Recent changes in Lake Erie Trophic Status? Jan J.H. Ciborowski University of Windsor & Gerald Matisoff Case Western Reserve University

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1 Recent changes in Lake Erie Trophic Status? Jan J.H. Ciborowski University of Windsor & Gerald Matisoff Case Western Reserve University

2 Important Variables and Issues Phytoplankton - primary producers - typically controlled by nutrients Total Phosphorus - key nutrient -controlled by inputs & recycling Dissolved oxygen - essential element Biological oxygen demand --> oxygen depletion (water & sediment) Control of phosphorus inputs --> improved trophic status ( s)

3 Water Mixing in Central Lake Erie Spring and Fall Epilimnion Summer and Winter Hypolimnion

4 M. Charlton Environment Canada

5 D. Rockwell - US EPA

6 Key Trends of Concern Very low phytoplankton biomass in central and eastern basins 2. Total phosphorus concentrations seem to be rising, even though 3. Inputs of Total phosphorus to Lake Erie have not risen much. 4. Oxygen demand in the central basin has not changed. 5. Central basin oxygen depletion continues in the hypolimnion. WHY?

7 A. Possible Environmental Influences i) Reduced size and/or increased persistence of hypolimnion Possible causes: warmer than normal summers (warmer surface water) longer than normal summers (more time for depletion) greater heating due to - clearer water - greater penetration by UV light (ozone depletion) 2002 Observations -late formation due to record cold May -rapid thinning due to wind &?warm summer --> rapid DO depletion -complete erosion by end of August

8 B. Possible Limits on Primary Production High grazing pressure (especially by zebra & quagga mussels)? -Possibly: lowest Chl a in nearshore (analysis in progress); but dreissenid densities are declining - Phytoplankton biomass increasing, but size much reduced - Significant hypolimnial primary production Nutrient limitation in subsurface epilimnetic water? (phosphorus or nitrogen) - limited evidence later in summer (minor); not spring Trace metal limitation (iron, copper or zinc)? - nothing conclusive; picoplankton most responsive UV + contaminant-induced inhibition? - lab evidence; not evaluated in 2002

9 C. Increased Phosphorus Loadings? Recent calculations ( Dolan & McGunagle 2002) suggest minimal increases from point sources. Loadings driven by largely weather. Uncertainty due to: i). - possible under-reporting from point sources - less sensitive detection limits (unlikely to be significant) - reduced data from tributaries (sample frequency & number of tributaries) ii). -unusually strong autumn storms - increased runoff from land (nonpoint sources) - erosion and resuspension of sediments in deltas (umeasured pulses of total phosphorus?)

10 Preliminary Results: C. Increased Phosphorus Loadings? Direct Industrial Discharge Direct Municipal Discharge Atmospheric Adjustment for Unmonitored Area Indir Ind Disch Indir Mun Disch Tributary Monitored Lake Huron Input Dolan & McGunagle (UWGB)

11 Lake Erie Tributary Loading Monitored-Unmonitored Locations Uncertainty due to reduced data from tribs. (sample frequency & number of tributaries) Dolan & McGunagle (UWGB)

12 D. Increased Rates or New Pathways of Internal Cycling? Noel Burns (trend analysis of EPA & EC data) Eutrophy has trended downward over the past 18 years (Carlson Trophic State Index values ) Deseasonalized TP has been falling by 0.2 mg/m 3 /y (Burns) but spring TP has been dramatically increasing since 1995 Deseasonalized water temperature has risen by 0.4 degees in 18 years Deseasonalized hypolimnial oxygen demand has been rising by 0.03 mg/m 3 /y.

13 Food web disruptions caused by Invaders? Nearshore shunt model R. Smith et al. Univ. of Waterloo External loading Nearshore Pelagic Benthic Zebra mussels established Profundal Buried

14 Preliminary Results: D. Increased Rates/New Pathways of Internal Cycling? Possibly: Hypolimnial increases in [Chl a] in late summer (Ostrom) Evidence of high hypolimnial and benthic primary production & equally high respiration in C & E basins (Ostrom) Cyanobacterial abundances significant in several locations - those with highest dreissenid densities (Smith et al.) Consistent evidence of algal benthification (various) Biologically mediated altered particle dynamics?

