skip to main content

Attention:

The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 11:00 PM ET on Thursday, October 10 until 2:00 AM ET on Friday, October 11 due to maintenance. We apologize for the inconvenience.


Title: Hydrology on high: Assessing the effect of ski resort expansion and changing climate at the Mount Mansfield paired‐catchment study in Vermont, USA
Abstract

A paired‐catchment study began in 2000 to assess the hydrologic effects of high‐elevation development on Mt. Mansfield, Vermont's highest summit (1340 m). West Branch Little River drains 12.08 km2and encompasses a large ski resort. Adjacent Ranch Brook drains 9.83 km2of minimally disturbed second‐growth forest. The two catchments have similar elevation, aspect, surficial and bedrock geology, and vegetation. The resort was well established before this study, but it underwent a major expansion during the period 2004–2008. The expansion included new ski lifts and trails, a large hotel, roads and second home development, a 435 000‐m3snowmaking storage pond and a nine‐hole golf course, increasing the extent of cleared/open land from 17% to 24%. Runoff from the developed West Branch Little River catchment was 21% greater than Ranch Brook over the duration of the study, but varied widely each year from 10% to 42%. This high variability occurs both on the interannual and individual storm scales, and is consistent with expectations from future climate projections. Hydrologic variability is on the rise, as shown by an increase in stream flashiness in both catchments over the 20 years of our study. Resort expansion, which provided for stormwater management, had no discernible effect on the overall runoff difference nor the flow distribution at the scale of the catchments, but sedimentation, water quality impacts and localized erosion cannot be ruled out. Forest clearing, impervious and hardened surfaces, and skier‐compacted and machine‐made snow may all cause enhanced runoff. However, the greater runoff at West Branch, which occurs primarily during snowmelt and summer, may arise partly from greater precipitation capture in the complex mountain topography. Development pressure on the mountain landscape continues to mount, but managers may also need to consider the confounding effects of a changing climate.

 
more » « less
NSF-PAR ID:
10367446
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Hydrological Processes
Volume:
35
Issue:
10
ISSN:
0885-6087
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    We applied an eco‐hydrologic model (Regional Hydro‐Ecologic Simulation System [RHESSys]), constrained with spatially distributed field measurements, to assess the impacts of forest‐fuel treatments and wildfire on hydrologic fluxes in two Sierra Nevada firesheds. Strategically placed fuels treatments were implemented during 2011–2012 in the upper American River in the central Sierra Nevada (43 km2) and in the upper Fresno River in the southern Sierra Nevada (24 km2). This study used the measured vegetation changes from mechanical treatments and modelled vegetation change from wildfire to determine impacts on the water balance. The well‐constrained headwater model was transferred to larger catchments based on geologic and hydrologic similarities. Fuels treatments covered 18% of the American and 29% of the Lewis catchment. Averaged over the entire catchment, treatments in the wetter central Sierra Nevada resulted in a relatively light vegetation decrease (8%), leading to a 12% runoff increase, averaged over wet and dry years. Wildfire with and without forest treatments reduced vegetation by 38% and 50% and increased runoff by 55% and 67%, respectively. Treatments in the drier southern Sierra Nevada also reduced the spatially averaged vegetation by 8%, but the runoff response was limited to an increase of less than 3% compared with no treatment. Wildfire following treatments reduced vegetation by 40%, increasing runoff by 13%. Changes to catchment‐scale water‐balance simulations were more sensitive to canopy cover than to leaf area index, indicating that the pattern as well as amount of vegetation treatment is important to hydrologic response.

     
    more » « less
  2. Abstract

    Stream and shallow groundwater responses to rainfall are characterized by high spatial variability, but hydrologic response variability across small, agro‐forested sub‐catchments remains poorly understood. Conceivably, improved understanding in this regard will result in agricultural practices that more effectively limit nutrient runoff, erosion, and pollutant transport. Terrestrial hydrologic response approaches can provide valuable information on stream‐aquifer connectivity in these mixed‐use watersheds. A study was implemented, including eight stream and co‐located shallow groundwater monitoring sites, in a small sub‐catchment of the Chesapeake Bay watershed in the Northeast, USA to advance this ongoing need. During the study period, 100 precipitation‐receiving days (i.e., 24‐hour periods, midnight to midnight) were observed. On average, the groundwater table responded more to precipitation than stream stage (level change of 0.03 vs. 0.01 m and rainfall‐normalized level change estimate of 3.81 vs. 3.37). Median stream stage responses, groundwater table responses, and response ratios were significantly different between sub‐catchments (n = 8;p < 0.001). Study area average precipitation thresholds for runoff and shallow groundwater flow were 2.8 and 0.6 cm, respectively. Individual sub‐catchment thresholds ranged from 0.5 to 2.8 cm for runoff and 0.2 to 1.3 cm for shallow groundwater flow. Normalized response lag times between the stream and shallow groundwater ranged from −0.50 to 3.90 s·cm−1, indicating that stormflow in one stream section was regulated by groundwater flow during the period of study. The observed differences in hydrologic responses to precipitation advance future modelling efforts by providing examples of how terrestrial groundwater response methods can be used to investigate sub‐catchment spatial variability in stream‐aquifer gradients with co‐located shallow groundwater and stream stage data. Additionally, results demonstrate asynchronous stream and shallow groundwater responses on precipitation‐receiving days, which may hold important implications for modelling hydrologic and biogeochemical fate and transport processes in small, agro‐forested catchments.

