Special Issue "The Role of Macrobiota in Aquatic Nutrient Cycling"

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Biodiversity and Ecosystem Functioning".

Deadline for manuscript submissions: closed (31 December 2019).

Special Issue Editors

Prof. Paul Bukaveckas
E-Mail Website
Guest Editor
Department of Biology and Center for Environmental Studies, Virginia Commonwealth University, USA
Interests: hydrology; underwater optics; phytoplankton physiology; algal blooms; nutrient cycling; consumer energetics
Prof. Dr. Marco Bartoli
E-Mail Website
Guest Editor
Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Parma, Italy
Interests: nutrients; sediments; benthic biodiversity; macrofauna; macrophytes; ecosystem functioning

Special Issue Information

Dear Colleagues,

The combined action of macrofauna, inclusive of fish, macrophytes, and birds, is an important driver of aquatic nutrient cycling. Fish and birds supply and translocate nutrients via direct (excretion) and indirect pathways (bioturbation, sediment resuspension, predation) at rates comparable to other nutrient sources. Consumer-mediated recycling may support a large fraction of the nutrient requirements by primary producers thereby offsetting management efforts to mitigate eutrophication. Fish and birds also alter the relative availability and ecological stoichiometry of nitrogen, silica and phosphorus, with cascade effects on species composition and ecosystem functioning. Macrophytes retain nutrients in biomass via uptake processes and favor their burial and long term retention within sediments. Rooted macrophytes produce a number of indirect effects on pore water nutrients, by stimulating via radial oxygen loss biogeochemical processes such as coupled nitrification-denitrification or precipitation. The effects of fish, birds and macrophytes on aquatic nutrient cycling is a complex issue, as it involves multiple feedbacks and synergistic interactions, often understudied. These effects likely vary along environmental gradients, such as nutrient and organic matter availability, salinity and ecosystem size. This Special Issue targets contributions focusing on the effects of macrofauna, on nutrient cycling with the goal of providing a more comprehensive understanding of their importance among diverse aquatic systems.

Prof. Paul Bukaveckas
Prof. Marco Bartoli
Guest Editors

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Keywords

  • Nitrogen
  • Silica
  • Phosphorus
  • Ecological stoichiometry
  • Biogeochemical cycles
  • Macrofauna
  • Macrophytes
  • Fish
  • Birds
  • Inland aquatic ecosystems functioning

Published Papers (12 papers)

