Sediment Nutrient Concentrations Research Articles

Hydrodynamic and biogeochemical evolution of a restored intertidal oyster (Crassostrea virginica) reef

Oyster reef restoration is increasingly used as a tool for restoring lost ecosystem services in degraded aquatic systems, but questions remain about the efficacy of the practice and when/if restored reefs may behave similarly to intact natural reefs. In this case study, field observations highlighted short- (<1 month post-restoration) and longer-term (30 months; 3 recruitment cycles) transformations in canopy, hydrodynamic, and biogeochemical characteristics of a restored intertidal oyster reef relative to nearby intact and degraded reefs. Within 12 months of restoration, live oyster density (326 oysters/m2), mean shell length (47 mm), and mean canopy height (76 mm) did not differ significantly from those observed on a reference reef. Lowering of the reef crest during restoration reestablished over-reef flow and periodic tidal inundation, improving hydraulic connectivity between the channel and the reef surface. This immediately restored much of the reef's hydrodynamic function and eliminated the irregular flow patterns observed on the previously degraded reef. Results showed that mean flow (channel-to-reef flow attenuation: 98% / 62%; within/above canopy) and velocity normalized turbulence (w'2¯/U2: 10−1/10−2; ϵ/U3: 100/10−2 m−1) characteristics were similar across the restored and reference reefs within 1 year of restoration, with temporal changes in mixing within the canopy attributed to increases in live oyster density. Nutrient pools (mean total carbon, total nitrogen) on reference and restored reefs had similar magnitudes within 1 year (C: 39 & 33 g/kg, N: 1.5 & 1.8 g/kg), while increases in DOC and NH4+ were correlated with the presence of live oysters. Most changes that occurred on the restored reef were linked to oyster recruitment and canopy growth, which modulated hydrodynamics through direct flow interactions and controlled sediment nutrient and organic matter content through waste deposition and burial.

Ecosystem functioning is linked to microbial evenness and community composition along depth gradient in a semiarid lake

Lake level or water depth are key physical variables known to respond dramatically to climate change, especially in arid regions, and their fluctuations exert substantial influences on lake biodiversity and ecosystem functioning. However, it is unclear how multiple ecosystem functions (i.e., ecosystem multifunctionality, EMF) respond to changes in water depth and how aquatic community attributes, such as species richness, evenness and community compositions, are linked to EMF along water depth gradients. Lake Hulun, a representative of semiarid-region lake in China, has experienced serious lake area shrinkage over the past 20 years. Here, we explored the water-depth patterns of three microbial taxonomic groups of bacteria, archaea and fungi and nine ecosystem functions related to nutrient cycling in Lake Hulun. We further examined the relative importance of different community attributes on EMF variations. We found that the community compositions of bacteria, archaea and fungi showed consistent water-depth decay patterns, and EMF and most individual ecosystem functions involved in C, N, P and S cycling increased with water depth. Further, EMF was predominantly mediated by microbial evenness and community composition, but not species richness, as predicted by the traditional theory of biodiversity-ecosystem functioning relationships. In addition, water depth indirectly affected the relationships between the microbial community and EMF via sediment nutrient contents. These findings indicate that the water depth changes under climate change could substantially alter ecosystem structure and functioning in arid regions. We further emphasize the necessity of including multiple community attributes in biodiversity-EMF relationship research to clarify the biotic and abiotic forces underlying EMF variations.

Trends of Nitrogen and Phosphorus in Surface Sediments of the Lagoons of the Northern Adriatic Sea

The analysis of nutrient concentrations in surface sediments is a reliable tool for assessing the trophic status of a water body. Nitrogen and phosphorus concentrations are strongly related to the sediment characteristics but are mainly driven by anthropogenic impacts. The results of the determination of total nitrogen and total inorganic and organic phosphorus in surface sediments of the lagoons and ponds of the northwestern Adriatic Sea (Marano-Grado, Venice, Po Delta, Comacchio Valleys, Pialassa della Baiona) show the merit of this approach. Indeed, when previous data are available, the ratio between the actual and background values can provide useful information on the trophic changes that have occurred in the most recent times, and the results can also explain the conditions present in less studied environments. In this context, numerous studies performed in the Venice lagoon since the second half of the 20th century during different environmental scenarios provide mean concentration ranges and propose the main causes of changes. The results of single datasets available for the other lagoons fall into scenarios that occurred in the Venice lagoon. At present, the most eutrophic basins are Pialassa della Baiona, the Po Delta lagoons and ponds and the Comacchio valleys due to industrial effluents, fish farming and clam harvesting, respectively, whereas the Venice lagoon is now experiencing environmental recovery.

