Phytoplankton Ecology in Coastal Zones

of LakeOntario

Ian R. MacLeod [1], Michael R. Twiss2

Introduction

LakeOntario contains a diverse community of free-floating photosynthetic algae that forms the base of the food chain for this temperate freshwater body. Those phytoplankton populations that lie in the coastal zones of New YorkState are subject to nutritive and pollutant inputs from the population centers lying on the coast and along in-flowing rivers such as the industrial port cities of Rochester and Oswego.

As primary producers, phytoplankton form the first and arguably most important trophic level and thus yield information on the ecology of higher organisms, with species of the commercial fishery as an example. Phytoplankton respond to changes in their environment and thus serve as indicators of water quality. With the use of modern instrumentation, this information can be gathered more quickly and efficiently than comparative older methods. This study seeks to build an understanding of the phytoplankton communities and their environments. Factors considered are:phytoplankton-type, number, health; location- inshore (littoral) vs. offshore (pelagic), shoreline features, anthropogenic influence; and water chemistry- nutrients, temperature, light extinction. This study was conducted as part of a small grant to determine the potential of using a novel array of instruments in conjunction with traditional sampling methods.

Methodology

During two trips to LakeOntario in June 2006, we collected data onboard the GreatRiversCenter research vessel R/V Lavinia. We visited eight sites on the southeastern coast of the lake ranging as far west as Olcott and east to Chaumont (see Figure 1). At each site, we sailed from an offshore position into the innermost part of the river or embayment collecting data continuously with the onboard instruments. At the start and end point of each transect we established fixed water collection stations.

The onboard instruments employed were the Fast Repetition Rate Fluorometer (FRRF; Mk I, Chelsea Instruments), FluoroProbe (Series 7; bbe Moldeanke, GmbH), and 10-AU (Turner Designs). The FRRF measures photosynthetic health of the phytoplankton by comparing variable to maximum fluorescence. The FlouroProbe identifies the amount of phytoplankton in each of four divisions by examining the fluorescence excitation spectrums resulting from the unique combinations of photosynthetic pigments present in each division. The 10-AU measures the quantity of colored dissolved organic matter (CDOM). Water passes through the instruments as it is pumped up from a 45kg steel “fish” submersed at a depth of 1.5m, into a flow-through ferry box (which houses the FluoroProbe) and then to the remaining instruments. The instruments are synchronized with the onboard GPS navigation system to provide accurate spatial and temporal coordinates for all readings.

Using the depth specific pumping system, water samples were acquired at each station and were used in various applications. Using laboratory analysis we determined nutrient levels at each station for chloride (Cl), nitrate (NO3), and total phosphorus (TP). Size fractionated filtration of water samples enabled us to group phytoplankton by specific size classes:>20, 20-2.0, and 2.0-0.2 micro-meters in diameter. Using a laboratory fluorometer, we then analyzed the photosynthetic pigment chlorophyll-a (Chl-a) by size class. Additionally, we measured the light extinction coefficient (Kd), which describes the turbidity of the water column, at each station using a 4п photometer at depths up to 22m in roughly 1 m increments. Lastly, we collected additional water samples for use in further analysis of bacteria, dissolved organic carbon (DOC), and stained-sample microscopy.

Figure 1. Map of LakeOntario with study sites indicated by arrows.

Results and Discussion

Figure 2. Data collected from the three onboard instruments on the OswegoRivertransect on June 9, 2006. The transect began offshore in LakeOntario at 14:15 and finished inshore within the river channel at 15:48 lasting ninety-three minutes.

The colored dissolved organic matter rises sharply when the effluent from the river was measured. The total Chl-a (indicative of phytoplankton biomass) rises slowly as we approached the river but then drops sharply as the river is reached. The photosynthetic health (represented by Fv/Fm) rises in conjunction with the CDOM but then decreases as the CDOM stabilizes in the far interior of the transect. This river was highly polluted and the Oswego Inshore station (OSI) claimed our 2nd and 3rd highest chloride (2603.45 nanomoles Cl) and nitrate (40.77 nanomoles NO3) nutrient values respectively.

Figure 3. Chlorophyll-a and total phosphorus at sixteen fixed water collection stations, representing the offshore and inshore positions of the eight sites.

Key: CB-ChaumontBay, SH-SacketsHarbor, SB-SodusBay, PB-PortBay, OS-Oswego, IB-IrondequoitBay, GR-GeneseeRiver, OL-Olcott (Eighteen Mile Creek).

Chlorophyll-a is an essential photosynthetic pigment found in all phytoplankton and serves as a surrogate of phytoplankton biomass. Phosphorus is an essential nutrient for phytoplankton (Kalff 247). TP is higher at the inshore station at all sites indicating that the coastal zones are a source of nutrients such as phosphorus, leaving the offshore areas less nutrient rich. The Oswego inshore station (OSI) has a high TP level which would seemingly promote algal growth. However, OSI Chl-a is significantly lower than the nutrient poor offshore station (OSO). The lower quantities of phytoplankton biomass at OSI can be explained by the high turbidity of the water which has a Kd equal to 1.12 m-1, our third highest of all sixteen stations, permitting little light to penetrate the water column for use in photosynthesis.

References

Kalff, Jacob. Limnology: Inland Water Ecosystems. Upper Saddle River, NJ: Prentice Hall, 2002.

Makarewicz, Joseph C. Elevated Levels of Nutrients and Algae in the Nearshore of LakeOntario.LakeOntario Coastal Initiative (Conference). SUNY Brockport.

1NSF-REU in Environmental Sciences and Engineering; Class of 2007, Departments of Biology and Environmental Science, WesleyanUniversity, ; Oral Presentation

2Research Mentor; Associate Professor, GreatRiversCenter, Department of Biology, ClarksonUniversity,