Novel ‘chemical cocktails' in inland waters are a consequence of the freshwater salinization syndrome

Abstract

Widespread changes in water temperatures, salinity, alkalinity and pH have been documented in inland waters in North America, which influence ion exchange, weathering rates, chemical solubility and contaminant toxicity. Increasing major ion concentrations from pollution, human-accelerated weathering and saltwater intrusion contribute to multiple ecological stressors such as changing ionic strength and pH and mobilization of chemical mixtures resulting in the freshwater salinization syndrome (FSS). Here, we explore novel combinations of elements, which are transported together as chemical mixtures containing salts, nutrients and metals as a consequence of FSS. First, we show that base cation concentrations have increased in regions primarily in North America and Europe over 100 years. Second, we show interactions between specific conductance, pH, nitrate and metals using data from greater than 20 streams located in different regions of the USA. Finally, salinization experiments and routine monitoring demonstrate mobilization of chemical mixtures of cations, metals and nutrients in 10 streams draining the Washington, DC–Baltimore, MD metropolitan regions. Freshwater salinization mobilizes diverse chemical mixtures influencing drinking water quality, infrastructure corrosion, freshwater CO 2 concentrations and biodiversity. Most regulations currently target individual contaminants, but FSS requires managing mobilization of multiple chemical mixtures and interacting ecological stressors as consequences of freshwater salinization. This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.

Multiple riparian–stream connections are predicted to change in response to salinization

“…Interdisciplinary research teams will have to work at multiple spatial scales and across large geographical gradients of salt deposition, land use and climate to fully address how salinization is altering 'brown webs'. At the watershed scale, multiple interacting stressors are the norm [156,157], where riparian composition and nutrients from fertilizers are interacting with salts in soils and freshwater, and rising water temperatures and altered hydrology all act to change detrital processing. Initial unravelling of some of these interactions has already resulted in unexpected synergistic effects driven by detrital composition and salt concentrations and identity in riparian [49], stream [14] and wetland communities [158].…”

Drivers of spatio-temporal patterns of salinity in Spanish rivers: a nationwide assessment

“…Agriculture has been long recognized as a major cause of soil and groundwater salinization [54], which reaches the rivers via surface runoff. Urbanization and its association with salinization has also been well-documented and can be linked to multiple sources such as storm water runoff, de-icing agents and wastewaters [55,56]. Further, although less documented, concrete weathering can substantially contribute to increase the concentration of certain ions in urban rivers and streams [13,44].…”

Combined salinity and acidity stressors alterDaphnia magnapopulation growth and structure under severe absence of photoperiod

“…Overall, our results corroborate the view advocated by Altshuler et al (2011) that a comprehensive understanding of the combined effects of multiple stressors will require the specific assessment of the effects of these stressors than only individually examining the effects of each stressor [23]. Further, a causative relationship between physico-chemical stressors may exist as changes in one stressor can lead changes in other stressors, e.g ., freshwater salinisation syndrome [4,77,112]. Hence, one could argue that complex toxic effects of stressor interactions may underlie our results.…”

“…Like changes in ion concentration in water [5,77], freshwater acidification is caused by multiple natural and anthropogenic, direct and indirect, short- and long-term causes [78–80], e.g. , acid rain [81] alongside with organic acids from land catchments and acid deposition on a local scale [78], pond draining [82] and drainage waters particularly in areas with soils originated from granite or weathering-resistant mineral aggregates [77,83], atmospheric and soil deposition of sulphur [78,80, 84], land use and management policies [80,83], afforestation [80] and mobilisation of acid anions, via heavy rain, following forest fires and draughts [80,85–87], use of nitrogen-based fertilisers [88], melt of snow rich in sulphuric and nitric compounds [81,83,84], and increased levels of carbon dioxide and pCO2 in water [70,89,90]. Indeed, water acidification are projected to lead to alarming ecological consequences overtime [70–72,75,89–91].…”

“…Light pollution effects, in terms of artificial light, sky glow and interference with daylight-night-time patterns, which increasingly affect aquatic ecosystems and ecological interactions [34,106], are becoming a serious concern associated with urbanisation and industrialised zones with increasing human population around the globe [30,34,107–110]. The far-reaching effects of extended light exposure [34] may not only lead to changes in vital phototactic behaviours with disruptive impacts on the aquatic system [30,34], but may also extend to how zooplankton respond to a cocktail of stressors [77,111].…”