ONONDAGA COUNTY DEPARTMENT OF
WATER ENVIRONMENT PROTECTION

 

VISION

To be a respected leader in wastewater treatment, stormwater
management, and the protection of our environment using state of-the-art,
innovative technologies and sound scientific principles as our guide.

 

MISSION

To protect and improve the water environment of Onondaga County in a cost-effective
manner ensuring the health and sustainability of our community and economy.


CORE VALUES

Excellence
Teamwork

Honesty

Innovation

Cost-Effectiveness

Safety

 

 

 

 

http://www.savetherain.us

 

 

 

Cover photo by C. Strait

 

 

 

ONONDAGA 2011 LAKE AMBIENT MONITORING PROGRAM

 

2011 ANNUAL REPORT

 

 

 

 

ONONDAGA COUNTY, NEW YORK

 

 

Final, February 2013

 

 

 

Prepared for

 

ONONDAGA COUNTY, NEW YORK

 

 

 

Prepared by

 

Upstate Freshwater Institute

224 Midler Park Dr.

Syracuse, NY 13206

 

 

 

 


Anchor QEA, LLC

Liverpool, NY

 

 

 

Lars Rudstam, Ph.D.

Cornell Biological Field Station

Bridgeport, NY

 


Onondaga County Department of Water Environment Protection

Syracuse, NY

 

 

EcoLogic, LLC

Aquatic, Terrestrial and Wetland Consultants

Cazenovia, NY

 



Key Features of this Report

This report presents the findings of Onondaga County’s Ambient Monitoring Program (AMP) for 2011.  The County’s annual monitoring program is designed to evaluate compliance with water quality standards and trends as improvements to the wastewater collection and treatment infrastructure are completed.  Each year, the Onondaga County Department of Water Environment Protection collects extensive water quality and biological data to characterize Onondaga Lake and its watershed.  This summary report of 2011 conditions provides a synopsis of the extensive data to the many stakeholders interested in Onondaga Lake.

The 2011 report was prepared and distributed as an electronic document.  Key results and supporting tables and graphics are included in the main document, with links to supporting tables, technical reports and graphics in an electronic library.  The report and supporting files are available on CD upon request and on the Onondaga County web site www.ongov.net/wep.  Throughout the document, the reader will find hyperlinks to additional detailed tables, graphs and related reports. These hyperlinks appear as blue underlined words in the print copy.  Simple definitions of many of the technical terms are included.  These words and phrases will appear as grey shaded in the print copy with blue underlined words.  They are hyperlinks to a glossary list.  These words are marked once in each chapter of the report.  If the user follows these links in the web browser, simply use the back arrow key in your web browser to return to the section of the report you are reading.

Once in the library of supporting documents, the reader can navigate back to the main report using browser navigation tools such as the back arrow.  There are more than 200 supporting tables and graphics in the library of supporting materials.  While each hyperlink has been checked, it is possible that some features will not be enabled on every computer’s operating system.  Feedback on the functionality of the electronic features of the document is welcome.  Please contact JeannePowers@ongov.net with comments.

 

 


 

