Ocean Intrusion Research Articles

The 1st method Parfait-Hounsinou used for the detection of saltwater intrusion in groundwater

This study presents the 1st method Parfait-Hounsinou, a method that makes it very easy to detect saltwater intrusion in groundwater. The method relies on the commonly sampled ion concentrations. This method involves several steps, namely: Chemical analyzes to determine the concentrations of majors ions and TDS in groundwater, production and study of the spatial distribution of chemical parameters in groundwater (TDS, Cl−…), delimitation of a probable area of saltwater intrusion in groundwater and the production and the study of spie chart where area of pie slices represents ions contents or group of ions content in the groundwater sample of the probable area of the saltwater intrusion in groundwater and radius length represents the Relative Content Index. The method is applied to groundwater data collected from the municipality of Abomey-Calavi in Benin. The method is also compared to other methods used for saltwater intrusion including the Scholler-Berkaloff and Stiff diagrams and the Revelle Index. Comparatively to Scholler-Berkaloff and Stiff diagrams, the 1st method Parfait –Hounsinou, at spie chart level, the area of pie slices make it easier to compare the major cations between them and the majors anions between them and the Relative Content Index of the chloride ion allows further confirmation of the saltwater intrusion and its extent.•There are frequent saltwater intrusion into groundwater which are important freshwater reserves for our planet.•Governments around the world should delineate the levels of ocean intrusion into groundwater using scientific methods such as this method and seek to limit this saltwater intrusion.•In this article we have proposed a simple and reliable method based on a series of irrefutable proofs of saltwater intrusion into groundwater.

An integrated assessment of water quality in a land reform settlement in northern Rio de Janeiro state, Brazil

The Zumbi dos Palmares land reform settlement lacks modern facilities for water and sewage treatment. Local farmers often use shallow wells as alternative source of water supply, because the water table is reasonably high in the region. This work presents a multivariate analysis assessment of physicochemical and bacteriological parameters and pesticide residues in water samples collected from these shallow wells. The physicochemical parameters analyzed were: conductivity, pH, DOC (dissolved organic carbon), nitrate, turbidity, and bacteriological analysis measuring total and fecal coliforms. The results show non-compliance with Brazilian legal standards in most samples where low pH values were found, characterizing the presence of acidic waters. Another example of non-compliance is the presence of total and fecal coliforms in for drinking water in most of the samples and, in some cases, very high values (2,400 CFU). Some wells showed high conductivity values, probably associated with a history of oceanic intrusion. Analyses determining the contamination by pesticides show the presence of ametrine, atrazine, methyl parathion, carbaryl and hexazinone. The concentration for these compounds ranged from 0.14 to 1.17 μg/L. Ordinance No 2914/2011 from the Brazilian Ministry of Health establishes the acceptable limits for atrazine and methyl parathion as 9 μg L−1 and 2 μg L−1. None of these exceeded the allowable Brazilian and European limits. However, for the other two pesticides, the European Legislation (Council Directive) recommends the maximum allowable concentration of 0.1 μg L−1 and, 0.5 μg L−1 for total pesticides. Our samples that were above the quantifiable limit of 50 ng L−1, were also above the European limit values. Our results therefore suggest that water gathered from shallow wells at the Zumbi dos Palmares settlement is not proper for consumption without proper disinfection treatments.

Can a future city enhance urban resilience and sustainability? A political ecology analysis of Eko Atlantic city, Nigeria

There is a consensus on the detrimental impacts of erosion and storm surges on the coast of Lagos, Nigeria but no agreement on whether the proposed Eko Atlantic City (EAC) adaptation project would lead to urban resilience and sustainability. This on-going modern city construction on the Atlantic Ocean is presented by its planners as a permanent solution to ocean intrusion and a model of adaptation, urban development, and economic growth, suggesting ‘all good things go together’ even in a changing climate. In this study, I explore the costs and risks of this future city to Greater Lagos in the broader context of resilience planning, capitalist urbanisation, disaster risk, and climate change. I draw on newspaper articles, in-depth interviews, and focus group discussions to unravel the relations of power, politics, and discourses that have served to legitimize and re-position the project as a positive-sum adaptation despite public concerns over maladaptation. Informed by urban political ecology, this paper reveals that while the EAC might hold promises of short-term storm mitigation on Victoria Island, in the long run it will re-shape the physical, economic, political, and socio-cultural ‘riskscape’ of Lagos with particular implications for marginalized communities and future generations. This developing country case study presents an opportunity for further discussion on adaptation planning, disaster risk reduction, and city transformation.

