Can macrophyte harvesting from eutrophic water close the loop on nutrient loss from agricultural land?

Do new lakes behave like natural lakes regarding sediment composition and phosphorus fluxes?

Numerous new lakes have been established during the last few decades. Lakes established on former agricultural soils often have high legacy phosphorus (P)-content, which constitutes a risk for potential internal P-loading after the lake is formed. In this study, we compared the P release and sediment P-pools from 31 new lakes and 31 natural lakes, to assess their similarities and differences. A suite of other sediment characteristics was identified and compared for both natural and new lakes; catchment characteristics of the new lakes also were analyzed. P release from the sediment of new lakes was significantly lower than from natural lakes (13.2 mg P m-2 d-1) compared to new lakes (6.9 mg P m-2 d-1). The P release was found to be low when molar Fe:P ratios were above 10. A significant correlation was found between the content of mobile-P (loosely adsorbed P, iron-bound P, and leachable organic P) and TP in the sediment, irrespective of lake type. The composition of the mobile P-pool also differed, with the new non-excavated lakes showing a higher proportion of RP-BD; both new lake types had significantly (p = 0.021) lower proportions of nrP, compared to natural lakes in the uppermost 10 cm sediment. In addition, variance in P release and mobile-P content of new lakes could be explained in terms of the land use of the catchments. Most sediment characteristics of new lakes established without topsoil excavation reached the average levels of natural Danish lakes with respect to density, organic content and P content within 20-30 years, while excavated lakes showed no such tendencies.

How nutrient retention and TN:TP ratios depend on ecosystem state in thousands of Chinese lakes

Worldwide, anthropogenic activities threaten surface water quality by aggravating eutrophication and increasing total nitrogen to total phosphorus (TN:TP) ratios. In hydrologically connected systems, water quality management may benefit from in-ecosystem nutrient retention by preventing nutrient transport to downstream systems. However, nutrient retention may also alter TN:TP ratios with unforeseen consequences for downstream water quality. Here, we aim to increase understanding of how nutrient retention may influence nutrient transport to downstream systems to improve long-term water quality management. We analyzed lake ecosystem state, in-lake nutrient retention, and nutrient transport (ratios) for 3482 Chinese lakes using the lake process-based ecosystem model PCLake+. We compared a low climate change and sustainability-, and a high climate change and economy-focused scenario for 2050 against 2012. In both scenarios, the effect of nutrient input reduction outweighs that of temperature rise, resulting in more lakes with good ecological water quality (i.e., macrophyte-dominated) than in 2012. Generally, the sustainability-focused scenario shows a more promising future for water quality than the economy-focused scenario. Nevertheless, most lakes remain phytoplankton-dominated. The shift to more macrophyte-dominated lakes in 2050 is accompanied by higher nutrient retention fractions and less nutrient transport to downstream waterbodies. In-lake nutrient retention also alters the water's TN:TP ratio, depending on the inflow TN:TP ratio and the ecosystem state. In 2050 higher TN:TP ratios are expected in the outflows of lakes than in 2012, especially for the sustainability-focused scenario with strong TP loading reduction. However, the downstream impact of increased TN:TP ratios depends on actual nutrient loadings and the limiting nutrient in the receiving system. We conclude that nutrient input reductions, improved water quality, higher in-lake nutrient retention fractions, and lower nutrient transport to downstream waterbodies go hand in hand. Therefore, water quality management could benefit even more from nutrient pollution reduction than one would expect at first sight.

Engineering aquatic plant community composition on floating treatment wetlands can increase ecosystem multifunctionality

Phytoremediation using floating treatment wetlands (FTWs) is an emerging nature-based solution for freshwater restoration. However, the potential to design these systems by manipulating macrophyte community composition to provide multiple ecosystem services remains unexplored. Using a tank experiment, we simulated aquatic environments impacted by multiple pollutants and employed a comparative ecological approach to design emergent macrophyte communities using the trait of plant stature (plant height) to structure communities. Ecosystem functions were quantified, and a threshold-based method used to compute an ecosystem multifunctionality index that was weighted based on three different management-driven restoration objectives: equal importance, phytoremediation, and regulation and cultural services. Across all restoration scenarios, ecosystem multifunctionality was higher when community types performed more diverse functions. Small emergent plant communities outperformed all other community types due to their increased provision of both regulation and maintenance, cultural, and provisioning services. Conversely, large emergent communities that are more typical candidates for phytoremediation had the highest levels of multifunctionality only when function was lower. Arranging emergent macrophytes in mixed-statured communities led to intermediate or poorer performance both in terms of multifunctionality and specific functions, suggesting that diversity on the plant stature axis leads to negative plant interactions and represents a 'worst of both worlds' combination. Employing comparative ecology to generalise plant selection by stature demonstrates that large emergent macrophytes are more likely to better deliver provision-based services, while small emergent communities can provide additional benefits from cultural and regulatory services. Selecting macrophytes for FTWs employed in freshwater restoration by stature is a simple and widely applicable approach for designing plant communities with predictable outcomes in terms of (multiple) ecosystem service provision and highlights the need for environmental managers to closely align restoration objectives with potential community types.

WITHDRAWN: Unlimited possibilities to use Сladophora (Chlorophyta, Ulvophyceae, Cladophorales) biomass in agriculture and aquaculture with profit for the environment and humanity

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/policies/article-withdrawal). This article has been withdrawn at the request of the Publisher for legal reasons related to Elsevier's policy on Geographic Sanctions (https://www.elsevier.com/about/policies/trade-sanctions).

A planetary health innovation for disease, food and water challenges in Africa

Many communities in low- and middle-income countries globally lack sustainable, cost-effective and mutually beneficial solutions for infectious disease, food, water and poverty challenges, despite their inherent interdependence^1-7. Here we provide support for the hypothesis that agricultural development and fertilizer use in West Africa increase the burden of the parasitic disease schistosomiasis by fuelling the growth of submerged aquatic vegetation that chokes out water access points and serves as habitat for freshwater snails that transmit Schistosoma parasites to more than 200 million people globally^8-10. In a cluster randomized controlled trial (ClinicalTrials.gov: NCT03187366) in which we removed invasive submerged vegetation from water points at 8 of 16 villages (that is, clusters), control sites had 1.46 times higher intestinal Schistosoma infection rates in schoolchildren and lower open water access than removal sites. Vegetation removal did not have any detectable long-term adverse effects on local water quality or freshwater biodiversity. In feeding trials, the removed vegetation was as effective as traditional livestock feed but 41 to 179 times cheaper and converting the vegetation to compost provided private crop production and total (public health plus crop production benefits) benefit-to-cost ratios as high as 4.0 and 8.8, respectively. Thus, the approach yielded an economic incentive-with important public health co-benefits-to maintain cleared waterways and return nutrients captured in aquatic plants back to agriculture with promise of breaking poverty-disease traps. To facilitate targeting and scaling of the intervention, we lay the foundation for using remote sensing technology to detect snail habitats. By offering a rare, profitable, win-win approach to addressing food and water access, poverty alleviation, infectious disease control and environmental sustainability, we hope to inspire the interdisciplinary search for planetary health solutions¹¹ to the many and formidable, co-dependent global grand challenges of the twenty-first century.

