2.7 Tributaries

This section is authored by Dr. Radha Pyati, Dean of the College of the Sciences and Mathematics at West Chester University of Pennsylvania and Dr. An-Phong Le, Associate Professor of Chemistry at Florida Southern College.

2.7.1. About the Tributaries

Water quality data were examined in detail for 29 tributaries in the LSJRB. Their selection was based upon several factors. First, the basin was divided into the 11 Planning Units that were initially established by the SJRWMD and subsequently adopted by DEP (DEP 2002). These Planning Units include Crescent Lake, Etonia Creek, Black Creek, Deep Creek, Sixmile Creek, Julington Creek, the Ortega River, the Trout River, the Intracoastal Waterway, the north mainstem, and the south mainstem. Each Planning Unit is made up of several waterbodies (parts of the river system) referred to by their Waterbody Identification (WBID). Then, each Planning Unit was reviewed, in order to choose WBIDs for analysis. A WBID was selected for analysis if it had enough sampling sites at which data had been collected. Often, if a WBID was on the verified impaired list in 2004, 2009, or 2014 (DEP 2014e), it was selected for analysis. Some unimpaired WBIDs were chosen because they are historically important or used frequently for recreation.

For each of these 29 tributaries, data were extracted (by characteristic) from Florida STORET (for data from 1997-2017) and FDEP WIN (2018 onward) and organized by WBID. The datasets were filtered to remove data that was deemed to be “invalid” for one or more of the following reasons (values in quotes are written as they are found in Florida STORET data fields):

  • Data identified as “LEGACY STORET” (data is reported from 1997 onward).
  • Data reported as “Present < PQL,” where no Practical Quantitation Limit (PQL) was listed.
  • Data reported as “Non-detect,” where no Minimum Detection Level (MDL) was listed.
  • Data with a matrix of “Ground Water,” “Surface Water Sediment,” and ”Unknown.”

Prior to the 2013 River Report, all “Non-detect” data had been removed. While seemingly a logical approach, the effect tends to bias the quartiles calculated in the data analysis on the high side. As a result, “Non-detect” data (and data reported as zero concentration) has been included in the data analysis here with a value MDL/2 (see Helsel 2005). In a similar manner, values listed as “Present < PQL”, were included as (PQL+MDL)/2 if no “Actual value” was reported in the “Comments” field. If an “Actual value” was reported in the “Comments” field, it was used instead.

Total nitrogen was calculated by the sum of the Kjeldahl nitrogen and nitrate-nitrites in each sample.  To remain consistent with FDEP data handling protocols, data that fell between the MDL and PQL were replaced by the MDL; any values that fell below the MDL were replaced by one-half of the MDL.  Total nitrogen was calculated from data available in STORET from 1997-2016, and total nitrogen data for 2017 and 2018 were obtained directly from FDEP (Homann 2019).

In the ‘About’ sections for each of the 29 tributaries below, information/data was taken from the TMDL documents about each tributary respectively, the Florida DEP comprehensive verified impaired list (DEP 2014e), and the final verified list (DEP 2016j) and delist list (DEP 2016h) from the recent Group 2 basins Cycle 3 assessment (DEP 2016i).

In the water quality data tables below, dissolved oxygen (DO) water quality criteria (WQC) where either based on Site Specific Alternate Criteria (SSAC) (DEP 2014b) for marine portions of the river or the new freshwater DO criteria based on DO saturation in water (DOsat) (DEP 2013k). As both of these criteria definitions are calculation based, the WQCs indicated in the tables should be considered nominal values.

Finally, freshwater WQC’s for metals were based off of 100 mg CaCO3/L, the estimated hardness of the freshwater part of the LSJR (see Section 5.2.1 for more information).

Figure 2.23
Figure 2.28 Tributaries of the Lower St. Johns River Basin.
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