Archive for the category: Effects of reactive nitrogen on ecosystems

Beverly¹, A. Roberts², F.R. Bennett³

¹ Agriculture Research and Development Division, Department of Economic Development, Jobs, Transport and Resources, Victoria, craig.beverly@ecodev.vic.gov.au

² Natural Decisions Pty Ltd, Victoria.

³ Burnett Mary Regional Group for Natural Resource Management, Bundaberg, Queensland.

Abstract

This paper describes the construction of a bio-economic optimisation framework to evaluate the feasibility and net profit (or net costs) of achieving water quality targets in the Burnett-Mary region within the southern portion of the Great Barrier Reef (GBR), southern Queensland, Australia.  Key outcomes from the study were that current sediment, nitrogen and phosphorus load reduction targets could be achieved whereas more ambitious ecologically relevant targets required significant additional investment and were not feasible based on the model if individual basins must meet the targets.

N Robinson ¹, R Brackin¹, C Paungfoo-Lonhienne¹, T Lonhienne², M Westermann¹, M Salazar¹, YK Yeoh³, P Hugenholtz³, MA Ragan⁴, M Redding⁵, C Pratt⁵, WJ Wang⁶, A Royle⁷, L DiBella⁷, P Lakshmanan⁸, S Schmidt¹

¹ School of Agriculture and Food Science, The University of Queensland, Brisbane QLD 4072, Australia

² School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane QLD 4072, Australia

³Australian Centre for Ecogenomics, School of Chemistry and Molecular Biosciences, The University of Queensland

⁴ Institute for Molecular Bioscience, The University of Queensland, Australia

⁵ Department of Agriculture and Fisheries, 203 Tor Street, Toowoomba, Qld 4350, Australia.

⁶ Department of Science, Information Technology and Innovation, 41 Boggo Road, Dutton Park QLD 4102, Australia

⁷ Herbert Cane Productivity Services Limited, Ingham QLD 4850, Australia

⁸ Sugar Research Australia, Indooroopilly, QLD 4068, Australia

Abstract

The N pollution footprint of sugarcane cropping is large due to inefficiencies caused by mismatched N supply and crop N demand over sugarcane’s long N accumulation phase. The Great Barrier Reef lagoon receives excessive N loads that contribute to the rapidly declining reef health. Exceeding international average nitrous oxide emission rates several fold, sugarcane soils contribute significantly to Australia’s agricultural emissions. Nitrogen pollution reduction schemes over recent decades have mostly targeted reducing N fertiliser rates in line with expected yields and improving soil quality. Overall, these measures have not resulted in the desired N pollution reduction and further innovation is needed to address this problem. We present research that aims to aid agronomic innovation with (i) next-generation fertilisers that are based on repurposed nutrient-rich wastes and sorbent materials to better match N supply and crop demand and to improve soil function and carbon levels, (ii) understanding of soil N cycling and microbial processes, (iii) legume companion cropping as a source of biologically fixed N, and (iv) genetic improvement of sugarcane that more effectively captures and uses N. We conclude that evidence-based innovation has to support crop growers across climate and soil gradients in the 400,000 hectares of catchments of the Great Barrier Reef. This should include investment into new technologies to support ecologically-sound agriculture and a circular economy without waste and pollution.

Benjamin K. Nyilitya¹, Stephen Mureithi², Pascal Boeckx³

^{1 Department of Water Resources Management, Ministry of Water and Irrigation, Kenya (kyalob73@yahoo.com)}

^{2 Department of Land and Water Management, University of Nairobi, Kenya}

^{3 Department of Applied Analytical and Physical Chemistry, Ghent University, Belgium (pascal.boeckx@ugent.be)}

