Sherman Swanson

Flows for Floodplain Forests: A Successful Riparian Restoration

Abstract Throughout the 20th century, the Truckee River that flows from Lake Tahoe into the Nevada desert was progressively dammed and dewatered, which led to the collapse of its aquatic and riparian ecosystems. The federal designation of the endemic cui-ui sucker (Chasmistes cujus) as endangered prompted a restoration program in the 1980s aimed at increasing spring flows to permit fish spawning. These flows did promote cui-ui reproduction, as well as an unanticipated benefit, the extensive seedling recruitment of Fremont cottonwood (Populus fremontii) and sandbar willow (Salix exigua). Recruitment was scattered in 1983 but extensive in 1987, when the hydrograph satisfied the riparian recruitment box model that had been developed for other rivers. That model was subsequently applied to develop flow prescriptions that were implemented from 1995 through 2000 and enabled further seedling establishment. The woodland recovery produced broad ecosystem benefits, as evidenced by the return by 1998 of 10 of 19 riparian bird species whose populations had been locally extirpated or had declined severely between 1868 and 1980. The dramatic partial recovery along this severely degraded desert river offers promise that the use of instream flow regulation can promote ecosystem restoration along other dammed rivers worldwide.

The effect of herbaceous plant communities and soil textures on particle erosion of alluvial streambanks

Soil texture and plants are understood to be important determinants of erosion. However, there is a paucity of research on the quantitative effect of various soils, plants, or the interaction of the two, on streambank erosion. This study measures the influence of herbaceous plant communities and sandy loam, loam and clay loam soils on particle erosion rates. It demonstrates that the interaction of plants and soil are important. Seventy-one samples from the banks of 5 streams were tested using a flume. Multivariate regression analysis was used to analyze a dependent variable of erosion rate with independent variables of root density, soil texture, and plant communities. Autocorrelation was treated with the maximum chi-square method. Nebraska sedge (Carex nebrascensis) and Baltic rush (Juncus balticus) communities had the lowest erosion rates, followed by mixed sedge (Carex lanuginosa, C. rostrata and others) then mixed grass (Poa pratensis with Deschampsia caespitosa) communities. Silt had a negative effect on erosion for the Nebraska sedge, Baltic rush and mixed grass plant communities, but had no effect with the mixed sedge community due to a silt-by-sedge interaction. An increase in percent clay correlated with an increase in erosion. As percentages of clay or silt increased, root-volume density declined. Root-volume density was correlated negatively with erosion. Clay to silt ratio correlated negatively with erosion. Thus knowledge of both vegetation and soil texture are necessary to predict or manage strembank erodibility.

Rooting characteristics of four intermountain meadow community types.

Healthy meadow communities generally have excellent soil binding properties. However, belowground characteristics of these communities have seldom been evaluated. In 4 meadow community types (CTs) we measured root mass and root length density (RLD) at 10-cm intervals to 40 cm soil depth. The CTs occurred along a wet to dry soil moisture gradient. The ranking of CTs from wettest to driest was: Carex nebrascensis (CANE) > Juncus balticus (JUBA) > Carex douglasii (CADO) > Poa nevadensis (PONE). Total RLD and mass to 40 cm paralleled the order of soil wetness, i.e., there were more roots at the wetter sites. Values of total RLD and mass for the 4 CTs were: 95.6 cm cm-3 and 3,382 g m-2 respectively for CANE; 33.6 cm cm-3 and 2,545 g m-2 for JUBA; 25.7 cm cm-3 and 1,526 g m-2 for CADO; and 8.8 cm cm-3 and 555 g m-2 for PONE. Root mass and RLD declined with depth, a result consistent with other graminoid systems. The RLD values for CANE, JUBA, and CADO are exceptionally high compared to literature values from other graminoid plant communities. The high RLD of the wet CTs suggests that they have superior sitestabilizing characteristics.

