Event-scale flow and sediment generation responses to agricultural land cover change in lowland UK catchments

Agricultural land use can increase runoff and erosion leading to detrimental downstream impacts. This paper examines the impact of agricultural land cover change on runoff and sediment generation at event scales using a model-based approach. SHETRAN, a physically based, spatially distributed model, was applied in two southwest England catchments to represent: (a) changes in the land cover (cropland extent and spatial arrangement), (b) changes in crop type, and (c) use of riparian buffer strips. A total of 84 simulated events within a 4-year period were used to quantify flow and sediment generation impacts. We found past changes in land cover resulted in significant differences in sediment yield (p < 0.05). Linear regression showed an increase in flow and sediment yield proportional to increases in arable crop area (p < 0.001). The spatial arrangement of cropped fields and riparian buffer strips produced no significant differences in event flow or sediment yield (p > 0.05). However, buffer strip scenarios compared with the base run showed sediment load reductions in specific events, up to 20% and 15% for woodland and grass riparian buffers, respectively. When comparing crop types with and without the use of post-harvest cover crops, we observed non-significant differences (both Qv and Sy). However, large reductions in modelled sediment yields occurred for some events (e.g., up to 60% for winter cereals, 50% for maize and 74% for spring cereals). For these scenarios, examination of rainfall event magnitude emphasized the importance of ground cover in mitigating soil erosion for maize and spring cereals, but not for winter cereals. Our findings indicate that significant changes in sediment delivery at the event scale are associated with cropland extent and crop types, depending on rainfall magnitude, but not on the spatial arrangement of cropped fields or the use of riparian buffer strips.

Nitrogen removal by different riparian vegetation buffer strips with different stand densities and widths

The migration of nitrogen (N) from farmland to lake aggravates eutrophication. Riparian buffer strips (RBSs) are crucial in alleviating the nitrogen into water bodies. This study examined the impacts of different RBSs patterns on nitrogen removal. The effects of different RBSs of various widths (5, 15, 30, and 40 m), with different vegetation types (Taxodium Hybrid ‘Zhongshanshan’, poplar (Nanlin-95), and a mixed forest of T. Hybrid ‘Zhongshanshan’ and poplar) and at different densities (400, 1,000, and 1,600 plants·hm−2) on the TN, NH4+-N and NO3−-N removal rates in different depths of runoff water were studied. The results showed that the 15 m-wide RBS removed nitrogen the most effectively, with average removal rates of NH4+-N, NO3−-N and TN reaching 67.79%, 65.93% and 65.08%, respectively. Among the RBSs with different vegetation types, the poplars forest RBS removed the most NH4+-N (74.28%) and NO3−-N (61.71%). The mixed-forest RBS removed the most TN (65.57%). The RBS with 1,000 plants·hm−2 was more suitable in terms of the removal of NH4+-N (74.25%), NO3−-N (71.08%) and TN (62.67%). The conclusion can provide the basis of vegetation and width optimization for the design and construction of an RBS for maximum eutrophication nutrient removal.

Improvement of root morphological characteristics on water percolation rate in grassland soils of Yellow River riparian buffer strips

Soil water percolation is an important process required to meet plant water needs, determine soil water storage, and affect soil water quality in riparian buffer strips. However, the effects of plant roots on soil percolation in riparian buffer strips are not totally understood, and contradictory results have been carried out on the effects of the root system on soil percolation rates. This study aimed to investigate soil percolation in natural grasslands and evaluate the relationships between root morphological characteristics and percolation rates. Path analysis was used to provide information on the relative contribution of root characteristics on soil percolation rates. Three mixed grasslands (Imperata cylindrica + Phragmites australis, Imperata cylindrica + Cynodon dactylon, Imperata cylindrica + Juncellus serotinus) were selected in the Yellow River wetland natural reserves of Zhengzhou. Soil percolation rates (initial, average and steady infiltration rates) were measured by using double-ring methods, and plant root morphological characteristics were analyzed. Soil percolation rates and plant root characteristics parameters of Imperata cylindrica + Phragmites australis and Imperata cylindrica + Cynodon dactylon were higher than those of Imperata cylindrica + Juncellus serotinus. Initial percolation rate of Imperata cylindrica + Phragmites australis and Imperata cylindrica + Cynodon dactylon at 0-10cm depth was 58.06% and 95.55% higher than that of Imperata cylindrica + Juncellus serotinus, respectively. Percolation rates had a significant positive correlation with root characteristic parameters, and the main factor controlling soil percolation rates was root volume density. Mixed natural grasslands with more root volume density improved soil infiltration and percolation rates.

Analysis Effect of Cloud Cover, Wind Speed, and Water Temperature to BOD and DO Concentration Using QUAL2Kw Model (Case Study In Winongo River, Yogyakarta)

Winongo river is one of the rivers in the province of D.I. Yogyakarta that included in the category of contaminated. the research aims to learn on the effect variation of cloud cover, wind speed, and water temperature on BOD and DO concentrate in order to choose water quality management strategy at Winongo river. This research conducting a simulation with variating the cloud cover variables (0%, 69%, and 88%), wind velocity (0 m/second, 0,211 m/second and 1,22 m/second), and so the water temperature air (24,2°C, 28,14°C, and 30,6°C). The modeling result shows that cloud cover variables don’t affect the DO-BOD concentrate at Winongo river (sig = 0). While the wind velocity variables only have a small effect on the changed of DO and BOD at Winongo river (sig > 0,05). And for water temperature variables had the significant effect on the concentration changed of DO (sig < 0,05) and have a small effect on the changed of BOD at Winongo river (sig > 0,05). The DO and BOD management strategy can be done by making of riparian buffer strips or planting vegetation on the riverbank Winongo, build a WWTP Communal in every district along the river Winongo