Drivers and spatial structure of abiotic and biotic properties of lakes, wetlands, and streams at the national scale

Examining inequality in aquatic ecosystem services: Evidence from large-scale monitoring programs

We hypothesize that aquatic ecosystem services are likely to be inequitably accessible and addressing this hypothesis requires systematic assessment at regional and national scales. We used existing data from large-scale aquatic monitoring programs (National Coastal Condition Assessment, National Lakes Assessment) to examine relationships between ecosystem condition, approximating a subset of cultural and provisioning services, and inequality (population below poverty level, minority population). We also assessed whether monitoring sites equitably represented the gradient of socioeconomic backgrounds. Several water quality indicators were associated with significantly different minority and low-income percentages; however, the effect size was generally small, with the exception of nitrogen condition status. Minority communities were somewhat under-represented when comparing the distribution of all census blocks to those in proximity to monitoring sites. Analyses were sensitive to the skewed distribution of monitoring sites with a low frequency of observations at the more socially vulnerable part of the gradient. We discuss implications of these findings for improving the representation of vulnerable communities in large-scale monitoring programs.

Verifying the usefulness of macrophytes as an indicator of the status of small waterbodies

Small waterbodies are characterised by a high variability of physicochemical parameters. This has an impact on aquatic macrophytes, which are functional components of aquatic ecosystems that also exert a strong influence on other components of these ecosystems. Therefore, their importance in the classification of reservoirs is unquestionable. Unfortunately, the hydromacrophytes found in nutrient-rich small waterbodies in rural areas have a fairly wide ecological scale and are not suitable for a more accurate assessment of these reservoirs. In addition, indicators derived from the classification of lakes, such as phosphorus, nitrogen, chlorophyll-a, organic matter and trophic state indices, have turned out to be of little use in the assessment of small waterbodies. Only a canonical analysis taking into account both environmental variables and the occurring plant species allows satisfactory results to be obtained. Six small waterbodies located in the rural landscape of the Greater Poland Region were studied over three years. 115 plant taxa, 15 of which are hydromacrophytes, were found in the reservoirs and in their immediate vicinity. Three types of small waterbodies were identified in the CCA assessment: (i) those with high TOC, COD and ammonium nitrogen contents, dominated by pleustophytes, and in a saprotrophic state, (ii) those with high nutrient concentrations, dominated by phytoplankton, with a lack of macrophytes or with nymphaeids present, and in a hypereutrophic state, and (iii) those dominated by submerged macrophytes with low chlorophyll-a content, and in a eutrophic state. Thus, macrophytes turn out to be good indicators which support other variables in the classification of small waterbodies.

Rethinking discretization to advance limnology amid the ongoing information explosion

Limnologists often adhere to a discretized view of waterbodies-they classify them, divide them into zones, promote discrete management targets, and use research tools, experimental designs, and statistical analyses focused on discretization. By offering useful shortcuts, this approach to limnology has profoundly benefited the way we understand, manage, and communicate about waterbodies. But the research questions and the research tools in limnology are changing rapidly in the era of big data, with consequences for the relevance of our current discretization schemes. Here, I examine how and why we discretize and argue that selectively rethinking the extent to which we must discretize gives us an exceptional chance to advance limnology in new ways. To help us decide when to discretize, I offer a framework (discretization evaluation framework) that can be used to compare the usefulness of various discretization approaches to an alternative which relies less on discretization. This framework, together with a keen awareness of discretization's advantages and disadvantages, may help limnologists benefit from the ongoing information explosion.

Modeling hypolimnetic dissolved oxygen depletion using monitoring data

Eutrophication increases hypoxia in lakes and reservoirs, causing deleterious effects on biological communities. Quantitative models would help managers develop effective strategies to address hypoxia issues, but most existing models are limited in their applicability to lakes with temporally resolved dissolved oxygen data. We describe a hierarchical Bayesian model that predicts dissolved oxygen in lakes based on a mechanistic understanding of the factors that influence the development of hypoxia during summer stratification. These factors include the days elapsed since stratification, dissolved organic carbon concentration, lake depth, and chlorophyll concentration. We demonstrate that the model can be fit to two datasets: one in which temporally resolved dissolved oxygen profiles were collected from 20 lakes in a single state and one in which single profiles were collected from 381 lakes across the United States. Analyses of these two datasets yielded similar relationships between volumetric oxygen demand and chlorophyll concentration, suggesting that the model structure appropriately represented the effects of eutrophication on oxygen depletion. Combining both datasets in a single model further improved the precision of predictions.

Consistent metacommunity structure despite inconsistent drivers of assembly at the continental scale

A fundamental goal of community ecology is to understand the drivers of community assembly and diversity. Local factors acting on community assembly are typically related to environmental conditions while regional factors are typically related to dispersal. Previous research has not consistently demonstrated the importance of local or regional factors, but this is likely because these factors act in concert and not in isolation. Studies that simultaneously integrate local and regional factors into analyses of community assembly can be a useful avenue to further our understanding of this core concept in community ecology. Here, we aimed to identify metacommunity structure and diversity and the local and regional drivers of community assembly at the continental scale. We evaluated metacommunity structure and drivers of assembly of macroinvertebrate communities in 941 rivers and streams nested within nine ecoregions distributed across the conterminous United States. Pattern-based metacommunity analyses and boosted regression tree techniques were used to (a) assign metacommunity structures and (b) identify the environmental, landscape and network drivers of assembly. We also evaluated how biodiversity scaled across hierarchical levels and varied among ecoregions. Metacommunity structures were consistent for the conterminous United States and each of the nine ecoregion subsets, with each ecoregional metacommunity displaying a Clementsian structure. Environmental variables were the predominant drivers of assembly, suggesting the importance of species sorting and environmental filtering on community structure; however, the identity of the most influential environmental variables differed among ecoregions and suggested hierarchical filtering on assembly. Partitioned diversity was found to be lower at the local and ecoregional levels, but turnover in diversity among ecoregions was higher than expected. Our results demonstrate contingencies in community assembly, notwithstanding consistency in metacommunity structure and support the importance of environmental control over community assembly and biodiversity. Moreover, biodiversity at the continental scale is likely maintained through this inherent variation in the drivers of assembly and concomitant changes in community composition among ecoregions. We suggest that further work should evaluate the assembly of other facets of community structure and the underlying mechanisms of the contingency in assembly drivers.