stream solute export and biogeochemistry in the luquillo mountains, puerto rico
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Stream Solute Export and Biogeochemistry in the Luquillo Mountains, Puerto Rico. Richard L. Brereton William H. McDowell University of New Hampshire. University of New Hampshire. El Yunque National Forest, PR. The only tropical rainforest in the U.S. - PowerPoint PPT PresentationTRANSCRIPT
Stream Solute Export and Biogeochemistry in the Luquillo
Mountains, Puerto Rico
Richard L. BreretonWilliam H. McDowell
University of New HampshireUniversity of
New Hampshire
El Yunque National Forest, PRThe only tropical rainforest in the U.S.
70% of runoff is withdrawn (Crook 2005)
LTER since 1988
CZO since 2009
Tropical Montane Wet Forest
Two Very Different Watersheds
Rio MameyesVolcaniclastic bedrock
3.5 m/y of rainLower avg. elevation
Rio Icacos/BlancoGranodiorite
bedrock4.5 m/y of rain
Higher avg. elevation
Volcaniclastic:Rio Mameyes
Bisley watershedsQ. Sonadora
GranodioriteRio IcacosQ. Guaba
Quebrada Sonadora - low flow
Controls on stream chemistry
• Major ions reflect lithology and sea salt
• Dilution at high flows• Silica dilution is among highest
measured (Godsey et al. 2009)• TSS increases with flow• Biogeochemical puzzle: Carbon and
Nitrogen
Shanley, McDowell, and Stallard 2011 “Boomerang” effect of DOC in the Icacos
0
100
200
300
400
500
1980s1990s2000s
0.1 1 10Discharge, mm hr-1
DO
C c
once
ntra
tion,
µm
ol L-1
El Yunque, 1984
1989 – Hurricane Hugo
(Inches of rain)
Category 4 Hurricane:226 km/hr sustained
Study Area
Bisley Experimental WatershedsBefore Hugo After Hugo
Georges, 1998 Category 3, 175 km/hr sustained
Mameyes headwaters – 2005
Weathering products and DOC:no response to hurricanes
0 50 100 150Months Since Hurricane
0
1
2
3
4
5
DO
C, m
g/L
Icacos after Georges
Nitrate response in two small watersheds after Georges (1998-
2009)
0 50 100 150Months Since Hurricane
0
100
200
300
400
NO
3N
0 50 100 150Months Since Hurricane
0
100
200
300
400
NO
3-N
, ug/
L Volcaniclastic(Prieta)
Quartz diorite(Guaba)
Two larger basins, Sonadora (254 ha) and Icacos (326 ha)
after Georges (1998-2009)
0 50 100 150Months Since Hurricane
0
100
200
300
400
NO
3-N
, ug/
L
RIQS
SAMPLE_ID
Pre-Hurricanes1983-1986Rio Icacos
Q. Sonadora
What makes nitrate behave so differently from other
solutes?
Why the slower return to baseline in granodiorite
watersheds?
Biogeochemical controlson N flux to streams
• Hydrologic flow path – groundwater? surface runoff?
• Residence time – contact with soils• What is the matrix?• Redox conditions – climate• Riparian denitrificationNO3 N2O N2
Groundwater monitoring wells
Transects across catena
Bisley – volcaniclastic
Riparian zone:Denitrification “hotspot”periodically anaerobic
C sourcehigh retention time
Modified from McDowell et al. 1992
Icacos trib. – granodiorite watershed
55035
45030 20
370 20560
5560
Riparian Zone
Slope
Stream:10010
Flows into Icacos
Modified from McDowell et al. 1992
Key:NO3 NH4
Icacos – slow recovery
Conclusions• Luquillo stream chemistry reflects
lithology overlain by vegetation, climate, disturbance history
• Hurricanes cause dramatic shifts in forest biogeochemistry, reflected in stream nitrate peaks
• Riparian zones hold the key to understanding long-term nitrogen dynamics in the Luquillo Mountains
Acknowledgements• Funding from NSF-LTER, NSF
Ecosystems, NSF-CZO, USFS IITF, UPR, UNH
• Collaborators include F. Scatena, A. Lugo, D. Schaefer, C. Asbury, J. Merriam, J. Potter, and others
• Field and laboratory assistance from M. Salgado, M.J. Sanchez, J. Bithorn, J. Merriam, J. Potter, J. Orlando, and others
Questions?55035
45030 20
370 20560
5560
Riparian Zone
Slope
Stream:10010
Flows into Icacos
Modified from McDowell et al. 1992
Key:NO3 NH4