ENVS 305 exam 3 lecture notes

• Sedimentation


  A physical process during which solid material is moved and deposited in a new location - can be rocks and minerals (abiotic) and remains of plants and animals (biotic/organic)
• Total solids


  Total suspended solids(TSS)+total dissolved solids (TDS)
• Turbidity


  Describes the visual appearance of TS in water, can also be quantified
• Turbidimeter


  Instrument used for measuring the turbidity of a liquid suspension, usually as a means of determining surface area of the suspended particles
• Turbidimeter operation


  Light source is pointed to sample cell and light scattered by solids in sample and scattered light creates apparent absorbance detected by photometer and the remaining light returns and is detected
• High turbidity


  Not as clear and darker, less visible visual appearance
• Turbidity units


  Nephelometric turbidity units (NTUs)
• Erosion


  Movement of sediment from one location to another, generally a natural process, largest source of sediment supplied to rivers
• Erosion steps


  1. Detachment

  2. Entrainment

  3. Transport
• Detachment


  Particle or aggregate loosened from surface
• Entrainment


  Initiation of motion by flow
• Rill


  Concentrated overland flow
• Inter rill (sheetwash)


  Diffuse overland flow
• Natural erosion influenced by running water, wind, ice
• Elevated levels of sediment in surface waters can be problematic because of erosion
• Excess levels of sediment can fill lakes, dams, reservoirs and waterways
• Particles


  Can remain suspended in aqueous systems, rate of settling depends on particle size - stokes law used to calculate settling rates
• Particles<0.0005 mm


  Acts as colloids: do not settle due to force of gravity, can remain suspended indefinitely
• Soil particles


  Interact with many types of chemistries and microbial life in water, inorganic (soil) and organic particulates exhibit mostly negative (-) and some positive (+) surface charges - chemical and biological contaminants adsorb and desorb to/from soil particles
• Particulates can carry pollutants through surface water


  • Nutrients, metals, organic compounds (PAHs and PCBs), herbicides, insecticides, fuels, solvents, preservatives, microorganisms (including pathogens)
• Anthropogenic activities increase sediment levels in freshwater
• Trees


  Stabilize soil structure and increase infiltration into soils and root zones
• Removal of trees


  Decrease infiltration and increase runoff, leading to transport and sediment deposition
• How wildfires can negatively impact water quality

  1. Intense fires cause chemical reactions that release metals, nutrients and other toxicants into the soil. Subsequent rains can wash these contaminants into rivers and reservoirs, which can negatively affect wildlife, agriculture and humans

  2. Scorched hillsides are vulnerable to post wildfire rains which can create mudslides that wash huge amounts of ash, debris and toxicants into waterways

  3. Toxic chemicals from burned and melted infrastructure (PVC and HDPE pipes, lithium batteries and other plastics) leach into soil and groundwater

  4. Stream temperature increase from lack of shade (just temperature from stream- the body of water)

  5. More nutrients and warmer water temperature can cause bacterial blooms, depleting dissolved oxygen and suffocating fish
• Overgrazing


  Too many animals eat too much of the plant cover - impedes plant regrowth, a leading cause of soil degradation
• Government subsidies provide few incentives to protect rangeland
• 70% of the worlds rangeland is classified as degraded
• Effects of overgrazing


  • Impacts soil and damages structure which decreases water infiltration, decreases aeration (the introduction of air into a material), and invasive species gain foothold and outcompete natives in altered environment which leads to decrease grass growth and survival and removes native grass, exposing bare topsoil and also results in wind and water erosion
• Effects of urbanization on sediment

  In developed lands rain pours more quickly off of city and suburban landscapes, pavement and rooftops shed water, storm drains deliver water directly to waterways, streets act as streams, collecting storm water and channeling it into waterways, water pools in indentations and filters into the soil, roots anchor soil, minimizing erosion, trees and other vegetation break the momentum of rain help reduce surface erosion, pollutants collected on impervious surfaces are washed into streams, rivers and lakes
• Construction of new roads cause loss of sediment - 5x to 20x increase in sediment levels
• Soil destabilisation during mining leads to increased sediment levels in impacted freshwater
• Reducing sediment impacts on water: erosion control methods


  Revegetation: new plant growth restabilizes soil - decrease erosion, runoff, erosion control methods: protect soils from runoff, evaporation, provides air exchange for new plantings, turf reinforcement mats: protect soil surface, decrease erosion runoff
• Minerals


  Naturally occurring, inorganic solids (don't contain carbon), have specific chemical composition, definite crystalline structure
• Metallic minerals


  Minerals that contain metals in their chemical formula, have a shine of their own, are associated with igneous rocks, are quite ductile, can be extracted by melting
• Non-metallic minerals


  Minerals that do not contain any metal elements in their compounds, do not have a shine of their own, are associated with sedimentary rocks, are not ductile and can be broken upon a collision, do not yield new products upon melting
• Non-metallic mineral examples


  • Graphite, limestone, mica, dolomite
• Metallic mineral examples


  • Galena (silver), magnetite (iron), arsenopyrite (arsenic), beryl (beryllium), cadmium (zinc ores), mercury (cinnabar)
• Potentially toxic elements


  Recently proposed term instead of "heavy metals" as the term heavy often mixes metals, metalloids, and non-metals with no distinction - heavy is also associated with increased toxicity, when there are some metals that are essential for life at known levels
• Arsenic


  Enters waterways by weathering of soil and rock, anthropogenic activities (high levels of exposure = death), EPA maximum contaminant level for drinking water= 10ppb, odorless, tasteless, colorless- rat poison, formerly used for makeup and medicinal purposes, drinking water systems that rely mostly on groundwater most heavily impacted, by-product of metal smelting: arsenic trioxide (As2O3)- elemental arsenic (As) is produced, 70% of arsenic worldwide used as timber preservative (pest/pathogen control), 22% of arsenic worldwide used in agriculture (pest/pathogen control)
• Arsenic species


  As^+3 (arsenite) - more common under moderate reducing/anoxic conditions, As^+5 (arsenate) - predominant species in oxygenated waters, under alkaline conditions, As^+3 and As^+5 desorb from clays and ferric oxides and become highly mobile/more bioavailable, alkalinity impacted mostly by carbonate levels, both As^+3 and As^+5 are highly toxic