Search

Nutritional and contaminant stressors influence organismal physiology, trophic interactions, community structure, and ecosystem-level processes; however, the interactions between toxicity and elemental imbalance in food resources have been examined in only a few ecotoxicity studies. Integrating well-developed ecological theories that cross all levels of biological organization can enhance our understanding of ecotoxicology. In the present article, we underline the opportunity to couple concepts and approaches used in the theory of ecological stoichiometry (ES) to ask ecotoxicological questions and introduce stoichiometric ecotoxicology, a subfield in ecology that examines how contaminant stress, nutrient supply, and elemental constraints interact throughout all levels of biological organization. This conceptual framework unifying ecotoxicology with ES offers potential for both empirical and theoretical studies to deepen our mechanistic understanding of the adverse outcomes of chemicals across ecological scales and improve the predictive powers of ecotoxicology.

Membrane inlet mass spectrometry (MIMS) provides detailed measures of dissolved 28,29,30N2, O2, and argon (Ar) for estimating important gas fluxes and concentrations in aquatic ecosystems. Previous studies demonstrated a large O2 scavenging effect while using a MIMS, where varying concentrations of O2 can affect measured N2 : Ar because O2 interacts with N2 in the ion source to produce NO+ (m/z = 30), potentially decreasing the detected current for 28,29N2 and increasing the detected current for 30N2. A common solution is to use a muffle furnace heated to 600°C with a copper reduction column to reduce the concentration of O2 to minimal levels and accurately measure 28,29,30N2. However, this solution eliminates the detection of O2 in environmental samples, which is a major benefit of using a MIMS. We questioned whether the MIMS was sensitive enough to provide accurate O2 estimates when using the furnace and whether the O2 scavenging effect was real and consistent among MIMS. We conducted four separate experiments on three different MIMS to test the O2 scavenging effect and the potential detection of O2 when using a MIMS with furnace. The furnace removed ~ 99% of O2, and O2 scavenging had little to no detectable effect on N2 : Ar and an unclear effect on 29N2 : 28N2, but increased 30N2 : 28N2. In most cases, accurate O2 data could be retrieved despite using the furnace. The need for O2 reduction may be limited to measuring accurate 30N2 : 28N2 in isotope pairing studies, but without substantial loss of MIMS measurements used to describe O2 dynamics. [ABSTRACT FROM AUTHOR]

Quantifying net N2 flux, the balance between nitrogen (N) fixation and denitrification, may help inform the decades-long debate about the significance of N relative to phosphorus (P) limitation in pond, lake, and reservoir ecosystems. Dissolved N2:Ar ratios can provide information about the role of these two processes in lakes but have not been experimentally verified. We measured dissolved N2:Ar patterns in twelve experimental pond mesocosms representing a N:P gradient ranging from 7 to 835 (molar) that was driven by large differences in NO3-N availability. Mesocosms with NO3-N < 0.1 mg L−1 had N2:Ar saturation ratio values consistently below equilibrium (i.e., net N fixation), whereas mesocosms with NO3-N > 1 mg L−1 had N2:Ar values consistently above equilibrium (i.e., net denitrification, demonstrating a shift from N2 import to export as pond N availability increased). Both planktonic N fixation estimated from isotope mixing models and N2 fluxes measured by sediment core incubations confirmed a shift from net N fixation to net denitrification as NO3-N concentrations increased. N2:Ar saturation ratio values in the photic zone were negatively correlated with increasing measured N fixation while saturation ratios from benthic waters were positively correlated with increasing sediment N2-N flux. N2:Ar saturation ratios were consistently < 1 in mesocosms with low N availability and high contributions of fixed N. Mesocosms with high N loading and low N fixation had high saturation ratios indicative of denitrification in benthic samples but dissolved gases collected from the photic zone were less consistent. Our water column N2:Ar saturation ratio measurements combined with quantitative measures of N fixation and benthic N2 flux confirm that grab samples for dissolved gasses can provide critical information regarding the relative contribution of net N fixation and denitrification to balancing N availability within shallow lakes at broad scales. [ABSTRACT FROM AUTHOR]

