Non-Point Source Pollution in Pineview Watershed

CEE 6640 Term Paper

Prepared by Lindsey DeBoer

Introduction

Pineview Reservoir, shown in Figure 1, is situated in the Wasatch Front region, approximately eight miles east of Ogden City, UT.  The beneficial use of this reservoir is not met when stratification develops and anoxic conditions are created in the hypolimnion and exacerbated by decomposition processes and hypolimnetic draw-down.  Furthermore, once the reservoir mixes, nutrients made available by reducing conditions in the hypolimnion cause algae and cyanobacteria blooms.  The TMDL conducted by Tetra Tech (2002) reported that nitrogen and phosphorus are limiting in this system and suggested a reduction in the loading of both of these critical nutrients to this waterbody;  however, there are no point sources of nutrients in the watershed and sources of non-point pollution need to be identified. 

Figure 1. Pineview Reservoir Watershed dominates the eastern half of Weber County (ESRI Inc. n.d.).

The majority of the watershed is dominated by rangeland in the upper elevations that is subject to minimal human impact.  In contrast, the valley floor near the reservoir encompasses many uses such as agriculture, residential, and recreation and has been subject to many changes in recent years.  Hydrologically, this watershed is impacted by snowfall and runoff events.  Export coefficients based on land use can vary orders of magnitude (Lin 2004) based other factors such as soil type, geography, and climate.  As such, there is a need to quantify the location-specific nutrient export rates.  Future studies will focus on the hydrologic and chemical sampling and analyses required while this study presents a preliminary step in determining the sampling locations on one main tributary which will enable the quantification of the desired export coefficients. 

Objectives

The purpose of this project was to:

1)      Identify the dominant landscape types under the categories of irrigated lands, impervious surfaces, and rangeland, and quantify their prevalence in the watershed draining to the reservoir,

2)      Determine the areas for which non-point pollution can be attributed to two separate stream reaches using a bracketing technique,

3)      Using literature values for the export coefficients, calculate the nutrient load per year of total phosphorus (TP) and nitrogen (TN) to the reservoir, and

4)      Compare the two evaluated stream reaches to determine which monitoring sites will be the most efficient to quantify anthropogenic nutrient loads.

Methods

In order to conduct the geospatial analyses required to complete these tasks, the tools made available through ArcGIS 9 version 9.3.1 (ESRI Inc. 1999-2009) were utilized including the Arc Hydro (ESRI Inc. 2009) and TauDEM (Tarboton 2009) tools.

The approximate coordinates of sampling sites of interest were obtained in the field using a handheld GPS.  Monitoring sites are located on one of the main tributaries to the reservoir, the South Branch of the Ogden River, which splits into two forks lower in the valley.  Various datasets for the area were collected which included the following: a 30-meter National Elevation Dataset (NED) and the 2001 National Land Cover Dataset Impervious Surface from the USGS Seamless Server (U.S. Department of the Interior, U.S. Geological Survey 2009), a shapefile of the irrigated areas obtained from the National Resource Conservation Service (Mr. Cody Tusing, personal communication), and flowlines, waterbodies, and catchment boundaries (hydrologic region 16 unit b) from NHD Plus (Horizon Systems Corporation n.d.).  Aerial photography from ESRI Online (ESRI Inc. n.d.) was also used to help orient the location of shapefiles within the watershed. 

The datasets were added to ArcMap and projected as necessary to Albers Equal Area Conic (USGS version) to preserve the accuracy of the land surface area and unify the spatial reference.  The geographic coordinates of the proposed sampling sites were imported and converted to a feature class sharing the same spatial reference.  Figure 2 shows the result of these steps.

