Transport of nitrogen and phosphorus from Rhode River watersheds during storm events

David Correll, Thomas Jordan, and Donald WellerWater Resources Research, 1999. Vol. 35 No 8 pg 2513-2521

Why this paper?

•One of many papers from the SERC on the Rhode River Watershed since the 1970s

•Effects of land use, season, and storm characteristics on nutrient transport

Land Use effects: 4 watershedsWatershed 101 Mixed Use Land UseWatershed 109 CropsWatershed 110 ForestWatershed 111 Grazed

ForestRow cropsPasture and Hay fieldsResidentialOld Fields

Site Description

Site Description

Chemistry

• Phosphorus– PPi, Dpi, POP, DOP

• Nitrogen– NO3-, NH4, PON, DON

– Continuous baseflow samples and storm samples

– Collected and returned w/in 24 hr

– Filtered 0.45 m

Discharge

120° and 150 ° V notch weirsStilling wells, floats every 5 minutes

6 /1 2 /0 2 1 5 :3 0 6 /1 2 /0 2 1 7 :1 0 6 /1 2 /0 2 1 8 :4 9 6 /1 2 /0 2 2 0 :2 9 6 /1 2 /0 2 2 2 :0 90

0 .0 2

0 .0 4

0 .0 6

0 .0 8

0 .1D

isch

arge

(cm

s)

3 0

4 0

5 0

6 0C

oncentration (mg/l)

t

t

ii

o

QCL

Steps:1. Connect the concentrations using a linear

interpolation2. Integrate the instantaneous load for the period

between the first sample and the last using equation (1)

(1)

Loads: Linear interpolation

Base flow vs. Storm

Storm Particulate + Dissolved Fractions added

Characteristic Storms (WS 101)

P and N Dynamics June storm (WS 101)

P N

Storm P & N Dynamics (all 4)

P N

Seasonal P Comparison

WS 101: Mixed LU WS 109: Cropland LU

Seasonal N Comparison WS 101: Mixed LU WS 109: Cropland LU

Summer: Particulates

P c-Q relationships

N/P Relationships

Mainly due to increases in Particulate P

Discussion

Particulate nutrients related to soil, soil erosion.

Discussion

Peak water discharge correlated to mean particulate nutrient concentrations– Eliminating need to know rainfall volume or intensity

– Smaller 1st order catchments

– Shorter, more intense storm discharges

[NH4] increased with peak water discharge- slopes much lower

Discussion

• Sampling implications• 1 large summer storm

– 24% of TP for entire summer

– 18% of TPi for entire summer

– 30% of TOP for entire spring

– 18.5% of TON for entire spring

• 1 large spring storm– 39% of TP for entire

spring

– 41% of TPi for entire spring

– 38% of TOP for entire spring

– 12% of of TON for entire spring

Questions?????• Why do storms increase particulate nutrient

concentrations but do not influence dissolved concentrations?

• If sediment related, why isn’t rain (detachment) as important as flow?

• Implications for sampling: every storm? Or use different load estimation?

• Internal validity- are differences really seasonal and land use related

• External validity? – how is this applicable to other watersheds