1997 Cumulative Report: The South Florida Estuarine Water Quality Monitoring Network, Part One- Data Synthesis and Discussion

Jones, Ronald; Boyer, Joseph; Black, Nancy

One of the primary purposes for conducting long-term monitoring projects is to be able to detect trends in the measured parameters 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, the major impetus was the combination of a seagrass die-off, increased phytoplankton abundance, sponge mortality, and a perceived decline in fisheries beginning in I987. In response to these phenomena, a network of water quality monitoring stations was established in I989 to explicate both spatial patterns and temporal trends in water quality in an effort to elucidate mechanisms behind the recent ecological change. This report summarizes the existing data from the South Florida Estuarine Water Quality Monitoring Network. This includes water quality data collected 28 stations in Florida Bay, 22 stations in Whitewater Bay, 25 stations in Ten Thousand Islands, 25 stations in Biscayne Bay, and 49 stations on the Southwest Florida Shelf (Shelf). Each of the stations in Florida Bay were monitored on a monthly basis with monitoring beginning in March I99I at stations I through 24. (Except monitoring began at stations I4, I9, 22, and 23 in April I99I). In July I992, stations 25 through 28 were added in Florida Bay. Monthly sampling of stations 29 through 50 in Whitewater Bay were added to the monitoring program in September 1992. Biscayne Bay monthly monitoring began September I993 for stations 100-125. In May I996 an analysis of the data was performed to address the adequacy of spatial coverage. At that time, I0 station locations in the Biscayne Bay monitoring network were moved to provide coverage of North Biscayne Bay. The Shelf was sampled quarterly beginning in spring 1995. We have begun the systematic analysis and interpretation starting with the most extensive dataset: Florida Bay. We have analyzed the data for spatial trends, temporal trends, and for freshwater loading effects. Spatial trend analysis can be performed on data of relatively short period of record (POR); however, time series analysis requires a minimum 5 year POR before significant trends can be recognized over the background noise of interannual variability. Therefore, the type of analysis performed on each estuary is determined by the length of POR. Trend analysis is an ongoing process; ecosystems change with climate and management strategy, therefore, analytical results may change as more data is collected. It is also important to understand that trend analysis alone will not necessarily provide cause and effect relationships. One of the purposes of any monitoring program should be to use the data gained by routine sampling to extend our understanding of the system by developing new hypotheses as to the underlying processes which drive it. Much inference into the behavior of South Florida estuaries can be made from the observed magnitude and distribution of water quality parameters. This type of multivariate approach should prove useful to scientists and managers faced with the task of interpreting large water quality datasets.