Figure 2: Pineview Reservoir Watershed with Irrigated Lands, Impervious Surfaces, NHD Flowlines and Waterbodies, and Monitoring Sites

Watershed processing tools were employed on the DEM.  First, the NHD Flowlines were burned in and the pits were filled using Terrain Processing (ESRI Inc. 2009).  The D8 flow directions and slopes were calculated using TauDEM (Tarboton 2009).  In order to determine the fraction of upstream area associated with a specific land use, weight grids were created for each of the specific land cover categories within the irrigated lands raster and for impervious surfaces with a value greater than one.  This was achieved by using the Raster Calculator to isolate desired values and then reclassifying the selected feature as one and ‘no data’ values as zero.  The D8 contributing area was calculated and recalculated for each land use using the values determined previously with the weighted grid.  Dividing the D8 contributing area by each weighted contributing area yielded the fraction of upstream contributing area associated with the respective land use.  An example of this procedure using impervious surfaces is shown in Figures 3, 4, and 5.

Figure 3: Impervious Surfaces Weight Grid

Figure 4: Impervious Surfaces D8 Contributing Area

Figure 5: Fraction of Upstream Area Occupied by Impervious Surface

Results

Examining the outflow of the reservoir under natural conditions, total Pineview Reservoir Watershed area is approximately 79,000 hectares.  The contributing land uses associated with this upstream area is summarized in Table 1.  Area not classified under the categories of irrigated land (hay, alfalfa, pasture, idle, grain, and fruit) and impervious is attributed to rangeland.

Table 1: Land Uses Upstream of Reservoir Outlet

Land Use

Fraction

0-Grass Hay

0.0087

1-Alfalfa

0.0203

2-Pasture

0.0131

3-Idle

0.0026

4-Grain

0.0039

5-Fruit

0.0000

Other (Rangeland)

0.9401

Impervious

0.0112

As shown in Figure 6, the North and South Branches of the South Fork of the Ogden River are bracketed by Sites 5 and 4 on the upstream ends, respectively, and Sites 6 and 7 on the downstream ends. 

Figure 6: North and South Branch of the South Fork Ogden River Showing Monitoring Sites

The drainage area by land use associated with each site was determined and Figures 7 and 8 compare the upstream and downstream sites, respectively.

Figure 7: Comparison of Land Uses Draining to Sites 5 and 4

Figure 8: Comparison of Land Uses Draining to Sites 6 and 7

Using export values reported by Lin (2004), Reckow et al. (1980), and Porcella and Sorensen (1980) (see Appendix A), the anticipated nutrient load per year at each site was calculated.  By subtracting the load at the upstream site from the load at the downstream site, the corresponding load from each isolated reach was determined.  Table 2 displays the results for each reach according to land use and as a total.

Table 2: Nutrient Load from each Proposed Monitoring Reach

Monitoring Site

Land Use

Area (ha)

TP (kg/yr)

TN (kg/yr)

North Branch (6-5)

Grass Hay

13.77

14.87

71.47

Alfalfa

26.82

28.97

139.20

Pasture

33.12

49.68

286.49

Idle

19.44

1.94

66.10

Grain

0.00

0.00

0.00

Fruit

0.00

0.00

0.00

Other (Rangeland)

50.85

4.07

45.77

Impervious

4.32

8.25

43.07

Total

148.32

107.78

652.08

South Branch (7-4)

Grass Hay

108.09

116.74

560.99

Alfalfa

278.10

300.35

1,443.33

Pasture

87.48

131.22

756.70

Idle

41.76

4.18

141.99

Grain

22.41

24.20

116.29

Fruit

0.00

0.00

0.00

Other (Rangeland)

6,463.80

517.10

5,817.42

Impervious

14.76

28.20

147.18

Total

7,016.40

1,121.98

8,983.90

Figures 9 and 10 show the distribution of the sources contributing to the nutrient loads for the North and South Branches, respectively.

Figure 9: Land Uses Contributing to Nutrient Load of North Branch Monitoring Reach

Figure 10: Land Uses Contributing to Nutrient Load of South Branch Monitoring Reach

A similar procedure was used to determine the estimated nutrient export from the entire watershed under natural flow conditions (no inundation).  The rate of total phosphorus export was approximately 12,000 kg per year and the total nitrogen rate was 99,000 kg per year.

Discussion

Overall, the dominant landscape for this area is rangeland.  It is roughly approximated in Table 2 as 94%; however, Figure 2 shows that anthropogenic impacts on land use are realized more frequently on the valley floor near the reservoir. 

