Reduce Nutrient Inputs Research Articles

Extreme Climate Anomalies Enhancing Cyanobacterial Blooms in Eutrophic Lake Taihu, China

AbstractClimate warming in combination with nutrient enrichment can greatly promote phytoplankton proliferation and blooms in eutrophic waters. Lake Taihu, China, is a large, shallow and eutrophic system. Since 2007, this lake has experienced extensive nutrient input reductions aimed at controlling cyanobacterial blooms. However, intense cyanobacterial blooms have persisted through 2017 with a record‐setting bloom occurring in May 2017. Causal analysis suggested that this bloom was sygenerically driven by high external loading from flooding in 2016 in the Taihu catchment and a notable warmer winter during 2016/2017. High precipitation during 2016 was associated with a strong 2015/2016 El Niño in combination with the joint effects of Atlantic Multi‐decadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), while persistent warmth during 2016/2017 was strongly related to warm phases of AMO and PDO. The 2017 blooms elevated water column pH and led to dissolved oxygen depletion near the sediment, both of which mobilized phosphorus from the sediment to overlying water, further promoting cyanobacterial blooms. Our finding indicates that regional climate anomalies exacerbated eutrophication via a positive feedback mechanism, by intensifying internal nutrient cycling and aggravating cyanobacterial blooms. In light of global expansion of eutrophication and blooms, especially in large, shallow and eutrophic lakes, these regional effects of climate anomalies are nested within larger scale global warming predicted to continue in the foreseeable future.

Evidence for antifouling biocides as one of the limiting factors for the recovery of macrophyte communities in lakes of Schleswig-Holstein

BackgroundThe European Water Framework Directive (WFD) has been implemented to achieve a good ecological status in European water bodies requiring macrophyte community assessment as one of the biological quality elements (BQEs). While in several lakes in Schleswig-Holstein (Germany) different BQEs improved within recent years, no recovery of macrophyte communities in some lakes could be achieved, despite the reduction of nutrient input and eutrophication. Due to the fact that no impairment of phytoplankton could be observed, toxic stress due to sediment contamination was hypothesized as a possible limiting factor of macrophyte community recovery.ResultsSediment toxicity was investigated by performing an extensive chemical screening of sediment contamination and a risk assessment based on toxic unit (TU) summation, using equilibrium water concentrations and algal toxicity as surrogates for lacking data on macrophyte toxicity. Possible indirect risks via toxic pressure on grazer were assessed via TUs based on crustaceans. The study revealed algal TUs of more than one order of magnitude below chronic toxicity thresholds in lakes with high and good status of the macrophyte community and increasing concentrations and frequency of exceedance of toxicity thresholds for lakes with moderate-to-bad status. The antifouling biocides irgarol and diuron were identified as major risk drivers. In addition, PAHs and glyphosate could not be ruled out to contribute to toxic pressure on macrophytes. Despite exceedance of toxicity thresholds for crustaceans, no connection of the ecological status of the macrophyte communities with toxic risks to grazers could be observed.ConclusionsOur study suggests that in a multiple pressure situation the toxic pressure created due to the contamination of sediments with antifouling biocides is one of the limiting factors for the recovery of macrophyte communities in impaired lakes of Schleswig-Holstein. This finding is in agreement with a Europe-wide survey on almost 47,000 sites suggesting that no good ecological status can be observed at sites with contamination exceeding toxicity thresholds. Similar to the survey, our study indicates additional stressors preventing the achievement of a good quality status of the lake ecosystems.

Reconstructing primary production in a changing estuary: A mass balance modeling approach

AbstractEstuarine primary production (PP) is a critical rate process for understanding ecosystem function and response to environmental change. PP is fundamentally linked to estuarine eutrophication, and as such should respond to ongoing efforts to reduce nutrient inputs to estuaries globally. However, concurrent changes including warming, altered hydrology, reduced input of sediments, and emergence of harmful algal blooms (HABs) could interact with nutrient management to produce unexpected changes in PP. Despite its fundamental importance, estuarine PP is rarely measured. We reconstructed PP in the York River Estuary with a novel mass balance model based on dissolved inorganic nitrogen (DIN) for the period 1994–2018. Modeled PP compared well to previous estimates and demonstrated a long‐term increase and down‐estuary shift over the study period. This increase occurred despite reductions in discharge, flushing time, DIN loading, and DIN standing stock over the same period. Increased PP corresponded to increased water temperature, decreased turbidity and light attenuation, and increased photic depth and assimilation ratio, suggesting that phytoplankton in the York River Estuary have become more efficient at converting nutrients into biomass primarily due to a release from light limitation. The increase in PP also coincided with the increasing occurrence of late summer HABs in the lower York River Estuary, including the emergence of a second bloom‐forming dinoflagellate in 2007. Results demonstrate how changes concurrent with nutrient management could alter expected system responses and illustrate the utility of the mass balance approach for estimating critical rate processes like PP in the absence of observations.

