Disrupted Biogeochemical Cycles in the Great Lakes: Challenges and Opportunities for Aquatic Science

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1 Disrupted Biogeochemical Cycles in the Great Lakes: Challenges and Opportunities for Aquatic Science R.E. Hecky Large Lakes Observatory Biology Department University of Minnesota Duluth

2 Great Lakes of the World >60% of surface fresh water Canadian Great Lakes Laurentian Great Lakes Baikal African Great Lakes

3 The Great Lakes are easily visible from space and are the globe s most substantial freshwater resources.

4 All biogeochemical processes that occur in the oceans can occur in lakes Special characteristics of Great Lakes relative to coastal oceans: ) Unidirectional outflow ) Mass budgeting simplified at large spatial scales allowing geostrophic circulation and inertial currents of relevance to understanding coastal process ) Weak mixing relative to coastal ocean; absence of significant tides (affects of biogeochemical processes accumulate) 3) Nutrient concentrations are low especially P and therefore sensitive to change amplifying biogeochemical signal ) Logistically accessible; observations can be dense and at high resolution 5) Ionically dilute-simplifies geochemical modeling

5 Influence of internal cycling/recycling on lakes generally a function of Water Residence Time both on scale of whole lakes as well as locally within lakes while influence of external loading is associated with the Terrestrial Catchment to Lake Area (CA:LA) Water Residence Time (WRT=volume/inflows) CA:LA mean depth WRT NO 3 (m) (y) µmol/l Tanganyika <0.5 Malawi <0.5 Baikal Superior Great Bear Victoria. 0 3 <0.5 Michigan.6 99 Huron. 6 0 Ontario Erie.3.6 Kalff. 00. Limnology. Table 9-3 Bootsma and Hecky JGLR. Evans JAEHM. Weiss. 99. Nature.

6 Nutrient Inputs and Outputs External Loading: rivers, precipitation, dryfall N fixation Denitrification Recycling Internal Loading Outflow Burial Nutrient Loadings are measured per unit time: ) Easiest to measure Outflow ) Most difficult Internal loading 3) On a daily basis, most algal demand is met by recycling ) Concentrations are balance of internal and external loading

7 TP mol.l- 0 3 TN mol.l Victoria Arctic Ocean 3 Scotian Shelf Malawi 5 Slope 6 Sargasso NW Ont Large Lakes NW Ont Small Lakes 9 Superior Victoria Oceans Nyasa-Malawi Superior The GLOW cover the range of nutrient concentrations found in off shore surface waters of the oceans; Nyasa/Malawi has lowest TN and Victoria highest TP Guildford and Hecky 000

8 Common stresses among great lakes (and many smaller lakes): ) Eutrophication )Fisheries Exploitation 3) Exotic Species ) Contaminants 5) Climate Change

9 Great Lakes -Great Experiments 600s 00s 00s Exploration: Loss of innocence Exploitation: Forests, Fisheries, Mining and Transport Acculturation: Land Clearance, Agriculture, Settlement, Canalization, Urbanization Degradation: Disease, Collapse of Fisheries, Eutrophication, Contamination Restoration: GLFC, GLWQA, P and contaminant Management; habitat restored 990 Globalization: Faunal Marination and Climate Warming

10 Exploitation

11 >30 Demise of fisheries in deep lakes and extinction of 3 deepwater species; establishment of sea lamprey in the upper lakes from Christie (9) first official sighting of lamprey in the lakes

12 Acculturation

13 Great Lakes System Profile

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16 Degradation

17 Major ion concentrations were the first warning that biogeochemistry of the lakes was changing (Beeton, 96) Chapra et al. 0. JGLR.

18 P model of Chapra 9 for Lake Michigan from Schelske et al. 96 Modeling of P export from different landscapes and land uses as well as paleolimnological investigations could show that nutrient cycles of the water and air sheds of the lakes had been disrupted and the lakes were responding. Schelske and Hodell L&O

19 Chapra (9) Science

20 Restoration Dolan and Chapra (0) JGLR

21 GLWQA 9 asked governments to focus on reducing P emissions from point sources and removal of P from detergents to reduce eutrophication especially in the lower lakes (Erie and Ontario) Ohio Task Force on P in Lake Erie. 0.

22 Good News. Total Phosphorus (TP) Loading reductions have exceeded targets. Loading and its variability is now dominated by non-point sources (runoff) which respond to precipitation. The standard errors vary from.5 to 9% of the total lake load depending on the lake and the year. Lake Superior typically has larger standard errors (9.% of the load, on average), while Lake Erie has some of the smallest estimates (3.5% of the load, on average).

