Unit 2 - Coastal Physics and Ecosystems Flashcards
How do nutrient concentrations in river water compare to open-ocean water?
nutrient concentrations naturally higher in river water
What human activities in the watersheds elevate nutrient concentrations in estuaries?
agriculture and fertilizer runoff.
What are some local inputs that elevate nutrient concentrations in estuaries?
Human waste discharge and street runoff.
How does primary production in estuaries respond to nutrient loads?
Generally positive trend
What are the characteristics of bioavailable nitrogen in pristine river waters?
Pristine river waters generally have low levels of bioavailable N (NO3 and NH4)
How does salt marshes affect the bioavailable nitrogen in estuarine waters?
Bioavailable N is stripped from river water as it passes over salt marshes
Why can rainfall be a significant contributor to estuarine waters?
N-filtering by salt marshes is very efficient
Where does most of the bioavailable nitrogen in estuaries come from?
not new, but recycled from mineralization of OM within estuarine water column and sediments
Why may cessation of excess nutrient input not have an immediate effect in estuaries?
because of sediment storage of N and P, making bottom sediments a long-term source of N and P
How do increases in nutrients in the Mississippi River affect the Gulf of Mexico?
Enhanced nutrient transport to the Gulf of Mexico
What does excess nutrients in coastal areas promote?
Excessive primary productivity
Where do big rivers discharge most of their sediment?
Open continental shelf or the upper slope
What happens to sediment in smaller rivers with significant estuaries?
Trapped in the estuaries due to slow water flow
Why is sediment reactions in estuaries different from water column reactions?
Due to low redox conditions in the sediments
What is a Salt Marsh?
A relatively flat intertidal area along the margin of an estuary where fine-grained sediment is deposited and salt-tolerant grasses grow
What is the channelization in a salt marsh dependent on?
tidal range (more tide -> more channels)
What leads to large amounts of import and export with tidal creeks in salt marshes?
Tide-induced flushing combined with groundwater flow from land
How does tidal flow affect salinity in salt marshes?
Low tide brings low salinity flow due to freshwater runoff; high tide inundates marsh w/ seawater leading to highest observed salinities.
How do salt marsh soils change during the daily tidal cycle?
During high tide, soils are inundated leading to anaerobic conditions; during low tide, soils drain, high redox potential re-established in surface sediment.
What factors affect dynamic equilibrium in salt marsh vegetation?
Rate of sediment accumulation and rate of sea level rise (or coastal subsidence)
How does sediment accumulation impact salt marsh vegetation?
As deposits accumulate, erosion + organic matter oxidation ⬆️, slowing rate of further accumulation
How does sea level rise affect salt marsh vegetation?
As sea level rises, the marsh is inundated more frequently, leading to an increased accumulation rate of sediment and peat
What is the consequence when the rate of sedimentation does not keep up with sea-level rise in salt marshes?
Marshland is lost
How does sea level rise due to global warming impact salt marshes?
It could accelerate the loss of marshland
