This section was authored by Dr. Gretchen Bielmyer-Fraser, Associate Professor in the Chemistry department at Jacksonville University and Dr. An-Phong Le, Associate Professor of Chemistry at Florida Southern College.
Phosphorus and nitrogen are important and required nutrients for terrestrial and aquatic plants, including algae. Under optimal conditions, nutrients can stimulate immediate algal growth. Alternatively, if absent, nutrients can limit algal abundance. If the nutrient concentrations in a system remain high for extended periods of time, eutrophic conditions may result, potentially changing the entire ecosystem by favoring the growth of some organisms and changing the optimal water quality conditions for other organisms. The term “eutrophic” generally signifies a nutrient-rich condition, resulting in a high concentration of phytoplankton (Naumann 1929). The more recent definition characterizes eutrophication as an increase in organic matter loading to a system (Nixon 1995). Eutrophication can be a natural process, predominantly occurring in small, enclosed water bodies like ponds and lakes. However, anthropogenic (human-made) activities that increase the loading of nutrients into a waterway can greatly increase the level of eutrophication, even in rivers such as the LSJR and its tributaries.
2.3.1. Description and Significance: Nitrogen
Forms of nitrogen typically found in water bodies include nitrate, ammonia and organic nitrogen. These different forms convert to each other in organisms and in the environment (Wright and Nebel 2008). While the atmosphere contains 78% nitrogen gas by volume, this form of nitrogen is unreactive and unavailable to most organisms. An exception is “nitrogen-fixers.” These bacteria take up nitrogen from the atmosphere and convert it to forms usable by other organisms. Nitrogen-fixers can add significantly to the overall nitrogen loading to a system.
Nitrate (NO3−) is one of the most bioavailable forms of nitrogen and can be rapidly taken up by plants. Sources of nitrate in waterbodies include atmospheric deposition, stormwater runoff containing fertilizer from agriculture and residential areas, runoff from animal operations, and treated sanitary wastewater. In particular, failing septic tanks contribute to nitrate contamination of shallow groundwater and surrounding water bodies (Harrington et al. 2010). Nitrite (NO2−) and nitrate (NO3−) are converted from one to the other by microbes, depending on the availability of oxygen and the pH of the environment. Under typical environmental conditions, nitrite concentrations are very low compared to nitrate. Generally, both nitrate and nitrite are measured together, and the values reported as nitrate plus nitrite.
Ammonia also is taken up by phytoplankton (Dortch 1990) and is often converted to nitrate under the correct conditions. It is a waste product of aquatic organisms and naturally occurs in surface and wastewaters at concentrations ranging from 0.010 mg/L in some natural surface waters and groundwater, to 30 mg/L in some wastewaters (Clesceri 1989). Organic nitrogen, such as proteins and urea, can decompose to ammonia (Hutchinson 1944; Wetzel 2001).
Total ammonia consists of two forms: un-ionized ammonia (NH3) and ammonium ion (NH4+). They interconvert depending on environmental pH, temperature and salinity. High pH, high temperature and low salinity promote formation of the more toxic form, un-ionized ammonia. It is more toxic to aquatic organisms because of its ability to cross biological membranes.
Other human sources of nitrogen compounds primarily include industrial fixation in the manufacturing of fertilizers, and the combustion of fossil fuels which liberates nitrogen oxides into the atmosphere. The form of nitrogen that enters a waterway can give an indication of its source. However, as noted above, in aquatic systems several abiotic and biotic processes can change the form of nitrogen, so the source may not be as easily identified. Abiotic processes include acid-base reactions and complexation; biotic processes include nitrification, denitrification, and nitrogen fixation. Sediments may act also as a major reservoir of nitrogen, just as they do for phosphorus (Levine and Schindler 1992).
Unbalanced total nitrogen levels in a system can have severe impacts on the distribution of phytoplankton and the zooplankton that eat it. Excess nitrogen can markedly increase some types of phytoplankton. Nitrogen-fixers, such as some cyanobacteria, thrive in low-nitrogen conditions because they can convert inert atmospheric nitrogen to reactive nitrogen, which allows them to grow rapidly and outcompete other species (Smith 1983).
