Influence of Catchment Characteristics on Stream Nitrogen Transport to the Hood Canal

Osborne, S.N.; Brett , M.T.; Richey, J.E.;

Steinberg, P.D.; Newton, J. A.; and Hannafious, D.

Hood Canal Dissolved Oxygen ProgramUniversity of Washington

Outline• General Watershed

Characteristics-Hydrology-Land Cover

• Study Objectives-Estimate freshwater N loads (possible cause of Hood Canal hypoxia)

• Results-Seasonal variation in N loads/concentrations-Land cover effects on load/concentrations-Discharge effects on load/concentrations

• Drainage Basin Area– Hood Canal

Watershed (2119 km2)– Individual Catchments

(35)• (0.05 to 628 km2)

• Slope – Individual Catchments

• (2.6 to 30.3 degrees)

Watershed Characteristics

Surface Water Contribution from Hood Canal Streams

Skokomish ~ 35.7%

Dosewallips ~ 11.4%

Lake Cushman ~ *10%

Hamma Hamma ~ 10%

Duckabush ~ 8.1%

Big Quilcene ~ 7.7%

Tahuya ~ 3.6%

All Other Sites ~ 23.9%

Annual Precipitation

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Surface Water Hydrology

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Land Cover• 14 Categories

• Dominant LC Types

Hood Canal Watershed:– Mature Conifer

(48.2%)

– Deciduous/Mixed(10.9%)

– Young Conifer(8.3%)

– Sub-Alpine Forest

(5.5%)

Watershed Characteristics

• Estimate total freshwater nitrogen loading to Hood Canal

• Identify seasonal trends in surface water nutrient concentrations and loading

• Examine the effect of catchment characteristics on nutrient transport (i.e. land cover, soil type, drainage basin area, slope, and discharge)

• Compile a dataset that can be used to develop and calibrate a watershed biogeochemical model

Study Objectives

1) Analytes (Monthly Sampling and Storm Event Sampling): • Dissolved Nutrients (ORP, NO3-N, NO2-N, NH4-N, and SiO4-

Si) • Dissolved Organic Carbon & Total Dissolved Nitrogen• Particulate Organic Carbon & Total Particulate Nitrogen• Total Phosphorus• Total Suspended Solids

2) Data Management & QA/QC

3) GIS Analysis• Watershed and Individual Catchment Characteristics

» Land Cover, Soil Type, Drainage Basin Area, Slope

4) Field Discharge Measurements and Hydrologic Modeling

5) Statistical Analysis of Data

Methods

HCDOPMonthly Sampling

Program

• 38 Sampling Locations

• ~80% of surface water discharge to Hood Canal

ResultsNitrogen Load from Hood Canal Streams

• 2005: 935 metric tons TN (Dry year)Total Dissolved Nitrogen (760 mt/yr) Particulate Nitrogen (175 mt/yr)

(DIN ~ 75% of TDN = 570 metric tons)

TDN Composition

Nitrate-N (68±19%) DON (24±16%)

Ammonium-N (7±11%) Nitrite-N (0.3±0.2%)

• 1990-2004 Averages Discharges with 2005 Nutrient Data1250200 metric tons TN

(750 130 metric tons DIN)

• USGS Preliminary Assessment/Prediction 421 ± 162 metric tons (DIN)

2005 Nitrogen Loading and Speciation Hood Canal Streams

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NO3-N DON PN NH4-N NO2-N

2005 Nitrogen Concentrations and Speciation for Hood Canal Streams

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/L) NO3-N DON PN NH4-N NO2-N

Seasonality of Nitrogen Loads and Concentrations

– Peaks of loading and flow-weighted concentrations occur during rainy months

– Dry January/February 2005 resulted in lower loading and concentrations

– Nitrate is dominant fraction of TDN during months of low biological uptake (winter & fall), DON is dominant fraction of TDN during months of high biological uptake (summer).

2005 Seasonal Cycle of Nitrogen Transport and Speciation in Hood

Canal Streams

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/L) NO3-N DON PN NH4-N NO2-N

NO2-N 1 1 1 0 0 0 0 0 1 1 1 1

NH4-N 13 11 11 11 7 8 18 9 19 16 17 16

PN 21 6 13 16 18 20 7 1 2 5 20 49

DON 30 14 57 75 46 57 43 34 48 29 24 57

NO3-N 76 75 88 47 36 28 43 43 48 63 110 118

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

WINTER SPRING SUMMER FALL

Seasonal Cycle of Nitrogen Loads from Rivers/Streams to Hood Canal (2005)

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Loading Rates of Hood Canal Streams are Discharge Dominated

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1990-2004Average

Land Cover Effects on TDN Concentrations

y = 0.01x + 0.12

R2 = 0.39

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% Deciduous Mixed Forest

Aver

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TDN

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y = -0.01x + 0.49

R2 = 0.26

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% Mature Coniferous Forest

-Deciduous Mixed Forest Cover Type: Red alder (Alnus rubra), a nitrogen fixer, is a major species.

-Low to medium density residential areas (with septic systems) are included Deciduous Mixed Forest type at this resolution

Influence of Deciduous/Mixed & Mature Conifer Forests on Nutrient

Concentrations• Nutrient Rich: TDN > 600 mg/L• Nutrient Poor: TDN < 150 mg/L

% DMF

% MCF Sites Identified

Nutrient Rich Streams (n=4)

30 18 Tarboo, Seabeck, Devereaux, Little Quilcene

Nutrient Poor Streams (n=11)

7 57 Dosewallips, Duckabush, Big Quilcene, Fulton, Waketickeh, Jorsted, Miller, Skokomish R.,

Unnamed Drainage, and Twanoh

Deciduous Mixed Forest

Mature Conifer Forest

Rainwater reference

Rainwater reference

• 8 of the 12 streams identified as nutrient poor are located on the west shore of Hood Canal.

West shore streams have:• Larger average watershed areas (49.4 km2 vs. 5.7

km2),• Headwaters in Olympic National Park• Higher average discharges (1.9 vs. 0.3 m3/s)• Greater average slopes (19.9 vs. 6.5 degrees)• Lower average nitrogen concentrations and

greater loads

Other Characteristics of Nutrient Poor Streams

- Sample streams every 2 – 4 hours during 2 – 4 day storm events

- Estimate discharge effects on nutrient concentrations

- Refine N loading estimates

Next Step: Estimating Storm Event Effects on Nutrient Concentrations

100%

100% ~800%

100% ~800%

~150%

100% ~800%

~150% <50%

1) Land cover (vegetation and land use) influences stream nutrient transport.

-Catchments dominated by Mature Conifer Forest retained nitrogen more efficiently.

-Catchments dominated by Mixed Deciduous Forest had higher nitrogen concentrations.

-Catchments dominated by Open Forest Regrowth had higher particulate nitrogen concentrations.

Conclusions

2) Larger rivers with headwaters in Olympic National Park (predominantly mature conifer forest) were typically associated lower N concentrations, but larger N loads

3) In stream nitrogen concentrations were generally low (<1 mg/L) and nitrate was the dominant fraction of TDN.

4) Stream nitrogen concentrations patterns are strongly seasonal.

5) Total surface freshwater N load is higher than initial estimates.

Conclusions cont.