H21F-0883
Role of Nurse Logs in Forest Expansion at Timberline
Nurselogs, known to be key sites of forest regeneration in lower elevation temperate forests, may be important sites for seedling establishment at expanding timberline forests. To determine factors associated with seedling establishment and survival on nurselogs at timberline, fourteen sites, located across a precipitation gradient in the Washington North Cascades Mountains, were examined. Site attributes including seedling type and height, disturbance process introducing downed wood, wood decay type, shading, slope gradient, aspect, and temperature and water content of wood and adjacent soil were determined along 60 m long transects. Nurselogs were found at 13 out of 14 sites; sites typically associated with greater than 80% shade and downed wood having a high level of wood decay. Downed wood serving as nurselogs originated from blowdown, snow avalanches, and forest fires. In total, 46 of 136 downed wood pieces observed served as nurselogs. Seedlings on nurselogs included mountain hemlock (Tsuga mertensiana), Pacific silver fir (Abies amabilis), yellow cedar (Chamaecyparis nootkatensis), subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii), and western larch (Larix occidentalis). Nurselogs had significantly higher temperatures (p = 0.015) and higher moisture contents (p = 0.019) than the adjacent soil. Per equal volumes weighed, nurselogs had on average of 23.8 g more water than the adjacent soil. Given predictions of climate warming and associated summer drought conditions in Pacific Northwest forests, the moisture provided by nurselogs may be integral for conifer survival and subsequent timberline expansion in some landscapes.
H21F-0884
Impact of seasonal and year-to-year variations in rainfall on soil moisture dynamics in a tropical rainforest and a tropical seasonal forest in Southeast Asia
We examined the impact of both seasonal and year-to-year variations in precipitation on soil moisture dynamics at a tropical rain forest (TRF) site and a tropical seasonal forest (TSF) site in Southeast Asia, between which there is a clear difference in the precipitation regime, through a probabilistic ecohydrological model. All model parameters have apparent physical meanings and were obtained by field observations. Rainfall statistics as the primary model forcing term were constructed from long-term rainfall records, and their analysis revealed a close relationship between drought and El Niño events at the TRF site and a long- term drought trend at the TSF site. The model results further demonstrated that the studied ecosystem's robustness mainly concerning the plant water availability are attributed to functional factors such as soil texture for the TRF site and rooting depth and the dry season use of water from the preceding wet season for the TSF site.
H21F-0885
Controls on the Hydrologic Response to Climate and Land Cover Change of Headwater Streams
Headwater streams are the nexus of the terrestrial and riverine system, typically classified as Horton-Strahler first and second order streams. Though their cumulative length comprises a large percentage of total stream length within the United States, hydrologic controls on ecological conditions in headwater streams are still poorly understood. Currently, the unique ecosystems supported by headwater streams are being threatened by climate and land cover change. Understanding the effects that climate and land cover change will have on headwater streams, is of central importance to preserving these areas of unique habitat. Our initial work focuses on understanding controls on the baseflow-index in Pennsylvania watersheds.
H21F-0886
Feedbacks and stability along ephemeral rivers - an integrative ecohydrological approach.
Ephemeral rivers are characterized by temporal surface flows, which result from highly variable rainfall events in arid regions. The riparian vegetation along these rivers represents a water-limited ecosystem, which is sensitive to hydrological change. These linear oases in otherwise dry landscapes have long been of importance to people and wildlife living in its proximity. Today they still are central points of human development and natural biodiversity. For a sustainable resource management the ecological dynamic has to be considered. This requires a parallel modeling approach of ecology and hydrology. However, in general the environmental data base of arid regions is rare. Therefore a biochemical approach of coupling the transpiration rates on biomass production is not appropriated and the need for aggregated approaches increases. We present an integrative ecohydrological model for the Kuiseb River in Namibia. In the upper catchment floods arise and influence a riparian woodland in the middle part of the river. The dynamic vegetation structure is reflected in the unsaturated and saturated water storages. The ecological part of the model is a dynamic state of the art model. The hydrological part is based on a conceptual water balance model, which simulates the hydrological processes realistically. Both parts are coupled by the rain use efficiency and mortality of biomass. Applying the coupled model to the Kuiseb River we investigate feedbacks and mechanisms, which stabilize or destabilize the ecohydrological system. Our results suggest that under certain hydrological conditions synchronization between different tree species occurs.
