Phosphorus Dynamics Associated With Organic Carbon Mineralization by Reduction of Sulfate and Iron in Sediment Exposed to Fish Farming

The expansion of the aquaculture industry has resulted in accumulation of phosphorus (P)-rich organic matter via uneaten fish feed. To elucidate the impact of fish farming on P dynamics, P speciation, and benthic P release along with partitioning of organic carbon (Corg) mineralization coupled to sulfate reduction (SR) and iron reduction (FeR) were investigated in the sediments from Jinju Bay, off the southern coast of South Korea, in July 2013. SR in the farm sediment was 6.9-fold higher than the control sediment, and depth-integrated (0–10 cm) concentrations of NH4+, PO43–, and H2S in pore water of the farm sediment were 2.2-, 3.3-, and 7.4-fold higher than that in control sediment, respectively. High biogenic-P that comprised 28% of total P directly reflected the impact of P-rich fish feed, which ultimately enhanced the bioavailability (58% of total P) of P in the surface sediment of the farm site. In the farm sediment where SR dominated Corg mineralization, H2S oxidation coupled to the reduction of FeOOH stimulated release of P bound to iron oxide, which resulted in high regeneration efficiency (85%) of P in farm sediments. Enhanced P desorption from FeOOH was responsible for the increase in authigenic-P and benthic P flux. Authigenic-P comprised 33% of total P, and benthic P flux to the overlying water column accounted for approximately 800% of the P required for primary production. Consequently, excessive benthic P release resulting directly from oversupply of P-rich fish feed was a significant internal source of P for the water column, and may induce undesirable eutrophication and harmful algal blooms in shallow coastal ecosystems.

Towards a potential vorticity based mesoscale closure scheme

<p>With the advent of high-performance computing, we are now capable of simulating the ocean and climate system on decadal to centennial timescales. However, global and basin-scale simulations still lack the spatial resolution necessary to resolve the mesoscales (hereon referred to as mesoscale-permitting simulations), a scale roughly on the order of O(100 km). Here, we provide a first step towards a potential vorticity (PV) based mesoscale closure scheme in order to improve the representation of mesoscale eddies in such simulations by taking advantage of the thickness-weighted averaged (TWA) framework. In the TWA framework the total eddy feedback can be encapsulated in the Eliassen-Palm (E-P) flux divergence. This implies that mesoscale closure schemes aimed at representing the total eddy feedback should therefore be representing the E-P flux divergence. The TWA framework further elucidates that its divergence is equivalent to the eddy Ertel PV flux. In other words, if one is to parametrize the eddy Ertel PV flux, one has parametrized the total eddy feedback onto the mean flow. Using a 1/12° North Atlantic ensemble simulation with 24 members, which allows us to decompose the mesoscale variability from the forced dynamics, we show that the eddy Ertel PV flux can be related to the local-gradient of mean Ertel PV as an active tracer via an anisotropic eddy diffusivity tensor. What follows is that not only does the tensor bring together the isopycnal thickness skew diffusivity and isopycnic tracer diffusivity, the former known as the Gent-McWilliams (GM) parametrization and latter the Redi parametrization, but also incorporates the eddy momentum fluxes. Although the Redi parametrization has existed longer than GM, there has been much more development in the latter, leaving the Redi diffusivity poorly constrained. Being able to treat GM and Redi simultaneously is another strength of our framework.</p>

Impact of the Quasi-Biennial Oscillation on the Northern Winter Stratospheric Polar Vortex in CMIP5/6 Models

