Intent: The Creek Conditions Reports are meant to give an overall picture of ecosystem health. While ratings are based on the official water quality standards used by resource managers, they are for information and education only. Regulatory compliance is determined by the Florida Department of Environmental Protection which incorporates additional factors, including biological health, into its assessment. Biological data regarding floral/faunal populations are not available at this time, and thus are not included in the Creek Conditions Report. If available, those data would give a more complete picture of a stream’s ecological health.
Dissolved Oxygen Saturation Regulations:
For waters such as tidal creeks that fluctuate between fresh and marine, the applicable regulatory criteria are complex. The applicable standard is determined by the location of the creek (its “bioregion”) and its salinity at the time of the DO saturation measurement. This means that freshwater criteria may apply at some times while marine criteria will apply at other times1. While DO may be measured in milligrams/liter (mg/l) or as percent saturation (%), for regulatory purposes, percent saturation is used.
For freshwater streams in the peninsula bioregion where Sarasota is located, the regulatory minimum standard2 for DO saturation is a daily average of 38% (not to be exceeded more than 10% of the time). The regulatory standard for DO saturation in marine waters is comprised of three parts:
- a daily average of 42% (not to be exceeded more than 10% of the time),
- a 7-day average of 51% (not to be exceeded more than once in any 12-week period), and
- a 30-day average of 56% (not to be exceeded more than once per year).
For simplicity’s sake in creating the Creek Conditions Reports, we have elected to characterize each stream segment as either predominantly freshwater or predominantly marine1. An annual geometric mean of all DO measurements in a basin’s predominantly freshwater segments is calculated and compared to the 38% minimum, and an annual geometric mean of all DO measurements in a basin’s predominantly marine segments is calculated and compared to the 56% minimum.
1By Florida statute, marine criteria are used to assess streams when the chloride concentration of water is above 1,500 mg/l; this value is equivalent to specific conductance of 4,580 µmhos/cm, or salinity of 2.7 Practical Salinity Units (PSU).
2Note that because the DO standard is a minimum requirement, the limit is “exceeded” when the percentage falls below the limit. In other words, low oxygen conditions fail to meet the standard. Reference: F.A.C. 62-302.533