Decomposition Of Aquatic Macrophytes Research Articles

Underestimated indirect and persistent effects of decaying macrophytes on aquatic ecosystem through alteration of bacterial community structure and function

The rapid release of nutrients by aquatic macrophyte decomposition directly results in the degradation of water quality and the deterioration of aquatic ecosystems. However, decaying macrophytes have indirect negative effects, mediated by bacteria in aquatic ecosystems, which may have long been underestimated. In this study, 16S rRNA sequencing was used to investigate the structural succession, possible metabolic function shifts, and specific environmental drivers of the bacterial community during the decomposition of four typical aquatic macrophytes over 188 days. Results indicate that nutrients released by macrophyte residues alter the physiochemical properties of overlaying water and have dual concentration effects of low promotion and high inhibition on α- and β-diversity of bacteria, driving their succession in different directions. High nutrient concentrations not only resulted in more substantial changes in the abundance of dominant bacteria at various taxonomic levels, but also inhibited carbon and nitrogen metabolic functions while promoting the phosphorus and sulfur metabolic functions of the bacterial community, which was in contrast to the effects of low nutrient concentrations. These effects persisted for a long time, potentially leading to a decrease in redundant genes and the loss of rare functional genes. This, in turn, indirectly reducing the structural stability of aquatic ecosystems and their resilience to external disturbances. Our findings indicate that the indirect and persistent negative impacts of macrophyte decomposition on aquatic ecosystems should not be ignored and that macrophyte residues should be harvested and properly treated before they undergoing explosive nutrient release.

Effects of Submerged Macrophyte Decomposition on Water Quality

Submerged macrophytes play an important role in aquatic ecosystems and are widely used in aquatic ecological restoration. However, when submerged macrophytes fade, litter, or even decompose, they may cause adverse effects on water quality. In this article, indoor experiments were carried out to study the quantitative influence of submerged plant decomposition on water quality. Six submerged macrophytes commonly used in aquatic ecological restoration in Sichuan Province, including Elodea canadensis Michx., Potamogeton wrightii Morong, Potamogeton crispus L., Vallisneria spinulosa, Ceratophyllum demersum L., and Potamogeton pectinatus L., were selected to measure the change processes of nutrients during macrophyte decomposition at 10°C, 20°C and 30°C. The results showed that the decomposition of submerged plants released nutrients into the water body, causing water pollution. At 10°C, the total phosphorus (TP) concentration of water bodies containing submerged plant litter increased by 1.97 to 5.97 times on the 50th day compared to the 5th day, while the TP concentration of the blank control group without hydrophytes decreased from 0.39 mg.L-1 to 0.22 mg.L-1 due to self-purification. The ammonia nitrogen (NH3-N) concentration increased by 3.82-9.58 times on the 50th day compared with the 5th day, while the value in the blank control group decreased from 1.42 mg.L-1 to 0.78 mg.L-1. This result indicated that the water body had a certain self-purification ability, but the decomposition of aquatic macrophytes had a negative impact on this progress. Increasing temperatures could accelerate plant decay processes. Initially, the concentrations of NH3-N and TP were high with high temperatures. After 45 days of reaction, the NH3-N and TP concentration in the water bodies appeared to be 30°C<20°C<10°C, indicating that decomposition was further advanced when the temperature was higher. This study provides a theoretical basis for water ecological management and water quality protection.

Ecological Productivity Studies of the Dominant Aquatic Macrophytes in Kapla Beel, Assam North East India

The present research work was carried out to study the primary productivity of dominant aquaticmacrophytes with reference to water quality parameters during the year 2017 and 2018. Dominant aquaticplant species were found out based on IVI values. Among the dominant macrophytes, Eichhornia crassipesshowed the maximum productivity values (1134gm/m2) during the summer as well as the winter seasons(659gm/m2).While Hygroryzaaristata showed lowest productivity values (438gm/m2 and 376gm/m2) bothin summer and winter seasons respectively. The macrophytes showed positive correlation with temperature,pH and turbidity while they showed highly negative correlation with DO. Luxuriant growth of thesemacrophytes and their subsequent death and decay results the lower dissolved oxygen value of the waterbody. It is due to the fact that during decomposition of aquatic macrophytes, microorganisms uses most ofthe oxygen dissolved in water body. Therefore aquatic macrophytes can be used for indicators of waterquality and their presence may enhance the water quality due to their ability to absorb excess nutrientsfrom the water body.

