Spatio-temporal changes in water quality in the Guarapiranga reservoir (São Paulo, Brazil): insights from a long-term monitoring data series

The provision of drinking water in metropolises is a challenge that requires programs for continuous monitoring of water quality and processes that impact the land cover of the watershed. In this work, we investigated through multivariate statistical analysis the temporal and spatial trends of several variables, not yet explored in a data series that includes 42 years (1978-2020) of monitoring in the hydrographic basin of the Guarapiranga reservoir, in the São Paulo Metropolitan Region-SPMR (Brazil). This reservoir is the source of drinking water for 3.8 million people and plays a strategic role in the social, environmental, and economic structure at SPMR. Our results point to the continuous degradation of water quality in the reservoir, although with different causes and spatio-temporal aspects. Between the 1970s and 1980s, variables associated with erosion/silting played a more critical role. From the 1990s, the introduction of N and P intensified, and the concentration of thermotolerant coliforms increased. The loss of quality is mainly associated with the progressive advance of urban settlements without planning combined with the inefficient initiatives to control domestic sewage pollution. If there is no rapid and comprehensive intervention, there is a risk that the Guarapiranga reservoir may become unsuitable for drinking water supply and other types of use in the future. This scenario will represent a critical obstacle to regional development and the quality of life of the population.

Watershed degradation and management practices in north-western highland Ethiopia

Watershed degradation in Ethiopia has become a major environmental threat and caused significant damages both in the natural environment and the development of human society. This paper assesses an overview of the extent, causes, and effects of watershed degradation and the management actions in north-western highland Ethiopia, taking the Rib watershed as a case study site. The data were collected from field observations, interviews, and questionnaire surveys administered to 210 farmers. The results show that watershed degradation is a serious and widespread problem in the study site. The major causes of watershed degradation include population growth, uncontrolled grazing, unsustainable land use and management practices, and weak land ownership system. Watershed degradation, mainly in the form of soil erosion, has adversely reduced agricultural production and worsened food insecurity and poverty in the study area. Various watershed management practices that combine structural and biological measures have been practiced to curb the problem. However, the farmers' decisions to adopt and implement the measures have been highly influenced by a range of socioeconomic, biophysical, and institutional factors. Access to support services, size of the farmland, educational level, and plot ownership were found to influence farmers' decisions positively at a statistically significant (P < 0.01) level. It needs efforts to create farmer environmental awareness and develop strong watershed management standards and guidelines. The watershed could benefit from hand in hand efforts of local farmers, concerned governmental agencies, and researchers.

Differential responses of stream water and bed sediment microbial communities to watershed degradation

The importance of microbial communities in the function of lotic ecosystems is unequivocal. However, traditional watershed studies on biodiversity have mostly focused on benthic macroinvertebrates, macroalgae and fish assemblages. Here, we investigated the diversity and interaction patterns of microbial communities in water and bed sediment of streams impacted by intensive watershed activities versus streams with relatively pristine conditions via next-generation sequencing of 16S rRNA amplicons using Illumina HiSeq platform. Both water and sediment microbial communities at forested sites had higher mean alpha-diversity than developed sites. Although microbial alpha-diversity indices were generally higher in bed sediment than water, they were comparable at forested sites. In addition, losses of taxa important in nitrogen cycle were evident particularly in bed sediment of developed sites. Interactions among microorganisms visualized by microbial network were more complex at forested sites versus developed sites, with more keystone taxa predominantly from sediment. Together, these findings suggest stream water and bed sediment microbial communities may be affected by watershed disturbances in distinctive ways, and losses of important functional microbial players and keystone taxa in bed sediment may result in decline of ecosystem functions and services. Therefore, cautions should be taken when implementing remediation strategies such as sediment dredging, and reseeding contaminated sites with key microbial players may catalyze the recovery of ecosystems.