Springer 2005
Hydrobiologia (2005) 541: 175–188 DOI 10.1007/s10750-004-5706-1
Primary Research Paper
Aquatic macroinvertebrate assemblages in mitigated and natural wetlands Collin K. Balcombe1, James T. Anderson1,*, Ronald H. Fortney2 & Walter S. Kordek3 1
Division of Forestry, Wildlife and Fisheries Resources, West Virginia University, P.O. Box 6125, 322 Percival Hall, Morgantown, West Virginia 26506-6125, USA 2 Department of Civil and Environmental Engineering, West Virginia University, P.O. Box 6103, Morgantown, West Virginia 26506-6103, USA 3 West Virginia Division of Natural Resources, P.O. Box 67, Ward Road, Elkins, West Virginia 26241, USA (*Author for correspondence: E-mail:
[email protected]) Received 21 July 2003; in revised form 25 October 2004; accepted 29 October 2004
Key words: macroinvertebrates, invertebrates, mitigation wetland, wetland construction, wetlands, wildlife
Abstract Many wetlands have been constructed in West Virginia as mitigation for a variety of human disturbances, but no comprehensive evaluation on their success has been conducted. Macroinvertebrates are extremely valuable components of functioning wetland ecosystems. As such, benthic and water column invertebrate communities were chosen as surrogates for wetland function in the evaluation of 11 mitigation and 4 reference wetlands in West Virginia. Mitigation wetlands ranged in age from 4 to 21 years old. Overall familial richness, diversity, density and biomass were similar between mitigation and reference wetlands (p > 0.05). Within open water habitats, total benthic invertebrate density was higher in reference wetlands, but mass of common taxa from water column samples was higher in mitigation wetlands (p < 0.05). Planorbidae density from benthic samples in emergent habitats was higher in reference than mitigated wetlands. Benthic Oligochaeta density was higher across open water habitats in mitigation wetlands. All other benthic taxa were similar between wetland types. Among the most common water column orders, Isopoda density was higher in reference wetlands, but Physidae density was higher in mitigation wetlands. Within mitigation wetlands, emergent areas contained higher richness and diversity than open areas. These data indicate that mitigation and reference wetlands generally support similar invertebrate assemblages, especially among benthic populations. The few observed differences are likely attributable to differences in vegetative community composition and structure. Mitigation wetlands currently support abundant and productive invertebrate communities, and as such, provide quality habitat for wetland dependent wildlife species, especially waterbirds and anurans.
Introduction Wetlands provide important habitat for numerous species of wildlife, fish, waterfowl, shorebirds, and neotropical birds. Unfortunately, wetland destruction has plagued the U.S. for many decades, but recent legislation has mandated the protection of these valuable ecosystems. Today, wetlands and streams are the only ecosystems regulated on both public and private lands in the U.S. (National Research Council, 1995). After the Clean Water
Act of 1972, the ‘no net loss’ policy was enacted in the late 1980s with the goal of sustaining positive gains in the wetland resource base. On paper, the ‘no net loss’ policy appears to be working with an estimated 50,000 ha of wetlands in the U.S. being gained from October 1993 to September 1999 (Mitsch & Gosselink, 2000). However, these statistics only reflect compensation of the area of wetland lost, and do not pertain to gains or losses in wetland function. Numerous authors have written about our inability to successfully mitigate
176 for wetland destruction (e.g., Erwin, 1990; Reinartz & Warne, 1993). Although the definition of success varies depending upon project objectives, most agree that compensatory wetlands should replace functions lost during wetland destruction. To gain further insight into the success of our legislation in protecting wetlands, one must evaluate this success in terms of wetland function. Since the 1980s, numerous studies have sought to assess the success of mitigation wetlands in properly supporting hydrology, soils, vegetation, and wildlife (Jarman et al., 1991; Reinartz & Warne, 1993; Niswander & Mitsch, 1995; Wilson & Mitsch, 1996; Campbell et al., 2002). While these functions are crucial to wetland ecosystem integrity, it may be logistically impossible to evaluate all of these functions when determining the success of a mitigation wetland. While wetland creation and restoration has been conducted widely throughout the U.S., research has only begun to determine if compensatory wetlands are replacing invertebrate habitat and communities of natural wetlands destroyed by development (Streever & Crisman,1993; Scatolini & Zedler, 1996; Ashley et al., 2000; Fairchild et al., 2000). For a variety of reasons, invertebrates are extremely important in the functioning of wetlands, and thus can be viewed as surrogates for wetland health. First, from a logistic standpoint, they make good study specimens because they are abundant, readily surveyed, and taxonomically rich (Dodson, 2001). Long-term hydrologic cycles, water quality, and habitat type associated with wetlands influence many adaptive strategies of invertebrates (Wiggins et al., 1980; Doupe & Horwitz, 1995; Brooks, 2000; Anderson & Smith 2004). Hence, researchers have used invertebrates to quantify and qualify water quality in wetland ecosystems (Wallace et al., 1996). In turn, invertebrates contribute to other wetland functions by assisting in litter decomposition, nutrient cycling (Cummins, 1973; Merritt et al., 1984) and plant community regulation (Weller, 1994). Thus, invertebrates indirectly aid in the transfer of nutrients from the sediments, detritus, and water column to higher-level organisms. They also have direct impacts on wildlife species that depend on them for food. Because numerous avian species, particularly waterfowl and other waterbirds, depend on invertebrates for food (De Szalay & Resh, 1996; Gonzalez et al., 1996; Anderson & Smith,
1998, 1999; Anderson et al., 2000), researchers can assess avian productivity by sampling invertebrates. As well, they are important in the diets of anurans (Anderson et al., 1999; Lima & Magnusson, 2000). Recently, invertebrates have even been used as indicators in delineating wetland boundaries (Euliss et al., 2002). It is clear that invertebrates play a vital role in wetland function and thus, are integral in analyzing the health of these ecosystems. Despite numerous studies indicating the significance of invertebrates in shaping wetland ecosystem health, few studies have monitored the ability of restored and constructed wetlands in supporting healthy invertebrate populations in the Central Appalachian mountains or elsewhere (Johnson et al., 2000). Many studies that do exist preclude a comprehensive evaluation of all invertebrate taxa, and instead, focus on specific taxa deemed important to wetland health (Streever & Crisman, 1993; Streever et al., 1995, 1996; Ashley et al., 2000; Fairchild et al., 2000; Johnson et al., 2000). Data are needed on the invertebrate assemblages of mitigated wetland habitats to ensure that communities are developing similarly to naturally functioning wetlands. This study sought to evaluate the success of mitigation wetlands in supporting invertebrate communities in the Central Appalachian Mountains of West Virginia. Natural (reference) wetlands were used as standards of comparison since these areas are considered relatively stable and undisturbed (Brinson, 1993; Brinson & Rheinardt, 1996; Wilson & Mitsch, 1996). Thus, the objective of this study was to test the null hypothesis that invertebrate familial richness, diversity, density, and biomass were equal between mitigation and reference wetlands. A further objective was to test the hypothesis that invertebrate assemblages in mitigated wetlands were equal between emergent and open water habitats. These data should be helpful in the creation of future mitigation wetlands, and also in the establishment of monitoring protocols for these and other wetlands in the region. Materials and methods Study sites Eleven mitigation (Walnut Bottom, VEPCO, Buffalo Coal, Elk Run, Leading Creek, Sugar
177
Figure 1. Site locations of mitigation and reference wetlands in West Virginia, 2001–2002.
