Phosphorus enrichment in floodplain subsoils as a potential source of freshwater eutrophication

Authors

Christoph Weihrauch, Collin Joel Weber

Despite decades of management efforts, freshwater eutrophication has not been effectively mitigated in each affected ecosystem. This might be due to insufficient knowledge of the sources of phosphorus (P) inputs into surface waters. We sampled 2 m-deep soil profiles in four floodplain areas under differently managed grassland in Germany under dry and moist conditions regarding soil moisture and precipitation. Four soil P fractions of decreasing solubility were determined. We found systematic enrichment of easily soluble P forms in the floodplain subsoils (average: from 87.5 cm depth). Water-soluble P in these “deep P stocks” was positively correlated with total phosphorus concentrations in the adjacent surface waters. Our data cautiously suggest increased P mobilization from deep P stocks under moist conditions. Drier conditions coincided with increased P retention, resulting in relatively large amounts of easily soluble P which could readily be desorbed and lost at the next stronger precipitation event. We found no effects of grassland management on deep P stock features and dynamics. Deep P stocks might be considered a new source of diffuse P losses from soils. To effectively mitigate freshwater eutrophication, best management practices need to be developed to minimize P transfer from deep P stocks.

Optical water types found in Brazilian waters

Authors

Edson Filisbino Freire da Silva, Evlyn Márcia Leão de Moraes Novo, Felipe de Lucia Lobo, Claudio Clemente Faria Barbosa, Mauricio Almeida Noernberg, Luiz Henrique da Silva Rotta, Carolline Tressmann Cairo, Daniel Andrade Maciel & Rogério Flores Júnior

Optical water types (OWTs) can represent diverse ranges of Chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) concentrations, which make them extremely useful for monitoring water quality, for example, detecting eutrophic conditions or tuning remote sensing algorithms. In this study, the objective is to assess OWTs found in Brazilian waters using in situ remote sensing reflectance (R_rs), acquired for water bodies encompassing a wide range of optical characteristics. Eight OWTs are obtained based on R_rs spectral shape and magnitude, which represent different limnological characteristics of Brazilian waters. The OWT 1 is clear waters with low TSM, Chl-a, and CDOM (median (x~x~): TSM of 2.64 g m⁻³, Chl-a of 6.04 mg m⁻³, and CDOM of 0.6 m⁻¹); OWT 2 represents moderate turbid waters (TSM x~x~: 5.14); OWTs 3, 4, and 5 are characterized by waters with high Chl-a concentration (x~x~: 33.1, 39.6, and 180.4 mg m⁻³, respectively); OWT 6 is characterized with the highest CDOM concentration (x~x~: 4.07 m⁻¹); OWTs 7 and 8 consist of waters with the highest TSM concentrations from terrestrial input (x~x~: 19.55 and 93.25, respectively). Hence, those OWTs could support satellite monitoring by helping to tune algorithms and also providing wide spatial–temporal monitoring.

Exploring the relative changes in dissolved organic matter for assessing the water quality of full-scale drinking water treatment plants using a fluorescence ratio approach

Authors

Tahir Maqbool, Yanling Qin, Quang Viet Ly, Jiaxing Zhang, Chengyue Li, Muhammad Bilal Asif, Zhenghua Zhang

This study aims to extend and demonstrate the application of fluorescence spectroscopy for monitoring the water quality of three differently operated full-scale drinking water treatment plants located in the Shenzhen city (China). A ratio of fluorescent dissolved organic matter (FDOM), which describes relative changes in humic-like to protein-like fluorescence, was used to explain mechanisms behind the physicochemical processes. The fluorescence components obtained through individual and combined parallel factor analysis (PARAFAC) modeling revealed the presence of humic-like (C1) and protein-like (C2) structures in the DOM. The C1/C2 ratio provided a direct relationship between the seasonal variations and DOM composition. Wet season generated DOM enriched with humic-like fluorescence, while dry season caused a higher release of protein-like fluorescence. The fluorescence ratio presented unique patterns of DOM in treatment trains. The chemical pretreatment and disinfection unit processes showed a higher tendency to remove the humic-like fluorescence. However, the C1/C2 ratio increased during physical treatment processes such as coagulation-precipitation and sand filtration, indicating preferential removal of protein-like fluorescence. The DOM composition in influent directly (R² = 0.77) influenced the relative intensities of fluorescence components in the treated water. Compared to the dry season, the wet season caused significant changes in DOM composition and produced treated water enriched with humic-like fluorescence. This fluorescence ratio offers an approach to explore the role of different treatment units and determine the factors affecting the composition of DOM in the surface water and drinking water treatment plants.

