The direct and indirect effects of watershed land use and soil type on stream water metal concentrations

Abstract

Identifying the factors controlling stream water pollutants is challenged by the diversity of potential sources, pathways, and processes. This study tests the effects of watershed characteristics on stream water metal concentrations across environmental gradients. By using an extensive data set of 83 watersheds in southern Finland and structural equation modeling (SEM), the direct and indirect effects of land use and soil type on metal concentrations were explored. Both land use and soil type resulted in statistically significant direct effects on metals; for example, land use was found to control dissolved metal concentrations, whereas soil type had the strongest links for total metal concentrations. The consideration of indirect correlation further strengthened the effects of soil type up to 50%, thus suggesting the dominant role of soil across land use intensities. Moreover, the results indicate that modified landscapes mediate the effect of natural soil processes in controlling stream metal concentrations. This work highlights the benefits of structural equation model framework, as the underlying paths for water quality are more likely to be identified, compared to traditional regression methods. Thus, the implementation of SEM on water quality studies is highly encouraged.

Mineral and Anthropogenic Indicator Inorganics in Urban Stormwater and Snowmelt Runoff: Sources and Mobility Patterns

“…Taka et al (2016) expressed a similar idea for metal concentrations in streams but used different descriptions of causative factors: the watershed soil type and land use. In this connection, two groups of inorganics are of interest: those of primarily mineral origin and those serving as indicators of anthropogenic activities, such as trace metals.…”

“…From a general perspective, stormwater runoff can be described as a process occurring across the urban landscape and hence reflecting both the local geology and anthropogenic activities (Frost et al, 2015 ; Taka et al, 2017 ). Taka et al ( 2016 ) expressed a similar idea for metal concentrations in streams but used different descriptions of causative factors: the watershed soil type and land use. In this connection, two groups of inorganics are of interest: those of primarily mineral origin and those serving as indicators of anthropogenic activities, such as trace metals.…”

Direct and indirect effects of rainfall and vegetation coverage on runoff, soil loss, and nutrient loss in a semi‐humid climate

“…The structural equation model identifies the direct, indirect, and total effects of the influence of the independent variable on the dependent variable via statistical analysis. It has been used to solve complex environmental problems, while few studies have applied this method to soil nutrient loss (Chamizo et al, 2012; Rodríguez‐Caballero et al, 2013; Taka et al, 2016). In this sense, we assumed that: (1) There are thresholds for vegetation cover to control soil erosion and nutrient loss; (2) factors such as rainfall and vegetation cover jointly drive soil erosion and nutrient loss.…”

Direct and indirect effects of rainfall and vegetation coverage on runoff, soil loss, and nutrient loss

“…The structural equation model identifies the direct, indirect, and total effects of the influence of the independent variable on the dependent variable via statistical analysis. It has been used to solve complex environmental problems, while few studies have applied this method to soil nutrient loss (Chamizo, Cantón, Rodríguez-Caballero, Domingo, & Escudero, 2012;Rodríguez-Caballero, Cantón, Chamizo, Lázaro, & Escudero, 2013;Taka, Aalto, Virkanen, & Luoto, 2016). This study takes slope runoff under natural rainfall events as the research object, quantifies the impact of vegetation on runoff sediment and nutrient loss through a large number of monitoring data, and uses the structural equation model to quantitatively analyze the direct and indirect impacts of various factors on slope runoff and erosion.…”