- Email: [email protected]
Ecological evaluation of weir removal based on physical habitat simulations for macroinvertebrate community
Ecological Engineering 138 (2019) 362–373
Contents lists available at ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Ecological evaluation of weir removal based on physical habitat simulations for macroinvertebrate community
T
⁎
Seung Ki Kim, Sung-Uk Choi
Department of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Republic of Korea
A R T I C LE I N FO
A B S T R A C T
Keywords: Weir removal Macroinvertebrate Physical habitat simulation Functional habit group Habitat suitability curve
In Korea, rapid urbanization has changed the land use in rural areas, which has resulted in an increase in the number of weirs that are left untended in streams. Previously, changes in stream morphology and fishes were studied following the removal of such weirs. The present study was conducted to investigate changes in the habitat of the macroinvertebrate community after weir removal using physical habitat simulations (PHSs). The functional group approach was used in the PHSs for the macroinvertebrate community. In the functional group approach, macroinvertebrates are classified based on the traits of their food acquisition (i.e., the functional feeding group) or habitat selection (i.e., the functional habit group). In the present study, macroinvertebrate species were divided into the functional habit groups (FHGs) of swimmers, clingers, burrowers, and sprawlers. Hydraulic simulations and habitat simulations were carried out using the River2D model and habitat suitability curves (HSCs), respectively. The distributions of the composite suitability index (CSI) for the FHGs were obtained over the entire study area, and the changes in the suitability of the habitat for the target FHGs were evaluated. The simulation results indicated that habitat suitability for swimmers, clingers, and sprawlers was improved. However, habitat suitability for burrowers was degraded after the weir was removed. Consequently, the removal of the weir increased the diversity of the macroinvertebrate community, thus improving the health of the aquatic ecosystem.
1. Introduction The construction of instream barriers, such as dams and weirs, results in significant changes in stream environments. That is, sediment deposition takes place in the increased water depth and the decreased velocity upstream of the barrier. However, in the downstream reach, the bed experiences degradation with coarsening sediment particles (Brandt, 2000). Dams and weirs affect not only these hydraulic variables but also the habitats of fish and macroinvertebrates. In addition, instream barriers obstruct the longitudinal movements of these aquatic organisms in feeding and spawning, which leads to decreases in their populations (Baxter, 1977; Larinier, 2001). Attempts have been made to restore degraded stream environments by removing dams and weirs that no longer serve their original purpose. It was reported that there are more than 90,000 dams in the US (US Army Corps of Engineers, 2018). Approximately 1300 dams have been removed since the early 20th century, 70% of which have been removed in 21st century. In Europe, at least 4000 dams and weirs have been removed since the mid-1990s (Gough et al., 2018). In Korea, there are about 34,000 weirs, including small dams. More than 3800 weirs
⁎
have been removed since the 1980s. Approximately 5900 weirs were reported to be out of service and left untended (Korea Rural Community Corporation, 2013). It was not until the 1980s that engineers paid attention to the morphological changes and effects on the habitats of aquatic animals after dams were removed (Bender, 1997). Removing instream barriers significantly contributes to stream restoration. Sediment particles deposited upstream of the barrier are flushed, and a portion of them are deposited on the degraded bed downstream of the barrier after its removal. Therefore, the discontinuity in the bed slopes upstream and downstream of the barrier disappears gradually, and the bed slope approaches the original slope before the barrier was constructed (Doyle et al., 2003). The improved river connectivity might restore the fragmented habitats of fishes and macroinvertebrates (Magilligan et al., 2016). Regarding fishes, the removal of barriers changes lentic habitats to lotic habitats upstream of the barrier, which are the habitats of native fishes (Kanehl et al., 1997; Catalano et al., 2007; Im et al., 2011) and increases the population of migratory fishes (De Leaniz, 2008). However, the knowledge about the effects of barrier removal on the macroinvertebrate community is limited.
Corresponding author. E-mail addresses: [email protected] (S.K. Kim), [email protected] (S.-U. Choi).
https://doi.org/10.1016/j.ecoleng.2019.08.003 Received 25 March 2019; Received in revised form 30 July 2019; Accepted 5 August 2019 Available online 12 August 2019 0925-8574/ © 2019 Elsevier B.V. All rights reserved.
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 1. Study area.
Fig. 2. Change of the thalweg elevation.
decreased significantly downstream of the dam. In previous research, field observations have been conducted to demonstrate the changes in the macroinvertebrate assemblage after weir removal. However, compared with field observations, the habitat modeling approach provides a quantitative assessment of habitat quality following changes in physical habitats. In the literature, the modeling for fish habitat (Im et al., 2011; Im et al., 2019) has been conducted, whereas no previous study has focused on the habitat of macroinvertebrates. This study was conducted to investigate the impact of weir removal on the macroinvertebrate community using the physical habitat simulation (PHS). The novelty of the present study is a use of the functional group approach in the PHS, which is an efficient tool for simulating the entire macroinvertebrate community. The study area, which is about 0.6 km in length, is located in the Gongneung-cheon Stream in the Hangang River basin, Korea. In 2006, a weir that was located in the middle of the study area was removed. First, the macroinvertebrate community was divided into four functional habit groups (FHGs) based on the data collected in the Han-gang River basin. Then habitat suitability curves (HSCs) for the FHGs were constructed using field monitoring data collected in the Han-gang River basin. Finally, the PHSs were carried out. Composite suitability index (CSI) distributions and normalized weighted usable areas (WUAs) were determined before and after the weir was removed.
Previous studies confirmed that weir removal changes stream morphology and physical habitat variables, which results in changes in macroinvertebrate assemblages (Stanley et al., 2002; Thomson et al., 2005; Hansen and Hayes, 2012; Chiu et al., 2013). For example, Stanley et al. (2002) studied changes in the channel form and macroinvertebrate assemblages due to the removal of a low-head dam in the Baraboo River in Wisconsin in the US. Before the removal, they observed that lentic taxa, such as tubificid worms, and lotic taxa, such as net-spinning caddisflies, were dominant upstream and downstream of the dam, respectively. However, after the removal, they found that the dominant macroinvertebrate species changed from lentic assemblages to lotic assemblages upstream of the dam. Thomson et al. (2005) investigated the changes in macroinvertebrate assemblages after the removal of a small dam in the Manatawny Creek in Pennsylvania in the US. They observed that the dam removal induced the sedimentation of sand downstream of the dam. This sedimentation reduced the macroinvertebrate density downstream, and the downstream macroinvertebrate assemblages became similar to the upstream assemblages. Chiu et al. (2013) studied the short-term effects of the removal of a check dam on the density and richness of macroinvertebrates in the Dajia River in Taiwan. After the check dam was removed, sediment particles deposited upstream of the dam were transported and deposited in the downstream reach. They found that the density of the macroinvertebrates increased upstream but decreased downstream of the dam immediately after its removal. In addition, they observed that the macroinvertebrate richness decreased only slightly upstream but 363
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 3. Change of bed material before and after the weir removal.
2. Materials and methods
2.2. Monitoring data
2.1. Study area
2.2.1. Channel morphology and bed material Geomorphological surveys were carried out before and after the weir removal. Fig. 2 shows the longitudinal changes in the thalweg elevation before and after the weir removal. The bed elevation was greatly lowered upstream of the weir after it was removed. The maximum erosion of 0.8 m occurred at a location 35 m upstream from the weir. This is mainly because the increased shear stress caused the flushing of bed materials in the upstream reach of the weir (Choi et al., 2009). In the downstream reach, aggradation occurred with the maximum deposition of 0.4 m at a location 15 m downstream from the weir. The changes in the composition of the bed materials before and after the weir removal are shown in Fig. 3. The overall change indicates that the bed material was coarsened over the study area after the weir removal. Before the weir removal, sand comprised over 80% of the bed material immediately upstream of the weir because of the deposition of the fine sediment by the weir. After the weir removal, sand comprised less than 50% of the bed material at the same location. In the downstream reach of the weir, after the weir removal, coarse gravel and cobbles increased by 9.9–28.3% and 1.2–5.1%, respectively. Specifically, in the upstream reach, D15.8 , D50 , and D84.1 changed from 0.25, 0.48, and 1.83 mm to 0.62, 1.88, and 7.61 mm, respectively, and in the downstream reach, they changed from 0.39, 2.59, and 8.47 mm to 1.07,
The study area is a 0.6 km long reach located at the Gongneungcheon Stream, which is a tributary of the Han-gang River (Fig. 1). The total length and watershed area of the Gongneung-cheon Stream are 45.0 km and 253.1 km2, respectively. The bed slope of the Gongneungcheon Stream ranges between 0.00022 and 0.012. The study area is located in the upper reach of the Gongneung-cheon Stream and the average slope of the study reach is 0.0031 (Choi et al., 2009) The discharges of the drought flow (Q355 ), low flow (Q275 ), normal flow (Q185 ), and high flow (Q95 ) are 0.28, 0.51, 0.91, and 1.73 m3/s, respectively (Korea Institute of Construction Technology, 2008). Here, Qn denotes the average flow discharge, which is exceeded on n days of the year. Gongneung Weir-2 was located 0.58 km upstream from the confluence with the Sunyu-cheon Stream. The weir was built in the 1970s to supply the nearby area with irrigation water. The height, width, and length of the weir were 1.5 m, 75 m, and 8.8 m, respectively. However, the weir became redundant because the land use in the nearby area was changed. Following the agreement of the local government and nearby residents, the weir was removed completely on 14 April 2006.
