Northeastern Naturalist 222 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 22001188 NORTHEASTERN NATURALIST 2V5(o2l). :2252,2 N–2o3. 52 Impacts of Recreational Flow Releases on Macroinvertebrate Drift at Different Distances Downstream from Abanakee Dam, New York Randall L. Fuller1,*, Jaime Dennison1, Gretchen Swarr1, Kelli Weichert1, Carrie Griego1, and Martin W. Doyle2 Abstract - We examined macroinvertebrate drift at 4 sites downstream of Abanakee Dam on the Indian River, NY, on separate days at base-flow conditions and following days during recreational releases (rapid releases supporting white-water rafting enterprises). Macroinvertebrate drift rates were highest near the dam due to high numbers of drifting Simuliidae at both base flow and during a release. At the other 3 sites, Simuliidae were less abundant in the drift, and Chironomidae and Sphaeriidae had especially high drift densities during a release, suggesting a greater vulnerability to catastrophic drift. Macroinvertebrate drift was not affected by differences in stream gradients or shear forces that did differ between sites. Our drift densities during the recreational releases were higher than observations from other studies during natural floods, suggesting greater drift vulnerability to rapid increases (~15 min) in discharge when flood gates are opened. Introduction Invertebrate drift is an ecologically significant, fundamental process, critical to the maintenance of benthic invertebrate populations and a key mechanism of resource delivery to drift-feeding fishes (Brittain and Eikeland 1988). The propensity of stream macroinvertebrates to voluntarily enter the water column and drift downstream was first termed “behavioral drift” after studies showed an increase in drift of macroinvertebrates after sunset and a cessation of drift post sunrise (Waters 1972). Various studies have identified mechanisms that might explain this periodicity. Flecker (1992) observed a clear diel periodicity in streams where fish were present; however, in upstream sections that were fishless, invertebrate drift was aperiodic. Other studies have observed similar drift patterns of mayflies and caddisflies in the presence of fish (Huhta et al. 1999, 2000; McIntosh et al. 2002) and invertebrate predators (Huhta et al. 1999; Malmqvist and Sjostrom 1987; Peckarsky 1980, 1986). In contrast, catastrophic macroinvertebrate drift occurs when natural floods increase discharge and higher shear forces on substrata cause involuntary drift (Crisp and Robson 1979; Gibbins et al. 2007, 2010; Hay et al. 2008; Perry and Perry 1986). Perry and Perry (1986) observed an increase in drifting invertebrates as velocity increased in experimental streams, especially when velocities were rapidly 1Biology Department, Colgate University, Hamilton, NY 13346. 2Nicholas School of the Environment, Duke University, Durham, NC 27708. Corresponding author - rfuller@colgate.edu. Manuscript Editor: Thomas Maier Northeastern Naturalist Vol. 25, No. 2 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 223 increased. Other studies have focused on macroinvertebrate drift rates that increase when bed sediments were mobilized during a flood, resulting in catastrophic drift (Brittain and Eikeland 1988; Bruno et al. 2016; Gibbins et al. 2005, 2007, 2010). Gibbins et al. (2007), using portable flumes in a natural stream, observed that drift remained low until velocities increased to the point that sediment was mobilized; at which point, invertebrate drift increased markedly, suggesting that increased drift during a flood likely results from some degree of bed movement. Most of the rivers in the northern hemisphere (>75%) possess some type of dam, with flow regulated in some form (Dynesius and Nilsson 1994, Nilsson et al. 2005, Poff et al. 2007). Dams store water, and many alpine river dams are operated with an emphasis on hydropower generation (Meile et al. 2010), while dams on other rivers may be managed for inland navigation, flood control, or to provide water for irrigation or water supplies for cities (Poff et al. 2007). All dams alter the flow regime and thermal regime, trap sediments, and impact macroinvertebrate composition, although to varying degrees, depending on the size and type of dam (Bunn and Arthington 2002, Poff et al. 1997, Tonkin and Death 2013). Hydropower facilities release water to generate electricity during peak periods of demand, and these hydropeaking events