Effects of Salt Contamination and Exotic Species Invasions on a Large, Freshwater Marsh in the Lake Erie Basin
Project Number: R/ER-056-PD, Progress Report
Start Date: 3/1/2000
Completion Date: 3/1/2001
Revision Date: 11/27/2000
|Principal Investigator(s)||1.||Lisa E. Park, University of Akron*|
|Co-Principal Investigator(s)||2.||Bryce Dingman, University of Akron*|
|This shows the current affiliation and may not match affiliation at time of participation. *|
|Source: Ohio Sea Grant College Program|
|Source Fund||State Match||Pass Through|
|Total||$ 7,642.00||$ 6,256.00||$ 0.00|
When did the marsh form, particularly with respect to Lake Erie high or low stands?
What is the current water quality in the marsh and how has it changed since the remediation was completed in 1988?
Is Phragmites encroachment a 'natural' phenomena or is it solely due to salt contamination?
What are the other plant species in the marsh and at what abundance are they?
What invertebrate species inhabit the marsh and how has the number and type of species changed since salt contamination in the 1950's?
How does plant diversity compare or contrast to other marsh communities?
In light of the documented long term changes in the marsh, what effects will proposed mitigation (i.e. the creation and enhancement of several ponds in the eastern end of the marsh) have on the overall ecosystem?
Mentor Marsh is the largest marsh within the Lake Erie basin (3.24 km2) entering the lake near the Grand River. It serves as an important nesting ground for migrating waterfowl, a spawning area for fish, and a habitat for various aquatic invertebrates. Some of its inhabitants such as the spotted turtle, sharp-skinned hawk and king rail, are on the Ohio endangered species list (Isard, 1966; Bernstein, 1974).
Physiographically, the marsh is 200 m above sea level and about 6-7 m above Lake Erie. The eastern basin of the marsh is approximately 1 m above the western basin. There are a few open water areas within the marsh, the largest being Shipman Pond, with two smaller ponds located along a boardwalk in the western part of the marsh. There are several tributaries entering the marsh, the primary ones being Marsh Creek, the Grand River outlet and Blackbrook Creek. The latter became the primary point source of contamination for the marsh.
The Salt Contamination Event
Salt contamination of the marsh in the late 1950's and early 1960's led to a dramatic disruption of it's ecosystem, resulting in die-offs of invertebrate, vertebrate and native plant species. Changes in the water quality also allowed for the invasion of exotic plant species, primarily the reed grass Phragmites australis.
The contamination event was attributed to the dumping of 165,000 tons of salt mine tailings in a landfill area adjacent to Blackbrook Creek. In 1981-82, a baseline survey funded through the Northeast Ohio Areawide Coordinating Agency (NOACA) investigated the conditions of the marsh as a basis for evaluating future development projects. This survey involved inventories of fish and two-winged fly species, as well as an initial geological evaluation of the marsh that included a salt budget model. From this study, a remediation effort was implemented as part of litigation against the primary salt contaminator. The direct result of these efforts was the re-routing of Blackbrook Creek (completed in Spring, 1988) that had previously flowed directly through the salt mine tailings and was the main source of salt contamination.
Need for Study
Since the re-routing of Blackbrook Creek in 1988, the water quality of the marsh has significantly improved, returning, in some areas, to the same ionic concentrations as before the salt contamination event. However, much more work needs to be done to better understand the water chemistry of the marsh, and more importantly, the effects of the salt contamination on the fauna and flora of this ecosystem. This has particularly acute relevance now, as the marsh is faced with mounting pressure of urbanization, and the Mentor Marsh Board, which owns and manages the marsh, faces important decisions with respect to remediation plans within the watershed. For such decisions to be made, details are needed on the geologic history of the marsh, the extent of the impact of the invasion of Phragmites australis, as well as the long-term impact on the diversity and abundance of aquatic invertebrates. Such information can be used to determine what areas of the marsh need to be protected the most and which would be most responsive to remediation efforts vis a vis mowing of the Phragmites and enhancing and/or creating ponds within the marsh.
Two vibracores were extracted near the Wake Robin trail boardwalk. Grain size, composition and clays were analyzed throughout the core, and two peat layers were sampled for 14C dating and analyzed at the University of Arizona Radiometric Dating Lab.
B.Assessing Phragmites Encroachment
We used aerial photo coverage from 1937-1994 to map the Phragmites distribution through time. Using this approach, we evaluated the amount of increase in Phragmites encroachment after the initial salt contamination event (circa 1959) and determine its significance.