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Research

Open AccessCommunication
Benthic Metabolism in Fluvial Sediments with Larvae of Lampetra sp.
Water 2021, 13(7), 1002; https://doi.org/10.3390/w13071002 - 06 Apr 2021
Viewed by 311
Abstract
Lampreys spend their larval stage within fine sand fluvial sediments, where they burrow and act as filter feeders. Lamprey larvae (ammocoetes) can significantly affect benthic-pelagic coupling and nutrient cycling in rivers, due to high densities. However, their bioturbation, feeding and excretion activities are [...] Read more.
Lampreys spend their larval stage within fine sand fluvial sediments, where they burrow and act as filter feeders. Lamprey larvae (ammocoetes) can significantly affect benthic-pelagic coupling and nutrient cycling in rivers, due to high densities. However, their bioturbation, feeding and excretion activities are still poorly explored. These aspects were investigated by means of laboratory incubations of intact sediments added with ammocoetes and of animals alone. Oxygen respiration, nutrient fluxes and excretion rates were determined. Individual ammocoete incubations suggested that biomass-specific oxygen consumption and ammonium, reactive phosphorus and silica excretion were size-dependent, and greater in small compared to large individuals. The comparison of ammocoetes metabolic rates with rates measured in intact sediments revealed that ammocoetes activity decreases significantly when they are burrowed in sediments. Furthermore, results suggest that a major fraction of ammonium excreted by ammocoetes was assimilated by benthic microbes or microalgae to overcome in situ N-limitation. Alternatively, part of the excreted ammonium was oxidized and denitrified within sediments, as nitrate uptake rather increased along with ammocoetes density. Ammocoetes excreted reactive phosphorus and silica but such production was not apparent in bioturbated sediments, likely due to microbial or microalgal uptake or to immobilization in sediments. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessCommunication
Contrasting Effects of Bioturbation Studied in Intact and Reconstructed Estuarine Sediments
Water 2020, 12(11), 3125; https://doi.org/10.3390/w12113125 - 07 Nov 2020
Cited by 1 | Viewed by 470
Abstract
Macrofauna can produce contrasting biogeochemical effects in intact and reconstructed sediments. We measured benthic fluxes of oxygen, inorganic carbon, and nitrogen and denitrification rates in intact sediments dominated by a filter and a deposit feeder and in reconstructed sediments added with increasing densities [...] Read more.
Macrofauna can produce contrasting biogeochemical effects in intact and reconstructed sediments. We measured benthic fluxes of oxygen, inorganic carbon, and nitrogen and denitrification rates in intact sediments dominated by a filter and a deposit feeder and in reconstructed sediments added with increasing densities of the same organisms. Measurements in reconstructed sediments were carried out 5 days after macrofauna addition. The degree of stimulation of the measured fluxes in the intact and reconstructed sediments was then compared. Results confirmed that high densities of bioturbating macrofauna produce profound effects on sediment biogeochemistry, enhancing benthic respiration and ammonium recycling by up to a factor of ~3 and ~9, respectively, as compared to control sediments. The deposit feeder also increased total denitrification by a factor of ~2, whereas the filter feeder activity did not stimulate nitrogen removal. Moreover, the effects of deposit feeders on benthic fluxes were significantly higher (e.g., on respiration and ammonium recycling) or different (e.g., on denitrification) when measured in intact and reconstructed sediments. In intact sediments, deposit feeders enhanced the denitrification coupled to nitrification and had no effects on the denitrification of water column nitrate, whereas in reconstructed sediments, the opposite was true. This may reflect active burrowing in reconstructed sediments and the long time needed for slow growing nitrifiers to develop within burrows. Results suggest that, in bioturbation studies, oversimplified experimental approaches and insufficient preincubation time might lead to wrong interpretation of the role of macrofauna in sediment biogeochemistry, far from that occurring in nature. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessArticle
Monthly Abundance Patterns and the Potential Role of Waterbirds as Phosphorus Sources to a Hypertrophic Baltic Lagoon
Water 2020, 12(5), 1392; https://doi.org/10.3390/w12051392 - 14 May 2020
Cited by 2 | Viewed by 613
Abstract
Compared to external loads from tributaries and sediment recycling, the role of waterbirds as phosphorus (P) sources in estuaries is overlooked. We performed monthly ship-based surveys of waterbird abundance in the Lithuanian part of the Curonian Lagoon, calculated their potential P excretion, and [...] Read more.
