eutrophication on natural water

Eutrophication promote excessive plants growth leading to many effects on water quality such as increased biomass of phytoplankton, increases in blooms of gelatinous zooplankton, decreas

Environmental Chemistry

REPORT Eutrophication on natural water

Group 6

Students: Dang Minh Son, Cu Thi Hien, Le Nam Thanh, Nguyen Ngoc Khanh, Phan

Lam Tung, andNguyen Quang Van

Class:K55 TT KHMT, Faculty of Environmental Science, VNU University of Science Instructor: Assoc Prof Nguyen Thi Ha

Hanoi, 14thMay 2013

Abstract

The paper is about eutrophication on natural water systems Eutrophication is water pollution as the result of the excess of one or more nutrient(s) in a water-body Eutrophication promote excessive plants growth leading to many effects on water quality such as increased biomass of phytoplankton, increases in blooms of gelatinous zooplankton, decreases in water transparency (increased turbidity), color, smell, and water treatment problems, dissolved oxygen depletion, loss of desirable fish species…Eutrophication can be human-caused or natural Untreated sewage effluent and agricultural run-off carrying fertilizers are examples of human-caused eutrophication However, it also occurs naturally

in situations where nutrients accumulate (e.g depositional environments), or where they flow into systems on an ephemeral basis Nitrogen is one of two main agents that causes almost eutrophication Nitrogen pollution has increased remarkably over the past several decades as a result of increased creation of reactive N for fertilizer use and, inadvertently, from combustion of fossil fuels The paper makes clear of the sources where nitrogen (N) came from; its transformation, transportation and conversion processes in the system; the impacts of eutrophication on systems

1. Introduction

During the last four decades,

eutrophication has undoubtedly been the

most challenging threat to the quality of

our freshwater resources Survey of the

International Lake Environmental

Committee has indicated in the early

1990s that some 40-50% of lakes and

reservoirs are eutrophicated Many of

these water bodies are extremely

important for drinking water supply,

recreation, fishery, and other economic

purposes One of the most dominant substances causing eutrophication is Nitrogen (N2) Therefore, early recognition of eutrophication, understanding all processes relating to transformation of nitrogen in natural water during occurring eutrophication processes and impacts of it are so important to manage and minimize nutrient enrichment

in almost water bodies This paper will give more knowledge for eutrophication in

natural water, especially nitrogen that

cause this phenomenon

2. Definition of eutrophication

In the most basic terms, eutrophication is

nutrient pollution When an ecosystem

experiences an increase in nutrients,

primary producers reap the benefits first

In aquatic ecosystems, species such as

algae experience a population increase

(called an algal bloom) Algal blooms

limit the sunlight available to

bottom-dwelling organisms and cause wide

swings in the amount of dissolved oxygen

in the water Oxygen is required by all

aerobically respiring plants and animals

and it is replenished in daylight by

photosynthesizing plants and algae Under

eutrophic conditions, dissolved oxygen

greatly increases during the day, but is

greatly reduced after dark by the respiring

algae and by microorganisms that feed on

the increasing mass of dead algae When

dissolved oxygen levels decline to

hypoxic levels, fish and other marine

animals suffocate As a result, creatures

such as fish, shrimp, and especially

immobile bottom dwellers die off In

extreme cases, anaerobic conditions

ensue, promoting growth of bacteria such

as Clostridium botulinum that produces toxins deadly to birds and mammals Zones where this occurs are known as dead zones

3. Sources

Eutrophication can be human-caused or natural Untreated sewage effluent and agricultural run-off carrying fertilizers are examples of human-caused eutrophication However, it also occurs naturally in situations where nutrients accumulate (e.g depositional environments), or where they flow into systems on an ephemeral basis Eutrophication generally promotes excessive plant growth and decay, favoring simple algae and plankton over other more complicated plants, and causes

a severe reduction in water quality

Eutrophication was recognized as a water pollution problem in European and North American lakes and reservoirs in the mid-20th century Since then, it has become more widespread Surveys showed that

54% of lakes in Asia are eutrophic; in

Europe, 53%; in North America, 48%; in

South America, 41%; and in Africa, 28%

[1] Many ecological effects can arise

from stimulating primary production, but

there are three particularly troubling

ecological impacts: decreased

biodiversity, changes in species

composition and dominance, and toxicity

effects

For further understanding about

eutrophication, let us consider one case of

eutrophication which is cause by the

excess of nitrogen in the system

Nitrogen is one of two main agents (the

other is Phosphorus) that causes almost

eutrophication (N for saltwater

ecosystems and P for freshwater

ecosystems) Nitrogen pollution has

increased remarkably over the past several

decades as a result of increased creation of

reactive N for fertilizer use and,

inadvertently, from combustion of fossil

fuels [2] There are many sources where N

can come from including the following

five sources [3] [4]

