Managing microcystin: identifying national‐scale thresholds for total nitrogen and chlorophyll <i>a</i>

Yuan, Lester L.; Pollard, Amina I.; Pather, Santhiska; Oliver, Jacques L.; D’Anglada, Lesley V.

doi:10.1111/fwb.12400

Cited by 67 publications

(40 citation statements)

References 62 publications

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“…To address our study objective, we selected local, lake‐specific explanatory variables previously identified in the literature as potential drivers of pelagic MC concentrations (Beaver et al, ; Yuan et al, ). In particular, we tested the importance of variables measured within the water column (total nitrogen [TN], total phosphorus [TP], TN:TP ratio, chlorophyll a [Chl a ], cyanobacterial biomass, alkalinity [acid‐neutralizing capacity, ANC; conductivity], dissolved organic carbon [DOC], turbidity, colour, and surface water temperature), as well as site and catchment characteristics [maximum depth, lake origin, drainage ratio, percentage agricultural land cover].…”

Section: Methodsmentioning

confidence: 99%

Predicting microcystin concentrations in lakes and reservoirs at a continental scale: A new framework for modelling an important health risk factor

Taranu

Gregory‐Eaves

Steele

et al. 2017

Global Ecol. Biogeogr.

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Aim Scientists, governments and non‐governmental organizations are increasingly moving towards the collection of large, open‐access data. In aquatic sciences, this effort is expanding the scope of questions and analyses that can be performed to further our knowledge of the global drivers of water quality. Cyanotoxin concentration is one variable that has received considerable attention, and although strong local‐scale models have been described in the literature, modelling cyanotoxin concentrations across broader spatial scales has been more difficult. Commonly used statistical frameworks have not fully captured the complex response of toxic algal blooms to global change, limiting our ability to predict and mitigate the impairment of freshwaters by toxic algae. Here, we advance our understanding of emergent drivers of cyanotoxins across a structured landscape by applying a hierarchical “hurdle” model. Location Lakes and reservoirs in the conterminous United States [n = 1127]. Methods We studied cyanobacteria and their toxins [microcystins] during the 2007 summer period. We applied a hierarchical zero‐altered model to test the importance of multi‐scale interactions among environmental features in driving microcystin concentrations above the limit of detection. We then used boosted regression trees [BRTs] to identify environmental thresholds associated with severe impairment by microcystins. Results Accounting for numerous non‐detections, spatial heterogeneity and cross‐scale interactions substantially improved continental‐scale predictions of bloom toxicity. Our model accounted for 55% of the variance in the probability of detecting microcystins across the United States, and 26% of the variability in microcystin concentrations once detected. BRTs further showed that although both local and regional drivers were associated with microcystin concentrations at low to intermediate provisional guidelines, only local drivers came into play when predicting higher limits. Main conclusions Identifying the interaction between local and regional processes is key to understanding the heterogeneous responses of microcystins to environmental change. Our framework could increase the effectiveness of continental‐scale analyses for many different water variables.

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Section: Methodsmentioning

confidence: 99%

Predicting microcystin concentrations in lakes and reservoirs at a continental scale: A new framework for modelling an important health risk factor

Taranu

Gregory‐Eaves

Steele

et al. 2017

Global Ecol. Biogeogr.

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“…As such, the targets for TN and TP derived in this way represent the overall mean concentrations of TN and TP across the NLA data set, or within a particular lake group. Other approaches for selecting individual management targets are possible, including examining the upper and lower bounds of the possible combined values of TN and TP (Yuan et al ., ), and the final approach selected depends on the management objectives.…”

Section: Discussionmentioning

confidence: 99%

“…The nutrient targets described here pertain only to the occurrence of excessive densities of cyanobacteria, and other considerations regarding the health of a lake likely yield different nutrient targets. For example, the extent of hypoxia in the lake (Yuan & Pollard, ) or the occurrence of high concentrations of microcystin (Yuan et al ., ) may be relevant endpoints to consider when making the management decisions.…”

Section: Discussionmentioning

confidence: 99%

Deriving nutrient targets to prevent excessive cyanobacterial densities in U.S. lakes and reservoirs

