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Paleoecology and ecosystem restoration: Case studies from Chesapeake Bay and the Florida Everglades

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Paleoecology and ecosystem restoration: Case studies from Chesapeake Bay and the Florida Everglades

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Abstract

Climate extremes that cause droughts, floods, or large temperature fluctuations can complicate ecosystem restoration efforts focused on local and regional human disturbance. Restoration targets are often based primarily on monitoring data and modeling simulations, which provide information on species' short-term response to disturbance and environmental variables. Consequently, the targets may be unsustainable under the spectrum of natural variability inherent in the system or under future climate change. Increasingly, ecologists and restoration planners recognize the value of the long temporal perspective provided by paleoecological data. Advances in paleoclimatology, including better climate proxy methods and temporal resolution, contribute to our understanding of ecosystem response to anthropogenic and climatic forcing at all time scales. We highlight paleoecological research in the Chesapeake Bay and the Florida Everglades and summarize the resulting contributions to restoration planning. Integration of paleoecological, historic, monitoring, and modeling efforts will lead to the development of sustainable, adaptive management strategies for ecosystem restoration.

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... They linked a dramatic increase in the late 20th Century, and a corresponding decline in the abundance of Elphidium selseyensis and Ammobaculites, to environmental changes related to fertilizer use, nutrient loading and oxygen depletion. However, the Ammonia record yielded evidence of seasonal anoxia in some years between 1900 and 1960 and episodically in the main channel between 1600 and 1900 (Willard and Cronin, 2007) (Fig. 4), as is also evident in the ostracod record (see below). A similar relationship between Ammonia and Elphidium on the inner shelf of the Gulf of Mexico (Rabalais et al., 1996) was used by Sen Gupta et al. (1996) ...
... Land use also profoundly influences vegetation, hydrologic pathways and patterns, nutrient runoff, and precipitation, with important consequences for eutrophication and hypoxia. Proxies for land use may include pollen shifts and salinity indicators as well as the other proxies discussed above (Willard and Cronin, 2007). ...
... Areas of seafloor overlain by naturally oxygen-depleted water masses are widespread in deeper water, e.g. the Cariaco and Santa Barbara Basins, the Black Sea, Kau Bay, and oxygen minimum zones, and greatly exceed those affected by anthropogenically-induced hypoxia (Naqvi et al., 2000; Helly and Levin, 2004). In shallow water, natural decadal or multidecadal climatic shifts linked to changes in indices such as the North Atlantic Oscillation (NAO) can have a major impact, particularly on coastal ecosystems where seasonal hypoxia can develop as a result of increased water column stratification during the summer linked to increased precipitation and freshwater runoff (Saegner et al., 2006; Cronin and Walker, 2006; Willard and Cronin, 2007; Leipe et al., 2008). Although the trend in most river-dominated coastal systems is for an increase in the N and P loads over the last half century (Boesch, 2002; Turner et al., 2003 a, b), hypoxia may also develop naturally off the mouths of major rivers (Van der Zwaan, 2000). ...
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Under certain conditions, sediment cores from coastal settings subject to hypoxia can yield records of environmental changes over time scales ranging from decades to millennia, sometimes with a resolution of as little as a few years. A variety of biological and geochemical indicators (proxies) derived from such cores have been used to reconstruct the development of eutrophication and hypoxic conditions over time. Those based on (1) the preserved remains of benthic organisms (mainly foraminiferans and ostracods), (2) sedimentary features (e.g. laminations) and (3) sediment chemistry and mineralogy (e.g. presence of sulphides and redox-sensitive trace elements) reflect conditions at or close to the seafloor. Those based on (4) the preserved remains of planktonic organisms (mainly diatoms and dinoflagellates), (5) pigments and lipid biomarkers derived from prokaryotes and eukaryotes and (6) organic C, N and their stable isotope ratios reflect conditions in the water column. However, the interpretation of these indicators is not straightforward. A central difficulty concerns the fact that hypoxia is strongly correlated with, and often induced by, organic enrichment caused by eutrophication, making it difficult to separate the effects of these phenomena in sediment records. The problem is compounded by the enhanced preservation in anoxic and hypoxic sediments of organic microfossils and biomarkers indicating eutrophication. The use of hypoxia-specific proxies, such as the trace metals molybdenum and rhenium and the bacterial biomarker isorenieratene, together with multi-proxy approaches, may provide a way forward. All proxies of bottom-water hypoxia are basically qualitative; their quantification presents a major challenge to which there is currently no satisfactory solution. Finally, it is important to separate the effects of natural ecosystem variability from anthropogenic effects. Despite these problems, in the absence of historical data for dissolved oxygen concentrations, the analysis of sediment cores can provide plausible reconstructions of the temporal development of human-induced hypoxia, and associated eutrophication, in vulnerable coastal environments.
... These studies indicate that drier intervals have been influenced by southward shifts of the Inter-tropical Convergence Zone, and wetter intervals have been influenced by the positive phase of the North Atlantic Oscillation. Such climatic changes have been associated with shifts in hydroperiod and hence composition of wetland plant communities (Willard and Cronin, 2007;Bernhardt and Willard, 2009;Willard and Bernhardt, 2011). Similar vegetation shifts attributed to variation in climate have also been suggested by other studies in south Florida and the Caribbean region (Islebe et al., 1996;Donders et al., 2005;van Soelen et al., 2012). ...
... In presentday south Florida wetland habitats, such increases have been noted after natural lightning-ignited fires (Slocum et al., , 2010 and hurricanes (Armentano et al., 1995), when open space is generated and colonized by species like Amaranthus australis (Schmitz et al., 2002). Increases of Amaranthaceae in other pollen diagrams have also been attributed to periods of drought (Willard et al, 2001;Willard and Cronin, 2007). Therefore the shift to an herbaceous community in this subzone suggests frequent major fires, perhaps in conjunction with periods of droughts; such intense fires have burned out willow thickets in the present-day Everglades (Beckage et al., 2003;Slocum et al., 2007). ...
... Linings of foraminifera start to appear with greater regularity at the top of this zone, while mangrove taxa increase in abundance beginning at 3800 cal yr BP, indicating increased seawater flooding (Scott et al., 2003;Sabatier et al., 2008;Gonzalez et al., 2010). Additionally, the abundance of Amaranthaceae and microscopic charcoal fragments diminishes, while Sagittaria and Typha pollen decline to trace values during this period, indicating a changing environment (less fresh water and fewer fires) with more marine influence (Willard et al., 2001;Willard and Cronin, 2007). These palynological data clearly show a period of marine transgression from~3800 to 2200 cal yr BP. ...
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Palynological, loss-on-ignition, and X-ray fluorescence data from a 5.25 m sediment core from a mangrove forest at the mouth of the Shark River Estuary in the southwestern Everglades National Park, Florida were used to reconstruct changes occurring in coastal wetlands since the mid-Holocene. This multi-proxy record contains the longest paleoecological history to date in the southwestern Everglades. The Shark River Estuary basin was formed ~ 5700 cal yr BP in response to increasing precipitation. Initial wetlands were frequently-burned short-hydroperiod prairies, which transitioned into long-hydroperiod prairies with sloughs in which peat deposits began to accumulate continuously about 5250 cal yr BP. Our data suggest that mangrove communities started to appear after ~ 3800 cal yr BP; declines in the abundance of charcoal suggested gradual replacement of fire-dominated wetlands by mangrove forest over the following 2650 yr. By ~ 1150 cal yr BP, a dense Rhizophora mangle dominated mangrove forest had formed at the mouth of the Shark River. The mangrove-dominated coastal ecosystem here was established at least 2000 yr later than has been previously estimated.
... Fossil pollen and charcoal records spanning tens to thousands of years can provide a unique, long-term perspective for biodiversity conservation efforts aimed at conserving processes, habitats, or species (Willis and Birks 2006;Gavin et al. 2007;Willard and Cronin 2007). Such studies are increasingly being used to inform natural resource management and conservation planning at local, regional, and global scales (Horn 1998;Swetnam et al. 1999;Willard et al. 2001;Willis and Birks 2006;Willard and Cronin 2007). ...
... Fossil pollen and charcoal records spanning tens to thousands of years can provide a unique, long-term perspective for biodiversity conservation efforts aimed at conserving processes, habitats, or species (Willis and Birks 2006;Gavin et al. 2007;Willard and Cronin 2007). Such studies are increasingly being used to inform natural resource management and conservation planning at local, regional, and global scales (Horn 1998;Swetnam et al. 1999;Willard et al. 2001;Willis and Birks 2006;Willard and Cronin 2007). For example, long-term fire histories can provide important baseline information on the range of natural variability of fire activity prior to human disturbance, such as land use change or fire suppression (Gavin et al. 2007). ...
... A number of recent paleoecological studies have provided information important for biodiversity conservation, including recommendations on wildfire, climate change, and management within thresholds of natural variability (e.g., Chambers et al. 1999;Willard et al. 2001;Willard et al. 2006;Burney and Burney 2007;Gavin et al. 2007;Willard and Cronin 2007). Horn (1998) (Horn 1989(Horn , 1993(Horn , 1997(Horn , 1998League and Horn 2000). ...
... Debates continue about what constitute baseline and reference conditions, and what are the appropriate spatial and temporal scales for studies; and new debates have emerged about novel ecosystems, no-analog communities, and how to define sustainability (Jackson and Overpeck, 2000;Willard and Cronin, 2007;Williams and Jackson, 2007;Jackson and Hobbs, 2009;Watson et al., 2011), but paleoecology has entered the realm of applied science in the twenty-first century. Opportunities for collaboration between paleoecologists and the emerging field of conservation paleobiology offer the potential to further our understanding of interactions between evolutionary patterns, the environment, and biodiversity 2 . ...
... Large-scale estuarine restoration projects have utilized information on historical variability for several decades. Numerous paleoecologic analyses have been conducted in the Chesapeake Bay region, eastern U.S.A. (summarized in Willard and Cronin, 2007). These studies have indicated (1) the effects of deforestation and the centuries-long impact of land-use on the Chesapeake region (Cooper and Brush, 1993;Brush and Hilgartner, 2000;Willard et al., 2003); (2) the combined effects of climate and land-use (Cooper and Brush, 1993;Cronin and Vann, 2003;Willard et al., 2003;Brush, 2009); and (3) measures of water quality, such as salinity, eutrophication, hypoxia and anoxia (Cooper and Brush, 1993;Karlsen et al., 2000;Cronin and Vann, 2003;Willard et al., 2003;Brush, 2009). ...
... He concluded that it is a realitythe past can serve as the key to the future. The examples provided above reinforce Kowalewski's and others' conclusions (for example, Folke et al., 2004;Willis and Birks, 2006;Willard and Cronin, 2007;Jackson and Hobbs, 2009;Gell, 2010;Willis et al., 2010;Dietl and Flessa, 2011;Seddon et al., 2014;Dietl et al., 2015) that studying changes to Earth's ecosystems over centennial to millennial time scales is essential as we move forward with restoration and resource management programs in the twenty-first century. In addition, these examples illustrate implementation of the initiatives outlined in 2005 in the U.S. National Academy of Sciences Committee report on The Geologic Record of Ecological Dynamics (NRC, 2005) by documenting past responses to ecosystem change under a range of conditions; by providing information that can be used to predict biological responses to future changes; and by highlighting potential changes to ecosystems due to anthropogenic impacts. ...
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Resource managers around the world are challenged to develop feasible plans for sustainable conservation and/or restoration of the lands, waters, and wildlife they administer—a challenge made greater by anticipated climate change and associated effects over the next century. Increasingly, paleoecologic and geologic archives are being used to extend the period of record of observed data and provide information on centennial to millennial scale responses to long-term drivers of ecosystem change. The development of paleoecology from an emerging field investigating past environments to a highly relevant applied science is reviewed and general examples of the application of paleoecologic research to resource management questions in diverse habitats and regions are provided. Specific examples of the application of paleoecologic research to the restoration of the Greater Everglades Ecosystem of south Florida (U.S.A) are presented. Conducting valuable scientific research that would benefit resource management decisions, however, is not enough. Scientists and resource managers need to be engaged in collaborative discussions from the beginning of the research process to ensure that management questions are being addressed and that the science reaches the people who will benefit from the information. Paleoecology and related disciplines provide an understanding of how ecosystems and individual species function and change over time in response to both natural and anthropogenic drivers. Information on pre-anthropogenic baseline conditions is provided by paleoecologic research, but it is the detection of long-term trends and cycles that allow resource managers to set realistic goals and targets by moving away from the fixed-point baseline concept to one of dynamic landscapes that anticipates and incorporates an expectation of change into decision-making.