H21F-0887
Interannual variations in soil moisture and productivity of boreal forest in Eastern Siberia
Interannual variations in soil moisture and vegetation parameters were observed for 9 years in a larch forest near Yakutsk, Russia in Eastern Siberia, to investigate the response of the ecosystem. Soil moisture varied depending on both the amount of summer rainfall in the year and soil moisture at the end of the previous summer carried over as ice. The annual water budget of soil moisture (dQs) from the previous August to the current year primarily corresponds to precipitation, with a deviations caused by runoff (decrease in dQs), limited transpiration and/or upward transport of ice meltwater from the bottom of the active layer (increase in dQs). The source of water for transpiration was inferred from sap water delta18O. Snow meltwater with low delta18O preset in spring was used in early summer (June) every year, while, summer precipitation with high delta18O was transpired in a wet summer and ice meltwater with low delta18O was a major contributor to transpiration during droughts. Tree growth (GBH increment) correlated with soil moisture in August of the same year, and there was no correlation observed with the date of snow thaw. Larch needle delta13C showed negative correlation with soil moisture in the previous August, indicating lowering of stomatal conductance during a drought and carrying over of carbon until the following year. Litter fall production seems to increase with a two-year time lag behind the increase in soil moisture due to carrying over of soil moisture and response of vegetation. Larch needle delta15N (-1.3?n on average) negatively correlated with C/N ratio, possibly caused by water and nutrient availability.
H21F-0888
An eleven-year validation of a physically-based distributed dynamic ecohydorological model tRIBS+VEGGIE: Walnut Gulch Experimental Watershed
A coupled, dynamic vegetation and hydrologic model, tRIBS+VEGGIE, was applied to the semiarid Walnut Gulch Experimental Watershed in Arizona. The physically-based, distributed nature of the coupled model allows for parameterization and simulation of watershed vegetation-water-energy dynamics on timescales varying from hourly to interannual. The model also allows for explicit spatial representation of processes that vary due to complex topography, such as lateral redistribution of moisture and partitioning of radiation with respect to aspect and slope. Model parameterization and forcing was conducted using readily available databases for topography, soil types, and land use cover as well as the data from network of meteorological stations located within the Walnut Gulch watershed. In order to test the performance of the model, three sets of simulations were conducted over an 11 year period from 1997 to 2007. Two simulations focus on heavily instrumented nested watersheds within the Walnut Gulch basin; (i) Kendall watershed, which is dominated by annual grasses; and (ii) Lucky Hills watershed, which is dominated by a mixture of deciduous and evergreen shrubs. The third set of simulations cover the entire Walnut Gulch Watershed. Model validation and performance were evaluated in relation to three broad categories; (i) energy balance components: the network of meteorological stations were used to validate the key energy fluxes; (ii) water balance components: the network of flumes, rain gauges and soil moisture stations installed within the watershed were utilized to validate the manner in which the model partitions moisture; and (iii) vegetation dynamics: remote sensing products from MODIS were used to validate spatial and temporal vegetation dynamics. Model results demonstrate satisfactory spatial and temporal agreement with observed data, giving confidence that key ecohydrological processes can be adequately represented for future applications of tRIBS+VEGGIE in regional modeling of land-atmosphere interactions.
