Effects of Stream Phosphorus Loading on Nutrient Export Pathways

EPA Grant Number: F07E10864
Title: Effects of Stream Phosphorus Loading on Nutrient Export Pathways
Investigators: Small IV, Gaston Elvin
Institution: University of Georgia
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2007 through January 1, 2010
RFA: STAR Graduate Fellowships (2007) RFA Text |  Recipients Lists
Research Category: Aquatic Ecology and Ecosystems , Fellowship - Aquatic Biogeochemistry , Academic Fellowships


Nutrient pollution is one of the most significant threats to freshwater ecosystems. Extensive research has gone into understanding the capacity of streams to remove nutrients; however, the emergence of aquatic insects into terrestrial ecosystems has rarely been considered in stream nutrient budgets. Furthermore, phosphorus (P) availability has been shown to control growth rates of aquatic insects in freshwater ecosystems, so phosphorus-loading in streams has the potential to control rates of nitrogen (N) and P export through insect emergence. The aim this study is to quantify the flux of nutrients in emerging aquatic insects relative to other nutrient fluxes (e.g. microbial denitrification) in tropical headwater streams at La Selva Biological Station, Costa Rica. These streams vary widely in dissolved P (2-200 μg/L soluble reactive phosphorus) due to differential inputs of solute-rich groundwater. The effects of stream P on the export of N and P through emerging insect biomass will be measured along this natural P gradient.


Emerging insects will be sampled using emergence traps placed along eight streams which vary widely in dissolved P during the wet season and dry season. Emergence samples will be collected intensively for one month during the dry season and wet season each year, and monthly samples will be collected in a subset of these streams throughout the year to understand seasonal dynamics. Insects will be sorted to family level, dried, weighed, and analyzed for carbon, nitrogen, and phosphorus content. Denitrification potential will be measured at these eight sites using the acetylene-block technique to estimate maximum levels of denitrification, so that microbial N-export can be compared to N-export through emerging insects along this P-gradient.

Expected Results:

The flux of N and P exported through insect emergence is expected to increase with increasing P availability due to increased insect production in P-rich streams. Preliminary results suggest that nutrient export through emerging insects is a significant component of the nutrient budget of small tropical streams.

Supplemental Keywords:

phosphorus, insect emergence, ecological stoichiometry, aquatic-terrestrial exchange,

Progress and Final Reports:

  • 2007
  • 2008
  • Final