Dynamics Of Detritus Research Articles

Microbial-mediated contribution of kelp detritus to different forms of oceanic carbon sequestration

Kelp is one of the most important primary producers in the coastal oceans. When it matures or begins to decay, a substantial amount of detritus sinks and is degraded by microorganisms. However, the fate of these detritus after long-term microbial degradation, which is closely related to their ultimate carbon sequestration function, is not yet clear. Here, by studying the long-term (210-day) microbial degradation dynamics of kelp detritus, we reveal that the bioavailable components of kelp detritus (when kept in the dark) persisted for over four months. This left a considerable amount (in total, ca. 8.85%) of different forms of stable carbon that could function in long-term carbon sequestration. Among them, recalcitrant dissolved organic carbon (RDOC), recalcitrant particulate organic carbon, dissolved inorganic carbon, particulate inorganic carbon, and residual large particulate carbon accounted for 1.27%, 0.12%, 6.00%, 0.04%, and 1.41% of the initial kelp detrital carbon, respectively. The remaining organic carbon resisted further degradation due to the high content of humic-like substances, polycyclic aromatics, and highly aromatic compounds. Microbial community structure showed obvious successional characteristics during the long-term degradation process, driving the gradual transformation of the detritus-derived organic carbon from labile to recalcitrant. Notably, microbial transformation of the bioavailable components of kelp detritus contributed 28.7% of the remaining RDOC molecular species. This study provides novel insights into the contribution of the microbial-mediated degradation of kelp detritus to different forms of carbon sequestration.

Binary plantings as a factor of reducing the technogenic load of agrocenosis

The results of research conducted by Voronezh State Agrarian University to determine the effect of binary sunflower plantings in combination with postharvest sideration on the content of plant residues in the soil, on the number of soil microorganisms, on the dynamics of detritus, sunflower infestation and yield are presented. The positive effects of the studied complex of biological function was well established to increase the content of organic matter sources in soil (by 4.64 of 5.67 t/ha), contributing to the increase in the content in the soil detritus (4.7 and 9.9%) on the growth of soil microorganisms, which in combination with the reduction of planting infestation (by 9-18 pcs/m2) has led to significantly higher yields of sunflower (0.18-0.51 in t/ha) compared with the traditional technology of cultivation. As binary components of sunflower, it is recommended to use perennial legumes of yellow melilot and purple alfalfa, and oil radish as a postharvest sideral crop.

Adaptation and multiple parameter optimization of the simulation model SALMO as prerequisite for scenario analysis on a shallow eutrophic Lake

SALMO (Simulation by means of an Analytical Lake Model) describes the seasonal dynamics of PO4-P, NO3-N, detritus, chlorophyta, bacillariophyta, cyanophyta and cladocerans of the epilimnion and hypolimnion of stratified lakes by complex ordinary differential equations. This study adapted the model for shallow polymictic lakes and developed a real-coded genetic algorithm to optimize key parameters identified by sensitivity analysis. Meiliang Bay of Taihu Lake is taken as a study case, and 5 years data were collected for model calibration and validation. Given the good performance of the adapted and optimized SALMO, the model was applied to analyze four management scenarios for the Meiliang Bay, including 50% reduction of external nutrient loads, 50% reduction of internal nutrient loads, 50% reduction of zooplankton mortality and 1°C increase of water temperature. The study showed: the adapted SALMO model is applicable to shallow polymictic and hypertrophic lakes; the real-coded genetic algorithm significantly improved the model efficiency and accuracy; reduction of nutrients from sediment release appears to be a key measure for controlling cyanobacteria blooms in Lake Taihu; biomanipulation is very delicate and can only be implemented with sufficient investigation and great caution; the increase of algae biomass due to water temperature rise indicates extra potential threat from climate change to lake ecosystems.