Biomanipulation as a strategy for minimizing ecological risks in river supplied with reclaimed water

Reclaimed water is an effective method for addressing water pollution and shortages. However, its use may contribute to the collapse of receiving water (algal blooms and eutrophication) owing to its unique characteristics. A three-year biomanipulation project was conducted in Beijing to investigate the structural changes, stability, and potential risks to aquatic ecosystems associated with the reuse of reclaimed water in rivers. During the biomanipulation, the proportion of Cyanophyta in the community structure of phytoplankton density in river supplied with reclaimed water decreased, and the community composition shifted from Cyanophyta and Chlorophyta to Chlorophyta and Bacillariophyta. The biomanipulation project increased the number of zoobenthos and fish species and significantly increased fish density. Despite the significant difference in aquatic organisms community structure, diversity index and community stability of aquatic organisms remained stable during the biomanipulation. Our study provides a strategy for minimizing the hazards of reclaimed water through biomanipulation by reconstructing the community structure of reclaimed water, thereby making it safe for large-scale reuse in rivers.

Driving forces and recovery potential of the macrophyte decline in East Taihu Lake

Macrophytes are of key importance to the structure and ecological services of shallow lakes and are sensitive to anthropogenic and natural perturbations. Ongoing eutrophication and hydrological regime change affect macrophytes through changes in water transparency and water level, which lead to a dramatic decrease in bottom light availability. Here an integrated dataset (2005-2021) of multiple environmental factors is used to demonstrate the driving forces and recovery potential of the macrophyte decline in East Taihu Lake by using a critical indicator, which is the ratio of the Secchi disk depth to the water depth (SD/WD). The macrophyte distribution area showed a remarkable decrease from 136.1 ± 9.7 km² (2005-2014) to 66.1 ± 6.5 km² (2015-2021). The macrophyte coverage in the lake and in the buffer zone decreased by 51.4% and 82.8%, respectively. The structural equation model and correlation analysis showed that the distribution and coverage of macrophytes decreased with the decrease in the SD/WD over time. Moreover, an extensive hydrological regime change, which caused a sharp decrease in SD and an increase in the water level, is likely to be the driving force that brought about the decline of macrophytes in this lake. The proposed recovery potential model shows that the SD/WD has been low in recent years (2015-2021), and that this SD/WD cannot ensure the growth of submerged macrophytes and is unlikely to ensure the growth of floating-leaved macrophytes, especially in the buffer zone. The approach developed in the present study provides a basis for the assessment of macrophyte recovery potential and the management of ecosystems in shallow lakes that suffer from macrophyte loss.

Aquatic macrophytes show distinct spatial trends in contaminant metal and nutrient concentrations in Coeur d'Alene Lake, USA

Coeur d'Alene Lake (the Lake) has received significant contamination from legacy mining. Aquatic macrophytes provide important ecosystem services, such as food or habitat, but also have the ability to accumulate contaminants. We examined contaminants (arsenic, cadmium, copper, lead, and zinc) and other analytes (e.g., iron, phosphorus, and total Kjeldahl nitrogen (TKN)) in macrophytes from the Lake. Macrophytes were collected in the Lake from the uncontaminated southern end to the outlet of the Coeur d'Alene River (main contaminant source) located northward and mid lake. Most analytes showed significant north to south trends (Kendall's tau p ≤ 0.015). Concentrations of cadmium (18.2 ± 12.1), copper (13.0 ± 6.6), lead (195 ± 193), and zinc (1128 ± 523) were highest in macrophytes near the Coeur d'Alene River outlet (mean ± standard deviation in mg/kg dry biomass). Conversely, aluminum, iron, phosphorus, and TKN were highest in macrophytes from the south, potentially related to the Lake's trophic gradient. Generalized additive modelling confirmed latitudinal trends, but revealed that longitude and depth were also important predictors of analyte concentration (40-95% deviance explained for contaminants). We used sediment and soil screening benchmarks to calculate toxicity quotients. Quotients were used to assess potential toxicity to macrophyte associated biota and delineate where macrophyte concentrations exceeded local background concentrations. Exceedances (toxicity quotient > one) of background levels by macrophyte concentrations were highest for zinc (86%), followed by cadmium (84%), lead (23%), and arsenic (5%).

Process variables that defined the phytofiltration efficiency of invasive macrophytes in aquatic system

Phytofiltration is an eco-friendly and cost-effective approach to the management of pollutants in aquatic system. The present study aimed at elucidating the process variables that defined the phytofiltration efficiency of invasive macrophytes in aquatic system. The invasion of macrophytes, such as Pistia stratiotes, of water bodies is an undesirable experience because of the challenges synonymous with their occurrence. Owing to the unfettered proliferation, high and rich biomass generation, and nutrient uptake capability, these macrophytes outcompete the native vegetation and reduce the distinctiveness of the biological communities at various scales. However, these same intrinsic features positioned them as an ideal phytofiltration species for the decontamination of polluted aqua systems. Herein, we provided an overview of the process of phytofiltration in an aquatic system, and the need to create a balanced ecological system through the exploitation of the potentials of macrophytes as phytoremediators. The translocation factor, type, and concentration of pollutants in the matrix, pH value, type of macrophyte employed are among the factors identified as determinants of the success or failure of invasive macrophytes as pollutant remediators in the aqua system. Therefore, the optimization of these variables, to enhance the phytoremediation potentials of the different macrophytes were critically appraised.

