Sec.22a-426-6. Lake trophic categories

(a) The ranges of Total Phosphorus, Total Nitrogen, Chlorophyll-a, and Secchi Disk Transparency appearing in the table in this section titled “Parameters and Defining Ranges for Trophic State of Lakes in Connecticut” shall be assessed collectively to determine the trophic state of a lake. In addition to water column data, the trophic state of a lake shall be determined by the percentage of the surface area covered by macrophytes in accordance with subsection (b) of this section. For the purpose of determining consistency with the Connecticut Water Quality Standards, the natural trophic state of a lake shall be compared with the current trophic state to determine if the trophic state of the lake has been altered due to excessive anthropogenic inputs. Lakes in advanced trophic states which exceed their natural trophic state due to anthropogenic sources shall be considered to be inconsistent with the Connecticut Water Quality Standards.

Parameters and Defining Ranges for Trophic State of Lakes in Connecticut
Trophic State Based on Water Column Data	Parameters	Defining Range
Oligotrophic	Total Phosphorus	0-10 ug/l spring and summer
	Total Nitrogen	0-200 ug/l spring and summer
	Chlorophyll-a	0-2 ug/l mid-summer
	Secchi Disk Transparency	6 + meters mid-summer
Mesotrophic	Total Phosphorus	10-30 ug/l spring and summer
	Total Nitrogen	200-600 ug/l spring and summer
	Chlorophyll-a	2-15 ug/l mid-summer
	Secchi Disk Transparency	2-6 meters mid-summer
Eutrophic	Total Phosphorus	30-50 ug/l spring and summer
	Total Nitrogen	600-1000 ug/l spring and summer
	Chlorophyll-a	15-30- ug/l mid-summer
	Secchi Disk Transparency	1-2 meters mid-summer
Highly Eutrophic	Total Phosphorus	50 + ug/l spring and summer
	Total Nitrogen	1000 + ug/l spring and summer
	Chlorophyll-a	30 + ug/L mid-summer
	Secchi Disk Transparency	0-1 meters mid-summer

(b) Aquatic Macrophytes

(1) Macrophytes are aquatic plants large enough to be seen without magnification. Macrophyte distribution and abundance data shall be reviewed in conjunction with the water column data to determine the trophic states of lakes and ponds.

(2) If macrophyte growth is very extensive (75 - 100% of water body area) and dense, the trophic state of a lake or pond shall be considered "highly eutrophic" regardless of the water column data.

(3) If macrophyte growth is extensive (30 - 75% of water body area) and dense, the trophic state shall be considered "mesotrophic" when the water column indication is oligotrophic, and the trophic state shall be considered "eutrophic" when the water column indication is mesotrophic or eutrophic.

(Effective October 10, 2013)