Quantifying anthropogenic nutrient sources and loadings within a small catchment with conservation interests, eastern Scotland

Abstract

ABSTRACT1. This paper demonstrates the possibility of quantifying sub-catchment nutrient budgets from routinely monitored hydrological and hydrochemical data. The relative importance of a number of potential anthropogenic nutrient sources was quantified for a small catchment in Scotland. Within the catchment there are two Sites of Special Scientific Interest, including two lochs and a floodplain mire. The study was undertaken to provide information for prescribing strategies to safeguard the conservation interests of these aquatic systems.2. The principal source of nitrate was found to be groundwater. Phosphate and ammonium loadings were greatest in surface run-off. The evidence indicates that the greatest contributor towards these nutrient sources is agriculture. Even when conservative estimates of losses were applied, current fertilizer and animal inputs could account for present day nutrient loadings. In addition, changes in the area under arable farming and under individual crops during the past 30 years are consistent with trends in nitrate and phosphate loads.3. Nutrient inputs from sewage works overflows and septic tanks within the catchment were estimated to be small. Leachate from a landfill site within the catchment was also not considered to be a major source of nutrients, but a more intensive water quality monitoring programme would be needed to confirm the absence of leachate plumes.4. The only long-term solution to reducing nutrient loadings to the aquatic systems is a reduction in agricultural activities within the catchment and avoidance of fertilizer and slurry applications near water sources. Diversion of drainage ditch waters supplying the floodplain mire is also a possibility but the hydrological consequences of such an action could induce more severe degradation than that due io nutrient enrichment.