Coastal inputs of nutrients and contaminants impact phytoplankton community composition and health in localized and large areas of coastal Lake Ontario. Advanced fluorimetric instrumentation (Fast Repetition Rate Fluorimeter [FRRF], FluoroProbe) was used during June 2006 to assess the in situ phytoplankton community of eight tributaries of Lake Ontario (Chaumont Bay, Sacketts Harbor/Black River, Oswego River, Port Bay, Sodus Bay, Irondequoit Bay, Genesee River, and Eighteen Mile Creek) representing a range of geomorphological features (rivers, protected embayments, open embayments). The instrumentation enabled high resolution (160 m) continuous monitoring of phytoplankton community composition (FluoroProbe) and photosynthetic efficiency (FRRF) along 1 m deep transect from nearshore (coastal Lake Ontario, > 7 m depth) to inshore (within the tributary, < 7 m depth). Limnological parameters such as water temperature, colored dissolved organic matter content (CDOM), total phosporus, nitrate, chloride, light extinction coefficient, and extracted size fractionated (0.2–2 μ m, 2–20 μ m, > 20 μ m) chlorophyll a concentrations were also determined. Results from this study illustrate the strong environmental gradients that exist along tributary transition zones into Lake Ontario. Offshore water quality was homogeneous and reflected nutrients levels (e.g. total phosphorus) that were below the Great Lakes Water Quality Agreement target value (10 μ g per litre), whereas most tributary inputs had elevated nutrient and chloride levels. Phytoplankton community composition differed between inshore and offshore sites and the transition coincided with changing water quality (followed using water temperature and CDOM concentrations) at the interface of the surface water masses. The greatest observed photosynthetic efficiencies occurred in the inshore environment; this is attributed to the greater nutrient availability rather than lower light levels. Fluorimetric applications provide useful techniques for monitoring water quality. Given the observed diversity of phytoplankton community and health among these tributary inputs, it follows that monitoring capabilities using the instrumentation applied here should be enhanced to observe these systems.

Introduction

The Great Lakes/St. Lawrence River system has benefited from phosphorus controls mandated by the Great Lakes Water Quality Agreement of 1978. Phosphorus enrichment was shown to enhance primary production throughout Lake Ontario (Mills et al., 2003) and particularly, the near shore environment. The reduction of phosphorus levels to the 10 μg l−1 (323 nM) water quality guideline has brought Lake Ontario to the mesotrophic/oligtrophic status in the pelagic regions of this lake. In contrast, coastal ecosystem health along New York States Lake Ontario shoreline is impaired by many factors including: land use issues (e.g. erosion, non-point source nutrient sources), inefficient waste water treatment facilities, failing septic systems, and pollution legacies (Landre et al., 2006). Thus, although nutrient inputs are primarily from the inshore area, the large size of this lake (average depth 80 m) effectively dilutes inputs into the pelagic region where large scale mixing events occur. However, geomorphic coastal features, horizontal coastal currents, thermal bars, and near shore P-shunt (Hecky et al., 2004) are expected to exacerbate nutrient impacts on the coastal area of Lake Ontario.

The purpose of this investigation is to demonstrate the impacts that coastal inputs have on Lake Ontario ecosystem health. Recent technological advances in fluorimetry enable aquatic scientists to establish qualitative and quantitative assessments of the phytoplankton community. Traditional methods to establish the health of a phytoplankton community require intensive water sampling efforts, and labor-intensive sample analysis (phytoplankton identification, pigment analysis) and experimentation, e.g. the use of light:dark dissolved oxygen method, [14C]-NaHCO3 method, [18O]-H2O to measure gross photosynthesis (Ostrom et al., 2005), and time and space consuming experiments to establish photosynthetic efficiency on discrete water samples. In addition, analysis of phytoplankton population composition requires equally intensive microscopic examination or extracted pigment analysis by HPLC or staining and analysis by analytical flow cytometry or light microscopy (Makarewicz, 1987) on discrete samples.

In this study we employed fluorimeters capable of measuring the quantity of specific algae and cyanobacteria (Gregor and Maršálek, 2004), the photosynthetic efficiency of these phytoplankton (Smyth et al., 2004), and colored dissolved organic matter, a tracer of tributary influence on coastal water quality (McKnight et al., 2003). These instruments were coupled together for examining the ecological and environmental gradients that exists in coastal regions of Lake Ontario.

