Journal Articles

Posted: January 26, 2020
Meadows of the Sierra Nevada and Cascade mountains of California, USA, support diverse and highly productive wet-meadow vegetation dominated by sedges, rushes, grasses, and other herbaceous species. These groundwater-dependent ecosystems rely on the persistence of a shallow water table throughout the dry summer. Case studies of Bear Creek, Last Chance, and Tuolumne meadow ecosystems are used to create a conceptual framework describing groundwater-ecosystem connections in this environment. The water requirements for wet-meadow vegetation at each site are represented as a water-table-depth hydrograph; however, these hydrographs were found to vary among sites. Causes of this variation include ( 1) differences in soil texture, which govern capillary effects and availability of vadose water and ( 2) elevation-controlled differences in climate that affect the phenology of the vegetation. The field observations show that spatial variation of water-table depth exerts strong control on vegetation composition and spatial patterning. Groundwater-flow modeling demonstrates that lower hydraulic-conductivity meadow sediments, higher groundwater-inflow rates, and a higher ratio of lateral to basal-groundwater inflow all encourage the persistence of a high water table and wet-meadow vegetation, particularly at the margin of the meadow, even in cases with moderate stream incision.

Posted: January 26, 2020
We present a new algorithm for mapping evapotranspiration (ET) that requires only local weather-station data including the ground beat flux and high resolution airborne thermal imagery. This ET mapping algorithm (ETMA) is based on the surface energy budget and partitions the available energy between the latent and sensible heat fluxes. Two parameters T-latent and T-sensible are defined as the surface temperatures at which all of the turbulent heat flux is accounted for by the latent and sensible heat fluxes, respectively. These points are used to develop linear relationships between surface temperature and ET at specified times. Maps of ET at two times during the day are then used to model and integrate the diurnal pattern of ET using the Penman-Montieth and Jarvis-Stewart models of ET and surface resistance. The resulting maps of daily integrated ET have 1-m spatial resolution that is rarely available, yet important to the fields of hydrology, ecology, forestry, and agriculture. Our results comparing ET values to porometry-based local measurements within the meadows suggest that the mapped ETday values are accurate to within 10% of the potential ET rate or within 0.7 mm absolute error; however, under different conditions the error may be larger. The purpose of developing this algorithm was to investigate the hydroecology of restored and degraded meadows in the Sierra Nevada of northern California, USA. The pond-and-plug method of riparian restoration aims to raise the water table and re-establish native mesic vegetation that has been replaced by sagebrush and dryland species due to land-use practices over the past 150 years. By comparing the ET regime of two restored and two degraded meadows, we show that daily ET in the restored meadows (5-6.5 mm/day) was approximately twice that of the degraded ones (1.5-4 mm/day). The detailed images of ET show local impacts of land-use change and re-vegetation efforts.

Posted: January 26, 2020
Restoration of degraded wet meadows found on upland valley floors has been proposed to achieve a range of ecological benefits, including augmenting late‐season streamflow. There are, however, few field and modelling studies documenting hydrologic changes following restoration that can be used to validate this expectation, and published changes in groundwater levels and streamflow following restoration are inconclusive. Here, we assess the streamflow benefit that can be obtained by wet‐meadow restoration using a physically based quantitative analysis. This framework employs a 1‐dimensional linearized Boussinesq equation with a superimposed solution for changes in storage due to groundwater upwelling and evapotranspiration, calculated explicitly using the White method. The model and assumptions gave rise to predictions in good agreement with field data from the Middle Fork John Day watershed in Oregon, USA. While raising channel beds can increase total water storage via increases in water table elevation in upland valley bottoms, the contributions of both lateral and longitudinal drainage from restored floodplains to late‐summer streamflow were found to be undetectably small, while losses in streamflow due to greater transpiration, lower hydraulic gradients, and less laterally drainable pore volume were likely to be substantial. Although late‐summer streamflow increases should not be expected as a direct result of wet‐meadow restoration, these approaches offer benefits for improving the quality and health of riparian and meadow vegetation that would warrant considering such measures, even at the cost of increased water demand and reduced streamflow.

