Rocky Mountain Watershed Research Articles

Southern Rockies Watershed Project

The Southern Rockies Watershed Project was initiated in 2003 to describe the impacts of severe natural disturbance by wildfire on a broad range of headwaters, larger river basin scale, and downstream water resources (Phase I). This watershed research is unique in that trans-disciplinary linkages between hydrology, biogeochemistry, aquatic ecology, downstream river basin processes, implications for human water use, and economic implications are providing broad insights into wildfire effects on water. A second phase of the research (Phase II) focuses on evaluating the effects of several alternative forest harvesting practices on these same water resource “values”. Collectively, this research is providing comprehensive information on watershed function after forest disturbance in Rocky Mountain watersheds.

Evidence of climate-induced range contractions in bull trout Salvelinus confluentus in a Rocky Mountain watershed, U.S.A.

Many freshwater fish species are considered vulnerable to stream temperature warming associated with climate change because they are ectothermic, yet there are surprisingly few studies documenting changes in distributions. Streams and rivers in the U.S. Rocky Mountains have been warming for several decades. At the same time these systems have been experiencing an increase in the severity and frequency of wildfires, which often results in habitat changes including increased water temperatures. We resampled 74 sites across a Rocky Mountain watershed 17 to 20 years after initial samples to determine whether there were trends in bull trout occurrence associated with temperature, wildfire, or other habitat variables. We found that site abandonment probabilities (0.36) were significantly higher than colonization probabilities (0.13), which indicated a reduction in the number of occupied sites. Site abandonment probabilities were greater at low elevations with warm temperatures. Other covariates, such as the presence of wildfire, nonnative brook trout, proximity to areas with many adults, and various stream habitat descriptors, were not associated with changes in probability of occupancy. Higher abandonment probabilities at low elevation for bull trout provide initial evidence validating the predictions made by bioclimatic models that bull trout populations will retreat to higher, cooler thermal refuges as water temperatures increase. The geographic breadth of these declines across the region is unknown but the approach of revisiting historical sites using an occupancy framework provides a useful template for additional assessments.

Spectral evaluation of watershed DOM and DBP precursors

Dissolved organic matter (DOM) quantity and character from eight locations, including rivers and managed‐flow sites, within two northern Colorado Rocky Mountain watersheds were examined using fluorescence and absorbance spectroscopy to characterize changes in DOM quantity and quality. River sites exhibited strong seasonal variability, containing higher concentrations of more aromatic DOM during spring runoff. Reservoir‐influenced, managed sites had year‐round stability and were less aromatic compared with the rivers. Total trihalomethane formation potential (TTHMFP) was used as a measure of DOM chlorine reactivity. Fluorescence compositional metrics (fluorescence index [FI] and Peak C/UV340 ratios) correlated with TTHMFP yields. River sites showed increased TTHMFP concentrations during runoff but little change in TTHMFP yield. Managed sites showed little seasonal variation in both TTHMFP and TTHMFP yield. The results show that fluorescence parameters provide additional information on DOM character not available from conventional measures and may be useful in facilitating watershed management and treatment decisions.

Terrain-based Predictive Modeling of Riparian Vegetation in a Northern Rocky Mountain Watershed

Research focused on improving our understanding of riparian habitat distribution is becoming increasingly important for assessing nutrient buffering potential within developing mountain watersheds. We used field-based vegetation data and digitally-derived terrain variables to (1) assess the usefulness of digital terrain variables for modeling the cross-valley extent of riparian vegetation, (2) compare the strength of hillslope versus fluvial terrain predictors for vegetation prediction, (3) determine a threshold elevation above the channel to be used for coarse delineation of the riparian zone, and (4) implement predictive vegetation models spatially across a 212 km2 watershed. Elevation above the channel, topographic wetness index and site gradient were the strongest vegetation predictors. In a single-predictor model, the extent of riparian vegetation was estimated at 1.2 m and 2.5 m elevation above the stream for 2nd and 3rd order streams, respectively. Predictors of vegetation composition shifted from fluvial/lateral to primarily lateral with decreasing stream size. Recognizing that optimum grid size depends on landscape complexity and the study variable of interest, our study suggests an optimum grid size of 20–30 m for calculating the topographic wetness index for identification of the transition from riparian to upland vegetation within low-gradient valley bottom areas in this mountain watershed.