Assessment of bioavailable nitrogen and phosphorus content in the sediments of Indian mangroves.

Efficient nutrient cycling and adequate sediment bioavailable nutrient supply are considered to be the two most important factors regulating the high productivity and subsequent carbon sequestration by mangrove ecosystems. We assessed spatial variability and the possible regulating factors of sediment bioavailable nutrients (nitrogen (N) and phosphorus (P)) and surface water-dissolved nutrients (N, P and silicate (Si)) in the five ecologically important mangrove ecosystems along the east and west coast of India during dry season. Higher bioavailable nitrogen concentrations in the sediments were recorded in Coringa mangroves (36.27 ± 14.7 μg g-1) and Bhitarkanika (18.54 ± 5.9 μg g-1) mangroves in the east coast followed by Karnataka (15.51 ± 8.26 μg g-1), Goa, (10.18 ± 9.96 μg g-1) and Kerala (6.36 ± 5.05 μg g-1) mangroves in the west coast. The dissolved inorganic nutrients in the mangrove waters ranged between 5.1 and 220.9 μmol l-1 for N and 0.07 and 3.9 μmol l-1 for P. These results indicated that terrestrial inputs, in situ remineralization and prevalent anoxic conditions regulated sediment nutrient content in these ecosystems, whereas the higher ammonium in the sediments was attributed to the greater nutrient adsorption by finer particles. The stoichiometry of the bioavailable nutrients (N, P) in the mangrove sediments deviated drastically from the Redfield ratio, and strong P limitation was recorded in most of the ecosystems. The results highlighted the potential role of sediment particle size and physiochemical (salinity and pH) properties in regulating bioavailable nutrient dynamics in mangrove sediments.

Metals in sediments and their accumulation in Zostera japonica in different sediment habitats of the Yellow River estuary

This research aims to study the ecological risk of metals to Zostera japonica and focuses on two typical sediment environments in the Yellow River estuary, namely, sediment erosion and deposition areas. Two different sediment habitats of Z. japonica were selected in this research from southern and northern sites in the Yellow River estuary. The plant growth and nutrient and metal concentrations in the sediments and Z. japonica tissue were investigated in the growth period of Z. japonica from April to October 2019. The shoot height of Z. japonica was measured with a centimetre-scale measuring stick, and the dry shoot weight was obtained after drying at 70 °C for 24 h. The total carbon (TC) and total nitrogen (TN) concentrations in the Z. japonica tissue and sediment were determined with an elemental analyser (Vario Macro Cube, Elementar Company, Germany). The total phosphorus (TP), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), lead (Pb), chromium (Cr) and cadmium (Cd) contents in the digested solutions were measured by high-resolution inductively coupled plasma atomic emission spectrometry (HR-ICP-AES, Spectro Company, Germany). The growth of Z. japonica was different at the two study sites, with a higher biomass at the southern site than that at the northern site due to higher sediment nutrient concentrations at the southern site. The Cu, Zn, Pb, Cr and Cd concentrations in the sediments at the southern site were 25.1 μg g−1, 74.2 μg g−1, 21.4 μg g−1, 65.4 μg g−1 and 0.32 μg g−1, respectively, which were higher than the levels at the northern site of 13 μg g−1, 47.6 μg g−1, 12.4 μg g−1, 46.4 μg g−1 and 0.17 μg g−1, respectively. However, among the metals, only Cd was bioconcentrated in the Z. japonica tissue, with bioconcentration factor (BCF) values of 5.59 and 10.85 at the southern and northern sites, respectively. The sediments at the southern site in the estuary are composed of clays enriched in nutrients, thus supporting more sustainable growth and higher biomass than the coarse-particle sediments at the northern site in the estuary. Moreover, the sediments at the southern site were also enriched in metals, resulting in high levels of metals in the Z. japonica tissue. Overall, the ecological risk was low except for Cd, which should be considered because of its potential impacts on this seagrass and its related food webs in the estuary ecosystem.

