Abstract
Abstract. A data mining, regression tree algorithm M5 was used to review the role of mutual hydrological and seasonal settings which control the streamwater nitrate flushing during hydrological events within a forested watershed in the southwestern part of Slovenia, characterized by distinctive flushing, almost torrential hydrological regime. The basis for the research was an extensive dataset of continuous, high frequency measurements of seasonal meteorological conditions, watershed hydrological responses and streamwater nitrate concentrations. The dataset contained 16 recorded hydrographs occurring in different seasonal and hydrological conditions. Based on predefined regression tree pruning criteria, a comprehensible regression tree model was obtained in the sense of the domain knowledge, which was able to adequately describe most of the streamwater nitrate concentration variations (RMSE=1.02 mg/l-N; r=0.91). The attributes which were found to be the most descriptive in the sense of streamwater nitrate concentrations were the antecedent precipitation index (API) and air temperatures in the preceding periods. The model was most successful in describing streamwater concentrations in the range 1–4 mg/l-N, covering large proportion of the dataset. The model performance was little worse in the periods of high streamwater nitrate concentration peaks during the summer hydrographs (up to 7 mg/l-N) but poor during the autumn hydrograph (up to 14 mg/l-N) related to highly variable hydrological conditions, which would require a less robust regression tree model based on the extended dataset.
Highlights
In recent years, the export of nitrogen from forested watersheds has become an important research area and a public policy issue since nitrogen leaching can strip nutrients from forest soils, acidify streams and cause eutrophication (Vitousek et al, 1997; Fenn et al, 1998; Lovett et al, 2002; Wade et al, 2004; Fitzhugh et al, 2003)
A data mining, regression tree algorithm M5 was used to review the role of mutual hydrological and seasonal settings which control the streamwater nitrate flushing during hydrological events within a forested watershed in the southwestern part of Slovenia, characterized by distinctive flushing, almost torrential hydrological regime
The model performance was little worse in the periods of high streamwater nitrate concentration peaks during the summer hydrographs but poor during the autumn hydrograph related to highly variable hydrological conditions, which would require a less robust regression tree model based on the extended dataset
Summary
The export of nitrogen from forested watersheds has become an important research area and a public policy issue since nitrogen leaching can strip nutrients from forest soils, acidify streams and cause eutrophication (Vitousek et al, 1997; Fenn et al, 1998; Lovett et al, 2002; Wade et al, 2004; Fitzhugh et al, 2003). Accumulation of labile dissolved inorganic nitrogen in excess of physical and biological retention capacity tends to occur (Likens and Boremann, 1995; Cirmo and McDonnell, 1997; Lovett et al, 2002; Vanderbilt et al, 2003). Both autumn and spring streamwater nitrate pulses are usually observed, with autumn increases in the nitrate concentration associated with a greater amount of precipitation and diminished biological assimilation, whereas spring pulses are reported mainly from watersheds with snowmelt driven hydrology
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