Grantee Research Project Results

2010 Progress Report: Elevated Temperature and Land Use Flood Frequency Alteration Effects on Rates of Invasive and Native Species Interactions in Freshwater Floodplain Wetlands

EPA Grant Number: R833837
Title: Elevated Temperature and Land Use Flood Frequency Alteration Effects on Rates of Invasive and Native Species Interactions in Freshwater Floodplain Wetlands
Investigators: Richardson, Curtis J. , Qian, Song S. , Ho, Mengchi , Flanagan, Neal
Current Investigators: Richardson, Curtis J. , Flanagan, Neal , Ho, Mengchi
Institution: Duke University , Nicholas School of the Environment and Earth Sciences
EPA Project Officer: Packard, Benjamin H
Project Period: April 1, 2008 through March 31, 2011 (Extended to March 31, 2012)
Project Period Covered by this Report: April 1, 2010 through March 31,2011
Project Amount: $598,107
RFA: Ecological Impacts from the Interactions of Climate Change, Land Use Change and Invasive Species: A Joint Research Solicitation - EPA, USDA (2007) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Aquatic Ecosystems , Climate Change

Objective:

The primary objective is to assess how predicted climate and land use driven changes in hydrologic flux and temperature regimes of floodplain ecosystems affect plant communities in terms of their vulnerability to the establishment and spread of invasive species, and in turn ecosystem functions and services. Future climate scenarios for the southeastern United States predict that surface water temperatures will warm (in concert with air temperature) and that stream flows likely will decrease, with a greater proportion of annual watershed hydrologic yield occurring during major storm events. Land use changes (urban vs. forested, etc.) have been shown also to raise water temperature and increase pulsed water releases during storms.

Progress Summary:

Regional floodplain hydrology and temperature shifts experiments:

We have identified nine synoptic sites located on river flood plains throughout North Carolina and southern Virginia (Roanoke River Basin). These sites are in three categories of water temperature: a) Warm: three sites are located downstream of reservoirs used as flood storage and cooling water supplies for coal-fired or nuclear power plants where regulated outflow is drawn from warmer surface water layers of the reservoir (Cowan’s Ford, Kerr and Gaston Dams); b) Cold: three sites are located downstream of hydroelectric plants where regulated outflow is drawn from deeper (cooler) strata nearer the lake bottom (Catawba, Smith Mountain, and Philpott Dam [VA]); and c) Reference: three sites are located on rivers with no dams and have normal regional water temperatures and rainfall patterns of water flow rates.

Floodwaters in the first group of sites are significantly warmer than those from the second group by >5°C. For example, during most summer periods, the water temperatures released from the sites in the cold treatment (Smith Mountain Lake, Philpot Dam, Catawba Dam) plant are less than 20ºC, while summertime water temperatures at warm treatment sites exceed 25ºC. We use differences in temperature and hydroperiod (flood storage dams versus hydroelectric dams) to examine the effects of temperature and flood frequency on floodplain riparian plant communities and ecosystem functions, with an emphasis on the effects of warmer water on invasive species and plant community shifts. Soil temperatures are being used to calculate accumulated soil growing degree days (SGDD) that are being used to compare the thermal balances between warm and cold riparian sites. These results showed significant (P < 0.05) differences in the soil heat accumulation within the sites with substantial differences in the heat accumulation at our cold, warm and reference sites (640, 1050 and 1380 SGDD, respectively). Species richness was highest at the warm treatment sites, intermediate at the reference sites and lowest at the cold sites. The degree of invasion was highest in our cold treatment, moderate in the reference treatment, and lowest in warm treatment. There was little difference in the degree of invasion between the Riparian and Emergent zones.

To explain these trends, we used several statistical approaches to evaluate relationships between plant community data and environmental variables monitored at our sites. Random Forest models were used to examine the strength of the relationship between a single site specific measure of alpha diversity and a suite of environmental (independent) variables to identify those with the greatest predictor importance at influencing model accuracy. The Random Forest model explained 51% of variance in species richness and 36% of variance in non-native stem density. Soil degree days by far were the most important environmental variable explaining invasive species while pulsed water and duration of hydrology were next in importance. As expected, duration of hydrology explained most of the species richness but the variation and frequency of hydrology were next in importance. SGDDs was next in importance in determining species richness. In summary, variables related to hydrology (flood duration, standard deviation of depth, flood frequency) were the most important factors explaining species richness, followed by SGDDs. Temperature (SGDD) was the most important predictor of degree of invasion followed by hydrology and exchangeable nitrogen. The most important hydrologic variable explaining degree of invasion was “pulse.” These findings have important ramifications if climate change increases the temperature and pulsing of river waters as predicted by the Intergovernmental Panel on Climate Change (IPCC) reports.

Future Activities:

We will continue data collection using our established protocols and applying adaptive management approaches as required. Due to the late funding date for this project, we have asked for and received a 1-year no-cost extension. In year four, we will present the final results at national meetings and prepare manuscripts for submission to peer-reviewed scientific journals.

Journal Articles:

No journal articles submitted with this report: View all 9 publications for this project

Supplemental Keywords:

wetlands, watershed, land use, climate change, invasive species, temperature shifts, pulsed water, water quality, altered stable states, nonlinear thresholds, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, climate change, Air Pollution Effects, Monitoring/Modeling, Regional/Scaling, Environmental Monitoring, Atmospheric Sciences, Ecological Risk Assessment, Atmosphere, coastal ecosystem, biodiversity, environmental measurement, ecosystem assessment, meteorology, global change, anthropogenic, climate models, UV radiation, greenhouse gases, environmental stress, coastal ecosystems, water quality, habitat diversity, invasive species, ecological models, climate model, Global Climate Change, land use, regional anthropogenic stresses, atmospheric chemistry, stressor response model, climate variability

Relevant Websites:

Duke University Wetland Center website www.env.duke.edu/wetland Exit .

Progress and Final Reports:

Original Abstract

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.