Gary Fahnenstiel RECENT CHANGES IN PRIMARY PRODUCTIVITY AND PHYTOPLANKTON DYNAMICS

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1 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

2 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

3 REMOTELY SENSED PRODUCTION----- WIM-GLPPM ( I o, K d, Chl, P-E)---- Field Measurements Shuchman et al. 2013a

4 FEAST/FAMINE--- EUTROPHICATION/OLIGOTROPHICATION IN GREAT LAKES 1950s-1970 Increase in P loading to lakes Mandated P reductions, P loadings reduced and water quality improves (lower P, Chl and 1 0 Production, fewer algal blooms) Dreissenid mussels invasion and colonization of all lakes. First zebra mussels in shallow regions and then quagga mussels in deeper water Quagga mussel populations explode in profundal regions of all lakes except Superior

5 Primary Production (mg/m2/d) Typical Zebra Mussel Shallow Water Impact in 1990s- Saginaw Bay, Lake Huron Saginaw Bay Primary Producers After Zebra Mussels Phytoplankton Benthic Algae (450 mg/m2/d) 600 Zebra Mussels Year

6 Creation of new microhabitat in Dreissenid areas (Increased nutrient cycling and water transparency) NEARSHORE SHUNT--- Hecky et al Nearshore/shallow water impact of mussels PRE RETENTION OF NUTRIENTS NEARSHORE-more algae SAGINAW BAY Cha et al POST

7 >900 Trillion Dreissenids in Lake Michigan (99% Quaggas) Nalepa

8 Offshore Pelagic Primary Productivity Trends (mgc/m2/d) SE Lake Michigan ( m stations) Tremendous decrease in spring 2007/10 (60-70%) Annual decrease > 30%

9 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 c C SUMMER 3.00 EARLY FALL a a a 2.00 a a a Large decrease in spring isothermal period 2007/09 (70%)

10 Phytoplankton Compositional Changes in 2007/10 Diatom biomass (mg/m3) Cyanobacteria biomass (mg/ m3) Spring diatoms decreased significantly especially large net diatoms Spring Diatoms 10.0 Cyanobacteria (BGs) did not decrease (only group) Low absolute abundance in 1980s and 1990s but now similar to diatoms s 1990s 2007/08 per iod Spring BGs s 1990s 2007/08 period Large Relative Increase in Autotrophic Picoplankton (<2µm) Biomass Pre-Quagga (1990s) Post Quagga (2009) >2 µm Phyto Picoplankton 5 4

11 Secchi Disk LESS PHYTOPLANKTON - LARGE INCREASE IN WATER CLARITY 20.0 Spring Isothermal Secchi Disk / / /10 In 2010 Secchi disk transparency as high as 32 m in northern LM

12 WHY BIG CHANGES IN SPRING?? Only time of year Dreissenid filtering is linked to entire water column (mixing period).. Isothermal mixing

13 Chl a (ug/l) Temperature (C) 2011 to 2012 Moored thermistors and fluorometer at M Series1 Series2 1m above bottom 100 m above bottom (10 m from surface) m off bottom Julian Day

14 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

15 What happened to Deep Chlorophyll Layer in Lake Michigan?? Why??- Relationship to Spring Diatom Bloom and less P

16 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 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)

17 Silica (mg/l) Lake Michigan Seasonal Si Utilization (Indicator of Diatom Production) Spring Drawdown Summer EPA_GLNPO data Closed symbols, northern basin Open symbols, southern basin

18 Silica utilization (mg/l) MI/HU Silica Drawdown Becoming like Lake Superior Michigan Huron Superior EPA_GLNPO data Closed symbols, northern basin Open symbols, southern basin

19 Silica utilization (mg/l) MI/HU Silica Drawdown Becoming like Lake Superior Michigan Huron Superior EPA_GLNPO data Closed symbols, northern basin Open symbols, southern basin

20 Nearshore Shunt and Nearshore/shallow water impact of mussels PRE Hecky et al 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 NWF REPORT

21 28% of mapped nearshore habitat in Lake Michigan is occupied by Cladophora or other SAV Shuchman et al. 2013b

22 GREAT LAKES Lake Total mapped area (km 2 ) Area of mapped SAV (km 2 ) Percent SAV Michigan Huron Erie Ontario What about 70% of nearshore zone that does not have significant Cladophora or other benthic algae Shuchman et al. 2013b

23 Primary Production (mgc/m2/d) 1500 Lake Michigan Primary Production 2009 Stations M15 Nearshore M45 Mid Depth M110 Offshore Julian Day No strong variation in nearshore-offshore production

24 Primary Production (mg/m2/d) 1600 Nearshore Primary Production Black and Blue lines from Fee 1973 (redrawn) 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

25 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, 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

26 TP:Chl 5 NUTRIENT STUFF-Spring But Phytoplankton Physiological Indicators Suggest More P Deficient Communities After Quaggas Pre-Quaggas Post-Quaggas 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 (?)

27 Mean Density (No. m -2 ) Mean Quagga Mussel Density, m Lake Ontario Lake Michigan Lake Huron Year Source Lake Ontario data: Watkins et al. (2007), Lozano (unpubl.) lakes Huron and Michigan T. Nalepa

28 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