5 research outputs found
Increases in Picocyanobacteria Abundance in Agriculturally Eutrophic Pampean Lakes Inferred from Historical Records of Secchi Depth and Chlorophyll-a
Phytoplankton size structure has profound consequences on food-web organization and energy transfer. Presently, picocyanobacteria (size < 2 µm) represent a major fraction of the autotrophic plankton of Pampean lakes. Glyphosate is known to stimulate the development of picocyanobacteria capable of degrading the herbicide. Due to the worldwide adoption of glyphosate-resistant crops, herbicide usage has increased sharply since the mid-1990s. Unfortunately, there are very few studies (none for the Pampa region) reporting picocyanobacteria abundance before 2000. The proliferation of µm sized particles should decrease Secchi disc depth (ZSD). Therefore ZSD, conditional to chlorophyll-a, may serve as an indicator of picocyanobacteria abundance. We use generalized additive models (GAMs) to analyze a “validation” dataset consisting of 82 records of ZSD, chlorophyll-a, and picocyanobacteria abundance from two Pampean lakes surveys (2009 and 2015). In support of the hypothesis, ZSD was negatively related to picocyanobacteria after accounting for the effect of chlorophyll-a. We then fitted a “historical” dataset using hierarchical GAMs to compare ZSD conditional to chlorophyll-a, before and after 2000. We estimated that ZSD levels during 2000–2021 were, on average, only about half as deep as those during 1980–1999. We conclude that the adoption of glyphosate-resistant crops has stimulated outbreaks of picocyanobacteria populations, resulting in lower water transparency
Individual biovolume of some dominant copepod species in coastal waters off Buenos Aires Province, Argentine Sea
Diel patterns of total suspended solids, turbidity, and water transparency in a highly turbid, shallow lake (Laguna ChascomĂșs, Argentina)
Can space-for-time-substitution surveys represent zooplankton biodiversity patterns and their relationship to environmental drivers?
Space-for-Time-Substitution surveys (SFTS) are commonly used to describe zooplankton community dynamics and to
determine lake ecosystem health. SFTS surveys typically combine single point observations from many lakes to evaluate the
response of zooplankton community structure and dynamics (e.g., species abundance and biomass, diversity, demographics
and modeled rate processes) to spatial gradients in hypothesized environmental drivers (e.g., temperature, nutrients,
predation), in lieu of tracking such responses over long time scales. However, the reliability and reproducibility of SFTS
zooplankton surveys have not yet been comprehensively tested against empirically-based community dynamics from longterm
monitoring efforts distributed worldwide. We use a recently compiled global data set of more than 100 lake
zooplankton time series to test whether SFTS surveys can accurately capture zooplankton diversity, and the hypothesized
relationship with temperature, using simulated SFTS surveys of the time series data. Specifically, we asked: (1) to what
degree can SFTS surveys capture observed biodiversity dynamics; (2) how does timing and duration of sampling affect
detected biodiversity patterns; (3) does biodiversity ubiquitously increase with temperature across lakes, or vary by climate
zone or lake type; and (4) do results from SFTS surveys produce comparable biodiversity-temperature relationship(s) to
empirical data within and among lakes? Testing biodiversity-ecosystem function (BEF) relationships, and the drivers of such
relationships, requires a solid data basis. Our work provides a global perspective on the design and usefulness of (long-term)
zooplankton monitoring programs and how much confidence we can place in the zooplankton biodiversity patterns observed
from SFTS surveys.info:eu-repo/semantics/publishedVersio