Exuviae as Indicators of Wetland Restoration Success In Waterloo Region, Ontario

Abstract

Restoration is currently playing a vital role in reviving ecologically important wetland features. However, the time- and cost-intensive nature of important restoration projects often weighs on their economic feasibility. By establishing biotic indicators of wetland habitat and water quality, ecologists can increase the efficiency of assessing and monitoring such sites. Odonata have long been studied as an order that plays an important role in the balance of aquatic invertebrate communities, and their general visibility, diversity and abundance around lentic waters makes them an ideal candidate for development as a group of ecological indicators. Three wetland sites were examined over two years for this study: a recently restored wetland, a protected or natural wetland and a highly impacted storm water management wetland. By using exuviae as the study subject, disturbance to these sensitive habitats was kept to a minimum. Regressions of the Odonata species assemblages against various water quality parameters showed that while a general measure of abundance has little potential for use in indicating water quality, a high diversity of species is strongly correlated with good quality aquatic environments containing low turbidity (100-120 NTU), moderate conductivity (700-900 mS/cm) and high dissolved oxygen levels (7-8 mg/L). Additionally, six species – Anax junius, Enallagma civile, simplicicollis, Ischnura verticalis, Lestes disjunctus, and Nehalennia Irene – were found to be highly responsive to changes in water quality. Through these results, a great potential exists for further exploration and development of these species as indicators of water quality on a local scale.

Introduction

Wetlands can play a significant role in maintaining the ecological integrity of a region. While they cover less than 9% of the global land area, they provide a disproportionately wide range of functions, including support for biodiversity, improvement of water quality, flood abatement, and sequestration of carbon (Zedler & Kercher 2005). Wetlands are also highly valued for their aesthetic qualities, especially in urban landscapes (Ehrenfeld 2000). However, it is estimated that approximately half of the world’s wetlands have been lost through human disturbances such as increased urbanization and intensification of agriculture (Zedler & Kercher 2005), making the restoration of degraded wetlands an increasingly important topic.

Over the last two decades, restoration ecology has emerged as a strong academic field based in well-established ecological principles and concepts (Young et al. 2005). While the probable success of a project can be estimated before its implication using pre-restoration feasibility studies (Hopfensperger et al. 2007), post-restoration monitoring and assessment is extremely important as well. However, methods for monitoring and assessing restoration success are K. Domsic – Odonata as Indicators of Wetland Restoration 2

often time- and cost-intensive, lacking standardization. Thus, methods are often created on a site-by-site or project-by-project basis depending on what resources and expertise are available (An et al. 2007). As the number and range of restoration efforts expands, the need for better assessment tools and endpoints to evaluate restoration success is also expanding (D’Amico et al. 2004).

Since the abundance and diversity of species that colonize and establish populations in wetlands is the ultimate indicator of successful wetland management (Steward & Downing 2008), determining sensitive species or taxonomic groups that can be used to indicate the health of ecosystems is a logical step in the progression of this field. By determining species or groups of species that are indicative of good or poor quality aquatic environments, restoration and conservation specialists can introduce consistency among wetland studies and cut back on the costs associated with monitoring by increasing their efficiency (Davis 1987; Briers & Biggs 2003). Additionally, by establishing criteria that is based on biological responses to pollution and restoration, rather than being solely focused on chemical and physical factors, restoration and conservation specialists will be better enabled to protect biological integrity (Lougheed et al. 2007).

Insects often make good indicators because they are present in some capacity in almost every type of habitat (Whitehouse et al. 2008) and many are habitat specialists (Lewis & Gripenberg 2008). While a lack of data has historically excluded the use of many taxa as possible indicators (Sahlen & Ekestubbe 2001), a growing number of studies on the habits and distributional patterns of certain is making their use increasingly suitable.

