Decrease In Nutrient Concentrations Research Articles

Natural and Engineered Ocean Inflow Projects to Improve Water Quality Through Increased Exchange

Globally, the health of coastal water bodies continues to be threatened by climate change and mounting anthropogenic pressures related to population increase and associated development. Land use changes have increased the direct runoff of freshwater, nutrients, and other contaminants from watersheds into coastal systems. Exacerbated by increased temperatures, these changes have contributed to a worldwide decline in seagrass coverage and losses of critical habitat and ecosystem functions. For restricted estuaries and lagoons, the influx of nutrients is particularly damaging due to high water residence times and impaired flushing. The result is eutrophication and associated declines in water quality and ecosystem function. To mitigate degraded water quality, engineered ocean–estuary exchanges have been carried out and studied with examples in Australia, New Zealand, India, Denmark, the Netherlands, Portugal, and the United States of America. Based on successes including decreased nutrient concentrations, turbidity, and chlorophyll and increased faunal abundance in some past studies, this option is considered as a management tool for combatting worsening water quality in other estuaries including the Indian River Lagoon, a subtropical, lagoon-type estuary on the central east coast of Florida, USA. Decreased residence times, lower nutrients, higher dissolved oxygen (DO), higher salinity, lower temperature, and lower turbidity all combine for improved ecosystem health. In this review, the successes and failures of past projects intended to increase ocean–estuary exchanges, including biological and geochemical processes that contributed to observed outcomes, are evaluated. The primary indicators of water quality considered in this review include nutrient contents (e.g., nitrogen and phosphorus) and dissolved oxygen levels. Secondary indicators include changes in temperature and salinity pre- and post- engineering as well as turbidity, which can also impact seagrass growth and overall ecosystem health. Each of the sites investigated recorded improvements in water quality, though some were more pronounced and occurred over shorter time scales. Overall, enhanced ocean exchange in restricted, impaired water bodies resulted in system-specific response trajectories, with many experiencing a net positive outcome with respect to water quality and ecosystem health.

Remarkable shifts in the megabenthic community structure over four decades in Tokyo Bay, Japan, in relation to environmental variations

We investigated long-term changes in the megabenthic community in Tokyo Bay, Japan, using data from fisheries-independent trawl surveys conducted from 1977 to 2023. In addition, we examined the potential relationship between changes in biotic communities and environmental conditions. The total abundance and biomass exhibited an increasing trend until 1987, followed by a substantial decline from the late 1980s to the 1990s due to a decrease in small to medium-sized fish and crustacean species. Meanwhile, a marked increase in the number of large fish (including elasmobranchs), mollusks, and echinoids, was observed in the 2000s. These shifts in the megabenthic community structure were correlated with an increase in water temperature and a decrease in nutrient concentrations and copepod densities. Cumulative evidence suggests that a remarkable shift in the megabenthic community structure occurred between the 1970s and the 2020s, which was possibly associated with variations in the environmental conditions in Tokyo Bay.

Drivers and resilience of methane-derived carbon contribution to chironomid biomass in boreal lakes

General mechanisms underlying the pathways of methane (CH4)-derived carbon in aquatic food webs are often associated with eutrophication-driven anoxia. Yet, the influence of changing nutrient availability on CH4 cycling has been mainly investigated during the increasing phase (i.e. onset of anthropogenic eutrophication), thus leaving unclear whether nutrient reduction can lead to a simple reversion of the observed effects on CH4 cycling. We combined stable isotopes of chironomid remains (δ13CHC) and sedimentary ancient DNA of methanotrophic bacteria (MOB) to unravel the drivers of biogenic CH4 contribution to chironomid biomass in boreal lakes. Using a spatial dataset, our study shows that δ13CHC values were more depleted in hypoxic lakes and were positively associated with methanotrophic bacteria belonging to the γ-proteobacteria class (MOB type I), therefore supporting the view of higher utilization of CH4-derived carbon in anoxic environments. However, this space-for-time substitution approach failed to provide any reliable information on whether lake food webs follow the same pathway in forward and reverse directions. Using downcore reconstruction, our results show that despite a drastic mitigation-induced decrease in nutrient concentrations and strong evidence of biological recovery of algal and chironomid communities, chironomid biomass remained highly subsidized by methanotrophic bacteria throughout the study period. Results therefore suggest that mechanisms underlying the pathways of CH4-derived carbon in aquatic food webs are likely not the same during perturbation and recovery trajectories and that complex feedback mechanisms can stabilize lakes in this CH4-based food web state.