... Numerous lines of evidence have shown that marine ecological degradations, for example, biodiversity loss, population collapse, invasion of exotic species, and various faunal/floral changes, are now apparent in most, if not all, marine ecosystems (Lotze et al. 2006; Halpern et al. 2008; Jackson 2008). Causes include increased nutrient loads resulting in zones of low dissolved oxygen and other symptoms of eutrophication (Kemp et al. 2005; Diaz and Rosenberg 2008; Breitburg et al. 2009), fisheries exploitation (Jackson 2001; Jackson et al. 2001; Worm et al. 2006), physical habitat destruction (Jackson 2001; Jackson et al. 2001; Coleman and Williams 2002), ocean acidification (Orr et al. 2005; Hoegh-Guldberg et al. 2007; Fabry et al. 2008), pollution (Shahidul Islam and Tanaka 2004), land clearance/modification (Lotze et al. 2005; Airoldi and Beck 2007; Willard and Cronin 2007), and global warming (Hoegh-Guldberg and Bruno 2010). Meta-analyses have detailed the general historical process of marine ecological degradation for the last 3000 years using fisheries, ecological, historical, archeological , and paleontological records, and have revealed rapid biodiversity and population loss starting at ~1800, the onset of industrialization (Lotze et al. 2006; Worm et al. 2006). ...
... Thus, they are useful proxies or model organisms to infer states of whole marine ecosystems in the past (Thomas and Gooday 1996; Cronin and Raymo 1997; Yasuhara and Cronin 2008; Yasuhara et al. 2008). Although several researchers have shown the importance of microfossils in understanding marine ecological degradation (Tikkanen et al. 1997; Willard and Cronin 2007; Yasuhara et al. 2007; Tsujimoto et al. 2008), many studies focused on microfossil-based reconstruction of pollution history (Sen Gupta et al. 1996; Clarke et al. 2006; Gooday et al. 2009) rather than reconstruction of the biotic response to pollution. This situation is similar to that in paleolimnology. ...
... In Europe, eutrophication footprints on faunal/floral composition extend back to ~1550 in a Norwegian fjord (Alve 2000) and to the mid-19th century in the Baltic Sea (Andrén 1999; Andrén et al. 1999). Initial ecological degradation in the 1700s in Chesapeake Bay in North America is indicated by disturbances to diatom flora and submerged aquatic vegetation associated with European land clearance (Brush and Hilgartner 2000; Willard and Cronin 2007; Brush 2009). In contrast, no marine ecological degradation was detected from pre-1900 sediments in Asia. ...
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We analyzed published downcore microfossil records from 150 studies and reinterpreted them from an ecological degradation perspective to address the following critical but still imperfectly answered questions: (1) How is the timing of human-induced degradation of marine ecosystems different among regions? (2) What are the dominant causes of human-induced marine ecological degradation? (3) How can we better document natural variability and thereby avoid the problem of shifting baselines of comparison as degradation progresses over time? The results indicated that: (1) ecological degradation in marine systems began significantly earlier in Europe and North America (∼1800s) compared with Asia (post-1900) due to earlier industrialization in European and North American countries, (2) ecological degradation accelerated globally in the late 20th century due to post-World War II economic growth, (3) recovery from the degraded state in late 20th century following various restoration efforts and environmental regulations occurred only in limited localities. Although complex in detail, typical signs of ecological degradation were diversity decline, dramatic changes in total abundance, decrease in benthic and/or sensitive species, and increase in planktic, resistant, toxic, and/or introduced species. The predominant cause of degradation detected in these microfossil records was nutrient enrichment and the resulting symptoms of eutrophication, including hypoxia. Other causes also played considerable roles in some areas, including severe metal pollution around mining sites, water acidification by acidic wastewater, and salinity changes from construction of causeways, dikes, and channels, deforestation, and land clearance. Microfossils enable reconstruction of the ecological history of the past 10(2)-10(3) years or even more, and, in conjunction with statistical modeling approaches using independent proxy records of climate and human-induced environmental changes, future research will enable workers to better address Shifting Baseline Syndrome and separate anthropogenic impacts from background natural variability.
... Initial signs of ecological degradation were the change in diatom abundance and flora in approximately 1700 due to European settlement and deforestation that resulted in increased river discharge and initial eutrophication (Cooper, 1995;Cronin & Vann, 2003;Yasuhara et al., 2012). Diatom diversity decreased by around 1800 (Cooper, 1995) because of further deforestation (Brush, 2009;Cronin & Vann, 2003;Willard & Cronin, 2007) and perhaps industrialization (Yasuhara et al., 2012). After that, the largest ecological changes occurred at around 1960, probably because of urbanization and substantial increase in population and fertilizer use (Brush, 2009;Cronin & Vann, 2003;Willard & Cronin, 2007). ...
... Diatom diversity decreased by around 1800 (Cooper, 1995) because of further deforestation (Brush, 2009;Cronin & Vann, 2003;Willard & Cronin, 2007) and perhaps industrialization (Yasuhara et al., 2012). After that, the largest ecological changes occurred at around 1960, probably because of urbanization and substantial increase in population and fertilizer use (Brush, 2009;Cronin & Vann, 2003;Willard & Cronin, 2007). The resulting eutrophication and deoxygenation, that have become much more severe and widespread since approximately 1960, have caused serious ecosystem degradation as represented by the ostracod and foraminiferan faunal and diatom floral changes (Brush, 2009;Cooper, 1995;Cronin & Vann, 2003;Karlsen et al., 2000;Willard & Cronin, 2007). ...
... After that, the largest ecological changes occurred at around 1960, probably because of urbanization and substantial increase in population and fertilizer use (Brush, 2009;Cronin & Vann, 2003;Willard & Cronin, 2007). The resulting eutrophication and deoxygenation, that have become much more severe and widespread since approximately 1960, have caused serious ecosystem degradation as represented by the ostracod and foraminiferan faunal and diatom floral changes (Brush, 2009;Cooper, 1995;Cronin & Vann, 2003;Karlsen et al., 2000;Willard & Cronin, 2007). The long core record covering the past 8000 years indicates that Chesapeake Bay deoxygenation is not purely a humaninduced phenomenon, and natural deoxygenation existed, though to a much lesser extent, especially in deep channels during the pre-Anthropocene Holocene (Yasuhara et al., 2012). ...
... Resource managers on federal lands in the United States and in other countries use the historical range of variability (HRV) as a dynamic management target (Keane et al. 2009). Paleoecological records with relatively high-i.e., annual to decadal-resolution (with minimal time-averaging per sampled assemblage) can be used to identify the HRV in specific settings (Landres et al. 1999) and enable managers to discriminate variability around a stationary mean from variability associated with a long-term trend (Willard & Cronin 2007, Smol 2010. For example, Wolfe et al. (2001) studied sediment cores from two alpine lakes in the Colorado Front Range and showed that an increase in the abundance of mesotrophic diatoms and increasingly 15 N-depleted sediments were responses to excess nitrogen derived from agricultural and industrial sources since the 1950s. ...
... Conservation paleobiology provides information on ecological conditions before human disturbance, thereby providing valid targets for mitigation and restoration efforts and a means to evaluate success (Brenner et al. 1993, Jackson & Hobbs 2009). Paleoecological studies are consequently playing an increasing role in ecological restoration efforts (Steadman 1995, Burney & Burney 2007, Willard & Cronin 2007, and they contribute to discussions regarding feasible restoration targets in a changing environment ( Jackson & Hobbs 2009). For example, Volety et al. (2009) used geohistorical baseline data from Holocene oyster (Crassostrea virginica) reefs off the coast of south Florida to establish that populations diminished largely as a consequence of reduced freshwater discharge from the Everglades. ...
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Humans now play a major role in altering Earth and its biota. Finding ways to ameliorate human impacts on biodiversity and to sustain and restore the ecosystem services on which we depend is a grand scientific and societal challenge. Conservation paleobiology is an emerging discipline that uses geohistorical data to meet these challenges by developing and testing models of how biota respond to environmental stressors. Here we (a) describe how the discipline has already provided insights about biotic responses to key environmental stressors, (b) outline research aimed at disentangling the effects of multiple stressors, (c) provide examples of deliverables for managers and policy makers, and (d) identify methodological advances in geohistorical analysis that will foster the next major breakthroughs in conservation outcomes. We highlight cases for which exclusive reliance on observations of living biota may lead researchers to erroneous conclusions about the nature and magnitude of biotic change, vulnerability, and resilience.
... For the twentieth century, the paleoecologic studies indicate a reduction in freshwater supply to both the upstream and downstream components of the system. This decrease in freshwater corresponds to the time period of construction of water control structures, and it is clearly documented in the changes in the fauna and flora present in both the estuarine and wetlands cores (see Willard et al. (2001a), Willard and Cronin (2007), and Bernhardt and Willard (2009) for a discussion of changes to the wetlands). Many of the estuarine sites examined show significant faunal shifts around the turn of the century and again between 1950 and 1960, in contrast to the more gradual changes seen in the lower parts of the cores. ...
... In light of IPCC (2007) projections of climate change and sea level rise, an understanding of the long-term (centennial-scale) natural patterns of change allows us to estimate the future trajectory of an unaltered system, and then generate potential future conditions under various IPCC scenarios (Fig. 22.3). These efforts, based on paleoecological data, increase the likelihood that the Everglades restoration efforts will be sustainable because they take the natural system variability into account (Willard and Cronin 2007). ...
Chapter
Paleoecological analyses of biotic assemblages from cores collected throughout south Florida’s estuaries indicate gradually increasing salinities over approximately the last 2000 years, consistent with rising sea level. Around the beginning of the twentieth century these gradual patterns of change began to shift, corresponding to the beginning of human alteration of the environment via canal construction, railroad construction and other land use changes. Between 1950 and 1960, at a time of significant construction of water management structures another distinctive shift in the biological assemblages occurred. Analysis of the assemblages provides essential information on long-term patterns of change in the estuaries and provides a basis for predicting future trajectories of change. Paleosalinity estimates derived from the cores are providing input to linear regression models to determine related freshwater flow into the estuaries of south Florida. These analyses are being used to help establish performance measures and targets for the Comprehensive Everglades Restoration, established following an Act of Congress in 2000. Restoration of south Florida’s ecosystems is slated to be a 30–50 year effort that will require detailed knowledge of past decadal to centennial-scale changes in climate, freshwater flow and salinity. This historical perspective provides information that allows land managers to set realistic and sustainable goals for restoration, and provides insight into the potential response of south Florida’s ecosystem to various future scenarios of global change.
... The period around the fifteenth century has apparent SLR rates of up to 2.7 millimeters per year in Greenland and 1.5 millimeters per year in Maine, but glacioisostacy affects the former and chronological uncertainty affects the latter. In North America, colonial land clearing and other human activities have influenced coastal faunal and floral communities [Willard and Cronin, 2007], complicating the interpretation of marsh sediment records. In summary, marshes contain potential evidence that sea level varied during the past several millennia, but more work is needed to establish better high-resolution regional sea level curves. ...
Article
Sea level rise (SLR) ranks high on the list of climate change issues because the expected acceleration from the current rate (about 3.1 millimeters per year) poses threats to coastal regions. Tide gauge, salt marsh, and archaeological records, and modeling of glacioisostatic adjustment (GIA) have led to the widely accepted idea that late Holocene (the past ∼2000 years) sea level was stable prior to acceleration beginning around 1850-1900 C.E. For instance, according to the Intergovernmental Panel on Climate Change Fourth Assessment Report, before the last century, sea level had “stabilized” over the past 2000 years, rising at a mean rate of 0-0.2 millimeter per year [Bindoff et al., 2007]. Others maintain that sea level was “nearly stable” over the past few thousand years [Nicholls and Cazenave, 2010], pre-twentieth century rates were “close to zero” [Church et al., 2008], or “stable from at least BC 100 until AD 950” and “stable, or slightly falling” from 1350 until the nineteenth century [Kemp et al., 2011].
... Examples include the Baltic Sea, Sweden (Andrén 1999;Andrén et al. 1999), along the Norwegian coastal zone (e.g. Alve 1991; Dale & Fjellsa 1994;Dale 2000;Alve et al. 2009) and Chesapeake Bay, USA (Brush & Hilgartner 2000;Cronin & Vann 2003;Willard & Cronin 2007;Brush 2009). However, anthropogenic pollution and eutrophication did not reach Asia until the twentieth century (e.g. ...
