A Framework for Setting Realistic Expectations for Water Quality Improvements - Capel

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