1UNESCO-IHE, Institute of Water Education, Delft, The Netherlands. 2Royal University of Bhutan, Thimphu, Bhutan. 3National Water and Sewerage Corporation ...
Controls of denitrification in papyrus wetlands in Kenya and Tanzania Gretchen M. Gettel1, Kuenzang Tshering2, Hawa Nakitende3 1UNESCO-IHE,
Institute of Water Education, Delft, The Netherlands 2Royal University of Bhutan, Thimphu, Bhutan 3National Water and Sewerage Corporation, Kampala, Uganda
Ecosystem Services
How do we balance the competing demands for ecosystem services?
Figure from: http://www.metrovancouver.org/planning/development/ecologi calhealth/Pages/default.aspx
Cyperus papyrus wetlands
Cyperus papyrus wetlands
Provisioning, Regulating and Supporting Services of Papyrus Wetlands Papyrus wetlands are at the crux of balancing provisioning and regulating services.
Denitrification as part of the Nutrient Retention • Requires organic carbon
• Requires anaerobic conditions
Are regulating services lost as wetlands are converted to agricultural land uses? Objectives: 1. Assess C and N limitation of denitrification in agricultural and papyrus vegetation (Proximate controls) 2. Relate potential denitrification in natural vegetation and agricultural land uses and relate to soil characteristics (Distal controls)
Papyrus Wetland Zones (HGMUs) River discharge
Lake Victoria
Agriculture/ grazing Temporarily flooded
Figure: Edwin Hes
Permanently flooded Groundwater recharge
Study area: Nyando wetland, Kenya
Nyando basin Nyando wetland
: 3587 km2 : ±50 km2
Kisumu
Nyando river
Nyakach Bay (Lake Victoria)
Sampling locations: Nyando River Ogyena Site – Daily influx of water from the Lake, moderately impacted Singida Site – Floods with river during the wet season, lightly impacted
Papyrus
Maize
Sugarcane
Rice
Study area: Mara wetland, Tanzania
Sampling locations: Mara River 10 m
Agriculture/ Grazing HGMU
Temporarily flooded HGMU
Permanently flooded HGMU
Floating vegetation
III rd sampling
10 m
II nd sampling
I st sampling
Transact I: At Mangorey
T Sampling site
P Sampling site
Main River Channel
Methods: Field sampling
Sampling Frequency: Three times at each site December 2010 – January 2011
Data Analysis
Water (Permanent Wetland)
pH, EC, DO, temp. DOC, NO3, NH4, SUVA
Soil Sample (top 5 cm)
pH, % Moisture, AFDM, TOC, NH4, NO3
Denitrification
C vs. N limitation of Denitrification
ANOVA, Tukey Post-hoc
Potential Denitrification
Multivariate Analysis
Acetylene inhibition method - DEA +C+N
• Potential Denitrification
+N
+C - Anaerobic conditions with chloremphenicol - Acetylene blocks conversion of N2O to N2 - Denitrification rate was calculated from linear regression of N2O produced during incubation period. - Three replicates for each treatment
Potential Denitrification Rate 9
a
Nyando
PDR (ug N-N20/g DW/hour)
8 7 6
a
5
4 3 2
b
b b
1 0 Ogenya WL
4.5
Singida WL
Maize field
S.C Field
Rice field
a
Mara
PDR (ug N-N20/g DW/hour)
4 3.5 3
2.5 2
b
1.5 1
b
0.5 0 Permanent
Temporary
Agriculture
Limiting factors for potential denitrification 8
7
7
6
a
5
4 3 2
b
1
6
a a
5 4 3
b
2 1 0
0 +C+N
+N
+C+N
+C
+N
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Sugarcane
a a
b
+C+N +N
+C
+C
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
a b
a
3.5
3.5
3.0
3.0
a
2.5 2 1.5
a
1 b
0.5 0
+C+N +N
+C
+C+N +N
Agricultural
1.0
4.0
a
Rice 3
Temporarily Flooded
Permanently Flooded 4.0
Maize
N2O-N ug/g DW/hour
8
N2O-N ug/g DW/hour
9
a N2O-N ug/g DW/hour
N2O-N ug/g DW/hour
Nyando
9
Singida Wetland
N2O-N ug/g DW/hour
Ogenya Wetland
