LCZO at AGU 2012

MONDAY, DECEMBER 03, 2012

V13G. V13G. Tracing Earth Surface and Deep Processes Using Innovative Isotopic Approaches I: Cosponsored by

MSA

Convener(s): Xiao-Ming Liu (University of Maryland), Philip Pogge von Strandmann (Oxford University), Kangjun Huang

(China University of Geosciences) and Kangjun Huang (China University of Geosciences)

1:40 PM - 3:40 PM; 303 (Moscone South)

WEDNESDAY, DECEMBER 05, 2012

B31B. B31B. Global Soil Change: New Frontiers for the Biogeosciences II Posters

Convener(s): Sharon Billings (Univ Kansas), Daniel Richter (Duke University) and Marc Kramer (Portland State University)

8:00 AM - 12:20 PM; Hall A-C (Moscone South)

B31C. B31C. Mercury Cycling in Heterogeneous Environments: Global and Local Factors III Posters

Convener(s): Michael Bank (Harvard Medical School), James Shanley (USGS) and Noelle Selin (MIT)

8:00 AM - 12:20 PM; Hall A-C (Moscone South)

EP33E. EP33E. Tracers, Transport, and Topography: Theory and Technology for Tractive Tracking II

Convener(s): D Bradley (U.S. Geological Survey), Lindsay Olinde (University of Texas) and Marwan Hassan (Univ British

Columbia)

1:40 PM - 3:40 PM; 2003 (Moscone West)

2:10 PM - 2:25 PM

V13G-03. How does a single precipitation event erode a landscape? Clues from meteoric 7Be and 10Be analysis of suspended sediments and soils Marcie Occhi; Jane K. Willenbring; James M. Kaste; Martha A. Scholl; James B. Shanley

8:00 AM - 8:00 AM

B31B-0412. Minerals vs. Microbes: Biogeochemical Controls on Carbon Storage in Humid Tropical Forest Soils Steven J. Hall; Whendee L. Silver

8:00 AM - 8:00 AM

B31C-0443. Just passing through --- high Hg deposition to Puerto Rico forest moves quickly off the landscape James B. Shanley; Jane K. Willenbring; James M. Kaste; Marcie Occhi; William H. McDowell

THURSDAY, DECEMBER 06, 2012

EP41I. EP41I. The Deep Critical Zone and the Inception of Surface Processes I

Convener(s): Suzanne Anderson (Univ of Colorado), Clifford Riebe (University of Wyoming) and W Steven Holbrook (Univ

Wyoming)

8:00 AM - 10:00 AM; 2008 (Moscone West)

A42B. A42B. Coastal Fog: Atmosphere, Biosphere, Ocean, and Land Interactions I

Convener(s): Alicia Torregrosa (U S Geological Survey), Christopher Still (Oregon State University), Ian Faloona (UC Davis)

and Travis O'Brien (Lawrence Berkeley National Lab)

10:20 AM - 12:20 PM; 3010 (Moscone West)

FRIDAY, DECEMBER 07, 2012

H51C. H51C. Ecohydrology of Tropical Forests: Processes, Feedbacks, and Change I Posters

Convener(s): Georgianne Moore (Texas A&M University), Gretchen Miller (Texas A&M University) and Heidi Asbjornsen

2:55 PM - 3:10 PM

EP33E-06. Deterministic and stochastic dynamics of bed load tracer particles in a coarse grained river Colin B. Phillips; Raleigh L. Martin; Douglas J. Jerolmack

8:00 AM - 8:15 AM

EP41I-01. Weathering of Fractured Rock in the Deep Critical Zone (Invited) Heather L. Buss; Ekaterina Bazilevskaya; Susan L. Brantley; Frederick N. Scatena; Marjorie S. Schulz; Art F. White

8:15 AM - 8:30 AM

EP41I-02. Probing the Architecture of the Weathering Zone in a Tropical System in the Rio Icacos Watershed (Puerto Rico) With Drilling and Ground Penetrating Radar (GPR) Joe Orlando; Xavier Comas; Gregory J. Mount; Susan L. Brantley

11:50 AM - 12:05 PM

A42B-07. Stable Isotope Signatures Illustrate the Importance of Fog and Cloud Water in Ecohydrological Processes (Invited) Martha A. Scholl

(University of New Hampshire)

8:00 AM - 12:20 PM; Hall A-C (Moscone South)

V53F. V53F. Earth Materials at the Mesoscale: Nature and Processes II: Cosponsored by MSA

Convener(s): James Watkins (Berkeley), Shaun Brown (Lawrence Berkeley Lab), Lawrence Anovitz (ORNL U Tennessee)

and Hongwu Xu (Los Alamos Natl Lab)

1:40 PM - 3:40 PM; 310 (Moscone South)

H53L. H53L. Ecohydrology of Tropical Forests: Processes, Feedbacks, and Change II

Convener(s): Heidi Asbjornsen (University of New Hampshire), Georgianne Moore (Texas A&M University) and Gretchen

Miller (Texas A&M University)

1:40 PM - 3:40 PM; 3014 (Moscone West)

8:00 AM - 8:00 AM

H51C-1353. Impact of large storms on runoff from leeward and windward watersheds, eastern Puerto Rico Sheila F. Murphy; Robert F. Stallard

