Originally published in our September 2011 newsletter.
By Jon Dittmar, Cardno JFNew
Wolf Lake is a 3.2 km² natural lake located on the Indiana/Illinois border near Hammond, Indiana. In pre-settlement days Wolf Lake was part of a vast complex of dunes, lakes, marshes, and wooded uplands. Ecologists refer to this area as the Lake Plain as it was once the bed of Lake Michigan. Development impacts, including dredging to obtain construction fill, filling with construction spoil, industrial discharges, invasive species encroachment, and other nonpoint sources of pollution have significantly altered Wolf Lake. In the 1950s the Indiana Toll Road (I-90) was built through the middle of the lake.
Despite these anthropogenic impacts, Wolf Lake still attracts fishermen, boaters, wind surfers, birders, and other nature admirers. It also offers habitat for a wide variety of wildlife and plants, including species listed as threatened or endangered such as the lake sturgeon (Acipenser fulvescens) and banded killifish (Fundulus diaphanus).
The Wolf Lake Aquatic Ecosystem Project was initiated by the U.S. Army Corps of Engineers (USACE) Chicago District under Section 206 of the Water Resources Development Act of 1996, which gives USACE authority to undertake restoration projects in aquatic ecosystems.
The city of Hammond, Indiana was the project owner and a major project collaborator. The city provided part of the matching funds for this 6.5 million dollar project and is responsible for long-term maintenance. Major project features include restoring 1.6 km of eroded shoreline, creating 0.10 km2 of aquatic and upland native plantings by constructing more than 30 sand islands, restoring natural water levels, improving boat channels, and controlling invasive plants. In 2009 the city of Hammond received a Conservation and Native Landscaping Award from the U.S. EPA and Chicago Wilderness.
The Restoration Plan
The Wolf Lake Aquatic Ecosystem Restoration Project is unusual in that wetland and upland habitats were created in shallow open water lake areas by constructing islands by hydraulic dredging of bottom sand. Material removed from the lake bottom created deep holes, which enhanced benthic diversity of the lake bottom. The extracted sand created islands with elevations suitable for emergent wetlands, wet prairie, and sand prairie depending on the elevations.
The benthos of Wolf Lake contains little organic matter or nutrients and as a result it is a less than ideal planting medium. We also anticipated that the lake’s high winds would hinder stabilization of the newly formed sand islands. Wave and ice action accompanying these winds had been destructive to previous shoreline restoration and stabilization efforts. Herbivory, particularly by muskrats, carp, and the resident Canada goose population was also expected to be a challenge for establishing plants on the islands.
The project plan used several methods to mitigate the potential effects of a less than ideal planting medium, wind erosion, and herbivory. Erosion blankets anchored with 46 cm landscape pins were installed along the shoreline of the newly created islands to protect the wet prairie seed. Emergent plant plugs were secured with 20 cm steel staples. Plant species selected for the seed and plug mix included fast-growing stabilization workhorses like Chairmaker’s rush (Scirpus pungens) and Softstem bulrush (Scipus validus), along with annual rye (Lolium multiflorum) and oats (Avena sativa) for quick cover. The plant and seed mix contained more than 100 native species in the hope that it would result in a diverse native plant community representative of pre-settlement ecosystems. A system of 46 cm tall chicken wire fencing and nylon cord was also installed to protect the 4.6 m wide emergent planting zone from predatory geese, muskrats, and carp. In critical energy zones, unvegetated sacrificial barrier islands were created to protect vegetated islands during the early plant establishment years.
Island construction began in late summer 2006 and seeding and planting commenced in spring 2007. The prime contractor was Luedtke Engineering of Frankfort, Michigan and they were responsible for performing the hydraulic dredging and island construction. Cardno JFNew provided all plant materials, installation, and initial vegetation maintenance.
Many planting and seeding areas were lost or damaged by agents of nature despite all the protective features incorporated into the design of the sand lakes. Some of the problems that occurred:
- There were some pockets of organic sediment that provided neither adequate base nor sufficient cohesive material for island construction. Preliminary soil borings of the lake bottom had not predicted this problem. As a result several of the islands had to be eliminated because they were to be located within zones containing these organic sediment deposits.