Hydrologic Calibration and Validation of SWAT in a Snow‐Dominated Rocky Mountain Watershed, Montana, U.S.A.1

Abstract: The Soil and Water Assessment Tool (SWAT) has been applied successfully in temperate environments but little is known about its performance in the snow‐dominated, forested, mountainous watersheds that provide much of the water supply in western North America. To address this knowledge gap, we configured SWAT to simulate the streamflow of Tenderfoot Creek (TCSWAT). Located in central Montana, TCSWAT represents a high‐elevation watershed with ∼85% coniferous forest cover where more than 70% of the annual precipitation falls as snow, and runoff comes primarily from spring snowmelt. Model calibration using four years of measured daily streamflow, temperature, and precipitation data resulted in a relative error (RE) of 2% for annual water yield estimates, and mean paired deviations (Dv) of 36 and 31% and Nash‐Sutcliffe (NS) efficiencies of 0.90 and 0.86 for monthly and daily streamflow, respectively. Model validation was conducted using an additional four years of data and the performance was similar to the calibration period, with RE of 4% for annual water yields, Dv of 43% and 32%, and NS efficiencies of 0.90 and 0.76 for monthly and daily streamflow, respectively. An objective, regression‐based model invalidation procedure also indicated that the model was validated for the overall simulation period. Seasonally, SWAT performed well during the spring and early summer snowmelt runoff period, but was a poor predictor of late summer and winter base flow. The calibrated model was most sensitive to snowmelt parameters, followed in decreasing order of influence by the surface runoff lag, ground water, soil, and SCS Curve Number parameter sets. Model sensitivity to the surface runoff lag parameter reflected the influence of frozen soils on runoff processes. Results indicated that SWAT can provide reasonable predictions of annual, monthly, and daily streamflow from forested montane watersheds, but further model refinements could improve representation of snowmelt runoff processes and performance during the base flow period in this environment.

Lakes and Forests as Determinants of Downstream Nutrient Concentrations in Small Mountain Watersheds

ABSTRACTLakes are dynamic processors of nutrients and may hold an active role in modifying the water chemistry of stream systems. In this study, we examine the influence of lakes and an important terrestrial component—forest cover—on the nutrient levels of stream water in 11 Rocky Mountain (Idaho) watersheds. Water samples were collected from the inflow and outflow of lakes with varying amounts of upstream lakes and forested area during spring runoff and summer base flow. During base flow, mean total nitrogen concentrations at the inflow of final lakes were significantly related to relative upstream lake area, increasing from 34 to 103 µg N L−1 as upstream lake cover in the watersheds increased from 0% to 4%. Forest cover was not significantly correlated with total nitrogen concentrations exported from the watersheds. However, similar to other studies, inflow nitrate concentrations were negatively correlated with relative forest cover. At the scale of individual lakes, dissolved organic carbon and dissolved organic nitrogen increased, and nitrate was significantly reduced from inflows to outflows. The results indicate a potentially critical role of mountain lakes in governing nitrogen flux downstream, and suggest the role of lakes as nitrogen sinks or sources may reverse between spring runoff and summer base flow.

Complementation of Habitats for Bonneville Cutthroat Trout in Watersheds Influenced by Beavers, Livestock, and Drought

AbstractMultiple age‐classes of Bonneville cutthroat trout Oncorhynchus clarkii utah throughout two Rocky Mountain watersheds were influenced by interactions among geomorphology, land use, activity by beavers Castor canadensis, and drought. Age‐0 trout were present in a limited portion of the watersheds, and their distribution became increasingly restricted as drought conditions developed over a 3‐year period. The Coal Creek watershed (including Huff Creek) produced the most age‐0 trout in the first 2 years of the drought, lacked beaver activity, and was affected by land use, suggesting that spawning habitat was determined by geomorphology rather than land use or beaver activity. However, the high abundance of age‐0 cutthroat trout in Huff Creek did not result in a high abundance of juvenile and older age‐classes of fish in subsequent years, most likely because of the lack of complementary habitats providing refuge for older fish. A nearby watershed and its major stream, Water Canyon, had less spawning habitat and produced fewer age‐0 fish during the first 2 years of the study but had more trout in the juvenile and adult age‐classes, most likely because of a higher degree of habitat complementation. In Water Canyon, less‐intense livestock grazing and the presence of beavers allowed for the development of pools and woody riparian vegetation that provided cover for older trout. Water Canyon was also the only stream to produce age‐0 trout during the most severe year of drought, suggesting that streams with more natural habitat may provide a spawning refuge during low‐flow conditions that occur periodically in the region. These results demonstrate that habitat complementation is important for the coexistence of multiple age‐classes of fish and that the adjacency of spawning habitat and refugia is crucial for the persistence of fish in the face of environmental stress associated with drought.