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The term 'Anthropocene' has been proposed to indicate a geological interval characterized by global anthropogenic environmental change. This paper attempts to recognize a method by which the Anthropocene can be defined micropalaeontologically. In order to do this, microfloras and microfaunas (diatoms, macrophytes, dinoflagellate cysts, foraminifera and ostracods) from nearshore waters through to paralic and freshwater aquatic milieux are considered, and biotic variability with an anthropogenic causation identified. Microbiotic change can be related to anthropogenically induced extinctions, pollution-related mutation, environmentally influenced assemblage variability, geochemistry of carapaces/tests, floral change related to lacustrine acidification, faunal and floral correlation to industrial and agricultural signatures and introduction of exotic species via shipping. The influence of humanity on a local scale can be recognized in assemblages as far back as 5000 years BP. However, widespread anthropogenic change took place in Europe and America, particularly in the nineteenth and twentieth centuries, although in Asia (e.g. Japan) it cannot be observed prior to the twentieth century. Profound and global biotic change began in the midtwentieth century and, if the Anthropocene is to be defined in this way, then the period 1940-1945 might encompass the biotic base of the interval.
... Chesapeake Bay is one of the largest estuaries in North America, with a length of 320 km. Episodic hypoxia has occurred in Chesapeake Bay since at least 1600 and seasonally since 1900 (Zimmerman and Canuel, 2002;Willard and Cronin, 2007;Gooday et al., 2009). Seasonal hypoxia increased in extent, duration and intensity during the 20th century (Breitburg et al., 2001;Vann, 2003, Hagy et al., 2004). ...
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Coastal hypoxia (<1.42 ml L<sup>−1</sup>; 62.5 μM; 2 mg L<sup>−1</sup>, approx. 30% oxygen saturation) occurs seasonally in many estuaries, fjords, and along open coasts subject to upwelling or excessive riverine nutrient input, and permanently in some isolated seas and marine basins. Underlying causes of hypoxia include enhanced nutrient input from natural causes (upwelling) or anthropogenic origin (eutrophication) and reduction of mixing by limited circulation or enhanced stratification; combined these lead to higher surface water production, microbial respiration and eventual oxygen depletion. Advective inputs of low-oxygen waters may initiate or expand hypoxic conditions. Responses of estuarine, enclosed sea, and open shelf benthos to hypoxia depend on the duration, predictability, and intensity of oxygen depletion and on whether H<sub>2</sub>S is formed. Under suboxic conditions, large mats of filamentous sulfide oxidizing bacteria cover the seabed and consume sulfide, thereby providing a detoxified microhabitat for eukaryotic benthic communities. Calcareous foraminiferans and nematodes are particularly tolerant of low oxygen concentrations and may attain high densities and dominance, often in association with microbial mats. When oxygen is sufficient to support metazoans, small, soft-bodied invertebrates (typically annelids), often with short generation times and elaborate branchial structures, predominate. Large taxa are more sensitive than small taxa to hypoxia. Crustaceans and echinoderms are typically more sensitive to hypoxia, with lower oxygen thresholds, than annelids, sipunculans, molluscs and cnidarians. Mobile fish and shellfish will migrate away from low-oxygen areas. Within a species, early life stages may be more subject to oxygen stress than older life stages. Hypoxia alters both the structure and function of benthic communities, but effects may differ with regional hypoxia history. Human-caused hypoxia is generally linked to eutrophication, and occurs adjacent to watersheds with large populations or agricultural activities. Many occurrences are seasonal, within estuaries, fjords or enclosed seas of the North Atlantic and the NW Pacific Oceans. Benthic faunal responses, elicited at oxygen levels below 2 ml L<sup>−1</sup>, typically involve avoidance or mortality of large species and elevated abundances of enrichment opportunists, sometimes prior to population crashes. Areas of low oxygen persist seasonally or continuously beneath upwelling regions, associated with the upper parts of oxygen minimum zones (SE Pacific, W Africa, N Indian Ocean). These have a distribution largely distinct from eutrophic areas and support a resident fauna that is adapted to survive and reproduce at oxygen concentrations <0.5 ml L<sup>−1</sup>. Under both natural and eutrophication-caused hypoxia there is loss of diversity, through attrition of intolerant species and elevated dominance, as well as reductions in body size. These shifts in species composition and diversity yield altered trophic structure, energy flow pathways, and corresponding ecosystem services such as production, organic matter cycling and organic C burial. Increasingly the influences of nature and humans interact to generate or exacerbate hypoxia. A warmer ocean is more stratified, holds less oxygen, and may experience greater advection of oxygen-poor source waters, making new regions subject to hypoxia. Future understanding of benthic responses to hypoxia must be established in the context of global climate change and other human influences such as overfishing, pollution, disease, habitat loss, and species invasions.
... Soils in low-energy coastal systems preserve historical conditions of plant community dynamics and maintain a record of natural and anthropogenic disturbances. Soil stratigraphy is frequently used as a tool in ecological studies to reconstruct past ecosystem dynamics and to elucidate patterns, causes, and rates of change (Willard and Cronin, 2007). Rates of sediment, nutrient, and heavy metal accumulation (DeLaune, Reddy, and Patrick, 1981;Reddy et al., 1993), the timing and frequency of episodic events (e.g., fires and hurricanes) (Liu and Fearn, 2000;Liu, Lu, and Shen, 2008), and shifts in hydrology and vegetation (Brenner, Schelske, and Keenan, 2001;Kim and Rejemánková, 2002) can all be determined from soil records. ...
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Mild winter temperatures are facilitating the expansion of black mangrove (Avicennia germinans) into smooth cordgrass (Spartina alterniflora) marshes along the northern Gulf of Mexico. These expansions have the potential to alter soil development because of differences in productivity and tissue chemistry between Spartina and Avicennia. Here, we examined changes in soil-nutrient chemistry at 2-cm intervals in 30-cm soil cores collected from Spartina and Avicennia habitats at two different sites in Fourchon, Louisiana. Beginning in 1959 and continuing through 2009, our chronology shows that the species shift had no effect on bulk density (mean +/- standard error [SE]: 0.68 +/- 0.02 g cm(-3)), organic matter (mean +/- SE: 8.36 +/- 0.29 %), or nitrogen content (mean +/- SE: 1.15 +/- 0.03 mg cm(-3)). Phosphorus densities were significantly greater in Avicennia habitats (mean +/- SE: 0.32 +/- 0.01 mg cm(-3)) than they were in Spartina habitats (mean +/- SE: 0.28 +/- 0.01 mg cm(-3)), which we attributed to Avicennia occurring at higher elevations in more oxidizing soils. We observed significant variability with depth (proxy for time) and between sites in all soil properties measured. This variability can be attributed to the dominance of allochthonous sediment deposition from natural and anthropogenic disturbances compared with the lesser influence of vegetation on autochthonous soil development. In the highly disturbed region of Fourchon, Louisiana, the shift from Spartina marshes to scrub Avicennia stands does not appear to affect the chemistry of soil development.
... The chemical composition of lake sediments and its biological remains constitute an archive of historical data. Changes in chemical and biological parameters can be used to understand the relationship between ecological disturbances in lake systems and their impact on ecosystem health (Willard and Cronin 2007). Disturbances of lake systems can be physical or chemical. ...
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Measurements of chemical composition and biological parameters of sediment cores are used as proxies for changes in past environmental conditions and more recently the human impact on ecosystem health. In this study, endospore-forming bacteria are proposed as a new biological proxy for such paleoecological reconstructions. A sediment core providing a record for the past 90 years (137Cs and magnetic susceptibility dating) was retrieved from the Rhone Delta of Lake Geneva. X-ray fluorescence was analyzed at a 0.2-cm resolution, while DNA extracts, elemental geochemistry and grain size were obtained at 4-cm intervals. The total number of bacteria and endospore-forming bacteria were quantified by qPCR using the 16S rRNA gene and the endosporulation-specific spo0A gene. Furthermore, a spo0A fragment was subjected to amplicon sequencing to define OTUs (operational taxonomic units) and the phylogenetic affiliation of the endospore formers. The results showed that despite the fact that the quantity of extracted DNA decreased with the age of the sediment, the abundance of endospore-forming bacteria remained constant. However, the diversity of this group of bacteria changed significantly, reflecting the eutrophication of the lake from 1960 to 1990. The shift in community composition was linked to the dominance of anaerobic clostridia-like endospore formers. This trend has reversed in the last 10 years of the record, suggesting a recovery after perturbation. This study shows that the abundance and diversity of endospore-forming bacteria can be used as proxies to reconstruct lake history. We hereby successfully introduce a new strategy for paleoecology that could also be applied to ocean sediments and long sediment cores.
... At the long-term timescale and perspective, paleoecological archives provide the means to reveal how natural systems have responded to climatic changes through time. This information cannot be resolved from any monitoring data, which usually consist of only short period of observation compared to paleoecological deposits [2,3]. In addition, sedimentary records provide a unique perspective on how today's ecosystems are likely to respond to future changes [4]. ...
Article
We examined a sediment core from a climatically sensitive High Alpine lake Unterer Giglachsee in the Niedere Tauern Alps in Austria. Our aim was to investigate long-term climate change impacts on aquatic invertebrates (Chironomidae, Cladocera) with a special focus on the ending of the Little Ice Age and the present climate warming. Although the changes in faunal assemblages were relatively subtle through the sedimentary record, a mutual faunal breakpoint at ∼1900 AD was distinguished. In addition, the faunal dynamics correlated closely with instrumental Alpine temperature records and with reconstructed Northern Hemisphere climate development over the examined time period. In particular, significant relationships between relative taxa abundance and temperature were found with chironomids Sergentia, Paracladius, Paratanytarsus austriacus-type, Cricotopus (I.) intersectus-type, and Cricotopus cylindraceus-type and with cladocerans Daphnia and Alonella excisa. Our results also suggested that the most recent assemblages represent unique community compositions. We conclude that our study lake is sensitive to climate warming and the composition of the aquatic ecosystem in Unterer Giglachsee has changed due to the impact of increasing temperatures. We predict that the further increasing temperatures will have direct but also cascading effects on the sensitive lake, potentially causing an ecosystem turnover where the key taxon Paracladius may play an important role.
... The Everglades is comprised of elongated, flow-parallel ridges and sloughs that formed several thousand years ago (Willard and Cronin, 2007;Bernhardt and Willard, 2009) (Fig. 1). The topographic and vegetation features are strikingly similar to other low-gradient, floodplain wetlands found worldwide that are valued for their relatively high biodiversity and high connectivity of habitats (e.g. ...
Article
Flow interactions with aquatic vegetation and effects on sediment transport and nutrient redistribution are uncertain in shallow aquatic ecosystems. Here we quantified sediment transport in the Everglades by progressively increasing flow velocity in a field flume constructed around undisturbed bed sediment and emergent macrophytes. Suspended sediment < 100 μm was dominant in the lower range of laminar flow and was supplied by detachment from epiphyton. Sediment flux increased by a factor of four and coarse flocculent sediment > 100 μm became dominant at higher velocity steps after a threshold shear stress for bed floc entrainment was exceeded. Shedding of vortices that had formed downstream of plant stems also occurred on that velocity step which promoted additional sediment detachment from epiphyton. Modeling determined that the potentially entrainable sediment reservoir, 46 g m− 2, was similar to the reservoir of epiphyton (66 g m− 2) but smaller than the reservoir of flocculent bed sediment (330 g m− 2). All suspended sediment was enriched in phosphorus (by approximately twenty times) compared with bulk sediment on the bed surface and on plant stems, indicating that the most easily entrainable sediment is also the most nutrient rich (and likely the most biologically active).
... Soils in low-energy coastal systems preserve historical conditions of plant community dynamics and maintain a record of natural and anthropogenic disturbances . Soil stratigraphy is frequently used as a tool in ecological studies to reconstruct past ecosystem dynamics and to elucidate patterns, causes, and rates of change (Willard and Cronin, 2007). Rates of sediment, nutrient, and heavy metal accumulation (DeLaune, Reddy, and Patrick, 1981; Reddy et al., 1993), the timing and frequency of episodic events (e.g., fires and hurricanes) (Liu and Fearn, 2000; Liu, Lu, and Shen, 2008), and shifts in hydrology and vegetation (Brenner, Schelske, and Keenan, 2001; Kim and Rejemánková, 2002) can all be determined from soil records. ...
