Phosphorus seasonal sorption-desorption kinetics in suspended sediment in response to land use and management in the Guaporé catchment, Southern Brazil

Presence of pharmaceuticals and bacterial resistance genes in river epilithic biofilms exposed to intense agricultural and urban pressure

The continuous discharge of pharmaceutical compounds into the aquatic environment has raised concerns over the contamination of water resources. Urban activities and intensive animal breeding are important sources of contamination. The accumulation of antibiotics may lead to the transfer or alternatively maintain the presence of resistance genes in natural microbial communities existing in epilithic biofilms. The objective of this study was to evaluate the pharmaceutical contamination levels and the presence of resistance genes in biofilms from a South Brazilian watershed. The Guaporé watershed exhibits a high diversity of land use, including agricultural and urban areas with differing levels of anthropogenic pressure. Seventeen sites along the Guaporé watershed were monitored. Biofilm samples were collected in two seasons (winter and summer), and the pharmaceutical concentration and quantity of resistance genes were analyzed. All monitored sites were contaminated with pharmaceuticals. Agricultural activities contribute through transferring pharmaceuticals derived from the application of animal waste to agricultural fields. The most contaminated site (pharmaceuticals and bacterial resistance genes) was located in an urban area exposed to high pressure. Decreases in the contamination of biofilms were also observed, exemplifying processes of natural attenuation in the watershed. The quality of the biofilms sampled throughout the watershed served as a useful tool to understand and monitor environmental pollution.

Strategies for identifying pollution sources in a headwater catchment based on multi-scale water quality monitoring

Rural headwater catchments are important to describe the connectivity of pollution sources to water bodies. Strategies to optimize water quality monitoring networks, as parameter definition, sampling, and statistical approach, have been widely discussed. The objectives of this study were to describe the spatial and temporal dynamics (intra- and inter-events) of water quality and to establish its implications for environmental monitoring programs. The monitoring was carried out in a rural headwater catchment (1.2 km²) with shallow soils, high slopes, and intense agricultural activity in Southern Brazil. To better describe the impact of agriculture on water resources, the monitoring strategy was based on definition of the best set of parameters and different sampling frequency to incorporate intra- and inter-event variability and statistical analysis approach. We also analyzed parameters in different sub-basins with physiographic traits. Three hydrological compartments were analyzed: surface flow, groundwater, and base flow. Physico-chemical parameters, the concentration of elements associated with agricultural activity, and biological parameters were evaluated. Total phosphorus and turbidity were the parameters most affected by agricultural activity. They reflected on the inter- and intra-events, the impacts of soil and water degradation by agricultural activity, and the precarious rural sanitation conditions. Spatiotemporal variability of the parameters characterizes the different mechanisms for transferring pollutants from diffuse sources to water bodies. Spatial and temporal patterns in water quality changes were used to discuss environmental monitoring strategies, such as parameter and sampling frequency definition, to improve soil and water conservation programs at the catchment scale.

Pesticide bioaccumulation in epilithic biofilms as a biomarker of agricultural activities in a representative watershed

Brazil is one of the largest consumers of pesticides in the world. The high rainfall rate and inadequate soil use and management promote the transfer of these compounds to the aquatic system. The aim of this study was to identify and quantify pesticides present in epilithic biofilms in order to evaluate the effectiveness of this matrix as a bioindicator able to discriminate areas and periods with different inputs of pesticides. Among the 25 pesticides analyzed in the biofilms, 20 compounds were detected. The epilithic biofilms picked up pesticides independent of their polarities, even in the period of lower use. The frequency and median concentration of five herbicides (2,4-D, atrazine, desethyl-atrazine, simazine, nicosulfuron), three fungicides (carbendazim, epoxiconazole, tebuconazole), and one insecticide (imidacloprid) were highest in biofilms sampled in summer crops during the growing period. Biofilms collected in the upper region of the catchment, where genetically modified soybean and corn cultivated in a no-tillage system prevail, the highest frequency and median concentration of three herbicides (2,4-D, thifensulfuron, isoproturon), four fungicides (carbendazim, epoxiconazole, tebuconazole, metconazole), and one insecticide (imidacloprid) were observed. Despite the excessive amounts of pesticides used in the catchment, the median values of all pesticides in the epilithic biofilm were considered low. The lower diversity and concentration of pesticides observed in the autumn/winter season is representative of lower use of pesticides, barriers to pesticide transfer from soil to water, and the biofilm's resilience capacity to decompose pesticides.

Remote Sensing Retrieval of Total Phosphorus in the Pearl River Channels Based on the GF-1 Remote Sensing Data

Total phosphorus (TP) concentration is one of the indicators for surface water quality evaluation. In this study, an indirect algorithm was proposed to retrieve TP concentration. This algorithm retrieves the TP concentration in urban waters based on Gaofen-1 (GF-1) remote sensing data. The algorithm uses the correlation between remote-sensing reflectance, optically significant constituents of water (chlorophyll, suspended sediment, and organic matter (excluding algae)), and TP to establish a retrieval model. First, the concentrations of optically active components are retrieved using a semi-analytical model. Second, the correlation between TP and optically active components is used to retrieve the TP concentration in waters. The GF-1 remote sensing data for 7 August 2015 were used to perform remote sensing retrieval of TP concentration in the Pearl River channels in Guangzhou, China. The results show that the TP concentration in most areas of the Front Channel, Western Channel, Guangzhou Channel, and the western part of the Back Channel was higher than 0.2 mg/L, while the TP concentration in the middle and eastern parts of the Back Channel was generally lower than 0.2 mg/L. The mean absolute percentage error of the retrieval is 24.18%. The experimental results show that the model is suitable for remote sensing retrieval of TP in urban waters in Guangzhou.