Using 16 CMIP5/6 models with a spontaneously generated quasi-biennial oscillation (QBO)-like phenomenon, this study investigates the impact of the QBO on the northern winter stratosphere. Eight of the models simulate a QBO with a period similar to that observed (25–31 months), with other models simulating a QBO period of 20–40 months. Regardless of biases in QBO periodicity, the Holton–Tan relationship can be well simulated in CMIP5/6 models with more planetary wave convergence in the polar stratosphere in easterly QBO winters. This wave polar convergence occurs not only due to the Holton–Tan mechanism, but also in the midlatitude upper stratosphere where an Elissen–Palm (E-P) flux divergence dipole (with poleward E-P flux) is simulated in most models. The wave response in the upper stratosphere appears related to changes in the background circulation through a directly excited meridional–vertical circulation cell above the maximum tropical QBO easterly center. The midlatitude upwelling in this anticlockwise cell is split into two branches, and the north branch descends in the Arctic region and warms the stratospheric polar vortex. Most models underestimate the Arctic stratospheric warming in early winter during easterly QBO. Further analysis suggests that this bias is not due to an overly weak response to a given QBO phase, as the models simulate a realistic response if one focuses on similar QBO phases. Rather, the model bias is due to the too-low frequency of strong QBO winds in the lower stratosphere in early winter simulated by the models.

Reduction of Internal Phosphorus Load in New Lakes by Pretreatment of the Former Agricultural Soil—Methods, Ecological Results and Costs

New lakes are established or reestablished to provide ecosystem services such as limiting floods and nutrient discharge and to improve biodiversity. New lakes are often established on fertilized land formerly used for agricultural purposes, thereby posing a risk of issues such as phosphorus (P) release when inundated. Release of P from agricultural soil affects both the developing ecosystem of the new lake and may increase downstream eutrophication. To decrease P release following inundation, three simple and cost-effective soil pretreatments were tested through laboratory soil–water fluxes from the test sites in the new Lake Roennebaek and the fluxes of P, nitrogen (N), and iron (Fe) were compared. The pretreatments compared were sand-capping, depth-plowing, and addition of the commercial iron product CFH-12® (Kemira). Untreated agricultural soil incubated under laboratory conditions released 687 ± 88 mg P·m−2 over 207 days and 85% was released within 60 days from inundation followed by low soil–water P exchange during the remaining incubation period. However, P was still released from the untreated soil 180 days after inundation within the lake. The cumulated P flux of the three pretreatment methods was in comparison negative, between −12 ± 3 and −17 ± 4 mg P·m−2 over 207 days incubation and showed negative P fluxes from cores collected within the lake 180 days after inundation. This study showed that the release of P when establishing new lakes on former agricultural land could be minimized using these simple and cost-effective methods, which may improve the ecological status of future lakes and enable the establishment of new lakes without threatening vulnerable downstream ecosystems.

A Concept for Capturing and Docking Spacecraft with Flux-Pinned Interfaces

Flux-pinned interfaces for spacecraft leverage the physics of magnetic flux pinning to govern the dynamics betweenclose-proximity spacecraft. The behavior of this interface enables a magnet to be held at a distance in up to six degrees of freedom relative to a type-II superconductor without contact or active control systems. This behavior is the result of a magnetic potential well with an equilibrium set by designer of the interface. When applied to a conceptual sample capture scenario, this approach offers several unique advantages over traditional mechanical capture systems, including robustness to control failures and the ability to preferentially orient the capture target without mechanical keying features. However, as a passive system, it is important to characterize the depth and shape of the potential well in order to bound the acceptable relative motion between a notional spacecraft and a notional sample cache to ensure a successful capture. This paper presents the results of a series of air bearing experiments designed to determine these bounds. Extrapolating from the ground testing environment, it was determined that the FPI is expected to work at a range of 50 cm in orbit around Mars, and operates best in a path angle of 0 degrees. It can tolerate a total relative translational velocity of up to 4.7 cm/sec or a total angular rate of 24 deg/sec between a spacecraft and a sample cache.