H21F-0889
Topographic Control on Soil-Vegetation-Atmosphere Interactions and its Impact on Numerical Weather Prediction
Accurate initialization and representation of the land surface is of critical importance for increasing skill in regional weather and climate prediction. This paper presents a coupled land atmosphere model that emphasizes topographic control on partitioning of mass and energy fluxes at the land atmosphere boundary. The TIN (Triangulated Irregular Network)-based Real-time Integrated Basin Simulator (tRIBS) is a physically based, spatially distributed eco-hydrological model and serves as the land surface boundary of the WRF (Weather Research Forecasting), a mesoscale regional atmospheric model. The tRIBS–WRF coupled model has been implemented in a parallel computing framework to allow fine scale simulations over large spatial domains. This talk presents short term simulations of the tRIBS-WRF model over the South Western United States. The coupled model atmospheric (WRF) conditions are initialized using North American Regional Reanalysis datasets while the land surface model (tRIBS) is initialized by conducting offline simulations using several years of meteorological forcing (NCDC hourly surface observations) data. These offline simulations are carried out for two cases, seasonally prescribed vegetation and fully dynamic vegetation which , each providing different initial conditions for the land surface boundary within the coupled model. For the two initial land surface conditions, we analyze the coupled model predictive skill in reproducing a large precipitation event observed on August 5th, 2002 in our simulation domain. The tRIBS-WRF simulations are also contrasted with equivalent simulations of the WRF using the NOAH land surface model.
H21F-0890
Inference of Hydrologic and Plant Interactions From Unsaturated Zone Chemical and Physical Data
Plant systems and deep moisture percolation are inextricably tied by their competition for incoming rainwater, especially in dry environments where moisture is limited. Unsaturated zone chloride concentrations have proved to be robust indicators of long term average subsurface flux in semi-arid to arid settings. Since these fluxes are residual amounts remaining after root uptake, this study demonstrates that chloride measurements can also be used to infer plant dynamics in a rain-fed cotton region in the semi-arid Southern High Plains of Texas. Interactions between plant and moisture flux operate on seasonal to storm-scale resolutions, making direct analysis impossible with chloride concentrations, which represent time-integrated conditions. Thus, we temporally downscale that information by conditioning fine time-scale soil-plant-atmosphere model simulations and plant parameters on unsaturated zone chloride and soil moisture data. Our estimates suggest that over the last ~75 years since the conversion to agriculture, nearly all precipitation during the peak growing season is taken up by evapotranspiration at the data sites, preventing any notable amounts of potential recharge. However, non-mature roots are unable to capture most moisture inputs during very intense spring storms, which consequently yield episodic percolation spikes. Such by-passing of roots is particularly prominent following unusually rainy winters that leave wet antecedent soil conditions, thus indicating high susceptibility to interannual variability in precipitation occurrence. Overall, these results reveal the crucial timing coordination of storm events and the growing season that determines the partitioning of rain inputs between plants and recharge. Understanding these control mechanisms can help plan for both plant growth and groundwater system impacts from changing meteorological conditions.
H21F-0891
Identification of Ecological Flow Regime Related to Fish Community: A Quantitative Ecology Approach
The pivotal difficulty in developing ecological flow regime is how to take into account the interaction and relation between flow regime and river ecosystem. In this study we propose a framework of considering the relation between ecological flow regime and fish communities based on the gradient analysis technique used in quantitative ecology theory. Dummy variables for representing synthetic environment gradient could be used to identify ecohydrological niche of each specific fish species. The main advantages of this technique are: (1) identify the patterns of variation in community composition that can be explained best by ecohydrologic indicators, (2) based on Gaussian response model, and (3) separate the effects of explanatory environment variables. This technique is then extended herein to build the optimal multi-objective operation model in Shihmen Reservoir by considering the maintenance of natural flow regimes and human needs. This research provided a framework that contributes to develop water resources management criteria to satisfy aquatic ecosystem.
