H51K-01
Developing Methods to Test the Influence of Critical Zone Development on Watershed Hydrology and Biogeochemistry
The Boulder Creek Critical Zone Observatory in the Front Range of Colorado, USA, is designed to study the development and function of the near-surface weathered profile. The critical zone is the interface between bedrock and the atmosphere, where water and terrestrial ecosystems drive chemical transformations, and where weathering and erosion transform landscapes and shape the critical zone itself. In Boulder Creek catchment, erosion rates and processes vary dramatically over the 2600 m elevation range from the Colorado piedmont to the headwaters at the continental divide. The topographic, climatic, erosional and ecologic variations result in a critical zone that ranges from thin, fracture-dominated, weathered profiles truncated by glacial erosion to slowly eroding, deeply weathered mantles. Quantifying these variations in critical zone development, and understanding how erosion and weathering processes produce these variations, are primary goals of the Boulder Creek CZO. Against this backdrop, we will use hydrochemistry to examine how critical zone development influences fluxes of water, solutes, and nutrients to streams. We expect that reaction progress will be low in glacially truncated critical zone profiles in the headwaters, since water residence times are expected to be low in the thin fracture-dominated weathered zone. In contrast, we expect deeply weathered profiles on post-Laramide low-relief surfaces to yield long residence time water that approaches saturation with respect to minerals present. Dissolved organic matter (DOM) will likely show the most evidence of microbial processing in the deeply weathered profiles. We will use a suite of tools to test these expectations. Water will be collected from streams, wells and soil water samplers arrayed in three subcatchments. Our headwater site is coincident with the Niwot Ridge LTER high elevation site and will be managed jointly. In the case of dry regolith, we will use laboratory soil water extracts to test compositions of subsurface water. Major element concentrations in these waters will be analyzed with respect to mineral suites present as determined from quantitative XRD. The Proterozoic age of the crystalline parent rocks in this area should make strontium isotopes a useful tool in deconvolving mineral weathering sources. DOM sources will be identified with fluorescence spectroscopy. Isotopic sampling and hydrologic simulation will constrain water residence times within our study subcatchments. Rates of processes will be constrained by elemental and mineral budgets for individual soil profiles, and by solid and solution fluxes at the watershed scale. Through standardized sampling within three subcatchments, we hope to identify how critical zone development- the size and state of the reactor- affects the fluxes out of the critical zone.
H51K-02 INVITED
Southern Sierra Critical Zone Observatory (CZO): hydrochemical characteristics, science and measurement strategy
The Southern Sierra CZO is a platform for integrated, multi-disciplinary research that will provide a process-level understanding of the critical zone, establish a foundation for long-term hydrologic, (bio)geochemical and ecological studies, and improve the predictive ability of Earth system models. An underlying hypothesis is that the distribution of soil moisture throughout the catchments controls (bio)geochemical processes, including weathering and the extent of coupling among the carbon and nitrogen cycles. Mixed conifer forest dominate the CZO, which is located in the rain-snow transition zone (1,600-2,100 m), a zone that characteristically undergoes rapid seasonal changes, going from snowcover to wet soil to dry soil over a 1-2 month period. Steep gradients in temperature and precipitation patterns, along both elevation and aspect, result in a distinct lag in spring runoff in going from lower to higher elevation. Streams draining the catchments are primarily sodium and calcium bicarbonate waters. Stream total ion concentrations measured at the top of the catchments above are about half of those at lower elevation. The higher elevation streams exhibit a larger average pH range (6.7-7.1) than do those at lower elevation (7.2-7.1). The stepped topography is a landscape that provides links between soil formation and weathering rates to landform evolution Our spatial sampling strategy is to capture key topographic features (slope, aspect, elevation, soil depth, streams) and use multiple tracers to characterize both longer term processes (millennia) and short term responses to current conditions. Our specific geochemical measurement strategy includes: i) year-round sampling of stream dissolved and suspended material, ii) isotopic, geochemical sampling to infer water sources, flowpaths and residence times, iii) temperature and electrical conductivity measurements at high frequency and high spatial resolution in streams, iv) geochemical and cosmogenic radionuclide measurements to provide a longer-term context in which to assess extreme events and their associated material fluxes, v) seasonally integrated measurements of deposition, and vi) soil-water sampling in different landscapes and along flowpaths. http://snri.ucmerced.edu/CZO