Biological metasurfaces based on tailored Luria Bertani Agar growth medium formulations for photonic applications.

Biodegradablealternatives to classic solid-state components are rapidly taking place in front-end photonic systems like metamaterials, meta-surfaces and photonic crystals. From this point of view, numerous solutions have been proposed involving eco-friendly compounds. Among them, the Luria Bertani agar (LBA) growth medium has been recently proposed as a functional option with the remarkable advantage of allowing the growth of fluorescent protein expressing bacteria. Such a possibility promises to lead to development of a new generation of biological and eco-sustainable optical sources based on meta-surfaces. There is, however, still a main drawback to address, related to the highly scattering nature of these compounds. To ensure adequate nutritive elements for cell growth, LBA hosts several compounds like NaCl, yeast extracts and tryptone. The presence of these components leads to very scattering LBA films, thus hindering its performance as an optical polymer. A trade-off arises between nutritive capacity and optical performance. In this paper, we successfully address this trade-off, demonstrating that a reduction of the basic nutrients (net Agar concentration) of LBA largely enhances the optical properties of the film as a photonic polymer without compromising its cell-viability. We considered two new LBA formulations with two- (LB2A) and four-fold (LB4A) reduction of the nutrients and replicated a square-lattice meta-surface used as a benchmark architecture. We demonstrated that both the replica molding performances and the optical properties (absorption, scattering and diffraction efficiency) of LBA formulations increase with decreasing nutrient concentration, without losing their cell-growth capability. To demonstrate this fundamental aspect, we inoculated the most critical case of LB4A with green-fluorescent-protein-expressing E. coli bacteria, verifying both their vitality and good photoluminescence properties. These results overcome one of the main limitations of LBA as a functional biopolymer for optical applications, unlocking its use in a new generation of biological quantum optical frameworks for all-biological weak and strong light-matter interactions.

Long-term warming and human-induced plankton shifts at a coastal Eastern Mediterranean site

Plankton are key ecological indicators for assessing the impacts of human-induced pressures like climate change and waste-water discharge. Here, 26 years (1988–2015) of biweekly in-situ chlorophyll-a concentration, mesozooplankton biomass and remotely-sensed sea surface temperature (SST) data are utilized to investigate long-term changes of plankton biomass and timing of growth (phenology) in relation to warming, in a coastal region of the Saronikos Gulf (Aegean Sea). A Waste-Water Treatment Plant (WWTP) was established in 1995, leading to decreased nutrient concentrations circa 2004. Overall, the results indicate an interplay between warming and changes in ecological status. During higher nutrient input (1989–2004), a temporal mismatch between zooplankton and phytoplankton, and a positive zooplankton growth—SST association, are evident. Conversely, in the warmer, less mesotrophic period 2005–2015, an earlier timing of zooplankton growth (related to copepod abundance) synchronizes with phytoplankton growth, including a secondary autumn growth period. Concurrently, an abrupt negative interannual relationship between SST and mesozooplankton, and a summer biomass decrease (linked with cladoceran abundance) are observed. This work provides evidence that current warming could alter plankton abundance and phenology in nearshore Eastern Mediterranean ecosystems, suggesting shifts in plankton community composition that could trigger potential cascading effects on higher trophic levels.

