n the 1920s. Greater access to the everglades led to unrestricted hunting when waders and other water birds suffered greatly, especially egrets, which were killed for their glorious plumes. The piecemeal drainage and conversion to agriculture and urbanisation has increased pollution from run off and fertilisers in the water that remains.
Haarlemmermeer (The lake of Haarlem) is one of the biggest, if not the biggest, drainage project ever accomplished. Situated in the Netherlands it once covered over 150 square kilometres and was drained by successive projects finally being dry in 1852. It is thought that around one thousand billion litres of water were removed to drain the lake.
Mangroves are another habitat that waders find of great value for foraging and roosting, and they are under threat across the globe particularly in Asia where they are being converted into agricultural land, aquacultural areas and removed for building development, particularly in the tourism sector. On the other hand, mangroves have been spreading across saltmarshes and tidal mudflats removing vital feeding areas of open mudflats and marsh from the waders’ choice of feeding area. Mangroves are restricted in their range by temperature requirements, as the planet warms they are able to access new areas and invade new coastal marshes and mudflats that are critical to the survival of migrating and wintering waders.
Peat bogs naturally hold a lot of water, and carbon. In order to extract the peat the area needs to be drained and then the peat extracted. The draining of the peat causes greater run off and that water is altered containing augmented suspended material and dissolved organic matter and increases in nutrient and metal content, colour and pH are to be found. Small scale hand dug peat extraction may not have caused too much harm, but the mechanised wholesale destruction of entire habitats in the last thirty years has had a devastating effect, particularly in Ireland where it has been instrumental in the decline in Curlew numbers.
River and coastal management
Degradation of habitat can also occur by the altering of water flowing from a river or along a coastline. Many estuarine mudflats exist because for millions of years the rivers have been depositing sediment at their final destination, the sea. But naturally that sediment is also washed away so needs constant replenishment. If a river is dammed or dredged to control the flow, altering its speed and volume, it will inevitably affect the amount of sediment deposited. Damming can reduce the flow to such an extent that the mud flats will simply disappear or at least change their character. Sediments may settle further upstream in slower moving water or be trapped by the dam itself and existing mudflat may erode, the sediment being transported and deposited elsewhere changing the physical form of the flats.
Dredging has the opposite effect where fast flowing water carries larger, heavier sediment which washes away smaller particles preventing them from settling. From a waders point of view deeper faster moving water is far less suitable for feeding than shallow slow-moving or still water.
If the flow of the water is changed it will therefore alter the deposition of the sediment and can change mud flats into sandy flats if the flow increases and vice versa if it is reduced. In addition a change of water level and velocity can render some islands in the middle of rivers, which were hitherto unreachable to land mammals, accessible if water levels drop or they can be washed away if the speed and level increases.
At the mouth of a river, where it meets the sea, the fresh water mixes with the salty sea water and salinity levels are increased. There are creatures in that environment that require the diluted salinity to thrive, so, if river flows are reduced the salinity increases and some life forms will not be able to survive. These victims may well be those that the waders are feeding upon again reducing the suitability of the habitat for waders.
River flow will also impact upon floodplains where pe