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Effects of Lake Michigan Water Levels on Wetland Soil Chemistry and Distribution of Plants in the Straits of Mackinac
J. Great Lakes Res. 12(3):175-183 Internat. Assoc. Great Lakes Res., 1986
EFFECTS OF LAKE MICHIGAN WATER LEVELS ON WETLAND SOIL CHEMISTRY AND DISTRIBUTION OF PLANTS IN THE STRAITS OF MACKINAC
John G. Lyon Department of Civil Engineering The Ohio State University Columbus, Ohio 43210 Ronald D. Drobney Center for Environmental and Estuarine Studies The University of Maryland Frostburg, Maryland 21532 Charles E. Olson, Jr. School of Natural Resources The University of Michigan Ann Arbor, Michigan 48109 ABSTRA CT. The effects of short-term or summer season water level fluctuations on wetlands were determined from measurements of flooding, relative soil chemistry, and the presence of plants. Analyses demonstrated higher relative concentrations of plant-available soil nutrients and higher density ofplants on flooded emergent wetlands as compared to infrequently flooded, unconsolidated shore sites. Flooding resulted in anaerobic soil conditions and increased concentrations of nutrients for wetland plants. The density of emergent wetland plants was highest where the topographic conditions and water level led to duration offlooding between 50 and 85% of the growing season. The effects of long-term water level fluctuations on wetlands were measured from historical aerial photographs of low, average, and high lake level conditions (1938 to 1980). An increase in water levels of 0.3 m reduced the extent of coastal wetlands by 18%. Historical aerial photos demonstrated and a model predicted that 13% of the total wetlands measured at low lake levels remained in the study area at the highest lake level sampled. This result was verified during the high lake levels of May 1985. ADDITIONAL INDEX WORDS: Coastal zone management, aerial photography, remote sensing, plant communities.
Lyon et al. 1985, Prince and D'Itri 1985, Whillans 1985). The quantity and variety of wetlands are thought to be influenced by both short- and longterm water level fluctuations. Short-term or summer season effects were evaluated in this study by measuring seasonal water levels, duration of flooding, soil characteristics, and the distribution of plants. Effects of long-term or multiple year fluctuations in water level were evaluated with historical wetland and water level data (Lyon and Drobney 1984). Evaluations of each time-frame
INTRODUCTION The potential effects of natural and humaninduced fluctuations on coastal resources are poorly understood. This prompts questions regarding effects of water levels and flooding on coastal resources. One concern is the potential for loss or gain of wetlands. Several studies have demonstrated change in wetlands resulting from water level fluctuations (IGLLB 1973, Jaworski et al. 1979, Lyon 1979, Lyon 1980, Harris et al. 1981,
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LYON et al.
176
provided information on both short- and longterm causative factors. The data were then used to develop a predictive model of long-term effects of water levels on a coastal wetland. METHODS Waugoshance Point and Sturgeon Bay are located on the south side of the Straits of Mackinac between Lakes Michigan and Huron (Fig. 1). Elevational, hydrologic, and geomorphologic conditions have resulted in a variety of wetland, shore, and beach habitats. Plant, soil, and hydrological measurements were taken within a 33,708 m2 grid composed of 144 cells 15.3 x 15.3 m in length (Fig. 2). At the intersection of grid lines (grid nodes), relative elevation was measured and referenced to a U.S. Lake Survey benchmark. Elevation measurements from all grid nodes were recorded in cm above or below the standard elevation of 254.0 cm. A water level gauge was established at Waugoshance Point to measure on-site fluctuations in water levels from mid-June to mid-August, 1980. The strip-chart records were digitized at hourly intervals to supply water level data for statistical analyses. Local water level and flooding data were collected during the period above. Several times per week the on-site gauge was read and the extent of local flooding was checked at each grid node. The
2 months of data were used to calculate flooding frequency for each node, and flood-frequency relative to elevation. The duration of flooding was calculated for each grid node using data on frequency of flooding relative to elevation and hourly water levels from the local water level gauge. In 1979, preliminary studies of monthly change in soil chemistry and texture were conducted to determine the optimal time and conditions to sample (Lyon 1981). An August date was selected because average monthly lake levels and soil nutrient concentrations were high. Furthermore, the common wetland species had matured and achieved most of their yearly stem production. Concurrent studies of soil chemistry and depth indicated that most plant-available soil nutrients occurred within the upper 20 cm of the soil. Most plant roots were also found within that range of depth, so a sample depth of the first 20 cm was selected. Soil samples were taken from grid intersections or nodes, frozen, and chemically analyzed in September, 1980. All soil chemical determinations were conducted using standard techniques (USGS 1977, Wetzel and Likens 1979, Lyon 1981). Soil variables included: 1) total organic matter content measured by weight loss after oxidation in a muffle furnace; 2) molybdate-phosphorus reaction for spectrophotometric analysis of plant-available or soluble-reactive phosphorus (Wetzel and Likens 1979); and 3) exchangeable or plant-available cat-
Mackinaw City STRAITS
OF MACKINAC
Waugoshance
C'.~~~~p"",,0:-i;nrt-+_~-..
Sturgeon Bay
Cross Village
•
Skm
FIG. 1. The Waugoshance Point study site. The area between arrows is the 6.1 km of shore used for historical analysis. The box shows the location of Figs. 2-4.
EFFECTS OF LAKE MICHIGAN WATER LEVELS ON WETLANDS
177
FIG. 2. Aerial photo of: (A) emergent wetlands, (B) vegetated and (C) nonvegetated unconsolidated shore, (D) washover channel containing emergents, and (E) low dunes. The sampling grid location is shown by the box, and the water level gauge was at (F). The photo was taken at average water conditions (23 April 1954, 176.54 m).
ions calcium, magnesium, and potassium as extracted from soil with a IN ammonium acetate solution (UGSG 1977) and measured by atomic absorption spectrometry using a Perkin-Elmer model 403 (Norwalk, CT). The grid nodes were also sampled during early August, 1980, for oxidation-reduction potential (redox), pH, and temperature. The pH of marsh soils was measured with an Orion pH meter by insertion of the electrode to a depth of approximately 9 cm. Redox and temperature were sampled at the same depth as the pH measurement. Redox potential was measured with the Orion meter using a platinum redox electrode. The meter was calibrated prior to sampling with a standard redox buffer solution of 0.0033 M K3 Fe(CN6 ) and 0.0033 M K4 Fe(CN6) in 0.1000 M KCI (Ponnamperuma 1972, USGS 1977). PH and temperature were used to correct redox measurements for temperature variation and to standardize them at 25°C. At each grid node, the number of species and stem density were measured within a 0.63 m 2 sampling frame. The results were reported as the average of five random replicates at each node. Stem
density counts provided a measure of relative cover for comparing plant characteristics with soil and hydrological parameters (Mueller-Dombois and Ellenburg 1974). Wetland community types were determined from field sampling and statistical evaluation of eight soil chemistry and hydrological variables. The variables included duration of flooding, elevation, redox potential, organic matter, and plant available forms of phosphorus, potassium, calcium, and magnesium. Groups were developed from: 1) Kellman tau-b rank correlations between presence of plant species and the variables; 2) Mann-Whitney U tests of pairwise species combinations and similarity of plant distributions related to soil chemistry and hydrological variables (Conover 1971); and 3) species combinations exhibiting similar distributions of the variables, as determined using Kruskal-Wallis tests of similarity. Pair-wise hypothesis tests of plant species distribution versus the eight variables indicated similar types (Ho:sustained). Dissimilarities between individual variables (Ho:rejected) facilitated the identification of differences between plant communities. Soil, plant, and flooding variables were
LYON et al.
