Upland Watersheds Research Articles

A coupled modeling approach to evaluate nitrogen retention within the Shanmei Reservoir watershed, China

To simulate impacts of nitrogen retention in the reservoir on nitrogen nutrient transported from the upland watershed to the ocean, a coupled watershed-reservoir modeling system, consisting of a watershed distributed model (SWAT) and a two-dimensional water quality model (CE-QUAL-W2), was developed. The coupled modeling system was well calibrated, and simulated values mainly agreed with observed data, demonstrating that the SWAT and CE-QUAL-W2 coupled modeling system can be used to assess hydrodynamic and water quality processes in a complex watershed comprised of an upland watershed and a downstream reservoir. Applying the coupled model, a long time simulation was conducted to analyze the temporal characteristics of nitrogen exported from the watershed and to reveal the effect of nitrogen retention in the reservoir at annual, monthly and daily scales. The results showed that nitrogen export from the watershed is closely associated with precipitation and runoff. The wet season was the critical period of nitrogen loss, whereas the dry season is the critical period for water quality management. The reservoir serves mainly as a nitrogen sink at annual scale due to the effect of nitrogen retention, but within the year, it may act as a sink during the wet season and a source during the dry season, which is significantly influenced by inflow runoff, nitrogen load and reservoir regulation.

Quantifying the time scale of elevated geomorphic response following wildfires using multi-temporal LiDAR data: An example from the Las Conchas fire, Jemez Mountains, New Mexico

Sediment yields commonly increase following wildfires in mountainous landscapes. Quantifying the magnitude and duration of elevated sediment yields following wildfires is important for quantifying the relative importance of wildfire-affected versus non-wildfire-affected erosion in the long-term evolution of landscapes and for understanding the processes of post-wildfire erosion. In this study we use bi-annual terrestrial laser scanning (TLS) surveys conducted over a 2-yr period together with repeat airborne laser scanning (ALS) surveys conducted over a 1-yr period to estimate the dependence of sediment yield on time following the high-severity Las Conchas fire of 2011 within two small (approximately 1.3km2) watersheds. The dependence of sediment yield on time since the wildfire was quantified using DEMs of Difference (DoDs) of the upland watersheds (to measure erosion) and of the adjacent piedmonts (to measure the deposition of eroded sediment). Over the 2-yr study period, sediment volume decreased linearly with time and sediment yield decreased exponentially with time in one watershed, while the other watershed showed a more complex relationship with time influenced by the specific sequence of rainstorms that impacted that watershed. Both watersheds had a recovery time of approximately 1yr, suggesting that vegetation regrowth and the stabilization of incised valley bottoms were primarily responsible for the decline in sediment yield versus time following the wildfire. Multi-temporal DoDs of the piedmonts show how they responded to the delivery of elevated sediment yields from the upland watersheds, i.e. by (1) incision of the proximal portion of the piedmont, triggering distal deposition, (2) infilling of the incised channel and avulsion, and (3) incision of the distal portion, creating an incised channel connecting the proximal and distal ends of the piedmont. The dynamic nature of incision/aggradation and channel shifting on piedmonts following wildfires has important implications for post-wildfire flood-hazard assessments.

The importance of the objective functions and flexibility on calibration of parameters of clark instantaneous unit hydrograph

The paper compares the results of automatic calibration of Clark’s synthetic unit hydrographs. Optimal values of model parameters were determined by the objective functions: percentage error in peak flow (PEPF), percentage error in volume (PEV), peak-weighted root mean square error (PWRMSE), sum of absolute residuals (SAR) and sum of squared residuals (SSR). The last part of the analysis assesses the flexibility of studied model. The research was performed in the upland watershed of Grabinka – left tributary of the Wisloka river located in Southern Poland. The analysis reveals that the smallest differences between the maximum flow in the observed and calculated flood culmination were obtained when applying PWRMSE function. This paper also indicates, that Clark’s model was efficient for describing the analyzed floods.

