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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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2015 September

Contents

What Does Recovery from Eutrophication Look Like?
Wrack Line Inverts Impacted by Shoreline Armoring in Puget Sound
Migratory Waterbirds Respond to Habitat Shifts in Yangtze
Managing Marshes in the Face of Climate Change

What Does Recovery from Eutrophication Look Like?

Holistic look at Danish estuaries finds encouraging trends in some, but not all, parameters

Many nutrient loading reduction programs have now been in place long enough that it is fair to ask, “Are they working?” The answer for a set of 45 Danish estuarine and coastal systems is basically “yes,” although recovery might not always look like what we expect.

Researchers examined trends in a number of parameters related to nutrient loading and eutrophication in the estuaries, which were impacted by nutrient loading from sewage and agricultural sources from the 1950s through the 1980s. Multiple nutrient reduction programs were instituted beginning in the late 1980s, leading to significant loading reductions (loadings from land declined about 50% for nitrogen and 56% for phosphorus). These loading reductions resulted in significant and parallel declines in nutrient concentrations in estuarine waters, a decline in chlorophyll a, and an increase in macroalgal beds.

But the story was not completely straightforward. Secchi depths increased, but not significantly. Average bottom water DO did not change. Overall benthic macroinvertebrate biomass decreased, especially that of filter feeders, but deposit feeder biomass increased. The authors theorize that recovery was complicated by oceanographic processes: wind velocity was low during the study period, decreasing water mixing and increasing stratification, and explaining the lack of recovery in bottom DO. The strong stratification also seemed to reduce availability of phytoplankton to filter feeding benthos.

The overall news is good: managers can expect direct positive responses to nutrient controls. However, some parameters may recover more slowly than expected thanks to feedback loops in food webs, shifting baselines, or overarching oceanographic drivers.

Source: Riemann, B., J. Carstensen, K. Dahl, H. Fossing, J. W. Hansen, H. H. Jakobsen, A. B. Josefson, D. Krause-Jensen, S. Markager, P. A. Staehr, K, Timmerman, J. Windolf, and J. H. Andersen. 2015. Recovery of Danish coastal ecosystems after reductions in nutrient loading: A holistic ecosystem approach. Estuaries and Coasts (May 2015). DOI:  10.1007/s12237-015-9980-0.

Study finds fewer invertebrates and altered invertebrate communities in beach wrack at estuarine armored sites

Beach wrack may look like little more than a line of debris on the sand deposited by the tide, but it is actually a significant source of habitat and organic matter on many kinds of beaches. Because sources of wrack line debris are often both marine and terrestrial, the wrack line serves as an important connection between ecosystem types as well. A growing body of research indicates that shoreline armoring – rip rap, seawalls, etc. – may decrease the amount of valuable wrack found on beaches. If the wrack declines, do wrack-associated invertebrate communities decline along with it? A recent study took up this question by surveying paired armored and unarmored sites in Puget Sound, WA.

Unarmored beaches had more invertebrates living in the local wrack line, as well as a higher species diversity. A separate analysis found that armored beaches harbored fewer mobile species (insects, amphipods, springtails). The relative paucity of invertebrates at armored beaches could represent a decrease in subsidy of prey items and organic material to both the adjacent nearshore and terrestrial ecosystems, perhaps leading to cascading trophic effects beyond the beaches themselves.

Source: Heerhartz, S. M., J. D. Toft, J. R. Cordell, M. N. Dethier, and A. S. Ogston. 2015. Shoreline armoring in an estuary constrains wrack-associated invertebrate communities. Estuaries and Coasts (May 2015). DOI:  10.1007/s12237-015-9983-x.

Migratory Waterbirds Respond to Habitat Shifts in Yangtze

As habitats have changed, so have bird communities in this ecologically sensitive region

The Yangtze River Estuary has been referred to as one of the 50 most ecologically sensitive regions in the world. At the mouth of the river lies the Chongming Dongtan wetlands, one of the Yangtze’s most prominent wetland areas and a global treasure, designated as a wetland of international importance by the Ramsar Convention. These wetlands host thousands of migrating waterbirds annually, but the wetlands, as well as the bird populations that use them, have been declining over the past decade. A recent study analyzed the relationship between changes in populations of the four dominant waterbird families that use the wetlands (Charardriidae (plovers), Ardeidae (herons), Laridae (gulls), and Anatidae (ducks and geese)) as well as changes in their habitats. The authors acquired bird survey data for natural wetland sites and surveyed aquaculture pond sites themselves. Satellite imagery was used to quantify changes in six habitat types: deep water, mudflat/shallow water, Scirpus (bullrushes), Phragmites, Spartina, and aquaculture ponds.

Relationships varied by species/habitat pairing, but overall, bird population fluctuations were correlated with changes in habitat types. For example, all populations were significantly positively correlated with extent of Scirpus, but negatively correlated with Phragmites. Anatidae populations were positively correlated with aquaculture pond area, while Charardriidae and Laridae were positively correlated with deep water habitat but negatively correlated with Spartina. Some relationships varied by season. The authors conclude that careful management is necessary for this area to sustain waterbird populations. Their recommendations include limiting reclamation of wetlands for agriculture and industry, controlling the spread of Spartina, and undertaking wetland restoration projects in the region.

Source: Zou, Y., C. Tang, J. Niu, T. Wang, Y. Xie, and H. Guo. 2015. Migratory waterbirds response to coastal habitat changes: conservation implications from long-term detection in the Chongming Dongtan Wetlands, China. Estuaries and Coasts (May 2015). DOI:  10.1007/212237-015-9991-x.

Managing Marshes in the Face of Climate Change

Climate Change Adaptation Strategy for a Rhode Island marsh provides a perfect case study for helping waterlogged wetlands

Climate change and associated sea level rise are not future concerns in coastal New England: they are immediate issues, affecting coastlines now in the form of increased storm surge, coastal erosion, and drowned coastal marshes. Just when coastal communities need the flood protection properties of these marshes the most, environmental forces are conspiring to drown the marshes in place as sea levels rise and marsh accretion is limited by decreasing sediment supplies and compromised health of plant communities. A robust management approach to improve resiliency of these critical habitats is vitally important. One case study in successful marsh management is the Climate Change Adaptation Strategy used to manage and monitor progress in the Narrow River Estuary in Rhode Island. This adaptive, flexible, data-based approach led by the U.S. Fish & Wildlife Service shows promise.

The strategy began with presenting stakeholders with the best available data and modeling information on the past, present, and projected future of the estuary, and then soliciting input on appropriate goals for the project and specific actions that could be taken to achieve those goals. Participants also defined suitable metrics for monitoring of the site. Specific projects undertaken in the estuary as a result of this planning include natural bank stabilization, sediment placement to raise marsh elevation, and excavation of new runnels and sinuous creeks in some reaches of the estuary. All projects will be monitored and adjusted as necessary over time, and a broader environmental monitoring program will also be implemented. An adaptive management approach will be employed in which data collected on the health and status of the estuary will be used to evaluate results and adjust actions as needed.

Only time will tell how successful these projects are. The authors of a recent paper about the program emphasize that institutional barriers to implementation of this type of strategy must be addressed, such as lack of funding and fragmentation of jurisdictional control. Bottom-up community planning and top-down national strategies will need to be implemented, and meshed together, to result in successful coastal marsh resilience.

Source: Wigand, C., T. Ardito, C. Chaffee, W. Ferguson, S. Paton, K. Raposa, C. Vandemoer, and E. Watson. 2015. A climate change adaptation strategy for management of coastal marsh systems. Estuaries and Coasts (June 2015). DOI: 10.1007/s12237-015-0003-y.