While numerous studies have examined pollution sources and seasonal effects on surface water quality independently, the complex interactions between these factors remain understudied. This research aimed to fractionate and quantify pollution sources and examine their interactive effects with seasonal variations on surface water quality in Khanh Hoa, Vietnam. The current study was based on 1080 surface water samples taken from three common water bodies - lakes, rivers, and canals across dry and rainy seasons and analyzed for 13 physiochemical properties. Findings revealed that surface water quality was influenced by four primary pollution sources: agricultural activities, residential areas, onsite erosion, and climatic factors. Agricultural sources dominated canal water quality (93.0-94.7%) but had less impact on lakes and rivers (12.8-23.8%). Residential sources significantly affected lakes and rivers (30.23-32.66%) but minimally influenced canals (2.6-5.6%). Onsite erosion sources had greater impacts on lakes and rivers typically during the rainy season and exhibited minimal impacts on canals. Lakes and rivers maintained consistent and higher water quality across seasons (water quality index (WQI) 9.1 to 9.3 out of 1.0 - excellent), while canals exhibited substantially lower quality in the dry season (WQI 0.75) compared to the rainy season (WQI 0.78). These interactive impacts were mitigated by self-purification, water residence time in lakes and rivers, dilution effects, and fast pollutant transport in canals. Our findings highlight the importance of effective management of these key pollution sources in interaction with seasonal variation for maintaining water quality and ensuring environmental sustainability.

The extreme conditions in arid ecosystems make these environments sensitive to environmental changes. Particularly, land use and seasonal changes are determinants of their soil carbon dynamics. The effect of those elements on soil respiration (RS) is still poorly known in several arid regions of the world. This study investigates the seasonal effect on the R(S )and its controlling factors throughout different land use systems in northeastern Mexico. RS and 34 biotic and abiotic variables were measured across agricultural crops, natural shrublands, livestock farms, walnut orchards, and industrially influenced soils during the dry and wet seasons. Six variables (soil water content, soil organic matter, soil temperature, silt, and pH) were found as drivers of R(S )on both local and regional scales. Seasonal and land use had a transversal effect on R-S and its controlling factors. R-S dynamics were primarily modulated by soil water content, with the wet season and managed lands showing increased sensitivity to climatic and anthropogenic changes. These results indicate that land management strategies are critical for carbon cycling, particularly in water-limited regions like northeastern Mexico, where land use changes are occurring at an accelerated pace.

Rainfall variability, waterlogging and frequent natural hazards are the major obstacles for cropping system intensification in heavy textured soils of the coastal areas of Bangladesh. While earlier monsoon rice harvesting by introducing short duration varieties created opportunities for cultivating low water demanding non-rice crops in the dry season, such crops failed in many instances because of heavy rainfall and waterlogging. To address such issue, we have analysed dry season (Nov-Apr) rainfall patterns of six meteorological stations of coastal Bangladesh for studying the feasibility of growing irrigated rice and non-rice crops that can be harvested by April. Very heavy rainfall (>20 mm) occurred in 18-23% of the studied years and heavy rainfall (>10 mm) in 42-43% of cases creating the risk of water stagnation and damage to non-rice crops. The return intervals between occurrences of heavy rainfall and very heavy rainfall in November to December were 1.3-1.4 years and 1.5-2.5 years, respectively. These rainfall events generally delay establishment of non-rice crops. Similarly, in March and April, the return periods for heavy and very heavy rainfall were 1.3-1.5 years and 1.6-2.1 years, respectively. These rainfall events had a detrimental impact on non-rice crops, especially during their ripening stages. Such rainfall events during field experiments at the study locations were found in three years out of four cropping seasons that reduced sunflower and maize yields by 50-64% and sweet gourd and watermelon yields by 55-84% compared to their absence. The probability of high yield of non-rice crops was <25% and the yield variability was very high (40-75%) compared to general rice yield variability (5-6%). Risk factor analysis also revealed that dry season rice is less risky compared to other non-rice crops. To enhance risk management, intensification of cropping systems can be achieved by promoting cultivation of dry season irrigated rice where there is sufficient stored water for irrigation and encouraging farmers to grow pre-monsoon rice.