1:55 PM - 2:10 PM

V53F-02. Using Neutron Scattering to Understand How Porosity opens in Weathering Rocks to Form Regolith (Invited) Susan L. Brantley; Ekaterina Bazilevskaya; Lixin Jin; Gernot Rother; David R. Cole; Alexis Sitchler; Xin Gu

2:00 PM - 2:15 PM

H53L-02. The sources of water transpired by mahogany species along elevational, topographic, and moisture gradients in southwestern and northeastern Puerto Rico Jaivime A. Evaristo; Frederick N. Scatena

H54B. H54B. Ecohydrology of Tropical Forests: Processes, Feedbacks, and Change III

Convener(s): Gretchen Miller (Texas A&M University), Heidi Asbjornsen (University of New Hampshire) and Georgianne

Moore (Texas A&M University)

4:00 PM - 6:00 PM; 3014 (Moscone West)

TITLE: How does a single precipitation event erode a landscape? Clues from meteoric 7Be and 10Be analysis of suspended sediments and soils

AUTHORS (FIRST NAME, LAST NAME): Marcie Occhi1, Jane K. Willenbring

1, James M Kaste

2, Martha A Scholl

3,

James B Shanley4

INSTITUTIONS (ALL): 1. University of Pennsylvania, Philadelphia, PA, United States. 2. The College of William and Mary, Williamsburg, VA, United States. 3. USGS, Reston, VA, United States. 4. USGS, Montpelier, VT, United States. ABSTRACT BODY: Stream sediment contains a history recorded in isotopes that cling to suspended particles. In this study we exploit this recorded history in order to understand how a single precipitation event erodes the landscape at two watershed sites (Bisley I and Mameyes) within the Luquillo Critical Zone Observatory, Puerto Rico. We use fallout cosmogenic radionuclides Beryllium-7 (7Be) and Beryllium-10 (10Be) to determine the provenance of suspended sediment at various stages of a hydrograph. Sediments from source areas within the watersheds, such as stable ridge crests and active landslide scars, were also sampled and analyzed. Exploiting the large difference in half-life, the 10Be/7Be ratio of suspended sediments coupled with the concentration and nature of organic material present show original depth of mobilized stream sediment in the hillslope. The storm hydrographs of a one-month recurrence interval storm on June 7th, 2011 were sampled at both watersheds. In the small watershed (0.067 km2), storm discharge and total suspended solids (TSS) show short lag times between the initiation of precipitation and the initial rise of the hydrograph and no lag time between peak discharge and peak TSS. The larger site (17.8 km2) had a lag time of approximately 30 minutes between the initiation of precipitation and a rise in discharge and had a 15-minute lag between peak stage (which occurred first) and peak TSS, highlighting the longer travel distances that particles must take to reach the stream sampling point in the larger basin. We compare fallout 7Be nuclide concentration in source sediments and assume a simple, two end-member model to mix these sources in the stream. Soil sediments collected from stable ridge crests (‘old’) have relatively high average 7Be concentrations of 2.7x106 atoms/g±10% and sediments collected from active landslide scars (‘new’) have relatively low 7Be concentrations of 4.0x104 atoms/g±15%. Suspended sediments had an average 7Be concentration of 7.2x105 atoms/g±8%, indicating a mixing of sediment pools. Results from the two-component mixing-model indicate that, in the small watershed, new sediments accounted for 84% of newly mobilized total suspended sediments while old sediments only accounted for 16% as a discharge weighted mean over the entire hydrograph. The highest peak of old sediment (24% of TSS) at this site corresponds to the peak in stage, with old sediment percentages decreasing from peak stage

4:00 PM - 4:20 PM H54B-01. Ecohydrology of the Luquillo Mountains of Northeast Puerto Rico (Invited) Frederick N. Scatena

4:20 PM - 4:35 PM

H54B-02. The Relative Importance of Convective and Trade-wind Orographic Precipitation to Streamflow in the Luquillo Mountains, Eastern Puerto Rico Martha A. Scholl; James B. Shanley; Marcie Occhi; Frederick N. Scatena

to the end of sampling. Peak new sediment occurred at the rising limb (81% of TSS) and immediately after the receding limb (84% of TSS) of the hydrograph. These results are consistent with the fact that landslide scars mar the small watershed and expose bare, non-vegetated, deep-sourced material for transport off of the hillslopes during storm events. In the large watershed, the storm mobilized more stable soils (36%) and less new sediment (64%) than in the small watershed. Peak old sediment is witnessed after the peak stage within the larger watershed site, where it stabilizes around 50% for approximately an hour, then decreases with the receding limb of the hydrograph. Conversely, peak new sediment occurred during the rising limb, then decreased during peak flow, then began to increase during the later portion of the receding limb.