     
    more » « less
  3. Abstract

    Trees shape the critical zone and modulate terrestrial water storage yet observed streamflow responses to forest cover change vary. Differences in catchment area, soil water storage, management practices, tree species, and climate are among the many explanations proposed for heterogeneous hydrologic responses. We addressed evidence for the hypothesis that mean annual temperature (MAT) and the phase shift between precipitation and enhanced vegetation index (EVI) peaks,θ, explain a significant amount of the variation in hydrologic response to forest cover loss. We selected 50 catchments with daily streamflow records spanning eight nations and seven climate regions. Categorical clustering of catchments was performed with MAT, θ, minimum EVI, catchment area, and percentage forest loss. Similar storm event runoff ratio responses to deforestation were best clustered by MAT andθ. High MAT tropical monsoonal catchments (Brazil, Myanmar, and Liberia) exhibited minimal evidence of increasing runoff ratios (increases observed in 9% of catchments). Low MAT subarctic, cold semi-arid, and humid continental catchments (US, Canada, and Estonia) showed consistent runoff increases around the time of snowmelt (94%). The deforestation runoff responses of temperate and subtropical catchments with Mediterranean, humid, and oceanic climates depended strongly onθ. We observe increased runoff following forest loss in a majority of catchments (90%) where precipitation peaks followed peak growing season (max EVI) (US). In contrast, where precipitation peaks preceded the growing season (South Africa and Australia) there was less evidence of increased runoff (25% of catchments). This research supports the strategic implementation of native forest conservation or restoration for simultaneously mitigating the effects of global climate change and regional or local surface runoff.

     
    more » « less
  4. Abstract

    Uncertainty in the estimation of hydrologic export of solutes has never been fully evaluated at the scale of a small‐watershed ecosystem. We used data from the Gomadansan Experimental Forest, Japan, Hubbard Brook Experimental Forest, USA, and Coweeta Hydrologic Laboratory, USA, to evaluate many sources of uncertainty, including the precision and accuracy of measurements, selection of models, and spatial and temporal variation. Uncertainty in the analysis of stream chemistry samples was generally small but could be large in relative terms for solutes near detection limits, as is common for ammonium and phosphate in forested catchments. Instantaneous flow deviated from the theoretical curve relating height to discharge by up to 10% at Hubbard Brook, but the resulting corrections to the theoretical curve generally amounted to <0.5% of annual flows. Calibrations were limited to low flows; uncertainties at high flows were not evaluated because of the difficulties in performing calibrations during events. However, high flows likely contribute more uncertainty to annual flows because of the greater volume of water that is exported during these events. Uncertainty in catchment area was as much as 5%, based on a comparison of digital elevation maps with ground surveys. Three different interpolation methods are used at the three sites to combine periodic chemistry samples with streamflow to calculate fluxes. The three methods differed by <5% in annual export calculations for calcium, but up to 12% for nitrate exports, when applied to a stream at Hubbard Brook for 1997–2008; nitrate has higher weekly variation at this site. Natural variation was larger than most other sources of uncertainty. Specifically, coefficients of variation across streams or across years, within site, for runoff and weighted annual concentrations of calcium, magnesium, potassium, sodium, sulphate, chloride, and silicate ranged from 5 to 50% and were even higher for nitrate. Uncertainty analysis can be used to guide efforts to improve confidence in estimated stream fluxes and also to optimize design of monitoring programmes. © 2014 The Authors.Hydrological Processespublished John Wiley & Sons, Ltd.

     
    more » « less
  5. Abstract

    In snowmelt‐driven mountain watersheds, the hydrologic connectivity between meteoric waters and stream flow generation varies strongly with the season, reflecting variable connection to soil and groundwater storage within the watershed. This variable connectivity regulates how streamflow generation mechanisms transform the seasonal and elevational variation in oxygen and hydrogen isotopic composition (δ18O and δD) of meteoric precipitation. Thus, water isotopes in stream flow can signal immediate connectivity or more prolonged mixing, especially in high‐relief mountainous catchments. We characterized δ18O and δD values in stream water along an elevational gradient in a mountain headwater catchment in southwestern Montana. Stream water isotopic compositions related most strongly to elevation between February and March, exhibiting higher δ18O and δD values with decreasing elevation. These elevational isotopic lapse rates likely reflect increased connection between stream flow and proximal snow‐derived water sources heavily subject to elevational isotopic effects. These patterns disappeared during summer sampling, when consistently lower δ18O and δD values of stream water reflected contributions from snowmelt or colder rainfall, despite much higher δ18O and δD values expected in warmer seasonal rainfall. The consistently low isotopic values and absence of a trend with elevation during summer suggest lower connectivity between summer precipitation and stream flow generation as a consequence of drier soils and greater transpiration. As further evidence of intermittent seasonal connectivity between the stream and adjacent groundwaters, we observed a late‐winter flush of nitrate into the stream at higher elevations, consistent with increased connection to accumulating mineralized nitrogen in riparian wetlands. This pattern was distinct from mid‐summer patterns of nitrate loading at lower elevations that suggested heightened human recreational activity along the stream corridor. These observations provide insights linking stream flow generation and seasonal water storage in high elevation mountainous watersheds. Greater understanding of the connections between surface water, soil water and groundwater in these environments will help predict how the quality and quantity of mountain runoff will respond to changing climate and allow better informed water management decisions.

     
    more » « less