Salinization alters fluxes of bioreactive elements from stream ecosystems across land use

Abstract

Abstract. There has been increased salinization of fresh water over decades due to the use of road salt deicers, wastewater discharges, saltwater intrusion, human-accelerated weathering, and groundwater irrigation. Salinization can mobilize bioreactive elements (carbon, nitrogen, phosphorus, sulfur) chemically via ion exchange and/or biologically via influencing of microbial activity. However, the effects of salinization on coupled biogeochemical cycles are still not well understood. We investigated potential impacts of increased salinization on fluxes of bioreactive elements from stream ecosystems (sediments and riparian soils) to overlying stream water and evaluated the implications of percent urban land use on salinization effects. Two-day incubations of sediments and soils with stream and deionized water across three salt levels were conducted at eight routine monitoring stations across a land-use gradient at the Baltimore Ecosystem Study Long-Term Ecological Research (LTER) site in the Chesapeake Bay watershed. Results indicated (1) salinization typically increased sediment releases of labile dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), total dissolved Kjeldahl nitrogen (TKN) (ammonium + ammonia + dissolved organic nitrogen), and sediment transformations of nitrate; (2) salinization generally decreased DOC aromaticity and fluxes of soluble reactive phosphorus from both sediments and soils; (3) the effects of increased salinization on sediment releases of DOC and TKN and DOC quality increased with percentage watershed urbanization. Biogeochemical responses to salinization varied between sediments and riparian soils in releases of DOC and DIC, and nitrate transformations. The differential responses of riparian soils and sediments to increased salinization were likely due to differences in organic matter sources and composition. Our results suggest that short-term increases in salinization can cause releases of significant amounts of labile organic carbon and nitrogen from stream substrates and organic transformations of nitrogen and phosphorus in urban watersheds. Given that salinization of fresh water will increase in the future due to human activities, significant impacts on carbon and nutrient mobilization and water quality should be anticipated.

A review of the species, community, and ecosystem impacts of road salt salinisation in fresh waters

“…Road salt can also increase the leaching of soil nutrients (Mg 2+ , K + , Na + ), potentially inhibiting the recovery of forested catchments affected by acid rain-induced soil acidification (Schweiger, Audorff, & Beierkuhnlein, 2015). Road salt concentrations ranging from 500 to 10,000 mg Cl − /L in urban watershed networks can also cause the release of Ca 2+ , K + , dissolved organic carbon, dissolved inorganic carbon, total dissolved Kjeldahl nitrogen (as NH 4 + + NH 3 + dissolved organic nitrogen), and can increase the water column concentration of soluble reactive phosphorus released from freshwater sediments or soils (Duan & Kaushal, 2015;Haq, Kaushal, & Duan, 2018). Concentrations of 2,500 mg Cl − /L in stream ecosystems can reduce denitrification rates, potentially decreasing the number of nitrate sinks in streams (Hale & Groffman, 2006).…”

“…Concentrations of 2,500 mg Cl − /L in stream ecosystems can reduce denitrification rates, potentially decreasing the number of nitrate sinks in streams (Hale & Groffman, 2006). Thus, in addition to the species-and community-level effects, road salt can disrupt nutrient and energy flow in contaminated stream watersheds through the mobilisation of nitrogen and carbon (Figure 3; Duan & Kaushal, 2015).…”

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

“…The positive relationship between specific conductance and pH suggests that the pH change is embodied by an increase in alkaline salts. This relationship may result from mobile anions, such as chloride and nitrate, transported together as chemical mixtures and ion exchange reactions in soils [17,18]. There was a cyclical relationship between nitrate concentrations and specific conductance during a discrete snowstorm demonstrating a flushing effect in an urban stream and the nearby Potomac River (electronic supplementary material, figure S5).…”

“…There was a cyclical relationship between nitrate concentrations and specific conductance during a discrete snowstorm demonstrating a flushing effect in an urban stream and the nearby Potomac River (electronic supplementary material, figure S5). Winter flushing of urban contaminants indicates potential water quality impacts from snowstorms which have been less studied than urban rainstorms [17,18]. Inverse and more complex relationships between specific conductance and nitrate at other sites were probably related to shifts in nitrate and other ion sources across streamflow and season (e.g.…”

“…CO 2À 3 [39,40]. Alkaline conditions favour the release of phosphorus from oxyhydroxides in sediments and soils which contribute to freshwater eutrophication [17,18]. Microbial nitrification and denitrification are both stimulated at slightly alkaline pH in soils and sediments affected by road salts, which contributes to either nitrogen transformations and/or coastal eutrophication (e.g.…”