Estuaries types

Aluminium anodes comprise essentially three generic types Al-Zn-In, Al-Zn-Hg and Al-Zn-Sn. Since Al-Zn-Sn alloys have largely been superseded, they will not be discussed further. Indium and mercury are added to aluminium to act as activators, i.e. to overcome the natural passivation of aluminium. Despite this, aluminium anodes are not suitable for low chloride environments which would lead to passivation. These anodes are therefore not used for land-based applications (although examples of use in environments such as swamps do exist). Similarly their use in low chloride aqueous environments such as estuaries must be viewed with caution. 

As in the case of power stations, where there is known to be considerable variation in operating conditions due to tidal changes, or in estuary waters variations in salinity, automatic control systems may be desirable. For such systems the current output of the transformer-rectifier is controlled by thyristor or transductors. Sensing electrodes are permanently installed on selected piles and transmit the electrode potential of the steel back to the controlling device. This type of system enables the most economic amount of current to be provided under all operating conditions. 

While an exact number of site clusters has not been proposed, the authors consider from approximately 3 to 10 clusters of sites to be appropriate. These clusters should represent different ecoregions with different ecological characteristics as well as different loadings (both in amount and source) of mercury deposition. Care should be taken to monitor different types of water bodies and watersheds (e.g., seepage lakes, drainage lakes, old reservoirs, rivers, and estuaries). Areas that should be considered as potential cluster site locations include lakes in northern New England/the Adirondacks, lakes in the upper Midwest, rivers and streams in the southeastern coastal plain, lakes in south-central and southeastern Canada, western... 

Saiinity gradients and direction of water flow in (a) sait-wedge, (b) partiaiiy mixed, (c) fjord-type, and (d) weii-mixed estuaries. Saiinity is given in parts per mii. 

Table 3.8 lists the arsenic concentrations of different types of marine and estuary sediments from various locations. Overall, low organic-carbon carbonate muds, oxidizing sands, and coarser-grained sediments have relatively little arsenic. In contrast, reducing marine sediments may contain as much as 3000 mg kg-1 of arsenic (Mandal and Suzuki, 2002), 202. Arsenic also tends to be enriched in fine-grained silicate-rich sediments, such as deep-sea clays and marine muds. In most cases, arsenic-rich sediments contain abundant arsenic-accumulating (oxy)(hydr)oxides, organic matter, or sulfides. 

To illustrate one type of speciation research, i.e. the determination of the apparent complexation capacity for copper (CCqu) and the conditional stability constant (K1), examples are given for three marine areas, viz. the Scheldt estuary, the Southern Bight of the North Sea and the open north Atlantic Ocean. A hypothetical model is presented giving the complexation capacity across the land-sea boundery from river to ocean. 

Various workers have assembled relatively complete assessments of the annual input of the major biological nutrients (C, N, P), certain heavy metals (Mn, Cd, Pb, Cu), and petroleum hydrocarbons to Narragansett Bay. Other studies have developed inventories of the amounts of these materials in the sediments of the Bay. We have brought these data together with information on sediment accumulation rates in the Bay to determine the degree to which this one estuary serves as a sink for different types of materials in their passage between land and the coastal ocean. 

A consideration of the annual mass balances summarized in Table 1 and the differing behavior of the various types of material discussed in the preceding section suggests that there are three general types of substances that differ markedly in the extent to which they will be retained within or transmitted through an estuary. 

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