Observed dissolved and particulate nitrogen concentrations in a mini flume

Abstract

Previous measurements of the benthic nitrogen (N) flux from resuspended estuarine particles in the Thames Estuary appeared to underestimate benthic inputs. This study attempted to address experimental limitations by using a mini-annular flume. The flume has a 45 l capacity and was prepared in order to facilitate trace chemical analysis of N. Sediment (S1) and suspended particulate material (SPM; S2) were collected from the Tamar Estuary, UK, and added to prepared, low-N, freshwater and seawater solutions to give a final particle concentration of 500 mg l−1. Two tidal cycles were simulated and SPM and total dissolved N (TDN) were measured at a range of turbulent shear stresses (0.06–0.9 Pa) representative of the sampling sites. A large increase in TDN concentration was measured after particle addition and initial mixing, due to release of loosely bound particulate N (PN). The TDN concentration increased as the experiment progressed (up to 12 μM), but did not appear to be systematically linked to either salinity or SPM concentration. The flume system and experimental protocol provided reproducible physical data and low detection limits for TDN, which demonstrates its potential for studying relationships between estuarine particle transport and macronutrient cycles.