Addition Of Inorganic Nutrients Research Articles

Aphotic N2 Fixation in the Eastern Tropical South Pacific Ocean

We examined rates of N2 fixation from the surface to 2000 m depth in the Eastern Tropical South Pacific (ETSP) during El Niño (2010) and La Niña (2011). Replicated vertical profiles performed under oxygen-free conditions show that N2 fixation takes place both in euphotic and aphotic waters, with rates reaching 155 to 509 µmol N m−2 d−1 in 2010 and 24±14 to 118±87 µmol N m−2 d−1 in 2011. In the aphotic layers, volumetric N2 fixation rates were relatively low (<1.00 nmol N L−1 d−1), but when integrated over the whole aphotic layer, they accounted for 87–90% of total rates (euphotic+aphotic) for the two cruises. Phylogenetic studies performed in microcosms experiments confirm the presence of diazotrophs in the deep waters of the Oxygen Minimum Zone (OMZ), which were comprised of non-cyanobacterial diazotrophs affiliated with nifH clusters 1K (predominantly comprised of α-proteobacteria), 1G (predominantly comprised of γ-proteobacteria), and 3 (sulfate reducing genera of the δ-proteobacteria and Clostridium spp., Vibrio spp.). Organic and inorganic nutrient addition bioassays revealed that amino acids significantly stimulated N2 fixation in the core of the OMZ at all stations tested and as did simple carbohydrates at stations located nearest the coast of Peru/Chile. The episodic supply of these substrates from upper layers are hypothesized to explain the observed variability of N2 fixation in the ETSP.

Bacterial carbon dependence on freshly produced phytoplankton exudates under different nutrient availability and grazing pressure conditions in coastal marine waters.

The effects of grazing pressure and inorganic nutrient availability on the direct carbon transfer from freshly produced phytoplankton exudates to heterotrophic bacteria biomass production were studied in Mediterranean coastal waters. The short-term incorporation of ¹³C (H¹³CO₃) in phytoplankton and bacterial lipid biomarkers was measured as well as the total bacterial carbon production (BP), viral lysis and the microbial community structure under three experimental conditions: (1) High inorganic Nutrient and High Grazing (HN + HG), (2) High inorganic Nutrient and Low Grazing (HN + LG) and (3) under natural in situ conditions with Low inorganic Nutrient and High Grazing (LN + HG) during spring. Under phytoplankton bloom conditions (HN + LG), the bacterial use of freshly produced phytoplankton exudates as a source of carbon, estimated from ¹³C enrichment of bacterial lipids, contributed more than half of the total bacterial production. However, under conditions of high grazing pressure on phytoplankton with or without the addition of inorganic nutrients (HN + HG and LN + HG), the ¹³C enrichment of bacterial lipids was low compared with the high total bacterial production. BP therefore seems to depend mainly on freshly produced phytoplankton exudates during the early phase of phytoplankton bloom period. However, BP seems mainly relying on recycled carbon from viral lysis and predators under high grazing pressure.

Assessing changes in microbial respiration, bacterial growth efficiency, and bacterial production with nutrient addition to batch cultures

Dissolved organic carbon (DOC) provides an important source of energy in lotic systems that can regulate food chain dynamics. It is thought that inorganic nutrient addition to stream culture samples will increase microbial respiration and bacterial growth efficiency (BGE). Nutrient limitation may prevent microbial communities from reaching their full potential in terms of biomass and efficiency, which could limit organisms at higher trophic levels. This study utilized batch cultures to assess changes across a variety of water quality and nutrient parameters in an effort to assess the role of inorganic nutrient addition in regulating microbial activity in headwater streams. Treatments of phosphorus addition (+ P) and nitrogen plus phosphorus addition (+ N + P) were used to assess changes in microbial activity in samples collected from forested and agricultural headwater streams. Phosphorus limitation was observed only at a single site, suggesting that a secondary limiting nutrient (e.g. nitrogen) may affect microbial activity at the other sites. Combined phosphorous and nitrogen additions demonstrated that nitrogen did limit microbial respiration at many of the study sites. BGE was highly variable and did not seem to be controlled by inorganic nutrient concentration. We did observe increased carbon production with nutrient addition at some of the study sites. The results of this study indicate that small streams could export more carbon through respiration rather than by incorporating available DOC into biomass.

