Critical Shifts in Trace Metal Transport and Remediation Performance under Future Low River Flows

Abstract

Exceptionally low river flows are predicted to become more frequent and more severe across many global regions as a consequence of climate change. Investigations of trace metal transport dynamics across streamflows reveal stark changes in water chemistry, metal transformation processes, and remediation effectiveness under exceptionally low-flow conditions. High spatial resolution hydrological and water quality datasets indicate that metal-rich groundwater will exert a greater control on stream water chemistry and metal concentrations because of climate change. This is because the proportion of stream water sourced from mined areas and mineralized strata will increase under predicted future low-flow scenarios (from 25% under Q45 flow to 66% under Q99 flow in this study). However, mineral speciation modelling indicates that changes in stream pH and hydraulic conditions at low flow will decrease aqueous metal transport and increase sediment metal concentrations by enhancing metal sorption directly to streambed sediments. Solute transport modelling further demonstrates how increases in the importance of metal-rich diffuse groundwater sources at low flow could minimize the benefits of point source metal contamination treatment. Understanding metal transport dynamics under exceptionally low flows, as well as under high flows, is crucial to evaluate ecosystem service provision and remediation effectiveness in watersheds under future climate change scenarios.

Identification and quantification of diffuse groundwater pollution in a mineralised watershed

“…Apportionment of mine pollution sources to streams under low flow conditions is important to identify diffuse subterranean sources of metal pollutants and also to consider the potential impacts on river water quality of future low flows, which are predicted to become more extreme and frequent due to climate change. 13,14 Failure to consider low and extremely low streamflow events in source apportionment studies and in subsequent mine site remedial activities may result in persistent metal pollution after remediation. 15 The aim of this paper is to assess the utility of the tracer dilution and synoptic sampling approach in identifying and quantifying sources of metal pollution, including diffuse groundwater sources, during very low streamflows, using the Nant y Bai stream at the abandoned Nantymwyn mine (Carmarthenshire, Wales) as an exemplar catchment.…”

“…Apportionment of mine pollution sources to streams under low flow conditions is important to identify diffuse subterranean sources of metal pollutants and also to consider the potential impacts on river water quality of future low flows, which are predicted to become more extreme and frequent due to climate change. 13,14 Failure to consider low and extremely low streamflow events in source apportionment studies and in subsequent mine site remedial activities may result in persistent metal pollution after remediation. 15…”

The impacts of spatio-temporal variation of natural and agricultural influences on the environmental water quality in a fluvial-lacustrine watershed in China

“…Natural factors, such as regional meteorology, physical geography, hydrology and river network data, make the spatial pattern of pollutant emissions heterogeneous, especially for large-scale watersheds ( Xiong et al, 2022;Varekar et al, 2021;Byrne et al, 2020;Cheng et al, 2019;Grizzetti et al, 2015). The erosion and scouring of rainfall promote pollutants entering the river with soil particles and other suspended solids, which leads to the NPS pollution.…”

Identification and Prioritisation of Mine Pollution Sources in a Temperate Watershed Using Tracer Injection and Synoptic Sampling

“…Recognising the challenges of identifying sources of mine pollution in temperate-oceanic watersheds, this work sought to demonstrate the tracer dilution and synoptic sampling methodology in an exemplar temperate study site in Scotland. Understanding mine pollution dynamics in temperate watersheds is also important as projected changes in precipitation patterns due to climate change will likely modify sources and transport processes (Byrne et al 2020). Our specific objectives were to: (1) locate and rank the principal sources of mine pollution in the study watershed; (2) discriminate the relative importance of point and diffuse sources of mine pollution under steady-state flow conditions, and; (3) estimate potential improvements in stream water quality following hypothetical mine site remediation scenarios.…”