364
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
and September 2006, which corresponded to before and after the weir removal, respectively. Before the weir removal, 10 and 33 species were observed among 111 and 2457 individuals in the upstream and downstream reaches, respectively. However, after the weir removal, the number of species changed to 17 and 32 among 187 and 4598 individuals in the upstream and downstream reaches, respectively (Kil, 2008). The sampling results revealed that the post-removal composition of the macroinvertebrate species had changed significantly. That is, before the removal, Chironomidae sp. 2 was the predominant macroinvertebrate species in the study area. They accounted for 58.6% and 52.2% of the total macroinvertebrate species in the upstream and downstream reaches of the weir, respectively. After the removal, Chironomidae sp. 2 was found to be predominant in the upstream reach, which accounted for 43.9% of the macroinvertebrate species. However, in the downstream reach, the predominant species was changed to Uracanthella rufa, followed by Baetis fuscatus, which accounted for 28.6% and 15.7% of the macroinvertebrate species, respectively (Kil, 2008). In the present study, the functional group approach was used to categorize the macroinvertebrate community. This approach was first introduced to evaluate or measure the diversity and composition of macroinvertebrate communities in the 1970s (Cummins 1973, 1974). In the functional group approach, two classification methods are used to categorize macroinvertebrates: the functional feeding group (FFG) and the functional habit group (FHG). The FFG is a method used to classify macroinvertebrates based on their food preference and feeding strategy. The FFG includes gatherers, filterers, herbivore-piercers, predators, scrapers, shredders, etc. (Merritt et al., 2002). The FHG is a method used to classify macroinvertebrates based on habitat characteristics, dwelling style, and adaptation strategy. The FHG includes skaters, swimmers, clingers, sprawlers, climbers, burrowers, etc. In this study, the FHG method was adopted. Fig. 4 shows the changes in the composition of the FHG before and after the weir removal. The observed swimmers included Baetis fuscatus, Baetis ursinus, etc. The clingers included Uracanthella rufa, Hydropsyche kozhantschikovi, etc. Examples of the observed burrowers were Chironomidae and Ephemera orientalis, and examples of the observed sprawlers were Caenis KUa and Mystacides KUa. In the upstream reach of the weir, burrowers accounted for 92.7% before the removal, which decreased to 68.4% after the removal. The number of sprawlers increased to 19.3%, and swimmers and clingers newly appeared, which accounted for 9.6% and 2.7%, respectively. In the downstream reach of the weir, the number of burrowers decreased drastically from 79.3% to 13.2%. In contrast, the number of swimmers increased from 0.9% to 27.9%. In addition, the number of clingers increased dramatically from 19.8% to 56.9%, and sprawlers newly appeared, which accounted for 2.0% after the removal.
Fig. 4. Changes of FHGs before and after the weir removal.
Table 1 Grouping macroinvertebrate species for constructing HSCs. Groups
Species
Swimmers Clingers
Baetis fuscatus, Baetis ursinus, Acentrella sibirica, Baetiella tubercularta Hydropsyche kozhantschikovi, Cheumatopsyche brevilineata, Epeorus pellucidus, Hydropsyche valvata Caenis KUa, Potamanthellus chinensis, Caenis nishinoae, Stenopsyche marmorata Chironomidae, Limnodrilus gotoi, Ephemera orientalis, Psychoda KUa
Sprawlers Burrowers
10.16, and 39.63 mm, respectively (Choi et al., 2009). The coarsening of the bed material downstream of the weir seemed to be caused by a flood with the peak discharge of 412.0 m3/s in July 2006 (Korea Institute of Construction Technology, 2008), which swept out deposited fine particles and transported gravels and cobbles from sites further upstream. The geometric standard deviation σg (=D84.1/ D15.9 ), which indicates uniformity of a sediment mixture, changed from 2.70 to 3.49 and 4.66 to 6.08 in the upstream and downstream reaches of the weir, respectively, suggesting that the size of the bed material was more widely distributed after the weir removal (Choi et al., 2009).
2.3. Physical habitat simulation 2.3.1. Hydraulic simulation In this study, the River2D model (Steffler and Blackburn, 2002) was used in the hydraulic simulation. The River2D model solves 2D shallow water equations using the finite element method. The shallow water equations consist of the following continuity and x - and y -momentum equations:
2.2.2. Macroinvertebrates Field monitoring campaigns of macroinvertebrate species were conducted at two sites in the upstream and downstream reaches of the weir. The monitoring sites are marked by inverted triangles in Fig. 1. The macroinvertebrates were sampled using a Surber sampler (30 × 30 cm, mesh size 0.2 mm). In each site, three replicates were sampled. The collected samples were preserved in Kahle’s solution. The taxonomic groups were identified and enumerated by visual inspection using a stereomicroscope (Kil, 2008). The macroinvertebrate samplings were conducted in March 2006
∂qy ∂qx ∂H =0 + + ∂y ∂x ∂t
(1)
∂vqx ∂uqx ∂qx g ∂H 2 1 ∂Hτxx 1 ∂Hτxy + = gH (Sox − Sfx ) + + + + 2 ∂x ρ ∂x ρ ∂y ∂y ∂x ∂t (2) 365
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 5. Distribution of FHGs against velocity, flow depth, and substrate.
∂vqy ∂uqy ∂qx g ∂H 2 1 ∂Hτyx 1 ∂Hτyy + + = gH (Soy − Sfy ) + + + 2 ∂y ρ ∂x ρ ∂y ∂y ∂x ∂t
the measured data. Detailed information is given in Im et al. Regarding the eddy viscosity coefficient in the River2D model, such default values as ε1 = 0 , ε2 = 0.5, and ε3 = 0 were used.
(3) where t is time, x and y are streamwise and transverse directions, respectively. H is the flow depth, (u , v ) are the depth-averaged velocities in the ( x , y ) directions, respectively, (qx , qy ) are the unit discharges in the ( x , y ) directions, respectively, (Sox , Soy ) are the bed slopes in the ( x , y ) directions, respectively, (Sfx , Sfy ) are the friction slopes in the ( x , y ) directions, respectively, τij is the horizontal turbulent stress tensor, ρ is the water density, and g is the gravitational acceleration. The x - and y components of the friction slope are estimated, respectively, as follows:
Sfx =
n2u u2 + v 2 n2v u2 + v 2 , Sfy H 4/3 H 4/3
2.3.2. Habitat simulation Habitat simulation is a procedure that evaluates the suitability of the habitat to the target specie using the habitat suitability model. In the present study, HSCs were used in the habitat suitability model, and the physical habitat variables were flow depth, velocity, and substrate. Habitat suitability is indicated by the CSI. The values of the CSI range from zero to unity, which represent the minimum and optimal conditions of the physical habitat, respectively. Various methods are used to calculate the CSI, such as the multiplicative aggregation method, the geometric mean method, the minimum method, and the weighted mean method. In the present study, the following weighted mean method was used to compute the CSI:
(4a,b)
where n is Manning’s roughness coefficient. In the same study area, Im et al. (2011) carried out the calibration of the roughness coefficient for a wide range of discharges. They proposed n = 0.027 or the effective roughness height ks = 0.11 m, which was used in the present study. They measured the water surface elevation and velocity using large scale particle image velocimetry. They also validated the River2D model by comparing the computed results with
CSI = f (H )a × f (V )b × f (s )c
(5)
where f (HV ) is the suitability value for each physical habitat variable HV . Here HV includes flow depth H , velocity V , and substrate s . In Eq. (5), a , b , and c are weighting factors for H , V , and s , respectively. 366
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 6. HSCs for FHGs. 367
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 7. Flow depth and velocity before the weir removal.
Fig. 8. Flow depth and velocity after the weir removal. k
In macroinvertebrates, the substrate is the most crucial among the physical habitat variables (Jowett and Richardson, 1990; Quinn and Hickey, 1990; Beisel et al., 1998; Brooks et al., 2005). Therefore, different weighting factors should be applied to Eq.(5) in order to consider the relative importance of the physical habitat variables. Li et al. (2009) suggested the weighting factors such as a = 0.260, b = 0.327, and c = 0.413 for the weighted mean method to compute the CSI for macroinvertebrates. These were obtained from the so-called analytic hierarchy process. Later, Kim and Choi (2018) carried out PHSs for four target macroinvertebrates using the weighting factors proposed by Li et al. (2009) in the same study area. They found that CSI values for each macroinvertebrate species from PHSs match well to observed populations. In this study, the weighting factors suggested by Li et al. were used. The WUA is obtained using CSI values. The WUA means the quantity of the available habitat for the target species in the study area. The WUA is the overall quantity of the wetted area weighted by CSI values. It is estimated as follows:
Normalized WUA =
∑ CSIi × Ai i=1
k
∑i = 1 Ai
(7)
which yields the average value of the CSI in the study area, indicating the average quality of the physical habitat of the target species. 2.4. Habitat suitability curves for the FHG To construct the HSCs for the target FHG, monitoring data obtained from the Han-gang River basin were used (Ministry of Environment/ National Institute of Environmental Research, 2011). The total number of monitoring data is 340. The data included the population of macroinvertebrates, water temperature, turbidity, flow depth, velocity, and substrate. For convenience, the monitored populations of the macroinvertebrates were converted into population density (population/m2), which is the number of individual macroinvertebrates per unit of bed area. Table 1 lists the groups and macroinvertebrate species sampled in the Han-gang River basin. The species in the table are the most abundant and representative species in each group. As Table 1 shows, the monitored macroinvertebrate species were grouped into four FHGs, namely swimmers, clingers, sprawlers, and burrowers. The four representative species of each FHG were selected based on the monitored populations. Fig. 5 shows a 3D scatter plot of the monitored habitat use data for the FHGs, which were used to construct HSCs for the FHGs in this study.
k
WUA =
∑i = 1 CSIi × Ai
(6)
where k is the total number of cells and Ai is the area of the i -th cell. The normalized WUA is calculated as follows:
368
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 9. Distribution of CSI for FHGs before the weir removal.
resisting fast flow, inhabit riffles. Burrowers create caves using sand and silt, where they reside. Sprawlers live mainly on silt-free beds. The HSCs shown in Fig. 6 indicate that swimmers, clingers, and sprawlers preferred running water, compared with burrowers, which favored high flow velocity and shallow water depth.
