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Coastal & Estuarine Science News (CESN)

Coastal & Estuarine Science News (CESN) is an electronic publication providing brief summaries of select articles from the journal Estuaries & Coasts that emphasize management applications of scientific findings. It is a free electronic newsletter delivered to subscribers on a bimonthly basis.

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2013 October


Culture Clash: Incorporating Cultural Modeling into Decision-Making in the Chesapeake Bay
Muddy Waters not Muddy Enough? Declining Sediments and Rising Seas Could Drown Some Tidal Wetlands
What is a Healthy Tampa Bay Worth? Millions per Year or More, Says One Study
How Much Chlorophyll a is too Much? Chesapeake Study Suggests Some Guidelines

Culture Clash: Incorporating Cultural Modeling into Decision-Making in the Chesapeake Bay

The Chesapeake Bay Modeling System (CBMS) is a massive network of numerical models that has been built and refined over the past three decades. Until recently, it was used by managers and policy-makers to guide voluntary efforts to reduce nutrient and sediment loadings into the bay, with the ultimate goal of reducing eutrophication and its accompanying ecological impacts. However, the model is now being used to set Total Maximum Daily Loads and to guide and evaluate the implementation of Watershed Implementation Plans at the state and county levels. These initiatives will not be voluntary. Consequently, stakeholders are now questioning the validity of the model, scrutinizing and criticizing the model and its projections more vocally than before. A recent legal challenge, including a proposal to use an alternate model developed by contractors to the Agriculture Nutrient Policy Council (an industry interest group), exemplifies the controversy over the model’s use and outcomes.

Social scientists, working with natural scientists, have examined the CBMS and the controversy surrounding its current applications. In a recent paper in Estuaries and Coasts, they suggest two social science approaches, research on cultural models and science and technology studies, that could help with model discussions. Cultural models study the complex interaction of stakeholder groups’ attitudes, beliefs, values, and modes of understanding, with the goal of improving understanding of conflicting cultural values, promoting collaboration and group learning. Science and technology studies seek to understand the social, historical, political, and cultural contexts of scientific research and knowledge. The authors advocate the use of these two approaches to facilitate stakeholder participation, to develop effective outreach campaigns, and ultimately to build understanding and support of the CBMS. They note that integration of social science into modeling and management efforts will be most effective if it is done as early as possible in the process.

Source: Paolisso, M., J. Trombley, R. R. Hood, and K. G. Sellner. 2013. Environmental models and public stakeholders in the Chesapeake Bay watershed. Estuaries and Coasts 36 (June 2013). DOI: 10.1007/s12237-013-9650-z.

 Muddy Waters not Muddy Enough? Declining Sediments and Rising Seas Could Drown Some Tidal Wetlands

Despite that fact that tidal wetlands enjoy state and federal protection from the indiscriminate filling and draining that took place decades ago, these critical ecosystems are not yet safe. One challenge to wetland preservation is inundation by sea level rise. If supplies of suspended sediments to marshes are not enough to keep up with sea level, the marshes will drown in place. Sediment delivery, particularly from the watershed, is a key factor in this balancing act. But is there enough sediment reaching the coast to sustain these habitats?

One recent study tackled this question on a large scale. In order to assess sediment delivery to tidal wetlands, the author of this study obtained more than 20 years of suspended sediment measurements from US Geological Survey stations in 61 watersheds on the East and Gulf Coasts. He examined these data, along with information on river discharge, land use, human population density, and the presence of dams and reservoirs to determine the risk of wetland inundation in each system. He found that suspended sediment concentrations have declined over time in 25 of the 61 watersheds studied, and increased in only 4. Of the parameters examined, including changes in agricultural land use, only the presence of dams and reservoirs was significantly correlated with this decrease. The author determined that marshes in the Mississippi and western Gulf of Mexico regions are increasingly vulnerable to wetland loss because of a combination of decreased sediment concentrations and high rates of sea level rise. Sea level rise along the mid-Atlantic coast makes that region vulnerable as well; Florida and the eastern Gulf are less vulnerable due to slight increases in sediment availability and lower rates of sea level rise.

The author points out that historical human influences on these ecosystems could, ironically, have actually created many of the wetlands that are now subject to inundation and loss. The large-scale deforestation of the eighteenth and nineteenth centuries, undertaken to create agricultural land, enhanced the delivery of sediments to some coastal areas. It may therefore be that future loss of these wetlands is largely unavoidable.

