Transcript Chris Lenhart SWCS Nov. 13-15, 2012  Issues  Theory  Methods  Phos loading at multiple scales  Case Studies  Approaches to quantifying P load.

Chris Lenhart
SWCS Nov. 13-15, 2012
 Issues
 Theory
 Methods
 Phos
loading at
multiple scales
 Case Studies
 Approaches to
quantifying P load
 Increased
loading of sediment from
channels
 Most P carried attached to soils
 Soluble P contributes to eutrophication
 Need practical way to quantify channel
loading of sediment and phosphorus for
TMDLs
HYDROLOGIC CHANGE
Blue Earth River, MN
CHANNEL WIDENING
EQUILIBRIUM

Erosion on outer bend
balanced by deposition &
nutrient processing
DISEQUILIBRIUM




Increased flows
Channel widening
Loss of sinuosity
Reduced retention
To develop approach to prioritize sites for
sediment and phos reduction in TMDLs
To understand mechanical and hydrologic
processes of channel erosion
 How
do sed and phos loading by
streambanks vary by soil properties and
by ecoregion?
PHOSPHORUS CYCLE




Geologic cycle
Most (95%) P lost in
particulate form
P In soil – 200-900 mg/kg
P in streambanks thought
to be lower than farm
fields
EUTROPHICATION

Limiting nutrient in fresh
H2O; SRP a key to
eutrophication (low in
streambanks)
 Approach
 Phos
Sampling
• Streambanks
• Floodplain and
sandbar
• By depth
 Phosphorus
tests
• Total P, n=65
(streambanks)
• Olsen P, n=50
95% correlation with
SRP (Fang et al. )
 Loading
estimates
• Measure historic
migration, change in
width in GIS
• Develop regionspecific BANCS
indices
• Monitor select sites
to verify
• BSTEM modeling for
comparison
GIS -CHANNEL MIGRATION
BANCS MODEL PREDICTION
Median TP by watershed
(ppm)
Olsen P by watershed or
stream type (ppm)
714
30
643
553
548
423
15
13
6
4
Elm Cr
Whitewater
Buffalo
Minnesota
Steep MN
tribs
Elm Cr
Whitewater
Buffalo
Minnesota
Steep MN
tribs
% sand in streambanks vs. total Phosphorus
Total Phos. (mg/kg)
1000.00
800.00
600.00
400.00
200.00
R² = 0.507
0.00
0.0
20.0
40.0
60.0
% sand
MN River
80.0
100.0
CROSS SECTION
ELM CREEK STREAMBANK
0.0
0
-10.0
-20.0
-30.0
-40.0
Depth
(inch)
-50.0
-60.0
-70.0
-80.0
-90.0
-100.0
5
10
15
20
Olsen P (mg/kg)
Minnesota River Valley
Blue = high TP
Red = low TP
 Loss of sinuosity
(Verry 2001; Yan et al.; 2010;
Lenhart et al. 2011)
 Entrenchment
 Less
P deposited
 More P downstream
Elm Cr15% loss of
length
Explains why water
quality improvements
may lag behind land
management
SEDIMENT SOURCES
Streambanks and adjacent
features (bluff and ravines)
comprise 70% of sed. load,
(900,000 tons/year)
STREAMBANK EROSION




Up to 4 m/year on outer
bends
Net widening of 1-2% per
year since 1938 from
Mankato to St. Paul
Load from bank erosion in
lower river alone is
280,000 tons (1/3 of total
load) (over 1938-2009)
1000 m
Chatfield Road
monitoring site
67 m -> 91 m
Lower MN River
1938-2009
2008 channel
1938
channel
62 m ->
129 m
58 m -> 100 m
Increase in
channel slope
due to cut-off
 TP
avg. 548 mg/kg
 Olsen P 13 mg/kg
 Total
load
153 Mg/year from
lower MN River (not
counting upper MN
river and tribuatries)
16% of total P load (908
tons/year)
Buffalo
Elm Creek
Whitewater
PHOS CONCENTRATION


TP – 714 mg/kg
Olsen P – 15mg/kg
BANK EROSION RATES
PHOS CONCENTRATION


TP – 643 mg/kg
Olsen P – 30 mg/kg
BANK EROSION RATES
PHOS CONCENTRATION


TP – 553 mg/kg
Olsen P – 4 mg/kg
BANK EROSION RATES
ST. LOUIS RIVER

northern forest region
MAUMEE RIVER

Glacial lake plain
 Watersheds
undergoing
hydrologic change
and channel
adjustment with
erodible soils tend to
have high P-loads
 Many regions will
have small loads of
streambank P
 Streambanks
in our
dataset have similar
TP levels to uplands
but lower Olsen P
 Difficult to scale-up
local results to whole
river basins
 Net transport hard to
quantify
 Standardize
methods
 Scale up BANCS via LiDar, GIS
 Targeting from a technical standpoint
• Scaling up field data for GIS
• Which sites make sense / are“restorable”?
 Targeted
policies to reduce P
• Reduce streamflow
• Near channel practices - Targeted Buffers
• In-channel work for highest loading sites and
with additional benefits
SCIENCE


How to account for
deposition? Can’t use
remote sensing.
Transformation of P in
rivers; sources and sinks
IMPLEMENTATION


Where to target?
BMPs at hotspots vs. landuse policies?
 Funders
 Collaborators
• MN Department of
• Dr. John Nieber, BBE
Agriculture (2011-2014
• MN Corn Growers
Association (20102011)
• MN Pollution Control
Agency – Ravine, Bluff,
Streambank erosion
study
Professor
• Jason Ulrich, BBE
fellow
 Workers
• Ben Underhill
• Nick Moore
• Laura Triplett