As shown in Fig. 5, the observed population densities of the FHGs were plotted against flow depth, velocity, and substrate, and the size of the bubbles indicates the population density. In the present study, Gosse’s (1982) method was used to construct the HSCs. The data in Fig. 5 were used to build the HSCs for the FHGs. First, the frequency distribution was obtained for each habitat variable. Then, the values of the suitability index 1.0, 0.5, 0.1, and 0.05 were given to the values of the habitat variable that encompass 50%, 75%, 90%, and 95% of the total populations, respectively. As Fig. 6 shows, swimmers preferred the ranges of 0.19–0.25 m, 0.50–0.78 m/s, and 4 (fine gravel) for the flow depth, velocity, and substrate, respectively. The range of each habitat variable preferred by clingers and sprawlers were found to be similar to the optimal ranges of swimmers. However, the ranges preferred by burrowers appear to be different, i.e., 0.15–0.25 m, 0.42–0.56 m/s, and 3 (sand) for the flow depth, velocity, and substrate, respectively. These findings indicate that burrowers prefer slow-water and fine substrate habitats, compared with the other groups. The constructed HSCs appeared to reflect the characteristics of each FHG described in Merritt et al. (2002), Johnson et al. (2003), and Herbst et al. (2018). That is, swimmers tend to swim in a relatively short period and cling to the riverbed. Clingers, which are capable of
3. Results 3.1. Hydraulic simulation Hydraulic simulations were carried out using the 2D hydraulic model for the normal flow of Q = 0.91 m3/s. Figs. 7 and 8 show the simulation results before and after the weir removal, respectively. The weir removal significantly changed the flow in the upstream reach of the weir. The weir had created a large wetted area with a deep water depth of about 1.0 m and a low velocity less than 0.1 m/s. However, after the weir removal, the wetted area upstream of the weir was reduced with the decreased water depth and increased flow velocity. Even though the weir was removed, the pool habitat remained in the middle of the study area. After the removal, the flow rarely changed in the downstream reach of the weir. That is, the water depth remained shallow, and the velocity of the water was high. 369
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 10. Distribution of CSI for FHGs after the weir removal.
the CSIs computed for burrowers were high. These results are consistent with the monitoring data, which showed that the number of burrowers was larger than that of the other FHGs. After the weir removal, the CSIs for swimmers, clingers, and sprawlers were increased by 0.03 – 0.07, indicating that the quality of the habitat of these FHGs was enhanced slightly. The monitoring data indicated that swimmers and clingers newly appeared, and the number of sprawlers was increased slightly after the weir removal. In the downstream reach of the weir, the computed CSIs and the observed number of individuals were larger than those in the upstream reach. Similar to the upstream site, the CSI for burrowers was higher, and the observed number of burrowers was larger before the weir removal. After the weir removal, the CSIs for swimmers, clingers, and sprawlers were increased, but the CSI for burrowers was decreased significantly. The monitoring data supported the simulation results. Fig. 12(a) and (b) show the normalized WUA for each FHG before and after the weir removal in the upstream reach and downstream reach, respectively. The normalized WUA denotes the WUA divided by the wetted area. The wetted areas of the study area before and after the weir removal were 6.42×103 m2 and 3.22×103 m2, respectively. In the upstream reach, it was observed that the normalized WUAs for swimmers, clingers, and sprawlers were increased slightly after the weir removal. This result indicates that the weir removal contributed slightly to the increase in habitat suitability for these FHGs. However, the normalized WUA for burrowers was decreased slightly. A similar trend was observed in the downstream reach. Before the weir removal, habitat suitability for all FHGs in the downstream reach was greater than that in the upstream reach. Similarly, after the weir removal, habitat suitability for swimmers, clingers, and sprawlers was increased in the downstream reach. However, habitat suitability for burrowers was decreased significantly.
3.2. CSI Distribution and normalized WUA Based on the results of the hydraulic simulations, CSIs were calculated before and after the weir removal. CSI distributions of the FHGs before and after the removal are shown in Figs. 9 and 10, respectively. In the figure, the white and gray colored areas denote zero CSI and dry regions, respectively. Fig. 9 shows that habitat suitability for swimmers, clingers, and sprawlers was high in the downstream reach of the weir. The reason is that these FHGs prefer shallow water and high flow velocity. In contrast, habitat suitability for burrowers was the highest in the study area. The reason is that in the study area, the substrate was mainly sand, which is preferred by burrowers. Fig. 10 shows the CSI distributions after the weir removal. The suitability of the physical habitat for swimmers, clingers, and sprawlers increased in both the upstream and the downstream reaches of the weir. The main reason is that the substrates were coarsened over the entire study area after the weir removal. In addition, the reduced water depth and increased flow velocity enhanced habitat suitability for these groups in the upstream reach of the weir. However, habitat suitability for burrowers decreased over the study area. The reason is that the coarsening of the substrate over the entire study area negatively affected habitat suitability for burrowers. The reduced water depth and increased velocity also negatively affected the habitat, especially in the upstream reach. Fig. 11 shows the computed CSIs and the monitored number of individuals, which were compared at two sites upstream and downstream of the weir. The two monitoring sites are denoted by the inverted triangles in Fig. 1. The field monitoring campaigns were conducted before (i.e., in March 2006) and after (i.e., in August and September 2006) the weir removal (Kil, 2008). At the upstream site of the weir, the CSIs computed for swimmers, clingers, and sprawlers were low. However, 370
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 11. Comparison of observed individuals and CSI.
Some additional PHSs were carried out for the low flow and the drought. It was found that the normalized WUA decreases as the discharge decreases for all FHGs because the flow depth and velocity decrease extremely. The results indicated that habitat suitability for all FHGs degrades for the low flow or the drought flow, compared to habitat suitability for the normal flow. For each flow, the change of the normalized WUA before and after the weir removal showed the same trend as is given in Fig. 12. In summary, the weir removal resulted in the degradation of the physical habitat regarding burrowers, which were dominant in the study area. However, the weir removal improved habitat suitability for the other three FHGs. This is due to coarsening of the substrate and flow change in the study area.
was degraded seriously, whereas habitat suitability for the other FHGs was improved slightly by the weir removal. The change in habitat suitability also affected the biological indices. Table 2 lists the dominance index and the diversity index before and after the weir removal. The dominance index is a measure of the degree to which one or a few species dominate the community, and the diversity index indicates the diversity of species within a community that consists of two or more species. In the present study, the dominance index and the diversity index were calculated by the methods in McNaughton (1967) and Pielou (1966), respectively. As Table 2 shows, the dominance index decreased in both the upstream and the downstream reaches after the weir removal. That is, the dominance index changed from “poor” to “fair” in the upstream reach and from “poor” to “good” in the downstream reach. This finding indicates that the percentages of the dominant and subdominant macroinvertebrate species decreased after the weir removal. The weir removal also affected the diversity index, which changed from “poor” to “fair” in the upstream reach and from “poor” to “good” in the downstream reach. This suggests that the number of macroinvertebrate
4. Discussion The results of this study revealed that the removal of the weir caused changes in the physical habitat and affected the composition of the macroinvertebrate community. Habitat suitability for burrowers 371
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
selective changes in the physical habitats of the macroinvertebrates. Specifically, habitat suitability for burrowers was decreased, but habitat suitability for the other FHGs was increased. In the same study area, Im et al. (2011) found that the number of individuals of lotic fishes, such as Rhinogobious brunneus and Zacco platypus, increased after the weir removal. The reason was that the weir removal actually restored riffles downstream of the weir, which led to the increase in the number of swimmers and clingers. The increase in the FHGs of the macroinvertebrate species improved the feeding conditions for lotic fishes, such as Rhinogobious brunneus and Zacco platypus. This finding indicated that the weir removal improved both the physical habitats and the feeding conditions of the fishes. 5. Conclusions This study presented the PHSs of the target FHGs to investigate changes in the habitats of the macroinvertebrate community after the weir was removed. The study area was a 0.6 km long reach in the Gongneung-cheon Stream, Korea, and Gongneung Weir-2 was located in the middle of the study reach. Gongneung Weir-2 was built in 1970 s to supply the irrigation water to the nearby area and was removed in April 2006 due to the land use change. The macroinvertebrate species in the study area were grouped into four FHGs such as swimmers, clingers, burrowers, and sprawlers, and their HSCs were constructed using monitoring data from the Han-gang River basin. PHSs for the four FHGs were carried out. The River2D model and the HSCs were used for hydraulic and habitat simulations, respectively. Hydraulics simulations for the normal flow revealed that the flow condition upstream of the weir changed significantly after the weir removal. That is, the water depth was decreased with the increased flow velocity. The results of the PHSs indicated that the habitat of burrowers was suitable over the study area before the weir removal. After the removal, habitat suitability for burrowers was decreased, whereas habitat suitability for the other FHGs was increased. The main reason is that the substrates were coarsened over the entire study area after the weir was removed. The improvement in the physical habitat for swimmers, clingers, and sprawlers increased the numbers of these macroinvertebrate species in the study area. Consequently, the diversity of the macroinvertebrate community was increased. Findings from some previous studies such as ones by Stanley et al. (2002) and Thomson et al. (2005) are contrary to those from the present study in that fine sediment transport from upstream of the weir degraded habitat quality for macroinvertebrates in the reach downstream of the weir. However, in the present study, the flood flow coarsened the substrates over the entire study area, leading to the selective changes in the physical habitats for macroinvertebrates. In addition, the weir removal restored riffles downstream of the weir, which brought out the increase of the populations of swimmers, clingers, sprawlers. This improved the feeding condition of the fish species, resulting in the increase in the number of individuals of lotic fishes, as reported in Im et al. (2011).
Fig. 12. Change of normalized WUA for each FHG before and after the weir removal.