Formation of N-nitrosodimethylamine precursors through the microbiological metabolism of nitrogenous substrates in water

Authors

Er Bei, Xiao Li, Fuhua Wu, Shixiang Li, Xinsheng He, Yufang Wang, Yu Qiu, Yu Wang, Chengkun Wang, Jun Wang, Xiaojian Zhang, Chao Chen

N-nitrosodimethylamine (NDMA) as one emerging disinfection by-product has been investigated globally since 1990s. However, its main precursors are still unclear. We found that NDMA formation potential (NDMAFP) of various water samples increased firstly and then decreased gradually during incubation with microorganism. We hypothesized that NDMA precursors could be produced through metabolism of nitrogenous components and then gradually be biodegraded. To verify this hypothesis, six amino acids (AAs), peptone and ammonium were separately incubated with microorganism and NDMAFP was measured regularly. The average molar yield of the substrates to NDMAFP were 60–200 × 10⁻⁶ for the AAs, 350 × 10⁻⁶ for peptone under aerobic condition. The extracellular fraction with molecular weight (MW) less than 1 k Dalton contributed the majority to NDMAFP in the peptone experiment, followed by that with MW between 10 k and 0.22 μm and the intracellular materials. Dimethylamine and methylamine were detected during the experiments but their contribution to NDMAFP is quite limited. The results indicate that the nitrosamine precursors may not be the direct metabolite of AAs or peptones but the excretion of living bacteria or the components in dead bacteria body. Our results inferred that AA metabolism may give an NDMAFP of 0.12 nmol/L (maximum) or 0.09 nmol/L (average) in water under aerobic condition. This estimation of NDMAFP from AA metabolism can account for 38% (maximum) or 27% (average) of the median NDMAFP in waters of China (0.32 nmol/L) reported before.

Formation of algal-derived nitrogenous disinfection by-products during chlorination and chloramination

Authors

X. Li, N.R.H. Rao, K.L. Linge, C.A. Joll, S. Khan, R.K. Henderson

Algal cells and algal organic matter (AOM) are a source of high dissolved organic carbon (DOC) and nitrogen (DON) concentrations. This poses a possible health risk due to their potential to form disinfection by-products (DBPs), some of which may be of health concern, after disinfection. While several studies have focussed on the formation of carbonaceous DBPs from AOM, only a few studies have focussed on the formation of nitrogen containing N-DBPs from AOM. Hence, the main aim of this study was to thoroughly investigate the N-DBP formation potential of the AOM from a species of cyanobacteria commonly found in natural waters, Microcystis aeruginosa. Three haloacetonitriles, two halonitromethanes, two haloacetamides, and eight N-nitrosamines were analysed by gas chromatography-mass spectrometry after chlorination and chloramination of the extracted AOM. To provide further insight into the influence of changing DON character on N-DBP formation potential, the AOM from three other species, Chlorella vulgaris, Dolichospermum circinale and Cylindrospermopsis raciborskii, were also tested. Dichloroacetonitrile (DCAN) was the DBP formed in the highest concentrations for both chlorination and chloramination of bulk AOM from all the species. Furthermore, during chlorination and chloramination, the high molecular weight fraction (>1 kDa) of AOM from M. aeruginosa had a greater DCAN formation potential (normalised to DOC or DON) than the AOM in the low molecular weight fraction (<1 kDa) of M. aeruginosa, regardless of growth stage. N-Nitrosamine formation from the bulk AOM of all species occurred only after chloramination. The molar concentration of N-nitrosodimethylamine (NDMA) was lower than the other N-nitrosamines detected. However, NDMA formation increased with culture age for all four species, in contrast to most other N-nitrosamines whose formation remained consistent or decreased with culture age. Overall, algal growth could result in elevated concentrations of N-DBPs due to the increasing concentrations of high molecular weight algal DON in the AOM. It is suggested that the AOM comprises precursors containing long C-chain amine (R₁-NH-R₂) or cyclic N-containing amine structures. Comparisons to previously measured N-DBP concentrations in drinking water suggest that the AOM from the algae and cyanobacteria examined in this study are not likely to be a major source of precursors for either DCAN or NDMA in real waters. However, AOM may present a major precursor source for other N-nitrosamines.

