Non-conservative Behavior Research Articles

Major ion concentrations and the inorganic carbon chemistry of the Humber rivers

Measurements of major ion concentrations in the main rivers draining into the Humber estuary show two dominant spatial patterns, related to anthropogenic sources from catchments draining urban/industrial areas and background weathering sources from the rural catchments. Most major ions exhibit dilution effects with flow, with higher concentrations at baseflow compared with stormflow conditions. This suggests a predominance of point (effluent) and/or groundwater (weathering) sources of major ions. An exception is NO 3 −, which exhibits higher concentrations under stormflow conditions in certain rural catchments, suggesting diffuse (catchment) sources, possibly derived from agricultural runoff. Inter-ion relationships were used for endmember mixing analysis to identify whether or not components were exhibiting conservative behaviour within the river. The dominant relationship between major ions is a straight line between baseflow and stormflow endmembers, indicative of conservative mixing processes. The chemical mixing patterns appear to be controlled by hydrology and the existence of distinct inter-ion ratios between baseflow and stormflow endmembers. In terms of the inorganic carbon system, HCO 3 − is the major component of dissolved inorganic carbon (DIC), with dissolved CO 2 (H 2CO 3 0 and CO 2(aq)) representing approximately 10% and CO 3 2− less than 1% of DIC. All river waters are oversaturated with respect to CO 2, with excess partial pressures of carbon dioxide ( E pCO 2) typically between 5 and 20 times atmospheric partial pressure. The elevated levels of E pCO 2 in the river water are sufficient to decouple the relationship between pH and alkalinity. E pCO 2 is related to microbial production of CO 2 by breakdown of organic carbon and the availability of nutrients (particularly NO 3 −) and is generally highest in the rivers draining urban and industrial catchments, together with the Derwent which receives high rates of agricultural runoff. E pCO 2 and pH do not exhibit simple mixing relationships and both determinands are inherently non-conservative in behaviour. These results provide important background information on which to base more detailed process studies and modelling work. The results imply that most of the major ions can be modelled using simple mixing relationships. In contrast the non-conservative behaviour of E pCO 2 and pH may require more thorough process evaluation for modelling the in-stream carbon system.

Distributions of dissolved manganese and fluorescent dissolved organic matter in the Columbia River estuary and plume as determined by in situ measurement

We deployed an instrument package consisting of a SeaBird 911 plus CTD, SeaTech 25-cm transmissometer, Chelsea AquaTracka fluorometer/nephelometer, Seapoint turbidity meter and ZAPS UV fluorometer/chemical sensor during a series of tows and lowerings within the Columbia River plume and estuary in 1994 and 1995. Simultaneous in situ measurements of Chl a, light attenuation, light scattering, and fluorescent dissolved organic matter (FDOM) or dissolved Mn collected along with CTD information provided new insight into the effects of mixing and non-conservative processes on riverine input to the coastal ocean. Inter-relationships among these parameters proved to be effective at delineating three coastal water masses: Columbia River Plume Water (CRPW), Shelf Deep Water (SDW), and Shelf Bottom Water (SBW). CRPW had variable amounts of FDOM, dissolved Mn, and Chl a as the plume mixed with coastal water. SBW was characterized by high concentrations of Chl a and low concentrations of dissolved Mn, suggesting a surface or near-surface source. The properties of SDW were intermediate between humic-rich plume water and turbid bottom water. FDOM displayed a quasi-linear and inverse relationship with salinity inside the estuary and nearshore coastal plume which supports previous work relating this parameter to the humic-rich terrestrial component of dissolved organic matter (DOM). There was, however, considerable evidence of lower FDOM levels within the estuarine turbidity maximum (ETM) and near the seaward boundary of the plume. There were also elevated levels of FDOM near the bottom at some locations on the shelf, suggesting that there may be a significant benthic flux of this material. Thus FDOM appears to be more reactive than previously thought when looked at in detail. Dissolved Mn also displayed non-conservative behavior in the estuary and across the plume showing significant input into surface waters. The sharpest Mn gradient on the shelf occurred near the seaward edge of the plume in an area of relatively high turbidity and Chl a, and relatively low FDOM. These distributions are consistent with the presence of a chemical front near the plume boundary where Mn-oxides are reduced during the oxidation of humic ligands. This process would release dissolved Mn and promote productivity in the turbid zone associated with the leading edge of the plume jet. This study demonstrates that chemical sensors can provide highly resolved, detailed information on trace substance distribution and variability in marine environments.

