《环境化学》课程PPT教学课件讲稿（英文版）Unit 15 Water Pollution-Plant nutrients

Water Pollution -Plant nutrients

Water Pollution-Plant Nutrients

Plant nutrients Plant growth requires various nutrients Major nutrient elements: CI N, P. trace elements: S, Si, Cl, I, and metallic elements(Fe, Mn, Cu, etc) The minor elements because of the low demand can usually be supplied at adequate rates in natural waters The required proportion of the major nutrient elements isC∴N:P=106:16:1 C despite the largest demand is plentifully supplied to phytoplanktons from CO2 in the atmosphere

Plant nutrients • Plant growth requires various nutrients. – Major nutrient elements: C, N, P. – trace elements: S, Si, Cl, I, and metallic elements (Fe, Mn, Cu, etc). • The minor elements, because of the low demand, can usually be supplied at adequate rates in natural waters. • The required proportion of the major nutrient elements is C:N:P=106:16:1. • C, despite the largest demand, is plentifully supplied to phytoplanktons from CO2 in the atmosphere

Natural nutrient cycling in aquatic ecosystem N,atmosphere) (soll; detergents; sewage nitrates(soil; sewage) COz(atmosphere) (usually limited) (possibly limited (usually plentiful) (Sufficient O2) Trace elements CO 〔Fe,Mn,Cu,etc.) Primary Prod FEE algae and other nitrogen fixing and photosynthetic organisms assimilate Bacterial Decomposition C N, Pin the atomic ratios of 106: 16: 1 of plant and animal debris Growth of fish ad ouer secondary producers (Sufficient O,) ag吗g Sedimentation of plant and animal debris

Natural nutrient cycling in aquatic ecosystem

N and p are often the limiting nutrients The limiting nutrient is the least available element in relation to its required abundance N is abundant in the form of N2, but N2 can only be utilized througl gh N2-fixing bacteria In waters where N2-fixing algal species are common, N is not usually limiting In regions where N2-fixing species are less abundant especially the oceans, N maybe the limiting nutrient This leaves P as the limiting element to plant growth This shortage keeps the spread of vegetation under control

N and P are often the limiting nutrients • The limiting nutrient is the least available element in relation to its required abundance. • N is abundant in the form of N2, but N2 can only be utilized through N2-fixing bacteria. • In waters where N2-fixing algal species are common, N is not usually limiting. – In regions where N2-fixing species are less abundant, especially the oceans, N maybe the limiting nutrient. • This leaves P as the limiting element to plant growth. • This shortage keeps the spread of vegetation under control

Phytoplankton productivity as a function of N and p concentrations and sunlight In winter low temperature and Phosphates and Phytoplankton sunlight are the nitrates at surface productivity limiting factors to talal phytoplankton productivity. In summer, nutriel become the limiting factor Decay of dead plant matter replenish nutrients leading to a secondary peak of phytoplankton winter Spring Summer Autumn winter productivity

Phytoplankton productivity as a function of N and P concentrations and sunlight In winter, low temperature and sunlight are the limiting factors to phytoplankton productivity. In summer, nutrients become the limiting factor. Decay of dead plant matter replenish nutrients, leading to a secondary peak of phytoplankton productivity

Consequences of excessive nutrient loading If a new source of n or p is introduced into the water, excessive plant growth occurs, and the algae population explodes (algae bloom), this phenomenon is called eutrophication Adverse consequences of eutrophication Waterways become clogged Algae might release unpleasant-smelling, bad tasting substances Decay of algae induces decrease in DO

Consequences of excessive nutrient loading • If a new source of N or P is introduced into the water, excessive plant growth occurs, and the algae population explodes (algae bloom), this phenomenon is called eutrophication. • Adverse consequences of eutrophication: – Waterways become clogged – Algae might release unpleasant-smelling, bad￾tasting substances – Decay of algae induces decrease in DO

Source of n Agriculture land treated with manure or nitrate fertilizers Slaughterhouses Stockyards Atmospheric deposition NOx from automobiles, power plants etc

Source of N • Agriculture land treated with manure or nitrate fertilizers • Slaughterhouses • Stockyards • Atmospheric deposition: – NOx from automobiles, power plants, etc

Source of P: Detergents TIDES IN. DIRTS OUT The two main ingredients in synthetic detergents are a surfactant and a builder Surfactants remove grease and dirt particles from clothing and dishes by solubilizing them into water. Cations Ca2+ and Mg2+ in water precipitates surfactants in detergents making scum Builders tie up polyvalent cations and thereby prevent them from precipitating the detergents

Source of P: Detergents • The two main ingredients in synthetic detergents are a surfactant and a builder. • Surfactants remove grease and dirt particles from clothing and dishes by solubilizing them into water. • Cations Ca2+ and Mg2+ in water precipitates surfactants in detergents, making scum. • Builders tie up polyvalent cations and thereby prevent them from precipitating the detergents

Detergents Surfactant structures Small ionic head (water soluble; hydrophilic) examples: carboxyl (-CO0- Na+) Long hydrocarbon tail (oil soluble; hydrophobic) sulfonate(一SO3Na+ hydroxyl (-OH) Natural soaps derived from animal fats Synthetic detergents Example: 0 Cl7H35-C CuH SOa Nat Sodium stearate Sodiurm alkylbenzene sulfonate

Detergents: Surfactant structures

Detergents: surfactant micelle Counter ions Water phase X+-Hydrophilic ion w dirt Water phase Organic phase Surfactant interface Hydrophobic hydrocarbon core (b)

Detergents: surfactant micelle