Past vegetation, invasive species expansion, climate variability, and human impacts on mid-Hudson estuarine marshes

Funded by the Hudson River National Estuarine Research Reserve and New York Sea Grant graduate fellowship, a part of my dissertation involves paleoecological/paleoenvironmental reconstruction of Hudson estuarine marshes to answer the following questions:

1) How much has climate change and human impact altered these important wetland and riparian ecosystems?

2) What can we expect from changes in the future? How will the ecosystems respond to expected sea level rise, climate change, and human disturbances?

3) How does this information impact our thoughts about preservation or restoration of these ecosystems? How should we restore these wetlands into? What was it like before major human disturbances? Will that be sustainable in the future?

Where?

Two major paleoecological study sites are Tivoli North Bay, Red Hook, NY and Stockport Flats, Stockport, NY. Recently, members in our lab have also conducted various paleoenvironmental studies at several Hudson River sites, including Piermont Marsh (Pederson et al., 2005), Iona Island (Peteet et al., 2006; Cleo Chou, 2009/Polgar fellow; Khoi Nguyen, 2010/Polgar Fellow), and Constitution Marsh (Sriya Sanderson/Columbia senior thesis).

How?

I use multiproxy analysis, including palynology, macrofossil analysis, C & N isotopic analysis, elemental analysis, radiometric methods, and other geochemical analyses to infer past vegetation, carbon and nutrient dynamics, sediment dynamics and landscape change, sedimentation rates, and chronologies.

Fig. 1: A comparison of the sum of percent pollen and spore of invasive and non-invasive wetlands species. Invasive species increases by up to 8 times the original concentration prior to the European Settlement. (Sritrairat et al., in prep)

Fig. 2: Wetland Vegetation Dynamics at Tivoli Bay (Sritrairat et al., in prep)

What did we find?

We found that during the past 1,000 years, anthropogenic alterations made the most significant impact on the watershed and the marshes. Native species, including ferns and sedges, are replaced by weedy and major invasive species, such as Typha angustifolia, Phragmites australis, and Lythrum salicaria during the past few centuries (Fig. 1&2). The trend is related with increase in nutrients and wastewater input and anoxia based on N isotope analysis and landscape changes, from deforestation, industrialization and human-induced landscape changes, which increases sedimentation rates in these marshes by 5-10 times the pre-European Settlement values (Fig.3). Though these wetlands maybe able to survive sea level rise because of high sedimentation rate, the high sedimentation rate may also dry these wetlands out, especially at Tivoli where we find significant increase in woody species during the recent century. The Medieval Warm Period with increased fire and the wet-and-cool Little Ice Age are observed at Tivoli, but ecosystem structure does not significantly change. Upland tree density significantly declined after the European Settlement in the 17^th century, but has recovered to similar species composition.

Fig. 3: Organic and inorganic fluxes into Stockport Flats, a freshwater tidal marsh of the Hudson

(Sritrairat et al., in prep)

Selected abstracts:

Environmental Changes of the Mid-Hudson Estuary in the Last Millennial

S. Sritrairat^{1, 3}; T. C. Kenna¹; D. M. Peteet^{1, 2}
1. Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, United States.
2. NASA Goddard Institute for Space Studies, New York, NY, United States.
3. Department of Earth and Environmental Sciences, Columbia University, New York, NY, United States.

The Hudson River serves many significant roles in the regional environment. It is important to understand how humans and climate have changed the ecosystems within such an important estuary. We use multiple proxies, including microfossils, to study the paleoecology and paleoclimate of two fresh tidal marshes -Tivoli North Bay (42º 02′N, 73º 55′W) and Stockport Flats (41º 19′N, 73º 47′W). These wetlands are two of four Hudson River National Estuarine Research Reserve (HRNERR) sites. Pollen, spores, macrofossils, charcoal, organic matter content, and radiometric chronologies at these sites reveal significant vegetation changes which reflect local and regional ecological and landscape alternation due to anthropogenic and climatic changes over the last 1000 years. European settlements are marked by a very abrupt shift in vegetation and sediment composition as a result of deforestation, invasive species introduction, land clearance, and infrastructure construction. Our data indicate that land use changes after European settlement significantly affected sedimentation patterns, resulting in the alteration of wetland hydrology and vegetative composition. At Tivoli, higher inorganic input appears to contribute to marsh composition changes from wetland herbaceous species to woody taxa throughout the most recent centuries. The structure of the upland forest slightly changed through time. After the 17th century, Betula dominates the forest in addition to Quercus and Pinus. Weedy and invasive species including Typha angustifolia, Phragmites australis, Ambrosia, Lythrum salicaria, Impatiens capensis, Chenopodiaceae and Gramineae drastically expand, replacing native ferns and sedges as human impact increases at both sites. At Stockport Flats, the area was not a marsh prior to the European settlement based on pollen, seeds, and LOI. At Tivoli, microscopic charcoal increases reflects drought during the Medieval Warm Interval which is recorded at other sites in the Northeast. We will present our data and discuss the relationship among human activities, ecosystem changes, and sedimentation pattern changes based on these microfossil records in comparison with other proxies.

Sritrairat, S. Peteet, D.M., and Kenna, T.C. Environmental Changes of the Mid-Hudson Estuary in the last Millennium. Geological Society of America, Northeast and Southeast Joint Meeting, 2010. Abstract 76-5