2.3.2. Description and Significance: Phosphorus
Phosphorus predominately occurs in natural freshwater areas as organically bound phosphate, within aquatic biota, or adsorbed to particles and dead organic matter (Clesceri 1989; Wetzel 2001); whereas, the dominant inorganic species, orthophosphate, accounts for about 10% of the total phosphorus in the system (Clesceri 1989). Orthophosphate is released by the breakdown of rock and soils and is then quickly used by aquatic biota, particularly bacteria and algae, and incorporated as organic phosphate (Newbold 1992; Kenney et al. 2002). Phosphorus can be released from biota by excretion and by the decaying of matter. Several other factors can influence the partitioning of phosphorus in aquatic systems. In oxygen-rich headwater streams of the LSJR, phosphorus may be bound to mobile particulate material; however, in the lakes and slower flowing freshwater parts of the river, phosphorus settles in sediments (Brenner et al. 2001). Many factors, such as wind, turbulence, DO, water hardness and alkalinity, sulfide concentration, salinity, and benthic (bottom-dwelling) organisms may potentially re-mobilize phosphorus into the water column (Boström et al. 1982; Boström et al. 1988; Lamers et al. 1998; Wetzel 1999; Smolders et al. 2006). When reaching the mouth of the river, sulfur may release phosphorus bound to sediments, thus making it potentially available to aquatic organisms (Lamers et al. 1998; Smolders et al. 2006). This occurs more commonly in anoxic areas where bacteria reduce sulfate to sulfide as they decompose organic matter (Lamers et al. 1998; Smolders et al. 2006).
Humans add to the naturally occurring phosphorus in aquatic systems. In central Florida, phosphorus is mined quite extensively, and is used in fertilizers, commercial cleaners and detergents, animal feeds, and in water treatment, among other purposes. Runoff can result in the addition of phosphorus into local waterways (Clesceri 1989; Wright and Nebel 2008). In the past, phosphorus was also often used in laundry detergents. Orthophosphate generally averages 0.010 mg/L whereas total dissolved phosphorus averages about 0.025 mg/L in unpolluted rivers worldwide (Meybeck 1982). Orthophosphate concentrations in rivers can increase substantially following a rainwater event to as high as 0.050‑0.100 mg/L from agricultural runoff and over 1.0 mg/L from municipal sewage sources (Meybeck 1982; Meybeck 1993).
The drainage basin for the river consists of agricultural lands, golf courses, and urban areas, all of which add to the phosphorus loading in the river. Those inputs, plus effluents from municipal wastewater treatment plants and other point sources may contribute to eutrophic conditions in the LSJR.
2.3.3. Management of Nutrients
Nutrient excesses in the LSJR have led to algal overabundance and low dissolved oxygen levels throughout the river. To address the problems, a final TMDL report was drafted in 2008 by the DEP to reduce nutrient inputs into the LSJR so that algal blooms are reduced in the freshwater regions and healthy levels of dissolved oxygen are maintained in the marine portions of the river. A TMDL is a scientific determination of the maximum amount of a given pollutant (i.e., nutrients) that a surface water body can assimilate and still meet the water quality standards that protect human health and aquatic life (Magley and Joyner 2008; see Section 1). The nutrient TMDL indicates how much nutrients need to be reduced to meet water quality standards in the LSJR. Subsequent Basin Management Action Plans establish restoration strategies required to achieve the water quality standards. Government agencies are working with municipal and industrial wastewater treatment facilities and NPDES permitted facilities to reduce nutrient loadings from permitted discharges. Also, nutrient-rich waters coming from standard secondary water treatment plants may be recycled. These recycled waters can and have recently been used as a means for irrigation when nontoxic. This practice has been utilized in Clay County, within the LSJRB, as well as other areas of the U.S., mostly for irrigation of urban open spaces like parks, residential lawns and golf courses. A similar practice has been used in agriculture. Wastewater treatment improvements have been implemented in Palatka, Orange Park, Neptune Beach, Jacksonville Beach, Atlantic Beach, St. Johns County, and Jacksonville. However, there is evidence that the use of reclaimed water can introduce nutrients (such as nitrogen and phosphorus) that can run off into adjoining areas (Harris and Hendrickson 2019).
