the thermal regime of shallow groundwater and a ...

Congrès annuel de la Société canadienne de génie civil Annual Conference of the Canadian Society for Civil Engineering Moncton, Nouveau-Brunswick, Canada 4-7 juin 2003 / June 4-7, 2003

THE THERMAL REGIME OF SHALLOW GROUNDWATER AND A SMALL ATLANTIC SALMON STREAM BORDERING A CLEARCUT WITH A FORESTED STREAMSIDE BUFFER A

A

B

C

M.D. Alexander , K.T.B. MacQuarrie , D. Caissie and K.E. Butler A Department of Civil Engineering, University of New Brunswick, Canada B Department of Fisheries and Oceans, Moncton, Canada C Department of Geology, University of New Brunswick, Canada

ABSTRACT: Groundwater temperature has an important influence on the thermal regime of streams with significant groundwater flow components. Groundwater is also an integral determinant in the thermal regime of the hyporheic zone of streams where groundwater and surface water mix. A variety of hydrogeological methods are being employed at Catamaran Brook to investigate groundwater flow and thermal transport through a shallow aquifer system, which receives recharge from a clearcut and a 60 m streamside buffer strip, and discharges to the hyporheic zone of the brook. Hydraulic head data suggest that upland recharge in the clearcut is contributing to groundwater discharge through the hydraulically connected hyporheic zone of Catamaran Brook. For the period studied the ground surface temperature in the streamside buffer strip was more stable and cooler (0.7± 2.2°C) than ground surface temperature measured in the clearcut. Groundwater and hyporheic water thermal plots all represented sine wave forms, with temperatures at shallow depths much more variable than temperatures at greater depths. A direct relationship in the data exists between lag period and depth; the lag period increased with increasing depth. Over the period of study, shallow and deep groundwater temperature mid-point in the buffer was, on average, 1.0±0.7°C and 0.7± 0.5°C cooler, respectively, than that measured for shallow and deep groundwater in the clearcut. Surface water and hyporheic zone differences, when compared to air temperature, were greatest during the winter. During that season, accumulated degree-days at depths of 10, 30, 70 and 150 cm in the hyporheic zone, respectively, were 173, 125, 154 and 274. Cross-correlation analysis showed that water temperatures in the hyporheic zone and stream during the fall and spring were more controlled by water at 150 cm in the hyporheic zone than by air temperature. During the winter water temperatures are highly uncorrelated or anticorrelated.

1.

INTRODUCTION

The principal component of stream flow, even under storm flow conditions, is often groundwater (GW) [Freeze and Cherry 1979], therefore it plays a critical role in the physical, chemical, and biological functioning of stream environments [Hynes 1970]. Groundwater-surface water (GW-SW) interaction within the hyporheic zone (HZ; Figure 1) is identified by many researchers as an important aspect to the ecological capacity of streams [e.g., Wroblicky et al. 1998; Woessener 2000]. The magnitude and extent of GW-SW interaction in the HZ is dependent on stream discharge, stream gradients, stream meanders, longitudinal bed surface profile and the magnitude and distribution of hydraulic conductivity of bed sediments [Wroblicky et al. 1998; Woessener 2000]. Interactions of GW-SW in the HZ are dynamic and complex. For example, interaction with GW in the HZ causes water that was once in the stream to have a changed set of water quality parameters [Hill and Lymburner 1998].