Creek, Sand Run, Triangle, Trus Joist MacMillan, Enoch Branch, and Bear Run) and 4 reference (Altona Marsh, Elder Swamp, Meadowville, and Muddlety) wetlands from the northern two-thirds of West Virginia were evaluated for this study (Fig. 1; Appendix A.1). Mitigation wetlands ranged in age from 4 to 21 years (x ¼ 10:0, SE ¼ 1.7), in size from 3.0 to 10.0 ha (x ¼ 5:8, SE ¼ 0.80), and in elevation from 265 to 1036 m (x ¼ 586, SE ¼ 75.9). Mitigation sites were created to compensate for wetland losses sustained in West Virginia for many human activities including highway and industrial development, as well as mining. Almost all mitigation study sites were located near some form of human disturbance. In fact, many were located adjacent to roads with moderate to heavy traffic. All were classified as either palustrine emergent or unconsolidated bottom wetlands with seasonally to permanently flooded hydrologic regimes (Cowardin et al., 1979). Reference wetlands were chosen based on their similarity in location and elevation to mitigation sites within that area (Balcombe, 2003; Balcombe
et al., in press a, b). All reference wetlands were undisturbed (i.e., lacked evidence of logging or grazing) and were typical of the palustrine scrubshrub and emergent wetlands with scrub-shrub borders that occurred in the region. Because the reference wetlands were relatively larger than mitigation sites, only portions of reference sites were selected for study. Reference wetlands ranged in elevation from 170 to 1000 m (x ¼ 582, SE ¼ 169.5) and ranged in size from 6.5 to 28.0 ha (x ¼ 15:1, SE ¼ 4.7). All were classified as palustrine emergent or scrub-shrub wetlands with seasonally to permanently flooded hydrologic regimes (Cowardin et al., 1979). Common rush (Juncus effusus L.) and broadleaved cattail (Typha latifolia L.) were the most common dominant plant communities in mitigated wetlands (Balcombe et al., in press b). Moreover, American bur-reed (Sparganium americanum Nutt.), mild water pepper (Polygonum hydropiperoides Michx.), reed canarygrass (Phalaris arundinacea L.), purple loosestrife (Lythrum salicaria L.), and rice cutgrass (Leersia oryzoides L.) were
178 common dominance types in mitigated wetlands (Balcombe et al., in press b). Broad-leaved cattail, soft-stem bulrush (Scirpus validus Vahl), tussock sedge (Carex stricta Lam.), American bur-reed, and common rush were the dominant communities in reference wetlands (Balcombe et al., in press b). Cover types on reference wetlands averaged 9.3% open water, 44.3% herbaceous vegetation, 41.1% scrub-shrub vegetation, and 5.3% trees. Mitigation wetland cover types averaged 40.6% open water, 54.0% herbaceous vegetation, and 5.4% scrub-shrub vegetation. Invertebrate sampling We conducted invertebrate sampling according to Anderson & Smith (1996, 2000, 2004) during the summers of 2001 and 2002. Specifically, we collected 300 samples during July 2001, September 2001, April 2002, and June 2002. Samples were collected at different times both years to collect a greater diversity of taxa. Wetlands were stratified based on wetland classification (Cowardin et al., 1979), and specimens were collected at 10 random points within open water and emergent areas of each wetland. At each point, we used a 5 cm diameter core (15 cm deep) and a 7.5 cm diameter water column sampler (Swanson, 1983) to collect benthic and water column specimens, respectively (Anderson & Smith, 1996, 2004). Water column samples were sieved in the field using a 500-micron sieve (Huener & Kadlec, 1992) and preserved in 70% ethanol. Benthic samples were placed in bags, refrigerated, and processed using an elutriator (Magdych, 1981) within 10 days of collection (Anderson & Smith, 2000). Invertebrates were identified and counted to family using McCafferty (1981), Merritt & Cummins (1984), and Pennak (1989). Familial richness was expressed as the number of families/wetland, and abundance (no. individuals) was converted into density estimates (No/m2 or No/L). Biomass (g/m2 or g/l) was obtained by oven-drying samples at 55C for ‡48 h to a constant mass (0.0001 g) and using an analytical scale. Data analyses Mitigation and reference wetlands were compared using SAS (SAS Institute, 1988). Invertebrate
familial richness, diversity, biomass, and density were compared using a split-plot Analysis of Variance (ANOVA) model, with wetland type (mitigation versus reference) as the first split and time as the second split. We incorporated a repeated measures design for two survey periods, which were repeated both years. The independent variables tested were wetland type and sampling period and type · sampling period interactions with dependent variables being richness, diversity, biomass, and density. Familial diversity was calculated using the Shannon-Weiner Index (Shannon & Weaver, 1949). To decrease variability, geographic area (Fig. 1) was included as a blocking factor for all analyses, except when comparing invertebrate indices between subtypes (emergent versus open water) within mitigation or reference wetlands. In this case, site was used as a blocking factor. In addition to comparisons of all invertebrate taxa, comparisons were made between wetland types for the most abundant orders and families observed. All families used for this analysis contained at least 100 individuals. Assumptions of normality were tested with the univariate procedure in SAS (SAS Institute, 1988), and Levene’s test was used for homogeneity of variances. Rank and log transformations were used to convert dependent variables that did not meet the aforementioned assumptions (Dowdy & Wearden, 1991). Specifically, log transformations were used for within subtype comparisons, and rank transformations (Conover & Iman, 1981; Potvin & Roff, 1993) were used to analyze familial density and biomass of common taxa. All tests were considered significant at p < 0.05.