Deforestation effects on biological and other important soil properties in an upland watershed of Bangladesh

Deforestation occurs at an alarming rate in upland watersheds of Bangladesh and has many detrimental effects on the environment. This study reports the effects of deforestation on soil biological properties along with some important physicochemical parameters of a southern upland watershed in Bangladesh. Soils were sampled at 4 paired sites, each pair representing a deforested site and a forested site, and having similar topographical characteristics. Significantly fewer (p≤0.001) fungi and bacteria, and lower microbial respiration, active microbial biomass, metabolic and microbial quotients were found in soils of the deforested sites. Soil physical properties such as moisture content, water holding capacity, and chemical properties such as organic matter, total N, available P and EC were also lower in deforested soils. Bulk density and pH were significantly higher in deforested soils. Available Ca and Mg were inconsistent between the two land uses at all the paired sites. Reduced abundance and biomass of soil mesofauna were recorded in deforested soils. However, soil anecic species were more abundant in deforested soils than epigeic and endogeic species, which were more abundant in forested soils than on deforested sites.

Quantifying nutrient and suspended solids fluxes in a constructed tidal marsh following rainfall: The value of capturing the rapid changes in flow and concentrations

Coastal tidal wetlands are perceived to provide nutrient dissipation services and serve as the final buffer between excess nutrient loads coming from nearby upland watersheds and sensitive estuarine waters. The construction and restoration of tidal marshes has the potential to benefit coastal waters. However, the water quality services of tidal wetlands have yet to be established with any certainty. This is in part due to the difficulty of monitoring these systems where flow and concentrations vary widely with tidal ebb and flood along with rainfall events mobilizing nutrients in pulses from upstream watersheds. In this article, we show over a period of 10 days following a rainfall event, the value of high temporal resolution data to characterize the complex nutrient and flow dynamics and to reliably calculate material balances in a created coastal marsh in North Carolina. Ultraviolet–visible spectrometers were used to obtain 15-min concentration data for nitrate, total Kjeldahl nitrogen, dissolved organic carbon, total suspended solids, phosphate, and total phosphorus. Our results show that a pulse of nitrate moved through the marsh from upstream agricultural production following the rainfall event and 25% (13kg of 53kg) of the nitrate was retained in the marsh over a period of 10 days. No other material showed a clear pulse from the upstream agricultural production. The marsh acted as a sink for total suspended solids (40kg) and had near neutral mass balances for dissolved organic carbon, total Kjeldahl nitrogen, total phosphorus, and phosphate. Subsequent simulations indicated that different and erroneous results would have been obtained from 2-, 6- or 12-h sampling intervals. These results demonstrate, even on a short term basis, why high-frequency data acquisition is necessary in these tidal marsh systems to truly quantify their impact on water quality ecosystem services.

Aspect-dependent variations in regolith creep revealed by meteoric 10Be

Although variations in insolation and emergent feedbacks among soil moisture, vegetation, and soil cohesion are commonly invoked to explain topographic asymmetry that depends on aspect, few studies have directly quantified the efficiency of regolith transport along hillslopes of opposing aspect. We utilize meteoric 10 Be concentrations in regolith (n = 74) to determine mass flux along equatorial-facing and polar-facing hillslopes in three forested upland watersheds in and adjacent to the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania (USA). In combination with regolith depth measurements and high-resolution topography, these fluxes allow us to evaluate transport rate laws and the efficiency of regolith creep. Concentrations of meteoric 10 Be in regolith along six separate transects imply that regolith flux is similar along all hillslopes, despite differences in topographic gradient and regolith thickness. Comparison of flux with regolith depth and topographic gradient reveals that transport depends on regolith depth, and that regolith creep is twice as efficient along low-gradient, south-facing slopes with thin regolith as compared to steep, north-facing slopes mantled with thicker regolith. We suggest that the observed topographic asymmetry in these watersheds has evolved over geologic time as a result of differences in the frequency of freeze-thaw events between hillslopes of opposing aspect.

Shifting Cultivation Effects on Soil Environment in Upland Watershed of Bangladesh

This research reports the effects of shifting cultivation on soil environment collecting samples from 0-5 cm soil depth from five locations viz. at Burburichhara, Maichchari, Longadu, Sukurchhari and Muralipara in Rangamati district of Chittagong Hill Tracts (CHTs). Soil analyses showed that fungal and bacterial population, microbial respiration and active microbial biomass, maximum water holding capacity, conductivity and moisture contents were significantly (at least <TEX>$p{\leq}0.05$</TEX>) lower in shifting cultivated soil compared to adjacent mixed tree plantations at all the sites. On an average in soils of 5 different shifting cultivated lands fungal population was <TEX>$1.33{\times}10^5$</TEX> CFU/g dry soil and bacterial population <TEX>$1.80{\times}10^7$</TEX> CFU/g dry soil and in mixed plantations fungal population was <TEX>$1.70{\times}10^5$</TEX> and bacterial population <TEX>$2.5</TEX><TEX>1{\times}10^7$</TEX> CFU/g dry soil. Organic matter and exchangeable Ca and Mg contents were significantly (at least <TEX>$p{\leq}0.05$</TEX>) lower and bulk density significantly (at least <TEX>$p{\leq}0.05$</TEX>) higher in shifting cultivated land in most of the locations compared to adjacent mixed tree plantations. Ratios of microbial respiration and organic carbon as well as active microbial biomass and organic carbon were distinctly lower and pH higher at 3 locations in shifting cultivated soils compared to mixed plantations. Findings of various soil properties, therefore, suggest that shifting cultivation has deteriorating effects on soil environment.

