How global warming and climate change may be accelerating losses of Chesapeake Bay seagrasses.

Transcription

1 How global warming and climate change may be accelerating losses of Chesapeake Bay seagrasses. Dr. Ken Moore The Virginia Institute of Marine Science School of Marine Science College of William and Mary Gloucester Point, VA USA

2 What Are Underwater Grasses? Rooted, vascular plants does not include marsh grasses or algae Completely submerged Have flowers and seeds 17 common species in Chesapeake Bay Grow in fresh and salt shallow tidal waters Only one true seagrass species in Chesapeake Bay (eelgrass)

3 Underwater grasses of Chesapeake Bay Only True Seagrass

4 Underwater grass communities are important in Chesapeake Bay Food for waterfowl Increase water clarity Habitat for fish and crabs

5 Underwater grass communities are widely distributed in Chesapeake Bay York River St Mary s s River Zostera marina eelgrass Ruppia maritima widgeongrass

6 Underwater grass communities are by distributed salinity Chesapeake Bay Underwater Grass Communities Freshwater Potamogeton Moore, Wilcox, Orth (2000) Estuaries 23: Ruppia Zostera

7 Saltwater CHESAPEAKE BAY UNDERWATER GRASS COMMUNITIES ZOSTERA Community Zostera marina* Ruppia maritima Freshwater RUPPIA Community POTAMOGETON Community FRESHWATER Community *Dominant Species Ruppia maritima* Potamogeton perfoliatus Potamogeton pectinatus Zannichellia palustris Potamogeton perfoliatus* Potamogeton pectinatus* Elodea canadensis Potamogeton crispus Myriophyllum spicatum* Hydrilla verticillata* Vallisneria americana* Ceratophyllum demersum Heteranthera dubia Najas minor Elodea canadensis Najas guadalupensis Potamogeton crispus Najas gracillima Potamogeton pusillus

8 There are very few underwater grass species FRESHWATER SUBMERSED SPECIES TERRESTRIAL 250,000 + SPECIES SEAGRASS SPECIES FRESHWATER WETLAND?? SPECIES

9 Our only seagrass Zostera marina (eelgrass) Temperate coastal distribution Monoecious, Sub-surface pollination (threadlike pollen) Sexual reproduction through seeds Asexual reproduction through rhizomes High salinity tolerance (10-40)

10 Chesapeake Bay Eelgrass Meadow Landscape

11 Underwater grasses have declined in the Chesapeake Bay over the past 60 years. Less than 50% present today compared to 1950s Eelgrass populations have also declined

12 Pre 1930s 1960s 2000

13 Chesapeake Bay Historical Land Use Pre-1630 Forested Watershed; < 1% land cleared Initial European settlement; <20% land cleared Developing Agriculture; 20-40% land clearance s Intensive Agriculture 60-80% land clearance, mechanization, deep plowing, fertilization s Farm abandonment, re-forestation, 40% land clearance, initial urban growth, storms 1950s-Present Urban Growth (Tropical Storm Agnes 1972 and others) Brush and Hilgartner 2000

14 Recent Decreases in York River Eelgrass Bed Abundance and Density 2004 Seagrass

15 Loss of eelgrass in last 10 years is problematic Goodwin Island York River

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17 Effects of Climate Change on Chespeake Bay Seagrasses and Other Underwater Grasses Atmospheric Changes Rainfall Patterns Increase Nutrient and Sediment Inputs (100% loading increase for C. Bay) Frequency/Intensity of storms Sea Level Rise Salinity Changes Increases in Water Depth, Water Motion and Tidal Circulation Increased Shoreline Erosion Temperature Rise Physiology, growth, reproduction

18 A variety of components reflect or absorb sunlight in seawater Sunlight Light Intensity Algae Depth Sediment Epiphytes Color Seagrass

19 Seagrass responsive to light reductions Healthy seagrass Impacted seagrass Seagrass loss Physiological responses Amino acids Chl a/b δ 13 C Morphological responses Biomass Shoot density canopy height Root/shoot Period of light deprivation

20 The greater the underwater light The deeper the underwater grass growth and The greater the abundance

21 York River current and historical 0m 1m 2m Current Distribution Upper Estuary Historic Extent eelgrass depth distribution Reduced light has been a factor! 0m 1m 2m Current Distribution Mid Estuary Historic Extent 0m Lower Estuary 1m 2m Current Distribution Historic Extent

22 Restoration of SAV to 1 m MLW depths will initially require reduction in suspended solids concentrations Cerco and Moore 2001

23 Full storage of sediment in Conowingo Dam Reservoir in next years (Annual average sediment inputs will increase 3-fold) 3 Langland and Hainly 1997 Scour during storm events will increase estuarine sedimentation. (16x annual sediment inputs during one 1996 winter flood)

24 Excessive Nutrients Promote Excessive Growth of Epiphytes Image provided by Kawartha Fisheries Association

25 Impacts of storms on seagrass can be significant

26 AIR AND WATER IN MOTION Due to the higher density of water (998.2 kg m-3 freshwater) than air (1.2 kg m-3), the force exerted by the same velocity on an organism is 827 times stronger in the water than in the air.