Juvenile Oyster (Crassostrea virginica) Biodeposits Contribute to a Rapid Rise in Sediment Nutrients on Restored Intertidal Oyster Reefs (Mosquito Lagoon, FL, USA)

By filtering large volumes of water and releasing nutrient-rich biodeposits (feces and pseudofeces), oysters can locally enhance sediment biogeochemical cycling. An active Crassostrea virginica restoration program in Mosquito Lagoon, FL (USA), was leveraged to assess the immediate (first-year) effects of restoration on sediment nutrients. Measurements included extractable and total carbon, nitrogen, and phosphorus on dead, natural, and restored reefs using a before-after-control-impact design. To investigate an observed “age-nutrient paradox” in sediment nutrient concentrations, a laboratory experiment compared feeding rates and biodeposit nutrient content between juvenile and older oysters. The field study documented a 136% increase in ammonium, 78% increase in total nitrogen, 46% increase in total phosphorus, and 75% increase in organic matter concentrations 12 months post-restoration, with extractable nutrients responding more rapidly to restoration than total nutrients. Sediment nutrient increases were positively correlated with oyster density, shell length, and reef height. Moreover, the laboratory study indicated juvenile oysters had higher rates of chlorophyll-a removal and ammonium efflux and produced biodeposits with higher concentrations of dissolved organic carbon, nitrate, and ammonium than older oysters. Overall, this study documented increases in sediment nutrients on intertidal reefs within the first year of restoration, which may be explained by a greater filtration rate and more nutrient-enriched biodeposits contributed by young oysters as compared to older oysters. Sediment total nitrogen and ammonium content may be the most robust monitoring metrics for documenting the ecosystem service of enhanced biogeochemical cycling on restored oyster reefs.

Quality changes of fluvial sediments impacted by urban effluents in Ushuaia, Tierra del Fuego, southernmost Patagonia

Bottom sediments play a fundamental role in the eutrophication process because they are one of the most active compartments in the biogeochemical cycle of nutrients. In Ushuaia city, Tierra del Fuego, Argentina, sewage effluents have been discharged into natural watercourses without treatment for many years. Organic matter has been introduced until 2016 when improvements in sewage infrastructure were done. The quality of surface sediments from three watercourses with different degree of impact has been studied taking into account contrasting hydrological periods. pH, organic carbon (OC), total nitrogen (TN) and soluble reactive phosphorus (SRP) were measured in austral autumn and spring between 2013 and 2018 in three sections of each watershed. Nutrient content in sediments of upstream sites derives from the contribution of Nothofagus spp. forests through litter-fall. Middle and downstream sites were the most affected by wastewater discharges evidencing that fluvial sediments act as a receptor of the allochthonous organic loads. Particularly, sediments of Buena Esperanza Stream had the lowest mean pH (5.44) and the highest mean concentrations of OC (42.95 mg g−1), TN (2.53 mg g−1) and SRP (0.067 mg g−1), along with the lowest mean annual flow and the largest urbanized area. No differences between hydrological periods were found, although TN and SRP contents were higher in autumn than in the snowmelt season. Minimal differences in nutrients between before and after infrastructure improvement were found. Even when external contributions have been decreased, more time will be necessary to reduce eutrophic conditions of fluvial sediments in southernmost Patagonia.

Geochemistry, mineralogy and nutrient concentrations of sediment of River Pampa in India during a massive flood event

Kerala, the southern state of India, was severely hit by a massive flood in August 2018 affecting millions of people causing loss to the state exchequer. The aim of this paper was to study the impacts of this flood on mineralogy, geochemistry (grain size, and heavy metal content) and nutrient content (organic carbon, total and available nitrogen, and phosphorus) of sediment of flood affected Pampa river, Kerala. The study indicates that this large-scale flood results in a considerable reduction in the heavy metals and nutrient concentration of sediment. Frequency histograms for most of the sediment particle size showed unimodal distribution curve with the dominance of sand particles which may be due to wash of fine size fraction like silt and clay during flood. FTIR study indicates that Pampa river sediment is dominant with quartz, orthoclase and microcline feldspar, and kaolinite, along with other trace minerals. SEM study also indicates that quartz is the common occurring mineral and its shape varies from highland to downstream due to transportation. Ratio of carbon to nitrogen and phosphorus particularly at downstream stations indicates the considerable influence of macrophyte which leads to accumulation of terrestrial organic matter. The cluster analysis results indicate that there were some similarity in origin and migration behaviour among these metals and nutrients of the sediments.