Yuan

Pollard

2015

Freshwater Biology

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Summary High densities of cyanobacteria can interfere with the use of lakes and reservoirs for recreation and as sources for drinking water, and one approach for reducing the amount of cyanobacteria is to reduce nutrient concentrations in the waterbody. An approach is described for deriving numeric targets for concentrations of total phosphorus (TP) and total nitrogen (TN) that are associated with a pre‐specified probability of cyanobacterial biovolume that exceeds the recommended World Health Organization thresholds for recreation in the water. The analysis consisted of two phases. First, a divisive tree algorithm was used to identify groups of lakes in which the relationship between nutrients and cyanobacterial biovolume was similar. Second, hierarchical Bayesian models were used to estimate relationships between cyanobacterial biovolume, TP and TN, while partitioning the observed variance in biovolume into components associated with sampling variability, temporal variability, and among‐lake differences. The final model accounted for 91% of the variance in cyanobacterial biovolume among different lakes and was used to identify nutrient concentrations that maintain a low probability of excessively high cyanobacterial biovolumes. When no classes of lakes were specified and the relationship between cyanobacterial biovolume and nutrient concentrations was modelled using a national data set, mean targets of 87 and 1100 μg L−1 were derived for TP and TN, respectively, to maintain cyanobacterial biovolume below moderate risk levels as defined by the World Health Organization. After classification, mean nutrient targets in lakes that were found to be most susceptible to high biovolumes of cyanobacteria (i.e. deep lakes) were 61 and 800 μg L−1 for TP and TN, while higher nutrient thresholds were observed for other classes of lakes.

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“…For instance, there are small or hand held fluorometers that measure chlorohpyll a . Additionally, chlorophyll a is a very commonly measured component of water quality that is also known to be positively associated with microcystin-LR concentrations 11, 12 . Yuan et al (2014) explore these associations in detail and control for other related variables 12 .…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, chlorophyll a is a very commonly measured component of water quality that is also known to be positively associated with microcystin-LR concentrations 11, 12 . Yuan et al (2014) explore these associations in detail and control for other related variables 12 . In their analysis they find that total nitrogen and chlorophyll a show the strongest association with microcystin.…”

Section: Introductionmentioning

confidence: 99%

Associations between chlorophyll a and various microcystin-LR health advisory concentrations

Hollister

Kreakie

2016

F1000Res

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Cyanobacteria harmful algal blooms (cHABs) are associated with a wide range of adverse health effects that stem mostly from the presence of cyanotoxins. To help protect against these impacts, several health advisory levels have been set for some toxins. In particular, one of the more common toxins, microcystin-LR, has several advisory levels set for drinking water and recreational use. However, compared to other water quality measures, field measurements of microcystin-LR are not commonly available due to cost and advanced understanding required to interpret results. Addressing these issues will take time and resources. Thus, there is utility in finding indicators of microcystin-LR that are already widely available, can be estimated quickly and in situ, and used as a first defense against high concentrations of microcystin-LR. Chlorophyll a is commonly measured, can be estimated in situ, and has been shown to be positively associated with microcystin-LR. In this paper, we use this association to provide estimates of chlorophyll a concentrations that are indicative of a higher probability of exceeding select health advisory concentrations for microcystin-LR. Using the 2007 National Lakes Assessment and a conditional probability approach, we identify chlorophyll a concentrations that are more likely than not to be associated with an exceedance of a microcystin-LR health advisory level. We look at the recent US EPA health advisories for drinking water as well as the World Health Organization levels for drinking water and recreational use and identify a range of chlorophyll a thresholds. A 50% chance of exceeding one of the microcystin-LR advisory concentrations of 0.3, 1, 1.6, and 2 g/L is associated with chlorophyll a concentration thresholds of 23.4, 67.0, 83.5, and 105.8, respectively. When managing for these various microcystin-LR levels, exceeding these reported chlorophyll a concentrations should be a trigger for further testing and possible management action.

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Managing microcystin: identifying national‐scale thresholds for total nitrogen and chlorophyll a

Cited by 67 publications

References 62 publications

Predicting microcystin concentrations in lakes and reservoirs at a continental scale: A new framework for modelling an important health risk factor

Predicting microcystin concentrations in lakes and reservoirs at a continental scale: A new framework for modelling an important health risk factor

Deriving nutrient targets to prevent excessive cyanobacterial densities in U.S. lakes and reservoirs

Associations between chlorophyll a and various microcystin-LR health advisory concentrations

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