Effects of Nutrient Management Scenarios on Marine Eutrophication Indicators: A Pan-European, Multi-Model Assessment in Support of the Marine Strategy Framework Directive

A novel pan-European marine model ensemble was established, covering nearly all seas under the regulation of the Marine Strategy Framework Directive (MSFD), with the aim of providing a consistent assessment of the potential impacts of riverine nutrient reduction scenarios on marine eutrophication indicators. For each sea region, up to five coupled biogeochemical models from institutes all over Europe were brought together for the first time. All model systems followed a harmonised scenario approach and ran two simulations, which varied only in the riverine nutrient inputs. The load reductions were evaluated with the catchment model GREEN and represented the impacts due to improved management of agriculture and wastewater treatment in all European river systems. The model ensemble, comprising 15 members, was used to assess changes to the core eutrophication indicators as defined within MSFD Descriptor 5. In nearly all marine regions, riverine load reductions led to reduced nutrient concentrations in the marine environment. However, regionally the nutrient input reductions led to an increase in the non-limiting nutrient in the water, especially in the case of phosphate concentrations in the Black Sea. Further core eutrophication indicators, such as chlorophyll-a, bottom oxygen and the Trophic Index TRIX, improved nearly everywhere, but the changes were less pronounced than for the inorganic nutrients. The model ensemble displayed strong consistency and robustness, as most if not all models indicated improvements in the same areas. There were substantial differences between the individual seas in the speed of response to the reduced nutrient loads. In the North Sea ensemble, a stable plateau was reached after only three years, while the simulation period of eight years was too short to obtain steady model results in the Baltic Sea. The ensemble exercise confirmed the importance of improved management of agriculture and wastewater treatments in the river catchments to reduce marine eutrophication. Several shortcomings were identified, the outcome of different approaches to compute the mean change was estimated and potential improvements are discussed to enhance policy support. Applying a model ensemble enabled us to obtain highly robust and consistent model results, substantially decreasing uncertainties in the scenario outcome.

Contiguous Low Oxygen Waters between the Continental Shelf Hypoxia Zone and Nearshore Coastal Waters of Louisiana, USA: Interpreting 30 Years of Profiling Data and Three-Dimensional Ecosystem Modeling.

The multidecadal expansion of northern Gulf of Mexico continental shelf hypoxia is a striking example of the adverse effects of anthropogenic nutrient enrichment on coastal oceans. Increased nutrient inputs and widespread shelf hypoxia have resulted in numerous dissolved oxygen (DO) water quality problems in nearshore coastal waters of Louisiana. A large hydrographic dataset compiled from research programs spanning 30 years and the three-dimensional hydrodynamic-biogeochemical model CGEM (Coastal Generalized Ecosystem Model) were integrated to explore the interconnections of low DO waters across the continental shelf to nearshore coastal waters of Louisiana. Cross-shelf vertical profiles showed contiguous low DO bottom waters extending from the shelf to coastal waters nearly every year in the 30+ year time series, which were concurrent with strong cross-shelf pycnoclines. A threshold Brunt-Väisälä frequency of 40 cycles h-1 was critical to maintaining the cross-shelf subpycnocline layers and facilitating the formation of a contiguous low DO water mass. Field observations and model simulations identified periods of wind-driven bottom water upwelling lasting between several days to several weeks, resulting in both physical advection of oxygen-depleted offshore waters to the nearshore and enhanced nearshore stratification. Both the upwelling of low DO bottom waters and in situ respiration were of sufficient temporal and spatial extent to drive DO below Louisiana's DO water quality criteria. Basin-wide nutrient management strategies aimed at reducing nutrient inputs and shelf hypoxia remain essential to improving the nearshore coastal water quality across the northern Gulf of Mexico.