KEYWORDS: [1150] GEOCHRONOLOGY / Cosmogenic-nuclide exposure dating, [1625] GLOBAL CHANGE / Geomorphology and weathering, [1825] HYDROLOGY / Geomorphology: fluvial. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: Contact Details CONTACT (NAME ONLY): Marcie Occhi CONTACT (E-MAIL ONLY): Occhim@sas.upenn.edu TITLE OF TEAM:

TITLE: Minerals vs. Microbes: Biogeochemical Controls on Carbon Storage in Humid Tropical Forest Soils

AUTHORS (FIRST NAME, LAST NAME): Steven J Hall1, Whendee L Silver

1

INSTITUTIONS (ALL): 1. UC Berkeley, Berkeley, CA, United States. ABSTRACT BODY: Humid tropical forest soils contain a substantial portion (~500 Pg) of the terrestrial carbon (C) pool, yet their response to climate change remains unclear due to mechanistic uncertainty in the biogeochemical controls on soil C storage in these ecosystems. Poorly-crystalline minerals have long been known to stabilize soil C, but few studies have explored their relative importance in comparison with other likely controls such as rhizosphere processes, oxygen deficiency (anaerobiosis), and C quality. We examined relationships among soil C and a suite of biogeochemical variables measured in 162 samples from surface soils (ultisols and oxisols) collected over scales of landforms to landscapes (m – km) in the Luquillo Experimental Forest, Puerto Rico. We measured iron (Fe), aluminum (Al), and manganese (Mn) oxides in 0.5M hydrochloric acid (HCl), sodium citrate/ascorbic acid (CA), and citrate/dithionite (CD) extractions, along with clay content, root biomass, C quality (C/N ratios), and anaerobiosis using HCl-extractable reduced iron (Fe(II)) concentrations as a proxy. We used mixed-effects models to compare the relative importance of the above variables (normalized by mean and standard deviation) as predictors of soil C, with random effects to account for spatial structure. Poorly-crystalline Al oxide concentrations (CA extraction), soil C/N ratio, and Fe(II) concentrations each had highly significant (p < 0.0001) positive relationships with soil C concentrations that conveyed equivalent explanatory power, assessed by comparing standardized regression coefficients. The optimal mixed model explained 82 % of the variation of the residual sum of squares of soil C concentrations, which varied between 2 – 20 % C among samples. Fine root biomass had a weak but significantly positive association with soil C concentrations (p < 0.05), while crystalline Fe oxide concentrations (CD extraction) displayed a negative correlation (p < 0.01), and clay contents had no significant relationship. The latter results are surprising given the documented role of Fe oxides and clay minerals in C stabilization, yet may indicate the importance of C supply via roots in controlling C concentrations in humid tropical ecosystems. Samples associated with high concentrations of crystalline Fe and high clay contents may represent soils from deeper in the soil profile exposed by landslides, characterized by poorly-developed aggregate structure and fewer C inputs since disturbance.

Our optimal mixed model suggested an equivalent importance of soil mineralogy, anaerobiosis, and C quality as correlates of soil C concentrations across tropical forest ecosystems varying in temperature, precipitation, and community composition. Whereas soil mineralogy may be relatively static over timescales of years to decades, O2 availability and the chemical composition of soil C inputs and can potentially vary more rapidly. Our model suggests that changes in temperature and precipitation regimes that alter O2 availability and/or increase the lability of C inputs may lead to decreased soil C storage in humid tropical forest soils.

KEYWORDS: [0428] BIOGEOSCIENCES / Carbon cycling. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: 0 Contact Details CONTACT (NAME ONLY): Steven Hall CONTACT (E-MAIL ONLY): stevenhall@berkeley.edu TITLE OF TEAM:

TITLE: Just passing through --- high Hg deposition to Puerto Rico forest moves quickly off the landscape

AUTHORS (FIRST NAME, LAST NAME): James B Shanley1, Jane K. Willenbring

2, James M Kaste

3, Marcie

Occhi2, William H McDowell

4

INSTITUTIONS (ALL): 1. U.S. Geological Survey, Montpelier, VT, United States. 2. University of Pennsylvania, Philadelphia, PA, United States. 3. The College of William & Marynia, Williamsburg, VA, United States. 4. University of New Hampshire, Durham, NH, United States. ABSTRACT BODY: Atmospheric mercury (Hg) in wet deposition at the Luquillo Experimental Forest in northeastern Puerto Rico, averages 28 µg m

-2 yr

-1, higher than any site in the USA Mercury Deposition

Network. Despite the high deposition, Hg content of soils, vegetation, and biota are below global averages. The low Hg content of watershed surfaces, coupled with exceptionally high stream total Hg flux, suggest that most of the Hg passes through the watershed with minimal retention. We assessed Hg dynamics in two adjacent watersheds, Rio Icacos underlain by quartz diorite, and Rio Mameyes underlain by volcaniclastic rocks. At both sites, high-flow Hg concentrations approached 100 ng L

-1, dominated by particulate Hg. In

order to assess the apparent pass-through nature of Hg in this tropical forest, we measured 7Be and

10Be

isotopes from natural, cosmogenic fallout adsorbed on stream suspended particles to constrain the Hg age /residence time and source (atmospheric vs. geogenic or legacy Hg from 19

th century gold mining).

Ubiquitous 7Be (half-life 53 days) and relatively high

7Be/

10Be ratios on suspended particles suggest that

stream Hg was dominated by erosion from exposed surfaces, supporting a short residence time. The low watershed retention of the high Hg throughput limits adverse biological effects in this tropical ecosystem.

