Differences In Processing Rates Research Articles

Year-round activity of microbial communities in cold-climate peatlands treating mining-affected waters

Pristine peatlands are typically low in nitrogen, sulfur and metal compounds. Thus, input of high concentrations of those compounds as a result of anthropogenic activity pose a huge challenge to peatland ecosystems. At a mine site in Finnish Lapland, mining-affected waters are purified in two treatment peatlands (TPs) before they are released into downstream waters. The TPs experience long winters and are snow- and partly ice-covered from October to May. Contaminants in inflow waters include nitrogen compounds, sulfate, metals and metalloids. The TPs were intensively monitored for >10 years, and monitoring data was complemented with laboratory experiments. High levels of multiple contaminants, often in the mM range, were measured in TP inflow. Removal of some contaminants such as nitrogen compounds and sulfate was higher in summer months while removal of other contaminants such as arsenic and antimony was similar throughout the year. Potential process rates as assessed in laboratory incubations were generally higher at higher incubation temperatures and decreased with decreasing temperatures, but processes still occurred at 0 °C. The composition of the potentially active microbial community as assessed by 16S rRNA amplicon sequencing varied more strongly between the two TPs and the two layers, while seasonal variability was minor. Potentially active microorganisms included genera known for nitrification, denitrification, sulfate reduction, iron reduction as well as arsenate and antimonate reduction. The collective results indicate that (i) microbial communities in mining-affected peatlands were exposed to high concentrations of multiple contaminants, (ii) microbially mediated processes contributed to contaminant removal throughout the year, and (iii) differences in process rates and contaminant removal likely stem from overall lower activities rather than from changes in microbial community composition.

Near-field variability of evaposublimation in a montane conifer forest

Methods that combine in-situ measurements, statistical methods, and model simulations with remotely sensed data provide a pathway for improving the robustness of surface flux products. For this research, we acquired eddy-covariance fluxes along a five-tower transect in a snowy montane forest over three consecutive winters to characterize near-field variability of the subcanopy environment. The novel experiment design enabled discriminating near-field evaposublimation sources. Boosted regression trees reveal that the predictive capacity of state variables change with season and storm cycle frequency. High rates of post-storm evaposublimation of canopy-intercepted snow at this site were constrained by short residence time of snow in the canopy due to throughfall and melt. The snow melt-out date for open vs. closed canopy conditions depended on total snowfall accumulation. Compared with low accumulation years, the snow melt-out date under the dense canopy during the high accumulation winter was later than for the open area, as shading became more important later in the season. The field experiments informed an environmental response function that was used to integrate ERA5-Land latent heat flux data at 20-km nominal resolution with USFS Tree Canopy Fraction data at 30-m resolution and showed near-field flux variability that was not resolved in model simulations. Previous evaposublimation results from experiments in alpine and subalpine environments do not directly translate to a montane forest due to differences in process rates.

Enhanced susceptibility to oiling may limit denitrification recovery in marshes subjected to woody encroachment

