Saving Dicken Woods -

The Thurston Nature Center

Below are the minutes from a recent (2002) meeting of the Thurston Nature Center Committee, including an informative overview of how the area was created and preserved.

Thurston Nature Center

Scott Dierks, hydrologist for Ayres, Lewis, Norris & May, Inc. explained the mission of the Millers Creek Action Team Working together to establish and implement socially, environmentally, and economically sustainable watershed management standards and practices that will improve the quality of the Millers Creek Watershed.

Miller's Creek Web Site -
Scott is interested in helping us meet our water goals.

Land Goals
TNC land Steward Report-Mike Conboy -Buckthorn removal is progressing slowly and will continue through the winter. Need to remove large dead limbs of weeping willow trees which extend over the path south of the pond. We are redoing the TNC brochure for 2003. If you have suggestions, additions, revisions or deletions please call Mike Conboy at 665-4027. Planned sprig tree planing include;Flowering Dogwood (replacement), Paw Paw, Largetooth Aspen, Blue Beech and Yellow Birch. Note:the TNC tree species inventory of 68 trees is based on the reference book "Michigan Tress Worth Knowing" by Norman F. Smith, republished eight times since 1948. Mile passed the table of contents to committee members.

Comments included proactive planting of shrubs, keeping in mind the wires above the willow tree "Dead zone". Transplant Tupelo tree to a wetter spot. Vickie Botek volunteered as the "Buckthorn removal person at large" Call her if you want to help. Suggestion to add Michigan Holly.

Water Goals
Update by Tom Edsall-Water Work Group (WWG) File: Thurston Pond Plan B2002

To: Water Work Group (WWG), Thurston Nature Center Committee (TNCC)
From: Tom Edsall, WGG
Subject: Thurston Pond Rehabilitation and Management Plan

As follow-up to the November TNCC meeting I offered to begin development of a draft plan for rehabilitating and managing Thurston Pond and to circulate the draft material for review and comment by the WWG and presentation to the TNCC at its December meeting. What I believe we need is a plan that addresses both short- and long-term needs for managing the pond ecosystem and that as a first priority provides an action plan to restore water quality in the pond. What follows is a proposed work schedule and a start on a plan that we can develop jointly.

Proposed Work Schedule:
  • 1. WWG outlines a draft conceptual plan for the restoration and management of Thurston Pond, consistent with the objective stated below, for consideration by the TNCC at the December 2002 meeting.

  • 2. WWG revises the plan as needed, so that it can be presented to the Miller Creek Watershed Group in January, 2003.

  • 3. Appropriate representatives of the TNCC interact with the Miller Creek Watershed Group to explore collaboration in a watershed-wide effort to help resolve the Thurston Pond water quality problem within the context of "downstream" rehabilitation programs and actions.

  • 4. WWG continues development of a more detailed conceptual plan and schedule for deepening and grading the Thurston Pond basin, as needed for the development of proposals to secure funding to cover the cost of the work. Complete the plan and present it to the TNCC at the March 2003 meeting.



To restore the ecological integrity and health of the Thurston Pond ecosystem as needed to permit the pond to be managed successfully as an open-water environment with fringing wetlands that supports a diverse and abundant community of desirable native plants and animals. This objective is consistent with the intended use of the pond ecosystem as (1) an outdoor teaching classroom for the Ann Arbor public school system, (2) the major aquatic ecosystem element of the Thurston Nature Center, a dedicated Conservation Education Reserve, (3) an important headwater feature of the Miller Creek watershed, and (4) a valued aesthetic resource available to the public for various non-consumptive recreational activities.

Background and Problem Statement: [This sort of material will probably be needed if we apply for funding to cover the proposed dredging. It obviously needs some fine tuning and addition of text by one of you educators to more fully accent the pond's use as an outdoor classroom.]

Thurston Pond is owned jointly by the City of Ann Arbor and the Orchard Hills subdivision. The pond was created in the mid-1960s when construction activities associated with the development of the Orchard Hills and Bromley subdivisions altered the drainage patterns in this headwater portion of the Miller Creek watershed, which until then was characterized by intermittent and seasonal surface water flows and several small temporal ponds with fringing wetland plant communities. During construction, surface water flows were channeled into storm sewers which discharged into the basin that now holds Thurston Pond. Elevation of the western side of the pond basin to accommodate subdivision construction and development activities contributed to the pooling of surface water flows and undoubtedly also increased retention of ground water. Jointly, these events created Thurston Pond. The subsequent construction of a berm along the west side of the pond helped to maintain pond level and create a walking path along that side of the pond.

