Nitrogen Release from Sediments in Agricultural Drainage Canals

Abstract

Many water quality conservation measures have been implemented in agricultural areas to reduce pollutant loading. We investigated agricultural drainage canals in three paddy-field districts around Lake Biwa. In this paper, we focus on nitrogen (N) and organic carbon (C) released from the sediments in the drainage canals. We collected sediment cores and conducted an incubation experiment. We measured temporal change in concentrations of N and organic C in the overlying water of the sediments. As a result, we found that the nitrogen is released mainly as inorganic nitrogen (ammonium N). Ammonium N flux for each sediment sampled from St. 1, St. 2 and St. 3 was 24, 13, and 41 mg N/m 2 /d, respectively. Nitrogen was released from the sediments mainly in an inorganic state. The C/N ratio of the sediments was about 10 and almost constant during the incubation period. It is suggested that the fraction of organic decomposed in the sediments was small during the incubation experiment.

Role of Organic Nitrogen and Carbon in Canal Sediments on Drainage Water in Paddy Fields

“…In particular, the drainage canal sediments can be NH 4 -N source because the ratio was high. Table 1 Mean water depth and N and organic C concentrations in the drainage water measured during the field investigation [4]. Site Parameter Depth (cm) Table 2 Mean N and organic C concentrations in the irrigation water measured during the field investigation.…”

“…Drainage water and irrigation water were sampled monthly at each site for two years since April 2011 [2,4]. Drainage water was analyzed for total N (T-N), total dissolved N (TD-N), ammonium N (NH 4 -N), nitrite N (NO 2 -N), nitrate N (NO 3 -N), total organic C (TOC), and dissolved organic C (DOC).…”

“…The experiments were performed in triplicate. In this paper, the concentrations of N and C released from the sediments, which was incubated for 28 days, were used for analysis because the release of N and C might reach the saturation concentrations [4]. After the incubation period, 50 mL of the overlying water was sampled and analyzed for T-N, TD-N, NH 4 -N, NO 2 -N, NO 3 -N, and DOC.…”

Historical changes in primary production in the Seto Inland Sea, Japan, after implementing regulations to control the pollutant loads

“…For example, Harima Nada is next to Osaka Bay and the Kii Channel, and nutrient transport from the Pacific Ocean is also well documented (Yanagi & Ishii, 2004). Sediment may also be a source of nutrients (Savchuk et al, 2009;Jikumaru et al, 2015;Nguyen & Maeda, 2016). In addition, seawater velocity may affect primary production by not only changing the retention of nutrients (Savchuk et al, 2009) but also light conditions (Wetsteyn & Kromkamp, 1994).…”