Early Life Stages of Fishes in Lake Taal, Philippines: Assessment and Implications for Biodiversity Management and Conservation

Lake Taal is the third largest lake in the Philippines and its fisheries provide livelihood to thousands of locals in its coastal areas. This study was conducted to recommend possible strategies and measures to conserve and protect the population of fishes, especially of the early life stages (ELS). The composition, abundance, and distribution of ELS and the environmental factors affecting these were investigated through monthly ichthyoplankton surveys and monitoring of water parameters, phytoplankton, and zooplankton abundances in 12 equidistant stations from January 2015 to December 2018. A total of 26,345 fish eggs and 9,140 fish larvae were collected, of which 88.9% of the fish larvae were morphologically identified into eight families, while the rest were unidentified. Families Terapontidae (44.5%) and Gobiidae (37.0%) numerically dominated the identified larvae catch. Distribution of the egg, yolk sac, and pre-flexion stages (ELS) significantly varied across stations. Three stations on the northern basin of the lake showed the highest fish egg abundance (731.82, 246.47, and 381.28 ind 100 m–3) while stations on the west, northwest, and eastern bay of the lake showed the highest abundance of fish larvae (153.76, 121.28, and 94.64 ind 100 m–3). The temporal distribution of ELS was highly associated with zooplankton, green algae, and salinity while spatial distribution was highly associated with the majority of the water parameters and chlorophyll a. Seasonal and annual distribution of ELS showed significant variation, which reveals possible spawning patterns of the identified fish larvae and the influence of varying environmental conditions to the distribution of ELS. Based on these, the identified possible spawning and larval foraging grounds are recommended as protected zones. Reduction of nutrient inputs to minimize changes in the lake trophic condition is also recommended.

Green hydrogen: The only oxygen and water balanced fuel

The use of any fuel depletes the oxygen content of the atmosphere, with one exception: hydrogen produced from water. Water electrolysis liberates oxygen from water in the precise stoichiometric ratio required to oxidise (and hence release energy from) the co-produced hydrogen. As a commercial fuel production process, electrolysis is unique in providing the oxidant as well as the fuel; electrolytic oxygen can thereby replenish the consumption of atmospheric oxygen due to hydrogen use. Furthermore, the amount of water consumed during electrolysis is reproduced when the hydrogen is oxidised. So the use of electrolysers and electrolytic hydrogen does not affect global oxygen and water resources: ‘green’ hydrogen may thus be described as the only oxygen and water balanced fuel. Conversely, the use of hydrogen derived from fossil fuels (with or without carbon capture and storage, CCS) depletes the oxygen resource and increases water vapour emissions to the atmosphere, which enhances the rate of global warming. Therefore, a worldwide multi-TW deployment of electrolysers could provide very substantial amounts of hydrogen for the energy system, and oxygen for the global ecosystem. This should be done in combination with other measures for combatting oxygen depletion (such as reducing combustion, increasing forestation, and reducing nutrient inputs to the ocean from sewage and agriculture). In this way the long-term objective should be to stabilise, or even increase slightly, the concentrations of atmospheric and aquatic oxygen, and possibly speed up the decay of atmospheric methane. Clearly the production-and-use of hydrogen derived from fossil fuels contravenes this objective, and should cease without delay.

The land use legacy effect: looking back to see a path forward to improve management

Water quality has suffered as humans have increased nutrient inputs across the landscape. In many cases, management actions to reduce nutrient inputs have not been met with concomitant ecosystem responses. These missed expectations are partly due to the continued slow delivery of nutrient-enriched groundwater pre-dating input reductions resulting from management actions. Land use legacies as expressed through this time lag are important to quantify in order to adjust management expectations. We present a novel coupling of nitrogen source maps with groundwater transport times to create a high-resolution (120 m) fully distributed estimate of the timing and magnitude of groundwater nitrogen deliveries to surface water across Michigan’s Lower Peninsula. This new view of the landscape has been designed around common management timelines for: elected officials looking to make a difference for re-election (<5 years), career managers hoping to see the fruits of their labor (5–30 years), and advocacy groups whose work can span generations (>30 years). One striking result is that after 100 years, in our study area, approximately 50% of the nitrogen that enters the groundwater system remains in transit. This means that actions taken now may not show the expected lower nitrogen loads to receiving ecosystems for decades to centuries. We show that differences in groundwater travel times create a heterogeneous patchwork over which managers can prioritize actions to best match their targeted response times. Across the highest nitrogen inputs in our study region, less than 10% had short enough groundwater legacies to match the management timeline of most government and agency work. Agricultural practices (manure and chemical fertilizer) are the main nitrogen contributors across the top three management classes; however, human contributions through septic tank effluent and lawn fertilizers contribute 5%–8% of nitrogen.

