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Formal definition of trophic status

(Image below is a generalization for illustration purposes; for formal definition, see below)

General explanation of trophic states

Soil & Water Conservation Society of Metro Halifax (SWCSMH)

June 18, 2016                                                             Narrative on Water Quality

Acknowledgements


Contents:


Trophic characterisation of lakes impairment of various uses: (OECD research)

Limnological characterisation Oligotrophic Mesotrophic Eutrophic
General level of production ........ low medium high
Biomass ............ low medium high
Green and/or blue-green algae fractions low variable high
Hypolimnetic oxygen content ..... high variable low
Impairment of multi-purpose use of lake little variable great


Source: Environment Canada (2004) derived from the OECD (Organization for Economic Co-Operation and Development)'s  peer-consensus research which was the outcome of several years' concerted effort by 18 Member countries


Trophic states (Environment Canada)



(
cf. Wetzel2001)

click photo of our recently departed Director    "Trophy of a lake refers to the rate at which organic matter is supplied by or to the lake per unit time."

Trophy, then, is an expression of the combined effects of organic matter to the lake. As developed originally and as largely used today, the trophic concept (e.g., TP, Cha, SD, and TN) refers to the pelagic-zone-planktonic portion of the lake ecosystem (cf. Tables 4.1 and 4.2, CCME & EC, 2004). The littoral flora and its often dominating supply of autochthonous organic matter to the system, was, and usually still is, ignored.

Prof. Dr. Bob Wetzel was a recipient of numerous awards in limnology, biology, and ecology among which were the Naumann-Thienemann Medal, the top medal in limnology, and the Hutchinson Award.



Trophic State Classification of Lakes with Aquatic Macrophytes (Canfield et al., 1983), and Assessing the Trophic Status of Lakes with Aquatic Macrophytes (Canfield and Jones, 1984):- "Conventional criteria for classifying trophic state emphasize conditions in the open water and ignore the nutrients, plant biomass, and production associated with macrophytes. A potential water column nutrient concentration can be determined through adding the nutrients contained in macrophytes to those in the water. Potential nutrient concentrations can be used in existing indices to classify lake trophic status."



The Corvallis LEI (Lake Evaluation Index)-composite trophic state index that includes Total Phosphorus (TP), Total Nitrogen (TN), Chlorophylla (Cha), Secchi Disk (SD), macrophyte coverage, and dissolved oxygen values in lakes.

click to hear Vollenweider  Vollenweider's dictum re the OECD Probability Distribution Diagrams: Notwithstanding the trophic state classifications based on pelagic parameters, listen to a 4-minute mp3 sound file of Dr. Richard Vollenweider promoting the use of the OECD probability distribution diagrams in order to establish trophic states with a high confidence level.

Dr. Richard Vollenweider was a recipient of the top medal in limnology, the Naumann-Thienemann Medal, among several other awards.



CCME (2004)- Phosphorus
: Canadian Guidance Framework For The Management of Freshwater Systems (6 p.); and Environment Canada's scientific supporting document (2004, 133p.)


Trophic State Indices (TSI)

  • TSI(TP) = 10(6-(ln(48/TP)/ln2))
  • TSI(Cha) = 10(6-((2.04-0.68lnCha)/ln2))
  • TSI(SD) = 10(6-(lnSD/ln2))
  • (TP and Cha expressed as g/l or mg/cu.m., and SD as metres)

  • Also see trophic status data evaluation methodology

  • *We thank all the sources for the info

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