Exchange of Polychlorinated Biphenyls between Sediment and Water in the Hudson River Estuary

Sediment-bound polychlorinated biphenyls (PCBs) measured at several sites in the lower Hudson River Estuary are above equilibrium with the overlying water, providing a thermodynamic driving force for exchange from sediment to water. The fluxes of PCB congeners are estimated for a number potential processes: diffusive release of dissolved and colloidal PCBs from the bed, resuspension and subsequent desorption from resuspended particles, and sediment accumulation and burial. All processes are potentially significant, at least for some congeners. The sediment exchange fluxes of PCB solutes for five sites between Governors Island and Haverstraw Bay are estimated to be 20–860 μm m−2 d−1, which is between 2 and 100 times more than the flux of dissolved PCBs coming down the river at Haverstraw Bay. Much of the exchange from sediment to water may be balanced by burial of sorbed PCBs by sediment accumulation. Advection down the river and sediment exchange dominate other potential sources of PCBs to the lower estuary under current loading conditions. The magnitude of the calculated fluxes is consistent with the nonconservative behavior of PCBs in the same region but is higher than earlier modeling estimates that employed different assumptions.

FLOW SEPARATION IN UNDISTURBED SOILS USING MULTIPLE ANIONIC TRACERS. PART 1. ANALYTICAL METHODS AND UNSTEADY RAINFALL AND RETURN FLOW EXPERIMENTS

Tracers provide one of the few ways of obtaining realistic information on the flows of water and solutes in undisturbed structured soils. Three fluorinated organic acids [pentafluorobenzoic acid, 2,6-diflurobenzoic acid and o-(trifluoromethyl) benzoic acid] and bromide were tested as anionic tracers in situations where the separation of different flow components is of interest. The fluorobenzoates were relatively conservative (approximately 90% for loam soil) although, in some instances, co-elution or complexation may lead to apparently non-conservative behaviour. Tracer mixtures applied to soils, were separated and quantified by high-performance liquid chromatography. The relative mobilities of the tracers were studied during unidirectional steady flow in large undisturbed soil columns brought back to the laboratory. The breakthrough curves showed highly dispersive behaviour, with very early breakthrough of solute and a long tail. Contributions to the column outflow of different simultaneous applications of rainfall and return flow, labelled with different tracers, were separated using multicomponent mixing equations. The results show the importance of preferential flow and relatively immobile storage in the transport process.

Nutrient elements in large Chinese estuaries

Based on comprehensive observations since 1983, this study summarizes major features of nutrient elements (nitrogen, phosphorus and silicon) in large Chinese river/estuary systems. Elevated nutrient element levels were observed in Chinese rivers, when compared to large and less disturbed aquatic systems (e.g. the Amazon, Zaire and Orinoco). Data from this study are similar to those obtained from the polluted and/or eutrophic rivers in Europe and North America (e.g. the Rho´ne and Loire). Nutrient elements may have either conservative or active distributions, or both, in the mixing zone, depending on the element and the estuary. For example, non-conservative behaviors were observed in the upper estuary, where nutrient elements may be remobilized due to the strong desorption and variations of the fresh water end-member, but conservative distributions were found afterwards in the lower estuary. Outside the riverine effluent plumes, nutrient elements may be depleted in surface waters relative to elevated bioproduction, whereas the regeneration with respect to decomposition of organic material and/or nitrification/denitrification offshore, may sustain high levels of nutrient elements in near-bottom waters. Laboratory experiment data generally compares well with field observations. The high fluxes and area] yields of nutrient elements from large Chinese rivers, indicate the extensive use of chemical fertilizers and domestic waste drainage over watersheds in China.