The specific objective was to examine water quality and the phytoplankton community at eight coastal Lake Ontario areas that represent a variety of geomorphic features (Table 1). The hypotheses tested are that the nearshore coastal environments have similar phytoplankton communities and that the tributaries have heterogeneous water quality, as indicated by chemical water quality parameters and phytoplankton community composition and health, as measured by photosynthetic efficiency. As used here, photosynthetic health reflects the photosynthetic efficiency of the entire phytoplankton community and is a reasonable indicator of the physiological condition of phytoplankton, as affected by such factors as nutrient stress or photo-inhibition (Pemberton et al., 2007).

Table 1.

Locations and site descriptions of coastal and pelagic areas studied on Lake Ontario in 2006.

Study Site (abbreviation), Hydrographic StationGeomorphic descriptionLatitude, Longitude at start and end of transect or stationDepth (m)Date (2006)
Eighteen Mile Creeka (EMC) Coastal, tributary Nearshore: 43° 21.461′, 78° 43.342′ Inshore: 43° 20.207′, 78° 42.985′ 20, 2.1 19 Jun 
Genesee Rivera (GeR) Coastal, tributary Nearshore: 43° 17.197′, 77° 34.584′ Inshore: 43° 13.986, 77° 37.064′ 21, 2.3 19 Jun 
Irondequoit Baya (IRB) Coastal, protected embayment Nearshore: 43° 16.007′, 77° 31.740′ Inshore: 43° 11.557, 77° 31.333′ 23, 6.4 19 Jun 
Sodus Bay (SoB) Coastal, protected embayment Nearshore: 43° 18.001′, 76° 58.300′ Inshore: 43° 14.153, 76° 56.337′ 21, 5.5 08 Jun 
Port Bay (PoB) Coastal, protected embayment Nearshore: 43° 19.182′, 76° 50.195′ Inshore: 43° 16.891′, 76° 49.423′ 7.9, 4.3 08 Jun 
Oswego Rivera (OsR) Coastal, tributary Nearshore: 43° 33.581′, 76° 32.949′ Inshore: 43° 27.510′, 76° 30.583′ 137, 4 09 Jun 
Black River-Sackets Harbor (BSH) Coastal, tributary into open embayment Nearshore: 43° 56.868′, 76° 10.922′ Inshore: 43° 58.920′, 76° 05.230′ 20, 3.4 07 Jun 
Chaumont River-Chaumont Bay (CCB) Coastal, tributary into open embayment Nearshore: 44° 01.329′, 76° 11.988′ Inshore: 44° 04.020′, 76° 08.603′ 9.1, 2.1 07 Jun 

aAreas of Concern, as defined by the Great Lakes Water Quality Agreement, Annex 2.

 
Study Site (abbreviation), Hydrographic StationGeomorphic descriptionLatitude, Longitude at start and end of transect or stationDepth (m)Date (2006)
Eighteen Mile Creeka (EMC) Coastal, tributary Nearshore: 43° 21.461′, 78° 43.342′ Inshore: 43° 20.207′, 78° 42.985′ 20, 2.1 19 Jun 
Genesee Rivera (GeR) Coastal, tributary Nearshore: 43° 17.197′, 77° 34.584′ Inshore: 43° 13.986, 77° 37.064′ 21, 2.3 19 Jun 
Irondequoit Baya (IRB) Coastal, protected embayment Nearshore: 43° 16.007′, 77° 31.740′ Inshore: 43° 11.557, 77° 31.333′ 23, 6.4 19 Jun 
Sodus Bay (SoB) Coastal, protected embayment Nearshore: 43° 18.001′, 76° 58.300′ Inshore: 43° 14.153, 76° 56.337′ 21, 5.5 08 Jun 
Port Bay (PoB) Coastal, protected embayment Nearshore: 43° 19.182′, 76° 50.195′ Inshore: 43° 16.891′, 76° 49.423′ 7.9, 4.3 08 Jun 
Oswego Rivera (OsR) Coastal, tributary Nearshore: 43° 33.581′, 76° 32.949′ Inshore: 43° 27.510′, 76° 30.583′ 137, 4 09 Jun 
Black River-Sackets Harbor (BSH) Coastal, tributary into open embayment Nearshore: 43° 56.868′, 76° 10.922′ Inshore: 43° 58.920′, 76° 05.230′ 20, 3.4 07 Jun 
Chaumont River-Chaumont Bay (CCB) Coastal, tributary into open embayment Nearshore: 44° 01.329′, 76° 11.988′ Inshore: 44° 04.020′, 76° 08.603′ 9.1, 2.1 07 Jun 

aAreas of Concern, as defined by the Great Lakes Water Quality Agreement, Annex 2.

