Effects of an invasive polychaete on benthic phosphorus cycling at sea basin scale: An ecosystem disservice

Macrofaunal activities in sediments modify nutrient fluxes in different ways including the expression of species-specific functional traits and density-dependent population processes. The invasive polychaete genus Marenzelleria was first observed in the Baltic Sea in the 1980s. It has caused changes in benthic processes and affected the functioning of ecosystem services such as nutrient regulation. The large-scale effects of these changes are not known. We estimated the current Marenzelleria spp. wet weight biomass in the Baltic Sea to be 60–87 kton (95% confidence interval). We assessed the potential impact of Marenzelleria spp. on phosphorus cycling using a spatially explicit model, comparing estimates of expected sediment to water phosphorus fluxes from a biophysical model to ecologically relevant experimental measurements of benthic phosphorus flux. The estimated yearly net increases (95% CI) in phosphorous flux due to Marenzelleria spp. were 4.2–6.1 kton based on the biophysical model and 6.3–9.1 kton based on experimental data. The current biomass densities of Marenzelleria spp. in the Baltic Sea enhance the phosphorus fluxes from sediment to water on a sea basin scale. Although high densities of Marenzelleria spp. can increase phosphorus retention locally, such biomass densities are uncommon. Thus, the major effect of Marenzelleria seems to be a large-scale net decrease in the self-cleaning capacity of the Baltic Sea that counteracts human efforts to mitigate eutrophication in the region.     

Indications of Recovery from Hypoxia in the Inner Stockholm Archipelago

Improved benthic conditions compared to the 1990s were found during benthic investigations, including sediment and benthic macrofauna in the inner Stockholm archipelago during 2008. In the 1990s, these areas were dominated by black and laminated surface sediments and very sparse fauna. A clear relationship was found when comparing sediment status with the benthic macrofauna. Reduced surface sediment and impoverished macroinvertebrate community was only found at one sampling station representing an enclosed part of the inner archipelago, whereas the other seven stations, with depths ranging from 20 to 50 m, had oxidized surface sediments and considerable biomasses of benthic macrofauna (6–65 g m⁻²) dominated by the invading polychaete Marenzelleria neglecta. An extrapolation of the results shows that, within the investigated area, the coverage of reduced surface sediments had decreased from approximately 17% in the late 1990s to 4% in 2008.     

Using benthic recruitment to assess the significance of contaminated sediments: the influence of taxonomic resolution

The use of small-scale experimental units as a means of evaluating the ecological effects of contaminated sediments was examined at the species, family, mixed and phylum levels of taxonomic resolution. Sediments were taken from various locations representing a range of contaminant loads. Containers with these sediments were placed in situ at a relatively uncontaminated location for 90 days. The containers were retrieved and the abundance of the macrofauna which recruited to the containers was estimated. The results showed that the composition of the benthic communities in the more highly contaminated sediments differed significantly from those in less contaminated sediments. Analyses at the different taxonomic levels showed that all but the phylum level data showed some differences in community structure among sediment types. The study showed that small-scale experiments are useful for examining the effects of contaminants and that higher levels of taxonomic resolution can be used to describe variations in the structure of benthic communities at this spatial scale.     

Hypoxia in the Baltic Sea: Biogeochemical Cycles, Benthic Fauna, and Management

Hypoxia has occurred intermittently over the Holocene in the Baltic Sea, but the recent expansion from less than 10 000 km² before 1950 to >60 000 km² since 2000 is mainly caused by enhanced nutrient inputs from land and atmosphere. With worsening hypoxia, the role of sediments changes from nitrogen removal to nitrogen release as ammonium. At present, denitrification in the water column and sediments is equally important. Phosphorus is currently buried in sediments mainly in organic form, with an additional contribution of reduced Fe-phosphate minerals in the deep anoxic basins. Upon the transition to oxic conditions, a significant proportion of the organic phosphorus will be remineralized, with the phosphorus then being bound to iron oxides. This iron-oxide bound phosphorus is readily released to the water column upon the onset of hypoxia again. Important ecosystems services carried out by the benthic fauna, including biogeochemical feedback-loops and biomass production, are also lost with hypoxia. The results provide quantitative knowledge of nutrient release and recycling processes under various environmental conditions in support of decision support tools underlying the Baltic Sea Action Plan.     

