This document summarizes a study that tested the effects of agricultural buffer strips on surface water quality. The study: 1) Sampled 52 paired stations (A next to buffer strip, B as control) in northeastern Netherlands to test if buffer strips reduced nutrient and contaminant loads using a paired t-test. 2) Found that stations next to buffer strips (A) had significantly lower concentrations of total nitrogen, nitrate, ammonium, chloride and conductivity. 3) Detected a higher ecological quality ratio for macrophyte species composition at stations next to buffer strips in 2009, but no other clear water quality differences between the stations. 4) Concluded that pairwise testing is effective for determining

1. Jan H. Wanink, Ronald Bijkerk, Marian van Dongen, Jetty Noordam
www.koemanenbijkerk.nl
j.h.wanink@koemanenbijkerk.nl
r.bijkerk@koemanenbijkerk.nl
www.hunzeenaas.nl
m.dongen@hunzeenaas.nl
j.noordam@hunzeenaas.nl
Koeman en Bijkerk bv, Ecological Research and Consultancy, P.O. Box 111, 9750 AC Haren, The Netherlands
Water Board Hunze en Aa's, P.O. Box 195, 9640 AD Veendam, The Netherlands
Testing for effects of agricultural buffer strips
on the ecological quality of adjacent surface waters
Dutch national policy
● Reduction of nutrient and herbicide emission to surface waters
Measures
● Application of buffer strips between farmland and adjacent watercourses
● Fertilization and spraying of the strips prohibited
Research questions
● Are buffer strips effectively reducing phosphorus and nitrogen loads?
● Is buffer strip management effectively improving ecological water quality?
Disadvantage of monitoring and trend analysis
● Large seasonal fluctuations in nutrient loads inhibit trend detection
Our solution
● One-time sampling of many paired stations; using paired Student’s t-test
Variable
H1
t
n
p
● Northeastern Netherlands: 35 farmers constructed 160 km buffer strips in 2006
● We sampled 52 paired stations A (buffer strip) and B (control) in 2008/2009
Total P
A<B
1.08 41
0.8573
Total N
A<B
- 2.42 50
0.0095
Variable
Ammonia
A<B
- 2.21 37
0.0169
Chloride
A < B - 2.47 48 0.0085
EQR
macrophytes
A>B
0.31 16
0.3796
Nitrate
A<B
- 2.18 40
0.0175
Conductivity A < B - 2.33 46 0.0122
EQR species
composition
A>B
1.76 16
0.0497
N characteristic
species
A>B
1.40 16
0.0908
H1
t
n
p
● Strips were 3 m wide, sewed with a mixture of grain, grasses and weeds
● Stations A (next to buffer strip) located at the downstream end of the strip
● A and B at opposite sides of same arable plot (identical management)
Variable (2009)
H1
t
n
p
EQR = Ecological Quality Ratio (Water Framework Directive)
Tested water parameters
● Temperature, transparency, conductivity, acidity, dissolved oxygen
● Nitrogen / phosphorus compounds; chloride
● Aquatic vegetation
Results
● A-stations: lower concentrations of total nitrogen, nitrate and ammonium
● A-stations: lower concentrations of chloride
● A-stations: lower conductivity
● A-stations: higher EQR macrophyte species composition (in 2009)
● No significant differences between A and B for the other parameters
Conclusions
● Pairwise testing is an effective method to determine intervention effects
● Absence of differences for P, attributed to internal fluxes from sediment
● For other parameters, attributed to spatial variation / small sample sizes
● A-stations: lower conductivity attributed to lower chloride concentrations
● Aquatic vegetation: response time longer than for chemical parameters