 

Methods

In this study, nearshore stations are defined as > 7 m depth, and inshore stations are < 7 m depth. A horizontal profiling mode was used to sample water continuously from offshore Lake Ontario (> 20 m isopleth) to the furthest reach possible in the tributary or embayment. A 45 kg steel “fish” was towed by the R/V Lavinia at a speed of 4 knots at a depth of 1 m. Water was pumped through a metal-less (Kynar®) magnetic drive electric impeller pump (March Pump model MDX-MT-3; March Mfg., Inc., Glenview, IL) continuously at a rate of 11 litres per minute through a butyl rubber hose into an 14.6 L polyvinylchloride “ferrybox” that provided an integrated water sample at a horizontal transect resolution of approximately 160 m at the transect sampling velocity of 4 knots. A FluoroProbe (Model II, Series 7; bbe Moldaenke, GmbH, Kiel-Kronshagen, DE), was submersed inside the ferry box and measured temperature and phytoplankton (see below). Water was drawn by gravity from the ferry box through a Fast Repetition Rate Fluorimeter (Mark I, Chelsea Technologies Group, West Molesey, UK) to measure photosynthetic efficiency (see below) and subsequently a fluorimeter that measured colored dissolved organic matter (see below). All data were time stamped and archived on a field computer (Panasonic model CF-29; Panasonic Corporation, Secaucus, NJ). The field computer contained navigational software (Offshore Navigator, ver. 5.07; Amesbury, MA) of the entire Lake Ontario coastline (NOAA chart set Region 84; Nautical Data International, Inc., St. John's, NL), and an integral geographic positioning system to record time stamped geographic location of the vessel during all transects.

A hydrographic station was sampled at the beginning and end of each transect. Water was drawn from a depth of 1 m directly from the pump and collected in trace-metal clean polyethylene containers. Water was filtered through 0.2-μ m polyethersulfone syringe filters (Puradisc™ 25 AS; Whatman Inc., Florham Park, NJ) for measurement of nitrate and chloride. Water was sampled for measurement of total phosphorus and size fractionated chlorophyll a (see below). For calibration of the FluoroProbe, 12–14 litres of water was pumped through a 0.45-μ m pore size polyethersulfone cartridge filter (Groundwater Sampling Capsule, Millipore Corp., Bedford, MA) into a clear food-grade polyethylene bag placed in a black opaque plastic bag contained in a rigid pail; the FluoroProbe was rinsed with filtered lake water before insertion into the filtered lake water then covered with the black bag prior to the calibration of site-specific yellow substances (see below). At each station, a light extinction coefficient was determined using a submersible photometer.

Instrumentation and analyses

FluoroProbe

The FluoroProbe is a submersible fluorimeter that assesses phytoplankton communities through the measure of photosynthetic pigment fluorescence at 5 wavelengths (Beutler et al., 2002). The FluoroProbe distinguishes phytoplankton into four groups: 1) Chlorophyta and Euglenophyta, 2) phycocyanin (PC)-rich Cyanobacteria, 3) Heterokontophyta and Dinophyta, and 4) Cryptophyta and phycoerythrin (PE)-rich Cyanobacteria (Beutler et al., 2002, 2003). The FluoroProbe was programmed to measure continuously every second for the duration of 1 second; thus, data were obtained at a frequency of 0.5 Hz. Data collected over a 4 minute period (approximately 490 m) at the beginning and end of each transect was averaged (n = 120 measurements).

