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- W4292304405 abstract "Nutrient dynamics play an essential role in aquatic ecosystems. Despite advances in sensor technology, nutrient concentrations are difficult and expensive to monitor in-situ and in real-time. Emerging data-driven methods may provide surrogate measures for nutrient concentrations. In this work, we use 4-years of water quality data with high-frequency (15-min) intervals acquired at 2 automatic stations in the German Danube River to train data-driven algorithms and build surrogate measures for nitrate ( <mml:math xmlns:mml=http://www.w3.org/1998/Math/MathML id=M1><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math> -N), ammonium ( <mml:math xmlns:mml=http://www.w3.org/1998/Math/MathML id=M2><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math> -N), and orthophosphate ( <mml:math xmlns:mml=http://www.w3.org/1998/Math/MathML id=M3><mml:msubsup><mml:mrow><mml:mtext>PO</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math> -P). Pre-processing of the data included removing outliers and filling missing values by linear interpolation. Multiple Linear Regression (MLR) and Random Forest (RF) are trained, cross-validated, and tested using dissolved oxygen (DO), temperature (Temp), conductivity (EC), pH, discharge rate (Q), and chlorophyll-a (Chl-a) as input futures. Additionally, we used time-series data to develop cyclical features to test improvements in the underlying relationship between data. This work presents a thorough description of the modeling workflow, including intermediate steps for feature engineering, feature selection, and hyperparameter optimization. In total, 12 surrogate models (2 algorithms * 3 constituents * 2 stations) are compared with R 2 and RMSE as error metrics. The results show that RF outperforms MLR when adding at least three predictors for all the surrogate models. The MLR models give R 2 -values for <mml:math xmlns:mml=http://www.w3.org/1998/Math/MathML id=M4><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math> -N 0.67 and 0.89, <mml:math xmlns:mml=http://www.w3.org/1998/Math/MathML id=M5><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math> -N 0.39 and 0.40, <mml:math xmlns:mml=http://www.w3.org/1998/Math/MathML id=M6><mml:msubsup><mml:mrow><mml:mtext>PO</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math> -P 0.34 and 0.54 of Pfelling station and Jochenstein station, respectively. RF models produce accurate predictions and low error performances for all the targets <mml:math xmlns:mml=http://www.w3.org/1998/Math/MathML id=M7><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math> -N ( R 2 = 0.99 and 0.99), <mml:math xmlns:mml=http://www.w3.org/1998/Math/MathML id=M8><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math> -N ( R 2 = 0.98 and 0.99), <mml:math xmlns:mml=http://www.w3.org/1998/Math/MathML id=M9><mml:msubsup><mml:mrow><mml:mtext>PO</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mn>3</mml:mn><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math> -P ( R 2 = 0.96 and 0.96). The percentage improvement of RMSE for RF compared to MLR in prediction nutrients ranges from 73 to 92%. This work demonstrates the usefulness of surrogate models using the RF algorithm when reproducing nutrient dynamics and serving as soft sensors for monitoring nutrient concentrations." @default.
- W4292304405 created "2022-08-19" @default.
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- W4292304405 date "2022-08-17" @default.
- W4292304405 modified "2023-09-26" @default.
- W4292304405 title "Predicting high-frequency nutrient dynamics in the Danube River with surrogate models using sensors and Random Forest" @default.
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