H51K-03
Using Integrated Hydrologic Models to Trace the Source and Dynamics of Fresh Water Discharge in a Coastal Watershed
Quantification of freshwater discharge to streams and estuaries is vital to coastal aquatic life, and is closely related to the salinity and chemical characteristic of the estuary. In this research, the Penn State Integrated Hydrologic Model (PIHM) is used to investigate the spatial and temporal behavior of freshwater discharge in Rhode River Basin, an experiment watershed operated by Smithsonian Environmental Research Center (SERC). PIHM is a multi-process, multi-scale hydrologic model where the major hydrological processes are fully coupled using the semi-discrete finite volume method. The model is used to partition surface and groundwater discharges to the estuary and streams. It is shown that the direct groundwater discharge is substantial (overall approximately 25% of total discharge) as compared to baseflow to streams. Noticeably, during dry periods baseflow to streams and coastline discharge are similar (direct discharge to the estuary is approximately 43% of the total discharge). It is also demonstrated that, forcing by precipitation and topography is largely controlled by tide stage. Ongoing research is developing a new tool for modeling the "age" of water through seasonal and longer term climate cycles.
H51K-04
Confidence interval in estimating solute loads from a small forested catchment
The evaluation of uncertainty in estimating mass flux (load) from catchments plays the important role in the evaluation of chemical weathering, TMDLs implementation, and so on. Loads from catchments are estimated with many methods such as weighted average, rating curve, regression model, ratio estimator, and composite method, considering the appropriate sampling strategy. Total solute loads for 10 months from a small forested catchment were calculated based on the high-temporal resolution data and used in evaluating the validity of 95% confidence intervals (CIs) of estimated loads. The effect of employing random and flow-stratified sampling methods on 95% CIs was also evaluated. Water quality data of the small forested catchment (12.8 ha) in Japan was collected every 15 minutes during 10 months in 2004 to acquire the gtrue valuesh of solute loads. Those data were measured by the monitoring equipment using FIP (flow injection potentiometry) method with ion-selective electrodes. Measured indices were sodium, potassium, and chloride ion in the stream water. Water quantity (discharge rate) data were measured continuously by the V-notch weir at the catchment outlet. The Beale ratio estimator was employed as the estimation method of solute loads because it was known as unbiased estimator. The bootstrap method was also used for calculating the 95% confidence intervals of solute loads with 2,000 bootstrap replications. Both flow-stratified and random sampling was adopted as sampling strategy which extracted sample data sets from the entire observations. Discharge rate seemed to be a dominant factor of solute concentration because the catchment was almost undisturbed. The validity of 95% CIs were evaluated using the number of inclusion of gtrue valueh inside CIs out of 1,000 estimations derived from independently and iteratively extracted sample data sets. The number of samples in each data set was set to 5,500, 950, 470, 230, 40, and 20, equivalent to hourly, 6-hourly, 12-hourly, daily, weekly, and biweekly sampling intervals respectively. As a result, 95% CIs worked properly only at the random sampling which contained 5,500 samples out of 34,000 entire observed data. In other case, 95% CIs could give much less confidence for both random and flow-stratified sampling. The width of 95% CIs seemed to be appropriate but only 50% to 80% of 95% CIs out of 1,000 estimations contained true value inside. It was concluded that the Beale ratio estimator made slightly biased estimation of solute loads and those bias and failure in deriving proper 95% CIs came mainly from sampling method. The difference between random and flow-stratified sampling was also insignificant except sodium which had a strong non-linear relationship between loads and discharge rates. Flow-stratified sampling was not enough to provide the i.i.d. (independent and identically distributed) sample data sets for the purpose of solute loads estimation.
