Hemispherical photography

Hemispherical photography is used to assess the canopy cover above each stream site. The photograph to the left shows a digital hemispherical photograph of a tree canopy. These photographs are analysed using computer software to quantify percentage canopy cover and estimate light availability for a range of different tree canopy densities and species.

Photosynthetically Active Radiation

The availability of Photosynthetically Active Radiation (PAR) for each of the different light regimes is measured using a Quantum Pyranometer attached to a datalogging device which records reading each second during daylight hours. These readings are then compared to a reference 'open site' so as to quantify the percentage of the total available PAR which can penetrate the canopy. This data is used to compliment the hemispherical photography 'canopy openness' data.

Macroinvertebrate surveys

In order to quantify the macroinvertebrate populations present at each of the shaded sites along the streams, surber samples are taken from the stream substrate. The samples are analysed in the lab to quantify population diversity and abundance.

Stone scrapings

Stones are sampled at random from sites along the reach of the river under different light regimes. The stones are collected in a tray and the invertebrates and algae are scraped off the upper stone surface into sample containers and are transported on ice in a dark container to the lab for analysis. The stone surface area is recorded and invertebrate density and community together with chlorophyll-a concentration is calculated per cm2for each of the stones.

Invertebrate grazing pressure

In order to assess the impact of grazing invertebrate communities on the overall biomass of epilithic algae, their numbers are reduced by applying high voltage fields across algal colonization tiles. This method combined with 'surber' counts of invertebrates is being used to assess grazing pressure and 'gross ungrazed' algal growth potentials across both nutrient and shade gradients.

IMPLANT Research Group

University College Cork