In the present study, the trophic state of lake water was assessed using selected trophic-related parameters such as Chl-a, TP, and TN, and evaluated by comparing them with the EPA National Eutrophication standards (Table 4). The results clearly indicated the levels of measured variables are notably higher than the EPA standards, which imply the eutrophic condition of lake water in both seasons (Table 5).

Table 4

Trophic condition of Mirik lake based on concentrations of Chl-a, TP, TN in different seasons, along with EPA National Eutrophication Survey (1974)

Classification of trophic state of lakes based on EPA National Eutrophication Survey (1974)
Chl-a (μg/L)Total phosphorous (μg/L)Total nitrogen (μg/L)Trophic condition
<7 <10 <400 Oligotrophic  
7–12 10–20 400–600 Mesotrophic  
> 12 >20 >600 Eutrophic  
Chlorophyll-a (μg/L) 
Season Min. Max. SD Trophic condition 
Pre-monsoon 46.50 78.40 11.87 Eutrophic 
Post-monsoon 22.90 43.80 8.50 Eutrophic 
Total phosphorous (μg/L) 
Season Min. Max. SD Trophic condition 
Pre-monsoon 80 2,100 740 Eutrophic 
Post-monsoon 20 1,200 550 Eutrophic 
Total nitrogen (μg/L) 
Season Min. Max. SD Trophic condition 
Pre-monsoon 3,600 7,200 1,320 Eutrophic 
Post-monsoon 90 2,800 1,000 Eutrophic 
Classification of trophic state of lakes based on EPA National Eutrophication Survey (1974)
Chl-a (μg/L)Total phosphorous (μg/L)Total nitrogen (μg/L)Trophic condition
<7 <10 <400 Oligotrophic  
7–12 10–20 400–600 Mesotrophic  
> 12 >20 >600 Eutrophic  
Chlorophyll-a (μg/L) 
Season Min. Max. SD Trophic condition 
Pre-monsoon 46.50 78.40 11.87 Eutrophic 
Post-monsoon 22.90 43.80 8.50 Eutrophic 
Total phosphorous (μg/L) 
Season Min. Max. SD Trophic condition 
Pre-monsoon 80 2,100 740 Eutrophic 
Post-monsoon 20 1,200 550 Eutrophic 
Total nitrogen (μg/L) 
Season Min. Max. SD Trophic condition 
Pre-monsoon 3,600 7,200 1,320 Eutrophic 
Post-monsoon 90 2,800 1,000 Eutrophic 
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Table 5

Pearson correlation matrix for the Mirik lake water variables

VariablespHECTSSTDSTATHDOBODCODCl−Chl-aFe
(a) Pre-monsoon 
pH 1 .891* .454 .891* .910* .868* .964** .957** .965** .993** .949** .463 .601 .701 .965** 
EC  1 .676 .999** .682 .980** .934** .979** .961** .893* .841* .444 .611 .756 .919** 
TSS   1 .679 .226 .732 .639 .581 .546 .415 .471 .674 .723 .598 .622 
TDS    1 .680 .976** .934** .978** .959** .895* .832* .440 .595 .755 .917* 
TA     1 .640 .785 .770 .789 .902* .872* .230 .515 .369 .806 
TH      1 .939** .964** .956** .848* .874* .581 .733 .824* .940** 
DO       1 .974** .975** .947** .925** .633 .685 .835* .993** 
BOD        1 .996** .954** .910* .490 .615 .795 .966** 
COD         1 .956** .937** .514 .639 .807 .975** 
Cl−          1 .909* .381 .510 .667 .937** 
           1 .571 .782 .716 .962** 
            1 .768 .819* .651 
             1 .605 .749 
Chl-a              1 .825* 
Fe               1 
(b) Post-monsoon 
pH 1 .940** .545 .943** .911* .888* .948** .937** .938** .861* .780 .691 .982** .835* .988** 
EC  1 .767 1.000** .938** .962** .932** .954** .950** .902* .882* .763 .963** .866* .971** 
TSS   1 .766 .735 .724 .668 .734 .720 .792 .884* .687 .585 .493 .646 
TDS    1 .945** .962** .940** .961** .956** .911* .885* .771 .964** .866* .973** 
TA     1 .954** .992** .982** .997** .936** .833* .916* .885* .860* .914* 
TH      1 .932** .929** .950** .847* .772 .877* .901* .941** .900* 
DO       1 .983** .996** .930** .816* .874* .911* .849* .939** 
BOD        1 .984** .975** .895* .837* .928** .843* .947** 
COD         1 .934** .838* .886* .910* .851* .940** 
Cl−          1 .951** .786 .859* .731 .890* 
           1 .639 .813* .602 .851* 
            1 .647 .797 .682 
             1 .863* .988** 
Chl-a              1 .815* 
Fe               1 
VariablespHECTSSTDSTATHDOBODCODCl−Chl-aFe
(a) Pre-monsoon 
pH 1 .891* .454 .891* .910* .868* .964** .957** .965** .993** .949** .463 .601 .701 .965** 
EC  1 .676 .999** .682 .980** .934** .979** .961** .893* .841* .444 .611 .756 .919** 
TSS   1 .679 .226 .732 .639 .581 .546 .415 .471 .674 .723 .598 .622 
TDS    1 .680 .976** .934** .978** .959** .895* .832* .440 .595 .755 .917* 
TA     1 .640 .785 .770 .789 .902* .872* .230 .515 .369 .806 
TH      1 .939** .964** .956** .848* .874* .581 .733 .824* .940** 
DO       1 .974** .975** .947** .925** .633 .685 .835* .993** 
BOD        1 .996** .954** .910* .490 .615 .795 .966** 
COD         1 .956** .937** .514 .639 .807 .975** 
Cl−          1 .909* .381 .510 .667 .937** 
           1 .571 .782 .716 .962** 
            1 .768 .819* .651 
             1 .605 .749 
Chl-a              1 .825* 
Fe               1 
(b) Post-monsoon 
pH 1 .940** .545 .943** .911* .888* .948** .937** .938** .861* .780 .691 .982** .835* .988** 
EC  1 .767 1.000** .938** .962** .932** .954** .950** .902* .882* .763 .963** .866* .971** 
TSS   1 .766 .735 .724 .668 .734 .720 .792 .884* .687 .585 .493 .646 
TDS    1 .945** .962** .940** .961** .956** .911* .885* .771 .964** .866* .973** 
TA     1 .954** .992** .982** .997** .936** .833* .916* .885* .860* .914* 
TH      1 .932** .929** .950** .847* .772 .877* .901* .941** .900* 
DO       1 .983** .996** .930** .816* .874* .911* .849* .939** 
BOD        1 .984** .975** .895* .837* .928** .843* .947** 
COD         1 .934** .838* .886* .910* .851* .940** 
Cl−          1 .951** .786 .859* .731 .890* 
           1 .639 .813* .602 .851* 
            1 .647 .797 .682 
             1 .863* .988** 
Chl-a              1 .815* 
Fe               1 

**Correlation is significant at the 0.01 level (two-tailed).

*Correlation is significant at the 0.05 level (two-tailed). Values highlighted in bold are indicate significant correlations.

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