AgricultureNitrogen is essential for crop

growth and human usually use mineral

fertilizer and livestock manure to provide and supplement Nitrogen for crops.Mineral fertilizers are the major source of nitrogen input in agriculture

However, we cannot know exactly the

amount of nitrogen which crops need and

we use fertilizer based on estimation So,

it is easy to make excessive nitrogen Nitrogen in commercial fertilizer is particularly soluble to facilitate uptake by crops Nitrogen which is not taken up by plants may be metabolized by micro-organisms in the soil to improve soil fertility This is a slow process however, and the major risk is that nutrients, particularly nitrate which is very soluble, will run off into surface water or percolate into groundwater Livestock manure is the second most important source of nutrient inputs to agricultural land Not all the nitrogen contained in excreted manure is spread on the land A certain amount is lost through volatilization of ammonia from stables and during storage This ammonia is a contributor to acidification

Acid rain Concentration of nitrogen

dioxide in the air rises more and more because of burning fossil fuel, deforestation, transportation, agricultural and industrial activities It combines with

water vapor to create nitric acid which

soluble into the rain water to make acid

rain It is also cause the rise in nitrogen

concentration in natural water

Wastewater Untreated wastewater and

wastewater treated by

mechanical-biological methods contain about 32mg/L

nitrogen So, waste water is a source of

nitrogen which causes of nitrogen

eutrophication in natural water

Aquaculture In aquaculture, excess fish

food pollutes the water as complete use of

the food cannot be achieved Nitrogen

present in the excess food is dissolved or

suspended in the water This process also

effect to the amount of nitrogen in natural

water

The sediment of water bodies like rivers,

lakes, marshes -its muddy bottom layer

-contains relatively high concentrations of

nitrogen These can be released to water,

particularly under conditions of low

oxygen concentrations The nutrients in

the sediment come from the past settling

of algae and dead organic matter

4. State and transformation

Chemical forms of nitrogen are most often

of concern with regard to eutrophication, because plants have high nitrogen requirements so that additions of nitrogen compounds will stimulate plant growth Nitrogen is not readily available in soil because N2, a gaseous form of nitrogen, is very stable and unavailable directly to higher plants Terrestrial ecosystems rely

on microbial nitrogen fixation to convert N2 into other forms such as nitrates However, there is a limit to how much nitrogen can be utilized Ecosystems receiving more nitrogen than the plants require are called nitrogen-saturated Saturated terrestrial ecosystems then can contribute both inorganic and organic nitrogen to freshwater, coastal, and marine eutrophication, where nitrogen is also typically a limiting nutrient The following part shows fate and transformation of nitrogen in the system

State

Nitrogen in water can take several forms The dominant combined N species in water are: dissolved inorganic N:NH4 , NO3-, NO2-; dissolved organic N; particulate N, which is usually organic but can contain inorganic N

In normal condition, transformation

process depending on water properties,

various inorganic nitrogen compounds

may be found In aerobic waters nitrogen

is mainly present as N2 and NO3- and

depending on environmental conditions it

may also occur as N2O, NH3, NH4 , HNO2,

NO2- or HNO3

Nitrification and de-nitrification processes

carried out by various microorganisms

Nitrification means ammonium oxidation

from protein decomposition processes by

bacteria, and subsequent conversion to

nitrates This requires oxygen, which is

added by aeration The water must be

aerated for a sufficient period of time

Ammonium is converted to nitrite, and

subsequently to nitrate The reaction

mechanism is a follows:

During the de-nitrification bacteria

decompose nitrates to nitrogen This does

not require aeration, as it is an anaerobic

process Nitrogen is eventually released

into air [5]

In excess nutrient contents, water

eutrophication is caused by the autotrophy

algae blooming in water, which composes

its bioplasm by sunlight energy and inorganic substances through photosynthesis—the process of eutrophication is described as follows:

According to above equation, it can be concluded that inorganic nitrogen and phosphorus are the major control factors for the propagation of algae, especially phosphorus Generally, the physical and chemical evaluation parameters were used

to assess water eutrophication, mainly nutrient concentration (N and P), algal chlorophyll, water transparency and dissolved oxygen The eutrophication or red tide occurs when N concentration in water reaches 300 μg/L and P concentration reaches 20 μg/L Richardson et al (2007) reported that exceeding a surface water mean TP threshold concentration of 15 μg/L causes

an ecological imbalance in algal, macro-phyte and macro-invertebrate assemblages

as well as slough community structure in the Everglades areas [6]

To further understand the fate of nitrogen

in the system and how it transform, let us take the look deeper in the process

Nitrogen cycling generally has 5 reactions

as shown in the following figure: Fixation,

Assimilation, Nitrification, Ammonification, and Denitrifilication [7]

Nitrogen fixation is a bacterially

mediated, exergonic reduction process

which convert molecular N to ammona:

In general, N fixation adenosine

triphosphate (ATP) which is generated by

photosynthesis, so this process is

inefficient at night However

cyanobacteria (primary Anabeana,

Aphanizomenon, Gloeotrichia) can fix

nitrogen directly

Assimilation of nitrogenThe importance

of plankton assimilation of nitrate was

demonstrate in Belham Tarm in English Lake District The author founded that added N-enriched sodium nitrate was removed from water within 14days The added N accumulated in resulting Microcytis bloom These result suggested that Nitrogen stripping by primary producers maybe important mechanism for removal of nitrate, although this depends on the ultimate fate of nitrogen once it reach the sediment because of N maybe available for re-release

Ammonification Ammonium production

occur both in the water column of rivers

and lakes and their sediment Microbial

decomposition convert organic nitrogen to

ammonia trial form This process is

oxygen-demanding and regenerates

available nitrogen for re-assimilation by

primary producer Ammonification can

result rapid in nitrogen cycling between

the sediment and the water column

Ammonia can exist as the ammonium

cation (NH4+) or as the un-ionied ammonia

molecule (NH3) High temperature and

high pH encourage the conversion of

ammonium to ammonia High

concentration of ammonia areusually only

associated with wastewater discharge

where biological treatment is minimum

Nitrification is a two stage oxidation

process mediated be chemoautotrophic

general

Nitrosomas (NH3 to NO2-) and nitrobacter

(NO2- to NO3-) The net reaction

The oxidation of ammonia to nitrite by

nitrosomonas is usually rate-limiting, so

nitrite is rarely present in appreciable concentration in fresh water Nitrate, the end product is highly oxidized, soluble and biologically available.Nitrification is oxygen demanding and can, in some aquatic systems, create anoxic conditions This is because of Nitrosomonas and nitrobacter are strict aerobes, requiring minimum oxygen concentration around 2mg/l to function efficiently

Denitrification Loss of nitrate can occur

through denitrification or dissimilatory nitrate reduction Denitrification is quantitative more important, particularly

in lake sediment and is high in summer month The rate and extent of denitrification is controlled by the oxygen supply and available energy provided by organic matter It is seen as an important mechanism in the reduction of nitrate concentration in reservoirs, but it is limited be the requirement for anaerobic condition and fixed bacterial carbon supply

Table 1: FACTORS RELATE TO EACH PROCESS OF NITROGEN

Nitrogen fixation Cyanobacteria at lake surface

Photosynthesis bacteria at anoxic zone

N fixation when soluble N concentration is low Mineralization More important in lake sediment

Rapid mineralization when plankton biomass dominate lake Nitrification Autotrophic in NH4+ and O2 dependent

Denitrification Seasonal, affected by NO3-supply

general occur in sediment-water interface Assimilation Phytoplankton, varies with NO3- concentration

NH4 can be assimilated if available

As mention in the previous part of the paper, many ecological effects can arise from stimulating primary production including the decreased biodiversity, changes in species composition and dominance, and toxicity effects Rather than impacts of nitrogen eutrophication, the below effects will give the whole picture of eutrophication in general to ecosystem [8]

5. Effects of eutrophication

Effect on water chemistry

Dissolved Oxygen (DO) Nutrient enrichment leads to excessive growth of primary

producers as well as heterotrophic bacteria and fungi, which increases the metabolic activities

of natural water and may lead to a depletion of dissolved oxygen (Mallin et al 2006) During the day, photosynthesis by primary producers provides a large amount of oxygen to the water At night, photosynthesis stops and elevated respiration by algae and bacteria continues to consume dissolved oxygen, which can deplete DO Furthermore, as primary producers die, they are decomposed by bacteria that consume oxygen Large populations of decomposers consume more dissolved oxygen, which increases the severity of DO depletion For example, daily oxygen fluctuations in enriched streams at low flow were reported to range from a high of approximately 25 mg/L at noon to a low of approximately

3 mg/L at night (Wong and Clark 1976)

pH During photosynthesis, carbon dioxide (CO2) and water are converted by sunlight into

oxygen and carbohydrate Hydroxyl ions (OH-) are produced, raising the water column pH

In addition, plants use a large amount of dissolved CO2 for photosynthesis, resulting in lower levels of carbonic acid (H2CO3) in the water column Thus, photosynthesis increases water column pH At night, increased respiration from biota increases the release of CO2 into the water, increasing the production of carbonic acid and hydroxyl ions, which, in turn, increases the acidity

Other chemicals Toxic effects of chemicals released from certain cyanobacteria have been

reported in lakes; very few studies have found cyanotoxins in streams Pfiesteria, a toxic substance produced by dinoflagellates that cause fish kills, has also been reported in coastal rivers associated with nutrient enrichment (Burkholder 1999) A relatively new golden alga, Prymnesium parvum, has been reported to be toxic in Texas The toxin prymnesin affects gill-breathing organisms including fish, tadpoles, and clams (Rhodes and Hubbs 1992) and has been responsible for an estimated 2.5 million dead fish and millions of dead clams in the Pecos, the Colorado, and Brazos river basins in Texas