Implementation and assessment of a model including mixotrophs and the carbonate cycle (Eco3M_MIX-CarbOx v1.0) in a highly dynamic Mediterranean coastal environment (Bay of Marseille, France) – Part 1: Evolution of ecosystem composition under limited light and nutrient conditions

Abstract. Many current biogeochemical models rely on an autotrophic versus heterotrophic food web representation. However, in recent years, an increasing number of studies have begun to challenge this approach. Several authors have highlighted the importance of protists capable of combining photoautotrophic and heterotrophic nutrition in a single cell. These mixotrophic protists are known to play an important role in the carbon cycle. Here, we present a new biogeochemical model that represents the food web using variable stoichiometry. It contains the classic compartments such as zooplankton, phytoplankton, and heterotrophic bacteria and a newly added compartment to represent two types of mixotrophic protists: non-constitutive mixotrophs (NCMs) and constitutive mixotrophs (CMs). We demonstrate that the model correctly reproduces the characteristics of NCMs and CMs and proceed to study the impact of light and nutrient limitation on planktonic ecosystem structure in a highly dynamic Mediterranean coastal area, namely the Bay of Marseille (BoM, France), paying special attention to the dynamics of mixotrophic protists in these limiting conditions. In addition, we investigate the carbon, nitrogen, and phosphorus fluxes associated with mixotrophic protists and showed the following: (i) the portion of the ecosystem in terms of the percentage of carbon biomass occupied by NCMs decreases when resources (nutrient and prey concentrations) decrease, although their mixotrophy allows them to maintain a carbon biomass almost as significant as the copepod one (129.8 and 148.7 mmol C m−3, respectively), as photosynthesis increases as a food source, and (ii) the portion of the ecosystem in terms of the percentage of carbon biomass occupied by CM increases when nutrient concentrations decrease due to their capability to ingest prey to supplement their N and P needs. In addition to providing new insights regarding the conditions that lead to the emergence of mixotrophs in the BoM, this work provides a new tool to perform long-term studies and predictions of mixotroph dynamics in coastal environments under different environmental forcings.

Conidia Fusion: A Mechanism for Fungal Adaptation to Nutrient-Poor Habitats.

Conidia fusion (CF) is a commonly observed structure in fungi. However, it has not been systematically studied. This study examined 2457 strains of nematode-trapping fungi (NTF) to explore the species specificity, physiological period, and physiological significance of CF. The results demonstrated that only six species of Arthrobotrys can form CF among the sixty-five tested NTF species. The studies on the model species Arthrobotrys oligospora (DL228) showed that CF occurred in both shed and unshed plus mature and immature conidia. Additionally, the conidia fusion rate (CFR) increased significantly with the decrease of nutrient concentration in habitats. The studies on the conidia fusion body (CFB) produced by A. oligospora (DL228) revealed that the more conidia contained in the CFB, the faster and denser the mycelia of the CFB germinated in weak nutrient medium and soil plates. On the one hand, rapid mycelial extension is beneficial for the CFB to quickly find new nutrient sources in habitats with uneven nutrient distribution. On the other hand, dense mycelium increases the contact area with the environment, improving the nutrient absorption efficiency, which is conducive to improving the survival rate of conidia in the weak nutrient environment. In addition, all species that form CF produce smaller conidia. Based on this observation, CF may be a strategy to balance the defects (nutrient deficiency) caused by conidia miniaturization.

Herbivory and warming have opposing short‐term effects on plant‐community nutrient levels across high‐Arctic tundra habitats

Abstract Environmental changes can rapidly alter standing biomass in tundra plant communities; yet, to what extent can they modify plant‐community nutrient levels? Nutrient levels and their changes can affect biomass production, nutrient cycling rates and nutrient availability to herbivores. We examined how environmental perturbations alter Arctic plant‐community leaf nutrient concentrations (percentage of dry mass, i.e. resource quality) and nutrient pools (absolute mass per unit area, i.e. resource quantity). We experimentally imposed two different types of environmental perturbations in a high‐Arctic ecosystem in Svalbard, spanning three habitats differing in soil moisture and plant‐community composition. We mimicked both a pulse perturbation (a grubbing event by geese in spring) and a press perturbation (a constant level of summer warming). After 2 years of perturbations, we quantified peak‐season nitrogen and phosphorus concentrations in 1268 leaf samples from the most abundant vascular plant species. We derived community‐weighted nutrient concentrations and total amount of nutrients (pools) for whole plant communities and individual plant functional types (PFTs). Spring grubbing increased plant‐community nutrient concentrations in mesic (+13%) and wet (+8%), but not moist, habitats, and reduced nutrient pools in all habitats (moist: −49%; wet, mesic: −31% to −37%). Conversely, summer warming reduced plant‐community nutrient concentrations in mesic and moist (−10% to −12%), but not wet, habitats and increased nutrient pools in moist habitats (+50%). Fast‐growing PFTs exhibited nutrient‐concentration responses, while slow‐growing PFTs generally did not. Grubbing enhanced nutrient concentrations of forbs and grasses in wet habitats (+20%) and of horsetails and grasses in mesic habitats (+19–23%). Conversely, warming decreased nutrient concentrations of horsetails in wet habitats (−15%) and of grasses, horsetails and forbs in moist habitats (−12% to −15%). Nutrient pools held by each PFT were less affected, although the most abundant PFTs responded to perturbations. Synthesis. Arctic plant‐community nutrient levels can be rapidly altered by environmental changes, with consequences for short‐term process rates and plant‐herbivore interactions. Community‐level responses in nutrient concentrations and pools were opposing and differed among habitats and PFTs. Our findings have implications for how we understand herbivory‐ and warming‐induced shifts in the fine‐scaled distribution of resource quality and quantity within and across tundra habitats.

