Key Words:
Cattle Access; Freshwater; Fencing; Macroinvertebrates

Introduction

Agriculture, particularly in intensively managed systems, can pose a risk to water quality via both diffuse and point sources. Unrestricted cattle access to streams and rivers is among these sources and can have potentially negative impacts on stream water quality as has been demonstrated both in the temperate European setting (Conroy et al., 2016a; O’Sullivan et al., 2019a & b) and internationally (Braccia and Voshell, 2007; Vidon et al., 2008; O’Callaghan et al. 2019, Raymond and Vondracek, 2011). Facilitating animal access to watercourses provides farmers with a cheap, low-maintenance source of water for their livestock.
Cattle access to streams has been linked with increases in levels of deposited sediment and habitat homogenisation (Herbst et al., 2012), hydromorphological changes (Belsky et al., 1999), degraded riparian conditions (Grudzinski et al., 2016), physico-chemical degradation (Arnaiz et al., 2011), alterations in biological communities such as aquatic macroinvertebrates (Braccia and Voshell, 2007; Conroy et al. 2016a) and increases in sediment concentrations of Escherichiacoli (Bragina et al., 2017).
Cattle access mediated changes in macroinvertebrate communities are driven primarily by changes in stream hydromorphology and riparian habitat conditions, and in elevated nutrient and sediment levels in streams (Li et al., 1994; Stone et al., 2005; Arnaiz et al., 2011; Miserendino et al., 2011; O’Callaghan et al. 2019). Increases in limiting nutrients such as phosphorus and nitrogen, as a result of cattle defecation both directly in streams and in the adjacent riparian zone, can lead to concentrations that are detrimental in themselves (Sarriquet et al., 2006), but can also result (in association with reductions in riparian cover/shade) in proliferations of instream algal communities (Braccia and Voshell, 2007). Damage to stream banks by the erosive action of cattle hooves as they enter and exit streams, and as they consume and trample streamside vegetation, contributes significantly to stream suspended sediment inputs and bed loads of fine sediment (Scrimgeour and Kendall, 2003; Braccia and Voshell, 2007; Ranganath et al., 2009; Schulte et al., 2009; O’Sullivan et al., 2019a,b; Rice et al., 2021). Habitat change as a result of algal proliferation and sediment induced stream bed homogenisation seriously alters macroinvertebrate communities in affected streams (Stone et al., 2005; Sarriquet et al., 2006; Braccia and Voshell, 2007). The environmental impact of cattle access to watercourses have been recognised in agri-environmental policy, with cattle exclusion being included in various schemes under Pillar I and Pillar II of the Common Agricultural Policy (see Kilgarriff et al., 2020). Fenced riparian buffer measures have been included in most European agri-environment schemes (Dworak et al., 2009), including Ireland’s, and are amongst the commonest mitigation measures to prevent cattle access to watercourses.
Various methods of limiting livestock access to waterbodies have been used and empirically tested. Miner et al. (1992), Bagshaw et al. (2008) and Rawluk et al. (2014) studied the use of alternative water sources to encourage cattle congregation away from streams and riparian areas. Legrand et al. (2011) examined the use of “cow showers” as a means of attracting cattle away from shaded riparian areas in the arid Californian climate. The impacts of varying grazing practices have been tested by Raymond and Vondracek (2011), where the benefits of reduced grazing intensity on stream ecosystems via rotational grazing methods were demonstrated. More commonly, however, has been the complete exclusion of cattle from watercourses via fencing (Li et al., 1994; Bewsell et al., 2007; Collins et al., 2010).
Various studies have cited how restriction of cattle access to streams has positively affected factors such as instream and riparian habitat (Weigel et al., 2000); stream hydromorphology (Agouridis et al., 2005), reduced sediment loads (Collins et al., 2010) and physico-chemical conditions (Batchelor et al., 2015; Line, 2003). Fewer studies have examined the response of stream biota to restricted cattle access and most of these studies are from North America (e.g. Raymond and Vondracek, 2011 (macroinvertebrates), Derlet et al., 2017 (microbial)). The efficacy of cattle exclusion as a means of improving stream water ecological quality has not been widely assessed in the context of the temperate northwest of Europe where pastoral farming predominates.
This study aimed to assess the environmental benefits of cattle exclusion via fencing in the short-term (one-year post-fencing), by examining changes in levels of deposited sediment, habitat condition and macroinvertebrate communities in streams in Ireland. Additionally, a case study on the longer-term responses to fencing (9 years) is also presented. Here, 2008 macroinvertebrate data from two sub-catchments (one which was entirely fenced as a part of a group water scheme in the following year), are compared to data collected nine years following exclusion. The results will help inform further development of programmes of measures to improve water quality in agricultural catchments.