Table 2 Biological indices before and after weir removal (Kil, 2008). index
dominance (DI )(1) diversity (H' )(2)
upstream reach of the weir
downstream reach of the weir
before removal
after removal
before removal
after removal
0.83 1.24
0.64 2.35
0.71 1.50
0.43 3.30
(1) Dominance index: excellent (< 0.25), good (0.25–0.5), fair (0.5–0.7), poor (0.7–0.9), and very poor (> 0.9). Here, DI = (N1 + N2)/ N with N = total number of individuals in all species, N1 and N2 are the number of individuals of the two most dominant species in a community. (2) Diversity index: excellent (> 4.0), good (3.0–4.0), fair (2.0–3.0), poor s (1.0–2.0), and very poor (< 1.0). Here, H ' = − ∑i = 1 (ni / N )ln(ni / N ) with ni = number of individuals in a species i of a sample and s = number of species.
Declaration of Competing Interest
species was increased after the weir removal. This is related to the fact that habitat suitability for burrowers was decreased, whereas it was increased for the other three FHGs. Previous studies by Stanley et al. (2002) and Thomson et al. (2005) indicated that habitat suitability for macroinvertebrates in the downstream reach of the weir was decreased after weir removal. This is because that the fine sediment deposited in the impounded region was transported and deposited in the downstream reach of the weir after the weir was removed. However, in the present study, the bed sediment was coarsened over the study area after flooding in July, which induced
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements This research was supported by a grant (18CTAP-C132929-02) from Infrastructure and transportation technology promotion research Program funded by Ministry of Land, Infrastructure and Transport of South Korean government. 372
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
New Zealand river and the development of in-stream flow-habitat models for Deleatidium spp. New Zeal. J. Mar. Fresh. 24, 19–30. https://doi.org/10.1080/ 00288330.1990.9516399. Kanehl, P.D., Lyons, J., Nelson, J.E., 1997. Changes in the habitat and fish community of the Milwaukee River, Wisconsin, following removal of the woolen mills dam. N. Am. J. Fish. Manag. 17, 387–400. https://doi.org/10.1577/1548-8675(1997) 017<0387:CITHAF> 2.3.CO;2. Kil, H.K., 2008. Effects of Dams on Benthic Macroinvertebrate Communities in Korean Streams (Doctoral dissertation). Seoul Women’s University, Seoul, Korea (in Korean). Kim, S.K., Choi, S.U., 2018. Prediction of suitable feeding habitat for fishes in a stream using physical habitat simulations. Ecol. Model. 385, 65–77. https://doi.org/10. 1016/j.ecolmodel.2018.07.014. Korea Institute of Construction Technology., 2008. The stream eco-corridor restoration and water quality improvement by weir removal with its function lost. Ministry of Environment, p. 402 (in Korean). Korea Rural Community Corporation, 2013. Statistical yearbook of land and water development for agriculture. Ministry for Food, Agriculture, Forestry and Fisheries (in Korean). Larinier, M., 2001. Environmental issues, dams and fish migration. FAO fisheries technical paper, 419, 45–89. Li, F., Cai, Q., Fu, X., Liu, J., 2009. Construction of habitat suitability models (HSMs) for benthic macroinvertebrate and their applications to instream environmental flows: a case study in Xiangxi River of Three Gorges Reservoir region, China. Prog. Nat. Sci. 19, 359–367. https://doi.org/10.1016/j.pnsc.2008.07.011. Magilligan, F.J., Graber, B.E., Nislow, K.H., Chipman, J.W., Sneddon, C.S., Fox, C.A., 2016. River restoration by dam removal: enhancing connectivity at watershed scales. Elem. Sci. Anth. 4. McNaughton, S.J., 1967. Relationship among functional properties of California grassland. Nature 216, 168–169. https://doi.org/10.1038/216168b0. Merritt, R.W., Cummins, K.W., Berg, M.B., Novak, J.A., Higgins, M.J., Wessell, K.J., Lessard, J.L., 2002. Development and application of a macroinvertebrate functionalgroup approach in the bioassessment of remnant river oxbows in southwest Florida. J. N. Am. Benthol. Soc. 21, 290–310. https://doi.org/10.2307/1468416. Ministry of Environment/National Institute of Environmental Research, 2011. Report on survey and assessment for health conditions of aquatic ecosystem. Ministry of Environment, National Institute of Environmental Research, p. 324 (in Korean). Pielou, E.C., 1966. The measurement of diversity in different types of biological collections. J. Theor. Biol. 13, 131–144. https://doi.org/10.1016/0022-5193(66)90013-0. Quinn, J.M., Hickey, C.W., 1990. Characterization and classification of benthic invertebrate communities in 88 New Zealand rivers in relation to environmental factors. N. Z. J. Mar. Fresh. 24, 387–409. https://doi.org/10.1080/00288330.1990. 9516432. Stanley, E.H., Luebke, M.A., Doyle, M.W., Marshall, D.W., 2002. Short-term changes in channel form and macroinvertebrate communities following low-head dam removal. J. N. Am. Benthol. Soc. 21, 172–187. https://doi.org/10.2307/1468307. Steffler, P., Blackburn, J., 2002. Two-dimensional depth averaged model of river hydrodynamics and fish habitat. In: River2D user’s manual, University of Alberta, Canada. Thomson, J.R., Hart, D.D., Charles, D.F., Nightengale, T.L., Winter, D.M., 2005. Effects of removal of a small dam on downstream macroinvertebrate and algal assemblages in a Pennsylvania stream. J. N. Am. Benthol. Soc. 24, 192–207. https://doi.org/10.1899/ 0887-3593(2005) 024<0192:EOROAS>2.0.CO;2. US Army Corps of Engineers. 2018. 2018 National Inventory of Dams (NID) database. U.S. Army Corps of Engineers. (Available from: https://nid.sec.usace.army.mil/ords/ f?p=105:19:487464404088::NO::: (accessed 28 July 2019)).
References Baxter, R.M., 1977. Environmental effects of dams and impoundments. Annu. Rev. Ecol. Evol. Syst. 8, 255–283. https://doi.org/10.1146/annurev.es.08.110177.001351. Beisel, J.N., Usseglio-Polatera, P., Thomas, S., Moreteau, J.C., 1998. Stream community structure in relation to spatial variation: the influence of mesohabitat characteristics. Hydrobiologia 389, 73–88. https://doi.org/10.1023/A:1003519429979. Bender, P.M., 1997. Restoring the Elwha, White Salmon, and Rogue Rivers: a comparison of dam removal proposals in the Pacific Northwest. J. Land Res. Envtl. L. 17, 189. Brandt, S.A., 2000. Classification of geomorphological effects downstream of dams. Catena 40, 375–401. https://doi.org/10.1016/S0341-8162(00)00093-X. Brooks, A.J., Haeusler, T.I.M., Reinfelds, I., Williams, S., 2005. Hydraulic microhabitats and the distribution of macroinvertebrate assemblages in riffles. Freshwater Biol. 50, 331–344. https://doi.org/10.1111/j.1365-2427.2004.01322.x. Catalano, M.J., Bozek, M.A., Pellett, T.D., 2007. Effects of dam removal on fish assemblage structure and spatial distributions in the Baraboo River, Wisconsin. N. Am. J. Fish. Manag. 27, 519–530. https://doi.org/10.1577/M06-001.1. Chiu, M.C., Yeh, C.H., Sun, Y.H., Kuo, M.H., 2013. Short-term effects of dam removal on macroinvertebrates in a Taiwan stream. Aquat. Ecol. 47, 245–252. https://doi.org/ 10.1007/s10452-013-9439-y. Choi, S.U., Lee, H.E., Yoon, B.M., Woo, H.S., 2009. Change in stream morphology after Gongneung weir 2 removal. J. Korea Water Resour. Assoc. 42, 425–432. https://doi. org/10.3741/JKWRA.2009.42.5.425. (in Korean). Cummins, K.W., 1973. Trophic relations of aquatic insects. Annu. Rev. Entomol. 18, 183–206. https://doi.org/10.1146/annurev.en.18.010173.001151. Cummins, K.W., 1974. Structure and function of stream ecosystems. BioScience 24, 631–641. https://doi.org/10.2307/1296676. De Leaniz, C.G., 2008. Weir removal in salmonid streams: implications, challenges and practicalities. Hydrobiologia 609, 83–96. https://doi.org/10.1007/s10750-0089397-x. Doyle, M.W., Stanley, E.H., Harbor, J.M., 2003. Channel adjustments following two dam removals in Wisconsin. Water Resour. Res. 39. https://doi.org/10.1029/ 2002WR001714. Gosse J.C., 1982. Microhabitat of rainbow and cutthroat trout in the Green River below Flaming Gorge Dam. Final report, Contract 81 5049, Utah Division of Wildlife Resources, Salt Lake City, p. 114. Gough, P., Fernandez Garrido, P., Van Herk, J., 2018. Dam Removal. A viable solution for the future of our European rivers. Dam Removal Europe. P. 38. Hansen, J.F., Hayes, D.B., 2012. Long-term implications of dam removal for macroinvertebrate communities in Michigan and Wisconsin Rivers, United States. River Res. Appl. 28, 1540–1550. https://doi.org/10.1002/rra.1540. Herbst, D.B., Cooper, S.D., Medhurst, R.B., Wiseman, S.W., Hunsaker, C.T., 2018. A comparison of the taxonomic and trait structure of macroinvertebrate communities between the riffles and pools of montane headwater streams. Hydrobiologia 820, 115–133. https://doi.org/10.1007/s10750-018-3646-4. Im, D., Kang, H., Kim, K.-H., Choi, S.U., 2011. Changes of river morphology and physical fish habitat following weir removal. Ecol. Eng. 37, 883–892. https://doi.org/10. 1016/j.ecoleng.2011.01.005. Im, D., Choi, B., Choi, S.U., 2019. Change in the composition of fish community following weir removal, field observations and physical habitat simulations. River Res. Appl. https://doi.org/10.1002/rra.3480. Johnson, L.B., Breneman, D.H., Richards, C., 2003. Macroinvertebrate community structure and function associated with large wood in low gradient streams. River Res. Appl. 19, 199–218. https://doi.org/10.1002/rra.712. Jowett, I.G., Richardson, J., 1990. Microhabitat preferences of benthic invertebrates in a
373
Contents lists available at ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Ecological evaluation of weir removal based on physical habitat simulations for macroinvertebrate community
T
⁎
Seung Ki Kim, Sung-Uk Choi
Department of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Republic of Korea
A R T I C LE I N FO
A B S T R A C T
Keywords: Weir removal Macroinvertebrate Physical habitat simulation Functional habit group Habitat suitability curve
In Korea, rapid urbanization has changed the land use in rural areas, which has resulted in an increase in the number of weirs that are left untended in streams. Previously, changes in stream morphology and fishes were studied following the removal of such weirs. The present study was conducted to investigate changes in the habitat of the macroinvertebrate community after weir removal using physical habitat simulations (PHSs). The functional group approach was used in the PHSs for the macroinvertebrate community. In the functional group approach, macroinvertebrates are classified based on the traits of their food acquisition (i.e., the functional feeding group) or habitat selection (i.e., the functional habit group). In the present study, macroinvertebrate species were divided into the functional habit groups (FHGs) of swimmers, clingers, burrowers, and sprawlers. Hydraulic simulations and habitat simulations were carried out using the River2D model and habitat suitability curves (HSCs), respectively. The distributions of the composite suitability index (CSI) for the FHGs were obtained over the entire study area, and the changes in the suitability of the habitat for the target FHGs were evaluated. The simulation results indicated that habitat suitability for swimmers, clingers, and sprawlers was improved. However, habitat suitability for burrowers was degraded after the weir was removed. Consequently, the removal of the weir increased the diversity of the macroinvertebrate community, thus improving the health of the aquatic ecosystem.
