Land Use Influences on Water, Sediment and Nutrients in the Napa Valley Watershed: Conceptual Models...
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Land Use Influences on Water, Sediment and Nutrients in the Napa Valley Watershed: Conceptual Models and Examples. Lester McKee (PhD) Watershed Program Manager San Francisco Estuary Institute (SFEI). San Francisco Estuary Institute. Presentation Outline.

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Lester McKee (PhD) Watershed Program Manager San Francisco Estuary Institute (SFEI)

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Land Use Influences on Water, Sediment and Nutrients in the Napa Valley Watershed: Conceptual Models and Examples

Lester McKee (PhD)

Watershed Program Manager

San Francisco Estuary Institute (SFEI)


San Francisco Estuary Institute

Presentation Outline

  • Historic conceptual model for water and sediment

  • Modern conceptual model for water and sediment

  • Examples of impacts

  • Conceptual models for nutrients

  • Examples of nutrient impacts


San Francisco Estuary Institute

Overview of Changes

  • Channel have been:

    • Straightened

    • Strengthened or lined

    • Connected

  • Drainage density has been increased

  • Result

    • More water drains of faster

    • Sediment supply is more connected

    • Nutrients and other chemical residues drain off faster


Soda - Realignment of Road and Creek


Lower Soda Creek Silverado-Napa R. Reach


Lower Soda Creek Silverado-Napa R. Reach

1942

1999


San Francisco Estuary Institute

St. Helena


Sulphur - Alluvial Fan Reaches

  • Storage of large volumes of sediment

  • Discontinuation of gravel mining in 2002

  • Aggradation and potential flood risks


Sulphur - Lowest Reaches

  • Highly affected by the town of St. Helena

  • Entrenched

  • Large amount of bank revetment

  • Water quality affected by runoff

  • Invasive species, primarily Arundo donax

  • Some areas with no riparian vegetation


Carneros Ck. Revetment


Carneros Ck. Bank Erosion


Carneros Ck. Bank Erosion


San Francisco Estuary Institute

Nutrients


San Francisco Estuary Institute

Null Hypothesis

H(0) Land use or human population have no influence on nitrogen or phosphorus concentrations in flowing water bodies within the Napa River watershed.

  • Accept H(0) if there was reasonable doubt that anthropogenic factors strongly influence water quality

  • If reject H(0) then we would need to develop and test alternate hypotheses (i.e. develop monitoring/management questions)


San Francisco Estuary Institute

Conceptual Models to Test Null Hypotheses Against

  • Nutrient concentrations should be below WQ standards

  • Seasonal variation should be minor (<10x)

  • Little spatial variation either between subwatersheds or in a downstream direction

  • Nitrate << organic nitrogen

  • Phosphate << organic phosphorus


SamplingLocations*selected for beneficial uses and coverage


WQ Guidelines

NOx 1,129 µg/L

TDN 500 µg/L

Phosphate 30 µg/L

TDP 30 µg/L


San Francisco Estuary Institute

Seasonal Variation


Downstream Variation


Reasons for Rejecting H(0):

  • Except in headwater reaches, concentrations of NOx, NH3 and PO43- were high relative to expected concentrations in pristine watersheds.

  • Concentrations of NOx varied greatly between sampling locations and increased in a downstream direction in relation to anthropogenic factors.

  • Total dissolved nitrogen was dominated by NOx and total dissolved phosphorus was dominated by PO43-.

  • Approximately 85% of the sampling locations exceeded EPA guidelines in Level III Eco-Region 6 for TN (500 µg/L) and ~92% of the sampling locations exceeded EPA guidelines in Level III Eco-Region 6 for TP (30 µg/L).

  • NOx concentrations were highest during the winter months indicating considerable seasonal variation greater than would be expected in a natural system.

  • NOx correlated significantly with population and urban environmental variables during the winter, spring and early summer and during the wet season only with agricultural and commercial land use variables


San Francisco Estuary Institute

Conclusions

  • Work to-date on water, sediment, and nutrients in the Napa River watershed suggests a level of impact associated with historic and current human land and water use

  • The questions that stakeholders and the public have to answer is:

    • Is this acceptable given multiple societal needs?

    • What goals do we set for the future?


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