The order Odonata represents one set of insects that is being widely studied for its potential in indicating environmental quality. Studies have included Odonata relationships with water quality (Azrina et al. 2006), biotope quality (Clark & Samways 1996; Clausnitzer 2003) and general species richness (Sahlen & Ekestubbe 2001, Briers & Biggs 2003), and the use of Odonata as indicators for wetland conservation (Bried et al. 2007), riparian management needs (Samways & Steytler 1996), wetland buffer width requirements (Bried & Ervin 2006) and shallow lake restoration (D’Amico et al. 2004). This is largely because many of the criteria of good indicator species, such as being taxonomically well-known, relatively easy to identify, and having distinct habitat requirements (Krebs 2001), are fulfilled by Odonata (Corbet 1999). However, the main reason Odonata were chosen as the focus of this study is their known status as early colonizers of new lentic habitats (Braccia et al. 2007), which is likely to translate into an ability to be early colonizers of successfully restored wetlands as well.

As a group of species that are especially sensitive to changes in their habitat, Odonata populations can also be indicative of the richness of other invertebrates and macrophytes (Corbet 1999, Bried & Ervin 2005). Furthermore, Odonata have become a focus of many conservation efforts as they tend to be large, colourful, and easily observable, making them an ideal subject of programs that are largely carried out by the public (Bybee 2005). Through such conservation efforts, Odonata can also act as umbrella species, facilitating the protection of habitat that is crucial for the survival of other species (Bried & Ervin 2005).

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While adult Odonata in flight are relatively easy to spot and identify, their movement among habitats limits their ability to indicate changes in water quality (D’Amico et al. 2004), and so they are not studied here. Alternatively, exuviae, or shed exoskeletons (Foster & Soluk 2004), can be sampled from emergent vegetation after larvae have molted out of the water. This method is ideal because it provides a clearer picture of which species are able to successfully breed in a particular habitat (D’Amico et al. 2004, Bried & Ervin 2005) and it also avoids the possibility of having detrimental impacts on sensitive or small Odonata populations, which may arise from directly sampling live larvae (Foster & Soluk 2004). Additionally, exuviae are generally easier to identify than early instar Odonata larvae (Foster & Soluk 2004).

Currently there is little data available on the relationships between Odonata assemblages and water quality. However, studies that have touched on these relationships have found evidence that water quality may impact adult Odonata assemblages (e.g. Sato & Riddiford 2008). Therefore, the objectives of this study are (1) to examine relationships among water quality and Odonata assemblages at a recently restored wetland, a natural protected wetland, and a degraded storm water management wetland in Waterloo Region, Ontario and (2) to determine the potential for using Odonata as indicators of wetland restoration success on a local scale.

Methods

Site Selection

This study was conducted in the Region of Waterloo, Ontario, Canada. Three wetland study sites were chosen: (1) a restored farm wetland in Wilmot Township (43°26’22 N 80°36’05 W), (2) a protected wetland in Environmentally Sensitive Policy Area (ESPA) 19 (43°27’43 N 80°35’34 W) and (3) a storm water management (SWM) wetland (43°27’08 N 80°34’37 W) located on the outskirts of a recent subdivision development in the City of Waterloo. The ESPA and SWM wetlands were chosen as the closest “natural” and “degraded” reference sites to the farm wetland which was known to have recently undergone restoration efforts.

Each of the wetlands is surrounded by sparse vegetation which has grown since past agricultural land uses ceased. However, the ESPA wetland also has some mid-successional cedar and oak forest nearby, and is located in the Waterloo Moraine. The other two wetlands are not directly in the moraine, but rather in the transitional zone from moraine to clay plain, which adds some variability to the hydrology of the three sites.

Field Data Collection

Each of the wetland sites was visited four times over two years. Environmental data and Odonata surveys were recorded during the peak emergence season (Burcher & Smock 2002), in June 2006, July 2006, June 2007 and July 2007 at each site. Since Odonata are known to go into hiding during and following precipitation storm events, specific dates and times were chosen to

K. Domsic – Odonata as Indicators of Wetland Restoration 4

be 4-4.5 days after the last precipitation event. The sampling dates were concentrated in the early summer between 1000-1700 h when sun was fullest since that is the time when most Odonata species are active in this region. At each site, five 2 m2 quadrats were established in the littoral zone, where emergent vegetation was present. All were chosen using a stratified random design and permanently marked with PVC pipe that was colour coded with a buried metal marker as a back up, to ensure the same quadrats could be located during each sampling date.

Environmental Data

Measures of pH, temperature, electrical conductivity, turbidity and dissolved oxygen, as well as observations of dominant vegetation types and corresponding percent cover were recorded on each sampling date in each quadrat at each site.