Characteristic length scales and time-averaged transport velocities of suspended sediment in the mid-Atlantic Region, USA

[1] Watershed Best Management Practices (BMPs) are often designed to reduce loading from particle-borne contaminants, but the temporal lag between BMP implementation and improvement in receiving water quality is difficult to assess because particles are only moved downstream episodically, resting for long periods in storage between transport events. A theory is developed that describes the downstream movement of suspended sediment particles accounting for the time particles spend in storage given sediment budget data (by grain size fraction) and information on particle transit times through storage reservoirs. The theory is used to define a suspended sediment transport length scale that describes how far particles are carried during transport events, and to estimate a downstream particle velocity that includes time spent in storage. At 5 upland watersheds of the mid-Atlantic region, transport length scales for silt-clay range from 4 to 60 km, while those for sand range from 0.4 to 113 km. Mean sediment velocities for silt-clay range from 0.0072 km/yr to 0.12 km/yr, while those for sand range from 0.0008 km/yr to 0.20 km/yr, 4–6 orders of magnitude slower than the velocity of water in the channel. These results suggest lag times of 100–1000 years between BMP implementation and effectiveness in receiving waters such as the Chesapeake Bay (where BMPs are located upstream of the characteristic transport length scale). Many particles likely travel much faster than these average values, so further research is needed to determine the complete distribution of suspended sediment velocities in real watersheds.

Comparison of Alternative Methods to Simulate Bacteria Concentrations with HSPF Under Low-Flow Conditions

<abstract><title><italic>Abstract. </italic></title> Low- or zero-flow conditions often occur in small, low-order, upland streams. Frequently these streams are in rural, agricultural areas where water quality may be impaired by excess bacterial concentrations. In Virginia, many of these streams require bacterial total maximum daily loads (TMDL). When developing TMDLs in these low-order, upland streams, model limitations often result in suspiciously high simulated in-stream bacteria concentrations. This study used the Hydrological Simulation Program-FORTRAN (HSPF) to compare three low-flow condition bacteria simulation methods and combinations to determine their effect on simulated in-steam concentrations. The three methods, Flow Stagnation (FS), Direct Deposit Stage Cut-off (SC), and Stream Reach Surface Area (SA), have all been used previously to develop EPA-approved bacterial TMDLs in Virginia. Violations of Virginia’s instantaneous and monthly geometric mean interim fecal coliform water quality criteria and the maximum simulated daily average in-stream fecal coliform concentration were used to compare each method and combinations of methods. Based on the assessment and comparison of the three low-flow condition bacteria modeling methods and how they interact, the FS method appears to hold the most promise for effectively simulating in-stream bacteria concentrations with HSPF in low-order, upland watersheds. If additional low-flow condition adjustment of simulated bacterial loads is required, combining the FS and SC methods is the most effective alternative of the evaluated combined methods.

Essential Terrestrial Variable data workflows for distributed water resources modeling

