Floating Marshes in Louisiana: Substrate and Hydrolic Characterization

Substrate characteristics and vertical mat movement were determined for maidencane (Panicum hemitomon), bulltongue(Sagittaria falcata) and wire-grass (Spartina patens) dominated marshes located progressively closer to the Gulf of Mexico in Barataria Basin, Louisiana, at Lake Boeuf, Lake Salvador and Bayou des Rigolettes, respectively. The near-surface substrate of the marshes at Lake Boeuf and Lake Salvador was characterized by high mean organic matter content (\u3e 90%, \u3e80%, gig dry weight x 100) and low mean mineral densities (0.007, 0.013 glee) respectively. Mean dry bulk density at these two marshes was low (0.065, 0.068 glee, respectively). Mean dry bulk densities were highest at Bayou des Rigolettes (0.14 glee); the shallow substrate contained approximately equal densities of mineral and organic material. Rubbed and unrubbed fiber contents in the upper 40 to 50 centimeters of mat were highest at Lake Boeuf (83%,73%), intermediate at Lake Salvador (68%,38%) and lowest at Bayou des Rigolettes (50%,29%). Buoyancy among the three sites roughly paralleled the gradient of increasingly fibric underground biomass. The Lake Boeuf marsh surface was above the water table and responded freely to changes in ambient water levels; the Lake Salvador marsh, while still responding freely, floated below the water surface. The wire-grass dominated marsh adjusted to increasing ambient water levels only to a small degree (3 - 4 em). Water levels and marsh-flooding events were compared among the three sites. Absolute water levels were high during the study interval. Under these conditiqns a trend of increasing duration of continuous flooding and total flooding was evident in an inland direction. The depth of flooding was greatest at the Lake Salvador marsh (measured relative to lowest marsh mat levels). The results presented in this study support the hypothesis of buoyant detachment of attached marsh from the subsiding solid substrate (O\u27Neil, 1949) as a response to marsh flooding and an absence of mineral sediment. This suggests that floating marshes are an integral and possibly large part of the Louisiana wetlands

Mat Movement in Coastal Louisiana Marshes: Effect of Salinity and Inundation on Vegetation and Nutrient Levels

The present research compared and contrasted the physical structure of floating and rooted marshes, their differing responses to open-water salinities and inundation, as well as the nutrient distribution in the porewaters and sediment. The effects of the physical differences in the two marsh types on the ocurrence of the dominant emergent vegetation was discussed. The main difference in physical structure of the two marsh types was the presence of a mineral, non-buoyant layer at 25-45 cm depth in the rooted marsh, which could serve as an anchor for the overlying highly organic mat layer found in both marsh types. Porewater salinities in floating marshes tracked open-water salinities more closely than they did in rooted marshes. Under the prevailing, mostly fresh conditions, porewaters in the rooted marsh contained significantly higher salt levels. Here also, there was a more pronounced vertical gradient in salt levels than found in floating marshes. With the three years of data it was possible to demonstrate the more extensive exchange of below-ground water with open waters in the floating marshes, rather than the rooted marsh. Surprisingly, the different hydrodynamics of floating and rooted marshes did not appear to affect inorganic porewater nutrient levels. It appeared that dominant above-ground vegetation determined these levels. The two dominant species of emergent vegetation have clearly contrasting tolerances to ambient salinites and flooding. Thus, the continued persistance of the bore salt-tolerant species in this mostly fresh area is thought to be attributable to the recurring, but infrequent years of high salinity. The significance of floating marshes in the rapidly subsiding Mississippi River Deltaic Plain, with concomittant increases in ambient salinities is obvious. Their potentially unique responses to these environmental forcing functions deserve closer attention when mitigation measures are conceptualized and implemented. It is quite possible that a majority of the low-salinity marshes in the deltaic plain may be floating

Non-Conservative Behavior of Select Naturally-Occurring Radionuclides and Metals in Coastal Waters.