Odonata Data

Exuviae surveys were also conducted on each of the four sampling dates in each quadrat at each site, by process of sweep netting through emergent vegetation.

The collected exuviae were then preserved in ethanol and later identified by comparison to a reference collection owned by Dr. Stephen Murphy, located at the Canadian Museum of Nature in Ottawa, Ontario.

For means of quality control, each of the species identifications was checked against multiple sources (Catling & Brownell 2000; Nikula et al. 2001; Carmichael et al. 2002; Ontario Odonata Atlas 2005) to find their likelihood of being observed in Waterloo Region. Questionable identifications were re-checked to ensure accuracy.

Data Analysis

In order to determine differences in water quality between the three wetlands, the differences in pH, temperature, conductivity, turbidity and dissolved oxygen were evaluated using analysis of variance (ANOVA) and two sample t-tests.

As an assessment of the Odonata assemblages at each site, abundance counts were analyzed with a Kruskall-Wallis test to find out whether there were significant differences in the number of Odonata at each of the three sites and Shannon diversity and evenness values were calculated and compared.

To determine whether any relationship exists between water quality and the diversity and abundance of Odonata, exuviae counts were pooled from all sampling dates and the resulting species diversity and abundance values were regressed separately against each of the environmental parameters.

K. Domsic – Odonata as Indicators of Wetland Restoration 5

Finally, in order to assess the possibility of using individual species as indicators of site health, the abundance of each species was regressed against each water quality parameter. Any species displaying strong correlations was then included in a repeated measures analysis of variance (RMANOVA), designed to quantify the species’ relationships with each of the water quality parameters and dominant vegetation types as well as to determine whether there were significant differences among results from the four sampling dates.

Results

Water Quality

The results of ANOVA testing show that pH, temperature, conductivity, turbidity and dissolved oxygen are all significantly different (p<0.001) among the three wetland sites (Table 1).

Table 1 Water quality data ranges and ANOVA results for differences in water quality at three wetland sites (1- Restored, 2-ESPA, 3-SWM). Site 1 Site 2 Site 3 df F-statistic F-critical P pH 7.0-8.0 7.1-7.6 6.9-7.3 2, 57 18.45 4.9981 <0.001 Temperature (°C) 16.4-17.8 17.0-17.8 19.0-20.0 2, 57 375.80 4.9981 <0.001 Conductivity (mS/cm) 660-830 730-830 380-460 2, 57 800.24 4.9981 <0.001 Turbidity (NTU) 79-88 79-87 105-120 2, 57 780.16 4.9981 <0.001 Dissolved Oxygen (mg/L) 7.1-7.7 7.1-7.6 4.9-5.5 2, 57 1107.68 4.9981 <0.001

Through the results of subsequent two-sample t-tests assuming equal variances, it was found that while no significant differences exist between sites 1 and 2 (p>0.01), both sites 1 and 2 are significantly different (p<0.001) from site 3 in terms of each environmental parameter (Table 2).

Table 2 t-test results for environmental parameters at three wetland sites (1-Restored, 2-ESPA, 3-SWM). Site 1-2: Ho: µ1 = µ2 Site 2-3: Ho: µ2 = µ3 Site 1-3: Ho: µ1 = µ3 df t-stat t-crit P t-stat t-crit P t-stat t-crit P pH 38 0.70 2.712 0.489 6.20 3.57 <0.001 5.28 3.57 <0.001 Temperature (°C) 38 -2.25 2.712 0.030 -27.77 3.57 <0.001 -22.27 3.57 <0.001 Conductivity (mS/cm) 38 -1.68 2.712 0.102 47.14 3.57 <0.001 31.60 3.57 <0.001 Turbidity (NTU) 38 1.11 2.712 0.274 -33.10 3.57 <0.001 -30.14 3.57 <0.001 Dissolved Oxygen (mg/L) 38 0.10 2.712 0.922 38.43 3.57 <0.001 40.20 3.57 <0.001

Odonata Abundance and Diversity

A total of 1797 Odonata exuviae were collected from 38 species, including Enallagma anna, for which the closest previous record was in Essex County (Carmichael et al. 2002). The two most abundant species were Erythemis simplicicollis (n=214) and Lestes disjunctus (n=189). The average exuviae abundances were 136, 200, and 111 (Figure 1), and the average species diversity was 29, 30, and 15 (Figure 2) at the restored, natural, and degraded sites, respectively.

