The last century saw the destruction of many hedgerows, particularly in farming areas like East Anglia.  The logic behind this was : to increase field size and  allow ease of access of machinery, like combine harvesters that were coming available at that time.   Whilst the loss of the hedgerows and the associated wildlife is well documented, the loss of ponds during this time has not attracted the same level of attention.  Many hundreds of ponds were filled in, to give a few more metres of arable land.  The whereabouts of some of these ponds can sometimes be found on old ordnance survey maps.  Many were located on farmland and their origins may extend back centuries to when they were created as marl or clay pits, sometimes for the watering of livestock.  Some were formed in depressions (pingos) left after the last ice age. There are still  thousands of ponds across the UK but many are polluted to a greater or lesser extent, or drained.  The pollution may be associated with the the surrounding land use or agricultural runoff. Runoff may take the form of nitrates / phosphates from the use of fertilisers.  In freshwater systems, these nutrients can cause eutrophication. Other agricultural chemicals may enter ponds and water courses - insecticides, fungicides, herbicides etc. Consequently, out of the thousands of ponds, only a very small number provide a suitable habitat for pond organisms such as the medicinal leech.  Leeches are rarely found for the reasons cited above but also because, as agriculture became more mechanised and less reliant on ‘animal power’ [horses, oxen], the ponds  (or wetlands) are no longer visited by these animals, which leeches would have fed on.  Leeches used to be abundant, but their number declined when their use in blood letting was largely abandoned, and their natural habitats were drained or damaged.  The medicinal leech is one of the largest leeches found in the UK, it can grow to a length of ten centimetres, and may have stripes / patterns on its body.  Some of the ponds that are home to medicinal leeches have been designated  Sites of Special Scientific Interest.  Since historic times, the extraction of blood by leeches was deemed to be a ‘healing process’ for patients. This practice of hirundotherapy / bloodletting spread widely and the collection of leeches resulted in the over-exploitation of many populations.  The leeches were used widely in the treatment of many conditions and  diseases such as cholera, regardless of whether or not they were effective.  At one stage, leeches were in such demand that there were ‘leech farms’, and  people could earn a living as leech collectors.  Indeed, so commonplace was leech collection that Wordsworth wrote about it in his poem Resolution and Independence : “He told, that to these waters he had come To gather leeches, being old and poor: Employment hazardous and wearisome! And he had many hardships to endure: From pond to pond he roamed, from moor to moor; Housing, with God’s good help, by choice or chance; And in this way he gained an honest maintenance.” Although the use of medicinal leeches was discredited and virtually abandoned for many decades, they are medically effective in certain circumstances.  The leeches produce a saliva which  contains a number of different proteins. These help the leech to feed by keeping the blood from clotting, and actually increasing blood flow to the leech at the point of attachment.  Some of these proteins act as anticoagulants (notably hirudin),   It is also possible that the saliva contains an 'anaesthetic / antiseptic' as leech bites are generally not painful. These leeches have now found a use in microsurgery.  They are used to stimulate the circulation in tissues which experience post-operative congestion.  They are helpful in finger reattachment and reconstructive surgery of the ear, nose, lip, and eyelid. The creation of a network of new or restored freshwater ponds across the landscape will be needed if natural populations of the leech are to expand. 