Table of Contents- AMP 2011

Key Features of this Report. iv

Executive Summary. 1

Section 1.      Introduction to the AMP. 17

1.1      Regulatory Requirements. 17

1.2      Classification and Best Use. 17

1.3      AMP Objectives and Design. 17

1.4      Amended Consent Judgment Milestones. 19

1.5      Projects to Address Legacy Industrial Pollution. 22

1.6      Use of Metrics to Measure and Report Progress. 23

Section 2.      Onondaga Lake and Watershed. 25

2.1      Watershed Size and Hydrology. 25

2.2      Land Use. 26

2.3      Morphometry. 26

Section 3.      Onondaga County Actions. 29

Section 4.      Tributary Water Quality: 2011 Results and Long-Term Trends. 35

4.1      Meteorological Drivers and Stream Flow.. 35

4.2      Compliance with Ambient Water Quality Standards. 36

4.3      Loads. 39

4.3.1        Calculations and Multi-format Results for 2011. 39

4.3.2        Selected Phosphorus Topics. 42

4.3.3        Recent Metro Performance. 45

4.3.4        Trends. 48

Section 5.      Onondaga Lake Water Quality: 2011 Results and Trends. 60

5.1      Sampling Locations. 60

5.2      Compliance with AWQS. 60

5.3      Trophic State. 63

5.3.1        Total Phosphorus. 64

5.3.2        Chlorophyll-a. 64

5.3.3        Secchi Disk Transparency. 65

5.3.4        Trophic State Indicators. 68

5.4      Dissolved Oxygen. 70

5.5      Ammonia, Nitrite, and Nitrate. 72

5.6      Recreational Quality. 73

5.7      Nearshore Trends. 74

5.8      Selected Lake Trends Coupled to Metro Improvements. 75

5.8.1        Indicators of Primary Production. 75

5.8.2        Phosphorus. 75

5.8.3        N to P Ratio. 78

5.8.4        Deep Waters. 80

5.9      All Other Parameters. 81

Section 6.      Biology and Food Web: 2011 Results and Trends. 82

6.1      Primary Producers- Algae and Macrophytes. 82

6.2      Zooplankton and Dreissenid Mussels. 86

6.3      Fish. 92

6.3.1        Richness and Diversity. 92

6.3.2        Reproductive Success. 93

6.3.3        Recreational Fishery. 96

6.3.4        Fish Size – Largemouth Bass. 96

6.3.5        Fish Size – Smallmouth Bass. 96

6.3.6        Fish Size – Sunfish. 97

6.3.7        Fish Size – Yellow Perch and Brown Bullhead. 98

6.4      Fish Abnormalities. 98

6.5      Additional Information Regarding the Fish Community. 99

6.6      Integrated Assessment of the Food Web. 99

Section 7.      Water Quality in the Three Rivers System.. 104

Section 8.      Progress with Related Initiatives. 110

Section 9.      Emerging Issues and Recommendations. 112

Section 10.   Acknowledgements. 114

Section 11.   Literature cited. 115

List of Acronyms and Glossary of Terms

Library of Supporting Materials

 


 

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LIST OF TABLES

Table EX-1.       Summary of metrics, Onondaga Lake 2011. 14

Table 1-1.          Overview of AMP data analysis and interpretation plan. 21

Table 1-2.          Metro compliance schedule. 22

Table 1-3.          CSO compliance schedule. 23

Table 3-1.          Summary (timeline) of significant milestones and pollution abatement actions and lake water quality conditions. 30

Table 3-2.          CSO remedial projects (gray infrastructure) planned. 33

Table 4-1.          Summary of tributary compliance (percent of observations in compliance) with ambient water quality standards AWQS, 2011. 37

Table 4-2.          Fecal coliform bacteria concentrations at selected tributary sampling sites in 2011. 39

Table 4-3.          Annual loading of selected water quality constituents to Onondaga Lake, 2011, Onondaga Lake tributaries with number of samples in parentheses. 41

Table 4-4.          Percent annual loading contribution by gauged inflow, 2011. 42

Table 4-5.          Flow-weighted average concentration of selected constituents in Onondaga Lake tributaries, 2011. 43

Table 4-6.          Tributary and Metro total dissolved phosphorus (TDP) loading and flow-weighted concentrations to Onondaga Lake for post-ActiFlo implementation. 45

Table 4-7.          Tributary and Metro total phosphorus (TP) Loading to Onondaga Lake and flow-weighted concentration, pre-ACJ and post-Actiflo® implementation. 50

Table 4-8.          Tributary and Metro soluble reactive phosphorus (SRP) loading to Onondaga Lake, and flow-weighted concentrations, pre-ACJ and post-Actiflo® implementation. 50

Table 4-9.          Ten-year trends in tributary concentrations (2002-2011) – summary, from application of seasonal Kendall test. 53

Table 4-10.        Ten-year trends in tributary loading (2002-2011) – summary, from application of the seasonal Kendall test. 55

Table 5-1.          Percentage of measurements in compliance with ambient water quality standards (AWQS) and guidance values in the upper mixed and lower water layers of Onondaga Lake in 2011. 61

Table 5-2.          New York State water quality standards for dissolved oxygen. 62

Table 5-3.          Percent of ammonia measurements in compliance with ambient water quality standards, Onondaga Lake, 1998-2011. 72

Table 5-4.          Summary of trends in lake concentrations during the 2002 to 2011 period, according to two-tailed Seasonal Kendall test. 76

Table 6-1.          Fish species identified in Onondaga Lake, 2000-2011. 92

Table 7-1.          Summary of non-compliance with ambient water quality standards for dissolved oxygen, nitrite, and total ammonia in Three Rivers System on discrete sampling dates of 7/13/2011, 8/31/2011, and 9/28/2011. 108

