Zones of untreatable water pollution call for better appreciation of mitigation limits and opportunities

Abstract

This opinion piece addresses subsurface legacy sources and their role in mitigation of large‐scale water pollution and eutrophication. We provide a mechanistic theoretical basis and concrete data‐based exemplification of dominant contributions from such sources to total recipient loads. We specifically develop a diagnostic test to detect such contributions, recognizing that they are inaccessible and associated with long transport times that tend to evade detection when homogeneous catchment models are calibrated to typically heterogeneous catchments. Dominant legacy‐source contributions are also in practice untreatable within the commonly short time frames given for compliance with environmental regulation. We therefore argue that, for considerable water quality improvements to be achieved within such short time frames, mitigation measures need to be spatially differentiated and directed to (sub)catchments without major legacy sources. The presented diagnostic test identifies dominant prevalence of such sources where there is linear temporal correlation between the nutrient/pollutant loads and the water discharges from a (sub)catchment. Confidence in this identification may be strengthened by independent quantification of long transport times and records of temporally extended presence of nutrient/pollutant sources in the same (sub)catchment. This article is categorized under: Science of Water > Water Quality Engineering Water > Planning Water

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

“…Ascott et al 2017, Van Meter et al 2018. Increased data availability and process-based theory are now paving the way to identifying (sub)catchments where such legacy sources are dominant in controlling water quality (Destouni and Jarsjö 2018). It is also becoming clear that the topic of water and health is no longer just of importance to the water chemistry and microbial research communities, but also to the hydrological community (Question 15), as reflected, for example, by the recent launch of the GeoHealth journal by the AGU.…”

Policy change implications for forest water protection in Sweden over the last 50 years

“…Finally, similar to findings from Angelstam et al (2011), the current proportion of protected riparian buffer forests in Sweden is presently too small in relation to the forestenvironmental policy ambitions, which is likely to weaken their impact. Research in very large watersheds with urban and agricultural influences has shown weak water quality effects of relatively recent protection efforts like riparian buffers (Quin et al 2015;Destouni and Jarsjö 2018), suggesting that the potential positive impacts from such forest management are not always measurable. Moreover, with predicted time lags in policy implementation, there could also be time lags in the response of water quality to mitigation due to legacy effects of historic land use, at least at large scales (Destouni and Jarsjö 2018).…”

“…Research in very large watersheds with urban and agricultural influences has shown weak water quality effects of relatively recent protection efforts like riparian buffers (Quin et al 2015;Destouni and Jarsjö 2018), suggesting that the potential positive impacts from such forest management are not always measurable. Moreover, with predicted time lags in policy implementation, there could also be time lags in the response of water quality to mitigation due to legacy effects of historic land use, at least at large scales (Destouni and Jarsjö 2018). Thus, we have the problem of needing to protect even more forest to secure water quality (Lidskog et al 2018), while simultaneously, climate change is placing additional demands on forests to provide biomass as a substitute for fossil fuel (Söderberg and Eckerberg 2013).…”

Watershed-Based Evaluation of Automatic Sensor Data: Water Quality and Hydroclimatic Relationships

“…On the one hand, loads of TN and TP are known to drive eutrophication and algae blooms [35][36][37], and are key variables for assessing hydro-ecological conditions and status [3,38]. On the other hand, nutrient load is the product of concentration and discharge, Q, with Q found to dominate nutrient load variability, while concentration levels are much less variable over time [3,39]. As such, nutrient concentrations may not correlate well with Q or with other water quality variables that are highly correlated with Q.…”