An Evaluation of Mitigation Measures to Reduce Impacts of Peat ...

An Evaluation of Mitigation Measures to Reduce Impacts of Peat Harvesting on the Aquatic Habitat of the East Branch Portage River, New Brunswick, Canada Marie Clément, André St-Hilaire, Daniel Caissie, Alyre Chiasson, Simon Courtenay, and Peter Hardie

Abstract: The evaluation of impacts of peat harvesting on riverine ecosystems is essential to the implementation of adequate mitigation measures. The objective of the present study was to determine the potential impacts of peat harvesting on the physical (e.g., flow, suspended sediment concentration (SSC), water temperature) and biological (fish abundance) parameters of the East Branch Portage River, New Brunswick. This study was initiated in 2005 and a before and after study design was used to assess impacts. When the operational activities were initiated (spring 2007), 19 ha of peatland (15% of the total area scheduled for harvesting) was drained. The exploited area was drained through a network of ditches which emptied into a sedimentation pond. Drained water subsequently flowed into a 250 m vegetated buffer zone and discharged into the East Branch Portage River. Drained water did not diffuse throughout the buffer zone as expected. Rather, water tended to concentrate in a natural depression (channel) in the buffer zone, thus connecting the outflow of the sedimentation pond directly to the river. Two main results deserve attention. First, elevated SSC events were recorded in the East Branch Portage River downstream of the confluence of the channel formed in the buffer zone and the river. Periods of elevated SSC could be attributed to poor maintenance of the sedimentation pond. However, elevated SSC events were also recorded after pond maintenance and were concurrent with the timing of ditching activities within the peatland. Secondly, fish abundance was lower in 2007 compared to 2006 (predevelopment period). However, potential impacts of peatland development on fish abundance should be interpreted with caution at this stage of the study. Résumé : L’évaluation des impacts de la récolte de la tourbe sur les écosystèmes lotiques est essentielle à la mise en œuvre de mesures d’atténuation appropriées. L’objectif de la présente étude était de déterminer Marie Clément1, André St-Hilaire2,3, Daniel Caissie1,3, Alyre Chiasson4, Simon Courtenay1,3, and Peter Hardie1 Fisheries and Oceans Canada, Gulf Region, Moncton, NB E1C 9B6 INRS-ETE, Université du Québec, Québec City, QC G1K 9A9 3 Canadian Rivers Institute, University of New Brunswick, Fredericton, NB E3B 5A3 4 Département de Biologie, Université de Moncton, Moncton, NB E1A 3E9 1 2

Submitted September 2008; accepted February 2009. Written comments on this paper will be accepted until June 2010. Canadian Water Resources Journal Revue canadienne des ressources hydriques

Vol. 34(4): 441–452 (2009)

© 2009 Canadian Water Resources Association

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Canadian Water Resources Journal/Revue canadienne des ressources hydriques

les impacts potentiels de l’exploitation d’une tourbière sur les paramètres physiques (par exemple, le débit, la concentration de sédiments en suspension (CSS) et la température de l’eau) et biologiques (abondance des poissons) de la rivière East Branch Portage, Nouveau-Brunswick. Cette étude fut initiée en 2005, suivant un protocole avant-après, afin d’évaluer les impacts. Lors du début des activités opérationnelles (printemps 2007), 19 ha de la tourbière (15% de la superficie totale prévue pour la récolte) fut drainée à l’aide d’un réseau de fossés qui se déverse dans un bassin de sédimentation. L’eau drainée ne s’est pas diffusée dans l’ensemble de la zone tampon, tel que prévu. Au contraire, l’eau s’est concentrée dans une dépression naturelle (chenal) dans la zone tampon, reliant ainsi l’exutoire du bassin de sédimentation directement à la rivière. Deux principaux résultats méritent une attention particulière. Tout d’abord, des événements élevés de CSS ont été enregistrés dans la rivière East Branch Portage, en aval de la confluence du chenal formé dans la zone tampon et la rivière. Certaines périodes de CSS élevées peuvent être attribuées à un mauvais entretien du bassin de sédimentation. Toutefois, des CSS élevées ont été enregistrées suite au nettoyage du bassin et coïncidaient avec les activités de creusement des fossés dans la tourbière. Deuxièmement, l’abondance des poissons a été plus faible en 2007 en comparaison à l’année 2006 (période de pré-développement). Toutefois, les impacts potentiels du développement d’une tourbière sur l’abondance des poissons doivent être interprétés avec prudence à ce stade de l’étude.

