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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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March 2010


Modified Shorelines May Harbor Modified Faunal Communities, Study Finds
Building a Better Shellfish Harvest Closure Decision Tool: Don’t Just Blame It On the Rain
Organic Pollutants, and The Problems They Cause, Are Here to Stay: H. T. Odum Synthesis Essay
How Will Future Climate and Sediment Supply Change the Shape of an Estuary? Projected Geomorphology in Suisun Bay, CA

Modified Shorelines May Harbor Modified Faunal Communities, Study Finds

Shoreline armoring – seawalls, rip-rap, and other modifications – is often carried out in the supratidal zone above mean higher high water (MHHW). Although this zone serves as a bridge between marine and terrestrial ecosystems, providing critical habitat for species from both, its ecology has often been overlooked. A recent study of insect and benthic macroinvertebrate communities in modified shorelines in Puget Sound, WA includes examinations of the impacts of shoreline modifications on this under-studied ecotone.

Investigators conducted paired sampling at beaches where the shoreline modifications occurred below MHHW (thereby reducing the extent of the intertidal) and adjacent unmodified areas. The supratidal zone of the armored sites exhibited coarser sediments than controls, providing less suitable habitat for benthic infauna and insects. Results indicated that the armored beaches had fewer amphipods, springtails, and insects, and greater abundance of benthic crustaceans. The unmodified sites in this part of the study had significantly more marine wrack, which provides important habitat for invertebrates. In a second part of the study the investigators conducted synoptic sampling at 26 sites, 10 natural and 16 modified above MHHW. However, faunal comparisons at these sites showed little difference.

The authors conclude that the impacts of armoring are more apparent the closer the modification is to the intertidal zone, which suggests that armoring above MHHW may have fewer direct impacts on supratidal communities, although the impacts to other shoreline processes were not studied.

Source: Sobocinski, K. L., J. R. Cordell, and C. A. Simenstad. 2010. Effects of shoreline modifications on supratidal macroinvertebrate fauna on Puget Sound, Washington beaches. Estuaries and Coasts 33(February 2010). DOI: 10.1007/s12237-009-9262-9.

Building a Better Shellfish Harvest Closure Decision Tool: Don’t Just Blame It On the Rain

If there’s one thing shellfish harvesters dread, it’s a rainy day. In many places, conditional closures of shellfish harvest areas are enforced for multiple days following a specified amount of rainfall and presumed accompanying microbial pollution. However, the assumptions underlying these closures may be incorrect, resulting in a pointless loss of income for harvesters and others. Managers have long wished for a better method that accurately predicts the need for conditional closures while maintaining simplicity of use. A recent study in four South Carolina estuaries developed new predictive models that could be useful for managing shellfish bed closures.

Analyses of the relationships underlying existing closure guidelines, which rely mostly on rain gauge precipitation data, revealed that the present model used in South Carolina is rarely valid. More accurate models were constructed using area-averaged rainfall data derived from NEXRAD archives in conjunction with temperature and salinity data. The best of these improved models were what the investigators consider “mid-complexity models,” relatively simple yet robust in all of the estuaries examined, which varied in degree of urbanization and relative contamination levels. The models worked best in areas of greater urban influence.

While the rainfall data used in the most successful models are readily available, the required salinity and temperature data would need to be collected either by hand or using platform or buoy-based instrumentation. The authors advocate the installation of such remote instrumentation in shellfishing areas to facilitate the development and use of these more accurate models. This modeling approach for managing shellfish bed closures might have additional utility in regulating closures at bathing beaches.

Source: Kelsey, R. H., G. I. Scott, D. E. Porter, T. C. Siewicki, and D. G. Edwards. 2010. Improvements to shellfish harvest area closure decision making using GIS, remote sensing, and predictive models. Estuaries and Coasts 22(February 2010). DOI: 10.1007/s12237-010-9264-7.

Organic Pollutants, and The Problems They Cause, Are Here to Stay: H. T. Odum Synthesis Essay

Nutrient enrichment, loadings of climate-changing greenhouse gases, trash in the oceans: there is no doubt that humans have had massive impacts on the marine environment. Among the most serious is the enhanced anthropogenic loadings of thousands of organic pollutants, many in concentrations too low to be easily detected. A recent essay in Estuaries and Coasts reviews this serious problem, and suggests that organic pollutants in coastal waters, sediments, and biota can have multiple, and often unknown, effects on ecosystems.

The sources of these chemicals can be categorized as primary (directly related to the use of the chemicals) and secondary (via cycling that occurs once the substance has entered the environment, such as release of PCBs from sediment into the overlying water column). In many cases, secondary sources are more important, and certainly more problematic. Once introduced to the environment, these chemicals can persist for decades to centuries. The essay points out that because there are so many of these contaminants, studying them can be daunting. Most studies of their effects use single compounds and model organisms observed in laboratory settings. Translating results of such studies to population- or ecosystem-level impacts is nearly impossible. The authors suggest the development of more sophisticated tests that can evaluate the impacts of mixtures of chemicals, and lobby for considering the effect of real mixtures of chemicals on both populations and ecosystems.

The paper makes a convincing case that introduction of organic pollutants is an important ecosystem driver, which will be shaping the marine environment for the foreseeable future. More scientific innovation is needed to continue to evaluate the problem and inform management.

Source: Dachs, J. and L. Méjanelle. 2010. Organic pollutants in coastal waters, sediments, and biota: a relevant driver for ecosystems during the Anthropocene? Estuaries and Coasts (February 2010). DOI: 10.1007/s12237-009-9255-8.

How Will Future Climate and Sediment Supply Change the Shape of an Estuary? Projected Geomorphology in Suisun Bay, CA

Factors that influence geomorphology of estuaries include climate, which is changing everywhere, and sediment supply, which is changing in many estuaries, including Suisun Bay, CA (a subestuary of San Francisco Bay). Such changes could influence availability of intertidal habitat, sediment transport, and even water quality. For example, as sea level rises and sediment supply declines, intertidal habitats might have a hard time keeping their heads above water. A recent paper provides estimates of geomorphic changes in Suisun Bay under four different scenarios: 1) present day conditions, 2) with sea level rise and freshwater flow changes projected for the year 2030, 3) with sea level rise and decreased watershed sediment supply of 2030, and 4) with sea level rise, freshwater flow changes, and decreased watershed sediment supply of 2030. In all simulations, net sediment deposition did not keep pace with sea level rise in shallow parts of the bay. Sedimentation declined in deeper parts of the bay in all scenarios relative to the base case, so that increase in water depth was more pronounced here than in the shallows. Many of the modeling results indicated the complexity of the interactions being investigated. For example, a few isolated areas of the bay became more erosional in scenarios with minor changes in freshwater flow timing, due to changes in water level and depth-dependent wind-wave resuspension.

The investigators also developed a dimensionless parameter, an estuarine geomorphic number, representing a balance between deposition and erosion. This parameter allows for comparisons of the effects of processes favoring deposition and erosion over a decadal time scale, and could easily be applied to other estuaries.

Source: Ganju, N. K. and D. H. Schoellhamer. 2010. Decadal-timescale estuarine geomorphic change under future scenarios of climate and sediment supply. Estuaries and Coasts (February 2010). DOI: 10.1007/s12237-009-9244-y.