Local utilities and government agencies have worked to reduce nutrient discharges since 2000 including a large public outreach campaign to reduce fertilizer use in residential landscapes. Individual homeowners may also introduce excess nutrients into the LSJR through failing septic tanks; therefore, the replacement of these septic tanks is one of the actions designated to achieve the proposed TMDL. Government agencies have been working with farming and silviculture operations to implement best management practices to reduce and treat runoff of nutrients. The reduction and treatment of urban stormwater runoff by municipal stormwater programs, improvement of development design and construction by commercial developers and homebuilders, and restoration projects by federal, regional, and state agencies may all influence the attainment of projected future goals of the TMDL program. These methods among others have been included in the DEP Nutrient TMDL and BMAP (Magley and Joyner 2008; DEP 2008a) and have widespread implications in reducing inputs of nutrients into the St. Johns River, provided government agencies, stakeholders, and the general public can meet this goal.
In August 2013, the FDEP and the Division of Environmental Assessment and Restoration reported to the Governor and Florida legislature on the status of efforts to establish numeric nutrient standards from narrative criteria (DEP 2013h). In August 2013, the FDEP also submitted a plan to EPA to implement numeric nutrient standards in Florida’s waters. The FDEP discussed how it developed numeric interpretations of existing State narrative criteria (DEP 2013d).
In this document, the site-specific numeric standards for the marine/estuarine areas of the LSJR, including marine tributaries, were expressed as TMDL loading per year, 1,376,855 kg TN/year and 412,720 kg TP/year. The numeric interpretation for chlorophyll-a is that the long-term annual averages will not exceed 5.4 µg/L. The site-specific criteria for the freshwater portion of the LSJR mainstem is 40 µg chlorophyll-a/L, not to be exceeded more than 10% of the time. For streams without site-specific interpretations required by TMDL stipulations, numeric thresholds and biological benchmarks were developed to assess nutrient status. The nutrient thresholds for peninsular Florida, based on analysis of reference streams, were 0.12 mg TP/L and 1.54 mg TN/L. These values are not to be exceeded more than once in a three-year period and are based on annual geometric means. Annual geometric means are similar to medians in that outliers (i.e., extremely high or extremely low values) influence the result less than they influence arithmetic means. Extensive biological assessment accompanies the numeric thresholds.
Progress towards meeting the TMDL goals for the LSJR mainstem was last separately reported in the 2015 LSJR Mainstem Basin Management Action Plan progress report (DEP 2016a). Beginning in 2017, progress has been reported in the Statewide Annual Report (STAR) (DEP 2020h). In late 2014, the FDEP Environmental Regulation Commission approved slightly different numeric criteria for the LSJR (DEP 2015b).
The nutrient content of the LSJR is influenced not only by the actions taken within the LSJRB but also by the actions of individuals and organizations upriver. Nutrient and dissolved oxygen TMDLs were adopted for the Middle St. Johns River Basin in 2009 (Gao 2009; Rhew 2009a). A draft report to develop an additional Nutrient TMDL for Bethel Lake, Lake Gem, and Lake Orlando in the Middle St. Johns River Basin was published in 2019 (Maeda 2019). Changes in nutrient loading upstream (both increases and decreases) could eventually flow into and affect the Lower St. Johns River Basin, impacting the work and projects already in progress.
Biosolids are materials produced from sewage sludge that has been treated and processed to limit the presence of heavy metals (such as arsenic and lead) and disease-causing pathogens (DEP 2019f). Biosolids are graded as class B, A, or AA based on the treatment methods used to reduce or destroy disease-causing pathogens and their concentrations of certain heavy metals (such as arsenic, cadmium, copper, and lead) (DEP 2010c). Class AA biosolids have the lowest heavy metal and pathogen content. Municipalities generally must pay to have these wastewater solids removed, although they may be able to recoup some wastewater treatment costs by selling this sewage sludge to farmers or fertilizer companies. These processed biosolids are attractive for use in agriculture as they are rich in nitrogen and phosphorus and can be less expensive alternatives to other chemical fertilizers. (Daprile 2017). In fact, class AA biosolids are marketed like other commercial fertilizers (DEP 2019f).