Table 7-2........ Summary of 15-minute dissolved oxygen (DO) data1 collected by the YSI sondes in 2011. 109

 


 

LIST OF FIGURES

Figure EX-1.      Annual time plot of the daily average Metro ammonia (NH3-N) loading to Onondaga Lake, 1990-2011. 2

Figure EX-2.      Contributions of Metro and the watershed to the total annual input of ammonia to Onondaga Lake, average for 1990-2004 compared to 2011. 3

Figure EX-3.      Annual time plot of the daily average Metro total phosphorus (TP) loading to Onondaga Lake, 1990-2011. 3

Figure EX-4.      Contributions of Metro and the watershed to the annual input of total phosphorus to Onondaga Lake, average for 1990-2004 compared to 2011. 4

Figure EX-5.      Annual average ammonia concentrations in the upper waters (0-3 meters) of Onondaga Lake, 1990-2011. 5

Figure EX-6.      Summer (June to September) average total phosphorus concentration in the upper waters (0-3 meters) of Onondaga Lake, 1990-2011. 6

Figure EX-7.      Summer (June to September) algal bloom percent occurrences in Onondaga Lake evaluated annually for the 1990 - 2011 period, based on chlorophyll-a measurements. 6

Figure EX-8.      Volume-days of anoxia (dissolved oxygen less than 0.5 mg/L) and hypoxia (dissolved oxygen less than 2 mg/L), in Onondaga Lake during the summer, 1992-2011. 7

Figure EX-9.      Minimum dissolved oxygen (DO) concentration in the upper waters (0-3 meters) of Onondaga Lake during fall turnover (October), annually 1990 – 2011. 7

Figure EX-10.   Aquatic plant coverage, 2000 and 2011. 9

Figure EX-11.   Bass (smallmouth and largemouth adults) captured by electrofishing in Onondaga Lake, 2000 – 2011. 9

Figure EX-12.   Average zooplankton size (all taxa combined) and alewife catch rates from electrofishing, 2000-2011, Onondaga Lake. Note:  error bars are standard error of the mean. 10

Figure EX-13.   Mean Secchi disk depth measurements and mean zooplankton size, Onondaga Lake, 1999 – 2011. 11

 

Figure 1-1.        Tributary and lake regulatory classifications and subwatershed boundaries. 18

Figure 1-2.        Map of routine AMP monitoring locations, Onondaga Lake and tributaries. 20

Figure 2-1.        Annual average inflows (gauged and ungauged) to Onondaga Lake, 2001-2011. 25

Figure 2-2.        Land cover classification map. 26

Figure 2-3.        Bathymetric map. 27

Figure 3-1.        Map of CSO areas. 34

Figure 4-1.        Monthly precipitation in 2011 compared to the long-term (1981-2010) average. 35

Figure 4-2.        Time series of fecal coliform bacteria counts for tributaries to Onondaga Lake, 2011. 38

Figure 4-3.        Evaluation of the dependence of the daily average total phosphorus load from the watershed (non-Metro), annually, on the annual precipitation for the 1990-2011 period. 44

Figure 4-4.        Metro effluent monthly average ammonia concentrations compared to permit limits for 2010 and 2011. 46

Figure 4-5.        Annual time plot of the daily average Metro ammonia (NH3-N) loading to Onondaga Lake, 1990-2011. 46

Figure 4-6.        Contributions of Metro and the watershed to the total annual input of ammonia to Onondaga Lake, average for 1990-2004 compared to 2011. 47

Figure 4-7.        Annual time plot of the daily average Metro total phosphorus (TP) loading to Onondaga Lake, 1990-2011. 47

Figure 4-8.        Metro effluent total phosphorus concentrations compared to permit limits for the 2006-2011 interval. Concentrations are monthly rolling average values for 12 months intervals. 48

Figure 4-9.        Contributions of Metro and the watershed to the annual input of total phosphorus to Onondaga Lake, average for 1990-2004 compared to 2011. 49

Figure 4-10.      Time series of fecal coliform bacteria counts for tributaries to Onondaga Lake, 1998-2011.  Annual geometric mean values are presented for six sampling sites: (a) Harbor Brook-Velasko, (b) Harbor Brook-Hiawatha, (c) Onondaga Creek-Dorwin, (d) Onondaga Creek-Kirkpatrick, (e) Ley Creek-Park, and (f) Ninemile-Route 48. 57

