Nitrogen Along the Urban Watershed Continuum: Riparian Zones to Rivers
Sujay S. Kaushal and Scientists of the Baltimore Ecosystem Study
Acknowledgements Collaborators/Co-authors: Ken Belt (USFS), Larry Band (UNC), Catherine Shields (UNC), Emily Elliott (Pitt), Carol Kendall (USGS), Paul Mayer (EPA), Peter Groffman (CIES), Claire Welty (UMBC), Jake Beaulieu (EPA), Clay Arango (CWU), Art Gold (URI), Liz Canuel (VIMS), Amy Shields (EPA), Philippe Vidon (SUNY), Ray Morgan (UMCES), Margaret Palmer (UMCES), Gary Fisher (USGS), Chris Swan (UMBC), Stuart Findlay (CIES), Michael Pace (UVA), Tamara Newcomer (UMD), Michael Pennino (UMBC), Shuiwang Duan (UMD), Rose Smith (UMD) Helpful Discussions: Rich Pouyat (USFS), Bill Stack (CWP), Steve Stewart (Baltimore County), Tom Schueler (CSN), Ed Doheny (USGS) Research Support: NSF, NASA, Maryland Sea Grant, D.C. Water, EPA
Alteration of the Watershed Continuum • Land development replaces natural drainage with infrastructure
Tile drains in Hancock County, Indiana
– Tile drain systems – Storm drain systems – Impervious surfaces
• Impacts on material and energy transport downstream and over time
Storm drains in Baltimore, Maryland (Courtesy Bill Stack)
Kaushal and Belt (2012), Kaushal et al. (In Press)
Why explore a new concept? • Expanded hydrologic connectivity • Evolution of urban watersheds over time • Need to consider infrastructure as part of ecosystems • No concepts to compare the ecological and biogeochemical functions between natural vs. urban watersheds across hydrologic flow paths
Kaushal and Belt (2012), Urban Ecosystems
3 Spatial Dimensions: Longitudinal, Horizontal, and Vertical Urban Watershed Continuum
Natural Watershed Continuum
? Altered DOM Amounts & Bioavailability: Natural DOM Amounts and Quality: Terrestrial Vegetation Storm Drains Algae Sewage Leaks Terrestrial Vegetation Algae
Urban Watershed Continuum Kaushal and Belt (2012) Urban Ecosystems
4th Dimension: Evolving over time
Nitrogen Along the Watershed Continuum How does hydrologic connectivity influence: 1. fluxes of N exported from watersheds? 2. sources of N exported from watersheds? 3. transformations of N in urban streams?
1. Fluxes of Watershed N Export?
Newcomer et al. (2012)
9
14
8
> 60% Urban > 60% Agriculture > 60% Forested 20-60% Urban
5
8
N - 3ON
10
NO3-N (mg/L)
6
NO3-N (mg/L)
12
7
4 3 2 1 0 0
10
20
6
30
40
50
60
% Impervious Surface
4 2 0 0
20
40
60
80
100
% CATCHMENT URBANIZATION
Kaushal et al. (2008), Envir. Sci. &Tech.
20-30% Nitrogen Retention Along Gwynns Falls Mainstem Spring
Summer
4.5
8.0
4.0
7.0
3.5
6.0
3.0
5.0
2.5
4.0
Concentration (mg/L)
2.0 1.5
3.0
1.0
2.0
0.5
1.0
0.0
0.0 0
5
10
13
16
17
18
21
27
31
0
Fall
6
20
25
30
36
Winter
4.5
4.5
17
13
4.0
4.0
3.5
3.5 3.0
3.0
2.5
2.5 2.0
2.0
1.5
1.5
1.0
1.0
0.5
0.5
0.0
0.0 0
6
13
17
20
25
30
36
0
11
17
21
27
32
Stream kilometer Nitrate - Main Stem
Nitrate - Tributaries
DOC - Main Stem
DOC - Tributaries
Kaushal et al. (2014), Biogeochemistry
Drought
Nitrate-N Export (kg/ha/y)
18 16
POBR (Forest)
14
GFCP (Urban)
12 10
GFGB (Suburb) GFVN (Suburb/Urban)
8 6 4 2 0 1998
Normal 2000
Wet 2002
2004
2006
Year
Kaushal et al. (2008), Envir. Sci. &Tech.
