Regional Effects of Agricultural Conservation Practices on Nutrient Transport

NATIONAL WATER QUALITY ASSESSMENT PROGRAM (NAWQA)

Ana Maria Garcia South Atlantic Water Science Center

Richard Alexander (USGS), Dale Robertson (USGS), Jeff Arnold (USDA-ARS), Mike White (USDA-ARS), Lee Norfleet (USDA-

NRCS)

Are we measuring the environmental benefits of established conservation practices?

Conservation Effects

Conservation Effects Assessment Program (CEAP) CEAP Cropland

Survey Current information on

farming practices including: crops grown, tillage practices, nutrient and pesticide application, conservation practices.

Regional Assessments for Cropland

Field-scale modeling

(APEX)

Regional-Scale Modeling

Environmental impact

of conservatio

n

SPAtially Referenced Regression On Watershed attributes (SPARROW) Non-linear least-squares regression on

catchments of a hydrologic framework to solve a mathematical expression of constituent mass.

Parameters of the regression equation are estimated by correlating stream water-quality records to spatially explicit data ▪ Inductive reasoning, the model informs on how the

system behaves

Monitoring Data323 stations

Model Predictions3627 catchments

Source factors, such as manure applied to farmland

Transport factors such as tile-drainage

SPARROW modeling process

α

β

Measure of conservation tested as a transport factor

BASELINE SCENARIO

APEX model results that account for conservation practices as reported in the CEAP Cropland Survey.

NO PRACTICE SCENARIO

APEX model results as if no conservation practiceswere in use.

The difference between these two scenarios is a measure of conservation adoption intensity.

Model DiagnosticsSPARROW

w/o conservation SPARROW withconservation

RMSE, log-transformed residuals 0.49 0.49

R2 of nutrient yield (log) 0.73 0.73

Predictor variables Estimate P-level Estimate P-level

Source variables

Permitted wastewater discharge (kg/yr) 0.80 < 0.001 0.80 < 0.001

Deposition of inorganic nitrogen (kg/yr) 0.55 < 0.001 0.54 < 0.001

Manure, confined livestock (kg/yr) 0.25 < 0.001 0.25 < 0.001

Manure, confined livestock, UMRB (kg/yr) 0.34 < 0.001 0.53 < 0.001

Area of cropland (km2) 12.1 < 0.001 12.3 < 0.001

Area of cropland, UMRB (km2) 19.3 < 0.001 22.1 < 0.001

Land-to-water

delivery

Conservation variable (kg/km2) -0.001 0.01

Drainage density (km/km2) 0.11 0.03 0.11 0.02

Precipitation (mm/yr) 0.002 < 0.001 0.002 < 0.001

Air temperature -0.03 0.08 -0.04 0.04

Fraction of catchment with with tiles 1.3 < 0.001 1.3 < 0.001

Average clay content 0.02 < 0.001 0.02 < 0.001

Stream loss (small streams) 0.43 < 0.001 0.44 < 0.001Stream loss (medium streams) 0.21 0.02 0.21 0.02Reservoir loss (m/yr) 5.3 < 0.001 5.4 < 0.001

Total Nitrogen SPARROW estimation results for the Upper Mississippi River Basin

Reductions in total nitrogen associated with conservation

4-Digi

t HUC HUC Name0701

Mississippi Headwaters

0702

Minnesota River Basin

0703

St. Croix River Basin

0704

Upper Mississippi-Black-Root Rivers

0705

Chippewa River Basin

0706

Upper Mississippi-Maquoketa-Plum Rivers

0707

Wisconsin River Basin

0708

Upper Mississippi-Iowa-Skunk-Wapsipinicon Rivers

0709

Rock River Basin

0710

Des Moines River Basin

0711

Upper Mississippi-Salt Rivers

0712

Upper Illinois River Basin only

0713

Lower Illinois River Basin

0714

Upper Mississippi, Kaskaskia and Meramec Rivers

Model diagnostics SPARROW model w/o conservationSPARROW w/ conservation

Root mean square error (RMSE), log-transformed residuals 0.49 0.49

R2 of nutrient yield (log) 0.73 0.73

Data set used to represent model variable Estimate P-level Estimate P-level

Source variables

Permitted municipal wastewater discharge (kg/yr)

1.06 <0.001 1.06 <0.001

Area in urban land (km2) 57.10 <0.001 56.50 <0.001

Area in forest land (km2) 15.40 <0.001 15.40 <0.001

Manure from unconfined livestock production (kg/yr)

0.03 <0.001 0.03 0.003

Manure from confined livestock production (kg/yr)

0.04 <0.001 0.05 0.002

Manure from confined livestock production (kg/yr) - UMRB

0.12 <0.001 0.12 <0.001

Commercial fertilizer applied to cropland (kg/yr) 0.04 <0.001 0.04 <0.001Commercial fertilizer applied to cropland (kg/yr) - UMRB

0.02 <0.001 0.02 <0.001

Land-to-water

delivery

Conservation intensity measure (kg/km2) -0.001 0.279Soil permeability -0.69 <0.001 -0.68 <0.001Fraction of catchment with with tiles -1.10 <0.001 -1.10 <0.001

In-channel attenuation

Stream loss in small streams 0.26 <0.001 0.26 0.001Stream loss in medium streams 0.31 <0.001 0.31 0.002Reservoir loss (m/yr) 5.14 <0.001 5.16 <0.0010

Total Phosphorus SPARROW estimation results for the Upper Mississippi River Basin

Reductions in total phosphorus associated with conservation

4-Digit HUC HUC Name0701 Mississippi Headwaters0702 Minnesota River Basin0703 St. Croix River Basin0704 Upper Mississippi-Black-

Root Rivers0705 Chippewa River Basin0706 Upper Mississippi-

Maquoketa-Plum Rivers0707 Wisconsin River Basin0708 Upper Mississippi-Iowa-

Skunk-Wapsipinicon Rivers

0709 Rock River Basin0710 Des Moines River Basin0711 Upper Mississippi-Salt

Rivers0712 Upper Illinois River Basin

only0713 Lower Illinois River Basin0714 Upper Mississippi,

Kaskaskia and Meramec Rivers

Inferences regarding nitrogen Conservation practice adoption signal is

mostly representative of soil management Results consistent with the hydrological

processes that could yield nitrogen reductions in streams. Increased hydraulic storage can lead to higher

denitrification rates when compared to equivalent areas without these practices.

Inferences regarding phosphorus The weak negative correlation between

conservation intensity and stream phosphorus loads may be potentially explained by the effects of several key factors. For phosphorus, the chemistry of agricultural

soils and more recent research on soluble phosphorus mobility and transport are leading to shifts in understanding.

Lags in response to nutrient management

Conclusions

The results provide some empirical evidence of regional-scale environmental benefit of conservation practices. environmental setting dictates the

effectiveness of conservation practices. These results present a corroboration of

some of the previous deductive work Application to other environmental setting

will further establish these conclusions