Spatial performance assessment of reed bed filtration in a constructed wetland

Constructed wetlands (CW) are implemented to improve water quality through filtration by plants (macrophytes), which sequester nutrients and contaminants. Macrophyte beds in CWs reduce the speed of water flow, aiming to improve the water quality by sedimentation and filtration with increasing distance from the inflow. Few studies have assessed spatial distribution and accumulation concentrations of nutrients and contaminants in CW macrophytes as a performance indicator for wetland functionality and management. Macrophytes and water were analysed for nutrient and contaminant accumulation in-situ at a stormwater-fed CW and water remediation site in South Australia. During the austral summer, macrophytes were sampled at 36 sites and water at 46 sites selected by a systematic GIS produced grid covering the entire wetland, which determined distance from the inflow for each site. A total of 144 Schoenoplectus validus (stems and roots) macrophyte samples (i.e. carbon-C, nitrogen-N, Trace elements) and 183 water samples (i.e. total suspended solids-TSS, total nitrogen-TN, total carbon-TC, nitrate-NO₃^-/ nitrite-NO₂^- and ammonia-NH₄⁺) were analysed. Concentrations of water chemistry parameters that significantly increased with distance away from inflow included; TC (P = 0.0008), TN (P = 0.0001), and NH₄⁺ (P = 0.0001), while there was significant decrease in TSS (P = 0.0001). The macrophyte S. validus significantly decreased in height (P = 0.0001) and biomass (P = 0.03) with distance from the inflow. Spatial mapping of nutrients and contaminants with distance from inflow identified increasing TC and C characteristics from inflow to outflow and identified where TSS were removed from the water column. Through this spatial assessment approach of the Oaklands CW, management has identified problem areas with flow regimes that require further investigation to enhance macrophyte water filtration performance which can be used in CWs elsewhere in the world.

Cost-benefit analysis of beach-cast harvest: Closing land-marine nutrient loops in the Baltic Sea region

Harvesting beach-cast can help mitigate marine eutrophication by closing land-marine nutrient loops and provide a blue biomass raw material for the bioeconomy. Cost-benefit analysis was applied to harvest activities during 2009-2018 on the island of Gotland in the Baltic Sea, highlighting benefits such as nutrient removal from the marine system and improved recreational opportunities as well as costs of using inputs necessary for harvest. The results indicate that the activities entailed a net gain to society, lending substance to continued funding for harvests on Gotland and assessments of upscaling of harvest activities to other areas in Sweden and elsewhere. The lessons learnt from the considerable harvest experience on Gotland should be utilized for developing concrete guidelines for carrying out sustainable harvest practice, paying due attention to local conditions but also to what can be generalized to a wider national and international context.

Circular Economy Framework for Energy Recovery in Phytoremediation of Domestic Wastewater

Circular economy (CE) strategy is crucial in developing towards sustainable growth. It was created to promote resource utilization and the elimination of waste production. This article aimed to study the possibilities of using the CE framework in wastewater bioremediation and energy recovery using hydroponic tanks. The integration of phytoremediation with bioenergy, construction and lifespan of hydroponic tanks in phytoremediation of wastewater, selection of aquatic plants and the expected challenges in the implementation of CE in phytoremediation of wastewater were discussed. The plant-based biomass harvested and the relative growth rate (RGR) of the selected plants from the phytoremediation process was evaluated. The findings obtained indicated that the selected plants tripled in weight after 14 days cultivation period at different retention times. E. crassipes recorded the highest growth with 2.5 ± 0.03 g g−1 d−1, followed by S. molesta with 1.33 ± 0.05 g g−1 d−1 and then P. stratiotes recorded 0.92 ± 0.27 g g−1 d−1 at the end of the cultivation period. Therefore, the selected plants have been identified as having the potential to be used in phytoremediation as well as a source of energy production. The outcome of our review suggested the adoption of a lifecycle assessment as the CE framework for the phytoremediation of wastewater.

External Phosphorus Loading in New Lakes

The water quality of lakes is highly dependent on external phosphorus (P) loading. The vast external loadings from sewage and other wastewater discharge that European lakes have historically received have been dramatically reduced today by improved wastewater treatment. Gaining knowledge of the catchment characteristics that influence external P-loading should enable predictions of the achievable water quality of lakes. In this study, we tested this proposition. Data from 90 new Danish lakes show no apparent relationship between the mean summer P-concentration and the size or land use of the catchments. The external P-loading and resulting annual P-concentration were further investigated on a representative subset of 12 of the new lakes, using six methods. Three of the methods used empirical estimates of P-transport from catchments, based on the national average P-transport, runoff-dependent P-transport, and crop-dependent P-transport, and the other three methods used different empirical models tested on the lakes. External P-loading was reliably predicted by several of the methods. The predictions of the annual P-concentration were highly dependent on the inclusion of annual runoff. However, the predicted P-concentrations were generally overestimated, most pronounced for the nutrient-poor and most recently established lakes. In these lakes, internal P-loading was found to be the most important factor in predicting achievable water quality.

Nutrient Remediation Efficiency of the Sedge Plant (Cyperus alopecuroides Rottb.) to Restore Eutrophic Freshwater Ecosystems

The current study investigated the nutrients removal efficiency of the sedge macrophyte Cyperus alopecuroides to treat water eutrophication, besides evaluating the recycling possibility of the harvested material. Samples of sediment, water, and plant tissues were taken seasonally from six polluted and three unpolluted locations for this investigation. The growth properties of C. alopecuroides showed remarkable seasonal differences in plant density and biomass, with the maximum values (7.1 individual/m2 and 889.6 g/m2, respectively) obtained during summer and the minimum (4.1 individual/m2 and 547.2 g/m2, respectively) in winter. In polluted locations, the above-ground tissues had an efficiency to remove more contents of N and P (11.9 and 3.8 g/m2, respectively) than in unpolluted ones (7.1 and 3.4 g/m2, respectively). The high-nutrient standing stock of C. alopecuroides supports its potential use for nutrient removal from eutrophic wetlands. The tissues of C. alopecuroides had the maximum nutrients removal efficiency to remediate great amounts of Na, K, and N in summer, and Ca, P, and Mg in spring. Above- and below-ground parts of C. alopecuroides from unpolluted locations can be considered as a rough forage for beef cattle, dairy cattle, goats, and sheep. The present study indicated the potential of C. alopecuroides in restoring eutrophic freshwater ecosystems, and, thus, it can be used in similar habitats worldwide.

Accounting for interactions between Sustainable Development Goals is essential for water pollution control in China

Meeting the United Nations' (UN's) 17 Sustainable Development Goals (SDGs) has become a worldwide mission. How these SDGs interrelate, however, is not well known. We assess the interactions between SDGs for the case of water pollution by nutrients in China. The results show 319 interactions between SDGs for clean water (SDGs 6 and 14) and other SDGs, of which 286 are positive (synergies) and 33 are negative (tradeoffs) interactions. We analyze six scenarios in China accounting for the cobenefits of water pollution control using a large-scale water quality model. We consider scenarios that benefit from synergies and avoid tradeoffs. Our results show that effective pollution control requires accounting for the interactions between SDGs. For instance, combining improved nutrient management, efficient food consumption, and climate mitigation is effective for simultaneously meeting SDGs 6 and 14 as well as other SDGs for food, cities and climate. Our study serves as an example of assessing SDG interactions in environmental policies in China as well as in other regions of the world.