H21F-0892
A minimal model of soil water–vegetation interactions forced by stochastic rainfall in water-limited ecosystems
A minimal model of soil water–vegetation interaction in dryland ecosystems is developed as a vehicle to show how stochastic differential equations can be applied to this problem. In contrast to previous works, which assume a constant rainfall, the system is forced using stochastic rainfall, and the stationary probability distributions of the soil water content and the vegetation density are derived analytically. Thence, a sensitivity analysis of the stationary probability distributions on rainfall and model parameters has been carried out. This analysis points out the influence of the rainfall process, soil and vegetation properties on the stationary probability distributions of soil water and vegetation. The approach can potentially be extended to address more complex models.
H21F-0893
Dryland ecosystems: The coupled stochastic dynamics of soil water and vegetation and the role of rainfall seasonality
In drylands the soil water availability is a key factor ruling the architecture of the ecosystem. The soil water reflects the exchanges of water among soil, vegetation, and atmosphere. Here, a dryland ecosystem is investigated through the analysis of the local interactions between soil water and vegetation forced by rainfall having seasonal and stochastic occurrence. The evolution of dryland ecosystems is represented by a system of two differential equations, having two steady states, one vegetated and the other unvegetated. The rainfall forcing is described by a diffusion process with monthly parameters. In each of the two possible steady states, the probability density functions of soil water and vegetation are derived analytically in terms of the rainfall distribution. The results show how the seasonality of rainfall influences the oscillation of the ecosystem between its vegetated steady state during the wet season and its unvegetated steady state during the dry season.
H21F-0894
The Influence of Hillslope Hydrology and Intermittent Tributaries on Hyporheic and Stream Temperatures in a Coastal Headwater Stream
As environmental temperatures rise, understanding the factors and mechanisms that help moderate stream and hyporheic zone temperatures will assist in the protection of fragile ecosystems. The stream temperature structure of a first order coastal New England stream was finely measured and analyzed to understand the components of the hydrologic system responsible for the moderation of temperature in a 500-meter study reach. An energy balance analysis coupled with the detailed geomorphic and temperature measurements of the stream, tributaries, groundwater and hyporheic zone illustrates the importance of groundwater, intermittent seeps, small wetlands and springs to stream temperature moderation and may shed light on the resulting nutrient loading in this and other similar coastal streams. Fiber Optic Distributed Temperature Sensing (FO-DTS) using a fiber optic cable was used as a survey tool in combination with discrete temperature measurements using thermocouple and thermistor sensors, and traditional hydrologic evaluation, to provide a description of the stream and hyporheic zone longitudinally and with depth along the 500-meter stream reach. LIDAR is also being used to map the watershed so that catchment, hillslope and stream geomorphology can be closely linked with the detailed temperature measurements. An analysis of 2007 field campaign data and 2008 NCALM LIDAR data will be presented.
H21F-0895
Identifying Hydrological Triggers of Green-Up in the Resilient and Widespread Creosotebush
The widespread creosotebush offers a predictable resource in an otherwise unpredictable and harsh environment. So that we might anticipate how climatic changes will effect this stable resource, we must improve our understanding of this species interacts with the water and carbon cycles. Specifically, our hypotheses include: (1) The green-up signal of creosotebush can be identified using time-lapse repeat digital photography (pheno-cams); (2) Green-up of creosotebush is driven by soil moisture within a deep reservoir (e.g. > 50 cm); and (3) Carbon-uptake is strongly correlated with the green-up signal of creosotebush. The study site is located in a creosotebush dominated ecosystem of the Santa Rita Experimental Range, southeastern Arizona. In addition to typical eddy covariance instrumentation, the site maintains continuous measurements of soil moisture in 6 one-meter profiles. Additionally, three pheno-cams have been installed within the footprint of the site. Here, we compare the green-up signal of creosotebush as detected by pheno- cams to net ecosystem exchange of CO2, soil moisture, and other micrometeorological data. Comparisons of continuous daily records of phenological events with micrometeorological records are expected to become an important step in our better understanding of hydrologic control on ecosystem function.
