Approaches for advancing scientific understanding of macrosystems

The emergence of macrosystems ecology (MSE), which focuses on regional- to continental-scale ecological patterns and processes, builds upon a history of long-term and broad-scale studies in ecology. Scientists face the difficulty of integrating the many elements that make up macrosystems, which consist of hierarchical processes at interacting spatial and temporal scales. Researchers must also identify the most relevant scales and variables to be considered, the required data resources, and the appropriate study design to provide the proper inferences. The large volumes of multi-thematic data often associated with macrosystem studies typically require validation, standardization, and assimilation. Finally, analytical approaches need to describe how cross-scale and hierarchical dynamics and interactions relate to macroscale phenomena. Here, we elaborate on some key methodological challenges of MSE research and discuss existing and novel approaches to meet them

Biodiversity change is uncoupled from species richness trends: consequences for conservation and monitoring

Global concern about human impact on biological diversity has triggered an intense research agenda on drivers and consequences of biodiversity change in parallel with international policy seeking to conserve biodiversity and associated ecosystem functions. Quantifying the trends in biodiversity is far from trivial, however, as recently documented by meta-analyses, which report little if any net change in local species richness through time. Here, we summarise several limitations of species richness as a metric of biodiversity change and show that the expectation of directional species richness trends under changing conditions is invalid. Instead, we illustrate how a set of species turnover indices provide more information content regarding temporal trends in biodiversity, as they reflect how dominance and identity shift in communities over time. We apply these metrics to three monitoring datasets representing different ecosystem types. In all datasets, nearly complete species turnover occurred, but this was disconnected from any species richness trends. Instead, turnover was strongly influenced by changes in species presence (identities) and dominance (abundances). We further show that these metrics can detect phases of strong compositional shifts in monitoring data and thus identify a different aspect of biodiversity change decoupled from species richness. Synthesis and applications: Temporal trends in species richness are insufficient to capture key changes in biodiversity in changing environments. In fact, reductions in environmental quality can lead to transient increases in species richness if immigration or extinction has different temporal dynamics. Thus, biodiversity monitoring programmes need to go beyond analyses of trends in richness in favour of more meaningful assessments of biodiversity change

Approaches to advance scientific understanding of macrosystems ecology

The emergence of macrosystems ecology (MSE), which focuses on regional- to continental-scale ecological pat- terns and processes, builds upon a history of long-term and broad-scale studies in ecology. Scientists face the difficulty of integrating the many elements that make up macrosystems, which consist of hierarchical processes at interacting spatial and temporal scales. Researchers must also identify the most relevant scales and variables to be considered, the required data resources, and the appropriate study design to provide the proper inferences. The large volumes of multi-thematic data often associated with macrosystem studies typically require valida- tion, standardization, and assimilation. Finally, analytical approaches need to describe how cross-scale and hierarchical dynamics and interactions relate to macroscale phenomena. Here, we elaborate on some key methodological challenges of MSE research and discuss existing and novel approaches to meet them

Building a multi-scaled geospatial temporal ecology database from disparate data sources: fostering open science and data reuse