AN INTEGRATED APPROACH TO MODELLING HYDROLOGY AND WATER QUALITY IN GLACIERIZED CATCHMENTS

The results are summarized of an integrated investigation of glacier geometry, ablation patterns, water balance, meltwater routing, hydrochemistry and suspended sediment yield. The ultimate objective is to evaluate the assumptions of lumped, two-component mixing models as descriptors of glacier hydrology, and to develop a semi-distributed physically based model as an alternative. The results of the study demonstrate that a reconstruction of probable subglacial drainage alignments can be achieved through a combination of terrain modelling based on estimated potential surface and dye tracing experiments. Recession curve analysis, evidence of the seasonal instability of the englacial and subglacial electrical conductivities assumed in a mixing model, evidence of the non-conservative behaviour of water chemistry in the presence of suspended sediment, and evidence of the seasonal evolution of the subglacial drainage system based on dye tracing all indicate that an alternative to a lumped, static model of the hydrology is necessary. The alternative presented in this paper is based on the combination of an energy balance model for surface melt which operates on an hourly time step and accounts for the changing spatial distribution of melt through the day as shading patterns change, and routing procedures that transfer surface melt to moulins on the basis of glacier surface gradients, then route water through reconstructed conduit systems using a hydraulic sewer-flow routing procedure.

Source and distribution of dissolved radium in the Bega River estuary, Southeastern Australia

Measurements of the activities of the four naturally occurring radium isotopes in the surface water and porewater of an estuary have yielded information on the release of radium from sediments and on the extent of surface water-porewater interaction in the estuary. Under low-flow conditions, the non-conservative behaviour of dissolved radium in the estuary is almost entirely due to the flux of radium from estuarine bed sediments. Radium accumulates in bottom sediment porewater, and is then mixed with estuarine surface water, probably as a result of tidal action. It is shown experimentally that the enrichment of the short-lived isotopes ( 224Ra and 223Ra) relative to 226Ra in estuarine porewater can be explained by the repeated leaching of radium from bottom sediments by saline water, and the rapid regeneration of the short-lived isotope activity from their sediment-bound parent nuclides. The leaching of radium from bottom sediments is apparently occurring on a time scale which is long (weeks-months) compared with the 224Ra and 223Ra half-lives, indicating that the amount of ion-exchangeable radium adsorbed to the sediments is large compared with the amount dissolved in porewater. By applying a simple 2-D steady-state multi-box model, 224Ra and 223Ra surface water and porewater concentrations have been used to estimate the daily flux of porewater crossing the sediment-water interface in the Bega estuary. This flux is found to be about 15% of the estuary volume.

Flocculation of dissolved Pb, Cu, Zn and Mn during estuarine mixing of river water with the Caspian Sea

This is the first study of the flocculation of dissolved Pb, Cu, Zn and Mn during mixing of river water with the largest lake in the world (the Caspian Sea). Flocculation of dissolved metals was investigated on a series of mixtures with salinities ranging from 3.2 to 7.4‰. The flocculation rates {Cu (74%) > Pb (61%) > Mn (58%) > Zn (34%)} are indicative of the non-conservative behavior of metals during estuarine mixing. Statistical analysis indicates that the flocculation of Pb and Mn is governed by salinity. The flocculation rates reveal that the overall metal pollution loads may decline by about 57% during estuarine mixing.

Metal Behavior during Surface-Groundwater Interaction, Silver Bow Creek, Montana

This work documents the geochemical character of the hyporheic zone in the bed sediment of a small creek underlain by acidic, metal-rich groundwater. Use of a unique in situ method of sampling the solid-phase chemistry (elemental composition of coatings on installed ceramic beads) combined with water chemistry data allowed us to build a more complete picture of the geochemistry during surface-groundwater interaction. A mixing ratio of 96 :4 surface water (pH ≃ 7.9-9.1, [Fe] ≃ 0.2 mg/L) to contaminated groundwater (pH ≃ 4.2 - 4.9, [Fe] ≃ 400 mg/L) can explain the composition of the ∼1 m thick hyporheic zone. Accumulations of metals on the ceramic beads support nonconservative behavior predicted by mixing ratios and show partitioning between the solid and aqueous phases. The behavior of metal contaminants in this system is discussed.