Figure 4-11.      Time series of fecal coliform bacteria counts for Onondaga Creek at Kirkpatrick Street, 1998-2011.  Annual geometric mean values are presented for three data sets: (a) all data, (b) dry weather data, and (c) wet weather data. 58

Figure 5-1.        Summer (June to September) average total phosphorus concentration in the upper waters (0-3 meters) of Onondaga Lake, 1990-2011. 64

Figure 5-2.        Summer (June to September) algal bloom percent occurrences in Onondaga Lake evaluated annually for the 1990 - 2011 period, based on chlorophyll-a measurements. 66

Figure 5-3.        Chlorophyll-a concentration, January to December, 1998-2011. 66

Figure 5-4.        Summer (June to August) average total phosphorus (TP) and chlorophyll-a concentrations in Onondaga Lake compared with selected regional lakes.  (a) The top panel shows Onondaga Lake concentrations pre-Actiflo® (1998-2005) and post-Actiflo® (2006-2011).  (b) The bottom panel represents the same data, scaled to show the 2007-2011 Onondaga Lake data and a best-fit trendline (R2 = 0.97) of the Finger Lakes concentrations (1996-1999). 67

Figure 5-5.        Secchi disk transparency, Onondaga Lake South Deep, 2011. 68

Figure 5-6.        TSI conditions based on summer average (June 1 – September 30) data, 1998-2011 (a) total phosphorus (0-3 meters) , (b) chlorophyll-a (upper waters), (c) Secchi disk transparency. 69

Figure 5-7.        Minimum dissolved oxygen (DO) concentration in the upper waters (0-3 meters) of Onondaga Lake during October, annually 1990 – 2011. 70

Figure 5-8.        First date of measured anoxic conditions at 15m depth, Onondaga Lake, 1990 – 2011.  No observation for 1993 because the lake failed to turnover in spring of that year. 71

Figure 5-9.        Volume-days of anoxia (dissolved oxygen less than 0.5 mg/L) and hypoxia (dissolved oxygen less than 2 mg/L), in Onondaga Lake during the summer, 1992-2011. 71

Figure 5-10.      Annual average ammonia concentrations in the upper waters (0-3 meters) of Onondaga Lake, 1990-2011.. 72

Figure 5-11.      Fecal coliform bacteria results for nearshore stations in Onondaga Lake, April – October 2011. 74

Figure 5-12.      Relationship between summer average lake total phosphorus (TP) concentrations (0-3 meters, June to September) for the 1999 to 2011 period and (a) Metro total phosphorus loading (based on water year) and (b) total (Metro + tributary) total phosphorus loading (based on water year). 79

Figure 5-13.      Summer average ratio of total nitrogen to total phosphorus (N:P) in the upper waters of Onondaga Lake, 1998‐2011. Error bars represent plus and minus 1 standard error. 80

Figure 5-14.      Time-series of concentration values in the deep waters of Onondaga Lake, 2000 to 2011: (a) daily average dissolved oxygen concentrations at 15 meters depth, and (b) lower water layer (LWL) nitrate concentrations and soluble reactive phosphorus concentrations from 15 meters depth. 81

Figure 6-1.        Onondaga Lake phytoplankton standing crop, 1998-2011. The heavy line is a 3 point moving average. 83

Figure 6-2.        Proportional biomass of phytoplankton divisions, 2011. 83

Figure 6-3.        Phytoplankton community structure and biomass, 2011. 84

Figure 6-4.        Macrophyte distribution, 2000 2011. 85

Figure 6-5.        Aquatic plant coverage, 2000 and 2011. 85

Figure 6-6.        Average zooplankton size (all taxa combined) and alewife catch rates from electrofishing, 2000-2011, Onondaga Lake. 87

Figure 6-7.        Mean Secchi disk depth measurements and mean zooplankton size, Onondaga Lake, 1999 – 2011. 87

Figure 6-8.        Average biomass of zooplankton, proportion of major groups. 88

Figure 6-9.        Biomass of various Daphnia species in Onondaga Lake. 88

Figure 6-10.      Average size of all crustacean zooplankton in Onondaga Lake, 1996 2011. Error bars represent standard error. 89

Figure 6-11.      Average crustacean zooplankton length (mm), 2009 through 2011.  Lines are the 2 point moving average for each year. 89