cause frequent floods that disrupt both the thermal and hydrologic regime (Bruno et al. 2013). Flood-control dams store peak flows and release more consistent flows over extended periods of time, while irrigation dams divert water for agriculture, and thus reduce flows downstream and increase temperatures (Rosenburg et al. 2000). Some dams also facilitate recreational activities, such as white-water rafting or kayaking, through rapid releases of water from dams that increase discharge to usually bank-full conditions. Regardless of their purposes, dam releases increase discharge, resulting in greater sediment transport, and potential increase in bed movement, changes in channel morphology, and macroinvertebrate drift (Castro et al. 2013, Holt et al. 2015, Kennedy et al. 2014). Flows from dam releases can be quite different from those that are caused by natural runoff events. Natural floods typically have a slower rising limb and falling limb, as compared to the abrupt rise and fall of flow releases from dams. Such gradual flow changes from natural floods may allow macroinvertebrates more time to seek refuge from higher shear stresses as discharge increases; however, during hydropeaking and recreational releases, the increase in discharge is more abrupt and the potential for increased catastrophic drift by macroinvertebrates is much greater (McKinney et al. 2009, Perry and Perry 1986). Some macroinvertebrate groups are better adapted for high shear-stress environments, and studies in frequently flooded rivers have shown shifts in taxonomic composition favoring species with adaptations that make them more resistant to high shear stresses (small body size or greater clinging abilities) or more resilient to flood-type disturbances (increased swimming abilities or shorter life cycles) (Jakob et al. 2003, Townsend and Hildrew 1994, Townsend et al. 1997). Both natural and dam-release floods create flow forces that differ longitudinally along an upstream–downstream gradient, with kinematic waves that can extend for hundreds of kilometers (Kennedy et al. 2016, Weile and Smith 1996). Northeastern Naturalist 224 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 Vol. 25, No. 2 Several macroinvertebrate drift studies have been done downstream of dams during experimental floods (Jakob et al. 2003, Shannon et al. 2001, Valdez et al. 2001). Jakob et al. (2003) observed high drift rates during experimental releases from a dam on an alpine river, but they did not observe any cumulative increase in macroinvertebrate drift density with increasing distance from the dam. Studies on distances traveled by drifting macroinvertebrates suggest distances as short as 1–3 m at velocities less than 10 cm/s, to distances of 5–10 m at higher velocities (Elliott 2002). Still other studies suggest drift distances of 10–40 m, depending on the taxa and discharge (Elliott 1968, Holomuzki and Van Loan 2002). Therefore, one may not observe increased drift of benthic invertebrates at increasing distances from a dam during experimental floods if the distances traveled are relatively short (less than 50 m). Our objectives were to examine invertebrate drift patterns at 4 sites downstream of Abanakee Dam on the Indian River on sequential days at base-flow conditions, and then the following day during a recreational-flow release. Our design allows a comparison across sites similar to Jakob et al. (2003) to further confirm or refute any potential increase in drift density with distance downstream during dam releases. Also, the geomorphology along a 4.5-km stretch of the Indian River varied with sites having either steeper gradients and narrow channel widths or lower gradients and wider channels. Thus, we sought to compare drift densities among dominant taxa and their relative vulnerability to catastrophic drift during releases and among sites because of their differences in geomorphology. Methods Study site The study was conducted below Abanakee Dam on the Indian River in the Adirondack Mountains, NY (Fig. 1). Abanakee Dam releases water from Abanakee Lake to the Indian River 4 d wk-1 from April to October, increasing discharge from base flows of 3–5 m3 s-1 to 35–45 m3 s-1 during a recreational release (duration: 1.5–2.0 h; Fig. 2). Discharge during flow releases was either at or slightly above bank-full discharge. The segment of the Indian River from the Abanakee Dam to the confluence with the Hudson River had 3 distinct geomorphic