Hydrographic maintenance of deep anoxia in a tidally influenced saline lagoon

2018 ◽  
Vol 69 (3) ◽  
pp. 432 ◽  
Author(s):  
S. Kelly ◽  
E. de Eyto ◽  
M. Dillane ◽  
R. Poole ◽  
G. Brett ◽  
...  
Keyword(s):  
Dissolved Oxygen ◽  
Deep Water ◽  
Oxygen Depletion ◽  
Exchange Flow ◽  
Dynamic Events ◽  
Basin Scale ◽  
Renewal Events ◽  
Term Data ◽  
Oxygen Concentrations

Low dissolved oxygen concentrations are of increasing concern in aquatic ecosystems, particularly at the interface between freshwater and marine environments. Oxygen depletion occurs naturally in many perennially stratified systems and it remains to be seen how climate change will affect these habitats. This is due, in part, to a lack of high-resolution, long-term data describing interannual variability in dissolved oxygen concentrations within stratified basins. Physicochemical parameters for Lough Furnace, an ecologically important tidal lagoon, were assessed using daily measurements (2009–14) from an undulating CTD (conductivity, temperature and depth) profiler and observations of tidal exchange flow. Continuous vertical saline stratification existed, with anoxia (<0.1mgL–1) typically persisting below 6m. Tidal inflows were generally restricted, with deep-water renewal events by intrusions of denser spring tidal water occurring episodically (three times in 6 years), following prolonged periods of low freshwater input. Although wind forcing alone was not sufficient to generate basin-scale mixing, the conditions that led to deep-water renewals may also be conducive to wind-driven upwelling events in nearshore areas. These findings have wider application to larger-scale two-layered stratified systems with deep anoxia because the ability to forecast such dynamic events is important for assessing the ecological implications of dissolved oxygen depletion.

scholarly journals The Relationship between Mollusks and Oxygen Concentrations in Todos Santos Bay, Baja California, Mexico

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
J. Gabriel Kuk-Dzul ◽  
Victoria Díaz-Castañeda
Keyword(s):  
Organic Matter ◽  
Dissolved Oxygen ◽  
Bottom Water ◽  
Organic Matter Content ◽  
Oxygen Depletion ◽  
Matter Content ◽  
The Other ◽  
Natural Conditions ◽  
The Relationship ◽  
Oxygen Concentrations

This study describes the relationship between mollusks, physicochemical properties of seawater, and sediments under natural conditions of low impact. Thirty-nine stations were sampled in October 1994 using a Van Veen grab (0.1 m−2). Temperature, salinity, and dissolved oxygen (DO) concentrations of bottom water were obtained with a CTD. Organic matter content and sediment grain analysis were determined. A total of 836 mollusks were collected. Gastropoda was the most abundant (52%) and diverse class with 27 genera, followed by Bivalvia with eight genera and Scaphopoda with only one genus. According to CCA analysis, dominant mollusks were significantly related with high DO concentrations.Donax,Natica,Acteocina,Bulla,Anachis,Odostomia, andCrucibulumcan be classified as sensitive genera because they were found mainly in high oxygen concentrations (3.1–5.6 mL L−1); on the other hand,Cardiomya,Nuculana,Laevicardium,Chione,Truncatella, andDentaliumcan be classified as tolerant genera (1.0–5.6 mL L−1). Todos Santos Bay hosts a diverse malacological fauna (36 genera); our results show that the dominant genera were mainly related to high dissolved oxygen concentrations. Mollusks can be a useful tool in environmental monitoring programs related with oxygen depletion in coastal areas.

