Inorganic Nitrogen Load Research Articles

Non-point source loadings of nutrients and dissolved organic carbon from an agricultural-suburban watershed in East central Florida

Unit area loadings for nitrogen, phosphorus and dissolved organic carbon were measured from four sub-watersheds and the entire 256 km 2 catchment area tributary to the Indian River Lagoon. The catchment area is a rapidly growing suburban area drained by 322 km of canals in east central Florida. One-third of the annual total nitrogen, one-half of the total phosphorus and one-fourth of the annual dissolved organic carbon were exported in the drainage canal water at the water control structure to downstream waters during a 6-week period when three major storms occurred. High annual loadings of dissolved inorganic (1.3 kg N/ha-yr) and organic (4.4 kg N/ha-yr) nitrogen were recorded for the rotational grazing sub-watershed; during storm events, the entire dissolved inorganic nitrogen load leaving the catchment basin originated from the agricultural sub-watershed. Annual total nitrogen and total phosphorus export coefficients from the agricultural sub-basin deviated considerably from published “national” averages, but were very similar to “regional” coefficients published for Wisconsin. Dissolved inorganic nitrogen and phosphorus had wide variances to the published “regional” coefficients, emphasizing the need for site-specific studies.

Oxygen concentrations and elimination of inorganic phosphorus and nitrogen in an experimental watercourse stocked with emergent macrophytes

The suitability of an experimental watercourse stocked with emergent macrophytes was investigated to serve as tertiary treatment alternative. Two designs were studied at subsequent periods. During design 1 (May–September 1977 and April–July 1978) an area of 0.42 ha (1800 m long × ca. 2.40 m wide) was covered with Schoenoplectus lacustris (L.) Pallas, Typha latifolia L. and Glyceria maxima (Hartm.) Holmb. The system was flooded (0.2–0.3 m depth, maximum flow 60 l s −1) with water from a ditch which received secondary effluents from a municipal sewage treatment plant of 3000 population equivalents. Oxygen concentrations during the night increased from 2 mg l −1 in the inflow to 9 mg l −1 in the outflow. Average concentrations of orthophosphate decreased from 0.063 mmol l −1 in the inflow to 0.011 mmol l −1 in the outflow, corresponding values for inorganic nitrogen (total of ammonia plus nitrate) from 0.603 to 0.257 mmol l −1. From these data a total nutrient elimination of 125 mol d −1 orthophosphate and 840 mol d −1 nitrogen was estimated for the growing season. This was equivalent to 64% of the orthophosphate and 72% of the inorganic nitrogen load discharged into the system by the municipal sewage treatment plant. After modification to design 2 (August–October 1978 and May–October 1979) when the macrophytes had been removed from half the profile, the enhancement of the oxygen concentrations during the night and the elimination of the inorganic nutrients were not significant.

Preliminary assessment of nutrient loads on lake Taupo, New Zealand

Abstract Lake Taupo is an oligotrophic lake of 612.4 km2 and 97 m average depth, situated in a catchment of 2849 km2 on the Central Volcanic Plateau of the North Island of New Zealand. Annual loads of reactive phosphorus and inorganic nitrogen were estimated from aerial, surface stream, and groundwater seepage sources. The specific surface load for phosphorus of 0.189 g·m−2·y−1 suggests a mesotrophic status, but the nitrogen load of 1.073 g·m−2·y−1 fits the observed oligotrophic condition of the lake. The overall ratio of nitrogen to phosphorus in the inputs was only 5.68 : 1. Most of the phosphorus is derived from natural sources, and in general greater quantities leave wooded land (covered with native forest, pine plantations, and scrub) than leave mostly pastoral areas. The major nitrogen loads originate from one part of the catchment. Substantial variations in nutrient loadings and ratios in surface flows occur seasonally, with variations in flow rates, and between sub‐catchments. Obvious associations between sub‐catchment nutrient loads and vegetative cover were not found. The low ratio of nitrogen to phosphorus in inputs to the lake suggests that nitrogen may prove to be an important growth‐limiting nutrient. Variable climate is likely to affect nutrient ratios and loading estimates for lakes without major sources of man‐made pollution.