Data from the UK Lake Ecological Observatory Network

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Air Temperature

Air Temperature - is the temperature of the air in degrees Celsius at about 3m above the lake surface. In the English Lake District, air temperatures of between a minimum of -16 and plus 35 degrees C have been recorded over the last few decades at Ambleside. Under standard conditions, water freezes at 0 degrees Celsius and boils at 100 degrees Celsius.

Barometric Pressure

Barometric Pressure - is the air pressure in mbar. The standard atmospheric pressure (1 atmosphere) is 1013.25 mbar which is equivalent to 760 mm Hg, 29.92 in Hg or 14.696 psi.

Wind speed

Wind speed - is the wind speed in metres per second at about 3m above the lake surface. Ten metres per second is equivalent to 22 mph or 19 knotts.

Wind Direction (from vector addition of unit length vectors)

Wind Direction - is the direction of the wind on a compass scale. North is represented by 0 and 360 degrees and South is represented by 180 degrees.

Solar radiation

Solar radiation - is the short wave energy from the sun measured in Watts per metre squared, which is equivalent to Joules per metre squared per second. Short wave radiation ranges from wavelengths of about 200 nm (ultraviolet) to 3000 nm (infra-red).

Surface photosynthetically available radiation

Surface photosynthetically available radiation - is sometimes also referred to as PAR or photon flux density. It is a measure of the amount of light from the sun between the wavelengths of 400 nm (blue) to 700 nm (red) which is also roughly the spectral band visible to the human eye. It has units of �mol photon per metre squared per second where 1 umol is 600,000,000,000,000,000 photons - tiny particles of light. On a very sunny day when the sun is overhead photosynthetically available radiation can reach a little over 2000 �mol photon per metre squared per second.

Surface water temperature

Surface water temperature - is the temperature of the water in degrees Celsius at the surface of the lake.

Temperature Profiles

Temperature Profiles - these record the water temperature in degree Celsius, at different depths in the water column. During the summer many lakes �stratify� into an upper warmer, less dense layer, the epilmnion, separated from a lower cooler more dense layer, the hypolimnion, by a region of sharp temperature change, the thermocline. In winter, inverse stratification sometimes occurs because water has a maximum density at about 4 degrees Celsius; water cooler than this is less dense and floats.

Underwater photosynthetically available radiation (1m)

Underwater photosynthetically available radiation (1m) - is sometimes also referred to as PAR or photon flux density. It is a measure of the amount of light from the sun between the wavelengths of 400 nm (blue) to 700 nm (red) which is also roughly the spectral band visible to the human eye. It has units of �mol photon per metre squared per second where 1 umol is 600,000,000,000,000,000 photons- tiny particles of light. This records the amount of photosynthetically available radiation at a depth of 1 metre after losses caused by reflection at the water surface and absorbance and scattering in the water column above the sensor.

Conductivity normalised to 25 degrees C

Conductivity normalised to 25 degrees C - is a measure of ability of water to conduct an electrical current and is affected mainly by the ionic content of the water and has the units of micro Siemen per cm. Pure water has a very low conductivity but water with more ions present has a much higher conductivity. Lake water typically has a conductivity between about 20 and 2000 micro Siemen per cm. Because temperature also has a slight effect on conductivity, values are usually corrected to a standard temperature such as 25 degrees Celsius (as here).

pH - is a measure of the acidity or alkalinity of a water. Pure water has a neutral pH of about 7, while water with a lower pH is acid and water with a higher pH is alkaline. Since pH is expressed on a logarithmic scale, lake water at pH 6 has a 10-fold higher acidity than lake water at pH 7. pH varies naturally among lakes from pH 2 in very acid lakes (often associated with volcanic activity) to over pH 10 in very productive lakes or in African �Soda lakes�; but most lakes have a pH between 5 and 9. Even in a given lake, pH can be highly variable because photosynthesis causes pH to increase by removing CO2 while respiration has the opposite effect.

Dissolved oxygen (% saturation)

Dissolved oxygen (% saturation) - when water is in equilibrium with air (dry air contains about 21% oxygen by volume), the concentration of oxygen (O2) is controlled by temperature, salinity and air pressure (altitude therefore has an effect); 100% saturation represents this equilibrium concentration. Biological processes can change the oxygen concentration. Respiration consumes oxygen so tends to reduce oxygen saturation while photosynthesis produces oxygen and so tends to increase the oxygen saturation. In very productive lakes, it is possible to find 200% saturation in the upper depths and 0% saturation at the lower depths as a result of these two processes.

Dissolved oxygen (mg per litre)

Dissolved oxygen (mg per litre) - is the concentration of oxygen in water as the mass of oxygen per litre. At equilibrium the concentration decreases with increasing temperature, salinity and altitude. Biological processes that consume oxygen (respiration) or produce oxygen (photosynthesis) tend to shift the dissolved oxygen concentration from the equilibrium concentration.

Dissolved carbon dioxide

Dissolved carbon dioxide - is expressed here as the concentration equivalent to the concentration in the atmosphere (parts per million). Before the start of the industrial revolution, atmospheric concentrations of CO2 were about 270 ppm but because of human activity, primarily linked to burning fossil fuels for energy, current atmospheric concentrations have reached about 400 ppm and are increasing by about 2 ppm per year. However, the concentration of CO2 in lakes can vary much more rapidly and to a greater extent when it is rapidly removed by photosynthesis and produced by respiration. On average, most lakes around the world are oversaturated with CO2 (i.e have a CO2 concentration greater than 400 ppm) because they receive carbon from their catchment, much of which is then lost to the atmosphere at the water surface.

Chlorophyll a concentration (relative units)

Chlorophyll a concentration (relative units) - Chlorophyll a is the green pigment responsible for harvesting energy from sunlight in all photosynthetic organisms. In the laboratory it can be measured accurately by extraction in an organic solvent and measuring light absorbance at specific wavelengths. In a lake it can be estimated approximately using fluorescence. When chlorophyll absorbs light in a leaf, for example, most of the energy is used in photosynthesis but a small proportion is re-released at a longer wavelength (shifted to the red end of the spectrum). This is called fluorescence and it can be measured to estimate the concentration of chlorophyll a. In addition to the amount of chlorophyll a, other factors can alter fluorescence, such as the rate of photosynthesis and the amount of light the cells have experienced. We are using it here to estimate the amount of phytoplanktonic algae but because it cannot provide an accurate value it is presented here as an arbitrary number. It is a very useful measurement however in detecting short-term changes in amount of phytoplanktonic algae.

Phycocyanin concentration (relative units)

Phycocyanin concentration (relative units) - Phycocyanin is a blue pigment used to harvest sunlight (in addition to chlorophyll a) that is present in cyanobacteria or blue-green algae. In planktonic cyanobacteria its concentration can be measured approximately by fluorescence: the emission of light by the pigment following light absorption. We are using it here to estimate the amount of cyanobacteria, but because it cannot provide an accurate value it is presented here as an arbitrary number. It is a very useful measurement, however, in detecting short-term changes in amount of cyanobacteria.

Bassenthwaite Lake

Blelham Tarn

Llyn Conwy

Llyn Tegid

Loch Leven

Loch Lomond

Lough Erne

Rostherne Mere

Round Loch of Glenhead

Windermere

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Please note: these are raw data. They have had basic automated quality checks only - they have not yet been through the full quality checking procedures.

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