15 Preliminary Results: Other Preliminary Observations Physical conditions play a major role in hypolimnial characteristics and persistence Sedimentary: Elemental analysis may permit reconstruction of historical oxygen demand Increasing R max through summer Planktonic: Strong spring epilimnetic bloom; high turbidity and TP (Rockwell) Hypolimnion seems to be biologically very active: both Ps and Respiration high in 2002 (Carrick) Little evidence that bacteria are P-limited; major limitation seems to be carbon (Heath)

16 Preliminary Results: Other Preliminary Observations Benthic processes: Hexagenia mayfly densities stable or declining (Ciborowski; Krieger) dreissenid densities declining; (Culver, Barton) quaggas only in E. basin; mostly quaggas in centre; zebras in W basin Gammarus densities declining (Barton, Ciborowski) Echinogammarus increase not continuing (Barton) significant loss of shoreline benthic diversity (caddisflies, mayflies) (Barton) Cladophora beds expanding; anoxic beneath (Hecky et al.) --> chironomids, worms, gammarids Consistent evidence of algal benthification (various)

17 Summary of Preliminary Findings Weather conditions are playing a significant role (short and long-term) Strong spring epilimnetic blooms; slowed settling rates Hypolimnion is biologically very active Dramatic changes in benthic processes in shallow and deep waters Possible key drivers: -climate change -consequences of habitat degradation -invaders

18 LAKE ERIE TROPHIC STATUS PROJECT - Strong Inference Summary Results Work consistent with in Possible Explanations: Explanation? Progress YES NO N/A 1. Observations may represent situations that have naturally occurred at regular or irregular intervals through time prior to that for which intensive monitoring data are available. G G G 2. Loading estimates are wrong/incomplete G G G 3. Climatic/physical/biogenic factors are increasing flux from sediments G G G 4. A) i) reduced size and/or G G G ii) increased persistence G G G of the central basin hypolimnion, possibly accompanied by B) increased rates of sediment oxygen demand or G G G C) a change in autotrophic:heterotrophic C fixation G G G 5) reduced benthic and/or planktonic primary production caused by A) high grazing pressure G G G B) nutrient limitation G G G C) trace metal limitation and/or G G G D) UV or contaminant-induced inhibition of photosynthesis G G G 6) increased net rates of organic C accumulation in hypolimnetic areas G G G Which of these linkages are controlling factors and which are cofactors?

19 LAKE ERIE TROPHIC STATUS PROJECT - Strong Inference Summary Results Work consistent with in Possible Explanations: Explanation? Progress YES NO N/A 1. Observations may represent situations that have naturally occurred at regular or irregular intervals through time prior to that for which intensive monitoring data are available. G G G 2. Loading estimates are wrong/incomplete G G G 3. Climatic/physical/biogenic factors are increasing flux from sediments G G G 4. A) i) reduced size and/or G G G ii) increased persistence G G G of the central basin hypolimnion, possibly accompanied by B) increased rates of sediment oxygen demand or G G G C) a change in autotrophic:heterotrophic C fixation G G G 5) reduced benthic and/or planktonic primary production caused by A) high grazing pressure [dreissenid-rich areas] G G G B) nutrient limitation G G G C) trace metal limitation and/or G G G D) UV or contaminant-induced inhibition of photosynthesis G G G 6) increased net rates of organic C accumulation in hypolimnetic areas G G G Which of these linkages are controlling factors and which are cofactors?

20 Variability in Total Phosphorus Concentration M. Charlton - Environment Canada CENTRAL BASIN Monthly Average 30 TP (uf) ug l Year

21 ACKNOWLEDGEMENTS Lake Erie Millennium Network