Physical Characteristics of Streams

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Paleolimnology
The study of long-term changes in lakes (and the
surrounding region) Recorded information only
goes back about 200 years But we can look at the
record stored in the sediments of lakes
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How do we tell the age of material at certain
depths in the sediments?
1. Annual layers called varves occur in some
lakes. Sediment carried with spring snow
melt High summer primary production 2. 14C
carbon dating good for layers 250 to 40,000 y old
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How do we tell the age of material at certain
depths in the sediments? (cont.)
3. 210Pb dating good for material less than 150
y old 4. Markers volcanic ash specific pollen
(e.g., ragweed, successional trees) 5.
Magnetic orientation -- changes in the earths
magnetic field
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Once we know the dates associated with specific
layers, what do we look at?
1. Inorganic materials a. Amount of inorganic
sediment/year erosion in the
watershed e.g., Lago di Monterosi Hutchinso
n et al. 1970 Via Cassia 171 B.C. b.
Specific inorganic elements Fe, Mn indicate
redox conditions P indicates P of
overlying water? e.g., Lake Washington,
Edmondson et al.
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2. Organic constituents a. Total organic
deposition lake productivity allochthonou
s inputs b. Plant pigments e.g.,
Oscillaxanthin is a pigment of Oscillatoria, a
blue-green alga. Blue-green algae generally
indicate eutrophic conditions Lake
Washington Edmondson et al.
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3. Pollen -- very resistant to decay -- often
can be identified to species -- can be used for
dating -- indicates whats happening in the
watershed
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3. Pollen e.g., Lake Windermere, Lake District
of England 10,000 BP -- retreat of last
glaciers 8,000 -- Pines ? oaks and
alders warming climate pines cut or burned by
early man? some grass -- cleared areas 3,000 --
much more grass human clearing? 1,000 --
agrarian society drained lowland alder and
birch wetlands and converted to sheep
pasture
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4. Algal remains a. Diatoms frustules highly
resistant to decay identifiable to
species ecology of many species well
known Centric diatoms -- oligotrophic
conditions Pennate diatoms -- eutrophic especiall
y the family Araphidineae (Fragilaria,
Asterionella) A/C ratio -- Araphidineae
(pennate)/ centric A/C large -- eutrophic A/C
small -- oligotrophic
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e.g., Lake Biwa, Japan (a graben lake) 200-m
core (part of a 1000-m core!) 500,000 y Melosira
solida -- large centric diatom, but this centric
species was present mostly during warm eutrophic
periods Fragilaria -- Araphidinate (pennate)
diatom Pennales -- pennate diatoms Careful of
generalizations about centrics and pennates (and
any other generalizations!) Eutrophication is
not a one-way process.
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4. Algal remains (cont.) b. Other algal
remains some green algae e.g., Staurastrum
(Lake Biwa) cysts of chrysophytes and
dinoflagellates heterocysts of
blue-greens (No, you dont need to know all these
details!)
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5. Animal remains a. Cladocerans exoskeleto
ns preserved studied by David Fry at Indiana
U. ecology well known Lake Biwa Bosmina
only in last 80,000 y
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5. Animal remains (cont.) b.
Insects Chironomid head capsules can be
identified to subfamily or
below Chironomus (bloodworms) - anoxic
Chaoborus -- usually indicates eutrophic
conditions Lake Biwa periodic appearance
of insects c. Mollusks -- well preserved but
not very useful because of broad environmental
tolerances
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Problems 1. Unequal sedimentation over lake
bottom -- depth -- proximity to inflowing
streams 2. Sediment focusing sediment
resuspended from shallow areas and
redeposited in deeper areas
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Problems (cont.) 3. Diagenisis
(decomposition) materials decompose at
different rates different rates in different
lakes different rates at different depths 4.
Bioturbation -- mixes materials from
different layers
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Problems (cont.) 5. Not everything preserved
A. A period of increasing productivity B.
Decreasing productivity? Or increasing
productivity with blue-greens replacing diatoms
(and the BGs arent preserved)?