23 Too much good news? Openlake annual median values have been below targets especially since 990 when a better fit to the observed data can be realized by using a higher settling coefficient e.g. 9 to 9 m/y in Ontario Unexpected increase in settling velocity attributed to dreissenids and result is that Michigan, Huron and Superior are converging in their trophic status Chapra and Dolan. 0. JGLR

24 Ohio Lake Erie Phosphorus Task Force Report (OLEPTFR) Ohio EPA 00

25 Ohio Lake Erie Phosphorus Task Force Report (OLEPTFR) Ohio EPA 00

26 0 Lake Erie algal bloom largest on record

27 Settling correction is especially clear for Lake Ontario which initially agreed well with the model and is less subject to interannual variability as Niagara River dominates loading Niagara River Loading has remained high despite declining TP concentrations in Lake Erie suggesting changing conditions at Erie outflow

28 Shoreline Fouling Aesthetic complaints Taste and Odour complaints High bacterial counts (E.coli) Tea Krulos Tourism/Recreation Property Values Cost of Clean up

29 Biomass (g DM m - ) Growth is rapid in late spring and early summer as waters warm Apr -May 3-Jul -Sep -Oct 0-Dec 9-Jan

30 State of Phosphorus in the Great Lakes: State of Confusion State of the Lakes 009 Red is poor Green is good Diamond unchanging Rt. Arrow improving

31 Life was good except-

32 Globalization

33 Dreissenid mussels, Epibenthic filtering organism now occupies much of hard bottom substrata in all the lakes except Superior (where it is in the harbors)

34 Q: What are the effects of dreissenid mussels on nutrient cycling in the nearshore of the Laurentian Great Lakes? To answer, turn to knowledge gained from estuarine and marine coastal environments.

35 Top-down effects of filter feeding bivalves Clear phytoplankton, small zooplankton, some detritus Clearance rate is a function of temperature, food flux to the bivalve bed (a function of physical processes and food density) Possible control of phytoplankton biomass when bivalve density is high, water residence time is longer than clearance time, phytoplankton not strongly nutrient limited

36 Bottom-up effects of filter feeding bivalves Concentrates nutrients into bivalve biomass, feces and pseudofeces ( biodeposits ), releases soluble nutrients at benthos Evidence of increased benthic fauna diversity and biomass Evidence of increase flora (seagrasses, red macroalgae)

37 dreissenid mussels have been credited with reengineering nutrient flux and distribution in the lower Great Lakes as well as improving nearshore water clarity Pre-mussels: Post-mussels: Nearshore Shunt Hypothesis: Hecky et al. Can. J. Fish. Aquat. Sci. 00

38 Depth (m) Dreisenna influences on Cladophora growth Increased Phosphorus to benthos -Increase in SRP + ug/l -Increase water clarity 0. kpar (m - ) (Markarewicz et al. 000; Higgins et al. 005) Improved light climate allows for growth at deeper depths 0 Biomass (g DM/m ) Model predicts X increase Post Dreissena in Lake Erie 6 0 Post Dreissena - ug/l SRP SRP and kpar

39 Phosphorus excretion by mussels was measured in benthic chambers Ozersky et al 0 JGLR

40 6,00 kg SRP,000 kg TP,600 kg SRP Dreissenid P excretion exceeds other P sources and P demand by Cladophora along rocky shorelines which host both organisms Ozersky et al JGLR Source of P presumed to be from lake based on C isotopes but P could also be regenerated from these same coastal sources different management implications for managing P fluxes in the coastal zone

41 Mussels have also reduced Total Phosphorus Export by 60 % from Inner Saginaw Bay to the Outer Bay. Saginaw Bay used to provide 0-0 % of total P loading to Lake Huron. To what extent has mussel interception of TP contributed to reduce concentrations in the lakes? Cha et al. 0. ES&T

42 What limits dreissenid growth? Instrumented coastal zone (5, 0, 0 m moorings; fluorometer, thermisters and ADCP) to look at dynamics of chlorophyll (phytoplankton) and mussel growth in cages Malkin et al. 0. L&O

43 Benthic boundary layer limits dreissenid access to water column food compared to suspended mussels Chlorophyll available near bottom (0.5 m) nearly 0x higher during first growth period.0 m below Negative growth on bottom in SFDM in second experiment suggests strong food limitation for much of summer period due to BBL 5 m 0 m above.0 m 0.5

44 Is the deep chlorophyll layer an important food resource during stratified season? How deep does the mussel interception of phytoplankton P remove TP from suspension? How effective is cross shelf transport from DCL to benthic boundary layer? Deep cage moorings (0 m) lost so no growth data available; but chlorophyll is higher at depth and cross shelf velocities higher than at shallower depths.