This paper discusses a prototype infrastructure, HydroTerre, that provides researchers, educators and resource managers with seamless access to geospatial/geotemporal data for supporting physics-based numerical models. The prototype defines the supporting data as Essential Terrestrial Variables (ETV's) and includes data fusion tools necessary to predict and manage surface and groundwater resources that resolve important dynamics of upland stream networks. The evaluation of ecosystem and watershed services, such as the detection and attribution of the impact of climatic change, provides one of many examples of the pressing need for high resolution, spatially explicit resource assessments in upland catchments. However, the current infrastructure for supporting models and data anywhere in the continental USA (CONUS) must overcome important problems of: efficient accessibility to high resolution geospatial datasets from multiple sources, scalability of geospatial data in support of distributed models and data-intensive computation for multi-scale, multi-state simulations.We discuss data workflows for web access to ETV data processing in support of catchment modeling, as part of a larger strategy for consuming this data within a framework that enables hydrological modelers to build and test models with fast data access at a United States Geological Survey (USGS) National Hydrography Dataset Hydrological Unit Code (HUC) level-12 scale. Given the prospect of petabytes of existing high resolution environmental data (NRC, 2012), we limit our investigation to a limited set of ETV's necessary to provide the first level of support for model implementation anywhere in the CONUS, and that resolve important features of upland watersheds (e.g. hill slopes within 1st–2nd–3rd order streams). The paper demonstrates HydroTerre tools for fast ETV data access to web users, and describes the computational resources necessary for using ETV's as the basis for implementing spatially distributed models at scales approaching the native resolution of the data (≥30 m). The Penn State Integrated Hydrologic Model (PIHM) serves as an example although other models are currently being considered.

Quantification of upland thermokarst features with high resolution remote sensing

Climate-induced changes to permafrost are altering high latitude landscapes in ways that could increase the vulnerability of the vast soil carbon pools of the region. Permafrost thaw is temporally dynamic and spatially heterogeneous because, in addition to the thickening of the active layer, localized thermokarst features form when ice-rich permafrost thaws and the ground subsides. Thermokarst produces a diversity of landforms and alters the physical environment in dynamic ways. To estimate potential changes to the carbon cycle it is imperative to quantify the size and distribution of thermokarst landforms. By performing a supervised classification on a high resolution IKONOS image, we detected and mapped small, irregular thermokarst features occurring within an upland watershed in discontinuous permafrost of Interior Alaska. We found that 12% of the Eight Mile Lake (EML) watershed has undergone thermokarst, predominantly in valleys where tussock tundra resides. About 35% of the 3.7 km2 tussock tundra class has likely transitioned to thermokarst. These landscape level changes created by permafrost thaw at EML have important implications for ecosystem carbon cycling because thermokarst features are forming in carbon-rich areas and are altering the hydrology in ways that increase seasonal thawing of the soil.

Hydrogeomorphology explains acidification‐driven variation in aquatic biological communities in the Neversink Basin, USA

Describing the distribution of aquatic habitats and the health of biological communities can be costly and time-consuming; therefore, simple, inexpensive methods to scale observations of aquatic biota to watersheds that lack data would be useful. In this study, we explored the potential of a simple "hydrogeomorphic" model to predict the effects of acid deposition on macroinvertebrate, fish, and diatom communities in 28 sub-watersheds of the 176-km2 Neversink River basin in the Catskill Mountains of New York State. The empirical model was originally developed to predict stream-water acid neutralizing capacity (ANC) using the watershed slope and drainage density. Because ANC is known to be strongly related to aquatic biological communities in the Neversink, we speculated that the model might correlate well with biotic indicators of ANC response. The hydrogeomorphic model was strongly correlated to several measures of macroinvertebrate and fish community richness and density, but less strongly correlated to diatom acid tolerance. The model was also strongly correlated to biological communities in 18 sub-watersheds independent of the model development, with the linear correlation capturing the strongly acidic nature of small upland watersheds (< 1 km2). Overall, we demonstrated the applicability of geospatial data sets and a simple hydrogeomorphic model for estimating aquatic biological communities in areas with stream-water acidification, allowing estimates where no direct field observations are available. Similar modeling approaches have the potential to complement or refine expensive and time-consuming measurements of aquatic biota populations and to aid in regional assessments of aquatic health.

Application of LiDAR Data for Hydrologic Assessments of Low-Gradient Coastal Watershed Drainage Characteristics

