Distinct variations in fluorescent DOM components along a trophic gradient in the lower Fox River-Green Bay as characterized using one-sample PARAFAC approach.

Variations in molecular weight distributions of dissolved organic matter (DOM) and PARAFAC-derived fluorescent components were investigated along a transect in the seasonally hypereutrophic lower Fox River-Green Bay using the one-sample PARAFAC approach coupling flow field-flow fractionation for size-separation with fluorescence excitation-emission matrix (EEM) and PARAFAC analysis. Concentrations of dissolved organic carbon and nitrogen, chromophoric-DOM, specific UV absorbance at 254 nm, and humification index all decreased monotonically from river to open bay, showing a strong river-dominated DOM source and a dynamic change in DOM quality along the river-lake transect. The relative abundance of colloidal DOM (>1 kDa) derived from ultrafiltration exhibited minimal variation, averaging 71 ± 4 % of the bulk DOM, across the entire estuarine transect although the colloidal concentration decreased in general. Using the one-sample EEM-PARAFAC approach, the identified major fluorescent components were distinct between stations along the river-estuary-open bay continuum, with four components in river/upper-estuary but three components in open bay waters. Among the four common fluorescent components (C475, C410, C320 and C290), the most abundant and refractory humic-like component, C475, behaved conservatively and its relative abundance (%ΣFmax) remained fairly constant (50 ± 4 %) along the transect, while the semi-labile humic-like component, C410, consistently decreased from river to estuary and eventually vanished in open Green Bay. In contrast, the two autochthonous protein-like components (C320 and C290) increased from river to open bay along the trophic gradient. The new results presented here provide an improved understanding of the diverse and fluctuating characteristics in DOM composition, lability, and estuarine mixing behavior across the river-lake interface and demonstrate the efficacy of the one-sample PARAFAC approach.

Partitioning and transformation of organic and inorganic phosphorus among dissolved, colloidal and particulate phases in a hypereutrophic freshwater estuary.

Phosphorus (P) loadings to the Great Lakes have been regulated for decades, but re-eutrophication and seasonal hypoxia have recently been increasingly reported. It is of paramount importance to better understand the fate, transformation, and biogeochemical cycling processes of different P species across the river-lake interface. We report here results on chemical speciation of P in the seasonally hypoxic Fox River-Green Bay system and variations in sources and partitioning of P species along the aquatic continuum. During midsummer when productivity is generally high, phosphate and dissolved organic P (DOP) were the major species in river water while particulate-organic-P predominated in open bay waters, showing a dynamic change in the chemical speciation of P along the river-bay transect with active transformations between inorganic and organic P and between colloidal and particulate phases. Colloidal organic P (COP, >1 kDa) comprised 33‒65% of the bulk DOP, while colloidal inorganic P was generally insignificant and undetectable especially in open bay water. Sources of COP changed from mainly allochthonous in the Fox River, having mostly smaller sized colloids (1-3 kDa) and a lower organic carbon to phosphorus (C/P) ratio, to predominantly autochthonous in open bay waters with larger sized colloids (>10 kDa) and a higher organic C/P ratio. The observed high apparent distribution coefficients (Kd) of P between dissolved and particulate phases and high-abundant autochthonous colloidal and particulate organic P in the hypereutrophic environment suggest that, in addition to phosphate, colloidal/particulate organic P may play a critical role in the biogeochemical cycling of P and the development of seasonal hypoxia.

Lakes at Risk of Chloride Contamination.

Lakes in the Midwest and Northeast United States are at risk of anthropogenic chloride contamination, but there is little knowledge of the prevalence and spatial distribution of freshwater salinization. Here, we use a quantile regression forest (QRF) to leverage information from 2773 lakes to predict the chloride concentration of all 49 432 lakes greater than 4 ha in a 17-state area. The QRF incorporated 22 predictor variables, which included lake morphometry characteristics, watershed land use, and distance to the nearest road and interstate. Model predictions had an r2 of 0.94 for all chloride observations, and an r2 of 0.86 for predictions of the median chloride concentration observed at each lake. The four predictors with the largest influence on lake chloride concentrations were low and medium intensity development in the watershed, crop density in the watershed, and distance to the nearest interstate. Almost 2000 lakes are predicted to have chloride concentrations above 50 mg L-1 and should be monitored. We encourage management and governing agencies to use lake-specific model predictions to assess salt contamination risk as well as to augment their monitoring strategies to more comprehensively protect freshwater ecosystems from salinization.

Automated Subdaily Sampling of Cyanobacterial Toxins on a Buoy Reveals New Temporal Patterns in Toxin Dynamics.

