November 24, 2003 — Old Woman Creek estuary is one of the few remaining natural areas along the Ohio shoreline of Lake Erie. Located on the south-central shore in Erie County, Ohio, it encompasses a total of 571 acres. Like many small creeks and streams in this region, agriculture is still the primary land use practice in the area. Lake Erie and its coastal zone are among Ohio's most valuable natural resources. Attracted by an abundant water and food supply and a variety of aquatic and terrestrial habitats, hundreds of species of plants, invertebrates, mammals, fishes and birds live in the estuary — including the endangered American bald eagle, as well as the eastern fox snake, sharp-shinned hawk and spotted turtle. As the state's once expansive coastal wetlands continue to disappear in the face of encroaching development, the preservation of these natural features becomes more critical. Fortunately, the area is protected as a State Nature Preserve by the Ohio Department of Natural Resources and was incorporated into the National Estuarine Research Reserve System in 1980 so that long-term research, monitoring and education could be conducted in this estuary. Today, the estuary serves as a field laboratory where scientists can study this naturally functioning system and as a place where students and the general public can learn about estuarine ecology in a natural setting.

OWC NERR is unique among the 26 reserves of the NERRS in that it is the only estuarine reserve located in the Great Lakes Biogeographic Region, thus making it the only Great Lake-type, freshwater estuary in the system. The reserve features freshwater marshes, swamp forests, a barrier beach, upland forest, estuarine waters, stream and nearshore Lake Erie. Estuaries are traditionally defined as areas where the land's fresh waters meet and mix with the saltwater of the sea and where water levels are affected by tides, however, in this case, Lake Erie is actually considered a freshwater “inland sea.” Although salt concentration or salinity is not a factor here, the waters of the lake and OWC combine in the estuary to form a third type of water, chemically different from that of either the creek or lake. Furthermore, even though the lunar tidal effect on Lake Erie is extremely small, lake levels are also affected by daily weather conditions. The Great Lakes are also affected by marked seasonal and annual changes in water levels as demonstrated in Figure 1.

Old Woman Creek Research
Although the Great Lakes have been well studied for the past 100 years, the coastal wetlands — and particularly the estuaries — have not received the scientific focus that they deserve. Therefore, the purpose of the OWC research program has been to identify the various components and processes within this freshwater estuary and to determine the role of this and other estuarine areas within the Great Lakes ecosystem. The program is also developing a database that can be used to evaluate the subtle, long-range changes in the Lake Erie system. Because agriculture is the major land use within the OWC watershed, research has also focused on the effectiveness of the estuary in mitigating storm runoff from agricultural lands. For example, studies have been conducted to track the movement of sediments from farm fields into the creek, and finally into the estuary. Other research projects are examining the function of the estuary in breaking down organic pollutants, particularly herbicides, before they move into Lake Erie. More recently, the marked decline in water levels in Lake Erie has allowed researchers to examine the impact of changing water levels on the coastal wetland environment. Likewise, changes in land use practices over the past few years has had a major impact on this estuary. The remainder of this article will focus on the impact of changing water levels; organic pollutants and land use changes on OWC NERR.

Changing Lake Water Levels Cause Marked Shifts in Vegetation
Great Lakes coastal wetlands are among the most dynamic wetland types due to changing lake levels. The impact of these changing water levels on aquatic vegetation has been significant over the years. In 1973, when lake levels were rising after an extended period of average water levels (Figure 1), the first detailed vegetative survey of the OWC estuary was conducted. In this survey, an emergent plant, Peltandra virginica (arrow arum), was one of the most common plants, as was the floating leafed plant, Nelumbo lutea (American water lotus). As a result of high water levels through the 1970s, P. virginica had largely disappeared by the time the reserve was established in 1980. By this time, N. lutea was the dominant aquatic macrophyte in the estuary and would remain so for the next two decades (the percentage cover by N. lutea varied from about 5 percent up to over 35 percent — with the other areas remaining open water). During this 20-year period, emergent vegetation was confined to a narrow band along the shoreline.

In 1999, Lake Erie water levels began a period of decline to average or slightly below-average water levels (Figure 1), and these low waters have continued to date. Once again, this change in water levels had a significant impact on local vegetation. In 1999, the estuary was still dominated by N. lutea, which covered about 30 percent of the estuary (Figure 2); and emergent vegetation was confined to shoreline areas around the perimeter of the estuary. By 2000, however, emergent plants covered nearly 45 percent of the estuary; and N. lutea coverage had declined by one-third (Figure 3). The dropping lake water levels exposed extensive mudflats during the spring of 2000 — allowing many of the emergent plant seeds to germinate successfully, and also those plants with rhizomes to spread rapidly. From 2000 through the summer of 2003, the relative extent of the emergent vegetation has increased only moderately, but the composition of the emergent plants has changed. The grasses of 2000 gave way to sedges and reeds during 2001 and 2002. Today, Phragmites australis (common reed), Bolboschoenus fluviatilis (river bulrush) and Sagittaria latifolia (broad-leaf arrow-head), as well as N. lutea, are now the most common plants in the estuary.

