Estimates of Natural Salinity and Hydrology in a Subtropical Estuarine Ecosystem: Implications for Greater Everglades Restoration

Disruption of the natural patterns of freshwater flow into estuarine ecosystems occurred in many locations around the world beginning in the twentieth century. To effectively restore these systems, establishing a pre-alteration perspective allows managers to develop science-based restoration targets for salinity and hydrology. This paper describes a process to develop targets based on natural hydrologic functions by coupling paleoecology and regression models using the subtropical Greater Everglades Ecosystem as an example. Paleoecological investigations characterize the circa 1900 CE (pre-alteration) salinity regime in Florida Bay based on molluscan remains in sediment cores. These paleosalinity estimates are converted into time series estimates of paleo-based salinity, stage, and flow using numeric and statistical models. Model outputs are weighted using the mean square error statistic and then combined. Results indicate that, in the absence of water management, salinity in Florida Bay would be about 3 to 9 salinity units lower than current conditions. To achieve this target, upstream freshwater levels must be about 0.25 m higher than indicated by recent observed data, with increased flow inputs to Florida Bay between 2.1 and 3.7 times existing flows. This flow deficit is comparable to the average volume of water currently being diverted from the Everglades ecosystem by water management. The products (paleo-based Florida Bay salinity and upstream hydrology) provide estimates of pre-alteration hydrology and salinity that represent target restoration conditions. This method can be applied to any estuarine ecosystem with available paleoecologic data and empirical and/or model-based hydrologic data.     

Geochronological (U–Pb,U–Th–total Pb,Sm–Nd) and geochemical (REE, <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr, δ<Superscript>18</Superscript>O, δ<Superscript>13</Superscript>C) tracing of intraplate tectonism and associated fluid flow in the Warburton Basin,Australia

The Warburton Basin of central Australia has experienced a complex tectonic and fluid-flow history, resulting in the formation of various authigenic minerals. Geochemical and geochronological analyses were undertaken on vein carbonates from core samples of clastic sediments. Results were then integrated with zircon U–Pb dating and uraninite U–Th–total Pb dating from the underlying granite. Stable and radiogenic isotopes (δ¹⁸O, Sr and εNd), as well as trace element data of carbonate veins indicate that >200 °C basinal fluids of evolved meteoric origin circulated through the Warburton Basin. Almost coincidental ages of these carbonates (Sm–Nd; 432 ± 12 Ma) with primary zircon (421 ± 3.8 Ma) and uraninite (407 ± 16 Ma) ages from the granitic intrusion point towards a substantial period of active tectonism and an elevated thermal regime during the mid Silurian. We hypothesise that such a thermal regime may have resulted from extensional tectonism and concomitant magmatic activity following regional orogenesis. This study shows that the combined application of geochemical and geochronological analyses of both primary and secondary species may constrain the timing of tectonomagmatic events and associated fluid flow in intraplate sedimentary basins. Furthermore, this work suggests that the Sm–Nd-isotopic system is surprisingly robust and can record geologically meaningful age data from hydrothermal mineral species.     

Breaking the impasse: towards a new regime for international climate governance

The reality of the current international order makes it imperative that a just and effective climate regime should balance the historical responsibility of developed countries with the increasing absolute emissions from many developing nations. The key pillars are briefly proposed for a new international climate architecture that envisions replacing the current annex system with two new annexes: Annex α, for countries with high current emissions and historically high emissions, and Annex β, for countries with high current emissions and historically low emissions. Countries in both annexes would implement legally binding targets under this framework. Additionally, this proposal includes alterations and revisions to funding and technology transfer mechanisms to correct for weaknesses and inequities under the current Kyoto architecture. The proposed framework stems from a belief that a top-down, international approach to climate policy remains the most effective for ensuring environmental integrity. Given the slow rate of institutional learning, the reform and improvement of the current system is held as a more efficient course of action than abandoning the progress already achieved. It is argued that the proposed framework could effectively accommodate key equity, environmental integrity, and political feasibility concerns.     