Back in the Nineteenth Century, John Bennet Lawes, a Victorian entrepreneur founded a research station at Rothamsted Manor.  It was to investigate the impact of organic and inorganic fertilisers on crop yield.  Lawes had a factory making some of the first artificial fertilisers.  The manor was to become the Rothamsted Experimental Station, now known as Rothamsted Research.  It has two of the longest running experiments - the Broad balk experiment and the Park Grass experiment - started in 1856. The Park Grass area was started by Lawes and Gilbert.  Its original purpose was to investigate ways of improving the yield of hay through the use of inorganic fertilisers or organic manures. Different strips of land received varying amounts of fertiliser to none.  It soon became clear that the different treatments had a dramatic effect on the species composition of what had been a uniform sward.  There are 35-45 plant species on the unfertilised plots but only 2 or 3 species on some of the fertilised plots. Fertilisers create conditions that allow fast growing grasses to dominate the vegetation.  More recently the plots have received attention (by Dr Balfour et al, Sussex University) for the number of pollinators that they support.  It was found that High levels of common fertilisers on grassland halves the pollinator numbers. Increasing the amount / availability of NPK (nitrogen phosphorus and potassium) on grassland reduces flower numbers five fold. Bee number were most affected.  There were 9 times more bees in untreated plants compared to plots with the most fertiliser input.   The number of bees, hoverflies, butterflies, wasps and flies on each experiment strip was counted. Whilst all pollinator types were present on untreated plots or with low fertiliser levels, only flies and beetles were present on high fertiliser plots. Interestingly, plots with lime added which changed the soil pH had more pollinators (50%) and flower species than those not treated with lime. as fertiliser use increases so there is a decrease in pollinator numbers.   Though these observations are for a specific area of managed grassland, they can be considered in a broader context.  Many grasslands and meadows, which offered homes to pollinators, have been lost in recent times,.  Over a similar period of time, farmlands across the country have extended (eg. hedgerow removal, ploughing meadows) and have been making significant use of fertiliser to improve crop yield, but the wider effects of these changes on insect populations and biodiversity in general has not received enough attention. The ‘excessive’ use of fertilisers can lead to soil eutrophication, air pollution, freshwater eutrophication and a loss of biodiversity.  It can favour botanical thugs )like nettles and invasive species.  We do know that there have been dramatic falls in insect numbers in recent years in what has been termed the ‘insect armageddon or the ‘insect apocalypse’.  Whilst there are many factors at play affecting insect numbers (such as the intensive use of pesticides), the maintenance or the reintroduction of natural areas [with low nutrient soil and native wild flowers] within farmland would at least offer sanctuary to many insects / pollinators that are vital for our crops.  Any reduction in the use of fertilisers would help reduce the CO2 emissions resulting from the Haber–Bosch process, used to produce ammonia and ammonium nitrate. Interesting fact : the institute employed Ronald Fisher in the 1920s to analyse data collected from many experiments.  His work and that of other statisticians means that many consider Rothamsted the birthplace of modern statistical theory (e.g. analysis of variance) and practice.  

Nitrogen is an important plant nutrient.  Generally, it is taken up in the form of nitrate (NO3) and it is used in the formation of amino acids, proteins and the constituents of the genetic material (DNA).  Some plants fix atmospheric nitrogen through the use of symbiotic bacteria in root nodules. However, modern / intensive farming involves the addition of nitrogen compounds in the form of manure, sewage sludge and chemical fertilisers. Couple this with the aerial deposition of nitrogen compounds, estimated at 400,000 tonnes / yr from car exhausts etc. (in the form of ammonia, nitrogen oxides) to give the total burden of nitrogen pollution. Pollution from such widespread sources is referred to as diffuse contamination. Read more...

Recently the blog commented on the loss of wild flowers from country lanes and roadsides - occasioned by seeing nettles and cow parsley for miles, and very little else.  This loss of diversity may be attributed in part to the use of nitrogenous fertilisers and aerial deposition of pollutants.  It is 'rare' to see poppies around the edges of fields nowadays.   So what is happening ? Obviously, the seed used by farmers nowadays has fewer "wild contaminants" but Plantlife is concerned that various agricultural management practices have placed arable plants under threat.  The need to make economic use of every bit of land, the increased use of herbicides (to control pernicious weeds - such as charlock, black grass, sterile brome) has a knock-on effect on many arable wild flower species, as has the greater use of winter planting.   In some parts of the country, a switch away from arable farming has also had its effects. Some 150 wild flowers are characteristic of,  or associated with arable farming;  many are now threatened.  The majority of the 'uncommon species' are found in the south-east (crudely speaking - draw a line from the Wash across to the Bristol Channel) Read more...