45 The African Great Lake Nearshore Shunt Andre et al. 003 JGLR

46 Water leaving radiance at 550 nm is correlated to suspended particle concentration and Secchi Disc depth. (Binding et al. 00. JGLR). Satellite imagery from early 90s can be compared with early 000s (March to October for spatially resolved ( km) evidence for changes in clarity

47 Great Lakes are becoming more transparent. Between early 90s and early 000s Change from to

48 Not only are lakes clearer on average but patterns of turbidity are altered with nearshore waters often clearer than offshore water; only in western and central basin of Erie has turbidity increased between these time periods Ontario Erie

49 Michigan NM Huron SM NH Superior SH Transparency of Upper Lakes is converging on Superior; greatest change in chlorophyll and transparency in the spring Barbiero et al. 0. JGLR SUP

50 Increased clarity has resulted in deepening of euphotic zone which allows better access to nutrient-rich deeper water in stratified season. True for both benthic and phytoplankton production in the Deep Chlorophyll Layers that form in the lakes. May be good news for cold water native stenothermal animals. Is energy being increasingly shunted to deep water food webs? Is there vertical Deep Water Shunt forming in the Great Lakes? Lake Michigan Lake Superior % PAR Barbiero et al. 00. JGLR House et al. In prep.

51 Dreissenids as calcifying organisms continuously producing shell have caused decreases in Ca and alkalinity concentrations in the lower lakes. If decline in Ca is all in mussel shells would reduce SRP by approximately 3 µg/l (based on Arnott and Vanni (996). Is the missing P in the lakes in mussel shells? Chapra et al. 0. JGLR.

52 Late summer whiting event (precipitation of CaCO 3 ) in Lake Michigan SeaWifs Image NOAA 6/seawifs_lake_mich_lrg.jpg In Lake Ontario, Ca and Alkalinity concentrations have fallen and summer whitings no longer occur (Barberio et al JGLR ); pelagic sedimentation may be declining

53 Challenge to the Workshop: Open the black box that has guided Great Lakes management and. address spatial and temporal complexity of internal transport and biogeochemical reactivity within the lakes. Challenges: ) Concurrent coastal eutrophication and pelagic oligotrophication ) Clarification and redistribution of nutrients and productivity within the lakes 3) Consequences of accelerated calcification on nutrient and trace element cycling ) Climate change on the biogeochemistry of the lakes June July Aug TP Chl SRP Leon et al. 0 JGLR ELCOM-CAEDYM

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55 Is the mussel shunt starving pelagic carbonate sedimentation and offshore sedimentation in general? Mass budgeting indicates sedimentation/settling coefficients are increasing while pelagic particulate concentrations are falling. Are we seeing a shift in the composition of offshore phytoplankton accelerating settling (e.g. more and larger diatoms) or is the increased settling a transfer of nutrient mass to the littoral? What are the consequences for nutrient and trace element cycling e.g. Total Hg concentrations in the lakes are falling. Eutrophication Oligotrophication Clarification Calcification

56 Open Lake Mercury Trends Lake Ontario Total Mercury Trend Lake Erie East Basin Total Mercury Total Mercury (ng/l) Lake Ontario Slope ng/l yr r = 0.55 Total Mercury (ng/l) Lake Erie East Slope ng/l yr r = Lake Huron Open Lake Total Mercury Trend Lake Superior Open Lake Total Mercury Trend Total Mercury (ng/l) Lake Huron Slope ng/l yr r = 0.3 Total Mercury (ng/l) Lake Superior Slope ng/l yr r =

57 Mussels grew slower on the bottom in experiment despite warmer temperatures; only other significant physical difference between experimental periods was higher near bottom stability measured as N which may have facilitated food depletion by mussels within the benthic boundary layer

58 5 m 0 m 0 m No difference between experimental periods near bottom velocity but second period was warmer Also no difference in near bottom stability, n, Ri, bottom shear velocity

59 Volume collected (m 3 ) Is it really resurgent? Yes Debris removed from cooling water intake filters at Pickering Nuclear Plant mostly Cladophora