While biosolids are not categorized based on their nutrient content, specific classes are thought to increase phosphorus pollution in some areas. For example, nutrient leaching from biosolid application on land is suspected to contribute to increases in phosphorus pollution in Blue Cypress Lake, the headwaters of the St. Johns River (Spear 2018; Patterson 2019a). Applications of class B biosolids to soil are regulated by the FDEP, while class AA biosolids fall under voluntary guidelines under the Florida Department of Agriculture with fewer restrictions on the amounts and the locations where they can be applied (Daprile 2017). In 2013, class B biosolids were banned from application onto agricultural land to protect watersheds in South Florida, and this led indirectly to a near doubling in biosolid application elsewhere in the Upper St. Johns River Basin (Treadway 2018; Treadway 2019). In its 2020 Consolidated Annual Report, the St. Johns River Water Management District identified the application of these class B biosolids as a significant source for the increase seen in total phosphorus concentrations in the Upper St. Johns River basin (SJRWMD 2020f).
Concerns regarding the impact that the land application of biosolids may have on the nutrient loading in water bodies led FDEP to establish a Biosolids Technical Advisory Committee in 2018 (DEP 2019e). The Committee was disbanded in January 2019 after recommending several changes to address the nutrient content and leaching from biosolids. These included recommendations to take nutrient loading of surface and groundwater into account during the permitting process, to increase inspections of biosolid applications, and to develop protocols to monitor nutrient migration. Legislation was proposed in February 2019 (and subsequently withdrawn in May 2019) to codify some of the Committee’s recommendations; although, this proposed legislation would not change the regulation of class AA biosolids (FloridaSenate 2019; Patterson 2019a). In 2019, FDEP held public hearings and published notice of proposed revisions to its biosolids rules to address concerns of the introduction of nutrients into water bodies from biosolid application (DEP 2019h). The St. Johns Riverkeeper submitted public comments during this rulemaking process highlighting the potential for significant increases in phosphorus loading into the Upper St. Johns River as a result of land application of biosolids (St. Johns Riverkeeper 2019). This increase would be on top of existing phosphorus sources in the Upper St. Johns River, while the Basin Management Action Plans for the Middle and Lower St. Johns River both call for reductions of total phosphorus loading from upstream in order to achieve applicable water quality standards. However, this proposed rule was withdrawn in March 2020 after passage of the so-called Clean Waterways Act (CS/SB 712) by the Florida House and Senate (which was signed into law by Governor DeSantis) (DEP 2020d; DEP 2020f; FloridaHouse 2020). FDEP then issued notice in April 2020 of the development of new rules that take into account provisions within the Clean Waterways Act (DEP 2020g).
2.3.4. Data Analysis
Because of the variability in the characteristics of the river extending from the mouth to the freshwater lakes, it is useful to examine the differences in nutrient profiles in different river regions. The section we refer to as the marine/estuarine reach spans from the mouth at WBID 2213A to WBID 2213H, which contains Doctors Lake (Figure 2.1). The section we refer to as the freshwater region extends from WBID 2213I upstream to WBID 2213N at the confluence of the Ocklawaha River.
The nutrients assessed include total nitrogen (TN), total phosphorus (TP), nitrate plus nitrite (NO3-NO2), ammonia, and orthophosphate (OP). The TN and TP parameters reflect total loading of nutrients into the system including different forms that are readily transformed and those that decay slowly. The sums of the dissolved and particle-bound forms are included in the TN and TP assessments. Orthophosphate, nitrate-nitrite, and ammonia are inorganic nutrients that are considered reactive because they can be taken up rapidly by biota and readily undergo chemical reactions in the environment. Chlorophyll-a is an indirect measure of biological responses to nutrient enrichment and is included in some discussions below. More detail about chlorophyll-a and its relationship to phytoplankton growth is provided in the following section on harmful algal blooms.