Nutrient removal and microbial community structure in an artificial-natural coupled wetland system

An artificial-natural coupled wetland was constructed at an estuary between an upstream river and a downstream lake to transport river water and reduce nutrient input load into a grass-type shallow lake. The removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) were as high as 43 % and 83 %, respectively. Their concentrations were reduced to 30.98 mg/L and 0.79 mg/L, respectively. The lotus pond had high microbial diversity and was key for water purification. It contributed 19 % and 49 % of the removal efficiencies of COD and TN, respectively. Most of the dominant microorganism in wetland were related to the transformation of C and N. Bacterial phyla containing phototrophic members accounted for three-quarters of the microorganisms and significantly contributed to bioactivity. Phylum Proteobacteria, the most abundant microbial species, were involved in both N and C cycling because of the metabolic versatility. The denitrification of the wetland depended on the classes Gammaproteobacteria, Deltaproteobacteria, Bacteroidia and Anaerolineae. Bacteria of the phyla Chloroflexi, Actinobacteria, Firmicutes, Spirochaetes, Bacteroidetes and class Alphaproteobacteria contributed to hydrocarbon mineralization and carbonate decomposition to promote C cycling. Therefore, this study provides insights to develop effective methods for reducing the risks of lake eutrophication and protecting the water ecological health.

Ongoing anthropogenic eutrophication of the catchment area threatens the Doñana World Heritage Site (South-west Spain)

Eutrophication is a major cause of wetland degradation worldwide. In recent decades, reductions in nutrient inputs have led to improvements in water quality in many rivers and lakes in central and northern Europe, but long-term trends are less clear in southern Europe. We conducted the first comprehensive study of water quality in Doñana (SW Spain), one of the most important wetland complexes in Europe and the Mediterranean region. The core area of Doñana is a large shallow, seasonal marsh (UNESCO World Heritage Site—WHS) that floods during rainy, cool winter months, then dries out during the summer. The marsh is fed by three main streams whose catchments are within a Biosphere Reserve but are impacted by greenhouses (for cultivating fruit, irrigated with groundwater), poorly treated urban wastewaters and tourism. From 2013 to 2016, we monitored nutrient (Total P, Total N, PO4−3, NH4+, NO3−, NO2−) and phytoplankton chlorophyll-a (chla) concentrations in surface waters of the Doñana marsh and the three main streams. We quantified changes in greenhouse cover since 1995 using satellite images. Nutrient concentrations in streams were consistently higher than in the marsh, particularly in the Partido and Rocina streams that regularly reached concentrations equivalent to a “bad physico-chemical status” under the EU Water Framework Directive (WFD), and whose catchments suffered a fivefold expansion of greenhouses from 1995 to 2016. The Partido was the most polluted stream, and the most affected by wastewater effluents, and had particularly high concentrations of NH4+ (Geometric Mean = 0.3 mg L−1) and NO2− (GM = 0.52 mg L−1) across seasons. Patterns in chla concentrations were less consistent, but streams (GM = 6.78 µg L−1) generally had higher concentrations than the marsh (GM = 4.27 µg L−1). Nutrient concentrations in spot samples within the marsh largely depended on a combination of evaporation (as revealed by higher stable isotope δ2H values in the water column) and spatial processes (concentrations increase close to stream entry points, where conductivity is lower). Anthropogenic nutrient pollution in entry streams is a serious problem in Doñana, with extensive stretches too toxic for fish. Reinforcement of policies aimed at reducing nutrient inputs to Doñana are urgently required to meet the biodiversity conservation and environmental objectives for the WHS and WFD, respectively. Paradoxically, the marsh is currently relied upon to purify the water entering from streams.