Long-Term Changes in Macrophyte Distribution and Abundance in a Lowland River

The aim of this study was to reveal the changes of macrophyte community over time and along the course of the Ižica River. In 1996, 2000, and 2016, we surveyed the distribution and abundance of macrophyte species in the lowland Ižica River, which originates in the town of Ig and then flows through an agricultural landscape. We calculated the River Macrophyte Index (RMI), which reflects the ecological status of the river. In 2016, ecomorphological conditions of the river, using the Riparian, Channel and Environmental inventory, were also assessed. In just 10.5 km of the river, we identified 27 taxa of macrophytes, among which Potamogeton natans, Sagittaria sagittifolia, and P. perfoliatus were the most abundant. Detrended correspondence analysis showed that, in 1996, the surveyed stretches differed more according to macrophyte composition than in the following years. The assessed environmental parameters explained 43% of the variability of the macrophyte species; riverbank stability explained 20%, riverbed structure 10%, while vegetation type of the riparian zone and bottom type explained 7 and 5%, respectively. The species composition of the macrophyte community revealed significant changes over the years of the riverine ecosystem. Comparison of RMIs in 1996 revealed better conditions in the upper and middle part of the river, while in 2016, the situation was the opposite, since the conditions in the upper part deteriorated significantly over time, while the lower part of the river had the best ecological status. These changes may be due to a considerable increase in the population of the settlement Ig, while better status in the lower course of the river may be a consequence of improvements in the infrastructure and the use of sustainable agricultural practices in the catchment due to the establishment of a formal area of protection.

A translocation analysis of organophosphate pesticides between surface water, sediments and tissues of common reed Phragmites australis

This study investigated the ability of common reed, Phragmites australis to take up organophosphate pesticides (OPPs). The study site was the agriculturally polluted Sundays Estuary in South Africa. Surface water, leaves, roots, and deep-rooted-sediments of P. australis were collected along the length of the estuary and analysed for 13 different OPPS. The extraction of OPPs in plant tissues was performed by QuEChERS method followed by GC-MS analysis. The highest concentration of OPPs was found in leaves (16.41-31.39 μg kg^-1 dw), followed by roots (13.92-30.88 μg kg^-1 dw), and sediments (3.30-8.07 μg kg^-1 dw). Of the 13 targeted OPPs, only one compound was not detected across the four sample matrices, thus reflecting widespread contamination in the Sundays Estuary. The biota sediment accumulation factor (BSAF) values of pyraclofos, quinalphos, fenitrothion, phosalone, EPN, diazinon, chlorpyrifos, pyrazophos, and isazophos were higher than one implying that P. australis possesses the ability to bioaccumulate these compounds. The root-leaf translocation factors (TF_r-l) of these pesticides were higher than 1, suggesting that P. australis possesses the capacity to move these pesticides from roots to leaves. The insignificant correlation observed between log BSAF and log K_ow and log TF_r-l and log K_ow implies that OPPs uptake by P. australis tissues were not dependent on log Kow. Our study demonstrates that P. australis possesses the potential to effectively remove OPPs from contaminated water and sediment.

The role of mechanical harvesting on the recession of aquatic vegetation under an extreme water level increase in a eutrophic shallow lake

Mechanical harvesting is quick and effective way to remove nuisance macrophytes and improve recreational use and aesthetics in shallow lake. However, applying mechanical harvesting to macrophytes in eutrophic shallow lake with weak resilience and strong perturbation raises concerns of the public and scientific communities. A combination of field investigation and remote sensing was used to determine the potential driving factors of macrophyte degradation in a eutrophic shallow lake from 2014 to 2017, including a comparative analysis of preserved and harvested areas to determine the impacts of mechanical harvesting. Over 95% of macrophytes had disappeared by 2017 in both preserved and harvested areas, with no significant difference in macrophyte distribution area or decline rate between the two by that time. The decline rate in the harvested area (76.7%) was slightly higher than in the preserved area (61.7%) in 2016 after performing the mechanical harvesting in 2015. The results demonstrate that mechanical harvesting is not the definitive driving factor for macrophyte loss, but it could accelerate the decline process. Bottom light availability (Secchi disk depth to water level), which decreased from 0.70 to 0.29 in 2015 and from 0.70 to 0.21 in 2016, is more likely the driving factor, caused by extreme water level increase events in two consecutive years (2015 and 2016) and decreased water clarity. Maintaining water clarity and low water level is crucial for macrophyte restoration.

The achievement of Water Framework Directive goals through the restoration of vegetation in agricultural canals

Decreasing nitrate concentrations is one of the most relevant Water Framework Directive (WFD) goals, which today is still unreached in several European countries. Vegetated canals have been recognized as effective filters to mitigate nitrate pollution, although rarely included in restoration programs aimed at improving water quality in agricultural watersheds. The Po di Volano basin (713 km², Northern Italy) is a deltaic territory crossed by an extensive network of agricultural canals (~1300 km). The effectiveness in buffering nitrate loads via denitrification was assessed for different levels of in-stream emergent vegetation maintenance by employing an upscale model based on extensive datasets of field measurements. The scenarios differed for the canal network length (5%, 20%, 40%, and 60%) where conservative management practices were adopted by postponing the mowing operations from the middle of summer, as nowadays, to the early autumn, i.e., the vegetative season end. The scenario simulations demonstrated that the capacity to mitigate diffuse nitrate pollution would increase up to four times, compared to the current condition (5% scenario), by postponing the vegetation mowing to the end of the vegetative season in 60% of the canal network length. By preserving the in-stream vegetation in 20% of the canal network, its denitrification capacity would equal the nitrate load reduction target required for achieving, from May to September, the good ecological status according to the WFD in waters delivered to the coastal areas. Changing the timing of vegetation mowing may create a large potential for permanent nitrate removal via denitrification in agricultural landscapes, thus protecting the coastal areas when the eutrophication risk is higher. Conservative management practices of in-stream vegetation might be promoted as an effective low-cost tool to be included in the WFD implementation strategies.

Re-Establishment Techniques and Transplantations of Charophytes to Support Threatened Species

Re-establishment of submerged macrophytes and especially charophyte vegetation is a common aim in lake management. If revegetation does not happen spontaneously, transplantations may be a suitable option. Only rarely have transplantations been used as a tool to support threatened submerged macrophytes and, to a much lesser extent, charophytes. Such actions have to consider species-specific life strategies. K-strategists mainly inhabit permanent habitats, are perennial, have low fertility and poor dispersal ability, but are strong competitors and often form dense vegetation. R-strategists are annual species, inhabit shallow water and/or temporary habitats, and are richly fertile. They disperse easily but are weak competitors. While K-strategists easily can be planted as green biomass taken from another site, rare R-strategists often must be reproduced in cultures before they can be planted on-site. In Sweden, several charophyte species are extremely rare and fail to (re)establish, though apparently suitable habitats are available. Limited dispersal and/or lack of diaspore reservoirs are probable explanations. Transplantations are planned to secure the occurrences of these species in the country. This contribution reviews the knowledge on life forms, dispersal, establishment, and transplantations of submerged macrophytes with focus on charophytes and gives recommendations for the Swedish project.

