Historical and current observations on macroalgae in the Hillsborough Bay Estuary

Transcription

1 University of South Florida Scholar Commons Reports Tampa Bay Area Study Group Project Historical and current observations on macroalgae in the Hillsborough Bay Estuary J.O.R. Johansson Bay Study Group, City of Tampa Follow this and additional works at: Part of the Environmental Indicators and Impact Assessment Commons Scholar Commons Citation Johansson, J.O.R., "Historical and current observations on macroalgae in the Hillsborough Bay Estuary" (2002). Reports. Paper This Statistical Report is brought to you for free and open access by the Tampa Bay Area Study Group Project at Scholar Commons. It has been accepted for inclusion in Reports by an authorized administrator of Scholar Commons. For more information, please contact

2 HISTORICAL AND CURRENT OBSERVATIONS ON MACROALGAE IN THE HILLSBOROUGH BAY ESTUARY (TAMPA BAY), FLORIDA. Johansson, J.O.R., Bay Study Group, City of Tampa, Tampa FL. Complaints from citizens of Tampa in the early 1960's about obnoxious odors emanating from decaying macroalgae (Gracilaria) along the western shore of Hillsborough Bay resulted in one of the earliest studies undertaken to control eutrophication of an estuary. Results from the study, which were published in 1969, linked the build-up of macroalgae along the shore, and poor bay water quality, to wastewater discharges to the bay with high nutrient and organic content. The study identified the City of Tampa s wastewater plant and the Central Florida fertilizer industry as the two major sources of nutrient pollution to the bay. The study concluded that large reductions of nutrient discharges were needed from these sources, specifically of nitrogen, to improve water quality and to restore a diverse ecosystem to the bay. From the mid 1970's to the early 1980's, local and state regulations, primarily aimed at reducing point-source nutrient pollution, resulted in large phosphate reductions and a near 65% reduction in dissolved inorganic nitrogen discharges to the bay. By the mid 1980's, Hillsborough Bay showed signs of lessened eutrophication. These signs included a near 50 percent decrease in phytoplankton biomass and new growth of submerged seagrass. Despite the nutrient reductions, macroalgae biomass appeared to remain high and odor complaints were still being received by the City of Tampa from citizens on the western side if Hillsborough Bay. In 1983, the city contracted for a year-long study of macroalgae biomass and distribution in the bay. Surprisingly, this study found areas with much higher biomass than that reported in the 1969 study. Attempts to link macroalgae biomass to bay water quality and other potentially important variables were inconclusive in this study. To improve the understanding of macroalgae dynamics it was recommended that long-term monitoring of the macroalgae in the bay be initiated. Subsequently, the City of Tampa initiated a Hillsborough Bay macroalgae monitoring program that since 1986 has been providing consistent monthly biomass and species composition information from five fixed transects. In addition to the transect monitoring, low level aerial observations are conducted on a near monthly schedule for estimations of bay-wide macroalgae and seagrass coverage. Results indicate that the annual bay-wide macroalgae coverage has decreased near steadily from about 300ha in the late 1980's to less than 30ha since Estimated average monthly bay biomass has decreased from a peak of near 150tons wet weight in 1988 to less than 1ton wet weight since Macroalgae species composition during the 15 year monitoring period has often been dominated both in terms of biomass and frequency of occurrence by Gracilaria spp. Other major species include: Spyridia filamentosa, Ulva lactuca, Agaridhiella tenera, and the attached alga Caulerpa prolifera

3 HISTORICAL AND CURRENT OBSERVATIONS OF MACROALGAE IN HILLSBOROUGH BAY (TAMPA BAY), FLORIDA CITY OF TAMPA BAY STUDY GROUP J.O.R. JOHANSSON W. M. AVERY G.V. PINSON K.B. HENNENFENT J.J. PACOWTA

4 TAMPA BAY AND WATERSHED

5 HILLSBOROUGH BAY

6 HISTORICAL BACKGROUND

7 BAYSHORE BLVD.

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12 DIN AND TP LOADING TO HILLSBOROUGH BAY IN DIN 91 mtons/yr 450 TP FERTILIZER IND+ALAFIA R CITY OF TAMPA OTHERS

13 TAMPA TRIBUNE NOVEMBER 16, 1969

14 ALAFIA RIVER PO4 CONCENTRATIONS PO4, ppm YEAR

15 DIN LOAD FROM COT WWTP AND NITRAM INC COT WWTP NITRAM INC. DIN LOAD, mtons/yr YEAR

16 DIN LOAD AND CHLOROPHYLL HILLSBOROUGH BAY DINLOAD CHLOROPHYLL 50 DIN LOAD, mtons/yr CHLOROPHYLL-a, ug/l YEAR 0

17 AUGUST 1991

18 OCTOBER 2001

19 JANUARY 1984

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21 CITY OF TAMPA MACROALGAE MONITORING TRANSECT SAMPLING

22 MONITORING TRANSECTS

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28 CITY OF TAMPA MACROALGAE MONITORING AREAL COVERAGE

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30 FLIGHT PATHS AND MACROALGAE AERIAL OBSERVATIONS

31 MONTHLY AREAL COVERAGE AND TRAWL ESTIMATED BIOMASS OF MACROALGAE IN HILLSBOROUGH BAY COVERAGE COVERAGE, ha TRANSECT BIOMASS TRANSECT BIOMASS, gw w /m YEAR

32 MACROALGAE AREAL COVERAGE AND BIOMASS IN HILLSBOROUGH BAY ANNUAL AVERAGE COVERAGE, ha COVERAGE BIOMASS ANNUALAVERAGE BIOMASS, m tonsw w YEAR

33 MACROALGAE COMPOSITION

34 GRACILARIA VERRUCOSA

35 GRACILARIA SP. 2

36 SPYRIDIA FILAMENTOSA

37 ULVA LACTUCA

38 AGARDHIELLA TENERA

39 CAULERPA PROLIFERA

40 MACROALGAE SPECIES OCCURRENCE AND BIOMASS (TRAWL COLLECTIONS) Spyr. fil. Ulva latac. Agar. tenera Grac. Sp.2 Chaetom. grac. Chaetom. crassa Caul. prolif SPECIES Grac. verr. TOTAL BIOMASS, gww/m2 COUNT OF OCCURRENCE BIOMASS OCCURRENCE

41 ANNUAL MACROALGAE SPECIES COMPOSITION (TRAWL COLLECTIONS) 80 BIOMASS, gww/m Grac. ver Grac. sp. 2 Agar. tenera Ulva lact. Spyr. fil YEAR

42 MACROALGAE COMPOSITION BY MONTH (TRAWL COLLECTIONS) 30 BIOMASS, gww/m Grac. verr Grac. sp. 2 Agar. tenera Ulva lact. Spyr. fil MONTH

43 CONCLUSION

44 MACROALGAE AND SEAGRASS COVERAGE, AND CHLOROPHYLL-a CONCENTRATIONS IN HILLSBOROUGH BAY YEAR MACROALGAE AND SEAGRASS COVERAGE, ha CHLOROPHYLL-a CONCENTRATION, ug/l MACROALGAE COVERAGE SEAGRASS COVERAGE CHLOROPHYLL-a CONC

45 Valiela, et al. 1997

46 THE END