A general one-dimensional vertical ecosystem model of Lake Shira (Russia, Khakasia): description, parametrization and analysis

A one-dimensional ecological model of the meromictic brackish Lake Shira (Russia, Khakasia) was developed. The model incorporates state-of-the-art knowledge about the functioning of the lake ecosystem using the most recent field observations and ideas from PCLake, a general ecosystem model of shallow freshwater lakes. The model of Lake Shira presented here takes into account the vertical dynamics of biomasses of the main species of algae, zooplankton and microbial community, as well as the dynamics of oxygen, detritus, nutrients and hydrogen sulphide from spring to autumn. Solar radiation, temperature and diffusion are modelled using real meteorological data. The parameters of the model were calibrated to the field data, after applying different methods of sensitivity analysis to the model. The resulting patterns of phytoplankton and nutrients dynamics show a good qualitative and quantitative agreement with the field observations during the whole summer season. Results are less satisfactory with respect to the vertical distribution of zooplankton biomass. We hypothesize that this is due to the fact that the current model does not take the sex and age structure of zooplankton into account. The dynamics of oxygen, hydrogen sulphide and the modelled positions of the chemocline and thermocline are again in good agreement with field data. This resemblance confirms the validity of the approach we took in the model regarding the main physical, chemical and ecological processes. This general model opens the way for checking various hypotheses on the functioning of the Lake Shira ecosystem in future investigations and for analysing options for management of this economically important lake.

Seasonal dynamics of benthic detritus and associated macroinvertebrate communities in a neotropical stream

The dynamics of benthic detritus and the structure, composition and functional feeding groups of as- sociated macroinvertebrate communities were followed at biweekly intervals over one year in a 4th-order Andean stream located in a forested hill in SW Colombia. The density of macroinvertebrates and the number of taxa showed a similar bimodal annual pattern with highest values occurring from January to mid-March and from July to mid- October. The accumulated benthic detritus and the invertebrate abundance and community structure were appar- ently controlled by stream discharge. This was confirmed by a cluster analysis of invertebrate assemblages over the year where three groups of sampling dates emerged. The first group occurred during high discharges, the second one under intermediate hydrological conditions and the third coincided with low rainfall and low discharges. Nu- merically, collectors dominated, whereas shredders represented less than 5.3 % of the invertebrates. Unexpectedly, benthic detritus and collector densities were negatively correlated; however, no relation between benthic detritus and the abundance of shredders was found, which may suggest that benthic detritus consisting mainly of plant remains was not a limiting resource in this neotropical stream. Macroinvertebrates appear to have a minor role in the decomposition of plant matter which is consistent with previous observations from the same and other tropical streams. As a consequence, macroinvertebrate dynamics in this stream were more influenced by hydrological vari- ations than by input of plant detritus.

Detrital stocks and dynamics of the seagrass Posidonia oceanica (L.) Delile in the Spanish Mediterranean

Previous studies have shown that most leaf production (>90%) of the seagrass Posidonia oceanica is shed after senescence and that a substantial percentage (up to 80%) may thereafter be exported off the seagrass meadows by waves and currents. It has also been reported that P. oceanica meadows can accumulate large stocks of belowground detritus due to slow decomposition rates. However, the generality of these results across broad spatial scales is poorly known. In this report, we examine the fate of leaf production and the magnitude and dynamics of belowground detritus in 16 P. oceanica meadows distributed along the Spanish Mediterranean. Herbivores removed a small percentage of leaf production in all the meadows (≤13%), with most leaf production (>85%) being shed after senescence. Most shed leaves (>90%) were exported off the meadows by physical agents, such as waves and currents. The amount of belowground detritus stored within 10–15 cm from the sediment surface varied from ca. 70 to 7500 g DW m −2 among the meadows examined, and they accumulated at rates ranging from ca. 65 to 650 g DW m −2 per year. These values are large when compared to other communities of aquatic and terrestrial macrophytes. Our results show that P. oceanica meadows in the Spanish Mediterranean support high values of secondary production in other systems by exporting large amounts of leaf detritus as well as acting as substantial carbon sinks by accumulating large reservoirs of belowground detritus. Therefore, the increasing anthropogenic threats on P. oceanica could entail an important loss of secondary production and carbon storage in Mediterranean coastal ecosystems.

