Spring Invertebrate Communities in a Restored Wetland

by Andrew Walnum

The goal of every restoration project is to restore degraded ecosystems as closely as possible to their pre-disturbed functions. For wetlands, restoring the hydrological function of the area is usually what restoration ecologists aim to achieve, often at a rate which quickly makes changes to the hydrology and chemistry of the landscape. Although ecological restoration is an important growing field, very little is known about the inter-habitat effects of restoration. Freshwater springs regularly form along wetland ecosystems but there have been no studies to find how restoration might affect these habitats. Illmonen et al.(2013) looks at the effects of restoring wetland on these non-target ecosystems by looking at macroinvertebrate diversity. Because these habitats are geographically scattered the authors believed that recovery time for these springs may be slow due to poor dispersing mechanisms for macroinvertebrates, although more cosmopolitan species may take over quickly.

Ilmonen and colleagues from the University of Oulu, Ruuhikoskenkatu, and the Finnish Environment Institute used impacted and control sites along with independent sites away from the restoration sites to perform a before-after-control-impact (BACI) study. Ditches were filled to prevent draining and restore the ecosystem back to its pre-disturbed mire state. Control springs were 5-10 meters away from restoration attempts. Independent control springs were located 300 km southwest of restoration activities but within the same ecoregion. Samples were taken in May 2001 before restoration occurred. Subsequent samples from the springs were collected in May 2003, 2005, and 2010. The macroinvertebrates were sorted to their lowest taxonomic level and then sorted into two categories: “freshwater generalist” and “spring specialist.” Using generalized linear mixed modeling, response variables of proportional abundance of crenophilous (spring and cold specializing) taxa compared to benthic invertebrates and total taxon richness, which was rarefied to 100 individuals.

Ensuing testing of macroinvetebrate richness after restoration indicated a large decrease in the number of crenophiles in both the impacted and controlled restoration sites. The marked decrease was more prominent in impacted sites then the controlled sites. However, by 2010, both sites had recovered their crenophile diversity to almost pre-restoration activity levels.

Ilmonen and colleagues recorded an increase in the spring of a few generalist species, particularly Psectrotanypus varius and Nemoura cinerea. Following restoration, P. varius abundance increased from no individuals to an average of 107 individuals per spring in 2003. The average number of individuals then decreased sharply to mean of 8.5 and 2.7 in 2005 and 2010 respectively. The number of individual N. cinerea also increased immediately following restoration and again corresponded to a decrease in crenophiles. Using the rarefied species richness results, there was an overall negative trend for restored springs. Remote springs showed an increase in species richness over time.

Overall, there was little change in the macroinvertebrate community of remote springs whereas all springs in the restored area showed a significant change after restoration and slowly recovered to pre-restored levels. Changes in the community of restored springs correlated with increasing changes of moss cover and water depth.

The results show that restoration can have a harmful impact on not only restored springs but also neighboring springs being used as controls. Although there was little impact on species richness over time, the community structure of the springs was greatly impacted. The after effects of restoration include an increase in the number of generalist freshwater taxa and a less marked decrease in crenophilous taxa. The lentic (still water) loving P. varius quickly established itself in the restored and control springs shortly after restoration occurred. In addition, there was a change in the abundance of species and taxa indicating that measuring species richness does not accurately convey changes in the ecosystem post-restoration. Species richness may reflect little change in the community over time but does not account for species turnover and a restructuring of the macroinvertebrate community. A comprehensive analysis of species abundance is a more accurate indicator of ecosystem changes. Off-site control springs showed almost no changes in species richness or abundance indicating that measured changes were caused by restoration activities.

The results also indicate the importance of time scale for these restoration based studies. Changes in disturbances can vary over time along with a slow response by flora and fauna to restoration. A short sampling timescale may not allow enough time to measure biological and chemical changes in a restored ecosystem. Also, it is important to have non-impacted control sites to measure changes in restored and adjoining ecosystems against. For all future restoration projects a pre-restored species list should be conducted in not just the target ecosystem but neighboring ecosystems. Based on the results a restoration project may not be considered justified if there are any red-listed species that might be affected by it.

Ilmonen, J., Virtanen, R., Paasivirta, L., Muotka,T. 2013.Detecting Restoration Impacts in Inter-Connected Habitats: Spring Invertebrate Communities in a Restored Wetland. Ecological Indicators. 30, 165-169.

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