The basin now occupied by Thurston Pond was previously a relatively flat, low, grassy area with a small (ca. 0.5-acre), shallow, seasonal pond with fringing wetland vegetation that was located in about the center of the northwest one-third of the present pond basin. During construction of the Orchard Hills subdivision and swimming pool, the eastern one-third of the basin of the present pond, which was owned by the developer, was graded and deepened. Surface soils were removed and the glacial till base (clay) was fully exposed. The remaining two-thirds of the pond basin, which is in City ownership, retains its original and topography and soils, except as they may have been modified by inundation.

Soon after the pond was created in the mid 1960s it developed a healthy compliment of aquatic plants and animals. Some migrated in from neighboring habitats and others were introduced by interested neighbors. School children planted the saplings that became the huge weeping willows that now border the south side of the pond. The pond water was clear and several species of fish, including largemouth bass, sunfishes, and bullheads were common to abundant. Children fishing from the shoreline at the end of Yorktown Street was a common sight. Frogs and toads could be heard chorusing in the spring. Painted turtles and snapping turtles became common. Diving and dabbling ducks and four species of herons frequented the pond and fed on the frogs and fishes. Tree swallows were abundant and the occasional migrating osprey was reported fishing in the pond in the spring. Muskrats burrowed in the pond banks and constructed offshore houses of aquatic vegetation that were readily apparent to even the casual observer.

By the mid 1970s, the pond was being stressed by nutrient additions, as evidenced by blanketing blooms of noxious filamentous algae. Efforts to control the algae by applying copper sulfate were largely unsuccessful and were eventually abandoned. Plantings of submersed (Elodea) and floating-leaved aquatic plants (pond lilies and pond weeds) were made by school children.

By the 1980s, the blooms of filamentous algae largely disappeared but the fish community had degraded to one that consisted largely of bullheads, carp, and goldfish, which are species that can survive in water with low oxygen content. Dragonflies and damselflies, whose juvenile life stages are aquatic, had become less abundant. The water was less clear and the submersed and floating-leaved plant community declined. Muskrats disappeared as the aquatic plants that were their food supply diminished. Canada geese began using the pond heavily as a roosting area from early fall until ice cover formed and 200 or more birds could often be counted on the pond at dusk. The significance of their contribution to nutrient enrichment has been debated, but studies elsewhere indicates it could be substantial.

By the 1990s, the water was almost constantly turbid, large aquatic insects were largely absent and the carp, goldfish, and bullheads had disappeared. Only turtles and crayfish remained abundant. Great blue herons and egrets were present only in small numbers and other fish-eating birds were rarely seen. Mallard ducks and Canada geese were abundant in the fall.

In late summer and early fall 2002, water clarity was extremely low. When the pond was calm and sediments were not stirred by wind, visibility into the pond water was about one inch. A rich bloom of floating, green, non-filamentous algae was present. Turtles were the only other apparent sign of aquatic life in the pond.

The present water level in the pond is the lowest seen since the pond was created in the 1960s. This low level probably reflects a lack of precipitation, which reduced storm water input and perhaps, by lowering the water table, also reduced storm water retention. In October, the water level had fallen to the point that the pond became three isolated pools, one in the northeast part of the basin, one in the south, and one in the northwest. These pools were separated by a large mud flat extending from south to north along the City-Orchard Hills property line and lying mostly on City property. Water depth in most of the pond, as estimated from depth soundings, made in 1999, was less that one foot.

The 1999 depth survey also, showed that the deepest portion of the pond basin was filling with soft, loose sediment and that this in-filling layer was 1-2 feet thick in the deepest portion of the pond. The in-filling material includes decaying plant matter produced in the pond (algae and rooted aquatic plants) together with that added from terrestrial and emergent aquatic plants along the shoreline (leaves and stems). It also includes mineral soils eroded from the shoreline, and from higher elevations of the pond bottom, and sediment transported into the pond through the storm drain at the northeast corner of the pond. Shoreline erosion of the till soil at the end of Yorktown Street is particularly severe and contributes to in-filling there and to decreased water clarity throughout the pond.

The present low water levels and in-filling will have continuing serious negative impacts on any remaining aquatic life in the pond. If the water levels remain low and we experience a cold winter, the ice cover in virtually all of the pond will extend to the pond bottom, leaving no water under the ice for aquatic organisms. Where the ice cover does not extend to the pond bottom, the oxygen demand from decaying plant material could easily remove the oxygen dissolved in the small amount of water remaining beneath the ice so that it cannot support aquatic life.