178
analyzed with non-parametric tests because the variance of flooded and non-flooded areas were not equal (Conover 1971). Historical Quantity of Wetland The quantity of wetland relative to lake levels was established through analysis of black and white aerial photographs for years of high (1952, 1973), average (1954, 1977), and low (1938, 1958, 1965) water levels. Wetlands were measured from seven sets of photographs (1:5,702 to 1:15,771 scale enlargements) in a 6.1-km-Iong section of the southern shore of Waugoshance Point (Fig. 1). For each year, boundaries of each of the wetland classes were identified with a stereoscope and traced onto Mylar. A random dot grid was used to measure the area within the wetland boundaries. These results were subsequently corrected for scale to yield the actual area measurements (Lyon 1981). Historic water level data were obtained from the gauge at Mackinaw City, Michigan, 16 km from the study site (NOAA 1978), and used to determine average water level for dates that aerial photographs were taken. Pearson correlations were used to evaluate the relationship between lake levels and area of wetland measured from aerial photographs (Netter and Wasserman 1974). A regression model was developed to predict the total area of wetland at a given Lake Michigan water level (y = -60.86x + 116281.46, x = water level in m, y = hectares or ha of total wetland). RESULTS AND DISCUSSION Long-term Water Levels and Extent of Wetland Wetland area measurements from seven sets of aerial photographs indicated a decrease of 154 ha of wetland from lowest to highest lake levels (Lyon and Drobney 1984). This 154-ha area represents 87010 of the total wetland present (178 ha) when measured at the lowest lake level studied (175.83 m). A model of long-term lake level versus quantity of wetland (F-statistic = 65.2, p < 0.001, R2 = 0.93) was developed to predict changes in wetland size at different water levels. At the lowest summer or growing season water level recorded (175.47 m, March 1964), the model predicted 228 ha of wetland. At the highest Lake Michigan water level recorded (177.18 m, July 1974) the model predicted 45 ha. Field evaluations and large scale aerial photographs from 20 June 1985 (177.02 m)
have verified the approximate quantity of wetland predicted by the model for the highest historical lake levels (Figs. 3 and 4). The wetlands studied at Waugoshance Point and adjacent Sturgeon Bay had a low gradient slope for 5 km with an average depth of 1.5 to 2.0 m. However, the wetlands and nearshore region of the bay have a locally uneven elevation, slope, and a convoluted shoreline due to the presence of numerous beach ridges. An aerial photographic method was employed here because actual measurements of historic wetland were possible despite the variation in elevation. Flooding and Soils The on-site water level gauge indicated a small change in the daily and hourly water level of wetlands during the summer of 1980. The 5-7 cm change had an approximate 2-hour period between peaks. These fluctuations were probably due to seiche or storm surge activity on Lake Michigan. The 2-hour period approximates the first traverse mode of oscillation for Lake Michigan (Fee 1968), and to wave periods recorded at Portage and Ludington, MI (Seelig and Sorensen 1977). Soils of the lacustrine emergent wetlands were composed of a think layer of peat over sandy, gravelly soils. These Entisols or Aquents (USDA 1975) experienced frequent flooding from June through September. The duration of summer flooding was governed by average lake levels and short-term, seasonal fluctuations. Seasonal fluctuations resulted in lake levels that were approximately 30 cm lower in winter than in summer. Because of the lower lake levels, emergent wetland soils were infrequently flooded from October through May, but were normally saturated due to a high water table. As the lake level rose to its mid-summer peak, emergent wetlands were often flooded to depths of 3 to 20 cm. In contrast to the soils of emergent wetland, lacustrine unconsolidated shore had Alpena gravelly loamy soils with no peat layer at the surface. Sediments in these areas were poorly sorted, and the texture of the sand was generally coarse to medium (Lyon 1981). These gravelly soils can experience long periods of drought due to low water retention and rapid percolation to a shallow water table (USDA 1975). They normally became very dry during low water months (October-May), but were frequently flooded or saturated as a result of high lake levels and a high water table during summer.
EFFECTS OF LAKE MICHIGAN WATER LEVELS ON WETLANDS
FIG. 3. (A) Emergent wetlands, (B) nonvegetated and (C) vegetated unconsolidated shore during high water in June 1985. The photo looks to the south.
FIG. 4. Low altitude aerial photo of near record high water levels (20 June 1985, 177.02 m). The photo looks to the west. (Symbols are the same as in Fig. 2b.)
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LYON et al.
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The bedrock of Waugoshance Point is composed of marl and dolomite from the Bois Blanc formation of the Devonian Period (Door and Eschman 1970). The high concentrations of exchangeable calcium and magnesium in the soils of the emergent wetland probably originated from the dolomitic bedrock (Table 2). Anaerobic conditions dur-
Areas that experienced a long relative duration of flooding had both a higher abundance of plantavailable phosphorus, potassium, calcium, and magnesium, and higher density of plants (Tables 1 and 2). Availability of these nutrients was correlated (p < 0.01) with anaerobic conditions (redox < - 300 mV) caused by flooding.
