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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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2012 January


Sea Level Rise Could Bring More Salt, More Water, or Both to Tidal Freshwater Marshes. How Will They Respond?
For Pelagic Fishes in San Francisco Estuary, What Doesn’t Kill You … Can Still Kill You
As Storm Frequency and Intensity Rise, Consequences for Marshes Could Be More Complex than Previously Thought
Got Benthic Maps? New Acoustic Techniques are Fast, Accurate, High-Resolution, and Cost-Effective in Shallow, Complex Environments

Sea Level Rise Could Bring More Salt, More Water, or Both to Tidal Freshwater Marshes. How Will They Respond?

Tidal freshwater marshes are resilient to environmental change. They have to be: they thrive in one of the most dynamic ecosystems on earth, where tides, storms, and river flow inundate them with salt water and fresh water on a range of time scales. But global climate change might represent a challenge to even these systems. How will these marshes react to being stuck between inundation by salt water as sea level rises and possible increases in freshwater flow?
Results from manipulating a marsh in South Carolina provide some insight. Researchers watered plots in a freshwater marsh with either fresh or salt water every 3-4 days, mimicking increased inundation with seawater, increased riverine flooding, or both, and reported on the first 20 months of the manipulation. The main impact of the salt water addition was a decrease in plant production. The freshwater–flooded plots exhibited a decrease in CO2 emissions, which the authors attribute to decreased microbial respiration in the soil. Net ecosystem production (NEP), the difference between gross primary production and community respiration, was calculated for each treatment. NEP is an indication of a marsh’s ability to accumulate organic matter:  Negative values mean that a marsh is losing C and therefore might not be able to “keep up” with sea level rise. In this study, experimental freshwater inundation led to an increase in NEP whereas salt additions led to a decreased NEP, indicating that marshes under these conditions could be susceptible to inundation. When salinity and hydrology were manipulated simultaneously, NEP did not change.

This study is ongoing, and further insights are likely to be gained. For example, results could change as community composition shifts to include more flood-tolerant species. If the observed trends hold, the study suggests that marshes will react differently to flooding with salt vs. freshwater, and that perhaps marshes flooded with freshwater might be better able to keep up with sea level rise.

Source: Neubauer, S. C. 2012. Ecosystem responses of a tidal freshwater marsh experiencing saltwater intrusion and altered hydrology. Estuaries and Coasts 35(January 2012). DOI: 10.1007/s12237-011-9455-x.

 For Pelagic Fishes in San Francisco Estuary, What Doesn’t Kill You … Can Still Kill You

Although contaminant loadings to water bodies are regulated based on the damage they do to species and ecosystems, mortality of an organism can rarely be directly link to a known chemical contaminant. Instead, contaminant effects are often sublethal, interactive, and depend on the life stage of the species in question as well as environmental conditions at the time of exposure. An extensive literature review recently examined the possible effects of contaminants and other stressors on different life stages of four species of pelagic fish (delta smelt, longfin smelt, striped bass, and threadfin shad) found in San Francisco Estuary. This issue is particularly relevant for San Francisco Estuary because its waters often violate state and federal water quality standards, and because declines in many fish species accelerated abruptly around 2002 with no obvious cause.

Rather than searching for evidence of direct mortality, which has not been observed since the 1980s, the authors evaluated how sublethal stressors could affect energy budgets of these species, a framework more appropriate to evaluating contaminant effects at a community level. A conceptual model of interactions between life stages and multiple stressors including contaminants indicates that the greatest overlap in threats to these species likely occurs during larval stages in the freshwater reaches of the Delta section of the estuary in late winter and spring. The analysis suggests that while sublethal contaminant effects are not the sole cause of fish declines in San Francisco Estuary, the chronic bioenergetic costs resulting from exposure to a variety of stressors are likely contributors. Rising water temperatures of the magnitude projected by climate change models could change these dynamics between stressors and fishes, but those impacts will likely vary among species. For example, warming water could increase metabolic rates, hastening elimination of some contaminants, whereas increases in respiration rates or food intake could result in higher doses of contaminants.

This bioenergetics approach is promising for evaluating sublethal effects of contaminants in the presence of other stressors, but predictive models will not be possible until additional data on water temperature, geochemistry, contaminant levels, fish abundances, age classes, and age/size ratios are collected on a regular basis.

