Identifying Riparian Zones Appropriate for Installation of ... · MLRA 108c: Steeper terrain,...
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MLRA 108c: Steeper terrain, moderately tiled and most incised Identifying Riparian Zones Appropriate for Installation of Saturated Buffers: A Multi-Watershed Assessment Introduction A key aspect of agricultural watershed conservation lies in matching practices to suitable locations where pollutant delivery to streams can be most effectively decreased. This is of vital importance in the U.S. Midwest, where nitrate losses from croplands are a dominant contributor to Gulf of Mexico hypoxia (USEPA, 2008, 2013; Schilling et al., 2015). Optimal practice- placement strategies could prove most useful if they can be trialed/demonstrated over a range of landscapes. This study compared extents of suitable locations for saturated buffers across nine HUC12 watersheds selected from three different major land resources areas (MLRAs) in Iowa (Fig. 1). Saturated buffers enhance denitrification by diverting subsurface tile flow into a vegetated riparian buffer (Fig 2). Criteria for suitable sites identify soil conditions that enhance denitrification and terrain attributes that minimize unintended consequences of bank sloughing and crop inundation. Methods • Nine HUC12 watersheds were randomly chosen from three MLRAs (Fig. 1). • The Riparian Denitrifying Practices tool from the Agricultural Conservation Planning Framework (ACPF) Version 2 Toolbox (Porter et al., 2016) was used to identify riparian assessment polygons (RAPs; Tomer et al., 2015) suited for saturated buffer placements (figure 2). Specified criteria include: • 35% of soils within 20 m of stream area must have average organic matter >1.7% from 0-100 cm depth, sand and gravel contents of <50% from 50-150 cm, and a seasonal water table depth of <1 meter (Apr-Jun). • At least 35% of the riparian zone must have slopes from 2-8% and estimated bank height must be ≤ 2.4 m. • Agricultural land cover (crop or pasture) must occur within the riparian zone. • The total numbers of RAPs, and those RAPS that met the above criteria, were mapped and counted. The number of agricultural fields expected to be tile drained was also estimated for each watershed using the ACPF. • Reasons that RAPs failed saturated buffer criteria were recorded. Results Figure 1. Three MLRAs in Iowa and randomly selected watersheds. HUC12 Name # Riparian Polygons % Agric. Fields Tile Drained / % RAPS Suited for Saturated Buffers 70200090101 Union Slough Ditch 120 79% / 21% 71000040401 Deer Creek 186 80% / 1% 71000061301 Greenbrier Creek 170 80% / 33% 70600060209 Spring Branch 158 35% / 0% 70802050901 Elk Run 262 63% / 49% 70802051401 Headwaters Prairie Creek 258 76% / 65% 70802090604 English River 156 34% / 27% 70801070101 West Fork Crooked Creek 430 63% / 63% 71000081506 Calhoun Creek 332 24% / 11% Table 1. Count of riparian zones, percent of tile drained ag fields, and percent of RAPs found suitable for saturated buffers within each HUC12 watershed. Reasons for saturated buffer disqualification are reported below. Figure 3. Riparian polygons are shown in white outline, riparian zones suitable for saturated buffers are highlighted in yellow. Where SOM criterion was the sole reason for failure, carbon enhancement (bioreactor walls) could be combined with the practice (light brown). Riparian Assessment Polygons (RAPs) are 90 by 250 m (Tomer et al., 2015). Fields likely to be tile drained are shown with pink cross-hatch. Reasons for saturated buffer disqualification (counts): 9 107 4 32 6 70600060209 15 45 9 10 3 13 702000090101 1 71 11 10 36 28 17 10 71000040401 45 15 13 3 28 3 7 71000061301 14 50 2 27 43 70802050901 2 18 16 4 26 13 4 20 70802090604 12 6 9 84 1 12 38 2 70801070101 13 73 4 70802051401 63 6 60 23 11 8 84 39 71000081506 Porter, S.A., M.D. Tomer, D.E. James, and K.M.B. Boomer. 2016. Agricultural Conservation Planning Framework: ArcGIS Toolbox User’s Manual Version 2. USDA Agricultural Research Service, National Laboratory for Agricultural and the Environment, Ames Iowa. Schilling, K.E., Wolter, C.F., and McLellan, E. 2015. Agro-hydrologic Landscapes in the Upper Mississippi and Ohio River Basins. Environmental Management, 55:646-656. Tomer, M.D., K.M.B. Boomer, S.A. Porter, B.K. Gelder, D.E. Jams, and E. McLellan. 