Posted: January 26, 2020
We discuss a recent paper which evaluated the hydrologic changes resulting from a pond-and-plug meadow restoration project in the Sierra Nevada Mountains of California. In the study, measurements of streamflow into and out of the meadow suggested late-summer baseflow increased as much as five-fold when compared with prerestoration conditions. However, the volume of streamflow attributed to the restored meadow (49,000–96,000 m3 over four months) would require that 2.5–4.8 m of saturated meadow soils drain during sum- mer months. The groundwater data from this meadow record only 0.45 m of change over this timeframe, which is less than might be expected from plant use alone (0.75 m), suggesting this restored meadow may be acting as a water sink throughout summer rather than a source.

Posted: February 15, 2017
Two pumiceous tephra layers, widespread in meadow topsoils of the southern Sierra Nevada, are correlated on the basis of radiocarbon dates and trace-element analyses with two eruptive centers at the northern and southern ends of the Mono Craters--Inyo craters volcanic chain in eastern California. Pumice and obsidian that were erupted in the northern part of the chain are uniform in trace-element content, whereas those erupted from the southern part are nonuniform and distinctly different, particularly in Sr content. Similar differences are recognized in the two most recent and widespread tephra layers originating from these sites. These tephra layers are the deposits of the most recent explosive eruptions of magma from the Mono Craters and the Inyo craters. Tephra 1, characterized by sanidine microphenocrysts and a Sr content of about 215 ppm, was erupted 720 {+/-} 60 yr B.P. Its distribution defines a south-trending lobe extending over the Sierra Nevada from the upper San Joaquin drainage area to the Little Kern drainage area. Sr, Rb, and Zr contents of the ash are similar to those of a tephra-ringed obsidian dome at the south end of the Inyo craters. Tephra 2, characterized by a lack of microphenocrysts and a Sr content of less than 20 ppm, was erupted 1190 {+/-} 80 yr B.P. It is encountered as a fine ash layer in the Sierra Nevada from northernmost Yosemite to Kings Canyon. Its low Sr content indicates geochemical affinity with the Mono Craters. Panum Crater, a tephra-ringed dome at the north end of the chain, appears to be its most likely source vent.

Posted: May 9, 2019
The wetlands of the Sierra Nevada were formed and are maintained by a feedback between soil, plant, and hydrologic processes. Primary production of plants builds soil organic matter and plant roots bind soil, preventing erosion during flooding. In turn, soil organic matter retains water and nutrients that support plant growth, while the hydrologic regime regulates soil organic matter decomposition, plant community makeup, and plant production. The relative stability of these interacting processes has built thick meadow soils over the past several thousand years. However, modern human impacts such as livestock grazing and water extraction have decoupled the interacting processes. Removal of plants by grazers exposes soil to water erosion and reduces production, the source of soil organic matter. Erosion gully formation and direct water extraction lower the wetland water table, speeding soil organic matter decomposition, altering plant community composition, and reducing production. Gully formation and loss of soil organic matter occur rapidly but are extremely slow to reverse by natural processes alone. Wetlands that have experienced these impacts enter alternative stable states that will not quickly return to their original configurations. In these cases, ecological restoration is necessary to repair human impacts and reestablish the stabilizing feedback of soil, plant, and hydrologic processes. This dissertation is composed of five chapters that explore wetland ecosystem function and restoration in the Sierra Nevada.

Posted: February 15, 2017
Study Region: We analyzed the effects of groundwater pumping on a mountain wetland complex, Yosemite National Park, California, USA. Study Focus: Groundwater pumping from mountain meadows is common in many regions of the world. However, few quantitative analyses exist of the hydrologic or ecological effects of pumping. New Hydrological Insights for the Region: Daily hydraulic head and water table variations at sampling locations within 100. m of the pumping well were strongly correlated with the timing and duration of pumping. The effect of pumping varied by distance from the pumping well, depth of the water table when the pumping started, and that water year's snow water equivalent (SWE). Pumping in years with below average SWE and/or early melting snow pack, resulted in a water table decline to the base of the fen peat body by mid summer. Pumping in years with higher SWE and later melting snowpack, resulted in much less water level drawdown from the same pumping schedule. Predictive modeling scenarios showed that, even in a dry water year like 2004, distinct increases in fen water table elevation can be achieved with reductions in pumping. A high water table during summers following low snowpack water years had a more significant influence on vegetation composition than depth of water table in wet years or peat thickness, highlighting the impact of water level drawdown on vegetation.

