2018 North Star Fen Hydrological Monitoring Report

prepared for: Pitkin County Open Space & Trails 806 West Hallam Street, Aspen, CO 81611

prepared by: Buscher Soil & Environmental, Inc. PO Box 156 Rollinsville, CO 80474 Pitkin County Open Space and Trails North Star Nature Preserve

Table of Contents

Section / Title Page

1.0 Introduction ...... 1 2.0 Objectives ...... 1 3.0 Methods ...... 1 4.0 Existing Conditions...... 2 4.1 Geology ...... 2 4.2 Hydrology ...... 2 4.3 Vegetation ...... 2 4.4 Soils ...... 3 4.5 Depth of Peat and Age of the Fen ...... 3 5.0 Hydrological Monitoring Results ...... 3 5.1 Results of First Fen Hydrological Monitoring Period, May 22, 2018...... 4 5.2 Results of Second Fen Hydrological Monitoring Period, July 10, 2018...... 4 5.3 Results of Third Fen Hydrological Monitoring Period, August 17, 2018...... 4 6.0 Recommendations ...... 4 7.0 References...... 6 8.0 Figures ...... 8 9.0 Photographs ...... 11

December 2018 – North Star Fen Hydrological Monitoring Report i Pitkin County Open Space and Trails North Star Nature Preserve

List of Figures

Number / Title Page

Figure 1. Project Location Map ...... 9 Figure 2. Fen Boundary and Saturation Map ...... 10

List of Photos

Number / Title Page

Photo 1. Encroachment of reed canarygrass. August 17, 2018 ...... 12 Photo 2. Water level in ditch below closed headgate. July 10, 2018 ...... 12 Photo 3. Drainage ditch with reed canarygrass along edges. August 17, 2018 ...... 13 Photo 4. Low water level in south pond with reed canarygrass along edge. August 17, 2018 ...... 13

December 2018 – North Star Fen Hydrological Monitoring Report ii Pitkin County Open Space and Trails North Star Nature Preserve

1.0 Introduction

Fens are peat-forming, ecologically important wetland resources that receive nutrients from sources other than precipitation: usually from upslope sources through drainage from surrounding mineral soils and from groundwater movement. Fens form where the rate of plant growth exceeds the rate of decomposition of organic matter due to saturation and cool temperatures, which both slow the rate of decomposition. Fens also play an important role in the global carbon cycle by functioning as long-term sinks of atmospheric CO2.

Groundwater levels at or near the soil surface during the growing season are a necessary component of organic matter accumulation and long-term fen health; if the water table drops, oxygen diffuses into the soil allowing aerobic decomposition of organic matter and potentially affecting the long-term stability of the fen.

The North Star fen is located in the North Star Nature Preserve Open Space just south of Aspen, Colorado (Figure 1) It is about 14 acres in size, of which 11.7 acres are on Pitkin County Open Space and the remaining 2.3 acres occur on private property on the north. It sits in the Roaring Fork Valley at an elevation of about 8,026 feet.

Historically, a drainage ditch was constructed through the North Star fen which partially drained it. However, in recent years a headgate was installed in the ditch, and the level of water in the fen was elevated. The extent to which this ditch has and is affecting long term hydrological functioning of the fen is unknown. It has been found that in fens in Colorado that have ditches through them, lowering the water table increases oxidation of surface peat and subsequently significantly increases organic matter decomposition rates (Chimner and Cooper 2003).

Reed canarygrass (Phalaris arundinacea) has been encroaching into the fen, which likely indicates that some areas of the fen may be drying out during critical times of the growing season (see Photo 1). Reed canarygrass cannot tolerate ponded water for prolonged periods during the growing season (Stannard 2003).