In Situ Monitoring of a Eutrophicated Pond Revealed Complex Dynamics of Nitrogen and Phosphorus Triggered by Decomposition of Floating-Leaved Macrophytes

To explore the influence of the decomposition of aquatic macrophytes on water quality in eutrophicated aquatic ecosystems and the interacting environmental factors that trigger nitrogen (N) and phosphorus (P) dynamics, a suburban pond with floating-leaved macrophytes (Pond A) as well as another nearby newly dug pond without any obvious aquatic macrophytes (Pond B) were studied. N and P levels together with a series of parameters relating to biomass, water and sediments were monitored during a period of 84 d that covered the entire decomposition process of plants. The results show that the decomposition of aquatic macrophytes can be divided into two phases, with the first phase having a faster decomposition rate and the second phase, a slower one. With the decomposition of biomass, the dissolved oxygen (DO), oxidation-reduction potential (ORP), and pondus hydrogenii (pH) of the water body increased, whereas the permanganate index (CODMn) decreased. Significantly higher levels of total phosphorus in both water and sediment (TPW and TPS) were detected in Pond A with macrophytes; TPW increased quickly during the first phase of biomass decomposition but decreased in the second phase, and TPS remained relatively stable during the first phase but increased slowly in the second phase. Total nitrogen in both water and sediment (TNW and TNS) was also significantly higher in Pond A but remained relatively stable. A structural equation model revealed that the decomposition of aquatic macrophytes, could, directly and indirectly, influence N and P cycles in an aquatic ecosystem through the regulation of pH and DO. Our study indicate that the decomposition of biomass exerted a greater influence on P than on N. Besides the direct release of P from decaying biomass, which caused a significant increase of P in water body, changes of DO and ORP and the subsequent redox state of the whole system during the process also indirectly affected the deposition and dissolution of P between sediment and water. P was the decisive factor that caused endogenous eutrophication in ponds containing aquatic macrophytes.

Integrating species mixture to improve insights into the home-field advantage of aquatic macrophyte decomposition in a eutrophic urban lake, China

Integrating species mixture to improve insights into the home-field advantage of aquatic macrophyte decomposition in a eutrophic urban lake, China

Vallisneria natans decomposition rates and associated macroinvertebrates, microbes and microalgae along a vertical depth gradient in an urban lake (Nanhu Lake, China)

ABSTRACTKnowledge on aquatic macrophyte decomposition has well developed, yet the decomposition and associated biotic factors along a vertical gradient in waters remain less examined. Here, we used Vallianeria natans leaves to investigate the decomposition rate and associated decomposers and microalgae at different vertical depths, by placing V. natans leaves into litterbags (0.5 and 5 mm meshes) and incubating them at the air–water interface (AW), sediment-water (SW) interface, and 10 cm (B10) or 20 cm (B20) burial in sediment over 60 days in a littoral zone of lake. Decomposition rates decreased with increased depths in each mesh size, with significant differences among and between AW (0.028 d−1), SW (0.022 d−1), B10 (0.014 d−1) and B20 (0.011 d−1) treatments in 0.5 mm litterbags and no significant difference between B10 (0.027 d−1) and B20 (0.025 d−1) in 5 mm litterbags. The average contribution of macroinvertebrates to biomass loss was highest in B20 (44.66%), lowest in AW (22.66%) and midst in both SW (25.35%) and B10 (38.78%), and was much less than that of both microbes and microalgae at each location. We show the importance of macroinvertebrates, microbes and microalgae in mediating macrophyte decomposition rate in response to different vertical locations in freshwaters.

