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Time Series Measurements in Lake Erie
Primary Investigator:
Nathan Hawley - NOAA/GLERL
Co-Investigators:
Brain Eadie (Emeritus) - NOAA/GLERL
Ram Yerubandi - National Water Research Institute (NWRI)*
Executive Summary of Rationale
Time series measurements of waves, currents, water temperature, dissolved oxygen, and water turbidity have been made in conjunction with scientists at the National Water Research Institute at 11 stations located in the three basins of Lake Erie between May and October (+ mooring coordinates). The observations will be used to assess the extent of the hypoxic zone in the lake, to determine the exchange of water and suspended material between the basins, and to assess the frequency and magnitude of sediment-water exchange in the lake. The observations will also be used to refine the present lake circulation model and to develop a coupled physical-biological model of the lower food web.
Proposed Work
Current/Ongoing
Due to personnel and financial constraints, none of the fieldwork or instrument evaluations originally planned for 2008 were conducted. The 8 mooring deployed in the summer of 2007 (Fig.1 ) were all successfully retrieved in October 2007. All data from these deployments was entered into the IFYLE time series data base.
Fig. 1 Location of moorings deployed in 2007
Data Analysis
Two manuscripts submitted last year (Hawley and Eadie 2007, and Rao et al. 2008) were published. The results from these investigations were described in the accomplishments for 2007. Preliminary analysis of temperature data from 2005 and 2007 shows the presence of a dip in the thermocline in the central basin (Fig. 2). This is contrary to observations in other lakes, which show that the thermocline bulges upwards away from shore. Analysis of this data will continue in 2009.
Fig. 2. Water temperatures along a transect from west to east in the central basin of Lake Erie in mid-August, 2005. Vertical lines show the locations of the vertical profiles from which the temperature field was interpolated.
2006 Plans
Analysis of the data collected during the winter of 2004-2005 will continue:
The first data set is the time series observations of surface waves, water
temperature, transparency, and current speed currently being collected
at two sets of moorings over the 04-05 winter, one in the central basin
and the other in the eastern basin of the lake. These moorings were deployed
in September 2004 and retrieved in late April of 2005, so the time series
measurements include the period during which the thermocline breaks down,
the isothermal period, and possibly the onset of the stratified period.
The data will be examined (in conjunction with GLERL's sediment trap data)
in order to determine the frequency and magnitude of sediment resuspension
events, and to determine whether or not the backscatter signal from the
adcps can be used as a reliable indicator of suspended sediment concentration.
The second data set is the current, temperature, and transparency data collected by the national Water Research Institute scientists at 7 stations from April-October of 2004. This data is being examined to determine the frequency and magnitude of resuspension events, the role of advection of suspended material, whether or not the backscatter signal from the adcps can be used as an indicator of suspended sediment concentration during the summer, and the time that the transmissometers can be left deployed before they become fouled. The last two of these objectives are vital to planning any further deployments during the stratified period in the lake.
Analysis of the data collected during the summer of 2005 will begin. The time series measurements made in 2004 and 2005 will be prepared for entry into the IFYLE data base.
2005 Accomplishments
Beginning in May, a series of moorings were deployed in Lake Erie to make time series measurements of waves, currents, suspended sediment concentration, water temperature, and dissolved oxygen. There were 6 adcp moorings, 1 current meter mooring, 3 strings of thermistors, and 5 bottom-resting tripods. The 5 tripod moorings were serviced monthly to clean the sensors and to download the data. All of the moorings were retrieved in late October.
Preliminary Lake Erie Moored Instrument Data Sets are now posted
+ view
data sets (login required)
2004 accomplishments
In conjunction with Brian Eadie (who deployed sediment traps at the sites), 5 moorings were deployed at two sites: one in the eastern basin, and the other in the central basin. The moorings will be left out over the winter and be retrieved in late April. Instrumentation at each site includes measurements of water transparency and turbidity at three elevations (1, 5, and 10 m) in the central basin, and 4 elevations in the eastern basin (1, 5, 10, and 30 m). A pressure sensor is also deployed at each site to measure wave activity. A 300 khz ADCP and a separate current meter (located near the bottom) are also deployed at each site to make measurements of the current velocities.
A LISST in situ particle size analyzer was borrowed from Ohio State University
and used to make measurements of the particle size distribution at several
locations in the western basin during a cruise in late June. The results
show that the particle size distribution is fairly uniform throughout
the western basin (Fig. 1 and Fig. 2), and that the mean particle size
is between 0.03 and 0.05 mm. A profile made in southern Lake Michigan
shows that the particles there are considerably larger (0.1-0.2 mm).
Fig. 1. Observations made at a station in the center of the western basin of Lake Erie. The lighter lines are measurements made with a CTD probe. The average diameter is in microns, the volume concentration is in microliters/liter.
Fig. 2. Time series measurements made at station 357
between June 18 (day 169) and June 23 (day 174). Units are the same as
in Figure 1. The lighter line is the standard deviation of the particle
diameter.
Scientific Rationale
The major theme of GLERL’s Lake Erie program
is the effect of hypoxic conditions in the lake on food web dynamics. In particular,
the effects of hypoxia in the central basin on fisheries production and exotic species
have been highlighted as one of the primary focuses of the program. Previous
determinations of the extent of hypoxic conditions have relied on point
measurements made several times a year at a limited number of stations.
Although valuable, the observations may be severely aliased and the resulting
extrapolations of the extent of the hypoxic are qualitative at best. Time
series measurements of dissolved oxygen and water temperature are needed
to better characterize the development and the extent of the hypoxic region
during a single year, and to assess its inter-annual variability. The
research proposed here will address this need by deploying (in conjunction
with scientists at CCIW) 11 stations at which time series measurements
of dissolved oxygen, water temperature, waves, currents, and water turbidity
will be made between May and September. Two stations will also be occupied
during the winter of 2004-2005. The oxygen, circulation, and temperature
data collected by this program will be used to assess the extent and inter-annual
variability of the hypoxic zone, and be used to develop numerical models
of the dynamics of the hypoxic region. The observations in the inter-basin
channels will be combined with the flow measurements made by our collaborators
at the National Water Research Institute to determine the transport of
suspended material between the western and central basins. The measurements
will also be used to determine the conditions necessary for sediment resuspension
in the lake. The current and wave measurements made over the winter will
aid in interpreting the trap data and in determining under what conditions
bottom material is resuspended. The backscatter data from the ADCP and
the transmissometer data will also be compared to the trap data to determine
what type of particles (large or small) are being collected by the traps.
In addition, if significant ice cover forms over the winter, the pressure
data will be used to determine the effect of ice cover on surface waves.
the particle size analyzer will be used to determine changes in particle
size during resuspension events.
Products
Publications
Hawley, N., and Eadie, B.J. 2007. Observations of sediment transport in Lake Erie during the winter of 2004-2005, Journal of Great Lakes Research, 33: 816-827.
Rao, Y.R., Hawley, N., Charlton, M.N., and Schertzer, W.M. 2008. Physical Processes and hypoxia in the central basin of Lake Erie, Limnology and Oceanography,53: 2007-2020.
Presentations
Hawley, N., 2008, Sediment transport observations in Lake Erie, presented at the 5th meeting of the Lake Erie Millenium Network conference, Windsor, ON.
Hawley, N., 2008,Sediment transport in Lake Erie, presented at the 2008 Ocean Sciences conference, Orlando, FL.
Hawley, N. and Eadie, B.J., 2006, Observations of sediment transport in Lake Erie during the winter of 2004-2005. Presented at the 49 Conference on Great Lakes Research, Windsor, ON.
*Link leads off GLERL's website