Results: 

Comparing conifers and grazing land at Plynlimon, we found:

Hydrology

Forests "use" more water than short vegetation.
This is related more to the evaporation of water from the tree canopy than to difference in root depth.
There is little effect on flood flows.

Sediments

Forested catchments contribute considerably more sediment to rivers than moorland areas. Suspended concentrations in the upland area are relatively low when compared to those recorded in lowland river reaches.
Some 80% of the suspended load in the forested areas, and 70% of the load in moorland areas is carried in less than 5% of the time.
Research projects have looked at the impact of forest harvesting in the instream sediment fluxes. These have contributed to the development of forestry guidelines in the UK.


Datasets

The combined datasets include river flow; rainfall, cloud and stream hydro-chemistry; meteorology; and a variety of detailed spatial datasets representing the topography, soils and rivers of the catchments. This dataset is a digital river network of the natural streams and rivers within the Plynlimon catchments. An additional dataset of artificial channels also exists.

To access the datasets, please go to the CEH Environmental Information Platform and search for Plynlimon.

Links to selected related papers can be foundin the Related Links section below.

 

Afon Cyff flume and hut

Scientific background

The infrastructure at Plynlimon was originally established in the1960s to investigate the impact of upland conifer plantations on the hydrological cycle. Over the years the Plynlimon Experimental Catchments have been expanded to cover a wealth of hydrological and hydro-chemical research by the Centre for Ecology & Hydrology.

Research overview

We conduct long-term measurements of weather, stream flow and chemical fluxes. We use this information to look for time trends, understand the processes operating, and investigate the impacts of land use on water resources, floods, drought flows, stream sediment and dissolved chemicals and acidification. 

Plynlimon altitude bandsOur work includes:

  • Effect of felling the first generation of plantation forestry for timber and its replacement by a more environmentally sensitive second generation forest.
  • Water quality – looking at effects of changes in atmospheric pollution levels on streamflow chemistry.
  • Use of novel high tech micro-meteorological instruments to directly measure evaporation from forest and grass and to study variations within each catchment involving altitude, slope direction, tree age and species.
  • CHASM (Catchment Hydrology and Sustainable Management).

Location

The catchments lie within the headwaters of the River Severn and the River Wye, approximately 20km inland of Aberystwyth on the mid-Wales coast. The catchments cover a combined area of 19.25 km2. More information on the Plynlimon monitoring site is available here.

Critical Zone Observatory

Plynlimon also acts as a satellite 'Critical Zone' (CZ) observatory site. The CZ is the environment that extends from the top of the tree canopy to the bottom of our drinking water aquifers; it is where terrestrial life flourishes and feeds most of humanity. The heart of the CZ is where soils are formed, degrade and provide essential ecosystem services. The Critical Zone observatory project aims to investigate and model the processes determining soil sustainability in Europe.

Data from the site will be used to test biogeochemical and nutrient models for SoilTrEC. Plynlimon is part of an international network of sites, located over similar geological units, studying processes of soil development across climatic and land use gradients; other sites are in the USA and China.

History of the Plynlimon catchment experiment

During the 1960s the former Institute of Hydrology, now the Centre for Ecology & Hydrology, instigated a major hydrological study to investigate the impacts of conifer plantations on the hydrological cycle.

The Plynlimon catchments were selected because they provide two, almost identical, adjacent catchments, with the exception that one is used for grazing sheep while the other is mostly under plantation conifer forestry. The findings are applicable to many upland areas in Britain where the land is used for water, wood and wool.

Map Locations: