CONCENTRATION-DISCHARGE RELATIONS IN CONNECTION WITH END-MEMBERS AND FLOW PATHS, IN A MODEL CATCHMENT

Open Access
Author:
Kakuturu, Sruthi
Area of Honors:
Environmental Systems Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Li Li, Thesis Supervisor
  • Mark Klima, Honors Advisor
Keywords:
  • concentration discharge
  • concentration
  • discharge
  • end member
  • end-member
  • end member mixing analysis
  • EMMA
  • flow path
  • mineral dissolution
  • nutrient transport
  • contaminant hydrology
  • hydrology
  • contaminant
  • adsorption
  • coupling
  • hysteresis
  • precipitation
  • intensity
  • model
  • catchment hydrology
  • 3-D printing
  • solidworks
  • geochemical
Abstract:
The goal of this research is to characterize concentration (C) – discharge (Q) relations for the species F-, Br-, Cl-, NO3-, SO42-, Na+, Mg2+, Ca2+, K+, pH and Dissolved Organic Carbon (DOC). Understanding CQ relationships are important for estimating solute and contaminant loads to rivers and streams and ultimately to the ocean. It also enables understanding of two overarching concepts: Flow Paths and End Members of chemicals. This experiment was performed in a physical model catchment (approximately 40 X 80 cm in area) resembling the real watershed Susquehanna Shale Hills Critical Zone Observatory (SSHCZO, 0.08 km2). The model catchment was 3D printed using the elevation and topographical data, soil from the real catchment was packed, and sprinkling experiments were conducted to simulate large rainfall events. The discharge from the model watershed was collected and analyzed to quantify water quantity and chemical composition. The advantage of the approach is that although soils are from a real watershed, the processes are not affected by ecological and microbiological processes at the watershed. With a deep groundwater component, the stream discharge primarily comes from two end members: rain fall with new water composition Cnew and soil water Cold. Three patterns of end member contribution were characterized. F- fell into Type A species, where rainfall is the dominant end-member and soil buffers the discharge load by retaining these species. Br- and NO3- fell into Type B species, where discharge load is similar to input load, therefore soil is neither dissolving nor retaining these species. Cl-, Ca2+, K+, Na+, Mg2+ and SO42- all fell into Type C species, where soil was the significant end member, and the soil gradually leached out these stored species during rainfall events with concentrations much larger than the rainfall input. Hysteresis patterns roughly show that F- mimicked chemodynamic behavior. Br-, Cl-, Ca2+, K+ show dilution behavior. Na+, Mg2+ and pH show chemostatic behavior. And NO3-, SO42- and DOC show crisscross CQ patterns that are in essence, chemostatic. These patterns together suggest that Cold is larger than Cnew for the most part, meaning the discharge load synchronizes itself with soil water composition. Time along each Run has the influence of connecting pores so that old water contribution can increase over the course of a precipitation event. Insights gained here will facilitate grouping of different behaviors of chemicals from different sources and predict solute loads and water quality in aquatic systems.