Anthropogenic Nutrient Loading Research Articles

The in situ Production of Aquatic Fluorescent Organic Matter in a Simulated Freshwater Laboratory Model.

Dissolved organic matter (DOM) is ubiquitous throughout aquatic systems. Fluorescence techniques can be used to characterize the fluorescing proportion of DOM, aquatic fluorescent organic matter (AFOM). AFOM is conventionally named in association with specific fluorescence “peaks,” which fluoresce in similar optical regions as microbially-derived proteinaceous material (Peak T), and terrestrially-derived humic-like compounds (Peaks C/C+), with Peak T previously being investigated as a tool for bacterial enumeration within freshwaters. The impact of anthropogenic nutrient loading on the processing of DOM by microbial communities is largely unknown. Previous laboratory studies utilizing environmental freshwater have employed growth media with complex background fluorescence, or very high nutrient concentrations, preventing the investigation of AFOM production under a range of more representative nutrient concentrations within a matrix exhibiting very low background fluorescence. We describe a laboratory-based model with Pseudomonas aeruginosa that incorporates a low fluorescence growth matrix consisting of a simulated freshwater (SFW), representative of low-hardness freshwater systems allowing controlled nutrient conditions to be studied. The effects of microbial processing of DOM as a function of available nitrogen, phosphorous, and dissolved organic carbon (DOC) in the form of glucose were investigated over 48 h at highly resolved time increments. The model system demonstrates the production of a range of complex AFOM peaks in the presence and absence of DOC, revealing no linear relationship between cell numbers and any of the peaks for the bacterial species studied, with AFOM peaks increasing with microbial cell number, ranging from 55.2 quinine sulfate units (QSU) per 106 cells to 155 QSU per 106 cells (p < 0.05) for Peak T during the exponential growth phase of P. aeruginosa under high nutrient conditions with 5 mg L−1 DOC. Nutrient and DOC concentration was found to cause differential production of autochthonous- or allochthonous-like AFOM, with lower DOC concentrations resulting in higher Peak T production relative to Peaks C/C+ upon the addition of nutrients, and high DOC concentrations resulting in higher Peak C/C+ production relative to Peak T. Our results show the production of allochthonous-like AFOM from a simple and non-fluorescent carbon source, and provide uncertainty in the use of Peak T as a reliable surrogate for specific bacterial enumeration, particularly in dynamic or nutrient-impacted environments, pointing toward the use of fluorescence as an indicator for microbial metabolism.

Nutrient loading effects on fish habitat quality: Trade‐offs between enhanced production and hypoxia in Lake Erie, North America

Abstract Across diverse systems, nutrient loading from anthropogenic sources into aquatic systems has increased over the past century. Such nutrient inputs may enhance system productivity and thereby increase resource availability but may also lead to undesirable conditions such as hypoxic zones. We examined the habitat quality trade‐offs associated with increases in phosphorus in a model system (Lake Erie, North America) with a history of anthropogenic nutrient loading. Using a water quality model and a bioenergetics growth rate potential model with fine vertical and temporal resolution, we assessed how the quality of habitat for multiple species of adult and juvenile fish changed across a range of phosphorus loading scenarios and across 19 different meteorological years. Increases in phosphorus loading increased invertebrate prey biomass, but also increased the duration and extent of the mid‐summer hypoxic zone. In general, phosphorus loading caused overall habitat quality to decline and only increased peak habitat quality (i.e., spatio‐temporal locations where temperature and prey abundance were already above average), but responses were species‐ and life‐stage specific. One challenge in ascertaining the effects of nutrient loading on fish habitat quality is separating the negative effects of hypoxia from the potential positive effects of increased prey densities. Through various model scenarios, we evaluated the individual effects of hypoxia and increased prey availability on fish habitat quality, demonstrating their potentially counter‐balancing effects. That is, the negative effects of low oxygen on fish habitat quality appear more severe if the prospect that increased hypoxia is accompanied by altered prey densities is not accounted for. Despite modelled responses to altered phosphorus loads, habitat quality responded more strongly to variation in annual meteorological conditions. Annual meteorological conditions such as temperature, vertical mixing, and timing of phosphorus loading had a greater effect on habitat quality for all species and life‐stages than changes in annual amount of phosphorus loading. This limited effect of changes in phosphorus loading on habitat quality probably partially reflects our focus on short‐term (1‐year) changes in loading. Thus, nutrient abatement programmes may not lead to obvious, rapid positive habitat quality responses, as short‐term meteorological effects may overwhelm effects related to nutrient reduction and changes in prey densities may partially offset the benefits of decreased hypoxic conditions.