Water column samples from three vastly contrasting coastal regimes (Framvaren Fjord, Norway, the Amazon and Mississippi River outflow regions) were analyzed to study the estuarine transport and scavenging processes of \sp{210}Pb, \sp{210}Po, \sp{234}U and \sp{238}U. The Amazon and Mississippi River outflow regions are two of the world\u27s largest river-ocean mixing systems that contrast each other sharply in many physiographical and geochemical features. The Amazon is a tropical, high energy, shelf environment where estuarine physico-chemical processes are strongly influenced by sediment-water interactions. The Mississippi system on the other hand discharges much of its load close to the shelf-break where estuarine geochemical processes are largely separated from benthic processes. The distribution of uranium in these two systems reflects the vastly contrasting environments. In the Amazon, U is consistently non-conservative--showing removal at all river discharge stages. Removal of U from this water column onto particulates involves scavenging by colloidal-sized metal oxides, flocculation and subsequent aggregation up the particle size spectrum. In the Mississippi River outflow region, U is conservative at all normal river discharge stages. However, during flood/drought conditions uranium does exhibit non-conservative estuarine behavior and U removal is thought to be a function of the reactivity of the carrier phase. Framvaren Fjord represents a unique environment in which to investigate estuarine chemistry. At about a salinity of 21 and a depth of 20 meters (well within the photic zone), a very sharp O\sb2/H\sb2S boundary controls the vertical distribution of a suite of trace metals and radionuclides. The uptake and release of such elements by dense communities of anoxygenic phototrophic bacteria (e.g., Chlorobium and Chromatium spp.) create very sharp concentration peaks at the redoxcline. Such bio-concentration at the O\sb2/H\sb2S boundary has been observed in the vertical profiles of \sp{210}Po, \sp{210}Pb, Fe, Mn, U, Ba and Sr. Mechanisms or processes to create such distributions must be biogenic and are most likely microbially mediated. Results from this study indicate that even elements once thought to be quite non-reactive in natural waters, such as uranium, can in fact be susceptible to both biotic and abiotic enrichment/depletion processes

Constraints on the utility of MnO2 cartridge method for the extraction of radionuclides: A case study using \u3csup\u3e234\u3c/sup\u3eTh

Large volume (102–103 L) seawater samples are routinely processed to investigate the partitioning of particle reactive radionuclides and Ra between solution and size-fractionated suspended particulate matter. One of the most frequently used methods to preconcentrate these nuclides from such large volumes involves extraction onto three filter cartridges (a prefilter for particulate species and two MnO2-coated filters for dissolved species) connected in series. This method assumes that the extraction efficiency is uniform for both MnO2-coated cartridges, that no dissolved species are removed by the prefilter, and that any adsorbed radionuclides are not desorbed from the MnO2-coated cartridges during filtration. In this study, we utilized 234Th-spiked coastal seawater and deionized water to address the removal of dissolved Th onto prefilters and MnO2-coated filter cartridges. Experimental results provide the first data that indicate (1) a small fraction of dissolved Th (\u3c6%) can be removed by the prefilter cartridge; (2) a small fraction of dissolved Th (\u3c5%) retained by the MnO2 surface can also be desorbed, which undermines the assumption of uniform extraction efficiency for Th; and (3) the absolute and relative extraction efficiencies can vary widely. These experiments provide insight on the variability of the extraction efficiency of MnO2-coated filter cartridges by comparing the relative and absolute efficiencies and recommend the use of a constant efficiency on the combined activity from two filter cartridges connected in series for future studies of dissolved 234Th and other radionuclides in natural waters using sequential filtration/extraction methods

Soil Shear Strength Losses In Two Fresh Marshes With Variable Increases In N And P Loading

We measured soil shear strength (SSS) from 2009 to 2018 in two hydrologically distinct freshwater marshes dominated by Panicum hemitomon after nitrogen (N) and phosphorous (P) were applied to the surface in spring. The SSS averaged over 100-cm depth in the floating and anchored marshes declined up to 30% throughout the profiles and with no apparent differences in the effects of the low, medium, and high N + P dosing. Plots with only N or P additions exhibited significant changes in SSS at individual depths below 40 cm for the anchored marsh, but not the floating marsh. The average SSS for the anchored marsh over the entire 100 cm profile declined when N and P were added separately or together. At the floating marsh, however, the SSS decreased when N and P were added in combination, or P alone, but not for the N addition. Increasing nutrient availability to these freshwater marsh soils makes them weaker, and perhaps lost if eroded or uplifted by buoyant forces during storms. These results are consistent with results from multi-year experiments demonstrating higher decomposition rates, greenhouse gas emissions, and carbon losses in wetlands following increased nutrient availability