Non-indigenous and Invasive Freshwater Species on the Atlantic Islands of the Azores Archipelago

Freshwater systems on remote oceanic islands are particularly vulnerable to biological invasions. The case of freshwater ecosystems in the Azores Archipelago is especially relevant considering the islands’ youth and remoteness, and low natural connectivity. This study presents a review of the introduction and presence of non-indigenous freshwater species in the Azores, retrieved from various historical records, paleoenvironmental reconstructions, published records, and field data from two decades of the Water Framework Directive (WFD) monitoring programs. At least 132 non-indigenous freshwater species have successfully established in the Azores, belonging to several taxonomic groups: cyanobacteria (10), synurophytes (1), desmids (1), diatoms (20), plants (41), invertebrates (45), amphibia (2), and fishes (12). Intentional and accidental introductions have been occurring since the establishment of the first human settlers on the archipelago, impacting freshwater ecosystems. The first reported introductions in the Azores were intentional fish stocking in some lakes. Non-deliberate introductions have recently increased through transport-contaminants (51%) associated with the aquarium trade or agricultural products. In the Azores, the highest number of non-indigenous species occur on the largest and most populated island, São Miguel Island (116), followed by Flores (68). Plants constitute the most representative group of introduced species on all islands, but invertebrates, diatoms, and fishes are also well established on most islands. Among invertebrates, non-indigenous arthropods are the most well-established group on all islands except on the smallest Corvo Island. Many non-indigenous species will likely benefit from climate change and magnified by globalization that increases the probability of the movement of tropical and subtropical species to the Azores. Present trends in international trade, importations, and enhanced connectivity of the archipelago by increasing flights and shipping will probably promote the arrival of new species. Augmented connectivity among islands is likely to improve non-indigenous species dispersal within the archipelago as accidental transportation seems to be an essential pathway for non-indigenous freshwater species already present in the Azores.

Primacy of ecological engineering tools for combating eutrophication: An ecohydrological assessment pathway

Eutrophication of freshwater bodies causes loss of earth's biological resources and aggravates climate change, thus assuming major environmental concern. Both endogenous and exogenous nutrient enrichment are responsible for eutrophication. Numerous monitoring and management studies conducted worldwide have resulted high-level technological innovations. These studies cumulatively uphold the significance of ecohydrological and ecological engineering approaches. However, holistic and insightful reviews with feasible recommendations of such huge academic outputs are rather scanty. Therefore, our main objective was to introduce a new perspective of eutrophication as an ecohydrological component; to discover all possibilities of monitoring and restoration of eutrophic water bodies. Furthermore, the present study critically analyzes various methods of treatment of eutrophication (physical, biological, chemical, and eco-engineering). Comprehensive volume of literature has been surveyed using search engines like Scopus, Google Scholar, PubMed, ScienceDirect etc. Meaningful keywords were used to obtain reliable information on methods of ecohydrological assessment in relation to eutrophication of freshwater bodies. According to our survey, ecohydrological research is diversified into conceptual knowledge (37.2%), assessment (32.6%), climate change (9.3%), algae/cyanotoxins (7%), engineering and restoration (7%), modelling (4.6%) and biodiversity (2.3%), in the instant decade (2010-2020). We have identified a clear trend of transition of restoration methods from traditional towards modern techniques over time. Moreover, this review recognizes a pool of biophysicochemical and ecological engineering techniques, which are very effective in regard to time, cost, and labor and have immense scopes of modification for improved results. This work focuses on the importance of ecohydrology and eco-engineering tools for restoration of eutrophic water bodies for the first time. We have highlighted how these approaches have emerged as one of the best suitable and sustainable water resource conservation routes in the present era.

Agricultural Innovations to Reduce the Health Impacts of Dams

Dams enable the production of food and renewable energy, making them a crucial tool for both economic development and climate change adaptation in low- and middle-income countries. However, dams may also disrupt traditional livelihood systems and increase the transmission of vector- and water-borne pathogens. These livelihood and health impacts diminish the benefits of dams to rural populations dependent on rivers, as hydrological and ecological alterations change flood regimes, reduce nutrient transport and lead to the loss of biodiversity. We propose four agricultural innovations for promoting equity, health, sustainable development, and climate resilience in dammed watersheds: (1) restoring migratory aquatic species, (2) removing submerged vegetation and transforming it into an agricultural resource, (3) restoring environmental flows and (4) integrating agriculture and aquaculture. As investment in dams accelerates in low- and middle-income countries, appropriately addressing their livelihood and health impacts can improve the sustainability of modern agriculture and economic development in a changing climate.

Uncoupling growth from phosphorus uptake in Lemna: Implications for use of duckweed in wastewater remediation and P recovery in temperate climates

Phosphorus (P) is an essential nutrient for crop growth and the second most limiting after N. Current supplies rely on P-rich rocks that are unevenly distributed globally and exploited unsustainably, leading to concerns about future availability and therefore food security. Duckweeds (Lemnaceae) are aquatic macrophytes used in wastewater remediation with the potential for nutrient recycling as feed or fertilizer. The use of duckweeds in this way is confined to tropical regions as it has previously been assumed that growth in the colder seasons of the temperate regions would be insufficient. In this study, the combined effects of cool temperatures and short photoperiods on growth and P uptake and accumulation in Lemna were investigated under controlled laboratory conditions. Growth and P accumulation in Lemna can be uncoupled, with significant P removal from the medium and accumulation within the plants occurring even at 8°C and 6-hr photoperiods. Direct measurement of radiolabeled phosphate uptake confirmed that while transport is strongly temperature dependent, uptake can still be measured at 5°C. Prior phosphate starvation of the duckweed and use of nitrate as the nitrogen (N) source also greatly increased the rate of P removal and in-cell accumulation. These results form the basis for further examination of the feasibility of duckweed-based systems for wastewater treatment and P recapture in temperate climates, particularly in small, rural treatment works.