Resource partitioning across a trophic gradient between a freshwater fish and an intraguild exotic

AbstractThe introduction of exotic species has the potential to cause resource competition with native species and may lead to competitive exclusion when resources are limiting. On the other hand, information is lacking to predict under what alternate trophic conditions coexistence may occur. Comparing diets of native yellow perch Perca flavescens and nonindigenous white perch Morone americana, we examined variation in resource partitioning and body condition across a prominent longitudinal nutrient gradient in Lake Erie (north‐eastern United States, Canada). As measured with Analysis of Similarity and Schoener's index, diet similarity declined monotonically from west to east tracking declines in nutrients, productivity and relative abundance of both species. Additionally, diet similarity increased from spring through fall, following seasonal development of stratification and hypolimnetic hypoxia—phenomena which tend to increase spatial overlap between these species. Finally, relative weights of both species peaked in the Central Basin (relative weights &gt; 0.85), which, on average, had intermediate values of prey diversity, ecosystem trophic status and water clarity. Our results highlight that native yellow perch coexist with invasive white perch under a wide range of trophic conditions. Of importance to fishery managers, mesotrophy in the Central Basin correlated with the highest body conditions and intermediate prey resource partitioning, although the effect size was small and variable. While competitive exclusion appears unlikely, the goal of reducing nutrient inputs in Lake Erie could affect not only the distributions of both species but also stakeholder decisions about where to fish.

Relaciones entre el uso del suelo y fracciones de fósforo y nitrógeno en condiciones de flujo base de un arroyo pampeano

During the last decades, population growth and the associated intensification of anthropogenic activities (agriculture, industrialization and urbanization) has increased nutrient inputs to Pampean lotic bodies. However few studies have evaluated the influence of these changes on water quality. The objectives of this study were to determine nitrogen (N) and phosphorus (P) fractions, trophic status and nutrient limitation of a typical Pampean stream, and to compare nutrient contents and speciation with different land uses (urban/industrial versus agricultural). Stream water samples were obtained monthly between 2010 and 2012 from six locations along the Pergamino stream. The stream was highly productive (eutrophic/hypertrophic) and nutrient concentrations were greater than the environmental quality standards from different parts of the world as a result of point and diffuse source inputs in addition to the naturally high baseline nutrient concentrations. In the case of N, organic and particulate fractions predominated in sites surrounded by agriculture, while inorganic forms predominated in sites dominated by urban/industrial effluent discharges. Nutrients spatial variation along the Pergamino stream presented the lowest concentrations in the headwaters, the highest concentrations when crossing the city of Pergamino and intermediate values towards the mouth. In this basin, despite being located in the most important agricultural region of Argentina, urban and industrial point source discharges resulted in greater impairment of water quality than diffuse sources linked to agriculture. Between the city of Pergamino and the stream mouth, total N and P concentrations decreased by 50% as a result of dilution due to increased flow and other natural self-cleansing mechanisms. It is imperative to design a monitoring programme and to adopt management strategies designed to reduce nutrient input to avoid saturating the stream’s capacity to retain and process nutrient inputs.

Selective survival of Escherichia coli phylotypes in freshwater beach sand.

Escherichia coli is used as an indicator of fecal pollution at beaches despite evidence of long-term survival in sand. This work investigated the basis for survival of E. coli through field microcosm experiments and phylotypic characterization of more than >1400 E. coli isolated from sand, sewage, and gulls, enabling identification of long-surviving populations and environmental drivers of their persistence. Microcosms containing populations of E. coli from each source (n=176) were buried in the backshore of Lake Michigan for 45 & 96 days under several different nutrient treatments, including unaltered native sand, sterile autoclaved sand and baked nutrient depleted sand. Availability of carbon and nitrogen and competition with the indigenous community were major factors that influenced E. coli survival. E. coli Clermont phylotypes B1 and A were the most dominant phylotypes surviving seasonally (>6 weeks), regardless of source and nutrient treatment, whereas cryptic clade and D/E phylotypes survived over winter (>300 days). Autoclaved sand, presumably supplying nutrients through increased availability, promoted growth and the presence of the indigenous microbial community reduced this effect. Screening of 849 sand E. coli from four freshwater beaches demonstrated that B1, but also D/E, were the most common phylotypes recovered. Analysis by qPCR for the Gull2, Lachno3 and HB human markers demonstrated only 25% of the samples had evidence of gull waste and none of the samples had evidence of human waste. These findings suggest prevalence of E. coli in the sand could be attributed more to long term surviving populations than to new fecal pollution.IMPORTANCE Fecal pollution monitoring still relies upon the enumeration of E. coli, despite the fact that this organism can survive for prolonged periods and has been shown to be easily transported from sand into surrounding waters through waves and runoff, thus no longer represents recent fecal pollution events. Here, we experimentally demonstrate that regardless of host source, certain genetically distinct subgroups, or phylotypes, survive longer than others under conditions typical of Great Lakes beach sites. We found nutrients were a major driver of survival and could actually promote growth, and the presence of native microorganisms modulated these effects. These insights into the dynamics and drivers of survival will improve the interpretation of E. coli measurements at beaches and inform strategies that could focus on reducing nutrient inputs to beaches or maintaining a robust natural microbiome in beach sand.

