Long term variation in water colour from Yorkshire catchments

Area of Science:

• Environmental Science
• Water Resource Management
• Analytical Chemistry

Background:

• Upland water colour is a significant issue in the UK.
• Recent variations in water colour necessitate long-term contextualization.

Purpose of the Study:

• To present site-specific conversion factors for water colour from absorbance units per metre (Au/m) to Hazen units.
• To analyze long-term trends and seasonal variations in water colour in Yorkshire catchments.

Main Methods:

• Collected water colour data from August 1997 to June 1998 for ten sites in the Yorkshire region.
• Calculated site-specific conversion factors (Au/m to Hazen units).
• Analyzed time series data from 1980 to 1998 to identify trends and drought impacts.

Main Results:

• Site-specific conversion factors were determined, with evidence of seasonal variation.
• A short-term upward trend in conversion factors was observed, potentially linked to post-drought recovery.
• Drought periods (1990-1992, 1995-1998, 1975-1976) disrupted seasonal colour patterns, followed by elevated colour levels, including unprecedented highs after 1995.

Conclusions:

• Long-term monitoring is crucial for understanding water colour dynamics in upland catchments.
• Droughts significantly impact water colour, leading to prolonged periods of high colouration.
• Site-specific data and conversion factors are essential for accurate water quality assessment and management.