13 nutrient pollution in aquatic ecosystems Flashcards
what are the nutrients in the aquatic environment?
chemical substances that provide nourishment and promote growth. Point of uptake into food webs:
1. via micro-organisms, e.g. bacteria and algae
2. via aquatic macrophytes (aquatic vascular plants)
-they include macro-nutrients such as N, P, C, Si
-they also include micro-nutrients such as Mg, Fe, Zn and Cu
-others? vitamins
are all nutrients equal in aquatic environments? (same impact on biological activity)
-some nutrients limit biotic productivity more than other (typically rate of algae growth)
-sometimes more than one nutrient may limit productivity
-bacterial and algal growth will be stimulated by the addition of a limiting nutrient
-for example, what happens when you add fertilizer to a lawn or a garden?
-stimulates grass/plant growth because we give it the limiting factor (nitrogen and phosphorus)
what is the example of factors that control primary productivity in aquatic ecosystems?
-classic whole ecosystem case study: fertilization of Lake 226 (ELA, Kenora, Ontario) commenced in 1969
-objective: which, if any nutrients (C, N and P) were limiting primary production
-lead to banning of P in detergents and reduction of P inputs from sewage treatments plants in Canada, the US and Europe (1970s)
what is the graph of lake ecosystems?
-lakes in temperate regions: phosphorus is a strong limiting nutrient
-algal biomass is used here as an index of primary production (both are strongly correlated)
-algal biomass is measured via chlorophyll concentration in water
what does the strong relationship in lake ecosystems mean?
-as a result of the strong relationship between algal biomass and phosphorus, the trophic status (or productive capacity) of a lake can be classified according to the quantity of phosphorus in a lake’s water column
-all of these can occur naturally
-natural eutrophication takes a long time (100 to 1000s of years)
-cultural eutrophication= anthropogenic causes for eutrophication
why are P and N limiting nutrients in freshwater?
demand for P and N by biota is greater than the environmental supply
why is N a limiting nutrient?
-our atmosphere is mainly nitrogen, but it is not bioavailable to most organisms (except some bacteria)
phosphorus
-no gaseous forms
-not really found in high levels in water
what is the chemistry of phosphorus?
-phosphorus is less mobile than nitrogen in the environment
-it combines readily with cations (e.g. Al+3, Fe+3, Ca+2) and clay
-forms insoluble products with the above elements and readily precipitates under oxic conditions (when O2 is plentiful)
-phosphate (PO4-3) is considered the bioavailable form of P, but occurs at extremely low concentrations in the natural environment because it readily precipitates out of solution (into sediments)
what is nitrogen in lakes?
-most common form of nitrogen in the biosphere is atmospheric N2 (78% of atmospheric gases)
-present at similar concentrations as O2 in the form of N2 in water
-important biomolecules: amino acids, nucleic acids, proteins and urea
-however, N2 can only be used directly by certain “nitrogen fixing prokaryotes”
-hence, N is another limiting nutrient
what is the forms of nitrogen found in lakes?
N exists in many oxidized and reduced forms
-NH4+: ammonium (preferred substrate for bacteria and algal uptake)
-NO3-: nitrate
-NO2-: nitrite
-ammonium is the reduced ionic form of N found in neutral to acidic
-under alkaline conditions, it is converted to ammonium hydroxide (NH4OH)
-NH4OH is toxic to many organisms (toxicity for fish is 0.3 mg/L)
what are unnatural sources of nutrients (pollution)?
point-source
-sewage and industrial discharge
-urban storm water
nonpoint-source or diffuse input
-agricultural and urban run-off
-atmospheric deposition
what is an example of a major problem of human impacts involving pollution?
-excess P applied to agricultural landscapes is carried into surface waters where it also causes excess algal and plant growth in lakes, river, estuaries and coastal systems (cultural eutrophication)
-PO4 binds quickly to soil and particles and tends to accumulate
-many agricultural landscapes are saturated with P
-as these soils erode, they carry P into water-bodies
what are the graphs of fertilizer usage and population growth?
what is cultural eutrophication?
the most obvious, persistent and pervasive water quality problem on earth is that of cultural eutrophication, or the enrichment of natural waters with nutrients by human activities
what are the impacts caused by cultural eutrophication?
anoxia and loss of habitat/biodiversity
-decrease in O2 concentration because algal population spikes and then crashes, leading to microorganisms degrading them, which consumes oxygen
-fish kills
-loss of recreation value
-loss of water quality: taste and odour problems
-most important: toxins (released by algae)
what is a prerequisite to understanding the impacts of cultural eutrophication?
thermal structure of lakes in summer
-epilimnion: warm, well mixed, well lit surface water
-metalimnion: region of rapid temperature and density change (slow mixing)
-hypolimnion: cold, oxygen-poor, dark zone that lies below the metalimnion, zone of little mixing
-effect is there is no mixing in the lake and oxygen diffuses very slowly
in lake ecosystems, what are potential oxygen gradients?