H21F-0896
Interactive Effects of Water level and Temperature on Tundra Carbon Flux Components
Arctic regions store important amounts of soil carbon in an unstable state because of saturated soils and low temperatures. Temperature and soil water may also strongly influence the productivity of tundra ecosystems. As a result, changes in water availability and temperature could have significant effects on the carbon balance. However, as the climate changes, the direction and the magnitude of changes in the carbon balance in response to these potentially interacting physical factors are uncertain. To evaluate the effects of water regime, we have initiated a large hydrological manipulation at Barrow, Alaska where we have maintained flooded, drained, and intermediate water levels in a drained thaw lake basin. To test the interactive effects of temperature and water level, we passively increased the temperature of the surface using open top chambers (OTCs) in each of the three water-level treatments. To quantify the effects of these treatments on the ecosystem carbon balance, we measured net ecosystem exchange (NEE) and its components, ecosystem respiration (ER) and gross primary production (GPP) using static chamber methods. Growing seasons differed strongly between 2007 and 2008, the being former hotter, brighter and drier. Interannual differences in water availability revealed an important reduction in ER for both OTC and non- temperature treated plots as a consequence of increased water table in 2008. The effect of increased water table on GPP was not as strong as the effect on ER. However, in areas where most the leaf area was submerged, GPP was strongly reduced. As a result, net ecosystem exchange (NEE) was greater (stronger sink activity) in 2008 than in 2007 for the non-temperature treated plots. The OTCs enhanced the effects of lower water availability on the flux components. During the dry year (2007) both the ER and GPP were positively affected with the stronger effect on GPP. As result the NEE was higher in the OTCs. In 2008, the combination of higher water table and lower light (fewer clear days in 2008 than in 2007) resulted in lower GPP. However, these conditions also had an important effect on carbon balance in the form of strongly reduced ER in 2008. Overall, increased water table lowers ER strongly by reducing soil oxygen availability and OTCs positively affect ER and GPP, especially in areas with little standing water. However, during very dry periods (such as those present in 2007) higher temperatures might increase transpiration and decrease the water table reducing water availability and negatively affecting GPP, especially that of the moss layer.
H21F-0897
Landform Mapping Using Multiscale Topographic Analysis
Many ecological and agricultural processes depend on topographic relationships. Topography strongly influences microclimate, the types and productivity of plants, biomass, evapotranspiration rates, carbon storage rates, and fire fuel accumulation. These factors in turn influence the water cycle, stream flow, water quality, and soil formation. Most previous topographic analysis methods have focused on the elevation of a given grid cell (pixel) and very localized measures of slope and aspect (e.g., computed from elevation in a 3x3 window). Some measures have moved beyond a strictly local relationship, such as the compound topographic index, which can be used as a soil wetness index. I introduce a new method of multiscale topographic analysis which can be applied to digital elevation model (DEM) data of any resolution. The method calculates slope and curvature (change of slope) of the land not only in relation to adjacent grid cells but also for much larger distances downstream. The algorithm uses a flow direction grid to create a synthetic stream network as a set of connected line segments (a vector dataset). The multiscale measures are stored on a node attribute table, where the nodes are the endpoints of line segments connecting the original DEM grid cells. A pointer is computed for directly accessing data for nodes at selected distances down the stream network. Baseline distances are selected by counting cells down the flow path by each power of two (1, 2, 4, 8, ... cells downstream). Slope and curvature measures are defined for each of these baselines and are queried to distinguish multiscale topographic characteristics. Several applications of these methods have been tested. A floodplain measure identifies areas that are relatively low on the landscape, even as elevation changes while moving from plains into hills or mountains (study area: South Dakota). The landscape may be partitioned to provide zones for ecological analysis, including selection of field sampling sites (study area: Yukon Flats area, Alaska). Calculations of slope length and slope for erosion modeling with the Universal Soil Loss Equation have been tested (study area: South Dakota). The multiscale slope and curvature measures can be combined with other land attributes to map landform classes which have ecological significance, such as for modeling carbon dynamics.