Introduction Peatlands have been subjected to significant anthropogenic impacts. Such impacts include peatland drainage to increase forest and agricultural productivity (Coulson et al., 1990; Minkkinen and Laine, 1998) and commercial peat harvesting (St-Hilaire et al., 2006; Pavey et al., 2007). In Canada, most of the peat produced is extracted using the vacuum harvesting

method (Daigle et al., 2001). This harvesting method requires the construction of a network of drainage ditches to lower the water table within the area to be harvested. The drainage can significantly alter the hydrological regime of the harvested peatlands (Shantz and Price, 2006). In some cases, drainage water with high sediment loads has been shown to have detrimental impacts on aquatic ecosystems (Ouellette et al., 2006). In studies of three New Brunswick harvested peatlands, the current provincial guideline of 25 mg/L for suspended sediment concentration (Thibault, 1998) was exceeded more than 60% of the time during three ice-free seasons (St-Hilaire et al., 2006; Pavey et al., 2007). The New Brunswick guidelines require that harvest sites located near watercourses contain sedimentation ponds downstream of the network of drainage ditches before the water is routed to the watercourse. One of the design criteria for sedimentation ponds, based on a study conducted by Gemtec Ltd. (1993), requires a volume of 25 m3 per hectare of drained peatland (Thibault, 1998). A buffer zone (undisturbed peatland) of 30 m between the outflow of the pond and the watercourse is generally a condition of the Approval to Operate issued by the New Brunswick Department of Environment. The original design of these ponds was in part based on the Rational Method (Dooge, 1973) for the estimation of peak flows, which in the case of peatlands is considered a crude approach (Gemtec Ltd., 1991). More accurate estimates are desirable. Hydrological conditions within harvested peatlands have been studied in eastern Canada (e.g., Shantz and Price, 2006) and a conceptual model to evaluate hydrological changes was proposed by Van Seters and Price (2002). However, such conceptual models have rarely been implemented for the purpose of flow forecasting. The PHIM model (Guertin et al., 1987) is perhaps the only tool that has been specifically developed to simulate flow conditions in both natural and harvested peatlands although it is limited to water quantity. Water quality (in particular SSC) was not considered in the PHIM model. The long-term objective of this study is to determine the potential impacts of peat harvesting on a riverine ecosystem by performing a before and after study of the physical (flow, SSC, and water temperature) and biological (fish abundance) parameters in the East Branch Portage River, New Brunswick.The study design provided a rare opportunity to quantify the natural state © 2009 Canadian Water Resources Association

Clément, St-Hilaire, Caissie, Chiasson, Courtenay, and Hardie

of the river during two consecutive years prior to the beginning of operational activities. Furthermore, the variations in the physical and biological parameters of the East Branch Portage River will be quantified during all crucial steps involved in peatland development and harvesting operations. The principal operational activities include ditching, drainage of the surface water, land preparation (vegetation removal, tilling, and harrowing) and peat harvesting. The results of the first three years of this study are presented in the present paper. Phase 1 (2005–2006) of the study quantified the natural variations in the physical and biological parameters of the East Branch Portage River (pre-development phase). Phase 2 (2007) quantified the effects of ditching, drainage of the surface water and land preparation for harvesting. The development and harvesting of additional sectors of the peatland is ongoing and further results will be reported in subsequent publications.