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Located at the northernmost extent of mangroves in the Gulf of Mexico, coastal Louisiana (LA) provides an excellent opportunity to study the effects of a climate-induced vegetation shift on nutrient cycling within an ecosystem. Climate throughout the Gulf Coast region is experiencing a general warming trend and scientists predict both hotter summers (+1.5 to 4 °C) and warmer winters (+1.5 to 5.5 °C) by 2100. Over the last two decades, mild winter temperatures have facilitated the expansion of black mangrove trees (Avicennia germinans) into the smooth cordgrass (Spartina alterniflora) along parts of the LA coast. Due to differences in morphology and physiology between these two species, the expansion of Avicennia has the potential to greatly alter sediment biogeochemistry, especially nutrient cycling. With such an extensive history of coastal nutrient enrichment and eutrophication in the Mississippi River delta, it is important to understand how nutrient cycling, retention, and removal in this region will be affected by this climate-induced vegetation expansion. We examined the effect of this species shift on porewater salinity, sulfide, and dissolved inorganic nutrient concentrations (nitrite, nitrate, ammonium, and phosphate) as well as sediment oxidation-reduction potential, bulk density, and nutrient content (carbon, nitrogen, phosphorus). We also measured net dinitrogen (N2:Ar), oxygen, and dissolved inorganic nutrient fluxes on intact, non-vegetated sediment cores collected from both Spartina and Avicennia habitats. Spartina sediments were more reducing, with higher concentrations of sulfides and ammonium. We found no significant difference between Spartina and Avicennia sediment dinitrogen, oxygen, or dissolved inorganic nutrient fluxes. Net dinitrogen fluxes for both habitat types were predominately positive, indicating higher rates of denitrification than nitrogen fixation at these sites. Sediments were primarily a nitrate sink, but functioned as both a source and sink of nitrite, ammonium, and phosphate depending on the season and light conditions. Further sediment analysis showed no significant difference in bulk density, carbon, nitrogen, or phosphorus content between Spartina and Avicennia sediments. Marine sediments high in bulk density and phosphorus content and low carbon and nitrogen content dominated the top several centimeters in both Spartina and Avicennia habitats. These surprising but reassuring results suggest that in a region where allochthonous sediment input dominates organic accretion from the primary producers, the climate-induced shift from Spartina to Avicennia will have little to no affect on littoral nutrient cycling.
... Everglades sloughs, likewise, may be experiencing the ratchet effect. Palaeoecological studies show that historically, sloughs contained less Eleocharis, and vegetation assemblages were characteristic of deeper water conditions (Willard et al., 2001;Willard and Cronin, 2007;Bernhardt and Willard, 2009). Additional studies show that Eleocharis cellulosa grown in deep-water conditions (54 cm depth) produces fewer shoots and lower biomass than Eleocharis cellulosa grown in shallower (7 cm depth) water (Edwards et al., 2003). ...
Article
Entrainment of sediment by flowing water affects topography, habitat suitability, and nutrient cycling in vegetated floodplains and wetlands, impacting ecosystem evolution and the success of restoration projects. Nonetheless, restoration managers lack simple decision-support tools for predicting shear stresses and sediment redistribution potential in different vegetation communities. Using a field-validated numerical model, we developed state-space diagrams that provide these predictions over a range of water-surface slopes, depths, and associated velocities in Everglades ridge and slough vegetation communities. Diminished bed shear stresses and a consequent decrease in bed sediment redistribution are hypothesized causes of a recent reduction in the topographic and vegetation heterogeneity of this ecosystem. Results confirmed the inability of present-day flows to entrain bed sediment. Further, our diagrams showed bed shear stresses to be highly sensitive to emergent vegetation density and water-surface slope but less sensitive to water depth and periphyton or floating vegetation abundance. These findings suggested that instituting a pulsing flow regime could be the most effective means to restore sediment redistribution to the Everglades. However, pulsing flows will not be sufficient to erode sediment from sloughs with abundant spikerush, unless spikerush density first decreases by natural or managed processes. Our methods provide a novel tool for identifying restoration parameters and performance measures in many types of vegetated aquatic environments where sediment erosion and deposition are involved.
... The historical record of human activities is characterized by a steady increase of pressure on Earth's ecosystems (Haber 2007;WWF 2004). Facing this situation, the detection of historical trends in ecosystems (i.e., paleoecology) is an important aspect of environmental research to document human impacts, to identify main stressors, and to design proper strategies of mitigation and management (Willard and Cronin 2007). Data obtained from sediment cores provide insights into past conditions, the natural range of variability, and the ecosystem response to change (Brewster-Wingard and Ishman 1999). ...
Article
The first paleoecological reconstruction of the biogeochemical conditions of the Gulf of Batabanó, Caribbean Sea was performed from (210)Pb-dated sediment cores. Depth profiles of 20 major elements and trace metals, organic compounds, grain size, and mollusk assemblage composition were determined from 9 stations encompassing unconsolidated sediments in the gulf. Spatial heterogeneity was evident for the geochemistry of sediments and for the mollusk assemblage composition. Our reconstruction indicates that pollution is not a critical threat to the ecosystem, although a slight historical increase of lead enrichment factor was detected probably due to long-range atmospheric fallout. Mollusk assemblages were composed by 168 species belonging to 59 families and no temporal trends in the species diversity or assemblage composition were detected, suggesting no depletion of diversity or habitat loss. Other signals of habitat loss such as changes in organic budget or increase of fine sediment fraction were absent or weak. Nitrogen retained in sediments changed by <1% in the century, indicating no historical events of eutrophication or oligotrophication in the gulf. Historical decrease of fine sediment fraction in the eastern sector would be linked to modifications in sedimentation rate, land use, and/or particle transport from the shelf border; this also suggests that both sectors have different sedimentary dynamics. Although, on theoretical grounds, historical fishery may have caused deleterious ecosystem effects by overexploitation of spiny lobster stocks, no evidence of habitat degradation or loss, caused by fisheries, could be detected.
... In the case of Manzala lagoon, pollen is used to interpret wetland responses to environmental modifications during the late-19th and 20th centuries and could serve as a baseline for studies that evaluate vegetation sensitivity to natural climate variability (cf. Willard and Cronin, 2007). ...
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The pollen record in a sediment core from Manzala lagoon on the Nile delta coastal margin of Egypt, deposited from ca. AD 1860 to 1990, indicates rapid coastal wetland vegetation responses to two primary periods of human activity. These are associated with artificially altered Nile hydrologic regimes in proximal areas and distal sectors located to 1200 km south of Manzala. Freshwater wetland plants that were dominant, such as Typha and Phragmites, decreased rapidly, whereas in the early 1900s, brackish water wetland species (e.g., Amaranthaceae) increased. This change occurred after closure of the Aswan Low Dam in 1902. The second major modification in the pollen record occurred in the early 1970s, after Aswan High Dam closure from 1965 to 1970, when Typha pollen abundance increased rapidly. Massive population growth occurred along the Nile during the 130 years represented by the core section. During this time, the total volume of lagoon water decreased because of conversion of wetland areas to agricultural land, and input of organic-rich sediment, sewage (municipal, agricultural, industrial), and fertilizer in Manzala lagoon increased markedly. Although the wetland plant community has continued to respond to increasingly intensified and varied human-induced pressures in proximal sectors, the two most marked changes in Manzala pollen best correlate with distal events (i.e., closure of the two dams at Aswan). The study also shows that the two major vegetation changes in Manzala lagoon each occurred less than 10 years after closure upriver of the Low and High dams that markedly altered the Nile regime from Upper Egypt to the coast.
... to algal blooms, seasonal hypoxia, and a shift from topdown to bottom-up trophic control of ecosystem structure (Brush 2001;Zimmerman & Canuel 2002;Willard & Cronin 2007). Many of the changes observed in the Chesapeake Bay are similar to those noted in bays and estuaries around the world Lotze et al. 2006;Beck et al. 2011). ...
Article
The search for novel approaches to establishing ecological baselines (reference conditions) is constrained by the fact that most ecological studies span the past few decades, at most, and investigate ecosystems that have been substantially altered by human activities for decades, centuries, or more. Paleobiology, archeology, and history provide historical ecological context for biological conservation, remediation, and restoration. We argue that linking historical ecology explicitly with conservation can help unify related disciplines of conservation paleobiology, conservation archeobiology, and environmental history. Differences in the spatial and temporal resolution and extent (scale) of prehistoric, historic, and modern ecological data remain obstacles to integrating historical ecology and conservation biology, but the prolonged temporal extents of historical ecological data can help establish more complete baselines for restoration, document a historical range of ecological variability, and assist in determining desired future conditions. We used the eastern oyster (Crassostrea virginica) fishery of the Chesapeake Bay (U.S.A.) to demonstrate the utility of historical ecological data for elucidating oyster conservation and the need for an approach to conservation that transcends disciplinary boundaries. Historical ecological studies from the Chesapeake have documented dramatic declines (as much as 99%) in oyster abundance since the early to mid-1800s, changes in oyster size in response to different nutrient levels from the sixteenth to nineteenth centuries, and substantial reductions in oyster accretion rates (from 10 mm/year to effectively 0 mm/year) from the Late Holocene to modern times. Better integration of different historical ecological data sets and increased collaboration between paleobiologists, geologists, archeologists, environmental historians, and ecologists to create standardized research designs and methodologies will help unify prehistoric, historic, and modern time perspectives on biological conservation. Integración de Paleobiología, Arqueología e Historia para Informar a la Biología de la Conservación La búsqueda de métodos nuevos para establecer líneas de base ecológicas (condiciones de referencia) está limitada por el hecho de que la mayoría de los estudios ecológicos abarcan las últimas décadas, cuando mucho, e investigan ecosistemas que han sido alterados sustancialmente por actividades humanas, por décadas, siglos o, posiblemente, más. La paleobiología, arqueología e historia proporcionan contexto ecológico histórico a la biología de la conservación, la remediación y restauración. Argumentamos que la integración explícita de la ecología histórica con la conservación puede ayudar a unificar disciplinas relacionadas de paleobiología de la conservación, arqueobiología de la conservación e historia ambiental. Diferencias en la resolución espacial y temporal y la extensión (escala) de datos prehistóricos, históricos y modernos aun son obstáculos para la integración de la ecología histórica y la biología de la conservación, pero las extensiones temporales prolongadas de datos ecológicos históricos pueden ayudar a establecer líneas de base más completas para la restauración, documentar un rango histórico de variabilidad ecológica y ayudar a la determinación de condiciones futuras deseadas. Utilizamos la pesquería del ostión oriental (Crassostrea virginica) de la Bahía de Chesapeake (E.U.A.) para demostrar la utilidad de los datos ecológicos históricos para dilucidar la conservación del ostión y la necesidad de un método de conservación que trascienda límites disciplinares. Los estudios ecológicos históricos de Chesapeake han documentado declinaciones dramáticas (tanto como 99%) en la abundancia de ostiones de inicios a mediados de los 1800, cambios en el tamaño de ostiones en respuesta a diferentes niveles de nutrientes del siglo dieciséis al diecinueve y reducciones sustanciales en las tasas de acreción de ostiones (de 10 mm/año a 0 mm/año) desde el Holoceno Tardío a tiempos modernos. Una mejor integración de diferentes conjuntos de datos ecológicos históricos y una mayor colaboración entre paleobiólogos, geólogos, arqueólogos, historiadores ambientales y ecólogos para definir diseños de investigación estandarizados y metodologías ayudarán a unificar perspectivas de la biología de la conservación prehistóricas, históricas y modernas.
... Paleoecological analyses have been used to establish pre-Anthropocene physical, chemical, and biological baselines (Willard & Cronin 2007), determine the timing and scope of diverse anthropogenic impacts (Richerson et al. 2008), suggest reference conditions beyond those provided by current and historical records (Feurdean & Willis 2008), and provide evidence for ecosystem-climate interactions on a range of time scales (Millar & Woolfenden 1999;Froyd & Willis 2008). Furthermore, such studies have helped conservation practitioners accept the notion that disturbance and change (due to climatic variability, fire, and geomorphic events like earthquakes and landslides) are natural, and in some cases, necessary parts of ecosystem function (Swetnam et al. 1999). ...