Predicting dissolved oxygen (DO) in lakes is important for assessing environmental conditions as well as reducing water treatment costs. High levels of DO often precede toxic algal blooms, and low DO causes carcinogenic metals to precipitate during water treatment. Typically, DO is predicted from limited data sets using hydrodynamic modeling or data‐driven approaches like neural networks. However, functional data analysis (FDA) is also an appropriate modeling paradigm for measurements of DO taken vertically through the water column. In this analysis, we build FDA models for a set of profiles measured every 2 hours and forecast the entire DO percent saturation profile from 2 to 24 hours ahead. Functional smoothing and functional principal component analysis are applied first, followed by a vector autoregressive model to forecast the empirical functional principal component (FPC) scores. Rolling training windows adapt to seasonality, and multiple combinations of window sizes, model variables, and parameter specifications are compared using both functional and direct root mean squared error metrics. The FPC method outperforms a suite of comparison models, and including functional pH, temperature, and conductivity variables improves the longer forecasts. Finally, the FDA approach is useful for identifying unusual observations. [ABSTRACT FROM AUTHOR]

Cyanobacterial harmful algal blooms (cyanoHABs) have been observed across the USA and worldwide, and even locally in Lake Fayetteville (Arkansas, USA) once we started monitoring for total microcystin. The goal of this research note was to present a framework that might help guide cyanoHAB and toxin public health advisories at Lake Fayetteville. We evaluated nonparametric change points (i.e., thresholds) and hierarchical structure (using classification and regression trees) between total microcystin concentrations, chlorophyll, and phycocyanin; chlorophyll‐a is a pigment in all algae, while phycocyanin is specific to cyanobacteria. Pigment concentrations and raw fluorescence units (RFUs) all showed significant thresholds with total microcystin concentrations, basically showing that as concentration or RFUs increased above the thresholds that total microcystin was greater at Lake Fayetteville. The regression tree with total microcystin concentrations showed a first split with phycocyanin RFUs at 4524, and then when phycocyanin RFUs were greater there was an optimal range for the phycocyanin to chlorophyll RFU ratio (0.64‐1.5). At this recreational lake, total microcystin concentrations were greatest when water samples met these criteria, providing a possible framework for when lake managers might suggest an increased risk for elevated cyanobacterial toxins. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are experiencing increased salinization. Adaptive management of harmful algal blooms (HABs) contributes to eutrophication/salinization interactions through the hydrologic transport of blooms to coastal environments. We examined how nutrients and salinity interact to affect growth, elemental composition, and cyanotoxin production/release in two common HAB genera. Microcystis aeruginosa (non‐nitrogen [N]‐fixer and microcystin‐LR producer [MC‐LR]) and Aphanizomenon flos‐aquae (N‐fixer and cylindrospermopsin producer [CYN]) were grown in N : phosphorus (N : P) 4 and 50 (by atom) for 21 and 33 d, respectively, then dosed with a salinity gradient (0–10.5 g L−1). Both total MC‐LR and CYN were correlated with particulate N. We found Microcystis MC‐LR production and release was affected by salinity only in the N : P 50 treatment. However, Aphanizomenon CYN production and release was affected by salinity regardless of N availability. Our results highlight how cyanotoxin production and release across the freshwater–marine continuum are controlled by ecophysiological differences between N‐acquisition traits. [ABSTRACT FROM AUTHOR]

Harmful cyanobacterial blooms are an increasing threat to water quality. The interactions between two ecophysiological functional traits of cyanobacteria, diazotrophy (nitrogen [N]‐fixation) and N‐rich cyanotoxin synthesis, have never been examined in a stoichiometric explicit manner. We explored how a gradient of resource N : phosphorus (P) affects the biomass, N, P stoichiometry, light‐harvesting pigments, and cylindrospermopsin production in a N‐fixing cyanobacterium, Aphanizomenon. Low N : P Aphanizomenon cultures produced the same biomass as populations grown in high N : P cultures. The biomass accumulation determined by carbon, indicated low N : P Aphanizomenon cultures did not have a N‐fixation growth trade‐off, in contrast to some other diazotrophs that maintain stoichiometric N homeostasis at the expense of growth. However, N‐fixing Aphanizomenon populations produced less particulate cylindrospermopsin and had undetectable dissolved cylindrospermopsin compared to non‐N‐fixing populations. The pattern of low to high cyanotoxin cell quotas across an N : P gradient in the diazotrophic cylindrospermopsin producer is similar to the cyanotoxin cell quota response in nondiazotrophic cyanobacteria. We suggest that diazotrophic cyanobacteria may be characterized into two broad functional groups, the N‐storage‐strategists and the growth‐strategists, which use N‐fixation differently and may determine patterns of bloom magnitude and toxin production in nature. [ABSTRACT FROM AUTHOR]

Introduction Landscape-scale patterns of the cyanobacterial toxin, microcystin, in Canadian lakes were recently analyzed by Orihel et al. (2012). The analysis of this comprehensive dataset was important for linking accelerated [...]