Effect of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; enrichment on bacterial metabolism in an Arctic fjord

Abstract. The anthropogenic increase of carbon dioxide (CO2) alters the seawater carbonate chemistry, with a decline of pH and an increase in the partial pressure of CO2 (pCO2). Although bacteria play a major role in carbon cycling, little is known about the impact of rising pCO2 on bacterial carbon metabolism, especially for natural bacterial communities. In this study, we investigated the effect of rising pCO2 on bacterial production (BP), bacterial respiration (BR) and bacterial carbon metabolism during a mesocosm experiment performed in Kongsfjorden (Svalbard) in 2010. Nine mesocosms with pCO2 levels ranging from ca. 180 to 1400 μatm were deployed in the fjord and monitored for 30 days. Generally BP gradually decreased in all mesocosms in an initial phase, showed a large (3.6-fold average) but temporary increase on day 10, and increased slightly after inorganic nutrient addition. Over the wide range of pCO2 investigated, the patterns in BP and growth rate of bulk and free-living communities were generally similar over time. However, BP of the bulk community significantly decreased with increasing pCO2 after nutrient addition (day 14). In addition, increasing pCO2 enhanced the leucine to thymidine (Leu : TdR) ratio at the end of experiment, suggesting that pCO2 may alter the growth balance of bacteria. Stepwise multiple regression analysis suggests that multiple factors, including pCO2, explained the changes of BP, growth rate and Leu : TdR ratio at the end of the experiment. In contrast to BP, no clear trend and effect of changes of pCO2 was observed for BR, bacterial carbon demand and bacterial growth efficiency. Overall, the results suggest that changes in pCO2 potentially influence bacterial production, growth rate and growth balance rather than the conversion of dissolved organic matter into CO2.

Effect of ocean acidification on the fatty acid composition of a natural plankton community

Abstract. The effect of ocean acidification on the fatty acid composition of a natural plankton community in the Arctic was studied in a large-scale mesocosm experiment, carried out in Kongsfjorden (Svalbard, Norway) at 79° N. Nine mesocosms of ~50 m3 each were exposed to 8 different pCO2 levels (from natural background conditions to ~1420 μatm), yielding pH values (on the total scale) from ~8.3 to 7.5. Inorganic nutrients were added on day 13. The phytoplankton development during this 30-day experiment passed three distinct phases: (1) prior to the addition of inorganic nutrients, (2) first bloom after nutrient addition, and (3) second bloom after nutrient addition. The fatty acid composition of the natural plankton community was analysed and showed, in general, high percentages of polyunsaturated fatty acids (PUFAs): 44–60% of total fatty acids. Positive correlations with pCO2 were found for most PUFAs during phases 2 and/or 3, with the exception of 20:5n3 (eicosapentaenoic acid, EPA), an important diatom marker. These correlations are probably linked to changes in taxonomic composition in response to pCO2. While diatoms (together with prasinophytes and haptophytes) increased during phase 3 mainly in the low and intermediate pCO2 treatments, dinoflagellates were favoured by high CO2 concentrations during the same time period. This is reflected in the development of group-specific fatty acid trophic markers. No indications were found for a generally detrimental effect of ocean acidification on the planktonic food quality in terms of essential fatty acids.

Temporal biomass dynamics of an Arctic plankton bloom in response to increasing levels of atmospheric carbon dioxide

