This QUEST project grew out of a collaboration between American and Japanese researchers when Ruth Yanai spent one month in Japan on a JSPS fellowship in June 2011. The three sites included in this analysis (Hubbard Brook, Coweeta, and Gomadan-san) are unique due to the replication of experimental watersheds within sites. This allows for a comparison of uncertainty in streamwater nutrient fluxes both within and between sites.
Sites and Participants:
Coweeta Hydrologic Laboratory and LTER (Otto, NC)
Hubbard Brook Experimental Forest and LTER (West Thornton, NH)
Carrie Rose Levine
Gomadan-san Experimental Forest, Totsukawa, Japan
Papers in Preparation:
A comparison of uncertainty in stream export of solutes from headwater catchments at Wakayama, Hubbard Brook and Coweeta Experimental Forests
Lead author: Ruth Yanai
In preparation for Hydrological Processes
Abtract: Uncertainty in estimation of hydrologic outputs of solutes in streamwater has never been fully evaluated at ecosystem scales. We used data from the Wakayama Experimental Forest, Japan; Hubbard Brook Experimental Forest, USA; and Coweeta Experimental Forest, USA to evaluate many sources of uncertainty, including measurements, spatial and temporal variation, and model selection error. Uncertainty in analysis of stream chemistry samples was generally small, but could be large in relative terms for solutes near detection limits, as for ammonium and phosphate at Hubbard Brook. Water fluxes deviated from the theoretical curve relating height to discharge by up to 10% at low flows at Hubbard Brook, but corrections to the theoretical curve amounted to only x% on an annual basis. Uncertainty at high flows has not been evaluated at these sites. Uncertainty in watershed area was x%, based on a comparison of digital elevation maps with ground surveys. Stream-to-stream variation in nutrient export was highest (x to x%) for solutes derived from mineral weathering (calcium, magnesium, postassium) and those affected by differences in vegetation type (hydrogen ions) and disturbance (nitrate). Year-to-year variation was due primarily to variation in annual stream flow. Uncertainty due to different methods of estimating stream chemistry between sampling dates was generally <x%, but for solutes with strong concentration-discharge relationships, simple models were biased by up to x% due to under-sampling of high-flow conditions. Uncertainty analysis can be used to guide efforts to improve confidence in estimated stream fluxes and also to optimize design of monitoring programs.