Data from: Cyanobacterial blooms in subtropical riverine and estuarine ecosystems of South America

Water quality impairment caused by toxic cyanobacterial blooms is a
growing global concern adversely affecting the biodiversity and
functioning of aquatic ecosystems, which can disrupt recreation and human
health. Recent studies indicate that factors such as eutrophication, dam
construction, and climate change are likely to increase the frequency and
intensity of these blooms in aquatic ecosystems worldwide. This trend
raises concerns in the subtropical South America (SA) region, where the
pampas ecosystem has registered a sustained increase in the surface used
by agroindustrial activities which leads to eutrophication of the Uruguay
River (UR) and the Río de la Plata estuary (RdlP) ecosystems. The UR-RdlP
system is crucial for recreational activities and serves as an essential
water source. Historical monitoring data indicate that currently, toxic
blooms are often documented in the UR and transported downstream to the
RdlP (Kruk et al., 2017; Martínez de la Escalera et al., 2017). 
In this context, it is imperative to develop comprehensive and coherent
reviewed datasets to analyze the spatio-temporal dynamics of toxic
cyanobacterial blooms effectively. Despite the availability of public
information, its accessibility and suitability for analysis are not always
guaranteed. Therefore, establishing and maintaining comprehensive
long-term databases in ecosystems frequented for recreational purposes is
crucial for studying the mechanisms associated with bloom formation and
predicting human health risks. Here, we provide historical records
(1963-2022) and indices of toxic cyanobacterial blooms at ca. 80 sites in
the subtropical region along the Uruguay River (UR) and Río de la Plata
(RdlP). The data compilation process involved gathering dispersed
information from open sources,  research projects, reports from
multiple water quality monitoring programs, and collaborative efforts with
research institutions in the country and the region. Data was checked for
consistency and included geospatial data on cyanobacterial cell abundance,
microcystin concentration, chlorophyll-a concentration, and risk levels
from field samples combined with relevant environmental, land use, and
climatic variables. This included in-situ measured environmental variables
(e.g., water temperature, salinity, turbidity, conductivity) and regional
climate and hydrology information (e.g., precipitation and flow rates), as
well as land use patterns in the UR basin (e.g., crops, forestation,
grasslands). A fundamental contribution of this dataset lies in the
consolidation and integration of variables reviewed from different
sources, facilitating its utilization to evaluate the frequency and
intensity of cyanobacterial blooms in a framework of productive
intensification and climate change, to analyze the causes and effects of
cyanobacterial blooms in riverine and estuarine recreational beaches and
their relation with human health risks, to understand the historical
dynamic of water quality experienced by users of these aquatic ecosystems,
and to model and improve early warning and national monitoring systems,
helping to mitigate potential public health risks. In short, various
studies utilizing the provided dataset reveal the following trends: over
the temporal analysis, there is a sustained increase in cyanobacteria
abundance from 1960 to the present, particularly marked by an exponential
growth around the year 2000 (Kruk et al., 2023). This shift is associated
with changes in land use, notably the transition to industrial crops (Kruk
et al., 2023). Cyanobacteria organisms and their bloom frequency of
occurrence increased also in estuarine waters (Martinez de la Escalera et
al., 2017; Kruk et al., 2017). Elevated salinity selects larger
cyanobacterial organisms with high toxicity (Kruk et al., 2019).
Cyanotoxin levels in UR and RdlP are significantly high, posing
substantial public health risks, especially to vulnerable populations
(Kruk et al., 2019). We highlight the potential of this dataset to explore
the interplay between environmental factors, anthropogenic changes, and
cyanobacterial dynamics at recreational beaches over an extended
historical period in which many relevant transitions were recorded that
promoted the rise and intensification of harmful algal blooms. Its
significance extends to aiding researchers and healthcare professionals in
establishing specific conditions for beach water quality management.