Abstract. Ocean acidification and carbonation, driven by anthropogenic emissions of carbon dioxide (CO2), have been shown to affect a variety of marine organisms and are likely to change ecosystem functioning. High latitudes, especially the Arctic, will be the first to encounter profound changes in carbonate chemistry speciation at a large scale, namely the under-saturation of surface waters with respect to aragonite, a calcium carbonate polymorph produced by several organisms in this region. During a CO2 perturbation study in Kongsfjorden on the west coast of Spitsbergen (Norway), in the framework of the EU-funded project EPOCA, the temporal dynamics of a plankton bloom was followed in nine mesocosms, manipulated for CO2 levels ranging initially from about 185 to 1420 μatm. Dissolved inorganic nutrients were added halfway through the experiment. Autotrophic biomass, as identified by chlorophyll a standing stocks (Chl a), peaked three times in all mesocosms. However, while absolute Chl a concentrations were similar in all mesocosms during the first phase of the experiment, higher autotrophic biomass was measured as high in comparison to low CO2 during the second phase, right after dissolved inorganic nutrient addition. This trend then reversed in the third phase. There were several statistically significant CO2 effects on a variety of parameters measured in certain phases, such as nutrient utilization, standing stocks of particulate organic matter, and phytoplankton species composition. Interestingly, CO2 effects developed slowly but steadily, becoming more and more statistically significant with time. The observed CO2-related shifts in nutrient flow into different phytoplankton groups (mainly dinoflagellates, prasinophytes and haptophytes) could have consequences for future organic matter flow to higher trophic levels and export production, with consequences for ecosystem productivity and atmospheric CO2.

Bioremediation of waste drilling fluid: comparison of biostimulation and bioaugmentation

Abstract In this study, waste drilling fluid was remediated by both biostimulation with the inorganic nutrient addition and bioaugmentation with the inoculation of a selected and well-adapted microbial consortium. The results showed that, compared to the non-bioaugmented system, the bioaugmented system exhibited considerably stronger pollution disposal abilities, with 95.2% total organic carbon degradation (TOC) and 91.2% total petroleum hydrocarbon (TPH) removal within 120 h. In contrast, in the non-bioaugmented system, the corresponding TOC and TPH removal efficiencies were 82.9% and 58.3%, respectively, within 120 h. The active role of the microbial inoculum in pushing the entire community towards an effective bioremediation has been proven through hydrocarbons analysis and metabolic profi ling at community level (Biologsystem).

Combined effects of inorganic nutrients and organic enrichment on intertidal benthic macrofauna: an experimental approach

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 461:59-70 (2012) - DOI: https://doi.org/10.3354/meps09819 Combined effects of inorganic nutrients and organic enrichment on intertidal benthic macrofauna: an experimental approach Jayne E. Fitch*, Tasman P. Crowe School of Biology and Environmental Science, Science Centre West, University College Dublin, Belfield, Dublin 4, Ireland *Email: jaynefitch@hotmail.com ABSTRACT: Marine environments are affected by multiple anthropogenic stressors, but research to date has focussed primarily on the impacts and indicators of individual stressors. Nutrient and organic enrichment can occur separately or in combination with each other, but their combined effects are not fully understood. In a field experiment on a sheltered, sandy-mud, sedimentary intertidal shore, 3 levels of inorganic nutrient addition (nutrient sticks) were crossed with 2 levels of organic matter enrichment (rusks), and benthic macrofauna were sampled at 2 times. Organic matter caused greater impacts on benthic macrofauna than nutrients and had a significant effect on taxon richness and Shannon diversity. Total abundance responded to the interactive effects of nutrients and organic matter. The response observed in total abundance was largely driven by the small opportunistic polychaete Capitella sp., which responded primarily to organic matter, but its response was mediated by addition of nutrients to the system. This highlights that its abundance varies in response to interactions among stressors, so cannot be easily interpreted. The performance of 2 biotic indices, the AZTI Marine Biotic Index (AMBI) and Multivariate AMBI (M-AMBI), varied, but M-AMBI proved to be the most effective at detecting the combined effects of nutrients and organic enrichment. These findings show that effective management of coastal environments must take account of the potentially complex combined effects of multiple stressors. KEY WORDS: Multiple stressors · Inorganic nutrients · Organic matter · Benthic · Intertidal · Macrofauna Full text in pdf format PreviousNextCite this article as: Fitch JE, Crowe TP (2012) Combined effects of inorganic nutrients and organic enrichment on intertidal benthic macrofauna: an experimental approach. Mar Ecol Prog Ser 461:59-70. https://doi.org/10.3354/meps09819 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 461. Online publication date: August 08, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Responses of microbial community from northern Gulf of Mexico sandy sediments following exposure to deepwater horizon crude oil

