1. Long term variations of land management
practices and their impacts on runoff and
water quality in a small agricultural
watershed in Atlantic Canada
Sheng Lia, Zisheng Xinga,b, Fanrui Mengb
a Potato Research and Development Centre
b University of New Brunswick
July 24-27, 2016, Louisville, Kentucky, USA
71st SWCS International Annual Conference - Great
River Landscapes

2. Outlines
• Introduction
• Description on site and long-term
monitoring
• Results and some critical findings
• Conclusions

3. What does matter at the
watershed level
 Soil erosion
 Nutrient loss
 Water quality
 Economic and
production
viability
 Environment
sustainability
Heavy storm
Rolling topography
Row cropping
Intensive mach…
Flood in 2008

4. Land management practices – To
address environmental issues
Notes: Mean numbers are % of each management practices over
total watershed area in the Black brook watershed from 1992 to
2013

5. Agriculture – Major driver
True? At watershed level?
Interactions among?
 topographic condition, soil condition
 climate change
 land management practices, cropping
system
 farmer preference, marketing, economy
Understand? need monitoring
Chow and Rees 2009, WEBs Annual Report

6. Watershed based long-term monitoring
 Monitored variables
 Land use, management, and
agricultural operation at a field basis
 Water discharge & flow rate at sub
watershed level
 Water quality parameters at sub
watershed level
 N, P, K, TN, TP, pH, sediment,
conductivity, water temperature
 Weather conditions
 Configurations
 Automatic stage measuring and
sampling
 Established in 1992
 11 stations - network
 9 in BBW (14.5 km2, agriculture
dominated area)
 1 in ULRW (380 km2, forested area)
 1 LRW
 Monitoring frequency
 Year around (1,2,3,12,14,8; heated)
 Stage proportional sampling

7. Land use (%) in subwatersheds 4, 8 and the
entire Black Brook watershed (1)
from 1992 to 2013
There is no much variation over years except for a slight decreasing of potato
area and a slight increasing area of grain

8. Our findings – climate conditions
y = 5.0193x - 8927.8
R² = 0.071
800
1000
1200
1400
1600
1990 2000 2010
Precip(mm)
y = -4.1155x + 8564
R² = 0.0928
0
200
400
600
800
1000
1990 1995 2000 2005 2010 2015
Snow depth
y = 8.06x - 15,327.25
R² = 0.16
400
600
800
1000
1200
1990 1995 2000 2005 2010 2015
Rainfall (mm)
Variable Tau
P‐
value
Kendall
Score (s)
Precipitation 0.21 0.18 49
Snow depth ‐0.15 0.34 ‐35
Rainfall (mm) 0.24 0.12 56
Rainfall (%) 0.23 0.14 53
Erosivity
(MJ mm ha‐1.hr‐1) 0.33 0.03 77

9. Monthly patterns of hydrological parameters in the
BBW; averages from 1992 to 2013

10. Subwatershed N (Kg/ha/yr) P(Kg/ha/yr) K (Kg/ha/yr) Ca (Kg/ha/yr) Mg (Kg/ha/yr)
1 25.71 0.34 8.71 268.70 23.14
4 9.79 0.18 4.24 181.19 16.46
8 27.60 0.37 10.32 225.89 19.62
Subwater
shed
Sediment
load
t/ha/yr
N
(Kg/ha/yr
)
P(Kg/ha/
yr)
K
(Kg/ha/yr
)
Ca
(Kg/ha/yr)
Mg
(Kg/ha/yr)
1 4.50 25.71 0.34 8.71 268.70 23.14
4 0.31 9.79 0.18 4.24 181.19 16.46
8 8.57 27.60 0.37 10.32 225.89 19.62
Yearly summary of chemical and sediment load to
stream water in the BBW; averages from 1992 to 2013

11. Characteristics of stream water in different
subwatersheds based on annual load
Weir 1 &
Wei 4
Weir 1 &
Weir 8
Weir 4 &
8
pH 0.442 0.908 0.395
Sedi.
load 0.02 0.529 0.005
Cond. 0.001 0.056 0
N 0 0.088 0
P 0.111 0.322 0.014
K 0.006 0.099 0
Mg 0.071 0.211 0.584
Ca 0.101 0.171 0.794
Numbers in the table are p-values of
mean difference t-test

12. Summary of stream water quality
observed from subwatershed 1, 4 AND 8
Weir 1 Weir 4 Weir 8
Flow weighted mean Mean
Standard
Error Mean
Standard
Error Mean
Standard
Error
pH 8.15 0.06 8.10 0.05 8.16 0.05
Sediment (g/L) 0.76 0.10 0.07 0.02 0.94 0.06
Conductivity (dS/m) 0.35 0.01 0.26 0.01 0.40 0.37
Nitrate (ppm) 4.34 0.23 2.01 0.16 5.02 0.40
Orth P (ppb) 55.45 9.07 35.03 8.21 68.26 9.87
K (ppm) 1.51 0.11 0.84 0.14 1.92 0.24
Mg (ppm) 4.11 0.27 3.39 0.22 3.61 0.34
Ca (ppm) 46.50 2.74 39.70 1.19 40.78 4.16
Similar results have been report in our previous paper
(Chow et al. 2011, Journal of soil and water conservation)

