Food web responses to habitat rehabilitation

Connectivity is a recurrent theme of my blog posts. Last year I wrote about plans for notching some of the redundant low mill weirs on a tributary of the River Aire, local to me. Those plans will come to fruition in the next few weeks as Pete Turner (Environment Agency) and I have had our bespoke environmental permit consented to progress the works, so I’ll report back to show you how the channel is evolving. I also wrote about making connections and how Mike Forty’s PhD research with Ribble Rivers Trust had thrown up some really interesting results, especially regarding the importance of free movement for precocious parr; the published work is available here.

To communicate the worth of habitat restoration work (in supporting the Ecosystem Service approach & Natural Capital principles) to the wider public and to potential future funders, and thus maintain, increase and maximise the potential impact, there is an urgent need for some simple and accessible assessments that a broad audience can appreciate. I have proposed to use the concept of the food web in this context because: a) the knock-on effects of habitat degradation translate into food web alterations very quickly; and b) the food web is recognised by a broad swathe of society (and from a very early age). Hence, measures of food webs can be used as an engagement & educational tool that will increase the understanding and value of restoration projects, as well as a tangible and effective measure for funding applications.

Bluebell Wood Weir on the Calder, Towneley Hall, Burnely

Yesterday, I spent a day putting this idea into action on the Calder at Towneley Hall, Burnley, with Gareth Jones of the Ribble Rivers Trust and keen volunteer, Tim Eldridge. As part of the Heritage Lottery-funded Ribble Life Project (part of a catchment-based approach to river basin management to help deliver the Water Framework Directive), we will use stable isotope analyses to characterise the food webs of short river sections to see how they respond to a weir removal. These will be compared to food webs on reference sections to determine the change associated with the actual weir removal. The weir will be removed in early 2017, so we were taking basal resource, invertebrate (riverfly), and fish samples yesterday to assess the situation prior to any intervention.

Weighing and measuring catch; and releasing a fine brown trout parr

It was encouraging to see some fine trout and eel specimens, as well as a reasonable diversity of invertebrates from a river which has been historically shunted to the side of the flood plain, shortened and steepened, fragmented by weirs, bordered with invasive plants, and formalised into a park in areas. Just imagine how good it could be with the barriers removed! 

Reference section of the R Calder — not perfect, but better than above!