KEYWORDS: [0478] BIOGEOSCIENCES / Pollution: urban, regional and global, [0489] BIOGEOSCIENCES / Trace element cycling, [1871] HYDROLOGY / Surface water quality, [0454] BIOGEOSCIENCES / Isotopic composition and chemistry. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: 25% at Biogeomon meeting in Maine, 2012 Contact Details

CONTACT (NAME ONLY): James Shanley CONTACT (E-MAIL ONLY): jshanley@usgs.gov TITLE OF TEAM:

TITLE: Deterministic and stochastic dynamics of bed load tracer particles in a coarse grained river

AUTHORS (FIRST NAME, LAST NAME): Colin B Phillips1, Raleigh L. Martin

1, Douglas J Jerolmack

1

INSTITUTIONS (ALL): 1. EES, University of Pennsylvania, Philadelphia, PA, United States. ABSTRACT BODY: Understanding the mechanics of a single coarse sediment particle, and the mechanics of sediment transport at the flood scale, is critical to linking event scale bed load transport rates to annual bed load fluxes. We present research on the dynamics of coarse sediment tracer particles tagged with passive radio transponder tags, observing motion resulting from individual floods and the cumulative transport over many floods spanning two years, in the Mameyes River in the Luquillo Mountains of Puerto Rico. This region presents an ideal study area due to the high frequency of coarse sediment mobilizing events, which allows us to field test the applicability of recently-proposed deterministic and stochastic theories for particle motion. Data for each flood are composed of (1) measured 'flight' lengths for each transported particle, (2) the fraction of tagged particles mobilized, and (3) high-resolution river stage measurements. At the single flood scale, measured tracer particle flight lengths are exponentially distributed, and modal flight lengths scale linearly with excess shear velocity. This is in quantitative agreement with recent theory and laboratory experiments, suggesting that moving particles' velocity is determined by momentum balance with the fluid. The fraction of mobile particles per event increases rapidly with flood stage, creating a logistic-like curve whose inflection point is used to empirically define the threshold of motion. This finding is in contrast to the linear relation observed in small-scale experiments and predicted from momentum balance between sediment and fluid; we use a particle Stokes number argument to suggest that a collision cascade from grain-grain interactions is responsible for the nonlinear relation between mobile fraction and fluid stress, in dynamical equivalence with aeolian sand transport. To examine particle dispersion and relate it to transport mechanics, it is necessary to remove the time over which the fluid stress is below the critical value to move sediment. We define a new dimensionless impulse time for unsteady flows – obtained by integrating the cumulative excess shear velocity over the duration of a flood (normalized by grain size) – and find that both mean travel distance and mean square displacement (MSD) collapse onto well-defined curves when plotted against it. The MSD of bed load tracer particles shows superdiffusive behavior. Using theory for random walks in asymmetric (downstream) transport, we infer a heavy-tailed distribution of rest times of particles between transport. Laboratory experiments in steady flow show heavy-tailed rest time distributions, which are controlled by the timescale of burial and excavation of tracers. Though perhaps fortuitous, the inferred rest time distribution from our field data matches that of experiments. The long-time super diffusive behavior is further supported through modeling results, and suggests that tracers in bed load transport behave similarly to tracers in other geophysical flows where particle waiting times are dominated by heavy-tailed distributions. The emerging model for bed load tracers is that of a mobile-immobile partition, with a residence time in the immobile phase that is controlled by erosion and deposition of the bed.

KEYWORDS: [1825] HYDROLOGY / Geomorphology: fluvial, [1862] HYDROLOGY / Sediment transport, [4468] NONLINEAR GEOPHYSICS / Probability distributions, heavy and fat-tailed. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: Field work methodology presented at AGU 2011 Fall meeting. Anomalous asymmetric tracer scaling presented at Gordon Granular Physics conference 2012 (by 3rd author). Contact Details CONTACT (NAME ONLY): Colin Phillips CONTACT (E-MAIL ONLY): colinp@sas.upenn.edu

TITLE OF TEAM: PennSeD Lab

TITLE: Weathering of Fractured Rock in the Deep Critical Zone (Invited)

AUTHORS (FIRST NAME, LAST NAME): Heather L Buss1, Ekaterina Bazilevskaya

2, Susan L Brantley

2, Frederick

N Scatena3, Marjorie S Schulz

4, Art F White

4

INSTITUTIONS (ALL): 1. School of Earth Sciences, University of Bristol, Bristol, United Kingdom. 2. Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, PA, United States. 3. Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA, United States. 4. National Research Program, US Geological Survey, Menlo Park, CA, United States. ABSTRACT BODY: The interfaces where intact bedrock physically and chemically weathers to form regolith, are often hidden deep within the critical zone and are thus difficult to access. However, weathering of primary minerals along bedrock fractures located in the groundwater or deep vadose zones may supply significant weathering products to streams and oceans and influence topography and soil fertility. We investigated the deep critical zone in the Bisley watershed at the Luquillo Critical Zone Observatory from two 9.6 cm diameter boreholes drilled with a hydraulic rotary drill to 37.2 and 27.0 m depth. Continuous core samples through coherent rock were taken using an HQ-wireline barrel. Bulk solid-state chemical analysis and quantitative XRD were performed on rock and saprock samples. Thin sections were examined by optical microscopy, SEM, EDS, and EPMA. A history of low- to moderate-grade metamorphism is reflected by the presence of epidote, prehnite, pyrite, and tourmaline in the fresh rock (visibly un-weathered). Fresh rock also contains abundant plagioclase and Mg-rich chlorite, with lesser quartz, K-spar, and pyroxene. The quartz is microcrystalline and present in variable quantities in the fresh rock, consistent with infiltration of Si-rich hydrothermal fluids. Evidence of reaction-induced porosity development is observed in the visibly un-weathered rock, but the majority of weathering occurs within weathering rinds (<15 mm thick). These rinds are developed on fracture surfaces (and the outer surfaces of exposed corestones) and contain abundant secondary Fe(III)-oxides, which fill pore space, decreasing porosity relative to the core-rind interface. In the case of exposed corestones, the rinds spall off, refresing the surface for continued weathering. In the case of subsurface corestones, rinds grow thicker and sometimes consume rock fragments entirely. Borehole cores revealed repeated zones of highly fractured rock, interpreted as subsurface corestones, embedded within layers of regolith. Some corestones are massive and others are highly fractured. Subsurface corestones are larger and less fractured in the borehole drilled under a ridge, compared to the borehole drilled near a stream channel. As corestone size is thought to be a function of fracture spacing, the location of the valleys and ridges in the watershed may be controlled by the fracture spacing of the underlying bedrock. Drilling terminated in coherent rock, thought to be bedrock based on a model that hypothesized a thickness for the corestone-regolith zone [1]. Both profiles indicate that weathering proceeds 10’s of meters below the stream channel; thus weathering depth is not controlled by local base level. Furthermore, weathering rinds on fracture surfaces at depth indicate that water and oxygen are transported below the stream channel; thus not all of the water in the watershed is discharged to the stream. [1] Fletcher and Brantley (2010) Amer. J. Sci 310, 131-164.

