Estimation of nitrogen budgets for contrasting catchments at the landscape scale

Abstract

Abstract.A comprehensive assessment of nitrogen (N) flows at the landscape scale is fundamental to understand spatial interactions in the N cascade and to inform the development of locally optimised N management strategies. To explore these interactions, complete N budgets were estimated for two contrasting hydrological catchments (dominated by agricultural grassland vs. semi-natural peat-dominated moorland), forming part of an intensively studied landscape in southern Scotland. Local scale atmospheric dispersion modelling and detailed farm and field inventories provided high resolution estimations of input fluxes. Direct agricultural inputs (i.e. grazing excreta, N 2 fixation, organic and synthetic fertiliser) accounted for most of the catchment N inputs, representing 82 % in the grassland and 62 % in the moorland catchment, while atmospheric deposition made a significant contribution, particularly in the moorland catchment, contributing 38 % of the N inputs. The estimated catchment N budgets highlighted areas of key uncertainty, particularly N 2 exchange and stream N export. The resulting N balances suggest that the study catchments have a limited capacity to store N within soils, vegetation and groundwater. The "catchment N retention", i.e. the amount of N which is either stored within the catchment or lost through atmospheric emissions, was estimated to be 13 % of the net anthropogenic input in the moorland and 61 % in the grassland catchment. These values contrast with regional scale estimates: Catchment retentions of net anthropogenic input estimated within Europe at the regional scale range from 50 % to 90 %, with an average of 82 % . This study emphasises the need for detailed budget analyses to identify the N status of European landscapes.

Ammonia Emissions May Be Substantially Underestimated in China

“…2 NH3 emitted to the atmosphere is either deposited directly or transformed into an ammonium aerosol (e.g., ammonium nitrates and ammonium sulfate) often transported over long distances. 3 Two types of NHx (NH3 (gas) + NH4 + (aerosol)) deposition usually occur: dry deposition of NH3 close to the emission sources, 4,5 and wet deposition of NH4 + that can occur at far distances downwind from the sources. 6 N biogeochemical cycles follow the principle of mass balance, and the Nr input to and output from the atmosphere system are normally balanced.…”

Chronic atmospheric reactive N deposition has breached the N sink capacity of a northern ombrotrophic peatbog increasing the gaseous and fluvial N losses

“…Assessing nitrogen budgets at the ecosystem scale can be an indicator of environmental pressures, with the determination of stock quantities and dynamics of Nr fluxes between air, soil and water, providing important information for designing effective environmental regulations for mitigating environmental pressures (Vogt et al, 2013). Although complete C budgets for bogs are now common in the literature (Billett et al, 2010;Moody et al, 2018;Nilsson et al, 2008;Worrall et al, 2018), comprehensive N budgets have received comparatively little attention.…”

“…While overall the system was found to be a sink of 1.9 kg N ha −1 y −1 , for 4 years the system acted as a net source of N, suggesting a transition from net N sink to net source. Similarly, Vogt et al (2013) and Drewer et al (2010) concluded that a moorland catchment in southern Scotland is showing signs of nitrogen saturation, defined as ecosystem N losses being equal or exceeding N inputs (Butterbach-Bahl et al, 2011), with a negative N balance of −1.6 to −2.4 kg N ha −1 y −1 . Despite a relatively low atmospheric N deposition rate (3.3 kg N ha −1 y −1 ) in a northern Minnesota bog, it was found that more than twice as much N was exported than received (Hill et al, 2016).…”

“…However, N inputs may have been underestimated since biological N 2 fixation (BNF) was not measured but a literature value of 0.5 kg N ha −1 y −1 (Urban and Eisenreich, 1988) was used instead, while denitrification N losses were estimated under laboratory conditions with the unreliable acetylene inhibition technique (Felber et al, 2012;Sgouridis et al, 2016). Due to a scarcity of reliable data, this is true for all recent N budget studies in bogs, which commonly rely on literature estimates of BNF (Vogt et al, 2013). In addition, uncertainty estimations of the N mass balance are often increased as in-situ measurements of gaseous N losses are commonly substituted for either literature estimates (Worrall et al, 2012) or calculated using highly uncertain emission factors (Vogt et al, 2013).…”

Reservoirs are hotspots of nitrogen cycling in peatland catchments

“…The use of nutrient input-output budgets as a method for evaluating the impacts of anthropogenic activities on the fluvial environment has long been recognized (Crisp, 1966;Winter et al, 2002;Cooper, 2005;Rothwell et al, 2008;Vogt et al, 2013). Freshwater acidification from high atmospheric sulphur (S) and inorganic nitrogen (N) deposition is a major water quality problem in many upland environments in the Northern Hemisphere (Stoddard et al, 1999;Curtis et al, 2000;Evans et al, 2000;Aherne et al, 2003;Skjelkvale et al, 2003).…”