Article
Estuarine restoration is a major focus of coastal management. To set estuarine restoration targets, coastal managers need to understand natural baselines and human modifications. The goal of this study was to characterize baseline environmental conditions for the purposes of restoration planning at Elkhorn Slough, a regionally significant California estuary. We reconstructed baseline salinity, sediment sources, sediment accumulation rates, and wetland plant distribution by collecting and analyzing sediment cores from the upper and lower reaches of the estuary, and marsh extent by synthesizing previously published stratigraphic descriptions of sediment cores. The results of this study show strong contrasts between current and baseline conditions. Sediment accumulation rates have recently increased, whereas flood deposits have disappeared from marsh sediments. Representation by freshwater and brackish plants has also declined. Extent of marshes increased in the recent past, likely as a result of anthropogenic sediment loading from early Euro-American land use changes. Many of these marshes have degraded in past decades, but marsh extent today is still higher than in previous periods. Reconstruction of natural baselines and processes suggests that restoration strategies for the estuary should focus on increasing sediment supply and freshwater inputs to the marshes in order to restore the processes that naturally sustained marsh accretion and diversity. This study highlights the importance of revealing human modifications when designing restoration strategies for dynamic and highly altered systems such as estuaries.
... In recent years the value of a palaeoecological approach for setting benchmarks for management has been realised at a policy level. In the USA, palaeoecological analyses are outlined in the United States Environment Protection Agency guidelines as a method to determine reference conditions (USEPA 2006) and have been used to provide management information and increase political and public awareness of estuarine eutrophication (e.g., Kemp et al. 2005;Willard and Cronin 2007). In Europe, the use of a palaeoecological approach is outlined in the European Union Water Framework Directive as a method to determine benchmark conditions (European Union 2000) and is being applied in a management context (e.g., SEPA SoE 2006). ...
Article
Addressing environmental problems in estuaries is a worldwide problem. Establishing benchmarks and targets for management is critical, whether the aim is conservation, restoration or sustainable use. Palaeoecological techniques have rapidly improved during the past decade, particularly with advances in methods that allow high resolution quantitative assessments of environmental change. Palaeoecology is a useful tool in environmental management as it allows pre-impact conditions, the rate, extent, direction and cause of change, and range of natural variability to be determined. Australian estuarine ecosystems are qualitatively different from the often more well-studied estuaries in North America and Europe, which means site-specific studies of Australian estuaries are needed to inform management. While a potentially useful and valuable tool, palaeoecological techniques have not yet been widely adopted and practically implemented as part of estuarine management strategies and policy frameworks in Australia.We discuss the role palaeoecological techniques have to play in estuarine management by providing two case studies undertaken in Australia that have provided management information. We aim to encourage communication and dialogue between scientists and environmental managers about the potential for widespread practical adoption and implementation of palaeoecological techniques into Australian estuarine science, management and policy frameworks.
... The Everglades is comprised of elongated, flow-parallel ridges and sloughs that formed several thousand years ago (Willard and Cronin, 2007;Bernhardt and Willard, 2009) (Fig. 1). The topographic and vegetation features are strikingly similar to other low-gradient, floodplain wetlands found worldwide that are valued for their relatively high biodiversity and high connectivity of habitats (e.g. ...
Article
The ridge and slough landscape of the central Everglades formed several thousand years ago and remained stable until relatively recently. These flow parallel features with a cross sectional wavelength of approximately 100 m are strikingly similar to topographic and vegetation features in other low-gradient, floodplain wetlands found worldwide. The ridge and slough landscape is valued for its relatively high biodiversity and high connectivity of habitats. Loss of the topographic and vegetative pattern started with drainage efforts that began decreasing flows a century ago. The year 2000 marked the beginning of one of the most ambitious restorations of an aquatic ecosystem ever attempted. Although progress has been made, the processes responsible for degradation of landscape topographic pattern remain uncertain. Our hypothesis of Everglades landscape formation and pattern maintenance is based on feedbacks between flow velocity, vegetative flow resistance, and shear stress. A key element within that feedback is the redistribution of sediment from topographically lower to higher areas, with consequent effects on water level and plant community that drive differential rates of peat accretion in sloughs and ridges toward an equilibrium height difference. However, both the velocity threshold needed to entrain and redistribute organic sediment from sloughs to ridges, and the role of the emergent macrophytes in intercepting suspended particulate material, have remained uncertain. We constructed experimental flumes (8-m long by 1-m wide) in the Everglades and equipped them with pumping systems to elevate velocity by an order of magnitude (covering the possible range in the pre-drainage Everglades) over five steps in velocity. Natural mobilization of flocculent detrital material (floc) from the bed occurred in our experiments at velocities between 3.2 and 5.3 cm s-1, i.e., velocities that are rare in the present-day Everglades where 90% of observations typically are below 1 cm s-1. These results suggest that pre-drainage patterns of sediment redistribution can be reinstated by adjusting water management practices to maximize water-surface slope, the main control on flow velocity. Modeling also suggests that decreasing the abundance of ridge and wet prairie vegetation that has invaded sloughs during the past century may also be necessary to reinstate the self-sustaining feedbacks that maintain a functional ridge and slough landscape.
... Conservation paleobiology is an important and active research area within paleoecology (Dietl et al., 2015). Using relatively young fossil records, paleobiologists have elucidated histories of human-induced ecosystem degradation, while pre-human fossil records will give us natural baseline information to compare with Anthropocene and present-day conditions (Willard and Cronin, 2007;Rick and Lockwood, 2013;Lotze and McClenachan, 2014;Dietl et al., 2015;Kidwell, 2015). Pollution, eutrophication, deoxygenation, and human-induced climate change have changed marine ecosystems, most dramatically after the industrialization (Yasuhara et al., 2012a). ...
... Ocean sediments are climatic and environmental archives, which preserve geochemical, microfaunal and sedimentary evidence that record globally relevant Earth system events, similar to other climate records such as the Greenland Ice Sheet Project [13]. Recent investigations reveal that paleoceanographic investigations hold valuable insight into modern environmental conservation and management [14,15]. ...
Article
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Climate-driven Oxygen Minimum Zone (OMZ) expansions in the geologic record provide an opportunity to characterize the spatial and temporal scales of OMZ change. Here we investigate OMZ expansion through the global-scale warming event of the most recent deglaciation (18-11 ka), an event with clear relevance to understanding modern anthropogenic climate change. Deglacial marine sediment records were compiled to quantify the vertical extent, intensity, surface area and volume impingements of hypoxic waters upon continental margins. By integrating sediment records (183-2,309 meters below sea level; mbsl) containing one or more geochemical, sedimentary or microfossil oxygenation proxies integrated with analyses of eustatic sea level rise, we reconstruct the timing, depth and intensity of seafloor hypoxia. The maximum vertical OMZ extent during the deglaciation was variable by region: Subarctic Pacific (~600-2,900 mbsl), California Current (~330-1,500 mbsl), Mexico Margin (~330-830 mbsl), and the Humboldt Current and Equatorial Pacific (~110-3,100 mbsl). The timing of OMZ expansion is regionally coherent but not globally synchronous. Subarctic Pacific and California Current continental margins exhibit tight correlation to the oscillations of Northern Hemisphere deglacial events (Termination IA, Bølling-Allerød, Younger Dryas and Termination IB). Southern regions (Mexico Margin and the Equatorial Pacific and Humboldt Current) exhibit hypoxia expansion prior to Termination IA (~14.7 ka), and no regional oxygenation oscillations. Our analyses provide new evidence for the geographically and vertically extensive expansion of OMZs, and the extreme compression of upper-ocean oxygenated ecosystems during the geologically recent deglaciation.
... Since direct measurements of long-term climate and sea level variability are unavailable, it is necessary to use indirect proxy indicators to reconstruct earlier changes. Paleoenvironmental research can provide a greater understanding of how coastal systems will respond to future environmental variability (Parr et al. 2003;Willard and Cronin 2007;Rick and Lockwood 2013). Additionally, in the interest of understanding the causes of global-scale environmental change, further research and data are needed for the tropics, an area for which few paleoenvironmental studies exist (Peros et al. 2007a;Peros et al. 2015). ...
... There are many specific issues that can only be resolved by understanding history. A long-term palaeoecological view is needed to enable visualisation of the prior nature and condition of the restoration site (Willard and Cronin, 2007;Saunders and Taffs, 2009), as well as the series of events that have led to the current condition, including the more recent history. This historical view needs to go beyond environmental change to include the social, cultural and economic context in which change has occurred (Alleway and Connell, 2015). ...
Article
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Accelerating declines in the extent, quality and functioning of the world's marine ecosystems have generated an upsurge in focus on practical solutions, with ecosystem restoration becoming an increasingly attractive mitigation strategy for systems as diverse as coral reefs, mangroves and tidal flats. While restoration is popular because it promises positive outcomes and a return to something approaching unimpacted condition and functioning, it involves substantial public and private investment, both for the initial restoration activity and for on-going maintenance of the restored asset. This investment often affords one big chance to get things right before irretrievable damage is done. As a result, precise, well considered and accountable decision-making is needed to determine the specific focus for restoration, the scale of restoration, the location for deploying restoration activities, and indeed whether or not restoration is necessary or even possible. We explore the environmental/ecological considerations and constraints governing optimal decisions about the nature, location and prioritisation of restoration activities in marine ecosystems, and in particular the constraints on achieving understanding of possible futures and the likelihood of achieving them. We conclude that action must be informed by a context-specific understanding of the historical situation, the current situation, the constraints on change, the range of potential outcome scenarios, and the potential futures envisioned.
... Changes over the last century to Everglades hydrology (Light and Dineen 1994;Steinman et al. 2002; see also Chap. 2, Volume I) have been found to influence biological changes evident in vegetation and fauna (McIvor et al. 1994;Sklar et al. 2002;Willard and Cronin 2007;Bernhardt and Willard 2009). These studies have found that altered hydrology has resulted in significant impacts to soils through changes in soil redox potential, organic matter losses in regions with reduced hydroperiods, and increases in organic matter (peat accumulation) in regions with increased hydroperiodsespecially when combined with increases in phosphorus loading (Craft and Richardson 2008). ...
Chapter
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Nutrient enrichment—particularly with respect to phosphorus—has long been a major concern in the Everglades (see Chap. 2, Volume I). This perturbation is of keen interest with respect to the Everglades mercury (Hg) problem because the biogeochemical cycling of Hg in aquatic ecosystems is intrinsically linked to trophic state through multiple pathways, including the effects of nutrient status on food web structure and dynamics, in situ particle production, and redox dynamics in surficial sediments (see Fig. 1.1, Chap. 1, this volume). As a result, decision makers charged with the responsibility of restoring the Everglades must also consider the resultant impacts of management strategies on not just trophic state dynamics, but also the linked effects of those strategies on Hg biogeochemical cycling and trophic transfer. This chapter thus reviews phosphorus enrichment in the Everglades and its effects on Hg biogeochemical cycling, including its effects on methyl mercury production related to perturbations in redox dynamics in particular.
... Unfortunately, the potential for more highly resolved ΔR estimates is limited because well-curated, known-age, pre-1950 C. virginica shells from Southwest Florida are surprisingly rare in museum collections--to our best knowledge consisting of the five specimens included in the current study. Attempts over the past 150 yr to drain, re-route, and control the Everglades have dramatically altered the flow of freshwater across most of South Florida (Willard and Cronin 2007;Krauss et al. 2011), undoubtedly affecting local reservoir ages. Any spatial patterning that might be discerned among the pre-bomb museum specimens would have little relevance to earlier times, when the flow of water was relatively unrestricted. ...
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In southwestern Florida, USA, terraformed landscapes built almost entirely of oyster shells (Crassostrea virginica) reflect a unique pre-Columbian tradition of shell-built architecture. The ability to reliably date oyster shells is essential to identifying spatial, temporal, and functional relationships among shellworks sites, yet to date there has been no systematic attempt to quantify or correct for carbon reservoir effects in this region. Here we present 14 radiocarbon (14 C) ages for 5 known-age, pre-bomb oyster shells collected between AD 1932-1948, as well as 6 14 C ages for archaeological oyster/charcoal pairs from the Turner River Mound Complex, Everglades National Park. We report our current best estimate of ΔR = 92 ± 74 yr for Greater Southwest Florida, and ΔR =-15 ± 42 yr for the Turner River archaeological site. Future research should focus on paired archaeological specimens to obtain spatially and temporally relevant estimates of ΔR.