Potential of invasive watermilfoil (Myriophyllum spp.) to remediate eutrophic waterbodies with organic and inorganic pollutants

Watermilfoil (Myriophyllum) is one of the world's most troublesome invasive aquatic weeds. Although current management practices may inhibit its expansion, it also impacts not only the quality of water but habitat deterioration. Therefore, the need for developing highly efficient and low-cost biotechnologies with resource recovery into the agriculture field as a complementary management strategy cannot be overstated. Here, we reviewe the scientific/grey literature to offer readers a precise and panoramic view of the invasive watermilfoil ecology, regional problems, impacts, ecosystem services, and management. In this regard, an in-depth review aimed to assess the potential for reducing non-point source inorganic and organic pollutants using invasive watermilfoil, with the sustainable approaches, while offering other services and mitigating ecological trade-offs is presented. Global distributions, growth, and current progress on the management and utilization of invasive watermilfoil biomass are summarized to develop the aim, which is to convey challenges during the implementation of large-scale weed use. In short, pollutant assimilation in plant and bacterial communities linked to this weed considerably contribute to the reduction and degradation of pollutants from both natural and artificial systems. Although several considerations in recycling and reusing biomass need to be considered, the potential reuse of the harvested material for livestock feed, compost and direct use in farming systems offer an additional strategy to achieve sustainable ecosystem restoration. Further research and development may focus on a more detailed economic modeling approach that integrates the costs (worker's wage, harvesting, transportation, and energy consumption), legal and regulatory barriers, health risks and ecosystem service benefits (biodiversity improvement, and pollutant removal) to holistically evaluate the economic, environmental, and societal value of reusing and recycling this waste material.

Valorization of farm pond biomass as fertilizer for reducing basin-scale phosphorus losses

Long-term fertilizer phosphorus (P) inputs are causing phosphorous saturation of agricultural soils globally. The saturation is spreading to the edge-of-the-farm stormwater detention systems (SDSs) from where the legacy P is potentially being released to downstream surface waters. We use site-specific and literature data for P-saturated SDSs, to develop and evaluate the biogeochemical and economic feasibility of a P recycling program that targets both low (LIC, sugarcane) and high intensity cropping (HIC, fresh-produce) systems within a watershed. The focus is to close the P cycle loop to rejuvenate P sink function of SDSs. It involves harvesting and composting the SDS's biomass and it's on-farm use as an organic fertilizer for crops. Results showed that harvesting-composting can conservatively increase the P retention from 50% to 77% for HIC and almost complete treatment for LIC. Beyond potentially increasing yield and improving soil health, compost use can further increase in-field retention of P (and water). Additional costs incurred in harvesting and composting can be offset by the economic value of compost and the reduction in State's expenditure on regional P treatment systems. Treatment costs were $26/kg of P for HIC and $42/kg for LIC, 10 times less than the current state expenditure of $355-$909/kg P using constructed wetlands. We propose an incentivized, payment for services (PS) program, where producers are paid for P recycling. The PS program considers the intensity of cropping systems and their location along the drainage network from headwaters to the outlet, to achieve basin-scale P load reduction. The LIC SDSs recover regional P by passing the public water through them while recycling is implemented at the HIC. The estimated basin-scale P retention with harvest-compost approach was 854 metric tons, 5 times the P that entered the Everglades Protection Area in 2018, at 88%-93% less cost than the State treatment systems.

Experimental harvesting of wetland plants to evaluate trade-offs between reducing methane emissions and removing nutrients accumulated to the biomass in constructed wetlands

Constructed wetlands built for water treatment often need biomass harvesting to remove nutrients from the system. Usually harvesting is done during the peak growing season to maximize the amount of nutrients removed from the system. This, however, can create huge methane fluxes that escape from plant tissues to the atmosphere. We used manual chambers and eddy covariance measurements to analyze the increase in methane emissions due to the harvesting of two common wetland species, Typha spp. and Schoenoplectus spp., in two climatically different constructed wetlands in Estonia and California. In addition, we determined the biomass nutrient and carbon concentrations from harvested biomass. We found that harvesting during the summer season, e.g. June and August, resulted in a significant release of methane at both sites. At the California site, baseline median methane emissions were 217.6 nmol m^-2 s^-1, and harvesting resulted in increases to 395.4 nmol m^-2 s^-1 that decreased to baseline emission within three days. Footprint modeling demonstrated that the emission increases measured by eddy covariance were dominated by contributions from the cut area to the total footprint signal. At the Estonian site, harvesting resulted in methane increases of 15.9 nmol m^-2 s^-1 to 110.4 nmol m^-2 s^-1 in August. However, in September and October the emission was significantly lower. Plant biomass analyses showed clear temporal dynamics in terms of nutrient concentration, being highest in summer and lowest in winter. Our experiments indicate that the optimal time for aboveground biomass harvesting is at the end of the growing season before nutrient translocation to belowground plant structures begins coinciding with lowest methane emissions. Therefore, strategic planning of the harvest timing may help reduce greenhouse gas emissions from managed wetlands and thus improve their multi-faceted ecological benefit.

Using hydrodynamic and water quality variables to assess eutrophication in a tropical hydroelectric reservoir

Few studies have examined the influence of reservoir hydrodynamics on the water quality of its limnological zones. In this study, the relationships between the operational phases and the water quality of the limnological zones were assessed for the Amazonian reservoir Tucuruí. Limnological zones were clustered by means of an artificial neural network technique, and inputs used were water quality variables, measured at twelve stations between 2006 and 2016. Generalized Linear Models (GLMs) were then used to identify the influence of the operational phases of the reservoir on the water quality of its limnological zones. The GLM with a gamma-distributed response variable indicated that Chlorophyll-a concentrations in the riverine and transitional zones differed notably from those observed in the lacustrine zone. Chlorophyll-a concentrations were significantly lower during the operational falling water phase than in the low water phase (p < 0.05). The GLM with an inverse Gaussian-distributed response variable indicated that Secchi depth was significantly lower in the riverine than in the lacustrine limnological zone (p < 0.05). Our results suggest that more eutrophic conditions occur during the operational rising water phase, and that the area most vulnerable to eutrophication is the transitional zone. We demonstrate that the use of GLMs is suitable for determining areas and operational phases most vulnerable to eutrophication. We envisage that this information will be useful to decision-makers when monitoring the water quality of hydroelectric reservoirs with dendritic patterns and dynamic operational phases.

An Appraisal of Potential for Sowing of Nasturtium officinale Into Streams to Mitigate Nutrient Pollution in Eastern Scotland

This study examines a farmer-led initiative to sow watercress (Nasturtium officinale) in field ditches. The objective was to assess the potential of this practice to mitigate summer nutrient loads in rivers. Two ditches—one seeded, the other unseeded—on a mixed-livestock farm in Eastern Scotland were monitored during the spring-summer of 2014–2016. The un-replicated trial design limited statistical analysis. However, changes in N and P concentrations along the two ditches were measured. In the watercress-seeded ditch, N retention of 0.092 g/m²/d (p < 0.001, SE = 0.020) and P retention of 0.0092 g/m²/d (p = 0.001, SE = 0.0028) occurred, while total organic C in the water increased along the ditch. Retention was close to zero for the unseeded ditch. The seeded ditch was also found to have more dry matter production and lower stream temperature. The impact of plastic covering (to increase spring temperature) on vegetation and nutrient removal was also assessed on replicate 5-m sections of the ditches. No significant impact on N and P removal was found; however, the release of C increased significantly in the plastic-covered sections. The rise in air temperature (up to > 30 °C) promoted a greater growth of opportunist species (nettle (Urtica), rush (Juncus), and grasses. These observations were used to make a simple assessment of the potential catchment scale impact of seeding watercress into first and second order streams in the nearby Lunan Water catchment. It was concluded that this could make a significant contribution to the reduction of nutrient loads.