Spatio-temporal distribution of organic and inorganic pollutants from Lake Geneva (Switzerland) reveals strong interacting effects of sewage treatment plant and eutrophication on microbial abundance

Variation with depth and time of organic matter (carbon, nitrogen, phosphorus), inorganic pollutant (mercury), as well as bacterial abundance and activity, were investigated for the first time in sediment profiles of different parts of Lake Geneva (Switzerland) over the last decades. The highest organic contents (about 32%), mercury concentration (27 mg kg⁻¹), bacterial abundance (in order of 9 × 10⁹ cell g⁻¹ dry sediment), and bacterial activity (1299 Relative Light Units (RLU)) were found in the highly polluted sediments contaminated by the waste water treatment plant (WWTP) discharge, which deposited during the period of cultural eutrophication. Such data, which contrast with the other sampled sites from deeper and more remote parts of the lake, prove that the organic matter and nutrients released from the municipal WWTP have considerable effects on bacterial abundance and activities in freshwater sediments. In fact, the relatively unpolluted deepwater sites and the coastal polluted site show large synchronous increases in bacterial densities linked to the anoxic conditions in the 1970s (lake eutrophication caused by external nutrient input) that subsequently increased the nutrient loading fluxes. These results show that the microbial activities response to natural or human-induced changing limnological conditions (e.g., nutrient supply, oxygen availability, redox conditions) constitutes a threat to the security of water resources, which in turn poses concerns for the world’s freshwater resources in the context of global warming and the degradation of water quality (oxygen depletion in the bottom water due to reduced deep waters mixing). Moreover, the accumulation of inorganic pollutants such as high mercury (methyl-mercury) concentration may represent a significant source of toxicity for sediment dwelling organisms.     

Oxygen,carbon, and nutrient exchanges at the sediment–water interface in the Mar Piccolo of Taranto (Ionian Sea,southern Italy)

In the shallow environment, the nutrient and carbon exchanges at the sediment–water interface contribute significantly to determine the trophic status of the whole water column. The intensity of the allochthonous input in a coastal environment subjected to strong anthropogenic pressures determines an increase in the benthic oxygen demand leading to depressed oxygen levels in the bottom waters. Anoxic conditions resulting from organic enrichment can enhance the exchange of nutrients between sediments and the overlying water. In the present study, carbon and nutrient fluxes at the sediment–water interface were measured at two experimental sites, one highly and one moderately contaminated, as reference point. In situ benthic flux measurements of dissolved species (O₂, DIC, DOC, N-NO₃ ^?, N-NO₂ ^?, N-NH₄ ⁺, P-PO₄ ^3?, Si-Si(OH)₄, H₂S) were conducted using benthic chambers. Furthermore, undisturbed sediment cores were collected for analyses of total and organic C, total N, and biopolymeric carbon (carbohydrates, proteins, and lipids) as well as of dissolved species in porewaters and supernatant in order to calculate the diffusive fluxes. The sediments were characterized by suboxic to anoxic conditions with redox values more negative in the highly contaminated site, which was also characterized by higher biopolymeric carbon content (most of all lipids), lower C/N ratios and generally higher diffusive fluxes, which could result in a higher release of contaminants. A great difference was observed between diffusive and in situ benthic fluxes suggesting the enhancing of fluxes by bioturbation and the occurrence of biogeochemically important processes at the sediment–water interface. The multi-contamination of both inorganic and organic pollutants, in the sediments of the Mar Piccolo of Taranto (declared SIN in 1998), potentially transferable to the water column and to the aquatic trophic chain, is of serious concern for its ecological relevance, also considering the widespread fishing and mussel farming activities in the area.     