Documenting the recovery of hydrologic functions following perturbations of a landscape/watershed is important to address issues associated with land use change and ecosystem restoration. High resolution LiDAR data for the USDAForestServiceSanteeExperimentalForestin coastalSouth Carolina,USAwas used to delineate the remnant historical water management structures within the watersheds supporting bottomland hardwood forests that are typical of the re- gion. Hydrologic functions were altered during the early1700’s agricultural use period for rice cultivation, with changes to detention storage, impoundments, and runoff routing. Since late1800’s, the land was left to revert to forests, without direct intervention. The resultant bottomlands, while typical in terms of vegetative structure and composition, still have altered hydrologic pathways and functions due to the historical land use. Furthermore, an accurate estimate of the watershed drainage area (DA) contributing to stream flow is critical for reliable estimates of peak flow rate, runoff depth and coefficient, as well as water and chemical balance. Peak flow rate, a parameter widely used in design of channels and cross drainage structures, is calculated as a function of the DA and other parameters. However, in contrast with the upland watersheds, currently available topographic maps and digital elevation models (DEMs) used to estimate the DA are not adequate for flat, low-gradient Coastal Plain (LCP) landscape. In this paper we explore a case study of a 3rd order watershed (equivalent to 14-digit hydrologic unit code (HUC)) at headwaters of east branch of Cooper River draining to Charleston Harbor, SC to assess the drainage area and corresponding mean annual runoff coefficient based on various DEMs including LiDAR data. These analyses demonstrate a need for application of LiDAR-based DEMs together with field verification to improve the basis for assessments of hydrology, watershed drainage characteristics, and modeling in the LCP.

Predicting the thickness and aeolian fraction of soils in upland watersheds of the Mojave Desert

Soil thickness and soil texture, and their spatial variability at hillslope scales, are important inputs for hydrologic models. Recent studies have demonstrated that mechanistic models can accurately predict the spatial distribution of soil thickness in areas where soil thickness varies gradually along hillslope profiles. To date, however, these models have not been tested in arid regions, where soils are often thin and highly variable at small scales (i.e., 1–10m) and where the influence of aeolian accretion on soil thickness and soil texture may be significant. In addition, most of the data available for the fraction of the soil derived from aeolian deposition (which can serve as a proxy for soil texture) originate from soils developed on stable depositional landforms; data for aeolian fractions from upland soils are scarce. In this study, we developed and tested a numerical model for the prediction of thickness and aeolian fraction of soils in arid upland areas. The model assumes a long-term balance between the rates of soil production from bedrock, aeolian accretion, and soil erosion. Rates of soil production are quantified in the model using the exponential and humped soil production functions, and soil erosion rates are quantified using the nonlinear depth- and slope-dependent transport functions, assuming that only the upper soil horizons (A+B) are capable of transport. The rate of aeolian deposition is assumed to be spatially uniform. We calibrated the three free parameters of the model at a site in the Mojave Desert with a granite lithology using a combination of 1) field-measured data for soil thickness and 2) estimation of the aeolian fraction in the soil using laboratory analysis of immobile element concentrations. We validated the model results in three nearby sites using a combination of measured soil thickness in soil pits and the presence/absence of soil, and laboratory analysis of the aeolian fraction of soil. The study area is characterized by generally thin soils (<1m) and extreme variability in soil thickness at small scales. The model does a relatively poor job of predicting the soil thickness on a point-by-point basis due to the extreme small-scale variability, but the model does a much better job at predicting the average soil thickness at the scale of tens of meters and greater. The model predicts soil thickness with a root-mean-square error of 15–32cm in regions characterized by poorly- to moderately-developed calcic soils, but fails to accurately predict soil thickness at a site characterized by well-developed soils (carbonate stages II–IV) and low-relief topography. The model predicts the aeolian fraction and content in soil with root-mean-square errors of 10–13% and 8cm, respectively. The prediction of aeolian content captures the overall pattern of increasing trend in aeolian content towards the lower portions of slopes. Our results show that the model can simultaneously predict the spatial variation of thickness and aeolian fraction/content of soils even in arid, dust-rich environments where soils are thin and spatial variability is extreme.

Fostering Incentive-Based Policies and Partnerships for Integrated Watershed Management in the Southeast Asian Uplands

This paper attempts to identify the major factors associated with some of the failures and successes of integrated watershed management policies and projects with a particular emphasis on the uplands of mainland Southeast Asia. It argues that many policy measures have been misguided by failing to acknowledge the multidimensional facets of sustainable watershed management and putting too much emphasis on command-and-control approaches to resource management and onesize-fits-all conservation models. Attempts to introduce soil and water conservation measures, for instance, have largely failed because they concentrated merely on the technical feasibility and potential ecological effects, while neglecting economic viability and socio-cultural acceptance. The production of agricultural commodities, on the other hand, has mostly been market-driven and often induced boom and bust cycles that compromised the ecological and social dimensions of sustainability. Purely community-based approaches to watershed management, on their part, have often failed to address issues of elite capture and competing interests within and between heterogeneous uplands communities. Drawing on a review of recent experience and on lessons from initiatives in a long-term collaborative research program in Thailand (The Uplands Program) aimed at bridging the various dimensions of sustainability in the Southeast Asian uplands, this paper discusses how a socially, institutionally and ecologically sustainable mix of agricultural production, ecosystem services and rural livelihood opportunities can be achieved through incentive-based policies and multi-stakeholder partnerships that attempt to overcome the (perceived) antagonism between conservation and development in upland watersheds of Southeast Asia.