reaches. We studied a total of 4 sites with different geomorphic and hydraulic characteristics (Fig. 1). Site 1 was ~500 m downstream from the dam, below a steeply incised gorge and ~4 m waterfall; substrata consisted of boulders and cobbles. Site 2 was 1.5 km downstream from the dam where the river channel narrowed (27 m), with a cobble–boulder-dominated substrata. Site 3 was 3 km from the dam where the channel widened (55 m), and the substrata consisted of mostly cobbles, pebbles, sand, and scattered boulders. Site 4 was 4 km downstream of the dam where the valley walls narrowed, as did the river channel (31 m), and the substrata was again dominated by boulders. The study sites were sampled at base flow on 19 July and 2 August 2006, and during a release on 20 July and 3 August 2006, respectively. Northeastern Naturalist Vol. 25, No. 2 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 225 Field methods Geomorphology and hydraulic measurement. We conducted cross-sectional surveys and longitudinal profiles at each of the sites at base-flow conditions during July 2006 to develop simple hydraulic models using standard survey and analysis techniques (Harrelson et al. 1994). We used high-water marks scoured during flow releases and resurveyed longitudinal profiles of these high-water marks to quantify Figure 1. Map showing 4 site locations downstream of Abanakee Dam on the Indian River, Adirondack Park, NY. Images depict typical flow conditions below Abanakee Dam at base flow and during a regulated release. Northeastern Naturalist 226 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 Vol. 25, No. 2 flow conditions during the flow releases. Using these depth profiles and the cross sectional and longitudinal surveys we could quantify shear stress at low and high flows, as: τ = γRS, Where τ is the shear stress exerted on the channel boundary, γ is the unit weight of water, R is the hydraulic radius, and S is the energy grade slope, assumed here to be the slope of the water surface profile. Bed mobilization and other scouring of the channel boundary (e.g., periphyton removal) is a function of shear stress, making this a primary independent variable for assessing the ef fect of flow releases. In addition, we calculated the Froude number (Fr), which is a non-dimensional hydraulic variable that has been used to characterize hydraulic habitat characteristics: Fr = (U / √gD), where U is velocity of flow, g is acceleration due to gravity, and D is depth of flow. Macroinvertebrate drift sampling. At base-flow conditions, we placed 5 drift nets (mesh size = 363 μm, area = 1350 cm2) equidistant along a transect across each river site between 10:00 am and 12:00 pm. We left the nets in the river for 10–30 min, depending on the amount of organic matter collecting in the nets. Duration of sampling time at a site was dependent on clogging of nets by algal and other debris accumulating in nets. We recorded the current velocity at the opening of each net using a Marsh McBierney Model 2000 current velocity meter. We used the area of net opening, velocity at net opening, and duration of drift sample to determine volume of water filtered for each drift net at each site. During a release, we held a drift net in the river for 2 min (~2 m from the shoreline for safety reasons); we collected 5 samples at each site using this procedure during a release. Shorter times were necessary during a release because of rapid clogging of nets due to accumulation of ___ Figure 2. Example of Indian River hydrograph for 1 July to 1 September 2006 showing instantaneous discharge calculated using stage height obtained from USGS Water Resources website (https://waterdata.usgs.gov/nwis/inventory/?site_no=01315080&agency_ cd=USGS). Northeastern Naturalist Vol. 25, No. 2 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 227 sloughed algal mats and other organic debris. We measured current velocities at the same point in the river where samples were taken during a release to calculate volumes filtered, thus allowing calculation of numbers of individuals per unit volume of water filtered by each net for samples taken during a release. All drift samples were preserved in glass jars with 5% formalin solution. Laboratory methods We filtered drift samples through a 250-μm mesh sieve and placed the collected material in a basin, where we removed all macroinvertebrates from the organic matter and stored them in 80% ethanol for quantification