Geography Reference
In-Depth Information
conditions more flow is generated from macropores and over the
land surface containing smaller base cation concentrations. The
availability of solute supply can vary with temperature during the
year or with plant growth (e.g. nitrate concentrations can be lowest
in spring and summer due to plant uptake). The concentrations of
chemicals within precipitation can also vary with time. In coastal
regions, precipitation is often enriched by sea salt during stormy
weather, increasing chloride concentrations in river waters.
Solute concentrations and
solute
fluxes
(total mass of a solute
moved) in rivers and lakes vary locally and globally. This is due to
local and regional differences in climate, geology, topography, land
management, soils and vegetation. Globally, patterns of solute con-
centrations are dominated by climate and geology. On a regional
level, land management, soil types and vegetation are more import-
ant. Land use affects solute concentrations by altering runoff pathways
and the amount and availability of dissolved chemical sources. It has
been estimated that human action has increased the total amount of
solutes transported by rivers across the planet by 12 per cent.
Agriculture has had a large impact on water quality, particularly
through increased erosion, and the leaching of nutrients, pesticides
and by-products of veterinary medicines into water courses. There
may be individual point sources of chemicals from leakage of pesti-
cides, slurry and wastes from storage facilities, or from more diffuse
pollution across the landscape. Manure is often spread on farmland
but when the plants cannot take up all of the nutrients provided
(i.e. too much has been applied) or if the manure is applied just
before heavy rain then leaching of soluble nitrogen and other
chemicals occurs. Drainage and ploughing can also increase leach-
ing rates and erosion.
Urbanisation and industrialisation are associated with increased
river concentrations of metals, nutrients, organic matter and salt in
the winter in cold climates where roads are treated. Vehicles are
responsible for a lot of urban metal pollution as they corrode depos-
iting materials on the urban surface. Urban drainage with rapid
removal of surface waters to rivers also means that there can be a
strong flush of chemicals that have built up on the surface at the start
of a rainfall event. Sewage effluent is also another major pollutant.
In many developed countries there are sophisticated wastewater
treatment techniques that clean the water before it is returned to