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Ecologically, the change in temperature of that water is one of the most important parameters [Power et al. 1999]. Clearcutting threatens the ecological integrity of stream environments by decreasing the connectivity of GW-SW interaction [Pringle and Triska 2000]. Early watershed research emphasized the impacts clearcutting can have on SW temperatures. In general, these studies showed that the loss of streamside vegetation increases the amount of solar radiation reaching the stream surface, which yields higher summer temperature maximums and increased diel and seasonal amplitudes [Brown and Krygier 1967; Hartman and Scrievener 1990]. Consequently, it has become standard practice to maintain forested riparian buffer strips between clearcuts and streams for eliminating or mitigating temperature increases [Rishel et al. 1982]. Frequently, buffer widths are prescribed on the basis of stream order. However, Loftin et al. [2001] evaluated numerous buffers and determined that a “one size fits all” approach should not be prescribed. Instead, buffer strip widths should account for individual site-specific characteristics. Lewis [1998] measured ground surface temperature (GST) increases of 1 to 2°C at sites in Western Canada when forest cover was removed. Peck and Williamson [1987] and Taniguchi et al. [1997] observed similar responses of GST following clearcutting. Although it is known that the GST increases as a consequence of clearcutting, the subsequent change in the thermal regime of shallow GW has received little consideration [Peck and Williamson 1987; Taniguchi 1997]. Previous researchers have not made a connection between increased infiltration through the warmer soil of a clearcut and the potentially increased GW temperatures that could be transmitted to the HZ of hydraulically connected streams, which could result in deleterious repercussions for aquatic biota. Curry et al. [2002] made the first attempt to address the affect of clearcutting on upslope GW temperature, but the study did not incorporate both a flow and thermal GW monitoring network in a clearcut, buffer strip and stream. The purpose of this study is to obtain an overall understanding of the hydraulic and thermal connections between clearcuts/forests and the HZ of streams in order to evaluate ecological effects.

A

A’

Stream Water Hyporheic Zone

Groundwater

C LEARCUT (WARMER RECHARGE W ATER)

SHALLOW UNCONFINED SANDA QUIFER

Clay Layer

60MF ORESTED BUFFERSTRIP (C OOLER RECHARGE WATER)

A A’

CLAY LAYER BEDROCK

Figure 1. Conceptual model showing the interaction of groundwater and surface water under the influence of upslope clearcutting. The inset details the hyporheic zone of the stream.

2.

STUDY SITE

The study is being conducted at Catamaran Brook, a tributary of the Little Southwest Miramichi River, located in central New Brunswick (46° 52.7’ N, 66° 06.6’ W; Figure 2). The Catamaran Brook drainage 2 rd basin is 52 km with a total main channel (3 order) length of 20.5 km, a stream gradient of approximately 1.3%, an average channel width of 10 m and an average depth of 0.4 m [Caissie et al. 1998].

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The second growth Acadian forest consists of 55.5% mature trees estimated at 65% coniferous and 35% deciduous species with a crown closure of 50% or more [Cunjak et al. 1990]. Since 1996, timber harvesting has resulted in 15.1% clearcut and 22.6% selectively cut lands in the basin. A 3.1 hectare (310 m x 100 m) portion of land clearcut in 1996 is the focus of the present research (Figure 2). Silurian and Devonian volcanic and sedimentary units comprise the basement rock of the basin [Anderson 1970; Rampton et al. 1984]. Pleistocene till and glaciofluvial deposits of loamy to sandy loam are found between a thin upper layer of Wisconsian moraine and the lower layer of basement rock. The streambed of the main catchment consists predominantly of glaciofluvial and alluvial sands and gravels that are generally 0.3 to 0.5 m thick [Rampton et al. 1984]. The long-term mean annual precipitation in the basin is 1142 mm [Cunjak et al. 1993]. Mean monthly air temperature (AT) ranges from a low in January of -11.8°C to a high in July of 18.8°C [Cunjak et al. 3 -1 1993]. Mean annual discharge was calculated to be 1.3 m s , which is equivalent to 66% of runoff [Caissie and El-Jabi 1995]. The highest flows are measured during the spring coincident with snowmelt and the lowest flows are measured in the summer during extended periods of no precipitation. Discharge from GW sources comprises the majority of stream flow during all seasons [Caissie et al. 1996]. Site

N

Little Southwest Miramichi River

Canada NB

Catamaran Brook

USA

Timber Management Block Key Plan

ry u ta Tri b

e On

MW-92-01

MW-92-03

Detailed Research Site

Catamaran Lake an B m ar Ca ta

ro o k

MW-92-04

Groundwater monitoring well

Scale 0 0.5 1

MW-92-04

Timber Management Block 2 Catamaran Brook basin (52km) Access road 2 km

Figure 2. Map of the Catamaran Brook drainage basin located in central New Brunswick. Shown are the locations of the groundwater monitoring wells, and the Timber Management Block (TMB) that is the focus of the research project. The inset details the extent of the research site within the TMB. 3.

