Physical limnology WETA151

Transcription

1 Physical limnology WETA151 L6 Pollution transport Contents Pollution? Modes of pollution point load and diffuse load accidental and continuous Turbulence, advection and dispersion Pollutant jets and near field Large scale transport Diffusion equation Case studies 2 1

2 Pollution? Water pollution: any addition to fresh or sea water that disrupts biological processes or causes a health hazard. Common pollutants include nitrate, pesticides, and sewage (see sewage disposal), though a huge range of industrial contaminants, such as chemical byproducts and residues created in the manufacture of various goods, also enter water - legally, accidentally, and through illegal dumping. Webster 3 Pollutting substances (Lillesand&Kipfer, 1999) Organic wastes consume oxygen through decomposition Infectious agents transmit deceases Plant nutrients promote nuisance growth of aquatic plants like algae and water weeds Synthetic organic chemicals detergents and pesticides toxic to aquatic life and potentially to humans Inorganic chemical or mineral substances from mining, manufacturing processes, oil plant operations and agricultural practices interfere with natural stream purification, destroy aquatic life, cause excessive hardness of water supplies, produce corrosive effects 4 2

3 Polluting substances.. Sediments fill streams, channels, harbours cause abrasion of hydroelectric power and pumping equipment, affect fish and shellfish population by blanketing fish nests and spawn as well their food supplies Radioactive pollution resulting from the mining and processing of radioactive ores, fallout of nuclear test Water temperature increases by cooling waters harmful effects on fish and aquatic life reduce the capacity of the receiving water to assimilate wastes 5 Modes of pollution entrainment: point source Ex: Municipal sewage plant, Industrial sewage plan, River mouth 6 3

4 Modes of pollution entrainment: diffuse load Large and dispersed entrainment area: Directly to lake with run off (agriculture, summer cottages, piers ), Via small rivers and creeks around the lake, Atmospheric pollution directly to lake surface 7 Modes of pollution entrainment: continuous Treated waste water from treatment plants In Finland the carrying capacity of recipient water is assessed before the permit is given The amount and content is controlled by actor and occasionally by Environmental Administration Loading amount (=volume*concentration) is reported and can be traced 8 4

5 Modes of pollution entrainment: accidental From industry purification chemicals over filling of tanks From treatment plants Sjas-river catastrophe in Russia Sahalahti From traffic cyanide lorry on the shore of Lake Issyk-Kul oil spillage on Baltic 9 Turbulence, advection and dispersion Laminar flow: -laminated structure -small velocities Turbulent flow: -Total velocity of water = mean velocity + chaotically fluctuating part of the flow -For each velocity component: f=f(mean)+f -Most environmental flow outside micro scale are turbulent 10 5

6 Importance of turbulence Primary cause of mixing in lakes, molecular diffusion is about 9 orders of magnitude less than turbulent diffusion Turbulence intensity is dependent on wind velocity, water density and currents in the lake Turbulence spectrum consists of eddies of different sizes Largest eddies are wind driven currents The smallest eddies are dissipated by viscosity of the water a: -no flow in ambient water and incoming fluid lighter than ambient -momentum jet -rising plume -level of equal density horizontal spreading 3.1.b: -main flow present -like 3.1.a but at the level of equal density advection downstream 3.1.c: -phases in the entrainment of a momentum jet -development range -fully developed flow 12 6

7 Large scale (> 100 m and >1h) Processes there determine the fate and transport of pollutant Can be studied by map survey, measurements or numerical flow model application Data on wind and river discharge are needed Data on pollutant temperature? density? aggregation? volatile? 13 Diffusion equation: simplest solution of transport Where: M=released mass (kg), u=velocity of ambient flow (=advection) (m/s), D=turbulent dispersion coefficient (m 2 /s), t=time (s), x=spatial coordinate (m) Tracer concentration in (M=D=1 and u=0) at time t= 1 and 10 after release, which happened at origin. Distribution is shown with one standard deviation. It grows as a function of time

8 Examples Onkivesi Lake Pyhäjärvi at Tampere 15 Lake Jyväsjärvi flow and particle transport model Two dimensional simulation model for water currents Vertical integration = mean velocity over the computational cell Driving forces: wind, tributary flow Resisting forces: internal and bottom friction Bouyant particles (floating with currents) Femflow2d.exe 16 8

9 Lake Võrtsjärv Present state and future fate of Lake Võrtsjärv. Results of Finnish- Estonian joint project in (Huttula and Nõges, eds., 1998) Master plan for restoration and protection of Lake Võrtsjärv (Bilaletdin and Arvonen, 2000) 17 Lake Võrtsjärv 18 9

10 Simulated flowfields of Lake Võrtsjärv with particle tracking applications. Wind: (a) - 4 m/s S, (b) - 4 m/s W, (c) - 4 m/s N, (d) - 4 m/s E. Simulation time = 5 days, dispersion coefficient = 0.2 m 2 /s. Source for particles is in the deepest part of the lake

11 Oil spillage on Baltic Ship traffic is increasing Many companies try to minimize harbour payments by leaking spillage water to sea Thin oil cover, floating on surface and transported by wind and currents International collaboration for tracking the oil floats control from air using mathematical models 21 11