Although there are considerable site-based data for individual or groups of ecosystems, these datasets are widely scattered, have different data formats and conventions, and often have limited accessibility. At the broader scale, national datasets exist for a large number of geospatial features of land, water, and air that are needed to fully understand variation among these ecosystems. However, such datasets originate from different sources and have different spatial and temporal resolutions. By taking an open-science perspective and by combining site-based ecosystem datasets and national geospatial datasets, science gains the ability to ask important research questions related to grand environmental challenges that operate at broad scales. Documentation of such complicated database integration efforts, through peer-reviewed papers, is recommended to foster reproducibility and future use of the integrated database. Here, we describe the major steps, challenges, and considerations in building an integrated database of lake ecosystems, called LAGOS (LAke multi-scaled GeOSpatial and temporal database), that was developed at the sub-continental study extent of 17 US states (1,800,000 km² ). LAGOS includes two modules: LAGOS[subscript]GEO , with geospatial data on every lake with surface area larger than 4 ha in the study extent (~50,000 lakes), including climate, atmospheric deposition, land use/cover, hydrology, geology, and topography measured across a range of spatial and temporal extents; and LAGOS[subscript]LIMNO , with lake water quality data compiled from ~100 individual datasets for a subset of lakes in the study extent (~10,000 lakes). Procedures for the integration of datasets included: creating a flexible database design; authoring and integrating metadata; documenting data provenance; quantifying spatial measures of geographic data; quality-controlling integrated and derived data; and extensively documenting the database. Our procedures make a large, complex, and integrated database reproducible and extensible, allowing users to ask new research questions with the existing database or through the addition of new data. The largest challenge of this task was the heterogeneity of the data, formats, and metadata. Many steps of data integration need manual input from experts in diverse fields, requiring close collaboration.Keywords: LAGOS, Integrated database, Data harmonization, Database Ecoinformatics, Macrosystems ecology, Landscape limnology, Water qualityKeywords: LAGOS, Integrated database, Ecoinformatics, Data harmonization, Water quality, Data sharing, Landscape limnology, Macrosystems ecology, Database documentation, Data reus

Relationship of chlorophyll to phosphorus and nitrogen in nutrient-rich lakes

<p>Nitrogen (N) and phosphorus (P) commonly co-limit primary productivity in lakes, and chlorophyll <i>a</i> (Chl-<i>a</i>) is predicted to be greatest under high N, high P regimes. Because land use practices can alter N and P biogeochemical cycles in watersheds, it is unclear whether previously documented phytoplankton–nutrient relationships apply where landscapes are highly disturbed. Here, we analyzed a lake water quality database from an agricultural region to explore relationships among Chl-<i>a</i>, total N (TN), and total P (TP) under extreme nutrient concentrations. Chl-<i>a</i> was weakly related to TN when TP was ≤100 μg L⁻¹ but displayed a stronger response to TN at higher TP. When TP exceeded 100 μg L⁻¹, Chl-<i>a</i> increased with increasing TN until reaching a TN threshold of ~3 mg L⁻¹ and decreased thereafter, resulting in a high nutrient, low Chl-<i>a</i> region that did not coincide with shifts in nutrient limitation, light availability, cellular Chl-<i>a</i> content, phytoplankton composition, or zooplankton grazing pressure. Beyond the threshold, nitrate comprised most of TN and occurred with reduced dissolved organic matter (DOM). These observations suggest that photolysis of nitrate may produce reactive oxygen species that damage DOM and phytoplankton. Reduction in N loading at high P could therefore increase Chl-<i>a</i> and decrease water clarity, resulting in an apparent worsening of water quality. Our data suggest that monitoring Chl-<i>a</i> or Secchi depth may fail to indicate water quality degradation by extreme nutrient concentrations. These findings highlight how extreme nutrient regimes in lakes can produce novel relationships between phytoplankton and nutrients.</p

Is limnology becoming increasingly abiotic, riverine, and global?

Abstract Scientists often debate on the evolving state of their fields and future research directions, but empirical studies on research trends are rare and this limits our capacity to disentangle perceptions from facts within the mass of available data. We used ecological and paleolimnological approaches to assess how the “community” of words most commonly used in limnological studies presented at the Association for the Sciences of Limnology and Oceanography (ASLO) meetings and published in Web of Science have evolved over the last decades. We found that the field of limnology has become increasingly focused on global abiotic research themes, especially in rivers, while there was a decrease in the proportion of organismal studies. We hypothesize that this results from both major influential publications highlighting the importance of framing limnology in a global context and the methodological limitations of organismal studies that prevent data from scaling up as quickly as their abiotic counterparts

Changing agricultural practices and regional lake sedimentation rates since European settlement, shown as decadal averages across all 32 lakes.