Yellow substance (YS) correction for the FluoroProbe

The FluoroProbe was calibrated for dissolved yellow substances (colored dissolved organic matter specifically measured by the FluoroProbe) using filtered (< 0.45 μ m) surface water (1 m). At each transect, a yellow substance calibration was determined by placing the rinsed FluoroProbe into this volume of filtered water and closing the black plastic bag to prevent any ingress of sunlight. The yellow substance corrections obtained for each transect were used to fit the data obtained from that transect using the Batch Fit function of the FluoroProbe software (ver. 1.8.3) such that the correction factors represented the water quality measured along the transect gradient (see results section).

Fast repetition rate fluorimetry (FRRF)

The FRRF measured photosynthetic efficiency at a frequency of 0.091 Hz. The program used for this instrument was identical to that developed by Pemberton et al. (2007) for use on Lake Ontario. The FRRF was programmed to measure the ratio of variable chlorophyll a fluorescence (Fv′) under ambient light conditions to maximal chlorophyll a fluorescence (Fm′) under ambient light conditions, calculated as:

formula
where, Fo′ = basal chlorophyll a fluorescence under ambient light conditions

Lake water collected during daylight hours and placed in the dark for at least 10 minutes will have a higher quantum efficiency (M.R. Twiss, unpublished data) than lake water that is assessed using FRRF immediately upon collection. The water residence time of the ferry box was 1.3 minutes (flow rate was approximately 11 litres per minute); thus, the phytoplankton in these transects would not have had adequate time to dark-adapt prior to measurement by the FRRF. Thus, measurements here reflect Fv′/Fm′ the indice of non-dark adapted photosynthetic efficiency.

Colored dissolved organic matter (CDOM)

Although the FluoroProbe can detect and correct for yellow substances in the lake water, an independent fluorimetric method was used to measure CDOM. Water from the ferry box was passed through a flow-through quartz cell on a fluorimeter (Turner Designs model 10-AU; Sunnyvale, CA) configured to measure CDOM (near UV Hg vapor lamp, 350 nm excitation filter and a 410–600 nm emission filter); measurements were made at a frequency of 1 Hz. The fluorimeter was calibrated with Suwannee River fulvic acid (SRFA; International Humic Substances Society, St. Paul, MN) and measurements from the fluorimetric were converted to FA units using the following equation: mg CDOMSRFA per litre = 1.622 × [CDOMraw]–0.3039.

Light extinction

At the beginning and end of each transect, a depth profile of photon flux density of photosynthetically active radiation (PAR; μ mol· m−2· s−1) was made using a submersible 4π sensor (LI-COR model 193; Lincoln, NB). The light extinction coefficient (λ; m−1) was determined as follows:

formula
where, z = depth (m).

Chlorophyll a

Chlorophyll a (Chl a) was measured as a proxy for photoautotrophic biomass. Total and size fractionated Chl a concentrations in the lake were analyzed fluorimetrically (Welschmeyer, 1994). Parallel filtrations using 47-mm-diameter filters were conducted in duplicate at each station within 1 hour of collection using the following sequence: 400 mL were collected onto a 20-μ m pore-size woven nylon filter; 100–250 mL were collected onto a 2-μ m pore-size polycarbonate filter; and 50 mL were collected onto a 0.2-μ m pore size polycarbonate filter. This approach provided details on the abundance of Chl a-bearing microplankton (> 20 μ m), nanoplankton (2–20 μ m), and picoplankton (0.2–2 μ m) fractions, respectively. Filters were extracted in 10 mL of 90% acetone in the dark at 4°C, for 8–24 hrs and Chl a was measured by fluorimetry (Welschemeyer 1994) using a calibrated fluorimeter (Turner Designs model TD-700; Sunnyvale, CA).

Total phosphorus

Phosphorus content was determined for duplicate unfiltered water samples. A fresh solution of potassium persulfate was added to each sample and the calibration standards to achieve a final concentration of 0.7% (mass:volume), and then digested in an autoclave (10 minutes at 121°C). Phosphorus was determined colorimetrically using the antimony/molybdate/tartrate method (Wetzel and Likens, 2000) and light absorption was measured (885 nm) using a 10 cm pathlength cuvette.

Nitrate and chloride

Total dissolved nitrate and chloride was quantified on filtered water (0.2 μ m) by ion chromatography (DX-500; Dionex Corp., Sunnyvale, CA). Replicate sample analyses had concentration differences < 2%; spike sample recovery was 100.7%.