TABLE 1. Plant and soil characteristics measured from a north to south transect across Waugoshance Point. Soil chemistry is reported as p.g/gm ofplant available forms (see Methods). Average Wetland Community Emergent Wetland (low elevation)
Most Common Plant
Number of Species
Number Stems/Sample
Redox Potential in mV
Soil Chemistry in ",g/gm P
Ca
Mg
K
S. validus
3
300
326
4,280
312
106
-150
Emergent Wetland (higher elevation)
C. mariscoides
3
160
260
4,044
242
89
-120
Unconsolidated Shore non-vegetated)
P. implicatum
9
32
35
3,062
74
9
-20
Unconsolidated Shore (vegetated)
C. aurea
11
38
38
1,212
80
13
>400
Beach Barrier
no plants
none
none
0
2,194
43
5
>400
TABLE 2. Site characteristics of plant species including mean values and standard deviation. Soil Chemistry is reported in p.g/g and organic matter in proportion. Frequency of Presence on Grid Sites
Elevation incm Relative to Standard
Duration of Flooding (Proportion)
Redox mV
X-
Potassium
u
0.9~
0.09
-135.5 59.2 326.4 257.3 54.1 41.2 3,979.6 1,414.3 212.1
0.27
251.3 2.2 0.75
0.37
-110.7 54.9 261.9 176.3 55.5 39.9 3,951.3
C. mariscoides 52
0.36
252.0 1.9 0.63
0.43
-106.4 67.6 260.3
U. cornuta
12
0.08
252.6 1.0 0.27
0.38
-55.4 80.3 119.2
X-
u
n
Proportion
S. validus
19
0.13
250.7 2.5
J. balticus
39
u
u
X-
Magnesium
Calcium
X-
Species
X-
Phosphorus
u
X-
u
X-
u
Organic Matter
X-
u
140.3 0.19 0.18
948.8 203.7 128.3 0.14 0.16
182.8 55.2 42.2 3,799.8 1,003.5 188.6 116.9 0.12 0.11 32.4 23.1
8.1 3,275.2
180.7
89.5
14.2 0.04 0.01
P. implicatum
20
0.14
253.3 0.5 0.04 0.08
-21.0 44.1
175.8 132.7 30.3 28.2 3,270.2
578.1
121.5
83.2 0.06 0.05
E. pauciflora
54
0.38
253.1
1.0 0.10 0.23
-26.3 50.1
104.0
58.7 18.0
8.7 3,114.1
406.7
85.7
21.1 0.04 0.01
C. aurea
51
0.35
253.1 0.6 0.17
-19.9 54.8 104.6
53.5 19.4
9.5 3,168.3
356.0
87.0
20.9 0.03 O.oI
0.31
EFFECTS OF LAKE MICHIGAN WATER LEVELS ON WETLANDS
ing flooding apparently resulted in solution of minerals such as dolomite, marl, hydroxyapatite, and other calcium and magnesium minerals (Cahill 1981) making them available in the plant root zone. The concentrations of phosphorus and potassium on non-flooded, unconsolidated shore (nonvegetated) were lower than the requirements of most plants (Gosselink and Turner 1978), and probably contributed to the low number of plants and low stem densities found in this wetland type. Low nutrient levels were also indicated by the presence of stunted cedar trees on neighboring sand dunes (Fig. 2) whose small height and diameter were caused by low concentrations of calcium (Cahill 1981, Lyon 1981). Wetland Categories The plants were grouped into three wetland types (Cowardin et al. 1979, Kraft et al. 1979) that included: (1) lacustrine emergent wetland found on washover fans and channels; (2) lacustrine unconsolidated shore (non-vegetated) or periodicallyflooded fans composed of washover deposits with little plant cover; and (3) lacustrine unconsolidated shore (vegetated) or infrequently flooded fans composed of higher-elevation washover deposits (Figs. 2, 3, Table 1). The predominant plant species in each wetland type included: (1) emergent wetland species,Cladium mariscoides, Juncus balticus, and Scirpus validus which were distributed in a similar manner with respect to soil chemistry and duration of flooding; (2) the regularly flooded, unconsolidated shore was populated with a sparse cover of Utricularia cornuta; and (3) the infrequently flooded, unconsolidated shore (vegetated) included Carex aurea, Eleocharis pauciflora, and Panicum impli-
catum. The wetland types each exhibited a characteristic duration of flooding as determined in this experiment. Emergent wetlands (l) were flooded from 51070 to 100% of the duration of the study, (2) the unconsolidated shore (non-vegetated) experienced 2070 to 51 % duration, and (3) infrequently flooded, unconsolidated shore areas (vegetated) were covered with water 1% to 26% duration of the study. Emergent wetland species (C. mariscoides, S. validus, and J. balticus) each had a distinctly different distribution relative to elevation and flood duration than plants found on the unconsolidated shore (Table 2). Distributions were related to char-
181
acteristic concentrations of phosphorus, calcium, and potassium resulting from anaerobic soil conditions. S. validus grew in areas of low elevation that had a long duration of flooding, relatively high concentrations of nutrients, and anaerobic conditions. C. mariscoides inhabited moderately anaerobic sites, with higher levels of potassium and phosphorus than on unconsolidated shore areas that were seldom flooded. J. balticus was commonly found on both infrequently flooded unconsolidated shores and flooded wetland sites, and it was found at slightly higher sites than S. validus (p < 0.001.). The species of unconsolidated shore areas (nonvegetated) exhibited discrete distributions relative to the soil and flooding variables measured. The duration of flooding in this wetland type was highly variable with 95% confidence intervals (CI) of 2% to 51 %, respectively (Table 2). U. cornuta was the only plant inhabiting the almost barren, frequently flooded unconsolidated shore, and was able to withstand the alternating drought and flood conditions of these areas. C. aurea, E. pauciflora, and P. implicatum were the predominant species on infrequently flooded, unconsolidated shore (vegetated). They were flooded 1% to 26% of the time, but were often subject to hourly influxes of water during the highest summer lake levels. These species were therefore subjected to periodic flooding of short duration, followed by drought due to high rates of insolation and evaporation. Flooding and drought produced an alternating aerobic and anaerobic soil environment. Distribution of Plants
Results indicated that both long-term and shortterm fluctuations in Lake Michigan water levels had an important influence on wetland plants. The two hydrological periods are related, with longterm lake levels operating as a primary variable to influence short-term soil and plant characteristics of the wetland at Waugoshance Point. Short-term or in-season differences in lake levels affected the distribution of plant species through flooding and anaerobic soil conditions. At Waugoshance Point, the flooded soils (Aquaents) of emergent wetland had a high concentration of nutrients (Table 1) as compared to infrequently flooded, unconsolidated shore (non-vegetated) soils. We found that with an increase in duration of flooding and anaerobic soil conditions, there
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LYON et ale