Uranium geochemistry on the Amazon shelf: Chemical phase partitioning and cycling across a salinity gradient

The size distribution of U was examined in surface waters of the Amazon shelf. Water samples were collected during a low discharge river stage across a broad salinity gradient (0.3–35.4%) and fractionated by planar filtration and tangential-flow ultrafiltration into (1) solution (Us, <10,000 MW; ∼1–10 nm), (2) colloidal (Uc 10,000 MW-0.4 μm), (3) dissolved (Ud, <0.4 μm), and (4) particulate (Up, >0.4 μm) phases.Concentrations of colloidal U comprise up to 92% of the dissolved U fraction at the river mouth and attain highest values (∼0.45 μg/L) in the productive, biogenic region of the Amazon shelf (salinities above ∼20%). Ud and Uc distributions are highly nonconservative relative to ideal dilution of river water and seawater, indicating extensive removal at salinities below ∼10%. The distribution of Us also shows some nonconservative behavior, yet removal, if any, is minimal. Saltwater-induced precipitation and aggregation of riverine colloidal material is most likely the dominant mechanism of U removal in the low salinity, terrigenous region of the Amazon shelf. There is evidence of a substantial colloidal U input (∼245% of the riverine Uc flux into surface waters above 5%. Such Uc enrichment most likely is the result of colloidal U-rich porewater diffusion/advection from the seabed and fluid muds or shelf-wide particle-colloid disaggregation. Removal of solution and dissolved phase U via a colloidal intermediate and Uc aggregation was examined in terms of coagulation theory. The highly reactive nature of all U phases on the Amazon shelf suggests that remobilization and fractionation of U may also occur in other river-influenced coastal environments.

Uranium geochemistry on the Amazon shelf: Chemical phase partitioning and cycling across a salinity gradient

The size distribution of U was examined in surface waters of the Amazon shelf. Water samples were collected during a low discharge river stage across a broad salinity gradient (0.3–35.4%) and fractionated by planar filtration and tangential-flow ultrafiltration into (1) solution (U s , <10,000 MW; ∼1–10 nm), (2) colloidal (U c 10,000 MW-0.4 μm), (3) dissolved (U d , <0.4 μm), and (4) particulate (U p , >0.4 μm) phases. Concentrations of colloidal U comprise up to 92% of the dissolved U fraction at the river mouth and attain highest values (∼0.45 μg/L) in the productive, biogenic region of the Amazon shelf (salinities above ∼20%). U d and U c distributions are highly nonconservative relative to ideal dilution of river water and seawater, indicating extensive removal at salinities below ∼10%. The distribution of U s also shows some nonconservative behavior, yet removal, if any, is minimal. Saltwater-induced precipitation and aggregation of riverine colloidal material is most likely the dominant mechanism of U removal in the low salinity, terrigenous region of the Amazon shelf. There is evidence of a substantial colloidal U input (∼245% of the riverine U c flux into surface waters above 5%. Such U c enrichment most likely is the result of colloidal U-rich porewater diffusion/advection from the seabed and fluid muds or shelf-wide particle-colloid disaggregation. Removal of solution and dissolved phase U via a colloidal intermediate and U c aggregation was examined in terms of coagulation theory. The highly reactive nature of all U phases on the Amazon shelf suggests that remobilization and fractionation of U may also occur in other river-influenced coastal environments.

Mineral Precipitation and Trace Oxyanion Behavior during Evaporation of Saline Waters.

Evaporation basins used for the disposal of agricultural drainage waters in central California contain elevated trace element levels that pose hazards to groundwater quality and wildlife visiting the ponds. A study was conducted to evaluate the solution dynamics of mineral-forming elements and trace oxyanions (U, Mo, and V) during evaporation of saline waters whose chemical compositions evolve according to two distinct chemical divides, and to characterize the evaporite minerals formed from the complete evaporation of these waters. The alkali and alkaline earth metals exhibited nonconservative behavior, forming evaporite minerals such as bloedite, calcite, aragonite, gypsum, halite, thenardite, and trona. Molybdenum behaved nonconservatively, while V exhibited conservative behavior that did not differ whether V was initially added as V(IV) or V(V). Uranium displayed conservative behavior under conditions of low U concentrations and high alkalinities. Nonconservative behavior was observed for U, however, under higher U concentrations and low alkalinities. We conclude that V and U in waters with alkalinities >10 mmolc L-1 will not accumulate in evaporation pond minerals. In ponds with low alkalinity, U will partition to a solid mineral phase.

