sandy beaches Flashcards
location
all over the earth
tide
intertidal
substrate
sand: Sediment particles have a diameter of 0.02 – 2 mm
Fine sand can retain water, but coarse sand allows water to
drain away
Not much detritus is retained in sand
source of sand
depends on the location
rocks on land and/or
calcium carbonate (CaCO3) skeletons of animals and coralline algae, including parrotfish poop
phys char: slope
variable over the seasons and varies with location
wave action
phys char: energy
moderate to high
Higher energy beaches have a steeper slope and larger sediment particles
DYNAMIC EQUILIBRIUM OF
SANDY SHORES
Beach shape & slope fluctuate about an equilibrium (which also
changes with time, but much more slowly)
Forces of erosion and deposition reach a dynamic equilibrium
Waves, tides, currents, and wind erode and transport sand
beach equilibrium profile for storm beaches
- typical of winter and after storms
- erosional
- coarser erosion sediment
- steeper slopes
- large, high berms
- narrow back shores
beach equilibrium profile for swell beaches
- typical of fair-weather conditions
- depositional
- finer-grained sediment
- gentler slopes
- small, lower berms
- broad back shores
light
absorbed or reflected by the surface layer of sand, so no light in sediment below surface but with some transparent particles and spaces between particles light penetrates deeper than in mud
temperature
within sand is quite stable
Just like mud, sand is a good buffer against temperature (and
salinity) changes
Below the first few centimeters, the temperature in the sand is the same as the surrounding seawater
salinity
within sand is also quite stable
Below the first 10-15 centimeters, the salinity in
the sand is the same as the surrounding seawater
Even with precipitation & run-off, the more dense
saltwater will sink below freshwater
nutrients
little to no nutrients in the sand as
nutrients move through with water and are used
quickly
BUT, waves do bring algae to beach
oxygen
lots due to high wave action / energy especially at high tide May be reduced in interstitial water at low tide as oxygen is
consumed by organisms
Fine-grained beaches do not allow oxygen to enter as quickly and therefore may become hypoxic at low tide
hydrogen sulphide
– little to none
Except at low tide in fine-grained beaches
biodiversity
low (except meiofauna)
few organisms are adapted to high energy shifting of sand particles
productivity
low (there are benthic diatoms in first few
millimeters of sand but producers get shifted around so much and nutrients are low)
biomass
low to moderate
meiofauna
Interstitial organisms (spaces between particles)
Size: 62 um to 0.5 mm
Benthic invertebrates (animals from many phyla)
importance of meiofauna
decomposition
nutrient cycling
food for many consumers at higher trophic levels
very sensitive to anthropogenic pollution, making them excellent
indicators
adaptations
Living among the shifting sands is the primary challenge here
– particles are always in motion
Burrowing is rapid & powerful (razor clam)
bio adaptations
camouflage
- Most organisms depend on waves to bring food & nutrients
e. g. mole crabs, sand dollars
Wrack line very rich in nutrients
Beach hoppers / amphipods
zonation
Just like in the rocky intertidal, there is a pattern of zonation
due to tides at sandy beaches
ECOSYSTEM SERVICES PROVIDED BY
SANDY BEACHES
sediment storage and transport;
wave dissipation and associated buffering against extreme weather events;
dynamic response to sea level rise;
breakdown of organic materials and pollutants;
water filtration;
nutrient mineralization and recycling;
storage of water in dune aquifers and groundwater discharge through
beaches;
maintenance of biodiversity and genetic resources;
providing a nursery area for juvenile fishes (e.g. sand lance, grunion);
nesting sites or rookeries for turtles, shorebirds, and pinnipeds;
prey for birds and other terrestrial wildlife;
scenic vistas and recreational opportunities;
functional links between terrestrial and marine environments
human impacts
Disturbance of species & sand
Beach grooming
Pollution, especially plastic!
Resource exploitation
Clams, crabs for food
Shrimps, worms for bait
Seaweed as compost
Shells & other treasures
Coastal development
Invasive / alien / introduced species
European green crab, Carcinus maenus
Climate change / sea level rise (erosion)
what’s the equilibrium beach profile?
Equilibrium beach profile (EBP) explains the balance between destructive and constructive forces acting on a beach.
what’s equilibrium?
The slope of the floor of a sea, ocean, or lake, taken in a vertical plane, when deposition of sediment is balanced by erosion.