Coastal salt marshes provide valuable ecosystem services but are subjected to multiple concomitant stressors that may impact their ability to provide those services. Global climate change has led to the poleward expansion of mangroves into salt marshes on each continent where mangroves and marshes co-occur. In the northern Gulf of Mexico, warming winter temperatures have resulted in the expansion of Avicennia germinans (black mangrove) into forb-dominated salt marshes, resulting in a shift in ecosystem structure that can impact the ecosystem services marshes provide, including biogeochemical processes such as nitrogen removal. There have been limited studies addressing how mangrove expansion impacts nitrogen removal rates in salt marshes, but it is possible that mangroves enhance microbial nitrogen removal capacity through more efficient oxygen translocation to sediments. However, mangroves are more sensitive to oiling (such as occurred during the 2010 Deepwater Horizon spill) than marsh plants, such as Spartina alterniflora, which have a higher turnover. Thus, even if they enhance nitrogen removal, if they cannot withstand disturbances such as oiling, there still may be a loss of function associated with woody encroachment. We conducted a field study to assess the impact of woody encroachment in mediating biogeochemical recovery 7 to 8 years after the Deepwater Horizon oil spill. We collected sediments from S. alterniflora- and A. germinans-dominated plots in the Chandeleur Islands (LA, United States), a chain of barrier islands in the northern Gulf of Mexico subjected to a range of oiling following the spill. We compared nitrate reduction rates (denitrification and dissimilatory nitrate reduction to ammonium), microbial community composition, and denitrifier marker gene abundance at sites subjected to light and moderate oiling using a combination of isotope pairing on sediment slurries, 16S sequencing, and qPCR. We predicted that overall, denitrification rates and microbial functional capacity would be enhanced in mangrove-dominated sediments. We also predicted that these enhancements would be diminished at the more intensely oiled site due to the higher susceptibility of A. germinans to oiling. Denitrification potential rates were higher in mangrove sediments at the lightly oiled site, whereas dissimilatory nitrate reduction to ammonium potential rates were higher in marsh sediments. Indicator analysis of 16S rRNA data selected putative sulfur cycling taxa as indicators of marsh sediments, suggesting that changes in oxygen availability associated with encroachment may be driving the differences in process rates. There was no difference in process rates between plant types at the moderately oiled site, where heavily weathered oil residue was still present. Sediment nutrient stocks were lower in moderately oiled mangrove plots than in lightly oiled mangrove plots, suggesting that sediment fertility recovery following the spill may have been slower in the mangroves, contributing to a change in ecosystem function. This study shows that woody encroachment has the potential to impact both the biogeochemical services that marshes provide and their response to and recovery from disturbances.

Denitrification in intertidal sediments of a tropical estuary subject to increasing development pressures

Darwin Harbour is a working port and the most populated city in the Northern Territory of Australia. This macrotidal estuary is located in the wet–dry tropics of Northern Australia and notwithstanding mounting development pressures in the region, is largely unmodified. The prevailing oligotrophic condition of estuarine waters suggest that biogeochemical cycling in sediments remain active, buffering the influence of anthropogenic inputs. We tested the hypothesis that nutrient hotspots exist in depositional low-velocity zones, with a gradient of high to low nitrogen processing from the upper to outer reaches of the estuary. A number of factors were examined for their influence on the effectiveness of denitrification in these depositional zones, a putative key process driving nitrogen removal, with particular emphasis on carbon-loading extremes in tidal creeks, spatial gradients along the estuary and the influence of seasonality. There were significant differences in process rates between hypereutrophic/eutrophic tidal creeks that receive the largest proportion of treated sewage loads in the region and the mesotrophic/oligotrophic tidal creeks that were comparatively undisturbed. Net benthic nutrient fluxes and dinitrogen efflux rates were more than an order of magnitude higher and lower, respectively, in degraded (hypereutrophic/eutrophic) tidal creek systems where denitrification efficiency (DE%) was < 40%. Denitrification (Dinitrogen efflux) rates in tidal creeks (mesotrophic/oligotrophic) and broader estuarine sites were high (~ 8 mmol N m−2 day−1) and denitrification efficiency remained > 65%, particularly during the wet season. On a whole-of-estuary basis, denitrification in conjunction with mechanisms such as burial could feasibly make a substantial impact, abating the influence of anthropogenic inputs. Although considerable variability was encountered, particularly across seasons, the hypothesis of elevated denitrification rates as nutrient hotspots in depositional zones along the estuary was not convincing. More influential are tidal creeks as potential ‘reactors’ for N cycling and removal, but their capacity can be degraded by overloading with nutrients.

Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

The effect of increased nutrient loads on biogeochemical processes in macrotidal, mangrove-lined creeks was studied in tropical Darwin Harbour, Australia. This study uses an integrative approach involving multiple benthic and pelagic processes as measures of ecosystem function, and provides a comparison of these processes in three tidal creeks receiving different loads of treated sewage effluent. There were significant differences in process rates between Buffalo Creek (BC) (hypereutrophic), which receives the largest sewage loads; Myrmidon Creek (MC) (oligotrophic–mesotrophic) which receives smaller sewage inputs; and Reference Creek (RC) (oligotrophic) which is comparatively pristine. Benthic nutrient fluxes and denitrification were more than an order of magnitude higher and lower, respectively, in BC and denitrification efficiency (DE) was <10%. Pelagic primary production rates were also much higher in BC but respiration exceeded primary production resulting in severe drawdown of O2 concentrations at night. Hypoxic conditions released oxide-bound phosphorus and inhibited coupled nitrification–denitrification, enhancing benthic nitrogen and phosphorus fluxes, leading to a build-up of excess nutrients in the water column. Poor water quality in BC was exacerbated by limited tidal flushing imposed by a narrow meandering channel and sandbar across the mouth. In contrast to BC, the effect of the sewage load in MC was confined to the water column, and the impact was temporary and highly localized. This is attributed to the effective flushing of the sewage plume with each tidal cycle. Denitrification rates in MC and RC were high (up to 6.83 mmol N m−2 day−1) and DE was approximately 90%. This study has identified denitrification, benthic nutrient fluxes and pelagic primary production as the biogeochemical processes most affected by nutrient loading in these tidal creek systems. Physical process play a key role and the combined influence of nutrient loading and poor tidal flushing can have serious consequences for ecosystem functioning.

No-till soil management increases microbial biomass and alters community profiles in soil aggregates

Aggregation is important for soil functioning, providing physical protection of organic matter and microbial inhabitants. Tillage disrupts aggregates, increases wind and water erosion of soils and exposes formerly protected organic matter to decomposition and losses. Microbial biomass and community dynamics in dry-sieved aggregate-size classes from long-term no-till (NT) and conventionally tilled (CT) soils were examined using phospholipid fatty acid analysis (PLFA). Bacterial, fungal, and total biomass were up to 32% greater in NT compared to CT aggregates. Aggregate size also affected microbial biomass, which was highest in the 1–2 mm size class. Arbuscular mycorrhizal fungi (AMF) were particularly affected by tillage disturbance with increases of 40–60% among aggregate-size classes in NT vs. CT, but glomalin related soil protein concentration was not different between tillage treatments or among aggregate-size classes. Bacterial stress biomarkers were higher in CT than NT aggregates but were not significantly correlated with total C, total N or C:N ratio, indicating that the physiological status of bacteria within aggregates was not simply governed by the quantity of available resources. Ordination analysis of PLFA profiles demonstrated a shift in microbial community structure between NT and CT aggregates, correlated with AMF abundance in NT aggregates and increased bacterial stress biomarkers in CT aggregates. Our results demonstrated greater microbial biomass and altered microbial community structure in NT vs. CT aggregates. This work demonstrates that tillage management influences microbial community structure within aggregates and may provide a potential explanation for differences in process rates observed in NT vs. CT soils. Further research into the processes that govern community structure in aggregates from NT and tilled soils is needed to better understand how the interaction of microorganisms with their physical environment affects nutrient turnover and availability.

Relationship between N-cycling communities and ecosystem functioning in a 50-year-old fertilization experiment

The relative importance of size and composition of microbial communities in ecosystem functioning is poorly understood. Here, we investigated how community composition and size of selected functional guilds in the nitrogen cycle correlated with agroecosystem functioning, which was defined as microbial process rates, total crop yield and nitrogen content in the crop. Soil was sampled from a 50-year fertilizer trial and the treatments comprised unfertilized bare fallow, unfertilized with crop, and plots with crop fertilized with calcium nitrate, ammonium sulfate, solid cattle manure or sewage sludge. The size of the functional guilds and the total bacterial community were greatly affected by the fertilization regimes, especially by the sewage sludge and ammonium sulfate treatments. The community size results were combined with previously published data on the composition of the corresponding communities, potential ammonia oxidation, denitrification, basal and substrate-induced respiration rates, in addition to crop yield for an integrated analysis. It was found that differences in size, rather than composition, correlated with differences in process rates for the denitrifier and ammonia-oxidizing archaeal and total bacterial communities, whereas neither differences in size nor composition was correlated with differences in process rates for the ammonia-oxidizing bacterial community. In contrast, the composition of nitrate-reducing, denitrifying and total bacterial communities co-varied with primary production and both were strongly linked to soil properties.

