Unit III

4/10/23 Lecture

Coastal Wetlands Primary Production

· Nutrients from freshwater tributaries and saltwater tides make estuaries especially rich

Global Patterns of Marine Primary Productivity

· Highest rates fond along continental margins, continental shelves

o Nutrient run-off from land

o Sediment disturbance

§ Grand banks:

· Mixing of Labrador and Gulf Stream currents in shallow water ® rich fishery – Cod, Haddock, Lobster, etc.

2. Chemical Cycling

· Ecosystems depend on the recycling of chemical elements

· Nutrients – chemicals organisms need to live, grow, and reproduce (e.g., C, N, P, S)

· Biogeochemical cycles move these chemicals through air, water, soil, rock, and organisms

· A chemicals specific route through an ecosystem depends on:

o Chemical (element)

o Type of ecosystem and its trophic structure

Nitrogen Cycle

· Nitrogen fixation converts atmospheric nitrogen gas (N2) to ammonia or ammonium (NH3 or NH4)

· Fixation done by some bacteria and by lightning

· Ammonia can then also be converted to nitrite (NO2-), and nitrate (NO3-)

· Plans can use NH4, NH3, NO3-, NO2-

· N important in all species for RNA, DNA, NAD, proteins, etc.

Application of N Fertilizer

· Already Reactive Forms

o Anhydrous ammonia: injected as gas into soils

o Urea: granules applied to soil

o Ammonium nitrate: NH4NO3 granules applied to soils (explosive)

o Others…

· Organic Forms Converted to Reactive Forms

o Manure

o Decaying organisms

Phosphorus Cycle

· No atmospheric pool

· Most in mineral deposits and marine sediments

o Much of this in forms not directly available to plants

· Slowly released in terrestrial and aquatic ecosystems via weathering of rocks

· Usable form: dissolved inorganic phosphate

Effects of Human Activities on Phosphorus Cycles

· Remove large amounts of phosphate from the earth to make fertilizer

· Reduce phosphorus in tropical soils by clearing forests

· Add excess phosphates to aquatic systems from runoff

4/14/23 Lecture

Phosphorus & Freshwater Primary Production

· Relationship between phosphorus and phytoplankton (and macrophyte) biomass

· Nutrient availability controls rate of primary production, especially P

o Aquatic systems: can have too much of a good thing

§ Too much P and/or N ® eutrophication

Nutrients and Decomposition

· Availability of nutrients depends on rate of conversion form organic to inorganic (useable) forms

o E.g., nitrogen comes in many forms

§ Only “fixed” nitrogen (ammonia; NH3) is usable by plants

· Decomposition may occur in steps

o A) Scavengers (ants, flies, vultures, hyenas, etc.)

o B) Bacteria, fungi

§ Rate influenced by temperature, moisture, and chemical composition

Decomposition in Aquatic Ecosystems

· Also carried out by scavengers, bacteria, fungi

Decomposition of Leaves in Aquatic Ecosystems

· Leaves with a higher lignin content decompose at a slower rate

o Lignin: fills in spaces in cell wall

Aquatic Ecosystems

Lakes and Ponds

· Standing bodies of water (lentic waters)

o Small ponds to very large lakes

· Formed through glacial, river, tectonic, and volcanic activity

4/17/23 Lecture

Lake Baikal Endemic Fauna

· World’s only freshwater seal, Phoca sibirica

· 344 species of amphipods

o Several exhibit gigantisms

Lake Baikal Issues

· Climate change: temp has risen 1.5C in 50 years

· Nutrient pollution (historically ultra-oligotrophic)

o Explosion of Spirogyra algae

o Altered zooplankton dynamics

· Cd pollution from mining upstream on one of its tribs

Chemosynthesis in Lake Baikal

· Frolikha Vent: Hydrothermal vent, heated water. Sulphates feed chemosynthetic bacteria

· Oils seep: Methane feeds chemosynthetic bacteria

Lakes and Ponds

· Horizontal zones:

o Littoral zone – from shore out toward center, as far out as sunlight penetrates to the bottom

§ You will find rooted plants here

o Limnetic zone – where sunlight does not penetrate to the bottom

· Vertical zones:

o Euphotic zone: where there is sunlight

o Aphotic zone: where there is no sunlight

Littoral Zone (“Shallows”)

· Submerged plants (chara, milfoil)

· Floating-leaved plants (lily pad, pond weed)

· Emergent plants (sedges, cattails)

Summer Stratification

· Stratifies (divides) due to differences in water density at different temps.

o Epilimnion: warmest, highest dissolved oxygen

o Metalimnion: rapid temperature change

o Hypolimnion: coldest, lowest dissolved oxygen (due to high biological oxygen demand (BOD) by decomposers)

Human Impacts to Lakes

· Eutrophication (high nutrient conc.)

· Invasive Species

Rivers and Streams

· Rivers and streams flow in one direction (lotic waters)

· Range from small headwater streams to very large rivers

· Streams and their watersheds form nested hierarchies

· Stream Order is a measure of stream size

o 1 – 12, one being the smallest and twelve being the largest (Amazon River)

o You need two streams of the same order to make it a higher order

§ E.g., two first order streams meet to create a second order stream.

· Most of “headwater” streams (1st to 3rd order)

· Mississippi River: 10th order

· Amazon River: 12th order

4/19/23 Lecture

Changes that occur longitudinally:

· Increase in size (width and depth)

· Increase in column (as tributaries flow in)

· From steep gradient to low gradient (flatter land)

3 sections to a large river (morphology of channel):

· Straight: stream order 1-3, small headwater streams

· Meandering: stream order 4-6, mid-reach streams

· Braided: stream order 7-12, large, low-gradient rivers

Floodplains and Floods

· Floodplain = flat land adjacent to a stream or river that experiences occasional or periodic flooding

· Flood magnitude defined in terms of return period, or recurrence interval

o E.g., “100-year flood”

· Just an average, based on historic data

· Can have back-to-back 500-year floods

“Stalking the Gentle Piranha”

· Essay by David Quammen

· Visited the Zabalo River, a tributary to the Amazon River

· Essay tells of relationship between fish & trees

· Part of every year, lowland Amazon Forest is covered by floodwater (up to 40 feet deep)

o 30,000 sq. miles

· During the flood

o Fish rely on seeds and fruit of those trees

§ Large jaws to break seeds open

o Trees rely on fish to disperse the seeds

· Implications for removal of forest

· Remove trees ® will remove fish ® will remove other trees whose seeds the fish disperse

Humans Impacts to Streams

· Channel alteration

· Dams

· Pollution

· Invasive species