Complex interactions between autotrophs in shallow marine and freshwater ecosystems: implications for community responses to nutrient stress

The relative biomass of autotrophs (vascular plants, macroalgae, microphytobenthos, phytoplankton) in shallow aquatic ecosystems is thought to be controlled by nutrient inputs and underwater irradiance. Widely accepted conceptual models indicate that this is the case both in marine and freshwater systems. In this paper we examine four case studies and test whether these models generally apply. We also identify other complex interactions among the autotrophs that may influence ecosystem response to cultural eutrophication. The marine case studies focus on macroalgae and its interactions with sediments and vascular plants. The freshwater case studies focus on interactions between phytoplankton, epiphyton, and benthic microalgae. In Waquoit Bay, MA (estuary), controlled experiments documented that blooms of macroalgae were responsible for the loss of eelgrass beds at nutrient-enriched locations. Macroalgae covered eelgrass and reduced irradiance to the extent that the plants could not maintain net growth. In Hog Island Bay, VA (estuary), a dense lawn of macroalgae covered the bottom sediments. There was reduced sediment-water nitrogen exchange when the algae were actively growing and high nitrogen release during algal senescence. In Lakes Brobo (West Africa) and Okeechobee (FL), there were dramatic seasonal changes in the biomass and phosphorus content of planktonic versus attached algae, and these changes were coupled with changes in water level and abiotic turbidity. Deeper water and/or greater turbidity favored dominance by phytoplankton. In Lake Brobo there also was evidence that phytoplankton growth was stimulated following a die-off of vascular plants. The case studies from Waquoit Bay and Lake Okeechobee support conceptual models of succession from vascular plants to benthic algae to phytoplankton along gradients of increasing nutrients and decreasing under-water irradiance. The case studies from Hog Island Bay and Lake Brobo illustrate additional effects (modified sediment-water nutrient fluxes, allelopathy or nutrient release during plant senescence) that could play a role in ecosystem response to nutrient stress.     

Projected future climate change and Baltic Sea ecosystem management

Climate change is likely to have large effects on the Baltic Sea ecosystem. Simulations indicate 2–4 °C warming and 50–80 % decrease in ice cover by 2100. Precipitation may increase ~30 % in the north, causing increased land runoff of allochthonous organic matter (AOM) and organic pollutants and decreased salinity. Coupled physical–biogeochemical models indicate that, in the south, bottom-water anoxia may spread, reducing cod recruitment and increasing sediment phosphorus release, thus promoting cyanobacterial blooms. In the north, heterotrophic bacteria will be favored by AOM, while phytoplankton production may be reduced. Extra trophic levels in the food web may increase energy losses and consequently reduce fish production. Future management of the Baltic Sea must consider the effects of climate change on the ecosystem dynamics and functions, as well as the effects of anthropogenic nutrient and pollutant load. Monitoring should have a holistic approach, encompassing both autotrophic (phytoplankton) and heterotrophic (e.g., bacterial) processes.     

Biogeochemical consequences of a changing Arctic shelf seafloor ecosystem

Unprecedented and dramatic transformations are occurring in the Arctic in response to climate change, but academic, public, and political discourse has disproportionately focussed on the most visible and direct aspects of change, including sea ice melt, permafrost thaw, the fate of charismatic megafauna, and the expansion of fisheries. Such narratives disregard the importance of less visible and indirect processes and, in particular, miss the substantive contribution of the shelf seafloor in regulating nutrients and sequestering carbon. Here, we summarise the biogeochemical functioning of the Arctic shelf seafloor before considering how climate change and regional adjustments to human activities may alter its biogeochemical and ecological dynamics, including ecosystem function, carbon burial, or nutrient recycling. We highlight the importance of the Arctic benthic system in mitigating climatic and anthropogenic change and, with a focus on the Barents Sea, offer some observations and our perspectives on future management and policy.     

Effects of light, microbial activity, and sediment resuspension on the phosphorus immobilization capability of drinking water treatment residuals in lake sediment

Drinking water treatment residuals (WTRs), nonhazardous by-products generated in a drinking water treatment plant, can be reused to immobilize phosphorus (P) to control the internal P loading from lake sediments for eutrophication control. Reasonably, before practical application, it is essential to determine the P immobilization capability of WTRs in lake sediments under various conditions. In this work, laboratory scale experiments were conducted to investigate the effects of light, microbial activity, and sediment resuspension on the P immobilization capability of WTRs. The results suggested that absence of light, low microbial activity, and sediment resuspension can increase the internal P loading from lake sediments. WTRs can, however, reduce the internal P loading significantly. Further analysis demonstrated that WTRs can stabilize P, decreasing the P bioavailability in the sediments under varied conditions. WTRs also presented little undesirable effects on the dissolved oxygen levels and pH of overlying water. Therefore, light, microbial activity, and sediment resuspension have little effect on the P immobilization capability of WTRs in lake sediments.     