Predicting Deep Water Intrusions to Puget Sound, WA (USA), and the Seasonal Modulation of Dissolved Oxygen

Observations and predictions regarding oceanic intrusions at the entrance to Puget Sound, WA (USA), are presented. Four years of seabed observations at Admiralty Inlet show episodic periods high salinity, coincident with landward residual currents near the seabed. The observed residual currents are consistent with an estuarine exchange flow during minimal tidal mixing, coincident with neap currents and maximum diurnal inequalities. These subtidal intrusions can carry dense water into Puget Sound and, thereby, renew the bottom water that is trapped landward of the sill. The oxygen concentration levels of these intrusions are often low, though not hypoxic, and may influence the oxygen levels in Puget Sound. The water mass properties of these intrusions are influenced strongly by regional dynamics, because the entrance to Puget Sound is connected to the open ocean via the Strait of Juan de Fuca. Coastal upwelling and discharge from the Fraser River discharge control the exchange flow in the Strait of Juan de Fuca and thus control the availability of dense water at the entrance to Puget Sound. The net effect of the tidal and regional dynamics is for intrusions with low oxygen levels to prevail in the late summer months. To predict intrusions in future years, an empirical method is developed and validated for daily application. The prediction method is based on publicly available operational data products and does not require in situ observations. In verification, 98% of intrusion events with dissolved oxygen less than 4.0 mg/L are successfully identified in a hindcast prediction for the 4-year observational record.

Imaging and mapping water mass intrusions and internal waves

Oceanic intrusions and internal waves can each be imaged with echo sounders for dynamics and flux studies. We have recently investigated signatures of intrusions, while internal-wave imaging is long established, with Farmer as a leader. Intrusive flow at fronts with counteracting temperature and salinity gradients along isopycnals is one of many mixing phenomena in the ocean. Advection within the intrusions is accompanied by diapycnal mixing above and below that may provide buoyant forcing. Probable double-diffusive mixing processes can create sharp interfaces and microstructure that can provide intrusion-following echo patterns. This backscattering is weaker than that from shear-generated turbulence microstructure, but it can be spatially coherent along intrusions and thus robustly detectable. Mapping of intrusion features with a shipboard system using this method may enable targeted physical measurements within intrusions to advance our knowledge, and can provide 2D structure maps if augmenting dropped probes are used. Note that plankton backscattering may mask these signals in some environments and seasons. Internal-wave imaging by recording the geometry of passive tracers moved vertically by the wave motions can be accomplished with even modest narrowband systems in plankton-rich environments, as shown with Quantifying, Predicting, and Exploiting Uncertainty program data from the East China Sea.

Turbulent high-latitude oceanic intrusions—details of non-smooth apparent isopycnal transport West of Svalbard

Filament intrusions are observed in high-resolution temperature (T) measurements from a 100-m and several month-long mooring in the Fram Strait in around 400-m water depth at the continental slope West of Svalbard (Spitsbergen, Norway). In this dynamic environment, a wide variety of intrusive layers are observed with thicknesses between 5 and 80 m with warmer water between cooler waters above and below. The layers typically last from several hours up to 1 day, exceeding the local buoyancy period but not lasting as long as intrusive layers in the open ocean. The intrusions are a result of an intermingling of Arctic and North-Atlantic waters and generated in the basins interior and locally via internal wave steepening upon the sloping bottom. Freely propagating semidiurnal lunar internal tides cannot exist without background vorticity at these high latitudes. Strongly nonlinear turbulent bores are not observed at the tidal periodicity, but wave fronts occur at the sub-inertial frequency of dominant baroclinic instability. The fronts are in part associated with near-buoyancy frequency internal waves (breaking). The details of the moored T observations and their spectral content demonstrate the non-smooth, relatively turbulent development including convective overturning and shear-induced instabilities when intrusions disperse in presumably salinity-compensated isopycnal layers.