2.0 Objectives

The objectives of this study included the following:

• Evaluate the groundwater and surface water hydrology of the fen throughout the growing season and determine the extent to which organic soils are seasonally saturated; • Determine the maximum depth of the organic material; • Determine the age of the fen using radiocarbon age dating (this objective was added in October 2018); and • Determine whether management activities, such as altering the water level of the fen by raising the headgate, filling in the drainage ditches, or installing a plug in the ditch downgradient of the fen are needed to ensure that this ecologically important resource and its functions are maintained.

3.0 Methods

Typically in Colorado fens, the water table is highest in May and lowest in fall and early winter, and soil saturation for a significant period of the growing season is the critical variable for peat formation (Cooper 1990). For this study, three hydrology monitoring periods were conducted throughout the 2018 growing season by a certified soil scientist, once in late May, once in mid-July, and once in mid-August.

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For this study, a fen, in part, is defined as having organic soils (Histosols). This requirement is also used by the U.S. Army Corps of Engineers to define fens. Histosols have at least 16 inches of accumulated organic material due to anerobic conditions (Soil Survey Staff 2006) and take 1,000s of years to form. Histosols were observed and delineated using a shovel and 2-inch hand auger. The Histosols boundary is approximate, as determining the exact extent of 16 inches of organic matter throughout the wetland was not practical, and Histosols tend to occur in a mosaic pattern at the edges of fens. Histosols were delineated only in Pitkin County Open Space and not in the private property on the north end. The extent of the fen on the private property was interpreted using aerial photography.

Saturation has two different definitions; for the purpose of this report, saturation occurs when all pores in a horizon are filled with water except those containing entrapped air, and this includes the capillary fringe. The capillary fringe occurs immediately above the water table where the soil water content is the same as below the water table. Water in the capillary fringe differs from that below the water table in that it has a pressure less than atmospheric pressure and is under tension or suction, and thus it does not enter wells or auger holes (Vepraskas and Sprechker 1997). Saturation is difficult to measure without using lysimeters or similar equipment, which was beyond the scope of this study. Depth of saturation was estimated from observing water seeping from a hand-held sample of peat from a given depth at atmospheric pressure.

Depths of peat were measured in seven locations using a 2-inch bucket auger to determine the maximum depth of the peat. These measurements were made near the center of the fen and in areas that were saturated in August; areas thought to have the most accumulation of peat. At the two locations with the thickest peat, it was decided in the field to collect samples of basal peat in case there was interest in determining the age of the fen. These two samples of basal peat were collected from about 50 to 53 inches and submitted to Geochron Laboratories in Chelmsford, Massachusetts for radiocarbon age dating. Samples were collected using a 2-inch hand bucket auger.

4.0 Existing Conditions 4.1 Geology The geologic setting of the North Star fen is a glacial carved valley composed of poorly sorted glacial deposits ranging from silt to boulders of the Pinedale glaciation (Bryant 1979). This material is overlain by alluvial deposits from the Roaring Fork River and also likely lake deposits from water blocked by the downgradient terminal moraine. The Pinedale glaciation began between 40,000 and 30,000 years ago and began receding 15,000 to 13,000 years ago (Benedict 1991). The North Star fen, as many Colorado mountain fens, sets behind a glacial terminal moraine.

4.2 Hydrology The hydrology of the fen is from several sources, including and most importantly 1) upslope sources from seeps and springs along the base of the mountainside on the west and southwest sides of the fen, 2) from ground water that discharges vertically up into the peat from the underlying alluvium, 3) from snow melt, and 4) from occasional flooding by the Roaring Fork River. In the spring, water from snow melt tends to pond and drain slowly into the peat due to frozen subsoil that acts like a temporary aquitard, limiting infiltration.

