Factors Governing Biodegradability of Dissolved Natural Organic Matter in Lake Water

Abstract

Dissolved Natural Organic Matter (DNOM) is a heterogeneous mixture of partly degraded, oxidised and resynthesised organic compounds of terrestrial or aquatic origin. In the boreal biome, it plays a central role in element cycling and practically all biogeochemical processes governing the physico-chemistry of surface waters. Because it plays a central role in multiple aquatic processes, especially microbial respiration, an improved understanding of the biodegradability of the DNOM in surface water is needed. Here the current study, we used a relatively cheap and non-laborious analytical method to determine the biodegradability of DNOM, based on the rate and the time lapse at which it is decomposed. This was achieved by monitoring the rate of oxygen consumption during incubation with addition of nutrients. A synoptic method study, using a set of lake water samples from southeast Norway, showed that the maximum respiration rate (RR) and the normalised RR (respiration rate per unit of carbon) of the DNOM in the lakes varied significantly. This RR is conceived as a proxy for the biodegradability of the DNOM. The sUVa of the DNOM and the C:N ratio were the main predictors of the RR. This implies that the biodegradability of DNOM in these predominantly oligotrophic and dystrophic lake waters was mainly governed by their molecular size and aromaticity, in addition to its C:N ratio in the same manner as found for soil organic matter. The normalised RR (independently of the overall concentration of DOC) was predicted by the molecular weight and by the origin of the organic matter. The duration of the first phase of rapid biodegradation of the DNOM (BdgT) was found to be higher in lakes with a mixture of autochthonous and allochthonous DNOM, in addition to the amount of biodegradable DNOM.

Catchment properties as predictors of greenhouse gas concentrations across a gradient of boreal lakes

“…It explained 6.88 and 28.8% of the total deviance explained in CO 2 and N 2 O models, respectively (Table 2). The positive correlation between the agricultural land cover (Cultivated) and CO 2 concentrations in boreal lakes has been pointed out previously (Kortelainen et al, 2006), likely reflecting inputs of easily degradable DOM (Crapart et al, 2021) as well as nutrient loads from croplands (Rantakari and Kortelainen, 2005). For N 2 O saturation, a positive correlation between N 2 O saturation and agricultural land cover has previously been reported previously for boreal lakes (Kortelainen et al, 2020).…”

“…This synoptic survey repeated previous campaigns conducted in 1986and 1995(Henriksen et al, 1998. The CBA dataset span a wide range of water quality properties (e.g., DOM, nutrients) (Crapart et al, 2021), catchment properties, and land use (Lie, 2021). Sampling was performed in late fall, during or after lake overturn.…”

Ecohydrology of two northern Wisconsin bogs

“…Recent experimental evidence suggests that such pathways may limit the mineralization rate of humic DOM in nature, explaining its apparent recalcitrance. In laboratory incubations, Crapart et al (2021) showed that DOM from dystrophic Scandinavian lakes can be degraded fairly easily if inorganic N and P are added in excess.…”

Distinguishing between Sources of Natural Dissolved Organic Matter (DOM) Based on Its Characteristics

“…Interestingly, the relative respiration rate of the DOM (Rel. RR, unpublished data), serving as a proxy for biodegradability [48], also exhibited a strong negative correlation with the proportion of VHA (Table 2). This adheres to the fact that the high molecular and aromatic VHA fraction has a lower biodegradability than other DOM moieties.…”