Organic Matter In Lake Water Research Articles

Recycled by leaf inhabitants: Terrestrial bacteria drive the mineralization of organic matter in lake water

AbstractTerrestrial organic matter subsidizes aquatic food webs and plays an important role in carbon cycling in lake ecosystems, where it is decomposed mainly by microbes. However, the contribution of terrestrial and aquatic microbiomes on terrestrial carbon cycling and their effects on the biochemical fate of carbon has remained understudied. Therefore, we explored the microbial carbon utilization of three chemically differing leaf species in lake water in microcosms and quantified the biochemical endpoints of leaf carbon in CO2, CH4, and microbial biomass. Additionally, we identified microbial taxa responsible for leaf carbon recycling and studied the role of epiphytic and endophytic leaf microbiomes in microbial community succession in lake water. Microbially utilized leaf carbon was mainly respired (82.7 ± 1.4%), whereas a small proportion (17.1 ± 1.4%) was assimilated into biomass. Carbon from nitrogen‐rich alder leaves was taken up at the fastest rate, whereas birch leaf addition produced the highest concentrations of CH4, suggesting that leaf chemistry affects the decomposition rate and biochemical fate of carbon. In particular, terrestrial bacteria shaped the succession of aquatic bacterial communities. The addition of leaves resulted in the equal contribution of epiphytic and endophytic bacteria in the lake water, whereas epiphytic fungi dominated the fungal community structure. Our results suggest that terrestrial bacteria originating from terrestrial leaves influence the microbiome succession in lake ecosystems and play a key role in linking terrestrial carbon to an aquatic food web and determining the quality of carbon emissions that are released into the atmosphere.

Factors Governing Biodegradability of Dissolved Natural Organic Matter in Lake Water

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.

Impact of hydrophyte decomposition on the changes and characteristics of dissolved organic matter in lake water

Abstract Hydrophyte decomposition can generate a large amount of decomposed organic matter that results in potential risks to water quality. Dissolved organic matter (DOM) collected from lake water induced by hydrophyte decomposition may play a key role in understanding the change in the water quality. Spectroscopic techniques can reveal the spectral properties of DOM and their impact on the water quality under oligotrophic and eutrophic growth conditions, such as the application of ultraviolet visible (UV–vis) spectra and fluorescence spectroscopy in combination with parallel factor analysis (PARAFAC) method. The results indicated that dissolved organic carbon (DOC), a350, and UV absorption in a unit of TOC at 254 nm (SUVA254) values under eutrophic growth conditions in summer are generally higher than those under oligotrophic conditions in winter. Five fluorescent components, including one humic-like substance (C4), one fulvic-like material (C3) and three protein-like materials (C1, C2 and C5) were obtained by PARAFAC analysis from hydrophyte-derived DOM samples under different growth conditions and in different seasons. The Fmax of the different fluorescent components were greatly influenced by hydrophyte decomposition, and varied under these different conditions. The results of water quality parameters also showed that dissolved oxygen (DO), chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN) concentrations for oligotrophic and eutrophic conditions in the summer (OS and ES) samples were generally higher than those in the winter samples. The characterization of hydrophyte decomposition DOM is of great importance in eutrophic lake management. Thus, much effort should be put into the study of hydrophyte-derived DOM characteristics and their potential risks as a carrier of hazardous pollutants. The study provides scientific guidance for lake clean water management.

Preferential sequestration of terrestrial organic matter in boreal lake sediments

AbstractThe molecular composition and origin has recently been demonstrated to play a critical role in the persistence of organic matter in lake water, but it is unclear to what degree chemical attributes and sources may also control settling and burial of organic matter in lake sediments. Here we compared the annual contribution of allochthonous and autochthonous sources to the organic matter settling in the water column and present in the sediments of 12 boreal lakes. We used the fluorescence properties and elemental composition of the organic matter to trace its origin and found a consistent pattern of increasing contribution of terrestrial compounds in the sediments as compared to the settling matter, with an annual average allochthony of ~87% and ~57%, respectively. Seasonal data revealed a predominance of in‐lake‐produced compounds sinking in the water column in summer. Yet only a slight concurrent decrease in the contribution of terrestrial C to lake sediments was observed during the same period, and sediment allochthony increased again to high levels in autumn. Our results reveal a preferential preservation of allochthonous matter in the sediments and highlight the role of lakes as sequesters of organic carbon primarily originating from the surrounding landscape.

