Water clarity changes

Changes in water clarity (or turbidity) due to changes in sediment & organic particulate matter and chemical concentrations. It is primarily related to activities disturbing sediment and/or organic particulate matter and mobilizing it into the water column.  Particle size, hydrological energy (current speed & direction) and tidal excursion are all influencing factors on the spatial extent and temporal duration. Salinity, turbulence, pH and temperature may result in flocculation of suspended organic matter. Changes in suspended sediment loads can also alter the scour experienced by species and habitats. Therefore, the effects of scour are also addressed here.

Benchmark: 
A change in one rank on the WFD (Water Framework Directive) scale, e.g. from clear to intermediate for one year (ranks are mean suspended particulate matter in units of mg/c: >300 - very turbid; 100-300 - medium turbidity; 10-100 - intermediate; <10 - clear.)
Examples: 
It could be 'natural' land run-off and riverine discharges or from anthropogenic activities such as all forms of dredging, disposal at sea, propeller wash, cable and pipeline burial, secondary effects of construction works, e.g. breakwaters. Anthropogenic sources are mostly short lived and over relatively small spatial extents. Shellfish and seaweed culture may actually improve water clarity through filtering or settlement of suspended particles.
Notes: 
Link with siltation (low) pressure. Excludes sewage discharge as regulations means is unlikely to meet benchmark.

Faroe Shetland Channel

The tables in this section reflect the output of the workshop (October 2019) when the pressures from human activities were assessed for the period 2014 to 2018 for the region. The summary text below the tables elaborates on some of the points that were made at the workshop.
This pressure assessment uses the FeAST classification which includes two abrasion pressures: surface abrasion & sub-surface abrasion. Some expert groups combined these as a single pressure "surface & sub-surface abrasion" whilst others focussed on using surface abrasion alone, hence there is a slight difference in handling for some regions.
The ranking of the pressures in terms of impact is a relative exercise within each region, and is not a statement of their absolute impact. Detailed comparison between regions on the basis of these relative pressure assessments is therefore not advisable.

Main pressures identified

Faroe Shetland Channel

Clyde

The tables in this section reflect the output of the workshop (October 2019) when the pressures from human activities were assessed for the period 2014 to 2018 for the region. The summary text below the tables elaborates on some of the points that were made at the workshop.
This pressure assessment uses the FeAST classification which includes two abrasion pressures: surface abrasion & sub-surface abrasion. Some expert groups combined these as a single pressure "surface & sub-surface abrasion" whilst others focussed on using surface abrasion alone, hence there is a slight difference in handling for some regions.
The ranking of the pressures in terms of impact is a relative exercise within each region, and is not a statement of their absolute impact. Detailed comparison between regions on the basis of these relative pressure assessments is therefore not advisable.

Main pressures identified

Clyde