METHODOLOGY

A shallow permanent GW observation network consisting of 91 drive point piezometers ranging in depth from 0.5 to 3.5 m was installed in the summers of 2000 to 2002. The network is used for monitoring the spatial and temporal distribution of hydraulic heads in the aquifer from within the clearcut, through the buffer strip and into the HZ of Catamaran Brook. The piezometers were normally installed in nests of two or more so that the vertical and horizontal hydraulic gradient can be determined. Piezometers for thermal measurements are installed in pairs at six locations so that GW temperatures at each location can be measured at depths of 0.75 m and, depending on location, either 1.50 or 1.75 m below the ground surface. Piezometers for thermal measurements are fitted with a TR Minilog temperature-logging probe (VEMCO Ltd., Shad Bay, Nova Scotia). The measurement range, resolution and accuracy of the TR loggers is –5 to 35°C, 0.2°C and ±0.3°C, respectively. Modified drive point piezometers are used for monitoring temperatures in the HZ located at the tail of a riffle. Model 107B thermistors (Campbell Scientific Canada Corp., Edmonton, Alberta) are housed inside of the modified piezometers for measuring temperature at 10, 30, 70 and 150 cm depths in the HZ. Thermistors are also used to measure air and stream water temperature at this location. The thermistors are connected to a shore based CR10 data logger (Campbell Scientific Canada Corp.). The measurement range, resolution and accuracy of the thermistors is –50 to 50°C, 0.1°C and ±0.2°C, respectively. Both AT (i.e., 1.5 m above the ground) and GST (i.e., 0.1 m above the ground) are measured in the clearcut and the buffer strip using TX Minilog probes. Those probes have a measurement range, resolution and accuracy of –35 to 40°C, 0.3°C and ±0.5°C, respectively. Prior to and after use, all of the Minilog probes are placed in a temperature controlled water bath and temperature differences/trends are observed over a range of temperatures. The calibration procedure

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checks for potential drift in the loggers. Using one probe as a baseline temperature, the temperature for each Minilog probe is adjusted accordingly. The thermistors were calibrated in a similar fashion before permanent installation in the streambed. During the field season (i.e., from May to November) hydraulic heads are measured on a monthly basis in the piezometer network to the nearest 0.25 cm. The measurement frequency of all Minilog probes is every hour on the hour everyday of the year, except when the probes are removed for calibration or maintenance requirements. Measurement frequency of the thermistors is also every hour. The hydraulic head data collected in the piezometer network is analyzed using the surface mapping program SURFER (Golden Software Incorporated, Golden, Colorado). Statistical methods are used for analyzing the collected thermal data. In addition to the standard methods of statistical analysis (e.g., mean, standard deviation, etc.) a method described by Malard et al. [2001], referred to as crosscorrelation analysis, is also used for comparing temperature patterns of the air, SW, HZ and GW.

4.

