Investigation of Phytoplankton Community Composition in Lake Erie

David Page 1., Michael Twiss 2.

Department of Biology

1. Class of 2006, Rochester Institute of Technology, participant in NSF-REU program in Environmental Science and Engineering

2. Project Mentor, Assistant Professor, Department of Biology, Clarkson University

Introduction

            Phytoplanktonic organisms are important to the structure and function of lake ecosystems.   In Lake Erie, phytoplankton abundance has diminished due to nutrient controls efforts in the 1960s and 70s and the arrival of the zebra mussel (Dreissena polymorpha) in the late 1980s. Phytoplankton composition, however, has varied over the decades.   Measurements of phytoplankton biomass and composition can be made from the fluorescence properties of chlorophyll-a (Chl-a), a photosynthetic pigment present in all species of phytoplankton, including eukaryotic and prokaryotic organisms.   One instrument that operates based on Chl-a fluorescence is the FluoroProbe (bbe-Moldaenke).   We used the FluoroProbe and a Geographic Information System (GIS) to conduct fine scale spatial mapping of phytoplankton community composition in Lake Erie during June 8-12, 2005.   Additionally, we examined the influence of UV-absorbing chromophoric dissolved organic mater ( CDOM) on phytoplankton biomass with the aid of the Field Fluorometer (AU-10CE Turner Designs).         

Materials and Methods

            Water was collected onboard the U.S. EPA R/V Lake Guardian from a depth of approximately 1.5 m, while in transect, through a submersed Teflon-lined polyethylene tube attached to a weight towed at depth.   Water was pumped into the chemistry lab onboard the ship using a pneumatically driven Teflon double diaphragm pump (Husky Model 307), where it was collected in a continuous flow through unit (the ferry box).   The FluoroProbe was submersed in water contained in the ferry box.   Water from the ferry box was provided to the Fast Repetition Rate Fluorometer (FRRF, Chelsea Instruments) and the AU-10 at a continuous flow rate through hoses connecting the ferry box to the instruments.   The internal clocks of the FluoroProbe, FRRF, and AU-10 were synchronized with the time stamped differential GPS ship log, so that all data could be referenced to specific locations along transects.   On 30 second intervals the ship log recorded time (GMT), date (ddmmyy), coordinates (latitude/longitude), speed over ground (SOG) (km/h, knots), depth under hull (m), and the water temperature (°C).   The flow rate through the ferry box (volume = 9.5 L) was calibrated to 4.65 L/min to obtain a turnover of lakewater in the ferry box within 0.5 km of linear distance traveled over the lake surface at a speed of 8 knots.   At the end of each transect, data was downloaded from the instruments and the ship log to our field computer (Panasonic, CF-29) for later processing.   Processed data was then entered into ArcGIS TM 8.       

Results

Total Chl-a concentrations were lowest in the south east transects with values ranging from 0.09-0.53 µg/L.   In the north east transects concentrations were higher (0.54-0.95 µg/L).   In the central transects most locations sampled ranged from 0.09-0.53 µg/L, but some locations ranged from 0.96-1.48 µg/L.   In the south central transects Chl-a ranged from 0.54-2.63 µg/L.   Total Chl-a concentrations were highly variable in the west transects ranging from 0.09-4.74 µg/L (Fig. 1.).  

Heterokontophyta and Dinophyta was the most abundant algal division (Fig. 2.).   Concentrations ranged from 0.00-0.29 µg/L (Chl-a equiv.) and 0.30-0.61 µg/L (Chl-a equiv.) in the east transects.   In the central and south central transects locations sampled ranged in concentration from 0.00-0.29 µg/L, 0.30-0.61 µg/L, 0.62-0.98 µg/L, and, in some locations, from 0.99-2.14 µg/L.   Concentrations in the west transects were similarly variable, but in some locations values were as high as 2.15-3.92 µg/L.  

Chlorophyta was the next most abundant division.   Concentrations ranged from 0.27-0.57 µg/L and 0.14-0.39 µg/L in the north east transects and from 0.00-0.26 µg/L in the south east transects.   Locations sampled in the central transects were highly variable in Chlorophyta concentration (0.00-0.57 µg/L).   Most locations sampled in the south central transects ranged from 0.14-0.57 µg/L, but for one 20 km stretch, east of Vermillion, OH, values ranged from 0.58-0.82 µg/L.   Concentrations in the west ranged from 0.00-0.82 µg/L.                    

Cyanobacteria concentrations were generally very low (0.00-0.08 µg/L) There was one 6 km stretch in the west transects where values ranged from 0.09-0.20 µg/L, and three 1 km stretches in the central transects and one 1 km stretch in the east transects, near the inlet to the Niagara River, where values ranged from 0.41-0.68 µg/L.

Cryptophyta concentrations in most sampled locations in the central and east transects ranged from 0.00-0.07 µg/L, and a few locations ranged from 0.08-0.16 µg/L.   In the west transects most locations sampled ranged in value from 0.08-0.16 µg/L, but some locations ranged from 0.34-0.55 µg/L.

CDOM ranged from 0.21-0.90 mg/L Suwannee River Fulvic Acid (SRFA) equivalents in the east transects, 0.21-1.19 mg/L in the central transects, and 0.91-1.63 mg/L in the south central transects.   In the west transects, most locations sampled ranged from 0.72-1.63 mg/L, but for one 6 km stretch, values ranged from 0.52-0.71 mg/L (Fig. 3).   We observed a significant positive correlation (r = 0.41, p < 0.0001, n = 5,727) between CDOM and total Chl-a (Fig. 4.).

Underway Sampling (1 m depth); Lake Erie June 8-12, 2005

Figure 1.   Total chlorophyll-a concentration in Lake Erie June 8-12, 2005.   Water was sampled from a depth of 1.5 m while underway onboard the R/V Lake Guardian.   Data was entered into ArcGIS TM 8.   

Lake Erie Phytoplankton Community Composition and Abundance and CDOM

Figure 2.   Phytoplankton community composition and chromophoric dissolved organic mater concentration (fulvic acid equivalents) in Lake Erie along transects.   Water was sampled from a depth of 1.5 m while underway.    

Underway Sampling (1 m depth); Lake Erie June 8-12, 2005

Figure 3.   Chromophoric dissolved organic mater concentration in Lake Erie June 8-12, 2005.   Water was sampled from a depth of 1.5 m while underway onboard the R/V Lake Guardian.   Data was entered into ArcGIS TM 8.     

CDOM vs Total Chlorophyll-a

Figure 4.   Positive correlation betweentotal chlorophyll-a and chromophoric dissolved organic mater.  

Conclusions  

Through the utilization of a GIS and advanced instrumentation, we have produced high resolution maps of phytoplankton community composition in Lake Erie.   Our results suggest that CDOM positively correlates with phytoplankton biomass.