Behaviour of uranium during mixing in the delaware and chesapeake estuaries

Unequivocal evidence is presented for the removal of uranium in two major estuarine systems of the north-eastern United States: the Delaware and Chesapeake Bays. In both the estuaries, during all seasons but mostly in summer, dissolved uranium shows distinctly non-conservative behaviour at salinities ⪯ 5. At salinities above 5, there are no deviations from the ideal dilution line. In these two estuaries as much as 22% of dissolved uranium is removed at low salinities, around salinity 2. This pronounced removal of uranium observed at low salinities has been investigated in terms of other chemical properties measured in the Delaware Estuary. In the zone of uranium removal, dissolved oxygen is significantly depleted and pH goes through a minimum down to 6·8. In the same low salinity regime, total alkalinity shows negative deviation from the linear dilution line and phosphate is removed. Humic acids, dissolved iron and manganese are also rapidly removed during estuarine mixing in this low salinity region. Thus, it appears that removal of uranium is most likely related to those properties of alkalinity and acid-base system of the upper estuary that may destabilize the uranium-carbonate complex. Under these conditions, uranium may associate strongly with phosphates or humic substances and be removed onto particulate phases and deposited within upper estuarine sediments.

Phosphorus, Silicon, and Some Trace Contaminants in the Ganges Estuary

Dissolved silica and phosphorous show a highly nonconservative behavior in the Ganges Estuary. In addition, phosphorous also shows seasonal variations, with winter levels higher than the levels in the monsoon. Mineral composition inducates enrichment of coarse quartz grains due to selective removal of finer clays in the estuary, either due to flocculation or due to dredging effects of the Port of Calcutta. Particulate P and Si show strong opposite trends, possibly indicating the presence of P in predominently nondetrial fractions in the sediments. Certain trace contaminants, such as Fe, Mn, Cu, Pb and Zn, show seasonal variability as well as enrichment in suspended particulate material relative to bed sediments. Levels of all these contaminents are still well below those reported for rivers such as the Rhine and other highly man-influenced systems.

Complex Formation and the Chemistry of Selected Trace Elements in Estuaries

The estuarine chemistry of several metals and anion-forming elements is compared. Differences in the estuarine behaviour of nickel and copper appear to be caused by differences in the stability and reaction rates of organic complexes of these metals. Nickel occurs partially in very stable organic complexes that have an estuarine pathway different from the electrochemically labile (weakly complexed) fraction as the two fractions are not in equilibrium on the estuarine time scale; whereas, the complexes of copper in the estuary are in equilibrium with each other. Titanium occurs largely in a nonlabile form and is subject to removal at low salinities; it is released again at intermediate salinities (25 practical salinity units) and behaves conservatively at higher salinities. Comparison of several anion-forming elements reveals differences; uranium, antimony, and molybdenum show nonconservative behaviour and selenium shows conservative behavior. Voltammetric measurements of the chemical speciation of molybdenum in estuarine waters indicated the unexpected presence of a nonlabile species for this element.

Distribution of trace metals in suspended matter of the Scheldt estuary

The distribution of trace metals (Ni, Co, Cr, Zn, Cu, Cd, Pb, Mn) in suspended matter and sediments collected in the Scheldt estuary is investigated as a function of grain size, Al and particulate organic carbon (POC) content. Normalized trace-metal content with respect to Al allows characterization of the origin of the solids and evaluation of their degree of contamination. The suspended matter exhibits strong changes in chemical composition in the tidal zone, indicating mixing of heavily contaminated particles of continental origin with less contaminated marine particles. Flood events strongly influence the trace-metal content of the suspended matter by inducing resuspension processes and intensive transfer of solid material from the river system to the sea. The evolution of the composition of the particles in the mixing zone of the estuary indicates that the trace elements do not behave conservatively and that they are also affected by the changing physico-chemical conditions (salinity, pH, redox) observed in the Scheldt. In order to gain a better understanding of the origin and behaviour of the particulate trace elements in the estuary, a mixing model of suspended matter based on the conservative property of Al is proposed, which enables quantification of the proportion of marine vs. continental solids and to detect non-conservative behaviour of trace elements.