Effects of pre, post, and simultaneous loading of natural organic matter on 2-methylisoborneol adsorption on superfine powdered activated carbon: Reversibility and external pore-blocking

Authors

Akiko Nakayama, Asuka Sakamoto, Taku Matsushita, Yoshihiko Matsui, Nobutaka Shirasaki

Three different natural organic matter (NOM)-loading methods were compared for the adsorptive removal of 2-methylisoborneol (MIB) by superfine powdered activated carbon (SPAC) and conventionally-sized powdered activated carbon (PAC). The three NOM-loading methods were: NOM adsorption followed by MIB (MIB adsorption on NOM-preloaded carbon), MIB adsorption followed by NOM (MIB adsorption on NOM post-loaded carbon), and simultaneous NOM and MIB loading (MIB adsorption on NOM-simultaneously loaded carbon). MIB removals were similar for the smaller-sized carbon (SPAC) at higher AC dosages and at lower initial NOM concentrations. The similar MIB removals indicate direct site competition between MIB and NOM with MIB adsorption reversibility (complete desorption of MIB by NOM). At lower AC doses, especially for PACs, and at higher initial NOM concentrations, the adsorption of MIBs depended on the sequence of MIB or NOM adsorption. MIB removal was lowest for the NOM-preloaded carbon, followed by NOM-simultaneously loaded carbon. The highest MIB removal was achieved by post-loading of NOM, indicating that the adsorption is irreversible. MIB adsorption on SPAC was more reversible than on PAC, although the pore size distributions of the two carbons were similar. The high degree of adsorption irreversibility for PAC compared with SPAC indicated that pore blocking occurs due to NOM loading at the PAC particle surface. Images of the external adsorption were obtained using isotope mapping and ¹⁵N-labeled effluent organic matter.

Pyrazines: A diverse class of earthy-musty odorants impacting drinking water quality and consumer satisfaction

Authors

Chunmiao Wang, Jianwei Yu, Daniel L. Gallagher, Julia Byrd, Wenchuo Yao, Qi Wang, Qingyuan Guo, Andrea M. Dietrich, Min Yang

The presence of earthy-musty odors in drinking water is a major concern for water suppliers and consumers worldwide. While geosmin and 2-methylisoborneol are the most studied earthy-musty odor-causing compounds, pyrazine and its alkyl and methoxy compounds possess similar odors and are widely distributed in nature, foods, and beverages. In this study, odor characteristics of pyrazines and their presence in natural and treated waters were determined. Pyrazine, 2,6-dimethyl-pyrazine (DMP), 2,3,5-trimethyl-pyrazine (TrMP), 2-ethyl-5(6)-methyl-pyrazine (EMP), 2,3,5,6-tetramethyl-pyrazine (TeMP), 2-isobutyl-3-methoxy-pyrazine (IBMP) and 2-isopropyl-3-methoxy-pyrazine (IPMP) were measured in source and finished drinking water across China. 2-Methoxy-3,5-dimethyl-pyrazine (MDMP), IBMP, and IPMP were investigated in rivers in Virginia, USA. The results showed that “musty” and “sweet” were the most common descriptors for pyrazine, DMP, MDMP, TrMP, and TeMP. While IBMP and IPMP were never detected in 140 source or drinking water samples from across China, pyrazine, DMP, MDMP, TrMP, and TeMP occurred throughout with concentrations of n.d.−62.2 ng/L-aq in source water and n.d.−39.6 ng/L-aq in finished water. IBMP, IPMP, and MDMP were present in two Virginia rivers; MDMP occurred in 18% of the samples with concentrations of n.d.−4.4 ng/L, many of which were above the aqueous odor threshold of 0.043 ng/L MDMP. The removal efficiencies through conventional water treatment were poor, ranging from negative removals to ∼10%. Advanced oxidation water treatment could only remove EMP and TrMP. The widespread presence of earthy-musty-sweet pyrazines in source and drinking waters on two continents, their poor removal during water treatment, and ng/L odor threshold concentrations confirm their potential to be T&O issues for consumers.