Figure 6-12.      Dreissenid mussel average density and biomass with standard deviation, 2002-2011. 91

Figure 6-13.      Relative abundance of dreissenid mussels, 2002-2011. 91

Figure 6-14.      Nesting survey map and comparison of north vs. south-2011. 94

Figure 6-15.      2011 Young-of-year Catch per Unit Effort (CPUE) distribution by stratum and species. Data indicate where young-of-year fish were caught in the lake during 2011, as well as the percentage of species captured in each stratum. 95

Figure 6-16.      Bass (smallmouth and largemouth adults) captured by electrofishing in Onondaga Lake, 2000 – 2011. 97

Figure 6-17.      Relative importance of brown bullhead in characterizing DELTFM abnormalities in Onondaga Lake fishes, 2003-2011. 100

Figure 6-18.      Fish space metric, 2010, for coldwater and coolwater species. 103

Figure 7-1.        The Three Rivers System, with AMP sampling locations and wastewater treatment plants identified. 104

Figure 7-2.        2011 hydrographs for Seneca River at Baldwinsville and Oneida River at Euclid, with survey dates identified. 106

Figure 7-3.        Dissolved oxygen patterns in the Three Rivers System on (a) 7/13/11, (b) 8/31/11, 9/28/11. 107

 

 

 


 

 

 


Executive Summary

Introduction

This Annual Report of Onondaga County’s Ambient Monitoring Program (AMP) describes the state of Onondaga Lake in 2011.  Conducted annually since 1970, the County’s monitoring program provides water resource managers, public officials, state and federal regulators, and the entire community a window into the significant changes evident in Onondaga Lake – both in the lake’s water quality conditions and in its biological community.

Changes in the lake ecosystem are the result of multiple factors.  Some of these factors reflect human intervention, notably, the significant investment in improved wastewater treatment technology and the ongoing efforts to remediate legacy industrial wastes.  Other changes in the Onondaga Lake ecosystem reflect biological factors such as the fluctuating population of the alewife and its cascading effects on the lake’s food web.  The 2011 Annual Report documents the input of water and materials (bacteria, sediment, nutrients, salts) to Onondaga Lake from the watershed and the Metropolitan Syracuse Wastewater Treatment Plant (Metro).  The lake’s response to these inputs is a focus of the annual program; the AMP examines water quality conditions, compliance with ambient water quality standards (AWQS), and long-term trends.  The AMP also examines the species composition and abundance of fish, phytoplankton, zooplankton, benthic invertebrates, aquatic plants, and dreissenid (zebra and quagga) mussels.

The Executive Summary highlights selected measures of the lake’s current water quality and biological conditions, and reports on long-term changes brought about by rehabilitation efforts.  Following this brief summary is the main body of the 2011 Annual AMP Report, where the results are discussed in more detail and supporting documentation is provided.

Report Format

The 2011 AMP annual report is a concise summary of major findings with hyperlinks to a library of related materials, including tables and graphs of historic data, and reports of biological sampling.  This paperless format was developed to advance two objectives: first, to reach a broader audience, and second, to continue to find ways to reduce our environmental footprint, through a commitment to green initiatives (for more information on Onondaga County’s green initiatives visit http://www.savetherain.us).  This format was envisioned as a means to enable Onondaga County leaders and citizens to learn about the condition of Onondaga Lake and its watershed.  Additional program information is available on the County web site http://www.ongov.net/wep/we15.html.  Annual reports from prior years are posted at http://www.ongov.net/wep/we1510.html.

Dramatic Reductions in Ammonia and Phosphorus Loading to Onondaga Lake from Improved Wastewater Treatment

Major reductions in the loading of ammonia (NH3-N) and phosphorus (P) to Onondaga Lake from Metro have been achieved through implementation of state-of-the-art wastewater treatment technologies.  Progressive improvements in treatment have been made since the 1970s.  The most recent Metro upgrades were designed to meet specific water quality goals in Onondaga Lake.  Total Maximum Daily Load (TMDL) analyses established the loading reductions required to meet these water quality goals.