In this report, the numeric standards for nutrients in peninsular Florida (0.12 mg TP/L and 1.54 mg TN/L; DEP 2013d), described above in Section 2.3.3, are compared to LSJR data to generally assess the status of the LSJR. However, the water body is not regulated under those standards; numeric criteria consist of total nutrient loading rates (1,376,855 kg TN/year and 412,720 kg TP/year) that cannot be compared to actual water concentrations.
Additionally, while nitrate is regulated for springs and drinking water, neither application is appropriate for the LSJR. There is no Florida orthophosphate criterion.
In the following analyses, the current status and time trends of the four nutrients are examined in different ways. Data are displayed in annual box and whisker plots, which show the distribution of the high and low concentrations each year. These plots consist of a five-number summary including: a minimum value, value at the first quartile, the median value, the value at the third quartile, and the maximum value. The size of the box is a measure of the spread of the data with the minimum and maximum values indicated by the whiskers. The median value is the value of the data that splits the data in half and is indicated by the horizontal blue line in the center of the boxes. Data are also displayed as annual arithmetic means ± standard deviations. In these graphs, the peninsular Florida numeric nutrient thresholds for streams, described above, are overlaid on the charts as a general reference point to assess the status of the LSJR.
Trends over time in annual average concentrations are identified by using the Spearman Rank 1-tailed test at p < 0.05.
All data from 1997 to 2017 were obtained from the FDEP STORET. Beginning in 2018 onward, new data were deposited in the FDEP Watershed Information Network (WIN). Both STORET and WIN are statewide computerized environmental data systems containing water quality, biological, and physical data. EPA methods 365.4 and 365.1 were used to measure total phosphorus in surface waters. Total Kjeldahl nitrogen (organic nitrogen plus ammonia), total ammonia, and nitrate plus nitrite were measured using EPA methods 351.2, 350.1 or 4500-G, and 353.2, respectively. Data for the entire LSJRB and tributaries were collected from FDEP STORET and WIN and culled for applicability to this study. Data were reviewed for quality and data points were discarded when samples appeared analytically compromised (contaminated blanks, poor recovery, poor replication, etc.) or were missing important information. Records with no analytical procedure listed were also removed. Negative values were removed. Values designated as present below the quantitation limit (QL) were replaced with the “actual value” if provided, or replaced with the average of the method detection limit (MDL) and practical quantitation limit (PQL) if the “actual value” was not provided. For “non-detect” values, half the MDL was used; and, for values designated as “zero” the MDL was used. All samples with qualifier codes K, L, O, Q, or Y, which indicate different data quality issues, were eliminated. Data designated with a matrix of “ground water,” “surface water sediment,” “stormwater,” or “unknown” were removed.
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).
2.3.5. General Characteristics
Nutrient profiles vary with the region of the river and depend on proximity to the mouth, rainfall, local sources, and upstream and tributary sources, as well as biological activity (Figure 2.7). The dilution of river water with lower-nutrient ocean water is evident for most nutrients because annual average concentrations sharply decrease as the river reaches the mouth in WBIDs 2213A-2213C. In most years, both forms of phosphorus and nitrate-nitrite concentrations increase as the fresh water moves downstream to estuarine areas, where it becomes diluted by ocean water. By contrast, TN gradually decreases as the river moves from freshwater to estuarine conditions (Figure 2.7). As a consequence of the different ratios of nitrogen to phosphorus, the downstream, saltier section is generally more susceptible to nitrogen pollution, and the upstream, more riverine section is more susceptible to phosphorus pollution.