Expansion of the model ‘Rostherne’ for fish and zooplankton: role of top-down effects in modifying the prevailing pattern of ecosystem functioning

This paper presents a new version of the well-established aquatic ecosystem model ‘Rostherne’, incorporating lake fish and zooplankton. The model currently comprises differential and algebraic equations describing processes and forcing functions most important for a freshwater ecosystem. These include seasonal changes of solar radiation and water temperature, processes of algal and cyanobacterial population dynamics and nutrient uptake, water and chemical budgeting, stratification of the water column and sedimentation of suspended particles, and dynamics of detritus and its chemical constituents. Although it was shown previously for some years that a reasonable simulation of changes in most state variables could be achieved without accounting for fish and zooplankton, in other years, consideration of these compartments improved the fit between observations and model simulations dramatically. This was particularly true for the year 1998, when the high zooplankton numbers in spring appeared to prevent any significant development of the diatom population. The latter, however, bloomed during the first part of the summer (following a decrease in zooplankton counts) causing an unusually delayed major drop in ambient Si levels. As biogoechemical cycles of Si, P and N are interconnected through the dynamics of the primary producers, such a delay has serious implications for the functioning of an aquatic ecosystem model. Since changes in zooplankton dynamics are heavily dependent on the variability in fish recruitment, simultaneous consideration of the two components is helpful both for modelling overall dynamics of the lake ecosystem and for implementation of the biogeochemical regulation proposed previously.

Nutrient stores and dynamics of woody detritus in a boreal forest: modeling potential implications at the stand level

Nutrient stores and dynamics of woody detritus in a boreal forest: modeling potential implications at the stand level

Nutrient stores and dynamics of woody detritus in a boreal forest: modeling potential implications at the stand level

Concentrations of 14 chemical elements (Al, B, C, Ca, Cu, Fe, K, N, Mg, Mn, Na, P, S, Zn) were measured in wood and bark of 126 sample trees representing different stages of decomposition in three major tree species of northwestern Russia: Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and birch (Betula pendula Roth.). Changes in nutrient stores in decay classes were calculated with adjustments for the loss of density and volume by dead trees. Although the concentration of many nutrients increased relative to the estimated initial level, the total amount of most nutrients contained in dead trees declined with decay. For example, nitrogen stores declined from decay class 1 to 4 by 45% for birch, 39% for spruce, and by 60% for pine. The rate and pattern of these losses varied by nutrient and by species and were primarily related to the patterns of bark loss. Pine lost bark early in the process of decomposition and released many essential nutrients (i.e., N, P, Ca) at the early stages, while birch retained most of its bark throughout the decomposition process and lost nutrients more gradually. The temporal dynamics of N, Ca, and K loss in pine were examined using a chronosequence approach, and the results were used in stand-level modeling. The analysis of modeling results suggests that, in northwestern Russia, post-disturbance release of nutrients from woody detritus can potentially supply a large proportion of the net N, Ca, and K accumulation in live forest biomass.

Seasonal dynamics of detritus and associated macroinvertebrates in a channelized boreal stream

This study documents various components of detritus dynamics in a channelized third order stream in Central Finland. Total annual litterfall entering the stream was 310g AFDM m -2 . Leaf fall, which comprised 86.7 % of total input, exhibited a distinct seasonal peak in September-October, with a maximum daily input rate of 13 g m -2 . The contribution of woody detritus to total input was only 5 %. The mean annual standing stocks of coarse (23.0 g AFDM m -2 ) and fine (1.76 g AFDM m -2 ) benthic organic matter are among the lowest reported for woodland streams. Macroinvertebrate standing stock peaked in February (1205 mg DW m -2 ), and the annual minimum (276 mg DW m -2 ) occurred in August. Shredding invertebrates did not reach their maximum biomass until March, although the availability of benthic leaf litter peaked already in October. In contrast, FPOM-collectors and predatory invertebrates tracked closely the seasonal availability of their food resources. Leaf release experiments showed that the stream had a low retention capacity: 13-40 % of 500 artificial leaves were retained within a 50m experimental section at discharges ranging from 0.46 to 1.52 m 3 s -1 . The stream is poorly retentive because it lacks effective retention devices (e.g. large woody debris). Due to the low retentivity of the stream bed and fast decomposition rates of the primary litter sources (birch and alder leaves), shredders probably face a severe springtime food limitation in this stream. We suggest that adding retentive devices to stream bed is a viable management strategy for restoration of channelized woodland streams.