2015. Agricultural Conservation Planning Framework: 2. Classification of Riparian Buffer Design Types with Application to Assess and Map Stream Corridors. J. Environ. Qual. doi: 10.2134/jeq2014.09.0387. United States Environmental Protection Agency (USEPA) 2008. Hypoxia in the Northern Gulf of Mexico, an update by the EPA ScienceAdvisory Board. EPA, Washington, DC. United States Environmental Protection Agency (USEPA) 2013. National rivers and stream assessment, 2008-2009, Draft Report. EPA, Washington, DC. Concluding comments • Proportions of RAPs suitable for saturated buffers found within watersheds varied within and among MLRAs. Landform region (MLRA) does not indicate the potential extent of the saturated buffer practice. However, the extents of tile drainage and of RAPs suited for the saturated buffer practice were correlated (R=0.99) in two MLRAs, but not MLRA 103 which is most heavily tile drained and most extensively ditched. • Major reasons for RAP disqualification varied but topography/high banks were major reasons in watersheds with steep and dissected landscapes. • The saturated buffer siting tool was evaluated in the field in about ten watersheds during the 2016 field season, with favorable results. Site specific investigations are required for site specific design and installation. References M.D. Tomer 1 , D.B. Jaynes 1 , S.A. Porter 1 , D.E. James 1 , T.M. Isenhart 2 , and J.D. Van Horn 1 1- USDA/ARS – NLAE, Ames, IA; 2- Iowa State Univ., Dept. Nat. Resour. Ecol. Mange., Ames, IA Figure 2. Basic design & function of a saturated buffer. Figure 4. Extents of tile drained fields and of RAPs suited as saturated buffers, by watershed, were correlated (R=0.99) in two of the three MLRAs MLRA 103: Flat terrain, heavily tiled and ditched MLRA 104: Rolling terrain, moderately tiled and incised 0 25 50 75 0 50 100 % RAPS suited % Fields tile drained MLRA 103 MLRA 104 MLRA 108c
Transcript of Identifying Riparian Zones Appropriate for Installation of ... · MLRA 108c: Steeper terrain,...
MLRA 108c:
Steeper terrain,
moderately tiled
and most incised
Identifying Riparian Zones Appropriate for
Installation of Saturated Buffers: A Multi-Watershed Assessment
Introduction
A key aspect of agricultural watershed conservation lies in
matching practices to suitable locations where pollutant delivery
to streams can be most effectively decreased. This is of vital
importance in the U.S. Midwest, where nitrate losses from
croplands are a dominant contributor to Gulf of Mexico hypoxia
(USEPA, 2008, 2013; Schilling et al., 2015). Optimal practice-
placement strategies could prove most useful if they can be
trialed/demonstrated over a range of landscapes. This study
compared extents of suitable locations for saturated buffers
across nine HUC12 watersheds selected from three different
major land resources areas (MLRAs) in Iowa (Fig. 1). Saturated
buffers enhance denitrification by diverting subsurface tile flow
into a vegetated riparian buffer (Fig 2). Criteria for suitable sites
identify soil conditions that enhance denitrification and terrain
attributes that minimize unintended consequences of bank
sloughing and crop inundation.
Methods
• Nine HUC12 watersheds were randomly chosen from three MLRAs (Fig. 1).
• The Riparian Denitrifying Practices tool from the Agricultural Conservation Planning
Framework (ACPF) Version 2 Toolbox (Porter et al., 2016) was used to identify
riparian assessment polygons (RAPs; Tomer et al., 2015) suited for saturated buffer
placements (figure 2). Specified criteria include:
• 35% of soils within 20 m of stream area must have average organic matter
>1.7% from 0-100 cm depth, sand and gravel contents of <50% from 50-150
cm, and a seasonal water table depth of <1 meter (Apr-Jun).
• At least 35% of the riparian zone must have slopes from 2-8% and estimated
bank height must be ≤ 2.4 m.
• Agricultural land cover (crop or pasture) must occur within the riparian zone.
• The total numbers of RAPs, and those RAPS that met the above criteria, were
mapped and counted. The number of agricultural fields expected to be tile drained
was also estimated for each watershed using the ACPF.
• Reasons that RAPs failed saturated buffer criteria were recorded.