Posted: February 13, 2017
A broad sample of 79 montane fens in the Sierra Nevada revealed that underlying geology and topography exert strong control over the distribution and vegetation of these ecosystems. Distinct granodiorite, metamorphic, volcanic, carbonate and serpentine bedrock geology resulted in very different water chemistry, which had significant effects on the particular plant species found at each site. Wide-ranging values of pH (4.28–8.00) and dissolved cation concentrations (1.6–62.0 mg L-1) spanned the categories of transitional poor– rich to extremely rich fens. The vegetation of a pair of fens on carbonate bedrock and two floating mat fens was markedly different from the vegetation recorded at any other study sites. Once these outlier fens were removed from the analyses, the environmental variables that correlated most closely with the vegetation data were pH, altitude, presence of volcanic bedrock and fen slope. The measured environmental parameters explained 9.7 % of the variability in the vegetation data. Species richness was primarily (and negatively) correlated with altitude. Peat thickness (15–253 cm) was constrained in smaller catchments and on steeper slopes, and was positively correlated with soil organic matter content (16–92 %). Of the four typical fen landforms (bedrock contact, slope, spring mound and basin), sloping fens were the most common (63 % of the 79-fen sample).

Posted: January 28, 2021
Beaver-related restoration is a process-based strategy that seeks to address wide-ranging ecological objectives by reestablishing dam building in degraded stream systems. Although the beaver-related restoration has broad appeal, especially in water-limited systems, its effectiveness is not yet well documented. In this article, we present a process-expectation framework that links beaver-related restoration tactics to commonly expected outcomes by identifying the set of process pathways that must occur to achieve those expected outcomes. We explore the contingency implicit within this framework using social and biophysical data from project and research sites. This analysis reveals that outcomes are often predicated on complex process pathways over which humans have limited control. Consequently, expectations often shift through the course of projects, suggesting that a more useful paradigm for evaluating process-based restoration would be to identify relevant processes and to rigorously document how projects do or do not proceed along expected process pathways using both quantitative and qualitative data.

Posted: February 15, 2017
Valley-fill deposits, exposed by Twentieth-Century dissection of a number of meadows on the west slope of the southern Sierra Nevada, contain a stratigraphic record strongly affected by secular variations in watershed hydrology during the Holocence. Meadows are situated in low gradient reaches, adequately supported by seepage water, where fine textured materials accumulate under present hydrologic conditions. Meadows do not necessarily owe their origin to glacial modification of drainage. Many meadows have formed in both glaciated and unglaciated valleys by a water table rise in valley-fill deposits. Ground water in any meadow drainage basin is annually recharged by snowmelt. Significant evapotranspiration by meadow plants causes diurnal fluctuations of growing-season water tables on the order of 0.2 to 0.5 ft and seasonal fluctuations of 2 to 4 ft. Growing-season water-table depths are characteristically different for the two major plant communities, being usually shallower that 2 feet for meadows, and deeper than 4 ft for conifer forests. This relationship and a ground-water model are used to interpret paleohydrologic variations recorded in valley-fill stratigraphy. Stratigraphy, radiocarbon dating, and tephrachronology indicate the following sequence in upper tributary valleys of the montane belt. Pre-Holocene cobbly alluvium rests upon bedrock. A paleosol developed upon this alluvium between 10,200 and 8700 radiocarbon years B.P., records an early post-glacial climatic interval that established forests in the present upper montane belt. The overlying sequence of coarse loamy materials associated with in situ conifer stumps indicates one or more intervals of good soil drainage and dry valley-bottom conditions between 8700 and 1200 years B.P. At some sites there is an abrupt change from forest soils to overlying wet-meadow deposits dated 2500 years at some sites and 1200 years at others, suggesting many meadows originated coincidentally with neoglaciation in the Sierras. A water-table rise of a few feet, resulting from late melting snows, could cause the change from forest to meadow conditions. Meadow deposits are composed of organic-rich, sandy-loam, topsoil layers intercalcated with sheets of well-sorted sandy gravels deposited by flood flows with recurrence intervals greater than 50 years. A plot of upstream catchment area and valley gradient for dissected and undissected meadows indicates the geomorphic domain of unstable meadows subject to gully erosion under present hydrologic conditions on the Sierra west slope. Two pumiceous tephra layers, widespread in meadow topsoils of the southern Sierra, are radiocarbon dated and attributed to tephra-ringed eruptive centers at opposite ends of the Mono-Inyo Crater chain of eastern California. Tephra 1, characterized by sanidine microphenocrysts and Sr content of 215 ppm, erupted 720 years B.P. Distribution of this tephra in confined to a south trending lobe extending 120 miles over the Sierra from the upper San Joaquin drainage to the Little Kern drainage. Trace element analysis of tephra 1 best match those of the tephra-ringed obsidian flow just south of Deadman Creek in the Inyo Craters. Tephra 2, characterized by a lack of microphenocrysts and Sr contents less than 20 ppm erupted from on the northern Mono Craters eruptive centers. These two tephras appear to represent the most recent explosive eruptions of magma from this 40-km long chain of Holocene volcanoes.