... In recent times, substantial efforts have been invested to preserve seagrass meadows, key in current European environmental policies. Posidonia meadows are protected as a priority habitat (Council Directives, 1992, as a species (Bern Convention, 1979;Barcelona Convention, 1976), under specific legal protection actions in individual countries (e.g., Albania, Croatia, France, Italy, Spain and Turkey), and included in marine protected areas along the Mediterranean Sea (UNEP-MAP-RAC/ the ecosystems' resilience to perturbations (e.g., Willard and Cronin, 2007;Benton and Harper, 2009;Davies and Bunting, 2010;López-Merino et al., 2012). Regime shifts are abrupt changes on several trophic levels leading to fast ecosystem reconfiguration, usually after abrupt climatic changes or anthropogenic impacts (Andersen et al., 2009). ...
Article
Posidonia oceanica is a marine phanerogam that buries a significant part of its belowground production forming an organic bioconstruction known as mat. Despite Posidonia seagrass mats have proven to be reliable archives of long-term environmental change, palaeoecological studies using seagrass archives are still scarce. Here we reconstruct four millennia of environmental dynamics in the NE coast of Spain by analysing the carbon and nitrogen stable isotopic composition of P. oceanica sheaths, the proportion of different seagrass organs throughout the seagrass mat and other sedimentological proxies. The palaeoenvironmental reconstruction informs on long-term ecosystem productivity and nutrient loading, which have been linked to global (e.g., solar radiation) and local (e.g., land-use changes) factors. The long-term environmental records obtained are compared with previous palaeoecological records obtained for the area, showing a common environmental history. First, a relative seagrass ecosystem stability at ~4000 and 2000 cal. yr BP. Then, after a productivity peak at ~1400–800 cal. yr BP, productivity shows an abrupt decline to unprecedented low values. The fluctuations in ecosystem productivity are likely explained by increases in nutrient inputs related to human activities – mostly in the bay watershed – concomitantly with changes in total solar radiation. Cumulative anthropogenic stressors after Roman times may have started to affect ecosystem resilience, dynamics and productivity, with more abrupt regime shifts during the last millennium. These results add into recent research showing the potential of seagrass archives in reconstructing environmental change and seagrass post-disturbance dynamics, hence providing unvaluable information for improving the efficiency in managing these key coastal ecosystems.
... In order to provide essential baseline data for the restoration of the hydrological conditions of the Everglades, numerous studies are being conducted along the coastal zones in the Everglades National Park (ENP) to understand the long-term ecological processes and developmental history of these natural wetlands. Recent paleoecological studies from the region suggest that the vegetation shifts in wetland communities during the middle and late Holocene are closely associated with the regional and globalscale climatic phenomena such as position of the Intertropical Convergence Zone (ITCZ) (Donders et al., 2005), the state of the North Atlantic Oscillation (NAO) (Willard and Cronin, 2007;Bernhardt and Willard, 2009), and the Holocene sealevel rise (Yao et al., 2015;Yao and Liu, 2017). To produce accurate results using fossil pollen analysis, it is important to understand how the modern vegetation and environmental gradients are represented in the modern pollen rain of the study area. ...
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This study aims to document the changes in modern pollen assemblages and soil elemental chemistry along broad edaphic, hydrological, and salinity gradients, including a previously undocumented secondary environmental gradient, in a vast mangrove-dominated wetland region in the Everglades, South Florida. Twenty-five soil surface samples were collected along an interior wetland transect and an estuarine mangrove transect across coastal zones in the Everglades National Park and subjected to palynological and XRF analyses. Modern pollen spectra from the sampling sites were classified into five a priori groups-wet prairie, pineland, inland mangroves, coastal mangroves, and fringe mangroves, based on the five vegetation types and sub-environments from which they were collected. Discriminant analysis shows that all (100%) of the samples are correctly classified into their a priori groups. On a broad scale, the modern pollen assemblages in surface samples collected from different vegetation types reflect the primary environmental gradient in the Florida Coastal Everglades. A distinct salinity and chemical gradient is also recorded in the XRF results, and the complexity of these gradients is captured at both regional and local scales. At the regional scale, concentrations of all the elements increase from terrestrial toward coastal sites. At the local scale, XRF results show a progressive decrease in most chemical concentrations and in the Cl/Br and Ca/Ti ratios away from the Shark River Slough at each individual site, suggesting that a secondary fluvial/tidal gradient also exists locally as a function of the distance from the river, the main carrier of these chemicals. This study provides new evidence to show that tidal flooding from the Shark River Estuary is directly related to the nutrient availability in the surrounding mangrove forests. These data will deepen our understanding of the environmental drivers behind the vegetation zonation in the region, especially in the mangrove ecosystems, and fill a gap in the pollen data network for the Everglades.
... With growing awareness of the necessity for nature conservation, the need for long-term ecological studies increases (Dietl and Flessa, 2011;Dietl et al., 2015). Setting goals for management and restoration plans, however, requires defining appropriate baselines that specify the composition of an undisturbed ecosystem (Alleway and Connell, 2015;Thurstan et al., 2015;Dietl and Smith, 2017;Tomašových and Kidwell, 2017) and to what extent it can realistically be restored together with the ecosystem services it provides (Willard and Cronin, 2007;Mann and Powell, 2007;Rick and Lockwood, 2013). Although the onset of industrialization may represent a baseline (Froyd and Willis, 2008;Wolfe et al., 2013), the human impact on ecosystems dates back to much earlier times (Lotze et al., 2011a). ...
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The molluscan assemblages in a sediment core from the north-eastern Adriatic show significant compositional changes over the past 10,000 yrs related to (1) natural deepening driven by the post-glacial sea-level rise, (2) increasing abundance of skeletal sand and gravel, and (3) anthropogenic impacts. The transgressive phase (10,000–6000 BP) is characterized by strongly time-averaged communities dominated by infaunal bivalves. During the early highstand (6000–4000 BP), the abundance of epifaunal filter feeders and grazers increases, and gastropods become more important. Epifaunal dominance culminates during the late highstand (4000–2000 BP) with the development of extensive shell beds formed by large-sized Arca noae and Ostrea sp. bivalves. This community persists until the early 20th century, when it falls victim to multiple anthropogenic impacts, mainly bottom trawling, and is substituted by an infauna-dominated community indicative of instability, disturbance and organic enrichment. The re-establishment of this unique shell-bed ecosystem can be a goal for restoration efforts.
... Palaeoenvironmental studies based on pollen and charcoal data in sediments of bay and estuarine environments have been used as an important tool for understanding changes in the vegetation cover caused by climate oscillations, sea level alterations, human activities and fire during the Quaternary period (Willard & Cronin 2007;Sritrairat et al. 2012). Guanabara Bay is one of the most important bays along the Brazilian coastline, and is also the second largest. ...
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Palynological and charcoal fragment analyses of Guanabara Bay sediments, as well as radiocarbon dating, were carried out on one 220 cm long sedimentary core collected from the northeast sector of the bay, near the São Gonçalo coast. This study aims at recognising and explaining the environmental history of this region during the mid-Holocene, and to identify the anthropogenic influences on it. The palynological data indicate the predominance of ombrophilous forest vegetation in the Guanabara Bay Hydrographic Basin at c. 6500 calendar years bp. During this period (pollen zone 1), the concentrations of pollen grains and spores may still have been controlled by the Holocene Maximum Transgressive Event. After a phase of low concentrations of palynomorphs, there was a considerable increase in the accumulation patterns of pollen and spore grains (pollen zone 2). This increase can probably be related to the retreat of the sea level event after the Holocene Maximum Transgressive Event. The 75 cm of the core top (pollen zone 3) provide clear evidence of human influence in the area, which is inferred from the significant reduction in ombrophilous forest pollen grains, the significant increase in herbaceous pollen grains, the presence of exotic pollen types (Eucalyptus and Pinus), and high concentration of carbonaceous particles.
... Sediment records are well suited for measuring changes in ecosystem processes in aquatic environments (Willard and Cronin 2007). Multiproxy approaches-including diatoms, magnetic susceptibility, biogenic silica, organic content, and nutrient fluxes to sediments-have been used to measure modern impacts of agriculture and the eutrophication of lakes and rivers (Edlund et al. 2009a;Engstrom et al. 2009) and then been applied to restoration goal setting (Edlund et al. 2009b). ...
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Historical information spanning different temporal scales (from tens to millions of years) can influence restoration practice by providing ecological context for better understanding of contemporary ecosystems. Ecological history provides clues about the assembly, structure, and dynamic nature of ecosystems, and this information can improve forecasting of how restored systems will respond to changes in climate, disturbance regimes, and other factors. History recorded by humans can be used to generate baselines for assessing changes in ecosystems, communities, and populations over time. Paleoecology pushes these baselines back hundreds, thousands, or even millions of years, offering insights into how past species assemblages have responded to changing disturbance regimes and climate. Furthermore, archeology can be used to reconstruct interactions between humans and their environment for which no documentary records exist. Going back further, phylogenies reveal patterns that emerged from coupled evolutionary-ecological processes over very long timescales. Increasingly, this information can be used to predict the stability, resilience, and functioning of assemblages into the future. We review examples in which recorded, archeological, paleoecological, and evolutionary information has been or could be used to inform goal setting, management, and monitoring for restoration. While we argue that long-view historical ecology has much to offer restoration, there are few examples of restoration projects explicitly incorporating such information or of research that has evaluated the utility of such perspectives in applied management contexts. For these ideas to move from theory into practice, tests performed through research-management partnerships are needed to determine to what degree taking the long view can support achievement of restoration objectives.
... The wetlands of the Greater Everglades ecosystem in South Florida (USA) [Willard and Cronin, 2007], which encompasses all area south of Lake Okeechobee including the coastal peatlands and Big Cypress swamp, form an important subtropical ecohydrological landscape with a large diversity of marshes, hammocks, sloughs, and swamps [Winkler et al., 2001]. The Greater Everglades' current protected status follows from significant losses of natural area due to drainage activities and land conversions that started in the 1880s [Davis and Ogden, 1994;Sklar et al., 2005]. ...
Article
The mechanisms involved in the initiation and development of the Greater Everglades peatland ecosystems remain a topic of discussion. In this study, we first present an overview of basal ages of peat deposits in South Florida, which shows two major episodes of peatland initiation between 7.0-4.5 kyr and 3.5-2.0 kyr. Our analysis of regional climate proxy datasets led to three alternative hypotheses that may explain the timing and duration of these two peatland initiation episodes: (1) decreased drainage due to relative sea level (RSL) rise during the Holocene (2) gradual increase in precipitation throughout the Holocene, and (3) a combination of increasing precipitation, rising RSL and oscillations in the climate system. We test whether these three hypotheses can explain the pattern of initiation and development of the Greater Everglades peatlands using models that simulate the non-linear processes involved in peat production and decomposition. The model results suggest that RSL-rise could explain the onset of peatland initiation and implies that the climate was wet enough for peat development also during the early Holocene. The first two hypothesized mechanisms in combination with climate oscillations may explain the onset of peat accumulation at 8.2 kyr BP. The two-phased character of peatland initiation maybe explained by the spatial distribution of local drainage conditions. As peatland development is highly non-linear, our model uncovers a mechanistic way how peats can suddenly shift from a dry high equilibrium to a wet low equilibrium resulting in lake formation as observed in paleo-ecological studies in the Greater Everglades.
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Sediments provide one of the best reservoirs of information of how aquatic ecosystems have been altered by natural (climate change) and human agents over time. This information is preserved in a variety of biogenic materials including macro- and microfossils, pollen and chemical proxies, which record ecological responses to past perturbations. Chesapeake Bay, the largest estuary in the United States, is particularly well-suited to paleoenvironmental studies due to high rates of sediment accumulation, good preservation potential and historical records that can be used to corroborate evidence of change over the past several centuries. Previous paleoecological studies in Chesapeake Bay have examined how climate change and human activities have modified vegetation, species composition, sediment supply and carbon delivery over time. In this chapter, we review a variety of paleoecological approaches that have been employed to understand how the Bay ecosystem has changed over time. These proxies include microfossils (benthic foraminifera and ostracods), pollen and seeds, chemical fingerprints (stable isotopes, lipid biomarker compounds and black carbon), and mollusk shells preserved in sediment core records.
