Chapter 11 – Riparian Integrity

Release Date: February 2013

Riparian zones are areas where the terrestrial landscape transitions to the aquatic environment of a flowing watercourse. These habitats are highly diverse, with numerous birds, mammals, amphibians, reptiles and insects making their home in the dense vegetation (Figure 1). The close interaction between the terrestrial and aquatic environments in riparian zones leads to greater habitat variability and consequently, increased plant and animal diversity (Maisonneuve and Rioux, 2001; Goebel et al., 2003). For example, riparian zones often have plant species normally associated with wetlands, forests, grassland, and disturbed habitats coexisting in a single location.

Riparian zones provide a variety of important ecological functions. These include retaining sediment and nutrients (Daniels and Gilliam, 1996; Butler et al., 2006), storing storage, flood attenuation (Tabacchi et al., 2000), bank stabilization (Naiman and Decamps, 1997), and regulating stream temperature (Moore et al., 2005). From a holistic perspective, riparian integrity can be defined by a site’s relative ability to provide all of these necessary ecological functions.

In addition to the forest and wetland terrestrial monitoring efforts with which it is associated, riparian monitoring remains a key element in integrated watershed health monitoring at CVC.

Figure 1. A Spotted Sandpiper (Actitis macularia), is a ground nesting shorebird commonly found in riparian zones.

Figure 1. A Spotted Sandpiper (Actitis macularia), is a ground nesting shorebird commonly found in riparian zones.

Riparian Monitoring

Riparian monitoring surveys began in spring 2009 and are presently conducted along 29 permanent monitoring stations distributed equally among the three physiographic zones (Figure 2). Riparian health is primarily assessed on plant communities because plants are important elements of the riparian zones and are known to be robust indicators of ecosystem health. Riparian monitoring employs a standardized plot-based methodology as recommended by Environment Canada’s Ecological Monitoring and Assessment Network (EMAN).

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

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

Riparian monitoring currently tracks changes in status of 6 community indicators: ground vegetation cover, woody regeneration, biodiversity, tree health, downed woody debris, and overhead canopy cover. Each of these indicators contains a series of parameters (or measures) related to specific aspects of the broader indicator. A Riparian Index of Biotic Integrity (IBI) incorporating several parameters is used to provide a comparative ranking for each monitoring station from good to poor (Miller et al. 2006).

Riparian Status (2011)

The Riparian IBI ranks 5 monitoring stations as good, 18 as fair, and 6 as poor. IBI rankings appear to be influenced by physiographic zone (Figure 3) and also show a correlation with stream order, namely whether the station is located on the Credit River or a tributary.

Range of riparian IBI values at the watershed scale and among the 3 physiographic zones. Box-plots show median (blue line), 25th and 75th percentile (red box) and range (black lines) of IBI values. Physiographic zones with different letters have statistically significant differences in their average IBI value (p<0.10).

Figure 3. Range of riparian IBI values at the watershed scale and among the 3 physiographic zones. Box-plots show median (blue line), 25th and 75th percentile (red box) and range (black lines) of IBI values. Physiographic zones with different letters have statistically significant differences in their average IBI value (p<0.10).

All 5 stations with good IBI rankings are located in the Upper and Middle Watershed and are associated with riparian swamps or small isolated streams on private property. Four of the 6 stations with poor rankings are located in urban areas of the Lower Watershed. The remaining 2 stations with poor rankings are located along roadside streams in the Upper and Middle Watershed where Reed Canary Grass (Phalaris arundinacea, Figure 4a) dominates the floodplain. This grass forms monocultures that out-compete other wet area vegetation.

The correlation of stream order with riparian IBI is evident when comparing high order (Credit River) and low order (headwater tributary) channels. Of the 7 monitoring stations located on the Credit River, 6 rank as fair and 1 as poor. In contrast, all 5 stations with an IBI ranking of good are located along narrower headwater tributaries (Figure 4b). These narrower streams tend to be located in rural areas of the Upper and Middle Watershed with less surrounding urbanization than the higher order streams.

Figure 4. Riparian monitoring stations with a) the bank and floodplain dominated by Reed Canary Grass (Phalaris arundinacea) and b) abundant woody vegetation, several species of ferns, native vegetation, and low proportions of non-native and disturbance tolerant plants. Using the Riparian IBI these particular stations ranked as poor and good respectively.

Figure 4. Riparian monitoring stations with a) the bank and floodplain dominated by Reed Canary Grass (Phalaris arundinacea) and b) abundant woody vegetation, several species of ferns, native vegetation, and low proportions of non-native and disturbance tolerant plants. Using the Riparian IBI these particular stations ranked as poor and good respectively.

Among the 8 constituent IBI vegetation parameters, 3 appear to be preferentially driving the station rankings: the Adjusted Floristic Quality Index (AFQI), the proportion of species that are non-native, and the proportion of species that are disturbance tolerant. The AFQI, which is associated with increased ecosystem integrity, is significantly higher in the Middle and Upper zones when compared to the urbanized Lower zone. Inversely, the proportion of non-natives per reach and the proportion of disturbance tolerant species, both of which are associated with decreased integrity, are significantly higher in the Lower zone when compared to the Upper zone (Figure 5).