Compared to external loads from tributaries and sediment recycling, the role of waterbirds as phosphorus (P) sources in estuaries is overlooked. We performed monthly ship-based surveys of waterbird abundance in the Lithuanian part of the Curonian Lagoon, calculated their potential P excretion, and compared its relevance to the riverine inputs. Phosphorus excretion rates for the censused species were assessed accounting for variations of body weights, daily feces production and their P content, and assigning species to different feeding and nutrient cycling guilds. During the study period (March–November 2018), 32 waterbird species were censused, varying in abundance from ~18,000–32,000 (October–November) to ~30,000–48,000 individuals (June–September). The estimated avian P loads during the whole study period varied between 3.6 and 25 tons, corresponding to an area load between 8.7 and 60.7 mg P m−2. Waterbird release of reactive P to the system represented a variable but not negligible fraction (1%–12%) of total external P loads, peaking in June–September and coinciding with cyanobacterial blooms. This study is the first in the Baltic Sea region suggesting that waterbirds are potentially important P sources to phytoplankton in large estuaries, in particular, during low discharge periods. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessArticle
Feces from Piscivorous and Herbivorous Birds Stimulate Differentially Phytoplankton Growth
Water 2019, 11(12), 2567; https://doi.org/10.3390/w11122567 - 05 Dec 2019
Cited by 5 | Viewed by 1008
Abstract
Aquatic birds may impact shallow ecosystems via organic and nutrient enrichment with feces. Such input may alleviate nutrient limitation, unbalance their ecological stoichiometry, and stimulate primary production. Herbivorous and piscivorous birds may produce different effects on aquatic ecosystems due to different physiology, diet [...] Read more.
Aquatic birds may impact shallow ecosystems via organic and nutrient enrichment with feces. Such input may alleviate nutrient limitation, unbalance their ecological stoichiometry, and stimulate primary production. Herbivorous and piscivorous birds may produce different effects on aquatic ecosystems due to different physiology, diet and feces elemental composition. We analyze the effects of droppings from swans (herbivorous) and cormorants (piscivorous) on phytoplankton growth via a laboratory experiment. These birds are well represented in the Curonian Lagoon, where they form large colonies. As this lagoon displays summer algal hyper-blooms, we hypothesize an active, direct role of birds via defecation on algal growth. Short-term incubations of phytoplankton under low and high feces addition produces different stimulation of algal growth, significantly higher with high inputs of cormorant feces. The latter produces a major effect on reactive phosphorus concentration that augments significantly, as compared to treatments with swan feces, and determines an unbalanced, N-limited stoichiometry along with the duration of the experiment. During the incubation period, the dominant algal groups switch from blue-green to green algae, but such switch is independent of the level of feces input and from their origin. Heterotrophic bacteria also are stimulated by feces addition, but their increase is transient. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessCommunication
Analysis of 15N-NO3 Via Anoxic Slurries Coupled to MIMS Analysis: An Application to Estimate Nitrification by Burrowing Macrofauna
Water 2019, 11(11), 2310; https://doi.org/10.3390/w11112310 - 04 Nov 2019
Cited by 1 | Viewed by 947
Abstract
The increasing use of the stable isotope 15N-NO3 for the quantification of ecological processes requires analytical approaches able to distinguish between labelled and unlabeled N forms. We present a method coupling anoxic sediment slurries and membrane inlet mass spectrometry to [...] Read more.
The increasing use of the stable isotope 15N-NO3 for the quantification of ecological processes requires analytical approaches able to distinguish between labelled and unlabeled N forms. We present a method coupling anoxic sediment slurries and membrane inlet mass spectrometry to quantify dissolved 15N-NO3 and 14N-NO3. The approach is based on the microbial reduction of 14N-NO3 and 15N-NO3 mixed pool, the determination of the produced 29N2 and 30N2, and the calculation of the original 15N-NO3 and 14N-NO3 concentrations. The reduction is carried out in 12 mL exetainers containing 2 mL of sediment and 10 mL of water, under anoxia. To validate this approach, we prepared multiple standard solutions containing 15N-NO3 alone or in combinations with 14N-NO3, with final concentrations varying from 0.5 to 3000 µM. We recovered nearly 90% of the initial 14N-NO3 or 15N-NO3, over a wide range of concentrations and isotope ratios in the standards. We applied this method to a 15N-NO3 dilution experiment targeting the measurement of nitrification in sediments with and without the burrower Sparganophilus tamesis. The oligochaete did not stimulate nitrification, likely due to limited ventilation and unfavorable conditions for nitrifiers growth. The proposed method is reliable, fast, and could be applied to multiple ecological studies. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessArticle
