Lars G. Rudstam Christopher Hotaling Russ D. McCullough Dave Lemon Web Pearsall Jana Lantry Michael J. Connerton Steve LaPan Zy Biesinger Brian F. Lantry Maureen Walsh Brian Weidel Kristen T. Holeck 2016 <ol><li>Offshore spring total phosphorus (TP) in 2015 was 4.2 μ g/L, the same as in 2014; this is lower than 2001 - 2013, but there is no significant time trend 2001 - 2015. Offshore soluble reactive phosphorus (SRP) was very low in 2015; Apr/May - Oct mean values were &lt;1 μ g/L at most sites. SRP has been stable in nearshore and offshore habitats since 1998 (range, 0.4 – 3.3 μ g/L). TP concentrations were low at both nearshore and offshore locations (range 4.2 - 8.1 μ g/L), and TP and SRP concentrations were significantly higher in the nearshore as compared to the offshore (6.8 μ g/L vs 4.8 μ g/L, TP; 1.1 μ g/L vs 0.7 μ g/L, SRP).</li><li>Chlorophyll-<i>a</i> and Secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll- a declined significantly 2000 - 2015. Nearshore chlorophyll- a increased 1995 - 2004 but then declined 2005 - 2015. Epilimnetic chlorophyll-<i>a</i> averaged between 0.9 and 1.9 1 μg/L across sites, and offshore concentrations (1.4 1 μg/L) were significantly higher than nearshore (1.1 μg/L). Summer Secchi depth increased significantly in the offshore 2000 -2015 and showed no trend in the nearshore, 1995 - 2015. Apr/May - Oct Secchi depth ranged from 5.0 m to 13.0 m at individual sites and was higher in the offshore (9.5 m) than nearshore (6.2 m).</li><li>In 2015, Apr/May - Oct epilimnetic zooplankton density, size, and biomass were not different between the offshore and the nearshore, but cyclopoid biomass was higher in the offshore (8.3 mg/m 3 vs 2.0 mg/m³) and <i>Bythotrephes</i> biomass was higher in the nearshore (0.17 mg/m³ vs 0.04 mg/m³).</li><li>Zooplankton density and biomass peaked in September, an atypical pattern. This coincided with peaks in calanoid copepod, daphnid, and <i>Holopedium</i> <i>Holopedium</i> biomass in the nearshore has increased significantly since 1995.</li><li>The predatory cladoceran <i>Cercopagis</i> continued to be abundant in summer in the nearshore (3.4 μ g/L) but not in the offshore (0.8 μ g/L). <i>Bythotrephes</i> biomass was very low (&lt;0.3 μ g/L) in both nearshore and offshore habitats. Combined biomass of these predatory cladocerans in the offshore was the lowest recorded since 2001.</li><li>Summer nearshore zooplankton density and biomass declined significantly 1995 - 2004 and then increased significantly 2005 – 2015. The decline was due to reductions in bosminids and cyclopoids and the increase was due mostly to a rebound in bosminids.</li><li>Summer offshore zooplankton density and biomass increased significantly 2005 - 2015. The increase was due to an increase in bosminids and cyclopoids. In 2015, offshore summer epilimnetic zooplankton biomass was 52 mg/m³ (2005 - 2014 mean=18 mg/m³).</li><li>Most zooplankton biomass was found in the metalimnion in July and in the hypolimnion in September. Cyclopoids and <i>Limnocalanus</i> dominated the metalimnion and <i>Limnocalanus</i> dominated the hypolimnion. Whole water column samples taken show a stable zooplankton biomass but changing community composition since 2010. Cyclopoids increased 2013 - 2015 and daphnids declined 2014 - 2015.</li></ol> application/pdf en New York State Department of Environmental Conservation 2015 status of the Lake Ontario lower trophic levels reports