K. Domsic – Odonata as Indicators of Wetland Restoration 6

Figure 1 Odonata exuviae abundance at each site during each sampling event at three wetland sites.

Figure 2 Odonata exuviae species diversity at each site during each sampling event at three wetland sites.

The cumulative abundances from the four sampling dates did not differ significantly between the restored (n=554), natural (n=798) and degraded (n=445) wetland sites (Kruskall-Wallis test; df=2, H=1.02, p>0.1). However, as shown in Table 3, Shannon diversity values (3.1, 2.8 and 1.9 at sites 1, 2 and 3, respectively) were significantly different among each pair of sites (p<0.01), with the most significant differences being between sites 1 and 3 (p<0.001) and sites 2 and 3 (p<0.001).

Table 3 t-test results for Shannon diversity values at three wetland sites (1-Restored, 2-ESPA, 3-SWM). df t-stat t-crit P Site 1 vs. Site 2 38915 2.95 2.576 <0.01 Site 1 vs. Site 3 32701 14.88 3.291 <0.001 Site 2 vs. Site 3 47903 33.14 3.291 <0.001

K. Domsic – Odonata as Indicators of Wetland Restoration 7

Odonata Responses to Environmental Conditions

Regressions showed moderately strong correlations between Odonata diversity and temperature (R2=0.73), conductivity (R2=0.76), turbidity (R2=0.75) and dissolved oxygen (R2=0.73) levels. When plotted against each water quality parameter, the differences in species diversity among the three wetland sites also became clearly visible, with Sites 1 and 2 being consistently grouped together and Site 3 being distinctly separate (Figure 3). However, pH levels were poorly correlated to diversity (R2=0.27), and none of the parameters had a strong correlation to Odonata abundance (all R2<0.3).

(a) (b)

(c) (d) Figure 3 Scattplots showing correlations between Odonata species diversity and (a) temperature, (b) electrical conductivity, (c) turbidity and (d) dissolved oxygen, as well as trends in diversity among three wetland sites.

When regressed individually, six species (Anax junius, Enallagma civile, Erythemis simplicicollis, Ischnura verticalis, Lestes disjunctus, and Nehalennia irene) were found to have distinctively strong relationships with some of the environmental parameters (Figure 4). These six species were typically found almost entirely at either both Sites 1 and 2 or at only Site 3 (Table 4). In order to test the strength of these observations, a Repeated Measures Analysis of Variance (RMANOVA) was conducted. The results of the RMANOVA testing show that each of the six species is significantly (p<0.01 to p<0.001) influenced by temperature, conductivity, turbidity, and dissolved oxygen levels (Table 5), and that there was no substantial variation in results among the four sampling dates. Only one of the species, Nehalennia Irene, was found to have a

K. Domsic – Odonata as Indicators of Wetland Restoration 8

significant relationship with vegetation types. However, the lack of correlation to dominant vegetation types among other species may be attributable to the typical response of Odonata to the structure or appearance of vegetation, rather than to vegetative species (Corbet 1999).

(a) (b)

(c) (d)

Figure 4 Scattplots showing correlations between the abundance of six Odonata species and (a) temperature, (b) conductivity, (c) turbidity and (d) dissolved oxygen.

Table 4 Species found to have a strong correlation to some water quality variables at three wetland sites (1-Restored, 2-ESPA, 3-SWM). Species With Strong Correlations to Species Abundance Water Quality Parameters Site 1 Site 2 Site 3 Associated with Poor Quality Water Anax junius 1 0 63 Enallagma civile 1 0 137 Ischnura verticalis 0 0 157 Associated with Good Quality Water Erythemis simplicicollis 85 128 1 Lestes disjunctus 87 101 1 Nehalennia irene 22 164 0