Silica Storage, Fluxes, and Nutrient Stoichiometry in Different Benthic Primary Producer Communities in the Littoral Zone of a Deep Subalpine Lake (Lake Iseo, Italy)
Water 2019, 11(10), 2140; https://doi.org/10.3390/w11102140 - 15 Oct 2019
Cited by 1 | Viewed by 1837
Abstract
Benthic vegetation at the land-water interface is recognized as a filter for silica fluxes, which represents an important but under-investigated subject. This paper aims to analyze stocks and fluxes of biogenic (BSi) and dissolved (DSi) silica in relation to nitrogen (N) and phosphorus [...] Read more.
Benthic vegetation at the land-water interface is recognized as a filter for silica fluxes, which represents an important but under-investigated subject. This paper aims to analyze stocks and fluxes of biogenic (BSi) and dissolved (DSi) silica in relation to nitrogen (N) and phosphorus (P) in the littoral zone of a deep lake. Specifically, we evaluated how different primary producers can influence BSi retention and DSi release. The study was performed from April to October in 2017, in three different benthic communities: submerged aquatic vegetation (SAV) and microphytobenthos (MPB), both occurring in soft bottom sediments, and epilithic macro- and microalgae (EA) on rocky substrates. The main result was that SAV and MPB were a DSi source and a N and P sink with the DSi efflux from SAV nearly three times as much as in MPB patches. These findings corroborate the hypothesis that SAV mediates the DSi transport from pore water to the water column. Conversely, EA communities were a DSi sink and a N and P source. Overall, these results highlight the fact that the littoral zone of lakes plays a key role in regulating aquatic Si cycling, which is likely to depend on the health status of SAV communities. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessArticle
Direct and Indirect Impacts of Fish on Crustacean Zooplankton in Experimental Mesocosms
Water 2019, 11(10), 2090; https://doi.org/10.3390/w11102090 - 07 Oct 2019
Cited by 4 | Viewed by 1120
Abstract
Understanding the factors that regulate phytoplankton and zooplankton is an important goal of aquatic ecologists; however, much remains unknown because of complex interactions between phytoplankton, zooplankton, and fish. Zooplankton, in particular cladocerans, can be regulated by bottom–up factors either via food quantity or [...] Read more.
Understanding the factors that regulate phytoplankton and zooplankton is an important goal of aquatic ecologists; however, much remains unknown because of complex interactions between phytoplankton, zooplankton, and fish. Zooplankton, in particular cladocerans, can be regulated by bottom–up factors either via food quantity or food quality in terms of polyunsaturated fatty acids (PUFA) or phosphorus (P) contents in phytoplankton. Fish can recycle nutrients and in turn change the PUFA and P contents of algal resources, thus modifying bottom–up regulation. Furthermore, fish can change phytoplankton structure through consumption of cladocerans which selectively graze phytoplankton. We conducted a mesocosm (300 L) experiment to determine how trophic state and fish affected crustacean dynamics. The mesocosms were filled with water containing natural plankton from the eutrophic Lake Jorzec and mesotrophic Lake Majcz (Northeastern Poland), and we manipulated fish presence/absence. We also conducted a complementary life-table experiment to determine how trophic state and fish nonconsumptively affected demographic parameters of the dominant cladocerans in the mesocosms. Small and large cladoceran species responded differently to food quantity and quality. Small-bodied Ceriodaphnia were regulated mainly by resource concentrations (i.e., food quantity), while large species were limited by PUFAs (i.e., food quality). Fish likely increased food quality in terms of PUFA, primarily eicosapentaenoic acids (EPA), thus providing conditions for more successful development of Daphnia than in the fish-free treatments. Phosphorus in the seston was likely limiting for zooplankton. However, food quality in terms of phosphorus was likely less important than PUFA because zooplankton can accumulate nutrients in their body. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessArticle
The Effect of Chironomid Larvae on Nitrogen Cycling and Microbial Communities in Soft Sediments
Water 2019, 11(9), 1931; https://doi.org/10.3390/w11091931 - 16 Sep 2019
Cited by 6 | Viewed by 1553
Abstract
The combination of biogeochemical methods and molecular techniques has the potential to uncover the black-box of the nitrogen (N) cycle in bioturbated sediments. Advanced biogeochemical methods allow the quantification of the process rates of different microbial processes, whereas molecular tools allow the analysis [...] Read more.