Morphological and biochemical responses of tropical seagrasses (Family: Hydrocharitaceae) under colonization of the macroalgae Ulva reticulata Forsskål.

BackgroundCoastal land development has deteriorated the habitat and water quality for seagrass growth and causes the proliferation of opportunist macroalgae that can potentially affect them physically and biochemically. The present study investigates the morphological and biochemical responses of seagrass from the Hydrocharitaceae family under the macroalgal bloom of Ulva reticulata, induced by land reclamation activities for constructing artificial islands.MethodsFive seagrass species, Enhalus acoroides, Thalassia hemprichii, Halophila ovalis, Halophila major, and Halophila spinulosa were collected at an Ulva reticulata-colonized site (MA) shoal and a non-Ulva reticulata-colonized site (MC) shoal at Sungai Pulai estuary, Johor, Malaysia. Morphometry of shoots comprising leaf length (LL), leaf width (LW), leaf sheath length (LSL), leaflet length (LTL), leaflet width (LTW), petiole length (PL), space between intra-marginal veins (IV) of leaf, cross vein angle (CVA) of leaf, number of the cross vein (NOC), number of the leaf (NOL) and number of the leaflet (NOLT) were measured on fresh seagrass specimens. Moreover, in-situ water quality and water nutrient content were also recorded. Seagrass extracts in methanol were assessed for total phenolic content (TPC), total flavonoid content (TFC), 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid radical cation scavenging activity (ABTS), and ferric reducing antioxidant power (FRAP).ResultsSeagrasses in the U. reticulata-colonized site (MA) had significantly higher (t-test, p < 0.05) leaf dimensions compared to those at the non-U. reticulata colonized site (MC). Simple broad-leaved seagrass of H. major and H. ovalis were highly sensitive to the colonization of U. reticulata, which resulted in higher morphometric variation (t-test, p < 0.05) including LL, PL, LW, and IV. Concerning the biochemical properties, all the seagrasses at MA recorded significantly higher (t-test, p < 0.05) TPC, TFC, and ABTS and lower DPPH and FRAP activities compared to those at MC. Hydrocharitaceae seagrass experience positive changes in leaf morphology features and metabolite contents when shaded by U. reticulata. Researching the synergistic effect of anthropogenic nutrient loads on the interaction between seagrasses and macroalgae can provide valuable information to decrease the negative effect of macroalgae blooms on seagrasses in the tropical meadow.

Long-term succession of Microcystis genotypes is driven by hydrological conditions and anthropogenic nutrient loading in a large shallow lake

Microcystis blooms that are caused by intensified human activities and global warming have become a challenging environmental problem in global lakes and reservoirs. Research has focused on Microcystis genotypes to understand their proliferation and the development of blooms, although knowledge gaps exist regarding how Microcystis genotype succession occurs over long-term time scales. In this study, high-throughput sequencing was used to investigate decade-long successional patterns of Microcystis genotypes in the large shallow Lake Chaohu that has long suffered from Microcystis blooms. Microcystis populations exhibited high overall genetic diversity, with 11,431 genotypes, and these were relatively stable over the last ∼70 years, with 339 shared core genotypes and 1 dominant genotype. Microcystis genotype succession exhibited three distinct historical phases corresponding to 1944–1960, 1964–1973, and 1976–2015. These successional patterns were clearly influenced by dam construction in 1963, and subsequent nutrient enrichment following the 1970 s. After dam construction, increased hydraulic retention times and slowing of hydrodynamic conditions influenced Microcystis genotype diversity by altering population composition and decreasing genotype richness. Populations and dominant genotypes rapidly returned after dam construction, combined with increased inferred interactions among genotypes. Network analysis also indicated that low abundance Microcystis genotypes, rather than dominant genotypes, may be keystone taxa across the decadal-scale co-occurrence network of Microcystis population.