Effects of invasive N2-fixing Acacia mearnsii on sediment nutrient concentrations in mountain streams: Implications of sediment geochemistry for ecosystem recovery

Widespread invasive nitrogen-fixing plant species pose major threats to water resources, biodiversity and nutrient dynamics of river catchments around the world. However, the impacts of invasive N2-fixing plants on in-stream sediment nutrient dynamics remain poorly understood. Here, we quantified the impacts of invasive N2-fixing Acacia mearnsii and A. mearnsii clearing on two mountain streams in South Africa’s Cape Floristic Region. Nutrients were measured in fine sediment that had infiltrated into the gravel bed and surface water in three reaches associated with natural fynbos shrubs, A. mearnsii invaded and cleared riparian ecotones. Results showed that the impacts of A. mearnsii invasions and Acacia clearing in riparian areas on in-stream sediment-associated nutrient concentrations are context-dependent. The difference in channel morphometry and sediment geochemical attributes at reach-scale contributed to the contrasting spatial patterns of sediment-adsorbed nutrients within these rivers. There was also an indication of a long-lasting effect of invasion on total phosphorus that could persist in river sediments ≥10 years after the removal of dense A. mearnsii stands in close proximity to streams. This could be a result of the complexation between phosphorus and immobile iron in sediment, resulting in the retention of ‘legacy phosphorus’. This underlines the importance of fine sediments in capturing nutrients and ultimately regulating nutrient concentrations in the water column.

Nutrient properties of tidal-borne alluvial sediments from a tropical mangrove ecosystem

Mangroves are inundated through tidal action, which mobilizes a large quantity of suspended and dissolved particles, including both decomposed mangrove and terrigenous materials. Sediments brought in by tidal water and trapped by mangrove roots contribute to the productivity of coastal, tropical mangrove ecosystems. They play an important role in the nutrient cycling of these ecosystems. However, there is limited information on sediment properties, inclusive of nutrients levels in tidal-borne sediments affecting mangrove ecosystems. Selected properties of sediment, including cation exchange capacity (CEC), texture, organic matter (OM) content, organic carbon (OC) content, and nutrient content (C, N, S, P, K, Ca and Mg) were studied, in a seasonal pattern, in tidal-borne sediment from Sibuti estuary mangrove. Sediment showed a high proportion of sand (range: 60%–65%) with high mean values of CEC 17 cmol/kg, a sediment OM content of 15%, and OC content of 13%. The mean average content of C was 15%, and mean concentrations of N, S, P, K, Ca, Mg and Na were 12, 10, 2, 3, 34, 18 and 16 (mg/kg), respectively. Significant positive relationships were found among nutrient concentrations in sediment and nutrient concentrations in leaf, stipule, flower, propagule, stem, bark, and root of both Rhizophora apiculata (Blume) and Xylocarpus granatum (Koenig) trees and their saplings. Seedlings are indicative of the growth, health, and productivity of the mangrove ecosystem, and are largely dependent on the phenomenon of nutritive aspects of tidal-borne sediments. The results of this study provide baseline information on the roles of nutrient productivity of a less disturbed tropical mangrove forest, adjacent to the South China Sea.

Assessment of nutrient and heavy metal concentrations in sediments and macrophytes of the Oroma wetland, Nigeria

Assessment of nutrient and heavy metal concentrations in sediments and macrophytes of the Oroma wetland, Nigeria

Enhancing ecological-economic efficiency of intensive shrimp farm through in-out nutrient budget and feed conversion ratio

In aquaculture systems, insufficient nutrients impede shrimp growth while excessive amounts of nutrient inputs lead to environmental degradation and unnecessary high investment. A study of in-out nutrient budgets in an intensive Litopenaeus vannamei farm was conducted in this work to measure the amount of nitrogen (N) and phosphorus (P) input and output from the system. The feed conversion ratio (FCR) was obtained to determine the level of nutrient input performance. Between September and December 2017, monthly water and sediment samples were taken within one crop cycle. Nutrient concentrations in sediment and water increased over 90 days. The total nitrogen concentration in the pond water and effluents were in accordance with wastewater quality control for aquaculture; however, the total phosphorus concentration failed to meet the water quality control from the water input through the end of the crop cycle. The nutrient budget model showed that the input/output contained 107.8 kg N and 178.4 kg P. Most of the N input came from shrimp diets (80%) while most of the P came from fertilizer (57%). Both N (46%) and P (54%) mainly deposited in the sediment as an output process. The FCR of this farm is 2.0. Based on the 1.8 FCR scenario, this farm could reduce 147 kg of feed in total, which accounts for 9.04 kg N and 2.21 kg P reduction. The farmer could save $1027 USD crop− 1 ($1 USD = 32.7 baht), as well as reducing uneaten food at the bottom of the pond. This study offers a simple and straightforward model that can practically reduce environmental impacts and increase the profitability of farms.