Modeling Hydrology in a Small Rocky Mountain Watershed Serving Large Urban Populations1

Abstract: This article describes the development of a calibrated hydrologic model for the Blue River watershed (867 km2) in Summit County, Colorado. This watershed provides drinking water to over a third of Colorado’s population. However, more research on model calibration and development for small mountain watersheds is needed. This work required integration of subsurface and surface hydrology using GIS data, and included aspects unique to mountain watersheds such as snow hydrology, high ground‐water gradients, and large differences in climate between the headwaters and outlet. Given the importance of this particular watershed as a major urban drinking‐water source, the rapid development occurring in small mountain watersheds, and the importance of Rocky Mountain water in the arid and semiarid West, it is useful to describe calibrated watershed modeling efforts in this watershed. The model used was Soil and Water Assessment Tool (SWAT). An accurate model of the hydrologic cycle required incorporation of mountain hydrology‐specific processes. Snowmelt and snow formation parameters, as well as several ground‐water parameters, were the most important calibration factors. Comparison of simulated and observed streamflow hydrographs at two U.S. Geological Survey gaging stations resulted in good fits to average monthly values (0.71 Nash‐Sutcliffe coefficient). With this capability, future assessments of point‐source and nonpoint‐source pollutant transport are possible.

Low Summer Water Temperatures Influence Occurrence of Naturalized Salmonids across a Mountain Watershed

AbstractWe investigated relationships between the absence of salmonids and low summer water temperatures across a 150‐km2 Rocky Mountain watershed. A model predicting maximum July water temperature (MJT) from measurements of perennial stream length, wetted width, and midrange basin elevation was developed from temperature data obtained at 20 sites across the watershed. The model was used to predict MJT in 75 reaches across the watershed where salmonids were sampled. The lowest predicted MJT in reaches where age‐0 and juvenile–adult brook trout Salvelinus fontinalis were observed was 9°C. The lowest predicted MJT in reaches where age‐0 progeny of the genus Oncorhynchus spp. (i.e., rainbow trout O. mykiss or cutthroat trout O. clarkii) were observed was 13°C and where Oncorhynchus spp. adults where observed was 12°C. The probability of occurrence of both age‐0 and adult brook trout and Oncorhynchus spp. increased as MJT increased above these thresholds. Our results indicate that low MJT in some portions of a mountain watershed can be related to the absence of salmonids. Consequently, data on MJT may provide managers with a means of assessing where summer water temperatures are not suitable for establishment of naturalized salmonid populations.

Factors Affecting Allopatric and Sympatric Occurrence of Two Sculpin Species across a Rocky Mountain Watershed

We assessed factors related to the occurrence of allopatric and sympatric Paiute Sculpin (Cottus beldingi) and Mottled Sculpin (Cottus bairdi) in the Salt River watershed of Wyoming and Idaho, 1996–1997. Sympatric occurrences of Paiute Sculpin and Mottled Sculpin were found in downstream segments of tributaries across a wide range of elevations, stream temperatures, channel slopes, and stream sizes. Allopatric Paiute Sculpin was found in small, high-elevation streams with low summer water temperatures, high channel slopes, large rocky substrates, and low densities of Brown Trout (Salmo trutta). Allopatric Mottled Sculpin occurred in spring streams that were wide and deep, dominated by fine substrate, and supported high densities of Brown Trout. Mottled Sculpin was absent from all tributaries on the eastern side of the drainage where streams have low summer water temperatures, high-gradient channels, and barriers that can influence upstream movements. This study suggests that stream geomorphology, thermal characteristics, local habitat conditions, and nonnative fishes differentially influence the occurrence of Paiute Sculpin and Mottled Sculpin.

