a framework for setting realistic expectations for water quality improvements - capel
TRANSCRIPT
A framework for setting realistic expectations for water quality improvements based on
changes in agricultural activities
Paul Capel and David WolockU.S. Geological Survey
Soil and Water Conservation Society Conference Greensboro, NC July 27-28, 2015
Chemicals and sediment from fields enter the stream network
Annual loads transportedto the Gulf of Mexico
Nitrogen:1000 – 2000 metric tons/year ~$1B
Phosphorus:150 – 250 metric tons/year
Sediment:600 – 1000 Million metric tons/year
A framework for setting realistic expectations for water quality improvements
Strategies for reduction of agricultural chemicals and sediment exported from fields to protect and improve water quality
Stop movement at/near sourceconservation practices, …
Reduce chemical usereduced N application rate, …
Remediate in real-timebiofilters, cover crops, …
Remove/retain in hydrologic networkconstructed wetlands, ….
A framework for setting realistic expectations for water quality improvements
How do chemicals and sediment get into the stream … coastal areas?
They move with the WATER (and wind) !
A framework for setting realistic expectations for water quality improvements
A framework for setting realistic expectations for water quality improvements
Framework for setting expectations
Transport
A framework for setting realistic expectations for water quality improvements
CHEMICAL: All agricultural chemicals are distributed between sediment and water
This distribution is an important control on the transport of the chemical.
Conceptual framework of watershed hydrology and chemical behavior
“Natural” flowpaths to a stream
Slowflowsourced(groundwater, wetlands, …)
Fastflowsourced
(stormflow, runoff, …)Different energies
Different interactions with surface and subsurface soil
Different mechanisms of chemical / sediment transport
Artificial flowpaths to the stream – surface and subsurface drainage
A framework for setting realistic expectations for water quality improvements
Artificial flowpaths to the stream – subsurface drainage
A framework for setting realistic expectations for water quality improvements
Conceptual space for water flowpaths to any agricultural stream
A framework for setting realistic expectations for water quality improvements
“Natural” stream
National Map of Primary Flowpaths on Cropped Land in the US
A framework for setting realistic expectations for water quality improvements
Conceptual framework of watershed hydrology and chemical behavior
Combining conceptual space for water flowpaths and for chemicals along a sediment-water distribution continuum
A framework for setting realistic expectations for water quality improvements
Examples of agricultural activities that can be used for the protection or improvement of water quality
Trapping Practices Terraces, Grassed waterways, Brims at edge of stream Buffer filter strips, Cover crops
Tillage Practices Conservation and no-till tillage Contoured plowing
Drainage Practices Controlled subsurface drainage Biofilters on subsurface drains Removal of subsurface drains and surface inlets to subsurface drains
Irrigation Practices Reduced volume and energy of irrigation water
Chemical Use Practices Reduction in chemical use Use of chemicals with short environmental lifetimes
Set-Aside Land for Conservation Conservation Reserve Program (Federal and state; e.g., USDA CRP) Constructed wetlands
A couple of examples of setting expectations for agricultural activities based on this framework
Conceptual framework of watershed hydrology and chemical behavior
Two sediment-water end-members
100% associated with sediment- soil particles~ total phosphorus~ DDT
100% associated with water- water- chloride- nitrate- atrazine
Assume no chemical transformation.
Conceptual framework of watershed hydrology and chemical behavior
A few example AMPs … Buffer strips
Fastflow Slowflow Drain flow
Solid Water Solid Water Solid Water
Buffer strip + +O O +O O O
Conceptual framework of watershed hydrology and chemical behavior
Example … No-till tillage
Fastflow Slowflow Drain flow
Solid Water Solid Water Solid Water
No-till + + O -O O -O
Conceptual framework of watershed hydrology and chemical behavior
Example … Reduction in use of the chemical
Fastflow Slowflow Drain flow
Solid Water Solid Water Solid Water
Reduction in use + + + + + +
A framework for setting realistic expectations for water quality improvements
Chemical behavior
Field: Engineered hydrologic setting
Field: “Natural” hydrologic setting
General effectiveness of management practice
A framework for setting realistic expectations for water quality improvements
Nitrate in Chesterville Branch, MD -- corn, soybean, nursery, … -- groundwater-sourced -- GW contaminated with nitrate
A framework for setting realistic expectations for water quality improvements
Sediment in DR-2 Drain, WA -- grapes, hops, apples, corn, dairy, … -- water from irrigation canal -- excess irrigation creates runoff -- SW contaminated with sediment+
A framework for setting realistic expectations for water quality improvements
Framework useful as a thinking, teaching, and policy tool
ProtectionImprovement
Transport