John Kovar USDA-ARS National Lab for Agriculture and the Environment

Tom Isenhart, Michael Thompson, and Jim Russell Iowa State University

NABS

Goals for the Presentation

1. Stream power (Lane’s equilibrium)

2. Stream bed and bank erosion

3. Management options

4. Phosphorus source-sink relationships

Impacts of Suspended and Bedded Sediments

1. Direct Effect on Aquatic Life • Visibility impairment (prey capture and avoidance,

reproductive cues)

• Physical abrasion

• Clogging of filtration and respiratory organs

• Smothering and entrapment

2. Indirect Effects on Physical Habitat • Decreased productivity

• Elimination of interstitial spaces used for reproductive

habitat, feeding, and cover

• Limit oxygen transport

3. Effect on Uses Other Than Aquatic Life • Recreation

• Drinking Water

Existing Iowa Water Quality Criteria for Sediment

61.3(2) General water quality criteria. The

following criteria are applicable to all surface

waters including general use and designated

use waters, at all places and at all times for

the uses described in 61.3(1)”a”.

f. The turbidity of the receiving water

shall not be increased by more than 25

Nephalometric units (NTU) at any point

source discharge.

Iowa DNR

Gully Erosion Stream Bank Erosion

Surface Runoff Cattle Access Points

USDA-NRCS

USDA-NRCS

ISU - NREM

ISU - NREM

Streams are Machines!

= Stream Power

(after Schumm, Harvey, Watson, 1984)

10 1930s 1990s 2007

Channel r esponse

1750 1850 1950 2050 Present

Stable?

Sediment Supply/

Transport capacity

Land use/

Management

Prairie/

Forest/

Wetland

Agriculture

Soil Conservation

Modified from Rakovan and Renwick, 2011

Channel r esponse

1750 1850 1950 2050 Present

Erosion Deposition Stable?

Sediment Supply/

Transport capacity

Land use/

Management

Prairie/

Forest/

Wetland

Sediment Supply

Modified from Rakovan and Renwick, 2011

Agriculture

Transport Capacity

Post-settlement alluvium

Changes Affecting Sediment Flux – Legacy Sediments

Pre-Row Crop Floodplain

Post-Row Crop Floodplain

Changes Affecting Sediment Flux – Legacy Sediments

Channelresponse

1750 1850 1950 2050Present

ErosionDepositionStable?

SedimentSupply/

Transportcapacity

Land use/Management

Prairie/Forest/

Wetland

Agriculture

Soil Conservation

SedimentSupply

Transport Capacity

Modified from Rakovan and Renwick, 2011

Increased sediment transport capacity resulting from

• Reduced water storage• Channel/floodplain

disconnection and loss of floodplain storage

• Increased frequency of intense precipitation

Decreased sediment supply resulting from

• Decreased cultivating of marginal/highly erosive land

• Soil conservation• Construction of ponds

and reservoirs

System-wide Channel Incision and Instability

Sediment & P loss from stream banks adjacent to crop fields, buffers, and

grazed pastures

• Six-year study

• Three ecoregions (NE, SE,

and Central IA)

• Erosion pin method

• Stream bank bulk density and P

ISU - NREM

ISU - NREM ISU - NREM ISU - NREM

• Length of eroding channels

• Rate of bank erosion

• Sediment yield

• Phosphorus contribution

• Land use categories

• Forest

• Pasture

• Cool-season/warm season grass

Recession Rates of Stream Banks with Differing Adjacent Land Use

Field Site Locations

Central Iowa

0

10

20

30

40

50

60

Row-cropped

fields

Continuous

pastures

Rotational

pastures

Grass filters Riparian forest

buffers

Treatments

Severe

Ero

din

g L

en

gth

s (

%)

Zaimes et al. 2008

0

50

100

150

200

250

300

350

Row-croppedfields

Continuouspastures

Rotationalpastures

Grass filters Riparian forestbuffers

So

il L

oss

es

(M

g k

m-1

yr-1

)

Treatments

Central Iowa

Zaimes et al. 2008

Naturally occurring radionuclides (7Be and 210Pb) as tracers to provide information regarding the sources of the sediment transported in streams

Proportions of the two radionuclides can be

used to differentiate between sediment

delivered from the landscape and from stream

bank failures, gullies, or re-suspended bed

material in the suspended sediment due to

different half-lives and erosion mechanisms in

each source area.