Erosion surfaces in northwestern Maine

Thesis (Ph.D.)--Boston University.In the progress of Boston University's geological mapping program in the Rangeley Lake region of northwestern Maine the occurrence of conspicuously level areas at varying, yet definite elevations was noted. Essentially horizontal or but slightly inclined areas, independent of structure and lithology, are found typically as breaks in slope on mountain flanks; others occur ar summit elevations of ridges or constitute the floors of certain basins and valleys. The striking occurrence of these levels of "terraces" was a stimulus toward the undertaking of the present studies which include the mapping of persistent levels and an attempt to explain their origin. The region under consideration is covered by the following quadrangle maps: Phillips, Rangeley, Stratton, Kennebago Lake, Oquossoc, and cupsuptic, Maine. The area includes the major part of the Blue Mountains, comprising isolated peaks and ranges which continue in general the northeasterly trend of the White Mountains of New Hampshire. Several peaks reach above 4000 feet elevation, such as Sugarloaf Mountain (4237 ft.), Bigelow Mountain(4150 ft.), Mount Abraham (4049 ft.), Saddleback Mountain (4116 ft.). There are many peaks reaching elevations of 3000 feet or more. Relief is highly variable, ranging from a few hundred feet to 3000 feet, owing to the irregular distribution of mountains. The region is maturely dissected, with major drainage to the east, southeast, and south, into the Kennebee and Androsooggin Rivers. [Truncated.

The magnitude and origin of groundwater discharge to Eastern U.S. and Gulf of Mexico coastal waters

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 44 (2017): 10,396–10,406, doi:10.1002/2017GL075238.Fresh groundwater discharge to coastal environments contributes to the physical and chemical conditions of coastal waters, but the role of coastal groundwater at regional to continental scales remains poorly defined due to diverse hydrologic conditions and the difficulty of tracking coastal groundwater flow paths through heterogeneous subsurface materials. We use three-dimensional groundwater flow models for the first time to calculate the magnitude and source areas of groundwater discharge from unconfined aquifers to coastal waterbodies along the entire eastern U.S. We find that 27.1 km3/yr (22.8–30.5 km3/yr) of groundwater directly enters eastern U.S. and Gulf of Mexico coastal waters. The contributing recharge areas comprised ~175,000 km2 of U.S. land area, extending several kilometers inland. This result provides new information on the land area that can supply natural and anthropogenic constituents to coastal waters via groundwater discharge, thereby defining the subterranean domain potentially affecting coastal chemical budgets and ecosystem processes.National Science Foundation Grant Number: EPS-1208909; NASA Carbon Cycle Science Grant Number: NNX14AM37G2018-04-2

Review of the scientific and institutional capacity of small island developing states in support of a bottom-up approach to achieve sustainable development goal 14 targets

Capacity building efforts in Small Island Developing States (SIDS) are indispensable for the achievement of both individual and collective ocean-related 2030 agenda priorities for sustainable development. Knowledge of the individual capacity building and research infrastructure requirements in SIDS is necessary for national and international efforts to be effective in supporting SIDS to address nationally-identified sustainable development priorities. Here, we present an assessment of human resources and institutional capacities in SIDS United Nations (UN) Member States to help formulate and implement durable, relevant, and effective capacity development responses to the most urgent marine issues of concern for SIDS. The assessment highlights that there is only limited, if any, up-to-date information publicly available on human resources and research capacities in SIDS. A reasonable course of action in the future should, therefore, be the collection and compilation of data on educational, institutional, and human resources, as well as research capacities and infrastructures in SIDS into a publicly available database. This database, supported by continued, long-term international, national, and regional collaborations, will lay the foundation to provide accurate and up-to-date information on research capacities and requirements in SIDS, thereby informing strategic science and policy targets towards achieving the UN sustainable development goals (SDGs) within the next decade