In the present study, microbial community responses to exposure to unweathered Macondo Well crude oil and conventional diesel in a sandy beach environment were determined. Biodegradation was assessed in mesocosm experiments with differing fuel amounts (2,000 and 4,000 mg/kg) and with or without inorganic nutrient amendment. Carbon dioxide production was measured daily for 42 d. Aerobic alkane, total hydrocarbon, and polycyclic aromatic hydrocarbon (PAH) degraders were enumerated in treated and control mesocosms and changes in their abundances were measured weekly. Hydrocarbon mineralization occurred in all treatments. In the inorganic nutrient-amended treatments, the degradation rates were 2.31 and 2.00 times greater in the 2,000 mg/kg diesel and crude oil treatments, respectively, and 3.52 (diesel) and 4.14 (crude) times higher for the fuel types at the 4,000 mg/kg fuel concentrations compared to unamended treatments. Microbial lag phases were short (<3 d) and alkane and total hydrocarbon degrader numbers increased by five orders of magnitude compared to the uncontaminated treatments within 7 d in most treatments. Hydrocarbon degrader numbers in diesel and in crude oil treatments were similar; however, the PAH degraders were more abundant in the crude oil relative to diesel treatment. These findings indicate that hydrocarbon degradation by extant microbial populations in the northern Gulf of Mexico sandy beach environments can be stimulated and enhanced by inorganic nutrient addition.

Large-scale and long-term decrease in fish growth following the construction of hydroelectric reservoirs

Hydroelectric reservoirs retain large volumes of water and have a global impact on sea level, elemental cycles, and biodiversity. Using data from a total of 90 historical and recent surveys in nine regulated and eight unregulated alpine and subalpine lakes, we show an additional large effect of reservoirs, i.e., that impoundment causes drastically decreased fish growth and thereby great negative consequences for inland fisheries in Scandinavia. Following a long period (40–65 years) after impoundment, the length and mass of Arctic charr ( Salvelinus alpinus ) of the single age class 4+ years was, on average, 35% and 72% lower, respectively, in impounded versus natural lakes in northern Scandinavia. The effect was stronger at higher altitudes and can be mitigated by addition of inorganic nutrients. We suggest that the decreased fish growth is a consequence of lowered ecosystem productivity, oligotrophication, caused by impoundment, resulting in erosion and loss of the littoral ecosystem as well as delayed flooding and leakage of nutrients from the riparian zone until after the growing season.

Study on Culture Condition Optimization and Kinetics for Crude Oil Degrading Strain SY2

Using crude oil degrading strain SY2 isolated from soil contaminated by crude oil as the starting strain, the optimum culture conditions of strain SY2 were obtained by the experiments of carbon source, nitrogen source, inorganic salt, and cultivation temperature. The biodegradation rate of crude oil can reach 43.20% under the condition of without the addition of inorganic nutrients. The enzyme-catalyzed kinetic model of strain SY2 degrading naphthalene was also established. The model was applied to guide the practical application of the crude oil degrading strain SY2.

Effects of different organic materials and mineral nutrients on arbuscular mycorrhizal fungal growth in a Mediterranean saline dryland

Arbuscular mycorrhizal (AM) fungi are root symbionts that enhance plant growth and improve soil fertility and soil structure in drylands. Even though AM fungi are obligate biotrophs, organic matter (OM) can stimulate their growth, but the mechanisms behind this are still unknown. Here, we compared the effect of nutrient patches of different OM sources to intrinsic components of OM such as inorganic nutrient supply and an improved soil water-holding capacity (WHC; via application of hydrophilic polymers), on AM fungal growth. Fatty acids extracted from in-growth mesh bags incubated in the field were used as biomarkers for AM fungi and other soil microbes. We found an enhancement of AM fungal growth in certain nutrient patches. Two out of three OM types stimulated AM fungal growth strongly, and also the addition of inorganic nutrients enhanced AM fungi, though to a lesser extent than OM. Enhanced soil WHC, on the other hand, did not influence AM fungal growth. AMF were more strongly enhanced by the mineral nutrients relative to other soil organisms. Intrinsic nutrients might be an important factor for AMF growth stimulation in OM additions, but there was no evidence that nutrients alone can explain this phenomenon.