Nutrient dynamics and the eutrophication of shallow lakes Kasumigaura (Japan), Donghu (PR China), and Okeechobee (USA)

We compared the nutrient dynamics of three lakes that have been heavily influenced by point and non-point source pollution and other human activities. The lakes, located in Japan (Lake Kasumigaura), People's Republic of China (Lake Donghu), and the USA (Lake Okeechobee), all are relatively large (> 30 km2), very shallow (< 4 m mean depth), and eutrophic. In all three lakes we found strong interactions among the sediments, water column, and human activities. Important processes affecting nutrient dynamics included nitrogen fixation, light limitation due to resuspended sediments, and intense grazing on algae by cultured fish. As a result of these complex interactions, simple empirical models developed to predict in-lake responses of total phosphorus and algal biomass to external nutrient loads must be used with caution. While published models may provide 'good' results, in terms of model output matching actual data, this may not be due to accurate representation of lake processes in the models. The variable nutrient dynamics that we observed among the three study lakes appears to be typical for shallow lake systems. This indicates that a greater reliance on lake-specific research may be required for effective management, and a lesser role of inter-lake generalization than is possible for deeper, dimictic lake systems. Furthermore, accurate predictions of management impacts in shallow eutrophic lakes may require the use of relatively complex deterministic modeling tools.     

Benthic ecosystem functioning in the severely contaminated Mar Piccolo of Taranto (Ionian Sea,Italy): focus on heterotrophic pathways

The benthic ecosystem functioning is a rarely applied holistic approach that integrates the main chemical and biological features of the benthic domain with the key processes responsible for the flux of energy and C through the system. For the first time, such conceptual model, with an emphasis on the heterotrophic pathways, has been applied to the sediments at four stations within one of the most polluted coastal areas in Italy: the Mar Piccolo of Taranto. The functioning of the benthic ecosystem was different according to the investigated site. Nearby the military arsenal, i.e., the main source of organic contaminants and heavy metals, the system seemed inhibited at all the investigated structural and functional levels. Slow microbial processes of C reworking together with very limited densities of benthic fauna suggested a modest transfer of C both into a solid microbial loop and to the higher trophic levels. On the other hand, the ingression of marine water through the “Navigabile” channel seemed to stimulate the organic matter degradation and, consequently, the proliferation of meiofauna and macrofauna. In the innermost part of the basin, the system functioning, to some extent, is less impacted by contaminants and more influenced by mussel farms. The organic matter produced by these bivalves fueled faster C reworking by benthic prokaryotes and enhanced the proliferation of filter feeders.     

Bioaccumulation of 51Cr, 63Ni and 14C in Baltic Sea benthos

The Baltic Sea is a species-poor, semi-enclosed, brackish sea, whose sediments contain a wide range of contaminants, including sediment-associated metals and radionuclides. In this study, we have examined and compared bioaccumulation kinetics and assimilation efficiencies of sediment-associated (51)Cr, (63)Ni and (14)C in three key benthic invertebrates (the deposit-feeding Monoporeia affinis, the facultative deposit-feeding Macoma baltica, and the omnivorous Halicryptus spinulosus). Our results demonstrate that (i) all radionuclides were accumulated, (ii) the different radionuclides were accumulated to various extents, (iii) small changes in organic carbon concentration can influence the accumulation, and (iv) the degree of accumulation differed only slightly between species. These processes, together with sediment resuspension and bioturbation, may remobilise trace metals from the sediment to the water and to higher trophic levels, and therefore should be taken into account in exposure models and ERAs.     

