RECENT CHANGES IN PRIMARY PRODUCTIVITY AND PHYTOPLANKTON DYNAMICS Gary Fahnenstiel Great Lakes Research Center Michigan Tech Research Institute Michigan Technological University And Water Center Graham Environmental Sustainability Institute University of Michigan COLLABORATORS: Mary Anne Evans USGS Tom Nalepa -UM Steve Pothoven- NOAA/GLERL Don Scavia - UM Bob Shuchman- MTU
Primary Productivity in Great Lakes Long History of Measurements Dominated by C-14 measurements First C-14 measurements in Grand Traverse Bay, LM in 1959 (Saunders et al. 1962) Over >50 studies have measured the rate of primary production (almost all in bottles) Reasonable In situ rates== (in vitro vs. in situ ) Many measurements but estimates limited to specific places and times Lake-wide estimates are lacking (i.e., large size, limited field measurements, etc.)- new approaches necessary that will use a combination of techniques Big Wind Event Day 153 (June 2) EPISODIC EVENT IN 1998 RESPONSIBLE FOR 25% OF ANNUAL PRODUCTION
REMOTELY SENSED PRODUCTION----- WIM-GLPPM ( I o, K d, Chl, P-E)---- Field Measurements Shuchman et al. 2013a
FEAST/FAMINE--- EUTROPHICATION/OLIGOTROPHICATION IN GREAT LAKES 1950s-1970 Increase in P loading to lakes 1972-1990 Mandated P reductions, P loadings reduced and water quality improves (lower P, Chl and 1 0 Production, fewer algal blooms) 1988-1997 Dreissenid mussels invasion and colonization of all lakes. First zebra mussels in shallow regions and then quagga mussels in deeper water 2000-2010 Quagga mussel populations explode in profundal regions of all lakes except Superior
Primary Production (mg/m2/d) Typical Zebra Mussel Shallow Water Impact in 1990s- Saginaw Bay, Lake Huron Saginaw Bay Primary Producers After Zebra Mussels 1200 1000 800 Phytoplankton Benthic Algae (450 mg/m2/d) 600 Zebra Mussels 400 200 0 75 80 85 90 95 Year
Creation of new microhabitat in Dreissenid areas (Increased nutrient cycling and water transparency) NEARSHORE SHUNT--- Hecky et al. 2004 Nearshore/shallow water impact of mussels PRE RETENTION OF NUTRIENTS NEARSHORE-more algae SAGINAW BAY Cha et al. 2011 POST
>900 Trillion Dreissenids in Lake Michigan (99% Quaggas) Nalepa
Offshore Pelagic Primary Productivity Trends (mgc/m2/d) SE Lake Michigan (100-110 m stations) Tremendous decrease in spring 2007/10 (60-70%) Annual decrease > 30%
Chlorophyll a (mg/m3) Chlorophyll a (mg/m3) Chlorophyll a (mg/m3) Phytoplankton biomass measured as chlorophyll a (surface-mixed layer) 4.00 a A SPRING 3.00 b 2.00 1.00 c 0.00 1983-87 1995-98 2007-08 2.00 C SUMMER 3.00 EARLY FALL a a a 2.00 a a a 1.00 1.00 0.00 1983-87 1995-98 2007-08 0.00 Large decrease in spring isothermal period 2007/09 (70%)
Phytoplankton Compositional Changes in 2007/10 Diatom biomass (mg/m3) Cyanobacteria biomass (mg/ m3) Spring diatoms decreased significantly especially large net diatoms 40.0 30.0 20.0 Spring Diatoms 10.0 Cyanobacteria (BGs) did not decrease (only group) Low absolute abundance in 1980s and 1990s but now similar to diatoms 0.0 4.00 3.00 2.00 1.00 1980s 1990s 2007/08 per iod Spring BGs 0.00 1980s 1990s 2007/08 period Large Relative Increase in Autotrophic Picoplankton (<2µm) Biomass Pre-Quagga (1990s) Post Quagga (2009) >2 µm Phyto. 40 6 Picoplankton 5 4
Secchi Disk LESS PHYTOPLANKTON - LARGE INCREASE IN WATER CLARITY 20.0 Spring Isothermal Secchi Disk 15.0 10.0 5.0 1985/89 1995/98 2007/10 In 2010 Secchi disk transparency as high as 32 m in northern LM
WHY BIG CHANGES IN SPRING?? Only time of year Dreissenid filtering is linked to entire water column (mixing period).. Isothermal mixing
Chl a (ug/l) Temperature (C) 2011 to 2012 Moored thermistors and fluorometer at M110 9 8 7 6 5 4 3 2 1 0 300 350 400 450 500 Series1 Series2 1m above bottom 100 m above bottom (10 m from surface) 2.5 2 1.5 40 m off bottom 1 0.5 0 300 350 400 450 500 Julian Day
What about below surface-mixed layer in summer??? DEEP CHLOROPHYLL LAYER in Lake Michigan (mid stratification feature) Relationship to Spring Diatom Bloom Spring diatoms settle out and are abundant in DCL
What happened to Deep Chlorophyll Layer in Lake Michigan?? Why??- Relationship to Spring Diatom Bloom and less P