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Under certain conditions, sediment cores from coastal settings subject to hypoxia can yield records of environmental changes over time scales ranging from decades to millennia, sometimes with a resolution of as little as a few years. A variety of biological and geochemical proxies derived from such cores have been used to reconstruct the development of eutrophication and hypoxic conditions over time. Proxies based on 1) the preserved remains of benthic organisms (mainly foraminiferans and ostracods), 2) sedimentary features (e.g. laminations) and 3) sediment chemistry and mineralogy (e.g. presence of sulphides and redox-sensitive trace elements) reflect conditions at or close to the seafloor. Those based on 4) the preserved remains of planktonic organisms (mainly diatoms and dinoflagellates), 5) pigments and lipid biomarkers derived from prokaryotes and eukaryotes and 6) organic C, N and their isotope values reflect conditions in the water column. However, the interpretation of these proxies is not straightforward. A central difficulty concerns the fact that hypoxia is strongly correlated with, and often induced by, organic enrichment (eutrophication), making it difficult to separate the effects of these phenomena in sediment records. The problem is compounded by the enhanced preservation in anoxic and hypoxic sediments of organic microfossils and biomarkers indicating eutrophication. The use of hypoxia-specific indicators, such as the trace metals molybdenum and rhenium and the bacterial biomarker isorenieratene, which have not been used often in historical studies, may provide a way forward. All proxies of bottom-water hypoxia are basically qualitative; their quantification presents a major challenge to which there is currently no satisfactory solution. Finally, it is important to separate the effects of natural ecosystem variability from anthropogenic effects. Despite these problems, in the absence of historical data for dissolved oxygen concentrations, the analysis of sediment cores can provide plausible reconstructions of the temporal development of human-induced hypoxia, and associated eutrophication, in vulnerable coastal environments.
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Hong Kong is one of the most urbanized coastal cities in the world. Yet, despite extensive anthropogenic impacts, adjacent marine environments harbour tremendous biodiversity. We investigated how the diversity, taxonomic composition, and biogeography of meiobenthic ostracods in Hong Kong's coastal waters vary in response to natural and anthropogenic factors. Our regression models indicated that metal pollution and mud content were the main factors structuring meiofaunal diversity, with eutrophication also playing a role. The highest diversity was observed in the Victoria Harbour region at the center of Hong Kong's urbanized seascape, and the lowest diversities were observed in Mirs Bay, Port Shelter, and Tolo Harbour. Ostracod diversity and biogeography patterns are congruent with published studies of other soft-sediment fauna, which also identified a diversity peak in Hong Kong's urban center and a vast southern water biofacies characterized by muddy and turbid conditions. These results do not apply to organisms that prefer oligotrophic conditions, such as hard corals. For those taxa, eutrophic waters in western Hong Kong are generally not habitable and higher diversities are observed in less productive, eastern waters. Our findings indicate that meiofaunal ostracods can be used as a bioindicator for the diversity of soft sediment benthos, more broadly.
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Hydrology is a key variable in the structure and function of a wetland; it is a primary determinant of wetland type, and it drives many of the functions a wetland performs and in turn the services it provides. However, wetland hydrology has been understudied. Efforts by scientists from Riparia, a wetland and aquatic systems research center at Penn State University, have advanced the understanding of wetland hydrology in the Mid-Atlantic Region over the past two decades primarily through a series of studies at a set of long-term monitoring sites. This work contributed to four primary issues in wetland hydrology: validation of regional hydrogeomorphic classification schemes, establishment of reference criteria for monitoring and assessment, identification of targets for restoration or mitigation, and evaluation of the hydrologic behavior of created vs. non-created wetlands. This chapter (1) summarizes some of the key findings of hydrologic studies of wetlands from the published and non-published research of wetland scientists associated with Riparia and secondarily, (2) describes general, seasonal, and inter-annual hydrologic patterns of the water level data that has been collected at some of the long-term monitoring sites or reference sites. © 2013 Springer Science+Business Media New York. All rights are reserved.
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IntroductionEcological History and HRVBeyond Baselines: The Extended HRV ConceptGeorge Webber's DilemmaAcknowledgmentsReferences
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Misuse of land and water resources has led to the degradation of many estuaries. As a result, present day management often focuses on developing strategies to reverse or contain these environmental impacts. However, a lack of long-term data on pre-impact conditions makes it difficult to define management goals and assess if management strategies have been, or are likely to be successful. Paleoecology is a useful tool in environmental management as it allows natural variability, pre-impact conditions, the rate, extent, direction and causes of change, and ecosystem responses to remediation and restoration attempts to be assessed. Paleoecological techniques have improved markedly during recent decades, particularly with regard to methodological advances, which allow studies to be tailored to estuarine management programs. What remains is for contemporary management approaches to consider the lessons available from historical change documented through paleoecology. This chapter outlines ways in which paleoecological approaches may be applied to estuarine management and the considerations for their integration into direct management outcomes.
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Climate changes throughout geological history have influenced estuaries and coastal systems in a variety of ways and over all timescales. Similarly, future climate change will influence estuaries, perhaps at an accelerated rate, notably through effects on salinity and temperature, dissolved oxygen concentrations, nutrient and sediment flux, biogeochemical processes, and coastal ecosystem functioning. Sea-level rise, altered rainfall patterns leading to extreme droughts and wet periods, and biogeochemical changes associated with ocean acidification are among the most important research topics associated with climate that will likely see great progress in the next few years.
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In this dissertation, I explore multiple tenets of the textural discontinuity hypothesis, which states that hierarchical landscape structures with scale-specific pattern entrain attributes of animals inhabiting the landscape. Landscapes form hierarchies that are structured by vegetative, geomorphological and contagious disturbance processes. The spatial and temporal patterns inherent in landscapes reflect numerous processes, interacting on distinct scales, which shape the assembly of animal communities. Analysis of body mass patterns and functional group distributions has been suggested as methods to provide insight about these underlying hierarchical processes. Scientists have posited that species at the edges of body mass aggregations may be exposed to highly variable resources. This dissertation focuses on the distribution of biological diversity in space and time and socio-ecological factors that are contributing to the worldwide increase in invasive and endangered species. I analyzed invasions and extinctions of birds and mammals across five Mediterranean-climate ecosystems and in 100 countries using an information-theoretic approach. All body mass distribution data analyzed were discontinuous. This work provided further support for Holling’s textural discontinuity hypothesis. Alpha diversity of function increased in 9 out of the 10 Mediterranean-climate ecosystems analyzed when NIS were introduced into the community. After the introduction of NIS, I observed a decrease in cross-scale redundancy of functional groups in mammals and when both taxonomic groups were combined. In Eocene Epoch mammal data, speciation events were not detected near body mass aggregation edges. Only 64% of the biomes in mammals had ecoregions with similar structure and only 50% of the biomes in birds had ecoregions with similar structure, which may be a result of coarse landscape classification schemes. GDP per capita was positively correlated with the proportion of NIS bird and mammal species within a country. Resilience of a country was correlated to life expectancy. As life expectancy increased, resilience of a country decreased. Results may help us make proper management decisions in monitoring particular non-indigenous species and focus conservation efforts on those native species.
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A molluscan analogue dataset is presented in conjunction with a weighted-averaging technique as a tool for estimating past salinity patterns in south Florida’s estuaries and developing targets for restoration based on these reconstructions. The method, here referred to as cumulative weighted percent (CWP), was tested using modern surficial samples collected in Florida Bay from sites located near fixed water monitoring stations that record salinity. The results were calibrated using species weighting factors derived from examining species occurrence patterns. A comparison of the resulting calibrated species-weighted CWP (SW-CWP) to the observed salinity at the water monitoring stations averaged over a 3-year time period indicates, on average, the SW-CWP comes within less than two salinity units of estimating the observed salinity. The SW-CWP reconstructions were conducted on a core from near the mouth of Taylor Slough to illustrate the application of the method.
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It is widely recognized that interactions between vegetation and flow cause the emergence of channel patterns that are distinct from the standard Schumm classification of river channels. Although landscape pattern is known to be linked to ecosystem services such as habitat provision, pollutant removal, and sustaining biodiversity, the mechanisms responsible for the development and stability of different landscape patterns in shallow, vegetated flows have remained poorly understood. Fortunately, recent advances have made possible large-scale models of flow through vegetated environments that can be run over a range of environmental variables and over timescales of millennia. We describe a new, quasi-3D cellular automata model that couples simulations of shallow-water flow, bed shear stresses, sediment transport, and vegetation dynamics in an efficient manner. That efficiency allowed us to apply the model widely in order to determine how different hydroecological feedbacks control landscape pattern and process in various types of wetlands and floodplains. Distinct classes of landscape pattern were uniquely associated with specific types of allogenic and autogenic drivers in wetland flows. Regular, anisotropically patterned wetlands were dominated by allogenic processes (i.e., processes driven by periodic high water levels and flow velocities that redistribute sediment), relative to autogenic processes (e.g., vegetation production, peat accretion, and gravitational erosion). These anistropically patterned wetlands are therefore particularly prone to hydrologic disturbance. Other classes of wetlands that emerged from simulated interactions included maze-patterned, amorphous, and topographically noisy marshes, open marsh with islands, banded string-pool sequences perpendicular to flow, parallel deep and narrow channels flanked by marsh, and ridge-and-slough patterned marsh oriented parallel to flow. Because vegetation both affects and responds to the balance between the transport capacity of the flow and sediment supply, these vegetated systems exhibit a feedback that is not dominant in most rivers. Consequently, unlike in most rivers, it is not possible to predict the “channel pattern” of a vegetated landscape based only on discharge characteristics and sediment supply; the antecedent vegetation pattern and vegetation dynamics must also be known.In general, the stability of different wetland pattern types is most strongly related to factors controlling the erosion and deposition of sediment at vegetation patch edges, the magnitude of sediment redistribution by flow, patch elevation relative to water level, and the variability of erosion rates in vegetation patches with low flow-resistance. As we exemplify in our case-study of the Everglades ridge and slough landscape, feedback between flow and vegetation also causes hysteresis in landscape evolution trajectories that will affect the potential for landscape restoration. Namely, even if the hydrologic conditions that historically produced higher flows are restored, degraded portions of the ridge and slough landscape are unlikely to revert to their former patterning. As wetlands and floodplains worldwide become increasingly threatened by climate change and urbanization, the greater mechanistic understanding of landscape pattern and process that our analysis provides will improve our ability to forecast and manage the behavior of these ecosystems.
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At Makauwahi Cave Reserve, on the south shore of Kaua`i, translocation decisions have been guided to a unique degree by the richly detailed fossil record of biota of recent centuries, which occurs on the site. To evaluate the efficacy of this strategy, ecological conditions and individual life histories for 3388 translocated native plants of 81 species have been monitored since 2005. Many species were selected on the basis of their prevalence as subfossils in the adjacent late Holocene cave sediments. Most of these species no longer occur on or near the abandoned farmlands and mine spoil used as a substrate for transplanted individuals. Records for each plant included location, date outplanted, flowering, fruiting, and, if applicable, mortality, including known or inferred cause. Also recorded was unaided recruitment, survival of transplanted recruits, and quantity of seed collected. Plant species selected for reintroduction on the basis of present occurrence near the site (many of which also occur there as fossils), and species not present but selected solely on the basis of fossil occurrence before European arrival, both show high survival rates in most cases. Species that fit neither of these criteria, but are judged suitable on the basis of their occurrence elsewhere on the island in similar habitats, generally showed lower survival rates. Primary mortality factors for nursery stock not surviving outplanting included transplant shock, irrigation failure, and human error (accidental cutting, pulling, or trampling). Much lower mortality rates were linked to insect damage, disease, and pig disturbance. Phenological records show that 80 % of translocated native species have flowered and 70 % produced seed. Unaided recruitment was observed for 43 % of the species with some rare species producing large numbers of volunteer seedlings. Translocated volunteer seedlings showed high survival rates. Insights from the fossil record have provided perspective on the site’s potential and limitations and enriched interest in a restoration by almost doubling the list of plant species used in restoration programs and adding a living history element to the interpretation of the site through the juxtaposition of the fossil evidence and the translocated native species.