1. Introduction The construction of instream barriers, such as dams and weirs, results in significant changes in stream environments. That is, sediment deposition takes place in the increased water depth and the decreased velocity upstream of the barrier. However, in the downstream reach, the bed experiences degradation with coarsening sediment particles (Brandt, 2000). Dams and weirs affect not only these hydraulic variables but also the habitats of fish and macroinvertebrates. In addition, instream barriers obstruct the longitudinal movements of these aquatic organisms in feeding and spawning, which leads to decreases in their populations (Baxter, 1977; Larinier, 2001). Attempts have been made to restore degraded stream environments by removing dams and weirs that no longer serve their original purpose. It was reported that there are more than 90,000 dams in the US (US Army Corps of Engineers, 2018). Approximately 1300 dams have been removed since the early 20th century, 70% of which have been removed in 21st century. In Europe, at least 4000 dams and weirs have been removed since the mid-1990s (Gough et al., 2018). In Korea, there are about 34,000 weirs, including small dams. More than 3800 weirs
⁎
have been removed since the 1980s. Approximately 5900 weirs were reported to be out of service and left untended (Korea Rural Community Corporation, 2013). It was not until the 1980s that engineers paid attention to the morphological changes and effects on the habitats of aquatic animals after dams were removed (Bender, 1997). Removing instream barriers significantly contributes to stream restoration. Sediment particles deposited upstream of the barrier are flushed, and a portion of them are deposited on the degraded bed downstream of the barrier after its removal. Therefore, the discontinuity in the bed slopes upstream and downstream of the barrier disappears gradually, and the bed slope approaches the original slope before the barrier was constructed (Doyle et al., 2003). The improved river connectivity might restore the fragmented habitats of fishes and macroinvertebrates (Magilligan et al., 2016). Regarding fishes, the removal of barriers changes lentic habitats to lotic habitats upstream of the barrier, which are the habitats of native fishes (Kanehl et al., 1997; Catalano et al., 2007; Im et al., 2011) and increases the population of migratory fishes (De Leaniz, 2008). However, the knowledge about the effects of barrier removal on the macroinvertebrate community is limited.
Corresponding author. E-mail addresses: [email protected] (S.K. Kim), [email protected] (S.-U. Choi).
https://doi.org/10.1016/j.ecoleng.2019.08.003 Received 25 March 2019; Received in revised form 30 July 2019; Accepted 5 August 2019 Available online 12 August 2019 0925-8574/ © 2019 Elsevier B.V. All rights reserved.
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 1. Study area.
Fig. 2. Change of the thalweg elevation.
decreased significantly downstream of the dam. In previous research, field observations have been conducted to demonstrate the changes in the macroinvertebrate assemblage after weir removal. However, compared with field observations, the habitat modeling approach provides a quantitative assessment of habitat quality following changes in physical habitats. In the literature, the modeling for fish habitat (Im et al., 2011; Im et al., 2019) has been conducted, whereas no previous study has focused on the habitat of macroinvertebrates. This study was conducted to investigate the impact of weir removal on the macroinvertebrate community using the physical habitat simulation (PHS). The novelty of the present study is a use of the functional group approach in the PHS, which is an efficient tool for simulating the entire macroinvertebrate community. The study area, which is about 0.6 km in length, is located in the Gongneung-cheon Stream in the Hangang River basin, Korea. In 2006, a weir that was located in the middle of the study area was removed. First, the macroinvertebrate community was divided into four functional habit groups (FHGs) based on the data collected in the Han-gang River basin. Then habitat suitability curves (HSCs) for the FHGs were constructed using field monitoring data collected in the Han-gang River basin. Finally, the PHSs were carried out. Composite suitability index (CSI) distributions and normalized weighted usable areas (WUAs) were determined before and after the weir was removed.
Previous studies confirmed that weir removal changes stream morphology and physical habitat variables, which results in changes in macroinvertebrate assemblages (Stanley et al., 2002; Thomson et al., 2005; Hansen and Hayes, 2012; Chiu et al., 2013). For example, Stanley et al. (2002) studied changes in the channel form and macroinvertebrate assemblages due to the removal of a low-head dam in the Baraboo River in Wisconsin in the US. Before the removal, they observed that lentic taxa, such as tubificid worms, and lotic taxa, such as net-spinning caddisflies, were dominant upstream and downstream of the dam, respectively. However, after the removal, they found that the dominant macroinvertebrate species changed from lentic assemblages to lotic assemblages upstream of the dam. Thomson et al. (2005) investigated the changes in macroinvertebrate assemblages after the removal of a small dam in the Manatawny Creek in Pennsylvania in the US. They observed that the dam removal induced the sedimentation of sand downstream of the dam. This sedimentation reduced the macroinvertebrate density downstream, and the downstream macroinvertebrate assemblages became similar to the upstream assemblages. Chiu et al. (2013) studied the short-term effects of the removal of a check dam on the density and richness of macroinvertebrates in the Dajia River in Taiwan. After the check dam was removed, sediment particles deposited upstream of the dam were transported and deposited in the downstream reach. They found that the density of the macroinvertebrates increased upstream but decreased downstream of the dam immediately after its removal. In addition, they observed that the macroinvertebrate richness decreased only slightly upstream but 363
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 3. Change of bed material before and after the weir removal.
2. Materials and methods
2.2. Monitoring data
2.1. Study area
2.2.1. Channel morphology and bed material Geomorphological surveys were carried out before and after the weir removal. Fig. 2 shows the longitudinal changes in the thalweg elevation before and after the weir removal. The bed elevation was greatly lowered upstream of the weir after it was removed. The maximum erosion of 0.8 m occurred at a location 35 m upstream from the weir. This is mainly because the increased shear stress caused the flushing of bed materials in the upstream reach of the weir (Choi et al., 2009). In the downstream reach, aggradation occurred with the maximum deposition of 0.4 m at a location 15 m downstream from the weir. The changes in the composition of the bed materials before and after the weir removal are shown in Fig. 3. The overall change indicates that the bed material was coarsened over the study area after the weir removal. Before the weir removal, sand comprised over 80% of the bed material immediately upstream of the weir because of the deposition of the fine sediment by the weir. After the weir removal, sand comprised less than 50% of the bed material at the same location. In the downstream reach of the weir, after the weir removal, coarse gravel and cobbles increased by 9.9–28.3% and 1.2–5.1%, respectively. Specifically, in the upstream reach, D15.8 , D50 , and D84.1 changed from 0.25, 0.48, and 1.83 mm to 0.62, 1.88, and 7.61 mm, respectively, and in the downstream reach, they changed from 0.39, 2.59, and 8.47 mm to 1.07,
The study area is a 0.6 km long reach located at the Gongneungcheon Stream, which is a tributary of the Han-gang River (Fig. 1). The total length and watershed area of the Gongneung-cheon Stream are 45.0 km and 253.1 km2, respectively. The bed slope of the Gongneungcheon Stream ranges between 0.00022 and 0.012. The study area is located in the upper reach of the Gongneung-cheon Stream and the average slope of the study reach is 0.0031 (Choi et al., 2009) The discharges of the drought flow (Q355 ), low flow (Q275 ), normal flow (Q185 ), and high flow (Q95 ) are 0.28, 0.51, 0.91, and 1.73 m3/s, respectively (Korea Institute of Construction Technology, 2008). Here, Qn denotes the average flow discharge, which is exceeded on n days of the year. Gongneung Weir-2 was located 0.58 km upstream from the confluence with the Sunyu-cheon Stream. The weir was built in the 1970s to supply the nearby area with irrigation water. The height, width, and length of the weir were 1.5 m, 75 m, and 8.8 m, respectively. However, the weir became redundant because the land use in the nearby area was changed. Following the agreement of the local government and nearby residents, the weir was removed completely on 14 April 2006.
