69th SWCS International Annual Conference July 27-30, 2014 Lombard, IL

1. Evaluating Wetland Impacts on
Nutrient Loads within Watershed
Systems Using AnnAGNPS
• Ronald L. Bingner, USDA-ARS, Oxford, MS
• Jill Kostel, The Wetland Initiative, Chicago, IL
• Jim Monchak, The Wetland Initiative, Chicago, IL
• Yongping Yuan, USEPA, Las Vegas, NV
• Henrique Momm, Middle TN State Univ.,
Murfreesboro, TN

2. Introduction
 Nutrient losses to surface waters are of great
concern on both national and regional scales.
 Large areas of hypoxia in the northern Gulf of
Mexico are due to excessive nutrients derived
primarily from agricultural runoff via the
Mississippi River.
 Excessive pollutant loading is also responsible for
algal blooms and associated water quality
problems in lakes and rivers.

3. Nutrient Management Approaches
Fertilizer management include improved timing of
N application at appropriate rates, using soil tests
and plant monitoring to split applications,
diversifying crop rotations, using cover crops
(Dinnes et al., 2002).
Creation of wetlands, riparian buffers or other
biofilters (Mitsch et al., 2001; Crumpton et al.,
2007); and integrated wetland riparian buffers.
Improved drainage management practices
(Skaggs et al., 2005).
Integrated drainage wetland systems.
Etc.

4. Implement wetland & riparian buffer
technology within watershed models for
an integrated watershed system
conservation management approach

5. Integrating Wetland & Buffer
Components within Watershed Models
Cell F
Cell E
Cell D
Cell CCell A
Cell B
watershed
outlet
feedlot
gully
A wetland is located on reach 2, buffer in reach 1, more wetlands
can be constructed on other reaches such as reach 1 and 3

7. 0.136
0.082
1.411
1.661Dormant season
Max farm
effluent load
0.04 0.05
0.55
1.08
N P
kg/ha
Outlet load
N P
kg/ha
Growing season
2004 – Ditch reduction capacity
N: 71% decrease
P: 40% decrease
N: 61% decrease
P: 35% decrease

8. • Modification of natural
wetland receiving
agricultural runoff by
adding water control
structures

9.  Comprehensive sampling of
vertebrates using these
habitats revealed that sites
with:
 large area, woody
vegetation, and permanent
pool yielded 65 to 82
vertebrate species
 smaller sites yielded only 11
to 20 species

10. Objective
Develop technology describing
wetland and riparian buffer
processes to evaluate their
effectiveness towards reducing non-
point source pollution leading to
evaluations of integrated
conservation practice within
watershed systems.

11. AnnAGNPS
(Annualized Agricultural Non‐Point Source) pollution model
Agricultural Research Service
A partnering effort between the USDA:
and
Natural Resource Conservation Service

12. AnnAGNPS
• Developed as a tool to evaluate the integrated
effect of all conservation practices within ungaged
watersheds, particularly for USDA‐NRCS
recommended practices, and identify sources of
water quality pollutants for:
• Water Quantity
• Sheet & rill erosion
• Gully erosion
• Channel erosion
• Chemical water quality
• Buffers and wetlands

13. Simulation of Wetland Nitrogen Removal
 Identify critical physical and chemical processes.
 Develop appropriate algorithms for simulating
these processes.
 Defining needed parameters for model simulation.
 Apply a mass balance approach is used to simulate
hydrologic and water quality processes in the
wetland.

14. Hydrology Balance
Where:
 Vi= amount of water per unit area in the wetland at the end of the day
(mm),
 Vi-1= amount of water per unit area in the wetland at the beginning of
the day (mm),
 Qinflow = amount of water added to the wetland during the day (mm),
 Qoutflow = amount of water released from the wetland during the day
(mm),
 P = precipitation on current day, from climate data information (mm),
 ET = daily evaporation or evapotranspiration (mm),
 I=daily infiltration, or seepage to the groundwater after inundation
(mm),
IETPQQVV outflowlowii   inf1
)1(
Wetland Component Development

15. Nitrogen Loss Calculation
Where:
 J = N loss rate (g m-2 day-1),
 K20 = the area based first order loss rate coefficient (m/day),
• C = the concentration of N in wetland (mg/L or g/m3),
• θ = the temperature coefficient for N loss, and
• T = water temperature (oC).
)20(
20 ** 
 T
CkJ 
A temperature dependent first-order model
developed by Crumpton et al., (1997) is used:
)3(

16. Where:
• S = N loss from the wetland on a given day (kg),
• J = N loss rate (g m-2 day-1), and
• Awetland = wetland surface area (m2)
1000
* wetlandAJ
S 
Nitrogen Loss Calculation
)4(

17. Simulation Sequence
 1) Simulate the amount of water and pollutant in
the wetland at the beginning of a day.
 2) Determine N loss during the day based on
equations 3 & 4.
)20(
20 ** 
 T
CkJ 
1000
* wetlandAJ
S  )4(
)3(

18. Simulation Sequence
 3) Determine the hydraulic head (H) is calculated
as a function of the water in the wetland:
)5(weirH
V
H 
1000
Where:
• H = hydraulic head on a given day (m),
• V = amount of water per unit area in a wetland on a
given day (mm), and
• Hweir = the height of a weir (m).