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Hydroecological feedback processes governing self-organization of the Everglades ridge and slough landscape
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Natural and anthropogenic factors shape present-day benthic marine ecosystems. Understanding their combined influence on benthic communities is limited, however, by a lack of biological monitoring. Using a conservation paleobiology approach, this study establishes biological baselines and assesses the effects of natural and anthropogenic environmental change on benthic communities in an urbanized subtropical seascape. We compared subsurface (“past”, covering approximately the last 50–100 years) and surface ("present", covering approximately the last 5 years) faunal assemblages in sediment grab samples in Hong Kong, one of the busiest ports and urbanized areas in the world. Results show that both natural (climate, monsoon) and anthropogenic factors (metal pollution, damming) were associated with recent faunal changes (dissimilarities between subsurface and surface faunal assemblages). Changes in freshwater and sediment discharge from the Pearl River due to monsoon rains and dams produced a strong west-east gradient in the turnover of rare species. Pollution from metals resulted in the turnover of abundant and dominant species in the central part of Hong Kong. Examining these data in the context of published results from other urbanized coastal areas around the world suggests that metal pollution may be important and understudied factor, responsible for benthic turnover in regions where pollution levels exceed thresholds for sediment toxicity.
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We synthesize existing evidence on the ecological history of the Florida Everglades since its inception ∼7ka (calibrated kiloannum) and evaluate the relative impacts of sea level rise, climate variability, and human alteration of Everglades hydrology on wetland plant communities. Initial freshwater peat accumulation began between 6 and 7ka on the platform underlying modern Florida Bay when sea level was ∼6.2m below its current position. By 5ka, sawgrass and waterlily peats covered the area bounded by Lake Okeechobee to the north and the Florida Keys to the south. Slower rates of relative sea level rise ∼3ka stabilized the south Florida coastline and initiated transitions from freshwater to mangrove peats near the coast. Hydrologic changes in freshwater marshes also are indicated ∼3ka. During the last ∼2ka, the Everglades wetland was affected by a series of hydrologic fluctuations related to regional to global-scale fluctuations in climate and sea level. Pollen evidence indicates that regional-scale droughts lasting two to four centuries occurred ∼1ka and ∼0.4ka, altering wetland community composition and triggering development of characteristic Everglades habitats such as sawgrass ridges and tree islands. Intercalation of mangrove peats with estuarine muds ∼1ka indicates a temporary slowing or stillstand of sea level. Although sustained droughts and Holocene sea level rise played large roles in structuring the greater Everglades ecosystem, twentieth century reductions in freshwater flow, compartmentalization of the wetland, and accelerated rates of sea level rise had unprecedented impacts on oxidation and subsidence of organic soils, changes/loss of key Everglades habitats, and altered distribution of coastal vegetation.
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A new, well-verified, multiproxy reconstruction of the winter North Atlantic Oscillation (NAO) index is described that can be used to examine the variability of the NAO prior to twentieth century greenhouse forcing. It covers the period A.D. 1400-1979 and successfully verifies against independent estimates of the winter NAO index from European instrumental and noninstrumental data as far back as 1500. The best validation occurs at interannual timescales and the weakest at multidecadal periods. This result is a significant improvement over previous proxy-based estimates, which often failed to verify prior to 1850, and is related to the use of an extended reconstruction model calibration period that reduced an apparent bias in selected proxies associated with the impact of anomalous twentieth century winter NAO variability on climate teleconnections over North Atlantic sector land areas. Although twentieth century NAO variability is somewhat unusual, comparable periods of persistent positive-phase NAO are reconstructed to have occurred in the past, especially before 1650.
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During the twentieth century, the natural landscape of the Florida peninsula was transformed extensively by agriculture, urbanization, and the diversion of surface water features. The purpose of this paper is to present a numerical modeling study in which the possible impacts of this transformation on the warm season climate of the region were investigated. For three separate July-August periods (1973, 1989, and 1994), a pair of simulations was performed with the Regional Atmospheric Modeling System. Within each pair, the simulations differed only in the specification of land-cover class. The two different classes were specified using highly detailed datasets that were constructed to represent pre-1900 natural land cover and 1993 land-use patterns, thus capturing the landscape transformation within each pair of simulations. When the pre-1900 natural cover was replaced with the 1993 land-use dataset, the simulated spatial patterns of the surface sensible and latent heat flux were altered significantly, resulting in changes in the structure and strength of climatologically persistent, surface-forced mesoscale circulations—particularly the afternoon sea- breeze fronts. This mechanism was associated with marked changes in the spatial distribution of convective rainfall totals over the peninsula. When averaged over the model domain, this redistribution was reflected as an overall decrease in the 2-month precipitation total. In addition, the domain average of the diurnal cycle of 2-m temperature was amplified, with a noted increase in the daytime maximum. These results were consistent among all three simulated periods, and largely unchanged when subjected to a number of model sensitivity factors. Furthermore, the model results are in reasonable agreement with an analysis of observational data that indicates decreasing regional precipitation and increasing daytime maximum temperature during the twentieth century. These results could have important implications for water resource and land-use management issues in south Florida, including efforts to restore and preserve the natural hydroclimate of the Everglades ecosystem. This study also provides more evidence for the need to consider anthropogenic land-cover change when evaluating climate trends.
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Long-term chronologies of precipitation can provide a baseline against which twentieth-century trends in rainfall can be evaluated in terms of natural variability and anthropogenic influence. However, there are relatively few methods to quantitatively reconstruct palaeoprecipitation and river discharge compared with proxies of other climatic factors, such as temperature. We developed autoregressive and least squares statistical models relating Chesapeake Bay salinity to river discharge and regional precipitation records. Salinity in northern and central parts of the modern Chesapeake Bay is influenced largely by seasonal, interannual and decadal variations in Susquehanna River discharge, which in turn are controlled by regional precipitation patterns. A power regressive discharge model and linear precipitation model exhibit well-defined decadal variations in peak discharge and precipitation. The utility of the models was tested by estimating Holocene palaeoprecipitation and Susquehanna River palaeodischarge, as indicated by isotopically derived palaeosalinity reconstructions from Chesapeake Bay sediment cores. Model results indicate that the early-mid Holocene (7055-5900 yr BP) was drier than the late Holocene (1500 yr BP-present), the 'Mediaeval Warm Period' (MWP) (1200-600 yr BP) was drier than the 'Little Ice Age' (LIA) (500-100 yr BP), and the twentieth century experienced extremes in precipitation possibly associated with changes in ocean-atmosphere teleconnections.
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Salinity oscillations caused by multidecadal climatic variability had major impacts on the Chesapeake Bay estuarine ecosystem during the past 1000 yr. Microfossils from sediments dated by radiometry (14C, 137Cs, 210Pb) and pollen stratigraphy indicate that salinity in mesohaline regions oscillated 10-15 ppt during periods of extreme drought (low fresh-water discharge) and wet climate (high discharge). During the past 500 yr, 14 wet-dry cycles occurred, including sixteenth and early seventeenth century megadroughts that exceeded twentieth century droughts in their severity. These droughts correspond to extremely dry climate also recorded in North American tree-ring records and by early colonists. Wet periods occurred every ~60-70 yr, began abruptly, lasted <20 yr, and had mean annual rainfall ~25%-30% and fresh-water discharge ~40%-50% greater than during droughts. A shift toward wetter regional climate occurred in the early nineteenth century, lowering salinity and compounding the effects of agricultural land clearance on bay ecosystems.
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Sediment cores as long as 20 m, dated by 14C, 210Pb, and 137Cs methods and pollen stratigraphy, provide a history of diatom productivity and sediment-accumulation rates in Chesapeake Bay. We calculated the flux of biogenic silica and total sediment for the past 1500 yr for two high-sedimentation-rate sites in the mesohaline section of the bay. The data show that biogenic silica flux to sediments, an index of diatom productivity in the bay, as well as its variability, were relatively low before European settlement of the Chesapeake Bay watershed. In the succeeding 300 400 yr, the flux of biogenic silica has increased by a factor of 4 to 5. Biogenic silica fluxes still appear to be increasing, despite recent nutrient-reduction efforts. The increase in diatom-produced biogenic silica has been partly masked (in concentration terms) by a similar increase in total sediment flux. This history suggests the magnitude of anthropogenic disturbance of the estuary and indicates that significant changes had occurred long before the twentieth century.
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Tree-ring data from Virginia indicate that the Lost Colony of Roanoke Island disappeared during the most extreme drought in 800 years (1587???1589) and that the alarming mortality and the near abandonment of Jamestown Colony occurred during the driest 7-year episode in 770 years (1606???1612). These extraordinary droughts can now be implicated in the fate of the Lost Colony and in the appalling death rate during the early occupations at Jamestown, the first permanent English settlement in America.
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We reconstructed paleoclimate patterns from oxygen and carbon isotope records from the fossil estuarine benthic foraminifera Elphidium and Mg/ Ca ratios from the ostracode Loxoconcha from sediment cores from Chesapeake Bay to examine the Holocene evolution of North Atlantic Oscillation (NAO)-type climate variability. Precipitation-driven river discharge and regional temperature variability are the primary influences on Chesapeake Bay salinity and water temperature, respectively. We first calibrated modern δ18 Owater to salinity and applied this relationship to calculate trends in paleosalinity from the δ18 Oforam, correcting for changes in water temperature estimated from ostracode Mg /Ca ratios. The results indicate a much drier early Holocene in which mean paleosalinity was ∼28 ppt in the northern bay, falling ∼25% to ∼20 ppt during the late Holocene. Early Holocene Mg/Ca-derived temperatures varied in a relatively narrow range of 13° to 16°C with a mean temperature of 14.2°C and excursions above 16°C; the late Holocene was on average cooler (mean temperature of 12.8°C). In addition to the large contrast between early and late Holocene regional climate conditions, multidecadal (20-40 years) salinity and temperature variability is an inherent part of the region's climate during both the early and late Holocene, including the Medieval Warm Period and Little Ice Age. These patterns are similar to those observed during the twentieth century caused by NAO-related processes. Comparison of the midlatitude Chesapeake Bay salinity record with tropical climate records of Intertropical Convergence Zone fluctuations inferred from the Cariaco Basin titanium record suggests an anticorrelation between precipitation in the two regions at both millennial and centennial timescales.
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Tree-ring data from Virginia indicate that the Lost Colony of Roanoke Island disappeared during the most extreme drought in 800 years (1587-1589) and that the alarming mortality and the near abandonment of Jamestown Colony occurred during the driest 7-year episode in 770 years (1606-1612). These extraordinary droughts can now be implicated in the fate of the Lost Colony and in the appalling death rate during the early occupations at Jamestown, the first permanent English settlement in America.
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Analysis of 170 pollen assemblages from surface samples in eight vegetation types in the Florida Everglades indicates that these wetland sub-environments are distinguishable from the pollen record and that they are useful proxies for hydrologic and edaphic parameters. Vegetation types sampled include sawgrass marshes, cattail marshes, sloughs with floating aquatics, wet prairies, brackish marshes, tree islands, cypress swamps, and mangrove forests. The distribution of these vegetation types is controlled by specific environmental parameters, such as hydrologic regime, nutrient availability, disturbance level, substrate type, and salinity; ecotones between vegetation types may be sharp. Using R-mode cluster analysis of pollen data, we identified diagnostic species groupings; Q-mode cluster analysis was used to differentiate pollen signatures of each vegetation type. Cluster analysis and the modern analog technique were applied to interpret vegetational and environmental trends over the last two millennia at a site in Water Conservation Area 3A. The results show that close modern analogs exist for assemblages in the core and indicate past hydrologic changes at the site, correlated with both climatic and land-use changes. The ability to differentiate marshes with different hydrologic and edaphic requirements using the pollen record facilitates assessment of relative impacts of climatic and anthropogenic changes on this wetland ecosystem on smaller spatial and temporal scales than previously were possible.
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Ecological extinction caused by overfishing precedes all other pervasive human disturbance to coastal ecosystems, including pollution, degradation of water quality, and anthropogenic climate change. Historical abundances of large consumer species were fantastically large in comparison with recent observations. Paleoecological, archaeological, and historical data show that time lags of decades to centuries occurred between the onset of overfishing and consequent changes in ecological communities, because unfished species of similar trophic level assumed the ecological roles of overfished species until they too were overfished or died of epidemic diseases related to overcrowding. Retrospective data not only help to clarify underlying causes and rates of ecological change, but they also demonstrate achievable goals for restoration and management of coastal ecosystems that could not even be contemplated based on the limited perspective of recent observations alone.
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Stratigraphic records from four sediment cores collected along a transect across the Chesapeake Bay near the mouth of the Choptank River were used to reconstruct a 2000-year history of anoxia and eutrophication in the Chesapeake Bay. Variations in pollen, diatoms, concentration of organic carbon, nitrogen, sulfur, acid-soluble iron, and an estimate of the degree of pyritization of iron indicate that sedimentation rates, anoxic conditions and eutrophication have increased in the Chesapeake Bay since the time of European settlement.