Ecology of aerobic anoxygenic phototrophic bacteria along an oligotrophic gradient in the Mediterranean Sea

Abstract. Aerobic anoxygenic phototrophic (AAP) bacteria are photoheterotrophic prokaryotes able to use both light and organic substrates for energy production. They are widely distributed in coastal and oceanic environments and may contribute significantly to the carbon cycle in the upper ocean. To better understand questions regarding links between the ecology of these photoheterotrophic bacteria and the trophic status of water masses, we examined their horizontal and vertical distribution and the effects of nutrient additions on their growth along an oligotrophic gradient in the Mediterranean Sea. Concentrations of bacteriochlorophyll-a (BChl-a) and AAP bacterial abundance decreased from the western to the eastern basin of the Mediterranean Sea and were linked with concentrations of chlorophyll-a, nutrient and dissolved organic carbon. Inorganic nutrient and glucose additions to surface seawater samples along the oligotrophic gradient revealed that AAP bacteria were nitrogen- and carbon-limited in the ultraoligotrophic eastern basin. The intensity of the AAP bacterial growth response generally differed from that of the total bacterial growth response. BChl-a quota of AAP bacterial communities was significantly higher in the eastern basin than in the western basin, suggesting that reliance on phototrophy varied along the oligotrophic gradient and that nutrient and/or carbon limitation favors BChl-a synthesis.

Temperature and the metabolic balance of streams

Summary 1. It is becoming increasingly clear that fresh waters play a major role in the global C cycle. Stream ecosystem respiration (ER) and gross primary productivity (GPP) exert a significant control on organic carbon fluxes in fluvial networks. However, little is known about how climate change will influence these fluxes. 2. Here, we used a ‘natural experiment’ to demonstrate the role of temperature and nutrient cycling in whole-system metabolism (ER, GPP and net ecosystem production – NEP), in naturally heated geothermal (5–25 °C) Icelandic streams. 3. We calculated ER and GPP with a new, more accurate method, which enabled us to take into account the additional uncertainties owing to stream spatial heterogeneity in oxygen concentrations within a reach. ER ranged 1–25 g C m−2 day−1 and GPP 1–10 g C m−2 day−1. The median uncertainties (based on 1 SD) in ER and GPP were 50% and 20%, respectively. 4. Despite extremely low water nutrient concentrations, high metabolic rates in the warm streams were supported by fast cycling rates of nutrients, as revealed from inorganic nutrient (N, P) addition experiments. 5. ER exceeded GPP in all streams (with average GPP/ER = 0.6) and was more strongly related to temperature than GPP, resulting in elevated negative NEP with warming. We show that, as a first approximation based on summer investigations, global stream carbon emission to the atmosphere would nearly double from 0.12 Pg C year−1 at 13 °C to 0.21 (0.15–0.33) Pg C year−1 with a 5 °C warming. 6. Compared to previous studies from natural systems (including terrestrial ecosystems), the temperature dependence of stream metabolism was not confounded by latitude or altitude, seasonality, light and nutrient availability, water chemistry, space availability (water transient storage), and water availability. 7. Consequently, stream nutrient processing is likely to increase with warming, protecting downstream ecosystems (rivers, estuaries, coastal marine systems) during the summer low flows from nutrient enrichment, but at the cost of increased CO2 flux back to the atmosphere.

Fire and Fertilization Effects on the Growth and Spread of Rhizome‐Transplanted Giant Cane (Arundinaria gigantea)

In the United States, clonal bamboo stands dominated by giant cane (Arundinaria gigantea), historically described as “canebrakes,” have been largely degraded or replaced by land conversion to agriculture. Due to limited and sporadic flowering and seed production of this species, restoration typically requires transplanting rhizomes, but there is limited information on establishment success and factors that influence growth and clonal spread of transplanted stock. We tested the effects of fertilization and prescribed fire applied alone and in combination on the growth and spread of giant cane in a 4‐year old planting. In rows containing transplanted rhizomes, multiple aspects of giant cane establishment (i.e., percent cover, culm density, height, diameter, and lateral spread) increased over time. Following 2 years of inorganic nutrient (N, P, and K) addition, there was a decrease in culm mortality. Giant cane exhibited reduced cover, height, and culm diameter over the short‐term in response to prescribed burning. Fertilization did not offset the short‐term negative impact of fire on these variables. However, burning increased culm density in planted rows and adjacent areas. In conclusion, fertilizing establishing giant cane may reduce mortality, and periodic burning can increase density and spread of this species, which should promote establishment over the long‐term.