Results and discussion

The stations were sampled over as short a time interval (12 days) as possible in order to reduce any seasonal or weather induced variability. Nevertheless, high seas and a thunderstorm prevented the measurement of the light extinction coefficients at nearshore Eighteen Mile Creek and inshore Port Bay, respectively.

The proportion of FluoroProbe-specific phytoplankton measured in the nearshore sites is similar to the taxonomic composition of phytoplankton biomass reported in nearshore (> 30 m depth) and offshore (> 100 m depth) stations in Lake Ontario during the summer (Munawar and Munawar, 2003).

This June 2006 sampling regimen determined that the nearshore environment was relatively homogeneous with respect to nutrient levels, chloride concentrations and concentration of CDOM (Table 2). The GLWQA Guideline of 323 nM TP was exceeded only once in the eight nearshore zones surveyed (viz., Eighteen Mile Creek) yet in all inshore areas, except at the Black River/Sacketts Harbor tributary. The GLWQA TP guideline was exceeded at least 10-fold at Eighteen Mile Creek, the Genesee River, Irondequoit Bay, and Port Bay. Accordingly, these inshore sites with elevated TP had extractable Chl a concentrations exceeding average nearshore concentration of Chl a (2.91 ± 0.90 μ g per litre, mean ± standard deviation, n = 8) and elevated proportions of PC-rich cyanobacteria (Table 3). Nearshore sites had PC-rich cyanobacteria concentrations representing less than 12% of the total in situ Chl a concentration, determined using the FluoroProbe, with the exception of nearshore Eighteen Mile Creek (75%). However, the elevated phosphorus at this station may have indicated that the site was influenced by the tributary. Owing to foul weather, this transect was shortened to 2 km in total length, and thus the tributary may have affected the water at the deeper nearshore station at this study site.

Table 2.

Water quality parameters at stations nearshore (depths > 7 m) and inshore (depth < 7m) in the coastal zone of Lake Ontario (June 7–19, 2006). n.d. = not determined. Z = maximum depth at station TP = total phosphorus; CDOM = colored dissolved organic matter (mg Suwannee River fulvic acid per litre, equivalents), measured fluorimetrically; λ = light extinction coefficient of photosynthetically active radiation in water determined using a 4π sensor.

Sta.ZoneZ (m)Temp. (°C)TP (nM)NO3 (μ M)N:P (mol:mol)Cl (μ M)CDOM (mean ± SD)λ (m−1)
EMC Nearshore 20 20.7 346 15.7 45 660 0.21 ± 0.00 n.d 
 Inshore 2.1 23.7 5576 45.1 1 808 2.64 ± 0.04 1.04 
GeR Nearshore 21 19.1 242 13.6 56 671 0.24 ± 0.00 0.15 
 Inshore 2.3 24.4 2036 45.8 22 1 281 2.59 ± 0.01 2.00 
IRB Nearshore 23 19.5 282 13.7 49 668 0.25 ± 0.00 0.21 
 Inshore 6.4 23.6 1325 2.1 4 993 4.22 ± 0.05 0.81 
SoB Nearshore 21 17.8 194 20.8 107 733 0.31 ± 0.01 0.19 
 Inshore 5.5 21.8 594 2.2 790 1.60 ± 0.03 0.55 
PoB Nearshore 7.9 17.8 149 20.3 136 731 0.32 ± 0.02 0.31 
 Inshore 4.3 21.9 3622 3.6 917 6.87 ± 0.17 n.d. 
OsR Nearshore 137 15.3 135 19.1 141 722 0.25 ± 0.00 0.21 
 Inshore 20.4 1660 40.8 25 2 603 4.50 ± 0.01 1.12 
BSH Nearshore 20 18.1 205 20.9 102 640 1.54 ± 0.10 0.48 
 Inshore 3.4 14.3 286 22.6 79 643 1.42 ± 0.35 1.20 
CCB Nearshore 9.1 21.0 191 9.6 50 654 0.77 ± 0.02 0.49 
 Inshore 2.1 20.1 375 8.6 23 680 0.91 ± 0.03 0.70 
Sta.ZoneZ (m)Temp. (°C)TP (nM)NO3 (μ M)N:P (mol:mol)Cl (μ M)CDOM (mean ± SD)λ (m−1)
EMC Nearshore 20 20.7 346 15.7 45 660 0.21 ± 0.00 n.d 
 Inshore 2.1 23.7 5576 45.1 1 808 2.64 ± 0.04 1.04 
GeR Nearshore 21 19.1 242 13.6 56 671 0.24 ± 0.00 0.15 
 Inshore 2.3 24.4 2036 45.8 22 1 281 2.59 ± 0.01 2.00 
IRB Nearshore 23 19.5 282 13.7 49 668 0.25 ± 0.00 0.21 
 Inshore 6.4 23.6 1325 2.1 4 993 4.22 ± 0.05 0.81 
SoB Nearshore 21 17.8 194 20.8 107 733 0.31 ± 0.01 0.19 
 Inshore 5.5 21.8 594 2.2 790 1.60 ± 0.03 0.55 
PoB Nearshore 7.9 17.8 149 20.3 136 731 0.32 ± 0.02 0.31 
 Inshore 4.3 21.9 3622 3.6 917 6.87 ± 0.17 n.d. 
OsR Nearshore 137 15.3 135 19.1 141 722 0.25 ± 0.00 0.21 
 Inshore 20.4 1660 40.8 25 2 603 4.50 ± 0.01 1.12 
BSH Nearshore 20 18.1 205 20.9 102 640 1.54 ± 0.10 0.48 
 Inshore 3.4 14.3 286 22.6 79 643 1.42 ± 0.35 1.20 
CCB Nearshore 9.1 21.0 191 9.6 50 654 0.77 ± 0.02 0.49 
 Inshore 2.1 20.1 375 8.6 23 680 0.91 ± 0.03 0.70 
Table 3.