강수조건에 따른 도암호 부유물질 거동 평가

BACKGROUND: The Doam watershed in Korea has been managed for the reduction and the prevention of non-point source pollution since 2007. Especially, the water quality of the Doam reservoir is a primary issue related to the Doam dam reoperation. We have carried out the modeling to evaluate the water quality based on suspended solids (SS) of the Doam watershed and the Doam reservoir. Two powerful hydrological and water quality models (HSPF and CE-QUAL-W2) were employed to simulate the combined processes of water quantity and quality both in the upland watershed of the Doam reservoir and the downstream waterbody. METHODS AND RESULTS: The HSPF model was calibrated and validated for streamflow and SS. The CE-QUAL-W2 was calibrated for water level, water temperature, and SS and was validated for the only water level owing to data lack. With the parameters obtained through the appropriate calibration, SS concentrations of inflow into and in the Doam reservoir were simulated for three years (2008, 2004 and 1998) of the minimum, the average, and the maximum of total annual precipitation during recent 30 years. The annual average SS concentrations of the inflow for 2008, 2004, and 1998 were 8.6, 10.9, and 18.4 mg/L, respectively and those in the Doam reservoir were 9.2, 13.8, and 21.5 mg/L. CONCLOUSION(s): The results showed that more intense and frequent precipitation would cause higher SS concentration and longer SS's retention in the reservoir. The HSPF and the CE-QUAL-W2 models could represent reasonably the SS from the Doam watershed and in the Doam reservoir.

Structural organization of process zones in upland watersheds of central Nevada and its influence on basin connectivity, dynamics, and wet meadow complexes

The drainage network within upland watersheds in central Nevada can be subdivided into distinct zones each dominated by a unique set of processes on the basis of valley form, the geological materials that comprise the valley floor, and the presence or absence of surficial channels. On hillslopes, the type and structure (frequency, length, and spatial arrangement) of these process zones is related to the lithology and weathering characteristics of the underlying bedrock. Process zones dominated by sediment accumulation, storage, and groundwater recharge are associated with less resistant rocks that weather into abundant but relatively small particles. Sediment transport and runoff-dominated zones are associated with resistant, sparsely fractured rocks that produce limited but larger clasts. The type and structure of process zones along axial valleys depend on the characteristics of the process zones on the hillslopes. Numerous sediment storage-dominated reaches leads to a relatively high number of unincised fans located at the mouth of tributaries along the axial valleys and to frequent and lengthy unincised valley segments, both of which disconnect large sections of the drainage basin from channelized flows. In contrast, a relatively high density of transport-dominated process zones leads downstream to the incision of side-valley fans and axial valley deposits as well as a high degree of basin connectivity (defined by the integration of surficial channels). Connectivity also is related to the lithology of the underlying bedrock, with higher degrees of connectivity being associated with volcanic rocks that presumably yield high rates of runoff. Lower levels of connectivity are associated most frequently with extensively fractured, locally permeable sedimentary and metamorphic rock assemblages. Thus, basins underlain by volcanic rocks appear to be more sensitive to incision and produce more dynamic channels in terms of the rate of channel/valley modification than those underlain by other lithologies. Considerable attention has been devoted in recent years to the management of wet meadow ecosystems that serve as important riparian habitats within upland basins of central Nevada. The data presented here show that, within basins characterized by a high degree of connectivity, areas of wet meadow are minimal. Where they do exist in these basins, they tend to be severely degraded by incision or gully erosion and will be difficult to manage given the dynamic nature of the axial channel processes. Wet meadows within basins that exhibit a low degree of connectivity and high sediment storage-to-transport ratios on hillslopes will likely be more responsive to management activities because of the reduced threats of channel incision and, presumably, a larger supply of groundwater flow to the meadows created by an extensive network of recharge sites. Importantly, human activities that lead to an increase in basin connectivity can negatively impact downstream meadows through a decrease in groundwater recharge and an increase in stream dynamics, in spite of the fact that these activities may be physically separated from the wet meadow areas.

