Chapter 10 – Wetland Integrity

Release Date: February 2013

Wetlands provide numerous ecosystem functions, including reducing streamflow intensity, water purification, erosion control, groundwater recharge and carbon sequestration (Zedler and Kercher 2005; Mitsch and Gosselink 2007). Despite these benefits, wetlands are often viewed as waste areas, and many were drained and filled to accommodate other land uses (Grand River Conservation Authority 2003). For example, in southern Ontario, approximately 70% of the original wetland area is estimated to have been drained for agricultural development (Natural Resources Canada 2009).

Within the Credit River Watershed current stressors on wetland integrity include land use and climate changes, nutrient and contaminant (e.g. road salt) loading, and introduction of non-native species (Dougan and Associates 2009).

Figure 1. Wetland integrity monitoring in the Credit River Watershed.

Figure 1. Wetland integrity monitoring in the Credit River Watershed.

CVC’s Wetland Monitoring

The wetland monitoring program measures the structure and function of wetlands at three levels of organization (e.g. species, community, landscape; Figure 1) and at different spatial and temporal scales (Woodley 1993). Status and trends of wetland components are then used to evaluate overall integrity of wetlands in the Credit River Watershed.

Long-term monitoring of wetland components allows assessment of environmental conditions and how stressors such as habitat loss, non-native species and climate change alter these systems (Niemi and McDonald 2004). Monitoring data are used to inform management decisions that help maintain or improve ecosystem integrity throughout the Credit River Watershed.

To evaluate wetland integrity, plant and amphibian (frog and toad) communities are surveyed annually at 26 sites throughout the Credit River Watershed (Figure 2). Plant communities are surveyed at permanent monitoring stations following modified plot-based methodologies developed by Environment Canada’s Environmental Monitoring and Assessment Network (EMAN) and Credit Valley Conservation. Wetland amphibian communities are assessed according to Bird Studies Canada’s Marsh Monitoring Program (Konze and McLaren 1997).

Figure 2. Location and status (2011) of wetland integrity monitoring stations in the Credit River Watershed.

Figure 2. Location and status (2011) of wetland integrity monitoring stations in the Credit River Watershed.

Indices of Biotic Integrity (IBI), one developed for plants and one for animals, were used to evaluate wetland integrity. The IBI incorporates several parameters to provide a comparative ranking of wetland integrity as good, fair or poor. Plant communities are ranked using an IBI that was originally developed to evaluate the impact of anthropogenic disturbance on headwater wetlands (Miller et al. 2006). This IBI incorporates eight parameters employed to assess wetland plant community health (Table 1). Amphibian communities were ranked using an IBI developed for wetlands in the Credit River Watershed. The amphibian IBI builds off a similar index produced for coastal wetlands in Ontario (Crewe and Timmermans 2005) and incorporates five parameters (Table 2).

Wetland Integrity Status (2011)

In 2011 the status of wetland plant communities in the Credit River Watershed ranges from poor to good. Of the 26 stations sampled, 15 are classified as good, 8 are classified as fair, and the remaining 3 are classified as poor (Figure 2).

Plant Community

Wetland plant communities in the Middle and Upper Watershed have higher IBI rankings than wetlands in the Lower Watershed (Figure 3). The Lower Watershed has fewer native species, a higher proportion of non-native species and a greater number of invasive species compared to the Upper and Middle Watershed. The greater abundance of non-native plants in wetlands of the Lower Watershed may be a response to differing land use in the Lower Watershed, where 57% of land is in urban use (Credit Valley Conservation 2007). Disturbances caused by urban development often negatively impact native species while promoting establishment of non-native species that tend to do well in disturbed environments (McKinney 2006).

Amphibian Community

The status of wetland amphibian communities in the Credit River Watershed also ranges from poor to good. Of the 21 sites sampled in 2011, 11 are classified as good, 10 are classified as fair and 1 is classified as poor (Figure 2). Sites classified as good are all in the Middle and Upper Watershed. These sites are all located in wetlands that are part of larger, intact forest-wetland systems, which likely contribute to higher species richness observed at these monitoring stations.

All Lower Watershed monitoring stations have an amphibian IBI ranking of fair. These stations are dominated by common, disturbance tolerant species such as Green Frog (Lithobates clamitans) and American Toad (Bufo americanus). The larger proportion of urban land use and smaller wetland areas in the Lower Watershed may be driving the pattern of reduced diversity in this physiographic zone. It is well known that amphibian populations are negatively impacted by habitat loss and fragmentation which is often associated with urban development (Fahrig et al. 1995, Hecnar and M’Closkey 1996, Knutson et al. 1999, Cushman 2006). It is, therefore, not surprising that the Lower Watershed has a lower amphibian IBI score than the Middle and Upper Watershed (Figure 3).

Average wetland station integrity scores for plant and amphibian community IBI separated by physiographic zone for 2011. Bars with different letters indicate statistically significant differences among the means (p<0.10).

Figure 3: Average wetland station integrity scores for plant and amphibian community IBI separated by physiographic zone for 2011. Bars with different letters indicate statistically significant differences among the means (p<0.10).

