Citation:

Janousek, Chris, C. Folger, AND C. Mayo. Potential climate change impacts on tidal wetland plant and algal assemblages in the Pacific Northwest. Presented at Seminar, Oregon Institute of Marine Biology, University of Oregon, September 28, 2012.

Impact/Purpose:

Climate change may alter the structure and function of tidal wetland vegetation in the Pacific Northwest. Using survey and experimental data, we identified several potential impacts to estuarine wetlands due to relative sea-level rise and increased salinity: (i) changes in plant composition and a reduction in overall plant diversity, (ii) a reduction in plant productivity, and (iii) a shift in ratios of algal versus plant productivity toward greater algal importance. Each of these changes has potential consequences for coastal food webs and other wetland processes. These data provide important information for coastal ecologists and planners who wish to understand whole-ecosystem effects of climate change or coastal managers who are involved in decisions pertaining to wetland restoration or coastal development. In this seminar, I summarize our findings to date.

Description:

Tidal wetlands along the coast of the Pacific Northwest provide wildlife habitat and support important ecosystem functions such as primary productivity. The future structure and function of these ecosystems may be altered by sea-level rise (SLR) or other climate change effects. We combined field survey data and lab and field experiments to better understand potential changes to wetland vegetation due to SLR or changes in salinity. In 2010 we quantified spatial patterns of plant and algal composition and diversity in different wetland habitat types in several Oregon estuaries with different hydrologic regimes. For both macroalgae and plants, composition differed only modestly among estuaries, even though the sites differed substantially in their relative degree of freshwater inputs. Composition varied more strongly within estuaries (among habitat classes and along environmental gradients). Tidal elevation appeared to be a key factor structuring both groups of primary producers. Macroalgal abundance and diversity and benthic chlorophyll a peaked in lower elevation habitat. In contrast, plant diversity was greatest in higher tidal marsh. Salinity also appeared to affect primary producer composition, though many common species occurred across a broad salinity gradient. Fresher marshes had markedly different plant composition and also tended to have less macroalgae and chlorophyll a than more saline wetlands. In 2012 we conducted a series of lab studies to investigate salinity effects on vascular plant seed germination and a field study with transplanted seedlings to determine the combined effect of salinity and inundation on plant growth. Both experiments mimicked the increasing stress plants would endure with SLR. Germination frequencies confirmed that most species responded best to fresher conditions, but species varied in tolerance for elevated salinity. The negative effect of salinity was also apparent in growth rates of seedlings transplanted to the field, even for

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