Recognizing novel cyanobacterial diversity in marine benthic mats, with the description of Sirenicapillariaceae fam. nov., two new genera, Sirenicapillaria gen. nov. and Tigrinifilum gen. nov., and seven new species

ABSTRACT Marine benthic proliferations are increasing in occurrence, range and duration by way of anthropogenic nutrient loading and climate change. The spread of these cyanobacteria within a variety of regions has made it fundamental to recognize the diversity and the species involved in these blooms. To expand knowledge on marine cyanobacterial diversity and reveal their phylogenetic relationships, sampling and isolation of benthic proliferative events from underexplored regions were conducted in the USA (Florida) and France (Loire-Atlantique). Cyanobacteria were described with the polyphasic approach using morphology, 16S rRNA gene phylogeny, 16S–23S rRNA ITS secondary structures and pairwise distances. Sampling of marine cyanobacteria from seagrasses, lagoons and marine coastal waters from nine Florida localities, in addition to Florida freshwater canals and French salt flats, revealed floating, epipsammic and epiphytic mats. A total of 30 cyanobacteria were isolated of which 21 represented two novel genera, Sirenicapillaria and Tigrinifilum. Sirenicapillaria is a genus that is found in massive benthic blooms throughout the western and southern Florida Coast.

Responses of the benthic environment to reduction in anthropogenic nutrient loading in the Seto Inland Sea (Japan), based on M-AMBI assessment

Deterioration of the sediment environment and benthic ecosystem is an undesirable effect of eutrophication, but little is known about the response of macrobenthic communities to eutrophication and their long-term recovery. In the present study, temporal changes in benthic ecological status, associated with reductions in anthropogenic impacts on a largest semi-enclosed sea in Japan, were determined using long-term monitoring data from water and sediment quality based on the multivariate AZTI Marine Biotic Index (M-AMBI), focusing on spatial differences in anthropogenic impacts. Several sub-areas were classified based on Chlorophyll a (Chl.a) concentrations in surface water during the 1980s. Chl.a concentrations decreased in all sub-areas except the sub-area with <2 μg Chl.a L−1 from the 1990s–2010s. On the other hand, total organic carbon contents in sediment decreased and M-AMBI values increased in all sub-areas during this period may be due to reduced lateral organic matter advection from surrounding areas.

Globally consistent assessment of coastal eutrophication

Eutrophication is an emerging global issue associated with increasing anthropogenic nutrient loading. The impacts and extent of eutrophication are often limited to regions with dedicated monitoring programmes. Here we introduce the first global and Google Earth Engine-based interactive assessment tool of coastal eutrophication potential (CEP). The tool evaluates trends in satellite-derived chlorophyll-a (CHL) to devise a global map of CEP. Our analyses suggest that, globally, coastal waters (depth ≤200 m) covering ∼1.15 million km2 are eutrophic potential. Also, waters associated with CHL increasing trends—eutrophication potential—are twofold higher than those showing signs of recovery. The tool effectively identified areas of known eutrophication with severe symptoms, like dead zones, as well as those with limited to no information of the eutrophication. Our tool introduces the prospect for a consistent global assessment of eutrophication trends with major implications for monitoring Sustainable Development Goals (SDGs) and the application of Earth Observations in support of SDGs.