C.Plant Census and Diversity Measurements
Plot-quadrat transects along the marsh margin and cross-cutting the marsh were made in order to inventory the types of species present and determine their relative abundances. Random quadrats were chosen and all plants within the 1 m2 quadrat were sampled and identified. Chi-square tests were conducted to determine if there are significant associations or differences in the flora from inside to the outside sample quadrats along the transect.
D.Invertebrate Species Census and Diversity Measurements
Replicated samples of benthic invertebrates were taken using a collecting net and jars at distances of 1, 5 and 10 meters offshore at two week intervals. Samples were then wet sieved and picked for invertebrate material. Faunal inventory lists and relative abundance measurement were made and compared in space and time to determine if there are significant differences between sampling sites and sampling time periods.
E.Comparison of Flora to Other Marsh Communities
Floral species lists were qualitatively and quantitatively compared to another freshwater marshes in Ohio, Old Woman Creek using rank abundance and rarefaction analyses.
Benefits & Accomplishments
- Marsh History
Mentor Marsh was formed as a cutoff meander of the Grand River approximately 1,924 B.P. during a Lake Erie lowstand. According to core stratigraphy and historical records, it was most probably an open water system dominated by a swamp forest until 1959-1960, when it was contaminated by the dumping of 165,000 tons of salt mine tailings at a site adjacent to Blackbrook Creek, a main tributary to the marsh. This event caused the marsh water to become hypersaline, thus creating a massive die-off of flora and fauna. This die-off also allowed for the invasion of exotic species, most notably the reed grass Phragmites australis, whose encroachment has dramatically decreased the floral diversity in the marsh.
- Water Chemistry After Remediation
Remediation efforts were completed in 1988, when the rerouting of the Blackbrook Creek around the contaminated site was finalized. Since then, the chloride concentrations within the marsh have decreased considerably; however, Cl and Na remain the dominant ions in the marsh surface water. The decrease in Cl concentrations from the baseline study conducted in 1988 to the Cl concentrations in the marsh surface water in 1997 shows that remedial efforts of rerouting the Blackbrook Creek were successful. However, even with significant improvement in surface water quality, the marsh remains drastically altered from its natural state. Other remediation efforts involving removal of Phragmites and the creation of open water ponds will be necessary to allow the flora and fauna to respond more rapidly to the changes in the water chemistry.
- Floral Response After Remediation
Phragmites encroachment has dramatically reduced the floral diversity of the marsh, however, the creation of small ponds along the boardwalk adjacent to Wake Robin trail has allowed some rejuvenation of the seed bank. The results of our floral transect along the boardwalk indicate that once Phragmites is removed, floral diversity increases. This could be due to the fact that the Phragmites dominates available space and its great biomass overwhelms the rest of the flora. Future remediation efforts to remove the Phragmites should be successful if deep, narrow channels are created.
- Faunal Response After Remediation
The fauna had a dramatic die-off after the salt contamination event of 1959. Faunal surveys indicate a patchy distribution of benthic invertebrates, with Boardwalk Pond, a smaller, eutrophying pond having significantly lower diversity than the other sampling sites. Shipman Pond North and West were not as similar as previously thought, suggesting that distribution is not homogenous and that the Shipman North site is probably influenced by its proximity to the Grand River.
- Ostracodes and 'Ecological Rebound'
Ostracode surveys from the 1930's (pre-contamination event) reveal species adapted for freshwater environments. Species surveyed in 1989 (one year after the remediation was completed) showed planktonic species adapted for saline environments. Species surveyed in 1999 (10 years after the remediation event) reveal generalists who are adapted to a broader range of environments. It should be noted that those species found in 1989 were absent from the fauna. This indicates that rate of faunal turnover for ostracodes is fairly rapid. This 'ecological rebound' demonstrates that remediation efforts (i.e. rerouting the Blackbrook Creek) are effective in restoring the ecosystem diversity and that this response can be as short as 10 years.
Publications & Media
|Conference, symposia, or workshop proceedings, and summaries|
|Dingman, B.D., Park, L.E., and Fuller, N. 2000, Paleoenvironmental changes in a freshwater marsh: ecosystem response to salt contamination in Mentor Marsh, Ohio|
GSA Abstracts with Programs, v. 32(7), p. 286.
|Bryce Dingman (Graduate)|
Title: Assessing the Biodiversity Changes of a Salt Contaminated Marsh, Mentor, Ohio