Posted: January 26, 2020
In mountains of the western United States, channel incision has drawn down the water table across thousands of square kilometers of meadow floodplain. Here climate change is resulting in earlier melt and reduced snowpack and water resource managers are responding by investing in meadow restoration to increase springtime storage and summer flows. The record‐setting California drought (2012–2015) provided an opportunity to evaluate this strategy under the warmer and drier conditions expected to impact mountain water supplies. In 2012, 0.1 km2 of meadow floodplain was reconnected by filling an incised channel through Indian Valley in the central Sierra Nevada Mountains of California. Despite sustained drought conditions after restoration, summer baseflow from the meadow increased 5–12 times. Before restoration, the total summer outflow from the meadow was 5% more than the total summer inflow. After restoration, total summer outflow from the meadow was between 35% and 95% more than total summer inflow. In the worst year of the drought (2015), when inflow to the meadow ceased for at least one month, summer baseflow was at least five times greater than before restoration. Groundwater levels also rose at four out of five sites near the stream channel. Filling the incised channel and reconnecting the meadow floodplain increased water availability and streamflow, despite unprecedented drought conditions.

Posted: February 10, 2016
Measurements of groundwater–surface water exchange at three wetland stream sites were related to patterns in benthic productivity as part of the US Geological Survey’s Northern Temperate Lakes–Water, Energy and Biogeochemical Budgets (NTL–WEBB) project. The three sites included one high groundwater discharge (HGD) site, one weak groundwater discharge (WGD) site, and one groundwater recharge (GR) site. Large upward vertical gradients at the HGD site were associated with smallest variation in head below the stream and fewest gradient reversals between the stream and the groundwater beneath the stream, and the stream and the adjacent streambank. The WGD site had the highest number of gradient reversals reflecting the average condition being closest to zero vertical gradient. The duration of groundwater discharge events was related to the amount of discharge, where the HGD site had the longest strong-gradient durations for both horizontal and vertical groundwater flow. Strong groundwater discharge also controlled transient temperature and chemical hyporheic conditions by limiting the infiltration of surface water. Groundwater–surface water interactions were related to highly significant patterns in benthic invertebrate abundance, taxonomic richness, and periphyton respiration. The HGD site abundance was 35% greater than in the WGD site and 53% greater than the GR site; richness and periphyton respiration were also significantly greater (p%0.001, 31 and 44%, respectively) in the HGD site than in the GR site. The WGD site had greater abundance (27%), richness (19%) and periphyton respiration (39%) than the GR site. This work suggests groundwater–surface water interactions can strongly influence benthic productivity, thus emphasizing the importance of quantitative hydrology for management of wetland-stream ecosystems in the northern temperate regions.