Results Taxa occurrence A total of 10,824 individuals were sampled, 6350 of which occurred in mitigation sites and 4474 occurred in reference sites. Within benthic samples, 3173 individuals from 38 families were sampled in mitigation wetlands while 3799 individuals from 25 families were sampled in reference wetlands. Within water column samples, 3177 individuals from 70 families were sampled in
179 mitigation wetlands, and 675 individuals from 50 families were sampled in reference wetlands. A complete list of all families is located in Balcombe (2003). Mitigation versus reference wetlands Overall benthic (Table 1) and water column (Table 2) familial richness and diversity were similar across wetland complexes of mitigation and reference wetlands. Similar results were obtained across emergent and open water areas. Total benthic (Table 1) and water column (Table 2) density and biomass were similar between mitigation and reference wetlands. However, within open water areas benthic density was higher in reference wetlands, but water column density and biomass were similar between mitigated and reference wetlands. The nine most abundant benthic families (of four orders) included Diptera (Chironomidae), Gastropoda (Lymnaedae, Physidae, Planorbidae, Pomatiopsidae, Valvatidae, and Viviparidae), Pelecypoda (Sphaeriidae), and Oligochaeta (not taken to family). The top 13 water column families (of 9 orders) included Amphipoda (Talitridae), Cladocera (not taken to family), Diptera (Chironomidae), Ephemeroptera (Baetidae and Caenidae), Gastropoda (Physidae, Planorbidae, and Viviparidae), Hemiptera (Corixidae and Veliidae), Isopoda (Asellidae), Odonata (Coenagrionidae), and Pelecypoda (Sphaeriidae). The two most abundant benthic orders sampled in both wetland types were Gastropoda and Oligochaeta (Table 1). The two most abundant water column orders in mitigation wetlands were Gastropoda and Hemiptera while in reference wetlands, Isopoda and Diptera were most abundant (Table 2). Comparisons of each order individually yielded a higher benthic Oligochaeta density in mitigation wetlands across open water areas (Table 1). Within emergent areas, Hemipteran and Odonata water column density was higher in mitigation wetlands (Table 2). However, water column Isopoda density was higher in reference sites across entire wetland complexes (Table 2). This was attributed to higher numbers across emergent areas. Density and biomass for all other orders were similar between mitigated and reference wetlands.
An evaluation of the 13 common families from water column samples combined yielded a higher biomass in mitigation wetlands within open water areas (Table 2). Benthic Planorbidae density was higher in emergent areas of reference wetlands than in mitigated wetlands (Table 1). Physidae density in mitigated wetlands was greater than in reference wetlands (Table 2). This was attributed to higher numbers across open water areas. Physidae biomass from water column samples was higher in mitigation wetlands across entire wetland complexes as well as emergent and open water areas (Table 2). Asellidae density and biomass were higher in reference wetland complexes, but this was the only family observed within Isopoda, so results are already reflected above within order comparisons. Emergent versus open water habitats Familial richness, diversity, density, and biomass also were compared between emergent and open water areas within mitigation and reference wetlands (Table 3). In this comparison, richness and diversity were higher in emergent areas for mitigation wetlands. Overall water column density and biomass for total invertebrates and common taxa also were higher in emergent areas. Trends obtained for reference wetlands were similar to mitigation wetland results, but statistical differences were lacking due to the small sample size of reference wetlands.
Discussion Mitigation versus reference wetlands These data indicated equally abundant, diverse, and productive invertebrate communities in mitigation and reference wetlands. An examination of specific taxa based on order and family indicated several differences in abundance or biomass of invertebrates between mitigation and reference wetlands. What is most striking is that only three taxa (Physidae, Asellidae, and Odonata) varied between mitigation and reference wetlands, with two taxa (Physidae, Odonata) higher in mitigation wetlands and only one higher (Asellidae) in reference wetlands. However, mass of the 13 most
0.005 1.6
0.849
0.021 3.6
0.021
Mass Density
Mass
Sphaeriidae 0.012
0.012 1.7
1.6
0.079
6.8
0.028
2.0
2.99
0.849 34.6
0.02 1.64
2.217
2.217 34.4
35.0
0.009
5.0
0.288
8.7
2.215
2.215 33.0
33.6
0.004
1.9
0.286
8.3
0.005
1.217 0.4
25.4
1.795
35.8 0.259
0.097
0.041
0.424
0.230
0.894
0.293 0.923
0.115
0.750
0.876
0.298
0.778
0.311
0.633 0.212
0.220
0.365
0.221
0.61
1.95 0.47
0.42
0.43
1.37
1.00
0.33
0.49
0.454
0.193 0.507
0.531
0.527
0.269
0.341
0.580
0.501
2.22 0.168 <0.01 0.951
1.43
3.35
5.51
Note: Bold numbering indicates a significant difference (p < 0.05).