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There are lots of things we can measure, and we
need to measure all we can to get a complete
story. Example R.E. Brugam Paleolimnology of
Linsley Pond 1978 Linsley Pond Near New Haven,
Conn. Studied for many years by limnologists at
Yale (Riley, Hutchinson, Deevey, Patrick, Brooks,
Dodson, )
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Linsley Pond 9 ha Zmax 14.8 m, 6.7
m Formed about 13,000 BP as glaciers retreated.
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History 1. Precolonial -- up to about 1700 2.
Homestead period -- 1700-1810 original Linsley
home (1) no activity adjacent to lake
except clearing and pasturing 3. Mill and farm
-- 1810-1915 house and barn on lakeshore (2,
3) grist mill (4) and mill pond (5)
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History (cont.) 4. 1915-1950 dairy herd
increased Twin Lakes Rd paved 1938 -- 8
vacations cottages (6) 5. 1950-1970s 1954 --
24 houses on watershed 1972 -- 113 houses 1961
-- golf course
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Modern pond is extremely eutrophic surface TP
48 ?g/L Secchi summer Blue-green blooms Study based on a single
238-cm core taken in 1974.
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Dating 210Pb -- top 50 cm (1938, 1961) 14C -- 233
BP, 673 BP Pollen ragweed (Ambrosia) European
settlement, ca. 1700 Am. Chestnut (Castanea
dentata) chestnut blight, 1913 Establish depth
versus date curve
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I. Sedimentation rate Essentially constant until
1700 some increase 1700 big increases
in 1938 -- vacation cottages 1960 --
suburban homes
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II. Sediment Chemistry mineral before 1700 --
50 1700-1938 -- 65-70 since 1938 -- 90 Fe
and Mn follow deposition of sediment no evident
change in redox (sediments probably anoxic for
last 8,000 y)
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II. Sediment Chemistry (cont.) Phosphorus not
correlated with diatoms does not reflect
chemistry of water? correlated with Fe and
Mn precipitated with complexes as these
chemicals are eroded from watershed
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III. Diatoms Total diatoms very low prior to
1700 increase about 1820, then
decrease primarily Melosira, a large centric
diatom Centrics increase 1700 to 1820, then
decrease after 1915 Melosira disappeared
and all diatoms are Araphidinate (pennate) A/C
indicates eutrophication about 1915
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IV. Zooplankton Bosmina declined since
1100 peak 1945 Daphnia only in most recent
samples Chydorus (cladoceran) increased about
the time araphidinate diatoms came in
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IV. Zooplankton (cont.) Few changes in
zooplankton until after 1960 Alewife in lake for
last 1000 y (about) Many alewife died off in
1960s, perhaps due to extreme eutrophcation.
Daphnia only increased after this time.
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V. Insects Dicrotendipes -- Chironomid, not
Chironomus declined after 1915 generally
followed centric diatoms Chironomus and
Chaoborus increase after 1915 follow
araphidinate diatoms tolerant of low DO
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Summary 1. Presettlement mesotrophic, perhaps
moderately eutrophic presence of Chironomids 2.
Homestead deforestation small but significant
changes increased PP, increased
diatoms nutrient runoff from deforestation
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Summary (cont.) 3. Mill and farm more intense
land-use near pond barnyard manure increases in
Melosira and Dicrotendipes higher productivity,
but not hypereutrophic 4. 1915 - 1960 major
changes increase in dairy herd changes in
farming, fertilization? centric to araphidinate
diatoms Dicrotendipes to Chironomus and Chaoborus
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Summary (cont.) 5. 1960 - hypereutrophication
sub-urbanization of watershed What has happened
since 1974?
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What have we learned from this study? 1. An
example of paleolimnology 2. Value of using a
lot of different techniques 3. Cultural
eutrophication 4. Many indicators of
eutrophication