Abstract
Water resources are threatened by many pollution sources. The harmful effects of pollution can be evaluated through biological indicators capable of tracing problems in life forms caused by the contaminants discharged into the streams. In the present study, the effects on stream water quality of landscape configuration, season, and distance from contaminant emissions of diffuse and point sources were accessed through the evaluation of a Portuguese macroinvertebrate index (IPtIN) in 12 observation points distributed within the studied area (Ave River Basin, Portugal). Partial least-squares path models (PLS-PMs) were used to set up cause–effect relationships between this index, various metrics adapted to forest, agriculture, and artificial areas, and the aforementioned emissions, considering 13 distances from the contaminant sources ranging from 100 m to 56 km. The PLS-PM models were applied to summer and winter data to explore seasonality effects. The results of PLS-PM exposed significant scale and seasonal effects. The harmful effects of artificial areas were visible for distances larger than 10 km. The impact of agriculture was also distance related, but in summer this influence was more evident. The forested areas could hold onto contamination mainly in the winter periods. The impact of diffuse contaminant emissions was stronger during summer, when accessed on a short distance. The impact of effluent discharges was small, compared to the influence of landscape metrics, and had a limited statistical significance. Overall, the PLS-PM results evidenced significant cause–effect relationships between land use metrics and stream water quality at 10 km or larger scales, regardless of the season. This result is valid for the studied catchment, but transposition to other similar catchments needs to be carefully verified given the limited, though available, number of observation points.
Highlights
The growing population and demographic expansion threaten hydric resources, by inducing stressful water demands and because of the continuous surge of pollution sources.The response to anthropogenic pressures relies on proper management that should always stand on environmental research
This study has shown to be effective in demonstrating seasonal and scale impacts in the interplay between the effect of landscape metrics and contamination sources on water quality
As it was found in this study, the effect of metrics can be greater than contamination sources
Summary
The growing population and demographic expansion threaten hydric resources, by inducing stressful water demands and because of the continuous surge of pollution sources.The response to anthropogenic pressures relies on proper management that should always stand on environmental research. The potential contamination by wastewaters is frequently reduced in urban and industrial areas where treatment stations are efficient, but in many regions proper treatment is not applied [3] In those situations, surface waters are directly contaminated by bacteria [4], nutrient loads [5,6,7], heavy metals [8,9] and even microplastics [10]. The presence of forested areas or riparian vegetation can create a barrier that retains such flow of contaminants [12,13] Wildfires are another threat to water quality [14,15], because they can destroy the aforementioned barriers [16], and because soil erosion increases [17], and ash-derived contaminants are leached towards the streams [18]. Another factor that can affect water quality is land occupation planning
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