KEYWORDS: [1039] GEOCHEMISTRY / Alteration and weathering processes, [1886] HYDROLOGY / Weathering, [3617] MINERALOGY AND PETROLOGY / Alteration and weathering processes, [0486] BIOGEOSCIENCES / Soils/pedology. (No Image Selected)

(No Table Selected) Additional Details Previously Presented Material: 20% presented at Goldschmidt 2012, Contact Details CONTACT (NAME ONLY): Heather Buss CONTACT (E-MAIL ONLY): h.buss@bristol.ac.uk TITLE OF TEAM:

TITLE: Probing the Architecture of the Weathering Zone in a Tropical System in the Rio Icacos Watershed (Puerto Rico) With Drilling and Ground Penetrating Radar (GPR)

AUTHORS (FIRST NAME, LAST NAME): Joe Orlando1, Xavier Comas

2, Gregory J Mount

2, Susan L Brantley

1

INSTITUTIONS (ALL): 1. Geosciences, Pennsylvania State University, State College, PA, United States. 2. Florida Atlantic University, Davie, FL, United States. ABSTRACT BODY: Weathering processes in rapidly eroding systems such as humid tropical environments are complex and not well understood. The interface between weathered material (regolith) and non-weathered material (bedrock) is particularly important in these systems as it influences water infiltration and groundwater flow paths and movement. Furthermore, the spatial distribution of this interface is highly heterogeneous and difficult to image with conventional techniques such as direct coring and drilling. In this work we present results from a preliminary geophysical study in the Luquillo Critical Zone Observatory (LCZO) located in the rain forest in the Luquillo Mountains of northeastern Puerto Rico. The Luquillo Mountains are composed of volcaniclastic rocks which have been uplifted and metamorphosed by the Tertiary Rio Blanco quartz diorite intrusion. The Rio Blanco quartz diorite weathers spheroidally, creating corestones of relatively unweathered material that are surrounded by weathered rinds. A number of boreholes were drilled near the top of the Rio Icacos watershed, where the corestones are thought to be in the primary stages of formation, to constrain the regolith/bedrock interface and to provide an understanding of the depth to which corestones form. The depth of the water table was also a target goal in the project. Drilling reveals that corestones are forming in place, separated by fractures, even to depths of 10s of meters below ground surface. One borehole was drilled to a depth of about 25 meters and intersected up to 7 bedrock blocks (inferred to be incipient corestones) and the water table was measured at about 15 meters. Ground Penetrating Radar surveys were conducted in the same location to determine if GPR images variable thicknesses of saprolite overlying corestones. GPR common offset measurements and common midpoint surveys with 50, 100, and 200 MHz antenna frequencies were combined with borehole drillings in order to constrain geophysical results. We will compare drilling observations to GPR data to understand: 1) the lateral extent of the regolith-bedrock interface; 2) distribution of rindlets or spheroidal fracturing around corestones; and 3) presence and extent of corestones. This work has implications for understanding the rate of weathering advance and changes in permeability across rapidly eroding watersheds.

KEYWORDS: [0920] EXPLORATION GEOPHYSICS / Gravity methods. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: 0% Contact Details CONTACT (NAME ONLY): Joe Orlando CONTACT (E-MAIL ONLY): jjo167@psu.edu TITLE OF TEAM:

TITLE: Stable Isotope Signatures Illustrate the Importance of Fog and Cloud Water in Ecohydrological Processes(Invited)

AUTHORS (FIRST NAME, LAST NAME): Martha A Scholl1

INSTITUTIONS (ALL): 1. Water Resources, U.S. Geological Survey, Reston, VA, United States. ABSTRACT BODY: Fog and cloud water, when part of an ecohydrologically significant local climate pattern, can contribute to stream flow, groundwater recharge, soil moisture, and plant uptake in coastal and mountain watersheds. Stable isotopes of water,

18O and

2H, can be used to quantify different sources of

precipitation, and to assess the role of fog or cloud water within the ecosystem. Fog and cloud water are usually enriched in

