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.
May 2004
Contents
Evidence that Global Climate Change Does Act Locally in San Francisco Bay
Invasion of the Marsh Snatchers: Effectiveness of Invasive Plant Removal in Puget Sound
Study Supports "Thinking Outside the Dike"
Links Between Land Use and Estuarine Health: A Potential Statistical Crystal Ball
Evidence that Global Climate Change Does Act Locally in San Francisco Bay
One way of improving our understanding of the effects of long term climate change on coastal food webs is to focus on the more dramatic shorter term regional changes knows as "regime shifts." A recent study makes great strides in determining the mechanisms by which the Eastern Pacific regime shift of the late 1970s, long implicated in a decline in fisheries production along the West Coast, may have brought about declines in productivity in San Francisco Bay.
This study examined abundant existing data collected from 1975-1993 on water quality, phytoplankton, zooplankton, and various physical and chemical variables in the Bay. Correlations between these parameters and a climate index based on sea level pressure (which is related to rainfall and streamflow to the estuary) were examined using "coherence analysis," which removes statistical artifacts from the data that can result in spurious correlations among variables. The results of the analysis indicate that climate acted on the Bay's food webs via three different pathways: through influencing wind velocity, air temperature (and therefore water temperature) and, most clearly, changes in streamflow. The impacts included declines in organic carbon, diatoms and zooplankton. Sub-sections of the estuary responded differently, suggesting the impact of climate change was location-specific.
This mechanistic understanding may eventually improve our predictive capabilities with respect to climate change impacts, ultimately allowing managers to incorporate climate change effects into their decision-making processes.
Source: Lehman, P.W. 2004. The influence of climate on mechanistic pathways that impact lower food web production in northern San Francisco Bay estuary. Estuaries 27(2): 311-324. (View Abstract)
Invasion of the Marsh Snatchers: Effectiveness of Invasive Plant Removal in Puget Sound
How to get rid of that pesky introduced invasive cordgrass (Spartina anglica) in Puget Sound? First off, according to a new study, once a removal program is instituted, don't skip a year or the Spartina will grow back with a vengeance.
Researchers in Washington set out to study the effectiveness of different removal regimes (removal for three consecutive years vs. skipping a year of removal) in a variety of Puget Sound habitats (low salinity marsh, high salinity marsh, cobble beach and mudflat). They also examined recovery of native plant communities at these sites. Results of both an observational study of areas subject to a State removal program and an experimental study indicated that consistent removal in successive years is critical because Spartina has such resilient underground storage capacity. When removal was interrupted, even for one year, substantial regrowth occurred, in some cases exceeding growth in areas not subject to removal. Habitat type also influenced regrowth and reinvasion: Regrowth was greatest in the benign low salinity marsh habitat, and re-invasion by seedlings was highest in the low salinity marsh site where uninterrupted removal took place. The good news for managers is that with consistent removal, Spartina did decline slowly but significantly. While restoration of native vegetation was negligible at cobble beach, mudflat and high salinity marshes (probably due to sediment accretion previously caused by the Spartina), restoration was more successful at the low salinity marsh where the original plant community colonized.
This study underscores the necessity of committing resources to a removal program for the long term. If funding or other resources for invasive control programs disappear, the problem may grow to be even bigger. The authors also point out that even if there is strong financial, social and political backing for eradicating an invasive species, removal is likely to be unsuccessful if the species' ecology is not understood.
Source: Reeder, T.C. and S.D. Hacker. 2004. Factors contributing to the removal of a marine grass invader (Spartina anglica) and subsequent potential for habitat restoration. Estuaries 27(2): 244-252. (View Abstract)
Study Supports "Thinking Outside the Dike"
Habitat restoration projects that aim to remove or remediate the effects of dikes in estuarine areas may need to consider expanding the scope of their projects, based on the results of a recent study examining the effects of diking on areas outside (seaward) of a diked area. It has long been understood that removing the influence of tides by diking tidal wetlands to create agricultural land, control salinity, or manage waterfowl populations has a variety of negative results for the wetlands themselves and their associated wildlife. These effects range from changing sediment dynamics and biogeochemistry to decreasing abundances of various benthic species. But what happens to the areas seaward of the dike?
Using GIS, the author compared historic and modern aerial photos of three sites on Washington's Skagit River where dikes were constructed in the 1950s. The analysis revealed that dike construction caused a greater loss of tidal channel surface area on the seaward side of the dike than on the landward side. Channel sinuosity decreased and channel width increased compared to reference sites, likely due to loss of floodplain area which prevents dissipation of flood energy. In this system, changes to tidal channels are particularly troubling because migrating endangered salmon use the channels as well as the impacted estuarine areas landward of the dike.
The results of this study indicate that habitat impacts of dikes extend well beyond the area enclosed by the dike, which may need to be taken into account during restoration planning. Another caveat raised by this study: The use of areas outside and adjacent to dikes as reference sites in studies assessing dike impacts should be reconsidered, as these areas have likely been affected by dike construction as well.
Source: Hood, W.G. 2004. Indirect environmental effects of dikes on estuarine tidal channels: Thinking outside of the dike for habitat restoration and monitoring. Estuaries 27(2): 273-282. (View Abstract)
Links Between Land Use and Estuarine Health: A Potential Statistical Crystal Ball
Most coastal managers know all too well how expensive and time-consuming it is to mount a comprehensive monitoring program to track the health of an estuary. Wouldn't it be helpful if existing land use data could be used to predict which estuaries are at greatest risk from impacts of land use practices? Those estuaries could then be selected for targeted sampling of sediment contamination and toxicity, number and diversity of benthic and fish communities, and water quality parameters. Such a tool would also be useful for understanding the links between land use in the watershed and environmental condition in the estuary.
A recent study was able to make this link for 58 pairs of small estuaries and watersheds in the mid-Atlantic region. The authors examined the statistical relationships between land use characteristics of the estuaries' watersheds and benthic quality. Benthic condition was described by three indices: Benthic Environmental Quality (defined by chemical parameters), Benthic Index (which defines benthic condition by the numbers, diversity and species of benthic invertebrates present), and total number of bottom-dwelling species, which takes into account fish and macroinvertebrates. The land use parameters chosen for the models correctly classified the estuaries as degraded or not degraded (as defined by the values of these three indices) 75-86% of the time. More urbanized and agricultural watersheds were generally associated with degraded estuaries (lower scores of the indices outlined above) and watersheds with a higher percentage of wetlands tended to have higher values of the indices, indicating a more healthy benthos.
This work establishes a significant statistical link between land use and environmental quality. While these models need to be tested in other areas, they show great promise as predictive tools, and could represent effective and economical "first-cut" methods for identifying estuaries that may be at risk.
Source: Hale, S. S., J. F. Paul, and J. F. Heltshe. 2004. Watershed landscape indicators of estuarine benthic condition. Estuaries 27(2): 283-295. (View Abstract)
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