Examining Figure 7 shows that at the upstream sites (5 and 4), the North Branch is dominated by rangeland and the South Branch is split between alfalfa and rangeland.  In contrast, Figure 8 shows the downstream sites at which the South Branch is dominated by rangeland.  There is currently minimal influence due to impervious surfaces reflecting the large amount of open space still available in this valley.  Comparing the loads of Figures 9 and 10 reveals that the North Branch will exemplify nutrient loads more dominantly attributed to irrigated lands while the South Branch will be more dominated by the loads from rangeland.  TP and TN represent estimates since the actual values will depend on the local export coefficients which remain to be quantified and do not account for any in-stream processes.  As such, this estimates the combined load from the North and South Branches of the South Fork Ogden River contribute 10.2% and 9.7% of the TP and TN exported from the watershed under natural flow conditions.

Conclusion

The dominant landscape in the Pineview Reservoir Watershed is rangeland; however, land use patterns change near the reservoir.  Drainage areas were determined according to land use and nutrient loads were estimated using available export coefficients.  Two reaches on a main tributary were proposed for monitoring and associated loads were calculated for the sites and associated reaches.  By designating loads based on land use, it was found that the North Branch reach would exemplify loads from human impacts such as irrigated lands and the South Branch would be more characteristic of loads from rangeland.  While this is a main tributary hydrologically, it only accounts for approximately 10% the nutrient export from the Pineview Reservoir Watershed under natural flow conditions.

References

ESRI Inc. (1999-2009). ArcMap 9.3.1. ArcGIS Desktop Evaluation Edition 9.3.1 .

ESRI Inc. (2009). Index of ftp://RiverHydraulics@ftp.esri.com/ArcHydro/. Retrieved October 16, 2009, from ftp://ftp.esri.com/ArcHydro/

ESRI Inc. (n.d.). Layers containing online data. Retrieved November 26, 2009, from ArcGIS Resource Centers: http://resources.esri.com/arcgisdesktop/index.cfm?fa=content&tab=Layers

Horizon Systems Corporation. (n.d.). NHDPlus Data. Retrieved November 02, 2009, from National Hydrography Dataset Plus: http://www.horizon-systems.com/nhdplus/data.php

Lin, J. P. (2004, September). Review of Published Export Coefficient and Mean Concentration (EMC) Data. Retrieved November 28, 2009, from Wetland Regulatory Assistance Program: http://el.erdc.usace.army.mil/elpubs/pdf/tnwrap04-3.pdf

Porcella, D. B., & Sorensen, D. L. (1980). Characteristics of Nonpoint Source Urban Runoff and its Effects on Stream Ecosystems. U.S. Environmental Protection Agency , EPA/600/3-80-032.

Reckhow, K. H., Beaulac, M. N., & Simpson, J. T. (1980). Modeling phosphorous loading and lake response under uncertainty: a manual and compilation of export coefficients. U.S. Environmental Protection Agency , 440/5-80-011.

Tarboton, D. G. (2009). Terrain Analysis using Digital Elevation Models (TAUDEM). Retrieved October 09, 2009, from Utah State University Hydrology Research Group: David Tarboton: http://hydrology.neng.usu.edu/taudem/

U.S. Department of the Interior, U.S. Geological Survey. (2009, November 19). The National Map Seamless Server. Retrieved November 02, 2009, from USGS: http://seamless.usgs.gov/index.php

Appendix A

Land Use

Mean (kg/ha/yr)

Range (kg/ha/yr)

Sample Size

TP

TN

TP

TN

TP

TN

Row Crops1

4.46

16.09

0.26-18.6

2.1-79.6

26

11

Non-Row Crops1

1.08

5.19

0.10-2.90

0.97-7.82

13

10

Pasture1

1.50

8.65

0.14-4.90

1.48-30.85

14

13

Idle2

0.1

3.4

 

 

 

 

Rangeland3

0.08

0.9

 

 

 

 

Urban1

1.91

9.97

0.19-6.23

1.48-38.47

23

19

 

 

 

 

 

 

 

1

(Lin 2004)

 

 

 

 

 

2

(Reckhow, Beaulac, & Simpson 1980)

 

 

3

(Porcella & Sorensen 1980)