K. Domsic – Odonata as Indicators of Wetland Restoration 9

Table 5 RMANOVA results for key species and environmental parameters. Note: MS = mean square error. Dissolved Dominant Temperature Conductivity Turbidity Oxygen Vegetation MS F P MS F P MS F P MS F P MS F P Anax junius 11.0 8.1 <0.01 11.6 9.2 <0.01 14.1 10.9 <0.001 19.8 16.8 <0.001 3.9 2.0 0.215 Enallagma civile 11.2 8.5 <0.01 18.9 15.7 <0.001 18.5 14.9 <0.001 25.5 20.9 <0.001 4.2 2.7 0.174 Erythemis simplicicollis 15.6 12.7 <0.001 19.1 16.0 <0.001 28.4 23.3 <0.001 35.4 30.1 <0.001 4.1 2.5 0.188 Ischnura verticalis 10.2 7.9 <0.01 15.8 12.0 <0.001 20.6 16.8 <0.001 26.9 21.5 <0.001 4.0 2.4 0.196 Lestes disjunctus 17.8 14.0 <0.001 22.5 18.7 <0.001 31.2 25.3 <0.001 33.7 29.4 <0.001 3.3 1.6 0.279 Nehalennia irene 20.0 17.8 <0.001 17.2 14.0 <0.001 37.5 33.4 <0.001 24.1 19.8 <0.001 11.9 8.5 <0.01

Discussion

A general sense of parallelism has been found between the ESPA and restored wetland sites. Their similarities include both similar ranges in water quality parameters and similar Odonata assemblages and levels of diversity. At the same time, a general sense of separateness has been discovered through data obtained at the SWM wetland.

The differences found between the ESPA and SWM wetlands were expected, since the ESPA wetland is located in a protected area and exists in a relatively natural state, while the SWM wetland is highly impacted by nearby urban development. The subsequent results associated with the water quality measurements and Odonata assemblages at the restored site seem to indicate that the restored wetland is beginning to achieve the desired “natural” state. Therefore, it appears that the restoration of this wetland was highly successful.

Water Quality Parameters

Abiotic factors are known to be important in determining the species composition of Odonata assemblages (Corbet 1999). Accordingly, this study has shown strong correlations between some water quality parameters and Odonata diversity, similarly to the results that other similar studies have found (e.g. Sato & Riddiford 2008). However, it is likely that some of these factors may be confounded. For instance, while a moderately strong correlation was found between Odonata diversity and temperature (R2=0.73), water temperature has previously been found to have little effect on Odonata larvae, with acclimation accounting for one third of the variation in larval temperature tolerances (Martin et al. 1976), and some species having upper lethal limits as high has 35-45°C (Corbet 1999). Therefore, the correlation in Odonata diversity is likely linked more closely to the other environmental variables, with any correlations to temperature being more or less coincidental.

The variables likely having a greater impact on Odonata assemblages – conductivity, turbidity, and dissolved oxygen – are also highly linked (D’Amico et al. 2004, Steward & Downing 2008). Conductivity is only known to affect Odonata larvae if it is strong enough to interfere with osmoregulation (D’Amico et al. 2004), which was not determined through this study. However it

K. Domsic – Odonata as Indicators of Wetland Restoration 10

is likely that turbidity, and possibly conductivity as well, may have affected adult Odonata in their choice of where to oviposit, since these variables often serve as distant visual cues to adults detecting polarization and reflected light of suitable habitats (Bernath et al. 2002). Additionally, a recent and similar study by Steward and Downing (2008) found coarse particulate organic matter and turbidity to be the main limiting factors on invertebrate communities. Meanwhile, dissolved oxygen levels are also known to affect the behaviour, metabolism, and survival of Odonata larvae at a given temperature and pressure (Corbet 1999). However, the correlation between turbidity and dissolved oxygen makes it difficult to determine which variable is most accountable for the low Odonata diversity in the SWM wetland.

In order to better decipher these findings, further analysis should include a multivariate approach such as non-metric multidimensional scaling (NMDS) and laboratory-based testing of the effects of environmental changes. This would help determine which variables account for how much of the variation in Odonata assemblages among these three wetland sites.