3.7
0.104
Density
Mass
0.043
15.3
Density
Pelecypoda
Oligochaeta
Mass
<0.001<0.0010.005
3.7
Mass
Density
1.217 0.4
25.4
1.795
35.8
0.001 0.1
Viviparidae
114.9
10.030 10.030 0.69
34.6
Mass Density
0.001 <0.1
0.03
1.21
0.08
<0.0010.11
0.6
0.003
1.5
14.182 14.180 1.23 10.3 10.3 0.01
115.3
Valvatidae
0.545 0.3
1.71
0.90
1.71
16.409 16.394 1.14 4.2
0.3
0.874
8.1
0.981
5.7
0.015
1.479 0.3
15.7
0.080
147.5
1.4
16.423 16.391 0.24 156.3 147.2 1.78
1.740
<0.0010.001
0.5
0.001
0.7
1.484
1.484 18.6
0.060
4.8 160.6
Density
Mass
1.119
16.1
Density
0.6 18.4
Pomatiopsidae
Planorbidae
Mass
0.020
9.3
Density
Mass
Physidae
2.056 0.5
Mass Density
Lymnaedae
0.001
30.0
Density
Mass
0.003
2.0
Density
Gastropoda
Chironomidae
Mass
2.181
Mass
Diptera
4.7
2.190 50.9
Mass Density
Density
1.590
Diversity
Common 9 taxa
5.5
54.7
Density
0.043
0.043 3.8
3.8
0.200
12.3
0.001
0.5
0.000
0.001 <0.1
0.2
0.279
12.6
0.114
3.8
0.001
0.396 0.1
17.2
0.004
2.5
0.005
3.3
0.643
0.645 35.8
1.120
37.1
3.9
x
0.029
0.029 2.1
2.2
0.137
3.9
0.001
0.3
0.000
0.001 <0.1
0.2
0.225
8.1
0.105
2.7
0.001
0.331 0.1
11.2
0.002
0.7
0.002
0.7
0.343
0.343 11.4
0.100
11.5
0.5
0.479
0.481 14.5
17.9
0.015
3.2
1.859
26.2
0.120
0.300 9.7
21.0
2.074
48.6
0.068
5.8
0.174
4.594 4.4
115.7
0.001
1.5
0.001
2.0
5.089
5.092 134.9
1.200
139.5
3.6
x
0.479
0.481 14.3
17.7
0.011
1.6
1.859
26.0
0.120
0.300 9.7
21.0
2.057
47.2
0.068
5.8
0.174
4.577 4.4
114.1
0.001
0.9
0.001
1.1
5.066
5.068 128.8
0.420
132.1
2.0
SE
p
SE
F1,10
SE
SE x
Mitigation
Reference
Mitigation
x
Reference
Open water
Emergent
Total invertebrates Richness
Invertebrate taxa
0.939
0.083
0.005
0.102
0.368
0.061
0.084 0.126
0.132
0.391
0.253
0.218
0.348
0.324
0.743 0.430
0.332
0.215
0.129
0.216
0.092
0.386
0.825 0.057
0.945
0.042
0.062
p
0.11
0.747
1.06 0.327 <0.01 0.964
0.01
3.72
12.69
3.25
0.89
4.45
3.68 2.78
2.68
0.80
1.47
1.73
0.97
1.08
0.11 0.68
1.04
1.76
2.74
1.74
3.47
0.82
0.05 4.61
0.01
5.42
4.44
F1,10
0.001 <0.1
0.3
0.366
7.9
0.543
4.2
0.007
0.901 0.2
13.3
0.001
0.6
0.001
1.3
0.894
0.895 14.1
0.080
14.0
0.5
SE
0.032
0.032 3.7
3.8
0.152
13.8
0.022
2.1
0.018
0.018 1.9
1.9
0.074
4.0
0.014
1.1
0.220
139.8
1.4
SE
NA
1.93
0.09
F1,10
0.758 5.1
23.2
1.934
42.2
5.049
20.2
0.511
9.388 7.4
115.5
0.001
1.6
0.003
3.1
1.348
1.349 24.4
26.4
0.012
4.1
1.073
17.4
1.347
1.348 23.6
25.6
0.005
1.3
1.072
17.1
0.062
0.758 5.1
23.2
1.926
41.5
5.049
20.2
0.511
9.378 7.4
114.5
0.001
0.6
0.001
0.9
10.730 0.001
0.184
0.328
0.254
0.606
0.790
0.242
0.468 0.162
NA
0.195
0.769
p
0.916
0.086
0.126 0.122
0.106
0.216
0.105
0.377
0.228
0.28
1.56 0.31
0.29
1.96
4.93
0.03
0.611
0.240 0.591
0.603
0.192
0.506
0.862
<0.01 0.987
3.62
2.79 2.86
3.15
1.74
3.18
0.85
1.65
0.01
1.04 0.332 <0.01 0.985
2.04
1.06
1.47
0.28
0.08
1.54
10.757 10.730 0.57 145.6 138.0 2.28
1.470
150.0
4.8
x
Reference
<0.001<0.0010.062
0.001 <0.1
0.3
0.577
14.3
0.616
6.5
0.010
1.226 0.3
23.6
0.002
2.2
0.004
4.0
1.412
1.417 43.3
1.36
45.9
4.7
x
Mitigation
Total
Table 1. Benthic invertebrate richness (number of families/wetland), diversity, density (No/m2) and biomass (g/m2) between mitigation (n = 11) and reference (n = 4) wetlands across emergent areas, open water areas, and entire wetland complexes, 2001–2002 with comparisons of all invertebrate taxa and the 9 most common taxa (i.e., >100 individuals)
180
3.1
Viviparidae
1.0
0.005
Mass
0.207
Density
Mass
0.017
Mass
1.5
0.229 0.9
Mass Density
Physidae
Density
3.4
0.003
0.6
0.174
0.6
0.009
0.183 0.5
1.5
0.006
0.7
0.001
0.4
0.002
0.010 0.3
1.7
0.004
0.5
0.001
0.3
0.002
0.008 0.3
1.2
0.1
0.09
0.24
3.78
3.41
4.64
4.04 6.89
3.22
4.35
<0.001<0.001<0.001<0.0011.06
0.1
Mass
0.3
0.13
2.92
0.6
0.2
0.006
0.48 2.09
0.54
0.39
0.04