was a corresponding increase in nutrients as compared to dry, infrequently flooded sites. The anaerobic soil conditions apparently affected the type and availability of nutrients for plant uptake as suggested by Ponnamperuma (1972). Wetland plant distribution was related to elevation, duration of flooding, and effects of these variables on soil chemistry. Flooding influenced the distribution of plant species in emergent wetland and unconsolidated shore sites by increasing the availability of normally limited plant nutrients in these Entisol soils. Infrequently flooded, unconsolidated shore areas were characterized by a low number of stems and higher numbers of species. The plant cover was less than 30%, and often less than 10070. These shore areas, consisting of washover fans, beach barriers, and small sand dunes, were infrequently flooded and had low levels of plant available nutrients (Table 1). With decreasing elevation, there was an increase in flooding, soil nutrients, and density of plants. Therefore, long duration of flooding (50070 to 85070) leads to higher density of plants (Tables 1 and 2), and the variety and distribution of plants was dependent on elevation of the wetland and prevailing water levels (DeLaune et al. 1976). The relatively constant presence of wetland and shore areas through time indicated that early seral communities have been maintained by fluctuations of water levels and flooding. Fluctuating water levels are a perturbation similar to fire in prairie, boreal forest, or chaparral ecosystems. Low lake levels are historically followed by high lake levels which flood previously dry areas and kill nonwetland shrub and trees (Great Lakes Basin Commission 1975, Bruce 1984). Wetland plants recolonize these areas and wetland areas are maintained by the periodic disturbance of high water levels (Weller 1978, Harris et al. 1981, Lyon 1981). CONCLUSIONS
Change in Great Lakes levels due to water consumption, diversion, and precipitation can impact coastal resources. One concern is the potential for altering the quantity of wetlands by changes in Lake Michigan water levels. At the highest water level examined (177.06 m), only 13070 of the historic wetlands were present in the study area as compared to the lowest lake level studied (175.83 m). A model of water levels and wetlands indicated a 0.30 m rise in level will result
in an estimated decrease of 32 ha. Conversely, a decrease in water level results in a similar increase in wetlands. The model and analyses of historical aerial photographs indicated the quantity of wetlands was relatively constant at any given water level over the amplitude of water level fluctuations. The quantity and variety of wetlands were related to duration of flooding, elevation, and resulting anaerobic soil conditions. Floodinginduced anaerobic conditions resulted in a significantly higher amount of plant-available phosphorus, calcium, and potassium as compared to adjacent, infrequently flooded sites. At any given location in the study area, the extent and density of emergent wetland was highest when elevation conditions and water levels led to a duration of flooding between 50070 and 85 of the growing season. Duration of flooding outside this range results in low density of plants. Infrequent flooding resulted in low nutrient availability and variable soil moisture conditions. More than 85070 duration of flooding resulted in water too deep for most wetland plants (Figs. 3 and 4). The short-term or growing season variations in local lake levels influenced the distribution of plant species by changing concentrations of plant nutrients through anaerobic soil conditions. Long-term water levels altered the total area of wetlands and unconsolidated shore. The two time frames were related with long-term lake levels operating as a primary variable to influence short-term soil and plant characteristics.
ACKNOWLEDGMENTS
This research was sponsored by NOAA Office of Sea Grant, grant No. 04-MOI-134 (R/CW-7 and -3) to Michigan Sea Grant and grant No. NA81AA-D-0095 R/EM-2 to Ohio Sea Grant, and from appropriations by the Michigan and Ohio Legislatures. Additional support was provided by the OSU Seed Grant Program, three Conservation Fellowships from the National Wildlife Federation (1978-1981), The School of Natural Resources and Biological Station at The University of Michigan, the Department of Civil Engineering at The Ohio State University, and the Center for Environmental and Estuarine Studies at The University of Maryland. The assistance of Dr. Alfred Beeton, Dr. William Benninghoff, and Dr. James Boyle is gratefully acknowledged.
EFFECTS OF LAKE MICHIGAN WATER LEVELS ON WETLANDS REFERENCES Bruce, J. 1984. Great Lakes levels and flows: past and future. J. Great Lakes Res. 10:126-134. Cahill, R. 1981. Geochemistry of recent Lake Michigan sediments. IL Instit. of Nat. Res., IL Geological Survey Div. Circ. 517. Conover, W. 1971. Practical Nonparameteric Statistics. New York: J. Wiley and Sons. Cowardin, L., Carter, V., Golet, R., and LaRoe, E. 1979. Classification of wetlands and deepwater habitats of the U.S. Office of Biological Services. Fish and Wildlife Service, Washington, D.C. DeLaune, R., Patrick, W., and Brannon, J. 1976. Nutrient transformations in Louisiana salt marsh soils. Sea Grant Pub. LSU-T-760-009, Louisiana State Univ., Baton, Rouge, LA. Dorr, J., and Eschman, D. 1970. Geology of Michigan. Ann Arbor: Univ. Michigan Press. Fee, E. 1968. Digital computer programs for the Defant Method of seiche analysis. Rept. No.4, Great Lakes Studies Center, Univ. Wisconsin, Milwaukee, WI. Gosselink, J., and Turner, E. 1978. The role of hydrology in freshwater wetland ecosystems. In Freshwater Wetlands: Ecological Processes and Management Potential, R. Good, D. Whigham, and R. Simpson, eds., pp. 63-78. New York: Academic Press. Great Lakes Basin Commission. 1975. Water levels and flows. Appendix 11. Great Lakes Basin Framework Study. Ann Arbor, MI. Harris, H., Fewless, G., Milligan, M., and Johnson, W. 1981. Recovery processes and habitat quality in a freshwater coastal march following a natural disturbance. In Selected Proc. Midwest Conj. on Wetland Values and Man, pp. 363-379. Freshwater Soc., St. Paul, MN. International Great Lakes Levels Board. 1973. Regulation of Great Lake water levels. Intern. Joint Comm., Windsor, Ont. Jaworski, E., Raphael, C., Mansfield, P., and Williamson, B. 1979. Impact of Great Lakes water levelfluctuations on coastal wetlands. Inst. of Water Res., Michigan State Univ., East Lansing, MI. Kraft, J., Allen, E., Belknap, D., John, C., and Maurmeyer, E. 1979. Processes and morphologic evolution of an estuarine and coastal barrier system. In Barrier Islands, S. Leatherman, ed., pp. 149-183. New York: Academic Press. Lyon, J. 1979. Remote sensing of coastal wetlands and habitat quality of the St. Clair Flats, MI. In Proc.