Role of nematodes in decomposition processes: Does within-trophic group diversity matter?

The importance of biodiversity for the functioning of ecosystems is still very unclear. Many hypotheses, mainly based on terrestrial studies, have been formulated, focussing on the plant diversity-productivity relationship. In this study, diversity-related and species-specific effects of bac- terivorous nematodes on the decomposition rate of cordgrass detritus Spartina anglica and on the associated microbial community were investigated using laboratory microcosm experiments. Four bacterivorous nematode species (Diplolaimelloides meyli, Diplolaimelloides oschei, Diplolaimella dievengatensis and Panagrolaimus paetzoldi) were added either separately or in combinations of 2 or 3 species to the microcosms. In contrast with previous reports, no stimulation of the decomposition process was observed in the presence of nematodes. Still, clear differences in process rates were found between nematode treatments. P. paetzoldi, reaching considerably higher densities than the other nematode species, suppressed bacterial activity and diversity, probably due to overgrazing. This was, however, not translated into slower decomposition. Within treatments exclusively contain- ing monhysterid nematode species (D. meyli, D. oschei and D. dievengatensis), differences in micro- bial activity and decomposition rates were found, but again no link was observed between activity and decomposition. Our data did not support any hypothesis predicting enhancement of process rates with an (initial) increase in numbers of nematode species, or redundancy among the studied species. Rather, we obtained support for an idiosyncratic diversity model, as differences in the effect of bac- terivore nematode species and species combinations could not be predicted at the start of the exper- iment. This could be explained by the inhibitory interactions between nematode species.

Indirect effects of predatory trout on organic matter processing in detritus‐based stream food webs

Indirect effects of predators on basal resources in allochthonous‐based food webs are poorly understood. We investigated indirect effects of predatory brown trout (Salmo trutta) on detritus dynamics in southern beech (Nothofagus spp.) forest streams in New Zealand through predation on the obligate detritivore, Zelandopsyche ingens (Trichoptera, Oeconesidae). Trout presence/absence and Z. ingens density were manipulated in flow‐through tanks to investigate the lethal and sub‐lethal effects of trout on litter processing by Z. ingens. An experiment that allowed trout access to Z. ingens showed trout predation reduced densities of Z. ingens resulting in slower breakdown of coarse particulate organic matter (CPOM) and reduced production of fine particulate organic matter (FPOM). A second experiment that prevented trout access to Z. ingens, but allowed the transmission of trout cues, resulted in no change in litter processing rates in the presence of trout. Litter processing rates were higher in high Z. ingens density treatments compared to low density treatments. Thus, trout effects on litter processing were due to reduced Z. ingens densities, not trout‐induced modifications to Z. ingens feeding behaviour. Field assays of litter processing rates using artificial leaf packs in natural streams showed significant reductions in CPOM loss in trout streams compared to fishless streams. Z. ingens dominated biomass in fishless stream leaf packs, but a facultative shredder, Olinga feredayi, dominated trout stream leaf packs. Thus, the absence of Z. ingens drove differences in processing rates between trout and fishless streams and the indirect effects of trout on litter processing observed in mesocosms were evident in complex, natural food webs. Overall our study provides evidence that predators can influence resource dynamics in donor‐controlled food webs through their effects on consumers.

