Seasonal and photochemical changes of DOM in an acidified forest lake and its tributaries

Abstract

The concentration, composition, and photochemical changes of dissolved organic matter (DOM) were evaluated in surface and bottom layers, and surface and subsurface tributaries of Plešné Lake, Bohemian Forest, Czech Republic, during one hydrological year. DOM was fractionated using the Amberlite XAD-8 and ion exchange resins into five fractions: hydrophilic neutrals, hydrophilic acids, hydrophilic and hydrophobic bases, hydrophobic acids, and hydrophobic neutrals. Photochemical transformations of DOM by photosynthetically active radiation (PAR) were tested with in-situ experiments using water from the surface tributary. The fraction composition of DOM was dominated by hydrophobic acids in all samples, with annual averages of 54 -58 % of DOM. The surface tributary differed from the subsurface one in higher and lower percentages of hydrophobic neu- Aquatic Sciencestrals and hydrophilic neutrals, respectively. The surface and bottom water of the lake did not significantly differ in the composition of DOM fractions despite significantly higher DOM concentrations at the bottom. The results of in-situ photochemical experiments showed the significance of PAR in photochemical as well as biological transformations of allochthonous DOM in this lake. The net rates of photo-production of DIC and photochemical plus biological degradation of DOC ranged from 0.3 to 0.6 and 0.6 to 4.3 µmol L -1 day -1 , respectively, with maximum values in late spring. The hydrophobic acids fraction and the remaining DOM fractions were decomposed biologically (in dark bottles) and by combined photochemical and biological degradation (in transparent bottles) at similar rates, resulting in unchanged fraction composition of DOM in the experiments.

A key role of aluminium in phosphorus availability, food web structure, and plankton dynamics in strongly acidified lakes

“…The abundance of unicellular bacteria (range: 0.5-1.2×10 6 cells mL −1 , see Vrba et al, 1996Vrba et al, , 2003bHejzlar et al, 1998), however, matches common values of oligotrophic to mesotrophic lakes. Epilimnetic bacteria, present in high biomass, utilise also photodegraded allochthonous DOC (Kopáček et al, 2003;Porcal et al, 2004). Both low P supply (or availability) and allochthonous DOC input can alternate or interplay in the bottom-up control of the plankton dynamics in the lakes .…”

Element fluxes in watershed-lake ecosystems recovering from acidification: Plešné Lake, the Bohemian Forest, 2001–2005

“…More details on these processes in Plešné Lake are given elsewhere Porcal et al, 2004). The photochemical and microbial decomposition removed a significant part of DOC supplied by surface inlets (Tab.…”

Chemical composition of aquatic dissolved organic matter in five boreal forest catchments sampled in spring and fall seasons

“…Consequently, DOM of surface waters may exhibit a high percentage of hydrophilic compounds in case leachates from mineral subsoils represent the main source of DOM in the catchment. In addition, the seasonal variability of DOM in subsoil waters is expected to be minor generating a rather uniform input of DOM into surface waters (Solinger et al 2001;Porcal et al 2004;Yano et al 2004), especially in case of coniferous forest catchments (Hongve 1999;Hongve et al 2000).…”