Leveraging green infrastructure for efficient treatment of reclaimed water

Global water scarcity necessitates creative, yet practical, solutions to meet ever-growing demand. Green infrastructure is increasingly used in this context to provide water in environmentally friendly and sustainable ways. In this study, we focused on reclaimed wastewater from a joint gray and green infrastructure system employed by the Loxahatchee River District in Florida. The water system consists of a series of treatment stages for which we assessed 12 years of monitoring data. We measured water quality after secondary (gray) treatment, then in onsite lakes, offsite lakes, landscape irrigation (via sprinklers), and ultimately in downstream canals. Our findings show gray infrastructure designed for secondary treatment, integrated with green infrastructure, achieved nutrient concentrations nearly equivalent to advanced wastewater treatment systems. For example, we observed a dramatic decline in mean nitrogen concentration from 19.42 mg L−1 after secondary treatment to 5.26 mg L−1 after spending an average of 30 days in the onsite lakes. Nitrogen concentration continued to decline as reclaimed water moved from onsite lakes to offsite lakes (3.87 mg L−1) and irrigation sprinklers (3.27 mg L−1). Phosphorus concentrations exhibited a similar pattern. These decreasing nutrient concentrations led to relatively low nutrient loading rates and occurred while consuming substantially less energy and producing fewer greenhouse gas emissions than traditional gray infrastructure—at lower cost and higher efficiency. There was no evidence of eutrophication in canals downstream of the residential landscape whose sole source of irrigation water was reclaimed water. This study provides a long-term example of how circularity in water use can be used to work toward sustainable development goals.

Assessment of impacts of water transfer on lake flow and water quality in Lake Chaohu using a three-dimensional hydrodynamic-ecological model

Study regionLake Chaohu is a typically large shallow freshwater lake in China, experiencing long-term eutrophication and a short period of drought. Study focusThis study employs a three-dimensional (3-D) hydrodynamic-ecological model to assess the impacts of water transfer on lake flow, water quality, and their relationship, and then reveals optimal strategies for achieving improved water quality in Lake Chaohu. New hydrological insights for the regionResults indicated that clean water transfer could dramatically increase flow rate and decrease nutrient concentrations near the water transfer inlets, while the grade level of lake water quality is not changed. The degree of improvement in water quality parameters is not always proportional to lake flow rate. A clean water transfer through the eastern route (ZH) has the largest improvement effect on the average flow rate and water quality (total nitrogen (TN) and total phosphorus (TP)) of the entire lake. Winter water transfer improves TN and TP better than summer, while the opposite for ammonia nitrogen (NH3-N). Decrease of wind speed is essential for mitigating nutrient accumulation in western lake’s heavily polluted bay through weakening the reverse circulation and the northwest flow. Water transfer operations are revealed to improve water quality in Lake Chaohu: conduct water transfer through ZH in winter, strictly control NH3-N concentration in the donating water, and combine the effects of the low east wind.