Materials and Methods The experimental site is located within the ombrotrophic Peatland 324N (latitude: 47°01.351ʹN and longitude: 064°56.782ʹW). The peatland is located near Baie St-Anne (Northumberland County, New Brunswick; Figure 1). Two sectors of the peatland are presently being exploited by developers (Figure 1). The operations within Sector A of the peatland were initiated in 2007 and this study is designed to quantify the potential impacts of the development of Sector A. This sector is included in the East Branch Portage River drainage basin (total drainage area 11 km2) which flows into the Portage River, a tributary of the Miramichi Estuary (Figure 1). Another company has harvested Sector B since 2001 (Figure 1). Drainage water from Sector B was routed easterly via a distinct drainage system and does not flow towards the East Branch Portage River. The exploited area of Sector A will eventually cover a total area of 125 ha. Following the construction of the access road (winter 2007), a network of secondary drainage ditches (depth 1 m; width 2–3 m) was excavated at 30 m intervals to drain the surface water from the first 19 ha of the peatland being exploited. This area represents 15% of the total projected exploited area within Sector A. The secondary ditches join the primary draining channel (depth and width 2–3 m) which delimits the contours of the exploited

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area and connect to a sedimentation pond. With the expansion of the exploited area, surface water from a total of 38 ha will be drained into this sedimentation pond. According to the New Brunswick guideline of 25 m3/ha, a sedimentation pond volume of 950 m3 will be required to receive drainage water from the total 38 ha. The initial volume of the sedimentation pond was 700 m3, which complies with the New Brunswick guidelines for the initial 19 ha of exploited area. The length of the sedimentation pond was 90 m, the width at the base varied between 2–5 m and the top width varied between 7–10 m. The sedimentation pond empties into a 250 m wide buffer zone (undisturbed peatland located between the exploited area and the East Branch Portage River; Figure 1). As the harvesting activities progress and the area of exploitation increases, three additional sedimentation ponds will be constructed (see Premier Horticulture Ltd. (2000) for detailed site development plan). Three study sites were selected in the East Branch Portage River (Figure 1). Site 1 is located approximately 2 km downstream of Sector A, in an area with potential fish habitat (riffle-pool sequences). Site 1 will provide information on the distal downstream influence of peat harvesting. Site 1 is also located downstream of a marsh that may potentially serve as an additional sediment depositional zone. Site 2 was established downstream, and Site 3 upstream, of operational activities. Consequently, Site 3 does not presently receive drainage water directly from the western exploited area of Sector A (Figure 1). Following the eventual development of the southeast area of Sector A (after 2010), Site 3 will become influenced by harvesting. Data recorded at Site 3 will allow a comparison of the river characteristics before and after varying levels of harvesting activities. Three transects at 2 m intervals were established in each of the sites. Channel width was recorded and water depth was measured at five points along each transect. A water quality station equipped with an optical backscatterometer (OBS-3 or OBS-3+, D&A Instrument, Inc.) and a temperature sensor (8 bit Minilog TR 16K, Vemco) was installed at each site. The OBSs were moored vertically at mid-depth, with the emitter/receiver perpendicular to the flow. OBS were connected to a Campbell Scientific datalogger (CR10 or CR510) powered by batteries and solar panels. Water turbidity was recorded every 15 seconds and data loggers recorded hourly averages. OBS outputs © 2009 Canadian Water Resources Association

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Baie Sainte-Anne Sector B

Sector A

Miramichi estuary

Exploitation zone

Exploitation zone

East Branch Portage River

Sedimentation pond

Site 1

Site 2

Site 3

Portage River

Site CANADA

500 m

N

Figure 1. Location of the peat harvesting sectors and location of the study sites (1 to 3) established in the East Branch Portage River. The buffer zone represents the undisturbed peatland located between the sedimentation pond and the East Branch Portage River. Map modified with permission from Jacques Thibault, New Brunswick Department of Natural Resources, September 2008.

were expressed as DC voltages and were converted to SSC (mg/L) using calibration curves. The calibration for each OBS was performed using the methodology described by Pavey et al. (2007). In addition, hourly flow measurements were recorded at Site 1. Water levels were recorded using a pressure transducer (Keller model 173-L, Pressure System Inc.). A rating curve was used to calculate discharge from instantaneous flow measurements taken at different river stages using a flow meter (Flo-Mate model 2000, Marsh- McBirney Inc.). Water velocities measured near the OBS were relatively low (0.01 to 34 cm/s). Some fouling is known to have

occurred. Regular (i.e., weekly during summer) site visits were conducted to clean the probes and any data that were suspected of being influenced by fouling were removed from the data time series. River discharge was also measured on three occasions at the outflow of the sedimentation pond to quantify the amount of drainage water being released into the buffer zone. The water quality station at Site 1 was operational two years prior to drainage of the exploited area (Phase 1; 2005–2006). All three stations were operational during the initial peatland development (Phase 2; 2007). Daily operations at the peatland were recorded by the developer. © 2009 Canadian Water Resources Association


