Sources and
Cycling of Water,
Carbon and
Nutrients Urban
Watersheds
Larry Band
University of North
Carolina
Baltimore LTER
Baltimore LTER students and collaborators
• Jon Duncan, Monica Lipscomb, Catherine Shields, Tamara
Mittman – UNC
• Peter Groffman, Steward Pickett – Cary Inst Ecosystem Studies
• Sujay Kaushal - UMD
• Claire Welty, Andy Miller – UMBC
• Rich Pouyat, Morgan Grove – USFS
• Naomi Tague – UCSB
The Three Central Questions of the
Baltimore Ecosystem Study:
• FLUXES...
– What are the fluxes of energy and matter in urban ecosystems,
and how do they change over the long term?
• RELATIONSHIPS...
– How does the spatial structure of ecological, physical, and
socio-economic factors in the metropolis affect ecosystem
function?
• LINKAGES...
– How can urban residents develop and use an understanding of
the metropolis as an ecological system to improve the quality of
their environment and their daily lives?
Hydroclimate impacts on water quality
Chesapeake Bay Foundation (www.cbf.org)
• 2003 dead zone one of the most severe on record
• Extreme drought followed by extreme precipitation
• Flushing effect
Nitrogen export into the Chesapeake Bay
Baltimore LTER
• The Chesapeake Bay has significant eutrophication problems: low
water quality, algae blooms, anoxia, fishery declines, …
• Nitrogen is a limiting nutrient: consortium of five states, DC, federal
agencies collaborating on reducing N, P, sediment loads across
different sectors, land uses, locations
– urban sources N ~30-40%
• Baltimore City/County under consent decree to significantly reduce N
export including point and non-point in urban, suburban, rural
catchments
Need to prioritize restoration efforts to maximize N reduction,
balanced with economic/social equity
Population trends in
Baltimore
Population in Baltimore City and County, 1790 to 2000
1000000
900000
800000
700000
600000
City
500000
400000
County
300000
200000
100000
0
1750
1800
1850
1900
1950
2000
2
Nested, gauged catchments: regrowth forest, agricultural, dense urban
• What is the space/time distribution of nutrient sources in urban watersheds?
• Where do nutrient loads come from, and what are the sources?
• How are nutrient cycling and export coupled to carbon and water cycling?
• Under what hydroclimate conditions are nutrients mobilized, transported from
source areas? Low/high flow? Wet/dry conditions? Seasons?
• What key ecosystem processes and features determine sources and export?
High flows provide additional N, P sources through
pressurized surcharging of sanitary sewers
6/1/2008
2/1/2008
10/1/2007
6/1/2007
2/1/2007
10/1/2006
6/1/2006
2/1/2006
10/1/2005
6/1/2005
2/1/2005
10/1/2004
6/1/2004
2/1/2004
10/1/2003
6/1/2003
2/1/2003
10/1/2002
6/1/2002
2/1/2002
10/1/2001
6/1/2001
2/1/2001
10/1/2000
6/1/2000
-
14
8
0.1
6
4
0.01
2
0
0.001
NO 3 concentrations (mg/L)
12
2/1/2000
10/1/1999
6/1/1999
2/1/1999
10/1/1998
Runoff (mm/day)
Forested catchments, low flow and NO3
concentrations and variability
NO 3 concentration time series
01583570 - Pond Branch
-
10
Runoff
Predicted Concentration
Actual Concentration
10
1
6/1/2008