2.3.6. Current Status and Trends: Total Nitrogen
Figure 2.8 shows the median, minimum, and maximum concentrations of TN measured in the LSJR. Yearly arithmetic mean TN concentrations in the LSJR are compared to the water quality reference concentration of 1.54 mg N/L (used only for the purpose of this report) in Figure 2.9. The yearly mean TN concentrations have gradually declined in both freshwater and marine/estuarine sections of the river since 1997 (Figure 2.9). Yearly mean TN concentrations in the entire LSJR have been below the water quality reference concentration of 1.54 mg N/L since 1997; however, TN concentrations are not equally distributed in the LSJR and some areas have higher TN than others (Figures 2.8 and 2.9). The maximum values in the LSJR, particularly due to values reported in the tributaries and in saltwater areas of the mainstem, have continued to be above the TN reference value (Figure 2.8). Reductions in nitrogen loading are likely to be the primary reason for the observed decline of TN in the LSJR (DEP 2013a).
Relatively elevated levels of nitrogen have been frequently observed in several tributaries (see below); as well as specific locations in the mainstem of the LSJR, such as the Main St. Bridge, which receives a substantial upstream contribution, city storm drainage inputs and power plant effluent, as well as atmospheric deposition, making it difficult to identify a predominant source.
2.3.7. Current Status and Trends: Total Phosphorus
The median, minimum, and maximum TP concentrations in the LSJR are presented in Figure 2.10. The annual mean TP concentrations are presented in Figure 2.11. Annual mean values have been below the TP reference concentration of 0.12 mg P/L (used only for the purpose of this report) since 1997 in the mainstem (Figure 2.11B, C); with a decrease in mean TP values, since 2010 in the marine/estuarine section of the mainstem (Figure 2.11C). Mean TP values in the entire LSJR, particularly the tributaries, have fluctuated around the reference value, and maximum reported values in the tributaries have been above the reference TP value (Figures 2.10, 2.11).
Slight seasonal increases in TP concentration in the LSJR are generally observed in summer months particularly in the marine/estuarine portion of the mainstem (Figure 2.12). Fertilizers containing phosphorus are used on crops primarily during the winter; however, increased stormwater runoff during the summer adds phosphorus from soil, resulting in TP inputs into the LSJR several times throughout the year.
2.3.8. Current Status and Trends: Nitrate, Ammonia and Phosphate
The reactive inorganic nutrients ammonia, nitrate-nitrite, and orthophosphate are readily taken up by various organisms and released back into the environment. Concentrations of the nutrients vary widely with environmental conditions such as rainfall and phytoplankton growth. Median ammonia concentrations have been slightly reduced since 2014 in both the freshwater and marine/estuarine portions of the LSJR mainstem, and to some extent the entire LSJR (Figure 2.13). The median nitrate-nitrite concentrations in the LSJR have remained relatively stable in the entire LSJR (Figure 2.14). There is also a seasonal trend in the levels of nitrate-nitrite, with the highest concentrations occurring in the winter (Figure 2.15). This may be the result of limited uptake of nitrate for phytoplankton growth in winter months. Orthophosphate tends to be higher in the marine/estuarine section than in the freshwater section (Figure 2.16). Reactive inorganic nutrients were variable over time; however, some trends were evident. In the freshwater section of the LSJR mainstem, ammonia and orthophosphate concentrations have generally decreased, while the nitrate-nitrite concentrations have held roughly steady. In the marine/estuarine portion of the LSJR mainstem, ammonia concentrations have held roughly steady, while nitrate-nitrite concentrations have generally decreased. Orthophosphate concentrations in the marine/estuarine mainsteam have remained steady over the entire period from 1997 to 2019. However, these orthophosphate measurements from have generally increased from 2010 to 2019, although the data do vary (Figure 2.17). Ammonia concentrations in the freshwater and the marine/estuarine sections of the LSJR mainstem have held roughly steady the past several years. (Figure 2.17). An interesting feature of the time series is the lower concentrations in 2010-2011 corresponding to times of intense algal blooms. Significant phytoplankton growth and die-off contribute to the fluctuations as nutrients are consumed and released.
