Linking the uptake of best management practices on dairy farms to catchment water quality improvement over a 20-year period

Correlations between catchment-scale farm infrastructure densities and stocking rate to stream nutrient concentrations in dairy-dominant catchments

Nitrogen and phosphorus pollution is a critical environmental issue that causes eutrophication of water bodies. High concentrations of these nutrients primarily come from agricultural areas and are driven by catchment characteristics such as climate, hydrology, topography, geology, land use, and land cover. In addition to these factors, specific farming practices - particularly, the use of dairy farm infrastructure and management of stocking rate - also influence stream nutrient concentrations. However, the extent of the influence of specific farming practices and their relative importance in determining nutrient concentrations in waterways remain unknown. In this paper, we used data from an agriculturally-intensive dairy farming region to investigate these relationships. We used statistical analyses and modelling to determine relationships between concentrations of ammonium (NH4+), filterable reactive phosphorus (FRP), nitrogen oxides (NOx), total phosphorus (TP), and total nitrogen (TN) with 26 predictors which include farm infrastructure density and stocking rate. We found that farm infrastructure and operational characteristics such as effluent pond density, dairy shed density, and stocking rate are consistently important predictors that influence concentrations of NH4+, FRP, NOx, TP, and TN during both wet and dry weather periods. This paper has shown that in addition to established factors such as land use and land cover, specific farming practices also play a role in influencing stream nutrient concentrations. By identifying key infrastructure and stocking rate as drivers of stream nutrient concentrations, this research emphasized the need for targeted management strategies to mitigate the impacts of agricultural activities on water quality.

The relative importance of soil moisture deficit, land use intensity and fertiliser spreading regulations for stream water quality in agricultural catchments

Despite European-wide regulatory controls on fertiliser management that effectively close and open spreading periods, there are still ongoing stream water quality issues in agricultural catchments. Adjustments to these regulations largely relate to application rate and set-back distances from watercourses at the start of the open period to avoid sudden water quality impacts. Within this regulatory framework and using long-term datasets the aim of this study was to investigate the relative importance of Soil Moisture Deficit (SMD), land use intensity and fertiliser spreading regulation effects on stream water quality during the first weeks of the open spreading period. Fortnightly stream water samples were collected over 2009-2023 in twenty-four agricultural sub-catchments of major Northern Ireland rivers. Random Forest Regression models were developed to predict baseline stream water total phosphorus (TP), soluble reactive phosphorus and total oxidised nitrogen (TON) concentrations. SMD and land use intensity were the primary drivers of changes in phosphorus concentrations while land use intensity was the primary driver of changes in TON concentrations. SMD was a more important driver of changes in nutrient concentrations in the more intensively farmed sub-catchments. In the less intensive sub-catchments, land use intensity was at least 30% (for TP) to 85% (for TON) more important than SMD and fertiliser spreading regulation for explaining these changes. The study highlights the need to reduce the nutrient source pressure as a more effective step to improve water quality compared to small adjustments to fertiliser spreading protocols, and for policy reviews to account for changes in weather pressures.

Dairy effluent management systems as a potential persistence source of Shiga toxin-producing Escherichia coli (STEC) strains

Shiga toxin-producing Escherichia coli (STEC) is a group of pathogenic enterobacteria of significant public health importance due to their association with highly prevalent human diseases. STEC is ubiquitous in livestock environments, and its presence in the environment emphasizes the importance of properly managing agricultural effluents to reduce health risks from contamination. In order to detect STEC in the effluent treatment systems of two dairy farms ("A" and "B") in the southwest of Buenos Aires province, samples ("A", n=88; "B", n=72) were taken at two different times of the year (winter and spring) and at various points in the treatment systems. Analysis markers for virulence genes (stx, eae, saa, and ehxA) revealed the presence of STEC in 13.1% of the samples, showing an increase in spring and differences between dairy farms possibly related to their maintenance conditions. After manure, sediments showed the highest proportion of STEC-positive samples, which is relevant due to the ability of these strains to survive in the environment through biofilm formation. Eight genetic profiles were identified among all STEC-positive samples, which are associated with STEC strains that can cause hemolytic uremic syndrome (HUS) and other gastrointestinal diseases. This demonstrates the role of dairy farm environments in the region as reservoirs of pathogenic STEC strains and their impact on public health.

Assessing the eco-efficiency of milk production systems using water-energy-labor-food nexus

Globally, massive resource inputs and undesired outputs hindered the further development of the dairy industry. This study proposed a method applying data envelopment analysis to the water-energy-labor-food nexus to assess the eco-efficiency of the milk production system (MEE) from a systemic perspective. Using national statistics on scale farms for the period 2014-2021, we illustrated the effects of scale and intensification on MEE in China. In the study period, the production cost increased by 23 % and milk production rose by 30 % at the same time. Despite the increases in both water and energy inputs, the rise in milk production weakened the resource burdens and thus lifted MEE by 24 %. The resource investment pattern shifted from water- and labor-oriented to energy-oriented. Under current conditions, production technology and system management were at higher superiority to advance than farm scale, while mechanization and on-farm clean energy production are the keys to further lifting MEE.