<0.001<0.001<0.001<0.0010.08
0.4
0.001 0.8
0.8
0.002
0.8
Mass
Density
Planorbidae
0.97
Density
Gastropoda
Caenidae
0.001 1.2
1.3
0.003
2.3
<0.0010.006 0.2
0.1
<0.001<0.0010.69
0.2
0.3
0.001
Mass
0.001 0.3
0.9
0.001
1.0
0.001
0.8
Density
0.002 1.0
Mass Density
Ephemeroptera
Baetidae
1.8
0.002
Mass
Density
2.5
0.002
Mass
Density
Chironomidae
Diptera
1.6
<0.001<0.001<0.001<0.0011.88
Density
0.78
Mass
Cladocera
0.2
3.98
1.55
Talitridae
0.2
0.024
3.2
0.25 2.02
0.1
0.040
8.6
2.7 0.022
4.76 0.44
<0.001<0.001<0.001<0.0012.16 0.1 0.1 0.1 0.1 0.29
0.1
12.6 0.055
1.5 0.04
Mass Density
0.181
2.6
0.182
8.0 2.33
F1,10
Density
0.253
Mass
0.9 0.11
SE
Amphipoda
11.0
Mass
Density
14.8
0.259
Density
Common 13 taxa
11.2
2.46
x
0.770
0.632
0.081
0.095
0.057
0.072 0.025
0.103
0.328
0.064
0.782
0723
0.118
0.504 0.179
0.480
0.546
0.847
0.427
0.348
0.120
0.173 0.602
0.398
0.074
0.242
0.186
0.625
0.523
0.054
p 1.2
0.2
0.003
0.003 0.4
0.4
0.018
1.0
0.019
1.1
0.18
<0.1
0.003
0.003 0.8
0.8
0.005
2.1
0.007
2.4
1.16
4.1
x
0.1
0.2
1.7
0.1
0.000
<0.1
0.003
0.003 0.8
0.8
0.003
1.0
0.005
1.1
0.43
0.06
3.00
2.96
2.72
1.83 3.83
3.77
7.50
0.45
3.36
0.29
4.20
4.02
F1,10
0.1
0.2
0.1
0.06
0.1
<0.1
<0.1
4.01
<0.001<0.001<0.0010.52
0.1
0.3
0.3
0.17
<0.1
0.013
0.1
0.001
0.015 0.1
0.2
0.002 0.05
0.2
3.45 7.08
3.03
<0.1
4.47 0.2
0.1
4.77
<0.001<0.0016.60
<0.1
<0.001<0.0012.86
0.002 0.05
0.3
<0.001<0.001<0.001<0.0011.53
<0.1
0.015
0.2
0.002
0.017 0.1
0.3
<0.001<0.001<0.001<0.0010.19
0.2
<0.001<0.001<0.001<0.0013.86
0.2
0.001
<0.001<0.001<0.001<0.0010.77 0.4 0.2 0.3 0.3 0.49
0.2
<0.001<0.001<0.001<0.0011.43
0.2
<0.001<0.0010.000
0.3
0.003
0.003 0.4
0.4
0.022
2.0
0.023
2.4
1.95
6.2
x
SE
SE
SE
x
Diversity
Family
Reference
Mitigation
Mitigation
Reference
Open water
Emergent
Total invertebrates Richness
Order
0.248
0.057
0.030
0.064
0.125
0.096 0.026
0.116
0.676
0.686
0.081
0.076
0.490
0.404 0.502
0.820
0.263
0.809
0.117
0.120
0.133
0.209 0.082
0.084
0.023
0.521
0.100
0.602
0.068
0.073
p
0.2
<0.1
0.001
0.001 0.3
0.4
0.014
1.8
0.013
2.1
0.05
1.2
SE
2.28
0.73
1.27 0.21
0.03
5.07
0.82
1.66
0.4
0.002
0.5
0.61
1.39
0.01
0.3
0.2
0.006
0.02
3.24
<0.001<0.0010.91 1.2 0.8 1.14
0.7
0.003
1.5
0.1
0.2
0.2
2.98
0.002
0.5
0.111
0.8
0.009
0.123 0.5
1.9
0.002
0.3
0.094
0.3
0.005
0.099 0.3
0.9
0.003
0.4
0.001
0.2
0.001
0.006 0.2
1.0
4.26
4.41
3.10 6.48
4.02
0.002
0.3
0.13
0.17
<0.0014.78
0.1
0.001
0.005 0.2
1.0
<0.001<0.001<0.001<0.0010.59
0.4
0.626
0.076
p
0.725
0.693
0.054
0.066
0.062
0.109 0.029
0.073
0.461
0.115
0.775
0.894
0.102
0.364 0.310
0.454
0.265
0.945
0.280
0.162
0.414
0.285 0.660
0.862
0.048
0.387
0.226
<0.01 0.961
0.25
3.92
F1,10
<0.001<0.0011.31
0.1
0.001
0.001 0.4
0.4
0.022
5.7
0.036
8.7
2.45
6.1
x
<0.0010.006
0.001 0.2
0.4
0.001
0.5
0.001
0.4
0.001
0.001 0.2
0.2
0.100
1.6
0.100
1.9
0.10
0.9
SE
Reference
<0.001<0.001<0.001<0.0010.09
0.3
0.001
0.001 0.7
1.0
0.001
1.4
0.001
0.9
0.001
0.001 0.2
0.2
0.137
6.5
0.141
8.6
2.52
9.0
x
Mitigation
Total
Table 2. Water column invertebrate richness (number of families/wetland), diversity, density (No/l) and biomass (g/l) between mitigation (n = 11) and reference (n = 4) wetlands across emergent areas, open water areas, and entire wetland complexes, West Virginia, 2001–2002 with comparisons of all invertebrate taxa and the 13 most common taxa (i.e., >100 individuals)
181
0.9
F1,10
0.2 6.30
Density 0.002 0.3
0.5 0.001 0.2
0.3 0.02 2.38
5.18
7.09
13.00
4.36
13.00
0.7
0.007
Density
0.007
Mass
Mass
0.7
0.004
0.4
0.004
0.4
0.022
1.5
0.022
1.5
0.016
1.0
0.016
1.0
0.50
1.02
0.71
0.68
<0.001<0.001<0.001<0.0011.71
Density
Mass
0.001 0.1
0.2
0.005
1.2
0.005
1.2
0.31 2.46
Note: Bold numbering indicates a significant difference (p < 0.05).
