Multiscale Landscape Pattern Affecting on Stream Water Quality in Agricultural Watershed, SW Finland

摘要

Finnish arable land is typically located on flat areas, where the fields are mostly drained and sub-drained to control the water tables. These areas are highly susceptible to nutrient loss, which affects the water quality of rivers and lakes. Therefore, it is very important to understand current landscape pattern and processes controlling water quality, not only identifying factors affecting it, but also identifying strategies and restoring areas for mitigation. We studied linkage of 21 years (1990–2011) of water quality (WQ) data from 16 agricultural watersheds, using landscape indices at three functional scales: watershed-wide, saturation-excess zone, and riparian zone (of varying widths). The hydro-biogeochemical functional areas of watershed were obtained by digital terrain analysis. Statistical analyses by generalized linear model and multivariate redundancy analysis indicated that the fraction of watershed in agricultural use was linked to most of the studied water quality variables. The relationships varied across the seasons: they were strongest during high flow periods (spring and autumn) when also highest nutrient losses occur. Total suspended sediment concentrations were linked to critical source areas. Riparian vegetation index was important explaining nitrate concentrations in autumn. Terrain-based mapping of hydro-biogeochemical functional areas provides a rapid identification of potential sites to mitigate diffuse nutrient pollution, particularly in riparian zones.