Effects of preadsorption by carbon black on membrane filtration of natural organic matter

This study aimed to assess the performance of two carbonaceous adsorbents, i.e. self-dispersible carbon black (CB) particles (130 nm) and powdered activated carbon (PAC; 151 µm), in the hybrid treatment with microfiltration or ultrafiltration. It was revealed that, although the dissolved organic carbon (DOC) removal by CB was less than that by PAC, addition of CB prior to the membrane filtration significantly reduced membrane fouling, whereas PAC addition brought about a severe membrane fouling. The difference between these two adsorbents was explained by the dominance of aromatic organic matter in lake water, selective adsorption of organics by the adsorbents, and a change of the cake structure of the adsorbents during the membrane filtration.

Sudden enhancement of sedimentation flux of 210Pbex as an indicator of lake productivity as exemplified by Lake Chenghai

The fundamental assumption of 210 Pb sediment dating is the stable flux of 210 Pb ex , which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the 210 Pb ex activity in sediments will be exponentially reduced with sedimentation age. 210Pbex in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly in-creased, 210 Pb ex will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of 210 Pb dating; on the other hand, the sudden enhancement of 210 Pb ex flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of 210 Pb ex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of 137Cs activity is characterized by a tree-peak pat-tern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of 210 Pb ex activity displays a specific distribution of peaks, and is similar to the vertical profile of Corg. This phenomenon seems to be related to the mecha-nism of constraining the transfer of 210 Pb ex into lake sediments. The average atomic ratios of H org /C org and C org /N org in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition- de-composition-accumulation”, the sedimentation fluxes ( F (C org )) of organic carbon (C org ) since 1970 were calculated by modeling. The sedimentation fluxes of 210 Pbex ( F ( 210 Pb ex )) in different years display good synchronous relations with the sedimentation flux of organic carbon ( F (C org )), es-pecially in the years of 1972─1974 and 1986─1989. The variation of F (C org ) led to the variation of F ( 210 Pb ex ); the variation of F ( 210 Pb ex ) reflects, to some extent, the historical variation of lake pro-ductivity.

First derivative UV spectra of surface water as a monitor of chlorination in drinking water treatment.

Many countries require the presence of free chlorine at about 0.1 mg/l in their drinking water supplies. For various reasons, such as cast-iron pipes or long residence times in the distribution system, free chlorine may decrease below detection limits. In such cases it is important to know whether or not the water was chlorinated or if nonchlorinated water entered the system by accident. Changes in UV spectra of natural organic matter in lakewater were used to assess qualitatively the degree of chlorination in the treatment to produce drinking water. The changes were more obvious in the first derivative spectra. In lakewater, the derivative spectra have a maximum at about 280 nm. This maximum shifts to longer wavelengths by up to 10 nm, decreases, and eventually disappears with an increasing dose of chlorine. The water treatment system was monitored by this technique for over 1 year and changes in the UV spectra of water samples were compared with experimental samples treated with known amounts of chlorine. The changes of the UV spectra with the concentration of added chlorine are presented. On several occasions, water, which received very little or no chlorination, may have entered the drinking water system. The results show that first derivative spectra are potentially a tool to determine, in the absence of residual chlorine, whether or not surface water was chlorinated during the treatment to produce potable water.

