An overview of diffuse pollution inputs and their impacts upon organisms in the River Almond, Scotland

The Water Framework Directive (WFD), published by the European Union in 2000, implemented by SEPA in Scotland, has been the main force behind changes to river environments within Scotland. The main focus is on improving water quality by not just considering the chemical characteristics of water but also the ecological characteristics of the ecosystems. Diffuse pollution, in the form of nitrogen, phosphorus and sediment inputs, has a major influence on river water quality. Catchment land use is seen as a key driver of diffuse pollution, with an estimated 75% of Scotland’s diffuse pollution originating from agricultural inputs. The aim of this study was to assess the extent of diffuse pollution inputs and their effects on the River Almond, Scotland. This was achieved through a combination of catchment-scale assessment of diffuse inputs based on land use characteristics, a walkover survey quantifying key in-channel features, modification, pollution points and flow types and sampling and evaluation of macroinvertebrate communities at contrasting sites. The length of the river was further broken down into 12 sections of equal size and different riparian corridor levels, 25m, 50m, 100m, 200m and 500m to further analyse diffuse pollution impact at a local scale. Phosphorus data was used as the primary indicator of a ‘high’ or ‘low’ nutrient load as nitrogen coefficients lacked the specificity required to determine this accurately. To try and quantify the levels of diffuse pollution present within the Almond catchment, a walkover survey was conducted along the main stem inventorying key in-channel features, modification, pollution points and flow types. Variation in perceived pollution loads and habitat characteristics facilitated the selection of kick sampling sites for macroinvertebrate collection in order to assess the impact that diffuse pollution has upon habitat and water quality at a local level. Eighteen samples were collected in total in areas along the main stem consisting of 12 samples at high P input sites, 6 at riffle sites and 6 at pool sites, whilst 6 were sampled at low P input riffle sites. The aim of this was to assess how different flow types respond to diffuse pollution and whether differences between macroinvertebrate communities were evident between high and low P input sites. Analysis primarily consisted of the calculation of indices such as the Lotic-Invertebrate Index for Flow Evaluation (LIFE), Percentage of Sediment-sensitive Invertebrates (PSI), Biological Monitoring and Working Party (BMWP), Average Score Per Taxon (ASPT), Number of Taxa (N-Taxa) and abundance weighted metrics for WHPT ASPT and N-taxa where once calculated were compared to predicted values provided by River Invertebrate Classification Tool (RICT) – this allowed for Ecological Quality Ratings (EQR) to be calculated to assess water quality at these sites.Non-irrigated agricultural land was identified as the land use that contributes most significantly to overall predicted nutrient loading to the river. There were no clear relationships between nutrient loadings calculated based on land use characteristics and the quantity or extent of diffuse pollution sources recorded in the walkover survey. This would tend to indicate that catchment-scale analysis and walkover surveys provide complementary but different information regarding diffuse pollution inputs; a combination of both types of information is likely to be useful in assessing potential impacts.Non-significant results were found when looking for relationships between the number of diffuse points per section, the levels of erosion and the levels of poaching in relation to the P loading for that section at any riparian corridor level.Evaluation of the invertebrate communities between areas with high and low diffuse nutrient loading using Ecological Quality Ratios for several relevant biotic indices found no difference in quality. However, comparison of different habitat types (pools and riffles) within high nutrient loading areas showed significant differences in a number of metrics, with riffles having higher quality. The River Almond is subject to a range of other influences, notably point source pollution and hydromorphological modification which may obscure any response to variation in diffuse inputs. However, the observed differences between pools and riffles suggest that variation in local physical habitat conditions may modify the extent to which any impacts of diffuse pollution are evident