2.3.9. Summary and Outlook
The annual mean TN concentrations have declined through 2019 in the mainstem; however, maximum values in the LSJR, particularly due to values reported in the tributaries, have continued to be above the TN reference value. The geometric mean of the TN concentrations in both the LSJR mainstem and tributaries has been lower than the TN reference value for the past three years, in line with the nutrient thresholds for waterbodies in peninsular Florida not governed by a TMDL. (Nutrients in the LSJR are regulated by their loading each year as set by the TMDL, not by their measured concentration.) In examining the individual TN measurements reported for 2019, 1.2% of data from the LSJR mainstream (2 of 171 measurements) and 4.4% of data from the LSJR tributaries (19 of 430 measurements) exceeded the TN reference value. For these reasons, the overall STATUS of nitrogen in the mainstem and in the tributaries is Satisfactory.
The trend in TN was determined using measurements from 2015 to 2019 to better represent more recent changes caused by activity within the LSJR basin as well as upriver (Figure 2.18). During this time period, TN in the mainstem has trended downward. TN levels in the tributaries have been trending downwards, although TN concentrations spiked in 2017. Continued measurements over time will reveal whether the 2017 data point remains a discrepant data point or is indicative of a changing trend. For these reasons, the TREND of nitrogen in the mainstem is Improving, and the TREND of nitrogen in the tributaries is Improving.
Mean TP concentrations in 2019 were below the reference value in the LSJR mainstem, while mean TP concentrations were near the reference value in the tributaries. Maximum TP levels in both the mainstem and the tributaries continue to be above the reference value. The geometric mean of the TP concentrations in both the LSJR mainstem and tributaries has been lower than the TP reference value for the past three years, in line with the nutrient thresholds for waterbodies in peninsular Florida not governed by a TMDL. (Again, nutrients in the LSJR are regulated by their loading each year as set by the TMDL, not by their measured concentration.) In examining the individual TP measurements reported in 2019, none of the data from the freshwater portion of the LSJR mainstem (0 of 62 measurements) exceeded the TP reference value. However, 20.5% of the measurements from the marine/estuarine portion of the LSJR mainstem (36 of 176 measurements) and 22.8% of the measurements from the LSJR tributaries exceeded the TP reference value. For these reasons, the STATUS of phosphorus in the freshwater LSJR mainstem is Satisfactory, in the marine/estuarine LSJR mainstem is Unsatisfactory, and in the tributaries is Unsatisfactory.
The trend in TP was determined using measurements from 2015 to 2019 to better represent more recent changes caused by activity within the LSJR basin as well as upriver (Figure 2.19). During this time period, TP in the mainstem overall has increased. In the freshwater areas of the LSJR mainstem, TP averages jumped higher in 2018. but across the 2015 to 2019 timespan, TP levels have remained essentially the same. Further monitoring over time will reveal whether the jump in 2018 is a one-time occurrence. TP in the marine/estuarine areas of the mainstem has been increasing over the past five years. TP in the tributaries has remained roughly steady over that same time period. For these reasons, the TREND of phosphorus in the freshwater mainstem is Unchanged, the TREND of phosphorus in the marine/estuarine mainstem is Worsening, and the TREND of phosphorus in the tributaries is Unchanged.
Areas of the LSJR with frequently elevated levels of TN or TP may have an increased propensity for algal blooms and low DO events. Reductions in nitrogen loading are likely to be the primary reason for the observed decline of TN in the LSJR (DEP 2013a). The reactive inorganic nutrients, nitrate and orthophosphate, are generally higher in the marine/estuarine section than in the freshwater section of the LSJR mainstem; however, like nitrate, mean orthophosphate concentrations have also been decreasing slightly over time. The worsening trend in TN and TP observed in some parts of the LSJR basin may reflect changes in land usage or possibly changes in water quality upriver, although these data are not sufficient to establish a cause.
There are wide fluctuations of these and other nutrients due to phytoplankton growth and die-off as well as weather conditions. As stated in section 2.1, recent hurricane activity has increased flooding into the LSJR in 2017 and 208, which may also affect nutrient loading. Ongoing efforts to actively reduce nutrient loading into the LSJR may be lowering the concentrations of some forms of nutrients in the mainstem. Changes in nutrient concentrations typically correlate with changes in algal growth. Algal growth, as indicated by average annual chlorophyll-a levels, is discussed separately in Section 2.4.