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13th Intern. Sym. on Remote Sensing of Environ. pp. 1117-1129. Env. Res. Instit. of MI, Ann Arbor, MI. ____ . 1980. Data sources for analyses of Great Lake wetlands. In Proc. Annual Meeting, pp. 512-525. Amer. Soc. of Photog., St. Louis, MO. ____ . 1981. The influence of Lake Michigan water levels on wetland soils and distribution of plants in the Straits of Mackinac, MI. Doc. diss., Univ. Michigan, Ann Arbor, MI. ____ , and Drobney, R. 1984. Lake level effects as measured from aerial photos. J. Surveying Eng. 110: 103-111. ____ , Jaworski, E., Gauthier, R., and Greene, R. 1985. Monitoring of marsh regeneration using aerial photos, Landsat MSS and TM data at the Point Mouillee confined disposal facility, MI. In Proc. 5th Corps of Eng. Symp. on Remote Sensing, Ann Arbor, MI. Mueller-Dombois, D., and Ellenburg, H. 1974. Aims and Methods of Vegetation Ecology. New York: J. Wiley and Sons. National Oceanic and Atmospheric Administration. 1978. Great Lakes water levels, 1860-1975. U.S. Department of Commerce, Riverdale, MO. Netter, J., and Wasserman, W. 1974. Applied Linear Statistical models. Homewood: Irwin. Ponnamperuma, F. 1972. Chemistry of submerged soils. Adv. Agron. 24:29-46. Prince, H., and D'Itri, F. 1985. Coastal Wetlands. In Proc. Wetlands Colloquium. Michigan State Univ., East Lansing, MI (in press). Seelig, W., and Sorensen, R. 1977. Hydraulics of Great lakes inlets. no. 77-8, Coastal Eng. Res. Center, Corps of Eng., Ft. Belvoir, VA. U.S. Department of Agriculture. 1975. Soil survey of Emmet county, Michigan. Soil Conservation Service, Washington, D.C. U.S. Geological Survey. 1977. National handbook of recommended methods for water data acquisition. Office of Water Res., Washington, D.C. Weller, M. 1978. Wetland habitats. In Wetland Functions and Value, P. Greeson, J. Clark, and J. Clark, eds., pp. 210-234. Minneapolis: Amer. Water Res. Assoc. Wetzel, R., and Likens, G. 1979. Limnological Analyses. Philadelphia: Saunders. Whillans, T. 1985. Related long-term trends in fish and vegetation ecology of Long Point Bay and marshes, Lake Erie. Doc. diss., Univ. Toronto, Toronto.
EFFECTS OF LAKE MICHIGAN WATER LEVELS ON WETLAND SOIL CHEMISTRY AND DISTRIBUTION OF PLANTS IN THE STRAITS OF MACKINAC
John G. Lyon Department of Civil Engineering The Ohio State University Columbus, Ohio 43210 Ronald D. Drobney Center for Environmental and Estuarine Studies The University of Maryland Frostburg, Maryland 21532 Charles E. Olson, Jr. School of Natural Resources The University of Michigan Ann Arbor, Michigan 48109 ABSTRA CT. The effects of short-term or summer season water level fluctuations on wetlands were determined from measurements of flooding, relative soil chemistry, and the presence of plants. Analyses demonstrated higher relative concentrations of plant-available soil nutrients and higher density ofplants on flooded emergent wetlands as compared to infrequently flooded, unconsolidated shore sites. Flooding resulted in anaerobic soil conditions and increased concentrations of nutrients for wetland plants. The density of emergent wetland plants was highest where the topographic conditions and water level led to duration offlooding between 50 and 85% of the growing season. The effects of long-term water level fluctuations on wetlands were measured from historical aerial photographs of low, average, and high lake level conditions (1938 to 1980). An increase in water levels of 0.3 m reduced the extent of coastal wetlands by 18%. Historical aerial photos demonstrated and a model predicted that 13% of the total wetlands measured at low lake levels remained in the study area at the highest lake level sampled. This result was verified during the high lake levels of May 1985. ADDITIONAL INDEX WORDS: Coastal zone management, aerial photography, remote sensing, plant communities.
Lyon et al. 1985, Prince and D'Itri 1985, Whillans 1985). The quantity and variety of wetlands are thought to be influenced by both short- and longterm water level fluctuations. Short-term or summer season effects were evaluated in this study by measuring seasonal water levels, duration of flooding, soil characteristics, and the distribution of plants. Effects of long-term or multiple year fluctuations in water level were evaluated with historical wetland and water level data (Lyon and Drobney 1984). Evaluations of each time-frame
INTRODUCTION The potential effects of natural and humaninduced fluctuations on coastal resources are poorly understood. This prompts questions regarding effects of water levels and flooding on coastal resources. One concern is the potential for loss or gain of wetlands. Several studies have demonstrated change in wetlands resulting from water level fluctuations (IGLLB 1973, Jaworski et al. 1979, Lyon 1979, Lyon 1980, Harris et al. 1981,
175
LYON et al.
176
provided information on both short- and longterm causative factors. The data were then used to develop a predictive model of long-term effects of water levels on a coastal wetland. METHODS Waugoshance Point and Sturgeon Bay are located on the south side of the Straits of Mackinac between Lakes Michigan and Huron (Fig. 1). Elevational, hydrologic, and geomorphologic conditions have resulted in a variety of wetland, shore, and beach habitats. Plant, soil, and hydrological measurements were taken within a 33,708 m2 grid composed of 144 cells 15.3 x 15.3 m in length (Fig. 2). At the intersection of grid lines (grid nodes), relative elevation was measured and referenced to a U.S. Lake Survey benchmark. Elevation measurements from all grid nodes were recorded in cm above or below the standard elevation of 254.0 cm. A water level gauge was established at Waugoshance Point to measure on-site fluctuations in water levels from mid-June to mid-August, 1980. The strip-chart records were digitized at hourly intervals to supply water level data for statistical analyses. Local water level and flooding data were collected during the period above. Several times per week the on-site gauge was read and the extent of local flooding was checked at each grid node. The
2 months of data were used to calculate flooding frequency for each node, and flood-frequency relative to elevation. The duration of flooding was calculated for each grid node using data on frequency of flooding relative to elevation and hourly water levels from the local water level gauge. In 1979, preliminary studies of monthly change in soil chemistry and texture were conducted to determine the optimal time and conditions to sample (Lyon 1981). An August date was selected because average monthly lake levels and soil nutrient concentrations were high. Furthermore, the common wetland species had matured and achieved most of their yearly stem production. Concurrent studies of soil chemistry and depth indicated that most plant-available soil nutrients occurred within the upper 20 cm of the soil. Most plant roots were also found within that range of depth, so a sample depth of the first 20 cm was selected. Soil samples were taken from grid intersections or nodes, frozen, and chemically analyzed in September, 1980. All soil chemical determinations were conducted using standard techniques (USGS 1977, Wetzel and Likens 1979, Lyon 1981). Soil variables included: 1) total organic matter content measured by weight loss after oxidation in a muffle furnace; 2) molybdate-phosphorus reaction for spectrophotometric analysis of plant-available or soluble-reactive phosphorus (Wetzel and Likens 1979); and 3) exchangeable or plant-available cat-
Mackinaw City STRAITS
OF MACKINAC
Waugoshance
C'.~~~~p"",,0:-i;nrt-+_~-..
Sturgeon Bay
Cross Village
•
Skm
FIG. 1. The Waugoshance Point study site. The area between arrows is the 6.1 km of shore used for historical analysis. The box shows the location of Figs. 2-4.