4.3 Vegetation Vegetation of the fen is dominated by beaked sedge (Carex utriculata) with reed canarygrass (Phalaris arundinacea) occurring along the drier edges of the fen, on spoil piles, and places in the fen interior that dried out during mid-growing season (see Lotic Hydrological, et. al. 2018). Reed canarygrass is very competitive once established by depriving light to other herbaceous species. Its sprouts can grow in ephemeral ponded water in the spring, but ponded water for a prolonged period will eventually kill the roots because the reducing environment deprives oxygen to the roots (Stannard 2003). Beaked sedge,

December 2018 – North Star Fen Hydrological Monitoring Report 2 Pitkin County Open Space and Trails North Star Nature Preserve on the other hand, will tolerate about 3 feet of ponded water (Utah State University Extension 2017) and at least 7 inches of ponded water for a considerable portion of the growing season (Cooper 1990). Sedges develop air channels in their leaves, stems, and roots that allow oxygen from the air to be exchanged with the roots, allowing them to thrive in low oxygen environments (Prendusi 2018).

4.4 Soils Soils in the fen are classified as Histosols, or organic soils, with varying degrees of organic matter decomposition. Most of the fen is composed of slightly decomposed organic matter, or peat (fibric material). Near the bottom of the organic soil, organic matter decomposition is greater, ranging from moderately decomposed (hemic material) to highly decomposed (sapric material). Collectively these materials will be referred to as peat. The peat, regardless of the degree of decomposition, was likely derived primarily from sedge roots. Above-ground decomposition rates are great enough that most of this organic matter is oxidized and not incorporated into the peat (Chimner et al. 2002). Unlike the moderately and highly decomposed organic matter, slightly decomposed peat has large pores so that when the water table drops it drains relatively quickly when compared to more decomposed organic matter (Boelter 1968). Therefore, it is essential to maintain a high water table in peat soils to maintain saturation and minimize decomposition. Underlying the peat is a gray silty clay loam of alluvial origin.

Hummocks up to 1.5 feet tall occur in the east and northwest portions of the fen, which correspond to areas that tend to dry out later in the growing season. Hummocks can form from several processes, such as livestock grazing, differential frost heave, shrink-swell from wetting and drying, and plant biomass accumulation. Peat has a large swell capacity when saturated and when dry is highly compressible. The hummocks in the fen are likely the result of one or more of these processes.

4.5 Depth of Peat and Age of the Fen The maximum depth of organic material in the fen was found to be about 53 inches (4.4 feet). Typically in Colorado mountain fens, peat accumulates about 1 foot every 1,500 to 3,000 years (Cooper 1990; Janik 2014).

In Colorado, most mountain fens formed at the end of the last ice age (Pinedale glaciation) as glaciers retreated some 14,000 years ago. Age dates of Colorado fens related to the Pinedale glaciation range from 5,000 years to about 10,600 years (Chimner et al 2002; Madole 1976). This difference in age, in part, is due to the years that elapsed before peat began to form after deglaciation. One site in the Front Range showed about 3,500 years after deglaciation before peat began to form (Madole 1976). Another factor is that glacial recession took place at different times in different locations.

Two samples of basal peat were collected from about 50 to 53 inches for age dating. The age determined was 1,840 and 1,350 years before present, which is too young for the thickness of the peat. David Cooper, a regional fen expert at Colorado State University, suggested that the basal peat samples likely were cross contaminated with overlying younger peat (Cooper, pers. comm. 2018), especially given that it was collected well below the water table. Mr Cooper stated that from his research in Colorado Rocky Mountain and Sierra Nevada fens, peat accumulates at a rate of one foot per 1,500 years (Cooper, pers. comm. 2018). Assuming that the North Star fen had a similar accumulation rate, it would be about 6,700 years old.

5.0 Hydrological Monitoring Results

The hydrology of the fen was monitored three times during the 2018 growing season, on May 22, July 10, and August 17. It was also visited on September 25, 2017. Figure 2 shows the extent of the fen (Histosols) and surface saturation within the fen at the time of the monitoring periods. On May 22 and July 10, the site was in a moderate drought, and on August 17 it was in a severe drought (Western Regional Climate Center 2018).