Impacts on Estuarine Ecology
Open water accounted for more that 50 percent of the estuary before 1999, but in 2000 the open water area declined to 25 percent of the estuary, and this trend has continued through 2003. The marked shift in aquatic vegetation associated with this change is expected to have at least three major implications throughout the biota of the estuary:

• The decline in open water could shift the food web in the estuary from grazer-based to detrital-based. If the shift occurs, then the microbial link in the food web would become more significant in the estuary. This microbial link is currently being studied.
• The shift in vegetation could have an impact on the benthic macro-invertebrate communities in the estuary. These communities are also being examined.
• Changing vegetation could alter the availability of habitat for a variety of fish species; therefore, the fish populations are being monitored on a seasonal basis.

Management Issues
The recent shift toward emergent vegetation in the estuary has created some management concerns resulting from the rapid spread of P. australis (common reed). Historically, this species was reported in the earliest vegetative surveys in the area conducted before the beginning of the 20th century. By 1973, it was no longer reported in the estuary. However, in the mid-1980s it was again observed in the estuary near the barrier beach, which would suggest that this species entered the estuary from Lake Erie. In extensive vegetative surveys conducted in 1993 and 1994, P. australis was confined to small patches along the shoreline. Through 1999, this species remained confined to the shoreline, and expansion was minimal. With the inception of low lake levels in 2000 and onward, the expansion of this plant has been both rapid and extensive. Specifically, from 2000 through 2001 there was a greater than four-fold increase in the coverage of this species. By 2003, it became the dominant species in the estuary. The impact of this rapid expansion on macrophyte species diversity within the estuary is currently being evaluated. If management procedures are deemed necessary to maintain the integrity of the estuary, control measures — such as herbicide application — may be undertaken. The impact of herbicide application on non-target species (algae, macro-invertebrates, and fish) is currently being evaluated at a test site.

Water Levels Affect Pollution Amelioration
As lake water levels drop, the surface area of the estuary becomes smaller and vegetation increases. How might this change affect the estuary’s ability to process the pollutants as they pass through the estuary and on into Lake Erie? On the one hand, there is more vegetation available to process (trap, absorb, convert) the pollutants; on the other hand, there is a smaller area in which to process it. In the early 1990s, when lake levels were high and rooted vegetation was less prevalent, a study was conducted to examine pollutant loads and estuarine mitigation rates. The researchers and staff at OWC are seeking funding sources to undertake a similar study during low water conditions. This would allow researchers to compare the effectiveness of the estuary in mitigating the waters that pass through it both during high and low water conditions. Since many pollutants are attached to sediments, any mitigation study must incorporate a sediment component. A study, recently completed, examined the movement of sediments during two storms at different lake levels. This study, in conjunction with the proposed study of pollutant loads, would result in a better understanding of the impact of lake levels on the role of the OWC estuary in pollution amelioration.

Organic pollution has become an area of concern in the Lake Erie region. Agricultural practices are relying even more heavily on organic herbicides and pesticides than in preceding years. At OWC, research has been underway since the late 1990s to examine the role of the estuary in degrading these organic compounds. An excellent review of this work is in the March/April 2003 (Vol. 25/No. 2) issue of Twine Line, The Ohio Sea Grant newsletter. The impact of one organic pollutant (atrazine) on two important species of Lake Erie fish, Perca flavescens (yellow perch) and Ictalurus punctatus (channel catfish) is currently being examined.

Infrastructure Development Affects Land Use Activities
Although the OWC watershed has been agricultural for the past 150 years, land use practices are changing. Specifically, Erie County has proposed installing water lines along county roads. This will accelerate a shift in land usage in the watershed from agriculture to a combination of agriculture and low-scale urban development. In anticipation of this shift, an evaluation of land use change (including the increase in impervious surfaces) over a 10-year period (1993-2003) is being conducted. This study, in conjunction with one on best management practices in the watershed, provides groundwork for the evaluation of future impacts from development on the waters flowing into OWC estuary.

Changing lake water levels and land use activities have been important in developing research initiatives at OWC. The research program will continue to evolve to address other changing environmental conditions in the estuary and its watershed. However, within this evolution, the long-term goal of developing a comprehensive understanding of a freshwater estuary and its role in the Great Lakes ecosystem remains unchanged.

Relevant Web Sites
NOAA National Estuarine Research Reserve System

Old Woman Creek Estuary

Remote Sensing in Estuarine Education

Great Lakes Commission

NATIONAL ESTUARIES DAY CELEBRATION FOCUSES ON EDUCATION

Media Contact:
Glenda Tyson, NOAA Ocean Service, (301) 713-3066 ext. 191 or Ben Sherman, NOAA Ocean Service, (301) 713-3066 ext. 178