18O and

2H relative to rain at the same site, explained in part by the effect of temperature

on stable isotope fractionation – relatively higher temperatures close to the land surface tend to keep the vapor/condensed phase system from evolving to lower isotopic ratios. Land immersed in coastal fog or orographic clouds receives droplet sizes from fog to light rain. Isotopic composition of fog-sized droplets may be similar to the small raindrops, so stable isotopes reflect precipitation source to a greater extent than precipitation size. As a result, isotopic water balance determinations can show higher amounts of cloud water than determinations using fog collectors, canopy water balances, eddy covariance, and other methods. Examples from Hawaii and Puerto Rico illustrate the use of stable isotope methods in cloud forest studies. On East Maui in Hawaii, clouds intercept the mountain slopes between 600 and 2200 m on both windward and leeward sides of the island. Puerto Rico’s eastern mountains receive cloud water input at their highest altitudes, between 900-1100 m. At all sites, stable isotopes of cloud water and rain were measured using passive fog and rain collectors; weather stations and throughfall gages provided additional data. Estimates of cloud water as a fraction of total precipitation input from isotopic mixing models and the canopy water balance calculations were 29% and 15%, respectively, on leeward Maui and 27% and 32% on windward Maui. Cloud water input in the Luquillo Mountains of Puerto Rico was estimated to be 45-56% of total precipitation from isotope mixing model results, compared with 10-16% from studies using physical methods. Determination of cloud height and atmospheric temperature for individual rain events and for weekly rain samples confirmed the isotopic signature of orographic cloud water and helped quantify the importance of that weather pattern to the forest ecohydrology. Isotopic composition of stream water indicated that orographic cloud water is an important component of headwater streamflow year-round (62% in Puerto Rico, 37% in Maui). In Puerto Rico, quantifying the isotopic signatures of rain from different weather patterns showed that streams had a higher proportion of orographic precipitation than the bulk rainfall, highlighting the importance of low-intensity cloud water precipitation in maintaining baseflow. On Maui, ohia lehua (Metrosideros polymorpha) xylem water isotopic composition indicated different water use strategies by the trees at the windward and leeward sites, which had different precipitation regimes. Isotope analyses work very well for tracing the pathways of cloud water within watersheds, and results can lead to a better understanding of the role of fog and cloud water in coastal and mountain ecosystems.

KEYWORDS: [0315] ATMOSPHERIC COMPOSITION AND STRUCTURE / Biosphere/atmosphere interactions, [1813] HYDROLOGY / Eco-hydrology, [1637] GLOBAL CHANGE / Regional climate change, [1854] HYDROLOGY / Precipitation. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: 70% previously presented, various conferences Contact Details CONTACT (NAME ONLY): Martha Scholl CONTACT (E-MAIL ONLY): mascholl@usgs.gov TITLE OF TEAM:

TITLE: Impact of large storms on runoff from leeward and windward watersheds, eastern Puerto RicoAUTHORS

(FIRST NAME, LAST NAME): Sheila F Murphy1, Robert F Stallard

1INSTITUTIONS (ALL): 1. U.S. Geological Survey,

Boulder, CO, United States.

ABSTRACT BODY: Water supplies of eastern Puerto Rico are vulnerable to extreme weather events, from severe

droughts to powerful tropical storms that cause floods and landslides and damage vegetation and infrastructure.

The severity of these events may increase in the future: climate models forecast that the trend of increasing

dryness in Puerto Rico will continue, while storm strength may increase due to warmer ocean temperatures. In

order to effectively manage water supplies of eastern Puerto Rico, the impact of various weather events needs to

be assessed accurately. Precipitation and runoff data over a fifteen-year period were evaluated for four

watersheds in eastern Puerto Rico. These watersheds vary in geology, land cover, and location relative to the

Luquillo Mountains. Two watersheds windward of the Luquillo Mountains are much wetter, receiving about 4,000

mm precipitation annually, and precipitation is closely related to elevation. Two leeward watersheds receive about

half as much precipitation, and precipitation is not well correlated with elevation. Interannual variation in

precipitation and runoff is substantial in all four watersheds and is related to regional-scale weather patterns,

which are partly explained by large-scale climate oscillations. Greatest precipitation and runoff (both totals and

rates) are associated with major storms, such as hurricanes, tropical storms, and upper level troughs. Discharge

caused by such storms can be several hundred times greater than average discharge and is a substantial fraction of

annual discharge. Rainfall and runoff during the largest storms were similar among all four watersheds, suggesting

that higher annual precipitation and runoff in the windward watersheds is probably controlled by the frequent,

smaller rain events related to orographic precipitation. The windward/leeward effects dominate hydrologic

regimes in these watersheds and overwhelm differences related to bedrock geology or land cover. The impact of

reforestation or climate change over the study period cannot be distinguished from the large interannual

variations in weather and the passage of occasional large storms.

http://pubs.usgs.gov/pp/1789/

KEYWORDS: [1879] HYDROLOGY / Watershed, [1876] HYDROLOGY / Water budgets, [1854] HYDROLOGY /

Precipitation, [1817] HYDROLOGY / Extreme events.(No Image Selected)(No Table Selected)

Additional DetailsPreviously Presented Material:

Contact DetailsCONTACT (NAME ONLY): Sheila MurphyCONTACT (E-MAIL ONLY): sfmurphy@usgs.govTITLE OF

TEAM:

TITLE: Using Neutron Scattering to Understand How Porosity opens in Weathering Rocks to Form Regolith(Invited)

