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

saltwedge

partiallymixed

wellmixed

fjord-type estuary with a sill

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”STREAM-SIDEStream DischargeFreshwaterHigher Turbidity(FPOM, DOM, & Sediment)

OCEAN-SIDEWaves & TidesMarine WaterLower Turbidity (usually)

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 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 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

phytoplankton(including phytobacteria)

zoo-planktoncrustaceans &microzooplank.

collecting & grazing

annelids, crustaceans,

mollusks, nematodes, &some small

fishes

smallpredatory

mollusks &crustaceans, & fish (juv.)

Fishes and Birds

soft sediment& epiphyticperiphyton

estuary CPOM

fringing/emergent macrophytes

estuary FPOM

leaf litter

stream CPOM

stream FPOM & DOC

estuary DOC

bacteria& fungi

Salt Marsh

Salt Marsh(Protected Shallow Estuary with Spartina)

(Tropical) Mangrove Swamp Estuary

(Shallow Estuary with Rhizophora)

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.

ChesepeakeBay Species

& OxygenTolerances

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 streamchannelization.

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 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.