Integration of ecological monitoring protocols for ponds in the Brussels-Capital Region: Streamlining of methodologies for Water Framework Directive, Habitats Directive and Cyanobacterial surveillance

The ecological status of standing waterbodies in the European Union is the subject of various environmental regulations, with the Habitats Directive (HD; 1992) and Water Framework Directive (WFD; 2000) comprising two important legal instruments to safeguard freshwater natural heritage. Monitoring of ponds in the Brussels-Capital Region can be specifically directed towards addressing both directives and their translation into regional legislation, as well as be tuned for surveillance of cyanobacterial blooms.
In order to optimize efficiency and completeness of the scientific protocol for pond monitoring, ecological status of a series of ponds has been assessed in 2013 and 2014, followed by selection of relevant biotic and abiotic variables and occasional adjustment of previously employed thresholds. In total, 15 ponds with ecological status ranging from clear, macrophyte-dominated to intermediately or turbid were sampled. Assessment focused on environmental parameters, phytoplankton, periphyton, aquatic vegetation (macrophytes) and zooplankton. Monitoring of macroinvertebrates and fish was considered to be sufficiently validated during previous campaigns, while inclusion and added value of phytobenthos (benthic diatoms) should be tested as part of future studies.
Overall, many of the indicators for good or bad quality correlated significantly, although several variables remain highly informative even if partly redundant. In any case, monitoring in terms of HD and WFD objectives and cyanobacterial containment requires the inclusion of a particular set of parameters.
Concerning Cyanobacteria, the current protocol seems fit for toxic bloom surveillance and response. For the purpose of WFD monitoring, a number of changes to the original scheme are proposed based on (a) observed relevance, (b) literature sources on (hyper)eutrophic peri-urban ponds, (c) elements of the ECOFRAME methodology for shallow lakes, (d) mandatory features outlined within the WFD, and finally, (e) on certain aspects equally relevant to (and therefore aiding) HD status assessment.
Important alterations of the WFD protocol for ponds in the Brussels-Capital Region are:
- change of thresholds for a number of phytoplankton parameters;
- increased attention to submerged macrophyte composition, richness and fitness;
- grouping and addition of a number of supplementary variables (including abiotic factors,
variables describing cladoceran grazing potential and impact of invasive alien species) to evaluate the supportive state of the habitat.
Based on a ‘one out, all out’ assessment of phytoplankton, macrophytes and supplementary variables, three ponds attained the WFD objective of Good Ecological Potential: Leybeek-b (2013), Rood Klooster 5 (2014) and Woluwe Park 1 (long pond, 2013 and 2014). Compared to previous methodologies, the proposed protocol tends to increase the appreciation of a seasonally stable, clear-water equilibrium dominated by a diverse submerged macrophyte community.
The potential and occurrence of two aquatic habitat types described in the Habitats Directive, H3140 (“Hard oligo-mesotrophic waters with benthic vegetation of Chara spp.”) and H3150 (“Natural eutrophic lakes with Magnopotamion- or Hydrocharition-type vegetation”) was evaluated for Brussels ponds. A dominance of characean species in clear ponds probably corresponds to H3140, and indicates the (often delicate) potential of this habitat type within the Brussels-Capital Region. Assessment of the ecological state of H3140 seems less straightforward, as characean vegetation in
5Brussels mainly consists of tolerant taxa. Of those ponds studied in 2013 and 2014, Parc Roi Baudouin 1 (2013) and Leybeek-b (2013) contained vegetation similar to H3140, but both have since degraded considerably.
For assessment of H3150, we used the methodology developed in Flanders. Although the necessary combination of relic floating-leaved macrophytes and multiple accompanying species has been observed on several occasions in the Brussels-Capital Region (e.g. Woluwe Park 1 in 2013/2014), key diagnostic species of the habitat are lacking and H3150 merely reaches a degraded state. Given the current circumstances characterized by (hyper)eutrophic nutrient conditions, unbalanced fish communities and limited dispersal opportunities, the probability of attaining sufficient or good status for H3150 in Brussels appears rather low on short notice.
Apart from harmonizing cyanobacterial, WFD and HD monitoring, we investigated spatial and temporal aspects of pond assessment. In 2013, sampling was performed from shore and repeated using a boat, in order to compare the accuracy of both methods. Sampling location affected a number of parameters, and for several variables the absolute difference between shore and boat measurements positively correlated with pond size. To obtain a complete overview of the macrophyte community the sampling effort should focus on the totality of the waterbody, and therefore vegetation analysis by boat would be the preferred method. For small, turbid ponds monitoring from the edge could be a valid approach.
In years of monitoring, tendencies of ecological degradation within the growth season – with loss of macrophytes and increased turbidity – necessitate repeated visits in order to accurately evaluate the ecosystem status. It is advised to at least sample in May/June and again in July/August, to avoid under- or overestimating the ecological value of dynamic ponds. Considering longer-term follow-up, WFD and HD monitoring cycles (three and six years, respectively) most likely exceed the expected life span of a particular ecological state in ponds of the Brussels-Capital Region. To be in line with the intrinsic philosophy of HD and WFD, habitat status of ponds should at least be checked once every three years, ideally every year.