Abstract

A study was conducted in three major rivers (Nzoia, Nyando, Sondu) draining the Kenyan side of L. Victoria catchment to establish sources of excess nitrate deposition into the Lake using isotopic techniques and hydrochemistry. Results show spatial variation in isotope signatures with enrichment in δ¹⁵N and δ¹⁸O values near towns and industries. For instance R. Nzoia after Eldoret town had δ¹⁵N and δ¹⁸O values of 13‰, 6‰ respectively while the river after Mumias sugar factory had 9‰, 10‰ isotope values respectively. A plot of δ¹⁵N versus δ¹⁸O indicates that most of nitrate from the three catchments originates from Soil Nitrogen and manure or sewage. This may be due to deforestation, charcoal burning, untreated effluent discharges amongst other environmental degradation and poor sanitary practices rampant in the area. However, sewage and industrial effluents has high contribution to river and ground water nitrate near towns and densely populated areas as observed by the enriched δ¹⁵N values for Kisumu City Rivers ranging 10‰ to 18‰. Low nitrate content with corresponding high δ¹⁵N and δ¹⁸O signatures was observed in ground water near Kisumu city indicating denitrification takes place in the area. In addition, surface water in Kisumu had similar and enriched nitrate isotope signatures to ground water indicating high ground water susceptibility to pollution by surface water. This observation is supported by stable water isotope data (δ ¹⁸O, δ ²H) which show that the source of groundwater in Kisumu area is evaporated surface water.

Maryna Strokal^1,2, Carolien Kroeze², Mengru Wang^2,3, Ang Li^2,3, Lin Ma³

¹ Environmental Systems Analysis Group, Wageningen University, Droevendaalsesteeg 3, 6708 PB Wageningen, The Netherlands, https://www.wageningenur.nl/en/Persons/Maryna-M-Maryna-Strokal.htm?subpage=projects, maryna.strokal@wur.nl 

² Water Systems and Global Change Group, Wageningen University, Droevendaalsesteeg 3, 6708 PB Wageningen, The Netherlands

³ Key Laboratory of Agricultural Water Resource, Center for Agricultural Resources Research, Institute of Genetic and Developmental Biology, Chinese Academy of Sciences, Huaizhong Road 286, Shijiazhuang, Hebei 050021, China

Abstract

Chinese agriculture has been industrializing since the 1990s to produce enough food. This increased nitrogen (N) in Chinese rivers and coastal waters, resulting in eutrophication-related problems. We analysed three options to reduce future N pollution of coastal waters in China by 2050. We did it using the MARINA Nutrient model (a Model to Assess River Inputs of Nutrients to seAs). Two optimistic scenarios (OPT-1 and OPT-2) were developed, taking the Global Orchestration scenario (GO) of the Millennium Ecosystem Assessment as a baseline. These scenarios assume efficient N management in agriculture (OPT-1 and OPT-2) and sewage (OPT-2). We also assessed effects of the “Zero growth in fertilizer use after 2020” policy (the CP scenario). Results show that N management in agriculture is more effective to reduce future N pollution of coastal waters than N management of sewage. In GO, Chinese rivers are projected to export 38-56% more N in 2050 than in 2000 because of poor manure management. The current policy in agriculture (CP) may not be successful to reduce coastal water pollution. In contrast, our more optimistic scenarios project much lower river export of N in 2050 (at around levels of 1970 for northern rivers and 2000 levels for central and southern rivers). This is mainly because OPT-1 assumes high rates of manure recycling, leading to decreased use of synthetic fertilizers. Improved sewage management in OPT-2 can further reduce N export by northern rivers. Our results can serve as a basis for decision makers on N management.

Keryn Roberts¹, Michael Grace², Perran Cook²

¹ Water Studies Centre, Monash University, Wellington, Clayton, Victoria, 3800, Australia, roberts.keryn@gmail.com

² Water Studies Centre, Monash University, Wellington, Clayton, Victoria, 3800, Australia

Abstract

Estuaries provide the final stage of nitrogen processing before its release into coastal waters. However, residence time, oxygen conditions and hydraulic mixing determine the nitrogen removal capacity of an estuary. Long residence times can lead to low oxygen conditions significantly affecting nutrient transformation pathways including, but not limited to, inhibition of nitrification and the competition for nitrate between denitrification and dissimilatory nitrate reduction to ammonium (DNRA). The study site for this research, the Yarra River estuary, is a shallow (3 – 5m) salt wedge estuary prone to hypoxia resulting from the extended residence time of the bottom waters during low flow events. The estuary is one of the main freshwater nitrogen inputs into Port Phillip Bay (PPB), a nitrogen limited system. This research examined nitrogen processing over the period 2009 – 2011, extending over two summers of contrasting rainfall. Nitrogen loads were driven by rainfall in the catchment and ensuing freshwater inflow. NO₃^– was the main form of dissolved inorganic nitrogen (DIN) entering the system, being 87 ± 2 % of total DIN. Low oxygen conditions promoted nitrogen recycling within the system leading to an accumulation of NH₄⁺ in the stratified bottom waters of the estuary. Estimates of nitrogen removal were low for the Yarra River estuary at < 5% of total DIN compared to 20 – 50 % for other estuarine systems. This study highlights the importance of understanding estuarine specific conditions (residence time and oxygen) on nitrogen dynamics in the management of nitrogen loads into receiving waters.

