2.7 Tributaries

This section is authored by Dr. Radha Pyati Chancellor and Dean of Penn State Berks, Dr. An-Phong Le, Associate Professor of Chemistry at Florida Southern College, and Dr. Scott F. Jones, Assistant Professor of Biology at the University of North Florida.

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 2014c), 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. Data were reviewed for quality and data points were discarded when samples appeared analytically compromised (e.g., value qualifier codes K, L, O, Q, or Y). Records with no analytical procedure listed were also removed. Only surface water samples were analyzed. Replicate samples were removed. For samples where dissolved and total concentrations are reported from the same sampling event, only total concentrations were retained. “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 in two ways. First, if nitrogen data were available in WIN, total nitrogen was calculated as the sum of the average Kjeldahl nitrogen and average nitrate-nitrite concentrations for each tributary. In addition, total nitrogen data were obtained directly from FDEP. Total nitrogen data for 2017 and 2018 were obtained directly from FDEP (Homann 2019), and total nitrogen data after 2019 were calculated from data available in WIN. Data are presented as annual arithmetic means with standard errors for each analyte available.

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 2014c), and the final verified list (DEP 2016h) and delist list (DEP 2016f) from the recent Group 2 basins Cycle 3 assessment (DEP 2016g).

In the water quality data tables below, dissolved oxygen (DO) water quality criteria (WQC) were 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 2013j). 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 2.29 Tributaries of the Lower St. Johns River Basin.
Figure 2.30 Tributaries of the Lower St. Johns River Basin.