RAPID: Plant Species Effects on Rapid Stabilization of Nitrogen in Soil Organic Matter of Mangrove Ecosystems at Risk from the BP Deepwater Horizon Oil Spill

University Of South Florida, Tampa FL

Investigators

Abstract

This is a Rapid Research Response grant in relation to the BP Deepwater Horizon oil spill. Nitrogen (N) is an essential element for life. Because it is scarce in a biologically usable form, organisms are sensitive to increases in N availability. Human activities have increased the cycling of N in the biosphere, galvanizing interest in the ability of ecosystems to retain N. Nitrogen is effectively stored by the decaying remnants of vegetation, animals, and microorganisms - collectively known as soil organic matter, or SOM. The research described here investigates whether SOM can immobilize N quickly - within minutes to weeks - after N is first introduced to the soil. This research will test the hypotheses (1) that SOM quickly immobilizes N in the stable fraction, which is the subset of SOM that takes years to decompose, and (2) whether immobilization happens at different rates in different forests, which have different kinds of SOM. This research is conducted in intertidal, mangrove forests along the coast of west-central Florida near Tampa Bay, which are at risk for exposure to oil deposition from the BP Deepwater Horizon oil spill. In each forest, investigators will collect soil cores that are 15 cm deep, and inject N as a bio-available form into the cores. After a measured reaction time (hours to weeks), the amount of N incorporated into the stable SOM will be determined. This will allow scientists to calculate the rate at which N gets immobilized in stable SOM. One goal of this project is to determine whether N immobilization in stable SOM differs among forests, so the characteristics of each forest will be described in two ways: with ground surveys and with remote sensing from satellites. The ground surveys will be conducted following standard procedures of the U.S. Forest Service: identifying the species of each tree, measuring several dimensions of tree size (height, girth, canopy cover), identifying trees that have died or newly germinated, and analyzing the chemistry of leaf tissues. The remote sensing will use multispectral and hyperspectral imaging. Spectral signatures, which are the combinations of reflected and absorbed light across the light spectrum, will reveal tree size and the amount and chemistry of foliage. The hypotheses of this project will be supported if scientists discover that N is, indeed, quickly immobilized in stable SOM, and that the rate of N immobilization differs among forests because of difference in the forest characteristics. As oil moves beyond the northern Gulf, it may put Florida Peninsula's western coastline at risk. Oil can affect the functioning of these mangrove ecosystems and alter the interaction between N and SOM in several ways. Not only is oil toxic to plants and soil organisms, crude oil is a source of N and organic matter (hydrocarbons) in its own right, potentially upsetting the pre-existing balance. Understanding baseline conditions in the dynamics of N and SOM mandates that this research be conducted now. In roughly the last 80 years, food and energy production by humans have tripled the amount of biologically usable N circulating through the biosphere. The ecological consequences have been profound, including increases in atmospheric greenhouse gas and smog concentrations, shifts in the composition of forest plants, and conspicuous algal blooms and de-oxygenation in aquatic habitats like the Gulf of Mexico. This research directly elucidates a mechanism for preventing such adverse environmental effects of accelerated N cycling. Academic and public resource agencies will be brought in closer contact, as researchers from the University of South Florida and the University of Florida interact with park and property managers at the mangrove forest sites, and with Forest Service employees. The research also will afford graduate students and undergraduate protégés the opportunity to respond to the concerns of a diverse and engaged citizenry of a large urban area. Finally, the use of remote sensing in the project may lead to tools for rapidly quantifying the impacts of disturbance and targeting restoration effects across west-central Florida's vast and otherwise intractable mangrove forest inventory.