Differential responses of phytoplankton and heterotrophic bacteria to organic and inorganic nutrient additions in coastal waters off the NW Iberian Peninsula

The short-term effects of inorganic N and P (nitrate, ammonium, phosphate) and organic C and N (glucose, amino acids) input, added separately as well as jointly, on microplankton commu- nity structure and metabolism were studied in 6 microcosm experiments conducted from February to July 2008 in a eutrophic coastal embayment in NW Spain under contrasting hydrographic conditions. The responses of planktonic communities were highly variable. Strong positive effects of combined inorganic and organic nutrient enrichments for phytoplankton and heterotrophic bacteria were found. In most experiments enhanced phytoplankton biomass and productivity (primary production increased up to 5.5-fold) was measured after mixed (inorganic plus organic) additions but phyto- plankton responded only in one of the experiments after inorganic additions. Heterotrophic bacteria responded faster than phytoplankton to the additions but were never affected by inorganic nutrient additions, suggesting a C limitation of bacterial activity in this coastal environment. Heterotrophic bacteria biomass, productivity, and respiration responded to mixed additions (containing C, N, and P) in all the experiments (bacterial production increased from 14- to 34-fold) whereas its response to organic (containing C and N) additions greatly differed among experiments (bacterial production increased from 0.6- to 21-fold), which could be partially related to P availability. A general increase in bacterial growth efficiency occurred only after mixed additions (up to 2-fold). The tendency towards heterotrophy of the microbial plankton community was weaker after the mixed (Production/Respira- tion (P/R) ratio changes from 0.34- to 1.6-fold) than after the organic additions (P/R changes from 0.16- to 0.8-fold). Our results suggest that phytoplankton requirememnts for organic nutrients for growth and P deficiency of bacterial populations intermittently occur in this coastal area.

Chemical and microbial community analysis during aerobic biostimulation assays of non-sulfonated alkyl-benzene-contaminated groundwater

A chemical and microbial characterization of lab-scale biostimulation assays with groundwater samples taken from an industrial site in which the aquifer had been contaminated by linear non-sulfonate alkyl benzenes (LABs) was carried out for further field-scale bioremediation purposes. Two lab-scale biodegradability assays were performed, one with a previously obtained gas-oil-degrading consortium and another with the native groundwater flora. Results for the characterization of the groundwater microbial population of the site revealed the presence of an important LAB-degrading microbial population with a strong degrading capacity. Among the microorganisms identified at the site, the detection of Parvibaculum lavamentivorans, which have been described in other studies as alkyl benzene sulfonates degraders, is worth mentioning. Incubation of P. lavamentivorans DSMZ13023 with LABs as reported in this study shows for the first time the metabolic capacity of this strain to degrade such compounds. Results from the biodegradation assays in this study showed that the indigenous microbial population had a higher degrading capacity than the gas-oil-degrading consortium, indicating the strong ability of the native community to adapt to the presence of LABs. The addition of inorganic nutrients significantly improved the aerobic biodegradation rate, achieving levels of biodegradation close to 90%. The results of this study show the potential effectiveness of oxygen and nutrients as in situ biostimulation agents as well as the existence of a complex microbial community that encompasses well-known hydrocarbon- and LAS-degrading microbial populations in the aquifer studied.