Ecological Importance of Alkaline Phosphatase Activity in Changing Marine Environmental Conditions

The effects of changing hydrological and climatic conditions on the dynamics of phosphorus (P) were studied in the Northern Adriatic Sea (NA), a coastal system currently affected by these changes. P limitation is one of the key stresses in the NA and it is a globally important phenomenon in aquatic ecosystems. Therefore, the response to P stress by inducing alkaline phosphatase activity (APA) was studied in characteristic water types in the NA, formed by the changing freshwater input in different thermic conditions. APA was important in providing P for microbial growth in upper waters dominated by assimilation during the warmer part of the year in stratified conditions. Contrarily, APA was not important during mixing in the colder part of the year, as well as in waters dominated by regeneration. In waters influenced by freshwater, temperature had no effect on APA, while in high-salinity waters, temperature was an important factor for APA increase. The highest APA occurred during riverine nutrients supply, indicating that the alteration of anthropogenic nutrient loads might strongly change P status in this coastal system. Furthermore, predicted increases in winter sea temperature and summer Po River discharge could delay the water column mixing, prolonging periods of P limitation.

Biogeochemical and Hydrological Drivers of Heterogeneous Nutrient Exports From Subterranean Estuaries

Submarine groundwater discharge (SGD) to coastal zones contributes terrestrial freshwater and nutrients that may support harmful algal blooms (HABs). The magnitude of nutrient exports via SGD depends on volumes of fresh groundwater discharge, its chemical composition, and modifications by biogeochemical processing within subterranean estuaries. Thus, the ability to upscale SGD exports requires knowing the range of chemical composition of inland groundwater and how those compositions may be transformed as fresh and saltwater mix within subterranean estuaries. These processes may create heterogeneous magnitudes of solute exports, even at small spatial scales, and such heterogeneities have rarely been assessed for regional or global SGD nutrient export estimates. To evaluate heterogeneity in subterranean estuary processes and nutrient export, we collected seasonal pore water samples in 2015–2016 at three proximal (&amp;lt;20 km) subterranean estuary sites in Indian River Lagoon, FL. Sites have homogenous hydrogeological settings, but differ in land use and coastal features, and include a mangrove site, an urban site, and a site offshore of a natural wetland. All sites exhibit little variation through time in nutrient concentrations and modeled SGD rates. In contrast, each site exhibits significantly different nutrient concentrations of potential fresh groundwater sources, fresh groundwater discharge volumes, and nutrient transformations within subterranean estuaries. Groundwater specific discharge correlates with nutrient concentrations, suggesting that higher residence times in the subterranean estuary increase biogeochemical transformations that reduce anthropogenic nutrient loads but increase in situ nutrient sources derived from organic matter remineralization. The differences in transformations lead to SGD nutrient contributions that differ by orders of magnitude between sites and have N:P ratios that are greater than the Redfield ratio (15) for the mangrove (29) and urban sites (28), but less than the Redfield ratio for the wetland site (8). These results indicate that heterogeneity of both absolute and relative nutrient export via SGD complicates integration of nutrient fluxes across regional coastal zones and evaluations of its impacts to coastal ecosystems. A better understanding of the drivers of heterogeneity, including subterranean estuary processes, land use, coastal topography, and vegetation dynamics could improve assessments of regional nutrient loading and upscaling for estimates of global solute cycles.

Homogenization of reservoir eukaryotic algal and cyanobacterial communities is accelerated by dam construction and eutrophication

Extensive construction of dams and increased human activities have greatly accelerated the homogenization of regional biotic communities. The cumulative effects caused by dams and anthropogenic nutrient loading on the temporal turnover of phytoplankton communities are largely unexplored, but of critical conservation importance for understanding reservoir ecosystem functioning. Here, biodiversity patterns in eukaryotic algal and cyanobacterial communities were investigated in a large reservoir over the last ~80 years by sequencing DNA preserved in sediment cores. The succession of eukaryotic algal and cyanobacterial communities recovered by sequencing of rRNA gene markers exhibited a high degree of consistency, with both showing evidence for significant changes in the 1970’s and 2000’s based on univariate and multivariate analyses. Temporal turnover indicated a marked loss of the taxonomic and phylogenetic structures of communities, which became more similar through time due to the homogenous reservoir environment and concomitant ecological pressures from human activities. Specifically, temporal homogenization of algal communities could be attributed to the damming of the reservoir in the 1960s that then affected the hydrological conditions of the reservoir and nutrient retention, with increased anthropogenic nutrient loading favoring the growth of specific taxa like Microcystis, as evidenced from Random Forest machine learning and ecological network analyses. Thus, these results demonstrate accelerated homogenization of algal communities in the reservoir due to the impacts of damming and nutrient enrichment. These observations also call for a need to develop conservation strategies to maintain ecosystem resilience and prevent harmful blooms in reservoir systems.

