The State of Florida promulgated numeric nutrient criteria in 2013 because of a concern that nutrient enrichment had led to widespread increases in algal abundance and blooms. Chlorophyll was identified as a nutrient response variable and examination of historical chlorophyll trends was identified as one approach to help identify nutrient-impaired lakes. Examination of a 508-lake database with 10+ yr of data found that 371 (73%) lakes showed no statistically significant chlorophyll trends over time. Significant decreasing chlorophyll trends were identified at 67 (13%) lakes and 70 (14%) lakes had positive chlorophyll trends. For those lakes with significant trends, only 19 of the 67 lakes and 14 of the 70 lakes had R-2 values > 0.65. There were also 153 lakes with more than 20 yr of data, but only 53 had significant trends in chlorophyll concentration. Of those lakes, 32 had positive trends, but only 3 of those had R-2 values > 0.65. When the presence of an algal bloom was statistically defined as chlorophyll values exceeding two standard deviations of the individual lake's long-term average (geometric) chlorophyll or as a specific fixed chlorophyll value (> 20, > 40, > 80, or > 100 mu g/L), less than 5% of the lakes in the 153-lake database had increasing algal bloom trends. These lines of evidence suggest that there has not been widespread nutrient impairment of Florida lakes and that there is a frequent lack of nutrient limitation, suggesting why nonpoint nutrient control programs have yet to achieve management goals at some Florida lakes.

Muck: what it is, how it's distributed in water bodies, how to remove it. Plus the ontogeny of aquatic systems.

Measurements of photosynthesis and community respiration in Lake Apopka, Florida, U.S.A. indicate that this lake may be heterotrophic, and that the source of extra organic carbon is internal rather than external to the lake. This large and shallow lake (area 124 km 2 , mean depth 1.7 m) was dominated by macrophytes until hurricane-associated winds disrupted the plants in 1947, and the lake switched to a turbid, algal state. A layer of flocculent, organic sediments covers the lakebed to an average depth of 45 cm and winds regularly resuspend the upper portion into the water column. We used the diel oxygen curve method to estimate production and respiration and also reanalyzed the results of five past studies of production in the lake. The production measurements did not support the hypothesis that the flocculent layer represented excess algal production since 1947. Community respiration exceeded gross production on 60 out of 76 days sampled with statistically significant negative net production found in two of the three studies using the light and dark bottle oxygen method. External supplies of organic carbon are relatively small and are balanced by losses through the outlet. If the lake is heterotrophic, the excess respiration is most likely supported by the remains of macrophytes deposited in the sediments prior to the switch to an algal state. Similar sediment oxidation probably occurs in other shallow lakes that switch from the macrophyte to the algal state.