MB: Sediment Bottoms, Estuaries

Sediment grain size determines much about the style and quality of life in sediments

• sediment grain size?

• what does grain size determine?

• Sand (2-.062 mm), Silt (0.62-.004 mm), Clay (.004 mm)

Grain size determines:

• water retention, oxygen replenishment, burrowing ease, organic content

• set by local hydrodynamics

Organisms in Sediment (2 Types + species, feeding)

1. Macrofauna: annelids, molluscs (clams/snails), arthopods, echinoderms (holothurians, irregular echinoids)

2. Meoifuana: annelids, kinorhynchs, gastrotirchs, nematodes, cepepods)

Feeding: deposit feeding, suspension feeding, predation

Sediment modification- what disrupts sediment? (3)

without organisms in sediment, it can be completely homogenous for large areas

1. organsims continuously modify the sediment around them by burrowing, consuming, defecating, & building it into mounds or tubes’ this is reffered to as bioturbation

2. shallow areas- water movement is also continuously disrupting sediment

3. fine, organic-rich sediment can be anoxic just below the surface

What are Estuaries?

• semi enclosed areas influenced both by fresh water flowing off the land and salt water flowing in from the sea

Estuaries Characteristics

• geologically young (like rocky shores)

• more prevalent on passive margins of continents (UNlike rocky shores)

• high productivity & standing crop (due to high levels of nutrients from land and detritus

-Detritus is organic debris + bacteria & protists consuming it at the base (phytoplankton are important for zooplankton and benthic suspension feeders

Species Diversity of Estuaries tends to be low due to many abiotic challanges:

1. Fluctuating salinity (every tidal cycle)

2. big area, shallow depths= temperature fluctuations

3. Mud clogs filterers, this block sunlight from penetrating water columm

What is Hypoxia?

hypoxia: dissolved oxygen is so depleted that it cannot support animals

What is the main cause of hypoxia?

-Excess nutrients from fertilizers, sewage, etc

1. Nutrient flow into sea from land

2. phytoplankton are spurred to grow

3. zooplankton eat the phytoplankton

4. bacteria feeding on the dead algae (fecal pellets) deplete the water of oxygen

5. Stratification: surface waters are less dense due to being warmer and less salty so oxygen cannot be mixed from the surface to deeper water

6. mobile organsims escape, sedentary die

What is the average size of the hypoxic zone in the northern gulf of mexico over the last 30 years?

• about 5,300 square miles- second largest in the world

Deep Sea Sediment diversity

• sediment is much more diverse compares to deep sea vents