Lake Production, Succession, and Eutrophication - Hydro-Environmental Analysis: Freshwater Environments - page 461

TABLE 16.3
Forsberg and Ryding Criteria Lake Trophic Status

Oligotrophic Mesotrophic Eutrophic Hypereutrophic

Total chlorophyll (μg L -1 ) <3 3-7 7-40 >40

Total phosphorus (μg L -1 ) <15 15-25 25-100 >100

400-600 600-1500

Total nitrogen (μg L -1 ) <400 >1500

Water clarity (ft.) >13 8-13 3-8 <3

Source: Forsberg, C. and Ryding, S.O., Archiv Für Hydrobiologie , 89, 189-207, 1980.

have been found to work well in other areas. For example, Florida LakeWatch (coordinated through
the University of Florida) has adapted these criteria to track the trophic status of Florida lakes
(Table 16.3).

16.4.3 t ropHIc S tate
Other common metrics of trophic status based on nutrients and chlorophyll include the trophic
state classiication by the Organization for Economic Development and Co-Operation (OECD 1982)
and that for tropical lakes by Salas and Martino (1991). The OECD (1982) classiication has been
internationally accepted for nearly 30 years, including acceptance by the U.S. EPA (USEPA 2000,
2010). Table 16.4 shows these trophic classes, associated TP chlorophyll-a values, and consensus
assessment of use impairment.

16.4.4 c arLSon ' S tSI
One of the most widely used metrics for estimating the trophic status of lakes was developed by
Carlson (1977) and is referred to as Carlson's TSI. Carlson indicated that the factors impacting the
trophic status of lakes are multidimensional, and cannot be adequately characterized by a single
metric. He developed an index based on data on algal biomass (as indicated by chlorophyll-a con-
centrations) from primarily northern lakes and developed relationships between biomass and trans-
parency (as indicated by the Secchi depth) and the TP. He then based his classiication of the trophic
status on the doubling of biomass. A 10-unit change in the index then represents a doubling or

TABLE 16.4
OECD and Salas and Martino Trophic Categories
OECD (1982) Salas and Martino (1991)

Trophic Category TP (mg L -1 ) Chlorophyll-a ( μ g L -1 ) Use Impairment TP (mg L -1 ) Use Impairment

Ultraoligotrophic <0.004 <1.0 Low

Oligotrophic <0.010 <2.5 Little <0.028 Low

Mesotrophic 0.010-0.035 2.5-8 Variable 0.028-0.070 Variable

Eutrophic 0.035-0.10 8-25 Great >0.070 High

Hypertrophic >0.10 >25 Very high

Source: OECD, Eutrophication of Waters: Monitoring, Assessment and Control , Organization for Economic Development
and Co-Operation, Paris, 1982; Salas, H.J. and Martino, P., Water Research , 25(3), 341-350, 1991; USEPA,
Technical Support Document for U.S. EPA's Final Rule for Numeric Criteria for Nitrogen/Phosphorus Pollution
in Florida's Inland Surface Fresh Waters , U.S. Environmental Protection Agency, Washington, DC, 2010.