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.
September 2010
Contents
Resisting Phragmites Invasions: Diverse Native Plant Assemblages Might Help
Modeling Past, Present, and Future Nitrogen in Narragansett Bay
EXPO’98 Improvements in Portugal Estuary Stick Around After the Fair is Long Gone
Bringing Back the Oyster: Sometimes Impacts Can Be Hard to See
Resisting Phragmites Invasions: Diverse Native Plant Assemblages Might Help
As Phragmites australis continues to invade North American marshes, managers are often faced with the Sisiphysian task of curbing the plant’s expansion and restoring invaded marshes. However, there is some indication that competition with native species reduces the success of Phragmites, and that in general the diversity of native competitors plays a critical role in the success of invading species A recent experimental study in a New Hampshire salt marsh explored this possibility. Investigators planted experimental plots with Phragmites shoots alone, Phragmites and one native plant species, and Phragmites and four native species. Conditions at the field site were considered conducive to the establishment of Phragmites (restricted tidal flushing, located near residential and road development).
Phragmites grown in plots with one native species exhibited significantly reduced growth (aboveground biomass, shoot length, and density) and survival compared to Phragmites-only plots. Phragmites grown in plots with four native species had the lowest growth and survival. These results suggest that resource competition from natives can help resist invasion, and that this effect is enhanced by the presence of a high diversity of natives. While there are a multitude of factors that influence recovery in sites from which Phragmites has been removed, the message to managers here is that in order to impede re-invasion by Phragmites, post-removal plantings should include a diversity of native species.
Source: Peter, C. R. and D. M. Burdick. 2010. Can plant competition and diversity reduce the growth and survival of exotic Phragmites australis invading a tidal marsh? Estuaries and Coasts 33(August 2010). DOI: 10.1007/s12237-010-9328-8.
Modeling Past, Present, and Future Nitrogen in Narragansett Bay
The reduction of nitrogen (N) loading in order to address eutrophication and its associated ecosystem impacts is a common management goal for North American estuaries. In evaluating policy options for managing N and developing insight into N dynamics in a given system, it is helpful to understand current and historic spatial loading patterns. In a study of Narragansett Bay, RI, researchers used data on population, human waste disposal, livestock, fertilizer, and atmospheric deposition to determine N inputs to the bay for 1850-2000. Model results indicate that total N loads to the bay increased by 250% from 1850 to 2000, and 80% from 1900 to 2000. Dominant N sources shifted from non-point animal waste to human waste from sewage treatment facilities. Increases in N loading to the upper bay were much greater than those to the lower bay, primarily due to the growth of sewage systems serving populations in the upper bay watershed, including Providence, RI and Fall River and Worcester, MA.
The investigators also used the model to predict N loading for 2015 under four management scenarios, asking how far “back in time” various policies could take the ecosystem. According to the model, “business as usual” would produce a 6% increase in land-based loading. Improvements that have already been agreed-upon would lead to an 11% reduction below business as usual, to 1990 loading levels. “Reasonable additional reduction,” including application of agreed-upon targets to more sewage treatment facilities, would bring loadings down 27%, similar to estimated loadings in the 1970s. Under the most aggressive (and, of course, expensive) management scenario considered, Narragansett Bay could turn the clock back to the 1890s, with a 50% reduction in N loading. The results of this study could provide a guide for moving forward with N reductions by suggesting geographic areas of focus, pointing out the most significant loading sources, and providing estimates of environmental benefit relative to amount of effort and expense invested.
Source: Vadeboncoeur, M. A., S. P. Hamburg, and D. Pryor. 2010. Modeled nitrogen loading to Narragansett Bay: 1850 to 2015. Estuaries and Coasts 33(August 2010). DOI: 10.1007/s12237-010-9320-3.
EXPO’98 Improvements in Portugal Estuary Stick Around After the Fair is Long Gone
The theme of the special World’s Fair in Lisbon in 1998 (EXPO’98) was “The Oceans, a Heritage for the Future,” so it was entirely fitting that in addition to the buildings, pavilions, and metro stations constructed for the fair, sewage treatment and other improvements were undertaken to clean up the Tagus estuary. A long-term monitoring program tracked intertidal and subtidal benthic communities at sites near the EXPO’98 site for more than ten years (1996-2007), and found that measures of benthic community health improved along with water quality.
Researchers collected benthic samples along seven transects near the site at quarterly intervals for eleven years, and used multiple statistical measures of benthic community characteristics (taxonomic richness, density, biomass, diversity, and the AMBI index) to draw conclusions about changes in the estuary. They found significant positive trends in nearly all indicators for both subtidal and intertidal communities, attributable to the improvements resulting from the management steps taken for the fair. A reversal of the positive trend occurred briefly in 2001/2002, possibly in response to extreme high flows followed by a period of significant drought in 2002. This anomaly underscores the importance of long-term, consistent monitoring in understanding ecosystem function and evaluating the impacts of management actions. The authors also discuss the need for some adaptation and calibration of the metrics they used in order to account for differences in subtidal and intertidal communities, as there was a clear separation between them.
Source: Chainho, P., G. Silva, M. F. Lane, J. L. Costa, T. Pereira, C. Azeda, P. R. Almeida, I. Metelo, and M. J. Costa. 2010. Long-term trends in intertidal and subtidal benthic communities in response to water quality improvement measures. Estuaries and Coasts 33(August 2010). DOI: 10.1007/s12237-010-9321-2.
Bringing Back the Oyster: Sometimes Impacts Can Be Hard to See
Efforts along the Atlantic and Gulf coasts to restore depleted estuarine oyster populations have taken off in recent years, and everyone has a reason for wanting the bivalve back. They’re good to eat (for humans and others), they support economic activities, they are ecosystem engineers that create habitat for lots of other organisms, and, importantly, they can filter prodigious quantities of particulates from the water column, leading to improvements in water quality. However, this last function has not always been demonstrated effectively in the field. Along the Gulf coast, researchers undertook a study in conjunction with the Alabama Oyster Reef Restoration Project to assess the impact of restored eastern oyster reefs on primary production, nutrient dynamics, and water quality in shallow tidal creeks. The investigators looked at these factors in sediment and water in paired creeks (with and without restored oyster beds) over the course of two years post-restoration. Despite the investigators’ expectations, oyster presence only affected sediment chlorophyll a and water column nutrient concentration, and results were inconsistent across sites. Oyster reefs did not seem to reduce water-column particulates or affect phytoplankton biomass or productivity.
The authors state that their results do not suggest that oysters do not impact water quality. Rather, they provide a range of potential explanations for their results that highlight the importance of considering the type, spatial extent, and magnitude of expected changes when evaluating oyster reef restoration projects. For example, the authors propose that a significant difference in water-column chlorophyll a may have been detected if they had sampled at a finer scale, on the order of a few cm rather than the meter scale they employed. Monitoring programs need to take such factors into account. Stay tuned for the results of future studies on this topic that could provide further clarification.
Source: Plutchak, R., K. Major, J. Cebrian, C. D. Foster, M. C. Miller, A. Anton, K. L. Sheehan, K. L. Heck, Jr., and S. P. Powers. 2010. Impacts of oyster reef restoration on primary productivity and nutrient dynamics in tidal creeks of the north central Gulf of Mexico. Estuaries and Coasts 33(August 2010). DOI: 10.1007/s12237-010-9327-9.
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