and identification to the lowest taxonomic level possible (usually genus or subfamily for Chironomidae). Statistical analyses We used a 2-way ANOVA to compare drift density of each macroinvertebrate taxon across flow conditions and sites after we conducted tests to confirm data were normally distributed and had equal variances. When we found significant differences among sites, we used a Tukey pairwise comparison to determine differences in drift densities between sites (α = 0.05) (JMP 10.0 Statistical Software). Results Geomorphology and hydraulic conditions Site 1 had an intermediate slope and channel width which combined to increase shear stress and Froude numbers, both of which were slightly elevated at this site (Table 1). Site 2 also had a narrow channel width, with similarly elevated shear stress and Froude numbers, despite the slope decreasing slightly. Site 3 had a much wider channel and lower slope, resulting in the lowest shear stress and Froude numbers. At Site 4, channel width again narrowed, the slope increased, and hydraulic conditions again shifted toward high shear stress and Froude numbers. Macroinvertebrate drift We collected over 6000 macroinvertebrates in our drift samples, with slightly more than half occurring in drift samples taken during base-flow conditions. At base-flow conditions, Diptera accounted for 84% of all drifting macroinvertebrates, with Simuliidae comprising >37%; most of these (>80%) were drifting at Site 1. Table 1. Geomorphic features of 4 sites below Abanakee Dam on the Indian River, NY, July 2006. Feature of site Site 1 Site 2 Site 3 Site 4 Distance from dam (km) 0.5 1.5 3 4.5 Width of channel (m) 45 27 55 31 Slope (m/m) 0.0153 0.0105 0.0013 0.011 Froude number Base flow 0.59 0.51 0.21 0.51 During release 0.73 0.63 - 0.62 Shear stress at base flow (N m -2) - 25.04 4.04 31.73 Shear stress during release (N m-2) - 112.29 79.43 69.33 Northeastern Naturalist 228 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 Vol. 25, No. 2 Chironomidae were the other major dipteran group in the drift (>45% at base flow); especially abundant during a release (>55%). Sphaeriidae molluscs also were found drifting in higher numbers during a release (>12%) than at base flow (less than 4%) and they were most common at sites 2, 3, and 4, but were rare in the drift at Site 1. Ephemeroptera, Plecoptera, and Trichoptera were much less abundant in the drift than other taxa (~10% at base flow, less than 6% during a release). We pooled drift samples taken on different dates when a 2-way ANOVA (dates with similar flow conditions versus sites) showed no significant differences in drift densities (P > 0.52, F[base flow] = 0.422; P > 0.12, F[during release] = 2.61) between dates with similar flow conditions; drifting Simuliidae larvae at Site 4 during a release did have a significantly higher drift density (P < 0.05) in late July versus early August samples, but we still pooled these 2 samples for both dates with similar flow conditions for consistency and accepted the greater variability that was introduced for this macroinvertebrate category. Total macroinvertebrate drift density was significantly different among sites (F3,72 = 6.98, P < 0.001) and flow conditions (F1,72 = 31.85, P < 0.003), with no significant interaction (F3,72 = 3.58, P < 0.060) among sites and flow conditions (Table 2). Comparisons among sites showed that Site 1 had higher drift densities at base-flow conditions (F3,36 = 21.42, P < 0.001) than all other sites, but there were no differences in drift density among sites during a release (F3,36 = 1.52, P = 0.227; Table 3, Fig. 3). A similar pattern was observed for Simuliidae, with significant differences in drift density among sites (F3,72 = 37.51, P < 0.001), but not for flow conditions (F1,72 = 0.98, P = 0.325) and there was no significant interaction (F3,72 = 2.06, P = 0.113; Table 2). Comparisons of Simuliidae drift density among sites showed higher drift densities at both base flow and during Table 2. Summary of 2-way ANOVA results comparing across sites and flow conditions for pooled dates (base flow: 19 July and 2 August 2006; during a release: 20 July and 3 August 2006) for each taxonomic category. F df P Total macroinvertebrate drift Site 6.98 3 less than 0.003 Flow conditions 31.85 1 less than 0.001 Site x flow conditions 3.58 3 0.060 Simuliidae drift Site 37.51 3 less than 0.001 Flow conditions 0.98 1 0.325 Site x flow conditions 2.06 3 0.113 