Figure from Wilson and Kuhnle, 2003 USDA-ARS

76% 24%

ISU NREM USDA-NRCS

Most research conducted in western United States

Studies suggest very different answers for this

question Buckhouse et al. (1981) claimed no significant difference

between grazing treatments

Trimble (1994) found a six-fold increase in bank erosion

where cattle had full access to the stream

Differences could be related to location, weather, study

timeline, etc.

Six 30-acre pastures

Willow Creek flows through

each pasture

Three grazing treatments

Rotational (yellow)

Limited Stream Access

(red)

Full Stream Access (blue)

Fifteen cow/calf units on each

pasture from May to October

Net Erosion (in)1

June2 July August September October November Annual

CSU3 -0.39 -1.81 0.04 -0.98

e -0.87 0.24 -2.05

CSR -0.91 -0.31 -0.20 -0.20f

0.08 0.39 -1.10

RS -1.22 -1.50 -0.31 -0.12f

0.28 0.24 -3.19

Net Erosion (in)1

June2 July August September October November Annual

CSU3 -0.12 -0.12 -0.004 -0.28 0.04

e 0.28 -0.20

0.24 -0.16 -0.08 -0.04 0.16f 0.04 0.16 CSR

RS 0.08 -0.04 -0.02 0.04 -0.04e 0.12 0.14

Net Erosion (in)1

May2 June July August September October December Annual

CSU3 -2.1 -0.2 -0.4

a 0.1 -0.1 0.0 0.2 -2.5

CSR -3.4 -0.1 -0.3b 0.2 -0.1 0.0 0.0 -3.7

RS -1.3 -0.1 -0.1b 0.0 -0.1 0.2 0.0 -1.5

2006

2005

2007

1Negative values represent soil erosion; positive values represent deposition. 2May/June value indicates change from previous November; all other values are from the previous month. 3CSU = Continuous stocking with unrestricted stream access; CSR= Continuous stocking with restricted stream access; RS = Rotational stocking.

Rainfall events during the 2005 grazing season increased

creek stage more than those of the 2006 and 2007 grazing

seasons (big events = big losses)

During the study period (May, 2005 through December, 2007)

net soil erosion from stream banks averaged 0.01 cm of soil

per day and did not differ among treatments

After three years, grazing management had little effect on

net erosion or erosion pin activity measured in Willow Creek

stream banks – trend analysis indicated bank erosion was decreasing in RS system

• Sediment flux from a watershed is episodic

• Climate and hydrology are important drivers

• Adjacent land use may not be as important as stream

equilibrium and channel evolution stage

• Effect of conservation practices on hydrology –

trading surface for channel erosion?

• Time lag before change in management impacts

hydrology.

• In-channel practices to reduce energy imbalance?

• Role of different vegetation?

Stream Bed and Bank Contribution to Suspended and Bedded Sediment

Management Options?

1. Riparian landuse changes

• Buffer width?

• Narrow for small streams and

local impacts – outside the

meander belt for large rivers

2. Stream bank stabilization

3. Reduce stream power

• Landscape practices?

• Pool-riffle structures

• Re-meander stream

Restricting Stream Access

ISU - NREM

Stream Bank Stabilization

ISU - NREM

ISU - NREM

Photo from the Des Moines Register's Archive

From May, 1966: "This line of junked cars along a bend in the Iowa River south of Iowa City were placed there at least 15

years ago, according to the State Conservation Commission, by a farmer trying to control erosion of his corn field by the

river. Such river-bank junkyards have been utilized along several other streams with the approval of the Conservation

Commission."

