Mercury Pollution History in Tropical and Subtropical American Lakes: Multiple Impacts and the Possible Relationship with Climate Change

Sediment cores obtained from 11 tropical and subtropical American lakes revealed that local human activities significantly increased mercury (Hg) inputs and pollution levels. Remote lakes also have been contaminated by anthropogenic Hg through atmospheric depositions. Long-term sediment-core profiles revealed an approximately 3-fold increase in Hg fluxes to sediments from c. 1850 to 2000. Generalized additive models indicate that c. 3-fold increases in Hg fluxes also occurred since 2000 in the remote sites, while Hg emissions from anthropogenic sources have remained relatively stable. The tropical and subtropical Americas are vulnerable to extreme weather events. Air temperatures in this region have shown a marked increase since the 1990s, and extreme weather events arising from climate change have increased. When comparing Hg fluxes to recent (1950-2016) climatic changes, results show marked increases in Hg fluxes to sediments during dry periods. The Standardized Precipitation-Evapotranspiration Index (SPEI) time series indicate a tendency toward more extreme drier conditions across the study region since the mid-1990s, suggesting that instabilities in catchment surfaces caused by climate change are responsible for the elevated Hg flux rates. Drier conditions since c. 2000 appear to be promoting Hg fluxes from catchments to lakes, a process that will likely be exacerbated under future climate-change scenarios

Using palaeoecological and palaeoenvironmental records to guide restoration, conservation and adaptive management of Ramsar freshwater wetlands: Lessons from the Everglades, USA.

The Everglades, the largest Ramsar wetland in the USA, is a spatially complex mosaic of freshwater habitats heavily impacted by agriculture, urban land use, and efforts to manage water resources in southern Florida. Restoration and conservation of these habitats is challenging because they experience different threats, and require different water levels, hydroperiods and disturbances. Historically, Everglades hydrology was maintained by seasonal precipitation and surface-water flows, but was significantly altered in the 20th century to foster agriculture and urban growth. Everglades palaeoecological and palaeoenvironmental studies provide opportunities to examine spatial and temporal variability in wetland conditions, and document past climate and anthropogenic influences on plant succession and habitat persistence since the mid-Holocene. This paper summarises key Everglades palaeoecological and palaeoenvironmental research, and highlights lessons learned about the evolution of the ecosystem, historical variability, and natural and anthropogenic influences. These lessons have been used in defining reference conditions and community targets in current efforts to restore the Everglades. Palaeoenvironmental and palaeoecological studies enhance our understanding about properties that define and contribute to the ecological character of wetlands, and they can identify criteria that are important for restoration and conservation projects in Ramsar-listed wetlands

Using palaeoecological and palaeoenvironmental records to guide restoration, conservation and adaptive management of Ramsar freshwater wetlands: Lessons from the Everglades, USA.

The Everglades, the largest Ramsar wetland in the USA, is a spatially complex mosaic of freshwater habitats heavily impacted by agriculture, urban land use, and efforts to manage water resources in southern Florida. Restoration and conservation of these habitats is challenging because they experience different threats, and require different water levels, hydroperiods and disturbances. Historically, Everglades hydrology was maintained by seasonal precipitation and surface-water flows, but was significantly altered in the 20th century to foster agriculture and urban growth. Everglades palaeoecological and palaeoenvironmental studies provide opportunities to examine spatial and temporal variability in wetland conditions, and document past climate and anthropogenic influences on plant succession and habitat persistence since the mid-Holocene. This paper summarises key Everglades palaeoecological and palaeoenvironmental research, and highlights lessons learned about the evolution of the ecosystem, historical variability, and natural and anthropogenic influences. These lessons have been used in defining reference conditions and community targets in current efforts to restore the Everglades. Palaeoenvironmental and palaeoecological studies enhance our understanding about properties that define and contribute to the ecological character of wetlands, and they can identify criteria that are important for restoration and conservation projects in Ramsar-listed wetlands

Topical advances and recent studies in paleolimnological research.

Paleolimnology combines the disciplines of limnology, geology and ecology, but because of challenges that separate investigators from direct knowledge about past lake conditions, the field is multidisciplinary by necessity. As a result, paleolimnology is influenced continuously by advances in many disciplines. As with limnological studies in recent decades, paleolimnology has diverged largely from the ecological and theoretical focuses of early investigators, but recent studies demonstrate the need for more integration of ecological and paleolimnological research. This paper provides a brief overview of recent paleolimnological investigations that have addressed questions related to theoretical ecology, as well as applied lake-management and climate research issues. We examine the use of transfer function models for estimating past water-quality conditions, and important caveats expressed by investigators about limitations in the development and use of such models. Paleolimnological research has contributed new insights about biological, physical and chemical processes in lakes that have been subject to change because of climate drivers and anthropogenic influences. These findings are relevant to predicting how lakes will respond to climate change, and will require new management approaches in the future. As the range of paleolimnological studies expands, there will be greater need for basic limnological research in order for paleolimnological investigators to better understand how sediments reflect lake processes of those regions

Topical advances and recent studies in paleolimnological research.

