The impact of catchment scale afforestation on water quality and ecology

: a case study in the Arrow catchment, Warwickshire

Abstract

With increasing pressure from the Water Framework Directive (WFD) (2000/60/EC) to improve water quality, the implementation of catchment management and natural measures is increasing. Natural Flood Management (NFM) is a widely accepted range of methods for natural mitigation of accelerated climate change, rapid urbanisation and water pollution by working with natural, hydrological and morphological processes, features and characteristics to manage the sources and pathways of flood water (SEPA, 2015; Lane, 2017). NFMs are relatively novel in their implementation and research regarding these techniques typically focus on flood function and capacity. Although research exists in relation to ecology and water quality, these topics are frequently a minor comment with little scientific evidence (e.g. Short et al., 2018), therefore, a scientific baseline was needed. The Arrow catchment, Warwickshire hosts a large NFM woodland creation scheme implemented by The Heart of England Forest (HoEF). To assess the Arrow catchment NFM a multi-criteria approach was implemented, consisting of a 6-monthfield investigation of ecological and physico-chemical indicators. It was found that the NFM improved habitat availability and provided opportunities for a range of floral and faunal species, as larger populations of fauna were present after implementation. The NFM was found to support a range of mammals, amphibians, birds, invertebrates and plants. Visual and recorded evidence of Great Crested Newt (GCN) (Triturus cristatus) and other amphibians in the NFM ponds were also found, along with mammal pathways across the NFM and macro invertebrate populations of a moderate – high sensitivity to water pollution in NFM waterbodies. Furthermore, the NFM had no significant negative impact to the water quality of the catchment, as predominantly high-quality water was discharged from the NFM drainage channel into the river, suggesting the plantation was successful in retaining pollutants. Surface water quality also improved as water flowed through the main drainage channel of the NFM. However, the catchment remained impacted by nutrient eutrophication, most likely sourced from the nearby Water Treatment Works (WTW). Although the WTW did not exceed the legal maximum limits for pollutants, Total Reactive Phosphorus (TRP) concentrations failed the standards for good quality, Total Ammonia (TA) classified as ‘Poor’ in the river and Iron (Fe) concentrations exceeded boundary levels, remaining at a harmful level for aquatic life. A specific remediation scheme for the WTW is therefore needed in the Arrow catchment for the NFM to make any positive impact to the water quality of the River Arrow. The catchment also remained influenced by other factors such as heavy rainfall and seasonal variation, most likely from stormwater runoff from the agricultural land to the west of the River Arrow, as the NFM was located directly adjacent to the river in the east. This agricultural runoff is also a likely source of TA, as ammonia does not remain in form for great distances. It is therefore imperative that further research and monitoring of NFMs are conducted in the future to fully understand the capabilities of such installations.

Date of Award	Apr 2021
Original language	English
Awarding Institution	Coventry University
Supervisor	Michael Kennedy (Supervisor) & Craig Lashford (Supervisor)