Weir spacing

Pool-Riffle Structures

ISU - NREM ISU - NREM

ISU - NREM

41

M

B P

H

M=Honey Creek

B=Walker Creek

P=Ninemile Creek

H=West Jackson Creek

To evaluate sediment – water column P

relationships in streams within the Rathbun Lake

watershed in southern Iowa, specifically targeting

four representative creeks

To evaluate the relationship between sediment

properties and indicators of the risk of P loss to

determine whether environmental risk can be

predicted

Bi-weekly stream water grab samples at 13 sites, March-Nov., 2008-

2009

Dissolved P (DP), total P (TP), total suspended sediment (TSS,

2009) determined

Bed and bank sediments collected at 4 selected sites, July 2009

Sediments air-dried, sieved to 2 mm

Sediment pH, particle size, total C, total N, TP, Mehlich-3

extractable P, Fe, Al, Ca, and Mg, ammonium-oxalate P, Fe, and Al,

and citrate-bicarbonate-dithionite Fe and Al determined

Degree of P saturation (DPS) calculated

Equilibrium P concentration (EPC) estimated in wet sediments,

using indigenous stream water

Used to predict and rank the risk of P loss from agricultural land

Also known as P sorption index (PSI) or P saturation index (Psat)

100

oxox

ox

AlFe

PDPS

100

33

3

MM

M

AlFe

PDPS

100

3

3 M

M

Ca

PDPS

Acid soils

Alkaline soils

Delaware: DPS 15% (Sims et al., 2002)

Not yet defined!

EPC is a useful index to determine whether stream bank/bed sediments act as a sink (sorb) or a

source (release) of P in stream water

EPC > dissolved P EPC < dissolved P

SOURCE SINK

-5

0

5

10

15

20

0.0 0.1 0.2 0.3 0.4 0.5

C (mg L-1)

S (

mg

kg

-1)

EPC

Slope = PEBC 0

100

200

300

400

500

600

700

0 20 40 60 80

P remaining in solution (mg L-1)

P s

orb

ed

fro

m s

olu

tio

n (

mg

kg

-1)

Sediments pH TC sand TP PM3 FeM3 Pox Feox Alox

----- g kg-1 ----- ------------------------------ mg kg-1 ------------------------------

M-bed 7.3 8 500 314 37 300 253 3260 651

M-bank 7.2 10 330 278 26 358 211 2500 655

H-bed 7.5 3 920 177 32 157 203 2140 555

H-bank 6.5 10 350 284 36 446 315 2780 584

B-bed 8.0 3 820 454 28 148 551 8240 875

B-bank 6.5 12 290 209 25 437 145 1940 715

P-bed 8.2 2 940 314 17 85 596 8800 762

P-bank 7.2 7 490 306 68 208 281 2310 452

Iowa agronomic M3P threshold = 20 mg kg-1

Arkansas environmental M3P threshold = 150 mg kg-1

Sediments DPS-ox(Fe+Al)† DPS-M3(Fe+Al)‡ DPS-M3(Ca)

-------------------- % --------------------

M-bed 7 5 2

M-bank 6 5 2

H-bed 9 6 8

H-bank 7 3 3

B-bed 7 7 3

B-bank 5 3 2

P-bed 7 7 3

P-bank 12 8 5

Bed Mean 7a§ 6a 4a

Bank Mean 7a 5a 4a

†The Netherlands: DPS-ox(Fe+Al) = 25 % (van dee Zee et al., 1990)

‡Delaware: DPS-M3(Fe+Al) = 15 % (Sims et al., 2002)

§Within a column, values with same letter not significantly different at 0.05 level.

Sediments EPC Value Status†

mg L-1

M-bed 0.05 sink

M-bank 0.07 sink

H-bed 0.08 equilibrium

H-bank 0.03 sink

B-bed 0.12 source

B-bank 0.02 sink

P-bed 0.12 source

P-bank 0.10 source

† Mean stream water DP in 2009 = 0.08 mg L-1

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Mar Apr May Jun Jul Aug Sep Oct Nov

M-bed

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Mar Apr May Jun Jul Aug Sep Oct Nov

B-bed

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Mar Apr May Jun Jul Aug Sep Oct Nov

H-bed

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Mar Apr May Jun Jul Aug Sep Oct Nov

P-bed

Dis

solv

ed P

(mg

L-1)

Dis

solv

ed P

(mg

L-1)

Dis

solv

ed P

(mg

L-1)

Dis

solv

ed P

(mg

L-1)

Main Points:

PM3 and DPS indicated little risk of P loss from these

sediments

EPC values indicated some sediments could release P to

water, depending on stream water DP and time of year

Likelihood of P desorption from sediments increased with

increasing pH and sand content

Readily extractable P was retained by the sediments by Fe

that was, in turn, associated with organic matter

changes in land use within the riparian areas may, at least

initially, have little effect on P concentrations in the streams

leading to Rathbun Lake.