Nutrient availability induces community shifts in seagrass meadows grazed by turtles.

In the Caribbean, green turtles graze seagrass meadows dominated by Thalassia testudinum through rotational grazing, resulting in the creation of grazed and recovering (abandoned) patches surrounded by ungrazed seagrasses. We evaluated the seagrass community and its environment along a turtle grazing gradient; with the duration of (simulated) grazing as a proxy for the level of grazing pressure. The grazing levels consisted of Short-term (4 months clipping), Medium-term (8 months clipping), Long-term grazing (8 months of clipping in previously grazed areas), 8-months recovery of previously grazed patches, and ungrazed or unclipped patches as controls. We measured biomass and density of the seagrasses and rhizophytic algae, and changes in sediment parameters. Medium- and Long-term grazing promoted a shift in community species composition. At increasing grazing pressure, the total biomass of T. testudinum declined, whereas that of early-successional increased. Ammonium concentrations were highest in the patches of Medium-term (9.2 + 0.8 μM) and Long-term grazing levels (11.0 + 2.2 μM) and were lowest in the control areas (4.6 + 1.5 μM). T. testudinum is a late-successional species that maintains sediment nutrient concentrations at levels below the requirements of early-successional species when dominant. When the abundance of this species declines due to grazing, these resources become available, likely driving a shift in community composition toward a higher abundance of early-successional species.

Implications of nutrient enrichment for the conservation and management of seagrass Zostera muelleri meadows

Abstract Nutrient overenrichment in aquatic environments, or eutrophication, is increasingly affecting seagrass habitats around the world, leading to the degradation of seagrass ecosystems and the loss of associated ecosystem services. The resistance of seagrass to nutrient enrichment is believed to be site specific, yet the direct correlations between environmental factors and the resistance of seagrass meadows has not yet been adequately resolved. The response of seagrass beds to long‐term multiple‐level sediment nutrient enrichment represents a current research gap. This study therefore assessed the in situ long‐term influence of four levels of sediment urea fertilizer addition on Zostera muelleri plants using a manipulative experimental design at three sites with diverse sediment characteristics. Specifically, this study investigated the response of porewater nutrient concentration, seagrass morphology indices, and seagrass plant tissue carbon and nitrogen contents under experimental nutrient stress levels. Over a 13‐month experiment, sediment nutrient addition substantially increased the ammonium concentrations in the sediment porewater, significantly decreased seagrass morphology indices, and caused a carbon and nitrogen imbalance in plant tissues. Ammonium toxicity was more pronounced in seagrass meadows growing on sandy substrates with lower relative above‐ground biomass, which showed low resistance to eutrophication at sediment ammonium concentrations of up to 1 × 104 μM. Plants growing in muddy sand substrates with higher relative above‐ground biomass were more resistant to nutrient impacts, however, with a delayed negative response observed in response to higher nutrient concentrations (up to 1 × 105 μM). Our findings suggest that seagrasses in low‐nutrient sandy environments show more rapid responses to eutrophication, although seagrasses in both sandy and muddy substrates exhibited declines in response to a long‐term elevation of sediment nutrient concentrations. While continuing to assess the relative susceptibility of seagrass habitats across differing environments to inform coastal management, conservation efforts should allocate resources accordingly and prioritize reducing nutrient overenrichment in sensitive seagrass meadows.