Abundance and Diversity

The lack of significant differences in Odonata abundances found in this study implies that abundance is not a good measure of water quality or restoration success. It is possible that since the three wetlands are of similar sizes, the abundances may have reached a maximum based on territoriality (Bried & Ervin 2005), presence of fish (Gee et al. 1997, Braccia et al. 2007, Steward & Downing 2008), other predator-prey and competitive interactions (Fincke 1992), or a lack of an adequate food base (Braccia et al. 2007).

However, stronger results were found to be correlated with Odonata diversity, where highly similar levels of species diversity occurred at the ESPA and restored wetlands, while a significantly lower level of diversity was found at the SWM wetland. These results show that a high diversity of Odonata species may be a useful indication of good water quality.

Individual Odonata Species as Indicators

Perhaps the most useful finding of this study was the discovery of six local species that may be highly stenotopic, having a narrow range of environmental tolerances. By being known to exist only at sites with a certain level of water quality these species should make very good indicators on a local scale (Schindler et al. 2003). With three “good” quality indicators - Erythemis simplicicollis, Lestes disjunctus,and Nehalennia Irene - and three “poor” quality indicators - Anax junius, Enallagma civile and Ischnura verticalis, the identification of these species in the field could potentially be used by resource managers as a biotic complement to chemical water testing.

However, there is still some doubt in associating these species with the conditions they were found in, especially with those species correlated with poor quality environments. Generally, species are not found in poor quality habitats because it is their preference, but rather because

K. Domsic – Odonata as Indicators of Wetland Restoration 11

they are inherently ubiquitous or have a high tolerance for unfavourable conditions. This idea is in line with the demonstration that Odonata species are generally found in a “nested” distribution (Sahlen & Ekestubbe 2001) in which common species are found everywhere, and rare species are only found at the richest sites (Patterson & Atmar 1986). Therefore, it is likely that until further research confirms these findings, only those species correlated with good quality water should be used as environmental indicators.

In further research, it would be useful to study the similarities of I. verticalis to I. elegans, which has been found to be one of the most euryoecious European species, actually being quite adaptable and common in a wide variety of environments, yet also possibly indicative of heavily contaminated aquatic conditions (Hardersen 2008). However, on a local or regional scale, this nestedness relies on a number of factors including habitat heterogeneity and the quality of each habitat within a landscape (Kadoya et al. 2008).

Additionally, it may be useful to note that some of these species may be playing important roles in changing or controlling their biotic communities. A. junius, for example is known to achieve high production due to its large size, agility, and great ability to stalk prey (Braccia et al. 2007). A. junius may even play a role in controlling the density of smaller Odonata such as E. civile, even though E. civile is also known to have great stalking abilities (Braccia et al. 2007).

Conclusions

Some of the findings of this report may be very useful in developing the use of Odonata as indicators of water quality on a local scale in the Region of Waterloo. The results that are most relevant to this development are the positive relationships that good water quality has with high Odonata species diversity and three species in particular – Erythemis simplicicollis, Lestes disjunctus and Nehalennia Irene.

Some confounding factors are inescapable with field studies such as this one. For instance, the effects of certain environmental parameters like turbidity, conductivity and dissolved oxygen have been difficult to separate. These factors could possibly be better distinguished through a lab-based study of Odonata larvae responses to specific environmental changes over a short time scale. Additional work could also be done to gain a clearer understanding of the effects of vegetation type, or more importantly, vegetation structure, on the success of adult breeding and larval survival.

There is no doubt that the insect order Odonata has a great potential for use in efficiently indicating the quality of water in respect to its effects on biota, at least on a local scale. The mere presence of a high diversity of species at any newly restored wetland could be used as an indication of some level of return to a natural or ecologically functional state. However, Odonata should not yet be used as a sole indicator, but rather in conjunction with traditional chemical water analysis techniques and a general overview of the biotic composition of any given wetland site. Theoretically, Odonata surveys can be used widely by resource managers

K. Domsic – Odonata as Indicators of Wetland Restoration 12

and conservationists to assess site quality, monitor restoration, and mark incremental benchmarks of ecological quality.

Acknowledgements

Thank you to Joanna Smedes and Laura Sider for all of their field efforts, including habitat characterization and site restoration, and to Dr. Stephen Murphy for identifying the Odonata exuviae and all of his invaluable advice and assistance with the analysis involved in this project.

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