Sediment phosphorus release sustains nuisance periphyton growth when nitrogen is not limiting

Nuisance periphyton growth influences the aesthetics, recreation, and aquatic life of waterbodies. Partners Lake is a shallow spring-fed lake in the headwaters of the Illinois River Watershed in Cave Springs, Arkansas, that experiences nuisance growth of periphyton (i.e., Spirogyra spp.) each year. The ratio of dissolved nitrogen (N ~5.0 mg L-1) and phosphorus (P ~0.030 mg L-1) in the lake water (N:P≥288), as well as nutrient limitation assays, suggests that periphyton growth should be P-limited. While the water column lacks sufficient P to promote growth, the sediments have the ability to release P to the overlying water; P-flux ranged from 1.63 mg m-2 d-1 to over 10 mg m-2 d-1, reaching final concentrations of 0.08 to 0.34 mg L-1. However, soluble reactive phosphorus concentrations were consistently at or below 0.030 mg L-1, in the lake, suggesting that the periphyton were likely immobilizing P as quickly as it was released from the sediments. In the lab, maximal periphyton growth (~30 to 35 mg m-2) occurred in the 0.10 to 0.25 mg L-1 P treatments, over a 6 day incubation period. Similar levels of growth occurred when lake sediments were the P source, suggesting P released from the sediments is sufficient to support nuisance algal growth. We need to begin managing the legacy P stored in the sediments, in addition to external P loads, because internal P can sustain nuisance periphyton biomass when N is not limiting.

Flight-Experiment Validation of the Dynamic Capabilities of a Flux-Pinned Interface as a Docking Mechanism

Flux-pinned interfaces for spacecraft leverage the physics of superconductor interactions with electromagnetism to govern the dynamics between two bodies in close-proximity. Several unique advantages over traditional mechanical capture systems include robustness to control failures, contactless reorientation of the capture target, and collision mitigation. This study describes a series of experiments performed in a microgravity environment during a parabolic-flight campaign to measure the dynamic behavior of a flux-pinned interface in a flight-traceable environment. This paper presents the performance of a flux-pinned interface in the full six degrees of freedom in terms of several quantifiable metrics: success of capture at various energetic states, momentum change, system damping, and interface stiffness of the two spacecraft bodies.

Flux-Pinned Dynamics Model Parameterization and Sensitivity Study

Flux-pinned interfaces maintain a passively stable equilibrium between two spacecraft in close-proximity. Although flux-pinning physics has been studied from a materials-science perspective and at the systems level, the sensitivities and implications of system-level designs on the dynamics need to be better understood, especially in interfaces with multiple magnets and superconductors. These interfaces have highly nonlinear, coupled dynamics that are influenced by physical parameters including strength of magnetic field sources, field-cooled position, and superconductor geometry. Kordyuk’s frozen image model successfully approximates the characteristics of flux pinning dynamics but could provide more precise state prediction with the addition of these physical parameter refinements. This paper addresses that gap by offering parametric terms to improve the dynamics model, which may better simulate the behavior of a multiple-magnet-multiple-superconductor interface. The sensitivity of the general flux-pinned dynamics model is studied by varying the physical parameters and simulating the systems level dynamics. This work represents a critical step in the development of a model suited to spacecraft performance verification.

Solar Influences on Stratospheric Circulation Patterns

<p>The impact of the solar cycle on the NH winter stratospheric circulation is analyzed using<br>simulations of a Model of an idealized Moist Atmosphere (MiMA). By comparing solar minimum<br>periods to solar maximum periods, the solar impact on the stratosphere is evaluated: Solar<br>maximum periods are accompanied by warming of the tropics that extends into the midlatitudes<br>due to an altered Brewer Dobson Circulation. This warming of the subtropics and the altered<br>Brewer Dobson Circulation leads to an increase in zonal wind in midlatitudes, which is then<br>followed by a decrease in E-P flux convergence near the winter pole which extends the enhanced<br>westerlies to subpolar latitudes.<br>We use the transformed Eulerian mean framework to reveal the processes that lead to the<br>formation of this sub-polar zonal wind anomaly and its downward propagation from the top of the<br>stratosphere to the tropopause.</p>