Sphaeriidae
Pelecypoda
0.002 0.5
1.0
<0.001<0.0010.008
3.0
Mass
0.2
0.2
Density
Mass Coenagrionidae Density
Odonata
Asellidae
<0.001<0.0010.008
3.0
Mass
0.2
0.2
0.000 0.1
<0.001<0.001<0.001<0.0010.44
Density
0.000 0.2
Mass
Isopoda
0.010 0.5
0.65
0.012 0.8
<0.1
Mass Density
<0.1
Veliidae
0.9
0.5 <0.001<0.0010.19
1.0
0.010
SE
Density
2.4
0.012
Density
x
p
0.497
0.337
0.420
0.428
0.221
0.882 0.154
0.046
0.024
0.005
0.063
0.005
0.522
0.592 0.148
0.438
0.671
0.031
0.2
0.4
x 0.3
0.15
F1,10
<0.1
<0.1
<0.1
0.50
0.1
0.000
<0.1
0.000
<0.1
<0.1
2.83
<0.1
2.83
0.2
0.2
0.18
<0.001<0.0012.83
<0.1
<0.001<0.0012.83
<0.1
0.001
0.1
0.001
0.1
0.1
0.1
0.22
0.001
<0.1
0.1
0.22
<0.001<0.0010.25
0.1
<0.001<0.001<0.0010.34
<0.1
<0.001<0.001<0.001<0.0012.61
<0.001<0.001<0.001<0.0010.99 0.1 0.1 0.1 0.1 0.92
0.2
0.000
<0.1
0.000
<0.1
<0.001<0.001<0.001<0.0010.72
<0.001<0.001<0.001<0.0010.13 0.2 0.2 0.3 0.3 0.45
<0.1
<0.001<0.001<0.001<0.0010.01
0.3
x
SE
SE
SE
x
Mass
Family
Reference
Mitigation
Mitigation
Reference
Open water
Emergent
Corixidae
Hemiptera
Order
Table 2. (Continued)
0.629
0.650
0.574
0.650
0.141
0.347 0.364
0.685
0.127
0.127
0.127
0.127
0.417
0.728 0.518
0.498
0.914
0.709
p
0.005 0.3
0.5
0.005
0.5
SE 0.2
SE 3.65
F1,10
<0.1
0.63
<0.001<0.0010.27 0.2 0.2 1.02
<0.1
<0.001<0.0010.18
0.5
x
Reference
0.616 0.337
0.446
0.680
0.085
p
0.1
1.9
0.1
1.9 0.3
<0.0010.001 0.1 0.2
0.1
5.46
8.34
15.63
8.34
15.63
<0.0010.12 0.1 4.31
0.2
0.002
0.7
0.002
0.7
0.003
0.4
0.004
0.4
0.002
0.2
0.002
0.2
0.011
0.8
0.011
0.8
0.008
0.5
0.008
0.5
0.43
1.12
0.64
0.80
<0.001<0.001<0.001<0.0015.73
0.001 0.3
0.6
<0.001<0.0010.004
0.1
<0.001<0.0010.004
0.1
0.528
0.315
0.443
0.392
0.038
0.741 0.065
0.042
0.016
0.003
0.016
0.003
<0.001<0.001<0.001<0.001<0.01 0.970
0.006 0.5
0.5
0.006
1.3
x
Mitigation
Total
182
183 Table 3. Benthic and water column invertebrate familial richness (number of families/wetland), diversity, density (benthic: No/m2; water column: No/l) and biomass (benthic g/m2; water column: g/l) between emergent and open water areas of mitigation wetlands (n = 11) in West Virginia, 2001–2002 with comparisons of all taxa and for the nine most common (abundant) benthic and 13 most common water column taxa (i.e., >100 individuals) Water Columna
Benthica Emergent x
SE
Open water x
Emergent
SE
Fdfa
p
x
SE
Open water x
SE
Fdfa
p
Mitigation Total invertebrates Richness
Common taxa
5.5
0.6
3.9
0.5
10.04
0.010
11.2
0.9
6.2
1.2
21.24
0.001
Diversity
1.60
0.19
1.12
0.34
20.02
0.001
2.46
0.36
1.95
0.59
11.91
0.006
Density
54.72
18.45
37.15
11.49
0.71
0.412
14.81
3.06
2.36
1.13
58.22
0.001
Mass
2.19
1.48
0.64
0.34
0.36
0.55
0.26
0.18
0.02
0.01
29.19
0.001
Density Mass
50.90 2.18
18.58 1.48
35.76 0.64
11.42 0.34
0.11 0.06
0.748 0.808
10.98 0.25
2.58 0.18
1.98 0.02
0.99 0.01
46.34 19.16
0.001 0.001
Reference Total invertebrates Richness Diversity
Common taxa
a
4.8
1.4
3.6
2.0
0.57
0.389
8.0
1.5
4.1
1.7
7.30
0.114
1.74
0.08
1.20
0.42
2.12
0.283
2.33
0.04
1.16
0.43
13.08
0.069
Density
160.6
147.5
139.5
132.1
0.40
0.573
12.6
2.7
2.4
1.1
9.41
0.092
Mass
16.42
16.39
5.09
5.07
0.36
0.591
0.055
0.022
0.007
0.005
5.38
0.146
Density
156.3
147.2
134.9
128.8
0.04
0.856
8.6
3.2
2.1
1.0
16.95
0.054
Mass
16.41
16.39
5.09
5.07
0.01
0.928
0.040
0.024
0.005
0.003
9.32
0.093
The degrees of freedom are 1,10 for mitigation wetlands and 1,3 for reference wetlands.