364
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
and September 2006, which corresponded to before and after the weir removal, respectively. Before the weir removal, 10 and 33 species were observed among 111 and 2457 individuals in the upstream and downstream reaches, respectively. However, after the weir removal, the number of species changed to 17 and 32 among 187 and 4598 individuals in the upstream and downstream reaches, respectively (Kil, 2008). The sampling results revealed that the post-removal composition of the macroinvertebrate species had changed significantly. That is, before the removal, Chironomidae sp. 2 was the predominant macroinvertebrate species in the study area. They accounted for 58.6% and 52.2% of the total macroinvertebrate species in the upstream and downstream reaches of the weir, respectively. After the removal, Chironomidae sp. 2 was found to be predominant in the upstream reach, which accounted for 43.9% of the macroinvertebrate species. However, in the downstream reach, the predominant species was changed to Uracanthella rufa, followed by Baetis fuscatus, which accounted for 28.6% and 15.7% of the macroinvertebrate species, respectively (Kil, 2008). In the present study, the functional group approach was used to categorize the macroinvertebrate community. This approach was first introduced to evaluate or measure the diversity and composition of macroinvertebrate communities in the 1970s (Cummins 1973, 1974). In the functional group approach, two classification methods are used to categorize macroinvertebrates: the functional feeding group (FFG) and the functional habit group (FHG). The FFG is a method used to classify macroinvertebrates based on their food preference and feeding strategy. The FFG includes gatherers, filterers, herbivore-piercers, predators, scrapers, shredders, etc. (Merritt et al., 2002). The FHG is a method used to classify macroinvertebrates based on habitat characteristics, dwelling style, and adaptation strategy. The FHG includes skaters, swimmers, clingers, sprawlers, climbers, burrowers, etc. In this study, the FHG method was adopted. Fig. 4 shows the changes in the composition of the FHG before and after the weir removal. The observed swimmers included Baetis fuscatus, Baetis ursinus, etc. The clingers included Uracanthella rufa, Hydropsyche kozhantschikovi, etc. Examples of the observed burrowers were Chironomidae and Ephemera orientalis, and examples of the observed sprawlers were Caenis KUa and Mystacides KUa. In the upstream reach of the weir, burrowers accounted for 92.7% before the removal, which decreased to 68.4% after the removal. The number of sprawlers increased to 19.3%, and swimmers and clingers newly appeared, which accounted for 9.6% and 2.7%, respectively. In the downstream reach of the weir, the number of burrowers decreased drastically from 79.3% to 13.2%. In contrast, the number of swimmers increased from 0.9% to 27.9%. In addition, the number of clingers increased dramatically from 19.8% to 56.9%, and sprawlers newly appeared, which accounted for 2.0% after the removal.
Fig. 4. Changes of FHGs before and after the weir removal.
Table 1 Grouping macroinvertebrate species for constructing HSCs. Groups
Species
Swimmers Clingers
Baetis fuscatus, Baetis ursinus, Acentrella sibirica, Baetiella tubercularta Hydropsyche kozhantschikovi, Cheumatopsyche brevilineata, Epeorus pellucidus, Hydropsyche valvata Caenis KUa, Potamanthellus chinensis, Caenis nishinoae, Stenopsyche marmorata Chironomidae, Limnodrilus gotoi, Ephemera orientalis, Psychoda KUa
Sprawlers Burrowers
10.16, and 39.63 mm, respectively (Choi et al., 2009). The coarsening of the bed material downstream of the weir seemed to be caused by a flood with the peak discharge of 412.0 m3/s in July 2006 (Korea Institute of Construction Technology, 2008), which swept out deposited fine particles and transported gravels and cobbles from sites further upstream. The geometric standard deviation σg (=D84.1/ D15.9 ), which indicates uniformity of a sediment mixture, changed from 2.70 to 3.49 and 4.66 to 6.08 in the upstream and downstream reaches of the weir, respectively, suggesting that the size of the bed material was more widely distributed after the weir removal (Choi et al., 2009).
2.3. Physical habitat simulation 2.3.1. Hydraulic simulation In this study, the River2D model (Steffler and Blackburn, 2002) was used in the hydraulic simulation. The River2D model solves 2D shallow water equations using the finite element method. The shallow water equations consist of the following continuity and x - and y -momentum equations:
2.2.2. Macroinvertebrates Field monitoring campaigns of macroinvertebrate species were conducted at two sites in the upstream and downstream reaches of the weir. The monitoring sites are marked by inverted triangles in Fig. 1. The macroinvertebrates were sampled using a Surber sampler (30 × 30 cm, mesh size 0.2 mm). In each site, three replicates were sampled. The collected samples were preserved in Kahle’s solution. The taxonomic groups were identified and enumerated by visual inspection using a stereomicroscope (Kil, 2008). The macroinvertebrate samplings were conducted in March 2006
∂qy ∂qx ∂H =0 + + ∂y ∂x ∂t
(1)
∂vqx ∂uqx ∂qx g ∂H 2 1 ∂Hτxx 1 ∂Hτxy + = gH (Sox − Sfx ) + + + + 2 ∂x ρ ∂x ρ ∂y ∂y ∂x ∂t (2) 365
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 5. Distribution of FHGs against velocity, flow depth, and substrate.
∂vqy ∂uqy ∂qx g ∂H 2 1 ∂Hτyx 1 ∂Hτyy + + = gH (Soy − Sfy ) + + + 2 ∂y ρ ∂x ρ ∂y ∂y ∂x ∂t
the measured data. Detailed information is given in Im et al. Regarding the eddy viscosity coefficient in the River2D model, such default values as ε1 = 0 , ε2 = 0.5, and ε3 = 0 were used.
(3) where t is time, x and y are streamwise and transverse directions, respectively. H is the flow depth, (u , v ) are the depth-averaged velocities in the ( x , y ) directions, respectively, (qx , qy ) are the unit discharges in the ( x , y ) directions, respectively, (Sox , Soy ) are the bed slopes in the ( x , y ) directions, respectively, (Sfx , Sfy ) are the friction slopes in the ( x , y ) directions, respectively, τij is the horizontal turbulent stress tensor, ρ is the water density, and g is the gravitational acceleration. The x - and y components of the friction slope are estimated, respectively, as follows:
Sfx =
n2u u2 + v 2 n2v u2 + v 2 , Sfy H 4/3 H 4/3
2.3.2. Habitat simulation Habitat simulation is a procedure that evaluates the suitability of the habitat to the target specie using the habitat suitability model. In the present study, HSCs were used in the habitat suitability model, and the physical habitat variables were flow depth, velocity, and substrate. Habitat suitability is indicated by the CSI. The values of the CSI range from zero to unity, which represent the minimum and optimal conditions of the physical habitat, respectively. Various methods are used to calculate the CSI, such as the multiplicative aggregation method, the geometric mean method, the minimum method, and the weighted mean method. In the present study, the following weighted mean method was used to compute the CSI:
(4a,b)
where n is Manning’s roughness coefficient. In the same study area, Im et al. (2011) carried out the calibration of the roughness coefficient for a wide range of discharges. They proposed n = 0.027 or the effective roughness height ks = 0.11 m, which was used in the present study. They measured the water surface elevation and velocity using large scale particle image velocimetry. They also validated the River2D model by comparing the computed results with
CSI = f (H )a × f (V )b × f (s )c
(5)
where f (HV ) is the suitability value for each physical habitat variable HV . Here HV includes flow depth H , velocity V , and substrate s . In Eq. (5), a , b , and c are weighting factors for H , V , and s , respectively. 366
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 6. HSCs for FHGs. 367
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 7. Flow depth and velocity before the weir removal.
Fig. 8. Flow depth and velocity after the weir removal. k
In macroinvertebrates, the substrate is the most crucial among the physical habitat variables (Jowett and Richardson, 1990; Quinn and Hickey, 1990; Beisel et al., 1998; Brooks et al., 2005). Therefore, different weighting factors should be applied to Eq.(5) in order to consider the relative importance of the physical habitat variables. Li et al. (2009) suggested the weighting factors such as a = 0.260, b = 0.327, and c = 0.413 for the weighted mean method to compute the CSI for macroinvertebrates. These were obtained from the so-called analytic hierarchy process. Later, Kim and Choi (2018) carried out PHSs for four target macroinvertebrates using the weighting factors proposed by Li et al. (2009) in the same study area. They found that CSI values for each macroinvertebrate species from PHSs match well to observed populations. In this study, the weighting factors suggested by Li et al. were used. The WUA is obtained using CSI values. The WUA means the quantity of the available habitat for the target species in the study area. The WUA is the overall quantity of the wetted area weighted by CSI values. It is estimated as follows:
Normalized WUA =
∑ CSIi × Ai i=1
k
∑i = 1 Ai
(7)
which yields the average value of the CSI in the study area, indicating the average quality of the physical habitat of the target species. 2.4. Habitat suitability curves for the FHG To construct the HSCs for the target FHG, monitoring data obtained from the Han-gang River basin were used (Ministry of Environment/ National Institute of Environmental Research, 2011). The total number of monitoring data is 340. The data included the population of macroinvertebrates, water temperature, turbidity, flow depth, velocity, and substrate. For convenience, the monitored populations of the macroinvertebrates were converted into population density (population/m2), which is the number of individual macroinvertebrates per unit of bed area. Table 1 lists the groups and macroinvertebrate species sampled in the Han-gang River basin. The species in the table are the most abundant and representative species in each group. As Table 1 shows, the monitored macroinvertebrate species were grouped into four FHGs, namely swimmers, clingers, sprawlers, and burrowers. The four representative species of each FHG were selected based on the monitored populations. Fig. 5 shows a 3D scatter plot of the monitored habitat use data for the FHGs, which were used to construct HSCs for the FHGs in this study.
k
WUA =
∑i = 1 CSIi × Ai
(6)
where k is the total number of cells and Ai is the area of the i -th cell. The normalized WUA is calculated as follows:
368
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 9. Distribution of CSI for FHGs before the weir removal.
resisting fast flow, inhabit riffles. Burrowers create caves using sand and silt, where they reside. Sprawlers live mainly on silt-free beds. The HSCs shown in Fig. 6 indicate that swimmers, clingers, and sprawlers preferred running water, compared with burrowers, which favored high flow velocity and shallow water depth.