The complex ecology of the LSJR and its highly variable characteristics and weather patterns make it difficult to assess its overall status. As a result, assessments can differ when different methods of analysis are used. It is reported in the 2013 LSJR BMAP progress report that total nitrogen is decreasing at benchmark sites in marine and freshwater areas of the river (DEP 2014a). Total phosphorus is unchanged at the freshwater site but could be increasing at the marine site. To date, wastewater treatment facilities in the freshwater portion of the LSJR have achieved their total nitrogen and total phosphorus TMDL-required reductions; and wastewater treatment facilities in the marine portion of the LSJR have achieved their TMDL-required total nitrogen reductions. The next few years will be critical in definitively determining when the considerable effort and expenditures to reduce nutrients in the LSJR have been successful. Robust data sets are particularly critical for assessing trends.
Numerous projects have been carried out by multiple counties and agencies in the last several years to reduce nonpoint sources of nutrients from stormwater runoff, agricultural runoff, landscape fertilizer and septic tanks, as well as point sources such as wastewater treatment plants. Projects include wastewater treatment plant upgrades, reclaimed water projects, general drainage improvement, septic tank phase-outs, and the construction of regional stormwater treatment facilities. As nutrient point sources are identified and corrected, further improvements in water quality will depend on addressing nonpoint sources. However, the diffuse nature of these nonpoint sources make improvements more difficult to achieve.
These efforts are detailed in the LSJR Mainstem Basin Management Action Plan progress reports and Statewide Annual Reports (DEP 2016a; DEP 2020h). In addition, nongovernmental NPDES permit holders have also reduced the discharge of nutrients in their effluents to meet TMDL load reduction allocations. The SJRWMD has undertaken several projects around Lake Apopka to reduce phosphorus loading into the St. Johns River, including the conversion of former agricultural lands into wetlands along the North Shore and the construction of phosphorus removal and water management projects (SJRWMD 2020f). In an interesting, cost-effective restoration project in Lake Apopka and in Lake George, the SJRWMD is reducing the mobilization of phosphorus from sediments by harvesting gizzard shad, which disturb the sediments and release the phosphorus for uptake by algae (DEP 2014a; SJRWMD 2019a). Harvesting the shad also removes the phosphorus contained in the fishes’ own bodies and prevents it from being reintroduced into the water.
SJRWMD completed a demonstration project to remove TP from treated wastewater effluent entering Doctors Lake, and the project is expected to begin operation in the 2019-2020 fiscal year. At full scale, SJRWMD estimates that this process will prevent 6,500 pounds of phosphorus from being discharged into Doctors Lake annually (SJRWMD 2020f). There were also plans in the 2019-2020 fiscal year to switch 79 residences in Clay County from residential septic systems to the central sewer system, reducing TN loading by an estimated 1,486 pounds annually (SJRWMD 2020f).
As a consequence of all of these efforts, the lower basin stakeholders have made substantial progress in meeting their targeted nutrient load reductions required by the LSJR TMDL limits, a very positive development for the river. In its 2019 Statewide Annual Report, FDEP reported that 306 projects to reduce TN and TP loading in the Lower St. Johns River had been completed through December 31, 2018, with 47 additional projects planned or underway. The projects completed through the end of 2018 were estimated to achieve more than 100% of the nutrient reductions needed to meet the TN and TP TMDLs in the freshwater LSJR mainstem and the TN TMDL in the marine LSJR mainstem (DEP 2019a).
To determine whether load reductions and numeric criteria have achieved a real environmental benefit, reliable and consistent data is essential. There is a very clear need for continued and increased monitoring to assess the effectiveness of the nutrient TMDLs that have been implemented for the LSJR mainstem. Responses to TMDL efforts of other water bodies in the entire St. Johns River basin, particularly upstream and tributaries also need to be monitored if benefits are to be accurately assessed. It is critical to maintain adequate monitoring capacity for nutrients, chlorophyll-a, and other water quality parameters in the LSJR mainstem so that information that is essential for effective management is available.