SEGH Articles

Nutrient export coefficients and the Northern Ireland Environment Agency river nitrate data

21 March 2011
Judith Watson was the joint winner of the Hemphill prize for best oral presentation at Galway SEGH 2010.

Nitrate nitrogen (NO₃N) and, to a lesser extent, ammonium nitrogen (NH₄N) are important nutrients that can influence the nutrient enrichment (eutrophication) of surface waters and, to meet EU Directives, are subject to legislative controls. Nutrient export coefficients are widely used in water quality modelling assessments as they offer a means to assess the impacts of land use change on the eutrophication of both marine and freshwater systems. Queen's University Belfast and the Agri-Food and Biosciences Institute are analysing how river nitrate levels in Northern Ireland are changing and this PhD research is entitled, ‘spatial analysis approaches to modelling water quality in Northern Ireland'. This research involves deriving nitrogen export rates measured in rivers in Northern Ireland for CORINE landcover classes, with the main aim of updating CORINE-based annual NO₃N riverine export coefficients for 2003-2008 so as to compare them with coefficients determined in the 1990s.  A secondary aim is to estimate CORINE-based NH₄N export coefficients as these have not been previously derived.

In-stream NO₃N and NH₄N concentrations from 534 river monitoring stations for 2003-2008 were supplied by the Northern Ireland Environment Agency (NIEA).  Mean concentrations per catchment were calculated for two time periods: 2003-2005 and 2006-2008.  Using ESRI's ArcGIS software, river catchment boundaries were overlaid with UK Met Office long-term annual mean rainfall and potential transpiration grids for the period 1971-2000 to estimate mean annual flow rates per catchment.  Mean annual nitrate loadings for 2003-2005 and 2006-2008 were calculated by multiplying annual mean NIEA nitrate concentrations with estimated annual river flows on a catchment-by-catchment basis.  By allowing for the human N contribution from sewers and septic tanks, we were able to determine the agricultural nitrate load for each catchment.   CORINE landcover data were extracted by overlaying the CORINE landcover map with the river catchment boundaries to give a breakdown of CORINE landcover areas for each catchment. 

Independent, small agricultural catchments distributed across Northern Ireland were selected for regression analysis.  Using the CORINE landcover classification areas of these catchments as independent (x-axis) variables and mean annual agricultural nitrate loadings as dependent (y-axis) variables, mean annual nitrate export coefficients were derived for each landcover class using stepwise, backward linear regression.  Results obtained for NO₃N show a statistically significant decrease in newly-derived export coefficients of 3.64 kgN/ha/yr for improved grassland and 2.57 kgN/ha/yr for non-improved grassland, for the years 2003-2005, from pre-2000 levels.  Similarly, decreases from pre-2000 levels were also observed for the period 2006-08. To validate these results, a further regression of predicted (newly derived export coefficient) NO₃N loadings and observed NO₃N loadings (based on the NIEA data) was undertaken for the selected independent catchments, for each time period.  The slope of each regression was close to 1.0, with 99% significance, indicating that CORINE landcover-based nutrient export coefficients are a good indicator of riverine NO₃N loadings. 

In contrast, NH₄N export coefficients showed little variation between the dominant landcover classes of Northern Ireland viz. good pasture, poor pasture, coniferous forest and peat bogs. For the period 2006-2008, coefficients for NH₄N ranged from 0.54-0.67 kgN/ha/yr.  This range was similar for 2003-2005.  It was concluded that NH₄N is independent of landcover class and therefore riverine NH₄N loadings may be more closely related to other variables.  Future work will investigate the relationship of NO₃N and NH₄N catchment loadings to soil type and also to manure N from farm livestock.

The results of this research show how NO₃N exports vary between landcover types.  This is of potential use to water and land use managers as the updated export coefficient model can be used to assess both changes in loss of nutrients from specific land cover classes (which, in this study, were found to be declining) and to predict the effects of future land use change on riverine NO₃N and NH4N levels.  

Judith Watson, Queen's University Belfast.