Century-long records reveal shifting challenges to seagrass recovery.

Global losses over the 20th century placed seagrass ecosystems among the most threatened ecosystems in the world, with eutrophication, and associated deterioration of the submarine light environment identified as the main driver. Growing appreciation of the ecological and societal benefits of healthy seagrass meadows has stimulated efforts to protect and restore them, largely focused on reducing nutrient input to coastal waters. Here we analyze a unique data set spanning 135years on eelgrass (Zostera marina), the dominant seagrass of the northern hemisphere. We show that meadows in the Western Baltic Sea exhibited major declines relative to historic (1890-1910) reference due to the wasting disease in the 1930s followed by eutrophication peaking in the 1980s, but have only shown modest improvement despite major eutrophication mitigation, halving nitrogen input since the 1980s. Across the past century, we identified generally shallower colonization depths of eelgrass for a given submarine light penetration and, hence, increased apparent light requirements. This suggests that eelgrass recovery is limited by additional stressors. Our study indicates that bottom trawling and intense recent warming (0.5°C per decade, 1985-2018), which impact on deeper and shallower meadows, respectively, suppress eelgrass from fully recovering from eutrophication. Warming is most severe in shallow turbid waters, while clear-water areas offer eelgrass refugia from warming in deeper, cooler waters; but trawling can prevent eelgrass from reaching these refugia. Efforts to reduce nutrient input and thereby improve water clarity have been instrumental in avoiding a catastrophic loss of eelgrass ecosystems. However, local-scale future management must, in addition, reduce bottom trawling to facilitate eelgrass reaching deeper, cooler refugia, and increase resilience toward realized and further warming. Warming needs to be limited by meeting global climate change mitigation goals.

The case of Mar Menor eutrophication: State of the art and description of tested Nature-Based Solutions

The Mar Menor (SE Spain), the largest hypersaline coastal lagoon of the Mediterranean basin, suffers a severe eutrophication crisis due to the nutrients that receives from the Campo de Cartagena watershed, mainly nitrate from intensive agriculture. This paper updates the state of the art in relation with nutrient discharges to the Mar Menor, and summarizes results from different tested Nature-Based Solution (NBS). Specifically, we show i) results from a pilot plant with woodchip bioreactors for nitrate-enriched brine denitrification, and ii) the first results obtained in a pilot plant with bioreactors and constructed wetlands for treatment of agricultural drainage water and leachates, as well as other effluents. Nutrient discharges to the lagoon are highly variable and occur via drainage network, drains, stormwater pipes, direct groundwater discharges from the Quaternary aquifer, and others. For instance, between January 2017 and January 2018 measured daily superficial discharge (floods excluded) ofN-NO3− amounted from 119 kg d−1 to 1084 kg d−1. Estimations subsurface discharges ranged 815 to 3836 kg N-NO3− d−1 in 2018–2020. Field studies in coastal wetlands (e.g. inflow ≈20–30 mg N-NO3− L−1, removal ≈80–90%) and results from pilot plants with bioreactors (e.g. inflow ≈30–40 mg N-NO3− L−1, removal ≈90–95%) and constructed wetlands (e.g. inflow ≈30–40 mg N-NO3− L−1, removal ≈60–70%), showed the good performance of these systems for nutrient retention. Four strategies are considered for reducing nutrient inputs into the Mar Menor, which include a combination of nature-based solutions and best management practices. (i) Reducing the leaching of nitrate to the aquifer and export of nutrients and sediments following heavy rains by improving fertilization, and irrigation routines, and soil conservation measures in the agricultural fields. (ii) Development of effective and scalable tools for denitrification of nitrate-rich brine produced by on-farm desalination plants. (iii) Capture and treatment of polluted water discharged to the Mar Menor via hydrologic networks, subsurface flow, drainage ditches, and others. (iv) Preservation and restoration of coastal wetlands.

