Landscape diversity and forest edge density regulate stream water quality in agricultural catchments. (January 2017)

• Record Type: Journal Article
• Authors: Clément, Francis; Ruiz, Julie; Rodríguez, Marco A.; Blais, Daniel; Campeau, Stéphane
• Is Part Of: Ecological indicators. Volume 72(2017)
• Page Start: 627
• Page End: 639
• Publication Date: 2017-01
• Subjects: Landscape configuration -- Landscape metrics -- Land cover -- Water quality -- Diatoms -- Watershed management -- Biotic index; Environmental monitoring -- Periodicals; Environmental management -- Periodicals; Environmental impact analysis -- Periodicals; Environmental risk assessment -- Periodicals; Sustainable development -- Periodicals; 333.71405
• DOI: 10.1016/j.ecolind.2016.09.001
• Languages: English
• ISSNs: 1470-160X

Abstract

Highlights: Landscape configuration accounted for 48% of the total variation in water quality. The individual contribution of landscape configuration factors was 6.2%. A forest cover >47% is required to prevent the eutrophication of Canadian streams. In areas of intensive farming, high landscape diversity improves water quality. Woodlands with a complex shape (edge density >36 m/ha) benefit water quality. Abstract: It is well known that the composition of land cover within a watershed plays a large role in regulating stream water quality. However, there remains significant uncertainty regarding the effect of spatial configuration of different types of land cover on water quality. Using periphytic algae (diatoms) as indicators of stream trophic state, we investigated the relationship between landscape configuration and water quality in a large number of watersheds (590) at varying catchment scales in Eastern Canada. Variation partitioning analysis showed that landscape configuration explained 48% of the variation in water quality. However, since the physiographic setting constrains most agricultural activities, most of the variation was attributed to the shared influence of surficial deposits, land cover and landscape configuration (34%). The results from regression models showed that the geomorphological setting of watersheds (surficial deposits and slopes) and the proportion of different land cover types (mainly forests, wetlands, crops and urban areas) have a major impact on stream water quality. Nevertheless, a few configuration metrics emerged as important factors. Landscape diversity appeared to have a negative impact on water quality, whereas forest and wetland edge densities had a positive impact. Moreover, the influence of these lanscape metrics seems to occur at certain thresholds. In areas of intensive farming, streams with a forest area that covers at least 47% of the watershed have a better water quality. Below this threshold, eutrophic and meso-eutrophic conditions are more frequent in streams and rivers. The shape and location of forested patches were also found to be relevant. Woodlands and wetlands with an edge density higher than 36 m/ha and located along streams and gullies have a positive impact on water quality. For the same proportion of forest, complex patches will be more efficient filters than large regular patches. Forest edge density seems to control the extent of the interface with the agricultural sources and thus promotes the "sink" effect of forests on nutrients.