Reservoir management: an opinion to how the scientific community can contribute

Abstract Aim To report possible academic experiences as strategic contributions to help manage reservoirs ensuring multipurpose uses. Methods In this opinion article, we point out and discuss academic activities that are usually developed to assess environmental studies in reservoirs. Results Experience shows that various contributions can be highlighted in reservoir management, as well as direct contributions for decision-making of the environmental authorities involved, such as: i) development of experimental procedures to solve specific problems; ii) sampling planning activities; iii) analysis, integration and synthesis of data; iv) qualification of human resources, etc. It is important to mention that all academic activities reported in this article are potentially publishable in scientific journals (knowledge areas: environmental management, limnology, sanitation, public health and aquatic ecology). Conclusions According to the related activities, we identified strong academic orientation (water quality determination, greenhouse gas inventories and water quality simulation using mathematical models, aquatic macrophyte decomposition and growth experiments) for reservoir management.

The effects of litter quality and living plants on the home-field advantage of aquatic macrophyte decomposition in a eutrophic urban lake, China

The ‘home-field advantage’ (HFA) hypothesis states that litter decomposes faster in its ‘home’ habitat, i.e., in the same habitat as the plant species from which it was derived than it does ‘away’ from its home, i.e., in the habitat of a different plant species. However, studies pertaining to HFA in aquatic ecosystems are relatively few. One area not well-studied is whether the presence of living plants has an effect on the HFA of aquatic macrophyte decomposition in a eutrophic lake. Here, we conducted reciprocal litter transplanting experiments, coupled with removal of living plants, between a dominant submerged macrophyte (Myriophyllum spicatum) and a floating-leaved macrophyte (Trapa natans) in a eutrophic urban lake in China, for 50 days. Test plots were created at sites by removing the dominant macrophytes from their ‘home’ habitats to test the effect of living plants on decomposition rates and HFA effect. The water chemistry of the two sites was not significantly different. The initial litter qualities were significantly higher in M. spicatum than in T. natans. The decomposition rates of T. natans were significantly greater in both the control and test plots in its ‘home’ habitat, indicating a positive HFA effect, while the decomposition rates of M. spicatum were significantly greater in the ‘away’ habitat compared to its ‘home’ habitat in all treatments, indicating a home-field disadvantage effect. The removal of living plants had a noticeable effect on the abundance of associated-macroinvertebrates, but had an inconsistent effect on decomposition rates providing conflicting evidence for HFA. In total, 10 macroinvertebrate taxa from four functional feeding groups (FFGs) were collected during the experiment. Compared to macroinvertebrate communities, microbial activities showed less correlation with decomposition rates. Our results provide evidence to suggest that decomposition-based HFA is dependent upon litter quality, habitat, and their interactions in a eutrophic urban lake.

Decomposition characteristics of three different kinds of aquatic macrophytes and their potential application as carbon resource in constructed wetland

Decomposition of aquatic macrophytes usually generates significant influence on aquatic environment. Study on the aquatic macrophytes decomposition may help reusing the aquatic macrophytes litters, as well as controlling the water pollution caused by the decomposition process. This study verified that the decomposition processes of three different kinds of aquatic macrophytes (water hyacinth, hydrilla and cattail) could exert significant influences on water quality of the receiving water, including the change extent of pH, dissolved oxygen (DO), the contents of carbon, nitrogen and phosphorus, etc. The influence of decomposition on water quality and the concentrations of the released chemical materials both followed the order of water hyacinth > hydrilla > cattail. Greater influence was obtained with higher dosage of plant litter addition. The influence also varied with sediment addition. Moreover, nitrogen released from the decomposition of water hyacinth and hydrilla were mainly NH3-N and organic nitrogen while those from cattail litter included organic nitrogen and NO3−-N. After the decomposition, the average carbon to nitrogen ratio (C/N) in the receiving water was about 2.6 (water hyacinth), 5.3 (hydrilla) and 20.3 (cattail). Therefore, cattail litter might be a potential plant carbon source for denitrification in ecological system of a constructed wetland.