27 But, in highly wave exposed areas, seagrasses are limited to protected areas Japan, Zostera marina, 2 m waves Chesapeake Bay 1 m waves Dan et al. 1998

28 Scour and deposition lasting for weeks after storms can result in landscape scale changes to seagrass beds Post Storm Surface Deposition Scour Post Storm Surface 10 meters

29 The effects of tropical storms observed in eelgrass beds in lower Chesapeake Bay

30 York River Goodwin Islands June 2004

31 York River Goodwin Islands June 2003

32 York River Goodwin Islands October 2003

33 York River Goodwin Islands June 2004

34 Effects of Climate Change on Chespeake Bay Seagrasses and Other Underwater Grasses Atmospheric Changes Rainfall Patterns Increase Nutrient and Sediment Inputs (100% loading increase for C. Bay) Frequency/Intensity of storms Sea Level Rise Salinity Changes Increases in Water Depth, Water Motion and Tidal Circulation Increased Shoreline Erosion Temperature Rise Physiology, growth, reproduction

35 Salinity changes can modify underwater grass distribution and abundance Chesapeake Bay Underwater Grass Communities Freshwater Potamogeton Moore, Wilcox, Orth (2000) Estuaries 23: Ruppia Zostera

36 Waves appear to affect the minimum depth of distribution of seagrasses and sealevel rise can restrict shallow water habitat.

37 Shoreline erosion can create chronic turbidity for local waters.

38 Effects of Climate Change on Chespeake Bay Seagrasses and Other Underwater Grasses Atmospheric Changes Rainfall Patterns Increase Nutrient and Sediment Inputs (100% loading increase for C. Bay) Frequency/Intensity of storms Sea Level Rise Salinity Changes Increases in Water Depth, Water Motion and Tidal Circulation Increased Shoreline Erosion Temperature Rise Physiology, growth, reproduction

39 Global distribution of eelgrass (Zostera marina) Eelgrass near southern limits of range on Atlantic Coast of US

40 Light requirements of eelgrass increase with increasing temperatures Reprinted from Moore et al. 1997

41 Investigate if temperature or some other factor is affecting Chesapeake Bay Seagrass? 1. Quantify the patterns of inter-annual variability and spatial distribution of seagrass in areas of the lower Chesapeake Bay. 2. Compare the patterns of long-term change in these areas. 3. Relate these patterns to environmental and water quality conditions.

42 Monitoring Sites Gloucester Point GP 1 GP 2 GP 3 Goodwin Island GI 1 Fixed continuous WQ monitoring stations: DO, Phytoplankton, Turbidity, Salinity, ph, Temp GI 3 GI 2 Bi-weekly WQ sampling: Phytoplankton, Water Column Nutrients, Suspended Sediments, Underwater Light

43 Seagrass Sampling Methods Monthly Sampling Measurements made every 10 m PVC square (0.25m -2 diameter) tossed 3 times every 10 m Ring is placed in densest patch of vegetation within the square

44 York River Depth (cm MLLW) Bottom Topography Goodwin Island Goodwin Is Distance (m) York River Gloucester Point Depth (cm MLLW) Gloucester 0 Point Distance (m)

45 100 Goodwin Island Eelgrass Cover May 2004 July 2004 Oct 2004 Percent Cover Percent Cover April 2005 July 2005 Oct Distance (m)

46 Goodwin Island Eelgrass Cover April 2006 May 2006 July 2006 Percent Cover Distance (m) Re-growth largely from seedlings

47 Goodwin Island Eelgrass Bed 100 Mean Percent Cover Percent Cover /04 07/04 01/05 07/05 01/06 07/06 01/07 Date (mm/yy)

48 Gloucester Point Eelgrass Cover May 2004 June 2004 September 2004 Percent Cover April 2005 July 2005 October Distance (m)

49 Gloucester Point Eelgrass Cover April 2006 May 2006 July 2006 Percent Cover Distance (m) Very few seedlings found

50 Gloucester Point Eelgrass Bed 100 Mean Percent Cover 80 Percent Cover /04 07/04 01/05 07/05 01/06 07/06 01/07 Date

51 Is Turbidity a Factor? Goodwin Island Gloucester Point Turbidity (NTU) Turbidity (NTU) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Date (month) 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Date (month)

52 Turbidity Frequency Distribution for Goodwin Island and Gloucester Point Goodwin Island 2004 Goodwin Island 2005 Gloucester Point 2004 Gloucester Point 2005 Percent Time Turbidity (NTU)

53 Sources of oxygen for seagrass metabolism Light photosynthesis and water column Dark water column only

54 Water Column Dissolved Oxygen Goodwin Island Gloucester Point Dissolved Oxygen (mg l -1 ) Dissolved Oxygen (mg l -1 ) Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Date (month) 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Date (month)

55 Water Column Dissolved Oxygen Frequency Distribution for Goodwin Island and Gloucester Point July and August Goodwind Island 2004 Goodwin Island 2005 Gloucester Point 2004 Gloucester Point 2005 Percent Time Dissolved Oxygen (mg L -1 )

56 Are High Water Temperatures a Problem? 35 Goodwin Island 35 Gloucester Point Temperature (C) Temperature (C) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Date (month) 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Date (month)

57 Water Temp Frequency Distribution for Goodwin Island and Gloucester Point GI 2004 GP 2004 GI 2005 GP 2005 Percent Time Temperature (C)

58 HOURS PER DAY ABOVE SAV LIGHT COMPENSATION IS VERY IMPORTANT H comp (ho urs) Currently Vegetated Historically Vegetated Jan Jun De c Light below compensation for 20 days

59 Summary The remaining eelgrass beds have been experiencing increasing frequency of summertime diebacks in shallow and deep regions. Global warming and climate change can affect Chesapeake Bay eelgrass survival through multiple ways: Elevated temperatures can stress growth Increased frequency and intensity of storms Given the long term effects of increases in temperature and turbidity due to global warming and climate change are problematic for continued success of eelgrass populations in this system.

60 Thanks!