Feeding ecology of the freshwater detritivore Ptychoptera paludosa (Diptera, Nematocera)

1. We examined selected aspects of the nutritional ecology of larval Ptychoptera paludosa and their role in nutrient cycling in the Breitenbach, a first‐order stream in Hesse, Germany.2. Food preference experiments demonstrated significant preference for sediments with a high organic matter content and live bacteria.3. pH was circumneutral in all sections of the gut.4. Enzymatic activity (β‐glucosidase and amino‐peptidase) in different parts of the gut was measured using 4‐methylumbelliferyl‐β‐D‐glucopyranoside (MUF‐Glc) and leucine‐4‐methylcoumarinyl‐7‐amide (Leu‐MCA). β‐glucosidase activity was highest in the hindgut.5. The mean larval gut passage time was between 7 and 8 h.6. The egestion rate of last instar larvae was about 0.35 mg dry weight (DW) faeces per larva h–1 and about 1.25 mg ash‐free dry weight (AFDW) faeces per mg larval AFDW day–1.7. Larval faeces contained at least 4–18 times more organic matter than the average in the sediments in which they were feeding, that is, larvae fed selectively, extracting organic matter from sediments.8. P. paludosa larvae are important in the dynamics of detritus in slow‐flowing reaches of the Breitenbach. They gather organic material from the sediment to a depth of 3 cm, and release it as faeces onto the sediment surface. A total of 770 g DW faeces m–2 yr–1, comprising about 16% organic matter, was produced by the Ptychoptera population.

Dynamics of phytoplankton detritus in a shallow, eutrophic lake (Lake Loosdrecht, The Netherlands)

Dynamics of phytoplankton detritus in a shallow, eutrophic lake (Lake Loosdrecht, The Netherlands)

Fire and the dynamics of allochthonous detritus in a South African mountain stream

SUMMARY. Input of allochthonous material, standing stocks of benthic organic matter (BOM) and suspended paniculate organic matter (POM) were measured in a south‐western Cape mountain stream from March 1986 to February 1988. The surrounding fynbos‐dominated catch‐ment was subjected to a prescribed burn in March 1987. Litter‐fall in the pre‐burn year exhibited a distinct seasonal pattern, with peak falls during the early summer. Although the riparian canopy was not directly affected by the fire, in that it did not burn, a heavy, aseasonal leaf‐fall occurred shortly afterwards. The following summer, litter‐fall was less than half that of the pre‐burn summer. Standing stocks of BOM were significantly higher in autumn than in winter in the pre‐burn year and were inversely related to discharge. Despite the heavy post‐burn leaf‐fall and low litter‐fall during the post‐burn summer, there was no significant difference between pre‐ and post‐burn BOM standing stocks. Proportions and quantities of fine benthic organic matter (FBOM) in the soft BOM fraction were significantly higher in the post‐burn spring, and monthly accumulation of ultra‐fine benthic organic matter (UBOM) was also significantly higher in the post‐burn spring and summer. These results may reflect accelerated decay rates of BOM in response to enhanced post‐burn nitrate concentrations in stream water. Export of CPOM was low in comparison to FPOM and particularly to UPOM, and the stream appears to be highly retentive of CPOM. The natural resilience of the riparian vegetation minimizes the potentially disturbing effects of fire on the stream environment. As a result, the prescribed burn had a less than expected effect on both standing stocks of BOM and the stream environment in general.

Effects of water acidification on the decomposition of Juncus bulbosus L.

Several field and laboratory experiments were performed to study the impact of acidification on the decomposition of Juncus bulbosus L. The breakdown of coarse detritus of this aquatic macrophyte appeared to be very slow. After 7 weeks of incubation in an acidified and a circumneutral moorland pool the remaining fraction of Juncus leaves varied between 46 and 75% of the original organic weight. Differences in decay patterns were observed among both systems. Furthermore, the breakdown rates were highly dependent on the season. Highest weight loss rates were recorded at high pH during the summer period. In acidified water and during the winter period the breakdown rates were reduced. Nutrient dynamics of detritus in the circumneutral soft water and the acidified system differed remarkably. In litter bags laid down on the bottom surface of the acidified moorland pool the density and diversity of macroinvertebrate assemblages was generally lower than in the bags immersed in the non-acidified body of water. In particular, the abundance of detritivores and herbivores at low pH was strongly reduced. However, in winter qualitative and quantitative differences in the macrofauna in the litter bags did not significantly affect decay rates of detritus. Laboratory studies revealed that the pH, bicarbonate concentration and aluminium content of the water particularly influenced the rate of decomposition of the pre-dried Juncus material. The extent of leaching and autolysis and the relative importance of fungi and bacteria in the decomposition of fresh Juncus leaves were studied using antifungal and antibacterial agents. In the laboratory leaching and autolysis accounted for 28–32% of the organic weight loss of coarse detritus. Leaching and autolysis caused the highest weight loss in the strongly acid medium. After 37 days of incubation in control media with pH 3.5 and 5.6 total organic weight loss was 55 and 59%, respectively. At pH 3.5 and 5.6 microbial decomposition accounted for organic weight losses of 23 and 31%, respectively. At low pH microbial decomposition was dominated by fungi, whereas, at pH 5.6 both fungi and bacteria played an important role in the breakdown processes. The contribution of macroinvertebrates to the breakdown of Juncus detritus seemed to be of minor importance.