Biomass loss and nutrient release from decomposing aquatic macrophytes: effects of detrital mixing

Aquatic plant decomposition is typically studied on species held separately, whereas diverse plant communities are usually found in lake littoral zones and decomposition occurs as mixtures of multiple species. Here, we examined whether detrital mixing affects the rate of aquatic macrophyte decomposition. Specifically, we measured decomposition rates of detritus from four species (Myriophyllum heterophyllum, Ceratophyllum demersum, Typha × glauca, and Potamogeton robinsii) in single, double, triple, and quadruple species mixtures held over two summer months in a mesotrophic lake in southern Ontario, Canada. We measured detrital mass loss after different time periods for all combinations. There were limited effects of mixing on decomposition rates with inhibitory effects observed in only two of the eleven multi-species mixtures. Decomposition rates of single and mixed species detritus varied with initial C:N and C:P ratios with faster rates seen for more nutrient-rich detritus. Overall, there was no effect of detrital species richness on macrophyte decomposition rates other than smaller differences among the averages of more species-rich mixtures. Our results were inconsistent with interactive effects of mixing on decomposition rates of multiple aquatic plant taxa. Instead, we found decomposition rates of mixed species communities were largely predicted by biomass composition and single-species decomposition estimates. There were also no apparent effects of species mixing on N- or P-specific fluxes or the ratio of these fluxes that resulted during decomposition during our experiment. Our results indicate that future changes in aquatic plant biodiversity may affect rates of decomposition in these ecosystems, but these should be largely predictable based on changes in plant communities and their biomass-weighted stoichiometry.

Potential Methane Production Associated with Aquatic Macrophytes Detritus in a Tropical Coastal Lagoon

Anaerobic decomposition of aquatic macrophytes in the sediment of wetlands is a key source of methane to the atmosphere. An experiment was conducted in order to evaluate the potential methane production (PMP) in the sediment colonized by three species of aquatic macrophytes and in the limnetic region of a tropical coastal lagoon. The incubations were prepared and maintained (70 days) at 25.0 °C, and the PMP was measured by gas chromatography. The initial concentrations of dissolved organic carbon (DOC), carbohydrates and methane in the sediment were also measured. The sediment colonized by emergent aquatic macrophytes showed higher PMP due to the higher amounts of carbohydrates. On the other hand, PMP was lower in the limnetic region, which showed lower amounts of carbohydrates. The carbon found in the limnetic region is mainly originated from the refractory detritus of aquatic macrophytes that reaches the central region of the lagoon, with lower carbohydrate content. These results indicate that detritus quality, which means highest concentration of carbohydrates in the DOC, was the main controlling factor of methanogenesis.

Oxygen availability and temperature as driving forces for decomposition of aquatic macrophytes

The decomposition of organic matter constitutes a fundamental ecosystem process where microorganisms, affected by temperature and oxygen availability, play a fundamental role. The decomposition rates interfere in the global carbon cycle and therefore, in the potential feedback to climate change. We addressed the individual and combined effects of water temperature (15, 20, 25 and 30°C) and oxygen availability (aerobic and anaerobic) on the decomposition of three aquatic macrophytes (Eichhornia azurea, Eleocharis sp. and Salvinia auriculata) in microcosms carried out for 120 days. A first-order kinetic model was adopted to describe the kinetics of the decomposition. The decomposition had a biphasic pattern of mass loss: labile/soluble fraction (≈15.4; 10.6 and 10.7% for E. azurea, Eleocharis sp. and S. auriculata, respectively) and refractory (≈84.2; 89.4 and 89.0% for E. azurea, Eleocharis sp. and S. auriculata, respectively). Based on the decomposition kinetics, the leaching process was faster than the degradation of refractory compounds. Comparing the effect of temperature and the availability of dissolved oxygen, the latter seems more relevant for the decomposition process of these plants. Oxygen availability accelerated the decomposition 1.25 times compared to anoxic conditions, while a temperature increase of 10°C accelerated it by 1.35 times. However, it is important to consider that these environmental variables act synergistically in the regulation of decomposition and therefore all of them influence the decomposition rates.