H51K-05
Isotopes and Sustainability of the Shallow Groundwater System in Spring and Snake Valleys, Eastern White Pine County, Nevada
A critical component to managing water resources is understanding the source of ground water that is extracted from a well. Detail information on the source of recharge and the age of groundwater is thus vital for the proper assessment, development, management, and monitoring of the groundwater resources in an area. Great differences in the isotopic composition of groundwater in a basin and the basin precipitation imply that the groundwater in the basin originates from a source outside the basin or is recharged under different climatic conditions. The stable isotopes of oxygen and hydrogen in precipitation were compared with the isotopic composition of water from wells, springs, and creeks to evaluate the source of the shallow groundwater recharge in Spring and Snake Valleys, Nevada, as part of an evaluation of the water resources in the area. Delta deuterium and delta oxygen-18 composition of springs, wells, creeks, and precipitation in Spring and Snake Valleys show that groundwater recharge occurs primarily from winter precipitation in the surrounding mountains. The carbon-14 content of the groundwater ranged from 30 to 95 percent modern carbon (pmc). Twenty two of the thirty samples had carbon-14 values of greater than 50 pmc. The relatively high carbon-14 values suggest that groundwater in the area is recharged by modern precipitation and the waters have rapid travel times. Total dissolved solids content of the samples outside the playa areas are generally low, and suggests that the water has a relatively short travel time between the recharge areas and sample sites. The presence of tritium in some of the springs and wells also indicate that groundwater mixes with post 1952 precipitation. Hydrogen bomb tests which began in 1952 in the northern hemisphere added large amounts of tritium to the atmosphere and reached a peak in 1963. The stable isotopic composition, the high carbon-14 activities, and the presence of tritium, show that the shallow groundwater in Snake and Spring Valleys originates as modern recharge. The shallow groundwater in these valleys is thus a renewable resource and can be developed in a sustainable manner using the appropriate planning and management tools.
H51K-06
Using Pore Water Chemistry to Understand Critical Zone Mineral Weathering Reactions: A Comparison of Three Tropical Watersheds
Geochemical, physical, biological, and hydrologic processes are tightly coupled within the critical zone and impact global and local water cycles, solute movement, weathering rates, and nutrient bioavailability. The weathering of primary minerals in regolith and at bedrock-regolith interfaces directly impacts the availability of many important soil nutrients including Mg, Ca, K, PO4, and Fe. However, surprisingly little biogeochemical data exists as a function of depth in terrestrial regolith below the rooting zone. This shortage of data hinders quantification of the coupled processes that control nutrient fluxes. Installation of nested suction soil water samplers enables multiple researchers to measure biogeochemical parameters as a function of depth. Nested suction water samplers have been installed in soil and regolith at 0.15 m to as deep as 16.0 m in two watersheds in the Luquillo Mountains of Puerto Rico and in a watershed on Basse-Terre, Guadeloupe, in the French Antilles. All three watersheds are steep, rugged, humid, and tropical, have similar vegetation and land- use, and contain thick saprolites developed on volcanic materials: a quartz diorite intrusion in the Rio Icacos watershed, Puerto Rico; marine bedded volcaniclastics in the Bisley watershed, Puerto Rico; and a volcanic debris flow in the Bras-David watershed, Guadeloupe. The two Puerto Rican watersheds are part of the USGS Water Energy and Biogeochemical Budgets (WEBB) program and also constitute a Critical Zone Exploration Network (CZEN) seed site. The Bisley watershed is also part of the Luquillo Long Term Ecological Research (LTER) site. The Guadeloupean watershed is a Critical Zone International Scholar seed site and the surface water chemistry is monitored by the Observatoire Volcanologique et Sismologique de Guadeloupe and the Institut de Physique du Globe de Paris (IPGP). In the mid 1990's the Rio Icacos watershed was instrumented with regolith gas samplers, tensiometers, and nested suction water samplers, which have been used in numerous studies by both USGS and university-affiliated scientists. Similar equipment was installed in the Bisley watershed in 2006-2007 and in the Bras-David watershed in 2007. An overview of research findings facilitated by the nested suction water samplers installed in the Rio Icacos watershed will be presented along with data from the newly instrumented Bisley and Bras-David watersheds.
