Monday, 16 March 2009

Water in the Landscape

A sunny, spring like day finds me sitting up on the hill above Barton Le Clay, and then in farmland near Lilley, to reflect on water in the landscape.

Barton Hills:
I wonder how much of the landscape around me is affected by water. There is a fairly clear sky above me with hazy cirrus clouds and the inevitable white vapour trails that scratch across the blueness. Water put there by nature and water put there by man.

The edge of the Chilterns here is quite a spectacular sight with the land dropping down steeply below me in a series of deep gulleys that cut through the chalk. The steep slopes are covered with the barest of short grasses and I wonder how this chalk escarpment was originally formed; what action of water has taken place over the millennia to shape this landscape? I found a small leaflet on the web about the geology of the area and it described how the landscape here was formed. Originally the area would have been under water but geological movement meant the seas lowered and the land folded to create the chalk escarpment. The action of a huge ice sheet that covered the landscape and erosion (around half a million years ago) sculpted the chalk ridge into the current landscape.

Hawthorns cling to soil here, perhaps rooting in ground disturbed by rabbits and their burrows. I think about how rain falls on the soil, is taken up by the hawthorns, helps form their berries which will subsequently be eaten by birds. Many animals and birds only get water through the food they eat and this must certainly be the case for all the rabbits around here grazing on the fine chalkland grass.

The ground must be very permeable to water and able to hold vast quantities of water within its structure. There seem little signs of erosion so the chalk must absorb large quantities of rain quite quickly. In fact it is a freeze-thaw cycle causing soil creep that apparently causes soil erosion here, and the numerous small parallel ledges that run along the hillside carrying large masses of soil downwards. There is a small spring and stream at the bottom of the gulley I gather (where the water hits a more impermeable and clayey Lower Chalk) but I haven't seen it yet. The chalk itself is a product of ocean-dwelling organisms. The rabbits seem to be able to dig in the top soil and chalk here quite easily. Piles of soil and small crumbly pieces of chalk litter the grassland. Perhaps the soil here is reasonably deep, though on the nearby fields the white of the chalk is evident on the top most parts of the field where the plough has dug into the surface chalk.

There are piles of horse manure (I assume) up by a fence. A good source of organic matter to hold nutrients and water in the soil. I think of horse digestion and the role water/liquids has to play in it.

Trees and plants have a great ability to use soil bound water. Growing on such steep slopes must be a challenge and I look across at the woodland on the other side of the valley. As plants colonise the ground so the amount of water held within the soil must increase, making more available to the plants and the larger species to then add to the mix. The amount of organic matter held in the soil will increase and surface evaporation will probably be less. Plants can then use the water more efficiently rather than allowing it to run off or soak away.

The large fields around here may be good agribusiness with crop production and chemical input carefully controlled and monitored, but the amount of water available is not so easily manageable by the farmer. Water is a crucial factor in crop production but we can't control the weather. In dry soils like this the use of fertilizers and possibly drought resistant crops will probably enable crops to survive dry conditions. I expect the amount of water-holding organic matter in these fields is negligible.

Seen several bumble bees, speedwell, Brimstone butterflies (around and about) and violets (yesterday).

Lilley:
I gaze out over some fields and hedges and wonder "What place does water have in this landscape?"

I am immediately tempted to say that it helps plants to grow, but I decide to look for another answer.

Water is present in the air when it rains. The atmosphere is filled with water and humidity. The space it occupies changes under the effects of gravity, pulling the water to the earth and the plants upon which it falls. Subsequently most of the water will find its way into the particles of soil if it doesn't evaporate. The water then becomes an intrinsic part of the landscape - bonding with particles of soil, roots, organic material and living organisms. Something seen - the falling rain, suddenly becomes invisible to the eye, abosorbed into the darkness of the earth. So much water much be absorbed into the earth - the chalk deep below. Some will be evaporated by the wind and some will be taken up via plant roots into plant bodies and, again, later evaporated from the surface of leaves.

No comments: