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Tidal creeks (aka tributaries) are essential habitats in the Tampa Bay Estuary and serve as important focal points for understanding watershed inputs that affect water quality. A fundamental goal of the Tampa Bay Estuary Program is to develop effective nutrient management strategies to support the ecological function of tidal creeks. In partnership with Sarasota Bay NEP, Coastal & Heartland NEP, and local government and agency stakeholders, an open science framework has been developed for assessing the tidal creek condition based on a host of commonly collected water quality data [1–3]. These assessments can support tracking of water quality management goals and can help refine restoration and management plans in priority tributaries, including those in need of hydrologic restoration that can support critical nursery habitats for sportfishes.

The tbeptools package includes a simple features spatial data object of the population of tidal creeks in southwest Florida, called tidalcreeks(). This includes 609 polyline features designated by a water body ID (WBID), creek id (JEI), and FDEP class (class, 1 for potable water, 2 for shellfish harvesting or propagation, and 3F/3M for freshwater/marine fish consumption, recreation, propagation and maintenance of a healthy, well-balanced population of fish and wildlife).

mapview(tidalcreeks, homebutton = F, legend = F)

The tidal creek assessment framework was established based on data from the FDEP Impaired Waters Rule database run 56 available here which includes data collected through January 10th 2019. However, the this framework intends to link to future IWR databases to refresh the site with new data as it becomes available. Raw data from the IWR database required for assessment is provided in the tbeptools package in the iwrraw() data object.


The tidal creek assessment framework includes both a “report card” and “indicators” assessment which are provided as separate tabs in the dashboard. The report card provides an assessment of total nitrogen concentrations (the limiting nutrient in these creeks) based on annual geometric average concentrations relative to standards developed for contributing freshwater streams. The indicators are based a several water quality metrics derived as outcomes of our study to describe tidal creek condition and provide insights into site specific attributes of these creeks that may govern overall creek health.

Report card

The report card is similar to the TBEP water quality report card in that tidal creeks are assigned to categories within an assessment framework intended to serve as both a mechanism for evaluating data relative to the need for management action, and to identify stewardship goals that, if properly pursued, may preclude the need for any regulatory actions. These categories were established based principally on fish as a biological response indicator. Tidal creeks are assigned to one of five categories:

No Data: Data are unavailable for evaluation.

Monitor: Creek is at or below nitrogen concentrations that protect individual creek types within the larger population of creeks.

Caution: Creek nutrients showing signs of elevated nutrient concentrations that may increase risk of eutrophic condition.

Investigate: Creek nutrient concentrations above margin of safety to protect creek from potential impairment.

Prioritize: Creek nutrient concentrations have exceeded regulatory standard for associated freshwater portion of tributary indicating that actions are needed to identify remediative measures to reduce nutrients to the creek.

Conceptually, these thresholds appear in the figure below.

Scoring rubrik for tidal creeks based on nitrogen thresholds.

Scoring rubrik for tidal creeks based on nitrogen thresholds.

The Prioritize category was defined based on Florida’s freshwater stream numeric nutrient criteria (NNC).Two different freshwater stream NNC are applicable to our region; the West Central NNC of 1.65 mg/l and Peninsular region NNC of 1.54 mg/l. The histograms in the above figure represent a range of annual geometric mean (AGM) nitrogen concentrations associated with the Prioritize and Investigate categories which are based on the NNC. In the example above, the maximum expected distribution of AGMs not to exceed of 1.65 mg/l with a 1:3 exceedence probability (as defined in F.A.C. 62-303) was generated using monte carlo simulation and the highest observed standard deviation from data collected during the first creeks study. The Investigate category was then defined as an explicit margin of safety by adjusting the distribution to find the grand geometric average that would result in a 1:20 chance of exceeding 1.65 mg/l. Assignment of a creek into the Caution category depended on a creek length adjustment as described below to protect smaller creeks from elevated nutrient concentrations.

The tidaltargets() data object included in tbeptools includes these thresholds. Note that the “Caution” category is a function of creek length.

#>         region prioritize investigate
#> 1 West Central       1.65        1.38
#> 2    Peninsula       1.54        1.30
#>                                             caution
#> 1 1.38 - 0.0174 * (23.78 - (Creek_Length_m / 1000))
#> 2 1.30 - 0.0174 * (23.78 - (Creek_Length_m / 1000))

A scoring algorithm was derived to define the final report card outcome for each creek using the entire ten year record of available data based on the following criteria. A single exceedance of the Prioritize and Investigate categories in any year of the ten year record would result in a classification of that creek into the respective category unless at least three other years of data were below the threshold level for that category. Creeks were assigned the next lower category if only one AGM for TN was above a given level while multiple other years (i.e., more than two) were below the given levels defining the cutoff points for each category. For example, a creek with at least 4 years of data and only a single exceedance of the Prioritize threshold would be assigned the Investigate category. Outcomes are exemplified below.

Report card functions

The two primary functions for the tidal creek assessments are anlz_tdlcrk() to obtain the scores and show_tdlcrk() to view an interactive map of the results. The anlz_tdlcrk() function uses the included tidalcreeks() and iwrraw() datasets to estimate the scores:

results <- anlz_tdlcrk(tidalcreeks, iwrraw)
#> # A tibble: 609 × 10
#>       id wbid  JEI   name          class monitor caution investi…¹ prior…² score
#>    <int> <chr> <chr> <chr>         <chr>   <dbl>   <dbl>     <dbl>   <dbl> <chr>
#>  1     1 2052  CC01  Rock Creek    3M         10      NA        NA      NA Moni…
#>  2     2 1983B CC01  Rock Creek    2          NA      NA        NA      NA No D…
#>  3     3 1983B CC02  Oyster Creek  2          NA      NA        NA      NA No D…
#>  4     4 2067  CC02  Oyster Creek  3M         10      NA        NA      NA Moni…
#>  5     5 1983B CC03  Buck Creek    2          NA      NA        NA      NA No D…
#>  6     6 2068  CC03  Buck Creek    3M          9       1        NA      NA Moni…
#>  7     7 2078A CC04  Buck Creek    2          NA      NA         1      NA Inve…
#>  8     8 2078B CC05  Coral Creek   2           2      NA        NA      NA Moni…
#>  9     9 2078A CC05  Coral Creek   2          NA      NA        NA      NA No D…
#> 10    10 2065C CC06  Catfish Creek 2          NA      NA        NA      NA No D…
#> # … with 599 more rows, and abbreviated variable names ¹​investigate,
#> #   ²​prioritize

The results include a unique creek identifier (id, based on the wbid and JEI fields), the waterbody id (wbid), the creek ID (JEI), the FDEP class (class), and results from the assessment in the remaining columns. The columns monitor, caution, investigate, and prioritize indicate the number of years from 2011 to 2021 that the nitrogen values were within the ranges appropriate for the creek type as specified within tidaltargets(). The score column indicates the overall category assigned to the creek for the period of record. Note that many creeks are assigned a No Data value if sufficient data were unavailable. A summation of the four component columns (monitor, caution, investigate, and prioritize) provides the number of years for which data were available at a creek.

The show_tdlcrk() function can be used with the output of anlz_tdlcrk() to view an interactive map of the results. Creeks are color-coded by the exceedance categories, with “No Data” creeks shown in light blue.