Fish assemblage structure and relations with environmental conditions in a Rocky Mountain watershed

Fish and habitat were sampled from 110 reaches in the Salt River basin (Idaho and Wyoming) during 1996 and 1997 to assess patterns in fish assemblage structure across a Rocky Mountain watershed. We identified four distinct fish assemblages using cluster analysis: (1) allopatric cutthroat trout (Oncorhynchus clarki (Richardson, 1836)); (2) cutthroat trout – brook trout (Salvelinus fontinalis (Mitchell, 1814)) – Paiute sculpin (Cottus beldingi Eigenmann and Eigenmann, 1891); (3) cutthroat trout – brown trout (Salmo trutta L., 1758) – mottled sculpin (Cottus bairdi Girard, 1850); and (4) Cyprinidae–Catostomidae. The distribution of fish assemblages was explained by thermal characteristics, stream geomorphology, and local habitat features. Reaches with allopatric cutthroat trout and the cutthroat trout – brook trout – Paiute sculpin assemblage were located in high-elevation, high-gradient streams. The other two fish assemblages were generally located in low-elevation streams. Associations between habitat gradients, locations of reaches in the watershed, and occurrence of species were further examined using canonical correspondence analysis. The results suggest that stream geomorphology, thermal conditions, and local habitat characteristics influence fish assemblage structure across a Rocky Mountain watershed, and they provide information on the ecology of individual species that can guide conservation activities.

Production of stream habitat gradients by montane watersheds: hypothesis tests based on spatially explicit path analyses

We studied how the features of mountain watersheds interact to cause gradients in three stream attributes: baseflow stream widths, total alkalinity, and stream slope. A priori hypotheses were developed before being tested in a series of path analyses using data from 90 stream reaches on 24 second- to fourth-order streams across a fifth-order Rocky Mountain watershed. Because most of the conventional least squares regressions initially calculated for the path analyses had spatially correlated residuals (13 of 15 regressions), spatially explicit regressions were often used to derive more accurate parameter estimates and significance tests. Our final working hypotheses accounted for most of the variation in baseflow stream width (73%), total alkalinity (74%), and stream slope (78%) and provide systemic views of watershed function by depicting interactions that occur between geomorphology, land surface features, and stream attributes. Stream gradients originated mainly from the unidirectional changes in geomorphic features that occur over the lengths of streams. Land surface features were of secondary importance and, because they change less predictably relative to the stream, appear to modify the rate at which stream gradients change.

A HYPOTHESIS ABOUT FACTORS THAT AFFECT MAXIMUM SUMMER STREAM TEMPERATURES ACROSS MONTANE LANDSCAPES1

ABSTRACT: Temperature is an important variable structuring lotic biotas, but little is known about how montane landscapes function to determine stream temperatures. We developed an a priori hypothesis that was used to predict how watershed elements would interact to affect stream temperatures. The hypothesis was tested in a series of path analyses using temperature data from 26 sites on second‐order to fourth‐order streams across a fifth‐order Rocky Mountain watershed. Based on the performance of the first hypothesis, two revised versions of the hypothesis were developed and tested that proved to be more accurate than the original hypothesis. The most plausible of the revised hypotheses accounted for 82 percent of the variation in maximum stream temperature, had a predicted data structure that did not deviate from the empirical data structure, and was the most parsimonious. The final working hypothesis suggested that stream temperature maxima were directly controlled by a large negative effect from mean basin elevation (direct effect = ‐0.57, p < 0.01) and smaller effects from riparian tree abundance (direct effect = ‐0.28, p = 0.03), and cattle density (direct effect = 0.24, p = 0.05). Watershed slope, valley constraint, and the abundance of grass across a watershed also affected temperature maxima, but these effects were indirect and mediated through cattle density and riparian trees. Three variables included in the a priori hypothesis ‐ watershed aspect, stream width, and watershed size ‐ had negligible effects on maximum stream temperatures and were omitted from the final working hypothesis.

Production of stream habitat gradients by montane watersheds: hypothesis tests based on spatially explicit path analyses

We studied how the features of mountain watersheds interact to cause gradients in three stream attributes: baseflow stream widths, total alkalinity, and stream slope. A priori hypotheses were developed before being tested in a series of path analyses using data from 90 stream reaches on 24 second- to fourth-order streams across a fifth-order Rocky Mountain watershed. Because most of the conventional least squares regressions initially calculated for the path analyses had spatially correlated residuals (13 of 15 regressions), spatially explicit regressions were often used to derive more accurate parameter estimates and significance tests. Our final working hypotheses accounted for most of the variation in baseflow stream width (73%), total alkalinity (74%), and stream slope (78%) and provide systemic views of watershed function by depicting interactions that occur between geomorphology, land surface features, and stream attributes. Stream gradients originated mainly from the unidirectional changes in geomo...

