College aantekeningen
lecture notes geochemproc
- Vak
- Instelling
lecture notes voor geochemische processen aan het aardoppervlak
[Meer zien]Voorbeeld 4 van de 33 pagina's
Voorbeeld 4 van de 33 pagina's
In winkelwagen
In winkelwagen
Verkoper
Volgen
graaggedaan
Ontvangen beoordelingen
Voorbeeld van de inhoud
LecturesLECTURE 1 ESTUARIES
Estuary = Partly enclosed body of brackish water (diluted seawater), with input from rivers/streams
and a free connection with the sea. Place where fresh and sea water mix.
Why are estuaries important to society?
Of major economic interest:
• recreation
• fisheries
• our living environment
Sensitive to environmental change:
• Pollutants (e.g., Hg(mercury) in fish, plastics)
• Harmful algal blooms → fertilizers leak into the sea → nutrients trigger harmful algal
blooms → low oxygen in bottom waters → organic matter sinks and degrades into
deeper water layers→ oxygen supply and demand are out of balance
• Low oxygen in bottom waters
Why are estuaries important for Earth Sciences?
Trapping and processing of dissolved and particulate matter:
Examples (from the field of geochemistry):
• “Filter” for nutrients and carbon (but also pollutants)
(removal of nitrogen through denitrification; burial of phosphorus and organic
carbon)
Denitrification: NO3- → N2(g) (by organisms, nitrogen gas goes into atmosphere)
• Source of CO2 to the atmosphere(degradation of organic matter from rivers)
Degradation of organic matter: CH2O + O2 → CO2 + H2O
Types of estuaries:
• Based on geology: drowned coastal river
valley, delta, flooded glacial channels
• Water circulation in estuaries:
o Delta type systems: river flow
dominant, salt wedge estuary
below river flow, little tidal mixing
(numbers are salinity)
o River flow still dominates, but is
modified by tidal currents, highly
stratified. Fjords with deep sills,
deep estuaries.
o slightly stratified, river flow and tidal
, mixing equally important. More vertical salinity gradients. Shallow estuaries
Why does (higher)salinity move land inward in fall? salinity moves land inward in fall due to less river
runoff
o Well mixed, vertically homogenous
dominated by tidal currents, scheldt
estuary. Tidal oscillation in salinity,
outward/seaward increase in
salinity.
o Silled estuary, surface layer
flow, restricted flow at depth,
fjord with shallow sill/black
sea/Baltic Sea. Mostly stagnant
deep water → anoxic)
Residence time and flushing time:
• Residence time of constituents defined for steady state:
Black Sea: 500-1000 years
• Flushing time = volume of freshwater / river discharge
Well-mixed estuary: 1-10 days, fjord: decades
Biogeochemical processes in estuaries (sink/source)
• Dissolved components
• Suspended matter
• Chemical processes
o Adsorption/desorption
o Precipitation/dissolution
• Biological processes
o Production (of organic matter)
o Consumption/Transformation (of organic matter)
• Sediment-water exchange (influx, efflux, burial)
• Other: Inputs/removal in the estuary
(sewage, dredging)
Role of biological processes:
• Production of organic matter by diatoms and algae
• Removal of nutrients (N, P) from surface water (diatoms also Si)
• Primary production in estuaries(very high) is typically ~230g C/m2/yr in open ocean ~50g
C/m2/yr
• ‘Permanent’ removal in estuaries by sedimentation (C, N, P, Si), transformation to gaseous
forms (N, C)
C:N:P ratios and limiting nutrients in estuaries
, • Redfield ratio for organic matter: C:N:P = 106:16:1, molar ratio, phytoplankton
• N:P ratio of the water determines the limiting nutrient
• The limiting nutrient may vary from location to location depending on
o N:P in river loads
o Role of recycling (P recycled more easily, nitrogen lacks more easily)
o Denitrification (NO3- → N2(g))
o N-fixation (to store more N) → by phytoplankton for example, more N input into
estuary
Estuaries as a sink or source of elements
• How can we assess how river water is altered during transport through an estuary? Loss or
gain of solutes during mixing.
• Conservative behaviour: no loss or gain during mixing (no change in solutes)
• Non-conservative behaviour: removal or addition during mixing (change in solutes)
H4SiO4 = dissolved silica
, total = conservative, so if release of DIP from particles, then removal of P in estuary (Dissolved
Inorganic Phosphate)
Mixing models don’t always work
• Two-end member model only works if you have two well defined end members (e.g. river,
oceanic)
• The end member composition may vary with time
• Third end member (e.g. other tributary)
How humans are altering estuaries: eutrophication as an example
• Excess nutrients driving elevated production of organic material in surface waters
• Oxygen demand exceeds oxygen supply due to dead organic matter rain → low oxygen in
bottom waters
• Examples:
o Scheldt estuary in the past
o Baltic Sea at present
(denitrification removes
N, P is efficiently
recycled, N fixation by
cyanobacteria)
o Massive algal blooms
coastal zone of China
Physical processes also matter e.g.,
Suspended matter deposition/transport.
Factors include:
• Flocculation of clays, (Fe-
)aggregation at higher salinity
• Current velocity (tides, river
flow)
Voordelen van het kopen van samenvattingen bij Stuvia op een rij:
√ Verzekerd van kwaliteit door reviews
Stuvia-klanten hebben meer dan 700.000 samenvattingen beoordeeld. Zo weet je zeker dat je de beste documenten koopt!
Snel en makkelijk kopen
Je betaalt supersnel en eenmalig met iDeal, Bancontact of creditcard voor de samenvatting. Zonder lidmaatschap.
Focus op de essentie
Samenvattingen worden geschreven voor en door anderen. Daarom zijn de samenvattingen altijd betrouwbaar en actueel. Zo kom je snel tot de kern!
Veelgestelde vragen
Wat krijg ik als ik dit document koop?
Je krijgt een PDF, die direct beschikbaar is na je aankoop. Het gekochte document is altijd, overal en oneindig toegankelijk via je profiel.
Tevredenheidsgarantie: hoe werkt dat?
Onze tevredenheidsgarantie zorgt ervoor dat je altijd een studiedocument vindt dat goed bij je past. Je vult een formulier in en onze klantenservice regelt de rest.
Van wie koop ik deze samenvatting?
Stuvia is een marktplaats, je koop dit document dus niet van ons, maar van verkoper graaggedaan. Stuvia faciliteert de betaling aan de verkoper.
Zit ik meteen vast aan een abonnement?
Nee, je koopt alleen deze samenvatting voor €4,89. Je zit daarna nergens aan vast.
Is Stuvia te vertrouwen?
4,6 sterren op Google & Trustpilot (+1000 reviews)
Afgelopen 30 dagen zijn er 76710 samenvattingen verkocht
Opgericht in 2010, al 14 jaar dé plek om samenvattingen te kopen