Watershed Symposium 2017

Evidence of groundwater connectivity in the Jordan River, Utah, USA

Summary:
We explored whether groundwater connectivity is evident in the Jordan River, where wastewater effluent represents ~ 25-40% of total flow. Concentrations of unreactive anions and cations, dissolved inorganic carbon, and isotopic signatures of water suggest that groundwater inputs continue to play an important role in riverine water quality.

Full Abstract:
Arid and semi-arid regions face increasing challenges for provisioning water for human consumption and ecosystem services under a changing climate and population growth. The role of urban water diversions and inputs on water quality in rivers remains poorly understood in many cities. We explored whether historic surface and groundwater connectivity is still evident in the water quality of the Jordan River, where wastewater effluent represents ~ 25-40% of total flow. The Jordan River is an 83 km, 4th order river that traverses the Salt Lake Valley in the state of Utah, USA. The river drains seven montane tributaries and connects Utah Lake to wetlands of the Great Salt Lake. Area urban water systems include four facilities collecting drinking water from the montane tributaries and four facilities treating wastewater (WRFs), which discharge effluent into the Jordan River. A major drainage canal diverts river water to prevent flooding of densely populated areas. The high degree of connectivity between natural and human systems in this area contributes to large spatial and temporal variation in water discharge, temperature, dissolved oxygen, pH, major ions, and isotopic signatures of water and dissolved inorganic carbon. Synoptic surveys of the river conducted over three seasons during one year show that variation in discharge (0.9-17.9 m3/s) and temperature (12.4-27.2 °C) were associated with snowmelt runoff, river regulation, and effluent inputs. Dissolved oxygen ranged from 2-21 mg/L, with a consistent decline in values each season from 10 mg/L to 2 mg/L below the surplus canal diversion. Values of pH ranged from 7.0-8.8, with circumneutral values found in WRF effluent and the oil drain downstream of the most northern WRF studied. We observed variation in concentrations of unreactive anions and cations (e.g., 42.3-111.3 mg/L calcium and 8.8-87.5 mg/L magnesium), concentration of dissolved inorganic carbon (25.1-97.7 mg/L), and isotopic signatures of δ13C (-4.9 to -11.9), δ2H (-45.6 to -115.9), and δ18O (-2.6 to -15.2, suggesting that seasonal shifts in the proportion of snowmelt vs. groundwater inputs or in-stream processes continue to play an important role in determining the water quality of the river. That groundwater continues to influence water quality in this urbanized river despite the highly engineered context is notable, especially since groundwater has been estimated to be a small fraction of total inputs. Taken together, our results suggest that effluent-dominated rivers can be strongly influenced by human modifications to surface water but also still be connected to the regional hydrologic basin via groundwater exchange. This implies that resource managers may need to account for the quality and quantity of not only surface waters but also historically overlooked groundwater inputs, in order to address water quality concerns and pollution exceedances in urban rivers.