RESULTS

Groundwater Flow Regime Water table (shallow hydraulic head) contours measured on September 6, 2001 are shown in Figure 3. The water table contours closely resemble the land surface topography of the study region (data not shown). Hydraulic heads measured on all other dates (data not shown) very much resemble the results shown in Figure 3. Measurements of hydraulic head indicate that GW flow is to the north toward Catamaran Brook. Vertical hydraulic gradients (data not shown) indicate that, locally, GW flow is downward within the clearcut (i.e., region of highest hydraulic head) and in the more southerly region of the forested buffer strip. Within the northerly portion of the forested buffer strip (i.e., on the floodplain) and within the HZ of Catamaran Brook, measured vertical hydraulic gradients indicate that GW flow is upward. The hydraulic head results suggest that upland recharge in the clearcut is contributing to GW discharge through the hydraulically connected HZ of Catamaran Brook. Ground Surface Thermal Regime The difference in GST between the clearcut and the streamside buffer strip for the entire study period -1 (i.e., May 11, 2001 to September 30, 2002; n = 11926 hourly measurements location ) is shown in Figure 4. For the entire study period, the GST in the clearcut ranged from –20.0 to 38.7°C with a mean of 8.4±10.7°C. The GST in the streamside buffer was more stable, when compared to the GST in the clearcut, and was cooler by 0.7±2.2°C. The mean GST in the buffer was 7.6±9.7°C and ranged from – 17.4 to 33.9°C. Maximal and minimal difference of GST coincided with differences in AT. Warmer GST in the streamside buffer during the fall of 2002 and the early and latter part of winter 2002 is a result of increased terrestrial heat in the buffer (i.e., from forest flora; Figure 4). The somewhat anomalous period of cooler GST in the buffer during mid-winter 2002 was likely a result of persistent snow pack there and the lack of a snow pack in the clearcut (i.e., both related to the mid-winter thaw that typically occurs during the month of January in New Brunswick). Lower levels of solar radiation in the buffer would have allowed snow pack to persist there longer compared to the clearcut. The other large peak near the end of winter 2002 is also attributed to snow pack persistence during the spring snowmelt period (Figure 4). Groundwater Thermal Regime Groundwater temperatures measured at 75 and, depending on location, 125 or 150 cm in the clearcut and streamside buffer strip are shown in Figure 5. Not all thermal data collected at the field site is presented; however, temperature measured at the other clearcut station and the other two buffer strip stations resemble the data presented for the clearcut and buffer strip, respectively. The GW data plots mimic a sine wave with the peak occurring during the summer of 2001 and the trough occurring during the spring of 2002. Present in the thermal plot for each temperature monitoring station are two temperature convergences when a zero temperature gradient existed between the two measurement depths (i.e., in mid-October 2001 and mid-May 2002). Temperature measured at the two depths flip-flopped between these two convergences with respect to which was cooler and which was warmer. For example, shallow GW was warmer than deep GW at TW -01-01 from August 2001 to midOctober 2001 and again from mid-May 2002 to October 2002. However, shallow GW temperature was

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cooler than deep GW from mid-October 2001 to mid-May 2002. From the plots it is also apparent that deep GW temperature lagged the shallow temperature by approximately one-month (Figure 5). 1300

Catamaran Brook Hyporheic Station

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TW-01-06

Y-COORDINATE DISTANCE (m)

1250

TW-01-04

1200 LEGEND MW-92-04

1150

GROUNDWATER MONITORING WELL RIPARIAN BUFFER STRIP DELINEATION P IEZOMETER NEST TEMPERATURE W ELL NEST SCALE 0m

25m

50m

75m

1100 TW-01-01

1050

1000

MW-92-04

950 1000 1050 X-COORDINATE DISTANCE (m)

Figure 3. Contour plot showing the water table elevation (i.e., shallow hydraulic head; contour interval = 1 m) measured on the 6 September 2001. Shown also are the locations of the groundwater monitoring well (MW-92-04) the groundwater temperature monitoring stations of interest (e.g., TW -01-01) and the hyporheic zone monitoring station. Same depth GW temperature comparison provides insight about thermal differences in location of the same infiltration event (i.e., water that infiltrated within the clearcut versus water that infiltrated within the streamside buffer at the same time) [Appelo and Postma 1994]. The shallow GW temperature at each location was compared (data not shown) to the shallow GW temperature measured at the station in the clearcut (i.e., TW -01-01). Over the entire study period, shallow GW temperature measured at mid-point in the streamside buffer (i.e., TW -01-04) was, on average 1.0±0.7°C cooler than in the clearcut. For the station adjacent to the stream (i.e., TW -01-06), shallow GW temperature was 0.4±0.4°C cooler than that measured in the clearcut; however, this was 0.6±0.3°C warmer than that measured mid-point in the buffer. Temperature at the site adjacent to the stream may be somewhat influenced by stream temperature through GW-SW interaction in the HZ. Temperature measured at the site located at mid-buffer was almost consistently cooler, with the exception of winter 2002, than the other two locations. Conversely, the station in the clearcut was almost always warmer, again with the exception of winter 2002, than the other two locations. The thermal amplitude in the clearcut and at the station adjacent to the stream was identical, whereas that measured in the middle of the buffer was lower by 1.1°C. Additionally, shallow GW temperature measured at TW -01-04 was more stable than shallow GW temperature at the other two stations. Deep GW temperature at each location was compared (data not shown) to the temperature of deep GW measured at TW -01-01. Data show that the station adjacent to the stream experienced, on average,

