Back to Search
Start Over
Upstream Causes of Downstream Effects
- Publication Year :
- 2017
-
Abstract
- The United States Environmental Protection Agency considers nutrient pollution in stream ecosystems one of the U.S. most pressing environmental challenges. But limited independent replicates, lack of experimental randomization, and space- and time-varying confounding handicap causal inference on effects of nutrient pollution. In this paper the causal g-methods developed by Robins and colleagues are extended to allow for exposures to vary in time and space in order to assess the effects of nutrient pollution on chlorophyll a, a proxy for algal production. Publicly available data from the North Carolina Cape Fear River and a simulation study are used to show how causal effects of upstream nutrient concentrations on downstream chlorophyll a levels may be estimated from typical water quality monitoring data. Estimates obtained from the parametric g-formula, a marginal structural model, and a structural nested model indicate that chlorophyll a concentrations at Lock and Dam 1 were influenced by nitrate concentrations measured 86 to 109 km upstream, an area where four major industrial and municipal point sources discharge wastewater.
- Subjects :
- Statistics - Applications
Subjects
Details
- Database :
- arXiv
- Publication Type :
- Report
- Accession number :
- edsarx.1705.07926
- Document Type :
- Working Paper
- Full Text :
- https://doi.org/10.1080/01621459.2019.1574226