As shown in Fig. 5, the observed population densities of the FHGs were plotted against flow depth, velocity, and substrate, and the size of the bubbles indicates the population density. In the present study, Gosse’s (1982) method was used to construct the HSCs. The data in Fig. 5 were used to build the HSCs for the FHGs. First, the frequency distribution was obtained for each habitat variable. Then, the values of the suitability index 1.0, 0.5, 0.1, and 0.05 were given to the values of the habitat variable that encompass 50%, 75%, 90%, and 95% of the total populations, respectively. As Fig. 6 shows, swimmers preferred the ranges of 0.19–0.25 m, 0.50–0.78 m/s, and 4 (fine gravel) for the flow depth, velocity, and substrate, respectively. The range of each habitat variable preferred by clingers and sprawlers were found to be similar to the optimal ranges of swimmers. However, the ranges preferred by burrowers appear to be different, i.e., 0.15–0.25 m, 0.42–0.56 m/s, and 3 (sand) for the flow depth, velocity, and substrate, respectively. These findings indicate that burrowers prefer slow-water and fine substrate habitats, compared with the other groups. The constructed HSCs appeared to reflect the characteristics of each FHG described in Merritt et al. (2002), Johnson et al. (2003), and Herbst et al. (2018). That is, swimmers tend to swim in a relatively short period and cling to the riverbed. Clingers, which are capable of
3. Results 3.1. Hydraulic simulation Hydraulic simulations were carried out using the 2D hydraulic model for the normal flow of Q = 0.91 m3/s. Figs. 7 and 8 show the simulation results before and after the weir removal, respectively. The weir removal significantly changed the flow in the upstream reach of the weir. The weir had created a large wetted area with a deep water depth of about 1.0 m and a low velocity less than 0.1 m/s. However, after the weir removal, the wetted area upstream of the weir was reduced with the decreased water depth and increased flow velocity. Even though the weir was removed, the pool habitat remained in the middle of the study area. After the removal, the flow rarely changed in the downstream reach of the weir. That is, the water depth remained shallow, and the velocity of the water was high. 369
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 10. Distribution of CSI for FHGs after the weir removal.
the CSIs computed for burrowers were high. These results are consistent with the monitoring data, which showed that the number of burrowers was larger than that of the other FHGs. After the weir removal, the CSIs for swimmers, clingers, and sprawlers were increased by 0.03 – 0.07, indicating that the quality of the habitat of these FHGs was enhanced slightly. The monitoring data indicated that swimmers and clingers newly appeared, and the number of sprawlers was increased slightly after the weir removal. In the downstream reach of the weir, the computed CSIs and the observed number of individuals were larger than those in the upstream reach. Similar to the upstream site, the CSI for burrowers was higher, and the observed number of burrowers was larger before the weir removal. After the weir removal, the CSIs for swimmers, clingers, and sprawlers were increased, but the CSI for burrowers was decreased significantly. The monitoring data supported the simulation results. Fig. 12(a) and (b) show the normalized WUA for each FHG before and after the weir removal in the upstream reach and downstream reach, respectively. The normalized WUA denotes the WUA divided by the wetted area. The wetted areas of the study area before and after the weir removal were 6.42×103 m2 and 3.22×103 m2, respectively. In the upstream reach, it was observed that the normalized WUAs for swimmers, clingers, and sprawlers were increased slightly after the weir removal. This result indicates that the weir removal contributed slightly to the increase in habitat suitability for these FHGs. However, the normalized WUA for burrowers was decreased slightly. A similar trend was observed in the downstream reach. Before the weir removal, habitat suitability for all FHGs in the downstream reach was greater than that in the upstream reach. Similarly, after the weir removal, habitat suitability for swimmers, clingers, and sprawlers was increased in the downstream reach. However, habitat suitability for burrowers was decreased significantly.
3.2. CSI Distribution and normalized WUA Based on the results of the hydraulic simulations, CSIs were calculated before and after the weir removal. CSI distributions of the FHGs before and after the removal are shown in Figs. 9 and 10, respectively. In the figure, the white and gray colored areas denote zero CSI and dry regions, respectively. Fig. 9 shows that habitat suitability for swimmers, clingers, and sprawlers was high in the downstream reach of the weir. The reason is that these FHGs prefer shallow water and high flow velocity. In contrast, habitat suitability for burrowers was the highest in the study area. The reason is that in the study area, the substrate was mainly sand, which is preferred by burrowers. Fig. 10 shows the CSI distributions after the weir removal. The suitability of the physical habitat for swimmers, clingers, and sprawlers increased in both the upstream and the downstream reaches of the weir. The main reason is that the substrates were coarsened over the entire study area after the weir removal. In addition, the reduced water depth and increased flow velocity enhanced habitat suitability for these groups in the upstream reach of the weir. However, habitat suitability for burrowers decreased over the study area. The reason is that the coarsening of the substrate over the entire study area negatively affected habitat suitability for burrowers. The reduced water depth and increased velocity also negatively affected the habitat, especially in the upstream reach. Fig. 11 shows the computed CSIs and the monitored number of individuals, which were compared at two sites upstream and downstream of the weir. The two monitoring sites are denoted by the inverted triangles in Fig. 1. The field monitoring campaigns were conducted before (i.e., in March 2006) and after (i.e., in August and September 2006) the weir removal (Kil, 2008). At the upstream site of the weir, the CSIs computed for swimmers, clingers, and sprawlers were low. However, 370
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
Fig. 11. Comparison of observed individuals and CSI.
Some additional PHSs were carried out for the low flow and the drought. It was found that the normalized WUA decreases as the discharge decreases for all FHGs because the flow depth and velocity decrease extremely. The results indicated that habitat suitability for all FHGs degrades for the low flow or the drought flow, compared to habitat suitability for the normal flow. For each flow, the change of the normalized WUA before and after the weir removal showed the same trend as is given in Fig. 12. In summary, the weir removal resulted in the degradation of the physical habitat regarding burrowers, which were dominant in the study area. However, the weir removal improved habitat suitability for the other three FHGs. This is due to coarsening of the substrate and flow change in the study area.
was degraded seriously, whereas habitat suitability for the other FHGs was improved slightly by the weir removal. The change in habitat suitability also affected the biological indices. Table 2 lists the dominance index and the diversity index before and after the weir removal. The dominance index is a measure of the degree to which one or a few species dominate the community, and the diversity index indicates the diversity of species within a community that consists of two or more species. In the present study, the dominance index and the diversity index were calculated by the methods in McNaughton (1967) and Pielou (1966), respectively. As Table 2 shows, the dominance index decreased in both the upstream and the downstream reaches after the weir removal. That is, the dominance index changed from “poor” to “fair” in the upstream reach and from “poor” to “good” in the downstream reach. This finding indicates that the percentages of the dominant and subdominant macroinvertebrate species decreased after the weir removal. The weir removal also affected the diversity index, which changed from “poor” to “fair” in the upstream reach and from “poor” to “good” in the downstream reach. This suggests that the number of macroinvertebrate
4. Discussion The results of this study revealed that the removal of the weir caused changes in the physical habitat and affected the composition of the macroinvertebrate community. Habitat suitability for burrowers 371
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
selective changes in the physical habitats of the macroinvertebrates. Specifically, habitat suitability for burrowers was decreased, but habitat suitability for the other FHGs was increased. In the same study area, Im et al. (2011) found that the number of individuals of lotic fishes, such as Rhinogobious brunneus and Zacco platypus, increased after the weir removal. The reason was that the weir removal actually restored riffles downstream of the weir, which led to the increase in the number of swimmers and clingers. The increase in the FHGs of the macroinvertebrate species improved the feeding conditions for lotic fishes, such as Rhinogobious brunneus and Zacco platypus. This finding indicated that the weir removal improved both the physical habitats and the feeding conditions of the fishes. 5. Conclusions This study presented the PHSs of the target FHGs to investigate changes in the habitats of the macroinvertebrate community after the weir was removed. The study area was a 0.6 km long reach in the Gongneung-cheon Stream, Korea, and Gongneung Weir-2 was located in the middle of the study reach. Gongneung Weir-2 was built in 1970 s to supply the irrigation water to the nearby area and was removed in April 2006 due to the land use change. The macroinvertebrate species in the study area were grouped into four FHGs such as swimmers, clingers, burrowers, and sprawlers, and their HSCs were constructed using monitoring data from the Han-gang River basin. PHSs for the four FHGs were carried out. The River2D model and the HSCs were used for hydraulic and habitat simulations, respectively. Hydraulics simulations for the normal flow revealed that the flow condition upstream of the weir changed significantly after the weir removal. That is, the water depth was decreased with the increased flow velocity. The results of the PHSs indicated that the habitat of burrowers was suitable over the study area before the weir removal. After the removal, habitat suitability for burrowers was decreased, whereas habitat suitability for the other FHGs was increased. The main reason is that the substrates were coarsened over the entire study area after the weir was removed. The improvement in the physical habitat for swimmers, clingers, and sprawlers increased the numbers of these macroinvertebrate species in the study area. Consequently, the diversity of the macroinvertebrate community was increased. Findings from some previous studies such as ones by Stanley et al. (2002) and Thomson et al. (2005) are contrary to those from the present study in that fine sediment transport from upstream of the weir degraded habitat quality for macroinvertebrates in the reach downstream of the weir. However, in the present study, the flood flow coarsened the substrates over the entire study area, leading to the selective changes in the physical habitats for macroinvertebrates. In addition, the weir removal restored riffles downstream of the weir, which brought out the increase of the populations of swimmers, clingers, sprawlers. This improved the feeding condition of the fish species, resulting in the increase in the number of individuals of lotic fishes, as reported in Im et al. (2011).
Fig. 12. Change of normalized WUA for each FHG before and after the weir removal.
Table 2 Biological indices before and after weir removal (Kil, 2008). index
dominance (DI )(1) diversity (H' )(2)
upstream reach of the weir
downstream reach of the weir
before removal
after removal
before removal
after removal
0.83 1.24
0.64 2.35
0.71 1.50
0.43 3.30
(1) Dominance index: excellent (< 0.25), good (0.25–0.5), fair (0.5–0.7), poor (0.7–0.9), and very poor (> 0.9). Here, DI = (N1 + N2)/ N with N = total number of individuals in all species, N1 and N2 are the number of individuals of the two most dominant species in a community. (2) Diversity index: excellent (> 4.0), good (3.0–4.0), fair (2.0–3.0), poor s (1.0–2.0), and very poor (< 1.0). Here, H ' = − ∑i = 1 (ni / N )ln(ni / N ) with ni = number of individuals in a species i of a sample and s = number of species.