Keep up to date

SEGH Events

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

  • Biochar-based constructed wetlands to treat reverse osmosis rejected concentrates in chronic kidney disease endemic areas in Sri Lanka 2017-12-01

    Abstract

    The objectives were to investigate the potential remedial measures for reverse osmosis (RO) rejected water through constructed wetlands (CWs) with low-cost materials in the media established in chronic kidney disease of unknown etiology (CKDu) prevalent area in Sri Lanka. A pilot-scale surface and subsurface water CWs were established at the Medawachchiya community-based RO water supply unit. Locally available soil, calicut tile and biochar were used in proportions of 81, 16.5 and 2.5% (w/w), respectively, as filter materials in the subsurface. Vetiver grass and Scirpus grossus were selected for subsurface wetland while water lettuce and water hyacinth were chosen for free water surface CWs. Results showed that the CKDu sensitive parameters; total dissolved solids, hardness, total alkalinity and fluoride were reduced considerably (20–85%) and most met desirable levels of stipulated ambient standards. Biochar seemed to play a major role in removing fluoride from the system which may be due to the existing and adsorbed K+, Ca+2, Mg+2, etc. on the biochar surface via chemisorption. The least reduction was observed for alkalinity. This study indicated potential purification of aforesaid ions in water which are considerably present in RO rejection. Therefore, the invented bio-geo constructed wetland can be considered as a sustainable, economical and effective option for reducing high concentrations of CKDu sensitive parameters in RO rejected water before discharging into the inland waters.

  • Medical geology of endemic goiter in Kalutara, Sri Lanka; distribution and possible causes 2017-12-01

    Abstract

    This study assesses the distribution of goiter in the Kalutara District, Sri Lanka in order to find causative factors for the occurrence of goiter even after the salt iodization. A questionnaire survey was conducted at the household level and at the same time iodine and selenium levels of the water sources were analyzed. Questionnaire survey results indicated the highest numbers of goiter patients in the northern part where the lowest were found in the southern sector which may be due to the presence of acid sulfate soils. Females were more susceptible and it even showed a transmittance between generations. Average iodine concentrations in subsurface water of goiter endemic regions are 28.25 ± 15.47 μg/L whereas non-goiter regions show identical values at 24.74 ± 18.29 μg/L. Surface water exhibited relatively high values at 30.87 ± 16.13 μg/L. Endemic goiter was reported in some isolated patches where iodine and selenium concentrations low, latter was <10 μg/L. The formation of acid sulfate soils in the marshy lands in Kalutara district may lead to transformation of biological available iodine oxidation into volatile iodine by humic substances, at the same time organic matter rich peaty soil may have strong held of iodine and selenium which again induced by low pH and high temperature were suggested as the instrumental factors in the endemic goiter in Kalutara district. Hence, geochemical features such as soil pH, organic matter and thick lateritic cap in the Kalutara goiter endemic area play a role in controlling the available selenium and iodine for food chain through plant uptake and in water.

  • Nickel accumulation in paddy rice on serpentine soils containing high geogenic nickel contents in Taiwan 2017-12-01

    Abstract

    We investigated the extractability of nickel (Ni) in serpentine soils collected from rice paddy fields in eastern Taiwan to evaluate the bioavailability of Ni in the soils as well as for demonstrating the health risks of Ni in rice. Total Ni concentrations in the soils ranged were 70.2–2730 mg/kg (mean, 472 mg/kg), greatly exceeding the natural background content and soil control standard in Taiwan. Available Ni concentration only accounts for <10% of total soil Ni content; 0.1 N HCl-extractable Ni was the more suitable index for Ni bioavailability in the soil to rice than was diethylenetriaminepentaacetic acid (DTPA)-extractable Ni. The accumulation ability of rice roots was much higher than that of its shoots; however, compared with those reported previously, our brown and polished rice samples contained much higher Ni concentrations, within the ranges of 1.50–4.53 and 2.45–5.54 mg/kg, respectively. On the basis of the provisional tolerable Ni intake for adults recommended by the World Health Organization (WHO), daily consumption of this rice can result in an excessive Ni intake.