Authors: Susanne Rolinski Heidemarie Horn Thomas Petzoldt Lothar Paul
Publish Date: 2007/07/12
Volume: 153, Issue: 4, Pages: 997-1008
Abstract
Phenology and seasonal succession in aquatic ecosystems are strongly dependent on physical factors In order to promote investigations into this coupling methods of characterising annual time series of phytoplankton were derived and applied to a 31year data set from Saidenbach Reservoir Saxony Germany Field data are often scarce and irregularly sampled particularly in the transition period from winter to spring so reliable methods of determining cardinal dates in the time series are necessary The proposed methods were used to determine the beginning maximum and end of the spring mass development of phytoplankton by estimating the inflexion points A fitting a Weibulltype function B and fitting linear segments to the logarithmic values C For the data set from Saidenbach Reservoir all three methods proved to be relevant to the analysis of longterm trends Differences between the maxima determined by the different methods seemed small but there were deviations when the maximum was related to physical factors such as iceout The Weibulltype fit gave the most reliable and comprehensible results and is recommended for trend analyses For all methods longterm analysis of the duration of the spring mass development and the duration of the spring full circulation revealed a period of consistently low values 1975–1990 followed by a period of higher values 1990–2005 These periods were also identified for the date of iceout although in this case there was a period of high values followed by a period of low values A sensitivity analysis that compared results from subsampled time series with increasing time intervals indicated that a minimum of one sample every three weeks is needed to obtain reliable resultsThis study is supported by the German Research Foundation DFG under grant PA 1202/1 of priority programme 1162 AQUASHIFT The authors are grateful to Karsten Rinke and Stephan Hülsmann for fruitful discussions Otto Richter for bringing up the Weibull function and two anonymous referees for their detailed persevering and constructive suggestions and their encouragement of the sensitivity analysis
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