Processing of leaf matter by lake-dwelling shredders at low oxygen concentrations

Organic sediments in freshwaters are regularly subject to low concentrations of oxygen. The ability of detritivores to sustain their feeding in such conditions should therefore be of importance for the decomposition process. In the present study, aquaria were used to determine processing rates of five lake-dwelling shredders at three different oxygen concentrations; normoxic (9 mg O2 l−1) and two levels of hypoxia (1 and 2 mg O2 l−1). Discs of alder leaves (Alnus glutinosa (L.)) were used as food. Four species of caddisfly larvae (Trichoptera Limnephilidae) and the isopod, Asellus aquaticus (L.) were compared in the experiments. Significant differences in processing rates per g animal biomass were found both at normoxia and 2 mg oxygen l−1. At l mg O2 l−1 none of the invertebrates fed on leaf discs. The caddisfly larvae Halesus radiatus (Curtis), being one of the two most efficient shredders at normoxia, did not feed at 2 mg oxygen l−1. The other species fed at rates 15–50 of that at normoxia. The least efficient shredder at normoxia, A. aquaticus was similar to two of the trichopterans at 2 mg O2 l−1. This study shows that the importance of specific shredder species may shift in case of hypoxia. Species-specific traits regarding oxygen sensitivity may also be influential for distribution patterns of shredder species both within and between lakes.

Leaf breakdown in a regulated desert river: Colorado River, Arizona, U.S.A.

We compared processing rates (k d) for leaves of the native willow (Salix exigua Nutt.) and cottonwood (Populus fremontii Wats.) to those of the non-native salt cedar (Tamarix chinensis Lour.) in the regulated Colorado River, U.S.A. Leaf packs of each species were incubated at Lees Ferry, approximately 26 km below Glen Canyon Dam, Arizona. Leaf packs were processed at 2, 21, 46, 84 and 142-d intervals. Water temperatures remained relatively constant (10 °C, SE ± 1 °C) during the study. There were significant differences in processing rates between species, with P. fremontii showing the fastest breakdown. After 142 d, only 20% of the P. fremontii leaf mass remained, whereas 30% and 52% of leaf masses remained for T. chinensis and S. exigua, respectively. The k d value for P. fremontii was 0.0062 compared to 0.0049 and 0.0038 for T. chinensis and S. exigua, respectively. Invertebrate colonization was not significantly different between native and non-native plant species with oligochaetes the most abundant animal colonizing the leaf packs. Dual stable isotope analysis showed that leaf material was not the primary food for invertebrates associated with leaf packs. Processing rates for all leaf types were slow in the regulated Colorado River compared to rates reported in many other systems. This is likely due to the lack of caddisfly and stonefly shredders and perhaps slow metabolic rates by microbes.

Comparison of leaf processing rates under different temperature regimes in three headwater streams

1. We studied the effects of different temperature regimes on leaf litter processing in three forested Appalachian headwater streams of different pH (mean pH = 4.2, 6.5, 7.5).2. We compared leaf breakdown rates, microbial biomass and macroinvertebrate shredder density and biomass between two 12‐week processing periods (October–January and November–February) in each stream. Leaf processing rates were calculated both as k (day–1) and kd (degree day–1).3. There were no significant differences in processing rates (k day–1) between the two study periods for any leaf species in any stream. The average difference in temperature between the two study periods was 175 degree days. Shredder density was significantly higher during the earlier study period on 40% of the sample dates, but shredder biomass was not significantly different between the two study periods. ATP concentration was significantly higher during the early study period for 60% of the sample dates.4. More significant differences in these variables (shredder density and biomass, ATP concentration) were seen among the three study streams than between the two study periods. This indicates that in this study other factors, particularly stream pH, contributed more to processing rate variation than did differences in thermal regime.

