Michael J. McCormick

Phytoplankton Productivity in Saginaw Bay, Lake Huron: Effects of Zebra Mussel (Dreissena polymorpha) Colonization

Phytoplankton photosynthesis-irradiance parameters, chlorophyll concentrations, underwater extinction coefficients (kPAR), and surface irradiance were determined at 8–10 sites on 27 occasions in Saginaw Bay from spring 1990 through fall 1993 corresponding to a period before and after the establishment of large zebra mussel populations (began in summer 1991). Similar measurements, with the exception of the photosynthetic parameter, α, had also been made in 1974/75 at eight sites on nine occasions. In inner Saginaw Bay where zebra mussels were primarily found, chlorophyll and kPAR values decreased, while the photosynthetic parameters, Pmax and α, increased after zebra mussel colonization. At sites in the outer bay where no zebra mussels were found, chlorophyll and kPAR values did not change after zebra mussel colonization, whereas photosynthetic parameters increased. Decreases in chlorophyll and kPAR in the inner bay were related to the zebra mussel, but increases in photosynthetic parameters in both the inner and outer bay were not. Areal-integrated and volumetric phytoplankton productivity decreased by 38% and 37%, respectively, in inner Saginaw Bay after the establishment of zebra mussels; phytoplankton productivity at outer bay control sites was similar during the same period. Decreased phytoplankton productivity in the inner bay was attributable to the large decrease in chlorophyll as increases in underwater irradiance (increased kPAR) and photo synthetic parameters could not compensate for the chlorophyll effect. Increase in underwater irradiance produced a significant increase in light to the benthic region and contributed to increased benthic primary productivity; ratio of photic zone to station depth increased in inner Saginaw Bay, from 0.6–0.8 before the zebra mussel colonization (1974–1990) to 1.1–1.3 after colonization (1992–1993). Overall, primary productivity in the inner bay did not exhibit a notable change after zebra mussel colonization as decreases in phytoplankton productivity were accompanied by increases in benthic primary productivity. Thus, zebra mussels altered inner Saginaw Bay from a pelagic-dominated system to a benthic/pelagic system which will have long-term effects on food web structure and productivity at higher trophic levels.

Potential Changes in Thermal Structure and Cycle of Lake Michigan Due to Global Warming

Abstract I used a one-dimensional numerical model to estimate the present and possible future temperature structures in Lake Michigan. The estimates were based on model output from simulations of the 1981–1984 offshore temperature field. Once the water temperature climatology was estimated, I examined three scenarios based on general circulation models in which atmospheric CO2 was doubled. The models were those of the Goddard Institute for Space Studies (GISS), the Geophysical Fluid Dynamics Laboratory (GFDL), and Oregon State University (OSU). In general, simulations based on these three scenarios suggested that winter and summer heat contents of the lake would be higher than at present; the summer increase would be less than that in winter. The higher winter heat content would cause an earlier onset of full thermal stratification, and the season of stratification would increase by up to two months. The earlier onset of stratification, coupled with little change in the wind stress pattern, would yield st...

Short-term Water Mass Movements in Lake Michigan: Implications for Larval Fish Transport

ABSTRACT Water mass movement within the Great Lakes may rapidly transport fish larvae from favorable nursery areas to less favorable habitats, thereby affecting recruitment success. During 2001 and 2002, we released satellite-tracked drifting buoys in eastern Lake Michigan to follow discrete water masses, and used ichthyoplankton nets to repeatedly sample larval fish within these water masses. Observed nearshore water currents were highly variable in both direction and velocity. Current velocities far exceeded potential larval fish swimming speeds, suggesting that currents can potentially rapidly advect fish larvae throughout the lake. Evidence suggests that while paired drifters released during 2002 were able to track relatively small alewife (Alosa pseudoharengus) and yellow perch (Perca flavescens) larvae within an alongshore coastal current, paired drifters released during 2001 failed to track larger alewife larvae when flow was more offshore and highly variable. These results are consistent with the decorrelation scales associated with alongshore and offshore transport.

Relationship between Surface Water Temperature and Steelhead Distributions in Lake Michigan

Abstract Salmonines support valuable recreational fisheries and are the predominant predators in the open waters of the Great Lakes, yet the spatial distributions of salmonines in these systems have not been fully documented. We analyzed the horizontal distributions of steelhead Oncorhynchus mykiss in Lake Michigan from 1992 to 1997 and related these distributions to mean surface temperature and temperature variation. We used angler catch rate data from Lake Michigan natural resources agencies to index the spatial and temporal distributions of steelhead and obtained surface water temperature data from advanced very-high-resolution radiometer satellite imagery through the National Oceanic and Atmospheric Administrations CoastWatch Program. During most months, steelhead catch rates were negatively related to surface temperature and were highest in areas of high temperature variation (i.e., vertical thermal fronts and upwelling zones) where thermal conditions and prey densities may have been optimal for gro...

