A mere is a shallow lake, pond, or wetland, particularly in Great Britain and other parts of western Europe.
Derivation of the word
Etymology
The word mere is recorded in Old English as mere ″sea, lake″, corresponding to Old Saxon meri, Old Low Franconian *meri (Dutch meer ″lake, pool″, Picard mer ″pool, lake″, Northern French toponymic element -mer), Old High German mari / meri (German Meer ″sea″), Goth. mari-, marei, Old Norse marr ″sea″ (Norwegian mar ″sea″, Shetland Norn mar ″mer, deep water fishing qarea″, Faroese marrur ″mud, sludge″, Swedish place name element mar-, French mare ″pool, pond″). They derive from reconstituted Proto-Germanic *mari, itself from Indo-European *mori, the same root as marsh and moor. The Indo-European root *mori gave also birth to similar words in other European languages: Latin mare, ″sea″ (Italian mare, Spanish mar, French mer); Old Celtic *mori, ″sea″ (Gaulish mori-, more, Irish muir, Welsh môr, Breton mor); and Old Slavic morje.
Signification
The word once included the sea or an arm of the sea in its range of meaning but this marine usage is now obsolete (OED). It is a poetical or dialect word meaning a sheet of standing water, a lake or a pond (OED). The OED fourth definition ("A marsh, a fen.") includes wetland such as fen amongst usages of the word which is reflected in the lexicographers' recording of it. In a quotation from the year 598, mere is contrasted against moss (bog) and field against fen. The OED quotation from 1609 does not say what a mere is, except that it looks black. In 1629 mere and marsh were becoming interchangeable but in 1876 mere was "heard, at times, applied to ground permanently under water": in other words, a very shallow lake. The online edition of the OED quoted examples relate to: the sea: Old English to 1530: 7 quotations standing water: Old English to 1998: 22 quotations arm of the sea: 1573 to 1676: 4 quotations marsh or fen: 1609 to 1995: 7 quotations
Characteristics
Where land similar to that of Martin Mere, gently undulating glacial till, becomes flooded and develops fen and bog, the remnants of the original mere remain until the whole is filled with peat. This can be delayed where the mere is fed by lime-rich water from chalk or limestone upland and a significant proportion of the outflow from the mere takes the form of evaporation. In these circumstances, the lime (typically calcium carbonate) is deposited on the peaty bed and inhibits plant growth, therefore, peat formation. A typical feature of these meres is that they are alongside a river rather than having the river flowing through them. In this way, the mere is replenished by seepage from the bed of the lime-rich river, through the river's natural levée, or by winter floods. The water of the mere is then static through the summer, when the concentration of the calcium carbonate rises until it is precipitated on the bed of the mere.
Even quite shallow lake water can develop a thermocline in the short term but where there is a moderately windy climate, the circulation caused by wind drift is sufficient to break this up. (The surface is blown down-wind in a seiche and a return current passes either near the bottom or just above the thermocline if that is present at a sufficient depth.) This means that the bed of the shallow mere is aerated and bottom-feeding fish and wildfowl can survive, providing a livelihood for people around. Expressed more technically, the mere consists entirely of the epilimnion. This is quite unlike Windermere where in summer, there is a sharp thermocline at a depth of 9 to 15 metres, well above the maximum depth of 60 metres or so. (M&W p36)
At first sight, the defining feature of a mere is its breadth in relation to its shallow depth. This means that it has a large surface in proportion to the volume of water it contains. However, there is a limiting depth beyond which a lake does not behave as a mere since the sun does not warm the deeper water and the wind does not mix it. Here, a thermocline develops but where the limiting dimensions lie is influenced by the sunniness and windiness of the site and the murkiness of the water. This last usually depends on how eutrophic (rich in plant nutrients) the water is. Nonetheless, in general, with the enlargement of the extent of a mere, the depth has to become proportionately less if it is to behave as a mere.