Properties of phytoplankton community composition at stations nearshore (depths > 7 m) and inshore (depth < 7m) in the coastal zone of Lake Ontario (June 7–19, 2006). M = microplankton (> 20 μ m), N = nanoplankton (2–20 μ m), P = picoplankton (0.2–2 μ m); CHL = Chlorophyta and Euglenophyta, PCC = phycocyanin (PC)-rich Cyanobacteria, H&D = Heterokontophyta and Dinophyta, and C&P = Cryptophyta and phycoerythrin (PE)-rich Cyanobacteria.

Phytoplankton measured by size-fractionated filtration (SF)Phytoplankton measured by FluoroProbe (FP)
Sta.ZoneZ (m)Chl a SF (μ g L−1)% M%N%PChl a FP (μ g L−1)CHL (%)PCC (%)H&D (%)C&P (%)Fv′/Fm′ (mean ± SD, n = 22)
EMC Nearshore 20 2.56 24 69 1.34 75.1 24.8 0.38 ± 0.03 
 Inshore 2.1 4.78 19 33 48 3.09 99.8 0.2 0.38 ± 0.02 
GeR Nearshore 21 2.20 28 64 1.47 17.1 5.9 54.8 22.2 0.33 ± 0.04 
 Inshore 2.3 15.02 55 40 6.10 21.1 1.2 77.7 0.51 ± 0.01 
IRB Nearshore 23 2.13 28 64 1.56 13.2 7.2 55.1 24.4 0.35 ± 0.04 
 Inshore 6.4 22.08 21 15 63 7.82 30 11.2 41.3 17.5 0.41 ± 0.01 
SoB Nearshore 21 3.67 18 31 51 2.07 14.6 7.2 57.7 20.5 0.15 ± 0.06 
 Inshore 5.5 6.84 29 62 2.61 12.7 43.4 10.6 33.3 0.20 ± 0.03 
PoB Nearshore 7.9 3.07 14 28 59 2.40 6.6 5.7 87.6 0.32 ± 0.03 
 Inshore 4.3 18.08 41 55 11.61 23.5 12.5 63.9 0.34 ± 0.01 
OsR Nearshore 137 4.47 18 22 60 3.70 0.6 2.4 1.2 95.8 0.20 ± 0.03 
 Inshore 1.62 25 42 34 1.11 100 0.25 ± 0.04 
BSH Nearshore 20 3.34 14 30 57 0.90 17.5 10.8 71.1 0.6 0.39 ± 0.03 
 Inshore 3.4 1.73 20 50 31 1.02 5.5 40.1 40.1 14.3 0.39 ± 0.06 
CCB Nearshore 9.1 1.82 10 37 53 1.41 29.0 11.8 48.8 10.4 0.28 ± 0.08 
 Inshore 2.1 1.41 38 56 1.62 16.4 10.8 53.8 19.0 0.26 ± 0.08 
Phytoplankton measured by size-fractionated filtration (SF)Phytoplankton measured by FluoroProbe (FP)
Sta.ZoneZ (m)Chl a SF (μ g L−1)% M%N%PChl a FP (μ g L−1)CHL (%)PCC (%)H&D (%)C&P (%)Fv′/Fm′ (mean ± SD, n = 22)
EMC Nearshore 20 2.56 24 69 1.34 75.1 24.8 0.38 ± 0.03 
 Inshore 2.1 4.78 19 33 48 3.09 99.8 0.2 0.38 ± 0.02 
GeR Nearshore 21 2.20 28 64 1.47 17.1 5.9 54.8 22.2 0.33 ± 0.04 
 Inshore 2.3 15.02 55 40 6.10 21.1 1.2 77.7 0.51 ± 0.01 
IRB Nearshore 23 2.13 28 64 1.56 13.2 7.2 55.1 24.4 0.35 ± 0.04 
 Inshore 6.4 22.08 21 15 63 7.82 30 11.2 41.3 17.5 0.41 ± 0.01 
SoB Nearshore 21 3.67 18 31 51 2.07 14.6 7.2 57.7 20.5 0.15 ± 0.06 
 Inshore 5.5 6.84 29 62 2.61 12.7 43.4 10.6 33.3 0.20 ± 0.03 