Assessing the effectiveness of management measures in the Ria Formosa coastal lagoon, Portugal

The Ria Formosa is an important transitional and coastal lagoon on the south coast of Portugal that provides valuable ecosystem services. The lagoon is a protected area under national and international conventions. There is a great potential for Blue Growth sectors, such as aquaculture and coastal tourism, but these rely on good water quality. European environmental legislation, such as the Water Framework Directive, requires member states, such as Portugal to implement management measures if a surface water body is not of good ecological status. This work addresses the effectiveness of management measures, such as wastewater treatment plant implementation and dredging, on the water quality of the Ria Formosa coastal lagoon system. This is an important social-ecological issue, since management measures can be very expensive. The ecological status of Ria Formosa was evaluated, according to the physico-chemical and biological quality elements of the Water Framework Directive. The main indicators were the physico-chemical quality elements of nutrient and oxygen condition, and the biological quality element chlorophyll a, as a proxy for phytoplankton biomass, under the Water Framework Directive. The data for these quality elements from the Ria Formosa were analyzed for consistency with the classification for the Water Framework Directive water bodies. The data after the implementation of management measures was compared with historical data to evaluate if these measures had been effective. The relation between nutrient pressures, meteorological and hydrological conditions was addressed, especially rainfall and runoff. Results showed a decrease in nutrient concentration after the management interventions, despite the increase of population and intensifying agriculture in the catchment. The Ecological Status is spatially variable with an overall moderate status, indicating the need for further management measures. There is a significant reduction in nutrient pressure on the lagoon during drought years. This indicates that climate change may alter the structure and function of the lagoon in the future.

The tolerance of grapevine rootstocks to copper excess and to the use of calcium and phosphorus to mitigate its phytotoxicity.

High soil copper (Cu) concentrations in vineyards can cause phytotoxicity to grapevine rootstocks. In order to mitigate toxicity, the use of grapevine rootstock genetic variation and the application of amendments are possible strategies. The aim of this study is to assess the tolerance of grapevine rootstocks to Cu excess and whether phosphorus (P) and calcium (Ca) can reduce phytotoxicity caused by Cu. Grapevine rootstock seedlings were produced from selected stakes: Paulsen 1103 (Vitis berlandieri × Vitis rupestris); SO4 (Vitis berlandieri × Vitis riparia); IAC 572 ((Vitis Riparia × Vitis rupestris) × Vitis caribaea); and Isabel (Vitis labrusca). Seedlings were grown in nutrition solution added with the following treatments: 0.3µM Cu (control); 60µM Cu; 60µM Cu and 62mg L-1 P; 60µM Cu and 400mg L-1 Ca. High Cu concentration caused phytotoxicity in all rootstocks, impairing their growth and decreasing nutrient concentration and photosynthetic activity. P and Ca addition had positive effect on the photosynthetic activity of all rootstocks, although it was not enough to revert growth to levels comparable with controls. Overall, based on the results, the application of P and Ca was not efficient in mitigating Cu phytotoxicity in grapevine plants grown in solution. Isabel was the most sensitive rootstock to Cu phytotoxicity, whereas Paulsen 1103 and SO4 presented more tolerance and can be used, together with other management strategies, in contaminated vineyard areas. Therefore, careful genotype rootstock selection for use in high Cu soils is important, while Ca and P are not efficient mitigators of Cu toxicity.

Chlorophyll a variations and responses to environmental stressors along hydrological connectivity gradients: Insights from a large floodplain lake

