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Samenvatting lectures Paleoenvironments
- Instelling
- Universiteit Utrecht (UU)
Complete samenvatting van de lectures van Paleoenvironments
[Meer zien]Voorbeeld 4 van de 39 pagina's
Voorbeeld 4 van de 39 pagina's
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Voorbeeld van de inhoud
Lecture 1: introductionClimate change is majorly caused by humans.
But there are also natural climate changes,
like El Nino. Leading to for example many
dead fish because of oxygen shortages. There
is a relation between temperature and CO2,
so there is an overall correlation. The
hydrological cycle is also linked.
Oostbroek excursion
Oostbroek is a wetland because of old course of the river the Rhyne. The filled up dead branches of
the river are archives full of information. It became a lake while there was no flow anymore and the
lake fills up with sediments.
Oostbroek was a monastery, so the trees are planted. Upstream there are oaks, birches (berken) and
maple trees. And downstream the water table is higher, so there are different trees. It floods in
winter. There is still the maple bus also the alder (els), which is typical for organic, nutrient rich wet
conditions. A sample is taken here with the Edelman boor and a guts. The surface is organic rich and
very clayey with lots of roots. Deeper down it is less organic, and the soil is partly oxidized and
reduced. When the water table is reached it becomes greyer instead of brown. Then with the
Edelman, more sandy sediment is found. The active branch of the river (the sand) was closed off
because in WIjk bij Duurstede there was active control of the river, which lead to the river slowing
down in this area. There was not much energy, so clay was deposited. The peat has disappeared
because of oxidization.
There are also samples taken from the water with a plankton net (so all the algae are catched).
Invertebrates, diatoms, green algae and maybe pollen grains will be found. Furthermore, aquatic
vegetation is used to know what kind of benthic organisms are living here (diatoms and algae grow
attached). Lastly the gravity corer is used to sample aquatic sediment. The sediment is pushed down
in a controlled way and draw off the overlying water. The samples are taken with every centimetre.
Then all the samples were taken to the laboratory.
- Water sample: we siff out the bigger (250 um) samples. A lot of vertebrates are crawling
around. There are volvox (colonial algae), Cladocera (water fleas) and copepods. Also, several
large mayflies and aquatic beetles.
- Sediment in lake: there are leaves and small particles of debris and only a few animals. In the
larger fraction there are oligochaete worms, mayflies’ larvae and a few Cladocera. In the
smaller fraction there are various algae, diatoms and flagellates. There are abundant
filamentous green algae, pollen grains and dinoflagellates (eukaryotic algae). Rotifers (wheel
animals) are zooplanktonic and create water flow by rotating their mouth parts. They eat
particulate organic detritus, dead bacteria, algae and protozoans.
,Observations from the practicum
- Flowing water more & varied biological activity compared to standing water. Flowing water
has more algae, diverser diatoms, low concentration planktics and high concentration
macroinvertebrates (but only a few species).
- Sunlit and shaded environments differ in abundance of especially the algae. Diatoms, green
algae and flagellates have a higher abundance and diversity in sunny environments.
Macroinvertebrates occur in shady environments, but in low abundance.
- Aquatic plants: Mostly benthic diatoms, very varied groups. It is the most abundant and
diverse habitat, especially in flowing water, both micro-organisms and macroinvertebrates.
There is a high diversity in flowing water of benthic organisms but this varies between years.
- Sediment: significant living activity limited to top 1-2 cm. Sediments are poorer in
macroinvertebrates, but more diverse in diatoms and green algae. There is preservation of
chitinous and siliceous elements (like diatoms), plastics and plant material, but most organic
material is quickly broken down. Microfossils (diatoms/pollen) preserve relatively well, and
therefore relatively more abundant at depth.
General conclusions
Biota in wet habitats highly variable
- Important factors: nutrients, sun-shade, turbidity
- Stable habitat conditions increases diversity & abundance standing water in most years, but
nutrients can sometimes limit (like in this year likely)
- Benthic diatoms are the most diverse group, green algae second, nutrient flow in flowing
water likely important
- Vary from year to year; this year activity relatively high despite cool conditions and relatively
high activity in benthic communities in flowing water
Only small part of biological acitvity in top sediment compared to benthic community on plants and
in the water samples
- Oxygen and light levels are limiting at the sediment-water interface!