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the warmest temperature with a value of 6.6±3.5°C. Temperature at the station in the clearcut was slightly cooler than that with an overall study mean of 6.3±3.3°C. The coolest temperature was measured at the station located in the middle of the buffer strip (i.e., 5.9±3.0°C). In fact the temperature at TW -01-04 was consistently cooler than the other two locations. More stable temperature was observed at TW -01-04, which also had the smallest measured thermal amplitude. 5 Fall 2002

Winter 2002

Spring 2002

Summer 2002 Calibration Period

Summer 2001

Temperature Difference ( oC)

4

Buffer Cooler Than Clearcut 3

2

1

0

-1

Buffer Warmer Than Clearcut -2 May 2001

Sep 2001

Jan 2002

May 2002

Sep 2002

Figure 4. Smoothed differences (i.e., using a 24 hour moving average) between ground surface temperatures measured in the clearcut versus the streamside buffer strip. Note: the data gap during the summer of 2002 was because the temperature probes were removed for calibration procedures. Hyporheic Zone Thermal Regime Smoothed hourly temperature measurements of surface water and hyporheic water temperatures measured within Catamaran Brook are shown in Figure 6. The AT measured in the streamside buffer strip is shown also for comparison to temperature of the SW and in the HZ. Minimum temperatures occur either in mid-winter (i.e., air and stream water) or early spring (i.e., hyporheic water). The maximum temperatures would occur during the summer for all locations if complete data records were available. Data show that shallow temperatures are much more variable than deep temperatures and that there is a temperature dampening with depth. A direct relationship exists between lag period and depth; the lag period increases as depth in the HZ increases. Similar to GW temperatures measured in the aquifer, two periods of zero temperature gradient are present in the data when the thermal gradient in the HZ reversed. The SW and HZ temperature differences, when compared to AT, were greatest during the winter and least during the spring (data not shown). Water at 150 cm in the HZ was the warmest of all locations through the fall and winter and the coolest of all water monitoring locations in the spring (Figure 6). During the winter season accumulated degree-days was 173, 125, 154 and 274, respectively, for depths from 10 cm to 150 cm in the HZ. It is worth noting that temperature at 30 cm in the HZ was cooler and the thermal amplitude was lower during the winter than at the local boundaries (i.e., at 10 cm and 70 cm). Although AT attained a minimum of –32.2°C during the winter, water temperatures in the HZ only achieved a minimum temperature of 0.6°C. Conversely, AT reached a maximum of 35.2°C during the spring, but water temperature in the HZ only achieved a maximum of 18.4°C. The lower thermal amplitude of water, when compared to AT, reflects the differences in latent heat.

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A)

Groundwater Temperature at Clearcut Station (TW-01-01)

Calibration Period

14

o

Temperature ( C)

12 10 8 6 Deep Probe 150 cm

4 Shallow Probe - 75 cm

2 0 14

Groundwater Temperature at Streamside Buffer Station (TW-01-04)

Calibration Period

B)

o

Temperature ( C)

12 10 8 6 Deep Probe 125 cm

4 Shallow Probe - 75 cm

2 0

C)

Groundwater Temperature at Station Adjacent to Stream (TW-01-06)

Calibration Period

14

10

o

Temperature ( C)

12

Shallow Probe - 75 cm

8 6

Deep Probe 150 cm

4 2 0

Summer 2001

Aug 2001

Fall 2002

Dec 2001

Winter 2002

Spring 2002

Apr 2002

Summer 2002

Aug 2002

Figure 5. Groundwater temperatures measured in the clearcut (panel a) and in the streamside buffer (panel b and c) from August 2001 to October 2002. Note: the data gap during the summer of 2002 was because the temperature probes were removed for calibration.