PoB Nearshore 7.9 3.07 14 28 59 2.40 6.6 5.7 87.6 0.32 ± 0.03 
 Inshore 4.3 18.08 41 55 11.61 23.5 12.5 63.9 0.34 ± 0.01 
OsR Nearshore 137 4.47 18 22 60 3.70 0.6 2.4 1.2 95.8 0.20 ± 0.03 
 Inshore 1.62 25 42 34 1.11 100 0.25 ± 0.04 
BSH Nearshore 20 3.34 14 30 57 0.90 17.5 10.8 71.1 0.6 0.39 ± 0.03 
 Inshore 3.4 1.73 20 50 31 1.02 5.5 40.1 40.1 14.3 0.39 ± 0.06 
CCB Nearshore 9.1 1.82 10 37 53 1.41 29.0 11.8 48.8 10.4 0.28 ± 0.08 
 Inshore 2.1 1.41 38 56 1.62 16.4 10.8 53.8 19.0 0.26 ± 0.08 

During the June coastal surveys, gradients of CDOM encountered in the coastal transects required the application of the unique YS correction factors for the FluoroProbe to treat both the nearshore and inshore waters. Two transects (Irondequoit Bay and Genessee River) are selected here to illustrate differences in the applicability of the two discrete YS correction factors for a single transect. The transects in these areas were characterized by strong gradients in temperature and CDOM that defined a transition (mixing) zone between these two distinct water masses (Fig. 1 & Fig. 2). In Figure 1, the nearshore and inshore YS correction factors were both used; data were fitted using the inshore YS correction factor to the point where the nearshore concentration of CDOM increased by 25%. In this case, the transition was apparently seamless. A spike of phytoplankton was observed at the transition point (likely due to the pumping of a piece of vegetation with attached epiphytes into the ferry box) and Cryptophytes and PE-rich Cyanobacteria disappeared in the mixing zone of inshore and nearshore waters but they appeared again towards the head of Irondequoit Bay. In contrast, this same group of phytoplankton abruptly disappeared once the inshore YS correction factor was applied for the Genesee River (Figure 2). It is possible that a third YS correction factor, unique to this mixing zone was required for a more realistic interpretation of the fluorimetric response of the algae by the FluoroProbe in this tributary.

Figure 1.

Water quality along a transect from Lake Ontario into Irondequoit Bay, June 19, 2006. Water was sampled at a depth of 1 m with the vessel moving at approximately 2 m s−1. The average of ten measurements of phytoplankton groupings were made and presented in this figure.

Figure 1.