- Sediments reflect biological patterns from water and plants relatively well for siliceous
organisms, not very well for macroinvertebrates
Relevance: proxy data resemble 1-2% of actual biology in lake or swamp
- Bioturbation is important but not “destructive” for assemblages
- Limited “view” of fossils on the real diversity, especially macroinvertebrates
- Preservation in sediment is very selective, mostly silica and some resistant organic fossils
(pollen, insect head capsules, some algae)
- In varied landscapes a single sediment record is not representative enough, best still is
standing water with a large catchment (i.e. Not a very small lake)
- Flowing water regime with much oxygen is not a great place to preserve microfossils
,Lecture 2: Natural environmental archives
Natural environmental archives: source of information extending the instrumental period back in
time:
- Types of environmental records
- Sampling techniques
- Sedimentation process
- Sediment characterisation
One of the most visible changes in climate is glacier retreat (the
response is very rapid). Most glaciers are retreating. There can be given
ocean cores in the oceans. Also, tree rings, corals and ice cores can be
used. Furthermore, pollen and lake levels are used. Globally, lake
sediments are most abundant, so the focus is on that. Climate, geology
and land use control lake processes and depict the sedimentation
(mixing, decomposition and chemistry). (Varves are annual layers).
Coring methods: Choice depends on research question and the aim of the study
- Long corers (long records); multiple segments and larger setups
- Short gravity cores (human impact, proxy calibration): flexible and transportable. These are
like a meter long.
- Freeze corers (sedimentation patterns, calibration, undisturbed sediment-water interface).’
Types of corers:
- The Russian corers: a half tube with a flap. It can be put in a backpack and put in sediment
(not to sandy, so lake sediment and peat), and give it a half a turn. It is simple to use and
undisturbed samples, it is mobile but there are short sections.
- The piston cores: can be done on land and in water. You have a piston in a tube, and you
bring it to the depth you want. Then the piston is fixed and the core around it is pulled down,
and then the whole core can be pulled up. The piston causes suction, so the sediment does
not fall out. You can very good control at which height you are. Many times, two cores are
used with differences in heights so the gaps are minimal, and you can look at many meters.
- Lake piston corer: 3m sections with core liners.
- Free fall piston core: you can make one core and you let the piston fall down in a lake.
- Gravity core: free fall system but relative short. Is for undisturbed sediment/water interface.
- Freeze cores: high precision records, no disturbance. Sediment is frozen in place around a
blade. Requires more skill and is not very easy. You can get frozen sediment in place.
- Clymo peat core: large soil blade. Does not work in clastic, but very well in peat. Gives larges
volume but has limited length. It is important for macrofossil studies. For recent time scales.
Lake → filling in → overgrowing → fen (laagveen) → raised bog
, Sedimentation: It differs in location within a lake, so you want to look at the middle of the lake.
- Variability of accumulation rates
- Particle distribution is not homogenous (Stocke’s law = rate of settling of spherical particles
in a viscous fluid of known density) Particle size = energy level. The large particles are
jumping along the riverbed (rolling, saltation) and smaller particles (silt and clay) are
suspended load and only with a very low flow rate they will deposit. If small particles are
accumulated, it is harder to erode again and the velocity needed for transport has to be
larger, they are more resistant to erosion. So, larger particles deposit rapidly and small
particles not. But if small particles are deposited, they have more resistance to erosion.
- Single events (slumps, turbidite (rapidly deposited), homogenites) = high deposition in a
short time. Turbidites are rapidly deposited.
- Bioturbation: moving of sediment because of animals.
- Zonation (transition from a lake to bog succession). Typically, reed, which causes organic
material in the lake. The material and accumulation are depended on the type of lake and
determines which type of organisms there are. The type of lake determines information
content and sensitivities and the accumulation rate.
o Eutrophic: high in nutrients which lead to high productivity. Gyttja is produced. The
accumulation is generally rapid. E.g.: Willow, alder and marl.
o Mesotrophic: typical: menyathes, Betula and carex rostrata.
o Oligotrophic: low nutrients (so low productivity), with largely minerogenic
sediments. It happens slow and depends on the erosion rates in the catchment.
o Dystrophic: almost absent of nutrients, which causes gel-mud or dy. The
accumulation is very slow.
- Hiatus: some of the record disappeared.
o Climate: drier/wetter, lake level change or events like floods
o Tectonic: subsidence, earthquake
o Isostatic rebound
o Chemical: dissolution of bedrock (sinkhole)
o Sediment infill variation (accommodation space)
o Strong bottom currents
o Ice scouring
o Uneven distribution of lakes globally. Then there can be looked at oceans, local
vegetation or different types of deposits.
Other sources of palaeoecological information: it is discontinuous, but often very high quality. Often
related to animal behaviour (feeding, shelter) Represent short time periods.
- Amber inclusions (tree resin)
- Packrat middens
- Coprolites
- Mass morality (landslides, floods, tar pits).
Limnic: lake situation
Telematic: marsh (between low and high-water level)
Terrestrial: mires, land, above water table
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