Vulnerability of coral reefs to bioerosion from land-based sources of pollution

This paper is not subject to U.S. copyright. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 9319–9331, doi:10.1002/2017JC013264.Ocean acidification (OA), the gradual decline in ocean pH and [ inline image] caused by rising levels of atmospheric CO2, poses a significant threat to coral reef ecosystems, depressing rates of calcium carbonate (CaCO3) production, and enhancing rates of bioerosion and dissolution. As ocean pH and [ inline image] decline globally, there is increasing emphasis on managing local stressors that can exacerbate the vulnerability of coral reefs to the effects of OA. We show that sustained, nutrient rich, lower pH submarine groundwater discharging onto nearshore coral reefs off west Maui lowers the pH of seawater and exposes corals to nitrate concentrations 50 times higher than ambient. Rates of coral calcification are substantially decreased, and rates of bioerosion are orders of magnitude higher than those observed in coral cores collected in the Pacific under equivalent low pH conditions but living in oligotrophic waters. Heavier coral nitrogen isotope (δ15N) values pinpoint not only site-specific eutrophication, but also a sewage nitrogen source enriched in 15N. Our results show that eutrophication of reef seawater by land-based sources of pollution can magnify the effects of OA through nutrient driven-bioerosion. These conditions could contribute to the collapse of coastal coral reef ecosystems sooner than current projections predict based only on ocean acidification.USGS Coastal and Marine Geology Progra

Trace element cycling in a subterranean estuary : part 2. Geochemistry of the pore water

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 70 (2006): 811-826, doi:10.1016/j.gca.2005.10.019.Submarine groundwater discharge (SGD) is an important source of dissolved elements to the ocean, yet little is known regarding the chemical reactions that control their flux from sandy coastal aquifers. The net flux of elements from SGD to the coastal ocean is dependent on biogeochemical reactions in the groundwater-seawater mixing zone, recently termed the "subterranean estuary". This paper is the second in a two part series on the biogeochemistry of the Waquoit Bay coastal aquifer/subterranean estuary. The first paper addressed the biogeochemistry of Fe, Mn, P, Ba, U, and Th from the perspective of the sediment composition of cores (Charette et al., 2005). This paper uses pore water data from the subterranean estuary, along with Bay surface water data, to establish a more detailed view into the estuarine chemistry and the chemical diagenesis of Fe, Mn, U, Ba and Sr in coastal aquifers. Nine high-resolution pore water (groundwater) profiles were collected from the head of the bay during July 2002. There were non-conservative additions of both Ba and Sr in the salinity transition zone of the subterranean estuary. However, the extent of Sr release was significantly less than that of its alkaline earth neighbor Ba. Pore water Ba concentrations approached 3000 nM compared with 25-50 nM in the surface waters of the bay; the pore water Sr-salinity distribution suggests a 26% elevation in the amount of Sr added to the subterranean estuary. The release of dissolved Ba to the mixing zone of surface estuaries is frequently attributed to an ion-exchange process whereby seawater cations react with Ba from river suspended clay mineral particles at low to intermediate salinity. Results presented here suggest that reductive dissolution of Mn oxides, in conjunction with changes in salinity, may also be an important process in maintaining high concentrations of Ba in the pore water of subterranean estuaries. In contrast, pore water U was significantly depleted in the subterranean estuary, a result of SGD-driven circulation of seawater through reducing permeable sediments. This finding is supported by surface water concentrations of U in the bay, which were significantly depleted in U compared with adjacent coastal waters. Using a global estimate of SGD, we calculate U removal in subterranean estuaries at 20 x 106 mol U y-1, which is the same order of magnitude as the other major U sinks for the ocean. Our results suggest a need to revisit and reevaluate the oceanic budgets for elements that are likely influenced by SGD-associated processes.This research was supported by the National Science Foundation (OCE-0095384) to M.A.C. and E.R.S., and a WHOI Coastal Ocean Institute Fellowship to M.A.C