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Modeling Nutrient Loads From Poultry Operations in the Toledo Bend Reservoir and
Sam Rayburn Reservoir Watersheds
Carl Amonett, T. Dybala and T. MarekWater Resources Assessment TeamTemple, Texas
Project Location
Sam Rayburn Land Use
0%7%
21%
9% 5%
41%
17%
Toledo Bend Land Use
0%
5%
16%
10% 7%
43%
19%
Water Quality Management Plans
Objective:
Quantify Benefits of 674 Poultry CAFO WQMPs on 35,591 ha
Too Many Birds
Chickens / Year
Manure Production
Tonnes/Year
Applied to Pasture/Hay
No Cropland Applications
Nutrient Production
N (PAN) – 5,311 tonnes
P2O5 – 8,870 tonnes
K2O – 6,349 tonnes
Nutrient Values
N – $5,854,000
P2O5 – $7,822,000
K2O – $3,499,000
Conservation Practices (BMPs) Waste Utilization
Nutrient & Pest Mgt
Pasture & Hayland Planting
Buffer Practices
Prescribed Grazing
Forage Harvest Mgt
Waste Storage Facility
Tree Establishment
Other Forestry Practices
Methods
3,675 Planned Fields
Boundaries Delineated
Database Assembled
SWAT Land Use Map Overlaid
Special SWAT Landuses Reflect Soil P and Nutrient Mgt.
Nutrient Application (Manure)L M H VH
none 0 - 1 tons 1 - 3 tons 3+ tonsL 0 - 15 ppm TPLL TPLM TPLH TPLV
Soil P M 15 - 75 ppm TPML TPMM TPMH TPMVH 75 - 200 ppm TPHL TPHM TPHH TPHVVH 200+ ppm TPVL TPVM TPVH TPVV
Special Land Uses
A Few Other Landuses:TBAP Grass PlantingTBHA Hayland – Commercial FertilizerTBHQ Headquarters / Poultry HousesTBPA Pasture – Commercial Fertilizer
Calibration / Validation
Flow Calibration / Validation
Sam RayburnReservoir
Toledo BendReservoir
111 Subbasins2,876 HRUs
107 Subbasins2,523 HRUs
Flow Calibration / Validation
Gauge ENS PBIAS8034500 0.82 / 0.82 1.9 / 12.58033900 0.81 / 0.72 7.7 / 13.28037050 0.78 / 0.64 2.2 / 4.98037000 0.71 / 0.74 6.4 / 1.68038000 0.78 / 0.70 13.2 / 9.98039100 0.64 / 0.69 8.2 / 7.4
Sam Rayburn Watershed
Flow Calibration / Validation
Gauge ENS PBIAS8022070 0.69 / 0.79 -0.12 / 1.18022400 0.88 / 0.67 1.95 / 0.278022300 0.75 / 0.68 -3.62 / -4.738022500 0.97 / 0.96 -2.1 / 1.478023200 0.82 / 0.82 0.08 / -3.338024500 0.60 / 0.61 -11.96 / 1.988024400 0.90 / 0.90 -0.60 / -9.56
Toledo Bend Watershed
P Calibration
0
1
2
3
4
18302 SWAT 14477 SWAT 10532 SWAT 10633 SWAT 16076 SWAT 10475 SWAT 10474 SWAT 15253 SWAT 15361 SWAT
MG
/L
Sam Rayburn Watershed – Total P median with 25th and 75th percentile data
Nine Sampling Sites With Very Limited Data
N Calibration
Sam Rayburn Watershed – Total N median with 25th and 75th percentile data
Nine Sampling Sites With Very Limited Data
0
1
2
3
4
5
6
7
8
18302 SWAT 14477 SWAT 10532 SWAT 10633 SWAT 16076 SWAT 10475 SWAT 10474 SWAT 15253 SWAT 15361 SWAT
MG
/L
Baseline Condition
Reference scenario
Dry litter CAFOs
No regular soil tests for nutrient balance
Manure applied to same fields year after year
Excess P in soils – often 250 – 750+ ppm
Manure applied to dormant forages / saturated soils
No buffers on streams, ponds and wells
Open gate grazing
Modeling Conservation Practices
Nutrient application rate & timing – mgt files
Buffers – field borders, riparian & filter strips – mgt files
Curve number – fair to good condition on pasture & hayland – mgt files
New Ponds and grade structures – pnd files
Heavy Use Area Protection – CNs and mgt files
Tree planting & grass planting land use conversions
Results
Results Farm (HRU) Level
Sam Rayburn:
P loadings reduced 34 to 91 percent
N loadings reduced 16 to 87 percent
Sediment loadings reduced 42 to 78 percent
Toledo Bend:
P loadings reduced 64 to 84 percent
N loadings reduced 30 to 79 percent
Sediment loadings reduced 65 to 74 percent
Results Subbasin Level
Sam Rayburn:
P loadings reduced 0 to 33 percent
N loadings reduced 0 to 21 percent
Sediment loadings reduced 0 to 29 percent
Toledo Bend:
P loadings reduced 0 to 75 percent
N loadings reduced 0 to 39 percent
Sediment loadings reduced 0 to 75 percent
Percentage Reductions – Sam Rayburn Watershed
P
N
Sediment
At Four Subbasin Locations On the Main Channels
9.6
4.5
2.6
% Reduction
0.6 0.1 0.1
% Reduction
11.5
1.4 0.9
% Reduction
6.7
0.4 0.2
% Reduction
Percentage Reductions – Toledo Bend Watershed
14
2.90.1
% Reduction
15.5
8.9
4.4
% Reduction
9.3
20.1
% Reduction
P
N
Sediment
At Four Subbasin Locations On the Main Channels
29
14.3
8.7
% Reduction
Conclusions
674 WQMPs were modeled.
20 Special SWAT landuses were created for modeling soil P and nutrient application rates.
Two scenarios were modeled: (1) current conditions, and (2) post WQMP implementation.
P loadings at field level were reduced 35 to 90 percent.
P loadings at subbasin level were reduced 0 to 75 percent.
P loadings at watershed level were reduced from 1 to 29 percent.
SWAT 2005 worked well for modeling the hydrology, nutrients and sediment of these two watersheds.
Modeling Report:
C. Amonett, T. Dybala, T. Marek. 2008. Modeling Nutrient Loads From Poultry Operations in the Toledo Bend Reservoir and Sam Rayburn Reservoir Watersheds. Report to Texas State Soil and
Water Conservation Board, April, 2008.
http://www.tx.nrcs.usda.gov/technical/wrat/docs/Poultry_study_final_report_md.pdf