| Title: | Modeling pesticide and sediment transport in the Malewa River Basin (Kenya) using SWAT |
| Authors: | Abbasi, Y., C.M. Mannaerts and W. Makau |
| Year: | 2019 |
| Journal: | Water |
| Volume (Issue): | 11 |
| Pages: | |
| Article ID: | 87 |
| DOI: | 10.3390/w11010087 |
| URL (non-DOI journals): | |
| Model: | SWAT |
| Broad Application Category: | hydrologic and pollutant |
| Primary Application Category: | sediment loss and transport |
| Secondary Application Category: | pesticide, antibiotic and/or PFAS fate and transport |
| Watershed Description: | 1,600 km^2 Malewa River, which drains to Lake Naivasha in southeast Kenya. |
| Calibration Summary: | |
| Validation Summary: | |
| General Comments: | |
| Abstract: | Understanding the dynamics of pesticide transport in the Malewa River and Lake Naivasha,
a major fresh water resource, is critical to safeguard water quality in the basin. In this study, the soil
and water assessment tool (SWAT) model was used to simulate the discharge of sediment and
pesticides (notably the organochlorine residues of lindane, methoxychlor and endosulfan) into the
Malewa River Basin. Model sensitivity analysis, calibration and validation were performed for both
daily and monthly time steps using the sequential uncertainty fitting version 2 (SUFI-2) algorithm
of the SWAT-CUP tool. Water level gauge data as well as a digital turbidity sensor (DTS-12) for
suspended sediment transport were used for the SWAT calibration. Pesticide residues were measured
at Upper and Down Malewa locations using a passive sampling technique and their quantity was
determined using laboratory gas chromatography. The sensitivity analysis results showed that curve
number (CN2), universal soil loss equation erodibility factor (USLE-K) and pesticide application
efficiency (AP_EF) formed the most sensitive parameters for discharge, sediment and pesticide
simulations, respectively. In addition, SWAT model calibration and validation showed better results
for monthly discharge simulations than for daily discharge simulations. Similarly, the results obtained
for the monthly sediment calibration demonstrated more match between measured and simulated
data as compared to the simulation at daily steps. Comparison between the simulated and measured
pesticide concentrations at upper Malewa and down Malewa locations demonstrated that although
the model mostly overestimated pesticide loadings, there was a positive association between the
pesticide measurements and the simulations. Higher concentrations of pesticides were found between
May and mid-July. The similarity between measured and simulated pesticides shows the potential
of the SWAT model as initial evaluation modelling tool for upstream to downstream suspended
sediment and pesticide transport in catchments. |
| Language: | English |
| Keywords: | SWAT; hydrologic simulation; pesticide residues; passive sampling; sediment; Malewa River |