The Biological Aerated Filter (BAF) system, which came on line in January 2004, provides year-round nitrification of ammonia, a potentially toxic form of nitrogen (N).  This treatment resulted in a 98% decrease in the ammonia loading to the lake from Metro since the mid-1990s (Figure EX-1) and reduced Metro’s contribution to the total annual load (Metro + tributaries) from 91% to 42% (Figure EX-2).  Implementation of BAF treatment also reduced the loading of nitrite (NO2-N), another form of nitrogen that is a potentially toxic to aquatic organisms.  Loading of nitrate (NO3-N), yet another form of nitrogen, has increased as a result of the BAF treatment process.  However, this form of nitrogen is not a water quality concern in Onondaga Lake.  In fact, the increases in nitrate are having beneficial effects on the lake by diminishing the cycling of phosphorus and mercury in the lower waters and bottom sediments.

A physical-chemical High-Rate Flocculated Settling (HRFS) treatment technology, known as Actiflo®, came on line in February 2005 to provide additional phosphorus removal.  This treatment resulted in an 85% decrease in total phosphorus (TP) loading since the early 1990s (Figure EX-3) and a 99% reduction since the early 1970s.  Metro’s contribution to Onondaga Lake’s total annual phosphorus load decreased from 61% prior to implementation of Actiflo® (1990-2004) to 20% in 2011 (Figure EX-4).

 

Figure EX-1.  Annual time plot of the daily average Metro ammonia (NH3-N) loading to Onondaga Lake, 1990-2011.

 

 

 

Figure EX-2.    Contributions of Metro and the watershed to the total annual input of ammonia to Onondaga Lake, average for 1990-2004 compared to 2011.

 

 

 

Figure EX-3.    Annual time plot of the daily average Metro total phosphorus (TP) loading to Onondaga Lake, 1990-2011.

 

 

 

 

Figure EX-4.    Contributions of Metro and the watershed to the annual input of total phosphorus to Onondaga Lake, average for 1990-2004 compared to 2011.

 

 

Remarkable Improvements in Onondaga Lake from Metro Upgrades

The inputs of ammonia, nitrite, and phosphorus from Metro caused severely degraded conditions in Onondaga Lake during earlier portions of the monitored record.  Violations of water quality standards to protect against the toxic effects of ammonia and nitrite occurred frequently in the upper waters of the lake.  The high phosphorus loads caused a severe case of cultural eutrophication (major increases in the production of microscopic plants – phytoplankton).  Associated features of degraded water quality included: (1) high concentrations of phytoplankton, including nuisance conditions described as blooms; (2) low water clarity, as measured by a Secchi disk (SD); (3) high rates of deposition of oxygen-demanding organic material into the lower layers of the lake; (4) rapid loss of oxygen from the lower layers of the lake; and (5) depletion of oxygen in the upper layers of the lake during the fall mixing period.

In the context of lake rehabilitation examples from North America and beyond, the water quality improvements in Onondaga Lake have been extraordinary.  While lakes usually respond to reductions in nutrient inputs, the response is often slow and the degree of improvement less than expected (Cooke et al. 2005).  In contrast, water quality improvements in Onondaga Lake were both substantial and rapid following Metro upgrades.  Violations of the ammonia and nitrite standards were eliminated by implementation of the BAF treatment process.  The reductions in ammonia concentrations in the upper waters of the lake (Figure EX-5) have enabled a more diverse biota.  In 2008, New York State Department of Environmental Conservation (NYSDEC) removed Onondaga Lake from the state’s 303(d) list for impairment by excessive ammonia concentrations.

 

 

Figure EX-5.        Annual average ammonia concentrations in the upper waters (0-3 meters) of Onondaga Lake, 1990-2011.

 

 

Substantial decreases in the summer average (June to September) concentration of total phosphorus in the upper waters of the lake have been achieved from the Actiflo® upgrade (Figure EX-6).  The summer average concentration in 2011 matched the guidance value of 20 micrograms per liter (µg/L) established by New York State.  Values of less than 20 µg/L were observed in 2008 and 2009.  Similar total phosphorus concentrations are observed in several nearby lakes with intermediate levels of phytoplankton production.  Loading of soluble reactive phosphorus (SRP), a form of phosphorus immediately available to support algal growth, was also reduced significantly as a result of Actiflo® treatment.  Occurrences of phytoplankton blooms, subjectively defined as chlorophyll-a concentrations of 15 µg/L and 30 µg/L for minor (impaired conditions) and major blooms (nuisance conditions), respectively, have decreased dramatically since implementation of Actiflo® (Figure EX-7).  No major blooms have occurred since the upgrade, and no minor blooms have occurred during summer since 2008.  A minor bloom was observed in May of 2011, prior to the summer averaging period.  Water clarity has also improved, though biological (food web) effects also cause noteworthy variations in this water quality metric.