EFFECTS OF LAKE MICHIGAN WATER LEVELS ON WETLANDS
177
FIG. 2. Aerial photo of: (A) emergent wetlands, (B) vegetated and (C) nonvegetated unconsolidated shore, (D) washover channel containing emergents, and (E) low dunes. The sampling grid location is shown by the box, and the water level gauge was at (F). The photo was taken at average water conditions (23 April 1954, 176.54 m).
ions calcium, magnesium, and potassium as extracted from soil with a IN ammonium acetate solution (UGSG 1977) and measured by atomic absorption spectrometry using a Perkin-Elmer model 403 (Norwalk, CT). The grid nodes were also sampled during early August, 1980, for oxidation-reduction potential (redox), pH, and temperature. The pH of marsh soils was measured with an Orion pH meter by insertion of the electrode to a depth of approximately 9 cm. Redox and temperature were sampled at the same depth as the pH measurement. Redox potential was measured with the Orion meter using a platinum redox electrode. The meter was calibrated prior to sampling with a standard redox buffer solution of 0.0033 M K3 Fe(CN6 ) and 0.0033 M K4 Fe(CN6) in 0.1000 M KCI (Ponnamperuma 1972, USGS 1977). PH and temperature were used to correct redox measurements for temperature variation and to standardize them at 25°C. At each grid node, the number of species and stem density were measured within a 0.63 m 2 sampling frame. The results were reported as the average of five random replicates at each node. Stem
density counts provided a measure of relative cover for comparing plant characteristics with soil and hydrological parameters (Mueller-Dombois and Ellenburg 1974). Wetland community types were determined from field sampling and statistical evaluation of eight soil chemistry and hydrological variables. The variables included duration of flooding, elevation, redox potential, organic matter, and plant available forms of phosphorus, potassium, calcium, and magnesium. Groups were developed from: 1) Kellman tau-b rank correlations between presence of plant species and the variables; 2) Mann-Whitney U tests of pairwise species combinations and similarity of plant distributions related to soil chemistry and hydrological variables (Conover 1971); and 3) species combinations exhibiting similar distributions of the variables, as determined using Kruskal-Wallis tests of similarity. Pair-wise hypothesis tests of plant species distribution versus the eight variables indicated similar types (Ho:sustained). Dissimilarities between individual variables (Ho:rejected) facilitated the identification of differences between plant communities. Soil, plant, and flooding variables were
LYON et al.
178
analyzed with non-parametric tests because the variance of flooded and non-flooded areas were not equal (Conover 1971). Historical Quantity of Wetland The quantity of wetland relative to lake levels was established through analysis of black and white aerial photographs for years of high (1952, 1973), average (1954, 1977), and low (1938, 1958, 1965) water levels. Wetlands were measured from seven sets of photographs (1:5,702 to 1:15,771 scale enlargements) in a 6.1-km-Iong section of the southern shore of Waugoshance Point (Fig. 1). For each year, boundaries of each of the wetland classes were identified with a stereoscope and traced onto Mylar. A random dot grid was used to measure the area within the wetland boundaries. These results were subsequently corrected for scale to yield the actual area measurements (Lyon 1981). Historic water level data were obtained from the gauge at Mackinaw City, Michigan, 16 km from the study site (NOAA 1978), and used to determine average water level for dates that aerial photographs were taken. Pearson correlations were used to evaluate the relationship between lake levels and area of wetland measured from aerial photographs (Netter and Wasserman 1974). A regression model was developed to predict the total area of wetland at a given Lake Michigan water level (y = -60.86x + 116281.46, x = water level in m, y = hectares or ha of total wetland). RESULTS AND DISCUSSION Long-term Water Levels and Extent of Wetland Wetland area measurements from seven sets of aerial photographs indicated a decrease of 154 ha of wetland from lowest to highest lake levels (Lyon and Drobney 1984). This 154-ha area represents 87010 of the total wetland present (178 ha) when measured at the lowest lake level studied (175.83 m). A model of long-term lake level versus quantity of wetland (F-statistic = 65.2, p < 0.001, R2 = 0.93) was developed to predict changes in wetland size at different water levels. At the lowest summer or growing season water level recorded (175.47 m, March 1964), the model predicted 228 ha of wetland. At the highest Lake Michigan water level recorded (177.18 m, July 1974) the model predicted 45 ha. Field evaluations and large scale aerial photographs from 20 June 1985 (177.02 m)
have verified the approximate quantity of wetland predicted by the model for the highest historical lake levels (Figs. 3 and 4). The wetlands studied at Waugoshance Point and adjacent Sturgeon Bay had a low gradient slope for 5 km with an average depth of 1.5 to 2.0 m. However, the wetlands and nearshore region of the bay have a locally uneven elevation, slope, and a convoluted shoreline due to the presence of numerous beach ridges. An aerial photographic method was employed here because actual measurements of historic wetland were possible despite the variation in elevation. Flooding and Soils The on-site water level gauge indicated a small change in the daily and hourly water level of wetlands during the summer of 1980. The 5-7 cm change had an approximate 2-hour period between peaks. These fluctuations were probably due to seiche or storm surge activity on Lake Michigan. The 2-hour period approximates the first traverse mode of oscillation for Lake Michigan (Fee 1968), and to wave periods recorded at Portage and Ludington, MI (Seelig and Sorensen 1977). Soils of the lacustrine emergent wetlands were composed of a think layer of peat over sandy, gravelly soils. These Entisols or Aquents (USDA 1975) experienced frequent flooding from June through September. The duration of summer flooding was governed by average lake levels and short-term, seasonal fluctuations. Seasonal fluctuations resulted in lake levels that were approximately 30 cm lower in winter than in summer. Because of the lower lake levels, emergent wetland soils were infrequently flooded from October through May, but were normally saturated due to a high water table. As the lake level rose to its mid-summer peak, emergent wetlands were often flooded to depths of 3 to 20 cm. In contrast to the soils of emergent wetland, lacustrine unconsolidated shore had Alpena gravelly loamy soils with no peat layer at the surface. Sediments in these areas were poorly sorted, and the texture of the sand was generally coarse to medium (Lyon 1981). These gravelly soils can experience long periods of drought due to low water retention and rapid percolation to a shallow water table (USDA 1975). They normally became very dry during low water months (October-May), but were frequently flooded or saturated as a result of high lake levels and a high water table during summer.
EFFECTS OF LAKE MICHIGAN WATER LEVELS ON WETLANDS
FIG. 3. (A) Emergent wetlands, (B) nonvegetated and (C) vegetated unconsolidated shore during high water in June 1985. The photo looks to the south.
FIG. 4. Low altitude aerial photo of near record high water levels (20 June 1985, 177.02 m). The photo looks to the west. (Symbols are the same as in Fig. 2b.)
179
LYON et al.
