Onondaga Lake water quality continues to improve in response to reductions in nutrient loading from the Metro wastewater treatment plant. However, the 2006 Lake conditions demonstrate the effect of a wet year on nutrient loading. Nonpoint source phosphorus input to the Lake increased in 2006 as a consequence of the above-normal precipitation and runoff. In response, Lake phosphorus and algal abundance showed a slight increase over 2005 conditions.
Dissolved oxygen content of the Lake has increased to the point where water quality standards are now routinely met during fall mixing. Algal blooms are diminishing and cyanobacteria (blue-greens) represent a minor component of the algal community. Improvements in the Lake have allowed the beds of aquatic plants to greatly expand; this has increased the amount of nesting and nursery habitat for the warm water fish community.
|Average ammonia-N concentrations in Metro Outfall 001, seasonal basis, 1995-2006|
Improvements to the county's wastewater collection and treatment system at the Syracuse Metropolitan Wastewater Treatment Plant (Metro) are primarily responsible for the improved water quality conditions in the Lake. Significant investment in wastewater treatment technology has achieved far lower discharges of wastewater-related pollutants, particularly ammonia and phosphorus.
Onondaga Lake had exhibited high ammonia concentrations for decades. Monitoring results from 1970 to 2002 documented that ammonia levels in the Lake waters were above New York State's ambient water quality standards designed to protect aquatic life. Effluent from Metro was the largest source of ammonia to the Lake, averaging about 90% of the total annual input. Recent improvements to Metro were designed to reduce ammonia levels in the treated effluent and bring the Lake's water quality into compliance with state standards.
|Average annual Metro ammonia load, Outfall 001|
The final stage of the Metro improvements for ammonia treatment came on-line in early 2004. The biological aerated filter (BAF) system has resulted in year-round nitrification (conversion of ammonia to nitrate) in wastewater. Prior to this final stage, various improvements to the treatment system had resulted in substantial reductions, particularly in the summer ammonia levels.
|Average daily phosphorus discharge from Metro,|
Enhanced phosphorus removal from wastewater is another objective of the Metro improvements currently underway. A high-rate flocculated settling (HRFS) physical-chemical treatment system (known as Actiflo) came on-line in 2005 to reduce effluent total phosphorus (TP) concentration.
This stage of
phosphorus treatment is designed to meet a 12-month
rolling average TP limit of 0.12 mg/L. Evaluation of
compliance with this limit began in April 2006,
following 12 months of operation. In 2006, Metro
effluent TP concentration met the 0.12 mg/L limit.
|Average annual Metro TP load, Outfall 001|
In 2006 Metro contributed about 29% of the total external phosphorus load to Onondaga Lake through outfall 001 (26%) and outfall 002 (2.7%). The remainder of the phosphorus load came from nonpoint sources throughout the 285 square mile watershed.
Bacteria concentrations were monitored at a network of near shore stations as well as at South Deep (the primary water quality monitoring site). In 2006, bacteria concentrations within the Class B portion of Onondaga Lake met the New York State ambient water quality standard for fecal coliform bacteria, which is meant to assess suitability for water contact recreation. However, concentrations in the Class C portion of the Lake, near the major southern tributaries and Metro discharge, were elevated following storms during the rainy summer of 2006. This result highlights the need for continued progress with CSOs, as well as the need for improved storm water management to reduce nonpoint source pollution from urban areas.
Dissolved oxygen (DO) levels continued to show improvement in response to reduced productivity in the Lake. The DO concentrations in surface water during the fall mixing period, a historically critical period in Onondaga Lake, were in compliance with regulatory standards.
Phosphorus concentrations in the Lake are declining as loading reductions are achieved at the wastewater treatment plant. In 2006, the summer average total P concentration was approximately 39 µg/L in the Lake's upper waters.
Chlorophyll-a concentration averaged 16.5 µg/L during the summer of 2006; the annual peak of 35 µg/L was measured at the end of March. Spring algal blooms are typical in Onondaga Lake. Moderate and variable algal levels were measured through much of the summer recreational period; slightly more than half exceeded 15 µg/L, the state-designated threshold of impaired suitability for recreational use. In 2006, cyanobacteria comprised about 2% of the total algal biomass. Nuisance algal blooms have been steadily diminishing, presumably in response to reductions in nutrient loads.