Deep chlorophyll maximum and plankton community response to oceanic bottom intrusions on the continental shelf in the South Brazilian Bight

The continental shelf of the South Brazilian Bight (Lat 23–28.5°S) is subject to bottom intrusions of the oceanic and nutrient-rich South Atlantic Central Waters (SACW) in summer, to compensate for the Ekman transport of surface waters offshore by northeasterly winds. In winter, shelf waters tend to overturn vertically due to tidal circulation and Ekman convergence of outer-shelf waters driven by southerly winds. From 9 November 2005 to 22 June 2006 the shelf off Santa Catarina State was surveyed to investigate hydrographic conditions and the seasonal dynamics of the plankton cross-shelf distribution and community structure. A strong wind-driven onshore bottom intrusion of the SACW with the formation of two independent deep chlorophyll maximum (DCM) layers on the shelf was clear. Chlorophyll concentrations ranged from 0.07 to 6.2mgm−3 and phytoplankton carbon biomass from 0.2 to 511µgCL−1, mostly as large centric diatoms and in spite of the numerical dominance of small pennates. The mid-shelf DCM was 12m thick between 38 and 50m (1–5% of irradiance) with mean chlorophyll concentrations up to 1.8mgm−3. The DCM on the outer shelf was formed between 60 and 70m depth (1–0.01% surface light) by small pennate diatoms and small phytoflagellates, with chlorophyll concentrations of 0.5–0.7mgm−3. Both DCMs were maintained independently from January to April 2006, and dispersed in June due to water column turnover during cold seasons. In the mid-shelf, the DCM was geographically extended towards the inner shelf and became thicker compared to pre- and post-intrusion periods. The freshwater species Aulacoseira granulata and large centric diatoms including the invasive Coscinodiscus wailesii were frequent along the shelf throughout the sampling period. Oncaea waldemari, Ctenocalanus vanus and Oithona plumifera usually dominated the zooplankton, which ranged from 23 to 7970 individualsm−3. Abundances were always higher on the inner shelf regardless of the season of the year. Abundance on the mid-shelf peaked following the onset of the intrusion of the nutrient-rich oceanic SACW in the lower euphotic zone and the enhancement of the DCM. A 6-step circulation model of diatoms coupled with shelf hydrodynamics is proposed as the main mechanism of retention of diatoms in the shelf system. The model suggests that diatoms resuspended in the nearshore are transported offshore by Ekman forces toward oligotrophic waters, where they sink faster due to poor nutrient conditions. Sinking cells find better nutrient conditions in the pycnocline/nutricline layers, become shade-adapted and increase their buoyancy, contributing to the formation of the DCM. Resting cells sinking out of the euphotic zone reach near-bottom layers or the sediments, from where they are carried back onshore by oceanic intrusions of the SACW. We suggest how this hydrodynamic circulation pattern of diatoms may take place in other subtropical shelf systems dominated by western boundary currents.

Influence of a vinasse-distributing lake on water quality of the groundwater

A vinhaça é um resíduo, proveniente do processo de destilação do álcool, rico em matéria orgânica e nutrientes, que, se aplicado em doses excessivas, pode desequilibrar o complexo sortivo do solo e consequentemente contaminar o lençol freático. O objetivo deste estudo foi avaliar a influência de uma lagoa de distribuição de vinhaça na qualidade da água freática em uma área cultivada com cana-de-açúcar localizada no estado de Pernambuco, Brasil. Foram instalados dez poços de monitoramento distribuídos em três transectos paralelos localizados em uma área circunvizinha à lagoa de distribuição de vinhaça. Ao longo do experimento, avaliou-se a qualidade da água subterrânea no nível freático, assim como da água do rio Ipojuca para verificar-se possível intrusão salina advinda do oceano. Os parâmetros analisados foram: CE, SDT, pH, DQO, DBO, NO3-, NO2-, K+, Ca2+, Mg2+, Na+, Cl- e HCO3-. Concluiu-se que o armazenamento da vinhaça na lagoa de distribuição alterou os valores de CE, DBO, DQO e as concentrações de SDT, Cl-, K+, Ca2+ e Mg2+ da água do lençol freático.

Satellite-Derived Photic Depth on the Great Barrier Reef: Spatio-Temporal Patterns of Water Clarity