The main activities in 2007 included the construction of the primary and secondary channels (ditching), drainage of the surface water and land preparation (vegetation removal, tilling, and harrowing). Annual electrofishing surveys (4 October, 2006 and 18 September, 2007) were conducted at two sites (E1 and E2) which were located 200 m and 75 m downstream of Site 1, respectively (Figure 1). Two sites (E3 and E4) were electrofished near Site 2 and Site 3 in 2007 (Figure 1). Site E3 was located 10 m downstream of Site 2 whereas Site E4 was located 5 m upstream of Site 3. Sites E1 and E2 were chosen to include different habitat types (i.e., riffle, flat, and pool). Sites E3 and E4 were located in the peatland and these sites were of a relatively homogenous flat habitat type. All electrofishing sites were 50 m in length and were fished from bank to bank. Electrofishing was conducted in an upstream direction using the CatchPer-Unit-Effort technique (CPUE) (Hayes and Baird, 1994). The effort was quantified in terms of the amount of time the electrical current was applied to the water. A Smith-Root Model LR-24 backpack electrofisher was used. The voltage output settings varied between 350 and 500 volts (depending on water conductivity). The pulse frequency was 60 Hz with a 36% duty-cycle. Following capture and enumeration, fish were then released back into the site.

Results Site Characteristics and Water Temperature

Site characteristics and water temperatures are presented in Table 1. Only small variations in the

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water temperature regime were observed between years and sites. For example, mean water temperature (± SD) at Site 1 varied from 15.5 ± 3.01°C (2007) to 17.1 ± 3.36°C (2005), during a concomitant period (9 July to 12 October 12, 2005–2007). In 2007, water temperatures were recorded at all sites from May 8 to November 14. A difference in mean water temperature (± SD) of only 1°C was observed for Site 1 (14.4 ± 5.07°C) compared to Site 3 (13.5 ± 4.12°C). River Discharge and Suspended Sediment Concentrations

During the pre-development period (Phase 1, 2005– 2006), increases in river discharge (indicated by arrows in Figure 2) were frequently associated with an initial increase in SSC, followed by lower SSC. This was probably a result of a dilution effect and the exhaustion of sediment supplies (see Tramblay, 2009). However, increases in SSC were not systematically associated with increases in discharge (e.g., 16 August and 19 August, 2005; 22 June and 26 June, 2006; Figure 2). In 2006, increases in SSC were recorded during a 25-day period of low flow (6 September to 1 October, 2006; Figure 2b). Similar to the pre-development period, increases in SSC followed by lower SSC were observed at Site 1, particularly after 9 October, 2007 (Figure 3a). However, the SSC time series clearly shows that Site 2 (Figure 3b) had a higher frequency of elevated SSC events (> 100 mg/L) compared to Site 1 and Site 3 (Figures 3a and 3c, respectively). In early May 2007 (Phase 2; peatland development), drainage water exiting the sedimentation pond concentrated into a natural depression (channel width:

Table 1. Site characteristics and mean daily water temperature measured during a concomitant period in the East Branch Portage River. Mean water temperatures at Site 1 are compared between years (2005–2007) during a concomitant period (Period 1 (P1): 9 July to 12 October, 2005–2007) and between sites in 2007 (Period 2 (P2): 8 May to 14 November, 2007). NA: Not applicable. Site

1 2 3

Channel Width

Water Depth

Water Temperature ± SD (°C)

± SD (m)

± SD (m)

Year/Period

3.6 ± 1.01 1.8 ± 0.35 1.6 ± 0.33

0.49 ± 2.12 0.91 ± 0.64 0.6 ± 1.88

2005/P1

2006/P1

2007/P1

2007/P2

17.1 ± 3.36 NA NA

16.4 ± 3.95 NA NA

15.5 ± 3.01 NA NA

14.4 ± 5.07 13.8 ± 4.70 13.5 ± 4.12


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200 150

SSC (m g/ L)

0.7

SSC Discharge

Site 1 (2005)