Impact of Deferred Rotation Grazing on Stream Characteristics in Central Nevada: A Case Study

Abstract Three central Nevada streams were selected to study the watershed-scale effects on stream morphology and bank stability of deferred rotation cattle grazing, complete rest from grazing, and the presence of road crossings. The streams had gravel substrates, and their entrenchments, width : depth ratios, sinuosities and gradients were moderate. Based on statistical analysis of 1980 stream survey results, geologic basin features, and the occurrence of similar flooding, we concluded that the three streams had similar conditions at the start of the grazing treatment. Since 1980, deferred rotation grazing allowed much improvement of aquatic and riparian habitats but the improvement was limited by the presence of roads, which apparently added sediment to the streams. Complete rest from grazing without the presence of roads allowed the most improvement. Of the variables measured in the 1980 survey, streambank soil stability, type and amount of vegetation cover, and quality of pools improved most in all th...

Variability of pool characteristics with pool type and formative feature on small Great Basin rangeland streams

Abstract Land managers and stream restorationists often set goals or complete designs including specifications for pools that are unrealistic because of a lack of knowledge of the potential conditions of the stream. Using 36 study sites on 17 rangeland streams in Nevada in the western United States, we determined relationships among pool and nonpool length, gradient, pool spacing, pool type and formative feature and stream type. Step pools primarily were formed by boulders while backwater pools were formed by coarse woody debris. This led to most pools being randomly located because structural pool-forming features are too large to move by the flows on these small streams. Montgomery and Buffington (1993) stream type associated with pool type and feature because of the direct linkage between the stream type definitions and pool features. Pool spacing varied only with Montgomery-Buffington stream type presumably because of its linkage with pool type and formative feature. Pool length varied with both Rosgen (1994) and Montgomery-Buffington stream type because of the relations between stream type and pool type and feature. Meander bend pools tended to be deeper because they form in erosive, fine substrate and because the spacing of forced pools may not be optimal which leads to sedimentation. Pool area did not vary with stream type but did with various formative features and pool and nonpool length. Variation of pool area with gradient and ln(gradient) was significant but explained much less variation than did other parameters. Meander bend dominated reaches had the highest pool area. The variability of results and the dependence of pool measures on pool type and formative feature indicates that strict adherence to published equations or expectations due to stream type should be avoided. Land managers should set goals for pool measures based on site specific conditions rather than perceived aquatic species needs or stream type.

An ecological function and services approach to total maximum daily load (TMDL) prioritization

Prioritizing total maximum daily load (TMDL) development starts by considering the scope and severity of water pollution and risks to public health and aquatic life. Methodology using quantitative assessments of in-stream water quality is appropriate and effective for point source (PS) dominated discharge, but less so in watersheds with mostly nonpoint source (NPS) related impairments. For NPSs, prioritization in TMDL development and implementation of associated best management practices should focus on restoration of ecosystem physical functions, including how restoration effectiveness depends on design, maintenance and placement within the watershed. To refine the approach to TMDL development, regulators and stakeholders must first ask if the watershed, or ecosystem, is at risk of losing riparian or other ecologically based physical attributes and processes. If so, the next step is an assessment of the spatial arrangement of functionality with a focus on the at-risk areas that could be lost, or could, with some help, regain functions. Evaluating stream and wetland riparian function has advantages over the traditional means of water quality and biological assessments for NPS TMDL development. Understanding how an ecosystem functions enables stakeholders and regulators to determine the severity of problem(s), identify source(s) of impairment, and predict and avoid a decline in water quality. The Upper Reese River, Nevada, provides an example of water quality impairment caused by NPS pollution. In this river basin, stream and wetland riparian proper functioning condition (PFC) protocol, water quality data, and remote sensing imagery were used to identify sediment sources, transport, distribution, and its impact on water quality and aquatic resources. This study found that assessments of ecological function could be used to generate leading (early) indicators of water quality degradation for targeting pollution control measures, while traditional in-stream water quality monitoring lagged in response to the deterioration in ecological functions.

Influence of Livestock Grazing Strategies on Riparian Response to Wildfire in Northern Nevada