Life Cycle Assessment of Seaweed Cultivation Systems

Life cycle assessment (LCA) is a holistic methodology that identifies the impacts of a production system on the environment. The results of an LCA are used to identify which processes can be improved to minimize impacts and optimize production.LCA is composed of four phases: (1) goal and scope definition, (2) life cycle inventory analysis, (3) life cycle impact assessment, and (4) interpretation.The goal and scope define the purpose of the analysis; describe the system and its function, establish a functional unit to collect data and present results, set the system boundaries, and explain the assumptions made and data quality requirements. Life cycle inventory analysis is the collection, processing and organization of data. Life cycle impact assessment associates the results from the inventory phase to one or multiple impacts on environment or human health. The interpretation evaluates the outcome of each phase of the analysis. In this phase the practitioner decides whether it is necessary to amend other phases, e.g., collection of more data or adjustments of goal of the analysis. In the interpretation, the practitioner draws conclusions, exposes the limitations, and provides recommendations to the readers.The quality of LCA of seaweed production and conversion is based on data availability and detail level. Performing an LCA at the initial stage of seaweed production in Europe is an advantage: the recommended design improvements can be implemented without significant economic investments. The quality of LCA will keep improving with the increase of scientific publications, data sharing, and public reports.

Efficacy of batch mode rotary drum composter for management of aquatic weed (Hydrilla verticillata (L.f.) Royle)

Invasive aquatic weed management is one of the biggest challenges in the field of solid waste management. Eichhornia crassipes, Pistia stratiotes and Hydrilla verticillata (L.f.) Royle pose some of the world's most noted aquatic weed problems. Previously reported studies on management of H. verticillata, a submersed aquatic plant, have shown that temporary removal, chemical treatment or biological control methods each have advantages and disadvantages. Removal programs that propose to compost harvested H. verticillata biomass may provide a novel technique to manage this issue. However, the properties of such compost as an agriculture resource are unclear. This study presents the different mix proportions of H. verticillata, cow dung and sawdust used for the composting of 550 L rotary drum composter. This work characterizes the biological, physicochemical, and respirometry properties of the various mixes over a 20-day composting period. The results suggest that the biomass of H. verticillata can be beneficially utilized to produce stable compost for potential use in agricultural systems.

Decomposition of Wolffia arrhiza residues rapidly increases mineral nitrogen and decreases extractable phosphorus in acidic soils

While nutrient loads from anthropogenic sources upset aquatic ecosystem balance, Wolffia arrhiza (duckweed) has capacity to purge nutrient-rich water if continuously harvested. The nutrients accumulated in biomass have potential as soil fertility amendments. The objective of this study was to determine changes in release of nitrogen (N) and phosphorus (P), and the fate of P in soils after duckweed biomass amendment. An incubation experiment was conducted at 25 °C using three soils amended with proportions equivalent to 501, 1002 and 1503 mg N kg^-1 and 62, 124 and 186 mg P kg^-1. Soil samples were collected on 0, 3, 7, 14, 21, 28, 42 and 56 days, for ammonium-N, nitrate-N and extractable-P measurements. At the end of incubation, P pools were determined. At least 25 mg kg^-1 of ammonium-N was released on day 0, reaching a peak within the first 2 weeks. Nitrate- and mineral-N increased from 14 to 42 days, with a corresponding decrease in ammonium-N. Relatively fertile soil released more mineral-N at higher applied ratios of duckweed than the less fertile. About 10-80 mg kg^-1 of duckweed P was extractable on day 0 and amounts progressively declined over the incubation period. The combined percentage (0.5%) of tissue aluminium (Al) and iron (Fe) facilitated Al and Fe phosphate accumulation as the proportion of duckweed amendment increased. The results suggested that soil type and elemental composition of duckweed are important determinants for N and P release, and liming could improve P availability in soil.

Nitrogen removal and recovery from lagoon-pretreated swine wastewater by constructed wetlands under sustainable plant harvesting management

A series of three-stage pilot-scale surface flow constructed wetlands (CWs) planted with Myriophyllum aquaticum were fed with three strengths of lagoon-pretreated swine wastewater to study nitrogen (N) removal and recovery under sustainable plant harvesting management. The CWs had mean removal efficiency of 87.7-97.9% for NH₄⁺-N and 85.4-96.1% for total N (TN). The recovered TN mass via multiple harvests of M. aquaticum was greatest (120-222 g N m^-2 yr^-1) when TN concentrations were 21.8-282 mg L^-1. The harvested TN mass accounted for 0.85-100% of the total removal in the different CW units. Based on mass balance estimation, plant uptake, sediment storage, and microbial removal accounted for 13.0-55.0%, 4.9-8.0%, and 33.0-67.5% of TN loading mass, respectively. The results of this study confirm that M. aquaticum is appropriate for the removal and recovery of nutrients in CW systems designed for treating swine wastewater in conjunction with sustainable plant harvesting strategies.

Transfer kinetics of phosphorus (P) in macrophyte rhizosphere and phytoremoval performance for lake sediments using DGT technique

DGT (diffusive gradients in thin films) technique and DIFS (DGT induced fluxes in sediment) model are firstly designed for macrophyte-rhizobox system and in-situ macrophytes in Lake Erhai. Dynamics of phosphorus (P) transfer in Zizania latifolia (ZL) and Myriophyllum verticiilatur (MV) rhizosphere is revealed and phytoremediation performance for P in sediment is evaluated. Dynamic transfer process of P at DGT/sediment interface includes (i) diffusion flux and concentration gradients at DGT(root)/porewater interface leading to porewater concentration (C₀) depletion and (ii) P desorption from labile P pool in sediment solid to resupply C₀ depletion. Fe-redox controlled P release from Fe-bound P (BD-P2) and then NH₄Cl-P1 in rhizosphere sediment resupplies porewater depletion due to DGT (root) sink. K_d (labile P pool size in solid phase), r (resupply ratio) and kinetic exchange (Tc and k_-1) lead to change characters of DIFS curves of (1) r against deployment time and (2) C_solu (dissolved concentration) against distance at 24 h. They include two opposite types of "fast" and "slow" rate of resupplies. Sediment properties and DIFS parameters control P diffusion and resupply in rhizosphere sediment. Phytoremoval ability for sediment P in lake is estimated to be 23.4 (ZL) or 15.0 t a^-1 (MV) by "DGT-flux" method.