Water clarity of the Lake is variable both within and between years. A spring clear-water phase was evident from the mid-1990s through 2000 but is no longer typical. The loss of the clear water phase is attributed to biological factors, cascading from the proliferation of the alewife, as discussed below.
Zooplankton grazing is a significant factor affecting water clarity. Throughout the 1980s and 1990s, a spring clear-water phase was attributed to a seasonal peak in the abundance of larger zooplankton. However, larger zooplankton are now essentially absent from the Lake, and the spring clearing events have disappeared as well. Larger zooplankton, which are efficient grazers of phytoplankton, are the preferred food source of the fish species alewife. The reduction in population of the larger zooplankton taxa was evident in late summer 2002 when young-of-the-year alewives first became abundant. Alewives are now prolific in the Lake, and their effects are seen throughout the food web. Destruction of larger zooplankton by alewives caused a decline in total zooplankton biomass from 2003 to 2005 and a diminution in their average size. The average size of zooplankton is gradually improving from the minimum values measured in 2003.
are one of the most visible components of the
ecosystem. Results of the 2006 fish program indicate
that the community continues to be dominated by
warm water species. Popular game fish such as largemouth
and smallmouth bass are common and tend to be more
abundant in the northern basin. This spatial pattern
is consistent with the distribution of aquatic plants
and macroinvertebrates, demonstrating that the
northern basin provides better habitat quality. Other
game fish, such as walleye and northern pike, are
present but are far less common than bass. Pan fish,
such as yellow perch, pumpkinseed, and bluegill, are
abundant in near shore areas.
Of the twenty-nine fish species captured in Onondaga Lake in 2006, thirteen (45%) showed evidence of successful reproduction. The young-of-the-year community was dominated by largemouth bass, which represented 49% of the catch. Overall abundance of young fish was notably lower in 2006 compared with 2000-2005 results.
Alewife abundance was evaluated using hydroacoustics, gill nets, and electrofishing. Length frequency analysis indicated that a strong year class of alewife was produced in 2005 and is augmenting the strong 2002 year class. Abundance of alewives is high compared with regional lakes.
The New York State Department of Health (NYSDOH) produces an annual report detailing advisories for the consumption of fish and game in New York. The May 2007 report, "2007-2008 Health Advisories: Chemicals in Sport fish and Game," included a significant revision. The NYSDOH now advises that largemouth and smallmouth bass greater than 15 inches in length from Onondaga Lake should not be consumed because of elevated mercury concentrations.
Macrophytes (rooted aquatic plants and algae) have changed profoundly in recent years. The number of species has increased from five in 1991 to seventeen in 2005, although the community is still dominated by a few species. Percent cover of macrophytes increased about three-fold between 2000 and 2005. Year-to-year variability is evident from the annual aerial photographs; this variability is typical of other regional lakes. Much of the littoral zone has plant coverage within the ideal range for largemouth bass propagation. A notable feature of the 2006 macrophyte abundance was a collapse in July, most likely due to extreme rainfall and associated runoff.
Tributary macroinvertebrates were monitored in 2006. The combination of habitat degradation, nonpoint source pollution, and CSO discharges affects the streams' macroinvertebrate communities. In 2006 the macroinvertebrate communities of Onondaga Creek, Ley Creek, and Harbor Brook showed varying levels of impact. Sites in Ley Creek tended to be the most severely affected followed closely by Harbor Brook. Sites in Onondaga Creek tended to be the least affected. Only minor changes to the macroinvertebrate community have occurred since completion of baseline surveys in 1999-2000.
Onondaga County completed a focused water quality monitoring effort at selected stations along the Seneca-Oneida-Oswego river system in 2006. The wet summer of 2006 kept stream flow high in the Seneca River through most of the summer and prevented violations of ambient water quality standards for ammonia-N and nitrite-N. Frequent measurements using sondes detected brief periods where DO concentrations dropped below the standards. The river's water quality conditions continue to be strongly influenced by zebra mussels.