Abstract In 1999–2001 wildfires burned 1.13 million ha across northern Nevada, burning through many grazed riparian areas. With increases in wildfire frequency and extent predicted throughout the Great Basin, an understanding of the interactive effects of wildfire, livestock grazing, and natural hydrologic characteristics is critical. A comparison of pre- and postfire stream surveys provided a unique opportunity to statistically assess changes in stream survey attributes at 43 burned and 38 unburned streams. Livestock grazing variables derived from an extensive federal grazing allotment inventory were used to identify interactive effects of grazing strategies, fire, and natural stressors across 81 independent riparian areas. Differences between baseline and “postfire” stream survey attributes were evaluated for significance using the nonparametric Mann–Whitney test for paired data. Binary logistic regression models evaluated the influence of fire, grazing, and hydrologic characteristics on observed stream survey attribute changes. Grazing attributes contributed most significantly to the bankfull width increase and bank stability rating decrease models. The odds of bankfull width degradation (increase in bankfull width) decreased where there had been rest is some recent years compared to continuous grazing. As the number of days grazed during the growing season increased, the odds of bank stability degradation also increased. The occurrence of fire was not significant in any model. Variation in the riparian width model was attributed primarily to hydrologic characteristics, not grazing. For the models in which grazing variables played a role, stream survey attributes were more likely to improve over time when coupled with a history of rotational grazing and limited duration of use during the growing season. This supports long-term riparian functional recovery through application of riparian complementary grazing strategies.

Stochastic modeling of pool‐to‐pool structure in small Nevada rangeland streams

We developed, calibrated, and verified a compound Poisson process model of pool-to-pool spacing and size using an exponential distribution for spacing and gamma distributions for length and width on 12 rangeland streams in Nevada. Neither distribution parameter varied with simple stream morphologic or vegetation characteristics. We verified the model by comparing the first three moments and distributions of stream simulations with observed streams using two transect-based sampling schemes. Very small errors stemmed from an inability to reproduce autocorrelation of width at short distances, pool cyclicity, and additional density at the tails. We conclude that the presented model is accurate for small, Nevada, rangeland streams and for pools located randomly on small streams with forced pool-riffle or step-pool sequences and regularly on larger, pool-riffle systems. Simulated streams may be used for testing stream survey procedures and hypotheses regarding pool habitat, spacing, and length.

STREAM MORPHOLOGIC IMPACT OF AND RECOVERY FROM MAJOR FLOODING IN NORTH-CENTRAL NEVADA

Major floods cause channel changes ranging from complete cross-sectional change to small fluctuations in pool area. We used stream cross-section data on 30 heavily grazed rangeland streams in north-central Nevada to assess changes over a climatically variable 14-year period. There was an insufficient range in ungulate damage to consider differences caused by grazing. Flooding with return intervals exceeding 50 years caused major change on approximately 25% of the surveyed streams regardless of initial stream type. One-quarter of the changed streams continued to experience cross-sectional change during a six- to eight-year period of low-to-normal flows. On these streams, upper banks either receded to expose a new, lower floodplain or flattened to a less vertical slope. On streams that did not change type, flooding substantially reduced pool area, which did not recover during the succeeding period, presumably because energy was insufficient to form pools. High flows flushed fine sediment from the streams th...

CASE STUDY: Reducing cheatgrass (Bromus tectorum L.) fuel loads using fall cattle grazing

Wildfire is a major concern in the Intermountain West. Fuels management can lower the potential for negative wildfire effects. Cheatgrass (Bromus tectorum L.), a nonnative annual grass, invasion has resulted in a buildup of highly flammable fine fuels that promote frequent wildfire. Removal of cheatgrass standing crop through targeted, prescriptive grazing should provide a reduction in fire intensity and possibly frequency on a local basis. Spring cattle-grazing prescriptions have provided critical reductions in cheatgrass standing crop and seed production. However, annual fluctuations in timing of readiness and standing crop production pose planning difficulties for both producers and land managers. With fall grazing, the uncertainties are no longer planning obstacles. We examined the effects of pasture-scale fall grazing of cheatgrass by cattle on standing crop (fuel reduction), the perennial vegetation community, and cattle performance. Fall grazing removed significant amounts of cheatgrass standing crop during 2006 to 2009: 79, 80, 79, and 58%, respectively. Cumulatively, 675 kg/ha were removed from the fuel base, significantly reducing carryover fuels. With protein supplementation, cattle increased BCS and gained BW in all 3 yr of the assessment (0.17, 0.35, and 0.29 kg/d in 2007 to 2009, respectively). Cheatgrass seed bank decreased by 6-fold in the grazed treatment and a little more than 2-fold in the ungrazed area 2007 to 2009. Perennial plants increased standing crop production at the expense of cheatgrass production. Fall grazing of cheatgrass can remove significant amounts of fine fuel with beneficial effects to grazing animals and the perennial plant community.