8/10/2019 Method of Interpretations of Dissolved Oxygen Analysis for Assessing Aquatic Ecosystem

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Method of interpretations of

Dissolved oxygen analysis for

assessing aquatic ecosystem

Prabir Kumar Das, Susmita Bhattacharya and

*Phani Bhusan Ghosh

Department ofBasic Sciences and Humanities, Institute of

Engineering

&

Management, Y-12, Sector-V, Salt Lake

Electronic Complex, Kolkata-700091

Abstract

Oxygen is an essential element which interacts

intensively with the biotic and abiotic components of

an aquatic ecosystem. Accordingly, the presence or

absence of dissolved oxygen (DO), its level of

occurrence and the mode of interactions within the

medium provide many interesting information

regarding the ultimate status of an aquatic

environment. Simply, by monitoring of water quality

without any knowledge of interpretation of the analysis

of results, significant conclusions relating to existing

condition or the conditions expected in future can not

be made. For proper diagnosis of the health of an

ecosystem, an environmentalist always longs for as

many information as possible. In absence of this,

neither any remedial method for restoration nor any

future in-depth studies on the environment could be

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8/10/2019 Method of Interpretations of Dissolved Oxygen Analysis for Assessing Aquatic Ecosystem

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Prabir Kumar Das, Susmita Bhattacharya, Phani Bhu.sw\

G~.

... - -~-~ ~~~.3 s==,e ~dea about the presence of

- z,

- :.;.~~&e organic matter, which is

-c ... -: - =;::~~ i: l:.erms ofbio-chemical oxygen

:..~=;.::.;. ~:::: ~ 'a.;.er The absence or presence

.- 7 .::. -:-~.

::: ~rl.icates that there is higher

;::;. ..::.- -:. >:.eg:-;:1 '::i~:e~cmatterrepresented

- _~7=-~~~ ~xygen demand (BOD) and

=. .,..-o-.? 1:..gT-.er ::ontent of DO signifies lower

-

:

5::: ~:.;bus. showsan inverse relationship

.;.-,-~~=- ~: cmd B8:J. This relationship, in most

...~.;,.' -~, :::ee~regarded as universal and well

.:.

. - e:;;:,en by :he sciootific community during

~-=---=-~e~:..a: studies. However, it may be found

-..:..z~.-;'~,type of relationship does not always hold

~ ,=.e::,~cially in cases of natural aquatic systems

...:....::reaDlS, rivers, ponds and lakes where BOD

::..;;..~a:~y remains less than 10 ppm in absence of

~:: :m~-opogenic impacts. When analytical results

~ -H.. system are compared with the results of

a:..her day, sometimes it might be observed that DO

-a:ues increase along with BOD values. This type

cfanomaly is quite obvious because of the fact that

in these cases, the increment of organic matter

from natural sources are very low and the amount

of oxygen supply (AOS) by combined sources of

photosynthesis and aerial diffusion(6) is more than

the oxygen requirement for degradation (ORD). As

a result, both DO and BOD value may increase

showing a positive relationship between them.

When AOS equals to ORD, the levels of these

components remain same as before and at

conditions of AOS < 'ORD, there is negative or

inverse relationship. So, it is clear that in presence

oflarge amount of organic matter (BOD> 15), always

negative relationship will exist while in cases of

lower amount of organic matter positive

relationship might appear.

These are the most possible inferences that

could be made by single analysis of DO in an

ecosystem. But it does neither allow representing

any ecological significance in the study nor it inform

how much it is either less or more than the actual

value that the water should contain at the prevailing

environmental condition. This deviation from the

true value is very important on ecological point of

view. If these analysis results are expressed in terms

of saturation value of DO, more information

regarding the status of the system may be obtained.

Oxygen saturation value and it's importance

Oxygen saturation value can be defined as the

maximum amount of aerial O2present in a certain

volume of water at the prevailing conditions of

temperature, pressure and total dissolved solids

(TDS) and is normally expressed as saturated value

of DO or the solubility of O2. Its value is either

obtained by calculation from the formula - or fro

the table given in APHA(8) or by using th

nomogram(9) as outlined in the literature. This

saturation value in an idealized aquatic system

absence of biotic interferences is considered as lOW

and is initially attained solely by physical prOCe8