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

camonett@brc.tamus.edu