2/1/2008
10/1/2007
6/1/2007
2/1/2007
10/1/2006
6/1/2006
2/1/2006
10/1/2005
6/1/2005
2/1/2005
10/1/2004
6/1/2004
2/1/2004
10/1/2003
6/1/2003
2/1/2003
10/1/2002
6/1/2002
2/1/2002
10/1/2001
6/1/2001
18
Actual Concentration
12
2
10
1.5
8
6
1
4
0.5
2
0
0
NO3- concentrations (mg/L)
16
2/1/2001
10/1/2000
6/1/2000
2/1/2000
10/1/1999
Runoff (mm/day)
Low density suburban (2/3 forest) on septic,
low flow, high NO3, low variability
NO3- concentration time series
01583580 - Baisman Run
3
Runoff
Predicted Concentration
2.5
14
6/1/2008
2/1/2008
10/1/2007
6/1/2007
2/1/2007
-
70
Predicted Concentration
50
40
3
2.5
30
2
20
1.5
1
10
0.5
0
0
NO 3 concentrations (mg/L)
60
10/1/2006
6/1/2006
2/1/2006
10/1/2005
6/1/2005
2/1/2005
10/1/2004
6/1/2004
2/1/2004
10/1/2003
6/1/2003
2/1/2003
10/1/2002
6/1/2002
2/1/2002
10/1/2001
6/1/2001
2/1/2001
10/1/2000
6/1/2000
2/1/2000
10/1/1999
6/1/1999
2/1/1999
10/1/1998
Runoff (mm/day)
Medium density residential, high flow and [NO3]
variability
NO 3 concentration time series
01589180 - Glyndon
-
5
Runoff
4.5
Actual Concentration
4
3.5
Dead Run flow and NO3- concentration time series
Agricultural catchments, low flow, high NO3
concentrations, low variability
NO3- concentration time series
01589238 - McDonogh
12
50
Runoff
45
Predicted Concentration
10
35
30
6
25
20
4
15
10
2
5
0
4/1/2008
10/1/2007
4/1/2007
10/1/2006
4/1/2006
10/1/2005
4/1/2005
10/1/2004
4/1/2004
10/1/2003
4/1/2003
10/1/2002
4/1/2002
10/1/2001
4/1/2001
10/1/2000
4/1/2000
0
10/1/1999
Runoff (mm/day)
8
NO3- concentrations (mg/L)
Actual Concentration
40
TN, NO3 concentration (mg/L)
.
5
4.5
4
3.5
[TN]
[NO3-]
3
2.5
2
1.5
1
0.5
0
MD
PB
BR
VN
CP
Site
GB
GL
DR
Shields et al 2008, WRR
Mean annual TN, NO3 export
12.00
N export (kg N/ha/yr)
.
10.00
8.00
NO3
TN
6.00
4.00
2.00
0.00
Pond Branch
Baisman's Run
Villa Nova
Carroll Park
site
Gwynnbrook
Glyndon
Dead Run
Mean annual TN, NO3 load from unforested areas
.
20
18
16
N (kg/ha/yr)
14
12
NO3
TN
10
8
6
4
2
0
Baisman's Run
Villa Nova
Carroll Park
Gwynnbrook
Site
Glyndon
Dead Run
Cumulative export of N
with flow developed
from N concentrationdischarge relations and
flow duration
Pond Branch (forested reference)
[NO 3 - ] (mg/L)
0.30
0.20
0.10
0.00
0.01
0.1
1
10
100
q (mm/d)
Cumulative frequency distribution of discharge,
Pond Branch (forested reference)
Baismans Run (suburban)
0.9
% discharge
[NO 3 - ] (mg/L)
3.00
2.00
0.01
0.1
0.6
1.00
0.3
0.00
0
1
q (mm/d)
10
100
0.01
0.1
1
q (mm/d)
10
100
Export distribution varies with land cover
1
0.10 kg NO3-N/ha/yr
0.75
% NO 3 - load
5.28 kg NO3-N/ha/yr
0.5
4.37 kg NO3-N/ha/yr
0.25
Pond Branch
(forested
reference)
Baismans
Run
(suburban)
Dead Run
(urban)
0
0.01
0.1
1
q (mm/d)
10
100
Shields et al 2008, WRR
Glyndon – 81 ha, mix of older suburban, new developments
What are the sources of N?
N retention in lawns?
Steve Raciti, BU
• N sources to BES watersheds
– Fertilizer = ~14 kg/ha/yr
– Atm Deposition = ~12 kg/ha/yr
• Largely from fossil fuel combustion
• Tracer Experiment
– Simulate atmospheric N deposition
• Spray 15N ‘labeled’ nitrate on lawns & forests
– Compare N retention
• Labeled N?
