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.