Understanding the key drivers of eutrophication in floodplain lakes has long been a challenge. In this study, the Chlorophyll a (Chla) variations and associated relationships with environmental stressors along the temporal hydrological connectivity gradient were investigated using a 11-year dataset in a large floodplain lake (Poyang Lake). A geostatistical method was firstly used to calculate the hydrological connectivity curves for each sampling campaign that was further classified by K-means technique. Linear mixed effect (LME) models were developed through the inclusion of the site as a random effect to identify the limiting factors of Chla variations. The results identified three clear hydrological connectivity variation patterns with remarkable connecting water area changes in Poyang Lake. Furthermore, hydrological connectivity changes exerted a great influence on environmental variables in Poyang Lake, with a decrease in nutrient concentrations as the hydrological connectivity enhanced. The Chla exhibited contrast variations with nutrient variables along the temporal hydrological connectivity gradient and generally depended on WT, DO, EC and TP, for the entire study period. Nevertheless, the relative roles of nutrient and non-nutrient variables in phytoplankton growth varied with different degrees of hydrological connectivity as confirmed by the LME models. In the low hydrological connectivity phase, the Chla dynamics were controlled only by water temperature with sufficient nutrients available. In the high hydrological connectivity phase, the synergistic influences of both nutrient and physical variables jointly limited the Chla dynamics. In addition, a significant increasing trend was observed for Chla variations from 2008 to 2018 in the HHC phase, which could largely be attributed to the elevated nutrient concentrations. This study confirmed the strong influences of hydrological connectivity on the nutrient and non-nutrient limitation of phytoplankton growth in floodplain lakes. The present study could provide new insights on the driving mechanisms underlying phytoplankton growth in floodplain lakes.

Effect of Seychelles Dome intensity on nutrient supply to the mixed layer: Insights from a coupled physical-biological model

The seasonal and interannual variability in the vertical nutrient supply above the Seychelles Dome (SD) in the southwestern tropical Indian Ocean is examined using a high-resolution coupled physical-biological ocean model. Above the SD region, seasonal phytoplankton blooms occur from May to August (from Austral fall to early winter). This unique seasonal variability is caused by a significant increase in the nutrient concentration, which coincides with a significant deepening of the mixed layer depth. A nutrient budget analysis revealed that the seasonal nutrient variability in the mixed layer above the SD is controlled mainly by vertical processes, including entrainment and vertical diffusion during the blooming season. The sum of the vertical nutrient supply is nearly equivalent to what is biologically consumed and is consistent with satellite observations of the seasonal variation in surface chlorophyll. Additionally, the influence of the SD intensity on nutrient concentrations above the SD region was investigated at an interannual time scale. Composite analyses of the nutrient budget imply that nutrient concentrations decrease (increase) because of negative (positive) vertical diffusion anomalies from the Austral summer to early fall in weak (strong) SD years. This negative (positive) vertical diffusion anomaly is caused by a gentle (sharp) vertical nutrient gradient owing to the weaken (strengthen) subsurface SD. Conversely, seawater nutrients and surface chlorophyll concentrations during blooms do not differ significantly between years with weak and strong SDs because negative (positive) nutrient concentration anomalies formed by anomalous vertical diffusion in the Austral summer are not maintained as a result of a damping effect, which is a positive (negative) meridional nutrient advection anomaly during the early blooming season and can last several months. During these months, anomalous meridional nutrient gradient plays an important role by inducing a meridional nutrient advection anomaly via a southwestward Ekman transport forced by climatological trade winds. These anomalous meridional nutrient gradients are caused primarily by vertical diffusion anomalies during the Austral summer during the SD-event years. The results of this study imply that interannual variations in mixed layer nutrient concentrations and surface chlorophyll during the Austral summer are strongly related to the intensity of the subsurface SD via the vertical gradient of nutrients inside and below the mixed layer.

Effects of extreme water levels on nutrient dynamics in a large shallow eutrophic lake (Changhu Lake, China)

Changhu Lake, a large, shallow, eutrophic lake in central China, experienced an extremely low water level event from November 2015 to January 2016 followed by an extremely high water level event in July 2016. In this study, we examined the effects of two extreme water levels on the nutrient dynamics of Changhu Lake over five years. The nutrient parameters in Changhu Lake showed significant interannual variations, and the nutrient concentrations at the sites in the western part of Changhu Lake were 2–41% higher than those at the outlet of the lake. In late 2015, the effects of low water levels led to a 17–74% increase in nutrient concentrations. After July 2016, however, a high water level event occurred, leading to a 34–48% decrease in nutrient concentrations. These changes in nutrient parameters were strongly related to water level fluctuations (p < 0.05). As extreme water levels are likely to become more frequent during the twenty-first century, this work may provide some insights into the conservation and management of lake ecosystems in the face of climate change and human activity.