common water column taxa also was higher in mitigation wetlands. It is evident that invertebrate communities in mitigated wetlands are relatively similar to natural wetlands in our study. Of particular interest within mitigation wetlands was the abundance of Hemipterans in emergent areas. Corixidae and Veliidae are important components of the diet of dabbling ducks (Euliss et al., 1991; Batzer et al., 1993), and actually are known to benefit from fish presence (Zimmer et al., 2000). Although no formal surveys were conducted on fish abundance, 10 of 11 mitigation wetlands contained fish populations. Studies, in general, show mixed results regarding invertebrate responses to fish populations (Wilcox, 1992; Pierce & Hinrichs, 1997; Batzer et al., 2000). Despite high numbers of water column Physidae in mitigation wetlands, benthic Planorbidae density was higher in reference wetlands, specifically in areas with emergent vegetation. It is clear that the amount of open water and emergent vegetation played a key role in structuring Planorbidae populations among wetlands. Planorbidae are grazers and generally found in shallow areas
with moderate amounts of aquatic vegetation (Pennak, 1989). Mitigation wetlands generally had longer periods of inundation with a more even mixture of emergent vegetation to open water than reference wetlands. These conditions likely favored Gastropoda colonization and probably reflect their ubiquitous distribution throughout emergent and open water areas of mitigation wetlands. This phenomenon is not uncommon throughout wetland studies (Anderson & Smith, 2000; Nelson et al., 2000). This trend was evident because of such unproportionally high numbers of Planorbidae in emergent areas of Altona Marsh, a natural marl wetland with alkaline conditions. Reference wetlands also supported more Asellidae (Isopoda), and a more productive water column Odonata population. Brown et al. (1997) also observed higher Asellidae abundance in natural wetlands in New York. Asellidae generally avoid open water and remain hidden under rocks, emergent vegetation, or debris. Hence, lower proportions of open water (9.3%) in reference wetlands than in mitigation wetlands (40.6%) and higher proportions of herbaceous/scrub-shrub
184 areas in reference wetlands (85.4%) than in mitigated wetlands (59.4%) likely provided more refugia for these taxa (Balcombe et al., in press b). In fact, almost all Asellidae were sampled within emergent areas of both wetland types. The rapid colonization of invertebrate communities is common in created, restored, and recently flooded wetlands (Streever et al., 1996; Brown et al., 1997; Fairchild et al., 1999; Ashley et al., 2000; Anderson & Smith, 2004). The proximity of mitigation wetlands to rivers, streams, and other wetlands is known to facilitate colonization of invertebrates (Nelson et al., 2000). Almost all of the mitigation wetlands in this study, as well as reference wetlands, were located near major water sources. The complex trophic levels among invertebrate communities often dictate composition of invertebrate taxa. Predatory taxa, for instance, depend on colonization by prey, herbivory taxa often depend on vegetation succession, and taxa that collect fine algal and detrital particles may depend on the development of adequate substrate conditions (Lake et al., 1989; Fairchild et al., 2000). Because of the average 10-year development time of mitigation wetlands included in this study, we expected temporal and spatial development among mitigation wetlands across the state to be sufficient in supporting diverse invertebrate taxa. In fact, representative taxa of predators, herbivores, algivores, and detritivores all were present across mitigation wetlands. Differences in vegetation composition and community structure between mitigation and reference wetlands likely accounted for some differences observed in water column invertebrate abundance. Mitigation wetlands supported more diverse and species rich vegetation communities than reference wetlands, as well as more evenly mixed ratios of emergent vegetation and open water (Balcombe et al., in press b). Given the relatively higher number of invertebrates observed in mitigation wetlands, one may conclude that, to a certain extent, the percentage of aquatic vegetation may play less of a role in structuring invertebrate communities than vegetation composition. This assertion is supported by results obtained by Brown et al. (1988), where increases in invertebrate richness and density were observed with increasing diversity of aquatic vegetation communities. They, too, concluded that diverse
vertical structure associated with diverse vegetation communities was more important in structuring invertebrate populations than surface area of vegetation. Other studies have concluded similar results (Schramm et al., 1987; De Szalay & Resh, 1996). The profound difference in vegetative community composition between mitigation and reference wetlands likely plays a leading role in structuring invertebrate populations. These differences should decrease through time, however, as disturbed conditions in mitigation wetlands diminish and vegetation competitive interactions manifest to create similar vegetation community composition between wetland types (Balcombe et al., in press b). While abundant research exists pertaining to invertebrate use of wetlands, few studies have evaluated invertebrate assemblages in mitigation wetlands relative to naturally functioning reference wetlands (Rossiter & Crawford, 1981; Streever et al., 1996; Brown et al., 1997; Fairchild et al., 2000; Zimmer et al., 2000). Within these studies, no real trend has emerged regarding the success of mitigation wetlands in supporting abundant and productive invertebrate populations. Brown et al. (1997) and Zimmer et al. (2000) found overall similar invertebrate abundances between restored and natural wetlands. Likewise, Fairchild et al. (2000) observed similar Coleopteran richness and Streever et al. (1996) observed similar Dipteran densities between constructed and natural wetlands in Pennsylvania. Results of these studies are consistent with those obtained in our study. However, Rossiter & Crawford (1981) found higher invertebrate density and diversity in natural wetlands. Nelson et al. (2000) also observed higher invertebrate richness and abundance in natural wetlands, but only two constructed wetlands were evaluated. Although some of these studies stratified invertebrate sampling by vegetation communities or by vegetated and open water habitats, for statistical purposes, samples were pooled across habitats. Hence, statistics analyzing invertebrates individually within these habitats were not performed. Our study compared mitigation and reference wetlands, not only within wetland subtypes (vegetated and unvegetated), but across entire wetland complexes as well. For instance, upon pooling samples taken from wetland subtypes, no statistical differences emerged for either benthic or water column