175

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Figure 2. Hourly suspended sediment concentration (SSC) and river discharge recorded at Site 1 (2 km downstream of the exploited area) in 2005 (a) and 2006 (b) in the East Branch Portage River. The horizontal lines indicate the 25 mg/L threshold (New Brunswick’s guideline). Arrows indicate particularly high discharge events.

approximately 2–3 m) within the buffer zone instead of dispersing throughout the undisturbed peatland. A direct linkage between the sedimentation pond and the East Branch Portage River was therefore created. The drainage water discharged into the river, approximately 10 m upstream of Site 2. As a result, sediment transport occurred through the buffer zone. River discharge measured at the outflow of the sedimentation pond (9 May, 23 May and 7 June, 2007) varied between 0.01 to 0.02 m3/s. This discharge represented 11 to 20% of the main stream discharge measured at Site 1 during the same time period.

Based on the available information from the operational diary provided by the developer, most elevated SSC recorded at Site 2 can be associated with operational activities in the peatland, particularly to ditching (indicated by asterisks in Figure 3b). During high intensity of ditching activities ( July 724, 2007; Figure 3b), three events of increased river discharge occurred, although generally less than 0.2 m3/s (Figure 3a). This period coincided with the highest recorded SSC during the time series, with concentrations reaching 2090 to 2600 mg/L (Figure 3b). It should be noted, however, that these © 2009 Canadian Water Resources Association


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Figure 3. Hourly suspended sediment concentration (SSC) and river discharge recorded at a) Site 1 (2 km downstream of the exploitated area), b) SSC recorded at Site 2 (immediately downstream of the exploited area), and c) Site 3 (upstream of the exploitated area) in East Branch Portage River in 2007. The horizontal lines indicate the 25 mg/L threshold (New Brunswick’s guideline). Arrows indicate particularly high discharge events and asterisks indicate SSC events which could be associated with operational activities. © 2009 Canadian Water Resources Association

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maximum SSC values may have been overestimated due to peat accumulation on the OBS. Malfunction of the equipment at Site 1 prevented the determination of whether these elevated levels of SSC observed at Site 2 were localized or persisted over a distance of 2 km downstream of the exploited area (see interruption in SSC data from 9 July to 22 August, 2007; Figure 3a). The newly built sedimentation pond was observed to rapidly accumulate peat and mineral particles during ditching activities and was filled to almost capacity by July 2007. The pond was cleaned by the developer between 24 July and 1 August, 2007. Elevated SSC were nonetheless observed at Site 2 following the cleaning process (after 4 August, 2007; Figure 3b). It is also noteworthy that the increase in SSC observed at Site 2 (11 October and 7 November, 2007) could not be associated with operational activities but did coincide with increases in water discharge. High SSC values were also recorded at Site 1 and Site 3 during this period (Figures 3a and 3c). The percentage of time with SSC > 25 mg/L was computed during concomitant periods between years and sites. Exceedances at Site 1 varied from 3% in 2007 to 25% in 2006 (Table 2). When comparing the three sites sampled in 2007, exceedances varied from 5% at Site 3 to 25% at Site 2 (Table 3). Events of elevated SSC which occurred from 9 July to 22 August, 2007 at Site 2 were excluded from the data set because SSC were not recorded at Site 1 during this period (Figure 3a and 3b). When the entire time series was considered, exceedance of the New Brunswick guidelines was observed 36% of the time at Site 2 compared to 10% at Site 1 and 3% at Site 3. Table 2. Comparison among years (2005–2007) of percent time with suspended sediment concentration values in excess of the 25 mg/L threshold at Site 1 during concomitant period. Year

Sample Size

Percent Exceedance

(Hours)

2005 2006 2007

1249 1249 1249

4.32 24.50 2.56

Table 3. Comparison among sites of percent time with suspended sediment concentration values in excess of the 25 mg/L threshold during concomitant period in 2007. Site

Sample Size

Percent Exceedance

(Hours)

1 2 3

2513 2513 2513

9.83 24.55 4.78

Fish Abundance

Fish assemblages downstream of Site 1 (sites E1 and E2) were composed of brook trout (Salvelinus fontinalis), white sucker (Catostomus commersonii), lake chub (Couesius plumbeus), and brook stickleback (Culaea inconstans). No fish were captured in the electrofishing sites within the peatland (E3 and E4). Electrofishing was facilitated in 2007 (compared to 2006) by a lower amount of leaves within the stream. However, CatchPer-Unit-Effort, expressed as the number of fish captured during five minutes of electrofishing time, showed a sharp decline in fish relative abundance (sites E1 and E2 combined) in 2007 compared to the preharvest conditions in 2006 (Figure 4, paired t-test on log-transformed CPUE data, t = 3.42 and p = 0.048).

