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Research in the Luquillo Critical Zone Observatory

The Luquillo Critical Zone Observatory (LCZO) focuses on how water balances and mass fluxes differ in landscapes with contrasting lithology across a range of climatic and vegetation zones.  Parent material has been recognized as a state factor for landscape and soil development for over a century.  However, the influences of lithology on denudation, hydrologic routing, and the elemental cycles and flows is still poorly constrained in most studies.  The LCZO will use the natural laboratory of the Luquillo Mountains to determine how critical zone processes differ in watersheds underlain by quartz diorite (GD ) and volcaniclastic (VC) bedrock (Figure 1). Specifically, the LCZO will address how the bedrock is coupled to or decoupled from the hydrologic, geochemical and biogeochemical cycles in these watersheds.  A set of interrelated hypotheses (Figure 2, Table 1) will be tested taking advantage of the cohesive network of sampling sites (Table 2) and a unified data management system. This approach facilitates controlled comparisons across bedrock (GD, VC) types, landscape position (ridge, hillslope, riparian), depths (surface to bedrock), forest type (Tabonuco, Colorado, Cloud) and distance from the headwaters (upland to coastal).

Figure 1; Luquillo Critical Zone focus watersheds. With stream gages (water droplets). 

Short term responses (e.g. days to seasons) to be investigated include the influence of lithology on biogeochemical responses to storms and droughts, and the influence of lithology on hydrologic routing and watershed hydrologic budgets. Recent research indicates there are greater seasonal variations in the chemistry of atmospheric inputs and soils processes than previously expected (Heartsill et al 2007, Shanley 2008, Scholl in press).  These responses will be quantified using an improved network of weather stations, nested stream gages and multi-investigator event sampling campaigns.  Responses at intermediate time scales (e.g. decades to centuries) will be evaluated by quantifying stream channel dynamics and examining the conditions in the past recorded in the sediments of the floodplains and coastal zones.  The long-term influences of lithology on sediment generation, hillslope and landscape development will be evaluated in studies of bedrock weathering rates and rates of saprolite and soil formation.

Figure 2: Conceptual framework and relationships between the hypothesis and sampling nodes for the Luquillo Critical Zone Observatory.  Infrastructure is in red while hypothesis are in green.

Hypothesis 1: The rate of saprolite advance varies with regolith thickness and landscape position  and is fastest in GD valleys and slowest on VC ridges.  Over large areas, the rate of saprolite advance will equal the rate of denudation and can be predicted from bedrock chemistry, porefluids, and physical rock properties (Brantley, Buss, White, Heimsath, Willenbring,).
The rate of saprolite production increases with regolith thickness, which depends on landscape position and bedrock type.  The rates should be fastest in GD valleys and slowest on VC ridges. Over large areas, the rate of weathering will equal the rate of denudation resulting steady state landscape profiles.  The magnitude of the rates can be predicted from bedrock chemistry, porefluids composition, and physical rock properties

Hypothesis 2: In surface soils, chemical transformations of atmospheric inputs are decoupled from bedrock lithology and influenced by soil carbon, surface redox, and plant nutrient cycling.  Biotic influences on soil biogeochemistry decrease with storm intensity and soil depth and are greatest in surface soils of the VC during low intensity rainfalls (Johnson, Shanley, Silver, Scatena, UPR).

Hypothesis 3: The routing of water through the critical zone is determined by bedrock lithology. The residence time will be longer in areas underlain by GD and shorter in areas underlain by VC resulting in differences in water chemsitry.  However these differences will decrease with storm intensity and duration (Scholl, Scatena, Shanley, McDowell).

Hypothesis 4: Over seasonal time scales, iron reduction and the associated CO2 production will vary across the landscape based on differences in soil redox and organic matter content. Iron reduction will be greatest in riparian VC surface soils and lowest at depth on stable GD ridge tops.  At larger spatial scales and longer time scales deep weathering rates and iron cycling are closely linked to the frequency of low redox events and carbon availability (Silver, Brantley, Plante)

Hypothesis 5: The morphology and soil biogeochemistry of riparian and colluvial deposits varies systematically with lithology and distance from the headwaters.  In contrast, the vegetation and soil organic matter chemistry vary systematically with rainfall and temperature (McDowell, Plante, Silver, Scatena, Jerolmack).

Hypothesis 6: Surface erosion is the dominant source of sediment to the stream channel network across the entire landscape. While surface erosion is associated with rainfalls of moderate intensity in VC watersheds, in the GD watersheds sediment originates from the landslides associated with high intensity precipitation events (Jerolmack, Horton, Willenbring, Scatena, Shanley).

Hypothesis 7: The temporal resolution of the climatic disturbances and land use change recorded in coastal and fluvial sediments differs between lithologies.  The GD watersheds will have a higher resolution record than corresponding environments in the VC watersheds because of …(Horton, Willenbring, Jerolmack, Heimsath, Scatena).

Figure 1; Luquillo Critical Zone focus watersheds. With stream gages (water droplets). 

Figure 2: Conceptual framework and relationships between the hypothesis and sampling nodes for the Luquillo Critical Zone Observatory.  Infrastructure is in red while hypothesis are in green.

Research News


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21 Apr 2017 - AGU has published a collection of commentaries highlighting the important role Earth and space science research plays in society.


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06 Apr 2017 - 2017 CZO Webinar Series: Critical Zone and Society.


