Viewpoint pubs.acs.org/est
Prioritizing Waterbodies To Balance Agricultural Production and Environmental Outcomes Donnacha G. Doody,*,† Paul J. A. Withers,‡ and Rachael M. Dils§ †
Agri-Food and Biosciences Institute, Newforge Lane, Belfast BT9 5PQ, U.K. School of Environment, Natural Resources and Geography, Bangor University, Bangor, Gwynedd LL57 2UW, U.K. § Environment Agency, Red Kite House, Howbery Park, Wallingford, Oxon OX10 8BD, U.K. duly contested politically, ethically and legally within society, there are strong scientific arguments supporting this approach. ‡
The Catchment Specific Relationship between Agriculture and Ecological Status. The duality between intensive and extensive agriculture has resulted in the perception that only intensive agriculture poses a threat to aquatic ecosystems.2 While research has provided evidence of the relationship between farming intensity and water quality, it is increasingly recognized that this relationship is site specific, with inherent variability in catchment response because of inter alia climate, soil type, topography, ecological sensitivity, and hydrology. Water quality impairment may occur in catchments with more extensive agriculture, where the site suitability for agriculture is marginal because of altitude, wetness, or where sensitive aquatic ecosystems occur.2 In some cases it is not possible to farm intensively without causing nutrient enrichment even when adopting current agricultural best practice guidelines. In these areas it is unlikely that further agricultural intensification can be achieved in a sustainable way without impacting on ecological status.
T
Legacy Nutrients. The historical overapplication of nutrients to agricultural soils has resulted in a buildup of “legacy” nutrients in soils, sediments and groundwater. As a result, even under a scenario of zero agriculture, nutrients released from these sources will impact on water quality well into the future.4 While research is exploring options to maximize the utilization of soil legacy P by plants, enabling lower P fertilizer inputs, options to accelerate reductions in legacy nutrients held in sediments and groundwater are much less clear. Major aquifers used for drinking water are often deep beneath extensive unsaturated zones or poorly permeable strata, which can result in long travel times of nitrate before it reaches the groundwater. It can take many years for groundwater to respond to improved farming practices, and in some cases nitrate concentrations are still increasing despite the reduction in surface inputs. Farming on a negative surplus balance to reduce legacy soil P will eventually compromise agricultural output, especially on livestock farms. It is currently uneconomical to export manure nutrients to crop producing areas because of the geographical disconnect, but the alternative option of reducing livestock numbers is inconsistent with the policy objective of increasing agricultural production. Waterbodies which have large legacy N and P stores in their
he enrichment of aquatic ecosystems with nitrogen (N) and phosphorus (P) is a widespread environmental problem. Although a wide range of anthropogenic activities contribute to the poor chemical and ecological status of waterbodies, the role of agriculture in this “wicked” problem has received significant attention.1 This has resulted in a plethora of voluntary, incentivized, and regulatory strategies aimed at reducing nutrient exports to threshold values considered necessary for protecting human health or aquatic ecosystems. However, it is increasingly evident that achieving water quality objectives in certain areas may be unrealistic without impacting agricultural production and rural livelihoods.2 Here, we present the scientific arguments to support the concept of prioritization of waterbodies as a rationale approach to balancing agronomic and environmental objectives: To meet future global demands for food, agriculture must intensify but in a sustainable manner. While sustainable intensification is a key objective in many countries, evidence to suggest this is achievable remains scant, particularly within the context of complying with water quality targets. It can be argued that that the competing goals of agricultural intensification and protecting aquatic ecosystems are in many cases incompatible and that trade-offs may have to be considered.3 While the legitimacy of these trade-offs will be © 2014 American Chemical Society
Published: June 27, 2014 7697
dx.doi.org/10.1021/es5024509 | Environ. Sci. Technol. 2014, 48, 7697−7699
Environmental Science & Technology
Viewpoint
Figure 1. Framework for the prioritization of catchments for water quality protection or intensification of agriculture.