Source: Weston, N. B. 2013. Declining sediments and rising seas: An unfortunate convergence for tidal wetlands. Estuaries and Coasts 36 (July 2013). DOI: 10.1007/s12237-013-9654-8.

What is a Healthy Tampa Bay Worth? Millions per Year or More, Says One Study

Ecological restoration is an expensive undertaking, but it also amounts to preserving the goose that laid the golden egg: because humans get so much, economically speaking, from productive and healthy ecosystems, the return on this investment can make it worthwhile. Just how worthwhile has been a topic of interesting research at the intersection of ecology and economics in the past 15 years. A recent analysis of the economic value of the successful restoration projects in Tampa Bay estimated that habitats (marshes, seagrass beds, and mangrove forests) subject to restoration efforts generated “ecosystem goods” with benefits worth over $365 million in the time period 1990-2008. Ecosystem goods are tangible products of nature that are directly enjoyed, consumed, or used to yield human well-being, such as clean water and air.

The investigators estimated the economic benefits provided by the three habitat types via carbon sequestration and denitrification. Economic benefits were calculated in two ways: by estimating the replacement costs of achieving the same level of water quality if the habitats were not present (e.g., the cost of an engineering solution like upgrading a wastewater treatment facility), and by estimating the social cost of carbon, which is an estimate of the monetized damages associated with an incremental increase in carbon emissions for a given year. Using conservative values for ecosystem benefits, the combined value of C and N removal increased by about $3 million per year between 1990 and 2010. When restoration goals have been fully met, the annual cost savings realized by protecting and restoring these habitats is projected to be between $28 million and $3 billion per year.

The authors conclude that restoration in Tampa Bay has certainly been worth the money invested. This analysis could be expanded by inclusion of additional ecosystem benefits such as production of catchable fish and dampening of storm surges. In addition, future economic analyses could benefit from an examination of spatially-explicit demand for given ecosystem goods and services.

Source: Russell, M. and H. Greening. 2013. Estimating benefits in a recovering estuary: Tampa Bay, FL. Estuaries and Coasts 36 (August 2013). DOI: 10.1007/s12237-013-9662-8.

 How Much Chlorophyll a is too Much? Chesapeake Study Suggests Some Guidelines

Chlorophyll a is an excellent indicator of nutrient enrichment in coastal systems (especially those with long residence times relative to phytoplankton growth rates): it serves to integrate nutrient loadings, has broad implications for ecosystem function, and is relatively easy to measure. However, numerical criteria have seldom been developed, largely because chl a concentrations vary so much by estuary size, flushing rate, depth, local meteorology, and other factors. Probably the best candidate system for proposing numerical chl a criteria is Chesapeake Bay, where long-term data sets can contribute to criteria development. A team of investigators recently undertook just such an analysis, using the abundant Chesapeake Bay monitoring data to develop multiple lines of evidence to determine appropriate chl a limits.

First the investigators mined the immense historical monitoring database to determine baseline chl a levels for the 1960s (recognizing that the bay was not unimpaired at that time) for two seasons (spring and summer), three flow conditions, and three bay salinity zones. The means from this analysis were considered the “goal” for chl a and 90th percentile thresholds were suggested to represent “compliance limits.” This resulted in goals that ranged from 1.1 to 15 mg/m3 depending on salinity zone and season, with compliance limits from 3.3 to 53 mg/m3. The authors also examined statistical relationships between chl a and ecologically significant levels of dissolved oxygen, water clarity, and toxic algal blooms, and established similar suggested goals and compliance limits. The range of approaches resulted in reasonably consistent seasonal means for chlorophyll a criteria across salinity zones; goal values ranged from 1.4 to 15 mg/m3 and compliance limits ranged from 4.3 to 45 m/m3. The relatively good agreement among the sets of criteria developed independently suggests that this approach is robust and could be used in other similar systems.

Whether these goals can be attained is certainly an open question, especially because “shifting baselines” is likely to be an issue for the Chesapeake Bay, but the authors suggest that adherence to these chl a criteria will move the bay toward a less impaired condition.

Source: Harding, L. W. Jr., R. A. Batiuk, T. R. Fisher, C. L. Gallegos, T. C. Malone, W. D. Miller, M. R. Mulholland, H. W. Paerl, E. S. Perry, and P. Tango. 2013. Scientific bases for numerical chlorophyll criteria in Chesapeake Bay. Estuaries and Coasts 36 (June 2013). DOI: 10.1007/s12237-013-9656-6.