AUTHORS (FIRST NAME, LAST NAME): Susan L Brantley1, Ekaterina Bazilevskaya

1, Lixin Jin

4, Gernot Rother

3,

David R Cole2, Alexis Sitchler

5, Xin Gu

1

INSTITUTIONS (ALL): 1. Earth & Environ Syst Inst, Penn State Univ, University Park, PA, United States. 2. Ohio State University, Columbus, OH, United States. 3. Oak Ridge National Laboratory, Knoxville, TN, United States. 4. Univ TX El Paso, El Pas, TX, United States. 5. Colorado School of Mines, Golden, CO, United States. ABSTRACT BODY: At the Earth's surface, bedrock formed at high temperature and pressure re-equilibrates to surficial conditions. During this equilibration, a mantle of disaggregated rock known as regolith forms due to interactions between minerals, water, biota, organic matter, and gas. To understand the initial stages of regolith formation, we are making observations showing how pores open and become connected in low porosity rocks during weathering. Pores ranging in size from nanometers to microns are probed using

neutron scattering to investigate the mineral - pore interface. For example, we have used neutron scattering to analyze the interface between unweathered and weathered shale, andesite, diabase, and granite. Scattering intensity increases with extent of weathering as the porosity and surface area increases. The interface inside rocks that scatters neutrons can sometimes be characterized as a mass fractal while in other cases the interface is a surface fractal. Furthermore, in basaltic and granitic material, scattering occurs from both, i.e., from pores (mass fractal) and bumps on pore surfaces (surface fractal). In contrast, in scattering from shale, only one fractal is observed. The fractal dimensions also vary with the extent of weathering. For example, in several cases we have observed that weathering causes the mass fractal to transform to a surface fractal as pores become interconnected. We also hypothesize that surface fractal dimensions may decrease when weathering reactions are transport-limited. As we use neutrons to explore the interface of pores inside rocks during weathering, we hope to develop models for predicting these processes quantitatively.

KEYWORDS: [3617] MINERALOGY AND PETROLOGY / Alteration and weathering processes. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: 25% has been presented in published work or oral presentations Contact Details CONTACT (NAME ONLY): Susan Brantley CONTACT (E-MAIL ONLY): brantley@eesi.psu.edu TITLE OF TEAM:

TITLE: The Relative Importance of Convective and Trade-wind Orographic Precipitation to Streamflow in the Luquillo Mountains, Eastern Puerto Rico AUTHORS (FIRST NAME, LAST NAME): Martha A Scholl1, James B Shanley2, Marcie Occhi3, Frederick N Scatena3 INSTITUTIONS (ALL): 1. Water Resources, U.S. Geological Survey, Reston, VA, United States. 2. U.S. Geological Survey, Montpelier, VT, United States. 3. Earth & Environmental Science, University of Pennsylvania, Philadelphia, PA, United States. ABSTRACT BODY: Like many mountainous areas in the tropics, watersheds in the Luquillo Mountains of Puerto Rico (18.3° N) have abundant rainfall and stream discharge, but relatively little storage capacity. Therefore, the water supply is vulnerable to drought and water availability may be affected by projected changes in regional temperature and atmospheric dynamics due to global warming. To help determine the links between climate and water availability, precipitation patterns were analyzed, and stable-isotope signatures of precipitation from different seasonal weather systems were established to identify those that are most important in maintaining streamflow and groundwater recharge. Stable isotope data include cloud water, rainfall, throughfall, streamflow, and groundwater from the Rio Mameyes and Rio Icacos/ Rio Blanco watersheds. Precipitation inputs have a wide range of stable isotope values, from fog/cloud water with δ2H and δ18O averaging +3.2‰, −1.74‰ respectively, to tropical storm rain with values as low as −154‰, −20.4‰. Spatial and temporal patterns of water isotopic values on this Caribbean island are different than higher latitude, continental watersheds. The data exhibit a ‘reverse seasonality’, with higher isotopic values in winter and lower values in summer; and stable isotope values of stream water do not decrease as expected with increasing altitude, because of cloud water input. Rain isotopic values vary predictably with local and mesoscale weather patterns and correlate strongly with cloud altitude. This correlation allows us to assign isotopic signatures to different sources of precipitation, and to investigate which climate patterns contribute to streamflow and groundwater recharge. At a measurement site at 615 m in the Luquillo Mountains, the average length of time between rain events was 15 h, and 45% of the rain events were <2 mm, reflecting the frequent small rain events of the trade-wind orographic rainfall weather pattern. Long-term average streamflow isotopic composition indicates a disproportionately large contribution of this trade-

wind precipitation to streamflow, highlighting the importance of this climate pattern to the hydrology of the watersheds. Isotopic composition of groundwater suggests a slightly higher proportion of convective precipitation, but still smaller than in total rainfall. Hydrograph separation experiments yielded information on stormflow characteristics, with quantification of contributing sources determined from water isotopes and solute chemistry. The evidence that intense convective rain events run off and light trade-wind showers appear to contribute much of the baseflow indicates that the area may undergo a change in water supply if the trade-wind orographic precipitation dynamics in the Caribbean are affected by future climate change. KEYWORDS: [1041] GEOCHEMISTRY / Stable isotope geochemistry, [1804] HYDROLOGY / Catchment, [1655] GLOBAL CHANGE / Water cycles. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: 50% previously presented, various conferences Contact Details CONTACT (NAME ONLY): Martha Scholl CONTACT (E-MAIL ONLY): mascholl@usgs.gov TITLE OF TEAM: TITLE: Ecohydrology of the Luquillo Mountains of Northeast Puerto Rico (Invited)

