Aquatic Ecosystems

Types of Aquatic Ecosystems • Often divided into two major categories: • Marine Ecosystems – have a high salinity. • Freshwater Ecosystems – low salinity. • Terrestrial biomes are primarily determined by temperature and rainfall. • Aquatic biomes primarily determined by depth, salinity, and rate of flow.

Freshwater biomes • Two basic types: • Lentic or standing water. Lakes, ponds, marshes, swamps, and bogs. • Lotic or flowing water. Streams and rivers. • Most lentic ecosystems are freshwater but some can be saline.

Salinity • Salinity – measure of the amount of dissolved solids in water. • Measured in parts per thousand (ppt). • Ocean water typically 30 ppt. • Freshwater typically 0.5 ppt or less. • Water in between called brackish (slightly salty).

Lentic Ecosystems • Little net flow into & out of system. Usually have circulation within though. • Flow helps distributes warmth, oxygen, & nutrients through the system. • Can be stratified (layered). • Can have temperature stratification – thermocline. • Can have oxygen stratification.

Depth • Depth of ecosystem greatly influences the amount of sunlight that can penetrate. • Light penetration determines how many and what kinds of plants found. • Divide into zones: – Photic zone – where light penetrates. – Aphotic zone – where light does not penetrate. – Benthic zone – bottom or floor.

Abiotic Factors

Biotic Factors

Lake

Deepest type. May have aphotic zone. May be fed by aquifers.

Complex food webs. Main producers are floating algae & benthic plants on shoreline.

Ponds

Light reaches benthic zone. Simpler food webs. Main Fed by rainfall, may be producers algae & plants on seasonal. the bottom.

Marsh

Very shallow w/ exposed land. Water often low O2.

Swamp

Land soaked w/ water, poor Large trees & shrubs drainage. adapted to growing in muddy low O2 soils.

Bog

Inland wetland, little flow in/out. Soil acidic, decay slow.

Plants have roots below water, leaves above.

Sphagnum moss is dominant, accumulates as peat.

Lakes • Deep enough that plants cannot grow on the entire bottom. • Very often stratified by temperature. • Colder water more dense than warm water. • Cold water can hold more dissolved oxygen (D.O.) than warm water.

Lake Stratification • Deeper water usually cooler, more D.O. • Oxygen comes from air & photosynthetic plants. • Most decomposition occurs in the benthic layer – uses D.O. • D.O. in cooler, deep water tends to be anoxic (no oxygen).

Lake Turnover • Some lakes will have periodic turnover. • Lake turnover can occur because of surface water warming/cooling & by wind currents. • Around here lakes typically turnover twice a year (spring & fall). • Turnover allows for nutrients from the bottom to be distributed and replenish D.O.

Eutrophication • Lakes gradually accumulate sediments. • Start to fill in, allows more plant growth along the banks. • As plants die & are decomposed, more nutrients available. • More nutrients= more plankton, bacteria, & other microorganisms. • More microorganisms= more macroorganisms.

Eutrophication • All of these things are growing, dying, and decomposing. • More nutrients to feed the cycle. • All of these things use more D.O. • Over time lake will gradually fill in. • First becomes a marsh, then a meadow, eventually a forest.

Cultural Eutrophication • Runoff from farms rich w/ nutrients (fertilizers). • Greatly increases the available nutrients. • Causes dense growths of algae – algal blooms. • Bacteria & decaying algae use up D.O. rapidly, causing fish die offs. • Can cause the lake to “die”.

Lotic Ecosystems • Usually called rivers, streams, creeks, & brooks. • Primarily defined by flowing water. • Organisms that live in streams are adapted to live in flow. • Velocity can vary tremendously. Some streams are susceptible to flash flooding.

Stream Order • Streams are ordered by where they are spatially. • 1st order streams are the headwaters. • As other streams combine w/ them – form 2nd order streams. • Usually as stream order increases, depth increases & velocity decreases.

Stream Flow • Headwater streams tend to be shallow, cold, high D.O., high velocity. • Usually have pools & riffles. • As stream order increases, flow slows down. • Allows for sediments to deposit. • As streams meander, get erosional & depositional zones.

Stream Organisms • Most adapted to live in flowing water. • Insect use a combination of hooks, strings, & other modifications to stay in place. • Most insects fall into 1 of 4 categories: – – – –

Shredders – shred fallen plant matter. Scrapers – scrape biofilm from surfaces. Gatherers – collect deposited/floating materials. Predators – eat other insects/fish.

Vegetation • Riparian vegetation – all the vegetation found in the immediate areas around the stream. • Plants are tolerant of flooding. • Can provide energy to stream food chains. • Can affect degree of shading & water temps.

Decomposition • Food webs in streams are usually decompositional. • Material falling into the streams usually coarse (large). Coarse particulate organic matter (CPOM). • Some leaches out (DOM). • Some is eaten & broken down (FPOM). • Recursive process – particles of OM are reprocessed as it travels downstream. • Current transport nutrients downstream.

Nutrient Spiraling • Nutrients cycle between organic & inorganic forms. • As the cycle is turning, moving downstream. Forms a helix. • Current determines how close the loops are. • Slower current – more nutrients available. • Change current, change spiral distance.