Novel predictors related to hysteresis and baseflow improve predictions of watershed nutrient loads: An example from Ontario's lower Great Lakes basin

• Published in: The Science of the total environment 2022-06, Vol.826, p.154023-154023, Article 154023
• Main Authors: Biagi, K.M., Ross, C.A., Oswald, C.J., Sorichetti, R.J., Thomas, J.L., Wellen, C.C.
• Format: Article
• Language: English
• Subjects: Agricultural watersheds; atmospheric precipitation; base flow; basins; environment; Environmental Monitoring - methods; eutrophication; hydrograph; Hysteresis; Lakes; Lower Great Lakes; model validation; Nitrate; nitrates; Nutrient loads; nutrient management; Nutrients; Ontario; Phosphorus - analysis; regression analysis; Rivers; subsurface flow; Total phosphorus; turbidity; Water Quality; water quantity; watersheds
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.154023

Eutrophication has re-emerged in the lower Great Lakes basin resulting in critical water quality issues. Models that accurately predict nutrient loading from streams are needed to inform appropriate nutrient management decisions. Generalized additive models (GAMs) that use surrogate data from sensors to predict nutrient loads offer an alternative to commonly applied linear regression and may better handle relationship non-linearities and skewed water quality data. Five years (2015–2020) of water quantity and quality data from 11 agricultural watersheds in southern Ontario were used to develop GAMs to predict total phosphorus (TP) and nitrate (NO3−) loads. This study aimed to 1) use GAMs to predict nutrient loads using both common and novel predictors and 2) quantify and examine the variability in seasonal and annual nutrient loads. Along with routine surrogate model predictors (i.e., flow, turbidity, and seasonality), the addition of the baseflow proportion and the hydrograph position of flow observations improved model performance. Conversely, including the antecedent precipitation index minimally affected model performance, regardless of constituent. Seasonal and annual patterns in TP and NO3− load predictions mirrored that of the hydrologic regime. This study showed that parsimonious GAMs featuring novel model predictors can be used to predict nutrient loads while accounting for the partitioning of surface and subsurface flow paths and hysteresis between streamflow and water quality parameters that are frequently observed in a wide range of environments. Conceptual flow chart outlining the selection process for identifying the most favoured model from the 16 generalized additive models configurations evaluated in this study. Competing models include combinations of routine and novel predictors. [Display omitted] •Incorporating baseflow proportion & hydrograph position improved model performance.•Generalized additive models aptly handle nonlinearities and seasonality.•The hydrograph position predictor efficiently accounts for hysteresis.•Generalized additive models facilitate evaluations of predictor effects on nutrient loads.•Spring and winter had the largest nutrient fluxes.