More than a Concentration-Discharge Curve: Looking at Detailed Event Concentration Dynamics to Understand Changing Stream Sulfate Sources Across Flow Conditions and Land Use Gradients
Abstract
Sulfate is a complex solute with many natural and anthropogenic sources. We compared sulfate concentration dynamics during baseflow and stormflow in neighboring forested and suburban catchments in the Maryland Piedmont in order to explore sources of sulfate and potential ecological consequences of variations in sulfate concentrations in these systems. Both streams drain small, headwater catchments underlain by schist. Sulfate concentrations were consistently around three times greater in the stream draining the suburban catchment under baseflow conditions. The streams were sampled during a large, multi-peaked spring storm event. Over the course of the storm sampling period, from pre-event flow through recession, the suburban catchment has a significant negative logarithmic sulfate concentration-discharge relationship (C-Q), while the forested catchment has a negative linear sulfate C-Q relationship. Silica had similarly negative logarithmic and linear C-Q relationships for the suburban and forested catchments respectively. Silica is primarily derived from rock weathering and the C-Q relationship implies dilution by younger event-water. Indeed, the concentration dynamics over the course of the storm in the suburban catchment have a dilution signal for both silica and sulfate, with concentration declining during event flow. However, despite similar C-Q relationships, concentration dynamics over the course of the storm are markedly different between silica and sulfate in the stream draining the forested catchment. Sulfate concentrations in the forested catchment begin to increase during the rising limb of the first storm event and remain elevated long after recession. This may result from changing baseflow source water with changing catchment wetness conditions. Stable water isotopes were used to chemically separate the storm peak and the high sulfate baseflow following recession. The differing C-Q patterns between the two catchments is likely the result of the different land uses and sulfate sources. Sulfur isotopes were used to explore end members for the excess sulfate in the suburban catchment. Understanding sulfate sources to the stream and their sensitivity to flow condition is important for predicting the timing and concentration of sulfate fluxes and their ecological impacts.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H23E..09C
- Keywords:
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- 0432 Contaminant and organic biogeochemistry;
- BIOGEOSCIENCESDE: 0481 Restoration;
- BIOGEOSCIENCESDE: 1830 Groundwater/surface water interaction;
- HYDROLOGYDE: 1871 Surface water quality;
- HYDROLOGY