Critical Review of Methods Used to Estimate Agricultural Nitrogen Loadings into Puget Sound

Faith Dewitz and Joel Baker

University of Washington Tacoma

characteristics, and contaminate sources to estimate contaminate transport (Everything you need to know about SPARROW). SPARROW was created in 1997 and has been continuously modified. The model has not been revised since October of 2007 making Version 2.9 is the most up to date model available.

VELMA

Crop Coverage Area Calculations

Critical Review of Environmental Models:VELMA and SPARROW

Nitrogen Loading From Agriculture into the Puyallup River

Introduction• In the Puget Sound, nutrient loads, particularly nitrogen, have become stressors in

the environment. • Excessive nutrient loads have decreased the amount of dissolved oxygen in the water,

which has resulted in portions of Puget Sound to fall below State water quality standards for dissolved oxygen • Levels decrease when nitrogen levels increase because nitrogen intensifies algal

growth. When the algae die it undergoes decomposition, a process that uses dissolved oxygen

• Agricultural activities contribute to an increase in nitrogen into the Puget Sound from over application of fertilizer and manure that are capable of transporting through the watershed through rivers, runoff, and ground water

Description• The Visualizing Ecosystem Land Management Assessments, VELMA, is an

ecohydrological model that was designed by the USEPA • Simulates water, carbon, and nitrogen cycling and the transport of these nutrients

throughout a watershed • A grid-based model that aims to improve water quality through green infrastructure

• Can assess green infrastructure and predict its effectiveness.Strengths• Highly detailed for small scale regions• Capable of being applied to various ecosystems, simulating ecosystem services, and

multiple land use• Uses green infrastructure as a method to improve water quality• Simulates short and long-term changes in landscape variablesWeaknesses• Lacks data for phosphorous• Some instream processes that can retain and recycle nutrients within streams are not

accounted for• Lack of available data decreases the certainty of calculations• Unable to spatially vary depth and soil texture

characteristics, and contaminate sources to estimate contaminate transport (Everything you need to know about SPARROW). SPARROW was created in 1997 and has been continuously modified. The model has not been revised since October of 2007 making Version 2.9 is the most up to date model available.

SPARROWDescription• SPAtially Referenced Regression On Watershed attributes, SPARROW, is the USGS’s

model used for estimating nutrients entering watersheds• Created to understand and describe where pollutants enter the watershed and how

they transport• Uses monitoring data, watershed characteristics, and contaminate sources, non-point

and point, to estimate contaminate transport Strengths• Works best at a regional scale• Can extrapolate data to fit larger watersheds• Capable of relating upstream processes to downstream results

• Allows predictions of annual loadings from sources in the modeling areaWeaknesses• Missing the hydrological piece in the model that VELMA has• Lacks carbon data• Lack of data, low-quality data, and scaling-up increase uncertainty in calculations• Using a set calibration across seasons neglects to acknowledge seasonality

The amount of land used for each type of agriculture was calculated by using a given percent of the amount of land used for each crop within the drainage basin, 2,473 km2

Row Crop is 0.3% of the drainage basin. 003 ∗ 2,472𝑘𝑚! = 7.4𝑘𝑚!

Pasture/Hay is 3.1% of the drainage basin. 031 ∗ 2,472𝑘𝑚! = 76.7𝑘𝑚!

Orchard/Vineyard/Other is 0.2% of the drainage basin. 002 ∗ 2,472𝑘𝑚! = 4.9𝑘𝑚!

The nitrate for each type of crop was calculated by using the crop coverage area and a given net nitrate export level for each crop in Western Washington.

Row Crops Net Nitrate Export Level= 2,240 "#"$!%&'

2,240𝑘𝑔

𝑘𝑚! − 𝑦𝑟∗ 7.4𝑘𝑚! = 16,621

𝑘𝑔𝑦𝑟

Pasture/Hay Net Nitrate Export Level= = 1,800 !"!#!$%&

1,800𝑘𝑔

𝑘𝑚! − 𝑦𝑟∗ 76.7𝑘𝑚! = 137,993

𝑘𝑔𝑦𝑟

Orchard/Vineyard/Other Net Nitrate Export Level= = 1,890 !"!#!$%&

1,890𝑘𝑔

𝑘𝑚! − 𝑦𝑟∗ 4.9𝑘𝑚! = 9,356

𝑘𝑔𝑦𝑟

Nitrogen Runoff from Crops Calculations

Percentage of Total DIN Delivered by CropsThe amount of nitrogen runoff was then used to determine what percent of the total DIN, 768,325 kg/yr, per year was delivered from each crop

Row Crops

16,620.80 𝑘𝑔𝑦𝑟

768,325 𝑘𝑔𝑦𝑟

∗ 100 = 2%

Pasture/Hay

137,993.00 𝑘𝑔𝑦𝑟

768,325 𝑘𝑔𝑦𝑟

∗ 100 = 18%

Orchard/Vineyard/Other

9,355.50 𝑘𝑔𝑦𝑟

768,325 𝑘𝑔𝑦𝑟

∗ 100 = 1%

Goal• Conduct a critical review of literature regarding environmental modelsMethods• Conducted a critical analysis of the environmental modeling programs, VELMA and

SPARROW• Determine the effectiveness and accuracy of each model and their ability to replicate

conditions within the Puget SoundFindings• The current modeling techniques used in the Puget Sound work best under different

circumstances and the use of them depend on the project at hand• VELMA works best with projects at a smaller scale and requiring more detail• SPARROW works best when projects are taking a regional approach

Goals, Methodology, and FindingsGoals• Estimate the nitrogen loading from agriculture into the Puyallup watershed and the

extent of impact that human agricultural practices have on the WatershedMethods• Researched and calculated the amount of agricultural land used for specific crops and

the nitrogen runoff associated with each. • Used the amount of nitrogen runoff to determine what percent of the total DIN per year

was delivered from each crop Findings• Crops contribute 163,969 kg/yr of nitrogen per year or 21% of the total DIN in the

Puyallup river each year• The results fall within this range, 100,001-250,000 kg/yr, but not all types of agriculture

were calculated• Data was not available for the Puyallup watershed’s yearly nitrogen runoff. DIN, nitrite

and ammonia, was used which may have impacted the percentage calculations

Goals, Methodology, and Findings

ReferencesAcknowledgements

Special Thanks:

This project was accomplished in partnership the Center for Urban WatersI wouldn’t have been able to complete this project without the help of Julie Mazura and my peers being willing to help me edit and refine my project

McCarthy S. Puget Sound Nutrient Synthesis Report, part 2: Comparison of Watershed Nutrient Load Estimates. Washington State Department of Ecology 2019 October; p.19.Map showing total nitrogen (TN) load results from agriculture sources in Puget Sound for 2002 using the USGS SPARROW environmental model.

Mohamedali, T, et al. 2011. Puget Sound Dissolved Oxygen Model, Nutrient Load Summary for 1998-2008. Washington State Department of Ecology, Olympia; p.1.Map of Puget Sound Showing dissolved oxygen levels that are of concern or impaired as well as location of major cities

• Comparing more environmental models, such as the Salish Sea Model, would provide better insight on which model would be best for the Puget Sound

• When more data is available, other crops can be included to get more accurate results• The impacts of animal agriculture was not included in this study but do fall under the

category of animal agriculture. With the inclusion of animal agriculture, there would be an increase in yearly nitrogen loading

Future Work