Results
Figure 1. Three
MLRAs in Iowa
and randomly
selected
watersheds.
HUC12 Name# Riparian
Polygons
% Agric. Fields Tile Drained /
% RAPS Suited for Saturated Buffers
70200090101 Union Slough Ditch 120 79% / 21%
71000040401 Deer Creek 186 80% / 1%
71000061301 Greenbrier Creek 170 80% / 33%
70600060209 Spring Branch 158 35% / 0%
70802050901 Elk Run 262 63% / 49%
70802051401 Headwaters Prairie Creek 258 76% / 65%
70802090604 English River 156 34% / 27%
70801070101 West Fork Crooked Creek 430 63% / 63%
71000081506 Calhoun Creek 332 24% / 11%
Table 1. Count of riparian zones, percent of tile drained ag fields, and percent of RAPs found suitable for saturated
buffers within each HUC12 watershed. Reasons for saturated buffer disqualification are reported below.
Figure 3. Riparian polygons are shown in white outline, riparian zones suitable for saturated buffers are highlighted in yellow. Where SOM
criterion was the sole reason for failure, carbon enhancement (bioreactor walls) could be combined with the practice (light brown). Riparian
Assessment Polygons (RAPs) are 90 by 250 m (Tomer et al., 2015). Fields likely to be tile drained are shown with pink cross-hatch.
Reasons for saturated buffer disqualification (counts):
9
107
4
32
6
70600060209
15
45
9
10
3 13
7020000901011
71
1110
36
28
1710
71000040401
45
15133
28
37
71000061301
14
50
2
27
43
708020509012
18
16
4
26
13
4
20
70802090604
126
9
84
1
12
38
270801070101
13
73
4
70802051401
63
6
60
2311
8
84
39
71000081506
Porter, S.A., M.D. Tomer, D.E. James, and K.M.B. Boomer. 2016. Agricultural Conservation Planning Framework: ArcGIS Toolbox User’s Manual Version 2. USDA Agricultural Research
Service, National Laboratory for Agricultural and the Environment, Ames Iowa.
Schilling, K.E., Wolter, C.F., and McLellan, E. 2015. Agro-hydrologic Landscapes in the Upper Mississippi and Ohio River Basins. Environmental Management, 55:646-656.
Tomer, M.D., K.M.B. Boomer, S.A. Porter, B.K. Gelder, D.E. Jams, and E. McLellan. 2015. Agricultural Conservation Planning Framework: 2. Classification of Riparian Buffer Design
Types with Application to Assess and Map Stream Corridors. J. Environ. Qual. doi: 10.2134/jeq2014.09.0387.
United States Environmental Protection Agency (USEPA) 2008. Hypoxia in the Northern Gulf of Mexico, an update by the EPA Science Advisory Board. EPA, Washington, DC.
United States Environmental Protection Agency (USEPA) 2013. National rivers and stream assessment, 2008-2009, Draft Report. EPA, Washington, DC.
Concluding comments
• Proportions of RAPs suitable for saturated buffers found within watersheds varied within
and among MLRAs. Landform region (MLRA) does not indicate the potential extent of the
saturated buffer practice. However, the extents of tile drainage and of RAPs suited for the
saturated buffer practice were correlated (R=0.99) in two MLRAs, but not MLRA 103 which
is most heavily tile drained and most extensively ditched.
• Major reasons for RAP disqualification varied but topography/high banks were major
reasons in watersheds with steep and dissected landscapes.
• The saturated buffer siting tool was evaluated in the field in about ten watersheds during
the 2016 field season, with favorable results. Site specific investigations are required for
site specific design and installation.
References
M.D. Tomer1, D.B. Jaynes1, S.A. Porter1, D.E. James1, T.M. Isenhart2, and J.D. Van Horn1
1- USDA/ARS – NLAE, Ames, IA; 2- Iowa State Univ., Dept. Nat. Resour. Ecol. Mange., Ames, IA
Figure 2. Basic
design & function
of a saturated
buffer.
Figure 4. Extents of tile drained
fields and of RAPs suited as
saturated buffers, by watershed,
were correlated (R=0.99) in two of
the three MLRAs
MLRA 103:
Flat terrain,
heavily tiled
and ditched
MLRA 104:
Rolling terrain,
moderately tiled
and incised
0
25
50
75
0 50 100
% R
AP
S su
ite
d
% Fields tile drained
MLRA
103
MLRA
104
MLRA
108c