Natural and anthropogenic dispersal of cyanobacteria: a review

Authors

Emily Curren & Sandric Chee Yew Leong

Cyanobacteria are oxygenic photosynthetic organisms that are prevalent in freshwater and marine ecosystems. A proportion of the cyanobacteria in a given locality are known to be introduced from other regions and are able to cause harmful cyanobacterial blooms. However, the processes by which cyanobacteria is relocated are not well described. This review presents the various natural and anthropogenic methods of cyanobacterial transport, with emphasis on the dispersal of problematic taxa. Natural mechanisms for transport of cyanobacteria include meteorological phenomena such as dust storms and tsunamis, which facilitate the long-distance transport of cyanobacteria through the air and rafting debris in oceans, respectively. Cyanobacteria can also be transported by animals such as worms, seabirds and planktivorous fish. The influence of anthropogenic activities on cyanobacterial distributions is also discussed, with focus on transport through international shipping and on rafting surfaces provided by plastic pollution. In this study, a total of 150 species of cyanobacteria from 64 genera were identified to be transported across a combination of natural and anthropogenic methods. As cyanobacteria are organisms that are prevalent in many ecosystems, an understanding of these transport processes will allow for improved assessment and monitoring of introduced toxic cyanobacterial species.

 

Trophic control changes with season and nutrient loading in lakes

Authors

Tanya L. Rogers Stephan B. Munch Simon D. Stewart Eric P. Palkovacs Alfredo Giron‐Nava Shin‐ichiro S. Matsuzaki Celia C. Symons

Experiments have revealed much about top‐down and bottom‐up control in ecosystems, but manipulative experiments are limited in spatial and temporal scale. To obtain a more nuanced understanding of trophic control over large scales, we explored long‐term time‐series data from 13 globally distributed lakes and used empirical dynamic modelling to quantify interaction strengths between zooplankton and phytoplankton over time within and across lakes. Across all lakes, top‐down effects were associated with nutrients, switching from negative in mesotrophic lakes to positive in oligotrophic lakes. This result suggests that zooplankton nutrient recycling exceeds grazing pressure in nutrient‐limited systems. Within individual lakes, results were consistent with a ‘seasonal reset’ hypothesis in which top‐down and bottom‐up interactions varied seasonally and were both strongest at the beginning of the growing season. Thus, trophic control is not static, but varies with abiotic conditions – dynamics that only become evident when observing changes over large spatial and temporal scales.

Two years of post-wildfire impacts on dissolved organic matter, nitrogen, and precursors of disinfection by-products in California stream waters

Authors

Habibullah Uzun, Randy A. Dahlgren, Christopher Olivares, Cagri Utku Erdem, Tanju Karanfil, Alex T. Chow

We investigated the effects of two California wildfires (Rocky and Wragg Fires, 2015) compared to an unburned reference watershed on water quality, dissolved organic matter (DOM), and precursors of disinfection by-products (DBPs) for two years’ post-fire. The two burned watersheds both experienced wildfires but differed in the proportion of burned watershed areas. Burned watersheds showed rapid water quality degradation from elevated levels of turbidity, color, and suspended solids, with greater degradation in the more extensively burned watershed. During the first year’s initial flushes, concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium (NH₄⁺/NH₃), and specific ultraviolet absorbance (SUVA₂₅₄) were significantly higher (67 ± 40%, 418 ± 125%, 192 ± 120%, and 31 ± 17%, respectively) in the more extensively burned watershed compared to the reference watershed. These elevated values gradually declined and finally returned to levels like the reference watershed in the second year. Nitrate concentrations were near detection limits (0.01 mg-N/L) in the first year but showed a large increase in fire-impacted streams during the second rainy season, possibly due to delayed nitrification. Changes in DOM composition, especially during the initial storm events, indicated that fires can attenuate humic-like and soluble microbial by-product-like (SMP) DOM while increasing the proportion of fulvic-like, tryptophan-like, and tyrosine-like compounds. Elevated bromide (Br⁻) concentrations (up to 8.7 μM]) caused a shift in speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) to brominated species for extended periods (up to 2 years). Wildfire also resulted in elevated concentrations of N-nitrosodimethylamine (NDMA) precursors. Such changes in THM, HAA, and NDMA precursors following wildfires pose a potential treatability challenge for drinking water treatment, but the effects are relatively short-term (≤1 year).