Wetland Integrity Trends

In total, 379 plant species and 9 amphibian species were detected watershed-wide. Overall, wetland integrity appears fairly consistent between 2005 and 2011. Whereas most parameters remained fairly stable over the monitoring period, a few parameters did experience change. Over the monitoring period, the number of non-native species, particularly those considered invasive, increased watershed-wide (Figure 4). The data indicate that not only are non-native species spreading to more wetlands throughout the watershed, but that some of these species are also invasive (e.g. Purple Loosestrife; Lythrum salicaria and Common reed; Phragmites australis) and capable of altering the structure and function of wetland ecosystems.

Figure 4. Number of non-native plant species in wetlands in the Upper, Middle and Lower Watershed observed during the monitoring program (2005-2011).

Figure 4. Number of non-native plant species in wetlands in the Upper, Middle and Lower Watershed observed during the monitoring program (2005-2011).

For the amphibian community 2 parameters displayed statistically significant trends over the monitoring period. The first trend was that the distribution of the disturbance tolerant Green Frog increased in the Lower Watershed, suggesting greater habitat disturbance. In contrast, the Middle Watershed had an increase in the number of monitoring stations where a full chorus of frogs or toads were detected, suggesting improving amphibian community health in this region. These monitoring trends highlight the divergent land use patterns in the Lower and Middle Watershed as the Lower Watershed has undergone increased urban development over the monitoring period whereas the Middle Watershed has undergone a recent expansion of forest cover.

Conclusions

Overall, wetland integrity in the Upper and Middle Watershed is good and relatively stable for all but a few parameters. In contrast, in the Lower Watershed, wetland integrity is primarily ranked as fair to poor.

In general, patterns drawn from forest communities were paralleled in wetlands. Similar to forests, undesirable changes in wetland parameters were more severe in the Lower Watershed, suggesting a possible link with urbanization. It is anticipated that as urbanization intensifies, particularly in the Lower Watershed, wetland communities will continue to deteriorate unless further steps are taken to protect these sensitive landscapes. Similarly, increasing levels of non-native species in the watershed are of concern due to their ability to alter the structure and function of wetland ecosystems (Francis and Austin 2000).

It is important to consider, however, that although wetland integrity in the Lower Watershed has a lower IBI ranking, these wetlands are still important features of the Credit River ecosystem. It is therefore vital to protect and preserve the remnant wetland habitats that exist in the Lower Watershed to ensure persistence of these communities and the ecosystem functions they provide. This highlights the importance of maintaining wetland balance and the need for creating an integrated Natural Heritage System throughout the Credit River Watershed.

In the next chapter we continue the examination of terrestrial plants and focus on riparian health in the Credit River Watershed. The riparian zone is where the terrestrial landscape transitions to the aquatic environment and is a highly rich and diverse habitat. What is the status of riparian health in the Credit River Watershed?

Did you know?

The transitional nature of riparian vegetation communities can result in plant species normally associated with wetlands, forests, successional, grassland, and disturbed habitats existing in combination along a single reach.

 

Table 1. Wetland plant Index of Biotic Integrity (IBI) parameters.

Parameter

Classification

Relationship to Wetland Integrity

Adjusted Floristic Quality Index

Community

Positive

% Cover of tolerant plant species

Community

Negative

% Annual species

Functional Group

Negative

% non-native species

Functional Group

Negative

% Invasive species

Functional Group

Negative

% Trees

Functional Group

Positive

% Vascular cryptogams (ferns)

Functional Group

Positive

% Cover of  Reed Canary Grass (Phalaris arundincea)

Species-Specific

Negative

Table 2. Wetland amphibian Index of Biotic Integrity (IBI) parameters.

Parameter

Relationship to wetland integrity

Number of disturbance tolerant species

Negative

Number of disturbance sensitive species

Positive

Number of rare species

Positive

Total species richness

Positive

Maximum calling code

Positive

Definitions

Definition #1: Integrity

Integrity is a term used to describe ecosystems that are resilient and resistant to change, biodiverse, structurally and functionally diverse, provide habitat for large species and predators and are self maintained. Generally, high integrity ecosystems are subjected to low intensities of anthropogenic stressors and are comprised of components of a self-organizing system (King 1993). The loss of any key system component or change to their interactions results in a loss of integrity (Karr and Dudley 1981, Noss 1990, Aubin et al 2007, LaPaix et al. 2009).

Definition #2: Wetland Amphibian Guilds

Species

Disturbance Tolerant

Disturbance Sensitive

Rare

American Bullfrog
(Rana catesbeiana)

 

 

X

American Toad
(Bufo americanus)

X

 

 

Gray Treefrog
(Hyla versicolor)

X

 

 

Green Frog
(Lithobates clamitans)

X

 

 

Northern Leopard Frog
(Rana pipiens)

 

X

 

Pickerel Frog
(Rana palustris)

 

X

X

Spring Peeper
(Pseudacris crucifera)

X

 

 

Western Chorus Frog
(Pseudacris triseriata)

X

 

X

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