Particle-solution behaviour of plutonium in an estuarine environment, Esk Estuary, UK

The particle-solution ( K d ) relationships of Pu(III,IV) in the Esk Estuary are investigated, using new experimental data together with a synthesis of our earlier work. Adsorption of 236Pu(IV) by a suspension of intertidal mud (40 mg L −1) from the Esk Estuary was determined after 1 h, as a function of salinity and pH, in a series of controlled laboratory experiments. Desorption of 239, 240Pu(III,IV) from this environmentally contaminated sediment was determined concurrently. The short term (i.e., within a tidal cycle) non-conservative behaviour of Pu(III,IV) in both the laboratory experiments and the estuary appears to be dominated by a rapid, reversible surface complexation reaction, although only a small fraction (<5%) of the 239,240Pu(III,IV) activity of the environmentally contaminated sediment is able to participate in the reaction. The existence of this exchangeable or labile fraction can explain the apparent dependence of Pu(III,IV) K d on sediment concentration. Thus, a single K d value is able to describe both the observed adsorption and desorption behaviour and the effect of sediment concentration, when desorption is expressed with respect to the labile 239,240Pu(III,IV) fraction. For example, in R. Esk water, the adsorption of 236Pu(III,IV) and the desorption of 236,240Pu(III,IV), over a two order of magnitude concentration range of unwashed Esk Estuary sediment, can be accounted for by a single K d of ∼3 × 10 3 L kg −1. The K d for the labile Pu(III,IV) fraction varies mainly as a function of salinity. pH is not an important factor over the pH range 4–9, although H + ion exchange does occur, probably through a similar surface complexation reaction. The kinetic and equilibrium characteristics of the Pu (III,IV) sorption behaviour conform to the pattern observed by Jannasch et al. (1988) and other workers for a range of trace elements.

A Bilinear Variational Principle Governing Longitudinal Vibration of Rods With Frequency-Dependent Material Damping

The equations governing the longitudinal vibration of rods with frequency-dependent material damping are developed as the Euler equations of a bilinear variational principle. Frequency-dependent material damping and modulus are accommodated through the introduction of an augmenting thermodynamic field that interacts with the mechanical displacement field. These two primary dependent fields are supplemented with two corresponding adjoint fields for the purpose of addressing nonconservative system behavior. The variational function is nearly symmetric in the primary and adjoint variables, a formulation which may be particularly useful in computational simulation of system behavior using finite elements. The augmenting thermodynamic field is found to be effectively internal—no boundary conditions involve it alone.

Supply and Exchange of Water and Nutrients in the Grådyb Tidal Area, Denmark

Supply of nutrients to estuaries and coastal waters is an increasing problem because it can contribute to eutrophication of these environments. In the worst cases it may lead to oxygen depletion of the bottom water. For a micro-tidal area in western Denmark a water exchange model based on conservation of salt and water has been constructed. It is demonstrated how this model can be used for predicting the concentration of total N in the tidal inlet as a function of supplied quantities. The significance of the different nutrient sources are evaluated and by use of the model a net budget for total N is set up. Finally, it is suggested that this net budget can be used for a rough estimation of the annual mean net flux of total N from the sediment to the water. The result obtained compares well with mass balance studies of fine-grained sediment carried out in the same area. It is concluded that total P cannot be treated in the same way as total N because a substantial part of P in the water is adsorped to clay and silt particles suspended in the water leading to a non-conservative behaviour.

Optical absorption spectra of waters from the Orinoco River outflow: Terrestrial input of colored organic matter to the Caribbean

An extensive series of optical absorption spectra were recorded for waters in the eastern Caribbean Sea, the Gulf of Paria, and the Orinoco River Estuary during the high‐flow period of the Orinoco River in the Fall of 1988. Evidence for high levels of dissolved, colored organic matter (COM) was found throughout the eastern Caribbean, with these levels increasing substantially at stations nearer the Gulf of Paria and the Orinoco River. The dependence of the absorption at 300 nm (a300) on salinity exhibited conservative mixing behavior for transects through the Gulf of Paria. In contrast, transects through the Orinoco Estuary revealed that a300 remained approximately constant or slightly increased with increasing salinity up to 27‰, after which it decreased linearly with increasing salinity. This nonconservative behavior was not produced by COM release from suspended particulate matter at higher salinity, nor did it appear to originate from the sediment. Below 30‰, the slopes of the log‐linearized absorption spectra were independent of salinity (0.0140 nm−1). At higher salinities, the slopes apparently increased, suggesting that the COM is modified. Based on specific absorption coefficients measured for COM isolated from this area, COM input by the Orinoco River is estimated to be ∼ 2.5 × 1012 g C/yr, which represents about 1% of the total global transport of dissolved organic carbon to the ocean. This input is likely to influence substantially the carbon cycle, photochemical properties, and optical characteristics of the waters in this region.