Declaration of Competing Interest
species was increased after the weir removal. This is related to the fact that habitat suitability for burrowers was decreased, whereas it was increased for the other three FHGs. Previous studies by Stanley et al. (2002) and Thomson et al. (2005) indicated that habitat suitability for macroinvertebrates in the downstream reach of the weir was decreased after weir removal. This is because that the fine sediment deposited in the impounded region was transported and deposited in the downstream reach of the weir after the weir was removed. However, in the present study, the bed sediment was coarsened over the study area after flooding in July, which induced
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements This research was supported by a grant (18CTAP-C132929-02) from Infrastructure and transportation technology promotion research Program funded by Ministry of Land, Infrastructure and Transport of South Korean government. 372
Ecological Engineering 138 (2019) 362–373
S.K. Kim and S.-U. Choi
New Zealand river and the development of in-stream flow-habitat models for Deleatidium spp. New Zeal. J. Mar. Fresh. 24, 19–30. https://doi.org/10.1080/ 00288330.1990.9516399. Kanehl, P.D., Lyons, J., Nelson, J.E., 1997. Changes in the habitat and fish community of the Milwaukee River, Wisconsin, following removal of the woolen mills dam. N. Am. J. Fish. Manag. 17, 387–400. https://doi.org/10.1577/1548-8675(1997) 017<0387:CITHAF> 2.3.CO;2. Kil, H.K., 2008. Effects of Dams on Benthic Macroinvertebrate Communities in Korean Streams (Doctoral dissertation). Seoul Women’s University, Seoul, Korea (in Korean). Kim, S.K., Choi, S.U., 2018. Prediction of suitable feeding habitat for fishes in a stream using physical habitat simulations. Ecol. Model. 385, 65–77. https://doi.org/10. 1016/j.ecolmodel.2018.07.014. Korea Institute of Construction Technology., 2008. The stream eco-corridor restoration and water quality improvement by weir removal with its function lost. Ministry of Environment, p. 402 (in Korean). Korea Rural Community Corporation, 2013. Statistical yearbook of land and water development for agriculture. Ministry for Food, Agriculture, Forestry and Fisheries (in Korean). Larinier, M., 2001. Environmental issues, dams and fish migration. FAO fisheries technical paper, 419, 45–89. Li, F., Cai, Q., Fu, X., Liu, J., 2009. Construction of habitat suitability models (HSMs) for benthic macroinvertebrate and their applications to instream environmental flows: a case study in Xiangxi River of Three Gorges Reservoir region, China. Prog. Nat. Sci. 19, 359–367. https://doi.org/10.1016/j.pnsc.2008.07.011. Magilligan, F.J., Graber, B.E., Nislow, K.H., Chipman, J.W., Sneddon, C.S., Fox, C.A., 2016. River restoration by dam removal: enhancing connectivity at watershed scales. Elem. Sci. Anth. 4. McNaughton, S.J., 1967. Relationship among functional properties of California grassland. Nature 216, 168–169. https://doi.org/10.1038/216168b0. Merritt, R.W., Cummins, K.W., Berg, M.B., Novak, J.A., Higgins, M.J., Wessell, K.J., Lessard, J.L., 2002. Development and application of a macroinvertebrate functionalgroup approach in the bioassessment of remnant river oxbows in southwest Florida. J. N. Am. Benthol. Soc. 21, 290–310. https://doi.org/10.2307/1468416. Ministry of Environment/National Institute of Environmental Research, 2011. Report on survey and assessment for health conditions of aquatic ecosystem. Ministry of Environment, National Institute of Environmental Research, p. 324 (in Korean). Pielou, E.C., 1966. The measurement of diversity in different types of biological collections. J. Theor. Biol. 13, 131–144. https://doi.org/10.1016/0022-5193(66)90013-0. Quinn, J.M., Hickey, C.W., 1990. Characterization and classification of benthic invertebrate communities in 88 New Zealand rivers in relation to environmental factors. N. Z. J. Mar. Fresh. 24, 387–409. https://doi.org/10.1080/00288330.1990. 9516432. Stanley, E.H., Luebke, M.A., Doyle, M.W., Marshall, D.W., 2002. Short-term changes in channel form and macroinvertebrate communities following low-head dam removal. J. N. Am. Benthol. Soc. 21, 172–187. https://doi.org/10.2307/1468307. Steffler, P., Blackburn, J., 2002. Two-dimensional depth averaged model of river hydrodynamics and fish habitat. In: River2D user’s manual, University of Alberta, Canada. Thomson, J.R., Hart, D.D., Charles, D.F., Nightengale, T.L., Winter, D.M., 2005. Effects of removal of a small dam on downstream macroinvertebrate and algal assemblages in a Pennsylvania stream. J. N. Am. Benthol. Soc. 24, 192–207. https://doi.org/10.1899/ 0887-3593(2005) 024<0192:EOROAS>2.0.CO;2. US Army Corps of Engineers. 2018. 2018 National Inventory of Dams (NID) database. U.S. Army Corps of Engineers. (Available from: https://nid.sec.usace.army.mil/ords/ f?p=105:19:487464404088::NO::: (accessed 28 July 2019)).
References Baxter, R.M., 1977. Environmental effects of dams and impoundments. Annu. Rev. Ecol. Evol. Syst. 8, 255–283. https://doi.org/10.1146/annurev.es.08.110177.001351. Beisel, J.N., Usseglio-Polatera, P., Thomas, S., Moreteau, J.C., 1998. Stream community structure in relation to spatial variation: the influence of mesohabitat characteristics. Hydrobiologia 389, 73–88. https://doi.org/10.1023/A:1003519429979. Bender, P.M., 1997. Restoring the Elwha, White Salmon, and Rogue Rivers: a comparison of dam removal proposals in the Pacific Northwest. J. Land Res. Envtl. L. 17, 189. Brandt, S.A., 2000. Classification of geomorphological effects downstream of dams. Catena 40, 375–401. https://doi.org/10.1016/S0341-8162(00)00093-X. Brooks, A.J., Haeusler, T.I.M., Reinfelds, I., Williams, S., 2005. Hydraulic microhabitats and the distribution of macroinvertebrate assemblages in riffles. Freshwater Biol. 50, 331–344. https://doi.org/10.1111/j.1365-2427.2004.01322.x. Catalano, M.J., Bozek, M.A., Pellett, T.D., 2007. Effects of dam removal on fish assemblage structure and spatial distributions in the Baraboo River, Wisconsin. N. Am. J. Fish. Manag. 27, 519–530. https://doi.org/10.1577/M06-001.1. Chiu, M.C., Yeh, C.H., Sun, Y.H., Kuo, M.H., 2013. Short-term effects of dam removal on macroinvertebrates in a Taiwan stream. Aquat. Ecol. 47, 245–252. https://doi.org/ 10.1007/s10452-013-9439-y. Choi, S.U., Lee, H.E., Yoon, B.M., Woo, H.S., 2009. Change in stream morphology after Gongneung weir 2 removal. J. Korea Water Resour. Assoc. 42, 425–432. https://doi. org/10.3741/JKWRA.2009.42.5.425. (in Korean). Cummins, K.W., 1973. Trophic relations of aquatic insects. Annu. Rev. Entomol. 18, 183–206. https://doi.org/10.1146/annurev.en.18.010173.001151. Cummins, K.W., 1974. Structure and function of stream ecosystems. BioScience 24, 631–641. https://doi.org/10.2307/1296676. De Leaniz, C.G., 2008. Weir removal in salmonid streams: implications, challenges and practicalities. Hydrobiologia 609, 83–96. https://doi.org/10.1007/s10750-0089397-x. Doyle, M.W., Stanley, E.H., Harbor, J.M., 2003. Channel adjustments following two dam removals in Wisconsin. Water Resour. Res. 39. https://doi.org/10.1029/ 2002WR001714. Gosse J.C., 1982. Microhabitat of rainbow and cutthroat trout in the Green River below Flaming Gorge Dam. Final report, Contract 81 5049, Utah Division of Wildlife Resources, Salt Lake City, p. 114. Gough, P., Fernandez Garrido, P., Van Herk, J., 2018. Dam Removal. A viable solution for the future of our European rivers. Dam Removal Europe. P. 38. Hansen, J.F., Hayes, D.B., 2012. Long-term implications of dam removal for macroinvertebrate communities in Michigan and Wisconsin Rivers, United States. River Res. Appl. 28, 1540–1550. https://doi.org/10.1002/rra.1540. Herbst, D.B., Cooper, S.D., Medhurst, R.B., Wiseman, S.W., Hunsaker, C.T., 2018. A comparison of the taxonomic and trait structure of macroinvertebrate communities between the riffles and pools of montane headwater streams. Hydrobiologia 820, 115–133. https://doi.org/10.1007/s10750-018-3646-4. Im, D., Kang, H., Kim, K.-H., Choi, S.U., 2011. Changes of river morphology and physical fish habitat following weir removal. Ecol. Eng. 37, 883–892. https://doi.org/10. 1016/j.ecoleng.2011.01.005. Im, D., Choi, B., Choi, S.U., 2019. Change in the composition of fish community following weir removal, field observations and physical habitat simulations. River Res. Appl. https://doi.org/10.1002/rra.3480. Johnson, L.B., Breneman, D.H., Richards, C., 2003. Macroinvertebrate community structure and function associated with large wood in low gradient streams. River Res. Appl. 19, 199–218. https://doi.org/10.1002/rra.712. Jowett, I.G., Richardson, J., 1990. Microhabitat preferences of benthic invertebrates in a
373