Insights into agricultural influences and weathering processes from major ion patterns

Abstract

Karst areas and their catchments pose a great challenge for protection because fast conduit flow results in low natural attenuation of anthropogenic contaminants. Studies of the hydrochemistry of karst sources and river solutes are an important tool for securing and managing water resources. A study of the geochemical downriver evolution of the Wiesent River and its tributaries, located in a typical karst terrain, revealed unexpected downstream decreases of nitrate with maximum mean values of 30 mg/L at the source to minimum values of 18 mg/L near the river mouth. This trend persisted over the length of the river even though increased agricultural activities are evident in the downstream section of the catchment. This pattern is caused by fertilizer inputs via diffusive and fast conduits flow from karst lithology in the upstream area that may have reached the river's source even from beyond the hydrological catchment boundaries. Further downstream, these influences became diluted by tributary inputs that drain subcatchments dominated by claystone and sandstone lithologies that increased potassium and sulphate concentrations. Our findings indicate that bedrock geology remains the dominant control on the major ion chemistry of the Wiesent River and that agricultural influences are strongest near the headwaters despite increased land use further downstream, due to long‐term storage and accumulation in karst aquifers. This feature may not be unique to the Wiesent River system, as carbonates cover significant portions of the Earth's surface and subsequent work in other river systems could establish whether such patterns are ubiquitous worldwide.

Hydrochemical Characteristics and Water Quality Assessment for the Upper Reaches of Syr Darya River in Aral Sea Basin, Central Asia

“…However, in this study, the ratio of Na + /Cl − is much greater than 1, indicating that the excess Na + comes from the weathering of silicates due to the ion exchange process. The results are similar to studies in Kanding, southeastern China [63], the Yellow River source region, the northeastern Qinghai-Tibetan Plateau [56], and the results are different from studies in southern Germany [62], India [66] and China [67]. NH 4 -N was detected at each sampling point in different sampling periods, which reflected the influences of human activities.…”

“…Because the water samples from the upper reaches of Syr Darya River and its tributaries mainly belong to the calcium bicarbonate category, carbonate dissolution may dominate the hydrochemical composition. If only carbonate dissolution occurs, the values of Ca 2+ /HCO 3 − and (Ca 2+ + mg 2+ )/HCO 3 − will be close to 0.5 [62]. In this area, If the Ca 2+ originates from gypsum dissolution, the ratio of Ca 2+ /SO 4 2− will be nearly equal to 1 [63].…”

Dissolved oxygen isotope modelling refines metabolic state estimates of stream ecosystems with different land use background

“…5 ). Due to the proximity of both study sites to its spring, the observed dominance of R rates may also reflect a residual signal from upstream DO-undersaturated spring water that was also measured by van Geldern et al 90 .…”

“…Additionally, at the WIS stream elevated nitrate concentrations were derived from the nitrate-rich spring and groundwater input from agriculturally influenced land use. This was combined with reduced nutrient attenuation potential of the karstic bedrock 90 . The elevated nutrient concentrations in combination with reduced shading likely fueled the photosynthetic activity during day time even in the proximity of the spring.…”

Water Quality for Agricultural Irrigation and Aquatic Arsenic Health Risk in the Altay and Tianshan Mountains, Central Asia

“…However, in the present study, the Ca 2+ /SO4 2-ratio was much greater than 1 (Figure 9), indicating that the excess Ca 2+ came from the dissolution of carbonate or silicate minerals. When the basin water is mainly affected by carbonate weathering, due to the subsequent chemical weathering process, the (Ca 2+ + Mg 2+ )/HCO3 -equivalent concentration ratio is about 0.5 [37,58]. From the water equivalent For a single ion component, if the Ca 2+ originated from gypsum dissolution, the Ca 2+ /SO 4 2− ratio would be close to 1 [57].…”