Variability of phytoplankton biomass in a lowland river: Response to climate conditions

Abstract

a b s t r a c tThe results are presented of an intensive study of phytoplankton assemblage carried out in the Berounka River above its confluence with the Vltava River (Czech Republic) in the period 2002-2007. The annual and interannual changes of phytoplankton development (based on high frequency of sampling) and their relation to hydrological conditions and concentrations of main nutrients are analysed. A marked decline of nutrient concentrations was observed during the period 1996-2007. The annual mean values of total P decreased from 0.43 mg L −1 to 0.16 mg L −1 , those of N-NO 3 from 4.6 mg L −1 to 1.5 mg L −1 and N-NH 4 from 1.9 mg L −1 to 0.04 mg L −1 . Despite this, the phytoplankton biomass remained at a high level. The seasonal mean values of chlorophyll-a ranged from 51.0 g L −1 to 116.8 g L −1 in the same time period. An obviously stronger relationship was found of the phytoplankton biomass and pattern of its development to the variation of flow rates than to the existing level of nutrient concentrations. A significantly decreasing relationship (R 2 = 0.384, P < 0.001) of chlorophyll-a to flow rates and a significantly increasing relationship (R 2 = 0.359, P < 0.001) of chlorophyll-a to water temperatures were found, based on monthly mean values for the seasonal period 2002-2007. The results obtained indicate a remarkable increase of phytoplankton biomass and its prolongated occurrence in watercourses, which can be expected due to the consequences of the predicted climate change (i.e. higher occurrence of summer droughts and low precipitation amounts accompanied by a substantial drop of flow rates, increase of air and water temperatures), as described in the respective scenarios for the territory of the Czech Republic. Simulations by the regional climate models HIRHAM and RCAO and emission scenario SRES indicated the increase of air temperature by 2.5-5 • C, decrease of precipitation amount by 6-25% and decline of flows by 14-43% in the Berounka River for the scenario period 2071-2100.

Spatial and temporal changes in chlorophyll-a concentrations in the River Thames basin, UK: Are phosphorus concentrations beginning to limit phytoplankton biomass?

“…Significant reductions in chlorophyll concentrations (an indicator of phytoplankton biomass) have been observed following reductions in phosphorus concentrations of the River Rhine in The Netherlands and the Sacramento and San Joaquin rivers in California, USA (Van Nieuwenhuyse, 2007), which supports the hypothesis that phosphorus concentration is the key control of phytoplankton biomass. Conversely, other studies have shown little relationship between river nutrient concentration and either phytoplankton or periphyton biomass (Bernhardt and Likens, 2004;Figueroa-Nieves et al, 2006;Lewis and McCutchan, 2010;Royer et al, 2008;Yang et al, 2008), and reductions in river phosphorus concentrations in recent years have not resulted in the expected reduction in chlorophyll concentrations (Desortova and Puncochar, 2011;Neal et al, 2006).…”

Impacts of climate change, land-use change and phosphorus reduction on phytoplankton in the River Thames (UK)

“…Only two sources of climatic disturbance, or climatic stressors, were employed in this study, both uniform through the year: change in precipitation and in air temperature. This strategy was adopted because it was recognised that temperature and residence time (strictly dependent on water discharge, and thus on precipitation) are the likely to be the most significant factors affecting phytoplankton concentrations and composition, as widely recognised in literature (Garnier et al, 1995;Reynolds, 2000;Desortová and Punčochář, 2011;Bowes et al, 2012). Nevertheless, other sources of climatic alteration may be relevant for the purpose of this study.…”

Climate change and plankton phenology in freshwater: current trends and future commitments

“…Whether climate or nutrients have a stronger impact on plankton phenologies is a question that has not yet been answered: emerging evidence exists for either cases (Thackeray et al, 2008;Feuchtmayr et al, 2010;Desortová and Puncochár, 2011;Shimoda et al, 2011;Sipkay et al, 2012;Zhang et al, 2012).…”