Effects of agricultural land use on dissolved organic carbon and nitrogen in surface runoff and subsurface drainage

Abstract

Dissolved organic carbon (DOC) load in discharges from cultivated soils may have negative impacts on surface waters. The magnitude of the load may vary according to soil properties or agricultural management practices. This study quantifies the DOC load of cultivated mineral soils and investigates whether the load is affected by agricultural practices. Discharge volumes and concentrations of DOC and dissolved organic nitrogen (DON) were continually measured at three sites from surface runoff and artificial subsurface drainage or from combined total discharge over a two-year period (2012-2014). Two experimental sites in South-West Finland had clayey soils (with soil carbon contents of 2.7-5.9% in the topmost soil layer), and the third site in West-Central Finland had sandy soil (soil carbon contents of 4.3-6.2%). Permanent grassland, organic manure application, mineral fertilization, and conventional ploughing or no-till activities were studied. Furthermore, the biodegradable DOC pool of surface runoff and subsurface drainage water from no-till and ploughed fields was estimated in a 2-month incubation experiment with natural bacterial communities collected from the Baltic Sea seawater. The annual DOC and DON loads were affected by discharge volume and seasonal weather conditions. The loads varied between 25-52kgha and 0.8-3.2kgha, respectively, and were comparable to those from boreal forests with similar soil types. The DOC load increased with increasing topsoil carbon content at all sites. There were slightly higher DOC concentrations and DOC load from permanent grassland, but otherwise we could not distinguish any clear management-induced differences in the total DOC loads. While only 6-17% of the DOC in discharge water was biologically degraded during the 2-month incubation, the proportion of biodegradable (labile) DOC in surface runoff appeared to increase when soil was ploughed compared to no-till.

Recycling of Biogas Digestates in Crop Production—Soil and Plant Trace Metal Content and Variability

“…In 2016, a higher volume of manure was added (233 L per plot) than in 2015 because of a lower N concentration. An increase in DOC concentration over the growing season with the use of organic fertilizers (composts) has also been confirmed in a recent study (Manninen et al, 2018). The rather low watersoluble concentration of Mo in our study may be explained by the fact that the strongest adsorption of Mo to the soil occurs at around pH 5 (Smith et al, 1997), which is not different from the pH values measured in the samples from our field experiment in August.…”

A Synthetic Model to Quantify Dissolved Organic Carbon Transport in the Changjiang River System: Model Structure and Spatiotemporal Patterns

“…It is estimated that, on a global scale, the amount of DOC that the river networks transport to the oceans is approximately 0.17–0.36 Pg C/year (1 Pg is 10 9 t; Aitkenhead & McDowell, ; Dai et al, ; Harrison et al, ; Li et al, ; Ludwig et al, ). Due to its active biogeochemical properties, DOC can affect the transportation and transformation of other pollutants, such as the complexation of heavy metals, and the effects on the nutrient cycle, which may profoundly impact climate change, damage ecosystems, and increase environmental pollution (Brett et al, ; Manninen et al, ). Hence, riverine DOC has remained an important issue in the context of the global and regional carbon cycle and budget studies for the last few decades.…”

Nitrogen losses from two contrasting agricultural catchments in Norway

“…Nitrate-N was found to be the main type of N loss from agricultural land-use catchments [31]. Generally, the amounts of nitrate-N in runoff water are influenced by N mineralization, local precipitation, crop systems [32] and discharge [13], and soil freeze–thaw cycles during winter could be another dominant factor leading to high N losses and N concentrations in runoff water [33]. In this study, higher losses of nitrate-N were found in the Skuterud catchment than in the Naurstad catchment (figure 4), which may be due to the high temperature, more soil tillage, high N fertilizer application and N surplus in Skuterud, and therefore increased N mineralization [34].…”

“…Such a periodic variation is well known in areas dominated by annual crops [22]. Nitrogen loads in agriculture-dominant catchments depend on seasonal conditions [13]. Owing to increased uptake by plants, the lowest N concentrations were observed during the summer months (June–August) [5,10].…”

“…Soil tillage has been shown to increase N losses in agricultural soils due to increased mineralization and the absence of plant N uptake [11–13]. Furthermore, in Norway, the relatively high concentrations of nitrate-N in drainage water from fallow plots resulted from the large amounts of nitrate-N mineralized in the soil during the summer season [14].…”