H21F-0898
Fog and Rain Water Influences on Tree Physiology and Ecosystem Function in a California Redwood Forest
Fog is thought to influence ecological function in coastal forests worldwide, yet few data are available that illuminate the mechanisms underlying this influence. In a California redwood forest we measured water fluxes from horizontally moving fog and vertically delivered rain as well as redwood tree function. The spatial heterogeneity of water fluxes, water availability, tree water use, and water movement varied greatly across seasons. Across the forest as a whole, 98% of water flux to the soil occurred in the rain season and was relatively even across the whole forest. In contrast, below-canopy flux of fog water declined exponentially from the windward edge to the forest interior. Following large fog events, soil moisture was greater at the windward edge than anywhere else in the forest. Physiological activity in redwoods reflected these differences in inputs across seasons: tree physiological responses did not vary spatially in the rain season, but in the fog season, water use was greater, yet water stress was less, in trees at the windward edge of the forest versus the interior. In both seasons, vertical passage through the forest changed the amount of water, revealing the role of both the tree canopy and roots in processing atmospheric inputs. While total fog water inputs were comparatively small, they may have important ecosystem functions, including relief of canopy water stress and, where there is fog drip, functional coupling of above- and below-ground processes.
H21F-0899
Estimation of Net Groundwater Recharge Using Natural Drawdown Events in Subtropical Isolated Wetland Ecosystems
Restoration of ditched and drained wetlands in the Lake Okeechobee basin, Florida, USA is currently under study for possible amelioration of anthropogenic phosphorus enrichment of the lake. To date most research in this area has focused on the biogeochemical role of these wetlands. Here we focus on the dynamic hydrology of these systems and the resulting control on biogeochemical cycling. Four depressional wetlands in the basin were monitored for approximately three years to understand the interaction between wetland surface water and adjacent upland groundwater system. A coupled hydrologic-biogeochemical model was created to evaluate restoration scenarios. Determining wetland-scale hydraulic conductivity was an important aspect of the hydrologic model. Based on natural drawdown events observed at wetland-upland well pairs, hydraulic conductivities of top sandy soil layers surrounding the isolated wetlands were calculated using the Dupuit equation under a constrained water budget framework. The drawdown-based hydraulic conductivity estimates of 1.1 to 18.7 m/d (geometric mean of 4.8 m/d) were about three times greater than slug test- based values (1.5 ± 1.1 m/d), which is consistent with scale-dependent expectations. Model-based net groundwater recharge rate at each depressional wetland was predicted based on the estimated hydraulic conductivities, which corresponded to 50 to 72% of rainfall in the same period. These variances appeared to be due to the relative difference of ditch bottom elevation controlling the surface runoff as well as the spatial heterogeneity of the sandy aquifer. Results from this study have implications for nutrient loads to Lake Okeechobee via groundwater as well as water quality monitoring and management strategies aimed to reduce solute export (especially P) from the upstream catchment area to Lake Okeechobee.