Environmental patchiness and processing of maple leaf litter in a backwater of a mountain stream: riffle area vs. debris dams

Processing rates of Acer pseudoplatanus leaves were investigated in three types of patches - debris dams, buried and exposed, and a riffle area - of a backwater of the alpine stream Oberer Seebach. The results show a gradient of processing rates from slower, for the leaves buried in the debris dams, to the highest, in the riffle area, with significant differences between these two extremes. Shear stress near leaf bags was significantly higher in the riffle area than in debris dams; however, this probably does not reflect the internal conditions of the bags. It is argued that the accumulation of great amounts of plant debris against the bags in the riffle area, and the relatively hard texture and the uniform perimeter of the leaf discs used in the experiment, might minimize mass losses due to mechanical abrasion by the water current. Nitrogen and phosphorus dynamics of the leaf material suggest that microbial processing did not differ between patches. Likewise, density and biomass of shredders did not help to explain differences in processing rates between patches. Nevertheless, significant taxonomical differences in the shredder assemblages between patches were observed. Differential population dynamics, feeding styles and metabolic capacities of shredders and the different environments in which to obtain food between the studied stream patches may be of great importance in the differences between processing rates.

Colonization and processing of leaf litter by macroinvertebrate shredders in streams of contrasting pH

SUMMARY Leaf litter processing rates and macroinvertebrate shredder assemblages in leaf packs were compared in four streams on the Allegheny plateau in the central Appalachian Mountains, U.S.A.; these streams were characterized by different bedrock geology and streamwater pH. Leaf litter processing rates were fastest in the neutral streams, slowest in the acidic stream, and intermediate in the most alkaline stream. Slower processing rates in the acidic stream were associated with lower total shredder biomass, made up predominantly by small leuctrid and nemourid stoneflies. The differences in processing rates between the more alkaline stream and the neutral streams were not associated with differences in shredder biomass, but appeared to be related to taxonomic differences in the shredder assembiages. Insects were dominant in the neutral streams, and amphipods were dominant in the more alkaline stream.

The hurst effect and its implications for extrapolating process rates

AbstractIn long‐term records of climatic or hydrological events, persistent periods of high and low values are measured by the ‘rescaled range’, which is defined for a sequence of n consecutive values. As n increases the rescaled range for historic sequences increases as nH for 0·5 &lt; H &lt; = 1. This is the Hurst effect. Sequences of independent random events give H = 0·5, while sequences in which the values are successive positions of a random walk (i.e. the sum of independent events) give H = 1. Intermediate values of H may be obtained from fractal sequences, from sequences with a steadily changing mean, or through a storage model. In all but the fractal case H exceeds 0·5 for a time related to the duration of the changing mean or the response time of the store.An exponential storage model has been explored in some detail. Storage models have the advantage of offering a plausible physical mechanism for persistence. Analysis of simulated sequences shows that the Hurst effect is evident for about 30 x the response time of the store, so that relatively modest store sizes are enough to explain observed Hurst effects over available periods of record. Comparison with empirical values shows that high H values seem to be associated with large physical stores.Whether the Hurst effect is due to storage effects or climatic or other change imposed from outside, the effect on longterm process rates is strong. Short‐term measurements of process rates show compressed variances and simple extrapolation is likely to produce large errors. If it is assumed that long‐term rates are strongly influenced by climatic variables, then measurements may be used to obtain parameters of a climatic model for differences in process rates. Errors in extrapolation will be least where the model has a sound physical basis.A first implication for magnitude and frequency distributions is that the sequence of events may be as important as their distribution over time in determining process impact. A second conclusion is that the geomorphic history of an area is inevitably dominated by a sequence of larger and larger events receding into the past, and that the Hurst exponent over geologic time‐spans measures the extent of that domination.

Protease activity in fibromyoma and normal human myometrium.

The potential involvement of intracellular proteases in the pathophysiology of fibromyoma was studied by assay of activity of two proteolytic enzymes in fibromyoma and adjacent normal myometrium. Protease I, a soluble acid protease and protease II, a particulate protease optimally active at the neutral pH range are present in fibromyoma as well as in normal myometrial tissue. No consistent difference was observed between the specific activities of these enzymes in the fibromyoma and the surrounding myometrium. The large variation in the specific activity of the protease noted among normal and fibroid tissue samples from different patients cannot be ascribed to differences in cellularity. This variance might suggest differences in rate of processing of steroid hormones or different degrees of vascularization. The present findings do not support a major role for modulation of intracellular protease activities in the development of fibromyoma.