Source: Brooks, M. L., E. Fleishman, L. R. Brown, P. W. Lehman, I. Werner, N. Scholz, C. Mitchelmore, J. R. Lovvorn, M. L. Johnson, D. Schlenk, S. v. Drunick, D. M. Stoms, A. E. Parker, R. Dugdale, and J. I. Drever 2012. Life histories, salinity zones, and sublethal contributions of contaminants to pelagic fish declines illustrated with a case study of San Francisco Estuary, California, USA. Estuaries and Coasts 35(January 2012). DOI: 10.1007/s12237-011-9459-6.

 As Storm Frequency and Intensity Rise, Consequences for Marshes Could Be More Complex than Previously Thought

Sea level rise due to climate change may outpace marsh accretion in many places, such that marshes are drowned in place. But this problem may bring its own solution, as increased storms that might accompany climate change may deposit enough sediment in marshes to help with the accretion process. The current bout of sea level rise is not the planet’s first. What can historical records of storm tide variation and salt marsh accretion tell us about these dynamics?

Using multiple approaches to examining historical data, researchers reconstructed the biogeological record of salt marshes on the seaward shore of a barrier island in the North Sea’s German Bight, where sea level rise has been shown to be higher than the global average. They used radioisotopes, sedimentology, and aerial photographs to determine the spatial extent of the marsh, and analyzed marsh changes in light of sea level and the frequency and intensity of storms. While accretion rates have varied since the marshes were formed, the highest rates have occurred in recent years. These accretion rates appear to coincide with periods of increased storm activity. For this marsh, the effects of storm frequency and intensity differ, and depend on inundation depth. The investigators identified a critical inundation height of 18 cm, below which the strength of a storm seems to positively influence salt marsh accretion rates and above which the frequency of storms becomes the major factor. The authors surmise that this threshold occurs because vegetation in the marshes slows water movement below the 18-cm inundation, allowing for sediment accretion.

Climate change will likely change both storm frequency and intensity in most places, and fringing salt marshes are an important first line of defense for landward ecosystems and human development. Because of this vital role for fringing salt marshes, ecosystem management needs to focus on preserving healthy marshes. In addition, the complexity of the storm/accretion relationship at this single site points out the necessity of considering storm trends – past and projected – in designing marsh restoration projects.
Source: Schuerch, M., J. Rapaglia, V. Liebetrau, A. Vafeidis and K. Reise. 2012. Salt marsh accretion and storm tide variation: an example from a barrier island in the North Sea. Estuaries and Coasts 35(January 2012). DOI: 10.1007/s12237-011-9461-z.

 Got Benthic Maps? New Acoustic Techniques are Fast, Accurate, High-Resolution, and Cost-Effective in Shallow, Complex Environments

Many coastal management programs are turning towards marine spatial planning to document resource use, and the first step in this process requires accurate and complete maps of the areas to be managed. An acoustic mapping method was used recently to map Delaware Bay and nearby coastal waters, resulting in a detailed map of benthic habitats that will be invaluable to managers. The methods used in this system could easily be applied elsewhere.

Investigators used a phase-measuring bathymetric sonar (PMBS) mounted on an autonomous underwater vehicle (AUV) to rapidly map large areas of subtidal bottom at a high resolution (<1 m). Ground-truthing was carried out via targeted grab samples and ROV images. An auto-segmentation algorithm was used to group backscatter data into geological and biological categories. This integrated approach allowed the identification of physical structure as well as sediment type, and data were combined to generate biological assemblage maps. Species preferences for particular habitat types allowed identification of potential habitats without the need for identifying individual organisms. A prime example of the success of this overall approach is the very complete and detailed mapping the investigators were able to carry out for patchy oyster bed habitats in the bay.

An additional advantage of this approach is that use of the AUV platform allows for more easily repeatable sampling to examine trends or changes over time, thanks to the precise navigation capability of AUVs. Data products generated by the study are available in geoTIFF and kml format for viewing in GoogleEarth at http://cshel.geology.udel.edu/kml_files/DEBay/

Source: Raineault, N. A., A. C. Trembanis, and D. C. Miller. 2012. Mapping benthic habitats in Delaware Bay and the coastal Atlantic: acoustic techniques provide greater coverage and high resolution in complex, shallow-water environments. Estuaries and Coasts 35(January 2012). DOI: 10.1007/s12237-011-9457-8.