Boyer, Joseph N.

Jones, Ronald

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Florida International UniversityFIU Digital CommonsSERC Research Reports Southeast Environmental Research Center1999Long Term Trends in the Water Quality of FloridaBay ( June 1989-Dec. 1999)Joseph N. BoyerSoutheast Environmental Research Center, Florida International University, boyerj@fiu.eduRonald JonesSoutheast Environmental Research Center, Florida International UniversityFollow this and additional works at: http://digitalcommons.fiu.edu/sercrpPart of the Environmental Monitoring Commons, and the Water Resource ManagementCommonsThis work is brought to you for free and open access by the Southeast Environmental Research Center at FIU Digital Commons. It has been acceptedfor inclusion in SERC Research Reports by an authorized administrator of FIU Digital Commons. For more information, please contact dcc@fiu.edu.Recommended CitationBoyer, Joseph N. and Jones, Ronald, "Long Term Trends in the Water Quality of Florida Bay ( June 1989-Dec. 1999)" (1999). SERCResearch Reports. 73.http://digitalcommons.fiu.edu/sercrp/73                      4Long-term trends in the water quality of Florida Bay (June 1989 - Dec. 1999)  Joseph N. Boyer & Ronald D. Jones Southeast Environmental Research Center, Florida International University, Miami, FL 33199   One of the primary purposes for conducting long-term monitoring projects is to be able to detect trends in the measured variables over time.  These programs are usually initiated as a response to public perception (and possibly some scientific data) that 'the river-bay-prairie-forest-etc. is dying'.  In the case of Florida Bay during 1987, the impetus was the combination of a seagrass die-off, increased phytoplankton abundance, sponge mortality, and a perceived decline in fisheries.  In response to these phenomena, a network of water quality monitoring stations was established in 1989 to explicate both spatial patterns and temporal trends in water quality in an effort to elucidate mechanisms behind the recent ecological change.  A spatial analysis of data from our monitoring program resulted in the delineation of 3 groups of stations which have robust similarities in water quality (Fig. 1).  We have argued that these spatially contiguous groups of stations are the result of similar loading and processing of materials, hence we call them 'zones of similar influence'.  The Eastern Bay zone acts most like a 'conventional' estuary in that it has a quasi-longitudinal salinity gradient caused by the mixing of freshwater runoff with seawater.  In contrast, the Central Bay is a hydrographically isolated area with low and infrequent terrestrial freshwater input, a long water residence time, and high evaporative potential.  The Western Bay zone is the most influenced by the Gulf of Mexico tides and is also isolated from direct overland freshwater sources.    Climactic changes occurring over the data collection period of record had major effects on the health of the bay.  Precipitation rebounded from the drought during the late 80's being greater than the long term average (9.2 cm mo-1) for the last 7 of 10 years (Fig. 2).  The heavy line in Fig. 2 and others is a 12 month moving average which shows interannual trends and oscillations.  Over this period, salinity and total phosphorus (TP) concentrations declined baywide while turbidity (cloudiness of the water) increased dr matically.  The salinity decline in Eastern, Central and Western Florida Bay was 13.6, 11.6, and 5.6 ppt, respectively (Fig. 3).  Some of this decrease in Eastern Bay could be accounted for by increased freshwater flows from the Everglades but declines in other areas point to the climactic effect of increased rainfall during this period.  The Central Bay continues to experience hypersaline conditions (>35 ppt) during the summer but the extent and duration of the events is much smaller.  As mentioned previously, TP concentrations have declined baywide over the 10 year period.  The Eastern Bay has the lowest concentrations while the Central Bay is highest (Fig. 4).  Unlike most other estuaries, increased terrestrial runoff may have been partially responsible for the decrease in TP concentrations in the Eastern Bay.  This is because the TP concentrations of the runoff are at or below ambient levels in the bay.  The elevated TP in the Central Bay is mostly due to concentration effect of high evaporation.  It is important to understand that almost all the phosphorus measured as TP is in the form of organic matter which is much less accessible to plants and algae than inorganic phosphate (fertilizer).  Turbidity in Eastern Bay increased 2-fold from 1991-98, while Central and Western Bays increased by factors of 20 and 4, respectively (Fig. 5).  Generally, the Eastern Bay has the clearest water which is due to a combination of factors such as high seagrass cover, more protected                       5basins, low tidal energy, and shallow sediment coverage.  