Assessing the eutrophication of stormwater ponds using visible aerial imagery (Collier County, FL) Marissa Fischer, Environmental Studies B.A. Mentor: Dr. Serge Thomas Ph.D. Florida Gulf Coast University, College of Arts and Science

Since 1982, stormwater ponds are mandated in Florida to The goal of this research was to characterize community ponds south of 26.3º latitude in Collier County and • Load the digitalized Collier County Stormwater remove more than 80% of the pollutants from the runoff to assess which portion of such hydrosystems exhibit signs of eutrophication using aerial pictures taken Management Ponds and wetlands GIS layer and loading into them as well as mimic, through flow within the visible spectrum. attributes into Google Earth Pro regulation, the natural hydro-patterns. However, such • Google Earth Pro is used to identify the residential ponds are often mismanaged because of questionable ponds in Collier County. aesthetic practices which render them more eutrophic. • Each aerial picture of the pond is then identified Most sponsored water quality studies conducted on SW ponds and exported as a jpeg from the February 2017 Florida ponds have been conducted on 1.5% of the ponds layer in Google Earth. of Lee and Collier counties. It is unsure whether such • The jpeg was then opened in the GNU Image studies reflect the real inclusive water quality of all the Manipulation Program GIMP 2. other ponds since, generally, ponds are studied because of • Average RGB pixel, RGB (%), and RGB values their visual dystrophic state. Thus, this study uses visible (n=3) of the limnetic zone color of each pond were aerial Google Earth Pro pictures and utilizes the red, green determined using the “color picker” tool in the and blue (RGB) composition of the pictures of the limnetic software GIMP 2. zone of the ponds to determine their degree of • An algorithm used to calculate the concentration of eutrophication. Only 1401 residential ponds out of 4220 chlorophyll a in leaves using RGB pictures was then

(33%) were studied. The RGB measurement was Figure 1: Google Earth Pro Layer view showing a Figure 2: GIMP 2 color picker view of FID 1 pond. Pond used ChRGB = G−R/2−B/2 (Ali, 2013) conducted using the software GNU Image Manipulation few community ponds that were studied. attributes: R:55, G:54, B:68; R%: 21.6, G%: 21.2, B%: 26.7; • The ChRGB value was then converted to a water Program GIMP2. A review of the algorithms used to Algorithm: -7.5; Est. Chl a ug/l: 17.1; Est. TSI: 57.7. chlorophyll a concentration using an empirical linear determine the chlorophyll concentration using RGB function (EstChla) pictures was subsequently performed and an algorithm was • EstChla was then used to calculate the trophic status then selected to be used for our data. A simple linear index based on the chlorophyll a concentration in the relationship was then used to convert the algorithm results water (Brezonik, 1984) into chlorophyll a concentrations which were subsequently • The degree of eutrophication of all the ponds was transformed into Trophic Status Indexes using the proper then assessed. formula developed for Florida lakes. A histogram was then generated and showed that the vast majority of Collier pond seemed nutrients rich. The degree of eutrophication of the ponds seems to be slightly skewed to the right (i.e, overestimation). Because there is nearly no data on the water quality Algae in the freshwater of the local community ponds of of ponds in southwest Florida, it is not possible to Figure 3: A Google Earth Pro aerial image of a pond Figure 4: Example of a Hypereutrophic pond in Collier County, FID Collier County, have primarily been controlled though the showing characteristics of a transition stages from 2520. Pond attributes: R: 149, G: 151, B:68; R%: 58.4, G%: 59.2, groundtruth our findings. However, the method use of algaecides over the years. A side effect is the eutrophic to hypereutrophic B%: 26.7; Algorithm: 42.5; Est. Chl a ug/l: 118.3; Est. TSI: 85.5. used seems promising and therefore, aerial pictures plankton that historically will naturally maintain the algae taken in conjunction to water chlorophyll a samples levels via grazing are being suppressed in the process as (or estimates using hyperspectral imagery) should well (e.g. when copper based algaecides are used). This be planned. makes the treatment of ponds almost completely reliant on artificial maintenance once the cycle of eutrophication has begun. Further, the lack of submerged and emergent Trophic status (TSI) percentage Thank you to Dr. Serge Thomas Ph.D. for his guidance aquatic vegetation exacerbated eutrophication by not oligotrophic (30-40) 0.07 and supporting ideas for this research. Also for his providing the necessary ecological filtration of water mesotrophic (40-50) 0.29 connections to Collier County Stormwater Maintenance. I eutrophic (50-60) 5.35 entering such hydrosystems. The degree of eutrophication eutrophic + (60-70) 40.11 would also like to thank Collier County’s Senior Project of most of these ponds is however unknown as there is no hypereutrophic (70-80) 50.75 Manager, Steve Preston for the GIS Stormwater layer that real monitoring program in place. This research thus hypereutrophic + (>80) 3.21 was essential for this research. attempts to assess the eutrophication of all the residential detention and retention stormwater ponds of Collier Ali M.M., A.Al-Ani, D. Eamus, D.K.Y. Ta n. 2013. An Algorithm based on the RGB colour model to estimate plant chlorophyll County using an experimental algorithm which utilizes and nitrogen contents. 2013 International Conference on Sustainable Environment and Agriculture IPCBEE 57:52-56. Betts A.T., K.A. Alsharif. 2014. Assessment of a Countywide Stormwater Pond Improvement Program. Urban Water Journal aerial pictures of the ponds taken within the visible 11:11-19. Carlson R.E., J. Simpson. 1996. A coordinator’s guide to volunteer lake monitoring methods. North American Lake spectrum. If successful, this inexpensive method could Management Society. 96 pp. Hu H., J. Zhang, X. Sun, X. Zhang. 2013. Estimation of leaf chlorophyll content of rice using image color analysis. Canadian then be useful to assess synoptically large regions of Journal of Remote Sensing 39(2):185-190. Sarrafzadeh M.H., H.J La, J.Y Lee, D-H Cho, S.Y. Shin W.J. Kim, H.M. Oh. 2015. Microalgae biomass quantification by digital image processing and RGB color analysis. Journal of Applied Phycology 27:205–209. possibly eutrophied water bodies. Shaw G.R., D.P Moore, C. Garnett. 2003. Eutrophication and algal blooms. Environmental and Ecological Chemistry 2:1-21.