13. Sediment load variation with increasing terrace
coverage in the Black Brook Watershed

14. Discharge, precipitation, and sediment
load with terraces
Year

15. Regression model examination on sediment
load (t/ha/yr) under terrace protected area
Model Variables with coefficients R-
square
P value
1 Terrace protected area (-0.404) &
rainfall (-0.249)
0.297 0.050
2 Terrace protected area (-0.419) & snow
depth (cm)
0.344 0.028
3 Terraced protected area (-1.396),
terrace change (-0.237),
total discharge (0.489)
Potato area on terrace protected field (-
1.0),
potato area on non-terraced field (.196)
0.498 0.035

16. Regression models of flow-weighted
sediment concentration (g/L) under terrace
protected area
Model Variables with coefficients R-
square
P
value
1 Terrace protected area (-0.455) &
precipitation (-0.360)
0.362 0.013
2 Terrace protected area (-0.489) & snow
depth (cm)(0.247)
0.358 0.028
3 Terrace protected area (-0.367) & rainfall
(mm)(0.508)
0.365 0.003

17. Soil loss reduction at the watershed level
% of Terrace protected area over total watershed area
0 10 20 30 40 50
Reductionofsoilloss(Mgha-1)
0.04
0.05
0.06
0.07
0.08
0.09
Measurements
Fitted curve
r2=0.83**
y = 0.0788exp0.1352x

18. Take-home messages
 There is no obvious climate change trend detected from
our data except for erosivity
 The soil and water erosion display strong spatial and
temporal variations, mainly due to land management
practices and land use
 Among land management practices, terrace
construction has been determined as the most effective
one which can reduce soil erosion loss at watershed
level
 For every % increase of terrace protection area, the soil
loss can be reduced by 0.08 Mg/ha

19. Acknowledgements
Lien Chow (Retired Research scientist)
Herb W. Rees (Retired research
scientist)
John Monteith (Retired technician)
Sylvie Lavoie (Watershed technician)
Lionel Steven (Lab technician)

20. Monthly shares of annual total of
hydrological parameters in the BBW
Month
1 2 3 4 5 6 7 8 9 10 11 12
Share(%)
0
10
20
30
40
50
Precipitation
Erosivity
Discharge
Sediment
1992-2013

21. Introduction to
Long-term monitoring program at the Black Brook
Watershed, NB, Canada
Detailed information can be found
At http://www.agr.gc.ca/eng/?id=1298406458612

22. Monitoring report
Weather, land management and water quality
summary from long-term monitoring

23. Critical findings
At the watershed level

24. VARIABILITY OF LOAD DURING SNOWMELT SEASON
(DECEMBER TO APRIL) IN DIFFERENT
SUBWATERSHEDS
Notes: summarized from 1992 to 2013

25. Flow weighted chemical concentrations
time series during 1992 to 2013

26. FLOW WEIGHTED SEDIMENT
CONCENTRATION VS SNOW DEPTH AND
ACCUMULATIVE TERRACES

27. DISCHARGE RATE OF PER MM
PRECIPITATION AND TERRACE PROTECTED %

28. DISCHARGE, SEDIMENT LOAD, EROSIVITY,
AND TERRACE PROTECTION PERCENTAGE

29. SWAT SIMULATED EXCEEDANCE OF DAILY
TOTAL SUSPENDED SEDIMENT CONCENTRATION
Yang et al. 2011. Water Quality Research Journal of
Canada

30. Percentage of Reduction (%) by BMPs for water-
quality indictors compared with default scenario a in
terms of average concentrations

31. PERCENTAGE OF SNOW SEASON
LOAD, SUMMARIZED DURING
1992-2010
Variables Wr1 Wr4 Wr8
Mean
Std.
Error Mean
Std.
Error Mean
Std.
Error
Discharge 58.91 1.93 48.43 3.82 72.04 4.26
Suspended
sediment % 60.83 5.77 41.34 4.91 48.56 5.13
Nitrate 59.29 2.20 50.60 4.03 64.19 5.21
Ortho-P 59.30 2.16 46.11 5.51 61.29 5.84
Disolved K 60.50 2.98 50.11 4.30 72.41 3.58

32. LAND MANAGEMENT % CHANGE
OVER TIME FROM 1992 TO 2014

33. SEDIMENT LOAD VS RAINFALL AND
ACCUMULATIVE TERRACE PROTECTED AREA

34. SEDIMENT LOAD WITH SNOW DEPTH AND
ACCUMULATIVE TERRACE PROTECTED AREA

35. Sediment load and its interaction with
terrace and potato production

36. FLOW WEIGHTED CONCENTRATION
WITH PRECIPITATION AND
ACCUMULATIVE TERRACE

37. FLOW WEIGHTED SEDIMENT
CONCENTRATION VS RAINFALL AND
ACCUMULATIVE TERRACE AREA

38. LONG TERM VARIATIONS OF LAND MANAGEMENT
PRACTICES AND THEIR IMPACTS ON RUNOFF AND
WATER QUALITY IN A SMALL AGRICULTURAL
WATERSHED IN ATLANTIC CANADA
Presented at the 76th Annual Conference of Soil and
Water Conservation Society of American