Impact of aquatic macrophyte decomposition on sedimentary nutrient and metal mobilization in the initial stages of ecosystem development

The shifts and extent of aquatic macrophyte-mediated P and N regeneration, crucial in the initial stages of ecosystem development, were investigated using immature sediments which were poor in organic matter, P and N, but rich in Fe and Mn, obtained from a five-year-old artificial pond ‘Chicken Creek’, in east Germany. During the decomposition of indigenous plant materials (Phragmites australis (Cav.) Trin. ex Steudel, Potamogeton natans L., Potamogeton pectinatus L.) in a laboratory experiment, the concentrations of P, ammonium (NH4+), Fe and Mn in the sedimentary pore water increased with increasing fresh plant biomass amendments, and over time. Based on weighted average of the biomass added, there were no differences between species in the enrichment of pore water P (51- to 60-fold) and Mn (19- to 26-fold), compared to pure sediments. There was, however, a clear sequence in the NH4+ and Fe enrichment of pore water between control sediment and plant additions with P. pectinatus<P. natans<P. australis, increasing from 25- to 86-fold and 85- to 239-fold. In all cases, the extent of Fe mobilization exceeded that of P, as indicated by an increasing Fe:P ratio. Independent of the origin of solid Fe, this suggests a tendency towards the regeneration of mobile redox-sensitive Fe. Macrophytes can thus accelerate the transition from rather geochemically inert to more biogeochemically reactive sediments (P priming effect) by enhancing the mobilization and release of P to other biota. At a current relative Fe surplus, the equilibrium between the release and binding of P, after plant decomposition, shifts towards redox-sensitive P-binding, indicating a progressive P mobilization and availability.

Litter Decomposition of Six Macrophytes in a Eutrophic Shallow Lake (Baiyangdian Lake, China)

AbstractThe decomposition of aquatic macrophytes has important consequences for wetlands because it is closely related to organic matter accumulation and nutrient cycling. A field litter bag experiment was undertaken to investigate the decomposition rates of six dominant macrophytes. And the level of nutrient transfer from plant residues to lake water was also researched in Baiyangdian Lake, a typical macrophyte‐dominated lake in the Northern China Plain. Intact standing plants of Phragmites australis, Typha angustifolia, Nelumbo nucifera, Potamogeton pectinatus, Ceratophyllum demersum, and Chara sp. were collected and different plant tissues incubated near sediment traps. Litter bags were collected at days 6, 26, 60, 104, and 140 to follow biomass loss and nutrient release. Decomposition rates of different macrophytes calculated from an exponential model ranged from 0.0028 to 0.0110 day−1. For the same external environmental conditions, decomposition rates were significantly affected by initial litter chemistry. The remaining biomass was positively related to the C/N and C/P ratios and negatively related to the N and P concentrations and the N/P ratio. Both stems and roots showed a lower decomposition rate than the leaves of the same species due to the higher C/N ratio. The nutrient release from plant litter to the lake water was substantial. Over the incubation period, the release of N from the litter represented 18.10–88.79% of the initial content, and the release of P from the litter represented 24.26–92.83% of the initial content.

