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
What nutrients do salt marshes receive from rivers and groundwater?
NO3
What do salt marshes convert NO3 into?
DON, PON, NH4, and N2
Are salt marshes sources or sinks of C, N, and P to estuaries?
Sources
What is a common limitation in salt marshes?
Nitrogen limitation
What is the dominant form of nitrogen in most salt marshes?
NH4 (Ammonium)
What allows for significant rates of denitrification in salt marshes?
Flooded, anaerobic sediments
How does the contribution of new inputs compare to recycled nitrogen in salt marshes?
About equal – different from upland ecosystems where new inputs are much lower (~10%)
What organisms may contribute significantly to the nitrogen budgets of salt marshes?
Cyanobacteria and soil bacteria through N-fixation
What is the range of salinities in which salt marshes can exist?
Salt marshes can exist over a wide range of salinities.
How does the wide range of salinities in salt marshes affect their biogeochemistry?
There will be large variations in the biogeochemistry of different marshes.
What is the main reason for the active S cycle in estuarine sediments?
High concentration of SO42- in seawater (28 mM)
What contributes to the active S cycle in estuarine sediments besides high SO42- concentration?
Large inputs of land- and estuary-derived organic matter
What does LOICZ stand for?
Land-Ocean Interactions in the Coastal Zone
What are the characteristics of LOICZ as a modeling method?
Minimal data requirements, ability to work with secondary data, widely applicable uniform methodology
What is LOICZ informative about?
CNP processes and fluxes
What assumption does LOICZ budgeting make?
all materials are conserved
How is the difference between ∑inputs and ∑outputs explained?
processes within the system: [∑(sources - sinks) ]
What is the outline of the LOICZ budgeting procedure?
I. Define physical boundaries of system of interest
II. Calculate water and salt balances to determine physical dynamics
III. Estimate nutrient balances
IV. Derive apparent net biogeochemical processes
What are water and salt budgets used for in coastal systems?
Estimate water exchange
How are system biogeochemical fluxes measured?
Departure of nutrient budgets from conservative behavior
What is the assumption for nonconservative DIP flux?
Proportional to (primary production - respiration)
What does the mismatch from ‘Redfield expectations’ for DIP and DIN fluxes depend on?
Proportional to (nitrogen fixation - denitrification)
What is the formula for calculating net primary production (NPP)?
(p-r) = -∆DIP • 106(C:P)
What is the formula for calculating nitrogen fixation minus denitrification?
(nfix-denit) =∆DINobs -∆DINexp
What do derived net processes represent in stoichiometric calculations?
apparent net performance of system. Non-biological processes may be responsible for some nutrient uptake/release.
What does Net Ecosystem Metabolism represent?
Production - Respiration
How are the rates of Net Ecosystem Metabolism described?
Apparent, based on stoichiometric assumptions
What is the typical range of values for Net Ecosystem Metabolism?
Most values cluster near 0
What values of Net Ecosystem Metabolism are considered questionable?
Extreme values beyond ±10
As Primary Production increases, respiration tends to exceed production. What does this reflect?
Apparently reflects importance of sedimentary organic matter loading
What process dominates when values cluster near 0 in (nitrogen fixation-denitrification)?
Denitrification
What is indicated when apparent N fixation is greater than 5 in (nitrogen fixation-denitrification)?
Too high
