Recovery of marine ecosystems: Regime shifts, resilience and shifting baselines

Transcription

1 Recovery of marine ecosystems: Regime shifts, resilience and shifting baselines Jacob Carstensen Dept. of Bioscience, Aarhus University

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3 Phase I eutrophicatio n model Source: Cloern (001) Mar.Ecol.Prog.Ser.

4 Phase I eutrophicatio n model Oligotrophication Eutrophication Source: Cloern (001) Mar.Ecol.Prog.Ser.

5 Phase II: System attributes modulate responses Oligotrophication Eutrophication Source: Cloern (001) Mar.Ecol.Prog.Ser.

6 Phase III: Coastal ecosystems have complex response patterns to multiple stressors Oligotrophication Eutrophication

7 Phase IV: Regime shifts between alternative stable states Oligotrophication Eutrophication

8 Hypoxia can lead to alternativ e stable states X Source: Jeremy Testa X

9 Clear state Turbid state TN TN DIN DIN DON PON DON PON SS SS

10 Total nitrogen input (10 6 kg) Source: Updated from Conley et al. (007) Ecol.Appl. DEPARTMENT OF BIOSCIENCE What are the responses to 5 years of nutrient reductions? Diffuse sources Point sources Nutrient management plans

11 TN (µg l -1 ) TP (µg l -1 ) DEPARTMENT OF BIOSCIENCE Nutrient concentrations have gone down! Nitrogen input from land (10 6 kg) Phosphorus input from land (10 6 kg) A typical phase II response

12 TN (µg l -1 ) Hydrological year (Jul-Jun) TN (µg l -1 ) DEPARTMENT OF BIOSCIENCE 800 TN trajectories over time Nitrogen input from land (10 6 kg) Estuaries and coastal waters Nitrogen concentrations have responded to reduced nutrient inputs in a predictable manner

13 Chlorophyll a (µg l -1 ) Chlorophyll a (µg l -1 ) DEPARTMENT OF BIOSCIENCE 7 What are the phytoplankton responses? Estuaries and coastal waters TN concentration (µg l -1 ) Chlorophyll did not respond in a linear predictable way to reduced nitrogen conc.

14 Secchi depth (m) Secchi depth (m) DEPARTMENT OF BIOSCIENCE 5.0 Did the water get clearer? TN concentration (µg l -1 ) Estuaries and coastal waters No real improvement in water transparency after 1990!!!

15 TOC (µmol l -1 ) InorgSS (mg l -1 ) Secchi depth (m) PON (µmol l -1 ) DON (µmol l -1 ) DEPARTMENT OF BIOSCIENCE Why didn t the water get clearer in Skive Fjord? 5 1 Skive Fjord Skive Fjord Skive Fjord Skive Fjord Skive Fjord Source: Carstensen et al. (01) Hydrobiologia

16 Inorganic SS (mg l -1 ) DEPARTMENT OF BIOSCIENCE Is there a positive feed-back from loss of eelgrass? Skive Fjord Lovns Bredning Eelgrass cover 1- m (%) Risgårde Bredning Skive Fjord Lovns Bredning Risgårde Bredning : open symbols Source: Carstensen et al. (01) Hydrobiologia

17 Eelgrass depth limit (m) Eelgrass depth limit (m) Eelgrass depth limit (m) Eelgrass depth limit (m) DEPARTMENT OF BIOSCIENCE Trends in eelgrass depth limits 7 Coastal areas.5 Estuaries inner parts 6,5 6 5,5.5 5, Estuaries outer parts.5 Limfjorden

18 Depth (m) Eelgrass depth limit (m) Depth (m) Eelgrass depth limit (m) DEPARTMENT OF BIOSCIENCE Does eelgrass respond to Secchi depth? 6 5 Løgstør Bredning Løgstør Bredning 1 Eelgrass depth limit Secchi depth Nibe-Gjøl Bredning Eelgrass responds linearly to light conditions with no or little time delay Secchi depth (m) Nibe-Gjøl Bredning Eelgrass depth limit 1 Secchi depth but each ecosystem behaves differently Secchi depth (m)

19 Expected eelgrass cover (%) DEPARTMENT OF BIOSCIENCE Do the eelgrass meadows also spread? Nibe-Gjøl Bredning Depth (m)

20 Oxygen responses to nutrient inputs Danish Straits Chesapeake Bay Gulf of Mexico Source: Conley et al. (009) Hydrobiologia

21 Oxygen concentration (mg l -1 ) Oxygen concentration (mg l -1 ) DEPARTMENT OF BIOSCIENCE Oxygen conditions in Danish Straits over 9 the long term Shift in baseline due to temperature 7 6 Organic enrichment has a significant impact on oxygen conditions and nutrient feed-backs Nitrogen input (10 6 kg yr -1 )

22 AARHUS UNIVERSITY Conference on significant factors controlling WWTP inputs to the Stockholm archipelago

23 PO (mmol m - ) PO (mmol m - ) Biomass (g m - ) DEPARTMENT OF BIOSCIENCE Conference on significant factors controlling Trends in oxygen and phosphate AARHUS UNIVERSITY conc. (a) O (mg L -1 ) Others Marenzelleria 0 (b) y = -0.x Bottom R = Surface O (mg L -1 ) Source: Norkko et al. (01) Glob.Change.Biol.

24 Conclusions on recovery of Danish coastal waters Nutrient concentrations have declined as expected. Waters are still turbid despite large reductions in N and P inputs. Eelgrass has not recolonised. Hypoxia is still a problem. Dissolved organic carbon is (most likely) still leaking from sediments adding to the unclear water. Hypoxia, loss of eelgrass and mussel harvesting has created an unhealthy benthic environment. Reestablishing a healthy benthic community is key to recovery. Recovery is fast, provided environmental conditions are suitable.

25 AARHUS UNIVERSITY Conference on significant factors controlling Coastal ecosystem responses (phase I- IV)

26 Conclusions on management implications Management frameworks based on Phase I and Phase II conceptual models are inappropriate (even flawed) Coastal ecosystems are almost all affected by multiple stressors that will shift baselines Coastal ecosystems have feed-back mechanisms that may lead to sudden shifts between alternative regimes, particularly associated with hypoxia and loss of benthic fauna and vegetation Coastal ecosystem management should aim at defining targets based on the ecosystem function rather than reestablishing a historical status