180
The bedrock of Waugoshance Point is composed of marl and dolomite from the Bois Blanc formation of the Devonian Period (Door and Eschman 1970). The high concentrations of exchangeable calcium and magnesium in the soils of the emergent wetland probably originated from the dolomitic bedrock (Table 2). Anaerobic conditions dur-
Areas that experienced a long relative duration of flooding had both a higher abundance of plantavailable phosphorus, potassium, calcium, and magnesium, and higher density of plants (Tables 1 and 2). Availability of these nutrients was correlated (p < 0.01) with anaerobic conditions (redox < - 300 mV) caused by flooding.
TABLE 1. Plant and soil characteristics measured from a north to south transect across Waugoshance Point. Soil chemistry is reported as p.g/gm ofplant available forms (see Methods). Average Wetland Community Emergent Wetland (low elevation)
Most Common Plant
Number of Species
Number Stems/Sample
Redox Potential in mV
Soil Chemistry in ",g/gm P
Ca
Mg
K
S. validus
3
300
326
4,280
312
106
-150
Emergent Wetland (higher elevation)
C. mariscoides
3
160
260
4,044
242
89
-120
Unconsolidated Shore non-vegetated)
P. implicatum
9
32
35
3,062
74
9
-20
Unconsolidated Shore (vegetated)
C. aurea
11
38
38
1,212
80
13
>400
Beach Barrier
no plants
none
none
0
2,194
43
5
>400
TABLE 2. Site characteristics of plant species including mean values and standard deviation. Soil Chemistry is reported in p.g/g and organic matter in proportion. Frequency of Presence on Grid Sites
Elevation incm Relative to Standard
Duration of Flooding (Proportion)
Redox mV
X-
Potassium
u
0.9~
0.09
-135.5 59.2 326.4 257.3 54.1 41.2 3,979.6 1,414.3 212.1
0.27
251.3 2.2 0.75
0.37
-110.7 54.9 261.9 176.3 55.5 39.9 3,951.3
C. mariscoides 52
0.36
252.0 1.9 0.63
0.43
-106.4 67.6 260.3
U. cornuta
12
0.08
252.6 1.0 0.27
0.38
-55.4 80.3 119.2
X-
u
n
Proportion
S. validus
19
0.13
250.7 2.5
J. balticus
39
u
u
X-
Magnesium
Calcium
X-
Species
X-
Phosphorus
u
X-
u
X-
u
Organic Matter
X-
u
140.3 0.19 0.18
948.8 203.7 128.3 0.14 0.16
182.8 55.2 42.2 3,799.8 1,003.5 188.6 116.9 0.12 0.11 32.4 23.1
8.1 3,275.2
180.7
89.5
14.2 0.04 0.01
P. implicatum
20
0.14
253.3 0.5 0.04 0.08
-21.0 44.1
175.8 132.7 30.3 28.2 3,270.2
578.1
121.5
83.2 0.06 0.05
E. pauciflora
54
0.38
253.1
1.0 0.10 0.23
-26.3 50.1
104.0
58.7 18.0
8.7 3,114.1
406.7
85.7
21.1 0.04 0.01
C. aurea
51
0.35
253.1 0.6 0.17
-19.9 54.8 104.6
53.5 19.4
9.5 3,168.3
356.0
87.0
20.9 0.03 O.oI
0.31
EFFECTS OF LAKE MICHIGAN WATER LEVELS ON WETLANDS
ing flooding apparently resulted in solution of minerals such as dolomite, marl, hydroxyapatite, and other calcium and magnesium minerals (Cahill 1981) making them available in the plant root zone. The concentrations of phosphorus and potassium on non-flooded, unconsolidated shore (nonvegetated) were lower than the requirements of most plants (Gosselink and Turner 1978), and probably contributed to the low number of plants and low stem densities found in this wetland type. Low nutrient levels were also indicated by the presence of stunted cedar trees on neighboring sand dunes (Fig. 2) whose small height and diameter were caused by low concentrations of calcium (Cahill 1981, Lyon 1981). Wetland Categories The plants were grouped into three wetland types (Cowardin et al. 1979, Kraft et al. 1979) that included: (1) lacustrine emergent wetland found on washover fans and channels; (2) lacustrine unconsolidated shore (non-vegetated) or periodicallyflooded fans composed of washover deposits with little plant cover; and (3) lacustrine unconsolidated shore (vegetated) or infrequently flooded fans composed of higher-elevation washover deposits (Figs. 2, 3, Table 1). The predominant plant species in each wetland type included: (1) emergent wetland species,Cladium mariscoides, Juncus balticus, and Scirpus validus which were distributed in a similar manner with respect to soil chemistry and duration of flooding; (2) the regularly flooded, unconsolidated shore was populated with a sparse cover of Utricularia cornuta; and (3) the infrequently flooded, unconsolidated shore (vegetated) included Carex aurea, Eleocharis pauciflora, and Panicum impli-
catum. The wetland types each exhibited a characteristic duration of flooding as determined in this experiment. Emergent wetlands (l) were flooded from 51070 to 100% of the duration of the study, (2) the unconsolidated shore (non-vegetated) experienced 2070 to 51 % duration, and (3) infrequently flooded, unconsolidated shore areas (vegetated) were covered with water 1% to 26% duration of the study. Emergent wetland species (C. mariscoides, S. validus, and J. balticus) each had a distinctly different distribution relative to elevation and flood duration than plants found on the unconsolidated shore (Table 2). Distributions were related to char-
181
acteristic concentrations of phosphorus, calcium, and potassium resulting from anaerobic soil conditions. S. validus grew in areas of low elevation that had a long duration of flooding, relatively high concentrations of nutrients, and anaerobic conditions. C. mariscoides inhabited moderately anaerobic sites, with higher levels of potassium and phosphorus than on unconsolidated shore areas that were seldom flooded. J. balticus was commonly found on both infrequently flooded unconsolidated shores and flooded wetland sites, and it was found at slightly higher sites than S. validus (p < 0.001.). The species of unconsolidated shore areas (nonvegetated) exhibited discrete distributions relative to the soil and flooding variables measured. The duration of flooding in this wetland type was highly variable with 95% confidence intervals (CI) of 2% to 51 %, respectively (Table 2). U. cornuta was the only plant inhabiting the almost barren, frequently flooded unconsolidated shore, and was able to withstand the alternating drought and flood conditions of these areas. C. aurea, E. pauciflora, and P. implicatum were the predominant species on infrequently flooded, unconsolidated shore (vegetated). They were flooded 1% to 26% of the time, but were often subject to hourly influxes of water during the highest summer lake levels. These species were therefore subjected to periodic flooding of short duration, followed by drought due to high rates of insolation and evaporation. Flooding and drought produced an alternating aerobic and anaerobic soil environment. Distribution of Plants
Results indicated that both long-term and shortterm fluctuations in Lake Michigan water levels had an important influence on wetland plants. The two hydrological periods are related, with longterm lake levels operating as a primary variable to influence short-term soil and plant characteristics of the wetland at Waugoshance Point. Short-term or in-season differences in lake levels affected the distribution of plant species through flooding and anaerobic soil conditions. At Waugoshance Point, the flooded soils (Aquaents) of emergent wetland had a high concentration of nutrients (Table 1) as compared to infrequently flooded, unconsolidated shore (non-vegetated) soils. We found that with an increase in duration of flooding and anaerobic soil conditions, there