Detecting changes to the transparency of the water column is critical for understanding the responses of marine organisms, such as corals, to light availability. Long-term patterns in water transparency determine geographical and depth distributions, while acute reductions cause short-term stress, potentially mortality and may increase the organisms’ vulnerability to other environmental stressors. Here, we investigated the optimal, operational algorithm for light attenuation through the water column across the scale of the Great Barrier Reef (GBR), Australia. We implemented and tested a quasi-analytical algorithm to determine the photic depth in GBR waters and matched regional Secchi depth (ZSD) data to MODIS-Aqua (2002–2010) and SeaWiFS (1997–2010) satellite data. The results of the in situ ZSD/satellite data matchup showed a simple bias offset between the in situ and satellite retrievals. Using a Type II linear regression of log-transformed satellite and in situ data, we estimated ZSD and implemented the validated ZSD algorithm to generate a decadal satellite time series (2002–2012) for the GBR. Water clarity varied significantly in space and time. Seasonal effects were distinct, with lower values during the austral summer, most likely due to river runoff and increased vertical mixing, and a decline in water clarity between 2008–2012, reflecting a prevailing La Niña weather pattern. The decline in water clarity was most pronounced in the inshore area, where a significant decrease in mean inner shelf ZSD of 2.1 m (from 8.3 m to 6.2 m) occurred over the decade. Empirical Orthogonal Function Analysis determined the dominance of Mode 1 (51.3%), with the greatest variation in water clarity along the mid-shelf, reflecting the strong influence of oceanic intrusions on the spatio-temporal patterns of water clarity. The newly developed photic depth product has many potential applications for the GBR from water quality monitoring to analyses of ecosystem responses to changes in water clarity.

The Intrusion Depth of Density Currents Flowing into Stratified Water Bodies

AbstractTheory and laboratory experiments are presented describing the depth at which a density current intrudes into a linearly stratified water column, as a function of the entrainment ratio E, the buoyancy flux in the dense current B, and the magnitude of the stratification N. The main result is that Z ∼ E−1/3B1/3/N. It is shown that the depth of the intrusion scales as Z ∼ (3 ± 1)B1/3/N for laboratory experiments, and as for oceanic density currents. The velocity of a large-scale density current is controlled by a geostrophic balance defined as Ugeo = 0.25g′s/f, where s is the slope and f is the Coriolis parameter. The geostrophic buoyancy flux is then defined by Bgeo = g′Ugeoh, with g′ the reduced gravity and h the thickness of the current. The scaling herein implies that the depth of an oceanic intrusion is relatively insensitive to changes in source water properties but is very sensitive to changes in the stratification of the water column, consistent with the previous scaling of Price and Baringer. For example, if the buoyancy flux of a dense current were to double while the stratification remained constant, then there would only be a 25% increase in the intrusion depth, whereas doubling the stratification would result in a 50% decrease of the intrusion depth.

Life in the Hypoxic and Anoxic Zones: Metabolism and Proximate Composition of Caribbean Troglobitic Crustaceans with Observations on the Water Chemistry of Two Anchialine Caves

The interaction of freshwater, seawater, and limestone creates the unique environment of the anchialine cave. Anchialine cave systems are characterized by the presence of several strong density interfaces that isolate the cave system into components: regions of freshwater at the surface, a hydrogen sulfide layer, and a warm oceanic intrusion that is devoid of oxygen. These unusual physical parameters provide a challenging environment for the organisms that reside there. Within the hypoxic and anoxic regions of the cave system, a unique community of macrofauna has adapted to cope with constant low oxygen conditions and a depauperate food supply. We examined respiration rates and proximate compositions of individuals representing seven orders of troglobitic crustaceans collected from two Bahamian anchialine caves. In addition, we examined the physical conditions of both caves to determine ambient oxygen concentrations. Mass-specific respiration rates of the troglobites were more than an order of magnitude lower than those of comparably sized pelagic crustaceans. When compared to organisms residing in oxygen minimum zones, respiration rates of the troglobites were similar, or in some cases, lower. Enzymes of the troglobites were anaerobically poised with lactate dehydrogenase activities exceeding those of citrate synthase in all species. Malate dehydrogenase activities were greater than lactate dehydrogenase activities, indicating further evolutionary adaptations to an anaerobic environment.

Use of phytoplankton species indicators to track the origin of phytoplankton blooms in Willapa Bay, Washington

We focus on the question of whether high phytoplankton production events observed in a United States Pacific Northwest estuary consist of estuarine species blooms fueled by oceanic nutrient input or reflect offshore oceanic blooms that have advected into the estuary. Our approach is to use certain phytoplankton species as indicators associated with water mass origin, either estuarine or oceanic, to help resolve this question in Willapa Bay, Washington. We used species analysis and primary production data from 10 selected dates in May–September of 1998 and 1999, representing periods of high through low productivity. Out of 108 phytoplankton species identified from Willapa Bay, nine were selected and tested as indicators of oceanic species, six as estuarine, and two as surf zone. Our test results demonstrated the oceanic and estuarine species to be satifactory indicators of source waters. The prevalence of these species indicators in our samples revealed that the highest primary production and the appearance ofPseudo-nitzschia spp. were associated with oceanic intrusions of phytoplankton biomass into Willapa Bay. While the largest blooms were oceanic in origin, numerous medium-sized production events were from either oceanic, surf zone, or estuarine sources, indicating a complex situation.

