Nutrients in Chesapeake Bay: The Nutrient Diet is Working!

Transcription

1 Nutrients in Chesapeake Bay: The Nutrient Diet is Working! SERC 2017 Bay Optimism Lecture Series June, :1 Large Drainage Basin Only 0.2 acres per person for dilution of wastes Walt Boynton and Many Colleagues Center for Environmental Science, Univ MD

2 Key Bay Features Watershed huge compared to estuary (14:1) Bay is closely connected to the land (11,000 miles shoreline; 9 major rivers) Channel is stratified, isolating deep water Very shallow (mean depth = 27 feet) Most of its surface area is in tributaries & sounds Slow flushing (4-6 months) 0.15 acres of water per person.very dense from this perspective!

3 A Famous Chesapeake Bay Painting Clearly, Bay fish important Multiple fishing techniques and signs of large fish Emphasis on shallow waters Clear water and seagrasses From T. De Bry in Hariot 1588

4 A John Smith Diet Traded with natives for corn, venison, fish, oysters, nuts, beans, pumpkins traded swords for turkeys (a 1 for 1 deal probably not a good deal for the English) Tobacco it purges the superfluous phlegm and other gross humours and openeth all the pores and passages of the body from Harriot who died of a nasal tumor in 1621 the tobacco wars started early Jamestowners preferred a seaman s diet of pork, beef, fish, wheat and barley (even with the everpresent worms) Sturgeon (dried and pounded) The Starving Time (winter ) cats, dogs, horses and people this was a very tough life indeed! Hoobler 2006

5 And this had an important buffering effect between the land and the Bay All agree that the watershed was largely mature forests of one sort or another and wetter than it is now Photo: Virginia State Parks

6 Paleoecologists tell us Beavers were a key species regulating water and nutrients Credit: Bert Drake Pre-colonial landscape had MANY WETLANDS BEAVERS were important for cleaning the water One to 5 million of these busy rodents in pre-colonial watershed (~1940 human population) Restore the pre-colonial wet and marshy condition mimic the beavers with more conventional approaches From Brush 2008

7 Storm Water Management: Wet Pond Example Pollutant Removal Efficiencies: TSS: 46% TP: 46% TN: 32% There have been many of these constructed in the watershed We need to keep improving the efficiency of these beaverlike systems Credit: Michael J./Flickr

8 Patuxent River Estuary Circa 1832 Water Quality and Habitat Conditions can be much improved not to the 1832 condition and that may not be the optimal status So transparent are its waters that far out from shore you may see, in the openings of the seaweed forest, on its bottom the flashing sides of the finny tribe as they glide over the pearly sands. The Old Plantation by Hungerford (1859)

9 Costanza et al. 2000

10 Historical and Current Nitrogen Loads to the Patuxent River Estuary 8000 Nitrogen Loads, Kg N/day Before John Smith arrived Before intensive development Current Condition Time Periods Boynton et al., 1995

11 Credit: Lyntha Scott Eiler/US National Archives Credit: U.S. Department of Energy Credit: Chuck Gallegos/SERC, aerial support from LightHawk Credit: Chuck Gallegos/SERC, aerial support from LightHawk Agriculture Major Nutrient Sources Urban/Suburban Run-off Power generation, auto exhaust Point Sources (factories, sewage treatment plants) Summary All have increased during last 50 yrs Importance varies widely with location Most reductions with point sources

12 Figure by Walter Boynton

13 Figure by Walter Boynton

14 Nutrient Enrichment Effects: Estuarine Ecosystems Source: Global Warming and the Free State: Comprehensive Assessment of Climate Change Impacts in Maryland (p. 60)

15 Declining Nitrate (NO 3 ) and Ammonia (NH 3 ) deposition concentrations across the Bay watershed

16 Trends in Nutrient Loads from Long-Term Monitoring Sites in Chesapeake Bay 9 major rivers monitored for inputs to the Bay About 82% of entire watershed monitored by these sites Monitoring record includes last 3 decades more in some cases US-EPA Chesapeake Bay Program

17 Dissolved Phosphorus Dissolved Nitrogen Zhang et al., JAWRA, 2015

18 Testa et al. unpubl.

19 US-EPA Chesapeake Bay Program Boynton, et al Point Source N and P Loads are Decreasing Blue Plains TN Load: Huge decline in both TN and TP loads to the Potomac River from Blue Plains Back River (Baltimore, MD) TN loads reduced by ~ 50% Back River TN Load: In January, 2017 Back River loads will again be reduced by a further 50% Most P loads were reduced before N loads were reduced

20 Restoration of Mattawoman Creek: Potomac River estuary tributary strongly impacted by nutrients from 1970 mid-1990s large and persistent algal blooms, sea grasses rare Nutrient diet stimulated restoration Photo from Elena Gilroy