Classification of Buoyant River Plumes from Large Aspect Ratio Channels

AbstractThe dynamics of the Grand River plume, a major tributary of Lake Michigan, was studied in the vicinity of the Grand Haven coast on the east side of the lake. The river spread laterally from the mouth and formed a thin surface buoyant plume with various shapes that have not been previously reported. To understand the influence of different driving forces, primarily wind, buoyancy, and ambient currents, extensive field experiments were carried out over four periods in August and June 2006, and June and July 2007. They included aerial photography over the plume, acoustic Doppler current profiler (ADCP) deployments, meteorological buoys, drifters, SF6 and Rhodamine WT tracer releases, three-dimensional (3D) CTD profiling over the plume, and CTD casts at the river mouth. The results showed more flow classes than included in previous studies. A modified classification scheme based on the relative magnitude of the plume-crossflow length scale and a Richardson number were devised that includes longshore c...

MONITORING MIDLAKE WATER TEMPERATURE IN SOUTHERN LAKE MICHIGAN FOR CLIMATE CHANGE STUDIES

Recent studies of potential climatic change on Great Lakes fisheries (e.g. Meisner , 1987; Magnuson , 1990; Regieret al., 1990) and our general ignorance of the natural variability of the basic physical properties of the Great Lakes (McCormick, 1990) have demonstrated the need for a long-term observation program which is representative of the lake-wide environment. In April 1990 a site was established in Lake Michigan to continuously monitor the offshore thermal structure and vertical velocity profile. The site is located near the center of the lakes southern basin in 160 m of water. Temperature is measured at 16 depths (winter) to 28 depths (summer), and the horizontal velocity components are measured at 5 levels which allows us to characterize the offshore environment with high temporal resolution. The goals of this effort are to provide basic physical measurements to better describe the flow of energy through the lake ecosystem and to provide a basis against which future change can be better gauged.

Phytoplankton photosynthesis and biomass in Lake Superior: Effects of nutrient enrichment

Several investigators have measured the rate of photosynthesis in Lake Superior during the past two decades (PUTNAM & OLSON 1966, PARKOS et al. 1969, VERDUIN 1975, NALEwAjKO et al. 1981, FAHNENSTIEL & GLIME 1983, NALEwAJKo & VOLTOLINA 1986). Neither experimental approaches nor methods for data reporting have been consistent among investigators (FAHNENSTIEL et al. 1989) and thus, not all rates are comparable. Furthermore, the factor(s) controlling the rate of photosynthesis in Lake Superior may still be open to question. The role of nutrients and in particular, phosphorus, in controlling photosynthesis and phytoplankton yield in Lake Superior has been documented. SCHELSKE et al. (1972) performed a series of large enclosure experiments that were designed to determine the limiting element in the Great Lakes. In these experiments, large volumes of water (> 1000 I) were spiked with various combinations of plant nutrients and the response of the phytoplankton community in terms of chlorophyll, phytoplankton abundance, and photosynthesis was monitored. Results from these experiments suggested that phosphorus was the limiting element in the Great Lakes. These and other nutrient enrichment studies on the Great Lakes (SCHELSKE 1979) provided the scientific cornerstone for eutrophication control. More recent information, however, has questioned the role of phosphorus in controlling primary production and algal growth in Lake Superior. NALEwAjKO et al. (1981) suggested that phytoplankton growth in Lake Superior was not limited by phosphorus but by light, and even suggested that the entire concept of phosphorus control to maintain phytoplankton biomass at present levels may need to be reevaluated. Light control of primary production was suggested to occur even in the epilimnion during thermal stratification. In a subsequent paper, NALEwAjKO & VOLTOLINA (1986) suggested that physical factors were more important than phosphorus in controlling primary production during isothermal mixing periods.

A comparison of the formulation for eddy diffusion in two one-dimensional stratification models

Abstract Two models for thermal stratification based on turbulent diffusion concepts are analysed and compared. The models by Henderson-Sellers; and by McCormick and Scavia, are shown to be equivalent at large values of the Richardson number, R i . At small R i , the simpler model reverts to specification of the turbulent diffusion as a constant value. This simplification is also demonstrated to be a realistic approximation only at low wind speeds and for deep lakes. By comparison of these model types, a (previously empirically defined by McCormick and Scavia) parameter β is related conceptually to the lake depth, H .

Comparison of Phytoplankton Growth Constructs in the Context of Vertically Segmented Plankton Models

A previously developed and calibrated ecological model, extended to a finer vertical grid representation, was capable of simulating the vertical structure of Lake Ontarios phytoplankton, available nitrogen and silicon, but not available phosphorus. Measured phosphorus depletion extended to 40m whereas nitrogen and silicon depletion extended to only 5–10m. Analysis of models using different algal growth constructs demonstrated the ability of algal models based upon internal nutrient pools to simulate the observed divergence between phosphorus and other nutrient profiles.