T256 Urban Geochemistry

Friday, 30 October 2020
10:00 AM - 2:00 PM
Meeting Rooms

STREAMWATER LITHIUM ISOTOPE VARIATIONS IN AUSTIN, TX WATERSHEDS: ASSESSING URBANIZATION VS. GEOLOGIC CONTROLS

Paper number: T256-15
Program: Technical Sessions
Time: 1:10 PM – 1:20 PM

Authors

Abstract

The sustainability of water resources in urban environments is becoming increasingly important in the face of population growth and urbanization in the 21st century. Urbanization can have multivariate impacts on water quality, including those resulting from impervious cover and industrial and domestic wastewater inputs. Watersheds in Austin, Texas span a range of urbanization. Streamwater 87Sr/86Sr values in Austin indicate that in more urbanized watersheds streamwater contains a large component of municipal water, reflecting significant contributions from irrigation and/or failing infrastructure. Whereas Sr isotopes are useful for tracking the overall input of municipal water into a natural stream, they are not as diagnostic for differentiating municipal supply from wastewater inputs to streams. The 7Li/6Li isotope system has been applied to tracing wastewater impacts in streams. A global dataset of stream waters shows an inverse trend, ranging from high δ7Li values and low Li concentrations to low δ7Li and high Li concentrations. This trend has been ascribed to either (1) impacts of urbanization, whereby low δ7Li and high Li concentrations are diagnostic of municipal wastewater, or (2) geologic control, whereby low δ7Li and high Li concentrations result from weathering of shales relative to carbonate rocks. Stream water and municipal supply water in most rural and urbanized Austin watersheds have high δ7Li and low Li concentrations, indicating that the wastewater component in these watersheds is not a significant source of Li. In one urbanized watershed, by contrast, stream water has low δ7Li and high Li concentrations. Our preliminary results indicate this watershed’s streamwater composition may be a function of either urbanization or geologic control (i.e., (1) or (2) above). Further analysis of streamwater and bedrock Li isotope compositions and concentrations may provide a means to distinguish between these controls on streamwater Li.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-359387

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