The combination of biogeochemical methods and molecular techniques has the potential to uncover the black-box of the nitrogen (N) cycle in bioturbated sediments. Advanced biogeochemical methods allow the quantification of the process rates of different microbial processes, whereas molecular tools allow the analysis of microbial diversity (16S rRNA metabarcoding) and activity (marker genes and transcripts) in biogeochemical hot-spots such as the burrow wall or macrofauna guts. By combining biogeochemical and molecular techniques, we analyzed the role of tube-dwelling Chironomus plumosus (Insecta, Diptera) larvae on nitrification and nitrate reduction processes in a laboratory experiment with reconstructed sediments. We hypothesized that chironomid larvae stimulate these processes and host bacteria actively involved in N-cycling. Our results suggest that chironomid larvae significantly enhance the recycling of ammonium (80.5 ± 48.7 µmol m−2 h−1) and the production of dinitrogen (420.2 ± 21.4 µmol m−2 h−1) via coupled nitrification–denitrification and the consumption of water column nitrates. Besides creating oxygen microniches in ammonium-rich subsurface sediments via burrow digging and ventilation, chironomid larvae serve as hot-spots of microbial communities involved in N-cycling. The quantification of functional genes showed a significantly higher potential for microbial denitrification and nitrate ammonification in larvae as compared to surrounding sediments. Future studies may further scrutinize N transformation rates associated with intimate macrofaunal–bacteria associations. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessArticle
Effect of Species Invasion on Transport of Solutes at Different Levels of Soft Sediment Macrofauna Diversity: Results from an Experimental Approach
Water 2019, 11(8), 1544; https://doi.org/10.3390/w11081544 - 25 Jul 2019
Viewed by 1095
Abstract
Different irrigation or ventilation strategies by macrofauna may provide a competitive advantage to tolerant species invading impacted benthic systems and alter benthic-pelagic coupling. To comparatively analyze the effects of an exotic and a native polychaete burrower on sediment-water exchanges, two laboratory experiments were [...] Read more.
Different irrigation or ventilation strategies by macrofauna may provide a competitive advantage to tolerant species invading impacted benthic systems and alter benthic-pelagic coupling. To comparatively analyze the effects of an exotic and a native polychaete burrower on sediment-water exchanges, two laboratory experiments were performed. In the first experiment, the invasive spionid polychaete Marenzelleria neglecta was added to defaunated sediments and fluxes of the inert tracer (bromide, Br) were measured to quantify the effects of irrigation by the worm on the tracer transport. In the second experiment, M. neglecta or the native polychaete Hediste diversicolor were introduced to a relatively diverse Baltic soft-bottom macrofauna community. The effect of species on fluxes of reactive solutes (ammonium, NH4+, and phosphate, PO43−) and transport rates of Br was estimated. The results indicate different invasion effects depending on the characteristics of the recipient habitat. In defaunated sediments, a single specimen of M. neglecta significantly enhanced originally low solute exchange rates. Total tracer flux was significantly enhanced over diffusive flux by a factor of 1.6 ± 0.14 (n = 3). In natural sediments, on the other hand, the addition of either M. neglecta or H. diversicolor had no statistically significant effects on benthic fluxes. Tracer flux estimates between control and treatment incubations differed by less than 10% on average, and both reactive solutes tended to increase by 10 to 40% after additions. One specimen of M. neglecta in cores with defaunated sediment generated approximately 20% of the tracer flux produced by the relatively diverse macrofauna community. Estimated net tracer fluxes in two experiments corresponded well with the number of adult polychaetes found in sediments (r2 = 0.73, p = 0.005, n = 12). The invasive M. neglecta produced a small effect on fluxes in biodiverse sediments, comparable to those of H. diversicolor, but it may deeply alter porewater chemistry in azoic sediment. As M. neglecta tolerates chemically reduced and sulphidic conditions, its bioirigation may favor sediment reoxidation and ultimately the recolonization by less tolerant, native species. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessArticle
Estuarine Macrofauna Affects Benthic Biogeochemistry in a Hypertrophic Lagoon
Water 2019, 11(6), 1186; https://doi.org/10.3390/w11061186 - 07 Jun 2019
Cited by 6 | Viewed by 1369
Abstract
Coastal lagoons display a wide range of physico-chemical conditions that shape benthic macrofauna communities. In turn, benthic macrofauna affects a wide array of biogeochemical processes as a consequence of feeding, bioirrigation, ventilation, and excretion activities. In this work, we have measured benthic respiration [...] Read more.
