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Continental-scale increase in stream and lake phosphorus: Are oligotrophic systems disappearing in the U.S.?
Citation:
Stoddard, J., J. Van Sickle, A. Herlihy, J. Brahney, Steve Paulsen, D. Peck, R. Mitchell, AND A. Pollard. Continental-scale increase in stream and lake phosphorus: Are oligotrophic systems disappearing in the U.S.? ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 50(7):3409-3415, (2016).
Impact/Purpose:
Phosphorus has long been regarded as the most important nutrient controlling the eutrophication of freshwater lakes and streams. This paper describes widespread increases in stream and lake total phosphorus (TP) concentrations over the period 2000-2014 that were identified through periodic probability surveys of thousands of water bodies in the conterminous U.S. These data were collected as part of the National Aquatic Resource Survey (NARS) partnership between the Office of Water, ORD and the States/Tribes. The TP increases were most notable in relatively undeveloped catchments, which means that traditional mechanisms of accelerated TP delivery to aquatic habitats (runoff from agriculture, stormwater and wastewater) are unlikely drivers. We examine other possible drivers, such as changes in hydrology and atmospheric deposition, and conclude that increased atmospheric delivery of P to lakes and streams, especially through dust, is the only mechanism supported by the data and is worthy of further study.
Description:
Phosphorus (P) is one of two nutrients that most commonly limit the productivity of freshwater ecosystems. Widespread increases in stream and lake total phosphorus (TP) concentrations over the period 2000-2014 were identified through periodic probability surveys of thousands of water bodies in the conterminous U.S. The increases were most notable in sites where TP was initially low (e.g., less than 10 µg L-1); an analysis of sites with relatively undisturbed watersheds suggests median annual TP increases of +2.0 µg L-1 yr-1 for streams (2000 to 2014) and +1.7 µg L-1 yr-1 for lakes (2007 to 2012). Because increasing TP is observed in relatively undeveloped catchments, expected mechanisms of accelerated TP delivery to aquatic habitats, such as runoff from agriculture, stormwater and wastewater, are unlikely explanations for the observed increase over time. We examine other possible drivers, such as changes in hydrology and atmospheric deposition, and conclude that increased atmospheric delivery of P to these minimally-disturbed lakes and streams, especially through dust—an increasingly important but poorly studied source of P—is the mechanism best supported by the data and worthy of further study.