Nutrient streams in the North Pacific

The nutrient streams in the North Pacific were examined by analyzing the results derived from the inverse calculation of the World Ocean Circulation Experiment (WOCE)-revisit cruise data. The Kuroshio, Alaskan Stream, and Oyashio drive the most intensive nutrient transport within the basin. The upper portion of the nutrient stream (lighter than 26.2 kg/m3) contains mode waters and recirculates within the subtropical gyre, while the intermediate portion (26.2–27.15 kg/m3) relates to North Pacific Intermediate Water (NPIW) and contributes most to nutrient transport in the nutrient stream. The nutrient concentration in the nutrient stream increases in the subtropical gyre along the Kuroshio and Kuroshio Extensions but decreases in the subarctic gyre from the Alaskan Stream to the Oyashio region. This increase or decrease in nutrient concentration from the upstream region to the downstream region mainly results from lateral water exchange, although it also partly depends on biogeochemical processes and vertical diffusion. Specifically, the lateral exchange of the nutrient stream in the subarctic gyre with water from lower latitudes decreases the nitrate concentration of the Alaskan Stream and that with water from the Okhotsk Sea decreases the nitrate concentration of the Oyashio. For vertical nitrate transport, our estimation shows that the ventilation processes of subduction and induction are comparable to the sum of vertical advection and diffusion. This implies that nutrient transport related to the ventilation of the North Pacific is in a dynamic balance on an annual cycle and should be quantified in future work.

Effects of prolonged drought on water quality after drying of a semiarid tropical reservoir, Brazil

In semiarid regions is recurrent water depletion of some reservoirs during periods of prolonged drought, intensifying eutrophication. After water depletion events, new waters arrival and the trophic state improvement is expected. Therefore, the aim of this study was to evaluate the change of the trophic state after the reservoir’s drying due to a prolonged drought in the Brazilian semiarid region. It is expected that the trophic state improves after the water renewal by decreasing nutrient concentrations and algal biomass. This study was performed in a tropical, semiarid reservoir (Cruzeta Reservoir, Brazil), and was carried out during two different periods: 2012 (beginning of the prolonged drought) and 2019 (after the drying and reflooding). Analyses of Wilcoxon test and principal components analysis (PCA) were used to identify significant changes and patterns between the periods studied. The studied periods differed significantly (p < 0.05) with regard to maximum depth, pH, dissolved oxygen, conductivity, turbidity, inorganic and organic suspended solids, total phosphorus, soluble reactive phosphorus, nitrate and chlorophyll a. The hydrological regime of the Brazilian semi-arid region, governed by the prolonged drought period (from 2012 to 2019), contributed to significant changes in the volume and water quality in Cruzeta reservoir, increasing nutrients and algal biomass, intensifying the symptoms of eutrophication. Thus, contrary to the hypothesis of this study, despite the reflooding after the drought period, a worsening in the trophic state of the reservoir from eutrophic to hypereutrophic was observed.

Impacts of sediment resuspension on phytoplankton biomass production and trophic transfer: Implications for shallow lake restoration

Wind-induced sediment resuspension in shallow lakes may enhance nutrient availability while reducing light availability for phytoplankton growth, thereby affecting the entire food-web. Lake restoration projects that reduce wind-induced resuspension are expected to enhance trophic transfer efficiencies, thereby improving food-web structure and functioning. Yet, reduced resuspension may also lead to lower nutrient concentrations in the water column, promote benthic algae development, reduce phytoplankton biomass production and thereby reduce secondary production by zooplankton. Lake Markermeer is a shallow delta lake in The Netherlands subject to wind-induced sediment resuspension. Restoration project Marker Wadden consists of newly built islands aiming to reduce sediment resuspension and promote higher trophic levels. Here, we tested the effects of reduced sediment resuspension on phytoplankton biomass build-up, benthic algae development, and zooplankton abundances at different temperatures in a 14-day indoor microcosm experiment. We used Marker Wadden sediment with three resuspension intensities combined with three temperatures, to also test effects of higher temperatures in shallow sheltered waters. Reduced sediment resuspension decreased nutrient concentrations and phytoplankton biomass build-up, while increasing light availability and enhancing benthic algae biomass development. Reduced sediment resuspension furthermore increased zooplankton biomass. Enhanced sediment resuspension and higher temperatures synergistically interacted, maintaining a high level of inorganic suspended solids. Our experimental results are in line with long-term seasonal observations from Lake Markermeer. Our findings demonstrate that for shallow lakes suffering from wind effects, measures such as Marker Wadden aimed at reducing sediment resuspension can be effective in restoring secondary production and supporting higher trophic levels.

