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Transport of Agricultural Chemicals: Estimating Lag Times in Different Hydrologic Environments David Wolock and Paul Capel U.S. Geological Survey. U.S. Department of the Interior U.S. Geological Survey. Quantify lag time for three of the Agricultural Chemicals Team study areas

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Transport of Agricultural Chemicals:

Estimating Lag Times in Different Hydrologic Environments

David Wolock and Paul Capel

U.S. Geological Survey

U.S. Department of the Interior

U.S. Geological Survey


Objectives

Quantify lag time for three of the Agricultural Chemicals Team study areas

Lag time is the travel time of water and chemicals from the land surface to the stream

Show implications of hydrology for agricultural chemical management

Objectives


Agricultural chemicals team study
Agricultural Chemicals Team study Team study areas

Overland flow

Nebraska

Transport and lag time vary in different hydrologic systems

Tile-drain flow

Ground-water discharge

Indiana

Maryland


Overland flow dominated streamflow
Overland-flow-dominated streamflow Team study areas

Nebraska site

Basin area = 1.5 km2


Overland-flow-dominated streamflow Team study areas

Nebraska site

Streamflow (ft3/s)

3

13

18

23

28

13

8

June-July, 2003

Typical flow event lasts 1-2 hours.



Tile drain dominated streamflow
Tile-drain-dominated streamflow Team study areas

Basin area = 7 km2

Leary-Weber Ditch, central Indiana


Streamflow (ft Team study areas3/s),

12 13 14 15 16 17 18 19 20

June 2003

Typical flow event lasts 24-48 hours.



Maryland site ground water discharge dominated streamflow
Maryland site: Ground-water discharge dominated streamflow Team study areas

Basin area = 29 km2

Morgan Creek


Ground water discharge dominated streamflow
Ground-water discharge dominated streamflow Team study areas

Base-flow index = 70%

Streamflow (mm/d)

Precipitation (mm/d)

Ground-water discharge to stream is continuous.


Assume ground-water flow velocity is 0.1 m/day.


Hydrologic differences

Lag time Team study areas

Degradation potential

Fraction of basin contributing to streamflow

Age of streamflow

Hours

Low

Small

Young

Hydrologic differences

Nebraska:

Overland flow

Indiana:

Tile drains

Maryland:

Ground water

Hours

Low

Large

Young

Decades

High

Large

Old


Agricultural chemical management implications

Response to changes in chemical applications Team study areas

Minimum tillage effective?

Buffer zones near stream effective?

Quick

Yes

Yes

Agricultural Chemical Management Implications

Nebraska:

Overland flow

Indiana:

Tile drains

Maryland:

Ground water

Slow

No

No

Quick

No

No


Bottom line: Team study areas

Hydrology matters for managing agricultural chemicals

Overland flow

Nebraska

Tile-drain flow

Ground-water discharge

Indiana

Maryland



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