estuaries

definition of an estuary

a narrow, semi-closed coastal body of water which has a free connection with the open seas. salinity of the water is measurably different to salinity of the open ocean

the upper limit of an estuary

the head

the lower limit of an estuary

the mouth

what type of estuary are most estuaries

positive estuaries

vertically mixed estuaries

surface and bottom layers always move in the same direction

stratified and salt wedge estuaries

surface and bottom layers move in opposing direction

what affects circulation

river flow, tidal currents, morphology, bathymetry

gravitational circulation

driven by density differences and varies with stratification

how does salinity change in positive estuaries with large freshwater input

salinity changes due to mixing o freshwater and seawater

definition of flocculation

when small particles in suspension coagulate to form a larger particle

dominates non-conservative mixing

removal processes

how can inputs of material or contaminants be classed as diffuse

if they occur across the whole estuary and come from urban runoff into the estuary

what is each estuarine salinity vale paired with

either 1 freshwater fraction value or 1 seawater fraction value

chesapeake bay complex salinity is due to

high number of estuaries

basin morphology and hydrography result in

stratification of the estuary

what is a sill in an estuary

a mass that blocks the inflow of saline water, reducing bottom water exchange and drivers stratification

what type of mixed estuary is chesapeake bay

partially mixed

what are hypoxic conditions

less than 20% of expected dissolved oxygen at the surface

what are anoxic conditions

no dissolved oxygen

when phytoplankton primary production is highest

from spring to autumn

why is there a strong seasonal pycnocline in the summer

increase surface temperatures increase stratification, combined effects of temperature and salinity changes

what is estuarine flushing time

the time required to replace the freshwater in an estuary by reiver discharge

what concept is required to calculate freshwater residence times

budget concept

longer estuarine flushing times mean…

there is more time for uptake of nutrients, pollutants

consequence of long flushing times

long processing time for nutrients into the bay, vulnerability to eutrophication

the 2 methods of calculating flushing time

freshwater fraction method, tidal prism method

advantages of freshwater fraction method

most data is readily avaliable and accounts for all mixing processes as it uses salinity to calculate freshwater fraction

advantages of the tidal prism method

requires little input data, no salinity survey required

estuarine flushing time varies with…

tides, river discharge