The significance of denitrification in relation to external loading and nitrogen retention in a mountain reservoir

Abstract

Nitrogen retention (Nret) and denitrification were studied in the mesotrophic Solina reservoir (south-east Poland) between spring and autumn in 2002 and 2003. Nret was calculated on the basis of the input-output mass balance. The rate of denitrification was measured using the 15N isotope pairing technique in two types of areas; in deep areas, where the bottom sediment makes contacts with the hypolimnion (Dprof), and in the unstratified shallows (Dlitt). The calculated daily load of removed nitrogen (Dtot) varied somewhat from 11.0 to 19.1 mg N m–2 day–1 with a standard deviation of 3.0 mg N m–2 day–1. The limited oscillation noted for Dtot results from the major participation of the deep areas of the reservoir, which are characterised by stable Dprof, as distinct from Dlitt, which varied seasonally from 5.8 mg N m–2 day–1 in November to 109.9 mg N m–2 day–1 in August. The primary factor limiting the denitrification rate was temperature, the other being availability of substrates, mainly organic matter. Nitrogen retention ranged seasonally between –25.0 and 175.9 mg N m–2 day–1. The contribution of denitrification to Nret ranged from 9.0% to 49.8% (mean 16.4%). On average, only 4.9% of the nitrogen external load was denitrified (range 2.6–7.9%, s.d. 1.5%). After comparing obtained data with others available in the literature, we concluded that reservoirs, estuaries and highly-loaded lakes in a river system experience a more limited contribution of Dtot to Nload than is the case in natural lakes.

Microbial dinitrogen and nitrous oxide production in a small eutrophic reservoir: An in situ approach to quantifying hypolimnetic process rates

“…The vegetated littoral zone could contribute disproportionately to whole-system denitrification due to the prevalence of oxic microsites on plant roots, which support nitrification adjacent to anoxic sites supporting denitrifier communities (Christensen and Sorensen 1986). While some studies find no relationship between denitrification rates and the height of overlying water column (David et al 2006), a number of studies find higher N removal at littoral sites Koszelnik et al 2007). Littoral zones have also been identified as hot spots for N 2 O production (Wang et al Fig.…”

Partitioning whole‐lake denitrification using in situ dinitrogen gas accumulation and intact sediment core experiments

“…If these estimates were accurate for our study reservoirs, then approximately 40-75% of N retained would have been denitrified in the reservoirs in 2010, which would be among the highest reported rates of denitrification efficiency for aquatic ecosystems (Kozelnik et al 2007).…”

“…Fewer estimates of the contribution of denitrification to N retention in reservoirs exist. However, high area-specific nutrient loading (Kozelnik et al 2007) and high rates of carbon burial (Downing et al 2008) make man-made impoundments potential landscape-scale denitrification hotspots. Reservoirs that experience seasonal thermal stratification may also represent predictable hot moments for denitrification (Groffman et al 2009).…”

“…Inland freshwater networks transport terrestrial N to sensitive downstream ecosystems, but freshwater networks also retain up to 50% of watershed N inputs (Wollheim et al 2008). The magnitude of this ecosystem service differs between aquatic systems, with greater N retention efficiency in systems with long water-residence times, such as natural lakes and man-made reservoirs (Saunders and Kalff 2001;Kozelnik et al 2007). …”

Development and application of the Riparian Mapping Tool to identify priority rehabilitation areas for nitrogen removal in the Tully - Murray basin, Queensland, Australia

“…The underlying assumptions that underpin the RMT are that: (1) the riparian zones have a uniform width and run parallel to the stream network; (2) the groundwater table is parallel to the ground surface with a gradient towards the stream (gaining stream); (3) nitrate is removed via denitrification in the saturated part of the root zone with activity decreasing with depth; and (4) temperature effects are ignored, although they can be a limiting factor on the extent of denitrification (Koszelnik et al 2007). Although the profile of the denitrification potential is assumed to be constant in this study (point 3), each riparian cell would have a different nitrate removal potential because the hydrology is different (i.e.…”