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In terrestrial and aquatic ecosystems, organisms directly affect nutrient storage and cycling by sequestering nutrients via growth and remineralizing nutrients via excretion and egestion. Therefore, species introductions and extirpations can profoundly affect nutrient storage and remineralization rates, and present a challenge for conserving ecosystem function in fresh waters. The literature of consumer-driven nutrient dynamics is growing rapidly, but studies of consumer effects on nutrient storage and remineralization across species and among ecosystems are limited. We compared the effects of 3 grazing taxa, nonnative armored catfish in Mexican streams, native mussels in Oklahoma streams, and native tadpoles in Panamanian streams, on nutrient storage and remineralization. We examined interactions among organismal stoichiometry and biomass, nutrient storage, remineralization rates, and ecosystem size across these 3 groups following species decline (tadpoles and mussels) or introduction (armored catfish) to gain a better understanding of organism-specific effects on nutrient dynamics among freshwater ecosystems. Collectively, our results suggest that the ecosystem-level effect of consumer-driven nutrient dynamics is strongly influenced by environmental variables and is taxon specific. Major changes in biomass of stoichiometrically distinctive organisms can lead to subsequent changes in the flux and storage of elements in an ecosystem, but the overall effect of aquatic animals on nutrient dynamics also is determined by discharge and nutrient-limitation patterns in streams and rivers. [ABSTRACT FROM AUTHOR]

Foraminifera are commonly defined as marine testate protists, and their diversity is mainly assessed on the basis of the morphology of their agglutinated or mineralized tests. Diversity surveys based on environmental DNA (eDNA) have dramatically changed this view by revealing an unexpected diversity of naked and organic-walled lineages as well as detecting foraminiferal lineages in soil and freshwater environments. Moreover, single-cell analyses have allowed discrimination among genetically distinctive types within almost every described morphospecies. In view of these studies, the foraminiferal diversity appeared to be largely underestimated, but its accurate estimation was impeded by the low speed and coverage of a cloning-based eDNA approach. With the advent of high-throughput sequencing (HTS) technologies, these limitations disappeared in favor of exhaustive descriptions of foraminiferal diversity in numerous samples. Yet, the biases and errors identified in early HTS studies raised some questions about the accuracy of HTS data and their biological interpretation. Among the most controversial issues affecting the reliability of HTS diversity estimates are (1) the impact of technical and biological biases, (2) the sensitivity and specificity of taxonomic sequence assignment, (3) the ability to distinguish rare species, and (4) the quantitative interpretation of HTS data. Here, we document the lessons learned from previous HTS surveys and present the current advances and applications focusing on foraminiferal eDNA. We discuss the problems associated with HTS approaches and predict the future trends and avenues that hold promises for surveying foraminiferal diversity accurately and efficiently. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses the uses of molecular approaches in freshwater ecology.

The National Lakes Assessment (NLA) used relative and attributable risks to measure the apparent nationwide effects of excess N, reduced lakeshore habitat, and other stressors on planktonic assemblages in lakes. The risk measures, borrowed from human health research, use nontechnical language to compare the apparent effects of disparate lake stressors, thereby helping the public and policymakers identify stressors of greatest national concern. However, the investigators for the NLA and similar prior surveys of streams did not adjust their risk estimates of each stressor for possible confounding by other covarying stressors. As a result, the NLA point estimates overstate the risks of individual stressors and, thus, are unreliable for assessing their importance relative to that of closely related stressors. I used NLA data from 966 lakes to illustrate existing statistical methods of risk adjustment. Point estimates of adjusted relative risk for 7 stressor variables were 15 to 64% lower than unadjusted estimates. Adjusted attributable risks also were lower than unadjusted values, but for some stressors, they were very inconsistent across 3 adjustment methods. In addition, adjusted risk estimates used only part of the available data because each estimate was adjusted for many (6) covarying stressors. Closely related stressor variables (for example, N, P, and turbidity) can be combined into a bundle representing a broader type of stress (reduced water quality). For the NLA data, adjusted risk estimates for the stressor bundles (water quality and habitat) were more consistent across estimation methods and had lower relative uncertainty than estimates for their component stressors. In addition, closely related stressors with similar sources and modes of impact are more likely to be managed together rather than individually. For these reasons, I suggest evaluating stressor bundles in future aquatic surveys. [ABSTRACT FROM AUTHOR]

Aquatic research historically has focused on separate aquatic ecosystems (i.e., freshwater, estuarine, and marine). We argue that this separation into subdisciplines is artificial and may even be counterproductive. Instead, scientists should consider the physical linkages between different aquatic ecosystems and the many similarities in properties and processes among those ecosystems (conceptual linkages). The 4 papers in this J-NABS cluster demonstrate the value of integrating information from different aquatic ecosystems. For example, the papers illustrate that transformation and transportation of nutrients and energy physically and conceptually link all aquatic ecosystems and are facilitated by the characteristics of the medium that defines them all-- water. To promote the exchange of information within aquatic science, more interecosystem studies should be published in journals and books so that scientists will see parallels and linkages among freshwater, estuarine, and marine systems. Over the longer term, such studies would benefit from the funding and teaching of aquatic science as an integrated whole. [ABSTRACT FROM AUTHOR]