Improving Connectivity Within Typha-invaded Great Lake coastal wetlands

This aerial photograph shows the results of harvesting and crushing work conducted at Cedarville Marsh in Northern Lake Huron. Most of the visible vegetation is Typha, though large clumps of Carex aquatalis are also visible in the area that had received crush treatment. The smaller channels were cut using aquatic weedwackers and should help increase access to the interior part of the marsh. While this work was not a replicated experiment, it shows how combining aquatic connectivity channels with other restoration methods can greatly improve the accessibility of invaded Great Lakes coastal wetlands.

This aerial photograph shows the results of harvesting and crushing work conducted at Cedarville Marsh in Northern Lake Huron. Most of the visible vegetation is Typha, though large clumps of Carex aquatalis are also visible in the area that had received crush treatment. The smaller channels were cut using aquatic weedwackers and should help increase access to the interior part of the marsh. While this work was not a replicated experiment, it shows how combining aquatic connectivity channels with other restoration methods can greatly improve the accessibility of invaded Great Lakes coastal wetlands.

Improving Connectivity Within Typha-invaded GLCW

On a per-acre basis, coastal wetlands are one of the most important ecosystem types in the Great Lakes region. While they occupy a relatively small area along the waters’ edge, they provide a number of services that are vital to keeping the whole lake system healthy. Wetlands capture and hold nutrients like phosphorus and nitrogen, helping to prevent eutrophication. They provide habitat for a myriad of creatures, including insects and other invertebrates, frogs, salamanders, migratory songbirds, waterfowl, wading birds, muskrats, and fish. Many commercially important fish in the great lakes, such as perch and walleye, spawn in coastal wetlands, laying their eggs on the stems of aquatic and emergent plants. In fact, nearly 90% of the fish species in the Great Lakes use coastal wetlands at some point in their life cycle.

Many fish that spend their adult lives in the open lake system depend on coastal wetlands for spawning and nurseries. Pictured here from left to right are northern pike, yellow perch, and a juvenile walleye. 

Many fish that spend their adult lives in the open lake system depend on coastal wetlands for spawning and nurseries. Pictured here from left to right are northern pike, yellow perch, and a juvenile walleye. 

Wetlands that are dominated by invasive plant species like cattail (Typha sp.) and common reed (Phragmites australis) don’t provide very good habitat for a lot of the plants and animals that depend on Great Lakes coastal wetlands. These plants grow densely and quickly accumulate leaf litter, excluding other plants and preventing the movement of many fish and birds. If animals can’t move from one part of a wetland to another, and from the wetland to the open lake, they will need to migrate to a new wetland or they and their offspring will not survive.

As more coastal wetlands come to be dominated by invasive plant species, animal species that depend on relatively intact wetland plant communities suffer. Because exterminating established invasive species is very difficult and expensive, we are investigating ways to improve the habitat value of a wetland without entirely removing the invasive plants. We have identified decreased aquatic connectivity and litter accumulation as two of the biggest degradation mechanisms resulting from invasion. Theoretically we will be able to increase the habitat value of invaded wetlands if we can address these mechanisms.

In a project funded through the EPA and GLRI, we are restoring aquatic connectivity in sections of Typha-dominated wetlands and evaluating the impact this has on wetland biodiversity. In the summer of 2016, we located five Typha-invaded wetlands that were ideal for this project. We set up a landscape-scale study with four experimental treatments: channelized connection to more open lake habitat, litter-removing harvest, channelized connectivity combined with litter-removing harvest, and un-manipulated controls (See Figure 1). We set up a blocked experimental design, with each wetland containing at least one blocked replicate that includes each treatment. Our field team of Loyola students, researchers, and collaborators from the Sault tribe of Chippewa Indians’ Inland Fisheries and Wildlife division used aquatic weedwackers and a lot of elbow grease to cut channels through cattail stands. We had purchased a sickle-bar mower for our Loglogic Softrak aquatic harvester, but unfortunately it didn’t arrive in time for us to use it at many of our sites. Once we had the sickle-bar mower up and running, we were able to make quick work of the rest of our experimental treatments.

Over the next two years, we will evaluate the impact of increased aquatic connectivity and decreased leaf litter on wetland biodiversity. Working with collaborators from the Sault tribe, The Fish and Wildlife Service, Michigan Tech University, and Oregon State University, we are going to conduct surveys of juvenile and adult fish, frogs, birds, invertebrates, and plants. Because we have replicated this study at several study sites, our results should be generalizable to coastal wetlands throughout much of the upper Great Lakes region.

This shows one of the connective channels that leads out to a more open part of the wetland in Cheboygan Marsh.

This shows one of the connective channels that leads out to a more open part of the wetland in Cheboygan Marsh.

Aquatic connectivity channel project locations.

Aquatic connectivity channel project locations.

This study design uses a blocked replicate design. Each wetland study site includes at least one block of each of the four treatments: Control, Aquatic Connectivity Channel (AC), Harvest, and combined Harvest and Channel. The black circles indicate where sampling subplots are located.

This study design uses a blocked replicate design. Each wetland study site includes at least one block of each of the four treatments: Control, Aquatic Connectivity Channel (AC), Harvest, and combined Harvest and Channel. The black circles indicate where sampling subplots are located.

A team of Sault Tribe technicians and Loyola students work to clear a connectivity channel using aquatic weedwackers and rakes. This is the harvest/channel treatment plot in the blocked replicate at Munuscong Bay Marsh.

A team of Sault Tribe technicians and Loyola students work to clear a connectivity channel using aquatic weedwackers and rakes. This is the harvest/channel treatment plot in the blocked replicate at Munuscong Bay Marsh.