19. Simulation Sequence
 4) Determine the amount of flow out of the
wetland and the amount of N released with water
is calculated using equations 6 & 7.
)6(5.1
_ ** HLBQ outflowvolume 
1000
* _ outflowvolumeoutflow
outflow
QC
M  )7(
Where:
• Qvolume_outflow = total volume of water flow out of the
wetland on a given day (m3),
• B = the weir coefficient and it is determined by a user,
• L = width of the weir opening (m), and

20. Simulation Sequence
 5) the amount of water in the wetland is updated
using equation 1; and the amount of N in the
wetland is updated using equation 2.
)2(
)1(IETPQQVV outflowlowii   inf1
SMMMM outflowlowii   inf)1(
 6) The steps 1-5 are repeated for each day.

21.  Large wetlands relative to the contributing
drainage area can be most effective in
improving water quality.
 Highly sensitive to temperature and retention
time impacted by flow.
 Greatest nitrogen removal efficiency can be
achieved during low flow conditions with a
retention time of at least one-two weeks.
 Additional water quality benefits can be
obtained when wetlands are incorporated with
riparian buffers.
Wetland Nitrogen Removal Efficiency

22. March 2013 Watershed‐Scale Characterization of Riparian Vegetation as Potential Filter Strips using Multi‐Source Remote Sensing 22
In‐field and edge‐of‐field buffer types

23. Integration of Riparian Zones Within AGNPS
Riparian Buffer System
Stream
Field
Drainage with
transport of sediment
& chemicals

24. Influence of natural and/or planted riparian
(streamside) vegetative buffer strips
The amount of sediment/chemicals trapped by buffers is
affected by:
• Width of the riparian buffer
• Type of vegetation cover
• Amount and intensity of rainfall
• Runoff characteristics
• Local terrain slope

25. Trapping Efficiency of Grass Buffers
< 5% slope

26. Trapping Efficiency of Grass Buffers
> 5% slope

27. Trapping Efficiency of Forest Buffers

28. Buffer length needed
for mitigation
Chlorpyrifos 184-230 m
Atrazine 101-281 m
Metolachlor 100-400 m
Methyl Parathion (plants) 18.8 m
Methyl Parathion (no plants) 62.9 m

29. AGBUF
AGNPS‐GIS Buffer Utility Feature
Provides buffer characterization for
AnnAGNPS input parameters

30. AGBUF
Riparian Buffer GIS representation
AnnAGNPS cells &
reaches
Buffer

31. AGBUF (continued)
TE Estimation in AnnAGNPS Cells includes the effect of
concentrated flow paths through buffers (short‐circuits)
A
0
0
0
1 2
3 4
5 6 TE = 97%
Potential short‐
circuits
TE = 90%
TE = 47%
Varying widths & lengths

32. BIG BUREAU CREEK WATERSHED

33. Land Cover
 92% agriculture
 77% cultivated crops
BIG BUREAU CREEK WATERSHED

34. NUTRIENT REDUCTION
Nutrient Management Practices
 Nutrient management plans
 Conservation tillage practices
 Cover crops
 Prescribed grazing
 Fencing
 Grassed waterways and control structures
Nutrient Reduction Practices
 Riparian buffers
 Drainage water management systems
 Constructed wetlands
Source:USDAARSSource:USDAARS
Constructed Wetland for Tile Drainage
 Wetland size and positioning key to nutrient removal
 Positioned to capture high nutrient loads
 Sized to allow adequate residence time (0.5 – 5%)

35. BBC POTENTIAL WETLAND SITES
 Total Number of Wetland Complexes = 80
 Total Wetland Area = 225 ha
 Range of Wetland Sizes = 0.14 - 38.7 ha
 Total Wetland & Buffer Area = 351 ha
 Range of Wetland & Buffer Area = 0.54 – 46.5 ha
 Area : Total BBC Watershed Area = 0.3%
 % of Runoff of BBC Watershed = 23%

36. Model Input (Data)
 Climate – 30 year daily simulated weather
 Topographic – 10 m DEM
 Land use – 2009 Illinois Cropland Data Layer
 Soil type – USDA Soil Survey Geographic database (SSURGO)
 Point sources – Average Design Flow rates and estimated effluent
concentrations
ANNAGNPS MODEL

37. Baseline Results:
Nutrients
 TN Load = 2,542,400 kg
 TN Loss = 20.4 kg/ha
 NO3-N = 72%
 TP Load = 60,150 kg
 TP Loss = 3.7 kg/ha
 Attached P = 56%
 Dissolved Inorganic P = 14%
 TSS = 100,446 Mg
Point Sources
 TN = 0.70% increase
 TP = 0.66% increase
Seasonal Effects
 Spring and summer
seasons higher loadings
ANNUAL AVERAGE LOAD DELIVERED

38.  The 351 ha of wetlands plus buffer would reduce the entire
BBC watershed TN and TP load by an average annual of 14%
and 11%, respectively.
 NO3-N accounted for 84% of the TN removed by potential
wetlands plus buffer.
 Dissolved inorganic P accounted for only 14-17% of TP
removed by the potential wetlands plus buffer attached.
ANNAGNPSWETLAND & BUFFER FEATURE

39. ANNUAL LOAD DELIVERED-NITROGEN
_ g
0 - 8.288
8.288 - 18.74
18.74 - 25.655
25.655 - 36.675
36.675 - 93.317
 With Buffers and Wetlands Without Buffers and Wetlands
kg/ha/yr

40. Summary
• Technology has been developed within AnnAGNPS to
evaluate wetland and riparian buffer effects on
pollutant loads at a watershed‐scale
• AnnAGNPS incorporates source load technology to
assess wetland and buffer capability to reduce
pollutant loads at any location within a watershed

41. Questions