185 specimens, both for all taxa and for the most common taxa. However, overall differences did emerge upon comparing benthic and water column samples across wetland subtypes. Specifically, benthic density was higher in reference wetlands across open water habitats. Hence, these data reveal the importance of open water habitats in distinguishing invertebrate assemblages between mitigation and reference wetlands. Indeed, this discovery would have been ignored upon comparing invertebrate communities across entire wetland complexes. Comparisons of individual taxa also reflect the importance of these analyses. These data definitely provide a clearer picture of the spatial variation in invertebrate assemblages in wetlands. Emergent versus open water habitats The variation in invertebrate distribution throughout wetlands was exemplified by significant differences in composition between emergent and open water areas in mitigation wetlands. Reference wetlands showed similar trends; however, the small sample sizes precluded us from finding differences. It was not surprising that invertebrate abundance, diversity, and production was so much higher in emergent areas. Numerous studies have observed a direct relation between invertebrate production and aquatic vegetation (Wilcox, 1992; Streever et al., 1995; Zimmer et al., 2000). Specifically, Streever et al. (1995) sampled invertebrate populations between vegetated and non-vegetated areas in a constructed wetland in Florida and found higher abundances in emergent areas. These data, as well as results from our study, support the need to stratify wetlands by structure to account for spatial variation in invertebrate populations. Emergent areas likely support more invertebrates because of decreased risk of predation, increased vertical and spatial structure, and higher food resources, especially from submerged aquatic vegetation (Crowder & Cooper, 1982; Carpenter & Lodge, 1986). As well, emergent vegetation may increase survival of some invertebrate taxa by increasing egg viability or diapausing individuals (Wiggins et al., 1980). However, too much emergent vegetation may decrease dissolved oxygen levels by shading oxygen producing submergent vegetation, thus inhibiting invertebrate productivity, especially Dipteran
larvae (Streever et al., 1996; Nelson et al., 2000). In this study, reference wetlands contained higher percentages of emergent aquatic vegetation than mitigation wetlands (Balcombe et al., in press b), yet invertebrate production was relatively low. This may be attributable to lower dissolved oxygen levels from decreased amounts of open water. While emergent vegetation does provide important food and cover to invertebrates, the importance of open water cannot be overemphasized. Indeed, studies have shown that dissolved oxygen has a strong influence on invertebrate community structure (Nelson et al., 2000), and that open water habitats provide higher dissolved oxygen levels necessary for subsistence of productive invertebrate populations. Sartoris & Thullen (1998) suggested that even proportions of emergent vegetation and open water habitats (i.e., hemimarsh) create optimal habitat for invertebrates. They pointed out that hemimarsh conditions, in addition to providing a mosaic of habitats for wildlife, create alternating aerobic and anoxic environments for invertebrates and allow for nitrogen treatment and degradation of organic matter. In our study, wetlands with relatively equal amounts of emergent and open water (i.e., hemimarsh) appeared most productive. This indicates that micro-topographic variation and differences in hydrology are important considerations in wetland design for promoting wetland invertebrates. Acknowledgements Funding for this project was provided by the West Virginia University Davis College of Agriculture, Forestry, and Consumer Sciences McIntire-Stennis Program, the Environmental Protection Agency, and the West Virginia Division of Natural Resources. We thank G.E. Seidel for statistical assistance, and S.L. Helon, S.R. Lemley, J.D. Osbourne, T.J. Polesiak, and A.K. Zadnik for field assistance on this project. We thank J.S. Rentch, W.N. Grafton, and two anonymous referees for reviewing this manuscript. We also thank West Virginia Division of Highways, West Virginia Department of Environmental Protection and Trus Joist MacMillan for access to respective properties. This is scientific article number 2892 of the West Virginia University Agricultural and Forestry Experimental Station.
1995
1981
VEPCO
Buffalo coal
10.4
1995
1992
1992
1994
N/A
1997 1993
Leading creek
Sugar creek
Sand run
Triangle
Trus Joist MacMillan
Muddlety
Enoch branch Bear run
a
3.2
1995
Meadowville
4248480
4318340
4316950
4315060
4328850
4321563
4330920
4342000
4332100
4337900
4340000
4334210
4353000
UTM Y
Division of Hwys 4247300 WV Dept. Env. Prot. 4305780
N/A
TJM timber Co.
Division of Hwys
Division of Hwys
Division of Hwys
Division of Hwys
N/A
Island crk coal Co.
Davis trucking Co.
Va electric power
N/A
Division of Hwys
N/A
Source
514550 519750
516790
569560
568500
573140
591470
602550
593940
636250
630900
641300
642200
673914
768600
UTM X
Widen Glenville
Widen
Century
Buckhannon
Buckhannon
Belington
Montrose
Nestorville
Davis
Davis
Mt. Storm
Mt. Storm Lake
Old fields
Middleway
Quad
Site names in bold indicate reference wetlands for mitigation wetland sites (listed below) in each of four areas.
3.4 6.2
3.1
3.0
6.8
8.6
3.8 6.5
1981
N/A
Elk run
9.0
7.0
28.0
N/A
Elder Swamp
15.2
Size (ha)
9.5
N/A
Year
1997
a
Walnut bottom
Altona Marsh
Site name
Shenandoah river
Watershed
Blackwater river
Blackwater river
Blackwater river
Gauley River Little Kanawha
Gauley River
Tygart Valley
Tygart Valley
Tygart Valley
Tygart Valley
Tygart Valley
Tygart Valley
Muddlety creek Little Kanawha
Muddlety creek
Buckhannon river
Buckhannon river
Sand run
Laurel creek
Leading creek
Laurel creek
N. Branch of Potomac R. Elk run
Cheat River
Cheat River
Cheat River
S. Branch of Potomac R. S. Branch of Potomac R.
Shenandoah River
Basin
Appendix A.1. List of 11 mitigation and 4 reference wetland study sites in West Virginia, including site name, year constructed, size (ha), source builder, Universal Transverse Mercator (UTM) coordinates, 7.5 min quadrangle, basin, and watershed, 2001–2002
186
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