H21F-0900
Seasonal, Variably Saturated Flows in a Vernal Pool Wetland Ecosystem
Vernal pool complexes are an important seasonal wetland ecosystem in California. The pools form in shallow landscape depressions during the rainy winter season. Only under extremely wet conditions, pools become part of a surface drainage network. The surface drainage network is typically much shorter-lived than the pools. Pools may have standing water from as little as two weeks to as long as six months during the rainy season (late fall to late spring). While ecologically important, little is known about the subsurface hydrology associated with vernal pools. We have implemented an extensive hydrologic monitoring program to begin understanding the role of variably saturated flow within these vernal pools catchments. At our field sites on older tertiary alluvial terraces, we find that winter precipitation (PPT) is the principal contribution to a variably saturated aquifer on a shallow, duripan aquitard. During the onset of the winter season, infiltration throughout the local catchment results in a gradual wetting up of the relatively dry soil profile. Soil moisture content increases due to macropore flow in a clay layer overlaying the duripan, thus creating a bottom up increase in saturated soil. Overlying landscape depressions begin to expose surface water not as a result of surface runoff, but as a result of increasing perched water table elevation, thus creating the vernal pools. Subsequent fluctuations in pool basin water levels are primarily controlled by evapotranspiration (ET) within the pool and by subsurface gravitational flows, often into seasonal drainages. Multiple vernal pool basins within a catchment are shown to exhibit a high level of groundwater connectivity. Intense periods of PPT continue to supply the perched aquifer with water. Rapid fluctuations in soil moisture content can occur over periods of 10 to 30 minutes increasing surface soil moisture to near saturation levels. Macroporous clay loam soils in the A horizon quickly discharge water downward to the existing saturated zone. Recharge of the perched aquifer can similarly cause a rapid increase in the height of the saturated soil zone above the duripan. This is often reflected in a rapid increase in the depth of the vernal pool basin surface water, by as much as one foot within one hour. The upper zone of soil saturation has a highly variable peak elevation that is directly related to the frequency and amount of PPT. A significant amount of variation is observed for infiltration rates and moisture content during and following PPT events. These variations are a function of soil hydraulic properties within different stratigraphic layers in the soil profile. Microtopographic variation in the soil texture can cause seasonal variation in soil moisture retention and loss through ET. Vernal pool plant communities increase the pool basin ET. Particularly towards the end of the rain season, this accelerates the drying out of surrounding uplands. Once the season vernal pool plants have completed their life cycle and no longer actively transport water, evaporation and moisture diffusion into the surrounding uplands are the major fluxes out of the vernal pools.
H21F-0901
Geochemical Characterization of Moisture Sources Supplying a Forested Ecosystem in an Unchanneled Hillslope in the Northern California Coast Range
Coastal California annually experiences periods of nearly 6 months without rain, yet dense coniferous forests commonly develop on steep hillslopes mantled with thin soil. Much of the coast range is underlain by marine sandstones and mudstones that are intensely fractured in the near-surface environment. We hypothesize that the coniferous forest might meet its transpiration water demands not just from the thin soil layer, but supplemented by residual winter moisture residing in the underlying fractured rock. This "rock moisture" is undocumented and difficult to measure directly. In order to explore this and other hypotheses, an intensive monitoring program was initiated on a 2600 m2 unchanneled valley (mean slope 25 degrees) developed mostly on vertically bedded mudstones that drains into Elder Creek at the Angelo Coast Range Reserve. Annual precipitation averages 216 cm per year and falls almost entirely between October and April. Six wells were drilled, some extending nearly 30 m below the surface, and numerous soil moisture monitoring stations were established. In parallel with this effort, a water chemistry sampling program was initiated to identify chemical tracers of water sources and pathways. Preliminary aqueous geochemical samples have been collected in February and July, 2008 and include groundwater, surface water from Elder Creek, moisture samples from the upper 10 cm of soil and from cores taken at depths up to 1.9 m into the underlying saprolite, and xylem moisture from four Douglas-firs spaced along the drainage path. Sulfate, calcium and strontium analyzed in groundwater and stream samples show a general increase in concentration with distance from the top of the drainage basin to the creek. A temporal variation is also observed, with increased concentrations in dry summer samples relative to wet winter samples. Stable isotopes of hydrogen and oxygen analyzed in all groundwater, stream, soil moisture and xylem waters fall within a range of -70 to - 40‰ for δD and -11 to -4‰ for δ18O. Groundwater, stream and saprolite moisture samples plot along the Global Meteoric Water Line (GMWL), with characteristic evaporative trends exhibited in the surface soil of both winter and summer samples. Xylem water from both sample sets falls below the GMWL. The distinct spatial and temporal variations in chemistry show promise in documenting the importance of rock moisture to forest maintenance and in revealing the primary flow pathways through such systems.
