A one‐year study of the Rostherne Mere ecosystem: seasonal dynamics of water chemistry, plankton, internal nutrient release, and implications for long‐term trophic status and overall functioning of the lake

Abstract

Abstract:A study of Rostherne Mere (Cheshire, UK) was undertaken to reveal relationships among various ecosystem components and assess the progress in lake recovery following sewage diversion. An intensive monitoring programme included measurements of dissolved oxygen, T, pH, electric conductivity, K, Mg, Ca, Si, N and P species, Secchi depth, suspended solids, chlorophyll-a, phyto-and zooplankton counts. Recorded changes and the results of correlation analysis broadly confirmed to the classic limnoecological theory and allowed detailed interpretation of the dynamics observed. The Si level was used to estimate the amount of diatom detritus produced in spring. Chemical profiles were used to estimate the amount of nutrients accumulated in the hypolimnion during the stratified period. These estimates were compared with simulations made using the model of exponential decay, which showed a good performance in the case of Si but considerable underestimation in the case of P. The differences between the values simulated by the model and estimates based on field observations resulted from the additional P release from the sediments. This release could have been stimulated by a combination of factors, including the development of anoxic layers on the sediment-water interface and Si-induced desorption from Fe, Al and Mn oxides. Internal P loading during the stratified period was thus estimated at about 4-9 g/m 2 , suggesting that rapid changes in the lake's trophic status are at present unlikely. Certain aspects of this work (including interpretation of interrelationships between ecosystem components, estimation of the decomposition constant, analysis of factors controlling nutrient accumulation in the hypolimnion, and a low-cost method to estimate internal P release) may be useful for studies of other aquatic systems and have, therefore, general limnological applicability.

Importance of biological and abiotic factors for geochemical cycling in a freshwater eutrophic lake

“…Although this pattern was fully confirmed in our previous research (Krivtsov et al 2001d), in 1998 some notable differences were obvious. Despite the excessive availability of Si, the diatom peak in spring did not occur and the local peak of Chl recorded on the 3 Apr resulted from the increased concentrations of flagellates (Krivtsov 2000).…”

“…It is worth mentioning, however, that hypolimnion temperatures recorded by our previous research (i.e. 6-8 degrees -see Krivtsov et al 2001d) were typically lower than those recorded in this study (i.e. up to 12 degrees).…”

“…elevation, rotation, perspective) of the particular graphs were chosen to obtain maximum visibility of the data. This presentation of hydrochemical profiles follows the presentation adopted in our previous work (Krivtsov et al 2001d). Significant Pearson correlation coefficients for the monitored time series are listed in Table 1.…”

“…Rostherne Mere, arguably, is the best-studied British freshwater lake (for maps, general description and further references see, e.g., Woof and Wall 1984;Carvalho 1993;Krivtsov et al 1998Krivtsov et al , 2001dKrivtsov et al , 2002b. The previous studies have addressed the lake's water and nutrient budgeting (see Krivtsov et al 2001bKrivtsov et al , 2002b and references therein), and there is an impressive long term monitoring record of the lake's planktonic community (e.g.…”

“…compared to the research presented here) limited. Most of these studies (Grimshaw and Hudson 1970;Davison and Woof 1984) were carried out before sewage diversion (for details of sewage diversion see Carvalho 1993) rather a long time ago, whilst the recent research (Krivtsov et al 2001d), did not include analysis of Fe, Mn, S, Na, DOC and Al. The purpose of this paper is to provide an up to date information on the seasonal dynamics of biota and hydrochemical profiles, to analyse interrelations between the dynamics of biological community and geochemical turnover of C, P, N, Si, Ca, Mg, K, Na, S, Fe, Mn and Al, and to assess implications for long term trophic status of the mere.…”