Human-accelerated weathering increases salinization, major ions, and alkalinization in fresh water across land use

Sujay S Kaushal,Shuiwang Duan,Thomas R Doody,Shahan Haq,Rose M Smith,Tamara A Newcomer Johnson,Katie Delaney Newcomb,Julia Gorman,Noah Bowman,Paul M Mayer,Kelsey L Wood,Kenneth T Belt,William P Stack

doi:10.1016/j.apgeochem.2017.02.006

Abstract

Human-dominated land uses can increase transport of major ions in streams due to the combination of human-accelerated weathering and anthropogenic salts. Calcium, magnesium, sodium, alkalinity, and hardness significantly increased in the drinking water supply for Baltimore, Maryland over almost 50 years (p < 0.05) coinciding with regional urbanization. Across a nearby land use gradient at the Baltimore Long-Term Ecological Research (LTER) site, there were significant increases in concentrations of dissolved inorganic carbon (DIC), Ca2+, Mg2+, Na+, SO42−, Si, and pH with increasing impervious surfaces in 9 streams monitored bi-weekly over a 3–4 year period (p < 0.05). Base cations in urban streams were up to 60 times greater than forest and agricultural streams, and elemental ratios suggested road salt and carbonate weathering from impervious surfaces as potential sources. Laboratory weathering experiments with concrete also indicated that impervious surfaces increased pH and DIC with potential to alkalinize urban waters. Ratios of Na+ and Cl− suggested that there was enhanced ion exchange in the watersheds from road salts, which could mobilize other base cations from soils to streams. There were significant relationships between Ca2+, Mg2+, Na+, and K+ concentrations and Cl−, SO42-, NO3− and DIC across land use (p < 0.05), which suggested tight coupling of geochemical cycles. Finally, concentrations of Ca2+, Mg2+, DIC, and pH significantly increased with distance downstream (p < 0.05) along a stream network draining 170 km2 of the Baltimore LTER site contributing to river alkalinization. Our results suggest that urbanization can dramatically increase major ions, ionic strength, and pH over decades from headwaters to coastal zones, which can impact integrity of aquatic life, infrastructure, drinking water, and coastal ocean alkalinization.

Highlights

Human-dominated land use is increasing rapidly on a global level (Foley et al 2005, Grimm et al 2008) with major impacts on water quality in streams and rivers across time and space (e.g. Walsh et al 2005, Lyons and Harmon 2012, Kaushal et al 2014, Chambers et al.2016)
A growing number of studies suggest that dissolved inorganic carbon (DIC) and base cations can be significantly elevated in streams and rivers draining human-dominated watersheds compared with forested watersheds (e.g., Daniel et al 2002, Baker et al 2008, Peters 2009, Barnes and Raymond 2009, Aquilina et al 2012, Kaushal et al 2013)
There was temporal variability, concentrations of sodium, calcium, magnesium, potassium, silica, and DIC typically increased with watershed impervious surface cover across land use (Figure 4, Tables 2–3)

Summary

Introduction

Human-dominated land use is increasing rapidly on a global level (Foley et al 2005, Grimm et al 2008) with major impacts on water quality in streams and rivers across time and space (e.g. Walsh et al 2005, Lyons and Harmon 2012, Kaushal et al 2014, Chambers et al.2016). A growing number of studies suggest that dissolved inorganic carbon (DIC) and base cations can be significantly elevated in streams and rivers draining human-dominated watersheds compared with forested watersheds (e.g., Daniel et al 2002, Baker et al 2008, Peters 2009, Barnes and Raymond 2009, Aquilina et al 2012, Kaushal et al 2013). DIC and calcium concentrations in streams throughout the Eastern U.S have shown increasing trends over time (Raymond et al 2008, Kaushal et al 2013). These geographic regions include urbanized watersheds, which sometimes drain minimal or no natural carbonate lithology (Kaushal et al 2013, Kaushal et al 2015). Human activities have increased the flux of carbon from land to ocean primarily via rivers by 1 Pg/yr since preindustrial times (Regnier et al 2013), and carbon fluxes are usually dominated by dissolved inorganic carbon from weathering and anthropogenic inputs (Cole et al 2007, Stets and Striegl 2012, Kaushal et al 2013)

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