Link to lakewide and other lakes 1. Documented large changes in productivity and diatom abundance at two stations in southern basin of Lake Michigan- How representative of entire lake? Other lakes?? 2. GLNPO/EPA monitors 11-18 stations in offshore region lakes Michigan, Huron and Superior collecting a suite of limnological parameters. 3. Silica is required by diatoms and the depletion of dissolved silica can be used as a measure of diatom and phytoplankton production (silica depletion hypothesis) 4. Use difference between early spring and summer dissolved Si concentrations as indicator of diatom production in Lake Michigan (silica depletion hypothesis)
Silica (mg/l) Lake Michigan Seasonal Si Utilization (Indicator of Diatom Production) 1 0.9 0.8 0.7 Spring 0.6 0.5 0.4 Drawdown 0.3 0.2 Summer 0.1 0 1980 1985 1990 1995 2000 2005 2010 EPA_GLNPO data Closed symbols, northern basin Open symbols, southern basin
Silica utilization (mg/l) MI/HU Silica Drawdown Becoming like Lake Superior 0.7 0.6 Michigan 0.5 0.4 0.3 Huron 0.2 0.1 0 Superior 1980 1990 2000 2010 EPA_GLNPO data Closed symbols, northern basin Open symbols, southern basin
Silica utilization (mg/l) MI/HU Silica Drawdown Becoming like Lake Superior 0.7 0.6 Michigan 0.5 0.4 0.3 Huron 0.2 0.1 0 Superior 1980 1990 2000 2010 EPA_GLNPO data Closed symbols, northern basin Open symbols, southern basin
Nearshore Shunt and Nearshore/shallow water impact of mussels PRE Hecky et al. 2004 RETENTION OF NUTRIENTS NEARSHORE Abundant Populations of Quagga Mussels In Profundal Regions of Great Lakes--Decreased Phytoplankton Abundance and Productivity and Increased Water Clarity (BENTHIFICATION OF GREAT LAKES) POST Creation of new habitat in Dreissenid areas H. Bootsma Hinderer et al. 2011 NWF REPORT
28% of mapped nearshore habitat in Lake Michigan is occupied by Cladophora or other SAV Shuchman et al. 2013b
GREAT LAKES Lake Total mapped area (km 2 ) Area of mapped SAV (km 2 ) Percent SAV Michigan 4390 1220 28 Huron 4371 664 15 Erie 532 158 30 Ontario 789 317 40 What about 70% of nearshore zone that does not have significant Cladophora or other benthic algae Shuchman et al. 2013b
Primary Production (mgc/m2/d) 1500 Lake Michigan Primary Production 2009 Stations M15 Nearshore M45 Mid Depth M110 Offshore 1000 500 0 50 100 150 200 250 300 350 Julian Day No strong variation in nearshore-offshore production
Primary Production (mg/m2/d) 1600 Nearshore Primary Production Black and Blue lines from Fee 1973 (redrawn) 1200 800 400 0 50 100 150 200 250 300 350 Julian Day Large decrease in nearshore production->50% (likely as much as 70%) Much larger decrease than offshore and little/no increase in benthic algae production
FINAL POINTS Large decreases in phytoplankton productivity and abundance in last 25 years in Great Lakes due primarily to filtering activities of Dreissenid mussels (shallow nearshore zones-zebra, as well as deep profundal regions-quagga). Phosphorus load reductions also played a role but were masked by Dreissenid effect. In some shallow nearshore zones (< optic depth) a large increase in benthic algae (Cladophora) In most of the shallow nearshore regions primary productivity has decreased in last 25 years In deeper nearshore zones (> OD- < CD, 20-50 m for oligotrophic regions) benthic algal abundance and production uncertain-- large? Dreissenid mussels a large selective force on the structure of phytoplankton composition Recent changes in nutrient cycling in both offshore and nearshore region poorly understood Not Rocket Science-Much More Complicated - H. Vanderploeg
TP:Chl 5 NUTRIENT STUFF-Spring 4 3 2 1 0 1983-87 1995-98 2007-09 But Phytoplankton Physiological Indicators Suggest More P Deficient Communities After Quaggas Pre-Quaggas Post-Quaggas 1995-1999 2007-2010 Part. C:P Low Moderate Popt:Vmax Low Moderate Increased SRP and TDP SELECTIVE FORCES OF MUSSELS ON PHYTOPLANKTON GRAZING: Large (>200 µm) and Small (< 2 µm) Nutrient Recycling NEED WORK P kinetics (V max ) and Storage Lower P max and Growth Rates (?)
Mean Density (No. m -2 ) Mean Quagga Mussel Density, 30-90 m 15000 Lake Ontario Lake Michigan Lake Huron 10000 5000 0 1990 1995 2000 2005 2010 Year Source Lake Ontario data: Watkins et al. (2007), Lozano (unpubl.) lakes Huron and Michigan T. Nalepa
Zebra Mussel Quagga Mussel D. polymorpha D. rostriformis bugensis Intake Siphon >900 Trillion Dreissenids in Lake Michigan (99% Quaggas) Competitive Advantages -Cold water adapted (high filtering and reproductive rates) - Ability to live on soft substrates