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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.

October 2006

Look Landward for Sources of Water Body Impairment, Says CA Study
Sampling Frequency: What Might You Be Missing?
Horseshoe Crab Sex and the City: Restoration Potential in Jamaica Bay
Feeding Sediment-Starved Tidal Marshes: Signs of Success in North Carolina

Look Landward for Sources of Water Body Impairment, Says CA Study

Commerce, aesthetics, recreation, and other factors have always driven humans to live near the coast. It is not unusual for water quality surveys to indicate that in some places we may be loving coastal waters to death. A recent water quality survey at 14 California sites representing a range of salinities adds to the body of evidence that human development – whether urban or agricultural – can drag water quality down. For all study sites, salinities, and levels of development, the “cleanest” conditions were found in forested rather than agricultural and urban watersheds. For example, fecal coliform concentrations were significantly higher in agricultural or urban watersheds than forested ones, and nitrogen pollution and chlorophyll concentrations were significantly correlated with agricultural land use at all sites.

In addition to the traditional water quality parameters measured in the study, one “up and coming” contaminant was examined: perfluorinated organic compounds, used in textile coatings and fire fighting foams, were measured in some sediment samples. Concentrations of these compounds were strongly correlated with agricultural land use, perhaps because these compounds are commonly found in sewage sludge, which is often used to amend agricultural soils.

Fecal bacteria concentrations were correlated with measures of eutrophication at all salinities, suggesting that these two classes of contaminants may come from the same sources. The interrelationship of all of these indicators of contamination underscores the need for widespread use of Best Management Practices (BMPs) in agricultural and urban watersheds.

Source: Handler, N. B., A. Paytan, C. P. Higgins, R. G. Luthy, and A. B. Boehm. 2006. Human development is linked to multiple water body impairments along the California coast. Estuaries and Coasts 29(5): 860-870. (View Abstract)

Sampling Frequency: What Might You Be Missing?

Your water quality monitoring program gears up to sample once a week. Logistically, that’s about as frequently as you can get into the field. But what if the parameters you measure vary diurnally, or even more frequently? How can you be sure you are accurately capturing relevant trends, especially if you are particularly interested in maximum or average values? A recent publication provides insight into the error that can result from sampling at too coarse a temporal scale, and suggests a subsampling approach for evaluating and understanding that error. To illustrate these points, the research team sampled specific conductance, temperature, and chlorophyll at 10-minute intervals at two sites in an embayment of the Sacramento-San Joaquin River Delta. All three parameters exhibited intradaily oscillations, with periodicity varying with parameter, space, and time. A scaling process was used to examine the mechanisms driving periodicity for these parameters, which included interactions among tides, heating, wind, and biological factors. By subsampling the high-frequency data daily at 6 a.m., noon, and 6 p.m., the authors demonstrated how quantities needed by managers may be misrepresented by low-frequency sampling. In this case, data drawn from only the 6 p.m. sampling time deviated from the day-averaged chlorophyll values more than the morning and noon sample points.

While it’s not necessary, or feasible, to sample water quality parameters every 10 minutes year round, this study highlights the importance of knowing how parameters of interest vary over short time scales in order to determine optimal sampling times relative to time of day, tidal phase, and other variables. High-frequency periodicity may also affect estimates of processes, such as flux and transport. This type of analysis can also help estimate error and balance competing monitoring goals and errors when more than one period of variability is involved.

Source: Lucas, L. V., D. M. Sereno, J. R. Burau, T. S. Schraga, C. B. Lopez, M. T. Stacey, K. V. Parchevsky, and V. P. Parchevsky. 2006. Intradaily variability of water quality in a shallow tidal lagoon: mechanisms and implications. Estuaries and Coasts 29(5): 711-730. (View Abstract)

