techniques, are then used to hindcast the rate of sea-level rise in that area. Estimates of contemporary sea-level rise rates are often derived from tide gauge records. This approach allows identification of subdecadal variations in mean water level. Accumulation rates of both organic and inorganic sediments can also be derived at these time scales and studies from many coastal marshes demonstrate the episodic nature of inorganic sediment deposition. The frequency and spacing of these events does not necessarily coincide with periods of increased local sea level. In addition, short-term increases in sea level could result in marsh deterioration as soils become excessively waterlogged. A conceptual model of changes in geomorphic and ecological processes contributing to marsh sustainability during the Holocene has been developed for the Mississippi delta plain (MDP). The survival of some marshes in this area, despite high rates of subsidence, indicates that the combined effect of organic and inorganic accumulation processes can be adequate to sustain coastal marshes in the face of sea-level rise.