River inputs to estuarine systems Flashcards
What process regulates the concentration of atmospheric carbon dioxide?
Chemical weathering - due to feedbacks betw weathering and climate
What are dissolved components in rivers mainly derived from?
- Precipitation (rain), mainly contributing Cl- (cyclic salt) & SO42- (pollution)
- Chemical weathering (dissolution) of catchment bedrock
- Organic matter from soil
- Evaporation and precipitation (e.g. precip of CaCO3)
- anthropogenic sources increasingly important, may be the main source of some components
What is the composition of ~80% of river water controlled by?
- precipitation (low TDS, rel high Na)
- chemical weathering (higher TDS and Ca) of catchment bedrocks
- evaporation (high TDS, low Ca due to precipitation of CaCO3, CaSO4, etc)
What are the features of transport-limited silicate terrains?
TDS < 20mg/L
Drains intensely weathered cation rocks and soils
Enriched in Si, Al, Fe, org material and low pH
Extreme weathering leaves residues of Fe and Al oxides, stripping alkali & alkali earth elements plus silica
fresh rock unavailable bc of low erosion
What are the features of weathering-limited silicate terrains?
TDS = 20-40 mg/L
Rate of erosion exceeds rate of chem weathering
Availability of fresh rock results in higher number of moles of pos charge per L & TDS than in transport limited regimes
What are the features of carbonate terrains?
TDS 40-250 mg/L
Dissolved ions derived from weathering carbonates, pyrite and minor evaporites
What are the features of evaporite terrains?
TDS > 250 mg/L
Weathering of evaporites and CaCO3
High ionic strength
What are the main anthropogenic inputs into rivers?
- organic matter (sewage etc)
- excess nutrients (P, N)
- pesticides
- heavy metals from acid mine drainage (important in the Fal estuary)
What are the controls on weathering rates?
- Runoff
- Erosion rates
How does erosion rate create a dynamic link between weathering, temperature and CO2?
Higher CO2 -> higher temps -> more weathering -> lower CO2 -> lower temps -> less weathering -> higher CO2 …
Weathering of which minerals is congruent?
Carbonate and evaporite minerals.
Weathering of which minerals is incongruent?
Most silicate minerals. Results in formation of secondary minerals.
Riverine suspended particles are enriched and depleted in what?
Enriched in less soluble elements and depleted in more soluble elements, relative to the catchment bedrock.
Why do most major elements that are transported in particles have little effect on ocean chemistry?
They are mainly deposited in ocean margins.