0.9
2.5 2.0 1.5
a
1.0
0.0 ＋C＋N
＋N
2.5 2.0 1.5
a a
1.0
b
0.5
＋C
µg N2O/g DW /hour
µg N2O/g DW /hour
µg N2O/g DW /hour
Mara
0.8
0.6
a
0.5 0.4 0.3
a
0.2
b
0.5
0.7
0.1
b
0.0
0.0 ＋C＋N
＋N
＋C
＋C＋N
＋N
＋C
+C
Nitrate limits PDR in Wetland Sites 8
7
7
6
a
5
4 3 2
b
1
6
a a
5 4 3
b
2 1 0
0 +C+N
+N
+C+N
+C
+N
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Sugarcane
a a
b
+C+N +N
+C
+C
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
a b
a
3.5
3.5
3.0
3.0
a
2.5 2 1.5
a
1 b
0.5 0
+C+N +N
+C
+C+N +N
Agricultural
1.0
4.0
a
Rice 3
Temporarily Flooded
Permanently Flooded 4.0
Maize
N2O-N ug/g DW/hour
8
N2O-N ug/g DW/hour
9
a N2O-N ug/g DW/hour
N2O-N ug/g DW/hour
Nyando
9
Singida Wetland
N2O-N ug/g DW/hour
Ogenya Wetland
0.9
2.5 2.0 1.5
a
1.0
0.0 ＋C＋N
＋N
2.5 2.0 1.5
a a
1.0
b
0.5
＋C
µg N2O/g DW /hour
µg N2O/g DW /hour
µg N2O/g DW /hour
Mara
0.8
0.6
a
0.5 0.4 0.3
a
0.2
b
0.5
0.7
0.1
b
0.0
0.0 ＋C＋N
＋N
＋C
＋C＋N
＋N
＋C
+C
Carbon limits PDR in agricultural sites 8
7
7
6
a
5
4 3 2
b
1
6
a a
5 4 3
b
2 1 0
0 +C+N
+N
+C+N
+C
+N
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Sugarcane
a a
b
+C+N +N
+C
+C
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
a b
a
3.5
3.5
3.0
3.0
a
2.5 2 1.5
a
1 b
0.5 0
+C+N +N
+C
+C+N +N
Agricultural
1.0
4.0
a
Rice 3
Temporarily Flooded
Permanently Flooded 4.0
Maize
N2O-N ug/g DW/hour
8
N2O-N ug/g DW/hour
9
a N2O-N ug/g DW/hour
N2O-N ug/g DW/hour
Nyando
9
Singida Wetland
N2O-N ug/g DW/hour
Ogenya Wetland
0.9
2.5 2.0 1.5
a
1.0
0.0 ＋C＋N
＋N
2.5 2.0 1.5
a a
1.0
b
0.5
＋C
µg N2O/g DW /hour
µg N2O/g DW /hour
µg N2O/g DW /hour
Mara
0.8
0.6
a
0.5 0.4 0.3
a
0.2
b
0.5
0.7
0.1
b
0.0
0.0 ＋C＋N
＋N
＋C
＋C＋N
＋N
＋C
+C
NO3 & NH4 among different land uses 0.45
0.4
0.40
0.35
0.35
0.3
0.30
0.25
a a
0.2
b
b
b
NH4-N (mg/g )
NO3-N (mg/g)
0.45
Nyando
N-NH4
N-NO3
a
0.20 0.15
0.1
0.10
0.05
0.05
0
0.00
0.025
a
0.25
0.15
Ogenya Singida WL WL
a
b b
Ogenya WL
Maize S.C Field Rice field field
0.35
b
b
Singida WL
Maize field
S.C Field Rice field
a
0.30
0.020
mg NH4-N/g resin/day
Mara
mg NO3-N/g resin/day
b
0.015 0.010 0.005
a
a
a
0.25 0.20 0.15
b
0.10 0.05
0.000 Permanent
Temporary Land Uses
Agriculture
0.00 Permanent
Temporary Land Uses
Agriculture
TN and TOC among different land uses TOC
TN 120
12
a
8
100
b
b
6
TOC (mg/g)
Nyando
TN (mg g-1 DM)
10
d c
4
b
80
c c
60
20
0
0
a
35 30
14
a a
25
12
b b
8 6
g AFDW
Mara
mg N/g soil sample
16
10
c
40
2
18
a
20 15
b
10
4
5
2 0
0 Permanent Temporary Agriculture
Permanent Temporary Agriculture
Land Uses
Land Uses
Moisture Content 90
Nyando
% Moisture content
80
a b
70 60
e
50
c
40
d
30 20 10 0 Ogentya WL Singida WL Maize field
90
80
S.C Field
Rice field
a a
Mara
% moisture content
70 60 50
40 30
b
20 10 0 Permanent
Temporary And Uses
Agriculture
Dissolved Oxygen and SUVA in Wetland Sites 14
DO % Saturation
12
Nyando
10 8 6
Singida
4
Ogenya
DO ranged from 0.2 – 0.8 mg/L
2 0
Permanently flooded HGMU
0.09
Temporarily flooded HGMU
0.08
Mara
DO % saturation
5.0 4.0 3.0 2.0 1.0 0.0
SUVA (Specific UV Absorbance
6.0
0.07
a a
0.06 0.05 0.04 0.03 0.02 0.01 0 Permanent
Temporary Wetland Types
Stepwise Multivariate Analysis: Wetland Sites pH, SUVA, DOC, moisture content, AFDW, NO3-N, NH4-N and TN were used as predictors of PDR. Nyando: No significant relationships
Mara: -SUVA (R2 = 0.73, p = 0.03) and +DOC (R2 = 0.98, p < 0.01) related to PDR.
23
Multivariate Regression Analysis, Agricultural Land, Mara
Moisture content, Ash Free Dry weight/TC, NO3-N, NH4-N and TN, used as predictors of PDR Nyando: +TOC and +Moisture Content (R2=0.66, p