– N has 2 stable forms: 14N, 15N
•
•
Ambient: 0.4% 15N atoms
Labeled: 99.5% 15N atoms
– Can follow the N through the system…
Following the ‘Labeled’ Nitrogen
N2 gas
Leaves/stems
Thatch/L
L
Soil Organic
Matter
DON
15N
(Dissolved Organic N)
DIN
(Dissolved Inorganic N)
Roots
Microbial
Biomass
Raciti et al. 2008 (Ecological Applications)
• Retention of simulated atmospheric N deposition was
similar in lawns and forests
– Despite annual fertilizer applications to lawns
*
(Raciti et al. 2011a)
* statistically significant (p<0.05)
Residential soils had more carbon and nitrogen than forest soils.
Raciti et al, 2011
Lawn fertilization rates by watershed area (mpw),
residential area (mpr), lawn area (mpl)
Nested (sub)urban flux fields
• Regional annual precipitation/deposition: ~1000 mm
– ~8-10kg N/ha/yr
100% land area
• Lawn irrigation: 25mm/wk *20weeks ~ 500 mm 20-50%
– ~100kg N/ha/yr
30-50% land area
• Septic input: 600 l/day /100 m2 = 6 mm/day
–
uns
at
sat
~ .02-.03 kg/100 m2 /day
~900 kg/ha/yr (mpsa)
>2000mm / yr
~9kg/ha/yr (mpr)
Verhoef, Welty, et al
UMBC
High frequency UV-nitrate sensor monitoring of storm and
diel dynamics
VerHoef et al., 2011a,b; VerHo
Storm dilution and recovery of NO3- in Dead Run catchments.
Diel variations expressed differentially across streams
VerHoef et al., 2011a,b
Hi frequency SUNA measurements of diel variations of NO3-
Dual isotope signatures of nitrate from different
sources and catchments
Kaushal et al, 2011, ES&T
Mixing and transition of dominant N sources
with flow levels
Kaushal et al 2011, ES&T
RHESSys Flow diagram
Dead Run 5: Hi res object-oriented land cover
NLCD
observed flow mm (USGS rating curve)
35
streamflow (mm)
30
25
20
15
10
5
0
new modeled flow mm (bmiles)
When, what and where of nitrogen exports
Interaction with water, carbon cycling
Prospects for improved retention
• On site (septic) and sanitary sewer wastewater appear to dominate.
Lawns appear to be more conservative in carbon/nitrogen than expected
• Mixed low density areas beyond urban service boundary (extensive in
expanding suburbs/exurbs) have large export at moderate to low flow.
– Potential to increase in-stream retention if flow rates can be reduced
or contact with riparian areas can be restored.
• Highly developed catchment N export increases significantly at higher
flows, dominated by large events
– More limited potential to achieve N reduction through restoration
– Altering catchment flow regime, reduction at source required
• Drought promotes retention of developed catchment N, transport limited
Promotes export of forest catchment N – supply limited
hydroclimate impacts reversed
Conceptual model shows moisture and nutrient flux
within the ecosystem patch-hillslope scale for
undeveloped and developed catchments
Geomorphology and infrastructure as controls of the spatial and temporal patterns of
shallow soil moisture: locations of non-point N sources, hydrologic pathways
Baismans Run W3 Observed and Simulated NO3
5.00
4.50
3.50
3.00
W3 measured nitrate conc.
Modeled DIN conc. (T2D)
2.50
2.00
1.50
1.00
0.50
Ju
n
Ju
l
A
ug
Se
p
O
ct
N
ov
D
ec
ov
D
ec
Ja
n
Fe
b
M
ar
A
pr
M
ay
N
ct
O
Se
p
ug
A
l
0.00
Ju
DIN concentration (mg/L)
4.00
Soil Moisture Controls on N-Cycling
Increased source by nitrification at mesic soil moisture,
increased sink at near saturated conditions
Soil Moisture Scalar (0-1)
What are these patterns in the developed and undeveloped landscape?
Nnitrif = f(H20, NH4,T, C/N,…)
1
Ndenitrif = f(H20, C, T,NO3,…)
0.8
denitrification
nitrification
0.6
0.4
0.2
0
0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1
Soil Wetness (0-1)
(Century N-Gas Model, Parton et al., 1996)
other SM influences:
decomp, photosynthesis,
uptake, immobilization