Using the Soil and Water Assessment Tool to Simulate the Pesticide Dynamics in the Data Scarce Guayas River Basin, Ecuador

Abstract

Agricultural intensification has stimulated the economy in the Guayas River basin in Ecuador, but also affected several ecosystems. The increased use of pesticides poses a serious threat to the freshwater ecosystem, which urgently calls for an improved knowledge about the impact of pesticide practices in this study area. Several studies have shown that models can be appropriate tools to simulate pesticide dynamics in order to obtain this knowledge. This study tested the suitability of the Soil and Water Assessment Tool (SWAT) to simulate the dynamics of two different pesticides in the data scarce Guayas River basin. First, we set up, calibrated and validated the model using the streamflow data. Subsequently, we set up the model for the simulation of the selected pesticides (i.e., pendimethalin and fenpropimorph). While the hydrology was represented soundly by the model considering the data scare conditions, the simulation of the pesticides should be taken with care due to uncertainties behind essential drivers, e.g., application rates. Among the insights obtained from the pesticide simulations are the identification of critical zones for prioritisation, the dominant areas of pesticide sources and the impact of the different land uses. SWAT has been evaluated to be a suitable tool to investigate the impact of pesticide use under data scarcity in the Guayas River basin. The strengths of SWAT are its semi-distributed structure, availability of extensive online documentation, internal pesticide databases and user support while the limitations are high data requirements, time-intensive model development and challenging streamflow calibration. The results can also be helpful to design future water quality monitoring strategies. However, for future studies, we highly recommend extended monitoring of pesticide concentrations and sediment loads. Moreover, to substantially improve the model performance, the availability of better input data is needed such as higher resolution soil maps, more accurate pesticide application rate and actual land management programs. Provided that key suggestions for further improvement are considered, the model is valuable for applications in river ecosystem management of the Guayas River basin.

Small Patches of Riparian Woody Vegetation Enhance Biodiversity of Invertebrates

“…Multiple pressures threaten European stream ecosystems [1][2][3][4]. These pressures result from various human activities, such as modifications of river morphology [5][6][7] and hydrology [6,8,9], intensive agriculture [10][11][12][13][14], urbanization [13,15,16] and mining [17][18][19]. Together, these activities often lead to the degradation of stream ecosystems, reducing biodiversity, water security and ecosystem services [4,20].…”

Response of Variation of Water and Sediment to Landscape Pattern in the Dapoling Watershed

“…The SWAT model with a strong physical foundation is mainly used to simulate soil erosion [26,27], non-point source pollution [28,29], agricultural management measures [30,31], etc. Suitable for watersheds with different land use types [32], soil types [33] and topographic conditions [34], it can simulate areas with insufficient data, thus meeting the data richness requirements of traditional hydrological models and satisfying the requirements of simulation accuracy [35,36]. Many investigations are available which have analyzed the effects of land use change on runoff and sediment process simulation by the SWAT model [37][38][39][40][41].…”

“…Gassman et al pointed out that, one area of future research in the SWAT model is more realistic simulation of landscape transport processes [46]. SWAT-VRR (SWAT model with vegetation runoff regulation enhanced) is a distributed hydrological model, modified based on the SWAT model to better show the effect of land use landscape change on hydrological processes in the watershed [35]. It considers the change in the CN value of the land use type with different slopes and flow routing process by forest in different slope zones, thus depicting hydrological characteristics of the study area more accurately [47].…”

Modeling Impact of Climate Change on Surface Water Availability Using SWAT Model in a Semi-Arid Basin: Case of El Kalb River, Lebanon

“…Conceptual and physically based models to assess the impact of climate change on water resources have been used [5]. The Soil and Water Assessment Tool (SWAT), a physically based model, has been used for streamflow prediction [6][7][8][9][10][11]. SWAT is used to address watershed management questions by predicting the effects of changes in soil, land use, and climate on water quantity and quality [12].…”