Bio 346 - Freshwater Eco. (Chpt 20) --> Particle Sedimentation and Sediments Flashcards
What is the major determinant of the sediment suitability?
Its physical and chemical structure
What does algae do in shallow water?
Grow on sediments so the macrophytes can get nutrients
What lives on/within the space between sediment particles?
Heterotrophic bacteria and invertebrates
What do fish use sediment for?
Feeding, nesting and breeding
What largely determines whether the sediment surface will be oxic or anoxic and whether the apparent redox potential is high or low?
Sediment respiration
What does lake depth influence?
The length of time available for organic particles to decompose in the water column rather then become sediment
What is sediment?
Matter that settles to the bottom of a liquid
Where is lake sediment largely derived from?
Inflowing streams and rivers from the drainage basin
What does soil, vegetation cover, drainage ratio (CA:LA) and catchment slope determine? (2 things)
- Particle supply rate
2. Composition of sedimenting materials (organic vs. inorganic)
What are the characteristics related to catchment attributes? (4 things)
- Shape of lakes
- Size of lakes
- Their catchment morphometry
- Lake attributes correlated
What is the advantage of covariation?
The ability to develop simple empirical models capable of predicting a variety of sediment attributes
What is the disadvantage of covariation?
Confounds interpretations of “cause and effect”
What happens to profundal sediment is LA and max depth both increase?
Profundal sediment decreases
The organic content of the sediment is best predicted from, what?
The inorganic matter sedimentation rate
What do lake and catchment morphometry determine?
The location where most biological activity occurs in aquatic systems
What is closely associated with the sediments in shallow lakes, streams and wetlands?
Biota and its metabolism
Where is profundal sediments metabolism low?
In deep lakes
- Where high fraction of the organic matter is decomposed
Sediment organic content and lake depth, have what kind of relationship?
Negative
What happens to particles in small, low density and shallow water?
The particles get resuspended readily by turbulence and transported by currents in all aquatic systems
What is turbulence controlled by? (2 things)
- Lake size (fetch)
2. Wind speed
What happens to particles in deep lakes?
- Settle to the bottom
2. Little subject to resuspension
Sediment focusing
The process in which catchment derived sediment particles that enter lakes are transported toward low-energy sites of permanent deposition in the profundal zone
Zone of sediment erosion (ZSE)
A zone of high turbulence and dominated by coarse-grained inorganic settlements
Zone of sediment accumulation (ZSA)
A zone of low turbulence dominated by fine organic particles
Transition zone (also known as zone of transportation
The zone where sediment accumulation is interrupted by rare periods of resuspension and transport during major storm events
What serves as surrogates for the wave energy and experienced and underwater slope?
Max fetch or exposure
- Predicted by the deposition boundary depth (DBD)
What do steep slopes allow currents to do compared to shallow slopes?
Allows them to impact the sediments more directly and powerfully
What occurs at greater depths?
DBD (deposition boundary depth)
What happens to ZSA when the slope gets steeper?
ZSA gets smaller
What is DBD important for?
Determining where plant, nutrients, organic matter and contaminants are deposited and stored
Where is 1 site for long term sediment accumulation in deep lakes?
Profundal zone
- but also present in bays and macrophyte beds (low turbulences)
What is a good predictor of how much the turbulence is reduced and how much fine sediment can accumulate?
Plant biomass density (space occupied by the biomass)
What do macrophyte beds act as?
Net sinks (in the littoral zone)
What happens to organisms when particles decrease?
Decrease in likelihood of surviving
- Due to lower levels of O2 (low turbulence)
Sediment of lotic systems show great variation in particle size as a function of what?
Spacial and temporal variations in turbulences
Lake and reservoirs that are deep enough to have a profundal zone of sediment transport and accumulation serve as what?
Traps for fine sedimenting particles
Why are sediment traps suspended into the depths of the pelagic zone?
So there is less turbulence
- Just below the metalimnion
What are sediment traps used for?
