From hogs to HABs: impacts of industrial farming in the US on nitrogen and phosphorus and greenhouse gas pollution

Abstract

Nutrient pollution and greenhouse gas emissions related to crop agriculture and confined animal feeding operations (CAFOs) in the US have changed substantially in recent years, in amounts and forms. This review is intended to provide a broad view of how nutrient inputs-from fertilizer and CAFOsas well as atmospheric NH 3 and greenhouse gas emissions, are changing regionally within the US and how these changes compare with nutrient inputs from human wastewater. Use of commercial nitrogen (N) fertilizer in the US, which now exceeds 12,000,000 metric tonnes (MT) continues to increase, at a rate of 60,000 MT per year, while that of phosphorus (P) has remained nearly constant over the past decade at around 1,800,000 MT. The number of CAFOs in the US has increased nearly 10% since 2012, driven largely by a near 13% increase in hog production. The annualized inventory of cattle, dairy cows, hogs, broiler chickens and turkeys is approximately 8.7 billion, but CAFOs are highly regionally concentrated by animal sector. Countrywide, N applied by fertilizer is about threefold greater than manure N inputs, but for P these inputs are more comparable. Total manure inputs now exceed 4,000,000 MT as N and 1,400,000 MT as P. For both N and P, inputs and proportions vary widely by US region. The waste from hog and dairy operations is mainly held in open lagoons that contribute to NH 3 and greenhouse gas (as CH 4 and N 2 O) emissions. Emissions of NH 3 from animal waste in 2019 were estimated at[ 4,500,000 MT. Emissions of CH 4 from manure management increased 66% from 1990 to 2017 (that from dairy increased 134%, cattle 9.6%, hogs 29% and poultry 3%), while those of N 2 O increased 34% over the same time period (dairy 15%, cattle 46%, hogs 58%, and poultry 14%). Waste from CAFOs contribute substantially to nutrient pollution when spread on fields, often at higher N and P application rates than those of commercial fertilizer. Managing the runoff associated with fertilizer use has improved with best management practices, but reducing the growing waste from CAFO operations is essential if eutrophication and its effects on fresh and marine waters-namely hypoxia and harmful algal blooms (HABs)-are to be reduced.

Drivers of Hot Spots and Hot Moments of Denitrification in Agricultural Systems

“…The most poorly understood process in the nitrogen (N) cycle is denitrification, the dominantly anaerobic microbial conversion of nitrate (NO 3 − ) and nitrite (NO 2 − ) to the gases nitric oxide (NO), nitrous oxide (N 2 O), and dinitrogen (N 2 ; Almaraz et al., 2020). This process is of great interest because it can significantly reduce pools of reactive N (and thus productivity) in ecosystems and because NO 3 − , NO, and N 2 O cause diverse air and water pollution problems, with direct links to human health (Davidson et al., 2012; Glibert, 2020) and fertilization costs. Denitrification is difficult to quantify because of problematic measurement techniques (especially for N 2 due to high background signals and insufficient analytical precision), high spatial and temporal variability, and a lack of methods for scaling point measurements to larger areas (Groffman et al., 2000, 2006).…”

Florida’s Harmful Algal Bloom (HAB) Problem: Escalating Risks to Human, Environmental and Economic Health With Climate Change

“…Eight of the 10 cities in the United States identified as most susceptible to climate change costs are in Florida (Muro et al, 2019). Generalized as warming, acidification and deoxygenation (Gobler, 2020), the specific climate change impacts likely to impact Florida include sea-level rise (Reece et al, 2013), increasingly intense weather and heavy precipitation events (Knutson et al, 2010;Emanuel, 2013;Contento et al, 2018Contento et al, , 2019Marsooli et al, 2019), marine fishery declines (Cheung et al, 2009), water pollution (Moss et al, 2011;Glibert, 2020), and reef and habitat loss (Snedaker, 1995;Manzello et al, 2007;Tobey et al, 2010;Okazaki et al, 2017). There is a general consensus that climate change is predicted to increase the frequency of both freshwater (O'Neil et al, 2012;Havens and Paerl, 2015) and marine HABs (Hallegraeff, 2010) through a variety of direct and indirect mechanisms.…”

“…HAB increases are attributed to a variety of reasons that vary with the species and the geographical areas involved (Anderson, 1989;Hallegraeff, 1993;Burkholder, 1998;Glibert et al, 2005;Glibert and Burkholder, 2006). These include increasing coastal nutrient inputs and eutrophication, coastal development, industrial and agricultural intensification (Smayda, 1990;Anderson et al, 2002Anderson et al, , 2008Heisler et al, 2008;Glibert, 2020), ballast water transport (Hallegraeff and Gollasch, 2006;Doblin et al, 2007;Smayda, 2007), increases in shellfish aquaculture (Shumway, 2011), climate change (Dale et al, 2006;Moore et al, 2008;Hallegraeff, 2010;O'Neil et al, 2012;Gobler, 2020) and a potential observer effect. In most cases, there is probably not a single cause underlying increases in a HAB's frequency, distribution or toxicity, but rather a complex interplay between these external pressures and the unique physiology of the HAB species involved which allows it to dominate under certain conditions.…”

Phytoplankton Drivers of Dissolved Organic Material Production in Colorado Reservoirs and the Formation of Disinfection By-Products

“…Given the broad range of reservoirs and conditions represented in this study, we expect that these results will be useful for comparison to other regions that have both mountain and plains lakes, especially since monitoring and treating freshwater HABs is an increasingly important issue in the global drinking water supply (e.g. Backer et al, 2015;Schmale et al, 2019;Glibert, 2020). However, it should be noted that other regions may have different regional factors such as climate, altitude and precipitation patterns that may influence local water quality and treatment, warranting further investigation.…”

“…Freshwater HABs, such as in Lake Erie, can be large enough to be monitored by satellite remote sensing (Schmale et al, 2019). HABs are also increasing in frequency due to increased nutrient supplies (Ho and Michalak 2017;Del Giudice et al, 2018;Glibert, 2020) and warming temperatures (e.g. Pearl and Scott, 2010), leading to contamination of municipal water supplies (e.g.…”