Spatiotemporal water quality variations and their relationship with hydrological conditions in Dongting Lake after the operation of the Three Gorges Dam, China

Identifying the spatiotemporal characteristics of water quality and related driving factors is essential for lake water quality management. To further understand the unique relationship between hydrological conditions and water quality in river-connected lakes, we analysed the spatiotemporal variations of water quality and hydrological factors in Dongting Lake from 1991 to 2018 and identified the effects of the operation of the Three Gorges Dam (TGD) on lake water quality. The total nitrogen (TN) and total phosphorus (TP) concentrations showed general increasing trends in the pre-TGD period, in contrast to a significant increasing TN trend and a decreasing TP trend in the post-TGD period, the latter of which was closely linked to a prominent decrease of water and suspended sediment discharge after the initiation of TGD operation. TN concentrations showed significant spatial variations during the study period, with the highest concentration in East Dongting Lake and the lowest concentration in West Dongting Lake. Nutrient inputs were the dominant pollution source determining the water quality of Dongting Lake; water discharge and water level were also important factors controlling the spatiotemporal variability of water quality. The contribution of the four tributaries to lake water quality was much greater than that of the three channels, accounting for 89.94–92.25% of N inputs and 74.10–75.85% of P inputs. Moreover, the contribution of the three channels to lake water quality decreased after TGD operation, mainly because of reduced nutrient input, water discharge, and suspended sediment discharge. This study indicates that controlling pollutant effluents in tributaries and monitoring hydrological conditions within the lake are the key factors necessary to improve the water quality in Dongting Lake and may provide a practical reference for water quality management in river-connected lakes worldwide.

Stable isotopes used to assess pollution impacts on coastal and marine ecosystems of Cuba and México

Stable isotopes of nitrogen (δ15N) have been widely used around the world to evaluate the impact of anthropogenic activities on marine ecosystems; however, in the Caribbean Sea countries, such as México and Cuba, they are rarely used. Inputs of nutrients related to urban development and tourist activities along the coasts of the Caribbean Sea have the potential to deteriorate their fragile marine ecosystems. The use of isotopic tools and elemental analysis in sentinel organisms would be useful to provide evidence of the impact generated by anthropogenic nutrients. Measurements of δ15N (‰), carbon and nitrogen content, and C:N ratios, were conducted in different sentinel groups (macroalgae, seagrasses, gorgonians, and corals) collected in five marine ecosystems with different nearby coastal development pressure in both countries. The selected ecosystems, ordered according to the level of coastal areas development (low to high), were: Jardines de la Reina (JR), Gulf of Ana Maria (GAM), Cayo Coco (CC), and Laguna Larga (LL) in Cuba, and Puerto Morelos (PM) in México. Results evidenced that the majority of sentinels inhabiting near the most developed coastal areas, in terms of population and tourism, showed higher N contents, lower C:N ratios and higher values of δ15N (e.g., PM and LL) than those near less developed coastal ecosystems (e.g., GAM and JR). Land-based nutrients from municipal wastewater constitute the primary source of N pollution. Because eutrophication represents a significant threat to the integrity of valuable coastal ecosystems, there is an urgent need to accelerate progress in wastewater treatment systems, in terms of capacity and efficiency, to significantly reduce nutrient inputs to coastal ecosystems. Otherwise, more negative changes and deteriorations to the health of coastal ecosystems, including coral reefs, are expected along the Mexican Caribbean and numerous key points of Cuba and other Caribbean countries.

First Comprehensive Quantitative Multi-Parameter Assessment of the Eutrophication Status from Coastal to Marine French Waters in the English Channel, the Celtic Sea, the Bay of Biscay, and the Mediterranean Sea

The first quantitative and comprehensive assessment of the eutrophication status from coastal to offshore French waters was performed within the Marine Strategy Framework Directive (MSFD descriptor 5) for the English Channel, the southern bight of the North Sea, the Celtic Seas, the Bay of Biscay and the Western Mediterranean Sea. Based on a combination of different data sources (in situ, satellite, and modeling products), a fully-integrated dataset was generated over the period 2010–2016. Using the best available knowledge on the eutrophication process and definition, the assessment procedure was implemented considering nutrient pressures, and direct and indirect effects of excessive inputs. The different steps of the assessment were: (i) Establishment of assessment levels and thresholds, (ii) development of methodology for aggregation and integration of data, and (iii) qualification of the Environmental Status. We investigated how reliable this assessment procedure was when considering other complementary information. Results highlighted that, despite efforts in recent decades to reduced nutrient inputs, the pressure on coastal marine ecosystems was still high. We discuss options for improving the coherence between MSFD and other similar approaches and associated monitoring programs. This study identifies areas where an increased monitoring effort is needed to improve the assessment and where environmental management actions are of priority.