Environmental impact and recovery at two dumping sites for dredged material in the North Sea

The environmental impact and recovery associated with the long and uninterrupted disposal of large volumes of moderately contaminated dredged material from the port of Rotterdam was studied at nearby dumping sites in the North Sea. Observations were made on sediment contamination, ecotoxicity, biomarker responses and benthic community changes shortly after dumping at the 'North' site had ceased and at the start of disposal at the new dumping site 'Northwest'. During the period of dumping, very few benthic invertebrates were found at the North site. Concentrations of cadmium, mercury, polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs) and tributyltin (TBT) in the fine sediment fraction (<63 microm) from this site were 2-3 times higher than at the reference site. In four different bioassays with marine invertebrates the sediments showed no acute toxic effects. In tissue (pyloric caeca) of resident starfish Asterias rubens, residual levels of mercury, zinc, PCBs and dioxin-like activity were never more than twice those at the reference site. Four different biomarkers (DNA integrity, cytochrome P450 content, benzo[a]pyrene hydroxylase activity and acetylcholinesterase inhibition) were used on the starfish tissues, but no significant differences were found between North and the reference site. Minor pathological effects were observed in resident dab Limanda limanda. One year after dumping had ceased at the North site, a significant increase in the species richness and abundance of benthic invertebrates and a concomitant decrease in the fine sediment fraction of the seabed were observed. After 8.2 million m3 of moderately contaminated dredged material had been dumped at the new dumping site Northwest, the species richness and abundance of benthic invertebrates declined over an area extending about 1-2 km eastwards. This correlated with a shift in sediment texture from sand to silt. The contamination of the fine sediment fraction at the Northwest location doubled. It is concluded that marine benthic resources at and around the dumping sites have been adversely affected by physical disturbance (burial, smothering). However, no causal link could be established with sediment-associated contaminants from the dredged spoils.     

Equilibrium partitioning theory to predict the sediment toxicity of the anionic surfactant C(12)-2-LAS to Corophium volutator

The study of the effect of the sorption of linear alkylbenzene sulfonates (LAS) on the bioavailability to marine benthic organisms is essential to refine the environmental risk assessment of these compounds. According to the equilibrium partitioning theory (EqP), the effect concentration in water-only exposure will be similar to the effect concentration in the sediment pore water. In this work, sorption and desorption experiments with two marine sediments were carried out using the compound C₁₂-2-LAS. The effect of the sediment sorption on the toxicity of benthic organisms was studied in water-only and in sediment bioassays with the marine mud shrimp Corophium volutator. In addition, three common spiking methods were tested for its application in the toxicity tests, as well as the stability of the surfactant during the water-only and sediment-water test duration. LC50 values obtained from water-only exposure showed a good correspondence with the pore water concentrations calculated from the sorption and desorption isotherms in the spiked sediments.     

不同生物联合净化富营养化水体的效果

利用野外原位围隔研究了鱼类、底栖动物和水生植物的不同组合对富营养化水体的净化效果。研究结果表明,鲴鱼（Plagiognathops microlepis Bleeker）能有效削减水体中TN,高锰酸盐指数和Chl-a,其中15 g·m-3投加密度的实验组高锰酸盐指数和Chl-a的削减率提高了8%,效果优于密度7.5 g·m-3的实验组,但不利于TP的去除;螺（Bellamya aeruginosa）和蚌（Hyriopsis cumingii）的投加对水体营养盐的去除有较好的效果,其中对Chl-a的影响最为显著（pWaterspinach）和水芹（Watersfennel）对水体中营养盐的去除差异不显著（p>0.05）,蕹菜略好于水芹。本研究结果可为水生生态系统调控和修复提供科学依据。     

水源水库沉积物间隙水营养盐分布特征及扩散通量

为了阐明水源水库沉积物营养盐释放对水体富营养化的贡献,以周村水库为研究对象,探讨沉积物间隙水中氮、磷营养盐的分布特征,同时采用Fick第一定律对沉积物-水界面营养盐的扩散通量进行了估算。周村水库表层沉积物间隙水中NH4+-N的浓度为6.47 to 16.82 mg·L-1,PO43--P的浓度在0.13 to 0.56 mg·L-1之间,均远高于上覆水中的营养盐浓度,表明周村水库表层沉积物具有很大的营养盐释放潜能。Fick第一定律的计算结果表明,沉积物-水界面NH4+-N与PO43--P的扩散通量分别为62.831 to 133.231和0.364 to 1.271 mg·（m2·d）-1,研究区域中间隙水中的营养盐均由沉积物向上覆水扩散,沉积物是底层水体营养盐的重要来源。     