Oxygen uptake from aquatic macrophyte decomposition from Piraju Reservoir (Piraju, SP, Brazil)

The kinetics of oxygen consumption related to mineralisation of 18 taxa of aquatic macrophytes (Cyperus sp, Azolla caroliniana, Echinodorus macrophyllus, Eichhornia azurea, Eichhornia crassipes, Eleocharis sp1, Eleocharis sp2, Hetereanthera multiflora, Hydrocotyle raniculoides, Ludwigia sp, Myriophyllum aquaticum, Nymphaea elegans, Oxycaryum cubense, Ricciocarpus natans, Rynchospora corymbosa, Salvinia auriculata, Typha domingensis and Utricularia foliosa) from the reservoir of Piraju Hydroelectric Power Plant (São Paulo state, Brazil) were described. For each species, two incubations were prepared with ca. 300.0 mg of plant (DW) and 1.0 L of reservoir water sample. The incubations were maintained in the dark and at 20 ºC. Periodically the dissolved oxygen (DO) concentrations were measured; the accumulated DO values were fitted to 1st order kinetic model and the results showed that: i) high oxygen consumption was observed for Ludwigia sp (533 mg g-1 DW), while the lowest was registered for Eleocharis sp1 (205 mg g-1 DW) mineralisation; ii) the higher deoxygenation rate constants were verified in the mineralisation of A. caroliniana (0.052 day-1), H. raniculoides (0.050 day-1) and U. foliosa (0.049 day-1). The oxygen consumption rate constants of Ludwigia sp and Eleocharis sp2 mineralisation (0.027 day-1) were the lowest. The half-time of oxygen consumption varied from 9 to 26 days. In the short term, the detritus of E. macrophyllus, H. raniculoides, Ludwigia sp, N. elegans and U. foliosa were the critical resources to the reservoir oxygen demand; while in the long term, A. caroliniana, H. multiflora and T. domingensis were the resources that can potentially contribute to the benthic oxygen demand of this reservoir.

Decomposition of aquatic macrophytes from Cantá stream (Roraima, Brazil): kinetics approach

Decomposition of aquatic macrophytes from Cantá stream (Roraima, Brazil): kinetics approach

Emissions of methane and carbon dioxide during anaerobic decomposition of aquatic macrophytes from a tropical lagoon (São Paulo, Brazil)

AIM: Massive accumulations of aquatic sedimentary plant are the main source of CH4 and CO2 emissions in floodplain lakes. To examine this connection, this study measured CO2 and CH4 formation during anaerobic decomposition of aquatic macrophytes from a floodplain lake; METHODS: Methane formation was determined to the intrinsic characteristics of the debris, and the experimental (physical and chemical) conditions. Production of CH4 and CO2 were measured during anaerobic degradation of seven aquatic macrophytes: Cabomba furcata, Cyperus giganteus, Egeria najas, Eichhornia azurea, Ludwigia inclinata, Oxycaryum cubense, and Utricularia breviscapa, all of which inhabit the littoral zone of the lagoon studied; RESULTS: Overall, methanogenesis was more sensitive to temperature variation than gross anaerobic mineralization. Although the metabolic routes that generate CO2 were always predominant, as a competing process methanogenesis was favored by increasing temperature to the detriment of CO2 formation. Although several factors (such as pH, redox potential, salinity and nutrients availability) influenced yields of the final degradation products, temperature and detritus chemical composition were, in a first approach, the key factors in CH4 formation. In the oxbow lakes of the Mogi-Guaçu River Floodplain, especially Óleo Lagoon, on average, 10% of the total carbon can be regarded as the yield of CH4 formation derived from aquatic macrophyte decay, while the remaining carbon (90%) became CO2.

Decomposition of aquatic macrophytes from Cantá stream (Roraima, Brazil): kinetics approach