Potomac River Hurricane Juan
Annual Streamflow (cfs)
25000
Hurricane Isabel 1996 Flood
Hurricane Agnes
20000
15000
10000
5000 2010 Drought
0 1925
2002 Drought
1945
1965
1985
2005
Year
USGS monitoring allows us to put research into context regarding hydrologic variability.
USGS River Input Monitoring Kaushal et al. (2010), Kaushal et al. In Press
Part 1: Key Points Imperviousness is related to stream N concentrations Watershed N fluxes are related to runoff variability Magnitude of response can differ across land use
I. Land Use and Sources of Nitrogen Export
Nitrogen and Oxygen Isotopes •Atmospheric Sources: d15N of nitrate decreases while d18O increases •Fertilizer: d15N of nitrate is low and d18O is low •Wastewater: d15N of nitrate is +10 to 20, and d18O is low •Denitrification: d15N of nitrate increases while d18O increases
Suburban and Urban Watersheds 100 DRKR (Urban)
Atmospheric Deposition
GFCP (Urban) GFGR (Urban)
80
RGHT (Storm Drain) Atmospheric Deposition (NADP)
Atmospheric Deposition (NADP) δ 18O-NO3- (‰)
Lawn Lysimeters
60
GFGL (Suburban)
40
Storm Drain Mixing between Atmospheric and Wastewater N
Denitrification 20 Urban Lawn Lysimeters
Suburban
0 NH4 in Fertilizer and in Rain
Soil N
Wastewater
-20 -20
-15
-10
-5
0 5 δ 15N-NO3- (‰)
10
15
20
Kaushal et al. (2011)
Hydrologic Variability Alters N Sources
Dead Run Streamflow 8
Mean Daily Discharge (m3/s)
7
Isotope Sampling
6 5 4 Isotope Sampling
3 2
Isotope Sampling
1
0 27-Jun-05
07-Jul-05
17-Jul-05
27-Jul-05
Date
Kaushal et al. (2011)
06-Aug-05
Dead Run Urban Storms (6 Locations)
14
DR 1 12
DR 3.1
Wastewater WastewaterNN
DR 3.2
δ15N-NO3- (‰)
10
DR 4 8
DR 5 DRKR (Gauge)
6
Mixture of Atmospheric and Wastewater N
4 2 0 0.1
1 Low to Moderate
Atmospheric N Stormflow
10
100
High Stormflow
Runoff (mm/day)
Kaushal et al. (2011)
Sources of Nitrogen Export in Urban Streams
Site DR1 DR 3.1 DR 3.2 DR 4 DR 5 DRKR
% Wastewater N 7 - 50 13 – 53 24 – 90 11 – 76 18 – 95 13 – 79
% Atmospheric N 8 – 92 6 - 87 10 - 76 24 - 89 5 - 82 21 - 94
Kaushal et al. (2011)
Part 2: Key Points Hydrologic connectivity with sanitary infrastructure is important during baseflow and high stormflow Atmospheric N sources can be important during light and moderate storms due to impervious surfaces Nonpoint N sources shift with storms and runoff
3. N Transformations in Urban Streams?
Elmore and Kaushal (2008), FEE
Disappearing Streams?
Pennino et al. (2014), Biogeochemistry
Stream burial reduces hydrologic connectivity and residence time in transient storage
Pennino et al. 2014, Biogeochemistry
Headwater Burial Decreases Nitrogen Uptake
Pennino et al. 2014, Biogeochemistry
Part 3: Key Points Headwater stream burial decreases hydrologic connectivity between streams and floodplains Headwater stream burial decreases N uptake Daylighting or de-channelization may have impacts at watershed scale
Pennino et al. 2014 (Biogeochemistry)
CONCLUSION
• Hydrologic connectivity can alter fluxes, sources, and transformations of N in watersheds. • Hydrologic connectivity needs to consider both surface and subsurface flowpaths. • Salinization, warming, and alkalinization represent additional water quality concerns potentially influenced by impervious surfaces
Increased salinization of fresh water in the Northeastern US
Courtesy of Ken Belt
Mean Annual Chloride Concentration (mg/L)
Link between Urbanization and Salinization of Fresh Water 600
1998 2001
500
1999 2002
2000
400 R2 = 0.81 300
Chronic Toxicity to Freshwater Life
200
Toxicity to Most Land Plants
100
0 0
10
20
30
40
50
Percent Impervious Surface in Watershed
Kaushal et al. (2005) PNAS