Limitation of lowland riverine bacterioplankton by dissolved organic carbon and inorganic nutrients

Flow regulation in lowland rivers has reduced the amount of allochthonous dissolved organic carbon (DOC) entering main channels through less frequent wetting of benches, flood runners and floodplains. The hypothesis tested was that lowland riverine bacterioplankton are DOC limited when flow events are absent and simulating an increase in assimilable DOC similar to that expected during an environmental flow will lead to heterotrophic dominance. Experiments took place in the Namoi River, a highly regulated lowland river in Australia. Specifically, in situ microcosms were used to examine the responses of bacterioplankton and phytoplankton to various additions of DOC as glucose or leaf leachate, with and without additions of inorganic nutrients. The results indicated that ambient DOC availability limited the bacterioplankton for the three seasons over which we conducted the experiments. When DOC was added alone, dissolved oxygen concentrations decreased primarily because of increased bacterial respiration and bacterioplankton growth generally increased relative to controls. Additions of DOC alone led to a pattern of decreased chlorophyll a concentration relative to controls, except for willow leachate. Additions of inorganic nutrients alone increased chlorophyll a concentrations above controls, indicating limitation of phytoplankton. These findings support our hypothesis. Based on the present results, environmental flows should increase the duration of allochthonously driven heterotrophic dominance, thus shifting regulated lowland rivers to more natural (pre-regulation) conditions for greater periods.

Bioremediation of marine sediments contaminated by hydrocarbons: Experimental analysis and kinetic modeling

This work deals with bioremediation experiments on harbor sediments contaminated by aliphatic and polycyclic aromatic hydrocarbons (PAHs), investigating the effects of a continuous supply of inorganic nutrients and sand amendments on the kinetics of microbial growth and hydrocarbon degradation. Inorganic nutrients stimulated microbial growth and enhanced the biodegradation of low and high molecular weight hydrocarbons, whereas sand amendment increased only the removal of high molecular weight compounds. The simultaneous addition of inorganic nutrients and sand provided the highest biodegradation (>70% for aliphatic hydrocarbons and 40% for PAHs). A semi-empirical kinetic model was successfully fitted to experimental temporal changes of hydrocarbon residual concentrations and microbial abundances. The estimated values for parameters allowed to calculate a doubling time of 2.9 d and a yield coefficient biomass/hydrocarbons 0.39 g C biomass g-1C hydrocarbons, for the treatment with the highest hydrocarbon biodegradation yield. A comparison between the organic carbon demand and temporal profiles of hydrocarbons residual concentration allowed also to calculate the relative contribution of contaminants to carbon supply, in the range 5–32%. This suggests that C availability in the sediments, influencing prokaryotic metabolism, may have cascade effects on biodegradation rates of hydrocarbons. Even if these findings do not represent a general rule and site-specific studies are needed, the approach used here can be a relevant support tool when designing bioremediation strategies on site.

Salmon Carcasses Increase Stream Productivity More than Inorganic Fertilizer Pellets: A Test on Multiple Trophic Levels in Streamside Experimental Channels

AbstractInorganic nutrient amendments to streams are viewed as possible restoration strategies for re‐establishing nutrients and stream productivity throughout the western coast of North America, where salmon runs and associated marine‐derived nutrient subsidies have declined. In a mesocosm experiment, we examined the short‐term (6 weeks) comparative effects of artificial nutrient pellets and salmon carcasses, alone (low and high amounts) and in combination, on stream food webs. Response variables included dissolved nutrient concentrations, biofilm ash‐free dry mass (AFDM) and chlorophyll‐a levels, macroinvertebrate density, growth and body condition of juvenile coho salmon Oncorhynchus kisutch, and whole‐body lipid content of invertebrates and juvenile coho salmon. Most of the response variables were significantly influenced by carcass treatment; the only response variable significantly influenced by fertilizer pellet treatment was soluble reactive phosphorus (SRP) concentration. Ammonium‐nitrogen concentration was the only response variable affected by both (low and high) levels of carcass treatment; all others showed no significant response to the two carcass treatment levels. Significant treatment × time interactions were observed for all responses except nitrate; for most responses, significant treatment effects were detected at certain time periods and not others. For example, significantly higher SRP concentrations were recorded earlier in the experiment, whereas significant fish responses were observed later. These results provide evidence that inorganic nutrient additions do not have the same ecological effects in streams as do salmon carcasses, potentially because inorganic nutrient additions lack carbon‐based biochemicals and macromolecules that are sequestered directly or indirectly by consumers. Salmon carcasses, preferably deposited naturally during spawning migrations, appear to be far superior to inorganic nutrient amendments for sustaining and restoring stream productivity, including fish production, and should be chosen over artificial nutrient additions when feasible and practical.