Comparisons of nitrogen and phosphorus mass balance for tomato-, basil-, and lettuce-based aquaponic and hydroponic systems

Aquaponics is known to be one of the most efficient agriculture production systems by far; however, limited quantitative data are available on the level of efficiency, particularly in comparison to its counterpart, hydroponics. This study compared aquaponics with hydroponics to assess nitrogen (N) and phosphorus (P) distributions, N- and P-use efficiency (NUE and PUE), and potential environmental impacts. Cherry tomato, basil, and lettuce were cultured in recirculating tilapia (Oreochromis niloticus)-based aquaponic or stand-alone hydroponic systems over a 3-month period. N and P mass balances were developed by using N and P concentrations in fish feed, solid waste, wastewater, fish biomass, and plant biomass for aquaponic systems, and chemical fertilizer, wastewater, and plant biomass for hydroponic systems, which were to estimate N and P loss from each system via denitrification and P precipitations, respectively. In aquaponics, 59–70% of total N input was estimated to be lost via denitrification (45–50%), wastewater (14–20%), and solid waste (0.7–2%) and 30–41% was assimilated into biomass (21–24% fish; 9–17% plants). In hydroponics, 76–87% was estimated to be lost via denitrification (69–78%) and wastewater (7–15%), and only 14–24% was assimilated into biomass. Similarly, 38–54% of total P input in aquaponics was lost via wastewater (22–28%), precipitations (8–25%), and solid waste (2–7%) and 46–62% was assimilated into biomass (35–45% fish; 11–25% plants). In hydroponics, 79–89% of total P input was lost via wastewater (52–74%) and precipitations (15–27%), and only 11–21% was assimilated into plant biomass. Plant species had a significant impact on N and P distribution, and tomato was most effective in removing N from wastewater and reducing denitrification via higher biomass production compared to basil and lettuce. NUE was lower for aquaponics than for hydroponics when only edible plant parts were taken into consideration, but 71–114% higher when both fish and plant biomass were considered. Meanwhile, PUE was higher for aquaponics than for hydroponics even only when edible parts were considered and 336–369% higher when the biomass of both crops was considered. Our N and P mass balance analyses demonstrated for the first time that aquaponics is more efficient than hydroponics. Greater N and P losses in hydroponics were mainly due to higher N and P inputs, causing 2 times higher N loss via gas emission and up to 3 times higher P loss via inorganic P in wastewater compared to aquaponics. Therefore, reducing nutrient inputs is critical in improving NUE and PUE for both aquaponics and hydroponics, which should be combined with proper crop choice, operation conditions, and management practices to further improve the efficiency of the systems.

Plant architectural responses in simultaneous maize/soybean strip intercropping do not lead to a yield advantage

AbstractMaize/soybean strip intercropping is a commonly used system throughout China with high crop yields at reduced nutrient input compared to sole maize. Maize is the taller crop, and due to its dominance in light capture over soybean in the intercrop, maize is expected to outperform maize in sole cropping. Conversely, soybean is the subordinate crop and intercropped soybean plants are expected to perform worse than sole soybean. Crop plants show plastic responses in plant architecture to their growing conditions to forage for light and avoid shading. There is little knowledge on plant architectural responses to growing conditions in simultaneous (non‐relay) intercropping and their relationship to species yields. A two‐year field experiment with two simultaneous maize/soybean intercropping systems with narrow and wide strips was conducted to characterise architectural traits of maize and soybean plants grown as intercrop and sole crops. Intercropped maize plants, especially those in border rows, had substantially greater leaf area, biomass and yield than maize plants in sole crops. Intercropped soybean plants, especially those in border rows, had lower leaf area, biomass and yield than sole soybean plants. Overall intercrop performance was similar to that of sole crops, with the land equivalent ratio (LER) being only slightly greater than one (1.03–1.08). Soybean displayed typical shade avoidance responses in the intercrop, such as greater internode elongation and changes in specific leaf area, but these responses could not overcome the consequences of the competition with the taller maize plants. Therefore, in contrast to relay intercrop systems, in the studied simultaneous maize/soybean system, plastic responses did not contribute to practically relevant increases in resource capture and yield at whole system (i.e., intercrop) level.