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Hydrological Cycle. Estuaries. Estuary = semi-enclosed body of water where freshwater from land drainage dilutes sea water. Fresh  Brackish  Marine – extent of salinity types varies with stream discharge, wave action, tidal action, evaporation, etc. - VARIABLE. Types of Estuaries.

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Hydrological Cycle

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Hydrological cycle

Hydrological Cycle



  • Estuary = semi-enclosed body of water where freshwater from land drainage dilutes sea water.

    Fresh Brackish Marine – extent of salinity types varies with stream discharge, wave action, tidal action, evaporation, etc. - VARIABLE

Types of estuaries

Types of Estuaries







fjord-type estuary with a sill

Estuary substrates

Estuary Substrates

  • Substrates is estuaries usually are dominated by the sediment and FPOM transported by the stream input. (low tide may revel “mud flats”)

  • Sedimentation may form

    a delta if tidal and wave

    action is low enough.

    Mississippi delta

Estuary sides

Estuary “Sides”


Stream Discharge


Higher Turbidity




Waves & Tides

Marine Water

Lower Turbidity


Drought floods tides

Drought, Floods, & Tides

Drought = less freshwater; estuary becomes more saline and less sediment w/ FPOM.

High Tide = more marine water; estuary becomes more saline.

Floods = lots of freshwater; estuary becomes much less saline and sediment with FPOM may be deposited less in the estuary itself (“blown out” of the estuary)

Low Tide = less marine water; estuary becomes less saline.

In estuary primary production

In-Estuary Primary Production

  • High turbidity often reduces (or eliminates) in-estuary submerged photosynthesis closer to the stream input.

  • Salt-tolerant marginal emergent macrophytes undergoes significant production, especially in higher order streams. (e.g., Spartina)

  • Periphyton (microphytes) may be able to undergo in-stream photosynthesis on the substrate (mud) surface (often at low tide).

  • Phytoplankton often important in more protected estuaries and at the seaward side.

Allochthonous inputs

Allochthonous Inputs

  • In most estuaries the most nutrients come from surrounding terrestrial environments via stream discharge (allochthonous materials)

  • Most enters as FPOM or DOM. Limited CPOM, but some from surrounding emergent macrophytes.

  • Detritivores and decomposers are very important in most estuaries.

  • The flats (mud flats) of estuaries often are very productive.

  • Deoxygenation of sediments often occurs.

Estuary food web

Estuary Food Web





stream CPOM

stream FPOM & DOC

estuary CPOM

soft sediment

& epiphytic



(including phytobacteria)

estuary DOC

estuary FPOM


& fungi



crustaceans &


collecting & grazing




nematodes, &

some small fishes



mollusks &


& fish (juv.)

Fishes and Birds

Hydrological cycle

Salt Marsh

Salt marsh protected shallow estuary with spartina

Salt Marsh(Protected Shallow Estuary with Spartina)

Tropical mangrove swamp estuary shallow estuary with rhizophora

(Tropical) Mangrove Swamp Estuary(Shallow Estuary with Rhizophora)

Estuary animals

Estuary Animals

Freshwater Animals – Most have a low salinity-range tolerance (stenohaline) and are restricted to the upper estuary (salinity <7).

Stenohaline Marine Animals –have a low range of salinity tolerance are restricted to the outer estuary (salinity >25).

Euryhaline Marine Animals –have a high range of salinity tolerance and are found in most of the estuary (salinity >15).

Estuarine Animals – All have a wide range of salinity tolerance and many can inhabit much of the estuary (including hypersaline isolated areas). Most in salinity 5-18.

Chesepeake bay species oxygen tolerances

ChesepeakeBay Species& OxygenTolerances

Human impacts development

Human Impacts: Development

Low land in the estuary protected from flood or tidal inundation and developed.

Increases sedimentation in channel, water velocity, and estuary “cleaning” of water before it reaches the ocean.

Similar to stream


Human impacts barrages

Human Impacts: Barrages

Barrages block tidal and other increased water flow from entering from seaward.

-May protect from storm or flooding surges.

-May keep water fresh for use locally.

Increase sedimentation.

Change to more freshwater environment.

May prevent or impede spawning migrations.

Human impacts pollution

Human Impacts: Pollution

Many human population centers are in or drain to estuaries (sewage and other pollution).

Heavy metals in sediments are of concern.

Estuaries can be nutrient overloaded. Red Tides and other algal blooms.

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