21 ALGAL BIOMASS DECREASED WITH SUBSTANTIAL LAG TIME Drought Year More Algae No clear response for about 4 years followed by sharp decline in algae 10 0 After 2005 low levels of algae became normal Major Nutrient load reduction completed Boynton, et al. 2012

22 Clearer Water WATER CLARITY INCREASED ALSO WITH A LAG TIME Drought Year More Algae No clear increase for about 8 years followed by sharp increase in clarity Water clarity and algae highly correlated in shallow Chesapeake Bay systems Major Nutrient WWTP load load reduction reduction completed Boynton, et al. 2012

23 More SAV Clearer Water SAV INCREASED SHORTER LAG WITH THRESHOLD RESPONSE Drought Year More Algae Very low levels of SAV were present prior to nutrient load reductions ha SAV Major Nutrient load reduction completed Major expansion of SAV in 2002, a severe drought year SAV relatively stable after 2002; lag in SAV relatively short Boynton, et al. 2012

24 Water Clarity: Hints of clearer water Secchi Depth measure the light available for SAV but it is also an index of nutrient and sediment loading problems Testa et al. unpubl.

25 SAV off Poplar Island in late summer 2015 Photo: Peter McGowan/U.S. Fish & Wildlife Service

26 Area (hectares) Baywide SAV Pattern: Slow increases with strong inter-annual variability. Note strong increases during drought and posttropical storm Lee (2011). Drought Post-Lee US-EPA Chesapeake Bay Program

27 Area (hectares) The WHERE of SAV Recovery or not Note likely response to tropical storm Lee in freshwater and Oligohaline (low salinity) areas of the Bay Negative trend in Polyhaline (salty) portions of Bay likely related to temperature stress Orth et al., in review

28 Susquehanna Flats SAV at the Head of the Bay An unexpected piece of very good news A clear example of why long-term monitoring is so valuable for both trends and explanations This example also reminds us that once these habitats start to get better strong positive feedbacks can accelerate the restoration process Adapted from Gurbisz and Kemp 2014

29 Now this is a SAV bed! Huge expanse ~ 20 square miles (13,000 acres) Clear water Resilient to major storms; recovery from major storm = several years (not decades!) C. Gurbisz, UMCES

30 SAV in the Upper Chesapeake Bay: Drought response and storm resilience LOW FLOW LOW FLOW LOW FLOW LOW FLOW HIGH FLOW HIGH FLOW Figure from Cassie Gubisz Data: Orth/VIMS

31 Late Summer Anoxia Declining in Mainstem Bay Anoxia ( no oxygen ) occurs in the deepest Bay water No multicellular organisms in CB can tolerate these conditions Size of anoxic zone varies from year to year Source: eake_bay_dissolved_oxygen_forecast/

32 MD Bay Anoxia: September Data (0-0.2 mg/l) 1600 Anoxic Volume, 10 6 m Average Maryland late September anoxic 0 Year Source: Maryland Department of Natural Resources

33 Late Summer Anoxia Declining in Mainstem Bay Long-term decline in late summer anoxia ( no oxygen ) This decline larger than expected from modest declines in load Explanation likely related to nutrient diet kickin in Testa et al. in review

34 Ecosystem Degradation Tipping Points: Points where a system shifts from one stable state to another Some ecosystems recover from eutrophication in the same way as they degraded Delaware River, NY Harbor Other respond positively to load reductions, but the response only occurs upon reaching a threshold reduction Recovery may also follow a similar trajectory as degradation, but only after a delay a lag time Mattawoman Creek, Susquehanna Flats, Gunston Cove

35 Tipping Points: Oxygen Interactions with Nitrogen Lower oxygen (hypoxic) can cause higher ammonium (NH 4 ) Anammox Denitrification Algae Algae X X H 2 S Nitrification Source: Testa, et al. in review

36 Long-Term Bay Trends for O 2, NH 4, & NO 3 in Late Summer Significant trends over 3 decades Late-summer mean values Increasing dissolved oxygen Decreasing ammonium Increasing nitrate Hypoxic region of Bay is becoming less hypoxic an important sign of recovery Testa et al. in prep

37 Changing Land Uses in Maryland More hardened surfaces = more runoff Population increases continue to put pressure on natural buffers Over 100 years of forest re-growth reversed in late 1980s

38 So, that s a very brief story of the watershed and estuary There have been a heap of changes in the Bay since John Smith arrived in 1608 The Bay suffers from too much of a good thing too much nutrient and sediment input among other stressors This Bay can be fixed by doing enough of the right things reduce nutrient and sediment inputs, and prudently manage habitats and fisheries Evidence says we are making real progress we need to finish the job!