Explosive erosion during the Phoenix landing exposes subsurface water on Mars

While steady thruster jets caused only modest surface erosion during previous spacecraft landings on the Moon and Mars, the pulsed jets from the Phoenix spacecraft led to extensive alteration of its landing site on the martian arctic, exposed a large fraction of the subsurface water ice under the lander, and led to the discovery of evidence for liquid saline water on Mars. Here we report the discovery of the ‘explosive erosion’ process that led to this extensive erosion. We show that the impingement of supersonic pulsed jets fluidizes porous soils and forms cyclic shock waves which propagate through the soil and produce erosion rates more than an order of magnitude larger than that of other jet-induced processes. The understanding of ‘explosive erosion’ allows the calculation of bulk physical properties of the soils altered by it, provides insight into a new behavior of granular flow at extreme conditions and explains the rapid alteration of the Phoenix landing site’s ground morphology at the northern arctic plains of Mars.     

Comparison of dew point temperature estimation methods in Southwestern Georgia

Recent upward trends in acres irrigated have been linked to increasing near-surface moisture. Unfortunately, stations with dew point data for monitoring near-surface moisture are sparse. Thus, models that estimate dew points from more readily observed data sources are useful. Daily average dew temperatures were estimated and evaluated at 14 stations in Southwest Georgia using linear regression models and artificial neural networks (ANN). Estimation methods were drawn from simple and readily available meteorological observations, therefore only temperature and precipitation were considered as input variables. In total, three linear regression models and 27 ANN were analyzed. The two methods were evaluated using root mean square error (RMSE), mean absolute error (MAE), and other model evaluation techniques to assess the skill of the estimation methods. Both methods produced adequate estimates of daily averaged dew point temperatures, with the ANN displaying the best overall skill. The optimal performance of both models was during the warm season. Both methods had higher error associated with colder dew points, potentially due to the lack of observed values at those ranges. On average, the ANN reduced RMSE by 6.86% and MAE by 8.30% when compared to the best performing linear regression model.     

Carbonate concretions—explained

Carbonate concretions are common features of sedimentary rocks of all geological ages. They are most obvious in sandstones and mudstones as ovoid bodies of rock that protrude from natural outcrops: clearly harder or better cemented than their host rocks. Many people are excited by finding fossils in the centre of mudstone‐hosted concretions ( Fig. 1 ) but spend little time wondering why the fossils are so well preserved. While the study of concretions has benefitted from the use of advanced analytical equipment, simple observations in the field can also help to answer many questions. For example, in cliff sections, original sedimentary beds and sedimentary structures can be traced right through concretions ( Fig. 2 ): so it can be deduced that the concretion clearly formed after these depositional structures were laid down. In this article we explain how and where concretions form and discuss the evidence, ranging from outcrop data to sophisticated laboratory analyses, which can be used to determine their origins. The roles of microbes, decaying carcasses, compaction and groundwaters are highlighted. Concretions not only preserve fossils but can also subdivide oil, gas and water reservoirs into separate compartments.

Figure 1 Open in figure viewer PowerPoint An early diagenetic carbonate concretion split in half to reveal an ammonite retaining its original aragonite shell, from the Maastrichtian of Antarctica. Image courtesy of Alistair Crame (British Antarctic Survey, NERC). Lens cap is 6 cm.     

Mining soil databases for landscape‐scale patterns in the abundance and size distribution of hillslope rock fragments

