groundwater surface water interactions n.
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Groundwater-Surface Water Interactions

Groundwater-Surface Water Interactions

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Groundwater-Surface Water Interactions

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  1. Groundwater-Surface Water Interactions • Groundwater and surface water are intertwined • Different types of interactions of groundwater with: • streams and rivers • lakes • wetlands • oceans • Focus on groundwater-stream interactions • gaining vs losing • measurements • role of hyporheic zone

  2. Gaining reach Losing reach Groundwater-Stream Interactions Groundwater can discharge to streams (gaining stream) or streams can discharge to groundwater (losing stream). Gaining and losing reaches can occur along the same stream (see example above) Fetter, 2000

  3. Determine gaining/losing stream via equipotentials Gaining Stream: convex equipotential lines zones of groundwater discharge net increase in flow Losing Stream: concave equipotential lines zones of groundwater recharge net loss of flow Freeze and Cheery (1979)

  4. riparian hillslope floodplain active channel hyporheic zone ground water Hyporheic Zone: region between groundwater and surface water Defined as the portion of the groundwater interface in streams where mixture of surface and groundwater is found. Occurs beneath the active channel and within the riparian zone

  5. Key Components of the Hyporheic Zone interface of groundwater and channel water associated gradients in biogeochemical variables (pH, redox, microbial populations, organic content, light, temperature)

  6. Hyporheic zone: ground water habitat of stream ecosystems Original use by Orghidan (1959) as groundwater environment with distinctive biota Stygobromus: subterranean amphipod hyporheic mayfly

  7. Hyporheic zone metabolically active, impacts nutrient cycling, which impacts stream ecology Upwelling waters bring groundwater nutrients to stream channel Controls on upwelling vs. downwelling Streambed morphology Vertical Gradients Dahm and Valett, 1996

  8. Vertical Hydraulic Gradients measured using piezometers or manometers dh free water surface dh Upwelling dL dL dh Downwelling = ' + ' dL dh = ' - ' dL

  9. Temporal variations in gradients can be significant Influence of Floods Influence of ET downwelling 0.4 head (m) 0.3 VHG (cm/cm) 0.8m below stream bed 0.2 upwelling stream 0.1 1 2 3 4 5 6 7 8 9 Time (days) from Valett (1993) after Lee and Hynes (1977)

  10. Groundwater-stream interactions exert control on solute cycling, biota, and stream hydrology Can be better understood through: • delineating gaining (upwelling) and losing (downwelling) reaches through measuring vertical gradients • quantifying the upwelling or downwelling discharge (Q) using stream gauging methods • mass balance methods to assess the role of the hyporheic zone in impacting solute transformation, retention and/or release Challenge: spatial and temporal variability may be significant!

  11. Case Study 1: Hyporheic influences on Sycamore Creek, AZ (Valett et al., 1994) upstream algal communities (750 mg/m2 as Chl a) dominated by green algae 100 m downstream algal communities (98 mg/m2 as Chl a) dominated by bluegreen bacteria

  12. Flash flooding represents a disturbance that reduces Chl to below detection limit and kills 95-99% of all invertebrate fauna From Valett et al. (1994)

  13. Patterns of GW/SW Exchange: Sycamore Creek Dry Stream Bed VHG: 0 to -1 VHG: 0.1 - 0.7 VHG: ~ 0 From Valett et al. (1994)

  14. after Valett et al. (1994) From Valett et al. (1994)

  15. GW/SW Exchange and Ecosystem Resilience From Valett et al. (1994) after Valett et al. (1994)

  16. Case Study 2: Groundwater-stream interactions in a mine setting Brinton Arsenic Mine Watson, 1911 Lottig, 2005 Arsenopyrite-bearing schist Produced As2O3 1903-1919

  17. N 50 m Waste piles resulting from mining operations lie adjacent to a headwater stream Mine Foundation Waste piles Start Schreiber, unpublished Streamflow End

  18. stream Waste pile Groundwater contributes high concentrations of As to stream Gaining stream stream Schreiber, unpublished

  19. Gross groundwater load Groundwater discharge Groundwater arsenic concentration Is there any retention of arsenic in the HZ as groundwater discharges to the surface? Use a mass-balance approach. First, find the gross groundwater load . Stream Hyporheic zone [As] [As] B. Brown, unpublished

  20. Load leaving the study reach Net groundwater load Stream Hyporheic zone Load entering the study reach Now, find the net groundwater load: the difference between loads entering and leaving the study reach B. Brown, unpublished

  21. Now, calculate retention: the difference between the gross and net groundwater loads If RHZ = positive, => net retention in HZ If RHZ = negative, => net release in HZ Stream Hyporheic zone B. Brown, unpublished

  22. Stream Using the mass-balance method, whole reach retention of As can be calculated Process: (1) Delineation of hyporheic zone (2) Establishment of the spatial variability of groundwater discharge (3) Characterization of groundwater flowpaths (4) Preliminary assessment of subsurface arsenic concentrations B. Brown, unpublished