We argue that a minimum standard of good practice should be applied to maximize the efficiency of N and P use and provide a basic level of environmental protection. Thereafter, a graduated system of policy intervention should be implemented including advice and guidance, voluntary approaches, economic incentives and stricter regulations.5 Minimal regulations should be applied in catchments where agricultural production is prioritised or is not affecting ecological status, while stricter regulations are applied, on a targetted risk based approach, where the probability of ecosystem recovery is highest. A suitable methodology to prioritize waterbodies for protection needs to take into account the ontological and epistemic uncertainty related to catchment processing, climate change, and the future trajectory of land use activities. The process of prioritizing catchments should also evaluate whether the compliance gap could be met by nutrient reductions in wastewater discharges and urban runoff, which could be more easily achieved with greater cost-effectiveness and does not pose a threat to future food security.
catchments will require a long lag time for ecological recovery, even if solutions to nutrient disconnects are on the immediate horizon. Recovery Trajectories of Water bodies. There is significant uncertainty in the recovery trajectories of waterbodies, with the rate and direction of recovery depending on catchment characteristics, the type of multiple stressors and internal ecosystem processes.4 The evidence to identify the threshold values at which nutrients are no longer constraining ecosystem recovery is limited. Therefore, setting quantitative targets for nutrient reductions from agriculture to achieve specific water quality outcomes is extremely difficult and based on a high level of uncertainty. In addition, the agricultural contribution to nutrient loads during the ecologically active period is often much lower than for other nutrient sources, which reduces the likelihood of ecological recovery based on nonpoint source mitigation in lotic waterbodies.
■
Prioritizing Catchments for Protection or Agricultural Production. A key question for society is whether to continue to aspire to protect all aquatic ecosystems or accept inevitable causalities in the drive for global food security. Prioritizing waterbodies may be the “least worst” option and a pragmatic acceptance of the difficulties in balancing environmental and agricultural objectives. Our current understanding of anthropogenic pressures on catchment systems suggests that the highest probability of reversing water quality and ecological impairment is in catchments where there is a small compliance gap between current and target nutrient concentrations, low legacy nutrient stores, where agriculture can be adapted without compromising production, and where resilient ecological communities exist. (Figure 1)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
REFERENCES
(1) Patterson, J. J.; Smith, C.; Bellamy, J. Understanding Enabling Capacities for Managing the “Wicked Problem” of Nonpoint Source Water Pollution in Catchments: A Conceptual Framework. J. Environ. Manage. 2013, 128, 441−452.
7698
dx.doi.org/10.1021/es5024509 | Environ. Sci. Technol. 2014, 48, 7697−7699
Environmental Science & Technology
Viewpoint
(2) Doody, D. G.; Foy, R. H.; Barry, C. D. Accounting for the Role of Uncertainty in Declining Water Quality in an Extensively Farmed Grassland Catchment. Environ. Sci. Policy. 2012, 24, 15−23. (3) Moss, B. Water Pollution by Agriculture. Philos. Trans. R. Soc. B 2008, 363, 659−666. (4) Jarvie, H. P.; Sharpley, A. N.; Withers, P. J.A.; Scott, J. T.; Haggard, B. E.; Neal, C. Phosphorus Mitigation to Control River Eutrophication: Murky Waters, Inconvenient Truths, and “Postnormal” Science. J. Environ. Qual 2013, 42 (2), 295−304. (5) McGonigle, D. F.; Harris, R. C.; McCamphill, C.; Kirk, S.; Dils, R.; Macdonald, J.; Bailey, S. Towards a More Strategic Approach to Research to Support Catchment-Based Policy Approaches to Mitigate Agricultural Water. Environ. Sci. Policy 2012, 24, 4−14.
7699
dx.doi.org/10.1021/es5024509 | Environ. Sci. Technol. 2014, 48, 7697−7699