Hortonian Scaling of Coupled Hydrological and Biogeochemical Responses Across an Intensively Managed River Basin

Structural and functional attributes across fractal river networks have been characterized by well-established and consistent hierarchical, Hortonian scaling patterns. In most of the global river basins, spatial patterns of human settlements also conform to similar hierarchical scaling. However, emergent spatial hierarchical patterns and scaling of heterogeneous anthropogenic nutrient loads over a river basin are less known. As a case study, we examined here a large intensely managed river basin in Germany (Weser River; 46K km2; 8M population). Archived data for point-/diffuse-sources of total Phosphorus (Ptot) input loads were combined with numerical and analytical model simulations of coupled hydrological and biogeochemical processes for in-stream Ptot removal at the network scale. We find that Ptot input loads scale exponentially over stream-orders, with the larger scaling constant for point-source loads from urban agglomerations compared to those for diffuse-source contributions from agricultural and forested areas. These differences in scaling patterns result from hierarchical self-organization of human settlements, and the associated clustering of large-scale, altered land-cover. Fraction of Ptot loads removed through in-stream biogeochemical processes also manifests Hortonian scaling, consistent with predictions of an analytical model. Our analyses show that while smaller streams are more efficient in Ptot removal, in larger streams the magnitude of Ptot loads removed is higher. These trends are consistent with inverse scaling of nutrient removal rate constant with mean discharge, and downstream clustering of larger cumulative input loads. Analyses of six nested sub-basins within the Weser River Basin also reveal similar scaling patterns. Our findings are useful for projecting likely water-quality spatial patterns in similar river basins in Germany, and Central Europe. Extensions and generalizations require further examination of diverse basins with archetype spatial heterogeneities in anthropogenic pressures and hydroclimatic settings.

The effect of natural and anthropogenic nutrient and sediment loads on coral oxidative stress on runoff-exposed reefs

Recently, corals on the Great Barrier (GBR) have suffered mass bleaching. The link between ocean warming and coral bleaching is understood to be due to temperature-dependence of complex physiological processes in the coral host and algal symbiont. Here we use a coupled catchment-hydrodynamic-biogeochemical model, with detailed zooxanthellae photophysiology including photoadaptation, photoacclimation and reactive oxygen build-up, to investigate whether natural and anthropogenic catchment loads impact on coral bleaching on the GBR. For the wet season of 2017, simulations show the cross-shelf water quality gradient, driven by both natural and anthropogenic loads, generated a contrasting zooxanthellae physiological state on inshore versus mid-shelf reefs. The relatively small catchment flows and loads delivered during 2017, however, generated small river plumes with limited impact on water quality. Simulations show the removal of the anthropogenic fraction of the catchment loads delivered in 2017 would have had a negligible impact on bleaching rates.

Low denitrification rates and variable benthic nutrient fluxes characterize Long Island Sound sediments

