Redundancy in the ecological assessment of lakes: Are phytoplankton, macrophytes and phytobenthos all necessary?

Abstract

Although the Water Framework Directive specifies that macrophytes and phytobenthos should be used for the ecological assessment of lakes and rivers, practice varies widely throughout the EU. Most countries have separate methods for macrophytes and phytobenthos in rivers; however, the situation is very different for lakes. Here, 16 countries do not have dedicated phytobenthos methods, some include filamentous algae within macrophyte survey methods whilst others use diatoms as proxies for phytobenthos. The most widely-cited justification for not having a dedicated phytobenthos method is redundancy, i.e. that macrophyte and phytoplankton assessments alone are sufficient to detect nutrient impacts. Evidence from those European Union Member States that have dedicated phytobenthos methods supports this for high level overviews of lake condition and classification; however, there are a number of situations where phytobenthos may contribute valuable information for the management of lakes.

Benthic algal assessment of ecological status in European lakes and rivers: Challenges and opportunities

“…In practice, this would mean either a weak or no correlation between biological metrics and pressure gradient. However, diatom-based metrics generally show a highly significant and strong response to nutrient gradients (Kelly et al, , 2016a with correlation coefficients similar to or better than those shown by other biological elements (Birk et al, 2012). This, therefore, is not good grounds for excluding phytobenthos.…”

“…This, therefore, is not good grounds for excluding phytobenthos. Instead, the main reason stated by Member States is redundancy, noting that phytoplankton and macrophytes already address eutrophication pressure (Kelly et al, 2016a).…”

“…The 9th meeting breaks with tradition by including both rivers and lakes within its ambit, recognizing that many of the processes which influence the condition of algal assemblages in lake littoral zones and shallow rivers are similar (Cantonati and Lowe, 2014) and the methods adopted for their assessment also show considerable overlap (DeNicola and Kelly et al, 2014). The papers in the special series of papers allow a comparison with current approaches in the USA (Hausmann et al, 2016;Tang et al, 2016), present new methods for the assessment of acidification and ecological status (Juggins et al, 2016;Kelly et al, 2016b), discuss the importance of quantitative estimates of headwater stream productivity, provide tools for better management of petrifying springs (Cantonati et al, 2016), critically review the utility of phytobenthos for lake assessments (Kelly et al, 2016a), and test the utility of functional measures (such as biofilm phosphorus uptake capacity, PUC; Proia et al, 2016).…”

“…We identify four particular challenges related to the WFD implementation that will be discussed in more detail: (1) understanding and overcoming the limitations of methods that rely on a single group of algae (mostly diatoms) to the exclusion of other groups, (2) the relatively low level of adoption of phytobenthos for the assessment of lakes (Kelly et al, 2016a), (3) measurement of phytobenthos abundance, and (4) the approaches used to define boundaries between ecological classes.…”

Using benthic diatoms for estimating lake ecological quality: Comparing different taxonomic resolution

“…For each BQE, the value of a quality index should be compared to a reference value indicating minimal human impact to obtain an ecological quality ratio. Macrophytes and phytobenthos are components of freshwater flora and are included by Annex 5 of the WFD in a single BQE, but they are evaluated separately, as they can respond differently to human impact, in relation to site-specific conditions (Schneider et al, 2012;Kelly et al, 2016).…”