Investigating benthic impacts at salmon farms using eddy covariance measurements of benthic oxygen fluxes

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 11:337-357 (2019) - DOI: https://doi.org/10.3354/aei00317 Investigating benthic impacts at salmon farms using eddy covariance measurements of benthic oxygen fluxes David R. Plew* National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch 8440, New Zealand *Corresponding author: david.plew@niwa.co.nz ABSTRACT: Benthic oxygen fluxes were measured in situ using the eddy covariance method at 2 Chinook salmon farms located in the New Zealand Marlborough Sounds in 29-35 m depth and compared to sediment nutrient (C, N and P) and sulphide concentrations. Observations from 3 sites at a high-flow location (near-bed RMS velocities of 0.11 to 0.17 m s-1) showed oxygen fluxes increasing with sediment enrichment. Mean ± SE oxygen fluxes of -102 ± 4 mmol O2 m-2 d-1 were observed immediately adjacent the farm. Higher fluxes were observed at 120 m from the farm (-53 mmol O2 m-2 d-1) than at 50 m (-48 mmol O2 m-2 d-1), consistent with higher sediment nutrient concentrations at the more distant site, and reflecting the effect of currents on deposition patterns. Ratios of C, N and P in sediments indicated a reduction of N mineralisation rates as sediment enrichment increased. The low-flow site (near-bed RMS velocities of 0.033 m s-1) had similar oxygen fluxes (-108 ± 9 mmol O2 m-2 d-1) to the high-flow site closest to the farm, but sediments were more highly enriched with high sulphide concentrations. Oxygen fluxes at the low-flow site were close to the estimated maximum potential flux that could be achieved under the ambient hydrodynamic conditions. Less than 0.2% of surface PAR reached the sediments, and no evidence of benthic primary production was observed at any of the sites. By incorporating ambient hydrodynamic conditions, eddy covariance has the potential to obtain true in situ benthic oxygen fluxes, giving greater insight into aquaculture-environmental interactions. KEY WORDS: Aquaculture · Benthic impacts · Oxygen flux · Organic enrichment · Eddy covariance · Salmon Full text in pdf format PreviousNextCite this article as: Plew DR (2019) Investigating benthic impacts at salmon farms using eddy covariance measurements of benthic oxygen fluxes. Aquacult Environ Interact 11:337-357. https://doi.org/10.3354/aei00317 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 11. Online publication date: July 11, 2019 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2019 Inter-Research.

River nutrient water and sediment measurements inform on nutrient retention, with implications for eutrophication

The consideration of nutrients in pollution dynamics is important for environmental management and conservation. Developing countries are yet to appreciate the aquatic ecosystem pollution impacts on their economies and as such, information on water pollution dynamics is limited. This study assessed the spatio-temporal dynamics of nutrient loading and retention in stream water and sediments in the Bloukrans River system, Eastern Cape province, South Africa over the course of the wet and dry season. Sediment and water samples were analysed for total phosphorus (TP) and nitrogen (TN) concentrations, and were used in combination with river flow discharge, to determine nutrient loads. The study results highlight that river discharge plays a significant role in temporal differences in sediment and water column nutrient concentrations. The mean sediment nutrient concentration was high for the dry season, with high values being observed for the urban river system. Nutrient loads were high above the sewage treatment works outflow (i.e. urban sites), as such, a decreasing trend was observed with increasing distance from the urban environment. Nutrient loads were generally high for the dry season in comparison to the wet season indicating organic matter retention (i.e. accumulation from burst sewage pipes) most likely due to low flows. While it was evident that the ageing wastewater infrastructure contributed to the observed state of the Bloukrans River, the high natural nutrient retention capacity seemed to mitigate eutrophication of downstream aquatic ecosystems. As such, the nutrient retention capacity and management of the system is central to the entire Bloukrans River catchment management practices. Therefore, the study contributes to our understanding of water and sediment nutrient pollution dynamics in an arid temperate river landscape where vast spatio-temporal differences in base flow characterise the riverscape.

A Preliminary Study on A Novel Water Treatment Pond Design Using Dredged Sediment, Shrub Willow and Recycling Hand Pumps for the Restoration of Water Pollution

The treatment of polluted water and sediment often costs too much and has little benefit. In this study, we proposed a novel design using dredged sediment, shrub willow (Salix spp.) and recirculating hand pumps for the restoration of polluted river water in Changchun city, China. Sediment was filled as a matrix for plant growth, shrub willow was transplanted for the absorption of nutrients, and ten hand-pumped water wells were built for recycling the polluted water. During the 5-month experimental period, the shrub willow growth and nutrient contents, sediment nutrient concentration and water quality were measured. The results showed that this pond system could effectively decrease the sediment pollutant levels, and its removal efficiencies of organic matter (OM), total nitrogen (TN) and total phosphorus (TP) could respectively reach as high as 11%, 10% and 26%. The dissolved oxygen (DO) content increased by more than 90% in August, and the chemical oxygen demand (COD) and total nitrogen (TN) content decreased by 44.93% and 19.82%, respectively. This means that the treatment pond could efficiently work toward the purification of polluted river water. The benefits and feasibility of this system application were also analyzed, and we found that it could be widely used for the treatment of polluted water and sediment in urban areas.