AIM: This study aimed at describing and comparing the kinetics of aerobic and anaerobic decomposition of Eleocharis interstincta, Nymphaea sp. and Montrichardia arborescens; METHODS: The samples of aquatic macrophytes and water were collected in the Canta Stream (02° 49' 11 N and 60° 40' 24 W), Canta, Roraima, Brazil. The plant material was dried and triturated and for each experimental condition (aerobic and anaerobic) mineralization chambers were prepared with plant fragments and stream water. The volume of evolved gases in anaerobic mineralization was monitored during 78 days, while the oxygen consumption was measured for 121 days; RESULTS: The results of aerobic and anaerobic decomposition were fitted to first-order kinetics model. The oxygen consumption varied from 195.36 mg g-1 (DM) for E. interstincta to 629.46 mg g-1 (DM) for Nymphaea sp. The deoxygenation rate derived from mineralization of M. arborescens was higher (kD: 0.049 day-1), followed by E. interstincta (kD: 0.038 day-1) and Nymphaea sp. (kD: 0.027 day-1). For the anaerobic condition the evolution of gases presented two phases: the consumption and formation. According to temporal variations of mineralized carbon, the anaerobic decomposition of M. arborescens presents the higher mineralization coefficient (0.0047 day-1); followed by Nymphaea sp. (0.0035 d-1) and E. interstincta (0.0017 day-1); CONCLUSION: Based on these results we conclude that during the aerobic decomposition of these macrophytes, the Nymphaea sp. was responsible for the higher oxygen demand and M. arborescens generated the highest amounts of gases during the anaerobic mineralization. On average, the aerobic decay processes were 11-fold faster than anaerobic. Regarding to the materials fluxes in freshwater ecosystems, low rate of decomposition observed in anaerobic process when comparing to aerobic rates reflect that the sediment represent a very efficient sink of carbon in the organic matter cycling.

Emissions of methane and carbon dioxide during anaerobic decomposition of aquatic macrophytes from a tropical lagoon (São Paulo, Brazil)

AIM: Massive accumulations of aquatic sedimentary plant are the main source of CH4 and CO2 emissions in floodplain lakes. To examine this connection, this study measured CO2 and CH4 formation during anaerobic decomposition of aquatic macrophytes from a floodplain lake; METHODS: Methane formation was determined to the intrinsic characteristics of the debris, and the experimental (physical and chemical) conditions. Production of CH4 and CO2 were measured during anaerobic degradation of seven aquatic macrophytes: Cabomba furcata, Cyperus giganteus, Egeria najas, Eichhornia azurea, Ludwigia inclinata, Oxycaryum cubense, and Utricularia breviscapa, all of which inhabit the littoral zone of the lagoon studied; RESULTS: Overall, methanogenesis was more sensitive to temperature variation than gross anaerobic mineralization. Although the metabolic routes that generate CO2 were always predominant, as a competing process methanogenesis was favored by increasing temperature to the detriment of CO2 formation. Although several factors (such as pH, redox potential, salinity and nutrients availability) influenced yields of the final degradation products, temperature and detritus chemical composition were, in a first approach, the key factors in CH4 formation. In the oxbow lakes of the Mogi-Guacu River Floodplain, especially Oleo Lagoon, on average, 10% of the total carbon can be regarded as the yield of CH4 formation derived from aquatic macrophyte decay, while the remaining carbon (90%) became CO2.

HUMIFICAÇÃO E MINERALIZAÇÃO DE MACRÓFITAS AQUÁTICAS: UMA REVISÃO SOBRE ESSES PROCESSOS

The decomposition of aquatic macrophytes results in the production of an amount of microorganisms, water, minerals, gases and humic compounds. Humic compounds are humic and fulvic acids which are polar substances with elevated molecular mass and irregular appearance, of heterogeneous nature and with varied degrees of polymerization. In aquatic ecosystems these substances take part in the pool of dissolved and particulate organic carbon, thus they hold considerable ecological and physiological importance. In the process of formation of humic compounds (humification) from the detritus of aquatic plants, a relative predominance of SH in the particulate organic matter in comparison to dissolved organic matter is perceived, with fulvic acid being the predominant compound. Although humic substances present recalcitrant properties in biodegradation, mineralization of these substances is essential in humus cycling and in the global carbon cycle. The refractance index of these substances renders them slow to decay in natural conditions, thus sediments acquire a great amount of humic substances. The processes of mineralization and humification can thus be seen as antagonist processes that evolve at different rates according with ambient conditions.