IMPACTS OF URBANIZATION ON STREAM WATER CHEMISTRY ACROSS LATITUDES

Urbanization has altered the Critical Zone through impervious surface cover (ISC) introducing anthropogenic pollutants to stream and groundwater. Pollutants include chloride from deicing salts and nitrate from sanitary sewer, septic systems, and fertilizer. Urbanization and associated pollutants reduce water quality and biodiversity in streams. Prior studies have linked urbanization to altered stream chemistry, but few have compared urban streams across climate regimes and urbanization rates.

Using at least 20 years of data from each watershed, we are analyzing the impacts of urbanization on stream water chemistry, discharge, and specific conductance (electrical conductivity of the stream water normalized to 25°C). Three urban streams and one non-urban stream are being compared in the states of Maryland, Virginia, and North Carolina.

Key constituents include chloride (Cl) and nitrate (NO₃) while analysis of other constituents is ongoing.

Differences between winter and non-winter Cl concentrations show correspondence between road salt use and higher Cl concentrations in colder climates as well as increasing Cl concentrations over time. By contrast, the non-urban and southeastern streams show little to no seasonal or temporal change in Cl concentrations. Nitrate concentrations increased substantially with time in streams with higher ISC. All urban streams have higher Cl and NO₃ concentrations than the 100% forested stream. Preliminary results show that less developed watersheds have lower concentrations of NO₃ and Cl than more developed watersheds. Elevated Cl concentrations drive elevated specific conductance in colder climates. Nitrate is most elevated in streams with high ISC and associated sanitary sewer and septic infrastructure.

Winter high temperatures are 5°C warmer in North Carolina than in the northern streams and the trajectory for urbanization is expected to increase by 165% over the next 40 years. Urbanization started later in the NC region and is not as advanced as the MD stream location but based on preliminary analysis, it is anticipated that NC will see an increase in NO₃ concentrations with increasing ISC. The VA stream analysis is ongoing and is predicted to have Cl and NO₃ concentrations somewhere in between the MD and NC streams based on climate and urbanization rates.