If you have followed my blog for some time you will know that two of my professional interests are ensuring consistency in the implementation of environmental legislation across the European Union and trying to make ecological assessment as straightforward and understandable as possible. These two interests sometimes collide briefly, particularly when I am travelling, as I have an urge to grab a sample from lakes and rivers that I pass and to make a quick judgement on their quality (see “Lago di Maggiore under the microscope” and “Subsidiarity in action”). This isn’t quite as straightforward as it seems, as my specialism requires use of a microscope, and travelling light precludes carrying my field microscope on my travels. Instead, I bring small, discrete samples home and have a look at the diatoms in their live state. Enough are usually recognisable to allow me to make a rough calculation of the indices that we use to evaluate ecological status.
My visit to Romania included a trip to Lacul Cāldāruşani, on the flat lands of the Wallachian Plain about 40 kilometres north of Bucharest. It is a shallow lake, fringed by reeds (Phragmites australis) and it was from these that we collected our sample. The reed stems were all smothered with the green alga Cladophora glomerata which, in turn, hosted a rich diatom flora. Many of these could be either identified, or a plausible guess at their identity made, from the live state, so I was able to make a list of diatoms and, from this, to calculate the indices that we use in the UK to assess the quality of lakes. My conclusion was that that this was definitely an enriched lake, some way below the standards set by the Water Framework Directive, which agreed with the evidence that my Romanian hosts already had. That I can travel from near the western edge of the European Union to the eastern edge and still make a robust inference of the quality of the lake says much for the robustness of the methods with which we are dealing.
The most abundant diatom in the sample was Cocconeis pediculus, which lives on the surface of the Cladophora filaments. This means that it is, in this case at least, an epiphyte on an epiphyte, as the Cladophora was, itself, growing on the reed stems. Rhoicosphenia abbreviata is another diatom that lives epiphytically on Cladophora, and this was also common in the sample. As well as these, there were at least three species of Encyonema, mostly free-living but a few in tubes, plus Navicula tripunctata and at least one other species and a few cells of Epithemia sorex. There was also a rich assortment of green algae, but I had only limited time to dedicate to this sample, so these will have to wait for another day.
Cladophora-smothered sections of submerged stems of Phragmites australis collected from Lacul Cāldāruşani, Romania, June 2016; b. and c. Cocconeis pediculus growing on living and dead filaments of Cladophora glomerata from Lac Cāldāruşani. Scale bar: 10 micrometres (= 1/100th of a millimetre).
Diatoms from Lac Cāldāruşani, Romania, June 2016: a. two cells of Rhoicosphenia abbreviata on a stalk; b. Navicula sp.; c. Navicula tripunctata; d. Epithemia sorex; e. Encyonema sp (E. silesiacum?) growing in mucilaginous tubes. Scale bar: 10 micrometres (= 1/100th of a millimetre).
One difference between this lake and most lakes in the UK is that the Romanians have a taste for a far broader range of freshwater fish than we do. We enjoy salmon and trout, but there is not much enthusiasm for eating other freshwater fish here, in contrast to many parts of central and eastern Europe where fish such as carp are both farmed and eaten (we, in the UK, seem to have lost that taste, as many ruined monasteries have “carp ponds”). Lac Cāldāruşani has a commercial fishery, and this probably contributes to the poor quality of the water. Many shallow lakes and ponds are stocked with carp in the UK too, but for angling, not commercial fisheries. Many of these are too small to feature on the regular monitoring programs (which only covers water bodies that are at least 50 Ha in size). Carp, however, are fish that like to root around in the mud for food and, in the process, stir up the sediments releasing nutrients back into the water where they can be used by algae. The algae, in turn, die and sink to the bottom where they decay and release the nutrients back to the water, only for another carp to stir them up again. These shallow lakes are, in effect, not just polluted by this year’s inputs of nutrients, but also by pollution from the preceding decade, which is constantly being recycled as the fish search for food.
From here, we climbed back into the car to visit one other lake. The story of that lake, however, will have to wait for a future post.
References
More details about the methods for assessing lake ecological status using diatoms in the following two papers:
Bennion, H., Kelly, M.G., Juggins, S., Yallop, M.L., Burgess, A., Jamieson, J. & Krokowski, J. (2014). Assessment of ecological status in UK lakes using benthic diatoms. Freshwater Science 33: 639-654.
Kelly, M., Urbanic, G., Acs, E. Bennion, H., Bertrin, V., Burgess, A., Denys, L., Gottschalk, S., Kahlert, M., Karjalainen, S.-M., Kennedy, B., Kosi, G., Marchetto, A., Morin, S., Picinska-Fałtynowicz, J., Poikane, S., Rosebery, J. Schoenfelder, I., Schoenfelder, J., Varbiro, G.(2014). Comparing aspirations: intercalibration of ecological status concepts across European lakes for littoral diatoms. Hydrobiologia 734: 125-141.
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