The effects of acid rock drainage onCarex aquatilis leaf litter decomposition in rocky Mountain fens

Fens occur in many Colorado Rocky Mountain watersheds that have historically been affected by metal mining activities. A persistent effect of mining is acid rock drainage (ARD), which flows from mine adits and tailings piles. ARD water has low pH and high concentrations of heavy metals and can pollute surface and ground water supporting fens. There are few floristic differences between polluted and pristine fens, and it is unclear what long-term affects ARD has on fens. We investigated decomposition of native leaf litter and a standard litter for two years in fourCarex aquatilis-dominated subalpine fens. Two of the fens are affected by ARD, and their source waters have pH 6.0 and low metal concentrations. ARD significantly reduced native litter decomposition rates over two years (ANOVA, p <0.01) with 63% of the initial mass of leaf litter remaining at the most pristine site (Peru Creek fen), 47 % at a moderately polluted site (Argentine fen), and 23% at the most pristine site (Deer Creek fen). ARD also reduced the quality of litter produced. Standard litter decomposed more rapidly than native litter at all sites, particularly Peru Creek fen. Site, representing fen environment, and litter origin, representing native vs. standard litter, significantly affected decomposition rates (ANOVA, p < 0.0001) Pristine fens had decomposition rates comparable with boreal rich fens, while polluted fens had decomposition rates comparable with boreal poor fens and bogs. Acid rock drainage causes ecosystem-level responses in organic matter processing, peat accumulation rates, and most likely in nutrient cycling, which could have long-term affects on fen primary and secondary production and other functions.

WATERSHED RESPONSES TO CLIMATE CHANGE AT GLACIER NATIONAL PARK1

ABSTRACT: We have developed an approach which examines ecosystem function and the potential effects of climatic shifts. The Lake McDonald watershed of Glacier National Park was the focus for two linked research activities: acquisition of baseline data on hydrologic, chemical and aquatic organism attributes that characterize this pristine northern rocky mountain watershed, and further developing the Regional Hydro‐Ecosystem Simulation System (RHESSys), a collection of integrated models which collectively provide spatially explicit, mechanistically‐derived outputs of ecosystem processes, including hydrologic outflow, soil moisture, and snow‐pack water equivalence. In this unique setting field validation of RHESSys, outputs demonstrated that reasonable estimates of SWE and streamflow are being produced. RHESSys was used to predict annual stream discharge and temperature. The predictions, in conjunction with the field data, indicated that aquatic resources of the park may be significantly affected. Utilizing RHESSys to predict potential climate scenarios and response of other key ecosystem components can provide scientific insights as well as proactive guidelines for national park management.

Estimates of Evapotranspiration or Effective Moisture in Rocky Mountain Watersheds from Chloride Ion Concentrations in Stream Baseflow

The principle that atmospherically derived chloride is a conservative tracer in many watersheds can be used to calculate average annual evapotranspiration or effective moisture if estimates are available for (1) the average annual chloride input to the watershed, (2) the average annual precipitation, and (3) the baseflow chloride concentration are known. The method assumes that no long‐term storage of chloride occurs and there is no lithologic source of chloride, or that such source releases only insignificant amounts to groundwater compared to the atmospheric source. National Atmospheric Deposition Program estimates of chloride wet deposition, watershed precipitation records or hyetal map estimates of precipitation input to watersheds, and a single sample of chloride concentration in base flow were used to calculate evapotranspiration for diverse Rocky Mountain watersheds. This estimate was compared to evapotranspiration determined by subtracting mean discharge from precipitation. Of the 19 watersheds used to test the method, 13 agreed within 10%, 2 appear to have not met the lithology criterion, 1 appears to have not met the flow criterion, and 1 neither criterion. The method's greatest strength is the minimal data requirements and its greatest weakness is that for some watersheds it may be difficult to obtain reliable estimates of precipitation and chloride deposition. If reliable discharge data are available, the method may be used to estimate watershed‐average precipitation; this is especially useful in high‐altitude mountain watersheds where little or no precipitation data are available.