Lena Schulte-Uebbing¹, Wim de Vries^1,2

¹ Environmental Systems Analysis Group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands, www.wageningenur.nl, lena.schulte-uebbing@wur.nl
² Alterra, Wageningen University and Research Centre, P.O. Box 47, 6700 AA Wageningen, The Netherlands

Abstract

Agricultural nitrogen (N) use leads to nitrous oxide (N₂O) emissions, which contribute to climate change. However, elevated N deposition may also increase net primary productivity in N-limited terrestrial ecosystems and thus enhance the terrestrial carbon dioxide (CO₂) sink. This indirect effect can lead to a considerable reduction of the net climatic impact of agricultural N use.

We performed a meta-analysis on data from 63 forest fertilization experiments to estimate N-induced carbon (C) sequestration in above-ground tree woody biomass (AGWB), a relatively stable C pool with long turnover times. Results show that boreal and temperate forests respond strongly to N deposition and store on average an additional 23 and 12 kg C per kg N in AGWB, respectively. Sub-tropical and tropical forests show much weaker response to N addition (6 and 2 kg C per kg N, respectively).

We estimated global C storage in tree AGWB resulting from agricultural N use by multiplying the C–N responses obtained from the meta-analysis with ammonia (NH₃) deposition estimates per forest biome. We thus derive a global C sink of about 84 (47–120) Tg C yr^-1 in AGWB, which compensates on average 16 (9–23) % of N₂O emissions from agriculture (6.4 Tg N₂O yr^-1 or 520 Tg CO₂-C_eq yr^-1). Adding estimates for N-induced C sequestration in soils and below-ground woody biomass obtained by stoichiometric scaling, we estimate total forest C sequestration resulting from agricultural N use at 236 (147–341) Tg C yr^-1, or 40 (28–54) % of agricultural N₂O emissions.

Jana E. Compton¹, Daniel J. Sobota², Jiajia Lin³, and Mario Sengco⁴

1U.S. EPA Office of Research and Development, Western Ecology Division, Corvallis OR 97333
2 Environmental Solutions Division, Oregon Department of Environmental Quality, 811 SW 6th Avenue, Portland OR
3 National Research Council, National Academies of Science, Washington DC 20001, based at US EPA Western Ecology Division
4 U.S. EPA Office of Water, Office of Science and Technology, Washington DC 20460
Abstract

Nitrogen (N) release to the environment from human activities can have important and costly impacts on human health, recreation, transportation, fisheries, and ecosystem health. Recent efforts to quantify these damage costs have identified annual damages associated with reactive N release to the EU and US in the hundreds of billions of US dollars (USD). The general approach used to estimate these damages associated with reactive N are derived from a variety of methods to estimate economic damages, for example, impacts to human respiratory health in terms of hospital visits and mortality, willingness to pay to improve a water body and costs to replace or treat drinking water systems affected by nitrate or cyanotoxin contamination. These values are then extrapolated to other areas to develop the damage cost estimates that are probably best seen as potential damage costs, particularly for aquatic ecosystems. We seek to provide an additional verification of these potential damages using data assembled by the US EPA for case studies of measured costs of nutrient impacts across the US from 2000-2012. We compare the spatial distribution and the magnitude of these costs with the spatial distribution and magnitude of costs from HUC8 watershed units across the US by Sobota et al. (2015). We anticipate that this analysis will provide a ground truthing of existing damage cost estimates, and continue to support the incorporation of cost and benefit information into communication, outreach, and decision-making related to nutrient pollution.