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16 LEGEND Streamwater Temperature Hyporheic Water Temperature at 10 cm Depth Hyporheic Water Temperature at 30 cm Depth

14

20

Hyporheic Water Temperature at 70 cm Depth

Increasing Depth in Streambed

Hyporheic Water Temperature at 150 cm Depth

10

o

10

Air Temperature ( C)

o

Water Temperature ( C)

12

Air Temperature 8 0 6 4 -10 2 0

-20 Fall 2002

Winter 2002

Spring 2002

-2 Oct 2001

Dec 2001

Feb 2002

Apr 2002

Jun 2002

Figure 6. Smoothed temperatures (i.e., using a 24 hour moving average) for air measured in the streamside buffer strip, stream water and hyporheic water temperatures measured within Catamaran Brook. Note: The scale for air temperature (i.e., right-hand-side y-axis) differs from the water temperature scale (i.e., left-hand-side y-axis). Cross-correlation analysis was performed on the thermal data shown in Figure 6. The results demonstrate that air, stream water and temperature in the HZ were strongly correlated during the fall and spring but were mostly anticorrelated (i.e., negatively correlated) during the winter (Table 1). Pearson coefficients were greater for dependent variables through the fall and spring when correlated with temperature at 150 cm in the HZ, than when compared to correlations with AT (Table 1). Furthermore, no lag was calculated for any temperature when the independent variable used for the correlation was temperature at 150 cm in the HZ. On the other hand, dependent variables lagged by 0 to 19 hours in the fall and spring when they were correlated with AT. These results suggest that temperature at 150 cm exhibited more of a control, when compared to AT, on the other HZ temperatures and stream water. Results during the winter show that all temperatures were moderately anticorrelated with AT and were, with the exception of air and stream water temperature, moderately to highly correlated with temperature at 150 cm in the HZ (Table 1). Air and SW temperature was moderately anticorrelated with temperature at 150 cm in the HZ through the winter. Winter lags for the dependent variables ranged from –720 to 638 hours and from –724 to 332 hours using, respectively, AT and temperature at 150 cm in the HZ as the independent variable. 5.

CONCLUSION

Hydraulic head data suggest that upland recharge in the clearcut is contributing to groundwater discharge through the hydraulically connected hyporheic zone of Catamaran Brook. For the period studied the ground surface temperature in the streamside buffer strip was more stable and cooler (0.7± 2.2°C) than ground surface temperature measured in the clearcut. Groundwater and hyporheic water thermal plots all represented sine wave forms and temperatures at shallow depth were much more variable than temperatures at greater depths. A direct relationship in the data exists between lag period and depth; the lag period increased with increasing depth. Over the period of study, shallow groundwater temperature mid-point in the buffer was, on average, 1.0±0.7°C cooler than that in the clearcut. Deep groundwater measured at the middle of the buffer strip was consistently cooler than other locations and

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was, on average, 0.7± 0.5°C cooler than deep groundwater measured in the clearcut. Surface water and hyporheic zone differences, when compared to air temperature, were greatest during the winter. During that season, accumulated degree-days at depths of 10, 30, 70 and 150 cm in the hyporheic zone, respectively, were 173, 125, 154 and 274. Cross-correlation analysis showed that water temperatures in the hyporheic zone and stream during the fall and spring were more controlled by water at 150 cm in the hyporheic zone than by air temperature. During the winter water temperatures are highly uncorrelated or anticorrelated. Table 1. Lag times between hourly temperature measurements of air, stream water and hyporheic water. Also shown are the Pearson coefficients, significant at p