Temporal variability of toxins produced by cyanobacteria in lakes is relatively unknown at time scales relevant to public health (i.e., hourly). In this study, a water quality monitoring buoy was outfitted with an automated water sampler taking preserved samples every 6 h for 68.75 days over a drinking water intake. A total of 251 samples were analyzed by tandem mass spectrometry for 21 cyanotoxin congeners in 5 classes producing 5020 data points. Microcystins (MCs) were the most abundant toxins measured (mean ± sd = 3.9 ± 3.3 µg/L) followed by cyanopeptolins (CPs) (1.1 ± 1.5 µg/L), anabaenopeptins (APs) (1.0 ± 0.6 µg/L), anatoxin-a (AT-A) (0.03 ± 0.06 µg/L), and microginin-690 (MG-690) (0.002 ± 0.01 µg/L). Advanced time series analyses uncovered patterns in cyanotoxin production. The velocity of cyanotoxin concentration varied from -0.7 to 0.9 µg/L/h with a maximum positive velocity just prior to peak toxin concentration during nonbloom periods. A backward-looking moving window of variance analysis detected major increases in cyanotoxin concentration and predicted the two greatest increases in MC. A wavelet analysis identified a significant ( p < 0.01) 2.8-4.2 day periodicity in toxin concentration over a ∼25 day period during peak toxin production, which is partially explained by easterly wind velocity ( R = -0.2, p < 0.05). Diversity in congener profiles was explored with principle component analysis showing that cyanotoxin dynamics followed a seasonal trajectory where toxin profiles were significantly clustered (ANOSIM R = 0.7, p < 0.05) on a daily basis. Variability in toxin profiles was strongly correlated with time ( R = -0.8, p < 0.001) as well as the C:N ratio of the toxin pool ( R = 0.17, p < 0.05). The methods employed here should be useful for uncovering patterns in cyanotoxin dynamics in other systems.

Analysis of cyanobacterial metabolites in surface and raw drinking waters reveals more than microcystin.

Freshwater cyanobacterial blooms are becoming increasingly problematic in regions that rely on surface waters for drinking water production. Microcystins (MCs) are toxic peptides produced by multiple cyanobacterial genera with a global occurrence. Cyanobacteria also produce a variety of other toxic and/or otherwise bioactive peptides (TBPs) that have gained less attention including cyanopeptolins (Cpts), anabaenopeptins (Apts), and microginins (Mgn). In this study, we compared temporal and spatial trends of four MCs (MCLR, MCRR, MCYR, MCLA), three Cpts (Cpt1020, Cpt1041, Cpt1007), two Apts (AptF, AptB), and Mgn690 in raw drinking water and at six surface water locations above these drinking water intakes in a eutrophic lake. All four MC congeners and five of six TBPs were detected in lake and raw drinking water. Across all samples, MCLR was the most frequently detected metabolite (100% of samples) followed by MCRR (97%) > Cpt1007 (74%) > MCYR (69%) > AptF (67%) > MCLA (61%) > AptB (54%) > Mgn690 (29%) and Cpt1041 (15%). Mean concentrations of MCs, Apts, and Cpts into two drinking water intakes were 3.9 ±â€¯4.7, 0.14 ±â€¯0.21, and 0.38 ±â€¯0.92, respectively. Mean concentrations in surface water were significantly higher (p < 0.05) than in drinking water intakes for MCs but not for Cpts and Apts. Temporal trends in MCs, Cpts, and Apts in the two raw drinking water intakes were significantly correlated (p < 0.05) with measures of cell abundance (chlorophyll-a, Microcystis cell density), UV absorbance, and turbidity in surface water. This study expands current information about cyanobacterial TBPs that occur in lakes and that enter drinking water treatment plants and underscores the need to determine the fate of less studied cyanobacterial metabolites during drinking water treatment that may exacerbate toxicity of more well-known cyanobacterial toxins.

Spatial analysis of toxic or otherwise bioactive cyanobacterial peptides in Green Bay, Lake Michigan.

Cyanobacterial harmful algal blooms (cyanoHABs) are a growing problem in freshwater systems worldwide. CyanoHABs are well documented in Green Bay, Lake Michigan but little is known about cyanoHAB toxicity. This study characterized the diversity and spatial distribution of toxic or otherwise bioactive cyanobacterial peptides (TBPs) in Green Bay. Samples were collected in 2014 and 2015 during three cruises at sites spanning the mouth of the Fox River north to Chambers Island. Nineteen TBPs were analyzed including 11 microcystin (MC) variants, nodularin, three anabaenopeptins, three cyanopeptolins and microginin-690. Of the 19 TBPs, 12 were detected in at least one sample, and 94% of samples had detectable TBPs. The most prevalent TBPs were MCRR and MCLR, present in 94% and 65% of samples. The mean concentration of all TBPs was highest in the Fox River and lower bay, however, the maximum concentration of all TBPs occurred in the same sample north of the lower bay. MCs were positively correlated with chlorophyll and negatively correlated with distance to the Fox River in all cruises along a well-established south-to-north trophic gradient in Green Bay. The mean concentration of MC in the lower bay across all cruises was 3.0 +/- 2.3 µg/L. Cyanopeptolins and anabaenopeptins did not trend with the south-north trophic gradient or varied by cruise suggesting their occurrence is driven by different environmental factors. Results from this study provides evidence that trends in TBP concentration differ by congener type over a trophic gradient.