Organic matter (OM) loading drives benthic metabolism and controls nitrogen (N), phosphorus (P), and carbon (C) cycling in coastal sediments. To better understand the influence of OM on benthic metabolism, we conducted sediment core incubations in Long Island Sound, NY (USA), an estuary heavily influenced by anthropogenic nutrient loading. Cores were collected during the summer and winter at five stations along a west to east transect representing a gradient of high to low nutrient inputs and subsequent OM deposition. Here we provide a comprehensive analysis of environmental drivers of benthic fluxes as well as the first directly measured rates of sediment denitrification and N-fixation, thus providing a missing piece of the N budget for Long Island Sound. Our findings show greatest sediment oxygen demand (SOD) in the western basin during the summer. Sediments were a source of dissolved inorganic N and P. Compared to historic SOD and ammonium fluxes, our measurements were about 50% lower, potentially reflecting larger scale perturbations (e.g., warming temperatures, decrease wind speed) or reduced N loading through improved management of wastewater treatment facilities. Sediments were a source of nitrous oxide (mean (± standard error): 8.63 ± 3.18 nmol m−2 h−1) and methane (23.80 ± 18.05 nmol m−2 h−1). Net sediment denitrification rates were low (10.34 ± 7.61 µmol N2–N m−2 h−1) and did not vary significantly across stations or seasons. These sediments have a N removal efficiency of ~ 30% with the potential to remove approximately 9% of the total land-based N load entering Long Island Sound.

Can nutrient uptake by Carex counteract eutrophication in fen peatlands?

Ground- and surface-water-fed peatlands (i.e., fens) of temperate Europe face high anthropogenic nutrient loads from atmospheric deposition, agricultural catchment areas, and from peat decomposition, if drained. As a result, nitrogen loads may exceed a fen's natural nutrient removal capacity, leading to increased eutrophication of adjacent water bodies. Therefore, it is important to address possible means to decrease a fen's nutrient load, including nutrient uptake by fen plants. To assess how much fen plants can contribute to nutrient removal by uptake, nutrient stocks of above- and below-ground biomass need to be quantified. Therefore, we investigated nitrogen, phosphorous, and potassium uptake capacities of sedges (Carex species), which are common dominants in fen plant communities. We grew specimens of five Carex species with varying preferences in nutrient availability under controlled, different nutrient levels. We show that Carex above-ground biomass harvest can remove up to one third of a system's total nitrogen even at high loads of about 40 g nitrogen m−2. Species-specific differences in biomass production, rather than preferences in nutrient availability under natural conditions, were drivers of standing nutrient stocks: Highly productive species, i.e., C. acutiformis and C. rostrata, had highest nutrient standing stocks across all nutrient levels. Amounts of nutrients stored in shoots increased almost linearly with increasing nutrient levels, whereas below-ground nutrient stocks species-specifically increased, saturated, or decreased, with increasing nutrient levels. As a rough estimate, depending on the species, 6–16 cycles of annual above-ground harvest would suffice to decrease nitrogen concentrations from the highest to the lowest level used in this study. Overall, our results indicate that Carex biomass harvest can be an efficient means to counteract anthropogenic nitrogen eutrophication in fens.

Anthropogenic nutrient loads and season variability drive high atmospheric N2O fluxes in a fragmented mangrove system

Fragmented mangroves are generally ignored in N2O flux studies. Here we report observations over the course of a year from the Mangalavanam coastal wetland in Southern India. The wetland is a fragmented mangrove stand close to a large urban centre with high anthropogenic nitrogen inputs. The study found the wetland was a net source of N2O to the atmosphere with fluxes ranging between 17.5 to 117.9 µmol m−2 day−1 which equated to high N2O saturations of between 697 and 1794%. The average dissolved inorganic nitrogen inputs (80.1 ± 18.1 µmol L−1) and N2O emissions (59.2 ± 30.0 µmol m−2 day−1) were highest during the monsoon season when the rainfall and associated river water inputs and terrestrial runoff were highest. The variation in N2O dynamics was shown to be driven by the changes in rainfall, water column depth, salinity, dissolved oxygen, carbon, and substrate nitrogen. The study suggests that fragmented/minor mangrove ecosystems subject to high human nutrient inputs may be a significant component of the global N2O budget.

