1. SELECTION ANDPLACEMENT OFBEST
MANAGEMENT PRACTICES TOREDUCE
TOTAL PHOSPHOROUS RUNOFFINA
PASTURE-DOMINATED WATERSHED
HectorG.Rodríguez*
JenniePopp*
ChetanMaringanti**
IndrajeetChaubey**
Brown Bag Speaker Series
December 2, 2010
* Department of Agricultural Economics and Agribusiness, University of Arkansas
** Department of Agricultural and Biological Engineering, Purdue University

2. Presentation Outline
1. Water Quality Issues
2. Objective
3. Methodology
4. Findings
5. Conclusions
6. Implications
7. Study Limitations
8. Future Research

3. 1. Regional Issues
 Animal agricultural is the
economic agricultural driver in
this region
 Agricultural Basins in northwest
Arkansas are designated nutrient
surplus areas
 More nutrients produced in the
watersheds than what can be
assimilated by the current land
use
 Handling of excess nutrients is
one of the challenges in the
region

4. 1. Water Reports
Assessment Reports - Environmental
Protection Agency (EPA):
 Section 303(d)
 list of impaired water bodies
 Section 305(b)
 biennial inventories of conditions and trends of water
 Section 319
 non point source (NPS) pollution
 waters that cannot attain WQS
 Best management practices (BMPs) to control NPS
4

5. 1. Watersheds in Arkansas
Illinois River Watershed
Source: Arkansas Watershed Information System. Arkansas Natural Resources
Commission, 2009.
Source: Illinois River Watershed Partnership, 2010.
Lincoln Lake Watershed

6. 1. Study Site Description
Total Area: 32 km2
Lincoln Lake Watershed
Land Use %
Forest 48.6
Pasture 35.8
Urban 11.9
Water 2.2
Others 1.5
Source: Chaubey et al. (2010).

7. 1. Land Cover
Sources:
* Chaubey et al. (2010).
**Arkansas Watershed Information System. Arkansas Natural Resources Commission, 2009.
http://watersheds.cast.uark.edu/
7
Lland
Lincoln Lake Watershed – 2004* Illinois River Watershed – 2006**

8.  Land application of animal manure
 Land use changes
 303(d) list as impaired for aquatic life
 Primary concern - total phosphorous (TP)
 EPA – TP standard 0.037 mg/L
303(d) list as impaired for aquatic life
Primary concern - total phosphorous (TP)
EPA – TP standard 0.037 mg/L
1. Water Quality Issues

9. 2. Objective
 Evaluate
 Selection
 Spatial distribution
 Minimize
 TP runoff
 Total (BMP implementation) cost
 Optimize
 Non-dominated Sorted Genetic Algorithm
35 BMP Combinations

10. 3. Methodology
Pasture Management
 No Grazing
 Optimal Grazing
Buffer Zone
 0, 15, 30 m wide
Poultry Litter
 Quantity: 0, 2.47, 4.94, 7.41 tons/ha
 Timing: Spring, Summer, Fall
 Alum: Yes, No

11. 3. Methodology
 Soil and Water Assessment Tool (SWAT)
 TP loads output data for each of the 35 BMP
combinations
 Cost data for each BMP combination
 Non-dominated Sorting Genetic Algorithm (NSGA)
 Minimize TP and net cost
 Trade-off curves TP vs. net cost

12. 3. SWAT
72 Sub-basins
 69 (pasture sub-basins)
1465 HRUs
 461 (pasture HRUs)
SWAT output
 For each sub-basin
 35 BMP combinations
 TP (kg/ha) loads

13. 3. Genetic Algorithm (GA)
Optimization
BMP selection, spatial
distribution (placement), TP
reduction and cost of
implementation
Genetic
Algorithm
SWAT
Output
BMP
Cost
Genetic Algorithm (GA) seeks optimal solutions to solve a
search problem by using evolutionary principles of
reproduction, recombination and mutation.
Parameters: Generation, Population, reproduction,
recombination and mutation probabilities (Sensitivity
Analysis)

14. 3. GA
Search Space 35461

15. 3. Optimization

16. 3. Optimization Analysis
The two objective functions that need to be
optimized (minimized) are:
1. TP runoff
2. BMP cost required for placement of BMPs in the
watershed.

17. 3. Optimization Analysis
Trade-off curves that would provide near optimal
solutions for a range of objective function values.

18. 4. Findings
Progress of the trade-off curves for TP and net cost

19. 4. Trade-off Curve
TP vs. net cost – Generation 10,000

20. 4. BMP Combination Frequencies (%) Lowest,
Medium and Highest Cost Solutions
Net Cost
Lowest Medium Highest
Grazing
No 32.5 33.8 15.8
Optimal 64.2 65.7 84.2
Buffer Zone (meters)
0 10.6 1.7 0.4
15 59.2 50.3 22.8
30 26.9 47.5 76.8
Poultry Litter
Quantity (tons/ha)
0.0 3.3 0.4 0.0
2.5 64.9 65.3 48.8
4.9 29.3 31.5 46.2
7.4 2.6 2.8 5.0
Alum
No 86.3 88.3 66.8
Yes 10.4 11.3 33.2
Timing
Spring 45.1 42.1 38.0
Summer 36.4 43.8 43.4
Fall 15.2 13.7 18.7

21. 4. Spatial Distribution
Selection and Spatial Distribution of BMPs to Control TP under three
Cost Solutions for Generation 10,000

22. 4. Findings
 TP runoff could be reduced drastically.
 Optimal grazing management pasture systems are
preferred when TP runoff and net cost were
optimized simultaneously.
 Buffer zones are very effective in reducing TP runoff.
 Low poultry litter application rates (i.e., less than 5
tons per ha) are preferred in terms of TP runoff
reductions.

23. 5. Conclusions
 Implementation costs and spatial distribution of
BMPs within a watershed affect BMP selection.
 Similar results can be achieved with several optimal
solutions that place different combinations of BMPs
in different locations across the watershed.

24. 6. Implications
As stated in Section 319 (CWA), this research helped
to identify BMPs to control NPS pollution.
Specifically this study help to:
 identify optimal solutions to control pollution in
nutrient surplus areas
 weight trade-offs between TP runoff reduction and
net cost increase when selecting BMPs

25. 7. Study Limitations
 The cost data used represented average cost of
implementing BMPs.
 Producers were assumed to bear all the cost of
establishing and maintaining buffer zones. Some
producers are enrolled in cost-share programs.
 Results are watershed specific since modeling was
conducted under specific soil and weather
conditions.

26. 8. Future Research
 Enhancement of the economic component might
include more qualitative information that impacts
the producers’ abilities and desires to adopt BMPs:
 Number of producers enrolled in cost-share programs
 Willingness to invest in new BMPs
 Optimizing sediments, nutrients and net returns
simultaneously