Module 6.
The Chesapeake Bay
Where is the Chesapeake Bay?
Estuarine Ecosystems
Resources
Functions
Estuarine Problems
Resource exploitation - the American Oyster & Striped Bass
Urbanization & Suburbanization
Loss of Watershed Processing
Water Pollution Issues
Eutrophication
Pfiesteria - The Cell from Hell
The Chesapeake Bay
Baltimore
Washington, D.C.
Richmond
Norfolk
concepts:
• the Chesapeake Bay is North America’s largest estuary
• the estuary provides a suite of unique habitats
• the region is surrounded by the eastern megalopolis
Biology 106 Module 6
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The Chesapeake Bay Watershed
64,000 square miles providing water & nutrients
Estuary - a water passage where the
tide meets a flowing river
Unique habitat providing a dynamic
mixing of resources
salinity
nutrients
structure
Watershed - land area that delivers
water, sediment, and dissolved
substances via small streams to a major
river or estuary
Abiotic Factors in Aquatic Ecosystems
producers
consumers
decomposers
light,
temperature
dissolved
gases
depth
zone
potential organisms
nutrient
enrichment
bottom
material
salinity
producers
consumers
decomposers
motion,
size
resulting community
concepts:
• abiotic factors influence community structure
• these factors change over short times and distances in estuaries
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Species Differences in Estuaries
Salt Water
Fresh Water
Emergent Vegetation
Spartina sp
Arrow Arum
Scavenger
Blue Crab
Cray Fish
Top Carnivorous Fish
Largemouth Bass
Striped Bass
Upstream nutrients
An Estuarine Foodchain
Phytoplankton
Zooplankton
Bluegill,
Shiners,
Minnows
Largemouth Bass
Nutrients
Emergents
SAV
Algae
Decomposers
Nutrients
Crayfish
(Scavengers)
Snails
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Habitats in an Estuarine Watershed
Varying resources provide varying habitats
distance downstream
salinity
forest
marsh
river
estuary
salt
marsh
forest
concepts:
• distinct zonation occurs in response to resources
• zonation provides habitat for different organisms
• intact habitat variation is important for estuary function
Zonation in Tidal Estuaries
Vegetation mirrors influence of abiotic factors
upland
forest
cordgrass
marsh
mudflat
open
water
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Salinity Alters Species
Food web components remain the same
Fresh
Salt/brackish
arrow arum
cordgrass
crayfish
blue crab
largemouth bass
striped bass
Communities in Estuarine Watersheds
Contribute to whole system function
fluctuating
water
level
forest
marsh
salt marsh
open estuary
concepts:
• biogeochemical cycles vary across communities
• net primary productivity varies across community type
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Marshes
Filter water crossing the terrestrial-coastal ocean boundary
high water
low water
forest
marsh
salt marsh
open estuary
concepts:
• vegetation slows water flow, protects soil, increases infiltration
• marshes filter surface water
• clean water is released slowly to streams & estuaries
Threats to Estuaries
Local and distant activities affect estuary health
over harvesting
of resources
coastal development
pollution:
nutrients & sediment
global warming
concepts:
• human activity directly & indirectly affects estuaries
• estuary integrity is integrally linked to onshore activities
Biology 106 Module 6
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American Oyster & Striped Bass
Over-harvesting and habitat degradation deplete the resource
oyster
bass
12
10
catch
(millions
of bushels
or pounds)
Oyster
Commission
Cull
Law
restrictions lifted
restrictions enacted for Bay
purse seines
banned
otter trawlers
banned
B&O
railroad
restrictions enacted for seaboard
8
6
4
declared threatened species
shell-planting
regulations
2
lease
moratorium
fishing reopened
0
1840 1850 1860 1870 1880 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Date
concepts:
• intensive harvesting exceeded maximum sustainable yield
• habitat degradation led to loss of reproduction
Fishing techniques impacting Oysters
Purse seines
Otter trawlers
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Wetland Distribution in the United States
Loss of wetlands with population growth
1-5%
5-12%
12-25%
25-50%
1790
>50%
1980
concepts:
• as population grew, so did development pressure on wetlands
• misguided public works projects drained/filled wetlands
• wetlands are now protected, but constantly under attack
Marshes Under Siege
exhibit altered water, nutrient, & sediment movements
high water
low water
forest
marsh
salt marsh
open estuary
concepts:
• impermeable surfaces alter water flow
• altered hydrology alters nutrient and sediment flows
• nutrient-, toxicant-, and sediment-rich water is released rapidly
into streams & estuaries
Biology 106 Module 6
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Land Use Alters Water Quality
•
35
30
•
25
Nutrient
load
20
•
15
10
Hydrological, sediment, &
nutrient cycles interact
Intensive land use increases
losses from ecosystem
Nutrient and sediment loading
in aquatic systems will alter
resources & habitat
5
0
forest
pasture
crop
urban
Nitrogen (10's of lbs/acre/yr)
Phosphorus (lbs/acre/yr)
Sediment (100's of lbs/acre/yr)
Pollutants Impact Stream Fauna
addition
clean
zone
decomposition
zone
septic
zone
recovery
zone
clean
zone
algae
mayflies
bass
sludge
black flies
carp
sludge
fungi
sludge worms
sludge
black flies
carp
algae
mayflies
bass
10
8
oxygen
concentration
or
BOD
(mg/l)
6
4
BOD
dissolved oxygen
2
0
distance downstream
concepts:
• pollutant additions to water alter resources
• altered resources alter habitat, which alters organisms present
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Schematic of Wastewater Treatment Process
Thermocline
Thermocline –Zone of gradual temperature
(and oxygen) decrease between warm surface
and cold water at depth
Concepts:
•Limited mixing establishes distinct zones in the water column
•Zones differ in temperature, density, salinity, nutrients, oxygen
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Nitrogen in Chesapeake Bay
Reflects seasonal changes in inputs, water flow, & uptake
Dissolved Oxygen
A critical resource altered by eutrophication
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Pfiesteria in the Chesapeake
Distribution reflects altered resource availability
The Eastern Shore:
intensive agriculture
increases N in water
Pathogen Injury to Fish
Young menhaden with deep, gaping ulcers. These ulcers could be
caused by viruses, certain chemical agents, parasites, predators, or
dinoflagellates such as Pfiesteria.
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