Seasonal Variability of Dissolved Nutrients in the Humber–Ouse Estuary, UK

N2O seasonal distributions and air-sea exchange in UK estuaries: Implications for the tropospheric N2O source from European coastal waters

“…The NH 4 + and NO 2 − distributions give insight into the nature of the NO 3 − source. In all three surveys NH 4 + decreased rapidly downstream of a maximum (30–100 μ M) located just upstream of the NO 3 − maximum, as found previously [ Uncles et al , 1999b]; a >90% reduction in concentration was evident by salinity ∼4 (Figure 2). These data support the earlier contention of us and others [ Barnes and Owens , 1999; Tappin et al , 2003] that the upper Humber estuary is a site of permanent and strong NH 4 + nitrification.…”

“…NO 3 − behaved similarly in all three surveys; apparently conservative mixing seaward of a maximum ∼600 μ M at salinity <2 (Figure 2) coincident with the TMZ [ Uncles et al , 1999b; Barnes and Owens , 1999]. Uncles et al [1999b] reported lower DIN values in river water immediately upstream of the freshwater‐saltwater interface, consistent with our observations. The data imply a large in situ NO 3 − source at low salinity which subsequently undergoes apparently conservative mixing; any additional NO 3 − sources or sinks further downstream appear to be insignificant.…”

“…The total annual load of oxidized DIN (NO 2 − and NO 3 − ) is the highest of any UK estuary [ Nedwell et al , 2002]; NO 3 − concentrations ∼600 μ M are not uncommon [ Sanders et al , 1997]. Nonconservative addition of NO 3 − in the tidal Ouse and NH 4 + maxima of up to 70 μ M in the TMZ imply large in situ sources of NO 3 − and NH 4 + at low salinities [ Uncles et al , 1999b].…”

“…Fully anoxic conditions as required for the onset of denitrification would be atypical of our study estuaries. In the Humber, Forth and Tamar TMZs for example, lowest dissolved O 2 saturations are typically ∼10% during summer, coincident with high concentrations of SPM [ Morris et al , 1985; Law et al , 1992; Balls et al , 1996; Mitchell et al , 1999; Uncles et al , 1999b], and not conducive to denitrification. Figure 3 shows highest N 2 O saturations at highest SPM concentrations associated with the TMZ, consistent with greater N 2 O production at low dissolved O 2 saturation.…”

Rapid Nitrate Uptake Rates and Large Short-Term Storage Capacities May Explain Why Opportunistic Green Macroalgae Dominate Shallow Eutrophic Estuaries1

“…We conducted two separate mesocosm experiments with U. intestinalis and U. expansa to determine how nitrate uptake rate and accumulation of tissue nitrogen varied with initial algal tissue nitrogen status (enriched and depleted) and initial water nitrate concentration (low, medium, and high). Experiments were conducted in summer of 2001, and both initial tissue nutrient levels and N pulses were within the range of values measured in the dry season in southern California estuaries subject to algal blooms (Kennison 2008) as well as other eutrophic Mediterranean systems (Barnes and Owens 1998, Uncles et al. 1998).…”