Denitrification potential of organic, forest and grassland soils in the Ribble-Wyre and Conwy River catchments, UK

Abstract

Soil denitrification activity can be highly variable due to the effects of varied land use management practices within catchments on the biogeochemical regulators of denitrification. To test this assumption in the context of mixed-use rural catchments, it was hypothesised that the relative magnitude of denitrification activity may be regulated, among others, by a gradient of soil nitrate (low to high) between organic (peat bog, heathland, and acid grassland), forest (coniferous and deciduous), and grassland (improved and semi-improved) rural land use types. The denitrification potential (DP) of organic, forest and grassland soils, in two UK catchments was measured in the laboratory. Land use type significantly (p < 0.05) influenced the DP, which ranged between 0.02 and 63.3 mg N m(-2) h(-1). The averaged DP of organic and forest soils (1.08 mg N m(-2) h(-1)) was 3 and 10 times less than the DP of semi-improved (4.06 mg N m(-2) h(-1)) and improved (12.09 mg N m(-2) h(-1)) grassland soils, respectively; and among others, nitrate correlated positively (p < 0.05) with the DP. The results indicated that the difference in soil nitrate concentration between organic (naturally low in nitrate availability) and grassland soils (nitrate enriched due to land management) partially regulated the extent of DP. In the absence of N fertilisation, except for the atmospheric N deposition, the relatively low net nitrification potential (as a source of nitrate for denitrifiers) of organic and forest soils alone seem to have resulted in lower denitrifier's activity compared to grassland soils. Moreover, the interactions between soil organic carbon, pH, bulk density, water filled pore space, and texture, as these are influenced by the relative degree of land management, exerted additional controls on the DP. The results suggest that land management can have significant effects on denitrification, and thus needs to be considered when modelling and/or predicting the response of denitrification to land use change.

Soil Greenhouse Gas Fluxes, Environmental Controls, and the Partitioning of N2O Sources in UK Natural and Seminatural Land Use Types

“…In the case of the MW forest, which displayed the lowest WFPS and the highest availability of mineral N (Table 1), there was strong indication that nitrification rather than denitrification may be quantitatively more important as an N 2 O source Matson et al, 2009;Ullah & Moore, 2011). This is also supported by the highest nitrification potential of the MW shown in a preliminary study (Sgouridis & Ullah, 2014). This suggests that enhanced nitrification due to increased N inputs in well-drained forest soils could consequently lead to increased N 2 O emissions .…”

“…Fertilization and grazing with mineral nitrogen in the improved grasslands are the primary reasons for the higher N 2 O emissions from this land use type, and this dose-response relationship has been well documented in the literature (Cardenas et al, 2010;Rafique et al, 2011;Skiba et al, 2013) and likely explains Journal of Geophysical Research: Biogeosciences 10.1002/2017JG003783 the 3 times lower emissions from the unfertilized SIG. Conversely, the N 2 O emission from the OS was limited by nitrate supply as indicated by the MLR (Table 2) and also by the significantly lower nitrification and denitrification potentials compared to the other land use types (Sgouridis & Ullah, 2014).…”

“…Soil reactive N (labile organic bound N and inorganic N compounds) availability has been advocated as the major driver of N 2 O emissions from soils (Butterbach-Bahl et al, 2013), while soil moisture and temperature provide additional controls by regulating the availability of oxygen and microbial enzymatic activity, respectively (Butterbach-Bahl et al, 2013;Schaufler et al, 2010). The interaction of these environmental controls, particularly due to the opposing conditions (aerobic versus anaerobic) for N 2 O production, and the contribution of other distal controlling factors such as soil organic carbon quality, soil pH, and texture (Saggar et al, 2013;Sgouridis & Ullah, 2014) commonly lead to weak relationships between N 2 O fluxes and environmental variables measured in the field (Carter et al, 2012;Luo et al, 2012;Skiba et al, 2013), further hampering our ability to predict N 2 O fluxes at the landscape scale and in response to changing environmental conditions. Despite the wealth of studies that have investigated GHG fluxes and their controlling factors, the majority have focused on one or two land use types and only a few have considered all major GHGs across a range of natural and seminatural land use types in the laboratory (Schaufler et al, 2010), in meta-analysis (Mander et al, 2010), and under field conditions (Czóbel et al, 2010).…”

Application of the &lt;sup&gt;15&lt;/sup&gt;N-Gas Flux method for measuring in situ N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O fluxes due to denitrification in natural and semi-natural terrestrial ecosystems and comparison with the acetylene inhibition technique

“…These sites were an acid grassland (C-UG), an ombrotrophic peat bog (C-PB), a mixed deciduous and coniferous woodland (C-MW), and an improved grassland (C-IG). Further details on the location, land management status, and major soil properties for all study sites can be found in Sgouridis and Ullah (2014).…”

Delineating and mapping riparian areas for ecosystem service assessment

“…In this sense, ecosystem services may be incorrectly assigned due to strong correlation between land cover type and ecosystem service provision (Burkhard et al, ; Maes, Paracchini, & Zulian, ; Peterson et al, ). For example, Sgouridis and Ullah () established a link between land cover and land‐use management with denitrification potential. The importance of accurate habitat identification is also endorsed by studies like Tscharntke, Klein, Kruess, Steffan‐Dewenter, and Thies (), which showed that local habitats might be essential to improve the delivery of ecosystem services, enhancing local diversity and providing a natural corridor of special importance in simple landscapes dominated by arable fields.…”