H51K-07
Effect of Tsunami on Shallow Ground Water Quality in Sri Lanka; Field Observations and Geochemical Modeling
On December 26th 2004, the earthquake off the south coast of Sumatra in the Indian Ocean generated tsunami waves, resulting in severe devastation in the coastal regions of Sri Lanka. Changes in water quality of a sand aquifer on the east coast of Sri Lanka due to the tsunami, subsequent disturbance due to well pumping and flushing by precipitation were investigated to observe its "natural cleansing" response by precipitation and the effect of well cleaning and pumping of water for domestic uses. The selected field sites near Batticaloa, located on the east coast of Sri Lanka, are bordered by the sea to the east and a lagoon to the west. The two sites were classified as disturbed and undisturbed, based on groundwater pumping. Daily rainfall was measured at the site and changes in water table were monitored from October, 2005 to October, 2006. Water samples were collected from 15 dug wells and 20 piezometers, from the disturbed and undisturbed sites, respectively to evaluate the temporal and spatial trends in water quality. Observed values of electrical conductivity, alkalinity and concentrations of calcium, sodium, magnesium, potassium and sulphate in the disturbed site were slightly higher than that in the undisturbed site during the months of January, March, and October 2006. Furthermore, water quality parameter values in abandoned dug wells in the disturbed site have shown similar results as the undisturbed site. This was also evident from the geochemical inverse modelling using the U.S. Geological Survey code, PHREEQC. These findings support the hypothesis that well cleaning and abstraction of water for general purposes disturb the natural downward movement and the recession of the tsunami impacts and therefore, the imprint of the tsunami may have been prolonged in the disturbed site compared to the undisturbed site.
H51K-08
FerryMon: Using ferries as hydrochemical observatories in estuarine and coastal waters
Estuaries are among the most productive and resourceful aquatic ecosystems on Earth. They are strongly influenced by hydrochemical stressors, including nutrient enrichment and climatic factors such as droughts, storms and floods. Clarifying how estuaries respond to these stresses will provide an understanding of how hydrologic and chemical processes control ecological condition and change of these ecosystems. This understanding will greatly benefit from a spatially and temporally-intensive observational program, which, when coupled to modeling will help predict future responses to external anthropogenic (nutrient) and climatic (hydrologic) perturbations. North Carolina's Pamlico Sound System (PSS) is the Nation's second largest estuary. It exemplifies the impacts of human development (eutrophication) and large climatic perturbations (hurricanes). We are using 3 NC DOT ferries to conduct unattended hydrochemical monitoring of water quality, habitat and ecological condition of the PSS. This program, FerryMon (www.ferrymon.org), uses temperature, salinity, pH, dissolved oxygen, turbidity, and chlorophyll a sensors coupled to discrete sampling of nutrients, organics, photopigment and molecular indicators to assess water quality in a near real-time manner over a range of relevant physical, chemical and biological time scales. An autonomous vertical profiler (AVP), equipped with sensors similar to those on the ferries, provides complementary vertical profile data. This capability is timely given unprecedented human development and a period of elevated tropical storm and hurricane activity affecting coastal water quality and habitat conditions and fisheries resources. FerryMon is used to calibrate remotely sensed indicators of water quality (photopigments, turbidity), facilitating scaling up to the ecosystem level. It is integrated with complementary observational programs (LTERs, NEON, ORION, WATERS, SEACOOS), and it supports interdisciplinary research aimed at identifying and quantifying anthropogenic and climatic drivers of ecological change in large water bodies that are difficult to monitor and assess using conventional monitoring programs. http://www.ferrymon.org