Forest cover correlates with good biological water quality. Insights from a regional study (Wallonia, Belgium)

Abstract

Forested catchments are generally assumed to provide higher quality water in opposition to agricultural and urban catchments. However, this should be tested in various ecological contexts and through the study of multiple variables describing water quality. Indeed, interactions between ecological variables, multiple land use and land cover (LULC) types, and water quality variables render the relationship between forest cover and water quality highly complex. Furthermore, the question of the scale at which land use within stream catchments most influences stream water quality and ecosystem health remains only partially answered. This paper quantifies, at the regional scale and across five natural ecoregions of Wallonia (Belgium), the forest cover effect on biological water quality indices (based on diatoms and macroinvertebrates) at the riparian and catchment scales. Main results show that forest cover - considered alone - explains around one third of the biological water quality at the regional scale and from 15 to 70% depending on the ecoregion studied. Forest cover is systematically positively correlated with higher biological water quality. When removing spatial, local morphological variations, or population density effect, forest cover still accounts for over 10% of the total biological water quality variation. Partitioning variance shows that physico-chemical water quality is one of the main drivers of biological water quality and that anthropogenic pressures often explain an important part of it (shared or not with forest cover). The proportion of forest cover in each catchment at the regional scale and across all ecoregions but the Loam region is more positively correlated with high water quality than when considering the proportion of forest cover in the riparian zones only. This suggests that catchment-wide impacts and a fortiori catchment-wide protection measures are the main drivers of river ecological water quality. However, distinctive results from the agricultural and highly human impacted Loam region show that riparian forests are positively linked to water quality and should therefore be preserved.

Effects of Land Use on Stream Water Quality in the Rapidly Urbanized Areas: A Multiscale Analysis

“…The construction land area was an important factor to explain the change of TN concentration in stream waters ( Figure 6). Under the circular buffer scale, the industrial, commercial, road and urban greenspace land uses were the primary sources of nitrogen pollution, whilst the areas of forest, wetland and river had significant negative correlations with the TN, showing effective degradation and purification effects on nitrogen pollution [23,[51][52][53][54]. If only considering the TN, more than 80% sampled streams were beyond Class V, and this could be closely related with the densely distributed industrial land in this region, and further, the associated pollution might have exceeded the pollution load capacity of local aquatic ecosystems.…”

Using remote sensing to characterize riparian vegetation: A review of available tools and perspectives for managers

“…Despite covering a relatively small area, riparian vegetation provides many ecosystem services related to river flow (Dixon et al, 2016), sedimentary processes (Zaimes et al, 2004), biodiversity (Naiman and Décamps, 1997), water quality (Honey-Rosés et al, 2013, Brogna et al, 2018, cultural value (Décamps, 2001, Klein et al, 2015, Vollmer et al, 2015. However, riparian ecosystems experience multiple pressures (e.g.…”

Small Reservoirs, Landscape Changes and Water Quality in Sub-Saharan West Africa

“…The issue of whether land use near water bodies (local scale) is a better predictor of water quality than land use over the entire watershed has remained unsettled for a long time [115][116][117]. Two spatial scales (including the whole watershed and 1 to 5 km riparian buffers) are often used to interpret the relationship between the characteristics of watershed and water quality measures, but which one is better is still in big arguments [118,119].…”