<p>(A) Percent land in farms (brown), percent of wetlands drained (light blue), maize yield (t ha⁻¹) (yellow), and cumulative USDA financial assistance (inflation adjusted) for soil and water conservation programs in the USA (green). (B) Average regional lake mass accumulation rates for erosional (black) and in-lake (fueled by nutrient enrichment; yellow) derived sediment (g m⁻² yr⁻¹). The time for lakes to add one mm of sediment is also shown (dark blue; days). Error bars represent ±1 standard error. Agricultural data were summarized from the United States Department of Agriculture’s Census of Agriculture (1850–2007) and the National Agricultural Statistics Service. Annual maize yield data were fitted to a LOWESS model.</p

Phytoplankton taxonomic compositional shifts across nitrogen and phosphorus concentration gradients in temperate lakes

Nutrient and light availability, and their balance, can modify community composition and structure in pelagic communities. Previous studies have demonstrated contradictory findings about whether total phosphorus (TP) concentrations alone or the ratio of total nitrogen (TN) to TP concentrations (TN:TP) drive Cyanobacteria dominance in freshwater ecosystems, and influences of light availability are often overlooked. Here, we analyzed a 12 year, 137 lake database to test paradigms of phytoplankton compositional patterns across nutrient (TN, TP, TN:TP) and light availability gradients in an agricultural region. We hypothesized that (1) TN:TP ratios would better predict phytoplankton compositional shifts than TP concentrations alone, (2) Cyanobacteria relative abundance would increase at low TN:TP ratios, and (3) Cyanobacteria biomass fluctuations would be the primary driver of light climate. We found that TN:TP ratios better described phytoplankton compositional patterns than TP concentrations, with Cyanobacteria proportions decreasing with increasing TN:TP while other taxa increased. Contrary to expectations, Cyanobacteria always dominated community composition (&ge;80% biomass), regardless of TP concentrations. Despite these patterns, N-fixing Cyanobacteria proportions were not correlated to TN:TP, suggesting that shifts toward N-fixation were not solely driving phytoplankton compositional patterns. Although Cyanobacteria biomass decreased with increasing light availability, inorganic particles explained more variance in light than total phytoplankton biomass, suggesting that buoyancy-regulating Cyanobacteria may gain an initial competitive advantage in light acquisition before bloom development in turbid systems. These findings suggest that Cyanobacteria strongly influence pelagic community dynamics in nutrient-enriched lakes, and their ability to manipulate light and nutrient environments enable their persistent dominance across large environmental gradients

Watershed Sediment Losses to Lakes Accelerating Despite Agricultural Soil Conservation Efforts

<div><p>Agricultural soil loss and deposition in aquatic ecosystems is a problem that impairs water quality worldwide and is costly to agriculture and food supplies. In the US, for example, billions of dollars have subsidized soil and water conservation practices in agricultural landscapes over the past decades. We used paleolimnological methods to reconstruct trends in sedimentation related to human-induced landscape change in 32 lakes in the intensively agricultural region of the Midwestern United States. Despite erosion control efforts, we found accelerating increases in sediment deposition from erosion; median erosion loss since 1800 has been 15.4 tons ha⁻¹. Sediment deposition from erosion increased >6-fold, from 149 g m⁻² yr⁻¹ in 1850 to 986 g m⁻² yr⁻¹ by 2010. Average time to accumulate one mm of sediment decreased from 631 days before European settlement (ca. 1850) to 59 days mm⁻¹ at present. Most of this sediment was deposited in the last 50 years and is related to agricultural intensification rather than land clearance or predominance of agricultural lands. In the face of these intensive agricultural practices, traditional soil conservation programs have not decelerated downstream losses. Despite large erosion control subsidies, erosion and declining water quality continue, thus new approaches are needed to mitigate erosion and water degradation.</p> </div

Lake and watershed sizes, maximum ²¹⁰Pb ages at the bottom of cores (± SE), historic and modern sediment total (erosional+in-lake) mass accumulation rates (MAR; ±SE) for the sediment cores taken from 32 lakes in this study.

<p>Lake and watershed sizes, maximum ²¹⁰Pb ages at the bottom of cores (± SE), historic and modern sediment total (erosional+in-lake) mass accumulation rates (MAR; ±SE) for the sediment cores taken from 32 lakes in this study.</p