Distribuição espacial da concentração de nutrientes em sedimentos na Laguna hipersalina de Araruama – RJ, Brasil

The present study was carried out in Laguna de Araruama, Rio de Janeiro. Pollution in the lagoon has hampered the ecosystem structure and caused the eutrophication process to intensify. In order to improve water quality, it is proposed to open channels of the lagoon with the sea, but may result in the remobilization of the nutrients in the sediment to the water column. Considering the importance of sediment as a nutrient storage compartment, the objective of this study was to determine nutrient concentrations in sediments and interstitial water and their distribution in the sediments. Measurements of pH and Eh were made in the sediment, conductivity and temperature along the water column. The granulometry was determined and the concentrations of ammonium, nitrite, nitrate and phosphate in the interstitial water were determined, and the total concentrations of phosphorus, nitrogen and carbon in the sediments. Considering the granulometric results, most of the lagoon has sandy formations. The sediment presented temperatures between 22 °C and 25 °C, basic pH (7.1 - 8.2) and reducing characteristics (-400mV). In the stations near Sao Pedro da Aldeia and Araruama, there are high levels of total nitrogen in the sediment due to the high amount of sewage discharged into the rivers that flow into the lagoon. High concentrations of total phosphorus were also found in the region of the Itajuru Channel, closer to the sea, which due to its lower salinity has higher primary productivity. It is concluded that the lagoon presents a high degree of pollution by nutrients, in specific points, due to the contributions caused by the discharge of sewage

Nutrient Retention in the Swedish Coastal Zone

In this study, the average nutrient filter efficiency of the entire Swedish coastline is estimated to be about 54% and 70% for nitrogen and phosphorus, respectively. Hence, significantly less than half of the nutrient input from land (defined as river discharge and point sources) can be assumed to be exported from coastal waters to the open sea. However, some coastal areas retained more than 100% of the land load and thus, also filter the open Baltic Sea water. These areas with effective filtering of nutrients have low land load per unit coastal area. The filter efficiency was calculated from a 30-years model simulation (1985-2014) of water exchanges and nutrient cycling within the Swedish coastal zone. The average model skill was evaluated to be good or acceptable compared to observations. In addition to the entire Swedish coast, the retention of total nutrient loads in seven larger coastal sub-regions and selected key sites representing different coastal types was also estimated. The modelled long term nutrient retention was found to be associated with the physical characteristics of a water body, such as the surface area, but also the mean depth and residence time of water. In addition, high retention efficiency is associated with high ratio of sediment nutrient content to pelagic nutrient concentrations. On interannual timescales temporal changes in the coastal nutrient pool can have a large influence on perceived nutrient retention. At one site, the phosphorus filter efficiency was actually negative, i.e. the coastal zone transported more phosphorus to the open Baltic Sea than it received from land. The nutrient removal is most efficient close to land, where the area specific retention efficiency is the highest. The variability of both the filter and retention efficiency between coastal regions was found to be large, with a range of approx. 4-1,200% and 0.1-8.5%, respectively.

Evaluation of Nutrient and Heavy Metal Pollution in Maozhou River in Shenzhen City

The sediment of Shenzhen Mazhou River was collected and sieved with different particle sizes to determine the physicochemical properties, nutrient contents and heavy metal contents of sediment, interstitial water and oversize mud. At the same time, the single factor evaluation and potential ecological risk assessment of heavy metals were carried out on the sediment of Mazhou River. The experimental results show that the screening of different particle size has little influence on the physicochemical properties and nutrient content of sediment. Mazhou River nitrogen and phosphorus nutrients pose little ecological risk effect on the environment. The ecological risk ranking of heavy metals is Hg> Cd> Cu> Ni> As> Zn = Cr> Pb. Mazhou river sediment comprehensive potential risk index RI values are greater than 1200, indicating that Maozhou river was in extremely high risk. Among them, Hg contributes the most, which is the most important factor controlling the risk of heavy metal pollution in sediment.