Lecture 11 pt. 2: eutrophication and marine dead zones

Eutrophication

Excessive nutrient enrichment in water bodies leading to hypoxia

key nutrients

nitrogen, phosphorus, N:P ration, silica (diatoms)

natural eutrophication timeline

occurs over centuries or millennia

anthropogenic eutrophication timeline

rapidly occurs over decades

agricultural runoff

fertilizer application, animal waste, soil erosion with nutrient rich sediments

urban wastewater and sewage

muinciple wastewater, storm water runoff, lawn fertilizer, organic waste, phosphate detergents

industrial emissions

food processing, paper mills, chemical manufacturing, power plants

atmospheric deposition

NOx from vehicles and industry, ammonia from agricultural operations, long range transport of nutrients, acid rain

Municipal treatment plants N and P loading

80.3 t/yr nitrogen and 5/6 t/yr phosphorus

agriculture N and P loading

293 t/yr nitrogen and 55 t/yr phosphorus

eutrophication stage 1

initial increase in nutrients leads to increased primary productivity and phytoplankton growth

eutrophication stage 2

algal blooms develop and species composition changes as surface scum forms

eutrophication stage 3

Excess of dead biomass

eutrophication stage 4

proliferation of bacteria

eutrophication stage 5

lack of oxygen and suffocation, denitrification happens and nitrous oxide builds up which is a greenhouse gas’s and toxic

harmful algal blooms

toxins are produced and oxygen depleted, fish killed and shellfish contaminated

types of algae in algal blooms

chlorophyta, Cyanobacteria, dinoflagellates, chrysophytes

water chemistry changes

pH fluctuations, increased turbidity, carbon dioxide levels change and nutrient cycling is altered

oxygen dynamics

BOD increases and hypoxic conditions develop, diurnal oxygen fluctuations

impact on biodiversity

loss of sensitive species and dominance of tolerant species

food web disruption

altered predator prey relationships, energy flow changes and trophic cascade, toxins bioaccumulate

microcystis aeruginosa

toxic Cyanobacteria that produced microcystins which are chemically stable and toxic

nitrate health concerns

normally not very toxic but for infants can stop oxygen from carrying oxygen correctly causing blue baby syndrome

dead zones

Areas in water where oxygen is to low to support life

hypoxia

<2mg/L of oxygen

anoxia

no oxygen in the water

major dead zones

Gulf of Mexico, Chesapeake bay, Baltic Sea, Black Sea,

permanent hypoxia

very deep waters, oxygen always below 2mg/L

temporary hypoxia

exists for hours or days

seasonal hypoxia

occurs every year during warm moths only

diel cycling hypoxia

occurs in warm months at night

impact on fishing

reduced cates, lower quality, market decline

effect on tourism

beach closures, reduced recreational activitys, visual and odor issues, economic losses

public health concerns

seafood contamination, water illness, respiratory toxins, drinking water concern

Monitoring technologies

remote sensing satellites, autonomous underwater vehicles, real time monitoring buoys, water sensors

biological monitoring

species abundance surveys, phytoplankton composition, fish population studies

parameters measured

dissolved oxygen, chlorophyll, nutrients, temperature, turbidity

agriculture measures

nutrient reduction, manure management, improved irrigation

urban measures

advanced wastewater treatment, green infrastructure, storm water management, phosphate detergent bans

industrial measures

Improved process efficiency, waste reduction, water reuse systems, treatment upgrades

chemical treatments

adding Al or FE to bind dissolved P and organic matter which settles out, fast and cost effective but can change pH

aluminium sulphate

binds dissolved phosphorus

Dredging lake sediments

addressing internal P loading problem from P stored in sediments, is very dependent on the lake structure and costs a lot and takes a ton of time

ecological restoration

planting macrophages that release oxygen and reduce turbidity compete with algae for nutrients but takes a long time to establish and may not be a good fit

future challenges

climate change, population increase, emerging issues