Environmental Geoscience TEST 2

interglacial period

high sea level, deposition of of Fe-oxides, intensive Fe-oxide and sulfate reduction, pyrite formation (could lead to heavy metal contamination in water)

glacial period

low sea level, exposure of submerged sediment to air, leads to pyrite oxidation and excess production of H+ ions (acidification) HIGH ACID SULFATE SOIL PRODUCTION

Bay of Bengal

contaminated groundwater caused by heavy metal adsorption. Recommendation to allow groundwater to be fully oxygenated before use to allow Fe Oxide to precipitate and adsorb heavy metals

actual acid sulfate soils

soils containing highly acidic soil horizons resulting from oxidation of pyrite. has a pH <4.0.

potential acid sulfate soils

contain iron sulfides and have pH>4.0. If exposed to air/oxygen, may turn in to the more extreme version.

Ways to determine acid sulfate soil

pH (must be less than 4)

electrical conductivity (ASS will be more conductive)

redox potential

color: by adding peroxide can judge presence of pyrite by how orange the soil turns

Barker Inlet

local area was drained and exposed pyrite to the air. It was oxidized, causing acid sulfate soils, killing local vegetation and contaminating groundwater.

recommendation was to reflood the area.

106C:16N:1P

redfield ration

oxygen

best oxidant used by bacteria in surface sediment

other oxidants

nitrate, Fe-Mg oxide, sulfate

Denitrification and Phosphorus adsorption

2 processes that limit efficiency of recycling biologically available N and P

denitrification

conversion of available N into N2 gas (non reactive)

Phosphorus adsorption

binds P to sediment

australia causes of sea level rise

1. tides and storm surges

2. ocean currents

australia effects of sea level rise

1. inundation

2. erosion

3. salinization

two main causes of global sea level rise

1. melting of polar and glacier ice

2. thermal expansion

Atolls

rings of flat reef-formed islands around a protected lagoon, formed around extinct subsided volcanoes

why are atolls sinking?

sea level rise is at a much faster rate than other glacial cycles.

ocean temp rise and acidification harm the growth of the coral that forms the island—growth can’t keep up with rising sea level

ocean acidification

an excess of H+ ions are released in the decay of carbonic acid (H2CO3) into bicarbonate and carbonate.

aragonite

shell-making compound, depleted in conditions of lower pH and higher temperature. aka calcium carbonate

reef growth impediments

1. coral bleaching (warm water)

2. eutrophication (coral overgrown by algae)

3. invasive pests (crown-of-thorns sea star)

water table

border between unsaturated and saturated ground material

unconfined aquifer

water not held in by any constricting layers

confined aquifer

water held in by constricting shale layer on top

aquitard

shale barrier that prohibits water flow. causes confined aquifer.

cone of depression

phenomena where water pumping from well drains aquifer in a surrounding area

darcy’s law

rate of water flow through tube is…

1. proportional to difference in height of water between 2 ends of tube

2. inversely proportional to length of tube

3. proportion to coefficient K, hydraulic conductivity

hydraulic conductivity

ease with which water can move through pore spaces (a velocity)

permeability

capability of rock to allow passage of fluids

what is permeability affected by?

shape and size of pore spaces

what degree pore spaces are connected

grain shape and size

grain packing/cementation

low permeability

fine grained, well sorted, and well packed material (clay, silt)

high permeability

large grained, poorly sorted, loose material (gravel, etc)

threats to groundwater

over-depletion (agriculture)

contamination

sea water intrusion

artificial recharge

purpose by which natural groundwater growth is augmented. involves injecting water back in to subsurface or creating reservoir where water seeps back in to subsurface

water surface storage

australian farms are very dependent on this, and it is inefficient because of constant water loss due to evaporation

causes of variance in groundwater

rainfall seasonality

vegetation uptake seasonality (less in winter)

agricultural seasonality

seawater intrusion

caused by excessive groundwater extraction in coastal areas and/or sea level rise.

coastal wells become semi-saline, has occurred in all major australian cities.