Posted: January 26, 2020
Stream restoration efforts, particularly within meadow systems, increasingly rely on 'pond and plug' type methods in which (a) alluvial materials are excavated from the floodplain, forming ponds; (b) excavated alluvial materials are used to plug incised channels and (c) smaller dimension channels are restored to the floodplain surface. A commonly stated objective of these efforts is to restore ecologically significant hydrological processes to degraded riparian systems. However, little research has been conducted to evaluate and quantify the restoration of these hydrological processes. Direct comparisons of pre- and post-restoration hydrological observations are often misleading due to an inter-annual climatic variability. To overcome this issue and accurately quantify the hydrological effects of restoration, we developed, calibrated and validated a hydrological model of a 230 ha mountain meadow along a 3.6 km restored reach of Bear Creek in the northeastern California. We then applied the model to simulate the pre- and post-restoration scenarios by altering the floodplain topography and stream channel networks. Our results document three general hydrological responses to the meadow restoration effort: (1) increased groundwater levels and volume of subsurface storage; (2) increased frequency/duration of floodplain inundation and decreased magnitude of flood peaks and (3) decreased annual runoff and duration of baseflow. This study supports and quantifies the hypothesis that 'pond and plug' type stream restoration projects have the capacity to re-establish hydrological processes necessary to sustain riparian systems. In addition, the results of this study can be used to improve quantitative objectives for 'pond and plug' type stream restoration activities in similar settings. Copyright (C) 2008 John Wiley & Sons, Ltd.

Posted: January 26, 2020
Stream incision is altering the hydroecology of riparian areas worldwide. In the Last Chance watershed in the northern Sierra Nevada, California, logging, overgrazing, and road/ railroad construction have caused stream incision, which resulted in drainage of riparian meadow sediments and a succession from native wet meadow vegetation to sagebrush and dryland grasses. Restoration efforts have been initiated to reestablish the ecosystem function of these systems. Original field data including stream stage records, water table hydrographs, sediment hydraulic properties, topographic transects, and aerial imagery of vegetation patterning were used to develop a model of an archetype meadow. Hydrologic behavior was simulated with a finite element model of variably saturated groundwater flow. This model was coupled to an empirical, time-dependent, vegetation threshold relationship between vegetation type and depth to the water table. This was a two-way coupling requiring an iterative approach because water table depth is a determinant of vegetation type, yet the vegetation regime influences water table depth through evapotranspiration. The hydrology and vegetation patterns were analyzed under pristine, degraded (incised), and restored conditions. For the case of deep streambed incision, our hydroecological model predicts the observed shift from mesic (wetter) to xeric (drier) vegetation communities and reproduces their imaged longitudinal zonation. This patterning is explained as a response to groundwater drainage to the stream, which creates dry zones with xeric vegetation adjacent to the stream, while preserving sufficient moisture at the margins of the meadow to support holdout populations of mesic vegetation. The model further predicts the reestablishment of meadow vegetation when the incised channel is filled and a new shallow channel is restored. The coupling of a near-surface hydrologic model to a vegetation response model may be used to design stream restoration projects by predicting vegetation patterning.

Posted: April 10, 2019
Adding chipped wood to soil ameliorates compaction, allowing faster plant growth that is critical to successful wetland restorations. Following the filling and planting of an erosion gully in Halstead Meadow, Sequoia National Park, the tallest leaf height and maximum clone width of transplanted Scirpus microcarpus seedlings were negatively correlated with soil compaction. Plant height decreased by 9.8 cm and width decreased by 11.9 cm per MPa of soil compaction (range of 0.74–4.50MPa). We experimentally amended mineral soil in a test trench and found that every 0.10 cm3/cm3 addition of wood chips (range of 0.00–0.75 cm3/cm3) reduced compaction by 0.174MPa. Had the Halstead Meadow gully fill contained an equivalent volume of wood chips to the reference area soil organic matter content (0.64 cm3/cm3), we predict compaction would have been reduced by 1.11MPa, increasing individual transplant width spread by 36%, approximately doubling the vegetated area after two growing seasons. In a greenhouse phytometer experiment, conifer bark leachate (phenolics 211 mg/L) significantly reduced plant growth and, in the presence of added nutrients, increased the production of the enzyme polyphenol oxidase (PPO). However, phenolics concentration in bark-free conifer wood leachate (12mg/L), similar to field-sampled concentrations, did not affect plant growth or PPO production. Pure conifer bark is not recommended as a soil amendment, but the addition of low-bark-content wood chips to gully fill may be a feasible and effective means of reducing soil compaction, accelerating plant establishment, and lowering wetland restoration project costs.