ALBERT

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Millette, N. C., Kelble, C., Linhoss, A., Ashby, S., & Visser, L. Using spatial variability in the rate of change of chlorophyll a to improve water quality management in a subtropical oligotrophic estuary. Estuaries and Coasts, 42(7), (2019): 1792-1803, doi:10.1007/s12237-019-00610-5.

Description: Anthropogenic eutrophication threatens numerous aquatic ecosystems across the globe. Proactive management that prevents a system from becoming eutrophied is more effective and cheaper than restoring a eutrophic system, but detecting early warning signs and problematic nutrient sources in a relatively healthy system can be difficult. The goal of this study was to investigate if rates of change in chlorophyll a and nutrient concentrations at individual stations can be used to identify specific areas that need to be targeted for management. Biscayne Bay is a coastal embayment in southeast Florida with primarily adequate water quality that has experienced rapid human population growth over the last century. Water quality data collected at 48 stations throughout Biscayne Bay over a 20-year period (1995–2014) were examined to identify any water quality trends associated with eutrophication. Chlorophyll a and phosphate concentrations have increased throughout Biscayne Bay, which is a primary indicator of eutrophication. Moreover, chlorophyll a concentrations throughout the northern area, where circulation is restricted, and in nearshore areas of central Biscayne Bay are increasing at a higher rate compared to the rest of the Bay. This suggests increases in chlorophyll a are due to local nutrient sources from the watershed. These areas are also where recent seagrass die-offs have occurred, suggesting an urgent need for management intervention. This is in contrast with the state of Florida listing of Biscayne Bay as a medium priority impaired body of water.

Description: Data provided by the SERC-FIU/SFWMD Water Quality Monitoring Network is supported by SFWMD/SERC Cooperative Agreement #4600000352 as well as EPA Agreement #X7-96410603-3. This research was also funded by a NOAA/Atlantic Oceanographic and Meteorological Laboratory grant to the Northern Gulf Institute (award number NA160AR4320199).

Description: Within the past five decades, it has been realized that people significantly influence the water quality, which, in turn, affects the fisheries. Since the 1960s, Lake Victoria and its basin have come under increasing and substantial pressure from a variety of human activities. These include deforestation, over-fishing, intense cultivation, animal husbandry and introduction of exotic fish species. Human activities have disrupted biogeochemical cycles with have consequences for the water quality and fisheries of Lake Victoria. Measurements and theoretical analyses have clearly connected observed changes in the watershed and water quality and conclusions have been drawn that aquatic biota including fisheries are strongly influenced by disturbances around and within Lake Victoria The Lake Victoria basin has clearly shown signs of population pressure and associated land use changes to and within the lake. Nutrient enrichment in the water column, sediment and in rainfall over Lake Victoria accelerated after the 1960s. Phosphorus concentrations have risen by a factor of 2 to 3. Atmospheric loads of nutrients, especially of nitrogen (N) and phosphorus (P) have increased due to biomass burning and deforestation in the catchment. These high nutrient concentrations support elevated algal primary production and algal biomass that have risen by factors of 2, and 6 to 8 respectively. Algal and invertebrates species composition have responded to changes in water quality. Algae are now dominated by the blue-greens with types that are potentially toxic. Elevated algal production probably supports the 4 to 5-fold rise in fish production in the lake since the 1950s. Increased fish production is good as more local people have turned to the lake for their livelihood and fish exports to international markets earn foreign exchange for the riparian states. But problems associated with nutrient enrichment (eutrophication) impacts of elevated algal biomasses and proliferation of the obnoxious water hyacinth (Eichhornia crassipes) threatens continued beneficial use of the lake resources. High algal biomass and increased sediment have contributed to a 4-fold reduction in the lake transparency since the 1960s. Reduced lake transparency is believed to have accelerated hybridization of some cichlids that are picky in choosing mates and use visual cues of bright male coloration to identify suitors of their own species. Deoxygenation of deep waters is another undesirable change that has precluded a stable demersal fishery. Seasonal bottom oxygen deficiency created by decomposition of algal biomass and aggravated by stronger thermal stability directly affects the distribution of organisms including invertebrates and fish. Low oxygen has led to loss of approximately 50% of aerated fish habitat since the 1960s, and also lowers potential fish production. Among the invertebrates, Caridina nilotica has become a keystone species as it is resilient to low oxygen conditions. Low oxygen conditions (anoxia) and algal blooms are often associated with fish kills in Lake Victoria.

Description: Published