Horseshoe Crab Sex and the City: Restoration Potential in Jamaica Bay

Surrounded by Brooklyn neighborhoods and JFK International Airport, Jamaica Bay provides a critical oasis of estuarine habitat on the edge of one of the world’s largest cities. While the most famous spawning congregations of horseshoe crabs occurs on the shores of Delaware Bay, Jamaica Bay provides some spawning habitat for these ancient creatures, mostly consisting of small patches of sand within larger areas of rubble and bulkheading. Habitat restoration at some sites could provide additional viable spawning areas, according to a recent study. Twelve sites in the bay already proposed for restoration by the Army Corps of Engineers were evaluated for suitability as horseshoe crab spawning habitat. After refining the set of study sites based on geomorphology and vegetation (Phragmites-dominated sites have already been shown to be of limited value as horseshoe crab spawning habitat), spawning activity and egg viability were studied at five of these sites. Egg densities at some Jamaica Bay sites were comparable to spawning sites in Delaware Bay, and in lab experiments Jamaica Bay eggs developed and hatched equally well in Jamaica Bay and Delaware Bay water. These results indicate that Jamaica Bay’s horseshoe crab “carrying capacity” is likely to be enhanced if appropriate habitat restoration takes place, since spawning does not appear to be limited by water quality or other factors. Specific restoration strategies appropriate to each site are suggested, including debris removal and substrate grain size modification.

The authors noted that the suite of fouling organisms found on Jamaica Bay adult horseshoe crabs is similar to that found on crabs from nearby Sandy Hook Bay in New Jersey, perhaps indicating that Jamaica Bay individuals are part of a metapopulation encompassing the entire lower New York Harbor estuary. This finding, consistent with results of another study described in CESN 29(4) (Model Results Recommend Easing Up on Horseshoe Crab Harvest), should be considered as fisheries managers design horseshoe crab harvest regulations.

Source: Botton, M. L., R. E. Loveland, J. T. Tanacredi, and T. Itow. 2006. Horseshoe crabs (Limulus polyphemus) in an urban estuary (Jamaica Bay, New York) and the potential for ecological restoration. Estuaries and Coasts 29(5): 820-830. (View Abstract)

Feeding Sediment-Starved Tidal Marshes: Signs of Success in North Carolina

Tidal marshes on the Atlantic and Gulf Coasts are constantly fighting the dual enemies of sea level rise and diminished sediment supply in order to avoid being submerged and lost. One solution to this problem that has been explored in recent years is addition of thin layers of sediment to marsh surfaces to keep the marsh elevation high enough to combat inundation. This approach was taken at deteriorated (characterized by lower Spartina stem densities, shorter plants, lower marsh elevation, and lower redox potential) and non-deteriorated back barrier marsh sites in NC, with promising results. Sand was applied to experimental plots in thicknesses ranging from 2.5 cm to 10 cm. One year after the sand additions, stem densities of Spartina increased at all sites, regardless of the thickness of sand application. The greatest stem density increase, a doubling, was observed at the deteriorated sites, perhaps because the sediment addition led to greater soil aeration. Benthic microalgae also increased in abundance on the marsh surface in deteriorated and non-deteriorated plots, but the presence of grazers did not. The most oxidized sites were those at which medium and thick layers of sand had been placed, while the more reduced sediment profiles were found where the added sand layer was thinnest. Abundance and diversity of benthic organisms did not suffer at any sites due to sand addition, and the infauna in place in the treated sites reworked the sediment so that grain size profiles in the amended plots began to resemble those of the control sites one year after sediment addition.

The authors note that some or all of the post-amendment changes observed may be short-term – longer monitoring of amended sites should be undertaken, along with more large-scale research to determine optimum thickness and frequency of sediment application. For interested readers, another recent CESN-highlighted paper provides data on this type of marsh renourishment technique, with similarly positive results (CESN 28(4), Sediment Slurry Application Helps Delta Marsh Rise to the Challenge).

Source: Croft, A. L., L. A. Leonard, T. D. Alphin, L. B. Cahoon, and M. H. Posey. 2006. The effects of thin layer sand renourishment on tidal marsh processes: Masonboro Island, North Carolina. Estuaries and Coasts 29(5): 737-750. (View Abstract)