The percent of non-native species at a given riparian site (an average of 30.5%) is notably higher than that recorded in either the forest or wetland monitoring stations. The high sensitivity of riparian systems to plant invasions is a commonly observed phenomenon (Brown and Peet, 2003) and several factors may be contributing to the elevated presence of non-natives. Flooding and bank erosion, which occur naturally in riparian zones, create new substrates on which aggressive non-native species are more suited to colonize (Malanson 1993). Hydrological connectivity and channel flow may also be facilitating the transport of seeds (Gurnell et al., 2006) from non-native species within and between sites. Recreational activities may also increase the probability of seed dispersal, while the linear shape of riparian features themselves may increases the amount of habitat edge available for the introduction of non-natives.

Figure 5 Average percent non-native and disturbance tolerant species per monitoring station at the watershed scale and among the three physiographic zones. Bars with different letters have statistically significant differences in their average values (p<0.10)

Figure 5. Average percent non-native and disturbance tolerant species per monitoring station at the watershed scale and among the three physiographic zones. Bars with different letters have statistically significant differences in their average values (p<0.10)

Riparian Trends

Riparian monitoring is a relatively new program at CVC and an insufficient amount of data exists to report on trends at this time. CVC will continue to monitor riparian vegetation and as the length of the monitoring record grows, future reports will include statistical analysis of long-term trends.

Conclusions

Overall, analysis clearly demonstrates that riparian integrity is compromised in the Lower Watershed compared to the Upper and Middle Watershed. These results are likely reflecting both the intensity and the proximity of urban development on natural plant communities. Such impacts come about through fragmentation and isolation of habitat, alteration of streamflow, and transport of non-native species. CVC will continue to monitor riparian vegetation and future reports will include statistical analysis of long-term trends.

We will return to the aquatic environment to examine the water quality of the Credit River. Water quality plays an important role in both human and ecosystem health

Did you know?

During winter and spring, chloride concentrations of some urbanized streams in the Credit River Watershed can be as high as in the world’s Oceans.

 

Definitions

Riparian Index of Biotic Integrity

This is a vegetation-based index originally developed in Pennsylvania to evaluate headwater wetland condition in relation to anthropogenic disturbances (Miller et al. 2006). Professional judgment has been used in determining that the Pennsylvania wetland IBI can be applied with equal validity in a riparian context. This specific IBI incorporates eight plant parameters classified as either community-based, a functional group, or species-specific. The eight parameters include:

Parameter

Classification

Relationship to Riparian 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

 
An IBI specifically for riparian use is currently being developed at CVC.

 

References

Brown, R.L. and Peet, R.K. 2003. Diversity and invisability of Southern Appalachian plant communities. Ecology 84(1): 32-39.

Butler, D.M., Franklin, D.H., Ranells, N.N., Poore, M.H., Green, J.T. 2006. Ground cover impacts on sediment and phosphorus export from manured riparian pasture. Journal of Environmental Quality 35: 2178-2185.

Daniels, R.B. and Gilliam, J.W. 1996. Sediment and chemical load reduction by grass and riparian filters. Soil Science Society of America 60: 246-251.

Goebel, P.C., Palik, B.J.,Pregitzer K.S. 2003. Plant diversity contributions of riparian areas in watersheds of the northern lake states, USA. Ecological Applications 13(6): 1595-1609.

Gurnell, A.M., Boitsidis, A.J., Thompson, K., Clifford, N.J. 2006. Seed bank, seed dispersal, and vegetation cover: colonization along a newly created river. Journal of Vegetation Science 17(%): 665-674.

Malanson, G.P. 1993. Riparian Landscapes. Cambridge University Press, Cambridge, UK.

Maisonneuve, C. and Rioux, S. 2001. Importance of riparian habitats for small mammal and herpetofaunal communities in agricultural landscapes in southern Quebec. Agriculture, Ecosystems and Environment 83: 165-175.

Miller, S.J., Wardrop, D.H., Mahaney, W.M., and Brooks, R.P. 2006. A plant-based index of biological integrity (IBI) for headwater wetlands in central Pennsylvannia. Ecological Indicators 6: 290-312.

Moore, R.D., Spittlehouse, D.L., Story, A. 2005. Riparian microclimate and stream temperature response to forest harvesting: a review. Journal of the American Water Resources Association: 813-834.

Naiman, R.J. and Decamps, H. 1997. The ecology of interfaces: Riparian zones. Annual review of ecological systems 28: 621-658.

Tabacchi, E., Lambs, L., Guilloy, H., Planty-Tabacchi, A., Muller, E., Decamp, H. 2000. Impacts of riparian vegetation on hydrological processes. Hydrological Processes 14: 2959-2976.

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