H21F-0902
Understanding Multiscale Surface Water–Groundwater Interactions on Scott River Watershed Temperatures with the use of Distributed Temperature Sensing (DTS) in Support of the Coldwater Salmonid Fishery Beneficial Use
The Scott River is a major tributary to the Klamath River that provides cold water rearing habitat for wild salmonid populations, including coho salmon (Oncorhynchus kisutch), Chinook salmon (O. tshawytscha), and steelhead trout (O. mykiss). During the summer months (July through September), the main-stem Scott River becomes disconnected from its tributaries throughout much of Scott Valley and relies primarily on baseflow from the groundwater aquifer. Summer stream temperatures in the Scott River are currently at levels that are not considered sustainable for the native salmonid population, resulting in the enactment of a Total Maximum Daily Load (TMDL) for temperature. Two of the conditions affecting stream temperature have been identified as increases in solar radiation due to a reduction in riparian vegetation and decreased accretion of groundwater. In conjunction with a regional scale surface water–groundwater modeling effort to investigate the benefits of various conjunctive use management alternatives on mid- and late summer baseflow in the Scott River, we completed high-resolution field measurements of stream temperature over an approximately 1,050-meter reach. Temperatures were measured using Fiber-Optic Distributed Temperature Sensing (DTS) techniques. The DTS survey in combination with FLIR stream surface temperature data from 2003 indicate that groundwater discharge to the Scott River is highly localized throughout the valley. The results of the DTS survey depict highly localized areas of groundwater accretion, as well as prominent localized temperature effects from riparian vegetation and river geomorphology. While originally modeled as a well-mixed stream during FLIR analysis, the DTS data further suggest that locally strong, vertical thermal gradients are found near the bottom of the active stream channel. The high-resolution temperature measurements were paired with fish surveys in order to determine the correlation between areas of identified lower river temperatures, groundwater accretion and other beneficial salmonid habitat indicators. Our work suggests that understanding of local-scale groundwater-stream interaction and analysis of corresponding local-scale geologic and riparian vegetation controls are critical to understanding the basin-scale groundwater-stream interactions. Preliminary data reviews indicate that groundwater discharge leads to distinct cold temperature pools near the streambed, while the remainder of the stream column is thermally well mixed. This local-scale, three-dimensional understanding is necessary if strategies are to be developed that aim for effective water resource management practices and improved beneficial use habitat. A multi-scale field reconnaissance and modeling approach is suggested to develop water management practices that lead to better habitat protection throughout the watershed.
H21F-0903
Exploring topographic and climatic controls on vegetation dynamics in the North American Monsoon Region.
The North American Monsoon system controls climate in southwestern United States and northwestern Mexico, leading to an increment in seasonal precipitation in the region and a seasonal change in vegetation. Interactions between the onset and intensity of the monsoon with vegetation dynamics are highly variable in space and time. For this reason, it is crucial to understand how these climate and topographic variables are related with the spatiotemporal variability of vegetation phenology. In this work, we focus on the NAME TIER-I region (20-35 N, 105-115 W). To explore this interaction, we performed a classification of regions with similar vegetation dynamics using a cluster analysis based on statistical variations generated by principal component analysis (PCA) on AVHRR 16-day NDVI composites (1981-2006). Moreover, remotely-sensed vegetation metrics were calculated to quantify the phenology of these regions. We also characterized coherent climatic regions with similar precipitation patterns using daily 1-degree gridded precipitation data (1948-2005). Topographic organization was explored based on spatial information such as slope and aspect, generated using a 1 km Digital Elevation Model. To understand the link among vegetation-climate- topography, cross correlation structures at different temporal lags were determined in the generated sub regions. Preliminary results indicate the existence of regions with similar vegetation dynamics and climatic trends. Strong correlations exist between the observed phenology of the sub-regions with topographic and climate organizations. Knowledge generated will be important to understand the dynamics of the monsoon and its relation with land surface characteristics.