Land cover change on Mt. Pinatubo, the Philippines, monitored using ASTER VNIR

Ashfall and pyroclastic flows from the large eruption of June 1991 destroyed much of the vegetation on the flanks of Mt. Pinatubo. Subsequent vegetation recovery has helped stabilize slopes and reduce debris flow hazard. In this project, visible and near-infrared (VNIR) satellite imagery from the advanced spaceborne thermal emission and reflection radiometer (ASTER) captured at a similar time of year in 2001, 2004 and 2008 were used to quantify vegetation recovery within 22 upland watersheds on the mountain, 10–16 years after the eruption took place. Differences in the normalized difference vegetation index (NDVI) derived from these images were used to measure the areal extent of losses and gains in ground cover and derive average net rates of change in ground cover. The success of this approach was dependent on post-processing ASTER imagery to correct for the effects of variation in satellite-sun geometry and vegetation reflectance and to calibrate and adjust the derived NDVI images for the influence of different atmospheric conditions at the time of image capture. All watersheds showed a variable pattern of losses and gains in vegetation and ground cover. Losses were related to shifting cultivation practices and gully and channel migration, and these amounted to 1–12% of watershed areas. Gains were related to revegetation of pyroclastic flows, recent channel terraces, abandoned gardens and areas of burnt vegetation, and these amounted to 3–45% of watershed areas. Consistent overall net gains in ground cover were observed in all watersheds, with the average NDVI increasing by up to 0.074 over each consecutive 3-year period. The rates of change in NDVI were used to derive a vegetation recovery curve from bare ground. The result showed that it will take approximately 50 years for hillslopes to regain a dense vegetative cover in this climate. This supports published findings which indicate rapid recovery of vegetation in tropical environments following such large volcanic eruptions. Results additionally showed that the trajectory of change and the speed of recovery were influenced by terrain type, geology, watershed morphology and the activity of erosion and depositional processes. Prior to 2001, revegetation had been fastest on mountain slopes that helped protect vegetation from the effects of eruption. Gains in ground cover are now greatest in areas that were most impacted by the eruption.

Influences of watershed geomorphology on extent and composition of riparian vegetation

AbstractQuestionHow strongly do watershed morphometry and geology influence the extent and composition of vegetation along riparian corridors?LocationEighteen upland watersheds in central Nevada, USA.MethodsWatershed (drainage basin) morphometry and geology were derived from digital data sets (DEMs and geologic maps). Riparian corridors were classified into five vegetation types (riparian forest, riparian shrub, wet/mesic meadow, dry meadow and shrub dry meadow) using high‐resolution aerial photography. Regression and multivariate analyses were used to relate geomorphic characteristics to riparian vegetation extent and composition.ResultsRiparian extent ranged from 0.4% to 3.6% of watershed area, was positively related to percentage intrusive bedrock and drainage density, and was negatively related to percentage carbonate bedrock and relative stream power. Riparian forest and shrub types occupied more than 75% of the riparian corridor in 12 of 18 watersheds; meadow types comprised a smaller proportion. Watershed size, topography and geology were important in predicting riparian composition. Riparian forest and shrub types were more abundant in small, rugged watersheds of high relief. Meadow types were more abundant in large, low gradient and less rugged watersheds. The importance of woody vegetation increased with more volcanic and intrusive bedrock, whereas meadow vegetation increased with increasing alluvium, carbonate and metasedimentary rock types.ConclusionsWatershed geomorphology significantly constrains extent and abundance of woody versus herbaceous vegetation within the riparian corridor. Watershed variables related to riparian vegetation are likely indicators of run‐off regimes or water and sediment transport. Consideration of relationships between watershed‐scale geomorphology and riparian vegetation can improve prediction and inform restoration efforts.

Agricultural Water Security and Instream Flows for Endangered Species

We analyze the potential effects of listing threatened salmonid species on landowner behavior using parcel‐level data from Sonoma County, California. We estimate a bivariate probit model, representing the landowner's joint decision on land use and water management during the period 1973–2006, both before and after listing. Our results indicate that after listing, vineyard development with on‐site reservoirs became significantly less likely, particularly in upland watersheds with seasonal streams. This interseasonal shift from stored surface water in winter toward groundwater or direct diversion in summer may lead to negative unintended consequences on summer flows needed for juvenile fish survivorship.