The Effects of an Invasive Tropical Grass, Pennisetum purpureum, on Stream Nutrient Dynamics and Nitrogen Export

EPA Grant Number: FP917328
Title: The Effects of an Invasive Tropical Grass, Pennisetum purpureum, on Stream Nutrient Dynamics and Nitrogen Export
Investigators: Fraiola, Kauaoa
Institution: University of California - Berkeley , Ernest Orlando Lawrence Berkeley National Lab
EPA Project Officer: Lee, Sonja
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Ecosystem Services: Aquatic Systems Ecology


Stream and river ecosystems provide society with many ecosystem services, one of which is the uptake of nutrients from the water column, which helps to buffer coastal ecosystems from nutrient pollution. Given the knowledge that plants (vascular and non-vascular) can significantly impact the nutrient processes of streams, it is important to understand the impacts of invasive plant species on stream processes. This project will investigate the effects of a widespread invasive grass, Pennistum purpureum (Elephant Grass) on the downstream export of nitrogen and stream food webs.


A combination of a large-scale field manipulation and stable isotopic measurements in a Hawaiian stream will be used to investigate the effect that Elephant Grass has on nutrient dynamics and stream food webs. Measurements of nitrogen uptake/export and benthic primary productivity will be made using short-term nitrogen additions, routine water samples, upstream-downstream changes in dissolved oxygen and colonization tiles. These measurements will be taken before and after the manipulation, in both the control and manipulation stream sections. The role of Elephant Grass in stream food webs will be determined using C and N stable isotopes and a mixing model. Stable isotope measurements will be made using samples of stream biotic community and their potential food resources (detritus and algae) before the manipulation.

Expected Results:

The results of this research are expected to increase knowledge of how Elephant Grass affects nitrogen uptake and export to downstream ecosystems, as well as its contribution as a basal food resource to stream food webs. These results will help resource managers better weigh the cost and benefits of Elephant Grass, which will in turn help them make more well-informed management decisions. The large-scale and manipulative nature of the study design also strengthens the inferences that can be made and the confidence through which results can be applied to management decisions. Lastly, in many tropical areas around the world, scientific understanding lags in comparison to those in temperate zones. This study also will help to increase understanding of nutrient dynamics in tropical streams and provide data on which future hypotheses might be built.

Potential to Further Environmental/ Human Health Protection

This research may have the potential to further environmental protection in that it will help the understanding of how an invasive semi-aquatic plant species influences nutrient loading to coastal ecosystems. Findings from this research may spur more research into how invasive species impact this valuable ecosystem service, an understanding that is sorely lacking and lags behind the understanding of the effects of other anthropogenic impacts such as deforestation, wastewater and channelization. Understanding the broad impacts that invasive species, like Elephant Grass, have on the environment will help resource managers make well-informed decisions in the face of multiple stressors and multiple uses.

Supplemental Keywords:

Pennistum purpureum, Elephant Grass, invasive species, nitrogen, nutrient dynamics, nutrient pollution, water, tropical streams,

Progress and Final Reports:

  • 2012
  • 2013
  • Final