Other Diptera drift Site 1.73 3 0.169 Flow conditions 48.80 1 less than 0.001 Site x flow conditions 0.83 3 0.633 Sphaeriidae drift Site 6.93 3 less than 0.001 Flow conditions 58.73 1 less than 0.001 Site x flow conditions 6.78 3 < 0.001 Northeastern Naturalist Vol. 25, No. 2 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 229 a release at Site 1, and significantly lower Simuliidae drift densities at all other sites, at both base flow and during a release (Tables 2, 3; Fig. 3). Drift densities for “other Diptera” (i.e., a category designation in this study, excluding Simuliidae; >80% were Chironomidae, but also included Tipulidae, Athericidae, and Tabanidae) were significantly higher during a release, than at base flow (F1,72 = 48.80, P < 0.001), but there was no difference among sites (F3,72 = 1.73, P = 0.169) and no significant interaction between site and flow conditions (F3,72 = 0.83, P = 0.633) (Fig. 4). Sphaeriidae mollusk drift densities were significantly different among sites (F3,72 = 6.93, P < 0.001) and flow conditions (F1,72 = 58.73, P < 0.001), with significant interaction between site and flow conditions (F3,72 = 6.78, P < 0.001; Table 2). Sphaeriidae drift densities at base flow were low and similar among all sites (Fig. 4); however, during a release their drift density was low at Site 1, but significantly higher at all other sites (which were similar; P > 0.05; Table 3). Discussion Total macroinvertebrate drift densities below Abanakee Dam increased during rapid releases versus base-flow conditions at sites 2, 3, and 4. At Site 1, however, differences in total macroinvertebrate drift were not detected, regardless of flow conditions, primarily because Simuliidae comprised 80% of the total macroinvertebrate drift at this site, potentially masking any differences. High densities of Simuliidae have been observed below Abanakee Dam (Baldigo and Smith 2012), and this group is known to compete for space by displacing individuals (Hart 1986); thus, outlet drift densities of Simuliidae may have been high at base flow due to interspecific interactions for space that displace larvae, resulting in high drift densities, regardless of flow conditions. Diptera other than Simuliidae (>80% Chironomidae) had a 3-fold higher drift density during a release than at base flow at all 4 sites, suggesting that they were more vulnerable to the higher velocities and shear stresses during a release. Other studies have also shown Chironomidae to dominate the drift at base flow (Tonkin and Death 2013), during natural floods (Hieber et al. 2003), and during regulated releases (Bruno et al. 2013, 2016; Perry Table 3. Summaries of 1-way ANOVA comparisons followed by Tukey pairwise comparisons when significant differences were found among sites in the 2-way ANOVAs. Different letters among sites indicate significantly different drift densities. Site comparisons F df P 1 2 3 4 Across sites at base flow conditions Total macroinvertebrates 21.42 3 less than 0.001 A B B B Simuliidae 19.27 3 less than 0.001 A B B B Sphaeriidae 0.812 3 0.495 Across sites during a release Total macroinvertebrates 1.52 3 0.227 Simuliidae 4.71 3 0.007 A B B B Sphaeriidae 12.42 3 less than 0.001 A B B B Northeastern Naturalist 230 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 Vol. 25, No. 2 and Perry 1986). Also, their higher drift densities during a release may be related to the sloughing of algal mats that commonly occurs during such releases (Fuller et al. 2011), often rapidly clogging drift nets, as similarly observed in other studies Figure 3. Mean drift densities of total macroinvertebrates and Simuliidae at base flow and during a regulated release at 4 sites on the Indian River, Adirondack Mountains, NY, from July to August 2006. During a release, total macroinvertebrate drift is significantly higher at Sites 2, 3, and 4; Simulliidae drift is significantly higher at Site 1 versus all other sites. (Lines at the top of bars are +1 SE.) Northeastern Naturalist Vol. 25, No. 2 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 231 during high flow periods (Allan 1995, Gibbins et al. 2007). Sphaeriidae molluscs had the same drift pattern as Chironomidae for sites 2, 3, and 4, with higher drift densities during a release versus lower drift densities at base-flow conditions. Numbers of drifting Sphaeriidae at Site 1 were very low at all flow conditions, suggesting this group had low benthic densities at this site. Figure 