Reducing phosphorus losses from agricultural land to surface water

Phosphorus (P) enrichment of water impairs its quality by stimulating algal growth and eutrophication, affecting an estimated 1.7 billion people. Remediation costs are substantial, estimated at $1 billion annually in Europe and $2.4 billion in the USA. Agricultural intensification over the past 50 years has increased P use brought into the system from mined fertiliser sources. This has enriched soil P concentrations and loss to surface waters via pathways such as surface runoff and subsurface flow, which are influenced by precipitation, slope, and farming practices. Effective mitigation of losses involves managing P sources, mobilisation, and transport/delivery mechanisms. The cost-effectiveness of mitigation actions can be improved if they are targeted to critical source areas (CSAs), which are small zones that disproportionately contribute to P loss. While targeting CSAs works well in areas with variable topography, flatter landscapes require managing legacy sources, such as enriched soil P to prevent P losses.

Difficulties in using land use pressure and soil quality indicators to predict water quality

Intensive agriculture can impair river water quality. Soil quality monitoring has been used to measure the effect of land use intensification on water quality at a point and field scales but not at the catchment scale. Other farm scale land use pressures, like stocking rate and the value of land, which relate to land use intensity are now publicly available, nationally. We therefore tested whether point scale soil quality measures, together with newly available farm scale land use pressures (land valuation and stocking rate) and existing catchment and climatic characteristics could help predict the behaviour of water quality data across 192 catchments in New Zealand. We used a generalised additive model to make predictions of the change in nitrogen fractions (r2 = 0.65-0.71), phosphorus fractions (r2 = 0.51-0.70), clarity and turbidity (r2 = 0.42-0.46), and E. coli (r2 = 0.35) over 15 years. The state and trend of water quality was strongly related to a refined farm scale land use classification, and to catchment and climatic characteristics (e.g. slope, elevation, and rainfall). Relationships with point scale soil quality measures and the land use pressures were weak. The weak relationship with land use pressures may be caused by using a single snapshot in time (2022), which cannot account for lag times in water quality response but leaves room for additional temporal data to improve predictive power. The weak relationship to soil quality measures was probably caused by limited data points (n = 667 sites) that were unrepresentative of land use, and areas of catchment subject to processes like runoff or leaching. While national soil quality measures might be useful for evaluating environmental risk at the field or farm scale, without a large increase in sampling, they were not relevant at the catchment scale. Additional analyses should be performed to determine how many samples would be needed to detect a change using an environmentally focused soil test that can guide water quality management.

A review of the development and implementation of the critical source area concept: A reflection of Andrew Sharpley's role in improving water quality

Critical source areas (CSAs) are small areas of a field, farm, or catchment that account for most contaminant loss by having both a high contaminant availability and transport potential. Most work on CSAs has focused on phosphorus (P), largely through the work in the 1990s initiated by Dr. Sharpley and colleagues who recognized the value in targeting mitigation efforts. The CSA concept has been readily grasped by scientists, farmers, and policymakers across the globe. However, experiences and success have been mixed, often caused by the variation in where and how CSAs are defined. For instance, analysis of studies from 1990 to 2023 shows that the proportion of the annual contaminant load coming from a CSA decreases from field to farm to catchment scale. This finding is consistent with increased buffering of CSAs and greater contribution of other sources with scale, or variation in the definition of CSAs. We therefore argue that the best application of CSAs to target mitigation actions should be at small areas that truly account for most contaminant loss. This article sheds light on the development and utilization of CSAs, paying tribute to Dr. Sharpley's remarkable contributions to the improvement of water quality, and reflecting upon where the CSA concept has succeeded or not in reducing contaminant (largely P) loss.

Protecting and restoring freshwater biodiversity across urban areas in Aotearoa New Zealand: Citizens' reporting of pollution in stormwater drains and waterways

Urbanization poses numerous challenges to freshwater biodiversity. This paper describes two studies with the joint aim of demonstrating the benefits of applying a systematic behaviour change framework and providing the foundational knowledge to inform future behavior change work to protect and restore urban freshwater biodiversity. In Study 1 we used a mixed-methods research design, involving 14 key informant interviews followed by an online survey targeting 17 freshwater biodiversity experts and another targeting a representative sample of 550 urban residents, to identify and prioritize the most promising resident behaviors to target to reduce stormwater pollution and improve natural waterway habitats in urban areas. Study 2 focused on the top-ranked short-term behavior identified in Study 1, citizen reporting of pollution in stormwater drains and waterways. We surveyed a representative sample of 1901 urban residents across Aoteraoa New Zealand to identify four main determinants influencing this behavior: awareness and uncertainty about reporting, lack of opportunity to report, social motivation and personal motivation to report, and five potential target audiences: 'Supportive', 'Unaware but receptive', 'Motivated but lack support', 'Reluctant', and 'Not my problem'. We make recommendations for the most appropriate intervention designs to target each of these audience segments to promote the reporting of stormwater pollution in urban areas. This knowledge will allow for a more coordinated and effective approach for addressing the 'human element' that lies at the heart of many urban freshwater management problems.