title: Endpoint 'floating leaves' of potamogeton natans: a new method to evaluate the development of macrophytes in pond mesocosms.
abstract: OBJECTIVE
  One of the advantages of long-term mesocosm experiments as compared to short-term standard toxicity tests in the laboratory is the potential for detecting secondary effects due to the interaction of species and recovery with biomass of macrophytes being an important endpoint. However, generating biomass data by harvesting is often laborious, time-consuming, costly and restricted to the end of the experiment. Moreover, valuable information may get lost, in particular in single application studies, since maximal primary effects and secondary effects or recovery occur per se at different times. Potamogeton natans was used as an example in order to test whether number and area of floating leaves can be reliably measured and be used as intermediate and final end-points in mesocosm effect studies.
  
  
  METHODS
  Digital photos, which were taken of the water surface in the course of an indoor pond mesocosm study on herbicide effects, were subjected to image analysis. The results were compared to wet weight and ash-free dry weight of Potamogeton at the end of the herbicide study.
  
  
  CONCLUSIONS
  Both number and area of floating leaves indicated the same herbicide effects as wet weight and ash-free dry weight of Potamogeton. Error introduced by the different work steps is small and can be further minimised by a number of method improvements.
  
  
  CONCLUSIONS
  In indoor mesocosm studies, errors due to the perspective adjustment may be circumvented by taking the photos perpendicular to the water surface. Correction for lens aberration, identical light conditions and the use of fluorescence images are considered promising. Field applications are proposed.
authors.affiliation: Federal Environmental Agency, Schichauweg 58, 12307 Berlin, Germany. ruediger.berghahn@uba.de
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Berghahn
authors.forename: Silvia
authors.initials: S
authors.lastname: Mohr
authors.forename: Michael
authors.initials: M
authors.lastname: Feibicke
authors.forename: Stefan
authors.initials: S
authors.lastname: Meinecke
authors.forename: Erik
authors.initials: E
authors.lastname: Sperfeld
mesh_terms: D018533:Biomass; D017753:Ecosystem; D005618:Fresh Water; D006540:Herbicides / Q000633:toxicity*; D018515:Plant Leaves / Q000033:anatomy & histology / Q000187:drug effects / Q000254:growth & development; D031821:Potamogetonaceae / Q000033:anatomy & histology / Q000187:drug effects / Q000254:growth & development*; D012984:Software; D018675:Toxicity Tests / Q000379:methods
chemical_list: D006540:Herbicides