1999-10-07_AgendaPacket - Laserfiche WebLink

Home

and increased water clarity are not indicators of falling total phosphorus concentrations, however. Total phosphorus has not changed significantly over the period of record (p>0.05, Figure LW3). Concentrations of phosphorus since 1975 have generally fallen within the range expected in eutrophic (highly productive) systems, although three of the last four years indicate summer average total phosphorus concentrations in the mesotrophic range. Snail Secchi disk depth in Snail Lake has shown significant improvement (p<0.05) over the period of record (Figure SL1). Summer average Secchi depth fell in the range for eutrophic systems during the late 1970s, but has steadily improved to near oligotrophic conditions in recent years. The lake would be classified as mesotrophic (i.e., moderately productive) in terms of Secchi disk depth. Chlorophyll concentrations have also improved over the period of record (Figure SL2). The trend is significant at the 95% confidence level (p<0.05). The trend in chlorophyll concentration has been from eutrophic (i.e., high nutrients), to mesotrophic (i.e., moderate nutrients) during the period of record. Total phosphorus concentrations in Snail Lake have also shown a significant (p<0.05) decline over the period of record. Summer average total phosphorus concentrations four of the last five summers have fallen in the range expected for mesotrophic systems (Figure SL3). Overall trends for each water quality parameter are significant improvement over the period of record. L.a it Lake Emily Secchi disk depth has consistently fallen within the range expected for eutrophic systems (Figure LEl). There is no statistical trend for Secchi disk depth in Lake Emily (p>0.05). Total phosphorus concentrations, however, indicate a significant (p<0.05) increase since 1980 (Figure LE2). Total phosphorus concentrations in Lake Emily are well into the range for hypereutrophic systems (i.e., very highly productive). Secchi disk transparency in Lake Judy improved from 1980 to 1986, but still remained well within the range of hypereutrophic lakes (Figure LJ1). The slight improvement was not significant (p>0.05). Further data collection should be done to determine the current transparency of the lake, and to determine long-term trends. Total phosphorus concentrations also declined from 1980 to 1986, but the trend was not significant (p>0.05). The range of total phosphorus concentrations was well within the range of hypereutrophic systems (Figure LJ2). grass_lake_intro.doc Page 5 09/27/99