FILE: Thurston Pond Mgmt 12.18.02
[History: Moved to hard drive 01.07.03]

Dear WWG Members,

At the December TNCC meeting it was recommended that the Draft Thurston Pond Rehabilitation and Management Plan (November 25, 2002) be amended to include options in addition to managing the pond as a pond. I am attaching some draft narrative that addresses that recommendation. The attached material can also serve as an ad hoc agenda for the WWG meeting.
Hope to see you all on the 19th.
Tom Edsall

Management Plan Alternatives

1. Do nothing.

This option would allow the processes currently at work to continue. The pond would remain but further slow degradation of the aquatic environment would probably result in more frequent and persistent blooms of obnoxious algae. Water clarity would probably be further reduced for most of the ice-free season. If water levels remain low, due to low precipitation, the fringing wetlands could be expected to expand around the perimeter of the pond and wetland vegetation would colonize the mud flat in the middle of the pond. Three separate pond basins surrounded with emergent aquatic vegetation could be expected. Woody shrubs would also gradually colonize the exposed pond bed.

2. Manage the present pond area as a wetland.

This option would convert a (presumably) significant amount of the present open-water pond habitat into wetland habitat. In the simplest case, the amount of open-water and wetland habitat and the locations of those habitats would be determined by the existing shape of the pond basin and the water level. A new water level control structure would be needed to regulate water level. Channel dredging would be required to lower the water level to the point where an expanded wetland plant community could become established.

Additional dredging and grading could be done to change the shape of the pond basin and, thus, the relative amounts and locations of the open-water and wetland habitats that could be realized.

As a first step, exercising this option would require the installation of a new water level control structure. This would be followed by channel dredging and draw-down of water levels. If additional grading of the pond basin is to be undertaken, the pond bottom sediments must be given sufficient time to dry (consolidate) to the point that they will support heavy earth moving equipment. Dredging or grading will need to proceed incrementally, from the outlet structure. Pond bottom sediments displaced by dredging and grading would be deposited on site to enhance habitat diversity. Wetland management would require some degree of seasonal flooding of the basin to support a healthy wetland plant community and to discourage the establishment (encroachment) of woody vegetation.

3. Manage the pond as a pond.

This option would retain most of the existing open-water habitat while restoring water quality and aquatic plant and animal bio-diversity in the pond. In the simplest case, channel dredging would be required to allow the pond be fully de-watered whenever necessary (probably every 10 years) to compact and rejuvenate (oxidize) pond bottom sediments by direct exposure to the atmosphere. A new water level control structure would be needed.

Additional dredging to deepen selected portions of the pond basin from (1-2 feet to 3-4 feet) would create more deep-water habitat and improve the aquatic bio-diversity potential. It would remove substantial amounts of the in-filling material with high oxygen demand, thus further contributing to improved water quality.

As a first step, exercising this option would require the installation of a new water level control structure. This would be followed by channel dredging and draw-down of water levels. If additional dredging and grading of the pond basin is to be undertaken, the pond bottom sediments must be given sufficient time to dry (consolidate) to the point that they will support heavy earth moving equipment. Dredging and grading would need to proceed incrementally, from the outlet structure. Pond bottom sediments displaced by dredging and grading would be deposited on site to enhance habitat diversity. Some of this displaced material could also be used to strengthen and elevate the berm at the western end of the pond that presently helps maintain the water level in the pond.

The Next Step(s)
I believe the WWG should, as its first priority, select one of the above options and develop a supporting rationale, including a simple conceptual plan with maps and other illustrations as appropriate, and present that package to the TNCC at the January meeting. If the decision is to manage the pond as a pond (option 3), the WWG conceptual plan needs to address (at least) the following subject areas:

  • 1. Desired, benchmark, seasonal, high- and low-water levels in the rehabilitated pond.

  • 2. Water depths to be achieved by dredging and manipulation of the outlet control structure(s).

  • 3. Location and functional design features or performance criteria for a major new outlet control structure for the pond.

  • 4. Consideration of construction of a second minor outlet structure in west end of pond and designed to permit release of water in spring to support reproduction by frogs and toads in a small seasonal pond created between Thurston Pond and Prairie Street.

  • 5. Areas to be dredged.

  • 6. Areas NOT be dredged, (e.g., a firm-bottom area near the existing outlet, which supports a major reed, Scirpus acutus, bed).

  • 7. Slope of dredged pond bottom.

  • 8. Areas for use as on-site deposition of dredged materials.

  • 9. Areas NOT for use as on-site deposition of dredged materials.