4. Mean drift densities of other Diptera (excluding Simuliidae) and Sphaeriidae at base flow and during a regulated release at 4 sites on the Indian River, Adirondack Mountains, NY, from July to August 2006. During a release, other Diptera drift is significantly higher at all sites and Sphaeriidae drift is significantly higher at sites 2, 3, and 4. (Lines at the top of bars are +1 SE.) Northeastern Naturalist 232 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 Vol. 25, No. 2 Our drift densities were higher (~1000 individuals/m3) than densities observed in other studies during both natural flood conditions (Brittain and Eikelund 1988) and regulated releases (Hieber et al. 2003, Jakob et al. 2003, Perry and Perry 1986). These higher drift densities may have been related to the steep nature of the rising limb of the hydrograph during releases below Abanakee Dam. Most natural floods have a rising limb that progresses over a period of hours, whereas the increase to bank-full flood stage below Abanakee Dam occurs much more quickly (~15 min; Fig. 2). Imbert and Perry (2000) showed that abrupt increases in discharge (typical of our releases) result in much higher drift rates for some macroinvertebrates (e.g., for our study, Chironomidae and/or Sphaeriidae). Thus, it seems Chironomidae and Sphaeriidae are more vulnerable to catastrophic drift during both natural flooding events and those created by recreational flow releases. We did not observe an increase in macroinvertebrate drift at sites with higher reach-level gradients or higher shear stresses. Sites 1, 2, and 4 had higher shear stresses and steeper gradients than Site 3, but this did not affect drift densities, suggesting reach-level shear stress alone does not determine drift density in the Indian River. While other studies have shown increases in drift with increases in velocity and shear forces that mobilize substrata (Gibbins et al. 2005), the substrata at our high shear-stress sites were dominated by large cobbles and boulders, creating a static mosaic of heavily armored substrates (Fuller et al. 2011), different from the shifting mosaic typical of substrata in many rivers during a flood (Lancaster and Hildrew 1993a, b). We also did not observe an increase in macroinvertebrate drift with distance downstream from the dam. Drift distances are usually less than 100 m, so we would not expect to see a cumulative increase in drift with distance from the dam (Ciborowski 1987). Because our drift samples during a release were collected close to the shoreline (~2 m from shore), this may create a sampling bias. However, Jakob et al. (2003) studied downstream drift during and after experimental floods in an alpine Swiss river and also saw no increase in macroinvertebrate drift with distance from the dam, but they did observe large numbers of stream macroinvertebrates that settled into trays set out on flood plains after water levels began to recede. While we did not examine loss of macroinvertebrates due to such strandings, there was no indication of lower macroinvertebrate abundance resulting from the frequent floods. Fuller et al. (2011) observed higher densities of benthic macroinvertebrates in the Indian River (at Site 3) versus 3 other Adirondack Mountain rivers not experiencing recreational releases, suggesting there was no significant negative impact on benthic macroinvertebrate densities from frequent floods. It should be noted, however, that benthic macroinvertebrate diversity in the Indian River was lower than in other local rivers (Fuller et al. 2011), with the community in the Indian River being dominated by swimming or clinging Ephemeroptera, Trichoptera, and Plecoptera. The net-spinning Trichoptera, as well as the clinging Ephemerellidae and swimming baetid mayflies were likely better adapted to the frequent flooding regime, which might explain their relatively low numbers in the drift compared to dipteran and sphaeriid drift densities Northeastern Naturalist Vol. 25, No. 2 R.L. Fuller, J. Dennison, G. Swarr, K. Weichert, C. Griego, and M.W. Doyle 2018 233 during releases. Since our drift densities were higher than what has been observed during natural floods, it is important for resource managers to consider gradually increasing discharge during recreational flow releases to reduce potential catastrophic drift of some macroinvertebrate taxa (e.g., Chironomidae, Sphaeriidae). 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