The first research I did was in biomonitoring during my MSc in 1996 at the University of Leicester supervised by David Harper. I tested a river plant index of nutrient enrichment: the Mean Trophic Rank method of Nigel Holmes (Demars & Harper 1998). This led to another work placement at the University of Glasgow in 1997 with Kevin Murphy, where I also met Vicky Abernethy and Nigel Willby (now at University of Stirling, Scotland) - Willby et al (2000). I then followed this up with a review of aquatic macrophytes as bioindicators during my national service at the University of Metz (France) with Serge Muller, where I also met Gabrielle Thiébaut (now University of Rennes, France) - Haury et al 2001.

I then started my PhD at the University of Leicester, where I tested the effects of nutrient enrichment on aquatic plant assemblages using a comparative survey in the Rivers of Norfolk (England). Study sites were located upstream/downstream from weirs and sewage treatment work effluents, throughout the river network. I found some evidence for the influence of the weir and spatial connectivity (also supported by species traits), but nothing regarding the effect of phosphorus in those nitrate rich rivers. This seriously questioned the validity of aquatic macrophyte as bioindicators of phosphorus enrichment. 

Was this a general finding? I re-analysed the data of Gabrielle Thiébaut (sandstone geology) and showed that alkalinity and the partial pressure of CO2 (pCO2) in the water were better factors than phosphorus to explain plant distribution in the Northern Vosges (Demars & Thiébaut 2008). The pCO2 was also the dominant factor explaining plant distribution in the calcareous streams of the Rhine plain (Demars & Trémolières, 2009). Amphibious plants grew happily completely submerged where the pCO2 was high but were replaced by strictly submerged plants with the ability to uptake bicarbonate at low pCO2. The pCO2 macrophyte index performed much better on independent data than the phosphorus and ammonium indices. Finally, I also used the aquatic plant surveys of Nigel Holmes and chemistry data from SEPA (Scottish Environmental Protection Agency) and the EA (Environment Agency of England and Wales) to show that it was not possible to get a reliable (causative) direct correlation between nutrients and aquatic plant assemblages or the Mean Trophic Rank (Demars & Edwards 2009). I concluded this work with a review questioning the validity of the most recent indicators (Demars et al 2012 Freshwater Biology) and the response to a national consultation on the use of nutrient thresholds for the implementation of the UK WFD (Demars 2013).

More ecological thinking and more joint thinking is required to better link and protect rivers, lakes, estuaries and coastal systems from anthropogenic impacts. My view is that we should not have to monitor every kilometre of rivers, but base river management on general scientific principles and current scientific understanding.

What then? Along the way I developed a better understanding of the role of spatial connectivity, aquatic plant ecology and drivers of species composition and diversity at multiple spatial and temporal scales (e.g. Demars & Harper 2005, Demars et al 2014). Aquatic plants are also ecosystem engineers and can harbour a distinct set of macroinvertebrate traits, as I have shown in taking forward the concept of river biotopes (Demars et al 2012, see figure at the bottom of this page).

I am now taking my research further and into biogeography. I believe we need to better integrate history and evolution in biomonitoring (Gray et al 2015). We also need to assess ecosystem functioning directly and I have now spent many years working on whole stream metabolism, gas exchange, nutrient cycling, and hydraulics. Eventually I am hoping to link biogeography to ecosystem functioning.



River biotopes and associated macroinvertebrate species traits (Demars et al 2012 Ecological Indicators)