December 2018 – North Star Fen Hydrological Monitoring Report 3 Pitkin County Open Space and Trails North Star Nature Preserve

5.1 Results of First Fen Hydrological Monitoring Period, May 22, 2018. The first fen hydrological monitoring was conducted on May 22, 2018. Most of the fen was saturated to the surface with ponded water except for a few areas higher in elevation that appear to be detached from ground water (see Figure 2). These areas are 1 to 2 feet higher than the rest of the fen and are east of the south pond and on two small mounds, one mound immediately south of the north pond and the other on the northwest side of the fen. These areas are most likely not saturated for most of the growing season and thus experience a high rate of organic matter decomposition. As peat builds up, it can separate portions of the fen from ground water. The drainage ditch was full of water at this time and the headgate, although closed, was leaking at a rate of about 0.63 cfs (see Lotic Hydrological, et. al. 2018).

5.2 Results of Second Fen Hydrological Monitoring Period, July 10, 2018. The second fen hydrological monitoring was conducted on June 10, 2018. This is a critical time of the growing season for the fen to be saturated at the surface to prevent decomposition of the peat. The east and north portions of the fen had dried up, and the water table in these areas was about 38 inches deep and saturation was about 20 inches (see Figure 2). Along the north edge of saturation, only the upper 3 to 6 inches of the surface were saturated and the peat was not saturated again until about 20 inches in depth, and the water table was about 38 inches. The lack of precipitation during this time that could have saturated the surface and the large pores in peat suggests that the fen was draining vertically. The south end of the fen, next to the springs and seeps, remained well saturated with a few inches of ponded water. The water level in the drainage ditch was below the headgate, which remained closed (see Photo 2).

5.3 Results of Third Fen Hydrological Monitoring Period, August 17, 2018. The third fen hydrological monitoring was conducted on August 17, 2018. Most of the fen had dried up at this time except for the southeast portion of the fen, next to the springs and seeps (see Figure 2). Much of this area remained well saturated with an inch or two of ponded water. The water table in non- saturated areas typically was 36 inches to greater than 40 inches below the soil surface, and saturation was around 20 to 24 inches. The drainage ditch was generally dry with a few small areas of ponded water, and the headgate remained closed (see Photos 3 and 4 – note reed canarygrass along edges of drainage ditch and pond).

6.0 Recommendations

This study was a one-year monitoring period during a very dry year. Summer precipitation in 2018 was 56 percent of normal; 5.06 inches in 2018 compared to the summer average of 9.02 inches (NOAA 2018). During May and June, the site was in a moderate drought and during August in a severe drought. The same study conducted during a normal precipitation year would end up with very different results. For example, the site was visited on September 25, 2017 when the site was not in a drought but was abnormally dry (Western Regional Climate Center 2017), and although surface saturation was not delineated, it did resemble saturation on July 10, 2018. However, the encroachment of reed canarygrass in the drier portions of the fen (the north, east, and southeast sides and the west side north of the small pond), suggests that the fen, regardless of the dry year, is drier than it likely was prior to the construction of the drainage ditch, and that the drying due to the ditch is contributing to the encroachment of reed canarygrass.

Based on the information above recommendations to rehydrate the fen and to ensure long-term success include:

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1) Monitor saturation during the 2019 growing season (assuming a more normal precipitation year) and if the fen continues to be significantly dry, install a plug in the drainage ditch downgradient of the fen at the end of the 2019 growing season.

2) Monitor saturation for 2-3 years following restoration to ensure the fen remains suitably saturated during the growing season.

For details of plugging the drainage ditch and post-restoration monitoring refer to the Fen Wetland Restoration Plan (see Lotic Hydrological, et. al. 2018).

December 2018 – North Star Fen Hydrological Monitoring Report 5 Pitkin County Open Space and Trails North Star Nature Preserve 7.0 References

Benedict, A. D. 1991. A Sierra Club Naturalist’s Guide to the Southern Rockies: The Rocky Mountain Regions of Southern Wyoming, Colorado, and Northern New Mexico. Sierra Club Books, San Francisco, CA.