Simulating algal dynamics within a Bayesian framework to evaluate controls on estuary productivity

The Neuse River Estuary (North Carolina, USA) is a valuable ecosystem that has been affected by the expansion of agricultural and urban watershed activities over the last several decades. Eutrophication, as a consequence of enhanced anthropogenic nutrient loadings, has promoted high phytoplankton biomass, hypoxia, and fish kills. This study compares and contrasts three models to better understand how nutrient loading and other environmental factors control phytoplankton biomass, as chl-a, over time. The first model is purely statistical, while the second model mechanistically simulates both chl-a and nitrogen dynamics, and the third additionally simulates phosphorus. The models are calibrated to a multi-decadal dataset (1997–2018) within a Bayesian framework, which systematically incorporates prior information and accounts for uncertainties. All three models explain over one third of log-transformed chl-a variability, with the mechanistic models additionally explaining the majority of the variability in bioavailable nutrients (R2 > 0.5). By disentangling the influences of riverine nutrient concentrations, flows, and loadings on estuary productivity we find that concentration reductions, rather than total loading reductions, are the key to controlling estuary chl-a levels. The third model indicates that the estuary, even in its upstream portion, is rarely phosphorus limited, and will continue to be mostly nitrogen limited even under a 30% phosphorus reduction scenario. This model also predicts that a 10% change in nitrogen loading (flow held constant) will produce an approximate 4.3% change in estuary chl-a concentration, while the statistical model suggests a larger (10%) effect. Overall, by including a more detailed representation of environmental factors controlling algal growth, the mechanistic models generate chl-a forecasts with less uncertainty across a range of nutrient loading scenarios. Methodologically, this study advances the use of Bayesian methods for modeling the eutrophication dynamics of an estuarine system over a multi-decadal period.

Understanding the origins of herbicides metabolites in an agricultural watershed through their spatial and seasonal variations

The aim of this study is to understand the spatial and seasonal variations of persistent herbicides metabolites and to determine their origins in the Vilaine River watershed, Britany-France. Improving knowledge on herbicides metabolites sources and seasonality is important for drinking water resource management. Data were collected at 13 sampling stations during five sampling campaigns in 2016 and 2017. Relations between water quality parameters, herbicides and metabolites were analyzed using statistical methods. The influence of land use and wastewater treatment plants (WWTP) on streams water quality has been identified. Cluster Analysis revealed that two groups of sampling stations can be described as “urban” with stations downstream the urban area and as “agricultural” with stations located downstream of the watershed. Chloroacetamids metabolites have been associated together with nitrates and agricultural areas as could be expected. Thus, the drinking water treatment plant located in the estuary of the Vilaine River is exposed to high metolachlor ESA and nitrate loads all year long. Aminomethylphosphonic acid (AMPA) is associated to anthropogenic urban contamination and nutrient loads. AMPA has its major sources in both glyphosate and phosphonate detergents issued from WWTP. This can help to adapt surface water treatment process and water management policies concerning herbicides metabolites.

Contrasting Raz–Rru stream metabolism and nutrient uptake downstream of urban wastewater effluent sites

Understanding how key stream ecosystem functions respond to wastewater treatment plant effluent is critical for assessing the ability of stream ecosystems to ameliorate anthropogenic nutrient loading and to effectively manage and restore impacted systems. We evaluated instream metabolism, reactive solute transport, and nutrient uptake along two 1.5 to 2-km-long reaches of a 2nd-order stream in the urbanized suburbs of Philadelphia, Pennsylvania, USA, each directly downstream of a wastewater treatment plant outfall. We compared metabolism based on resazurin–resorufin (Raz–Rru) with nutrient uptake and dissolved oxygen (DO) metabolism calculations. Plateau co-injections of the Raz–Rru metabolic tracer system and fluorescein provided integrated stream metabolism measurement. We sampled tracer concentrations hourly along longitudinal profiles and recorded them continuously, along with DO, at 2 discrete locations. The smaller reach 1, characterized by higher nutrient concentrations and canopy cover, had higher short-term transient storage and Raz uptake velocity. In contrast reach 2, with lower nutrient concentrations and less canopy cover, had higher nitrate and phosphorus uptake along with higher rates of gross primary productivity (GPP) and ecosystem respiration (ER). Temporal analysis indicated nitrate uptake increased over the afternoon at reach 2, whereas Raz uptake declined at both reaches. Our results suggest that nutrient uptake and GPP are sensitive to excessive nutrient concentrations and light in our system. In contrast, lower light and higher transient storage are likely driving larger, reach-scale spatial differences in Raz-based ER. Increasing nitrate uptake at reach 2, which lags behind diel DO concentrations, is likely the result of assimilatory N uptake coupled to GPP moderated by nitrification and denitrification, whereas decreasing rates of Raz transformation are likely related to diel variation in heterotrophic uptake. Our ability to resolve sub-daily changes in ER illustrates one of the key advantages of the Raz–Rru tracer system. However, our results also show the need for further investigation into the drivers of sub-daily ecosystem metabolism in streams as well as the mechanistic differences between DO- and Raz-based estimates of ER. Contrasting results from different measures of metabolic activity between reaches and over time highlight the complexity of metabolic processes in high-nutrient systems.