Colloidal and dissolved organic matter in lake water: Carbohydrate and amino acid composition, and ability to support bacterial growth

Bacterial utilization of dissolved organic matter (DOM) was studied in water from a humic and a clearwater oligotrophic lake. Indigenous bacteria were inoculated into either 0.2 μm natural filtered lake water, or lake water enriched fivefold with colloidal DOM >100 kD but below 0.2 μm. Consumption of DOM was followed from changes in concentrations of total dissolved organic carbon (DOC), dissolved combined and free carbohydrates and amino acids (DCCHO and DFCHO, and DCAA and DFAA, respectively) and by uptake of monosaccharide and amino acid radioisotopes. DCCHO and DCAA made up 8% (humic lake) to 33–44% (clear-water lake) of the natural DOC pools, while DFCHO and DFAA contributed at most 1.7% to the DOC pools. Addition of >100 kD DOM increased the DOC concentrations by 50% (clearwater lake) to 92% (humic lake), but it only resulted in a higher bacterial production (by 63%) in the humic lake. During the incubations 13 to 37% of the DOC was assimilated by the bacteria, at estimated growth efficiencies of 4–8%. Despite the measured reduction of DOC, statistically significant changes of specific organic compounds, especially of DCCHO and DCAA, generally did not occur. Probably the presence of high molecular weight DOC interfered with the applied analytical procedures. Addition of radiotracers indicated, however, that DFAA sustained 17–58% and 29–100% of the bacterial carbon and nitrogen requirements, respectively, and that glucose met 1–3% of the bacterial carbon requirements. Thus, our experiments indicate that radiotracers, rather than measurements of concentration changes, should be used in studies of bacterial utilization of DOC in freshwaters with a high content of humic or high molecular weight organic matter.

Spring bloom in a hypereutrophic lake, lake Kasumigaura, Japan—III Phytoplankton abundance in standing stock of organic matter in lake water

The rapid increase of phytoplankton biomass was the major process for the increase of particulate organic matter in Lake Kasumigaura in 1980. During the first phytoplankton pulse in the bloom relative abundance of each component of organic matter in the lake water was: dissolved organic matter 100, phytoplankton 28, bacteria 27, and detrital particle 27. This relative abundance was maintained as a steady-state oscillation throughout the spring bloom similar to that usually observed in moderately eutrophic waters. Thus phytoplankton abundance in the standing stock of organic matter of the hypereutrophic water during the spring bloom does not show any marked difference from that of moderately eutrophic waters.

Dissolved Organic Matter in Lakewater: Characteristics of Molecular Weight Size-Fractions and Ecological Implications

The dissolved organic matter pool in a soft-water lake was fractionated into six molecular weight components using ultramembrane filtration. A statistical relationship was found between organic carbon concentrations and molecular weight ranges within individual size-fractions. In characterizing these fractions, high (> 100000-50000) and low (2000-0) molecular weight organic materials were found to be labile (about 50 % decomposed in 4 h), following exposure to UV-light, while intermediate sized fractions (50000-2000) were essentially refractory. Chelation-complexation capacity for inorganic iron (59Fe) by high and low molecular weight fractions was increased significantly following exposure to UV-light. Bacterial 14C-labelled extracellular products were found to decompose at different rates in comparison to 12C organic compounds in individual molecular weight fractions, following exposure to UV-light, suggesting they were qualitatively different from one another.

Effect of carbohydrates on the symbiotic growth of planktonic blue-green algae with bacteria.

PHOSPHORUS and nitrogen have been suggested to be limiting agents in the unwanted growth of Cyanophyta. Removal of phosphorus from sewage effluents is being considered as the preferred method to control eutrophication. The significance of organic matter in lake water has been largely disregarded, although carbonaceous material is always found in productive lakes, for example, from 22 mg to 99 mg/l. of dissolved organic matter in the Great Lakes1. Massive growths of blue–green algae have been documented before the use of industrial phosphates, and they probably occurred always after a heavy influx of organic matter. Maximum growth of phytoplankton does not require high concentrations of phosphorus. As little as 0.02 mg of phosphorus/l. in natural lake water may sustain it2. Additional phosphorus alone does not increase growth because algal growth will depend on the presence and availability of not less than fifteen essential elements3.