Used to examine sedimentation rate changes over time or depth in the profundal zone of single lakes
What time of the year is sedimentation in temperate lakes usually maximal?
In the summer time
- But polymictic lakes have great temporal variation in sedimentation
Depending on the system examined, seasonal variation in sedimentation can be attributed to variation in:
(5 things)
- Phytoplankton production
- Allochthonous particles carried by inflowing rivers and streams
- Calcite precipitation
- Organic aggregate formation through turbulence and microbial action with the sedimenting aggregates known as lack snow
- Resuspension of the bottom material followed by resedimentation
Disadvantages of sediment traps?
Can collect more materials than that was produced in the euphoric zone which can lead to an over estimation of sediment rate
What is very important for determining the rate of nutrient and contaminant removal from water to the sediment? (2 things)
- An accurate estimation of sedimentation rates
- To determine the time available for algal cells to decompose during sedimentation or to reach the bottom of the late without decomposing
What is the ideal situation for determine rate of nutrients and sedimentation?
Low turbulence
Where is the best area to get a good coring estimation?
In the middle
- Darker levels on top show us that it is oxic
Measured sinking velocities in nature of: (4 things)
- Rapidly sinking large diatoms
- Crystals of calcite
- Fecal pellets of copepods or large organic aggregates
- Inorganic-organic aggregates (e.g. Iron and Mg oxides)
What does sinking velocity depend on?
Depends on an organisms ability to control their buoyancy
- Larger particles sink faster
What are 6 biological indicators?
- Pollen
- Algae (diatoms, chrysophytes) –> not always a good indicator
- Plant macrofossils
- Cladocera
- Chironomids –> good indicator of oxic conditions
- Ostracods
What are 8 chemical indicators?
- Pigments
- C:N ratio
- Geochemistry
- Organic content
- Grain size
- Organic content
- Organic compounds (hydrocarbons)
- Carbon particels (fire history, carbon fuels)
What does C determine in C:N ratio?
Where primary production is located
What do know decay rates of particular long-lived radioactive isotopes released into the atmosphere allows to serve as?
Good markers for dating sediment
How is the age of a sediment core slice determined?
Determined by comparing an isotopes current specific depth in a core
Radioactive C (14C)
- 1/2 life of 5,730 years
- Widely used to date organic matter
- Not a good marker for recent sediment (less than 400 years)
- -> its too small for accurate readings
Lead-210 isotope
- 1/2 life of 22.3 years
- Produced during decay of Rado-222 gas escaping form earths crust
- Widely used for dating recent sediment deposits (up to 150 years) in lake sediments
Cesium-137
- 1/2 life of 30 years
- Useful marker
- 1986 explosion of nuclear power plant in chernobyl created widespread distribution 137Cs in Europe
What are 5 of the simple, less expensive core markers?
- Clearly defined sediment layers deposited during a record massive storm and resulting sediment runoff or the construction of a road for which records are available
- Historically dated mountain slides, volcanic eruptions or forest fires
- The rapid rise of stable 208Pb in cores associated with the onset of coal burning at the time of industrialization
- The first recorded presence of ragweed pollen in north temperate zone sediment profiles representing the recorded time of forest clearing of agriculture purposes, allowing weed to invade
- The first appearance in sediments of specific chemicals
Shawnigan Lake
- Faced extensive development since early 1900, more extensively since 1970s
- Forest harvesting
- Septic inputs
- Changes in fisheries through introduction of alien species
Smoke Reservoir
- Has been protected since early 1900
- Dams been raised 3 times (1910, 1970 & 2002)
- Intro of Leech river water through deception in 1988
What do lake sediments preserve? (2 things)
Part records of:
- Watershed changes
- Water quality
Land use activities and practices that cause changes?
7 things
- Agriculture/fertilizers
- Livestock farming
- Waste disposal
- Pesticides/herbicides
- Harvesting
- Housing
- Industries
Loading of what causes changes? (5 things)
- Nutrients
- Pathogens
- Metals/organics
- Humic compounds
- Pharmaceuticals