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Critical Zone Profile - JAIVIME EVARISTO (ecohydrologist, PhD student)

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Example Publications


Beyond clay: towards an improved set of variables for predicting soil organic matter content. Rasmussen C., Heckman K., Wieder W.R., Keiluweit M., Lawrence C.R., Berhe A.A., Blankinship J.C., Crow S.E., Druhan J.L., Hicks Pries C.E., Marin-Spiotta E., Plante A.F., Schädel C., Schimel J.P., Sierra C.A., Thompson A., Wagai R. (2018): Biogeochemistry (online) Cross-CZO


Concentration-Discharge Relations in the Critical Zone: Implications for Resolving Critical Zone Structure, Function and Evolution. Chorover, J., Derry, L. A., McDowell, W. H. (2017): Water Resources Research 53(11): 8654–8659 Cross-CZO National


Growing new generations of critical zone scientists. Wymore Adam S., Nicole R. West, Kate Maher, Pamela L. Sullivan, Adrian Harpold, Diana Karwan, Jill A. Marshall, Julia Perdrial, Daniella M. Rempe and Lin Ma (2017): Earth Surface Processes and Landforms 42 (14): 2498-2502 Cross-CZO National


Geochemical evolution of the Critical Zone across variable time scales informs concentration-discharge relationships: Jemez River Basin Critical Zone Observatory. McIntosh J.C., Schaumberg C., Perdrial J., Harpold A., Vázquez-Ortega A., Rasmussen C., Vinson D., Zapata-Rios X., Brooks P.D., Meixner T., Pelletier J., Derry L., Chorover J. (2017): Water Resources Research 53(5): 4169–4196 Cross-CZO National


Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth. Brantley, S.L., McDowell, W.H., Dietrich, W.E., White, T.S., Kumar, P., Anderson, S., Chorover, J., Lohse, K.A., Bales, R.C., Richter, D., Grant, G., and Gaillardet, J. (2017): Earth Surface Dynamics, 5, 841–860 Cross-CZO National


Reviews and syntheses: on the roles trees play in building and plumbing the critical zone. Brantley, Susan L., David M. Eissenstat, Jill A. Marshall, Sarah E. Godsey, Zsuzsanna Balogh-Brunstad, Diana L. Karwan, Shirley A. Papuga, Joshua Roering, Todd E. Dawson, Jaivime Evaristo, Oliver Chadwick, Jeffrey J. McDonnell, Kathleen C. Weathers (2017): Biogeosciences, 14, 5115-5142 Cross-CZO National


Controls on deep critical zone architecture: a historical review and four testable hypotheses. Riebe, C. S., Hahm, W. J., Brantley, S. L. (2017): Earth Surface Processes and Landforms, 42 (1): 128–156 Cross-CZO National


Special issue of The Earth Scientist about the Critical Zone and the US NSF Critical Zone Observatory (CZO) program. CZO Education/Outreach team (2016): The Earth Scientist, Volume XXXII, Issue 3, Fall 2016 Cross-CZO National


Variation of organic matter quantity and quality in streams at Critical Zone Observatory watersheds. Miller, Matthew P., Boyer, Elizabeth W., McKnight, Diane M., Brown, Michael G., Gabor, Rachel S., Hunsaker, Carolyn T., Iavorivska, Lidiia, Inamdar, Shreeram, Johnson, Dale W., Kaplan, Louis A., Lin, Henry, McDowell, William H., Perdrial, Julia N. (2016): Water Resources Research, 52 (10): 8202–8216 Cross-CZO


Reconstructing the transport history of pebbles on Mars. Szabó T., Domokos, G., Grotzinger, J.P., Jerolmack, D.J. (2015): Nature Communications


A field comparison of multiple techniques to quantify groundwater–surface-water interactions. González-Pinzón, R., Ward, A., Hatch, C., Wlostowski, A., Singha, K., Gooseff, M., Haggerty, R., Harvey, J., Cirpka, O., and Brock, J. (2015): Freshwater Science, 34(1) Cross-CZO


Analytical model for flow duration curves in seasonally dry climates. Müller, M.F., Dralle, D.N., and Thompson, S.E. (2014): Water Resources Research 50(7): 5510-5531. Cross-CZO

Critical zone structure controls concentration-discharge relationships and solute generation in forested tropical montane watersheds. Wymore, A.; Brereton, R. L.; Ibarra, D. E.; Maher, K.; McDowell, W. H. (2017): Water Resources Research 53, 6279–6295 Cross-CZO National

Mixing as a driver of temporal variations in river hydrochemistry: 1 Insights from conservative tracers in the Andes-Amazon transition. Torres, M.A.; Baronas, J.J.; Clark, K.E.; Feakins, S.J.; West, A.J. (2017): Water Resources Research 53, 3102–3119

Rapid iron reduction rates are stimulated by high-amplitude redox fluctuations in a tropical forest soil. Ginn, Brian, Christof Meile, Jared Wilmoth, Yuanzhi Tang, and Aaron Thompson (2017): Environmental Science & Technology 51 (6): 3250-3259

Optimized high-throughput methods for quantifying iron biogeochemical dynamics in soil. Huang, W., Hall S.J. (2017): Geoderma

Reassessing rainfall in the Luquillo Mountains, Puerto Rico: Local and global ecohydrological implications. Murphy SF, Stallard RF, Scholl MA, González G, Torres-Sánchez AJ (2017): PLOS ONE

Weathering and erosion of fractured bedrock systems. Lebedeva M.I., Brantley S.L. (2017): Earth Surface Processes and Landforms

Extreme storms drive riverine particulate organic matter export from tropical mountians of estern Puerto Rico. Kathryn E. Clark, Robert F. Stallard, Martha A. Scholl, Alain F. Plante, Sheila F. Murphy, Grizelle Gonzalez, and William H. McDowell (2017): ...

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