Experimental test of the pupation window model for development of detritivorous insects

Cohort size and food availability to larval detritivores are linked to pupal mass, and hence to adult fitness, by the pupation window model. Previous tests of this model have employed artificial food. This paper derives a version of the model that incorporates the dynamics of natural detritus. Tests of the model using cohorts of Aedes triseriatus Say led to successful predictions of numbers of pupae, female pupal mass, and female development time. However, it is recommended that model parameters be estimated separately for different types of leaf litter.

Nutrient dynamics of vegetation and detritus following two intensities of fire in the New Jersey pine barrens.

The nutrient dynamics of upland forest sites in the New Jersey Pine Barrens exposed to different fire intensities were determined. Nutrient concentrations and inventories in biomass, litter, humus, and standing dead wood were determined for an unburned site, two sites burned by severe wildfire and two sites burned by light prescribed burning. Humus nutrient levels were similar among sites despite differing fire histories. Amounts of calcium, magnesium, and potassium in biomass and in litter were lower in wildfire sites than in prescribed burn sites, all of which were lower than the control. Standing dead wood nutrient levels were much higher in the wildfire sites than in the other three sites. Output of nutrients to groudwater correlated poorly with the amounts of nutrients retained in humus or standing dead wood; however strong inverse correlations were found between nutrient output and nutrient storage in biomass or biomass plus litter and humus. These results emphasize the central role of nutrient immobilization in regrowing biomass in after fire on nutrient poor soils.

Benthic detritus dynamics in a mountain stream

The dynamics of sedimentary detritus was examined over a 17‐month period in a third‐order mountain stream in Colorado. Autumnal and vernal peaks in total detritus standing crop (197 g and 165 g AFDW m−2, respectively) were associated with leaf abscission and ice out. The flushing action of snowmelt runoff rapidly reduced benthic detritus to 14 g AFDW m−2. Detrital size classes differentially contributed to temporal fluctuations in total detritus. The autumnal maximum was largely comprised of coarse particulate organic matter (CPOM), primarily leaf litter. The large increase following ice out was mainly due to fine detritus (FPOM, 0.45–75 μm) which accounted for > 50% of benthic detritus during 9 months of the year. Evidence suggests that changes in standing crop and particle size distribution during the extended period of ice cover (November‐March) resulted from in situ processing rather than transport. Despite major differences in climate, geochemistry and hydrology, the Colorado stream exhibited patterns of detrital dynamics remarkably similar to an eastern deciduous forest stream.

Dynamics of Detritus in a Small Stream in Southern Sweden and Its Influence on the Distribution of the Bottom Animal Communities

Transport and availability of various size fractions of organic material along with bottom structure and benthic invertebrates, grouped with respect to feeding types, were examined along an 8 km long stream in southern Sweden. Transport of coarse particulate organic material (CPOM) was insignificant, while considerable amounts of fine particulate (FPOM) and dissolved organic matter (DOM) were carried downstream. DOM showed little variation and was constantly 2-3 times the energy of suspended FPOM. Export of DOM was 5 times as high as that of FPOM, total organic output being twice as high as leaf input. On a stony bottom shredders and scrapers dominated, whereas scrapers, deposit feeders and filter feeders were abundant where sedimentation was heavy. Downstream the section with most extensive sedimentation all categories including predators were well represented.