Impact of nutrient and water level changes on submerged macrophytes along a latitudinal gradient: a pan-european mesocosm experiment

Ersoy, Zeynep
Ongoing climate warming will affect freshwater ecosystems worldwide. In addition to a temperature rise, increased precipitation and enhanced nutrient runoff is anticipated for Northern Europe, whereas decreased precipitation, decreased water levels and intensified drought conditions are expected for Southern Europe and the Mediterranean region. We conducted a controlled Pan-European mesocosm experiment in six countries along a latitudinal temperature gradient from Sweden to Greece to elucidate the effect of climate on macrophyte growth in shallow lakes with contrasting depths (shallow and deep) and nutrient levels (low and high). Physico-chemical variables, light attenuation and percent volume inhabited (PVI %) of submerged plants were sampled monthly during one season (May-November 2011). At the end of the experiment, macrophytes were harvested and dried. Water level changed only marginally (ranging from -3 to +8 cm) in northern countries; whereas an average of 46 cm and 83 cm water level decrease occurred in Turkey and Greece, respectively. Mean air temperature was highest in Greece (23.4 oC), followed by Turkey (18.7 oC). During the experiment, submerged macrophytes grew in all shallow mesocosms irrespective of nutrient treatments. ). ANCOVA results indicated a significant effect of depth- nutrient and temperature-nutrient interactions on PVI%. High temperatures with low nutrient conditions gave rise to higher PVI% in shallow mesocosms which followed an increasing pattern from Sweden to Greece with an increase in mean air temperature. Shallow high nutrient mesocosms also exhibited high PVI% in Turkey, likely due to decreased water level, but not in Greece where extreme water level drop was detrimental for macrophyte growth. We conclude that the combined effects of water level decrease and temperature increase stimulated macrophyte growth even under unfavourable light environment and high nutrient conditions. Nonetheless, an extreme water level decrease had negative effects on macrophyte growth by means of sun exposure, desiccation and eutrophication. Our results therefore indicate that global climate warming and eutrophication may negatively affect the development of macrophytes, if longer and intense drought periods become more common.
Citation Formats
Z. Ersoy, “Impact of nutrient and water level changes on submerged macrophytes along a latitudinal gradient: a pan-european mesocosm experiment,” M.S. - Master of Science, Middle East Technical University, 2015.