Are laboratory-based stable isotope dosing experiments representative of field-based experiment outcomes when exploring the role of dissolved organic matter in freshwater ecosystems?

Within the EU, an estimated 1 billion tonnes of livestock-derived organic matter are produced annually. These products frequently enter streams via urination or defecation of livestock directly into streams or by leaching of manures and fertilisers through soil. Our recent research has shown that DOM can be highly bioavailable as a nutrient resource for freshwater biota. Investigating this uptake relative to inorganic nutrient uptake using stable isotope dosing in mesocosms is a novel approach developed by our group and applied in the field. Such experiments are often considered optimal as they run under natural ambient stream conditions, but they can be costly, requiring large amounts of staff time to set up and run. An alternative approach is to perform experiments in a controlled, laboratory setting which can minimize staff time needed to set up field-based equipment, while also allowing for tight control over key limiting factors such as temperature and light during the experiments. A common criticism is that such laboratory experiments do not represent natural conditions. Here, we report the results obtained from 2 stable isotope dosing experiments in replicate mesocosms conducted in both the field and laboratory in an attempt to investigate if laboratory-based experiments can produce findings comparable to those generated under field ambient conditions. Preliminary results suggest that similar patterns are observed in bulk ¹⁵N and ¹³C uptake in both biofilms and bryophytes in laboratory and field-based experiments, though absolute rates of uptake vary between the two approaches. Further work is currently underway to examine these patterns and determine how accurate laboratory mesocosm experiments are at simulating field-based experiments.

Presentation Preference: Poster

Primary Presenter: Sydney Enns, University of Bristol (sydneyenns@gmail.com)

Authors:

Penny Johnes, University of Bristol  (penny.johnes@bristol.ac.uk)

Ana Castro-Castellon, University of Bristol  (ana.castro-castellon@bristol.ac.uk)

Sydney Enns, University of Bristol  (sydney.enns@bristol.ac.uk)