Basin scale dissolved oxygen interannual variability of the Mediterranean Sea: Analysis of long-term observations

2020 ◽  
Author(s):  
Apostolia-Maria Mavropoulou ◽  
Vassilios Vervatis ◽  
Sarantis Sofianos
Keyword(s):  
Dissolved Oxygen ◽  
Mediterranean Sea ◽  
Interannual Variability ◽  
Biological Effects ◽  
Marine Ecosystem ◽  
Mediterranean Ecosystem ◽  
Biogeochemical Processes ◽  
Basin Scale ◽  
The Mediterranean

&lt;p&gt;The Mediterranean Sea is characterized by a combination of long-term trends and climatic shifts known in the literature as &amp;#8220;transients&amp;#8221;, that impact the biogeochemical processes. &amp;#160;We focus on the dissolved oxygen (DO) concentration, as it is an essential oceanic parameter for the marine ecosystem functioning. Dissolved oxygen distribution in the ocean interior is controlled by air-sea interaction processes, ocean circulation patterns, and biological effects. Understanding the related mechanisms and the variability of the above processes requires systematic oceanographic measurements over long periods and at high spatial resolution. Taking advantage of the Mediterranean monitoring systems, we can examine the sensitive physical and biogeochemical processes in the Mediterranean ecosystem. In this study, we investigate and combine all available data of temperature, salinity and dissolved oxygen over the period 1960-2011 (taking into consideration the scarcity of the available DO observations during the last years). In order to receive a direct and accurate evaluation of the interannual changes in the Mediterranean Sea, we constructed a gridded dataset interpolated into 1/8&lt;sup&gt;&amp;#959;&lt;/sup&gt; x 1/8&lt;sup&gt;&amp;#959;&lt;/sup&gt; grid using Data-Interpolating Variational Analysis (DIVA). At the surface layer, the solubility-driven changes determine the dissolved oxygen concentration. In deeper layers, the interannual variability is more related to dynamical processes that may involve dense-water convection, biological consumption or mixing, rather than temperature trends. The observed changes in minimum/maximum oxygen zones are mostly related to abrupt shifts. The attribution of the observed variability involves complex physical and biogeochemical processes as well as anthropogenic activities and requires further analysis using modeling techniques and available operational tools.&lt;/p&gt;

Deep winter ventilation dynamics in the south Adriatic convection area from in situ glider observations and model output

2020 ◽  
Author(s):  
Riccardo Martellucci ◽  
Elena Mauri ◽  
Riccardo Gerin ◽  
Giulio Notarstefano ◽  
Gianpiero Cossarini
Keyword(s):  
Dissolved Oxygen ◽  
Water Column ◽  
Deep Water ◽  
Inverse Correlation ◽  
Model Output ◽  
The South ◽  
Basin Scale ◽  
Oxygen Minimum ◽  
Ocean Processes

&lt;p&gt;Dissolved oxygen dynamics in the south Adriatic pit have been investigated between 2015 and 2019 through in situ measurements and numerical models. This area is characterized by a frequent occurrence of deep water convection phenomena during winter time. Such convection phenomena represent the main source of dense waters for the Eastern Mediterranean basin modulating the oxygen advection in the deep water.&lt;/p&gt;&lt;p&gt;In situ glider measurements in the south Adriatic pit were performed by the OGS Glider Team since 2013. Typically, these missions covered the transect from Bari to Dubrovnik. The glider missions aim to investigate the water masses before, during and after the convection period. Pre-convection missions were carried out between the end of November and the beginning of December. Convection missions were performed between the end of January and the beginning of May.&lt;/p&gt;&lt;p&gt;Over 3000 pro&amp;#64257;les from the surface to 950m depth were collected and used to better understand the physical and biogeochemical highly variable processes in the southern Adriatic pit.&lt;/p&gt;&lt;p&gt;During the pre-convection period the water column is generally stratified; recorded data show an inverse correlation between dissolved oxygen and salinity. The pre-convection periods in 2015 and 2016 present the highest variability; the water column is mainly characterized by vertical profiles with a double oxygen minimum, which corresponds to the highest salinity concentrations. During the 2017 pre-convex mission the water column is characterized by a vertical salinity gradient, whereas dissolved oxygen profiles show a double dissolved oxygen maximum both on the surface and at 300-400 m depth. The 2018 pre-convex mission shows a thin surface layer of low salinity and high dissolved oxygen, which extends from the surface down to 50 m depth. A nucleus of high salinity and low oxygen is present close to the Italian coast at about 80-200m depth.&lt;/p&gt;&lt;p&gt;The 2016 convex mission revealed an inverse correlation of oxygen and salinity profiles and a double oxygen minimum with slightly different characteristics with respect to the previous pre convection period. During 2018 and 2019 the missions occurred during the convection phenomenon. The water column is well mixed from the surface down to 600 m depth, suggesting the occurrence of deep winter convection, also confirmed by the increase in oxygen and salinity concentrations along the water column.&lt;/p&gt;&lt;p&gt;In order to fully understand the process development in the south Adriatic Pit, which are the combinatorial result of coastal and open ocean processes, we integrated our observations with numerical model outputs provided by the Copernicus Marine Environment Monitoring Services. As the sea glider allows us to observe a high degree of variability from mesoscale to sub-mesoscale, the model output was used to evaluate mesoscale and sub basin scale phenomena.&lt;/p&gt;&lt;p&gt;Such an integration of different datasets provide information at different temporal and spatial scales of water mass dynamics, thus underlying the fundamental role of integrating multi-platform contributions to gain knowledge of the ocean processes.&lt;/p&gt;