Turbidity in the Central and Western Bays have increased tremendously since 1991.  We are unsure as to the cause but the loss of seagrass coverage may have destabilized the bottom so that it is more easily disturbed by wind events.    Chlorophyll a concentrations, a proxy for phytoplankton biomass, were particularly dynamic and spatially heterogeneous.  In the Eastern Bay, which makes up roughly half of the surface area of Florida Bay, chlorophyll a declined by 0.9 µg l-1 or 63% (Fig. 6).  The isolated Central Bay zone underwent a 5-fold increase in chlorophyll a from 1989- 4, then rapidly declined to previous levels by 1996.  In Western Florida Bay, there was a significant increase in chlorophyll a, yet median concentrations of chlorophyl a in the water column remained modest (~2 µg l-1) by most estuarine standards.    Ammonium (NH4+) levels displayed large variability over the period of record and was much higher in the Central Bay than anywhere else (Fig. 7).  Only in Central Bay did the NH4+ pool increase substantially over time (3-6 fold).  Trends in nitrate (NO3-) concentrations (Fig. 8) mirrored those of NH4+ and were mostly due to the biological conversion of NH4+ to NO3- (nitrification) under aerobic conditions.  It is important to note that these changes in turbidity and chlorophyll a happened after the poorly-understood seagrass die-off n 1987.  It is likely that the death and decomposition of large amounts of seagrass biomass can at least partially explain some of the changes in water qu lity of Florida Bay but the connections are temporally disjoint and the processes indirect and not well understood.      ACKNOWLEDGMENTS  We thank all the field and laboratory technicians involved with this ongoing project especially Pete Lorenzo.  This project was possible due to the continued funding of the South Florida Water Management District through the Everglades National Park (SFWMD/NPS Cooperative Agreement C-7919 and NPS/SERC Cooperative Agreement 5280-2-9017).    This report is contribut on #T122 of the Southeast Environmental Research Center at Florida International University.   Maps of South Florida Water Quality Monitoring Network http://www.fiu.edu/~serc/jrpp/wqmn/datamaps/datamaps.html                           6   Figure 1. Zones of similar water quality in Florida Bay   Monthly Average Rainfall   Figure 2. Monthly average rainfall in the Florida Bay area. 0102030401989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000cm mo-1                      7Median Salinity    Figure 3. Monthly median salinity in the three Florida Bay zones. Eastern102030405060701989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000pptC e ntra l102030405060701989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000pptW este rn102030405060701989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppt                      8Median Total Phosphorus    Figure 4. Monthly median total phosphorus concentration in the three Florida Bay zones. Eastern0.000.020.040.060.081989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppmC e ntra l0.000.020.040.060.081989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppmW este rn0.000.020.040.060.081989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppm                      9Median Turbidity    Figure 5. Monthly median turbidity levels in the three Florida Bay zones. Eastern010203040501989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000NTUC e ntra l010203040501989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000NTUW este rn010203040501989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000NTU                      10Median Chlorophyll a    Figure 6. Monthly median chlorophyll a concentrations in the three Florida Bay zones. E a s te rn0246810121989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000mg l-1C e ntra l0246810121989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000mg l-1W este rn0246810121989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000mg l-1                      11Median Ammonium (NH4+)    Figure 7. Monthly median ammonium concentrations in the three Florida Bay zones. E a s te rn0.00.20.40.60.81.01989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppmC e ntra l0.00.20.40.60.81.01989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppmW este rn0.00.20.40.60.81.01989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppm                      12Median Nitrate (NO3-)    Figure 8. Monthly median nitrate concentrations in the three Florida Bay zones. E a s te rn0.000.010.020.030.040.051989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppmC e ntra l0.000.010.020.030.040.051989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppmW este rn0.000.010.020.030.040.051989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000ppm

Long Term Trends in the Water Quality of Florida Bay (June 1989-Dec. 1999)

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