AUTHORS (FIRST NAME, LAST NAME): Frederick N Scatena1

INSTITUTIONS (ALL): 1. Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA, United States. ABSTRACT BODY: Coastal humid tropical mountains are major sources of sediment, particulate organic carbon, and dissolved fluxes to the ocean. They are also important sources of food, fiber, municipal and agricultural water. Unlike water-limited drylands their ecohydrology is influenced by excess water and a high frequency of natural and hydrologically induced disturbances. However, like water-limited drylands, the spatial distribution of water across the landscape can play a fundamental role on biogeochemical and ecological processes. This paper reviews the influence of water on the critical zones and ecohydrology of the Luquillo Mountains of Northeastern Puerto Rico. Over a horizontal distance of 10 to 20 km, Luquillo life zones change from subtropical dry conditions at the coast to cloud enshrouded mountain peaks where the vegetation is stunted, evapotranspiration is reduced, and cloud water interception adds to annual precipitation such that annual rainfall approaches annual runoff. Along this elevational gradient there are systematic changes in climate, vegetation structure and diversity, gross and net primary productivity, carbon storage, and hydrologic and biogeochemical cycles. At the scale of hillslopes within the elevational gradients, soil nutrients, soil moisture, and soil oxygen vary systematically from ridge tops to adjacent valleys and topographic position is correlated to landscape stability and vegetation composition and structure. At landscape scales, hurricanes are the major control on forest age and structure and their associated defoliation and biomass loss can have large influences on both hydrologic and biogeochemical cycles. Nevertheless, because of the rapid re-growth of hurricane disturbed forests, the fluxes of most hydrologic pathways return to pre-hurricane rates within a year. Biogeochemical can take years to decades to return to pre-hurricane conditions. This presentation reviews these relationships and the challenges and opportunities related to measuring hydrologic and ecohydrologic properties in this and similar humid tropical mountains.

KEYWORDS: [1813] HYDROLOGY / Eco-hydrology, [0414] BIOGEOSCIENCES / Biogeochemical cycles, processes, and modeling. (No Image Selected) (No Table Selected) Additional Details

Previously Presented Material: 0 Contact Details CONTACT (NAME ONLY): Frederick Scatena CONTACT (E-MAIL ONLY): fns@sas.upenn.edu TITLE OF TEAM: Luquillo Critical Zone Observatory TITLE: The sources of water transpired by mahogany species along elevational, topographic, and moisture gradients in southwestern and northeastern Puerto Rico

AUTHORS (FIRST NAME, LAST NAME): Jaivime A Evaristo1, Frederick N Scatena

1

INSTITUTIONS (ALL): 1. Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA, United States. ABSTRACT BODY: Studies on the natural abundances of hydrogen (δD) and oxygen (δ18O) stable isotopes in water within plants have provided new information on water sources, competitive interactions, and water-use patterns under natural conditions, and highlighted the temporal and spatial variations of these processes as influenced not only by climate but also by plant morphology and physiology. However, although many studies looked at some temporal and spatial relationships between stable isotopes of water – δD in xylem sap and in soil water in many cases – and varying depths in the soil profile, virtually no study to date has looked into the possible relationships between soil-plant hydrology and elevation, topography, and moisture gradients across landscapes with similar climates but contrasting bedrocks. In addition, although the effects of moisture on plant ecophysiology in various physiographic settings have been relatively well understood, investigations into the same in environments with marked moisture gradients, particularly in the tropics, are relatively rare. δD and δ18O signatures of xylem sap from a total of 64 mahogany trees were sampled across nine physiographic sites, with varying elevation, topography, and moisture gradients, in southwestern and northeastern Puerto Rico. δD and δ18O as well as δ13C and δ15N signatures at 10-cm interval in 30-cm soil profiles were also determined in addition to leaf δ13C and δ15N. Preliminary results indicate that mahogany trees in the relatively drier sites in SW Puerto Rico utilized water from deeper parts of the soil; the δD and δ18O signatures of which closely tracked the LMWL of the site, with more pronounced effects in riparian plot than in slope and ridge plots. Conversely, mahogany trees in the relatively moist sites in NE Puerto Rico utilized water from shallower parts of the soil profiles, with increasingly more pronounced effects in riparian plots than in slope and ridge plots. Preliminary leaf δ13C results were more depleted in moist NE than in drier SW Puerto Rico, implying lower WUE in the former than in the latter site. Although leaf δ13C has been reported to vary in response to N availability, as was also tested in this study through the measurement of the natural abundances of 15N and 14N, soil moisture was found to be more important in leaf δ13C signatures in this study. Insights from investigations of this nature may prove useful for our understanding of the influences of topography, elevation, lithology, and moisture gradients not only on plant water-use patterns but also in modeling hydrological fluxes and storages that can ultimately aid in the formulation of integrated natural resource management interventions in both urban and forested systems.

KEYWORDS: [1813] HYDROLOGY / Eco-hydrology, [1852] HYDROLOGY / Plant uptake, [0483] BIOGEOSCIENCES / Riparian systems. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: Contact Details CONTACT (NAME ONLY): Jaivime Evaristo CONTACT (E-MAIL ONLY): evaristo@sas.upenn.edu