Discussion and Conclusion Results from the present study indicate that the sedimentation pond and the 250 m buffer zone were partially effective in retaining suspended sediment during the initial phase of peatland development at Sector A. These mitigation measures were not adequate to maintain the SSC below the New Brunswick guideline value of 25 mg/L. The inefficiency of the buffer zone to filter suspended sediment can be partially attributed to the concentration of flow in the natural depression within the buffer zone soon after the beginning of the drainage operations. This channel facilitated transport of sediment into the East Branch Portage River. Periods of elevated SSC observed at Site 2 in July 2007 could be attributed to poor maintenance of the sedimentation pond which rapidly filled with sediments. An increase in the frequency of © 2009 Canadian Water Resources Association


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CPUE (No. fish per 5 min.)

5

2006 2007

4 3 2 1 0

Brook trout

Lake chub

White sucker

Stickleback

Species

Figure 4. Mean Catch-Per-Unit-Effort (CPUE), expressed as number of fish captured per five minutes of electrofishing at sites E1 and E2 (n = 2) in 2006 and 2007. Vertical bars represent the standard deviation of the mean.

pond maintenance may be required during the early stages of peatland development. Nonetheless, events of elevated SSC were recorded at Site 2 in August 2007 (following pond maintenance). This suggests that elevated SSC were not only related to pond maintenance. During these events, high sediment loads were rather directly associated with ditching and subsequent drainage activities, which might have been amplified by increases in water discharge. Marttila and Kløve (2008) highlighted the influence of the presence of peat in the bottom of ditches. Rainfall events will induce higher sediment loads when channels are filled with deposited peat. In 2007, operational activities were occurring in 15% of the total area scheduled for harvesting (Premier Horticulture Ltd., 2000). As future operational activities progress towards the southeast area of the peatland and the East Branch Portage River, the amount of sediment loads discharged into the watercourse could increase. Other studies have shown that the 25 mg/L guideline can be exceeded more than 60% of the time in some harvested peatlands (e.g., St-Hilaire et al., 2006; Pavey et al., 2007). In this study, 25 mg/L was exceeded 36% of the time at the most impacted location (Site 2) in 2007 (entire time series considered). When comparing sites during concomitant periods in

2007, SSC exceeded 25 mg/L during 25% of the time at Site 2. The frequency of exceedance at Site 2 was three times higher than Site 1 and four times higher than Site 3. Although the percentage of exceedance observed at Site 2 was lower than previously recorded elsewhere (St-Hilaire et al., 2006; Pavey et al., 2007), accumulation of peat on the streambed at Site 2 was nevertheless noticeable. Such accumulations were not observed at Site 1 and Site 3. The low percentage of exceedance observed at Site 1 in 2007 suggests that the impacts from the peatland operations were localized. Most of the sediment transport occurred over a short distance (< 2 km) and deposition most likely occurred within the marsh located between sites 1 and 2. However, malfunction of OBS equipment at Site 1 during the highest SSC events recorded at Site 2 precluded the determination of whether elevated SSC observed at Site 2 could be detected at Site 1. The low percentage of exceedance observed at Site 3 also indicates that upstream harvesting operations conducted in Sector B caused negligible impacts at that study site. Suspended sediment concentrations measured at Site 1 during the pre-operational phase (2005–2006) also confirmed that a relatively undisturbed river can still exceed the 25 mg/L guideline. A 4% exceedance © 2009 Canadian Water Resources Association