Water quality along a transect from Lake Ontario into Irondequoit Bay, June 19, 2006. Water was sampled at a depth of 1 m with the vessel moving at approximately 2 m s−1. The average of ten measurements of phytoplankton groupings were made and presented in this figure.

Figure 2.

Water quality along a transect from Lake Ontario into the Genesee River, June 19, 2006. Water was sampled at a depth of 1 m with the vessel moving at approximately 2 m s−1. The average of ten measurements of phytoplankton groupings were made and presented in this figure.

Figure 2.

Water quality along a transect from Lake Ontario into the Genesee River, June 19, 2006. Water was sampled at a depth of 1 m with the vessel moving at approximately 2 m s−1. The average of ten measurements of phytoplankton groupings were made and presented in this figure.

The high percentage of Chl a attributed to PC-rich cyanobacteria reported here for the Oswego River and harbor (100%) is greater than, but consistent with, the proportion of abundance (based on cell numbers) of this group of phytoplankton observed by Makarewicz (1987) during three cruises in 1981 (late July, 84–94%; late August, 85–89%; and early October; 88%). Expert microscopic examination of water samples collected would be required to confirm the accuracy of the FluoroProbe. Microscopy would also be required to determine if the Heterokontophyta detected in the nearshore region in the Oswego River transect were halophiles, as reported by Makarewicz (1987).

In instances where there was a noticeable difference between non-dark adapted photosynthetic (quantum) efficiency (Fv′/Fm′) along the transect, the greatest observed photosynthetic efficiencies occurred in the inshore environment (Table 3). This increased photosynthetic efficiency can be attributed to the greater nutrient availability (Table 2; benefiting the phytoplankton physiology) and lower light levels (as indicated by CDOM concentrations and light extinction coefficients; Table 2) that likely reduced any photochemical damage to the phytoplankton caused by high PAR and ultraviolet radiation in the more clear nearshore waters. Here we attribute the influence to be that of nutrients since transects that showed the least change in Fv′/Fm′ (Chaumont Bay and Black River/Sacketts Harbor; Table 2) had the smallest difference in nutrients concentrations (TP and nitrate) despite large differences in the light extinction coefficient of photosynthetically active radiation (Table 3).

Photosynthetic efficiency (Fv′/Fm′) of phytoplankton sampled from a depth of 1m during lake wide surveys of Lake Erie in June July and September 2005 showed strong dield periodicity (M.R. Twiss, unpublished data). Mimimal Fv′Fm′ were observed shortly after sunrise and did not increase until after sunset. In the present study, all transects took place during daylight hours and at least four hours after sunrise. Thus, we expect no diel periodicity to have influenced the observations.

Light may have influenced the accuracy of the FluoroProbe. A plot of extracted chlorophyll a versus in situ chlorophyll a determined by the FluoroProbe shows that the FluoroProbe is measuring only about 42% of the extracted level of this pigment. During pelagic cruises in Lake Ontario in spring and summer 2006, the accuracy of the FluoroProbe to measure in situ Chl a at depths greater than 5 m was near 100% that of extracted chlorophyll a (M.R. Twiss, unpublished data). Since the pelagic samples were sampled from depths of at least 5 m it is possible that light may have caused photo-bleaching of Chl a in phytoplankton at depths of 1 m, sampled during the transects.

Conclusions

Fluorimetric applications provide useful techniques for monitoring water quality. Given the observed diversity of phytoplankton community and health among these tributary inputs, it follows that monitoring capabilities using the instrumentation applied here should be enhanced to observe these systems. However, there are limitations to the instrumentation used here. For example, the FluoroProbe is unable to distinguish between some major algal/cyanobacterial divisions, e.g. the Heterokontophyta and Dinophyta, and the Cryptophyta and PE-rich Cyanobacteria. Therefore, microscopic identification must be relied upon, in addition to the incorporation of new techniques, to establish indices of biodiversity that can be applied to reveal long term trends in water quality in Lake Ontario and tributaries.

Acknowledgements

This research was funded by a grant from the Lake Ontario Coastal Initiative (LOCI) to MRT. IRM was funded by the Clarkson University Environmental Science and Engineering Research Experience for Undergraduates, sponsored by the United States National Science Foundation. We thank Avery Twiss for technical assistance in the field. This is Contribution No. 341 of the Clarkson University Center for the Environment.

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