DOI: 10.5061/dryad.g1jwstqt5
title: Fencing farm dams to exclude livestock halves methane emissions and improves water quality

description: Agricultural practices have created tens of millions of small artificial
 water bodies (“farm dams” or “agricultural ponds”) to provide water for
 domestic livestock worldwide. Among freshwater ecosystems, farm dams have
 some of the highest greenhouse gas (GHG) emissions per m2 due to
 fertilizer and manure run-off boosting methane production – an extremely
 potent GHG. However, management strategies to mitigate the substantial
 emissions from millions of farm dams remain unexplored. We tested the
 hypothesis that installing fences to exclude livestock could reduce
 nutrients, improve water quality, and lower aquatic GHG emissions. We
 established a large-scale experiment spanning 400 km across south-eastern
 Australia where we compared unfenced (N = 33) and fenced farm dams (N =
 31) within 17 livestock farms. Fenced farm dams recorded 32% less
 dissolved nitrogen, 39% less dissolved phosphorus, 22% more dissolved
 oxygen, and produced 56% less diffusive methane emissions than unfenced
 dams. We found no effect of farm dam management on diffusive carbon
 dioxide emissions and on the organic carbon in the soil. Dissolved oxygen
 was the most important variable explaining changes in carbon fluxes across
 dams, whereby doubling dissolved oxygen from 5 to 10 mg L-1 led to a 74%
 decrease in methane fluxes, a 124% decrease in carbon dioxide fluxes, and
 a 96% decrease in CO2-eq (CH4 + CO2) fluxes. Dams with very high dissolved
 oxygen (&gt;10 mg L-1) showed a switch from positive to negative
 CO2-eq. (CO2 + CH4) fluxes (i.e., negative radiative balance), indicating
 a positive contribution to reducing atmospheric warming. Our results
 demonstrate that simple management actions can dramatically improve water
 quality and decrease methane emissions while contributing to more
 productive and sustainable farming.
description: In April 2021, we sampled farm dams across 400 km of the
 Australian South West Slopes bioregion in south-eastern New South Wales.
 The study region has a warm temperate climate, with hot dry summers and
 cool humid winters (the largest city of Albury has an annual mean
 temperature of 22°C and annual rainfall of 691 mm). Most of the area is
 dedicated to livestock grazing (especially beef cattle and sheep) and
 dryland cropping (mainly cereals and oilseed). We surveyed 64 farm dams
 located in pastures on 17 farming properties. Within each property, we
 established two experimental treatments: “unfenced” farm dams and “fenced”
 farm dams. For each experimental treatment within a farming property, we
 measured between 1 and 5 dams (depending on availability) on the same day.
 Unfenced farm dams (N = 33) received no management intervention to improve
 their ecological condition. Fenced farm dams (N = 31) were either entirely
 fenced (with a pump delivering water into drinking troughs) or partly
 fenced (providing water access through a hardened access point) for at
 least 2 years prior to sampling.
description: We used the statistical software R version 4.0.3 (R Core Team,
 2020) with the packages nlme (Pinheiro et al., 2020) and effects (Fox
 & Weisberg, 2018, 2019) for the statistical analyses, and dplyr
 (Wickham et al., 2018), plyr (Wickham, 2011), and ggplot2 (Wickham, 2009)
 for data manipulation and plotting.