Boelter, D.H. 1968. Important Physical Properties of Peat Materials. Available at: https://www.nrs.fs.fed.us/pubs/jrnl/1968/nc_1968_boelter_001.pdf.

Bryant, B. 1979. Geology of the Aspen 15-minute Quadrangle, Pitkin and Gunnison Counties, Colorado. Geological Survey Professional Paper 1073. U.S. Government Printing Office, Washington D.C.

Chimner, R.A. and D.J. Cooper. 2003. Influence of Water Table Levels on CO2 Emissions in a Colorado Subalpine Fen: An In-Situ Microcosm Study. Soil Biology & Biochemistry: Vol. 35, pp. 345-351.

Chimner, R.A., D.J. Cooper and W.J. Parton. 2002. Modeling Carbon Accumulation in Rocky Mountain Fens. Wetlands. Vol. 22, No. 1, pp. 100-110.

Cooper, D. J. 2018, November 30. Senior Research Scientist/Professor, Department of Forest and Rangeland Stewardship, Colorado State University. Personnel communication with David Buscher, Buscher Soil & Environmental, Inc.

Cooper, D.J. 1990. Ecology of Wetlands in Big Meadows, Rocky Mountain National Park, Colorado. Biological Report 90(15). Fish and Wildlife Service, U.S. Department of the Interior.

Janik. A. 2014. Rocky Mountain Wetland Provides Fen Tastic Habitat for High Altitude Plants and Wildlife. Available at: https://www.fs.fed.us/blogs/rocky-mountain-wetland-provides-fen-tastic-habitat- high-altitude-plants-wildlife.

Lotic Hydrological, Buscher Soil & Environmental, Inc., Peak Ecological Services, Colorado Wildlife Services, and DHM Design, Inc. North Star Preserve Fen Wetland Restoration Plan. 2018.

Madole, R.F. 1976. Bog Stratigraphy, Radiocarbon Dates, and Pinedale to Holocene Glacial History in the Front Range, Colorado. Jour. Research U.S. Geological Survey. Vol. 4, No. 2, pp. 163-169.

National Oceanic & Atmospheric Administration (NOAA). 2018. U.S. Department of Commerce National Oceanic & Atmospheric Administration. National Environmental Satellite, Data, and Information Service. Available at: https://www.ncdc.noaa.gov/cdo-web/

Prendusi, T. 2018. Water Sedge – Precious Prairie Plants. Available at: www.preciousprairieplants.com/water-sedge.html.

Soil Survey Staff. 2006. Keys to Soil Taxonomy: 10th Edition. Natural Resource Conservation Service, U.S. Department of Agriculture. Pocahontas Press, Inc. Backsburg, Virginia.

Stannard, M. 2003. Biology, History, and Suppression of Reed Canarygrass (Phalaris arundinacea L.). Available at: https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_043972.

Utah State University Extension. 2017. Rangeland Plants of Utah: Beaked Sedge. Available at: https://extension.usu.edu/rangeplants/grasses-and-grasslikes/beaked-sedge.

Vepraakas, M.J. and S.W. Sprecher. 1997. Overview of Aquic Conditions and Hydric Soils. In: Aquic Conditions and Hydric Soils: The Problem Soils. SSSA Special Publication Number 50. Soil Science Society of America, Inc. Madison, Wisconsin.

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Western Regional Climate Center. 2018. United States Drought Monitor. Available at: https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?High_Plains.

Western Regional Climate Center. 2017. United States Drought Monitor. Available at: https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?High_Plains.

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8.0 Figures

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Figure 1. Project Location Map

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Figure 2. Fen Boundary and Saturation Map

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9.0 Photographs

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Photo 1. Encroachment of reed canarygrass. August 17, 2018

Photo 2. Water level in ditch below closed headgate. July 10, 2018

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Photo 3. Drainage ditch with reed canarygrass along edges. August 17, 2018

Photo 4. Low water level in south pond with reed canarygrass along edge. August 17, 2018

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