Species-level associations of phytoplankton with environmental variability in the Neva Estuary (Baltic Sea)

Changes in phytoplankton communities due to anthropogenic nutrient load and climate change often lead to eutrophication and harmful algal blooms that can affect biogeochemical cycling. However, little is known about the specific responses of various species to environmental variables. 17-year long data on the midsummer phytoplankton biomass in the Neva Estuary were analyzed to show the changes in the composition of phytoplankton in relation to water depth, transparence, salinity, temperature, concentrations of total phosphorus and chlorophyll a, and plankton primary production. One hundred seventy-four species and forms from eight taxonomic classes were found in phytoplankton. Fifteen species were potentially harmful. The most diverse and abundant groups were cyanobacteria, green algae and diatoms. Canonical Correspondence Analysis showed that the biomass of various species from each phytoplankton group correlated differently with environmental factors. However, within each group, there were some predominant trends in the correlative response to changes in environmental variables. The biomass of cyanobacteria was high in the middle and lower reaches of the estuary and, in general, positively correlated with water salinity. The biomass of most species of green algae and diatoms correlated negatively with it. These algae showed a positive trend in biomass in the upper and middle reaches of the estuary during the last decades that may be explained by changes in weather conditions. Taking into account that climate models predict future increases in precipitation and temperature in the northern Baltic, the future expansion of freshwater phytoplankton species in estuaries of the northern Baltic Sea is very likely.

Landscape-scale patterns of nutrient enrichment in a coral reef ecosystem: implications for coral to algae phase shifts.

Nutrient pollution is altering coastal ecosystems worldwide. On coral reefs, excess nutrients can favor the production of algae at the expense of reef-building corals, yet the role of nutrients in driving community changes such as shifts from coral to macroalgae is not well understood. Here we investigate the potential role of anthropogenic nutrient loading in driving recent coral-to-macroalgae phase shifts on reefs in the lagoons surrounding the Pacific island of Moorea, French Polynesia. We use nitrogen (N) tissue content and stable isotopes (δ15 N) in an abundant macroalga (Turbinaria ornata) together with empirical models of nutrient discharge to describe spatial and temporal patterns of nutrient enrichment in the lagoons. We then employ time series data to test whether recent increases in macroalgae are associated with nutrients. Our results revealed that patterns of N enrichment were linked to several factors, including rainfall, wave-driven circulation, and distance from anthropogenic nutrient sources, especially human sewage. Reefs near large watersheds, where inputs of N from sewage and agriculture are high, have been consistently enriched in N for at least the last decade. In many of these areas, corals have decreased and macroalgae have increased, while reefs with lower levels of N input have maintained high cover of coral and low cover of macroalgae. Importantly, these patchy phase shifts to macroalgae have occurred despite substantial island-wide increases in the density and biomass of herbivorous fishes over the time period. Together, these results indicate that nutrient loading may be an important driver of coral-to-macroalgae phase shifts in the lagoons of Moorea even though the reefs harbor an abundant and diverse herbivore assemblage. These results emphasize the important role that bottom-up factors can play in driving coral-to-macroalgae phase shifts and underscore the critical importance of watershed management for reducing inputs of nutrients and other land-based pollutants to coral reef ecosystems.