Long-Term Assessment of Surface Water Quality in a Highly Managed Estuary Basin.

Anthropogenic developments in coastal watersheds cause significant ecological changes to estuaries. Since estuaries respond to inputs on relatively long time scales, robust analyses of long-term data should be employed to account for seasonality, internal cycling, and climatological cycles. This study characterizes the water quality of a highly managed coastal basin, the St. Lucie Estuary Basin, FL, USA, from 1999 to 2019 to detect spatiotemporal differences in the estuary’s water quality and its tributaries. The estuary is artificially connected to Lake Okeechobee, so it receives fresh water from an external basin. Monthly water samples collected from November 1999 to October 2019 were assessed using principal component analysis, correlation analysis, and the Seasonal Kendall trend test. Nitrogen, phosphorus, color, total suspended solids, and turbidity concentrations varied seasonally and spatially. Inflows from Lake Okeechobee were characterized by high turbidity, while higher phosphorus concentrations characterized inflows from tributaries within the basin. Differences among tributaries within the basin may be attributed to flow regimes (e.g., significant releases vs. steady flow) and land use (e.g., pasture vs. row crops). Decreasing trends for orthophosphate, total phosphorus, and color and increasing trends for dissolved oxygen were found over the long term. Decreases in nutrient concentrations over time could be due to local mitigation efforts. Understanding the differences in water quality between the tributaries of the St. Lucie Estuary is essential for the overall water quality management of the estuary.

Effects of Loblolly Pine Biochar and Wood Vinegar on Poultry Litter Nutrients and Microbial Abundance.

Simple SummaryDeveloping a sustainable agroforestry system requires the utilization of byproducts. Poultry production and forestry are the two largest agricultural industries in Mississippi (USA) with loblolly pine being one of the most predominant timber species in the southeast. Poultry litter is a high-nutrient waste generated in poultry systems that is used as a fertilizer. However, poultry litter can release pollutants that reduce air and water quality and carries a heavy microbial load. Biochar and wood vinegar effects on nutrient retention and microbial activity vary due to the source material, production conditions, and application rate. This research evaluated how loblolly pine biochar and wood vinegar influence nutrients and microbial activity over time. The study found that wood vinegar reduced microbial growth in poultry litter-biochar blends. Fungi thrived in higher biochar proportions and bacteria preferred less biochar. Nitrogen and phosphorous were retained in 10% and 20% biochar blends. Furthermore, 10% and 20% biochar treatments were observed to be less odorous and compact, and the high pH of the biochar would be an effective conditioner for acidic soils. This study provides valuable information to stakeholders on how to utilize these materials to meet their objectives using regionally generated waste streams in the southeastern USA.Biochar, wood vinegar, and poultry litter are waste streams that can be utilized as soil amendments and fertilizers. However, poultry litter releases several pollutants through nutrient leaching and carries heavy microbial loads, including potential human pathogens. Improving nutrient retention and reducing microbial load in poultry litter may help protect environmental and human health and improve its value as a soil amendment. The objectives of this study were to determine how blending varying proportions of loblolly pine (Pinus taeda L.) biochar, wood vinegar, and poultry litter affected nutrient profiles and microbial abundance over time. Biochar inclusion rates were 0%, 5%, 10%, and 20%, and wood vinegar was applied at 2% w/w. Samples were taken at Day 0, 57, and 112 to measure nitrogen, phosphorus, potassium, pH, total fungi, and total bacteria. Nutrient levels generally decreased with increasing biochar level; however, biochar inclusion rates of 10% and 20% retained nitrogen and phosphorus and exhibited improved physical properties. Overall, adding wood vinegar decreased nutrient concentrations and showed a biocidal effect for bacteria and fungi. Bacteria and fungi showed different relationships with biochar inclusion rates, with fungi preferring higher biochar inclusion rates and bacteria flourishing at lower biochar inclusion rates.