127 Climate Variability and Phytoplankton Production in PNW Coast Estuaries

The west coast of North America receives strong forcing from climate modes such as El Niño‐Southern Oscillation and the Pacific Decadal Oscillation. Estuaries are poised at a sensitive interface because estuarine biota and habitat will be affected by variability in properties and processes associated with the ocean, the watershed, and the local weather. Observations from the Washington coast and Willapa Bay illustrate these three arenas of influence. Variation in ocean upwelling and ocean thermocline depth associated with the 1997–98 El Niño versus the 1999 La Niña affected temperature and nutrient availability in Willapa Bay. Variation in river flow associated with the 2000–01 drought affected estuarine circulation and residence time. And, variation in prevailing wind direction and/or cloudiness was highly correlated with phytoplankton biomass. This situation is responsible for the complexity of understanding climate impacts on estuarine systems. In order to help evaluate which mechanisms, remote oceanic processes or local watershed/estuarine characteristics, most affected Willapa Bay's phytoplankton production, several phytoplankton species were used as indicators of water mass origin and compared with primary productivity data to assess whether phytoplankton blooms were dominated by endemic or imported species. Our analysis resolved that the highest primary production (and the appearance of Pseudo‐nitzschia spp.) was associated with oceanic intrusions of phytoplankton biomass into Willapa Bay. This result underscores the dominant role that variation in ocean and climate play in controlling Pacific Northwest estuarine production. However, while the largest blooms were oceanic in origin, numerous medium‐sized production events were from either oceanic or estuarine sources, indicating a complex picture.

The effect of vertical temperature and salinity gradients on double-diffusive interleaving

Theoretical and experimental work has been carried out to understand the almost horizontal oceanic intrusions that occur at density-compensating fronts, and in particular how the layer separation and slope of the intrusions depend on the vertical concentration gradients of the two diffusing components. In the experiments salt and sugar were used as analogues of ocean temperature and salinity, respectively. Matching stable linear density distributions were set up on the two sides of a vertical barrier, with an excess of sugar on one side and salt on the other. When the barrier was removed interleaving motions formed spontaneously. A similar experiment was performed by Ruddick and Turner (1979, Deep-Sea Research, 26, 903–913), but they assumed that the ensuing motion depended only on the total vertical density gradient and not on the relative contributions to this from the two components. In oceanic terms, the layer depth was found to be approximately independent of salinity gradient S z at constant total density gradient, except when S z was very small. For zero temperature gradient, T z = 0, h varied as S z to the power −0.7 ± 0.2. In all experiments the slope of intrusions was such that hot, salty water sank. A theoretical analysis is given of the dependence of the sense of layer slope on the ratio of the two vertical gradients, and suggestions are made for further experiments. Preliminary results of an optical investigation of the detailed structure of the layers are reported.

Oceanic intrusions: some limitations of the Ruddick and Turner (1979) mechanism

The Ruddick and Turner (1979, Deep-Sea Research, 26, 903–913) mechanism for double-diffusive interleaving at lateral thermoclinic fronts is examined on the S-0 diagram, revealing that for the oceanographically relevant pair of properties (heat-salt rather than salt-sugar), an alternating series of diffusive and finger interfaces does not form, but rather each interface is a fingering interface. Since active oceanic intrusions do exhibit regions of diffusive stratification between the salt fingering regions, it is concluded that they must have their origins in ‘smooth’ thermoclinic fronts, that is, fronts that are significantly wider than the height of an intrusion. This has direct implications for the way in which the diapycnal fluxes associated with double-diffusive interleaving are parameterized in ocean models.

Dominance, frequency and species richness patterns in occurrences of calanoid copepods in Moreton Bay, Queensland

Of 66 calanoid species recorded in Moreton Bay, the 11 which were most frequent (> 50%) were also amongst the most dominant. Greatest total number of species (56) and greatest species richness (per sample) was found in the oceanic-influenced eastern Bay regions, a decrease toward western Bay estuarine-influenced regions being correlated with a salinity (and temperature) gradient. Maximum species richness in all regions occurred in autumn, seasonal amplitude of change being greatest in the eastern Bay. These data are largely explained by increasing environmental stability in .eastern Bay waters, especially with autumnal oceanic intrusion.