Coastal lagoons display a wide range of physico-chemical conditions that shape benthic macrofauna communities. In turn, benthic macrofauna affects a wide array of biogeochemical processes as a consequence of feeding, bioirrigation, ventilation, and excretion activities. In this work, we have measured benthic respiration and solute fluxes in intact sediment cores with natural macrofauna communities collected from four distinct areas within the Sacca di Goro Lagoon (NE Adriatic Sea). The macrofauna community was characterized at the end of the incubations. Redundancy analysis (RDA) was used to quantify and test the interactions between the dominant macrofauna species and solute fluxes. Moreover, the relevance of macrofauna as driver of benthic nitrogen (N) redundancy analysis revealed that up to 66% of the benthic fluxes and metabolism variance was explained by macrofauna microbial-mediated N processes. Nitrification was stimulated by the presence of shallow (corophiids) in combination with deep burrowers (spionids, oligochaetes) or ammonium-excreting clams. Deep burrowers and clams increase ammonium availability in burrows actively ventilated by corophiids, which creates optimal conditions to nitrifiers. However, the stimulatory effect of burrowing macrofauna on nitrification does not necessarily result in higher denitrification as processes are spatially separated. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessArticle
Effects of Drying and Re-Wetting on Litter Decomposition and Nutrient Recycling: A Manipulative Experiment
Water 2019, 11(4), 708; https://doi.org/10.3390/w11040708 - 05 Apr 2019
Cited by 2 | Viewed by 1181
Abstract
Climate change and water abstraction may change stream flow from perennial into intermittent lotic systems, modifying their abiotic and biotic benthic environment and impacting ecosystem processes such as nutrient turnover. We conducted a microcosm experiment to investigate the interactive effect of water intermittency, [...] Read more.
Climate change and water abstraction may change stream flow from perennial into intermittent lotic systems, modifying their abiotic and biotic benthic environment and impacting ecosystem processes such as nutrient turnover. We conducted a microcosm experiment to investigate the interactive effect of water intermittency, macrofauna and leaf size (Populus nigra leaves) on nutrient mineralization and recycling. Leaf disks (1 or 5 cm diameter) were incubated for 40 days with or without the leaf-consumer, Potamophylax cingulatus larvae (Trichoptera, Limnephilidae) and with or without an intervening, 10-days simulation of stream drying and subsequent rewetting. Nutrient fluxes, residual leaf biomass and leaf elemental composition were measured to evaluate how intermittency, macrofauna and leaf size affect organic matter mineralization rates and stoichiometry. Results suggest that drying slows decomposition rates, impacting both the microbial and setting to zero macrofauna activities. The presence of macrofauna increases mineralization and nutrient (C, N and P) regeneration rates. Our findings also suggest that leaf disks with higher diameter display higher microbial activity and NH4+ regeneration. During the experiment, the C:N:P ratios of residual litter changed, as the leaf material became enriched with N and P. Our study suggests that increasingly frequent dry events might slow mineralization rates and downstream nutrient transport. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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Open AccessArticle
Contrasting Effects of an Alien Worm on Benthic N Cycling in Muddy and Sandy Sediments
Water 2019, 11(3), 465; https://doi.org/10.3390/w11030465 - 05 Mar 2019
Cited by 3 | Viewed by 1564
Abstract
The North American oligochaete Sparganophilus tamesis is widespread in European freshwaters. Its ecological effects on benthic nitrogen (N) biogeochemistry were studied in two contrasting environments: the organic-rich muddy sediments of the eutrophic Mincio River (Italy) and the organic-poor sandy sediments of the oligotrophic [...] Read more.
The North American oligochaete Sparganophilus tamesis is widespread in European freshwaters. Its ecological effects on benthic nitrogen (N) biogeochemistry were studied in two contrasting environments: the organic-rich muddy sediments of the eutrophic Mincio River (Italy) and the organic-poor sandy sediments of the oligotrophic Cazaux-Sanguinet Lake (France). Oxygen and inorganic N fluxes and denitrification rates (IPT) were measured by dark incubation of intact cores with different worm biomass. Sediment oxygen demand and denitrification were higher in muddy than in sandy sediments; however, at the two sites, bioturbation by the oligochaetes stimulated differing microbial O2 and NO3 respiration and NH4+ production. In particular, the relative effect of S. tamesis on sediment metabolism was greater in Cazaux-Sanguinet Lake than in the Mincio River. As a result, S. tamesis favored net N loss in the Mincio River, whereas it increased NH4+ recycling and lowered denitrification efficiency in the Cazaux-Sanguinet Lake. Our results suggest that the effects of S. tamesis on N biogeochemistry might differ depending on local trophic settings. These results have implications for the conservation of isoetids in the French Lake, whose persistence can be menaced by oligochaete-induced nutrient mobilization. Full article
(This article belongs to the Special Issue The Role of Macrobiota in Aquatic Nutrient Cycling)
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