  • 10. Use of dredged material (e.g., to strengthen and elevate berm on west side of pond and to create a shoreline footpath along the north side of the pond).

  • 11. Stabilizing the dredged material and pond shorelines with vegetation and other appropriate non-erodible materials.

  • 12. Creating new habitats within the pond basin (e.g., islands and nested wetlands).

  • 13. A rescue plan to capture the pond's turtles during de-watering, relocate them to suitable refugium, and reintroduce them into the pond after it is refilled.

  • 14. A plan for introducing or reestablishing desirable native species of plants and animals to the pond after it is refilled.

  • 15. A phased schedule for outlet construction, de-watering , and refilling of the pond.

Other WWG Tasks
1. The TNCC has expressed concern that dredging and grading could expose porous sediment layers underlying the pond bottom that could cause the pond to drain. This concern could be addressed by making pre-dredging borings of the pond bottom. These borings would show whether the proposed dredging and grading would expose porous sediment layers. We need someone to lead this task. At the last TNCC meeting the teacher (name) from Clague School volunteered to enlist students to do the borings and Scott Diericks (sp) volunteered to provide the boring equipment. Someone on the WWG needs to take the lead here to coordinate the work and report the results to the WWG. The work would be done this winter when there is sufficient ice cover to support the workers. Minimally, one boring should be done at the deepest point in each of the three pond basins. Boring depth should be at least 3-4 feet.

2. The TNCC has expressed concern that dredging of the pond bottom may require that we first conduct sediment testing for pollutants. I believe that someone from the GLERL-NOAA laboratory volunteered to do the testing. Of interest would be the nitrogen and phosphorus levels in the sediments. Testing might also be required to show there are no toxic materials present. Someone from the WWG needs to take the lead here. Contact the City of Ann Arbor to see what tests (if any) need to be run and then contact GLERL-NOAA or other testing service to see what to do and what it would cost.

3. I believe it would be appropriate to conduct monthly, under-ice measurements of the dissolved oxygen levels in the pond. One measurement should be made in each of the three basins of the pond. I can take the lead here. I have all of the needed equipment and instrumentation.

4. Elevation data is needed for the two storm water inlet pipes that discharge into the pond and for the outlet structure that was designed to serve as the drain for the pond. The City of Ann Arbor may be able to provide this data. Someone from the WWG needs to take the lead here and get the data.

NOTE: Exercising option 2 would involve addressing many of the same considerations as option 3.

FILE: Thurston Pond 12.20.02


We (I) did not generate a set of minutes. Maybe we should try to do that more formally in the future. Basically, the email I sent to all WWG before the meeting listing "Management Plan Alternatives" served as the agenda.

The meeting convened at the Great Lakes Science Center at 7:00 PM and ended at 8:30 PM. Attendees were Mike Tucker, Neal Foster, Bram and Lila vanLeer, Beth Caldwell, Jan Baty, and I.

We decided that option 3 (manage the pond as a pond) was the preferred action. Then I charged the group with developing a map showing which areas would be dredged and where the dredged material would be deposited. There was no immediate consensus, so that task became "homework" that would be presented at the next TNCC meeting.

We moved on to the list of "Other WWG Tasks" and made some work leader assignments. Mike Tucker argeed to provide oversight for the pond bottom borings (Task 1); Mike will contact Joe Hoeflinger (sp?) at Clague to develop a schedule involving student participation in the boring; he will also contact Scott Dierks to arrange to borrow the boring tools. Neal Foster volunteered to take the lead on the "contaminants-dredging" issue (Task 2). In today's earlier TNCC email (initiated by Scott Dierks) there is more discussion about that. I volunteered to handle the underice measurements of dissolved oxygen (Task 3). Beth Caldwell presented benchmark information for the pond area (Task 4). The closest (city) benchmark is located on Georgetown Blvd. near the Georgetown-Yorktown intersection. The WWG was encouraged to have a benchmark hunt over the holidays. No prizes were authorized for first sighting. Mike Tucker agreed to get and distribute information on permits required to dredge and deposit (Task 5, added). Dave Szczygie (sp?) had agreed earlier to get information on who actually owns the "school property" portion of the Nature Center (Task 6, added).

There was much additional about how to protect the ponds turtle population during pond rehabilitation (draining and dredging) and it was recommended that dewatering the pond be done in two phases that would leave a turtle refugium first in one basin and then in another (e.g., first drain and grade the west basin and then refill it and then drain and grade the eastern basin). The turtles would be invited to migrate to the available water.

That was about it.