Nutrient pathways and their susceptibility to past and future change in the Eurasian Arctic Ocean

Climate change is altering nutrient cycling within the Arctic Ocean, having knock-on effects to Arctic ecosystems. Primary production in the Arctic is principally nitrogen-limited, particularly in the western Pacific-dominated regions where denitrification exacerbates nitrogen loss. The nutrient status of the eastern Eurasian Arctic remains under debate. In the Barents Sea, primary production has increased by 88% since 1998. To support this rapid increase in productivity, either the standing stock of nutrients has been depleted, or the external nutrient supply has increased. Atlantic water inflow, enhanced mixing, benthic nitrogen cycling, and land–ocean interaction have the potential to alter the nutrient supply through addition, dilution or removal. Here we use new datasets from the Changing Arctic Ocean program alongside historical datasets to assess how nitrate and phosphate concentrations may be changing in response to these processes. We highlight how nutrient dynamics may continue to change, why this is important for regional and international policy-making and suggest relevant research priorities for the future.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-021-01673-0.     

Evaluation of the potential impact of polluted sediments using Manila clam Ruditapes philippinarum: bioaccumulation and biomarker responses

An assessment was made to monitor the short-term impact of heavily polluted sediments that may move out from the brackish man-made Lake Shihwa outside of the sea dike due to operations of a tidal power plant. Here, we exposed the Manila clam Ruditapes philippinarum collected from the western coast of Korea to natural sediment under lab condition for 96?h. Sediments were collected from Lake Shihwa and outside of the sea dike representing polluted and reference conditions, respectively. The results of chemical analysis revealed that the concentrations of nonylphenol and heavy metals in water and sediment from the inner region of Lake Shihwa were significantly higher than those of reference sediments. After 48 and 96?h of exposure, 30 specimens of clams were sampled from each experimental condition, and concentrations of nonylphenol and metals were measured in clams, water, and sediments. Several biomarkers, including concentrations of metallothionein-like proteins, and activities of the antioxidant enzymes glutathione S-transferase and catalase were determined in clams to characterize the effects of polluted sediments to clams. After 96?h of exposure, R. philippinarum assimilated nonylphenol up to 71 times compared to initial concentrations. However, there was no apparent uptake of heavy metals into the clams. Additionally, antioxidant enzymes exhibited higher activities in clams exposed to the polluted sediment. The results of the present study with physiological responses in R. philippinarum suggest that sediment transportation caused by the operation of a tidal power plant in Lake Shihwa will have striking effects on benthic organisms in the adjacent coastal area.     

Laboratory studies to characterize the efficacy of sand capping a coal tar-contaminated sediment

Placement of a microbial active sand cap on a coal tar-contaminated river sediment has been suggested as a cost effective remediation strategy. This approach assumes that the flux of contaminants from the sediment is sufficiently balanced by oxygen and nutrient fluxes into the sand layer such that microbial activity will reduce contaminant concentrations within the new benthic zone and reduce the contaminant flux to the water column. The dynamics of such a system were evaluated using batch and column studies with microbial communities from tar-contaminated sediment under different aeration and nutrient inputs. In a 30-d batch degradation study on aqueous extracts of coal tar sediment, oxygen and nutrient concentrations were found to be key parameters controlling the degradation rates of polycyclic aromatic hydrocarbons (PAHs). For the five PAHs monitored (naphthalene, fluorene, phenanthrene, anthracene, and pyrene), degradation rates were inversely proportional to molecular size. For the column studies, where three columns were packed with a 20-cm sand layer on the top of a 5 cm of sediment layer, flow was established to sand layers with (1) aerated water, (2) N(2) sparged water, or (3) HgCl(2)-sterilized N(2) sparged water. After steady-state conditions, PAH concentrations in effluents were the lowest in the aerated column, except for pyrene, whose concentration was invariant with all effluents. These laboratory scale studies support that if sufficient aeration can be achieved in the field through either active and passive means, the resulting microbially active sand layer can improve the water quality of the benthic zone and reduce the flux of many, but not all, PAHs to the water column.