Reconstructing a 180 yr record of natural and anthropogenic induced low-oxygen conditions from Louisiana continental shelf sediments

Osterman, Lisa E.; Poore, Richard Z.; Swarzenski, Peter W.; Turner, R. Eugene

doi:10.1130/g21341.1

Cited by 65 publications

(52 citation statements)

References 23 publications

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“…Together with previous authors (Nelsen et al, 1994;Blackwelder et al, 1996;Platon and Sen Gupta, 2001), Osterman (2003) observed that the combined percentage of three foraminiferal species (Pseudononion atlanticum, Epistominella vitrea and Buliminella morgani) was highest in surface sediment samples from hypoxic areas at mid-shelf depths (30-70 m) off Louisiana. She termed this percentage the PEB Index and used it to reconstruct trends in bottomwater oxygenation over a 180-year period (Osterman et al, 2005). Later, Osterman et al (2007) extended coverage of the PEB Index to other parts of the Lousiana shelf and also examined a much longer time period in three gravity cores, including one obtained within the modern hypoxic zone.…”

Section: Foraminiferasupporting

confidence: 77%

Historical records of coastal eutrophication-induced hypoxia

Jorissen²,

et al. 2009

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Abstract. 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 hypoxiaCorrespondence to: A. J. Gooday (ang@noc.soton.ac.uk) 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 humaninduced hypoxia, and associated eutrophication, in vulnerable coastal environments.

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Section: Foraminiferasupporting

confidence: 77%

Historical records of coastal eutrophication-induced hypoxia

Jorissen²,

et al. 2009

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“…Fluctuations in the amount of these low-oxygen-tolerant species between 1817 A.D. and 1910 A.D. correspond with increased discharge/flooding events in the Mississippi River drainage. In most cases, high river discharge correlates with high percentage values of the low-oxygen-tolerant PEB species (Osterman et al, 2005).…”

Section: An Evaluation Of An Enclosed Methods For the Determination Ofmentioning

confidence: 99%

“…Measurements of Louisiana continental-shelf waters have indicated that hypoxia (oxygen content <2mg/L) has increased since 1985 (Rabalais et al, 1999). Sediment cores taken from the Louisiana shelf have provided a record of hypoxic and low-oxygen conditions over longer time intervals of 50-100 years (Sen Gupta et al, 1996;Blackwelder et al, 1996;Osterman et al, 2005).…”

Section: An Evaluation Of An Enclosed Methods For the Determination Ofmentioning

confidence: 99%

USGS science in Florida: proceedings of Florida Integrated Science Center meeting, Orlando, Florida, May 3-5, 2005

2005

Open-File Report

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Human health and ecological concerns have arisen regarding Florida's spring waters as a steady increase in nitrate concentrations has been observed during the past 30 years. Springs discharge nearly 8 billion gallons per day and provide base flow for many rivers in Florida that flow toward coastal areas. Increased nitrogen loads in spring runs and streams have led to the formation of nuisance algal mats and exotic species of rooted aquatic plants. In response to these concerns by the State of Florida, several research studies have been using naturally-occurring isotopic and other chemical tracers to determine sources of nitrate contamination and age of ground water discharging from springs. Since 1997, more than 60 water samples have been collected from 44 springs and analyzed for isotopes ( 15 N, 3 H/ 3 He, 18 O, 2 H, 13 C) and other chemical indicators (chlorofluorocarbons (CFCs), major ions, dissolved gases, and SF 6 ). Delta 15 N values of nitrate ranged from 2.6 to 12.9 per mil (median = 5.8 per mil) and indicated that nitrate in most spring waters originated from synthetic fertilizers. Mean transit times of ground water from the Upper Floridan aquifer that discharges from these springs ranged from 5 to 39 years, based on measured concentrations of CFCs, 3 H/ 3 He, and SF 6 and various flow system models. Concentrations of these multiple transient tracers are consistent with a two-component hydrologic model with mixtures of varying proportions of young water (<8 years) from the shallow part of the aquifer and older water (20-50 years) from the deeper part of the flow system. Given residence times of 20 to 40 years for ground water discharging from most springs, it likely will take decades for nitrate concentrations to decrease to near background levels, even with immediate reductions in nitrogen inputs at the land surface. The landscape, hydrology, and ecology of Lake Wales Ridge, central Florida, are unique in many respects. The Ridge is the highest and most prominent topographic feature in peninsular Florida and contains one of the largest collections of rare and endangered species in the United States (Dobson and others, 1997), one of the highest concentrations of endemic species in North America (Martin, 1998), and more than 200 lakes, most of which are seepage lakes with significant ground-water inflow. Lake Wales Ridge (subsequently referred to as 'the Ridge') is also one of the most intensely cultivated citrus regions in the world, with citrus groves covering about 25 percent (170 square miles) of the land area. Geologically, the Ridge is underlain by highly permeable marine sands forming relict Miocene-Holocene paleoislands which support some of the oldest ecologic communities in Florida. Ground water and surface water are closely linked in this region where ground-water inflow contributes more than 80 percent of the net water input to some lakes (Sacks and others, 1998). Ground water is the primary drinking-water supply in this region. The unconfined surficial aquifer supplies drinking water for s...

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“…Extensive studies have shown that the loss comes from a combination of anthropogenic (e.g., artificial canal dredging, pond creation, and so forth) and natural mechanisms, involving relative sea level rise and wave attack on marshes fronting open water. While fossil records of low-oxygen-tolerant foraminifers suggest that the peak of hypoxia activity coincided with nutrient enhancement in the late 1950s, the peak also correlates well with the peak slope of wetland losses during the same time period [Osterman et al, 2005], so separating these effects remains difficult.…”

Section: River-dominated Marginsmentioning

confidence: 99%

Controlling Hypoxia on the U.S. Louisiana Shelf: Beyond the Nutrient‐Centric View

et al. 2008

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As the Earth's population continues to increase, the projected effects of contaminant loading and human encroachment on biodiversity remain unclear. One area of intense interest is coastal eutrophication and associated hypoxia events (with hypoxia defined as oxygen <2 milligrams per liter = 1.4 milliliters per liter = ˜63 micromoles per cubic decimeter). On average, the Mississippi River discharges to the northern Gulf of Mexico (GOM) 550 cubic kilometers of freshwater and approximately 60–70×109 moles of dissolved inorganic nitrogen per year [Dagg et al., 2004], which contains anthropogenic nitrogen derived primarily from agricultural fertilizer as well as effluent from animal feedlots.

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Reconstructing a 180 yr record of natural and anthropogenic induced low-oxygen conditions from Louisiana continental shelf sediments

Abstract: Figure 1. Locations of four cores discussed herein. Locations of hypoxia zone frequency taken from Committee on Environment and Natural Resources (2000), based on measurements done by N. Rabalais since 1985.

Cited by 65 publications

References 23 publications

Historical records of coastal eutrophication-induced hypoxia

Historical records of coastal eutrophication-induced hypoxia

USGS science in Florida: proceedings of Florida Integrated Science Center meeting, Orlando, Florida, May 3-5, 2005

Controlling Hypoxia on the U.S. Louisiana Shelf: Beyond the Nutrient‐Centric View

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