Biomethanation of water hyacinth biomass

The aim of this study was to test practical solutions to improve biogas yield during the anaerobic digestion of water hyacinth (WH) biomass. Increasing the WH (whole plant) solid content to ∼40% through sun drying (6 h), and its subsequent digestion increased biogas yield by 14% with a higher biogas methane (75%) content. Ensilation of dried WH (40% moisture) was found effective for its preservation to ensure its continuous availability even during offseasons, but the biogas yield from six months ensilated biomass was 20% less compared with fresh WH. Co-digestion of WH with waste activated sludge and food waste revealed ∼150 and ∼400 ml biogas/g VS respectively against ∼140 ml/g VS of WH alone. The practical approaches tested in this study like pre-treatment, preservation, and co-digestion of WH found to be effective to make its bio methanation more feasible.

Long-term assessment at field scale of Floating Treatment Wetlands for improvement of water quality and provision of ecosystem services in a eutrophic urban pond

Pollution of urban water bodies requires stringent control measures and the development of low-cost and highly efficient alternative technologies. In contrast to Constructed Wetlands, Floating Treatment Wetlands (FTWs) have the advantage of not requiring large surface of land since they operate in situ. However, there is limited information about their long-term evaluation while operating at field scale. The aim of this work was to assess the performance of FTWs using a combination of Pontederia sagittata and Cyperus papyrus for the improvement of the water quality and provision of ecosystem services of a eutrophic urban pond. The FTWs were built with low-cost material easy to acquire and to ensemble. Two FTWs (17.5m² and 33m²) located in Pond 1 within a complex of 4 urban artificial ponds were evaluated for two years. They promoted an increase in the dissolved oxygen (D.O.) within a range of 15 to 67%, a removal of fecal coliforms in the range of 9 to 86% and a nitrate removal in the range of 9 to 76%. The plant productivity reached a maximum of 363g_dmm^-2d^-1 in the FTW1 and 536g_dmm^-2d^-1 in the FTW2 during the period March-June 2016. The TKN and the TP content in the plant were in the range of 18.3 to 28.1 and of 0.05 to 0.196gkg^-1 dry matter, respectively. In conclusion, the tested FTWs have proved to be a very beneficial low-cost technology for the improvement of water quality and provision of ecosystem services.

Mowing Submerged Macrophytes in Shallow Lakes with Alternative Stable States: Battling the Good Guys?

Submerged macrophytes play an important role in maintaining good water quality in shallow lakes. Yet extensive stands easily interfere with various services provided by these lakes, and harvesting is increasingly applied as a management measure. Because shallow lakes may possess alternative stable states over a wide range of environmental conditions, designing a successful mowing strategy is challenging, given the important role of macrophytes in stabilizing the clear water state. In this study, the integrated ecosystem model PCLake is used to explore the consequences of mowing, in terms of reducing nuisance and ecosystem stability, for a wide range of external nutrient loadings, mowing intensities and timings. Elodea is used as a model species. Additionally, we use PCLake to estimate how much phosphorus is removed with the harvested biomass, and evaluate the long-term effect of harvesting. Our model indicates that mowing can temporarily reduce nuisance caused by submerged plants in the first weeks after cutting, particularly when external nutrient loading is fairly low. The risk of instigating a regime shift can be tempered by mowing halfway the growing season when the resilience of the system is highest, as our model showed. Up to half of the phosphorus entering the system can potentially be removed along with the harvested biomass. As a result, prolonged mowing can prevent an oligo-to mesotrophic lake from becoming eutrophic to a certain extent, as our model shows that the critical nutrient loading, where the lake shifts to the turbid phytoplankton-dominated state, can be slightly increased.

Phosphate and ammonium adsorption of the modified biochar based on Phragmites australis after phytoremediation

To effectively remove N and P from eutrophic water, the Phragmites australis after phytoremediation was harvested for preparation of modified biochar. The MgCl₂-modified biochar (MPB) was successfully synthesized at 600 °C under N₂ circumstance. The physiochemical characteristics, the adsorption capacity for N and P in the simulated solution, and their adsorption mechanism of MPB were then determined, followed by the treatment of eutrophic water of Tai lake and its inflow river from agricultural source. The results demonstrated that the MPB presented high adsorption capacity to both simulated NH₄-N and PO₄-P with the maximum adsorption capacity exceeding 30 and 100 mg g^-1, respectively. The entire ammonium adsorption process could be described by a pseudo-second-order kinetic model whereas the phosphate adsorption process could be divided into three phases, as described by both intra-particle diffusion model and the pseudo-first-order kinetic. It was further found that the dominant mechanism for ammonium adsorption was Mg²⁺ exchange instead of functional groups and surface areas and the Mg-P precipitation was the main mechanism for phosphate adsorption. The MPB also showed high removal ratio of practical TP which reached nearly 90% for both the water in Tai lake and its agricultural source. It suggested that MPB based on harvested P. australis was a promising composite for eutrophic water treatment and it could deliver multiple benefits. Graphic abstract.

Bioextraction potential of seaweed in Denmark - An instrument for circular nutrient management

The aim of the study is to assess the efficacy of seaweed for circular nutrient management to reduce eutrophication levels in the aquatic environment. We performed a comparative Life Cycle Assessment (LCA) of two reference waste management systems treating seaweed as biowaste, i.e. landfill disposal and combustion, and an alternative scenario using the seaweed Saccharina latissima as a resource for biobased fertilizer production. Life Cycle Impact Assessment (LCIA) methods were improved by using a cradle-to-cradle approach, quantifying fate factors for nitrogen and phosphorus loss from fertilized agriculture to the aquatic environment. We also differentiated between nitrogen- and phosphorus-limited marine water to improve the traditional freshwater impact category, making this indicator suitable for decision support in relation to coastal water management schemes. Offshore cultivation of Saccharina latissima with an average productivity of 150Mg/km(2) in Danish waters in 2014 was applied to a cultivation scenario of 208km(2). The bioresource scenario performs better than conventional biowaste management systems, delivering a net reduction in aquatic eutrophication levels of 32.29kgNeq. and 16.58kgPO4(3-)eq. per Mg (dry weight) of seaweed, quantified by the ReCiPe and CML impact assessment methods, respectively. Seaweed cultivation, harvest and reuse of excess nutrients from the aquatic environment is a promising approach for sustainable resource cycling in a future regenerative economy that exploits manmade emissions as a resource for closed loop biobased production while significantly reducing eutrophication levels in 3 out of 7 Danish river basin districts. We obtained at least 10% bioextraction of phosphorus manmade emissions (10%, 89% and >100%) and contributed significantly to local nitrogen reduction goals according to the Water Framework Directive (23%, 78% and >100% of the target).