Effects of watershed and riparian zone characteristics on nutrient concentrations in the River Scheldt Basin

Abstract

Abstract. The relative influence of a set of watershed characteristics on surface water nutrient concentrations was examined in 173 watersheds within two subcatchments (UpperScheldt and Nete) of the River Scheldt Basin (Flanders, Belgium). Each watershed was described by seasonal rainfall, discharge loading of point sources, morphological characteristics (area, average slope, drainage density, elongation), land use and soil properties (soil texture and drainage). Partial regression analysis revealed that soil drainage variables had the strongest influence on nutrient concentrations. Additional influence was exerted by land use and point source loading variables. Nitrate concentrations were positively correlated with effluent loadings coming from wastewater treatment plants and with the area of agricultural land. Phosphate concentrations were best explained by effluent loadings of industrial point sources and by the area of urban land. Land use close to the river was not a better predictor of nitrate and phosphate concentrations than land use away from the river. This suggests that the mediating impact of riparian zones is rather explained by the hydrologic pathways within the buffer strip.

Effects of Catchment and Riparian Landscape Setting on Water Chemistry and Seasonal Evolution of Water Quality in the Upper Han River Basin, China

“…Our results indicated that low catchment slope (<15°) and major element interactions were consistent with commonly observed pattern of their positive associations while those in the catchment with high slope (>15°) were somehow contradictory (Table 4). Though the negative correlations between base cations and alkalinity and steep slopes in unvegetated terrain were reported [16], [29], while Meynendonckx et al [15] concluded that there was no direct explanation for the negative associations. Thus, the slope influences on water chemistry were varying.…”

“…Compared to the rainy season, fewer variables had significant associations with land use within the entire catchment in the dry season, which was primarily contributable to anthropogenic inputs especially the point sources. Whereas, variables were strongly more associated with land use along rivers such as 100 m [23], 200 m and 500 m in the dry season (Table 3), suggesting that precipitation within the buffer zone had much higher explanative values to elements and hydrological pathways greatly mediated major element compositions [15].…”

“…It was established that watershed physical characteristics such as soil properties (soil texture and soil drainage), morphological variables (drainage density and elongation) [10],[13],[14],[15],[17],[30], particularly the surficial debris remarkably influenced water chemistry in river waters [16],[29], we therefore ascribed the abnormal interactions to their multicollinearity. Also, hydrological regime and the proportion of vegetation might be another important factor impacting their correlations [14],[15],[31]. This was confirmed by increasing proportion of vegetation coverage in its respective gradient as slope increases (Table 1), which primarily resulted in their negative relationships (Table 4).…”

“…Numerous studies have related landscape to water quality especially nutrients using empirical techniques such as correlation analysis and stepwise multiple linear regression models [7], [12]–[15], and indicated that basin physical characteristics such as land use types, morphological characteristics and local geology substantially influence the hydrology and water variables, and consequently mediate fluvial chemical compositions [10], [16], [17]. Their relative impacts on water chemistry depend on geographical scale (e.g., local, regional, national, continental and global) and sampling factors (e.g., random versus geostatistical; high versus low density).…”

Upstream to downstream: a multiple-assessment-point approach for targeting non-point-source priority management areas at large watershed scale

“…However, the nature of the interactions among those multiple river points still remains poorly understood. The relationship between the upstream and downstream assessment points has yet to be developed for those large-scale watersheds (Horton, 1945;Kang et al, 2008;Meynendonckx et al, 2006;Rodriguez-Iturbe and Rinaldo, 1997).…”