182
LYON et ale
was a corresponding increase in nutrients as compared to dry, infrequently flooded sites. The anaerobic soil conditions apparently affected the type and availability of nutrients for plant uptake as suggested by Ponnamperuma (1972). Wetland plant distribution was related to elevation, duration of flooding, and effects of these variables on soil chemistry. Flooding influenced the distribution of plant species in emergent wetland and unconsolidated shore sites by increasing the availability of normally limited plant nutrients in these Entisol soils. Infrequently flooded, unconsolidated shore areas were characterized by a low number of stems and higher numbers of species. The plant cover was less than 30%, and often less than 10070. These shore areas, consisting of washover fans, beach barriers, and small sand dunes, were infrequently flooded and had low levels of plant available nutrients (Table 1). With decreasing elevation, there was an increase in flooding, soil nutrients, and density of plants. Therefore, long duration of flooding (50070 to 85070) leads to higher density of plants (Tables 1 and 2), and the variety and distribution of plants was dependent on elevation of the wetland and prevailing water levels (DeLaune et al. 1976). The relatively constant presence of wetland and shore areas through time indicated that early seral communities have been maintained by fluctuations of water levels and flooding. Fluctuating water levels are a perturbation similar to fire in prairie, boreal forest, or chaparral ecosystems. Low lake levels are historically followed by high lake levels which flood previously dry areas and kill nonwetland shrub and trees (Great Lakes Basin Commission 1975, Bruce 1984). Wetland plants recolonize these areas and wetland areas are maintained by the periodic disturbance of high water levels (Weller 1978, Harris et al. 1981, Lyon 1981). CONCLUSIONS
Change in Great Lakes levels due to water consumption, diversion, and precipitation can impact coastal resources. One concern is the potential for altering the quantity of wetlands by changes in Lake Michigan water levels. At the highest water level examined (177.06 m), only 13070 of the historic wetlands were present in the study area as compared to the lowest lake level studied (175.83 m). A model of water levels and wetlands indicated a 0.30 m rise in level will result
in an estimated decrease of 32 ha. Conversely, a decrease in water level results in a similar increase in wetlands. The model and analyses of historical aerial photographs indicated the quantity of wetlands was relatively constant at any given water level over the amplitude of water level fluctuations. The quantity and variety of wetlands were related to duration of flooding, elevation, and resulting anaerobic soil conditions. Floodinginduced anaerobic conditions resulted in a significantly higher amount of plant-available phosphorus, calcium, and potassium as compared to adjacent, infrequently flooded sites. At any given location in the study area, the extent and density of emergent wetland was highest when elevation conditions and water levels led to a duration of flooding between 50070 and 85 of the growing season. Duration of flooding outside this range results in low density of plants. Infrequent flooding resulted in low nutrient availability and variable soil moisture conditions. More than 85070 duration of flooding resulted in water too deep for most wetland plants (Figs. 3 and 4). The short-term or growing season variations in local lake levels influenced the distribution of plant species by changing concentrations of plant nutrients through anaerobic soil conditions. Long-term water levels altered the total area of wetlands and unconsolidated shore. The two time frames were related with long-term lake levels operating as a primary variable to influence short-term soil and plant characteristics.
ACKNOWLEDGMENTS
This research was sponsored by NOAA Office of Sea Grant, grant No. 04-MOI-134 (R/CW-7 and -3) to Michigan Sea Grant and grant No. NA81AA-D-0095 R/EM-2 to Ohio Sea Grant, and from appropriations by the Michigan and Ohio Legislatures. Additional support was provided by the OSU Seed Grant Program, three Conservation Fellowships from the National Wildlife Federation (1978-1981), The School of Natural Resources and Biological Station at The University of Michigan, the Department of Civil Engineering at The Ohio State University, and the Center for Environmental and Estuarine Studies at The University of Maryland. The assistance of Dr. Alfred Beeton, Dr. William Benninghoff, and Dr. James Boyle is gratefully acknowledged.
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13th Intern. Sym. on Remote Sensing of Environ. pp. 1117-1129. Env. Res. Instit. of MI, Ann Arbor, MI. ____ . 1980. Data sources for analyses of Great Lake wetlands. In Proc. Annual Meeting, pp. 512-525. Amer. Soc. of Photog., St. Louis, MO. ____ . 1981. The influence of Lake Michigan water levels on wetland soils and distribution of plants in the Straits of Mackinac, MI. Doc. diss., Univ. Michigan, Ann Arbor, MI. ____ , and Drobney, R. 1984. Lake level effects as measured from aerial photos. J. Surveying Eng. 110: 103-111. ____ , Jaworski, E., Gauthier, R., and Greene, R. 1985. Monitoring of marsh regeneration using aerial photos, Landsat MSS and TM data at the Point Mouillee confined disposal facility, MI. In Proc. 5th Corps of Eng. Symp. on Remote Sensing, Ann Arbor, MI. Mueller-Dombois, D., and Ellenburg, H. 1974. Aims and Methods of Vegetation Ecology. New York: J. Wiley and Sons. National Oceanic and Atmospheric Administration. 1978. Great Lakes water levels, 1860-1975. U.S. Department of Commerce, Riverdale, MO. Netter, J., and Wasserman, W. 1974. Applied Linear Statistical models. Homewood: Irwin. Ponnamperuma, F. 1972. Chemistry of submerged soils. Adv. Agron. 24:29-46. Prince, H., and D'Itri, F. 1985. Coastal Wetlands. In Proc. Wetlands Colloquium. Michigan State Univ., East Lansing, MI (in press). Seelig, W., and Sorensen, R. 1977. Hydraulics of Great lakes inlets. no. 77-8, Coastal Eng. Res. Center, Corps of Eng., Ft. Belvoir, VA. U.S. Department of Agriculture. 1975. Soil survey of Emmet county, Michigan. Soil Conservation Service, Washington, D.C. U.S. Geological Survey. 1977. National handbook of recommended methods for water data acquisition. Office of Water Res., Washington, D.C. Weller, M. 1978. Wetland habitats. In Wetland Functions and Value, P. Greeson, J. Clark, and J. Clark, eds., pp. 210-234. Minneapolis: Amer. Water Res. Assoc. Wetzel, R., and Likens, G. 1979. Limnological Analyses. Philadelphia: Saunders. Whillans, T. 1985. Related long-term trends in fish and vegetation ecology of Long Point Bay and marshes, Lake Erie. Doc. diss., Univ. Toronto, Toronto.