-oxygen is not as readily available in water as in air
-epilimnetic waters may contain O2 at saturated concentrations
-but O2 does not diffuse rapidly across the water density gradient in the metalimnion
-and respiration by microbes in the metalimnion and, especially in the hypolimnion, can deplete O2 concentrations to create anoxic conditions by mid0summer
what is the decline of fisheries?
impact of cultural eutrophication
what is the example of O2 loss from the hypolimnion of lake ontario over summer?
what are other impacts of eutrophication?
various types of algae can flourish due to nutrient enrichment
what are algal bloom of blue-green algae?
such blooms can result in aesthetic, taste and odour problems resulting in poor water quality (e.g. for drinking or recreation)
-foul odor comes from geosmin, which are released from certain blue-green algae
what are cyanotoxins?
a serious problem in many canadian freshwater systems
-when: cyanobacteria can bloom and release hepatotoxins and neurotoxins, under warm and calm conditions in high nutrient waters
-result: contamination of livestock, fish, wildlife, and humans
-responsible organisms: many algal genera (e.g. Microcystis, Anaebaena, Aphanizomenon)
-exposure by: drinking, swimming, touching or even breathing airborne toxins can cause harm
what is microcystin?
a hepatotoxin produced by Microcystis sp. (cyanobacteria)
-protein phosphatases are found in our liver which regulated metabolic function of the liver
-microcystin blocks this group of enzymes=liver damage and dysfunction
what is a growing issue in canada?
cyanotoxins
what is happening in Lake Diefenbaker?
cyanobacteria blooms but doesn’t happen every year
what is cultural eutrophication in the marine environment?
-unlike freshwater systems, estuaries and coastal regions tend to be nitrogen limited
-these regions undergo cultural eutrophication from river and estuarine nutrient inputs (upstream agriculture)
-also, many coastal cities (e.g. Victoria, BC) released raw or untreated sewage directly into the ocean
what are red tides?
-reddish or brown hue of marine surface waters
-usually caused by a bloom of dinoflagellates
-color is caused by an accumulation of carotenoid pigments
-generally restricted to autotrophic genera
where are red tides found?
-common to tropical and subtropical coastlines and estuaries
-but can also be found in temperate coastal waters in lake spring and summer
-about 40 species create serious toxins
when do red tides occur?
-calm warm surface waters, low salinity and high nutrient conditions favor bloom development
-these conditions often occur after heavy rain storms (nitrogen in runoff into coastal waters)
-red tides are visible when cell densities reach 10-20 million cells/L
how toxic are red tides?
-toxins from these blooms can be lethal
-saxitoxin is a neurotoxin leading to paralysis (blocks voltage gated Na+ channels)
-called paralytic shellfish poisoning (PSP)
what are the effects of saxitoxin?
saxitoxin: a common red tide toxin causing PSP
-effects in humans: headache, nausea, vomiting and diarrhea with increasing muscular paralysis and pronounced respiratory difficulty
what are effects of some dinoflagellate toxins?
what is the increased occurrence of PSP worldwide?
what is ASP?
toxins: amnesic shellfish poisoning
-pseudo-nitzchia spp. can produce the amino acid and neurotoxin domoic acid
-when shellfish consume this diatom they may concentrate the toxin in their tissues (shellfish are unaffected)
-when humans consume such shellfish: memory loss, cramps, vomiting, disorientation, and death may result
-first known cases occurred in 1987 in PEI resulting in 4 deaths and 153 illnesses across canada
-another nutrient related issue
-glutamite is a neurotransmitter found found in CNS
-domoic acid is a mimic of glutamite
-it binds to glutamite receptors which causes overactivation, leading to disruption in CNS
what are domoic acid hotspots?
