Ecosystem Viltality Eutrophication

August 10, 2021 at 8:00 PM

Besides the parameters listed in the previous section, for lake or reservoir type systems, an additional indicator to monitor freshwater ecosystem health that could be considered is Eutrophication. Eutrophication (ETP) measures the total weight of living biological material (biomass) in a given water body, such as lakes, ponds and reservoirs.

Attributes

 

Scale of calculation:

Sub-basin/monitoring station, aggregate to basin

Range of Output:

100-70 indicates oligotrophic; 70-50 indicates mesotrophic; 50-40 indicates light-eutrophic; 40-30 indicates mid-eutrophic; <30 indicates hypereutrophic

Reference:

Methods for environmental quality assessment of surface water in China (2011)

Type/Class of Input required:

Chlorophyll a (Chl-a), total phosphorus (TP), total nitrogen (TN), Secchi depth (SD), and chemical oxygen demand permanganate index (CODMn)

Suggested source of ‘minimum’ data to enable calculation:

Local observation

 

Data Preparation:

  1. Time series data for ETP:

    Chlorophyll a (Chl-a), total phosphorus (TP), total nitrogen (TN), Secchi depth (SD), and chemical oxygen demand permanganate index (CODMn) are critical parameters to obtain the ETP value

  2. Calculate trophic level index of each parameter and corresponding weight:

    $$TLI(j) = {a \left(b+c \ln C(j) \right)}$$

    $$W_j = \frac{r^2_{ij}}{\sum_{j=1}^m r^2_{ij}}$$

    where TLI(j) is the trophic level index of parameter j, Wj is the weight of the TLI(j), m is the number of evaluated parameters, rij is the correlation coefficient between parameter j and Chl-a, C(j) is the concentration of parameter j. The coefficients of each parameter are listed below:

    Parameters

    a

    b

    c

    rij2

    Chl-a

    10

    2.5

    1.086

    1

    TP

    10

    9.463

    1.624

    0.7056

    TN

    10

    5.453

    1.694

    0.6724

    SD

    10

    5.118

    -1.940

    0.6889

    CODMn

    10

    0.109

    2.661

    0.6889

     

  3. Calculate ETP

    Combine the weights and trophic level index, and transform to FHI scale as follows:

    $$ETP = 100 -{\sum_{j=1}^m W_j*TLI(j)}$$

    Applicants will have to consider a suitable scheme to combine results from the general calculation with this result, depending on the case (i.e., prominence of the lakes/reservoir in the freshwater system).