Paleolimnology combines the disciplines of limnology, geology and ecology, but because of challenges that separate investigators from direct knowledge about past lake conditions, the field is multidisciplinary by necessity. As a result, paleolimnology is influenced continuously by advances in many disciplines. As with limnological studies in recent decades, paleolimnology has diverged largely from the ecological and theoretical focuses of early investigators, but recent studies demonstrate the need for more integration of ecological and paleolimnological research. This paper provides a brief overview of recent paleolimnological investigations that have addressed questions related to theoretical ecology, as well as applied lake-management and climate research issues. We examine the use of transfer function models for estimating past water-quality conditions, and important caveats expressed by investigators about limitations in the development and use of such models. Paleolimnological research has contributed new insights about biological, physical and chemical processes in lakes that have been subject to change because of climate drivers and anthropogenic influences. These findings are relevant to predicting how lakes will respond to climate change, and will require new management approaches in the future. As the range of paleolimnological studies expands, there will be greater need for basic limnological research in order for paleolimnological investigators to better understand how sediments reflect lake processes of those regions

Isotope record of anthropogenic lead pollution in lake sediments of Florida, USA.

We examined the anthropogenic lead (Pb) burden that accumulated in sediment of lakes in the southeastern USA during the last ~150 years. Mining, smelting, agriculture, and fossil-fuel combustion are known to have contributed to Pb pollution in lakes of other regions. Few studies, however, have examined Pb sequestered in lakes of the southeastern USA, particularly peninsular Florida, which is subject to less continental atmospheric influence than other regions of the eastern USA. We obtained sediment cores from Little Lake Jackson and Little Lake Bonnet in Highlands County, Florida and used Pb isotopes in the records to identify principal sources of Pb contamination. The sediment records showed that changes in Pb concentration and isotope ratios correspond temporally with gasoline consumption in the USA, as well as with changes in lead ores used to produce leaded gasoline. Lead concentrations in the study lakes showed temporal variations that were similar to those found in peat records from east-central Florida. Isotope trends were similar to the mean USA atmospheric Pb deposition record, and to Pb isotope records from Bermuda and Atlantic corals. We modeled the isotopic composition of the anthropogenic Pb in lake sediments and found that the overall trend is controlled by Pb that was released during leaded gasoline combustion. There is, however, additional Pb at each site that comes from sources that are not fully represented by the natural, background Pb. Lead isotope ratios and Pb/arsenic (As) ratios provide evidence that Pb deposition in lakes during the middle 1900s might have been influenced by lead arsenate applications to golf courses, a source that is often ignored in Pb isotope studies. Isotope evidence confirms, however, that following cessation of commercial lead arsenate use in the 1960s, atmospheric alkyl lead was again the primary influence on Pb in sediments of the study lakes

Isotope record of anthropogenic lead pollution in lake sediments of Florida, USA.

We examined the anthropogenic lead (Pb) burden that accumulated in sediment of lakes in the southeastern USA during the last ~150 years. Mining, smelting, agriculture, and fossil-fuel combustion are known to have contributed to Pb pollution in lakes of other regions. Few studies, however, have examined Pb sequestered in lakes of the southeastern USA, particularly peninsular Florida, which is subject to less continental atmospheric influence than other regions of the eastern USA. We obtained sediment cores from Little Lake Jackson and Little Lake Bonnet in Highlands County, Florida and used Pb isotopes in the records to identify principal sources of Pb contamination. The sediment records showed that changes in Pb concentration and isotope ratios correspond temporally with gasoline consumption in the USA, as well as with changes in lead ores used to produce leaded gasoline. Lead concentrations in the study lakes showed temporal variations that were similar to those found in peat records from east-central Florida. Isotope trends were similar to the mean USA atmospheric Pb deposition record, and to Pb isotope records from Bermuda and Atlantic corals. We modeled the isotopic composition of the anthropogenic Pb in lake sediments and found that the overall trend is controlled by Pb that was released during leaded gasoline combustion. There is, however, additional Pb at each site that comes from sources that are not fully represented by the natural, background Pb. Lead isotope ratios and Pb/arsenic (As) ratios provide evidence that Pb deposition in lakes during the middle 1900s might have been influenced by lead arsenate applications to golf courses, a source that is often ignored in Pb isotope studies. Isotope evidence confirms, however, that following cessation of commercial lead arsenate use in the 1960s, atmospheric alkyl lead was again the primary influence on Pb in sediments of the study lakes