scholarly journals Long-term changes in deep-water fish populations in the northeast Atlantic: a deeper reaching effect of fisheries?

2009 ◽  
Vol 276 (1664) ◽  
pp. 1965-1969 ◽  
Author(s):  
D.M. Bailey ◽  
M.A. Collins ◽  
J.D.M. Gordon ◽  
A.F. Zuur ◽  
I.G. Priede
Keyword(s):  
Deep Water ◽  
Marine Reserve ◽  
Population Data ◽  
Commercial Fishing ◽  
Natural Factors ◽  
Reserve Management ◽  
Major Impediment ◽  
Term Data ◽  
Unique Dataset

A severe scarcity of life history and population data for deep-water fishes is a major impediment to successful fisheries management. Long-term data for non-target species and those living deeper than the fishing grounds are particularly rare. We analysed a unique dataset of scientific trawls made from 1977 to 1989 and from 1997 to 2002, at depths from 800 to 4800 m. Over this time, overall fish abundance fell significantly at all depths from 800 to 2500 m, considerably deeper than the maximum depth of commercial fishing (approx. 1600 m). Changes in abundance were significantly larger in species whose ranges fell at least partly within fished depths and did not appear to be consistent with any natural factors such as changes in fluxes from the surface or the abundance of potential prey. If the observed decreases in abundance are due to fishing, then its effects now extend into the lower bathyal zone, resulting in declines in areas that have been previously thought to be unaffected. A possible mechanism is impacts on the shallow parts of the ranges of fish species, resulting in declines in abundance in the lower parts of their ranges. This unexpected phenomenon has important consequences for fisheries and marine reserve management, as this would indicate that the impacts of fisheries can be transmitted into deep offshore areas that are neither routinely monitored nor considered as part of the managed fishery areas.

Hydrogeological responses in tropical mountainous springs

2019 ◽  
Author(s):  
Ricardo Sánchez-Murillo
Keyword(s):  
Costa Rica ◽  
Isotope Composition ◽  
Central Valley ◽  
Distribution Functions ◽  
Geochemical Composition ◽  
Transit Times ◽  
Management Plans ◽  
Best Fit ◽  
Term Data

This study presents a hydrogeochemical analysis of spring responses (2013-2017) in the tropical mountainous region of the Central Valley of Costa Rica. The isotopic distribution of δ18O and δ2H in rainfall resulted in a highly significant meteoric water line: δ2H = 7.93×δ18O + 10.37 (r2=0.97). Rainfall isotope composition exhibited a strong dependent seasonality. The isotopic variation (δ18O) of two springs within the Barva aquifer was simulated using the FlowPC program to determine mean transit times (MTTs). Exponential-piston and dispersion distribution functions provided the best-fit to the observed isotopic composition at Flores and Sacramento springs, respectively. MTTs corresponded to 1.23±0.03 (Sacramento) and 1.42±0.04 (Flores) years. The greater MTT was represented by a homogeneous geochemical composition at Flores, whereas the smaller MTT at Sacramento is reflected in a more variable geochemical response. The results may be used to enhance modelling efforts in central Costa Rica, whereby scarcity of long-term data limits water resources management plans.

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