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was observed in 2005 but the percentage of exceedance reached 25% in 2006. The higher percentage of exceedance in 2006 can be attributed to elevated SSC recorded during a period of low flow which persisted over a period of 25 days.The exact cause of these increases in SSC remains unknown. However, sediments could have originated from the marsh located immediately upstream of Site 1 and the increased SSC values could have resulted from a reduction in the dilution effect by lower discharge. It is not uncommon to observe SSC values exceeding 25 mg/L in streams draining from natural peatland. For example, Pavey et al. (2007) showed that 25 mg/L was exceeded 30% of the time in this type of environment. Determining the causes of the decline in fish abundance observed in 2007 requires further investigation. The decline could be attributed to operational activities within Sector A or to natural fish abundance fluctuations. Except for a few isolated events of elevated SSC measured at Site 1 (located near fish habitats) in 2007, low SSC (< 25 mg/L) measured at this site suggests that the decline in fish abundance was not attributed to suspended sediment. Furthermore, juvenile fish generally seek refugias during elevated SSC events (see Newcombe and Jensen (1996) for a review). However, the level of impact is influenced by the duration of exposure to sediments and life stage (e.g., embryos survival in substrate during the incubation period). Water quality parameters other than suspended sediment (e.g., water chemistry) may have impacted fish abundance in this study. However, to determine a causal effect of peatland development on fish, comparison with abundance in natural stream would be required. Available data from other electrofishing surveys of nearby, undisturbed streams were not comparable to this study because these surveys focused on the determination of juvenile Atlantic salmon abundance. These surveys were mainly conducted in riffle habitat type (prime habitat for juvenile Atlantic salmon) as opposed to the inclusion of all available habitat types in this study. However, a new program was established in 2007 by the province of New Brunswick to monitor fish community abundance and composition in diverse habitat types. This new electrofishing program may allow comparison with fish abundance fluctuations in the East Branch Portage River in future years. Annual electrofishing surveys will be continued and will provide further information on the interannual

variations of fish abundance in the East Branch Portage River. SédibacsTM (Bio Innove Inc.) have been installed in each electrofishing site since 2006 to estimate the sediment deposition rates and their potential effects on fish habitats. Furthermore, benthic macroinvertebrate samples have also been collected in two habitat types (pool and riffle) in each electrofishing site since 2006. The analysis of the macroinvertebrate assemblages will eventually provide further information regarding the potential impacts of peat harvesting on aquatic biota. Additional data are also being collected (e.g., total and dissolved metals, major ions, nitrates, phosphorous, pH, conductivity, color, Biological oxygen demand, etc.) by Environment Canada. These analyses will also contribute to a better understanding of the impacts of harvesting on the riverine ecosystem. River thermal regime is an important fish habitat component (see for example Caissie, 2006). Only small variations in water temperature were observed among sites and years in this study. However, future expansion of the peatland exploited area may induce changes to the water temperature regime. With such a wide range of data being collected, it is expected that the necessary information will be available in the near future to assess the efficacy of current guidelines in New Brunswick and provide information for the improvement of mitigation measures. The present study, conducted on a gauged river basin and draining from peatland, will ultimately contribute to a better understanding of peatland hydrology. This information is essential in the development of predictive modelling tools for ungauged basins to assess potential environmental impacts of peatland harvesting. Most hydrological models were not developed for peatland environment ( Jutras et al., this issue). However, hydrological models such as PHIM could be coupled to sediment transport models to generate scenarios of sediment loads downstream of exploited peatland. Such combined tools would also be useful in improving the design of sedimentation ponds to minimize the impacts on fish and aquatic habitats. One of the challenges facing model developers within peatland environments is that most models with sediment yield components (e.g., models such as SWAT, Arnold and Fohrer, 2005) were developed for inorganic particles. The applicability of these models for organic matter, such as peat particles, will have to be tested in future work. © 2009 Canadian Water Resources Association


Acknowledgements This research was supported by the New Brunswick Wildlife Trust Fund, programme de coopération universitaire en enseignement supérieur et recherche Québec/Nouveau Brunswick, and NSERC. The contribution of Premier Horticulture Ltd. is also acknowledged. We would like to thank Jacques Thibault from the New Brunswick Department of Natural Resources for his advice throughout this project and for providing comments on an initial draft of this manuscript. Special thanks are also expressed to Sylvie Robichaud for her assistance in the field and data management.

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