The reductions in phytoplankton from decreases in phosphorus loading have led to less deposition of organic matter (settling phytoplankton) and thereby reduced oxygen demand in the lower layers of the lake.  As a result, the oxygen resources of the lower layers have improved, according to a metric termed “volume-days of anoxia” (Figure EX-8), which takes into account both the volume of the lake affected by low dissolved oxygen concentrations and the duration of these conditions.  Two different low oxygen thresholds are presented (Figure EX-8), corresponding to hypoxia (less than 2 milligrams per liter (mg/L) and anoxia (less than 0.5 mg/L).  Decreasing (improving) trends are shown for both thresholds.  The oxygen status of the upper waters through the fall mixing period has also improved substantially, as indicated by the recent higher annual minima in oxygen concentration (Figure EX-9).  Oxygen concentrations in the upper waters have remained well above the standard to protect aquatic organisms since Actiflo® was implemented.

 

Figure EX-6.      Summer (June to September) average total phosphorus concentration in the upper waters (0-3 meters) of Onondaga Lake, 1990-2011.

 

 

Figure EX-7.      Summer (June to September) algal bloom percent occurrences in Onondaga Lake evaluated annually for the 1990 - 2011 period, based on chlorophyll-a measurements.

 

 

 

Figure EX-8.    Volume-days of anoxia (dissolved oxygen less than 0.5 mg/L) and hypoxia (dissolved oxygen less than 2 mg/L), in Onondaga Lake during the summer, 1992-2011.

 

 

 

Figure EX-9.    Minimum dissolved oxygen (DO) concentration in the upper waters (0-3 meters) of Onondaga Lake during fall turnover (October), annually 1990 – 2011.

 


 

Improved Water Quality Reflected in a Changed Biological Community 

The reduction in phosphorus and algae has resulted in clearer water throughout the lake.  Light penetrates deeper into the lake, and supports the growth of macrophytes (rooted aquatic plants and bottom-dwelling algae) in nearshore shallow waters (littoral zone).  Macrophytes are an important component of the lake’s ecology; they produce food for other organisms, provide habitat for aquatic invertebrates, fish, and wildlife, and help stabilize sediments. The percent of the littoral zone with macrophytes has increased greater than four-fold since 2000 (Figure EX-10).  The increasing macrophytes provide spawning and nursery habitat, shelter and food for the fish community.  Electrofishing catch rates of gamefish such as largemouth bass have generally increased since 2000, while the catch of smallmouth bass is declining (Figure EX-11).

Several important metrics of the fish community consider the diversity and richness of the adult fish community, both littoral (near-shore) and pelagic (open water). Richness is a count of the number of species within a community, while diversity considers both the number of species present and their relative abundance. In Onondaga Lake, richness has fluctuated annually since the start of the AMP with 25 species captured during spring and fall electrofishing surveys in 2011.  Surveys conducted since 1987 have identified a total of 64 fish species in the lake, making the species richness of Onondaga Lake comparable to that of regional waters.  The lake is an open system, with easy migration into and from connected waterways through the Seneca River system. 

Diversity of the fish community fluctuates in response to the periodic peaks and crashes of two species of clupeid: the alewife (Alosa pseudoharengus) and gizzard shad (Dorosoma cepedianum). Abundance of these two species of the herring family is highly variable, as Onondaga Lake is near the northern edge of their range, and both species periodically exhibit significant winter mortality.  Extremes in recruitment are common; both species periodically produce very strong year classes that dominate the catch for years, as individual fish can live 10 years or longer.  In 2011, clupeids dominated the lake fish community, with alewife and gizzard shad combined representing 90% of the fish observed (boated and estimated number of fish combined), and 52% of the netted catch (fish boated and counted); yellow perch and pumpkinseed sunfish were the next dominant species.

Onondaga Lake’s aquatic food web continues to include new species, both native and exotic, with increasingly complex pathways of material and energy transfer among the different life stages.  This increasing complexity with regard to energy sources and energy flow results in an ecosystem that may be more resilient to environmental stress.  The results of the 2011 AMP indicate that this is an ongoing process and that more changes are likely to occur.  As lake water quality continues to improve, resulting in more diverse and higher quality habitat conditions, increases in aquatic species diversity, abundance, and interrelatedness can also be expected.