Robust Empirical Modeling of Chlorophyll-a in Streams and Rivers: Scaling by a Single Reference Observation
Abstract
Chlorophyll-a (Chl-a) is an important indicator of stream water quality and ecosystem health. Chl-a typically follows a diurnal pattern due to the variation in solar radiation and water temperature. We developed a scaling-based empirical model to robustly predict the diurnal cycles of stream Chl-a using a single reference observation as the scaling parameter. The scaling tranformed different Chl-a cycles — representing different days and streams — into a single dimensionless cycle, which was parameterized by using an extended stochastic harmonic algorithm (ESHA). Hourly Chl-a observations of growing season (May-October) from 26 USGS water quality monitoring stations were used for model parameter estimations, calibrations, and validations. The selected study sites represent a considerable gradient in land use (rural vs. urban vs. forest) and catchment size, encompassing different USEPA level I ecoregions. The modeling involved five parameters that demonstrated spatiotemporal robustness across the growing season days and streams. Chl-a predicted using the site-specific (temporal averages) and generalized (spatiotemporal averages across sites) ensemble parameter sets showed good model fitting efficiency and accuracy (Nash-Sutcliffe Efficiency =0.49-0.95 ). The model robustness was further demonstrated by relatively small parameter sensitivity and uncertainty measures. The developed model can robustly predict the diurnal cycles of hourly Chl-a from the corresponding single (or a set of limited) reference observations. The model is, therefore, a useful tool to dynamically assess stream water quality and ecosystem health across the continental U.S. and beyond.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.H53E1497S
- Keywords:
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- 1847 Modeling;
- HYDROLOGY;
- 1871 Surface water quality;
- HYDROLOGY;
- 1879 Watershed;
- HYDROLOGY;
- 1880 Water management;
- HYDROLOGY