- High water levels during the early planting stages inundated the emergent and wet prairie planting zones and delayed planting. The cause of the problem was three culverts on the Illinois side of the lake had been dammed by beavers. A concerted effort was required to keep the culverts open so planting could take place at the desired water levels.
- Low water levels during the 2007 mid- summer drought threatened the new plantings. This was particularly detrimental to the sand prairie seedings planted at the highest elevations. Installation of erosion blankets and irrigation, which were not part of the original design, were necessary in this zone to reduce plant mortality.
- High water levels from rainfall occurred after the plantings were completed in August 2007. These high water levels resulted in wave action and inundation that killed many of the newly planted emergent zone plants.
- Predation barriers were only marginally effective. Geese entered the enclosures from the upland side. Carp and muskrats were able to burrow underneath the predation barriers because the chicken wire mesh could not be securely pinned to the soft sand substrate.
- During the first year the most exposed reaches of newly created islands suffered severe erosion. Some areas adjacent to large open expanses of water that were exposed to prevailing winds lost large amounts of sand the first winter. In some cases the new shoreline was 23 m landward from the original location.
- Low levels of nutrients and organic matter in the sand meant slow growth of the stabilizing vegetation prolonged the period of erosive damage to the islands.
The restoration community may benefit from the lessons learned on this project. Future designs using dredged spoils to create sand islands within lakes should consider the following:
- Design island shapes for greatest area- to-perimeter ratio. Erosion on all sides of long, narrow islands can destroy the entire land mass before native vegetation can become sufficiently established to stabilize the substrate. In general, the larger and more circular the shape, the more resistant it will be to erosive attrition.
- Use erosion control blankets on all seeded areas. This will help conserve moisture and slow erosion from wind and rain for faster stabilization.
- Control construction timing to allow islands to settle before planting. Wait at least three months to allow the newly created sand islands to become consolidated before doing any planting.
- Build the islands larger than final desired dimensions. This will allow for erosive attrition to occur while still maintaining the form and function. Expect greater losses on sides adjacent to large fetches or drop-offs to deep water.
- Protect all shorelines that have exposure to particularly harsh wind and wave action. Use hard armor barriers such as log structures or sacrificial islands.
- Focus on establishing vegetation in the above-shoreline zone. Most vegetative stabilization at Wolf Lake occurred after a dense sod of native grasses, sedges, and forbs became established in the wet prairie zone adjacent to and immediately above the waterline. Plant establishment in the highly dynamic emergent zone was generally much slower and mortality much greater. In many areas erosion was not arrested until the wet prairie zone plants became well established.
- Limit emergent plantings. Focus simply on groupings or “pods” spaced along the shoreline. Completely surround the groups with at least 0.9 m tall netting.
- Size the emergent plant pods to discourage geese landing. Keep these areas small (i.e., no larger than 0.9 m wide by 1.8 m long). This sized pod can withstand herbivory after the plants mature and will spread vegetatively and by seed to other areas.
- Be prepared for nature to trump your plan. The final results delivered by the grand forces of nature may not conform to your plan, despite your best design efforts. Set reasonable vegetative cover goals, and be prepared to modify the goals to account for the unknowns.
As with any restoration project, ongoing management is essential to control the advances of non-native aggressive species and maintain biotic integrity. During project design the USACE developed an operations and maintenance manual that will guide long- term management of the native areas. Wolf Lake is particularly vulnerable to the advances of phragmites (Phragmites spp.), purple loosestrife (Lythrum salicaria), and Eurasian watermilfoil (Myriophyllum spicatum).
Project ownership has transitioned from USACE to the City of Hammond. The city is now responsible for managing these species and aggressive native plants like cottonwood and willow. In certain areas, wave and wind erosion requires periodic reinforcement of protective measures such as wave barriers and erosion control blankets, and replanting of native plant plugs. Periodic prescribed burning of upland areas is also planned.