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Spatial and temporal variations in nutrient concentration and speciation in Silver Bow Creek

Spatial and temporal variations in nutrient concentration and speciation in Silver Bow Creek. Chris Gammons, John Babcock, Bev Plumb, Steve Parker Montana Tech, Butte, MT. Monitoring databases for nutrients in surface waters often look like this. Why so messy?. Outline of talk.

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Spatial and temporal variations in nutrient concentration and speciation in Silver Bow Creek

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  1. Spatial and temporal variations in nutrient concentration and speciation in Silver Bow Creek Chris Gammons, John Babcock, Bev Plumb, Steve Parker Montana Tech, Butte, MT

  2. Monitoring databases for nutrients in surface waters often look like this Why so messy?

  3. Outline of talk • Site description • Synoptic variations • Seasonal variations • Diel variations • Lateral (bank to bank) variations • Implications for monitoring

  4. SBC-1 Above WWTP

  5. WWTP discharge

  6. SBC-3 3 km below WWTP

  7. Warm Springs Ponds

  8. Synoptic changes in nutrient concentration SBC-3 below WWTP, August, 2006 Nitrite (NO2-) forms as intermediate during oxidation of NH4+ to NO3- Nitrosomonas

  9. Synoptic changes (different years) • Decrease in NH4+ due to nitrification • Increase in NO3- due to nitrification • Decrease in DIN due to assimilation

  10. Seasonal changes in nutrient concentrations SBC at Warm Springs Ponds Winter months Nitrate + Nitrite Ammonium DIN Dissolved Inorganic N ■ WSPOU INLET ○ WSPOU OUTLET

  11. Diel changes SBC-3 below the Butte WWTP

  12. Nutrient isotopes: synoptic

  13. Nutrient isotopes: diel Δ = 14.1 ‰ Δ = 20 ‰ • NH4-oxidizing bacteria preferentially metabolize 14N • Isotopic separation is less during day (faster rates) • Isotopic trends inconsistent with denitrification

  14. Lateral variations in water chemistry USGS gaging station Silver Bow Creek WWTP discharge 1000 ft Silver Bow Creek How far below the confluence of SBC and WWTP before combined flow is mixed, bank-to-bank?

  15. Bank-to-bank profiles in specific conductance (SC)

  16. How far below the confluence of SBC and WWTP before combined flow is mixed, bank-to-bank? USGS gaging station Silver Bow Creek WWTP discharge 2400 feet 1000 ft Silver Bow Creek

  17. Implications for nitrate monitoring • The sample you collect is representative only of a given spot in a given stream reach on a given day and at a certain time of day • For streams like Silver Bow Creek, consider taking 24-h integrated samples, or sample at same time of day for long-term trend analysis • For highly polluted waters, be sure to sample for all nutrients (e.g., ammonium, nitrite) • Stable isotope signatures of nitrate are also affected by synoptic and diel variations • Be careful that you are not sampling water from a stream or river that is not completely mixed

  18. Acknowledgements • USGS 104b • Montana Water Center • Students • Bev Plumb • John Babcock • Stacey Wilcox • Erika Sholey • Brian Kuhn

  19. References • Plumb, B. (2009) Geochemistry of nutrients in Silver Bow Creek, MT. M.S. Thesis, MT Tech. • Gammons, C.H., Babcock, J., Parker, S.R., Poulson, S.R. (2011) Diel cycling and stable isotopes of dissolved oxygen, dissolved inorganic carbon, and nitrogenous species in a stream receiving treated municipal sewage. Chemical Geology, 283, 44-55. Questions??

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