Landscape‐scale variation in rock fragments on soil‐mantled hillslopes is poorly understood, despite the potential importance of rock fragments in soil weathering and coarse sediment supply to river networks. We explored the utility of soil survey databases for data mining, with the goals of identifying landscape‐scale patterns in the abundance and size distribution of rock fragments (diameter D > 2 mm) and potential controls on grain size production. We focus on data from three regions: the Hawaiian Islands, and the Sierra Nevada and Cascade Mountains, where elevation transects span a range of environmental conditions. We selected pedons from pits dug on hillslopes with active soil production and transport. For the 27 pedons selected, we constructed depth‐averaged grain size distributions and calculated the mass fraction of rock fragments (F_RF) and the median rock fragment grain size (D_50RF). We also categorized as bimodal, size distributions with a clear ‘breakpoint’ between fine and coarse modes. Several strong patterns emerge from the data. We find rock fragments in 85% of the pedons, primarily in distinct coarse modes within bimodal size distributions. Values of F_RF and D_50RF are strongly correlated, although the best‐fit power law scaling between F_RF and D_50RF differs between the warmer Hawaiian, and colder Sierra Nevada and Cascade Mountain sites. We also find a regional contrast in the variation in F_RF with elevation; F_RF declines with elevation in Hawaii, but increases in the mainland sites. Although this contrast could be an artifact of variable lithology, precipitation may influence many patterns in the data. Lower mean‐annual precipitation correlates with higher F_RF, dominantly bimodal distributions and surface enrichment in the vertical distribution of rock fragments. These observations may be useful in refining models of coarse sediment supply to rivers, and suggest opportunities for future work to test mechanistic hypotheses for rock fragment production on soil‐mantled hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.     

Coupling relationships: Hillslope–fluvial linkages in the Hodder catchment, NW England

Variations in the coupling of sediment transfer between different parts of a fluvial catchment, e.g., hillslope to axial stream, can hamper understanding but are an integral part of the geomorphological record. Depositional environments respond to a combination of land use, climate, storms (floods), and autogenic conditioning. The distribution of sediment in the upland landscapes of NW England is out of equilibrium with contemporary climate and geomorphological processes; more a function of peri- and paraglacial mobilisation of glacigenic deposits. Soil and vegetation development after deglaciation have interrupted any progression toward sediment exhaustion with sediment release controlled largely by extrinsic perturbation, with late Holocene anthropogenic activity, climate and extreme hydrological events the likely candidates. This paper presents a new radiocarbon-dated Holocene geomorphological succession for the River Hodder (NW England), alongside evaluating new palaeoecological and geoarchaeological data to discern the impacts of human activity. These data show a late Holocene expansion in human occupation and use of the landscape since the Iron Age (700–0 cal. B.C.), with more substantial changes in the character and intensity of upland land use in the last 1300 years. The geomorphological responses in the uplands were the onset of considerable and widespread hillslope erosion (gullying) and associated alluvial fan development. Interpretation of the regional radiocarbon chronology limits gullying to four, more extensive and aggressive phases after 500 cal. B.C. The downstream alluvial system has responded with considerable valley floor deposition and lateral channel migration that augmented sediment supply by remobilising the existing floodplain terraces and led to the aggradation of a series of inset alluvial terraces. The timing of these changes between states of aggradation and incision in alluvial reaches reflects the increased connectivity between the hillslope and alluvial systems. Aspects of both the regional climate and land use histories are conducive to increasing discharge and sediment flux, but the region wide lowering of erosion thresholds appears a key driver conditioning these sediment-rich conditions and producing a landscape that was more susceptible to erosion under lower magnitude flows.     

Robust chronologies for landform development

Obtaining chronological control for geomorphological sequences can be problematic due to the fragmentary and non‐sequential nature of sediment and landform archives. The robust analysis of ¹⁴C ages is often critical for the interpretation of these complicated sequences. This paper demonstrates a robust methodology for the ¹⁴C dating of geomorphological sequences using a case study from the lower Ribble valley, northwest England. The approach adopted incorporates using greater numbers of ages, targeting plant macrofossils, obtaining replicate measurements from single horizons to assess the extent of reworking and the use of Bayesian approaches to test models of the relative order of events. The extent of reworking of organic materials and space‐time dynamics of fluvial change means that it is critical that chronological control is sufficiently resourced with ¹⁴C measurements. As a result Bayesian approaches are increasingly important for the evaluation of large data sets. Assessing the conformability of relative order models informed by interpretation of the geomorphology can identify contexts or materials that are out of sequence, and focuses attention on problem materials (reworking) and errors in interpretation (outlier ages). These relative order models provide a framework for the interrogation of sequences and a means for securing probability‐based age estimates for events that occur between dated contexts. This approach has potential value in constraining the sequence of geomorphological development at scales that vary from individual sites to a catchment or region, furthering understanding of forcing and change in geomorphological systems. Copyright © 2008 John Wiley & Sons, Ltd.