Long-term chloride concentrations in North American and European freshwater lakes.

Anthropogenic sources of chloride in a lake catchment, including road salt, fertilizer, and wastewater, can elevate the chloride concentration in freshwater lakes above background levels. Rising chloride concentrations can impact lake ecology and ecosystem services such as fisheries and the use of lakes as drinking water sources. To analyze the spatial extent and magnitude of increasing chloride concentrations in freshwater lakes, we amassed a database of 529 lakes in Europe and North America that had greater than or equal to ten years of chloride data. For each lake, we calculated climate statistics of mean annual total precipitation and mean monthly air temperatures from gridded global datasets. We also quantified land cover metrics, including road density and impervious surface, in buffer zones of 100 to 1,500 m surrounding the perimeter of each lake. This database represents the largest global collection of lake chloride data. We hope that long-term water quality measurements in areas outside Europe and North America can be added to the database as they become available in the future.

Cyanobacterial Toxins of the Laurentian Great Lakes, Their Toxicological Effects, and Numerical Limits in Drinking Water.

Cyanobacteria are ubiquitous phototrophic bacteria that inhabit diverse environments across the planet. Seasonally, they dominate many eutrophic lakes impacted by excess nitrogen (N) and phosphorus (P) forming dense accumulations of biomass known as cyanobacterial harmful algal blooms or cyanoHABs. Their dominance in eutrophic lakes is attributed to a variety of unique adaptations including N and P concentrating mechanisms, N2 fixation, colony formation that inhibits predation, vertical movement via gas vesicles, and the production of toxic or otherwise bioactive molecules. While some of these molecules have been explored for their medicinal benefits, others are potent toxins harmful to humans, animals, and other wildlife known as cyanotoxins. In humans these cyanotoxins affect various tissues, including the liver, central and peripheral nervous system, kidneys, and reproductive organs among others. They induce acute effects at low doses in the parts-per-billion range and some are tumor promoters linked to chronic diseases such as liver and colorectal cancer. The occurrence of cyanoHABs and cyanotoxins in lakes presents challenges for maintaining safe recreational aquatic environments and the production of potable drinking water. CyanoHABs are a growing problem in the North American (Laurentian) Great Lakes basin. This review summarizes information on the occurrence of cyanoHABs in the Great Lakes, toxicological effects of cyanotoxins, and appropriate numerical limits on cyanotoxins in finished drinking water.

Salting our freshwater lakes.

The highest densities of lakes on Earth are in north temperate ecosystems, where increasing urbanization and associated chloride runoff can salinize freshwaters and threaten lake water quality and the many ecosystem services lakes provide. However, the extent to which lake salinity may be changing at broad spatial scales remains unknown, leading us to first identify spatial patterns and then investigate the drivers of these patterns. Significant decadal trends in lake salinization were identified using a dataset of long-term chloride concentrations from 371 North American lakes. Landscape and climate metrics calculated for each site demonstrated that impervious land cover was a strong predictor of chloride trends in Northeast and Midwest North American lakes. As little as 1% impervious land cover surrounding a lake increased the likelihood of long-term salinization. Considering that 27% of large lakes in the United States have >1% impervious land cover around their perimeters, the potential for steady and long-term salinization of these aquatic systems is high. This study predicts that many lakes will exceed the aquatic life threshold criterion for chronic chloride exposure (230 mg L-1), stipulated by the US Environmental Protection Agency (EPA), in the next 50 y if current trends continue.

Variable Cyanobacterial Toxin and Metabolite Profiles across Six Eutrophic Lakes of Differing Physiochemical Characteristics.

Future sustainability of freshwater resources is seriously threatened due to the presence  of  harmful  cyanobacterial  blooms,  and  yet,  the  number,  extent,  and  distribution  of  most  cyanobacterial toxins-including "emerging" toxins and other bioactive compounds-are poorly  understood.  We  measured  15  cyanobacterial  compounds-including  four  microcystins  (MC),  saxitoxin (SXT), cylindrospermopsin (CYL), anatoxin-a (ATX) and homo-anatoxin-a (hATX), two  anabaenopeptins (Apt), three cyanopeptolins (Cpt), microginin (Mgn), and nodularin (NOD)-in  six freshwater lakes that regularly experience noxious cHABs. MC, a human liver toxin, was present  in all six lakes and was detected in 80% of all samples. Similarly, Apt, Cpt, and Mgn were detected  in all lakes in roughly 86%, 50%, and 35% of all samples, respectively. Despite being a notable  brackish  water  toxin,  NOD  was  detected  in  the  two  shallowest  lakes-Wingra  (4.3  m)  and  Koshkonong (2.1 m). All compounds were highly variable temporally, and spatially. Metabolite  profiles were significantly different between lakes suggesting lake characteristics influenced the  cyanobacterial community and/or metabolite production. Understanding how cyanobacterial toxins  are  distributed  across  eutrophic  lakes  may  shed  light  onto  the  ecological  function  of  these  metabolites, provide valuable information for their remediation and removal, and aid in the  protection of public health.